March 1988

eitior000JO

Signal divider for satellite TV receivers

Computer -controlled slide fader

Uniphase loudspeaker system

UK £1.50IR £2.20

(incl. VAT)

EE

March 1988

BBC Micro Computer System8BC MASTER SERIES:AMB15 BBC MASTER 128K £346ADC06 Turbo (65C102) Card £95ADC08 512 Processor £185ADF14 Rom Cartridge E13ADF10 Econet Card £40ADJ22 Ref. Manual I £14ADJ23 Ref. Manual Part II _ E14ADJ24 Adv Ref Manual E18

(a)(dl(b)(d)(d)(c)(c)(c)

BBC ARCHIMEDESPlease enquire about availability anddetais of the s stem.

UPGRADE KITS:1.2 OS F1O1.) E15 (d)ONFS ROM . £19 (dlBASIC II ROM (BBC B) .. £22.50 (d)ADFS ROM E261770 DFS Kit E43.50Econet Kit (B&B+) E55 Id)ACORN ADD-ON PRODUCTS:Torch ZEP 100 £229 (a)512 2nd Processor £195 Ib)IEEE Interface £265 IS)Teletext Adapter £95 )b)Acorn 65CO2 Turbo E99 )b)

Ask for full detaas on our fua range of software

WORD PROCESSOR ROMs:VIEW 2.1 £35 Id) VIEW 3.0 .. £48 (c)Speamaster £49 (dl VIEW INDEX E12 (dlWORDWISE £24 (dl WORDWISE+ E38 Id)

SPELLCHECK IIIWYSIINIG+ E21 (d) £31 (dlINTERWORD £46 (di EDWORD II £43 (a)

LANGUAGE ROMS:Micro Prolog E62 (c) Microtext £52 (c)ISO PASCAL £51 lc) LOGOTRON £55 (c)LOGO £46 (c) MACROM £33 (dlLISP E39 (dl COMAL £43 (dl

Oxford Pascal £36 (c)COMMUNICATIONS ROMS:TERMULATOR £25 (dl).(ASTER TERMULATOR E34.75 (dlCOMMSTAR II (28 (d)MODEM MASTER Ell (d)COMMAND E34 Id/

UTILITY ROMs:DOTPRINT PLUS for FX RX compatiht.,qDOTPRINT DUAL for MX rangeAcorn Graphics Extension Rom E28Merlin with 57 disc unity commands100 page manual E37.50 (cl

MULTIFORM Z80 2nd Processor for the BBCThis unique Z80 2nd Processor running OS 1.1 will allow use of almost any standard CP.M software on the BBC micro. It is supplied with a number of different CPifil formats and includes autility to configure it to read other formats. This is pariicularty useful in environments where corn -autos with different CP/M formats are used and the data cannot be easily exchanged betweenthem. Mains powered (includes Pocket Wordstar & MSDOS (LW unity) E249 Ib)MS DOS Read Write Utility £49 Ic)

META Version 3 ASSEMBLERAssembles 17 of the popular processors. Over 70K long program on two roms and a disc andprovides complete Editing and Assembly facilities. It uses appropriate mnemonics for differentprocessors. Fully nestable macros, nestable conditional assembly (IFIELSEENDIF). modularsource code, true focal arid global labels, 32 bit labels arid arithmetic. 30 ways to send ohi;ettcode and 50 directives.A powerful editor with many features. Send for detailed leaflet. £145 (6)

BBC DISC DRIVES5.25" Single Drive:1 400K 40.80T DS: TS400 E90 Ibl PS400 vrtth peal £104 lb)5.25" Dual Drive:2 x 400K 40.80T DS: TD800 ....E170 (a) P0800 with psu E190 la)2 a 400K 40.801 OS with psu and built in monitor stand P08009 £209 lal3.5- Drives:

400K 80T DS TS35 1 E67 (b) PS35 1 with psu E85 lb)1 , 400X SOT DS with psu TD35 2 E126 lb( P035 2 with psu E149 it))

3M FLOPPY DISCSIndustry standard floppy discs with a life time guarantee. Discs in packs of 10:

5% DISCS 3% DISCS40T SS DD £8.20 Id) 40T DS DD £10.00 (dl SOT SS DD £15.00 (dl80T SS DDE12.25 (d) 80T DS DD. E13.00 Id) 80T DS DO £19.50 (d)

DISC ACCESSORIESSingle Disc Cable E6 (d) Dual Disc Cable E8.50 (d)10 Disc Library Case £1.80 Ic) 30 Disc Storage Box E6 (Cl40 Disc Lockable Box E8.50 (c) 100 Disc Lockable Box E13 (c)Eloppielene Drivehead Cleaning Kit with 20 disposable cleaning kits 5F." f 14 50 (dl; E16 Idi

BT APPROVED MODEMSMIRACLE TECHNOLOGY WS Range

WS4000 V21123. WS2000 V21A/23Mayes Compatible. Inter -vent. Auto Dial'Auto Answer) E135 lb) WS 2000 Auto Dial CardWS3000 V21123 Professional WS 2000 Auto AnswerAs WS4000 and with BELL standards arid WS 2000 SKI Kitbattery back up for memory . . £244 (b) %VS 2000 User Port LeadW53000 V22 ProfessionalAs WS3000 V21/23 but with 1200 baud fullduplex £409 falWS3000 V22 his Professional (Offer Ernited to current stodulAs V22 and 2400 baud full duplex E537 (alINS3000118C Data Lead E7 (dl

Manual Modern £92 (b)E27£27 Ml£5 Id)£5 Idl

SPECIAL OFFEREPROMs/RAMS

2764-25 £2.80 Id)27256 £5.00 Id)27512 £9.90 (dl6264LP-15 £2.6027128-25 (12.5 Vpp) £3.40 (dl27128-25 (21.0 Vpp) £4.80 Id1

PROJECTS:Junior Computer Kit £86 lb)Housekeeper kit £58 (b)Elekterminal Kit (1980) £50 (b)ASCII Keyboard kit £75 Ib)J C Books 1, 2, 3. & 4E6.90 lc) eaUniversal Terminal (65021 Kit £75 lb)Elekterminal Kit (19831 £70 lb)

101050 (136 col) E529 (alTAXAN KP815 (80 cob £269 fa)We hailin stock a large variety of printer attachments, interfaces anj con su m abzes.Pease write or phone for details.

PRINTERSEPSON KP915 (156 coil E369 !a)LX800 £189 le) BROTHER HR20 E349 la)FX800 E295 (a) STAR N110 1ParaBel !lace) . . . E179 lalEX 1000 E405 la) STAR NLIO Serial Interface) . E219 (a)EX800 E395 la) JUKI 6100 (Daisy Wheel) . ... £295 (alEX1000 £539 (a) INTEGREX (Colour) E549 lalL0850 (80 col) E439 (a) NAT PANASONIC KX P 1081_ E149 la)

NAT PANASONIC KX P 3131. £249 la)

ACCESSORIESBUFFALO 32K Buffer for Epson printers E75 (dl: FX80 plus sheet feeder £129 lb).EPSON Serial Interface: 8143 E30 IS); 8148 with 2K buffer E65EPSON Paper Roll Holder £17 lb); FX80.80- ,85 Tractor Attach £37 (0); RXTX80Dust Cover E4.50 (dl; LXBO Tractor Unit E20 (c); 10800 Tractor Feed E47 lb).EPSON Ribbons: MX/FIX,FX80 E5; MX,FIXTX100 E10 (dl: LX80 £4.50 Id%JUKI: Serial Interface E65 Id): Tractor Attach. £149 (a); Sheet Feeder E219 (a);Ribbon £2.50 (a): Spare Daisy Wheel £14 (dl.BROTHER HR20: Sheet Feed E229; Ribbons - Carbon or Won £3; Tractor Feed£116 (a): 2000 Sheets Fanfold with extra foie par. 9.5- - E13.50; 15" £17.50 lb).BBC Parallel Lead £6; Serial Lead E6 (dl: IBM Parallel Lead l2m) E12

MONITORSMICROVITEC 14" RGB1431 Standard Resolution E179 (al1451 Medium Resolution E225 (a)1441 Hi Res £365 (a)MICROVITEC 14" RGB:PAL & Audio1431 AP Standard Resolution E199 (a)1451 AP Medan Resolution £259 (a)MICROVITEC 20" RGEIPAL,Audo2030 CS std Res £380 (a)2040 CS Hi Res E675 (a)Mitsubishi 14" RGB Med Res IBBCIBM)

E219 (a)

TAXAN K12SV620 12" £269 lalTAXAN K125V625 12" . £319 la)12" MONOCHROME MONITORS:TAXAN:Taxan KX 117 12' Green P31 E 85 la)Taxan KX 118 12" Green P39 E 95Taxan KX 119 12" Amber E 95 la)PHILIPS:7502 Green Screen E 69 tai7522 Amber Screen E 75 la)7542 White Screen E 79 (a)AB Phelps Monitors scarified with swivelstand

BOOKSNo VAT

LANGUAGES:6502 Assy Lang Prog8086 BookAcorn BCPL User GuideAcorn FORTHAcorn LISPAcorn ISO Pascal Ref ManualIntro to COMALIntro to LOGOMicro Prolog Ref ManualIntroduction to Turbo Pascal.Prog the Micro with Pascal .

The UNIX BookUnix User GuideUnderstanding Unix

£19.95E23.95£15.00

£7.50E7.50

£10.00£10.00

E7.50E10.00E14.95

E8.5007.50

E19.95E18.45

BBC MICRO GUIDE BOOKSBBC User Guide Acorn £15.00BBC Plus User Guide E15.00Drawing your Own BBC ProgramsE6.95Inside Information C8.95Math Prog vt BBC Basic E7.95Toolbox 2 £10.95VIA 6522 Book 450PROGRAMMINGATIILITYAdvanced Sideways Ram UserGuide £9.95Advanced User Guide (BBC)Applied Ass./Lang on the BBC E9.95BBC Micro Sideways ROM's RAM'sE9.95Guide to the BBC ROM £9.95Beginners Guide to W.P £7.95

on books; Carriage (c)View 3.0 User Guide £9.00Viewstore £9.00Vrewstieet £9.00Wordwise Plus E9.95

SOUND & GRAPHICS:Mastering P4usic E6.95

DISC DRIVE SYSTEMS:Advanced Disc User Guide (14.95Disc Book E3.50Disc Programming Techniques £7.95Disc Systems E6.95File Handing on the BBC E6.95

APPLICATIONS:Interfacing PrOj for BBC E6.9588C and Small Business £5.75

PROFESSIONAL SOFTWAREWordstar made easy £16.95Introduction to Wordstar £17.95Wordstar Handbook E11.95dBase-II for the first time user E 16.95Understanding dBase-111 £22.95Multiplan Made Easy £18.95&summate Complete Grade £16.95ABC of LOTUS 123 £17.451-2-3 for Business £16.95Adv Tech in dBase 11111 . E22.95Mastering CPA( £17.95CPM Wale E16.50Introducing CPIM on BBC & ZEO E9.95MS PC DOS Prompt . __ £10.95

PROGRAMMED ROPROJ

503-N kir_ Computer Monitor2708 E 4.80

504 Disco fights 2708 E 4.80505 Chess Intelekt . 2 x 2716 E14.60506 J C Tape Monitor . 2716E 7.30507-N J C Printer Mon & PME

2716 E 7.30508 J C Bus Control 82S23 E 4.80510 150 MHz Freq Meter 2 x 82523

E 9.60514 Dank Room Camp:A.21 2716 E 7.30

MS FOR ELEKTORECTS516 TaScing Dice 2716 E 7.317521 CharGen & Video Routine for DOSJumor 2732 + 2716 £16.40522 CharGen & video; Routine for ex-tended junior 2732 2 x 2716 E24.00523 Char. Generator .. 2732E 9.00524 Otrantisiz' er 2732 E 9.00525 Universal Term 2732 E 9.00526 Wind Dir Ind 2716 E 7.30527 Babyrinth 2716 E 7.30530 Daisywheel Ifatie 2 2716 E11.00

ALL PRICESEXCLUDE VAT.Please add carnage 50p unless

indicated as follows:

falf8 0)1'2.50 (c/£1.501 (d/£1.00

TECHNOLINEVIEWDATA SYSTEM

Tel. 01-450 9764Using 'Neste type protocols.

For information and ordersavailable 24 hours. 7 days

a week.

SEE OUR PAGE 5 ADVERTISEMENT FOR COMPONENT PRICES

TECHNOMATIC LTDMAIL ORDERS TO: 17 BURNLEY ROAD. LONDON NW10 1ED

SHOPS AT: 17 BURNLEY ROAD, LONDON NW10(Tel: 01 208 1177, Telex 922800)

305 EDGWARE ROAD, LONDON W2. Tel: 01 723 0233

PLEASE ADD CARRIAGE AS PER CODE & 15% VAT

(Export. no VAT. p&p at CostlOrders from Government Depts. Er Colleges etc. welcome.

Minimum telephone order E5

14k1Detailed Price list on request.

Prices subject to change without notice

Sensors & actuatorsp. 14

13 Editorial

Components14 Sensors & actuators20 The reason for miniature transducers

by Mike Coope22 Infra -red detector for alarm systems

Computers

24 PROJECT: A 256 -colour adapter for theEGAby Peter Balch

28 Towards the Supernode computerby Dr Chris Jesshope

General Interest30 PROJECT: Computer -controlled slide fader

(1)

Audio & Hi-fi36 PROJECT: Uniphase loudspeaker system40 The value of silence

by Dr Dylan Jones and Dr Chris Miles

Radio & Television

43 PROJECT: Signal divider for satellite TVreceiversby R. van Terborgh

46 PROJECT: Low -noise preamplifier for FMreceivers

49 Radio & TV news52 PROJECT: Slave indication unit for intel-

ligent time standard

Design Abstracts60 Electronic compass

Computer -controlled slide faderp. 30

Uniphase loudspeaker systemp. 36

Test & Measurement62 Dual trace oscilloscopes: a review -

Part 4by Julian Nolan

68 A word in the hand makes the measure-ment firmby David Simpson

Information19 Events; 21-27-49-66 News; 57 Newliterature; 58 People; 59-73 New products;70 Readers services; 72 Terms of business

Guide lines76 Buyers guide 77 Switchboard 78 Classifiedads 78 Index of advertisers

In next month'sissue:The main theme willbe Electrophonics anda number of articleswill deal with thispopular subject,among them: Guitar fuzz unit Computer con-

trolled music gen-erator

MIDI code gen-erator

Further, Active loudspeaker

system Digital optical

transmitter Radio communi-

cations of thefuture

see pages 74 and 75for our specialoffer of three Crotechoscilloscopes

Front coverIn line with ourtheme of the month,our front cover thismonth shows aselection of ther-mocouple tempera-ture sensors.

4 EE

March 1988

NEW THIS MONTH'JIMMY'Exciting electronic football gameoriginally sold for £19.95, but thisprice included plastic grandstand.stickers etc. We can supply the420. 93mm neatly cased electronicscomprising keypad either end. 14 x

1988 CATALOGUEOUT NOW - 88 pages of bargains fromresistors to disco mixers. Price in -eludes latest bargain list, discountvouchers, order form. Don't be with.out your copy - send £1.00 now!!

.t. 8 1,-; to ri, a a5mm red LED's l'players'), TMS1000 v a . f "i e r. : IF ir

. taxiing:al,. 4.1.chip programmed to make odd noises - .. % a at avail& a awhilst playing and a tune when a goalis scored. also 2 x 7seg LED's to keepscore. Cardboard 'pitch' . instruc-

..._-,...asigailionapt * 31 is :2

tions supplied. £5.00 2810 KEYBOARD Really smart alphanumeric standard qwerty keyboard

WINTER SALE LIST with separate numeric keypad. fromA 16 page supplement combining ICL's 'One Per Desk'. Nicely laid outBargain Lists 33-35 + the 50% off keys with good tactile feel. Not en.supplement, with prices further re- coded - matrix output from PCB takenduced to 66% off!! It's FREE - send to 20 way ribbon cable. Made by Alps.large SAE for your copy now! Size 333. 106mm. 73 keys . . £8.95COMPASSES SPEAKERSPrecision spring bow 8Bmm long_ Max Z578 Sub -min speaker 30 . 30 x 3mrndia 70mm. Replaceable pencil lead & thick by Fuji. 16R 0.4W. 60p ea: 10steel tip. E 1.00 £3.70 25 £7; 100 E22: 1000 £180.

Z575 70 x 45mm 45R 0.5W 55p ea:VC1400 VIDEO COMPUTER 10 E3.30 25 £6 100 £20Z816 Games machine that used car- SOLDERtridges 'none available). Main console 500g reels resin cored. 1Bg .. £5.95contains UHF modulator + various 500g reels resin cored 22g . . £7.95chips. PSU has mains input, 15V LOGIC PROBE0.16A and 8V 1.22A output. 2 hand For TTL. CMOS etc. LED and sound in -held controllers each with joystick and dication. Pulse enlargement capability14 button keypad. All in original box. allows pulse direction down toNote: These are returns, and may be 25nsec. Max f = 20 MHz 4-16V. VPfaulty £12.50 Z:1?.1 £9.99FUSED UPPRESSORZ003 PSotted unit 60.45 .30 hasscrew term tip for mains, 2Orrimfuseholder & o/p tags for appliance

SOLDER SPECIAL! I.

* 15W 240V ac soldering iron99P * High power desolder pump

VIEWDATA LTU * Large tube solderZ697 Interface Panel 166x 150 with3>: Lf.1324, LM339. LM393, 4066, 11transistors, 3 reed relays etc. 3m leadwith BT plug attached. Supplied withcomprehensive data and ccts. £2.90

ALL FOR

£ 7 . 95Z620 68000 Panel. PCB 190,:45 be -REED SWITCHES

K569 A selection of about 15 types lieved to be from ICL's 'One per Desk'from 12 to 50mm long, mostly form A, computer containing MC68008P8few form C. Pack of 30 £2.75 I8MHz 16/8 bit microprocessor, + 42797 Min 15.3mm long. ROM's, all in skts; TMP5220CNL,20.11.50: 100/16: 250/112 74HCT245, 138, LSO8, 38 etc. £5.002798 Large 50.8mm long. Z625 32k Memory Board. PCB1011.50: 25/13: 100/(10 170 x 170 with 16 2k x 8 6116 staticZ799 Changeover 40mm long. RAM's. Also 3.6 V 100 mA511.50; 251E6: 1001E20 memopack nicad, 13 other HC/LSTOOLSScoop high

devices. 96w edge plug. 8 way DILswitch, R's. C's etc. E4.80purchase of quality surgical

instruments ideal for electronics use. SOLAR CELLSZ308 5- lightweight long nose pliers Giant size. 90mm dia giving 0.45V,

Z309 5'/-'a - as above but with ratchet.This enabes pliers to be lockedtogether - for holding small compo-

1.1A output. E4 each, 10+ £3.50.Mega size - 300 . 300mm. These in.corporate a glass screen and backingpanel, with wires attached. 121./

nents, or as heat shunt etc. £1.20 200mA output. Ideal for charging_ .

Other types on Bargain List 36 nicads_ £24.00Z662 COIN ACCEPTOR MECHANISM

ENTERPRISE PANELS Made by Coin Controls, this will accept2658 PCB 325 a 158 with 64k of RAM various size coins by simple adjust -18 .4864). 2130A microprocessor, + ment of 4 screws. Incorporates various21 other chips, UHF modulator, security features - magnet, bent coinspeaker etc. ROM and Nick andior rejector etc. Microswitch rated 5ADave chips missing supplied with cct 240V. Front panel 115 x 64. depthand data £8.00 130mm. Cost £10.85 Our price£4.00

if?

2004 Skeleton Joystick, switch type.Good quality, made by AB. Brass

Z811. Cumana Touch Pad for the BBCspindle has 44mm long black plastichandle attached. Body has 4 mountingholes. These really are a fantastic

computer_ This remarkable add-onenables you to draw on the screenusing a stylus with the touch sensitivebargain!! ONLY £1.00 pad. Supplied with 2 stylli. power/data

SWITCHED MODE PSU connecting lead & demo tape with 4Astec type AA7271. PCB 50 x 50mm progs. Contains state of the art elec-has 6 transistor cct providing current tronics. Originally being sold atoverload protection, thermal cut-out £79.95, later reduced to £49.95 -and excellent filtering. Input 8-24V but we can offer a limited quantity ofDC. Output 5V 2A. Regulation 0.2%. these brand new and boxed for just

£5.00 £19.95A pr:es Y-',,,lA vAT; just aid E1 .Et) P&P.

erda E10 M rn n. CWOL Official%Sn AccessMEW ords from schools etc. v.-4-

GREENWELD ..,Our shoo

_ mat en.-cci,x charge E10.has enormous stork, of components ads opus:

9-5.30 1,'^r, -Sat. Came and see uswELECTRONIC Send SAE for latest Ba::..,B.-r, LitCOMPONENTS 443E Millbrook Road Southampton

501 OHX Tel (0703) 772501/783740

AUDIOKITS PRECISION COMPONENTS

THE 30+30 INTEGRATED AMPLIFIER* DESIGNED FOR OUTSTAND;NG SOUND QUALITY* VERY HIGH QUALITY COMPONENTS SUPPLIED* LOW TEMPERATURE GENERATED DISTORTION* ULTRA LOW NOISE MC STAGE* STAR EARTHING - MAPPED ON PCB TRACKS* CLEAN SOUND RIGHT UP TO FULL OUTPUT* 7 SEPARATELY RECTIFIED POWER SUPPLIES GIVES OUTSTANDING STEREO

IMAGERY* LATEST KITS HAVE IMPROVED HEAT SINKS AND LOWER RESIDUAL NOISE

IMPROVED VERSION ALSO FEATURES* BULK FOIL RESISTOR IT Coefficient Sporn 'CI IN CRITICAL PLACES* HOLCO RESISTORS FOR OUTPUT TRANSISTOR EMITTER RESISTORS* POLYPROPYLENE AND POLYSTYRENE CAPACITORS* LONG LIFE ELECTROLYTIC CAPACITORS* KINtBER CABLE FOR INTERVAL WIRING* GOLD PLATED PHONO SOCKETS* EXTRA OUTPUT TRANSISTORS FOR 40 WATT OUTPUT

PRICES Standard 30+-30 kit £172 - £6 p&p = £178Standard with extra ofp transistors £185 - £6 p&p = E191Improved kit £380 - £6 p&p = £386

Export version to order with II0V or 220V primary transformers. P&P charges by quo-tation. Delivery 14 to 21 days. but can be longer as lead times for manufacture of caseor supply of some top quality parts used in improved version is much greater.

ETI VIRTUOSO PREAMP KITS. PCB'S AND ALL PARTS AVAILABLE.

oeta,.1s of Audio Kits cornponents and kits. pease send SAE '4-1 ioverseas 3 1RCs1 to:

AUDIOKITS, 6 Mid Close, Bonowash, Derby DE7 3GU. Tel: 0332 674929

Happy MemoriesPart type 1 off 25-99 100 up4116 (Pulls) 1 00 0.90 0.854164 150ns Not Texas 1.30 1.15 1.0541256 150ns 2.90 2.75 2.6041256 120ns 3.20 3.05 2.9041256 10Ons 3 75 3.55 3.4041464 120ns 3 45 3.20 2.992114 200ns Low Power 1.75 1.60 1.556116 15Ons Low Power 2.75 2.55 2.406264 150ns Low Power 3.25 2.95 2.8062256 12Ons Low Power 10.95 10.25 9.652716 45Ons 5 volt 3.20 3.05 2.952532 450ns 5 40 4.85 4.502732 450ns 3 20 3.05 2.952732A 250ns 3.95 3.70 3.502764 250ns Suit BBC 2.85 2.65 2.5027128 250ns Suit BBC 4.55 4.25 3.9527256 250ns 4.55 4.25 3.9527512 250ns 8.45 7.95 7.65

Low profile IC sockets: Pins 8 14 16 18 20 24 28 40Pence 5 9 10 11 12 15 17 24

Please ask for quote on higher quantities or items not shown.Data free on memories purchased. Enquire cost for other.

Write or 'phone for list of other items including our 74LS seriesand a DISCOUNT ORDER FORM.

Please add 50p post & packing to orders under £15 and VAT tototal. Access orders by 'phone or mail welcome.

Non -Military Government & Educational orders welcomefor minimum invoice value of £15 net.

Happy Memories (EL), FREEPOST, Kington,Herefordshire HR5 3BR. Tel: (054 422) 618

(No stamp required)

EE

March 1988

A Wolters Kluwer CompanyManaging Editor: Len SeymourPersonal Assistant: L VousdenTechnical Editor. J BuitingAdvertisement executive:Pauline O'Rourke

Editorial offices:1 Harlequin AvenueBRENTFORD TW8 SEWEnglandTelephone: 01-847 2618 (National)or +44 1847 2618 (International)Advertising: 01-847 2619Telex: 917490 (elektr g)Fax: 01-847 2610European offices:Postbus 756190 AB BEEK IL)The NetherlandsTelephone: +31 4490 89444Telex: 56617 Ielekt nilFax: +31 4490 70161Overseas editions:Pubiitron Publicacoes Tecnicas LtdaAv Ipiranga 1100, 9° anderCEP 01040 Sao Paulo - BrazilEditor: Juliano Barsali

Elektor sariRoute Nationale; Le Seau; B.P. 5359270 Bailleul - FranceEditors: D R S Meyer;G C P RaedersdorlElektor Verlag GmbHSiisterfeld-Strafle 255100 Aachen - West GermanyEditor: E J A KrempeisauerElektor EPEKaraiskaki 1416673 Voula - Athens - GreeceEditor: E Xanthoulis

Elektor Electronics PVT Ltd.Chhotani Building52 C, Proctor Road, Grant Road (ElBombay 400 007 - IndiaEditor: Surendra hirer

Elektuur B.V.Peter Treckpoelstraat 2-46191 VK Beek - the NetherlandsEditor: P E L Kersemakers

Ferreira & Bento Lda.R.D. Estefania, 32-1°1000 Lisboa - PortugalEditor: Jorge Goncalves

Ingeiek S.A.Plaza Republica Ecuador2-28016 Madrid - SpainEditor: A M Ferrer

Electronic Press ABBox 63182 11 Danderyd - SwedenEditor: Bill Cedrum

International co-ordinating& technical manager:K S M WalravenInternational editorial secretariat:G W P v Linden; M PardoDistribution:SEYMOUR334 Brixton RoadLONDON SW9 7AG.

Typeset & composed in theNetherlands by GBS, Beek (L).Printed in the Netherlands byNOB, Zoeterwoude.Copyright 1988 Elektuur B.V.

ABC

Sensors and medicine

Mention the United Kingdom Atomic Energy Authority's laboratory atHarwell to most people and they immediately think of nuclear engineeringand power stations. It would, no doubt, surprise them to hear that nuclearengineering is now but a relatively small part of the UKAEA's activities. Dur-ing the past decade, the laboratory has, in fact, become a research insti-tute for the whole of British industry, and is now one of the largest contractresearch organizations in Europe

One of the research programmes is devoted to discovering new devicesand materials for use in biosensors. These combine micro -electronics andbiochemistry to give novel types of detector. The surface of such a sensorhas to react with a specific substance to give a change that can bedetected and converted into an electrical signal.

One promising method is to mimic the human body's information trans-mission system, that is, to make an artificial nerve. The success of such adevice hinges on substances called ion gates. Normally, cells are sur-rounded by insulating membranes that exclude all unwanted molecules.Ion gates can upset this by opening up channels in the membranethrough which ions can pass. This is the crucial information transductionevent. Not only does the opening of a channel produce an electrical cur-rent (moving ions), but amplification as well. One gate can let millions ofions through at a time.

The most exciting artificial nerve sensor consists of an artificial membraneonly two molecules thick (3 to 5 nm). These form self -assembly, highlyordered systems that are very good electrical insulators. Specific detectormolecules, such as antibiotics, are incorporated into the membrane, andwhen the substances to be detected are bound to these, it is observed asa change in the gating characteristics.

One of the first uses of the Harwell device may be to detect humanpregnancy hormones; it will be possible to tell whether a woman is preg-nant much sooner than at present.

There is even greater potential for the device in other fields. As the originalidea for the sensor came from mimicking the human nerve, it seems asimple progression to create an artificial brain cell. Neuro-physiologists nowbelieve that learning and memory occur when the ionic transmissioncharacteristics of the membrane separating brain cells is semi -permanentlyaltered. Chemicals released by the body are responsible for this change,which occurs over a period of time.

This is similar to the way the new biosensor works and the way in whichfuture parallel computers may operate. if the devices are to work asmemory or switching elements, the binding of a messenger molecule to areceptor molecule in the cell membrane must be made more reversible.This is made possible by the use of artificial proteins.

The possible extension of the technology to computer and logic circuitslies outside the scope of the biosensor project, but Harwell is using its ex-pertise in computing to improve the current parallel computer processingalgorithms and is evaluating new applications in control and instrumen-tation.

V.D.rert AteerE -.SAU Caa.A.A7ONS

14 EE

March 1988

SENSORS & ACTUATORadiant, mechanical, thermal, magnetic, and chemical effects inour environment are nowadays normally detected and measuredby electronic means. The conversion of these (analogue) effectsinto (digital) electrical signals is invariably effected by sensors.

These transducers have become so important that without themlife on earth would almost literally come to a standstill.

Sensors come in a wide variety: it isestimated that there are close to 20,000different types produced by thousandsof manufacturers all over the world. Themost important types are used in thedetection or measurement of tempera-ture, pressure, gases, radiation, hu-midity, magnetism, acceleration, direc-tion, angle, flow, level, presence, pos-ition, displacement, and many more.The operation of most sensors dependson optics (lasers, optical fibre, infra -redemitters and detectors), semiconduc-tivity (photo transistors, photo diodes),thermoelectricity (thermocouples), orpiezoelectricity.The demands made on most sensors arehigh: they must be sensitive, corrosion-

resistant, inexpensive, precise, stable,easily integrated into a microelectroniccircuit, and preferably have a linear in-put/output characteristic.

Optic sensorsFibre optic sensors can be regarded ascomprising three parts: the opticaltransmitter, the optical modulator, andthe optical receiver. Each of the threeparts has one major "active" compo-nent. The transmitter has an emitter(such as the LED or a laser); the modu-lator has the stimulus sensor mechanism(such as a diaphragm or a specific op-tical property material); and the receiverhas a photodetector.The emitters employed in fibre optic sen-

A sensor, the popular name fortransducer, is a device that converts anon -electrical parameter into an elec-trical signal or vice versa. The variationsin the electrical signal parameter are afunction of the input parameter.Most transducers provide a linear,analogue output, but some provide adigital output in the form of discretevalues. Ivlost transducers are lineardevices, i.e., they provide an output thatis a linear function of the input.Like many networks, transducers may beconsidered as quadripole devices, butone pair of terminals is not necessarilyelectrical.Most transducers require external elec-trical excitation for their operation; ex-ceptions are piezo-electric, photovoltaic,and electro-magnetic sensors.

An actuator is a device that converts anelectrical signal into another form ofenergy, normally mechanical. It is thus aspecial type of transducer. Typicalexamples are loudspeakers, electronicswitches, and many measuring instru-ments.

sors can be classified as broadband (in-candescent), narrowband (LED), coher-ent (lasers), or blackbody radiators(emitting from inside or outside thefibre). The choice of which one to selectdepends solely upon the modulatormechanism being employed. For in-

stance, fluoroptic thermometers use tem-perature dependent fluorescence ofmaterials at the end of a fibre opticprobe. Many sensors for high tempera-ture measurements rely upon blackbodyradiation for ranges from 300 to 2000degrees Celsius. However, the vast ma-jority of applications use their own ex-ternal light sources in the form of anLED or a laser, primarily because of thespecific need to accurately control theemitter wavelengths, power outputs, andmodulation frequencies.Fibre optic sensors have been helpedsignificantly by developments in LEDs,super luminescent diodes (SLDs), andlasers used in the fibre optic communi-cations and optical disc industry. Semi-conductor LEDs can emit from eithertheir surfaces or their edges, dependingupon their design. Surface emittingLEDs (SLEDs) have a wide solid angleon the output beam, and the beam inten-sity is Lambertian. Edge emitting LEDs(ELEDs), on the other hand, have awaveguide mechanism inherent in theirstructure (as do lasers) and thus have anarrower Gaussian intensity beam.An SLD lies midway between an LEDand a laser. It possesses only a singlepass gain. As the current density is in-creased, even though an SLD shows agreater (super) luminescence than anLED, it still does not reach the thresholdfor multiple pass gain. However, becauselight is designed to undergo a single passin the active area of the SLD, its spec-trum is narrower than the LED's.

TABLE 1.

Comparison of Surface LEDs (SLEDs), Edge LEDs (ELEDs). SLDs, and Lasers

Characteristics SLED ELED SLD LaserSpectral width (nm) 80-100 75-80 10-20 0.8-2.5Typical optical power output(mW) at 100 mA (except lasers) 0.5-0.75 0.4-0.5 0.6-0.8 5-10Coupling efficiency of opticalpower into fibers Mediocre, needs lensing Small Better BestResponse time Ins) 10-50 5-15 5-15 1-2.5Stability to ambient temperature Least changes Sensitive Sensitive Least sensitiveLifetime expectancy in years 1000 1000 100 100Package options- Lenses Yes No No Special cases- Fibre connectors Yes Yes Yes Yes- Fibre pigtail Yes' Yes Yes Yes- Thermoelectric coolers &stabilization modules No Seldom needed Special cases For all critical

applications

The amount of power an emitter needsto generate for a fibre optic sensor appli-cation is a function of several design fac-tors. The power from an emitter mustfirst be transferred into an optical fibre.In many cases, it must be tailored ap-propriately (e.g., through a polarizer, asin the case of a fibre gyroscope) prior tosuch introduction.LEDs, SLDs, and lasers are not onlymade of the same semiconductormaterials but also have the same basicdevice structure. In principle, these semi-conductor devices have a p -n junction,which upon being forward biased leadsto a recombination of holes and elec-trons with the simultaneous emission ofphoton energy. The wavelength of thisemitted light is in turn governed by thecomposition of the semiconductor ma-terial. Thus, the amount of aluminiumdetermines the center wavelength of theemitted light.LEDs, SLDs, and lasers are in an as-cending order of sophistication (seeTable 1). An SLD can be regardedlas anemitter that is half -way between an LEDand a laser. An LED produces spon-taneous emission in its "active" regionand thus has a wide spectrum about acentral wavelength. A laser has a built-inmechanism in its structure so that lightproduced in its active region is made tooscillate between its specially designedfront and back facets, thus leading to aprimary wavelength or mode of oper-ation.An important application of the opticsensor is in robotics, since it makes poss-ible artificial vision, without whichrobots can not reach their full potential.Another application of the optic sensoris in seam tracking and process controlin arc welding. The sensor is inherentlyinsensitive to the arc light.An interesting application is the oxygensensor that measures oxygen saturationin the human blood so as to control therate of a pacemaker. The sensor is inte-grated in the stimulation catheter andlocated in the right ventricle of the heart.A new line of intelligent sensors prom-ises to rid cars, buildings, aircraft, andfactories of most of the increasinglycomplex wiring. One of these sensorsuses a multiplexable optical encoder chipproduced for Honeywell by its Optoelec-tronic Division in Richardson, Texas.This chip combines sensors and ana-logue and digital circuits on a singlewafer. The on -chip sensors can deter-mine direction or rotation, rotationalvelocity, and angular position.A new technique to measure physicalcorrelations in multi -use fluid transpor-tation systems has been developed by theBerg Akademie Freiberg in FederalGermany. In this, fibre optic probes areused to accurately measure particle con-centration, fluctuation, speed, size, andcross-sectional distribution - all criticalin process control and regulation.

Among the measurement said to bepossible with the system are impurities inwater, organic or inorganic liquids, gasbubbles in liquids, crystals in saturatedsolutions, and flocculants in pipes andother apparatus.Japan's Sofia University has developedan optic sensor that controls on -offswitching for use in optical computers.The optical switch needs no electric cir-cuits, since the optical signals are con-trolled by light beams. Remote controland information exchange are possible.The development is expected to ac-celerate the development of optical in-formation processing technology, whichforms the basis of optical computers andoptical communications.

Semiconductor sensorsSemiconductor sensors have two import-ant advantages over other types: they areinvariably produced from silicon, whichis a plentiful and well -researchedmaterial, and they can easily be inte-grated with amplifier and logic circuitsonto a single wafer.These sensors are normally encounteredin the form of photo transistors or photodiodes. A photo transistor is a detectorthat consists of a bipolar junction tran-sistor operated with the base regionfloating. The potential of the baseregion is determined by the number ofcharge carriers stored in it. The elec-tromagnetic radiation to be detected isapplied to the base of the transistor andproduces the base current. The transistoris operated essentially in a common -emitter configuration.A photo diode produces a current whenit is illuminated. There are two mainclasses of photo diode: depletion -layerand avalanche. Depletion -layer diodesconsist commonly of a reverse -biased p-it junction operated below the break-down voltage. The p-i-n and Schottkyphotodiodes are versions of the de-pletionlayer type. Avalanche photodiodes are reverse -biased p -n junctiondiodes that are operated at voltagesabove the breakdown voltage.Sensors for the detection of gases arenormally manufactured from othersemiconductors materials, such as tinoxide, zinc oxide, titanium oxide, andothers.

Thermocouple sensorsThermocouple sensors depend on thephenomenon that when two dissimilarmetals are joined at each end and thetwo resulting junctions are maintained atdifferent temperatures a voltage is devel-oped between them. Copper-constantanor iron-constantan thermocouples canbe used up to 500 °C. Temperatures upto about 1500 °C may be measured withthe aid of a platium/platinum-rodium

EE

March 1988

alloy thermocouple, and even highertemperatures may be measured with anirridium/irridium-rhodium alloy ther-mocouple.

Piezoelectric sensorsWhen certain materials are subjected tomechanical stress, an electrical polariz-ation is set up in the crystal and the facesof the crystal become electricallycharged. The polarity of the chargesreverses if the compression is changed totension. Conversely, an electric field ap-plied across the material causes it to con-tract or expand according to the sign ofthe electric field.Piezoelectric sensors are important sincethey couple electrical and mechanicalenergy and, therefore, are used asgramophone pick-ups, loudspeakers,microphones, to name but a few.

Practical applicationsTemperature sensors. As already men-tioned, many temperature sensors arebased on the Seebeck effect that occursin a thermocouple. They are normallyproduced in the shape of a probe: a widevariety of such probes is shown in Fig. 1.

\

Fig. 1. A selection of thermocouple tempera-ture probes. (Photograph courtesy OmegaInternational Inc.)

Another well-known type of temperaturesensor is the thermistor. This is basicallya resistor, made from semiconductormaterial, that has a negative temperaturecoefficient. This means that when theambient temperature rises, the elementbecomes more conductive (its resistancedecreases) and the consequent change involtage across it is a measure of the tem-perature rise. It should be noted thatthere are also thermistors with a positivetemperature coefficient, whose resist-ance, therefore, increases when the tem-perature rises.Temperature may also be measured by

16 EE

March 1988measuring infra -red (heat) radiation, forwhich an infra -red sensor as shown inFie. 2 is used. This technique, called

Fig. 2. Typical infra -red sensor.

thermal imaging or thermography, isbased on the property that each body orobject radiates heat. The technique, forwhich a camera with a suitable lenssystem may be used, does not requireany external source of illumination. It isused, for instance, in production tests todetermine whether any component heatsup too quickly (and is, therefore, almostcertainly faulty). It is also used inmedicine for diagnostic purposes todetermine whether any areas of the bodyhave an unusual temperature distri-bution.

Pressure/force sensors. Although thereare various methods of measuringpressure and force, the most commonone makes use of the piezoelectric effectas discussed earlier in this article. Themost widely used material for themanufacture of pressure/force sensors isquartz. This material has some import-ant advantages over others: (1) it isstrong; (2) it is cheap; (3) it is a goodelectrical insulator so that the electriccharge caused by the pressure collapsesonly slowly.

Fig. 3. Constituent parts of a piezo-elcctricpressure sensor. (Photograph courtesyTelefunken AG).

The parts making up a typical piezoelec-tric sensor are shown in Fig. 3. It con-sists of a wafer of silicon only 1 mm indiameter, onto which a tiny piezoelectric

crystal and four resistive tracks havebeen etched with the aid of ion implan-tation. When pressure distorts thecrystal, the resistance value of one ormore of the legs of the resistance bridgechanges. This type of sensor is versatile:it can be used for measuring absolute orrelative pressure, overpressure, andpressure difference. It is suitable forpressures up to 40 MPa.This type of sensor is, of course, widelyused in all sorts of weighing machine.Other areas of use are hydraulics, waterworks, refineries, filter plants, pressurechambers, and loudspeakers.Pressure sensors are also used in ac-celerometers, but there they operatesomewhat differently. Such a sensor formeasuring mechanical vibrations or im-pact contains a freely moving seismicmass and a piezoelectric element (nor-mally quartz)-see Fig. 6. When theseismic mass is accelerated in the direc-

1 metal base at enclosure2 Au-Sn solder joint3 silicon substrate

metal plate5 silicon substrate6 silicon epitaxial layer

(pressure -sensitive membrane)7 implanted resistor8 silicon oxide9 silican nitride10 metal block11 CVO nitride12 aluminium banding wires13 cavity; force compensation to

rear side of enclosure

Fig. 4. Construction of a typical piezo-electric pressure sensor. (Courtesy SiemensAG).

Lion of its axis, it exerts a force onto thequartz element that is proportional tothe acceleration. The element is then dis-torted and the consequent piezoelectricvoltage is used to charge a capacitor.This charge can be measured, but thishas to be done quickly as otherwisesome of the charge leaks away. At fre-quencies below the resonant frequencyof the sensor, the seismic mass followsthe vibrations faithfully. This type ofsensor usually contains an integratedpreamplifier.

Humidity sensors. Humidity sensors areused almost exclusively in hygrometers,

Fig. 5. A selection of typical pressure sensors.(Photograph courtesy Bruel + Kjaer).

i.e., instruments for measuring thehumidity of air. In the past, these sen-sors used a human hair, or a strand ofsilk, but nowadays they use a capacitor,a dew point mirror, or optical means.The dew point mirror sensor depends onthe effect that when a smooth surface iscooled it mists up. The moment thismisting up starts is determined optically.Since it is accurately known at whichpressure and temperature gases con-dense, this technique yields very accurateresults.Another type of dew point sensor con-sists of a very small wafer of resistivematerial which has been coated with ahygroscopic chemical. The wafer is fittedwith two electrical terminals. When mistforms on the coating the resistance ofthe wafer increases. This type of sensoris quite vulnerable, but because of itsvery small dimensions, it is used inSony's 8 mm Camcorder.Optical humidity sensors make use ofthe property that gas molecules absorbenergy at certain frequencies: watervapour does so in the infra -red region. Itis thus possible with the aid of an infra-red sensor to determine how muchenergy is absorbed. The higher thehumidity, the more energy is absorbed.This technique has the disadvantage thatthe infra -red sensor soils up easily andthen becomes unusable.Nowadays, the most important and best -value -for -money type of humidity sensor

Fig. 6. Construction of accelerometer sensor.M=seismic mass; P= piezo-electric element;B=underside; R=initial tension. (CourtesyBruel + Kjaer).

EE 111March 1988

Fig. 7. These twin axis gyros belong to arange of inertial sensors that includes rapidstart coasting displacement gyros, rate gyros,Dynamically Tuned Gyros, and linear ac-celerometers. (Photograph courtesy BritishAerospace).

high-grade steel membrane

high-grade steel enclosure

oil

silicon bridge circuil

sealing robber

666023 -6

Fig. 8. Construction of a combined pressureand temperature sensor. (Courtesy Sen-sortechnik Widemann).

Fig. 9. Selection of EPI Series pressure pro-bes. (Photograph courtesy Entran Ltd).

Fig. 10. Some tiny semiconductor humiditysensors. (Photograph courtesy VolvoPhilips).

is based on a capacitor. This is, ofcourse, a special capacitor which as adielectric that is sensitive to humidity. Inthe Valvo sensor-see Fig. 10-thedielectric is in the form of a foil that hasbeen coated at both sides with gold,which forms the electrodes. Humiditychanges the dielectric constant of thefoil and thus the capacitance of the ca-pacitor. Since this capacitor forms oneof the legs of a capacitive bridge, thechange in capacitance can be readilyconverted into an electrical voltage.

Gas sensors. As -stated before, gas sen-sors are normally based on a variety ofsemiconductor materials. Such materialshave the property that their resistancedecreases when certain gases are presentin the surrounding air. This effect iscaused by adsorption of gas moleculeson the surface of the semiconductormaterial. The consequent layer of gasmolecules influences the conductivity,and thus the resistance of the element.These sensors are very sensitive: concen-trations of only 1 ppm of the relevantgas in air are readily detected.A variant of this type of sensor isTelefunken's ISFET-see Fig. 12.Basically, this is a modified MOSFET inwhich the usual metal eate has been re-placed by a layer that reacts to the ionsof certain gases. ISFETs are un-breakable, small, have a low -impedanceoutput, have a large linear range of oper-ation, are temperature compensated,and provide an output signal that issuitable for driving a microprocessor.Many gas sensors still depend (and willcontinue to do so) on a chemical reac-tion to generate an electrical voltage,current, or resistance change. Yet othersensors use the heat generated by thecombustion reaction when a gas hits thesurface of the sensor. This heat is ap-plied to a platinum wire whose resistancethen changes.There are also optical gas sensors andthese are used particularly for the detec-tion of fire or smoke. They normally usea photo diode or photo transistor tomonitor the light absorption behaviourof the surrounding air. When smokedarkens the air, the photo transistorswitches off and this operates an appro-priate actuator.

Light sensors. Popularly probably thebest known type of sensor is the lightsensor. This can be based on a photo di-ode, photo transistor (see Fig. 13), p-i-ndiode, photo varistor, or solar cell. Allof these are made from the samematerial, silicon, and function in similarfashion at wavelengths from about400 nm to around 1000 nm.Photons enter the silicon and cause anumber of electrons to jump to a,differ-ent energy level. This in turn causes aphoto current which can be used tooperate an actuator.

Fig. 11. Some typical gas sensors. (Photo-graph courtesy Dragenverk AG).

Cartsci elect-rdE

Ilmnnul

Fig. 12. The ISFET is a modified MOSFETused as a gas sensor. (Courtesy TelefunkenAG).

Fig. 13. Some typical photo transistors within the centre an infra -red photo diode.

For wavelengths below 400 nm (ultra-violet light), photomultipliers are used.These are normally constructed as avalve and have the usual advantages ofelectron tubes: good bandwidth, lownoise factor, high amplification.Primary electrons, emitted from the

18 EEMarch 1988

cathode as a result of photon bombard-ment, are accelerated by the field be-tween anode and cathode and arrive atthe anode with great energy, causing acurrent in the anode circuit. The anodecurrent is much greater than the originalcathode current, whence the namephotomultiplier.Photo detectors as described were alsoused as light sensors in camera tubes,but nowadays they are largely super-seded by CCD (charge -coupled device)sensors, particularly in video cameras,medical cameras, and robotics. CCDsare small: typically, one the size of a 28 -terminal IC has a resolution of 60,000

Fig. 14. Photo diode used as a gas sensor.(Photograph courtesy Plessey Semiconduc-tor).

elements. Each of these elements con-sists of a photo diode with a light-sensitive area of only a few micrometres.Each photo diode is accompanied by aMOS capacitor that stores the generatedphoto electrons. The charge on thecapacitors is read at regular intervals bya shift register. Suitable circuits inte-grated on the device process the infor-mation to a suitable level for driving amicroprocessor.

Biological sensors. During the past fewyears, a new type of sensor has enteredthe fields of biology and medicine.These so-called biosensors consist ofbiological molecules, such as enzymesand antibodies. When such sensors reactto other substances, a small electricsignal is generated that can be detectedwith the aid of a suitable electrode(probe).

Remote sensing. Another interesting newfield where sensors are indispensable isthat of remote sensing. This exciting newtechnique has been made possible by theroutine availability of satellite infor-mation for the entire surface of theearth. Remote sensors on board satellitesprovide digital data in seven wavebandsof visible light, reflected infra -red radi-ation, and thermal infra -red radiation.Different surfaces reflect differentamounts of radiation, which is why theyappear in different colours and light in-tensities to us. In the same way that wedistinguish objects by their appearance(but in a more sophisticated manner),these remotely sensed images can beused to identify the land -cover typeswhich exist in an area. Since they recordin the infra -red region, many things wecannot normally see are shown. Cropcondition and the thermal properties ofbuildings or water can be 'seen' anddisplayed, for instance.Remote sensing enables scientists tostudy the earth's surface on a scalewhich was until recently only dreamedof. For a very small part of the time itwould take to survey a large area by con-ventional methods, digital informationcan now be used to identify and measurethe extent of crop types, major landuses, soils, properties of water bodies,geological structures, and vegetationconditions. In sparsely populated areas,the existence of certain surface featuresis being established for the first time,and over all areas of the world, whatwere previously partial surveys can nowbe completed. A great attraction ofremote sensing is the relatively low costof large-scale surveys. For instance, im-ages with ground resolution down to

Fig. 15. The DART (Dual Axis Rate Trans-ducer) is a miniature gyro particularly suitedfor stabilization of laser, infra -red, and radarseeker systems. The sensor, which is only40.6 mm long and has a diameter of 18 mm.uses a rotating piezo-electric crystal to sensethe applied rate. (Photograph courtesyBritish Aerospace).

10 m and covering 50 km x 50 km canbe obtained for less than £1,000.Much pioneering work on remote sens-ing has been carried out in Britain bySalford University.

A final thought. Although the scienceand technology of sensors and actuatorshas made vast strides in the past fewdecades, the most complex, reliable, andversatile sensor system remains man.Coupled with his intelligent data pro-cessing unit which almost certainly willnot be emulated during the life ofanyone alive today, he forms a for-midable system of intelligence. A pity wedo not always appreciate it.

We acknowledge with thanks the co-operation and help received from the fol-lowing organizations in the preparationof this article: British Aerospace; Bruel

Kjaer; Drdeerwerk AG; Entran Ltd;Hawker-Siddeley; IGI Consulting Inc.;Omega International Corporation;Plessey Semiconductor; Salford Univer-sity; Sensortechnik Wiedemann;Siemens AG; STC Mercator; Telefunken;Valvo Philips.

Anglo-Japanese agreementA formal trade agreement was signed re-cently between Fujisoku Electric ofJapan and Arrow Hart (Europe) Ltd, thePlymouth -based manufacturer ofspecial-purpose electrical components.Under the agreement, Fujisoku, aleading Japanese switch manufacturer,will purchase rocker switches fromArrow Hart and sell them on their homemarkets.

EE

March 198819

EVENTS EVENTS EVENTS EVENTS IEE meetings this month1 Recent developments in digital NDT

equipment design.2 Home automation.8 Control problems of spacecraft -

past, present, and future.8-10 Digital communications*.11 Mobile radio networks.16 Advances in sensors in biotech-

nology.18 Solid-state and smart sensors.21-24 Video, audio, and data recording.28 Expert systems in process control.Full details from The Institution of Elec-trical Engineers Savoy Place LON-DON WC2R OBL Telephone 01-2401871, except:* Secretariat IZS 88 Hasler AG TDS1 Belpstrasse 23 CH -3000Bern 14 Switzerland.

Electro-optics and Laser ShowAt the national Exhibition Centre, Birm-ingham from 22 to 24 March. Furtherdetails from Cahners Exhibitions Ltd Chatsworth House 59 London Road TWICKENHAM TW1 3SZ Tele-phone 01-891 5051.

InternepconAt the National Exhibition Centre,Birmingham from 22 to 24 March. Fulldetails from Cahners Exhibitions Ltd Chatsworth House 59 London Road TWICKENHAM TW1 3SZ Tele-phone 01-891 5051.

CADCAMAt the National Exhibition Centre,Birmingham from 22 to 24 March. Fulldetails from EMAP International Exhi-bitions Ltd Abbot's Court 34 Far-ingdon Lane LONDON EC1R 3AU Telephone 01-608 1161.

European & NationalStandardsThe third of a series of seminars organ-ized by BEAMA on the theme Europeanand National Developments in Qualityand Standards - Opportunity or Threat?will be held at the Selfridge Hotel, Or-chard Street, LONDON WI on 22March. It will be addressed by theMinister of Trade and Industry, the RtHon Kenneth Clarke, QC, MP.

Further details from BEAMA 8Leicester Street LONDON WC2H7BN Telephone 01-437 0678.

ICS courses this monthFibre optic communications 8-11 Parisand 15-18 London Integrated voice/datacommunications and ISDN 15-18 Paris.Details from ICS Publishing CompanyLtd Telephone 0800 282 353 (UKonly) or +44 372 379211 (outside UK);France: Integrated Computer Systems Telephone (I) 48 39 88 00.

Frost & Sullivan events thismonth (all in London)7-9 Artificial Intelligence14-16 Voice Processing21-23 An Introduction to Data Com-

municationsFrost & Sullivan Ltd Sullivan House 4 Grosvenor Gardens LONDONSW1W ODH Telephone 01-730 3438.

TO BE PUBLISHEDTHIS SPRING

Two new books from ELEKTOR ELECTRONICS

DATA SHEETBOOK 2

DATA SHEET BOOK 2ISBN 0 905705 27 0Price £8.25This book contains data on ICs as wellas on discrete transistors and diodes.Moreover, it gives an introduction tofast (HCMOS) devices and a review ofsymbolic logic as proposed inBS3939:Section 21.

MICROPROCESSORDATA BOOK

MICROPROCESSOR DATA BOOKISBN 0 905705 28 9Price £8.95This reference book gives a generaldescription, hardware block schematic.software structure. DC characteristics,and instruction sets for over 70 micro-processors.

RDPTransducer

Indicators

turn any transducer intoa measuring system

* Direct digital readout in engineeringunits

* Analogue and BCD outputs* High and low-level trips* Bench or panel mounting* Many options

RDP Electronics Ltd.GROVE STREET, HEATH TOWN, WOLVERHAMPTONUNITED KINGDOM. Tel: (0902) 57512.Telex: 335430 RDP-G.

20 EE

THE REASONS FOR MTVATURETRANSDUCERS

A statement made by a senior engineerin the aircraft industry recently summedup some of the reasons why many in-dustries have turned towards the use ofminiature transducers. "Years ago ouraircraft engine control electronics werethe size of a small suitcase but today thetotal package size has been dramaticallyreduced. This obviously means thatwhen we are testing these components,particularly for important vibrationtests, that the additional weight that weadd by employing transducers on to theunit can, if the size, and hence weight,are not minimal, completely change thetest performance. We must thereforelook for transducers, in this particularcase accelerometers, with the smallestpossible mass".The simple but important rule that ap-plies here is that F=m x a. Hence theadditional force that is applied to theitem under vibration test is dependent onthe mass and the distribution of mass inthe overall dimensions of the transducer.For instance, suppose that a conven-tional sized accelerometer is used for thevibration test. If it weighs 100 grams andis being used for 100 g acceleration, bycalculation in the F=m x a formula, afurther 10 kg is added to the weight ofthe component under test. This will con-siderably distort the results of the vi-bration tests.Entran designs and manufactures piezo-resistive semiconductor strain gage ac-celerometers which have the capabilityof measuring both steady-state dc andhigh response dynamic vibration inputs.The EGA range offers models withmeasuring ranges from 0-5 g up to 0-5000 g within a housing as small as0.140 x 0.140 x 0.270 in. (3.4 mm x3.5 mm x 6.75 mm) and weighing aslittle as 0.5 grams. The EGA Series hasthe desirable feature of fluid damping toprotect against resonant excitation. TheEGAX model the additional feature ofinternal overrange stops which give theaccelerometer the capability of acceptingan overload of ±10,000 g in either thenormal sensitive acceleration measuringaxis, or in all directions. This feature isavailable even on the lowest measuringrange of ±5 g. Not only will this over -range feature make the accelerometersuitable for many impact and guidanceapplications, but it will also protect avaluable measuring transducer fromday-to-day mishandling on the work -

, I

by Mike Coope-

shop floor where accidents will unfortu-nately happen.These particular features of low massand high overrange of the EGAX ac-celerometers have proved beneficial to aparticular area of research in the medicalfield. Various departments of MedicalEstablishments have the need to studythe features of muscular tremours anddiseases such as Parkinson's disease.With patient involvement, the need is foran unobtrusive and small vibrationmeasuring device to monitor themovements of the patient's limbs thathas the capability of withstandingseveral thousand 'g' should the acceler-ometer be inadvertently dropped to thefloor. This specification exactly fits theEntran EGAX Series of accelerometer,which has been used for many years byseveral Medical Establishments.Entran designs and manufactures a var-iety of semiconductor strain gauges, ofwhich the smallest is active over 0.020 in.(1.50 mm) length by 0.006 in.(0.150 mm) width. The distinct advan-tage of these resistive sensing elements is(a) their micro -miniature size and (b)their extremely high gauge factors. Theterm gauge factor (GF) is a measure ofthe incremental change in the resistanceof the strain gauge for a given incremen-tal change in the active length of thegauge, i.e. GF = AR/AIHence, gauge factor is a measure of thesensitivity or output performance of thestrain gauge. To give a comparison, stan-

:EGA

dard foil strain gauges typically have agauge factor of 2.0, whereas that for asemiconductor strain gauge can betypically 150. This means that whensemiconductor types are used, we can ex-pect improvements of outputs in theregion of approximately 75 times. En-tran takes full advantage of theseproperties of their strain gauges in theirextensive range of miniature transducers.In the accelerometer (Fig. 1) straingauges are bonded in pairs to the topand bottom surfaces of a single degreeof freedom cantilever beam. A mass isattached to the end of this beam and theresulting deflection of the beam whenexperiencing a 'g' force results in a linearsignal output when the strain gauges arewired into a Wheatstone bridge and anexcitation voltage is applied (Fig. 2).

The advantages of strain gauge proper-ties are also used in miniature pressuretransducers (Fig. 3) where the parameteris sensed by monitoring the deflection ofa metal diaphragm. To achieve thehighest possible dynamic response, thediaphragm must be small and its de-signed full scale deflection minimal.With their inherent high sensitivity andultra -miniature size, semiconductorstrain gauges can be used on a stiff, lowdeflection diaphragm to achieve thiscriterion. A further advantage of theminiature diaphragm is its low deflec-tion, resulting in low stress levels withinthe diaphragm material, and hencealmost infinite fatigue life. Thus Entranpressure transducers offer measurementof both static and high frequencydynamic inputs.The smallness of pressure has an import-ant bearing on their performance. Sizecan also be important on the overall ef-fects of the test. For instance, in thetesting of the aerodynamics of scalemodels of new military and civil aircraft,automobiles, aircraft components such

as helicopter blades, missiles, and gener-ally all transport where the efficiency ofmovement is important, the transducermust be as unobtrusive as possible so asnot to alter the original shape of the testpiece. Entran have ultra -miniature trans-ducers of low profile designs (EPL) witha thickness of 0.040 in. (1.02 mm),which are used in a recessed mourning togive original aerodynamic flow lines ofthe test model. Alternatively, all EntranEPI pressure transducers are availablewith diameters from 0.080 in. (2.03 mm)down to 0.050 in. (1.27 mm) and areused in many wind tunnel tests becausethey can be easily accommodated withinthe rivet head of an aircraft structurewithout affecting the structure and pat-tern of the normal air flow.Entran's specialization is in the designand manufacture of miniature trans-ducers for the measurement of acceler-ation, pressure, load and strain, butmany other models have been developedwith the requirements of Entran's cus-tomers in mind. Although standardmodels exist, it is accepted that many

transducer requirements fall outside thenormal specification and, for these situ-ations, Entran has special engineeringfacilities to provide the low-cost OEMstyle transducer or the ultra -sophisti-cated, latest -technology, quality -assuredtransducer.

EE 1/1March 1988

Within this framework of adaptation tomarket requirements, Entran offer arange of accelerometers and pressuretransducers which are the outcome oflong experience of transducer design.The new range of devices offers robuststyling, both internally and externally, aswell as the optional addition of internalminiature electronic circuits to give (a)amplified output up to 10 V FS; (b)supply regulation; (c) custom filtering.This short article emphasizes a few ofthe aspects that miniature transducerscan play in the latest fields of industrial,research, medical, aerospace, chemical,automotive and many other industries.Further information on ENTRAN sen-sors may be obtained from ENTRANLtd Sales & Technical Centre 5 Albert Road CROWTHORNERGI1 7LT Telephone (0344) 778848 Telex 847422 Fax (0344) 777991.

* Mike Coope is Technical Sales Directorof Entran Ltd.

COMPONENT NEWS

Thirty million TDA4600sSeven years ago, Siemens found a way ofintegrating the control circuit for switch -mode power supplies used in TV sets ona single 7 mm' chip. Since then, salesfigures have reached 30 million for thebipolar TDA4600 and 10 million for theTDA4601 version (with extended voltagerange: 80-270 V).Its ability to produce the requiredvoltages at varying input voltages andloads in an economical way has madethe TDA4600/4601 the unrivalled topproduct on the market, favoured bymore than 200 customers throughout theworld. An enhanced version, theTDA4605, using "Sipmos" transistorshas now reached the production stage.As early as 1972, engineers at the Appli-cations Research Laboratories ofSiemens had conceived the idea of usinga flyback converter as a power supply forTV sets. Until then, the standard prac-tice had been to provide a rigid, andcost -intensive, coupling with the line fre-quency circuit. The introduction of theflyback converter drastically reduced thecircuitry and components. The inte-gration of the entire control circuit onthe TDA4600 further simplified thepower supply section in the TV set. Theimproved reliability of power suppliesequipped with the TDA4600 is reflectedin the significant reduction in TV setfailures over the past several years.

Roxburgh Electronics becomeAlps distributorFollowing an agreement with ArmonElectronics LTD-official UK agents forAlps Electrical Company, Japan'slargest independent componentsmanufacturer -Roxburgh Electronicshave been appointed nationwidedistributors for the comprehensive rangeof Alps products.Further information from RoxburghElectronics Ltd 22 Winchelsea Road RYE East Sussex TN31 TEL

Telephone (0797) 223777.

Prototyping kit for membranekeyboardsNew from Highland Electronics is theDMC DT series of 'do-it-yourself'prototype keypad kits which contain allthe parts necessary to build a customisedmembrane switch/keyboard panel.Available in 4, 12, 16, 40, 80 and 102QWERTY key configurations, the kit in-cludes the basic switch unit, graphicsoverlay, colour pad, connector, bezel,and face plate. Options include drytransfer lettering to add numbers, letters,of function keys, depending on theuser's applications.The DT series of kits. is offered in achoice of key colour and lettering styles.Switch technology used in the keyboardscombines low cost with high reliabilityand tactile feedback is provided by astainless steel dome under each key pos-ition. Seven types of standard, switchlayouts can be cut into different con-figurations without disabling the re-maining keys.

The switches have been successfully triedand tested to over three million oper-ations at 24 VDC/5 mA.The DMC DT prototyping membranekeypad kit is available ex -stock fromHighland Electronics Ltd. AlbertDrive BURGESS HILL RH15 9TN.Telephone: (04446) 45021.

Liquid level sensorsGentech International have extendedtheir proven range of versatile liquidlevel sensors with a new externally fittedversion which is simply and economi-cally mounted using a compressiongrommet.

Externally assembled, with no awkwardthreading of cables through tanks, andfitted through a simple hole without athreaded flange or boss, this givessignificant potential for cost savings,particularly when mounting into lowcost plastic tanks with poor internal ac-cess.Gentech International LtdGrangestone Industrial Estate Girvan Ayrshire SCOTLAND KA26 9PS.

Telephone: (0465) 3581.

111

INFRA -RED DETECTOR FORALARM. SYSTEMS

As a follow-up to the design abstract on the Type PID-11 published last year ('), this article describes aversatile infra -red sensor which will find many applications in security and alarm systems.

The Type PID-11 infra -red sensor fromSiemens introduced in reference 1" is aversatile component that lends itself tobuilding a simple, yet effective and sensi-tive, transducer that detects heatemanating from mammals. To be able tounderstand the basic operation of thecircuit shown in Fig. 1, it is rec-ommended to read the sections Appli-cation tips and Some suggested circuitsin reference (".The infra -red sensor, ICz, is powered bya regulated 5 V supply. The referencevoltage available on pin 4 (2.2 V) is ap-plied to opamp Ai for comparison withthe voltage at pin 3. The voltage on pin2 of the comparator is held slightlybelow the reference with the aid ofpotential divider Ri-R2. In the non -activated state of the circuit, the outputof Ai is, therefore, high. When thesensor detects infra -red radiation, how-ever, the comparator supplies a short,low, pulse. Opamp A2 functions as amonostable multivibrator (MMV) and abuffer whose gain depends on the am-bient light intensity measured byphototransistor Ti. The triggerthreshold of Ai can be adjusted withpreset PI. The preset in network C5 -R5 -P2 at pin 6 of A2 enables adjusting the

mono time of the MMV, i.e., the holdtime of the circuit. Incident daylight onphototransistor Ti effectively raises thetrigger threshold for the MMV, andhence ensures automatic disabling of thealarm by reducing its sensitivity. Pins 5and 6 of the monostable are logic high inthe non -activated state of the alarm.When the PID-I 1 senses the infra -red

component in heat emanating from amammal, the voltage on pins 5 and 7 ofA2 drops abruptly to practically nought.The voltage on C5 is no longer main-tained by Di, and the capacitordischarges. At the end of the dischargeperiod, the monostable reverts to its in-itial state. Opamp A2 supplies a digital(TTL compatible) switch pulse at outputDIG. . The function of relay driver T2and alarm indicator 11 is self-evident.The maximum on -time of the relay thatcan be set with P2 is about 1 minuteafter detection of any single alarm pulsefrom the detector.

Construction, adjustment andapplicationsThe printed circuit board shown in Fig.2 holds all the components in the circuitdiagram, and so enables ready construc-tion of the compact detector unit. Thecompleted board is shown in Fig. 3.

1

ElAt, A2 .1C1 = TLZ72C01.1:12. IN41411

SV

Fig. 1 Circuit diagram of the PID-11 based infra -red detector for alarm systems.

EE 1/1March 1988

Note that the top of the phototransistor,Ti, and that of the alarm indicator, D3,is level with the top of the PID-11. Relaydriver T2 and regulator IC3 do not needheat -sinks. The completed board can befitted in a water resistant, strong ABSenclosure, with suitable grommets, strainreliefs and sockets for the connection ofthe wires for the relay, the mains, and thedigital output, if used.When the circuit is used as an automaticporch light controller, it is recommendedto fit it in a sheltered position over thefront door, paying due attention to safeand sound insulation. In many cases, itmay be safer (and cheaper) to use aseparate 8 V AC adaptor plugged into amains outlet in the home, rather than thePCB mounted mains transformer, Tn.The adjustment of the circuit, i.e., thesensitivity and the relay on -time, isgoverned by the application in question.Initially, it is recommended to test thecompleted circuit by adjusting Pi suchthat the circuit is just off in the absenceof an infra -red source. For this adjust-ment, it is necessary to temporarily coverthe phototransistor against incidentlight. The value of tantalum capacitorCs may be increased when the maxi-mum relay on -time of 30 to 60 secondsis too short for the given application. Itshould be noted that the PID-11 signalsdetection of an infra -red source by anoutput pulse of about 1.5 s rather thanby a continous logic level. The pulse,which can be measured on the output ofAi and A2, is positive or negative, in-dicating a cold -to -warm or a warm -to -cold transition, respectively.When fitting the IR detection unit, it isimportant to ensure that it can not detectheat from external sources (sunlight,heating systems, etc.). Also note that thesensitivity of the IR detector depends onthe ambient temperature. Strong mag-netic fields may cause interference in thesensor and hence spurious operation ofthe alarm. Finally, be sure to avoidoverloading the relay contacts byswitching too heavy loads. St

Reference:

(" Design abstracts: Passive infra -reddetector 73pe PID-11. Elektor Elec-tronics, March 1987, p. 24 ff.

Siemens distributor in the UK is ElectroValuelimited 28 St Judes Road EnglefieldGreen Egham Surrey TW20 OHB. Tele-phone: (0784) 33603. Telex: 264475.Northern branch: 680 Bumage Lane Manchester M19 1NA. Telephone: (061 432)4945.

Fig. 2 Track layout and component mounting plan of the PCB for buildin.. the IR detecwr.

Parts list

Resistors (±5%):

RI =2K2R2= 33KRa;R4=10KR5= 100KRs= 1K5R7 =680RRs = 390RRs=1MO131;132=4701( or 500K preset for horizontalmounting

Capacitors:

Cr =470p; 25 VC2=10p; 16 VC3= 220nC4 -100nCs = 15p; 16 V bead tantalum

Semiconductors:

Bi=840C400 or B40:01000DI;D2=1N414803= red LEOD4= 1N4001Ti =19103-3T2=BD140'Cr =11.272C or TLC272IC2=PID-11 (Siemens)IC3= 7805

Miscellaneous:

Fr = 50 mA delayed action fuse with PCBmount holder.

TRt = PCB mount transformer: 8 V; 150 mA.net = PCB mount SPDT relay; 5 V; e.g.Siemens V23127 -8001-A101.

2 -way PCB mount screw terminal.3 -way PCB mount screw terminal.PCB Type 87067 (available through the Readers

Services).

Fig. 3 The completed circuit board ready for fitting in the ABS enclosure.

24 EEM 88

A 756 -COLOUR ADAPTER FORTHE EGA

by Peter Balch

The IBM-PC enhanced graphics adapter (EGA) can display amaximum of 16 colours at a time. For many applications, such asthe creation of realistically shaded three-dimensional images, this

is simply not enough.

The 256 -colour board described in thisarticle is offered as a design idea to ad-vanced users of the IBM-PC XTequipped with an EGA. The extensionboard plugs into the EGA feature con-nector. It produces analogue RGBsignals, and TTL-level Hsync and Vsync.Many popular colour monitors accepteither TTL signals from the EGA, orRGB signals from the 256 -colour board,and can, therefore, be used both for thenormal EGA modes and the new 256 -colour modes.By default, the colour extension board isinactive, and the EGA works as normal:installing the board does not, therefore,affect the execution of existing pro-grams.

EGA modesA complete description of all the displaymodes offered by the EGA is, unfortu-nately, beyond the scope of this article.In mode 14, the card produces 640 by200 pixels, each of which can be assigned1 of 16 colours. In mode 16, it produces640 by 350 16 -colour pixels. The 256 -colour board combines pairs of these togive 320 x 200 or 320 x 350 pixels, each ofwhich can be assigned I of 256 colours.This is similar to the performance of theVGA card used in the new PS/2 range ofIBM PCs. In 256 -colour mode, a VGAcan display only 320 x 200 pixels.In modes 14 and 16, the EGA outputseach pixel as four TTL signals called R,G, B and I. The 256 -colour board com-bines pairs of pixels to give single 8 -bitpixels. These eight TTL signals are con-verted to red, green and blue analoguesignals by three D -A (digital to analogue)converters.

Feature connectorThe EGA card contains a 32 -pin socketcalled the Feature connector. This allowsaccess to several signals on the EGA

card. The proposed colour extensionuses 11 of these signals-see the pinassignment in Fig. I.

GND and +5 V provide power to the256 -colour board.

R, G, B and I are the EGA pixelcolour signals. R, G and B are the

primary red, green and blue signals,while I is used for either the secondarygreen, or the intensity signal.MI 14 MHz is a clock running at one

cycle per EGA pixel. The EGA pixelcolour signals change on the falling edgeof each clock cycle. ATRS/L is the attribute shift load

signal. This is a short, active low,pulse that indicates the loading of eachbyte into the EGA's pixel shift registers. HIN and YIN are the active high

horizontal and vertical synchroniz-ation signals (note: signals going into the256 -colour board are labelled 'IN') INTERNAL enables and disables the

256 -colour board. The signal is highwhen the EGA has disabled its internalvideo drivers.

Fig. I. The Feature connector on the IBMEnhanced Graphics Adapter (EGA).

Circuit descriptionThe circuit diagram of the 256 -colourboard is shown in Fig. 2. The RGBI bitsof the odd -numbered pixels of the EGAare latched into IC:. When the RGBIbits of the even pixels arrive, they arelatched into IC2 along with the odd-numbered pixel bits now stored in IC:.This means that 8 bits of pixel infor-

mation appear at the outputs of IC2 forevery two cycles of the 14 MHz clock.Clocking of IC: and IC2 takes place onthe rising and falling edges of a 7 MHzsignal, obtained by IC4 dividing the14 MHz signal by 2.

It is important that IC: stores the odd -numbered pixels, and IC2 the even -numbered ones, not vice versa. IC: iscleared by the low level on ARTS/Levery 8 pixels to maintain the correctphase relationship.

TimingThe timing of the clock signals appliedto IC: and IC2 is critical. The clockpulses must arrive when the RGBIsignals are stable. Delaying and invertingthe 14 MHz signal in a 7404 gate ensuresthe right timing and polarity. Similarly,the CLEAR signal for IC. is obtainedby delaying the ATRS/L signal in two7404 gates. Do not use a 74LSO4 in thisapplication: its propagation delay is tooshort. The way in which the correctdelays are obtained may be frownedupon for good reasons, but it is the onlyreasonable way of getting the timingright, given the signals available on theEGA's feature connector. The timingdiagram of the circuit is given in Fig. 3.

D -A convertersAn 8 -bit pixel appears at the outputs ofIC2 every 143 ns. These digital signalsmust be converted to analogue RGBlevels that drive the monitor. The mostadvanced way of obtaining analogueRGB signals would be to use a chip thatcombines the functions of colour paletteand multiple D -A converter. There areseveral such chips available, for instancethe Type TMS34070 from Texas Instru-ments (reference ")), or the TypeINISG170 from Inmos, which can dis-play any 256 out of 262,144 colours at aclock rate of up to to 50 MHz. 'A palettechip would require an interface to thePC bus, address decoding circuitry, and

EE

March 1988

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CEO5V P4

O IAN15t.

1RIS0tEMI

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0

5V

O me10k

Fig. 2. Circuit diagram of the low-cost 256 -colour extension for the EGA.

so on. The actual design of a palette in-terface is quite straightforward, requir-ing the data sheets of the palette chip,the technical reference manual of theIBM prototype card, and that for thePC -XT (part numbers are 1525015 and6938833, respectively).In fact, for realistic images, a variablepalette is often less useful than a fixedone, because it is always difficult todecide what colours to put into it. Thismade the author decide to do without apalette and use three D -A converters in-stead.Of the eight pixel bits, three determinethe red intensity, another three the green,and the remaining two the blue (thehuman eye is less sensitive to blue light).With so few bits for each analoguesignal, it is easy to build a D -A converterfrom resistors. In Fig. 2, RI . Rs incl.and Pi ...Ps incl. form the three D -Aconverters, which are dimensioned fordriving a Taxan Type KSI2R RGB moni-tor (V,..--1.5 Vpp in 600 Q). Different re-sistor values may be required for othertypes of monitor, and it is, therefore, rec-ommended to plug the resistors in a 16 -way IC socket with turned pins to

facilitate establishing the right values.Presets PI, P3 and P5 control the overallgains of the D -A converters, while P2,P4 and P. define the brightness of eachcolour when the pixels are set to zero.

Sync signalsA colour monitor typically requireshorizontal and vertical synchronizationsignals. The horizontal sync tells themonitor when to end each horizontalscan line, and when to start the next.Similarly, the vertical sync signal in-dicates the end of the vertical scan of thescreen, and the start of the next. Somemonitors require the horizontal and ver-tical sync to be combined to give com-posite sync.The horizontal sync signal produced bythe EGA is an active high TTL pulse.The polarity of the vertical sync signal isnot fixed, however, and depends on themonitor and video mode used. In the 16 -colour 640 x 200 mode, the vertical syncis an active high TTL pulse, while in the640 x 350 mode it is active low.The Taxan Type KS12R monitor canwork in three modes. In mode 1 (IBM-PC mode), it displays 16 colours usingactive high TTL horizontal and verticalsync signals. It can also be switched tomode 2 (Apple -II mode), which displaysanalogue signals and uses active lowTTL horizontal and vertical syncs. Thereis a separate connector on the monitorfor each of these modes. The two sets ofsync signals may not be applied simul-taneously.The HIN and VIN signals from the EGAare inverted by N1 -N2, and buffered byICI. When ICI is disabled, the Hsyncand Vsync outputs are switched to highimpedance, and no longer drive themonitor. When ICI is enabled, the EGAsets its own horizontal and verticalretrace output signals to high im-pedance. The control of ICI is revertedto below.Be sure to check the specification of themonitor used in respect of the polarityof the sync signals. If it needs positivegoing svncs in both modes, the inverterson the HIN and VIN lines must be re-moved. Alternatively, set the sync signal

1C.:

ATRS \

R,G,B,i

ICI 01_04

IC2 Q1-08

internal-J

K

VIM

\

880071-3

Fig. 3. Tithing of the main signals on the colour extension board.

26 EE

March 1988

polarities under software control bywriting to the Miscellaneous OutputRegister of the EGA.

Enabling the boardThe 256 -colour board can be switchedon and off under software control. Bit 4of the EGA's Miscellaneous OutputRegister controls the video and syncdrivers of the EGA. A logic 1 disablesthe output drivers on the EGA, andcauses INTERNAL on the Feature con-nector to go logic high. On the 256 -colour board, this high level is invertedby N3 and used for enabling the syncand pixel outputs on latches ICI andIC,. By default, INTERNAL is logiclow, so that 'the 256 -colour board is inac-tive at power -on, and the EGA works asnormal.

Construction and setting upThe construction of the colour extensioncard will present no difficulties toanyone who has completed any prolioushardware project. The physical layout ofthe board is not critical.The prototype was constructed onVeroboard, and plugs into the Featureconnector of the EGA as a daughter -board. Figure 4 shows a suggested ar-rangement. The board is suppported byan indirect connector which plugs intothe Feature connector, and by a bracket

Table 1

procedure graph lode;

var Regs: record

case boolean of

true: (ax,bx,cx,dx,bp,si,di,ds,es,flags:

false: (al,ah,bl,bh,cl,ch,dl,dh: byte);

end;*

begin

with reps do

begin

ax:=14:

intr(S10,rsgs);

end;

port[$3C2]:=$23+$10:

end;

integer);

bolted to the EGA 9 -pin D -type videoconnector.The outputs from the 256 -colour boardshould be taken to a separate connector.It is suggested to use a 15 -pin D -type soas not to confuse it with any of the othersockets on the rear panel of the com-puter. Remove the cover for the slot nextto the EGA to give access to the 256-colour board.The even -numbered presets are adjustedso that each colour is just off when thepixels are all zero. Then adjust the odd -numbered presets so that the screen is a

880071-4

Fig. 4. Suggested mounting of the 256 -colour board. 1: Feature connector. 2: EGA board. 3:Bracket. 4: 256 -colour board.

bright white when the pixels are all set to255 (FFF1).

SoftwareA complete description of the EGAhardware and software is available fromIBM. The comprehensive document iscalled Update Number I for the IBMTechnical Reference Options andAdapters. The IBM reference partnumber is 6138280.To get started with the colour extensionboard, use the BIOS calls to control theEGA, and write to the MiscellaneousOutput Register. Setting bit 4 in thisregister disables the video and syncdrivers on the EGA and enables thedrivers on the 256 -colour board.Table 1 shows a Turbo Pascal procedurewhich puts the EGA into 640x200 16 -colour mode, and enables the colour ex-tension. The procedure uses BIOS inter-rupt S10, function SOO, to set the displayto video mode 14. It then writes S33 tothe EGA Miscellaneous Output Register.For mode 14, the BIOS normally setsthis register to $23, but bit 4 must also beactivated here to enable the 256 -colourboard (for video mode 16, the BIOS nor-mally sets the Miscellaneous OutputRegister to SA7).Table 2 shows a Turbo Pascal procedurewhich draws a single pixel in one of 256colours. It uses integer variables r, g andb to calculate the value of the two"pixel" bytes to be written, then callsBIOS interrupt SIO, function SOC, towrite the lower and upper halves of the256 -colour value to the even and odd-numbered pixels of the EGA. Using theBIOS to set the display mode alwaysdisables the colour extension board,making it easy to return to the standard16 -colour graphics.It should be noted that the BIOS is ex-tremely slow to write pixels. Eventually,users of the colour extension board willwant to write software that gives directaccess to the EGA hardware. For this,

the above mentioned IBM manual onthe EGA is indispensable.

EE

March 1988

Table 2

Reference:

Digital colour palette. Elektor Elec-tronics, April 1986, p. 68 ff.

' Peter Balch is with Analogue InformationSystems Limited.

IBM, EGA, VGA, PC XT and PS/2 areregistered trademarks of InternationalBusiness Machines Corporation.Turbo Pascal is a trademark of Borland

Taxan is a trademark of Kaga Elec-tronics Company Limited.Veroboard is a trademark of BICC-VERO Elelectronics Limited.

procedure drav_point ( x,y ,r, gib: integer);

var pixel_Aspixel_B: integer;

Regs: record

case boolean of

true: (ax,bx,cx,dx,bp,si,di,ds,es,flags: integer);

- false: (al,ah,bl,bh,cl,ch,dl,dh: byte);

end;

begin

pixel_A:=(g and 7)+(b and 3)18+(r and 7)232;

pixel_8:=pixel_A and 15;

pixel_A:=pixel_A div 16;

with regs do

begin

ah:=E0C;

al:=pixel_13;

bh:=0;

CX:=X+X+1;

dX:=Y;

intr($10,regs);

end;

With regs do

begin

ah:=SOC;

al:=pixel_A;

bh:=0;

CX:=X-11;

dx:=y;

intr($10,regs);

end;

end;

New computer system forMetropolitan PoliceSystems Designers Scientific has beenselected by the Metropolitan to act asprime contractor in a £17 million projectto provide the Met's computerizedCrime Report Information System-CRIS. The new system will replace theMet's current paper -based crime reportsystem with a force -wide integrated com-puter network.The present crime report system has be-come unwieldy and costly in valuablepolice manpower. CRIS will cut downtime spent by officers supervising paper-work, allow complex searches throughdatabases, and provide each divisionwith instant access to crime reports fromthroughout the Metropolitan Policearea.CRIS will be available to around 30,000police officers and civil staff, 24 hours aday, seven days a week, for the im-mediate creation, updating, and inter-rogation of crime reports. Police person-nel will be able to access instantly crimereports from the past two years and ob-

tain, within four hours, crime reportsfrom the previous four years held in ar-chives.Nearly 2,000 computer workstations willbe placed in all Metropolitan PoliceDivisions, Sub -Divisions, Areas, En-quiry Centres, and in various HQbranches to access databases held on anetwork of 233 EC MicroVAX com-puters at the divisions and a central VAXcluster based around eight VAX8700mainframe machines.Further information from SystemsDesigners Centrum House 101-103Fleet Road Fleet Hampshire GU138PD.

High-performance portableAMT's portable IBM compatible, thePC SPORT PLUS, has a conventionalmemory of 256 K that can be increasedto 640 K, while a further 512 K memorycan be added on a separate memorybank. The computer runs at 8 MHz.The keyboard provides a standard layout

and in addition separate cursor keys(assisting numeric inputs to spread-sheets), ten function keys, and a resetbutton.A 360 K disk drive is built into the right-hand side of the machine and an exter-nal drive can be connected at the rear.Communications are available with twoserial RS232 ports, 25 -pin and 9 -pin re-spectively. This facility allows the use ofvarious modems without a converterlead. The display card is CGA (640 x200), while an EGA card will beavailable soon as an optional extra.The PC SPORT PLUS is priced at £499plus VAT. With DOS 3.2, 640 K RAM,and a monochrome monitor added, theprice goes up to £703 plus VAT.Further details from AppliedMicrosystems Technology Ltd 249-251 Cricklewood Broadway LON-DON NW2 6NX.

28 EE

March 1988

'IOWA S THE SUPERNODECOMPUTER

by Dr. Chris Jesshope, CEng, FBCS, MIEEDepartment of Electronics and Computer Science,

Southampton University

Esprit is a research programme sup-ported by the Commission of theEuropean Communities. It is currentlyfunding a collaborative project to de-velop and exploit a low cost, high per-formance supercomputer, in whichSouthampton University") is playing amajor role.Unlike conventional supercomputers,such as the Cray 1 and Cray 2, whichtend to use expensive ultra -fast circuits,the prototype being designed atSouthampton University makes use ofthe latest microprocessor technology.The Supernode supercomputer is basedon the revolutionary transputer, which isa modern microprocessor designed byINMOS (2) as a component of parallelprocessing systems.Parallel processing uses many processorsto obtain increased system performance.For example, the Supernode supercom-puter may eventually contain severalthousand transputers, all of which couldbe brought to bear on a single appli-cations problem. The research pro-gramme, as well as developing severalprototype supercomputers, will in-vestigate programming and applicationstechniques for this novel computer archi-tecture.The exploitation of such large scaleparallelism is by no means well estab-lished and the United Kingdom, like therest of Europe, has an active researchprogramme to ensure its informationtechnology industry remains competitiveduring this period of major change. Infact Southampton University was in-itially funded by Britain's Alvey pro-gramme to investigate the feasibility ofusing the transputer as a basis for asupercomputer. Other partners in theEsprit collaboration also had priorfunding for transputer research.

Prototype productionThe collaborators in this project comefrom Britain and France, and includeuniversities, small and large companies.and a government research establish-ment. The role of prime contractor withoverall project management is filled bythe Royal Signals and Radar Establish-ment (RSRE)(3). The remainder of the

plan is divided into work packageswhich involve the close cooperation ofsmall groups of collaborators.The prototype designing is being led bySouthampton with collaboration fromthe RSRE and the two industrial part-ners, Thorn EMI(4) and Telmat ofFrance. These two will manufactureseven small and four large machines forthe work, with commercial exploitationto follow. Provision for real time inputand output to the supercomputer is be-ing developed by collaboration betweenRSRE and Thorn EMI.The major component of the Supernodesupercomputer-also known as theReconfigurable Transputer Processor-is the newly announced T800 transputer,which was developed within a workpackage under this collaboration by IN-MOS.IMAG at Grenoble University, in France,is working on the system software for theSupernode machine in collaborationwith Southampton. They are also study-ing the implementation of high levellanguages such as Prolog on this novel

architecture.The remaining collaborators are workingon applications of the supercomputer,including image and signal processing,image generation by ray tracing, com-puter aided design (CAD) for very largescale integration (VLSI), computeraided manufacture (CAM), and appli-cations in science and engineering.

Transputer developmentThe T800 transputer is the major com-ponent in the Supernode. It is aderivative of the T414 transputer an-nounced by INMOS some two years ago.The major difference between these twochips is that the T800 contains an ad-ditional processing unit for handlingfloating point numbers. Floating pointor real numbers May have fractionalparts and have a very wide range ofvalues; most microprocessors handleonly integers (whole numbers), with op-erations for real numbers being providedby software, or alternatively by an ad-ditional special chip.

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L

Southampton University identified thelimitation of software floating point atan early stage in its feasibility study,based on its applications in science andengineering. This was basically a speedlimitation, for it should be noted that allsupercomputers provide support forrapid floating point computation and,inevitably, a software implementationwill not provide a comparable perform-ance.The T800 chip is about 1 cm2 and con-tains about 250,000 transistors. Unlikemore conventional microprocessors, itcan be used entirely on its own as it con-tains a simple but efficient 32 -bit integerprocessor, the floating point processorwhich handles numbers stored using upto 64 bits of information, some very fastrandom access memory (it can store4096 characters), and four high speed in-put and output channels.It is the latter communication channelsthat provide the key to the transputer'ssuccess as a parallel processing compo-nent. In any parallel processing system,the processors must be able to com-municate with each other, to share dataand to synchronise their activity. Thecommunication channels on the trans-puter provide both of these facilities.A single channel can transmit about twomillion characters per second in eachdirection over the three -wire circuit usedto connect transputers together. Thefour links provide the ability for anytransputer to talk to four others directly.This means that transputers could beconnected in a regular two-dimensionallattice.The limitations of such networks arethat communications between trans-puters that are not neighbours will haveto be provided by software, with in-termediate transputers acting as sortingoffices which forward data in con-veniently sized packets to a transputerthey can talk to but which is closer to thedata's destination. Being provided bysoftware, this mechanism is considerablyslower than a direct connection.

Powerful workstationThe problems faced in designing thesupercomputer all relate to communi-cation, for this is the key to all successfulparallel processor designs. Transputerscan only have direct connections to fourother devices although the sorting officeanalogy could provide a solution to thedifficulty of providing other channels.The problem is that the more transputersare included in the system the slowercommunication between distant trans-puters becomes. In programming thesupercomputer, what is ideally requiredis the ability to realize the direct connec-tions between transputers specified bythe program.One of the key features of the Supernodesupercomputer is the ability to realizethis aim. This is provided by switchingcircuits on the links. Each transputer hasits links connected into a switch throughwhich they may be connected to anyother transputer in the system. To pro-vide an alternative analogy, this issimilar to telephones when each user(transputer) is connected to an exchangefrom which he can make a call for agiven duration to any other free userconnected to the exchange.In practice, it is expected that the com-puter will be used with all of the connec-tions established at a given time, pro-viding a pattern of communication ornetwork that reflects the flow of data inthe applications program.One of the disadvantages of using theseswitching circuits is the cost of theswitch, which grows as the square of thenumber of inputs to the exchange. Thiscost function is avoided to some extentby deSigning the computer in modules,each with their own local exchange andof course with lines to other main ex-changes. A unit of about 30 transputerscan be constructed economically in thisway.This supertransputer, the Supernode,can stand alone as a powerful work-station, or can itself be used as the basis

EEMarch 1988

of a super-supernode. One transputeracts as a supervisor, setting the switcheson request. It talks to all other trans-puters within the node by means of acontrol bus which is used to synchronisemany transputers to a common event, sothat the switches may be reset.

29

The prospectsA single Supernode can contain 32worker transputers, each containingstorage for 256,000 characters, a con-troller, a memory server with storage for16 million characters, and a disk serverwith capacity limited only by disk drivetechnology. Such a node could performup to 50 million floating point oper-ations per second, the rate usually ob-tained from machines such as the Cray 1,a multi -million pound supercomputerdating from 1976.A Supernode supercomputer could bemanufactured for tens or perhaps hun-dreds of thousands of pounds, and a col-lection of 32 supernodes in a singlesupercomputer could produce a propor-tionally higher performance, in excess of1000 million floating point operationsper second. This is in the same league astoday's supercomputers which sell forabout £12.5 million. The Supernodesupercomputer could be marketed for afraction of this cost.

References:

1. Southampton University, Departmentof Electronics and Computer Science,Southampton, United Kingdom, S095NH.

2. INMOS Ltd, 1000 Aztec West,Almondsbury, Bristol, UnitedKingdom, BS12 4SQ.

3. Royal Signals and Radar Establish-ment, St Andrews Road, Malvern,Hereford and Worcester, UnitedKingdom, WR14 3PS.

4. Thorn EMI Research Laboratory Ltd,Dawley Road, Hayes, Middlesex,United Kingdom, UB3 1HH.

COMPUTER NEWS

Dataquest expects PC salesto exceed $200 billionThe personal computer market will totalmore than S200 billion over the next fiveyears, according to Dataquest. That isalmost double the industry's Sill billionincome from its inception in 1975 to theend of 1986. The expected increase willbe fuelled by two major factors: replace-ment of older units and a growingnumber of new computer users.Further information fromCochrane Communications Ltd CCLHouse 59 Fleet Street LONDON EC4Y

Microbeeb on targetMicrobeeb, the function -packed BBCBasic control computer from CambridgeMicroprocessor Systems, is finding itsway into more and more applicationswhere the user requires computationalpower with a complete range of I/Ofunctions. These may include full colourgraphics, digital and analogue I/O, step-per motor control, multiple serial chan-nels, and many others - all fully pro-grammable in BBC Basic and CMSMultibasic, the multi -tasking version ofBBC Basic.Further information fromCambridge Microprocessor Systems Ltd Brookfield Business Centre TwentypenceRoad Cottenham CAN1BRIF/GE CB44PS.

Cheaper transputer systemsThe cost of the Kuma K -Max TransputerDevelopment System for the Atari STSeries has been reduced from £995 to£695, excl. VAT. The standard K -Max issupplied with an Inmos T4I4, 256 KRAM, and an Assembler. It can beupgraded by adding a further T414 and256 K RAM and is supported by two Oc-cam products from Kuma: Occam-ST(£59.95 incl. VAT) and Cascade -XP(£199.50 incl. VAT).Further information fromKUMA Computers Ltd 12 HorseshoePark PANGBOURNE RG8 UM

3

COMPUTER-CONTROLLED SLIDEFADER (1)

Revenge yourself on giggling friends and relatives joined to watch and criticize your clumsy slidepresentation.

This project gives the creativity you put in your colour slides an extra dimension in the true sense ofthe word. A chance for all mindful photographers and slide makers to stun their audience with a

dazzling show of fading and dissolving images, sudden or gradual colour changes, the repeating of"theme" slides, and many more special effects, achieved by intelligent control of four slide projectors.

The main difficulty in making a slidepresentation is to capture the attentionof the audience. Television, the motionpicture, and modern advertisement tech-niques prove beyond doubt that thedegree of attention depends strongly onthe rate at which the human mind ap-pears to perceive changing images.While appreciating the difference incharacter and objective between a well -prepared slide presentation and, say, avideo clip, the former is often needlesslystatic. It is, of course, true that this isoften useful for educational purposes,where it is required that an image beshown as long as necessary to allow forexplanatory comments, but the showsoon becomes dreary when pictures areabruptly changed with the operator oc-casionally forced to go through all theprevious ones before he can pick out theslide that requires repeating for ad-ditional comment.The computer controlled slide fader de - Fig. 1. Functional blocks in the computer -controlled slide fader system.

scribed here is sure to add motion andliveliness to your next slide presentation.The effects that can be obtained with itare in the hands of the operator: in itsbasic version, the fader enables com-puter control of the lamp intensity in 64steps, and the reverse/forward motion ofthe slide caner in any one of up to fourslide projectors-see Fig. 1. The hard-ware required for this is relatively simple,and can be extended or simplified to per-sonal needs. The whole slide show canbe designed, directed and prepared byprogramming a computer in BASIC.Each slide projector requires its own 8 -bit output port. Not many computershave 4 such outlets, however, and requireequipping with extension circuits pub-lished, or to be published, in ElektorElectronics:

MSX systems:32 -bit I/O and timer cartridge: ElektorElectronics January 1987, p. 53 ff. Con-trols up to 4 projectors. 6502, 6800 and Z80 based systems:Universal I/O bus: Elektor Electronics,May 1985, p. 35 ff. 8 -bit 1/0 bus:Elektor Electronics, December 1985,p. 20 ff. Controls 1 projector. IBM PC XT and compatibles: to bedescribed in a forthcoming issue ofElektor Electronics. Controls 4 projec-tors. Centronics port: to be described in aforthcoming issue of Elektor Elec-tronics. Controls up to 4 projectors.

Circuit description of thelamp dimmerSlide images can be faded in and out,just like sound, if the intensity of theprojector lamp can be controlled insmall steps. Figure 2 shows the circuitdiagram of 1 of 4 identical dimmers. Atthe heart of the circuit is the TypeTCA280 dimmer chip, whose basic oper-ation is discussed in reference "1. Theintensity of the lamp driven by the triacis an inverse, but non-linear, function ofthe direct control voltage applied to pin5 of the chip. The minimum value of theinput voltage, +2.5 V, gives maximumintensity, while the lamp is quenched at+5 V. Circuitry on board the TCA280Aarranges for the perceived lamp intensityto vary gradually in accordance with thechange in the applied input voltage.The dimmer is powered from the avail-able 24 VAC connections on the lamptransformer in the projector. The triac isfitted as an external component to avoidhigh currents being carried on the PCB.The Types TIC236 and TIC246 are usedfor lamps of up to 150 W or 250 W, re-spectively.

Circuit description of thecontrol interfaceThe circuit diagram of Fig. 3 shows 4identical control channels: one for eachprojector used. The control informationfor each channel is obtained from an 8 -bit output port (A, B, C, or D). With

2

0

O

8

TrI

T

r -

RI

0.5W

1N4001

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131 11 9

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15

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10

12

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7 14

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270k

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6

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72

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1930

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Tr i I

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87259-2

al j j 9

a2

TIC236

(TIC246)

Fig. 2. Circuit diagram of the TCA280 based lamp dimmer.

EEMarch 1988

reference to the upper channel, A, 6 bits,A0... A5 incl., are used for controllingthe lamp intensity at a resolution of 64(26) steps. The 2 remaining bits, A6 andA7, control the relays for reverse andforward motion of the slide carrier onthe projector.Digital to analogue converter (DAC) ICIaccepts the 6 -bit binary informationfrom the computer, and translates thisinto a corresponding direct voltage be-tween 0 and +2.5 V on the output, pin4. The maximum value is derived from areference voltage source set up aroundR17 and 4 series -connected silicondiodes D9. . . D12 incl. The forward dropon each of these is approximately0.62 V. When the computer port sendscontrol value 00H, 40H, or 80H to theDAC, all 6 inputs DB0... DB5 incl. onthe DAC are pulled low, so that the con-verted analogue output voltage is 0 V.The maximum value of the output volt-age, Lire( (+2.5 V), is available when allDAC inputs are programmed logic high,i.e., when the computer sends 3FH, 7FH,or BFH (it makes no sense to activatebits 6 and 7 simultaneously).Opamp IC2 is set up as an invertingamplifier connected to the output of theDAC. Its function is to invert and shiftthe analogue output voltage span of 0 to+2.5 V into the corresponding dimmerinput span from +5 V down to +2.5 V.The amplification of the opamp is,therefore, -1.. With preset Pi set to thecentre of its travel, the voltage at thenon -inverting (+) input is +2.5 V. Thisis the lowest output voltage of theopamp, resulting in maximum illumi-nation of the lamp. The use of the in-verting and span shifting opampfacilitates the programming on the com-puter, since the lowest and highest valuessent to the DAC correspond to minimumand maximum illumination of the pro-jector lamp. A preset is used rather thana fixed potential divider to enable opti-mum matching of the dimmer to thelamp in the associated projector.Bits 6 and 7 in the byte sent to eachchannel arrange the forward or reversemotion of the slide carrier via relays Reiand Reg. The contacts of these form anSPDT switch connected to pins 3 and 5on the relevant 5 -way DIN socket at theoutput of the controller board. Theintensity control signals for the 4 dim-mer boards, and the system ground, arealso carried via the DIN sockets.The pin -out on 1{3 is in accordance withthat on the previously mentioned 32 -bitI/O and timer cartridge, so that this con-nects direct to the 4 -way slide controllerboard. For non-MSX computers, theconnection of the slide controller is, un-fortunately, a matter of finding the rightbits and connections at both ends of thecable.The 5 V supply for the circuitry on thecontroller board is obtained from thecomputer via pins 21 and 22 on K5.

EE

March 1988

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EE .111March 1988

Parts list

MAIN BOARD (CIRCUIT DIAGRAM: Fig. 3).

Resistors (±5%):

fit;112;Rs;Re;Rs;Rto;Ri3;R 14 = 120KR3;R4;R7;118;RII:R12;R15;R 1 6 = 6k8

Ftt7=2K7...P4 incl.=250K or 220K preset H

Capacitors:

Ci C4 incl. = 1n0Cs:C6=100p; 16 V

Semiconductors:

Di ...D12 1N4148T . Ts incl. =BC547BICI:IC3lCs;IC7=ZN436E (Ferranti)IC2;1C4:1C6;1C8 = CA3130

Miscellaneous:

Ki ... K4 incl.= 5 -way angled DIN socket(1809 for PCB mounting.

Ka= 50 -way angled header; 2 rows of 25 pins.for PCB edge mounting.

Ret ...Res incl.= SPDT relay for PCB mount-ing, e.g. Siemens V23101 -A0003 -B101.

PCB Type 87259 (see Readers Services page).

Parts list

DIMMER PCBs (CIRCUIT DIAGRAM: Fig. 2).

Resistors I ± 5%):

RI =470R: 0.5 WR2:R7= 100KR3= 22KR4= 330KRs=150KRe= 270Kfle=82KRs=150R

Capacitors:

Cr =470p; 16 VC2= 1p2 (see text)Ca=ln5

Semiconductors:

Di =1N4001ICt =TCA28OATrit =T1C236 or T1C246 (see text)

Fig. 4. This l'CB is used for building the interface and 4 dimmers.

34 EE

March 1988

Construction: 5 boards in 1The ready-made printed circuit board ofFig. 4 is cut in 5 pieces to obtain 1 inter-face board, and 4 dimmer boards.Commence the construction by popu-lating the dimmer boards according tothe component overlay and the parts list.Mount a 1pF and a 220nF capacitor inparallel if the 1.2pF type in position C2is difficult to obain. Electrolytic capaci-tor CI and triac Trill are fitted as exter-nal components. This enables the triacto be cooled effectively, while avoidingtracks carrying lamp currents of severalamperes. The dimmer board and thetriac should be mounted in a suitableloaction inside the slide projector. Ametal surface near the fan is, of course,ideal for mounting the triac because itforms a heat -sink (do not forget to insu-late the triac with the aid of a micawasher). Figures 5 and 6 illustrate themounting of the triac and the dimmerboard in a slide projector Type Diamator1500 AF.In some cases, the existing DIN socketon the slide projector may have to be re-wired in accordance with the pin -out onthe socket fitted on the controller board.If this is impossible, or less desirable, itis a relatively simple matter to mount anadditional DIN socket for ready connec-tion to the interface. Whatever solutionis adopted, be sure to know exactly howthe slide carrier control system is ac-tuated externally. In case of doubt, it isrecommended to consult the usermanual supplied with the projector.Universal 5 -way DIN cords as used foraudio equipment are perfectly adequatefor connecting the slide controller to theprojectors.The completion of the 4 -way controllerboard is straightforward. Note the use ofPCB mounted DIN sockets, which makefor a compact board, obviating the needfor extensive wiring. The unit can be fit-ted in a suitable ABS enclosure, observ-ing that the intensity span presets,PI. .. P. incl., are easily accessible foradjustment purposes. Figure 7 shows asuggestion for the front panel lay -out.

Over to you: softwareIn principle, all effects in a slide presen-tation are based on 3 operations, namelyvisual mixing of slides, arranging theorder of the slides, and lamp intensitycontrol. As already stated, the numberof possible effects depends solely on thecreativity put into the computer pro-gram. It is, for example, possible torevert to an early slide in the show by re-verse shifting of the slide carrier in pro-jector number 3, whose lamp is turnedoff, while projectors numbers 1, 2 and 4are used for the current images. Thiscalls for a software slide counter on eachchannel to keep track of the slide num-bers, and hence the forward/reverse mo-

18 SCRIENO : CLS TEST PROGRAM FOR SLIDE FADER

29 DEW A -Z

38 DIN D(15),C(15),I(15)

48 FOR 1=8 TO 3 ' ADDRESS INITIALIZATION

58 A=I'16

68 D(8+124)=4+A : D(14Is4)=54 : D(2+I14)=8+A : D(3+II4)=9+A

70 C(0 -014)=6+A : C(1+114)=7+A : C(2+I14)=18+A : C(3+Ig4)=11+A

88 NEXT

98 ON STOP GOSUB 590 : STOP ON

100 FOR X=0 TO 15 ' START CONDITIONS

110 OUT C(X),255 : OUT C(X),8 : OUT C(X),7 : OUT C(X),3

128 OUT D(X),8

130 I(X)=8

148 NEXT

158 P=0 : X=1

168 ON KEY GOSUB 260,300,340,370,400,430,460,498,520,550

170 FOR I=1 TO 18

1m KEY (I) ON

190 NEXT

208 KEY1,"OFF" : KEY2,"ON° : KEY3,"c" : KEY4,")" : KEYS," -"

210 KEY6,"PREVIOUS":KEY7,"NEXT":KEY8,"STEP-":KEY9,"STEP+":KEY18,"RESET"

228 KEY ON

230 LOCATE 18,6 : PRINT"PROJECTOR:";P+1;" " : LOCATE 10,8 :

PRINT"LEVEL:";I(P);" "

248 LOCATE 10,18 : PRINT"STEP SIZE";X;" ° LOCATE 10,12 :

PRINT"CHANGE:";X$;" "

250 GOTO 220

260 ' KEY 1 INTENSITY -

278 I(P)=1(P) -X : IF I(P)'0 THEN I(P)=0

2:.; OUT D(P),I(P) : X$="-°

290 RETURN

300 ' KEY 2 INTENSITY +

310 I(P)=I(P)+X : IF I(P))63 THEN I(P)=63

328 OUT D(P),I(P) : X$="-"

330 RETURN

340 ' KEY 3 CHANGE REVERSE

350 OUT D(P),64 : X$="<" : I(P)=0

360 RETURN

370 ' KEY 4 CHANGE FORWARD

388 OUT D(P),128 : X$=")" : I(P)=0

398 RETURN

400 ' KEY 5 CHANGE OFF

418 OUT D(P),0 : XA="-" : I(P)=8

420 RETURN

438 ' KEY 6 PREVIOUS PROJECTOR

448 P=P -1 : IF PO THEN P=15

458 RETURN

468 ' KEY 7 NEXT PROJECTOR

470 P=P+1 : IF P)15 TUN P4

488 RETURN

490 '

580 X=X-1 : IF Xcl THEN X=1

518 RETURN

528 '

538 X=X+1 : IF X)63 THEN X63

548 RETURN

550 '

568 P=0 : X=1 : X$="-"

578 FOR I=0 TO 15: OUT D(I),8 : 1(1)=8 : NEXT

588 RETURN

598

608 FOR 1=0 TO 15: OUT D(I),0: NEXT

618 DEFUSR=6H3E : A=USR(8)

620 CLS : END

KEY 8 REDUCE STEP SIZE

KEY 9 INCREASE STEP SIZE

KEY 18 ENT

STOP ROUTINE

Table 1. MS BASIC test program for the slide fader.

EE

March 1988

Fig. 5. The dimmer board fitted next to the fan motor in a slide projector. Ci is mounted atthe track side of the PCB.

tion of the carrier. A library of routinescan be written for fade-in and fade-outeffects timed by the CT'C (counter/timercontroller) on the MSX I/O & timerboard.Programmers should have little diffi-culty spotting and adapting the slidecontroller routines in the test program ofTable I. This program runs on MSXcomputers fitted with at least one I/O &timer cartridge. Part 2 of this article willdetail the use of 4 cartridges, so that thesame program tests and controls a maxi-mum of 16 projector channels.Non-MSX users will find lines 260 up toand including 580 useful for analysingthe ways in which the test program con-trols the interface. The instructions inlines 220, 230, 240 and 250 are executedin a loop. The ON KEY GOSUB state-ment does not form pan of this becausethe function keys on an MSX computercan be programmed to call the relevantsubroutine after generating an interrupt(see line 160).Key the program into the computer, andfamiliarize yourself with the functionsassigned to the function keys. Select aprojector, and quench the lamp byholding down the INTENSITY - key.Then adjust the relevant preset on thecontroller board such that the lamp justabout lights. This setting guarantees fastresponse to software -controlled intensityvariations while lengthening the usefullife of the lamp.Some projectors have single -key slidecarrier control. This can be simulated bythe interface board if the software en-sures the correct duration of the forwardand reverse pulses. Although it would bepossible to omit 1 relay on the board,this is not recommended because itmakes the controller less versatile. A bet-ter solution in this case is the connectionof pins 2 and 3 on the socket internal tothe projector in question.

The subject of software for the slidefader will be reverted to in part 2 of thisarticle. We will then discuss an advancedeffects program for no fewer than 16projectors.

Fig. 7. Suggested Front panel la -out.

Fig. 6. An ideal location for the hot triac.Some filing is required to fit the the heat -sinkbetween the sides of the fan enclosure.

References:

t' Halogen lamp dimmer. Elektor Elec-tronics July/August 1987, Supplementp. 55.(23 Articles on MSX extensions inElektor Electronics:I/O bus, digitizer and 8 -bit I/O bus:January 1986, p. 66 ff.Cartridge board. February 1986, p. 32ff.;Add-on bus board. March 1986, p. 55ff.;Bus direction add-on for MSX exten-sions. July/August 1987, Supplementp. 52.

Please refer to Past Articles on theReaders Services page in this issue.

EE

%larc- 198°

UNIPHASE UDSPEAKERSYSTEM

A loudspeaker system that is based on Audax drive units anduses a 12 dB Linkwitz filter. The closed box design enables the

drive units to be located in a straight acoustical line.

The use of a Linkwitz filter (Ref. 1) in aloudspeaker system makes sense only ifthe drive units are positioned in straightacoustical line.The three-way system presents nothingnew, but the drive units have somespecial characteristics as will be seenlater. Total costs for two loudspeakers(drive units, wood, filter components,etc.) is of the order of £250. Listeningtests in which the uniphase system wascompared with commercially availableproducts show that the quality is roughlythe same as that of a commercial systemcosting twice as much.The most noteworthy aspect of the boxis the staggered front, which is essentialto get the drive units in a straightacoustical line. This means that the driveunits are positioned in a manner whichensures that the acoustical output ofeach of the three drivers reaches thelistener at exactly the same time.It might be thought that to achieve thisit is sufficient to measure the depth ofeach cone to be able to calculate by howmuch each drivers must be displacedwith reference to one another. It's agood start, but unfortunately not suf-ficient. This is because the phasebehaviour of each drive unit is far fromideal-see Fig. 1 for a typical phasecharacteristic of a bass driver in a closedbox. Although W. Marshall Leach pub-lished a very interesting article on thephase behaviour of drive units in theJournal of the AES as long ago as 1980,it appears that in the practical systems ofmost manufacturers no notice has beentaken of the findings of Mr. Leach.

Fig. 1. Prototypespeaker system.

In an ideal loudspeaker system deVdmmust be a constant to obtain optimumpulse behaviour. With reference to thecurve of Fig. 1, it is seen that this is vir-tually impossible to attain. Any box that

of the uniphase loud -

contains more than one drive unit and across -over filter will have a phase behav-iour that causes impulse distortion. Evenin a wideband system without filter, it isvery difficult to attain optimum impulsebehaviour.

Is phase shift audible?During the past few years, there havebeen a number of investigations into thequestion whether phase errors are aud-ible or not. These investigations havefailed to agree. It is probable that thesensitivity to phase errors varies fromone person to another. And what aboutthe test methods? Our own experienceshows that serious phase deviations candefinitely be detected in the reproducedsound. Particularly the pronouncedphase jumps around the cross -over pointof the filter seem to be the culprits.These jumps also cause the loudspeakersto produce a different sound pattern atdifferent positions around the room.This is because the acoustic radiationpattern around the cross -over pointsshows large variations along its axis.We have the impression-shared with anumber of researchers-that mostlisteners are not not so much sensitive toabsolute phase deviations, but rather tosudden phase differences.

A matter of less than an inchAbove resonance, the loudspeakerbehaves capacitively at first and then, athigher frequencies, inductively. Thisbehaviour is caused by the voice coil.

12 DV,. V.2....1 RANGEi..110

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EE

March 1988The phase behaviour of each driver canbe measured with a good standardmicrophone. On the basis of the results,the drivers are then displaced with refer-ence to one another until their phasecharacteristics meet smoothly at thecross -over points. This cannot beachieved with 100% accuracy, but theresulting over curve approaches thetheoretical one very closely. Fig. 2 showsthe overall phase behaviour of theuniphase system after these correctionshad been introduced. In practice, thedrive units were positioned such that thepoints of origin of their cones lay in astraight line. This implies that only thespecified Audax drivers should be used,since otherwise the distances betweenthe drivers would be incorrect. In otherwords, if drivers other than the Audaxunits are used, the phase behaviour mustbe measured again, and the design of theenclosure adapted accordingly.

Three-way: an acceptablecompromiseA loudspeaker system in which accountis paid to the phase behaviour and theseparation of the drive units cannot verywell be realized with fewer than threedrivers. Also, the cross -over pointsshould be chosen at other than the stan-dard frequencies. In the present system,they lie at 370 Hz and 3,200 Hz. The lat-ter frequency was chosen deliberatelybecause a middle frequency driver, evenif it is small, gives more and more prob-lems with its phase behaviour above thatfrequency. Moreover, a 25 mm tweeterperforms very well at that frequency,particularly if it is remembered that thecross -over points here lie at -6 dB. Itshould be noted that the distances be-tween the drive units were determinedfor these frequencies: other values must,therefore, not be used.

The drive unitsThe bass unit is a 24 cm type on a castaluminium chassis. The magnet,although of reasonable size, is not par-ticularly large. Since the enclosure is aclosed box (which has better impulsebehaviour than a bass reflex), the mag-net should be not too large to avoid thefrequency response characteristic fallingoff too early.The middle frequency driver is a splen-did unit. To all outward appearances, itlooks like a conventional model, but itsmagnet is the same size as that of thebass unit, and its cone is made of TPX.An aluminium cone in the centre ensuresa better spread of the high tones. Its costis similar to that of the bass unit. Itshould, however, be borne in mind thatthis unit takes care of the most import-ant part of the audio range. In ourprototype, it performed beautifully.

3

distance between loudspeakers

(Al or A2343 phase difference-)

(fc1 or 1c2) x 360

wooferAlsquawker

I A2tweeter

Fig. 3. Displacing the drive units with respect to one another makes the phase characteristicsmeet more evenly.

4Lsl

C:1(Mitil 24P370.5/4

Cl

31$ 5, Ls3

1:1(I37W ICA725 FF

87365-4

Fig. 4. Circuit diagram of the Linkwitz filter.

Fig. 5. The Visaton Type UP70/3 PCB andpopulation plan.

The tweeter is a modernized version of awell -established unit, which has formedpart of Audax's range for many years. Itis, without doubt, still one of the besttweeters available. This version has fer-rofluid cooling and damping of the voicecoil. It reproduces the very high fre-quencies with just a little better defi-nition than the original model.

Components list

Resistors:

(all 5 W)RI;f14=10R2=1Rs;Rs= 8Q2Rs =242

Capacitors:

CI;C3=33 p; 50 V bipolarC2=15 p; 50 V bipolarC4 =15 p MKT or MKCCs = 5p6 (4117111p) MKT or MKCCs =10 p; 50 V bipolarC7=3119 MKT or MKC

Inductors:

L,=6 mH (wind on 20 mm pot core from0.9 mm dia. enamelled copper w

L2=0.5 mH (air -cored: 10 mm dia.; ...ind ircm1 mm dia. enamelled copper wirel

L3 = 2 mH (wind as LilL4 = 0.6 mH (wind as La)

Miscellaneous:

Bass drive unit: Audax Type MHD24P37RSMMiddle frequency driver: Audax Type

TX11 .25RSNTweeter: Audax Type DTW100T25FFFSynthetic cotton wool wadding (see text)Universal filter PCB Visaton Type UP70i3Fixing bolts, nuts, and crinkle washers for driveunits

Loudspeaker terminals (4)

The loudspeakers and filter PCB for this projectare available from CSI Electronicslsee page 78).

The filterThe present system uses a 12 dBLinkwitz filter-see Fig. 4, which is oneof the best passive filters. Next month weintend to publish an active version of theloudspeaker system that will make use ofthe active network published last year(Ref. 2). However, for those who are not

38 EE

March 1988

6

scale 1: 7.5

* loam rubber

50

4

45

4

Fig. 6. Construction plan of the enclosure. Required MDF board or chipboard, thickne-18 mm.

prepared to spend the extra money for anactive system with six output amplifiers,the passive system is an excellent choicethat offers very good sound quality.The design of the filter follows theearlier article (Ref. 1) fairly faithfully.The increasing impedance presented bythe bass unit at higher frequencies iscompensated by R, and C2. A similarnetwork is provided for the middle fre-quency drive unit, otherwise the filterwould not behave as predicted by theory.Furthermore, the middle frequencydriver and the tweeter have been given asmall attenuation network to matchthem more closely to the woofer.The resistances in parallel with the driveunits effectively flatten the resonancepeak of the impedance characteristic ofthe middle and high frequency drivers,since these peaks are close to the respect-ive cross -over points.Readers who check the values of the net-

work components will find that those ofC3 and L3 do not correspond with thetheoretical values. The cause for thisdiscrepancy is that the impedance of themiddle frequency unit rises sharply inthe vicinity of the cross -over point, inspite of the 8.2 ohm shunt resistor:consequently, during the design it wasfound that the practical values deviatesharply from the computed ones.

The enclosureThe enclosure is an upright, narrow boxof such a height that the middle andhigh frequency drivers are roughly at earheight. The narrow front keeps thenumber of reflections to a minimum. Asalready mentioned, the front surface isstaggered to make it possible for thedrive units to be placed at the correctdistances from one another.Otherwise, the construction is fairly con- prototype.

Fig. 7. Some stages in the construction of the

EE

March 198839

8

b

narLAY SCA).* Rama (:) i..,L e.,EI .0e-lluidvatnottGSPEED 1=1 E1

SisisS4OMR SPEEDpsevil = 1=1 Z:=1 SsOss

pEr ,2, in M. Pro ....0 a., 0 CO irn 1=1 = =2 S 13112S

03 03 V _ _100 200_ - SOO Is os 20s

- -

II 01 s

- - __

. -

1144p "

.

.-

_

-

_-- - -

__ -

I. . .

-Bailiff's 's EMIL' Il_III

01`ZSIS011OsI

EsSisf SCALE I RANGESeel

WA 200

Fawns. TIME II I

It

..111 a -El I WRITING SPEED 1=I 1=1 I ASPER SPEEDv.=,1 pv.V1...eacri ear 1 So t CP

lw 20k

1 I ]is -

CI CI .E1O =

NE 1...178:4PC sa

Uniphase:frequencyresponse

T,r-2, 3331

55 _ _ - Ka 201

- -

r esi-lial-laz.ism I mais '5. 203

SETE511 TIME 5,0

55 10S

1 1

14.1..rra1lt /MG

Idssicsieg Clopct

/ - Uniphase:impedance

sn

k /S

"r/7/,TO'S 3351

Fig. 8. Frequency characteristic (a) and impedance curve (b) of the uniphase loudspeaker system.

ventional. The volume of the woofercompartment is about 60 1, which is suf-ficient to obtain a Qrc of 0.7. The-3 dB point of the combination lies ataround 45 Hz. The section for themiddle frequency unit has a volume ofsome 15 1. Again, that is necessary toobtain a QTC for this section of 0.7.Furthermore, it ensures good impulsebehaviour over the middle frequencyrange.The box is made of MDF (medium den-sity fibre board), a material that re-sembles chipboard but has a muchgreater density. If this material cannotbe obtained, chipboard of the best qual-ity may be used.

ConstructionThe filter is constructed on Visaton'sType UP70/3 universal filter PCB asshown in Fig. 5. Some additional holeswill have to be drilled in this board.Inductors Li and L3 should be madewith a pot .core, otherwise they becometoo large for PCB mounting. All otherinductors are air -cored. Capacitors Cl,C2, C3, and C6 are bipolar electrolytictypes; all other capacitors are MKT

(metallized polytherephtalate) types(MKC-metallized polycarbonate-types are suitable alternatives).The construction plan for the box isshown in Fig. 6. The panels are intercon-nected with the aid of suitable dowelsand wood glue: bear in mind that thefinished box must be airtight. Apartfrom the panel separating the wooferfrom the other speakers and the panelhalfway up the bass unit compartment,no struts are required.The drive units are mounted with the aidof nuts, bolts, and crinkle washers. Sub-sequently, the cables between the driversand the filter are put in. Take care thatthe hole in the slanting separating panelthrough which the cables from themiddle and high frequency units to thefilter are fed is made airtight after fittingthe cables.The rear of the box is provided with agood quality terminal board.The filter is mounted on the inside rearpanel of the woofer compartment: takecare that all cables are connected cor-rectly!Next, the box is filled with wadding, forinstance, synthetic cotton wool which issold in bags. About 1 bag is needed for

the top compartment and 3 bags for thewoofer section.When all that is done, the box is closed,again using good quantities of woodglue to ensure an airtight closure. Fi-nally, the enclosure is finished to in-dividual taste (cloth, veneer, varnish,etc.).

FinallyThe enclosures may be positionedagainst a wall, but preferable not in acorner.

References:1. Linkwitz filters; Elektor ElectronicsApril 1987 p. 36.2. Active phase -linear cross -over net-work; Elektor Electronics September1987, p. 61.3. Designing a closed loudspeaker box;Elektor Electronics February 1986, p.68.4. Loudspeaker impedance correction;Elektor Electronics May 1986, p. 30.5. Loudspeaker efficiency; Elektor Elec-tronics June 1986, p. 52.

40 EE

March 1988

THE VALUE OF SILENCEby Dr Dylan Jones and Dr Chris Miles, Department of Applied Psychology, University of Wales

Institute of Science and Technology, Cardiff

Most people would agree that their concentration on readingand attempts to memorise information are made more difficultwhen someone nearby is speaking. One reason stems from thepart that hearing has played as a warning system in the courseof human evolution. Recent laboratory studies have produced

data showing the disruptive effect that speech can have in openplan offices, control towers and even on the flight decks ofaircraft, causing serious losses of efficiency. Research is also

helping psychologists to chart the flow of information in the brain.

"Under all speech that is good foranything there lies a silence that isbetter. Silence is deep as Eternity;

speech is as shallow as Time."Critical and Miscellaneous Essays,

vol. Iv, Sir Walter Scott,by Thomas Carlyle.

Silence is a precious commodity, themore so when we are trying to thinkclearly or read. Religious orders insist onit for periods of devotion and con-templation. Librarians demand it, too,but are often frustrated by people whoinsist on whispering.At our place of work we may find thatour ability to understand the writtenword, or the clarity of our thought pro-cesses, is muddied by ringing telephonesand the babble of voices in the back-ground. Of all the sounds that impingeupon us, the human voice is especiallyintrusive; from what is known of thepsychology of hearing there are goodreasons to suppose that speech is treatedin a slightly different way to othersounds.Abundant anecdotal evidence suggeststhat the human voice, even when whis-pered, makes reading difficult; this istrue even when the person tries to ignorethe sound, so it is clear that speech canintrude without invitation upon our con-sciousness. Although interference be-tween the written and spoken word is ob-vious and natural to the layman, it posesa range of significant questions for thepsychologist interested in how the brainprocesses information. First, we mustask why it is that information deliveredto two separate sensory organs, the eyeand the ear, somehow get mixed in thebrain. For interference to occur, thestreams of information coining from thetwo sense organs must share some com-mon pathway in the brain. Part of thepsychologist's interest is in locating theprecise point at which the interference

takes place. Second, what are thosefeatures of speech which make it so diffi-cult to ignore, and why are our strenuousattempts to suppress it usually of noavail?

Disrupting memoryFrom a series of experiments in variouslaboratories, a fairly clear picture is be-ginning to emerge of the way in which ir-

15

13

11

9

7

3

01',.._ ..

4. .........,-%

,.13

\ ...

.. Reversed speech

Normal speech

White noise

Quiet

\

1 2 3 4 5

POSITION WITHIN THE SEQUENCE OF PRESENTATION

6 7

Effects of different types of sound on memory. Speech, even when reversed, is seen to havea more disruptive effect than white noise, which has a similar effect to quiet. This shows thatdisruption is not simply due to acoustic stimulation.

EE

March 198841

relevant speech interferes with reading.Studies have proved fruitful for theacademic psychologist interested in theworkings of the brain and for all thoseinterested in the abatement of noise. Twodistinct strands of research on irrelevantspeech are discernible: the first examinesan effect, now well established in theliterature, of irrelevant speech on short-term memory; the second focuses on themore recently discovered effects on thereading process.Typically, short-term memory is testedby asking a person to recall a list of itemssuch as letters, short words or digits.Each list comprises up to nine items,presented visually at a rate of about oneper second. At the end of the list, orsoon thereafter, the person is asked towrite down the items in the order inwhich they were presented. The presenceof irrelevant speech during the presen-tation of the items appears to reduce thenumber recalled by about 20 per cent. Byany standards this is a significant degreeof impairment. The failure to rememberis roughly the same over the whole list;it is apparent only when ordered recall isrequired, but not when the items can berecalled in any order.Over the last ten years several features ofthis disruption have become more clearlyunderstood. First, the loss of efficiencydoes not depend upon the meaning ofthe interfering speech; the degree of im-pairment is similar if the speech is in alanguage that the person does not under-stand. Furthermore, reversed speech pro-duced by running a tape backwardsthrough a tape recorder is as disruptiveas proper speech. Second, it has beenshown that while the intelligibility ofspeech does not matter, sounds that arenot speech do not interfere. For example,white noise (which is a random mix ofhissing sounds like those heard from aradio or television set that is not tuned toa transmitting station), is not disruptive.Perhaps this is because white noise andspeech are composed of different kindsof acoustic signals. But there is at leastone exception to this general finding,which arises from a study we made ofthe disruptive effect of singing. We haveshown that the effect of sung words issimilar to that of spoken words. But ifthe tune is hummed rather than sung theeffect is less marked, which suggests thatthe sound has to be word -like rather thanmore broadly speech -like. Finally, theintensity of the speech is unimportant:speech as loud as a shout or as low as awhisper disrupts memory to the samedegree.

Phonological formWhat does this pattern of results tell usabout the processes responsible? Thefindings indicate that the brain mechan-ism discriminates on the basis of how

90 -

60

Normal speech r--1 Reversed speech

72per cent 68

per cent

One line

70per cent

Five lines One line

TYPE OF DISPLAY

85per cent

Eve lines

The influence that the number of lines in a visual presentation to a reader has on the effectsof irrelevant speech. There is a reduced advantage in viewing the text five lines at a time whennormal speech is interfering, but the reader can gain a 15 per cent advantage if the speechis meaningless.

closely the incoming signal approx-imates to speech. The more similar thesound and speech are to one another, thegreater the disruption. However, thismechanism fails to discriminate on thebasis of meaning, for the disruption oc-curs whether the passage heard is mean-ingful or not. More recent experimentshave shown that it is the similarity be-tween the irrelevant speech and thesound of the material being rememberedthat is crucial. Words which are read areconverted into a code which has asound -like basis, as if the person wasproducing 'inner speech'. For example, ifthe list of words has the sounds of run,nets; tree, sore, in common with irrel-evant speech such as one, two, three,four, then the disruption will be severe.This points to the possibility that thetwo streams of information, oneoriginally visual and the other auditory,are converging at a point where they areboth held in a so-called phonologicalform.The need for this conversion processbecomes evident if we reflect for a mo-ment on the way that we read. One wayof understanding reading is to think of itas a conversion process from letters andwords into sounds, into what we havealready referred to as inner speech.When learning to read, the child has toappreciate the appropriate set of rulesfor converting shapes on the page intothis inner speech. Some of the soundsassociated with words, and therefore in-ner speech, may already be known to thechild through hearing the language. Sohearing and reading share a commonlevel of analysis within the brain. Inadult life, whenever we are confronted

with the particularly difficult task ofremembering a list of words or letters inthe correct order, we make this type ofanalysis. Intrusion of a similar signal viathe ear will lead to confusion; the moresimilar the codes used in the two streamsare, the greater is the confusion whenthey are stored in memory.

Susceptibility of readingAnother line of our work has focused onthe effects that irrelevant speech has onreading. At the outset we suspected thatthe effects of speech on reading wouldbe different from those on memory. Toinvestigate this possibility we used thetechnique of playing speech of differentsorts while the person was proof-readinga text for spelling and grammatical er-rors. Typically, a volunteer would spend15 minutes or so looking for errorswhich we had deliberately and carefullyintroduced into the text. We measuredhow many of these errors they coulddetect under various conditions of am-bient sound.There are three main features to the out-come of these experiments. First, mean-ing of the speech in this instance is im-portant. This has been shown bymanipulating the speech in a variety ofways. For example, reversed speech pro-duces a roughly similar effect to silence.We were able to confirm this bydemonstrating that people bilingual inWelsh and English were disrupted by ir-relevant speech in either Welsh orEnglish when they read English text. Butthe reading of those English speakingreaders unable to understand Welsh was

42 EE

March 1988

not disrupted by irrelevant Welsh. Sec-ond, intensity of speech is not import-ant; just as in the results to do withmemory, a whisper has as much effect asa shout. Third, the effect does not de-pend on other physical features of thespeech, such as the number of voices, orwhether its source is stationary or mov-ing. The main point seems to be thatmeaning is important.

Discrete effectsThe conclusions from these findings arethat it is the meaning of the speech thataffects proof-reading. In contrast, short-term memory is affected by speech -likeproperties of the acoustic signal. Sothere seem to be two discrete effects, oneon reading and the other on memory.We were able to check this by developinga variant of the proof-reading task. \Veused a computer -based system, in whichtwo forms of the task were developed. Inone, a single line of text was displayed.The reader could examine each line anduse an electronic pointer to mark errors.When each new line was written -up onthe screen the old line was erased,preventing the reader from looking back.The other form displayed the two linespreceding and the two lines following theline under correction. The reader wasfree to check backwards and forwards.The two versions were used to examinewhether reading was being disruptedthrough reliance of reading on memory.Offering the reader five lines of textnecessarily reduces the immediate bur-den on working memory; the reader maycheck whether the grammar is correct byglancing back or forward to the entiresentence under scrutiny. In contrast, byproviding one line of text only, thereader is forced to remember parts of thesentence while examining it for errors.If reading is disrupted through the effectthat speech has on memory, it would bethought that the effect would be morepronounced where the burden onmemory is greater. The results of our ex-periments show just the opposite. Thefive -line version proved to be moresusceptible to disruption. We think thatthe fluency of reading is important: themore fluent the reading, as with fivelines of text, the more likely it is to bedisrupted by speech.

Evolution\Ve are now left with the question of pre-cisely why speech -like sound intrudesinto our thoughts. Part of the answercomes from an understanding of the rolethat hearing has played in human evol-ution. It has the characteristics of anearly warning system and has been de-scribed as the sentinel of the senses. Itcan receive information through theauditory channel in darkness; it can

wake a sleeping person and, unlike theeyes, the ears are omnidirectional. Theway we use our eyes is far more pur-poseful and directed; the ear, in com-parison, is a passive and automatic re-cipient of information. We know, too,that nerves from the ears connect withthose parts of the brain to do with alert-ness. Signals passed on by the ear are farmore likely to be significant to a person'ssurvival. All of these features suggest asystem tuned to act as a vigilant guard-ian but one through which, nevertheless,a great deal of intelligent information istransmitted. So speech may take advan-tage. of the ear's guardianship of ourconsciousness because it can gainprivileged access to our thoughts.The next stages of our research will focuson what it is in the nature of the speechsignal that determines the degree ofdisruption. To begin with, this will meanlooking at two features of the speechsignal, both of which have the potentialto interfere. The first is the possibilitythat speech has a certain combination ofsounds, spaced at particular intervals,that characterise speech only. It is likelythat the nervous system is tuned to re-ceive such features while rejectingothers. The second is that the so-calledprosodic features, those increases anddecreases in intensity of speech that giveit a rhythm of its own, might be respon-sible. These changes of intensity, whichare peculiar to speech, might also besubject to tuning by the nervous system.

Practical outcomeWhat are the practical implications ofour findings? Wherever people areengaged in activities like those we havealready described, it seems likely thatthey run the risk of being distracted byirrelevant speech. Workers in open-planoffices, where there is little or noacoustic isolation, are likely to have theirefficiency impaired. Activities such asreading, composing text and performingmental arithmetic are all likely to sufferto some extent.Most recommendations for the officeenvironment take scant regard of whathas already been found out by psychol-ogists. It is usually assumed that thedegree of interference by speech issimilar to that induced by white noise.That is, it is taken for granted that theinterference can be predicted by knowingthe ratio of the intensities of signal andnoise. But we know that the effect ofspeech does not depend on its intensityand is therefore largely independent ofits distinguishability from backgroundnoise. This probably explains the dis-crepancy that has often been found be-tween objective acoustic measurementsin offices and complaints by the peopleworking there.

Control roomsIn any complex system where anoperator is exposed to material whichhas to be read and interpreted, the in-trusive effects of speech may be at work.More important is that in control rooms,where streams of speech and text aremixed haphazardly, there is a chancethat irrelevant speech will impair thememory of instrument readings and se-quences of events. In air traffic controltowers and in the control rooms ofpower stations the intake of visual infor-mation is at risk. In these settings, onlysome of the speech heard will be relevantto the task at hand, so there is goodreason to recommend that some kind ofcontrol be exercised over incomingspoken messages. In person -to -personcommunication it could be done bychannelling speech via microphones andheadphones, so that there is some degreeof control over reception.In control systems using advanced tech-nology, machine -generated speech willbe used more and more to pass messagesfrom the machine to the user. Inter-ference from such sources can be keptdown by queuing messages within acomputer system so that the operatorcan listen to them at a convenient timewhen the workload is low enough.

Most profoundIt is during the development of readingskills that the effect of irrelevant speechmay have its most profound effects. Inprimary schools the trend has beentoward classrooms of the open-plantype. Though data are not yet available,there is every possibility that in such set-tings fluent reading is being disruptedand the faltering steps of learners are be-ing impaired.Of all our experimental findings, thesingle most important is that the disrupt-ing effect of speech is independent ofintensity. This means that the traditionalidea of abating it ought to be supplantedby eliminating it. Reducing the level ofnoise by modest degrees is relativelycheap; getting rid of ambient noisealtogether is an extremely difficult andexpensive enterprise. Yet there may besettings such as the flight deck of an air-craft where the potential costs ofdisrupting work might be so high thatsuch a course should be seriously con-sidered.

`And silence, like a poultice, comes Toheal the blows of sound." The MusicGrinders, by Oliver Wendell Holmes.

43

SIGNAL DIVIDER FOSATELLITE TV RECEIVERS

by R. van Terborgh

Our first application of a monolithic microwave integrated ampli-fier (MMIC) from Avantek is a wideband amplifier and splitter thatmakes it possible to connect two satellite TV receivers to a singleoutdoor unit. In other words: this is your chance to share the cost

of a dish plus LNB with your next-door neighbour!

As stated in the introductory article onMivIICs (reference ffi), these new devicesare eminently suited to building highperformance wideband amplifiers withonly a handful of components. In thepresent application, a single MMIC isused for amplifying the IF output signalof a commercially available low noiseblock down converter (LNB or LNC).The standardized IF bandwidth of LNBsis 950-1750 MHz, but it should benoted that these are not absolute bandedges. Most LNBs have a relatively highconversion gain (55 dB typ.), but this isoften found to decrease with frequency.Similarly, the attenuation of thedownlead coax cable increases with fre-quency, so that the highest down -converted transponder signals are almostinvariably of lower absolute amplitudethan those further down in the IF band,while C/N figures are still roughly thesame because reduced gain results in lessnoise (compare the S -meter reading ofSuper Channel to that of, say, TeleclubSwitzerland).The foregoing observations have conse-quences for the design of a cable ampli-fier/signal divider for use in satellite TVreceiving systems:

1. The amplifier should have a relativelyhigh drive margin to prevent it being

"blocked" by the high output levels sup-plied by the LNB.2. The frequency response of the ampli-

fier should be as flat as possibleacross the entire IF band.Both requirements are met by the pro-posed amplifier/splitter based on theType MSA0404 MMIC, which ensuresan output power of +12 dBm at I dBcompression, and a third -order interceptpoint of +26 dBm (0 dBm=t--1 mW in50 Q).The 2 -way signal divider described hereprovides a modest, but often welcome,insertion gain of about 4 dB on bothoutputs, and allows relatively inexpens-ive coax cable to be used for connecting

the indoor units. Still, do not be temptedinto using, say, 30 m RG-58, or ubi-quitious "TV coax": the massive at-tenuation such a cable introduces is im-possible to overcome by the best cableamplifier or IDU input stage. Stick togood quality COAX12, COAX6, or H43cable (all 75 Q), terminated in BNC, Nor F connectors. Green or yellow coaxcable occasionally seen in TV and radiodistribution networks is also suitable,but appropriate plugs may be difficult toobtain.

Circuit descriptionThe circuit diagram of Fig. 1 shows thesingle -chip amplifier and 2 -way signaldivider. The LNB is connected to BNC,N or F socket ICI; the 2 indoor units(IDUs) to IC2 and K3. Amplifier ICI is aType MSA0404, whose technicalcharacteristics can be found in Fig. 5 in". Gain of the MMIC is 8 dB; inputand output impedance are 50 Q. Themismatch between the 75 Q cable and

the 50 Q input of the amplifier (K1;MMIC), is of no practical consequence(referenceThe amplified wideband signal is ap-plied to a resistive splitter, 112-R2, forfeeding to the indoor units. Given theamplification of the MM IC, and the lossin the splitter, the net gain on each chan-nel is still about 4 dB (do not forget thatthe MM1C has a 50 Q output, and thatK2 and Ki are terminated in 75 Q).More gain is not desirable here becauseit would lead to overdriving of the inputstage in the IDU.Output IC2 on the amplifier/splitter ac-cepts the LNB supply voltage carried onthe downlead coax cable to the IDU.This supply voltage is also used forpowering the MMIC via RI -L2, and ap-pears on Ki after passing throughchokes L3 and Li. Indoor unit 1 (IDU 1)connected to K2 powers the LNB andthe signal divider. The supply voltage onthe coax cable should not disappearwhen IDU 1 is switched off, because thiswould make make reception on IDU 2impossible. The Elektor Electronics in-door unit (reference ffi) causes no prob-lems in this respect: the LNB supplyvoltage is present on the RF input aslong as the unit is connected to themains, i.e., irrespective of the position ofthe ON/ OFF switch.Capacitors C2, C3, Co and C. ensure ad-equate supply decoupling, while CI,and C5 are DC blocking capacitors witha low reactance and stray inductance atthe frequencies involved.

Series resistor RI should be dimen-sioned in accordance with the LNBoperating voltage supplied by the IDUon the downlead coax cable. The MMICdraws about 50 mA at the recommendedsupply voltage of 5.5 V, so that

RI .(1/LN-B - 5.5)/0.05 [2].

The value of 220 Q shown in the circuitdiagram ensures safe operation of the

EE

March 1988

Fig. I. Circuit diagram of the wideband amplifier and splitter for satellite TV receivers.

amplifier when connected to the Elek torElectronics IDUNa=15 V).Warning: some indoor units supply anLNB voltage as high as 18 V or' even24 V. Always measure Visa on thecentre tip of the RF input connector ofyour IDU with the LNB connected to thedownlead coax cable. Then calculate RIas shown above.The dimensioning of RI is not critical:calculate the theoretical resistance, selectthe next higher value from the E12series, measure the voltage on theRF OUT/BIAS terminal of the MMIC,and decrease the resistor value if re-

quired, until the operating voltage is be-tween +5 V and +6 V. Be sure to use anordinary '/2 W carbon film resistor: itsinductance is essential in this appli-cation.

ConstructionPrepare the small Eddystone enclosureshown in the photographs prior to start-ing any soldering work. Study the lo-cations of Ki, K2 and K3 on the PCBbefore drilling the holes for these flange -type BNC sockets, which are fitted ontothe lid as shown in Fig. 3. You may have

3

Fig. 3. Side view of a prototype of the signaldivider, showing the PCB and the RF con-nectors secured onto the lid of a diecastenclosure.

Fig. 2. The small, double sided, printed circuit board for the signal divider is available ready-made through Elektor Electronics' ReadersServices.

Parts list

Note : SMD = surface mount device.

Resistors I 5%):

Capacitors:

CI:Cs:Cs= 68p SMDC2;C3;Cs=1n0 SMDC7 =10p; 25 V tantalum bead

Semiconductor:

RI =220R: 0.5 W carbon film (see text). ICI =MSA0404 (Avantek; distributors are listedR2;R3=22R SMD in reference ill).

Inductors:

1.1;L2;1.3= home made -see text.

Miscellaneous:

10:1(2;K3= BNC socket (flange type).PCB Type 880067 (see Readers Services page).Diecast enclosure (Eddystone; dimensionsapprox. 112 r 64 x 30 mm).

to provide new mounting holes on thePCB if you intend to use Type N or Fsockets instead of BNC. Mount asuitable clamp to the box to enable at-taching this near, or onto, the dish aerialstand, if this is the most favourable lo-cation for the splitter considering thelengths of the downlead cables. Providelettering on the lid to rule out anylikelihood of erroneous connections.Now proceed with the completion of theprinted circuit board shown in Fig. 2.Less experienced constructors shouldnote that all parts, with the exception ofthe 3 sockets, are fitted direct onto thetrack side of the board. The leads ofC-, RI and the 3 inductors should bekept as short as possible.The tvIMIC is seated in a 04 mm hole,and its 4 leads are soldered straight ontothe relevant copper areas. All capacitors,with the exception of tantalum bead typeC-7, are surface mount devices, securedin place by fast soldering with a low -power iron. The same goes for dividerresistors R2 and R3.

The 3 home-made inductors in theamplifier are identical. The winding dataare as follows:Li; 1_2; L3 = 12 turns 00.5 mm(SWG25) enamelled copper wire; close -wound; internal diameter: 2.5 mm.Use a sharp knife to remove the protec-tive PTFE collar around the centre pinwhere this protrudes from the BNCsocket. The 3 sockets are held against the

Fig. 4. All parts, with the exception of the RFconnectors, are fitted at the track side of thePCB. The small, greyish, rectangular, blocksare surface -mount resistors and capacitors(prototype).

EE

March 1988outside of the lid, and the PCB is pushedonto the centre pins that protrude at theinside. Press the PCB firmly against thelid, and push the twelve M2.6 screwsthrough the holes in the PCB. Carefullytighten the screws, and solder the centrepins of the RF sockets onto the copperislands at the track side of the board.Finally, be sure to terminate outputIDU 2 in 75 Q at all times. In mostcases, the attenuation of the downleadcable is high enough to ensure propertermination of the amplifier if IDU 2 isdisconnected in the home. If, for somereason, the downlead cable to IDU 2 istemporarily disconnected from theamplifier output, this must be ter-minated in a 75 Q dummy load (a 75 Qresistor fitted in the RF plug). Ingeneral, the signal divider should be fit-ted as close as possible to the LNB.RGK

References:

45

") MMICs revolutionize wideband RFamplifier design. Elektor Electronics,January 1988, p. 38 ff.

Loss encountered when interconnec-ting cables having the incorrect im-pedance. By Dr P. Brumm. VHF Com-munications, 3/1974.") Indoor unit for satellite TV recep-tion, parts 1, 2 and 3. Elektor Elec-tronics, October 1986, November 1986,January 1987.RF module for IDU. Elektor ElectronicsJuly/August 1987, Supplement p. 10.

ELECTRONICS NEWS ELECTRONICS NE n

S

Videodisc market in EuropeA report from Frost & Sullivan. TheVideodisc Market in Europe (#E870)does not deal with the consumer market,which failed to materialize in the early1980s-in fact, one of the blazingmistakes made by videodisc makers thenwas to chase the general public.Videodiscs aimed at the film -viewingpublic experience virtually non-existenttake-up because of the rapid penetrationof videocassette recorders (VCRs).Instead, the study sees the emergingvideodisc arena as one primarily aimedat the professional audio-visual marketfor industrial, institutional, and com-mercial organizations. The mostfavoured and developed applications arefor training and point -of -sale advertisingand information. The study predicts thatgrowth rates will average close to 25% ayear through 1991, with more than 5350million worth of machines installed inEurope by then.Frost & Sullivan Ltd Sullivan House 4 Grosvenor Gardens LONDON

SW1W ODH Telephone 01-730 3438.

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Scandinavia Other

46_Eja,

LOW-NOISE PREAMPLIFIER FORFM RECEIVERS

First in a short series of articles on simple to build RF preamplifiersis a tuneable aerial booster for the FM band.

The RF preamplifier described here is in-tended for fitting as close as possible tothe FM band aerial. It is a tuneable,rather than a wideband, amplifier, whichis fed and tuned via the downlead coaxcable. The amplification and the noisefigure of the FM aerial booster are25 dB and about 1 dB, respectively. Allpreamplifiers described in this series arepowered and tuned by a commonsupply/tuning unit installed at an appro-priate location in the home.

Circuit description

The circuit diagram of Fig. 1 shows thatthe preamplifier is a conventional designbased on a VHF MOSFET tetrode TypeBF981. The preamplifier input can beconnected to unbalanced (60...75 2) aswell as balanced (240...300 Q) aerialsor feeder systems. The balanced inputallows the preamplifier to be connecteddirect to the dipole element. In this case,the preamplifier can take the place of thebalun removed from the ABS, water-resistant, enclosure that houses thedipole terminals. This solution ensuresthe lowest possible input loss, and ob-viates the need for a separate preampli-fier enclosure on the mast.The balanced or unbalanced aerialsignal is applied to winding a of tuneableinductor Li. Varactors DI -D2 form theadjustable capacitance across winding b,so that the tuning range of Li is about86...109 MHz. Gate 2 of DG MOSFETTi is held at about +4 V by potentialdivider R2 -1b. The bias voltage is effec-tively decoupled by surface mount ca-pacitor Ci. Blocking capacitor CO takesthe amplified RF signal from a half-impedance tap on drain inductor L2.The MOSFET is fed with a constantoperating voltage of 12 V, supplied byregulator ICI. The direct voltage on thedownlead coax can be varied between15 V and about 26 V by means of thesupply/tuning unit near the receiver.Zenerdiode D3 in the preamplifier en-sures that the tuning voltage for varac-tors DI -D2 is the voltage on the

downlead coax minus 12 V. Example: ifthe downlead coax carries +18 V, thetuning voltage at junction Di -D2 is+6 V with respect to ground. The lowestdownlead voltage is about 15 V to ensurethe minimum voltage drop across regu-lator ICI. Choke L3 forms a high im-pedance for the amplified RF signalssuperimposed on the tuning/supplyvoltage.

Construction

Commence the construction of the pre-amplifier with winding the inductors.Input inductor LI is wound on theformer in the Type 10V1 inductor as-sembly from Neosid-see Fig. 2. First,close -wind Lit, as 11 turns, 00.6 mm

enamelled copper wire. Study the com-ponent overlay on the PCB (see Fig. 3)to find the 2 pins on the base that con-nect to Lib. Close -wind Li. as 4 turns,00.6 mm enamelled copper wire ontoLib, starting at the base of the plasticformer. The tap is made after 2 wind-ings. Stretch the turns, and carefullyscratch off a small area of the enamelcoating approximately half -way the in-ductor. Solder a short wire to this point,and point it down towards the base.Press the inductor together again. Con-nect the end wires and the tap wire to thebase pins, and verify continuity andorientation of the completed inductor.Drain inductor L2 is wound as 4 turns00.3 mm enamelled copper wirethrough a small 'ferrite bead. The centretap is made after two turns by twisting

BF981

0

03

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650C42 - I

Fig. 1. Circuit diagram of the tuneable VHF preamplifier.

Fig. 2. The Type 10V1 inductor assemblyfrom Neosid.

3 cm or so of the wire before making thethird and fourth turn. The twisted wire isthen cut to length, the enamel coating isscratched off, and the connection iscarefully pre -tinned.Choke L3 is the simplest to make: it iswound as 6 turns 00.2 mm enamelledcopper wire through a small ferrite bead.The three home-made inductors in thepreamplifier are shown in the photo-graph of Fig. 4.

The PCB for this project is a double -sided, but not through -plated, pre -tinned type. The four resistors aremounted upright. Ascertain the pinningof MOSFET Ti before fitting it on theprinted circuit board: depending on themake of the device, it may be necessaryto mount it with the type indication fac-ing the PCB.The ground terminal of R2, R4, ICI, C:,C3, C4, C5, the source terminal of Ti,the anode of 132, input pin 2, the 2solder tabs on the shielding can of Li,and the output ground terminal, aresoldered at both sides of the PCB. Theonly component at the track side of theboard is SMD capacitor CI. This issoldered direct across the GATE 2 andSOURCE connections of the MOSFET. Fita 15 mm high brass or tin metal screenwith a small clearance for the MOSFETas shown on the component overlay.

Supply/tuning unit

The circuit diagram of the simple,regulated and adjustable, power supplyfor the downlead-powered preamplifiersis shown in Fig. 6. The output voltage ofintegrated regulator ICI is adjusted be-tween 15 V and 26 V with tuning controlPi. The tuning and supply voltage foreach preamplifier is applied to the centrecore of the respective downlead coaxcable by a choke -resistor combination.The tuning/supply unit is built on thedouble -sided, pre -tinned printed circuitboard shown in Fig. 7. Construction

Cl

L1 --E) Q-q3 R2

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Fig. 3. The PCB for building the VHF preamplifier.

Parts list

FM BAND PREAMPLIFIER. CIRCUIT DIAGRAM:FIG. 1.

Resistors ± 5%):

RI:113= 100KR2 = 56KR.4= 10K

Capacitors:

CI =1n0 (surface mount assembly)C2=1n0 ceramic (pitch: 5 mm)C3 = 1p0; 16 V; axialCo= tp0; 40 V; axialCs=47p; 35 V; axialCe=560p ceramic (pitch: 5 mm)

Semiconductors:

D1;02=80405

Da= zenercriode 12 V; 400 mWICI =78L12TI=BF981

Inductors:

Winding data ae given in the text.

Li = inductor assembly Type 10V1. Neosid partnumber: 15955100. (Neosid Eduard House Brownfields Welwyn Garden City Herts AL7 1 AN. Telephone: (0707) 325011.Telex: 25423).

2 off small, single -hole. ferrite beads (length:approx. 3 mm).

Miscellaneous:

Suitable waterproof enclosure.PCB Type 880042 (see Readers Services page).5 off soldering pins.

should not present problems: groundedcomponent leads or terminals aresoldered at both sides of the PCB. FitICI with a TO220-style heat -sink, butmake sure that this is insulated from theground area.

The winding data for the 3 chokes on theboard are as follows:

= 6 turns 00.2 mm enamelled

copper wire through a small ferrite bead(length: approx. 3 mm).The tuning control, Pi, is convenientlyfitted onto the 3 soldering pins to goround a 3 -wire connection. The as-sembled board, the 24 VAC power trans-former, mains switch and fuse are hous-ed in a small enclosure with a slopingfront panel. Omit DI...D4 incl., andCI -C2, when a 24 VDC source, such as a

Fig. 4. A close look at the home-made inductors.

48 EE

March 1988

Fig. 5. Prototype of the completed low -noisepreamplifier.

mains adapter, is already available-connect this to the points marked + and0. The tuning control can be fitted witha vernier and a scale for the frequencyranee of each preamplifier.

Fig. 6. Circuit diagram of the tuningisuppl)

Testing

Connect the AC input of the completedtuning/supply unit to the secondary ofthe 24 VAC mains transformer, apply

unit.

power, and verify the presence of the ad-justable direct voltage on the threeDC/RF terminals. Check whether Pisets the voltage between +15 V and+26 V.

7

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Parts list

TUNINGiSUPPLY UNIT. CIRCUIT DIAGRAM:FIG. 6.

Resistors (±5%):

RS =220RR2=1K8Ra;114:115=47R

Pt =2K5 or 2K2 linear potentiometer

Capacitors:

CI;C2=47nC3= 1000p; 40 VC4= 1p; 40 VCs;C6;C7 = 220pCa= 10p; 40 V

Inductors:

1.1;t2;1_3= home made on 3 mm ferritebeads-see text.

Semiconductors:

Di...04 incl.=1N4001ICI =LM317 (T0220 enclosure)

Miscellaneous:

T0220 -style Heat -sink for ICI.11 off soldering pins.PCB Type 880041 (see Readers Services page).

Fig. 7. The printed circuit board for the tuning/suppl) unit.

Tune the FM receiver to a relatively weaktransmission at about 108 MHz, andmake a note of the signal strength. Con-nect the input of the completed pre-amplifier to the aerial, not a cable net-work outlet. The preamplifier output isconnected to the appropriate solderingterminal on the tuning/supply board viaa short length of coax cable. Similarly,connect the unbalanced (75 Q) input ofthe FM receiver to the RF (RX) outputon the tuning/supply board. Set Pi to+26 V on the cable to the preamplifier.Verify the presence there of +12 V onC3, and +14 V on C5. Use a plastic trimtool to adjust the screw core in Li foroptimum reception. Vary the supply

voltage between 22 V and 26 V to checkthat this tunes the preamplifier.

Set the supply to +15 V, and tune the re-ceiver to a signal at the lower band edge,i.e., approximately 88 MHz. Check thatLi is still adjusted for optimum recep-tion by carefully adjusting the core. Tuneto a number of stations at regular fre-quency intervals in the FM band, op-timize reception by adjusting Pi in thetuning/supply unit, and make notes ofthe downlead voltage. If necessary, redothe adjustment of Li to ensure that thespan of the tuning voltage covers the en-tire FM band. For optimum tracking of

EE

March 1988the resonance frequency with the tuningvoltage applied to the varactors, the corein Li should be turned to about half-way the aerial winding. This completesthe initial adjustment of the FM bandpreamplifier, which is ready for fittinginto a waterproof enclosure.

49

The next instalment in this series willdeal with preamplifiers for the short-wave, VHF and UHF TV bands.

RADIO & TV NEWSDistance learningProfessor Bill Spence, head of UlsterUniversity's Communications Depart-ment, recently demonstrated how newtechnology is presenting opportunitiesfor distance learning and teleconferenc-ing by giving an hour-long lecture to theInternational Technology Conference inPerth, western Australia, from his officein Northern Ireland.Professor Spence has been sponsored bythe British Council to carry out researchinto distance learning. This has resultedin visits to Laval University, Quebec, andRutgers University, New Jersey.has a similar problem to Ulster Univer-sity in that it consists of four campuses,each about 96 km apart, and is trying toimprove communications with the latesttechnological aids, such as advancedtelephone conferencing, closed circuittelevision, electronic mail, and docu-ment publishing.As a result of Professor Spence's visit,the communications department atUlster University now has access to theNorth American computer networkknown as Bitnet through arrangementsmade by the Office of Television andRadio at Rutgers University as a con-tribution towards the further collabor-ation of both universities in the field ofdistance learning.

Land mobile services throughINMARSATAt last October's INMARSAT Assemblyin London, the INMARSAT Councilwere requested to examine the commer-cial, technical, and operational feasi-bility of providing land mobile satelliteservices. The organization is already in-troducing telephone, telex, facsimile,and data services for aircraft operationsand passengers later this year.As part of the feasibility study, aspecially equipped van is touring Europeto demonstrate to truck and bus manu-facturers, and the media, the reliability

and potential of satellite transmissionsto a moving vehicle. The equipmenton the van consists of a small, roof -mounted, omni-directional antenna, acar -radio sized receiver, and a printer.The van's route is taking it throughsouthern England, Federal Germany,Belgium, the Netherlands, and Switzer-land.

In -orbit delivery of BritishsatelliteThe European Telecommunications Sat-ellite Organization, EUTELSAT, hastaken formal delivery in orbit ofEUTELSAT I F-4 after a series of rigor-ous acceptance tests.EUTELSAT I F-4, originally calledECS-4, was built by a European consor-tium led by British Aerospace. It was

launched by Ariane rocket lastSeptember from Kourou in FrenchGuiana and has now been placed in itsfinal geostationary orbital position at10° East.The spacecraft will complementEUTELSAT I F-1 (ECS-1) and EUTEL-SAT I F-2 (ECS-2), also manufacturedby British Aerospace as prime contrac-tor, which provide a range of telecom-munications services to Europe, includ-ing telephony, business services, and TVdistribution. '

EUTELSAT I F-4 is the 11th communi-cations satellite to be launched in theseries of 18 which have been developedfrom the Orbital Test Satellite. It willoperate at 14/11,GHz and 14/12 GHz,and its transponders will be used mainlyfor TV distribution.

Produced to a demanding Interspace of France requirement for vibration testing of a spacesatellite, the Environmental Engineering Department of British Aerospace Army WeaponsDivision have designed a dual head vibration fixture to a Ling Dynamic Systems specification.

With a diameter of 2.111I the satellite vibration test fixture couples a three tonne specimen totwo electromagnetic vibrators. A maximum weight, minimum static stiffness and a minimumlowest resonant frequency were specified for the fixture. The major problem was to devise afixture that would transmit the motion of the vibrators to the lest piece faithfully, without dis-torting the motion as a result of the fixture's own physical characteristics.

50 EE

March 1988

RADIO & TV NEWS

Multi -standard MAC decoderannouncedNordic VLSI of Norway, in co-operationwith the Norwegian Telecommuni-cations Administration, have succeededin producing the first working C/D/D2MAC (multi -MAC) compatible chip forreception of TV services via satellite.The first prototypes of the VLSI chipwere combined with MAC satellite re-ceiving equipment produced by Tand-berg Telecom. The prototype chip, whichhad 230,000 transistors on board,worked first time without any need forredesign or modification. Following thissuccess, Nordic teamed up with PlesseySemiconductors and Philips to develop acomplete Multi -MAC transcoder con-cept with provisions for decrypting andconditional access decoding. In thisjoint venture, Plessey Semiconductorswill manufacture three of tim full -custom VLSI CMOS ASICs at the heartof the decoder and also supply a Teletextfull -custom VLSI CMOS ASIC. Tocomplete the decoder, Philips will de-velop the operating software (includingdecryption) and supply ICs from theirextensive bipolar and MOS ranges toperform the analogue signal processing,computer control and data conversionfunctions.This unique cooperation has led to theavailability of the first -ever chip -set forconstructing an advanced multi -stan-dard MAC decoder which can enor-mously increase the market applicabilityof TV sets through its most innovativefeature - multi -standard operation thatmeets all the requirements of today'sEuropean satellite TV market.

Unique features of a decoder built withthe chip -set: Implements the full CMAC/DMAC/

D2MAC packet standard Can handle the standard MAC for-

mat for picture plus up to eight monoor four stereo sound channels

Is compatible with any TV set archi-tecture

A conditional access control featureallows descrambling and decryptionof sound and vision signals (Pay TV)and of Teletext. This feature canhandle several broadcasts simul-taneously and meets the requirementsof the new Part 6 of the EBU specifi-cation. Entitlements can be ad-dressed over -air, via a smart -card orvia a keyboard

Single- and double -cut conditionalaccess descrambling of the visionsignal as specified by the EBU

I Very flexible packet multiplexingallows full -field sound/data transferof up to 50 high quality sound chan-nels at a rate of nearly 20 Mbit/s

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MI The configuration data can bechanged without disrupting the ser-vice

II Can handle Teletext in accordancewith the EBU specification duringthe frame interval or in the packetmultiplex

A second vision signal aspect ratioand decompression ratio will allowfuture high -definition TV (aspectratio 16:9) to be accommodatedwhilst retaining compatibility withpresent standards (aspect 4:3)

Linear or companded sound signalscan be decoded

II Processing of 1st and 2nd level errorprotection of the sound signal, in-cluding error concealment

Digital mixing allows simultaneousprocessing of stereo sound and com-mentary channels

Sound quality comparable with com-pact disc

The decoder is software controlled.

Main functions of the multi -standardMAC decoderThe main part of the decoder comprisesfour full -custom VLSI CMOS ASICsfrom Plessey Semiconductors; MACcontrol circuit MV1720, MAC video cir-cuit MVI710, MAC sound circuitMV1730 and MAC Teletext circuitMV1740. These are complemented byseveral Philips ICs; a MAC ANalogue(MACAN) circuit TDA8734 which per-forms analogue signal processing and in-cludes functions such as data slicing,

clock recovery and video clamping, amicrocomputer comprising a micropro-cessor (e.g. the 16 -bit 68070) plus RAMand ROM, and a conditional access con-trol module incorporating a PCB80C518 -bit microcontroller. Standard PhilipsICs are also used for D to A and A to Dconversion of the video signal (3 xTDA8702 and TDA8703 or PlesseySP94308 respectively), D to A conver-sion of the stereo sound signal (dualDAC TDA1541A), and for filtering thesound signal (SAA7220).The conditional access control modulehandles both over -air and/or local ad-dressing for decryption. It can either bedetachable or can form a permanentpart of the TV set. In either case, it'sconnected to the microcomputer via theEBU interface.

The user interface, in its minimum form,consists of pushbuttons and LEDs. Amore advanced version would incor-porate a keyboard for controlling menusand service identification data displayedon the screen of the TV set.

Nordic VLSI, together with TandbergTelecom and Elektrisk Bureau, has alsoformed the Crypto-MAC consortium,which will produce encoders and com-plete receivers using Nordic VLSI chips.The consortium has already signedmajor contracts for delivery of suchequipment.

Philips expect to commence productionof the multi -MAC decoder in June ofthis year.

CCIR is 60 years old

Sixty years ago, the ITU Plenipoten-tiaries of 80 states meeting inWashington D.C. (USA) from 4 Octoberto 25 November 1927, turned a page ofthe Union's history by creating the Inter-national Radio Consultative Committee(CCIR).Taking advantage of the presence ofseveral CCIR delegates gathered inGeneva for interim study groupsmeetings, the CCIR held a celebrationtoday to commemorate the event.In the years following the setting up ofthe Union, international agreements inthe field of radiocommunications couldbe made by international conferenceswithout much difficulty. However, as aresult of the rapid development of thetechniques used and their increasingcomplex nature, it became clear in the

1920s that preliminary studies and coor-dination of the work undertaken in eachMember country in telecommunicationsresearch and development would be re-quired by international conferences toenable them to reach agreements withinreasonable periods of time.It is against this background that the de-cision was made to establish in 1927 apermanent body within the ITUSecretariat to deal with these questions.The role of the CCIR today is to studyand issue Recommendations on techni-cal and operating questions relating toradiocommunications. The First PlenaryAssembly - the policy -making bodymade of representatives of Member ad-ministrations - was held in The Haguein 1929 and the first post-war Assembly,which reorganized the work of theCCIR, was held in Stockholm in 1948.Over 300 Recommendations adopted

EE 111March 1988

throughout its 60 years of history arestill in force to date.CCIR's Recommendations cover nearlyevery domain of the use of radio tech-nology, including radio relay systems intelecommunications networks, satellitesystems for communications, radio andtelevision broadcasting, and mobile ser-vices such as maritime, aeronautical andland vehicle mobile communications.Some basic aspects of radiocommunic-ation are also studied, as radio wavespropagation and technical means thatwould lead to a better and more econ-omical use of the frequency spectrum.The CCIR is headed by a Directorelected at Plenipotentiary conferencesand is assisted by a specializedsecretariat. The present Director of theCCIR is Mr. Richard Kirby from theUnited States.

The International Telecommunication Union (111.) was founded in 1865 and as such is the oldest specialized agency of the United Nations. It now has amembership of 163 countries. It is the international organization responsible for the planning of telecommunications worldwide, for the establishment ofequipment operating standards, for the coordination of data required for the planning and operation of telecommunications services and, within theUnited Nations system, for the development of telecommunications..

Cultural television channelexpands in EuropeBritain's Satellite Television Arts Chan-nel, which broadcasts cultural program-mes to cabled homes in western Europe,has added West Germany and Austria toits 'footprint' as from 1 January thisyear. From that date, it will also beavailable in many more households inBelgium, Denmark, the Republic ofIreland, Luxembourg, Finland, Norway,the Netherlands, Sweden, andSwitzerland, as well as in Britain.The expansion follows the conclusion ofan agreement between the two-year oldchannel and Skychannel, whichpioneered satellite transmissions of fam-ily entertainment within Europe andprovides for Arts Channel programmesto be transmitted via Sky's Eutelsat Flsatellite transponder. The three hours ofcultural programmes are scheduled fortransmission at 2330 UTC, althoughtrailer highlights will be shown duringthe day so that viewers who do not wantto stay up can set their video recorders.Arts Channel makes about one fifth ofits own programmes and 95% of thetotal output is of European origin. Therange includes ballet, opera, drama,music, and visual arts. The channel iscurrently filming a major four-partdocumentary, William and Mary, mark-ing the 300th anniversary later this yearof the accession to the British throne ofDutch Prince William of Orange and hisEnglish wife Princess Mary. This Anglo-Dutch programme will describe thearchitecture, painting, and music of theperiod.The Arts Channel P.O. Box 7 Ebbwsale Gwent Wales United Kingdom.

et -7i

Buzzbox attracts the deafThe problem of how to attract the atten-tion of a deaf child has been solved by aUK engineering product designer. Hehas produced a vibrating bracelet that isworn by the child and radio controlledby the parent.Mr Paul Fearis developed the Buzzboxduring his final year at South BankPolytechnic, London, in response to aproblem raised by the UK RoyalNational Institute for the Deaf. It con-sists of two units -a transmitter wornby the parent, and a receiver worn by thechild, both running off rechargeable bat-teries.The vibrating bracelet is connected tothe receiver by a wire. Both units areabout the size and weight of a smallcalculator, are moulded in plastic and

are water resistant. "I used the sort ofrugged radio -control apparatus used inaeroplanes" explained Mr Fearis, "so itshould survive being dropped".The transmitter sends a signal within thestandard Citizen's Band frequency butthis does not create any interference withCB radio, sines the Buzzbox signal isdigitally encoded. The signal is then re-ceived and decoded by the child's re-ceiver, triggering the vibrator in thebracelet. The system will work up to adistance of 1.6 km in an open area, or0.4 km in a heavily built-up area.The parent can send a signal on two dif-ferent channels, each of which will lightup a different light -emitting diode(LED) on the child's receiver, one redand the other green. The parent andchild agree as to the meaning of the twodifferent signals. The LED and vibratorwill automatically switch off after 16seconds if a child does not switch themoff first. The 16 second period can bechanged by changing the resistance andcapacitance of the trigger circuit.The vibrator itself consists of a smallDC motor driving an off-centre weight,so that the velocity of the motor controlsthe frequency of vibration felt by thechild. (200 Hz is thought to be the fre-quency to which humans are mosttouch -sensitive.)Blind people could also use the system,says Mr Fearis, if the red/green LEDswere replaced by two different types ofvibratory signal. The child could receivea pulsed vibration, for instance, by send-ing a square -wave radio signal.The Buzzbox is to be manufactured byMentmore Industries, workshop for thedisabled in Hackney, London, and willretail for about £47.

rch,98.

SLAVE INDICATION UNIT FINTELLIGENT TIME STANDARD

sr 7t41E STANDARDELEKTOR

The serial data output of the Intelligent Time Standard describedlast month is geared to driving a number of auxiliary time and

date indication units installed at some distance from the masterclock.

Applications of the indication unit described here can be foundin and around the home, in studios, offices, laboratories, schools,

workshops, or any other building in which accurate, central,timekeeping is a must.

The slave indication unit described hereis an optional extension to the IntelligentTime Standard (DCF77 clock) describedin "'. The unit has large time and datedisplays with automatic brightness regu-lation, and is connected to the TimeStandard via a 2 -wire cable.

Circuit descriptionAt the heart of the present circuit is apre-programmed microcontroller Type87481-1 from Intel. The "invisible"program that controls the operation ofthe indication unit has been designedand loaded into the EPROM on boardthe 8748H by Elektor Electronics. Theinternal machine code enables themicrocontroller to combine the func-tions of:1. serial data receiver;2. ASCII to 7 -segment decoder;3. intelligent display multiplexer and

refresh timer.

Hence, software is used in this appli-cation to make for a remarkably lowchip count in a circuit whose operationis, none the less, relatively complex.With reference to the circuit diagram ofFig. 1, serial data at TTL level trans-mitted by he Intelligent Time Standardenters the circuit of the slave indicationunit via buffer/inverter T,, which drivesthe INT (interrupt) input of themicrocontroller, ICI. Figure 2 shows thecircuit diagram of the display unit,which consists of two multiplexed rowsof 7 -segment LED displays, and 7discrete LEDs. Port PI of the 8748Hcontrols the segments of the upper 6 dis-plays (time), and the 7 LEDs (day of theweek), while port P2 controls the lower8 displays (date). IC; and ICs containpower buffers inserted between the portoutputs of the microcontroller and thecathodes of the display segments and thediscrete LEDs. The display 'unit ismultiplexed by databits DB0... DB7 anddarlington transistors T2...T9 incl.

The brightness of the displays is con-trolled automatically as a function ofambient light intensity. This function isrealized by phototransistor Tit in con-junction with voltage regulator IC3 (ref-erence 01). The common -anode voltagefor the displays, Ud, is directly relatedto the ambient light intensity measuredby Tu. The minimum brightness of thedisplays can be set to individual require-ment by increasing the value of R.i to220 Q, and reducing R4 to 560 Q.The regulated 5 V power supply for theslave indication unit is of conventionaldesign, and merits no further comment.The alternating input voltage(9...10 VAC) is obtained from a mainsadapter, or a suitable power transformer.

Construction: two boardsThe slave indication unit is built on twoequally sized printed circuit boards thatcan be fitted in a sandwich construction

1

7. 270

1000)01-1

'Cl

211.11

zDm

S

ULN

2000

5V

7. 7 of7

v

(5

0111

M°.0. 251

roVCC YCO

" P16-2

52P

21 P1.2as 71.5as 16.2

16.7

EME

1.2

5V

00

7.

0SV

322

P2.2Pil

it P2.2P1..1

3dP2-2

31

a 727

6D676

c t

BC -517

PIT

PISEN

6.00

272.1 -

IC I

8745/4

DS I

2C.53

CS.

755

CM

DS7

SS

n --

5V

:Li =A* c

-T 1.

/2 222 ((at

u 22 130(C31) (222) t0221 (CM) (CAS) (C.2.5) tun tem'

CC

5I0

222

11-1711SSA

A

05

72-T5= S. 1317675

Of = aan 3676.6.61:7 = aP ren snot ets.6

x=212PCs t9

Up(3V -.5-5V)

0

f=1

17125_1

Fig. 1. Circuit diagram of the remote indication unit for the Elekior Electronics IntelligenTime Standard.

2

Kt!tt]1,11

I2,1

LD 1

I_II -I

12? I 127 7,5

r upDal

66)

1.681"16S,000

LD

=kJLi

vac 2

1.011

LDS 1D 5

CM

1-1LI

12011D&T

Pa

rC6

10121 LD

I-1 IIIII0 0 I I0ri

TUESDAY

WEDNESDA

1152152.21

FRIDAY

LD11022 .77S 7751DI -DO. LSD

.74 -

SATURDAY

SLIMLY

EE

March 1988to allow the use of a relatively flatenclosure (see the introductory photo-graph). For ease of wiring and access,the boards are mounted with facingtrack sides. It is also possible to use thecontrol board for driving other displayunits, such as the Jumbo Displays (refer-ence 0)), provided the necessary altera-tions are made to this circuit.If the sandwich construction is used, theboards are best interconnected withshort lengths of strong, solid wire. Forother mounting arrangements, it is rec-ommended to use a 5 cm long connec-tion made in flatcable.The two sets of pull-up resistors,R12...R1S incl. and R19...R25 incl., arepreferably mounted as 9 -pin, single -in -line, resistor networks, but it is alsopossible to use 16 miniature (0.125 \V)resistors, mounted vertically and com-moned by a horizontally running wire tothe positive supply line (see Fig. 3).The component mounting plan for thecontrol board is shown in Fig. 4. Thereare 6 fixed, and 2 variable, wire links,whose function is shown in the circuitdiagram. Fit links A -C (century: 19xx)and E -F (no zero suppression).All segment control outputs are made insoldering terminals. Common -anodedriver transistors T2...T9 incl. are fittedin a neat row on the PCB, and can dowithout a heat -sink. Be sure to check themounting position of these transistorsagainst the pin -out shown in the circuitdiagram, Fig. 1. Voltage regulators IC2and IC3 need heat -sinks of the style andsize indicated on the component overlay.It is not necessary to insulate the metaltabs of the regulator chips from the heat-sinks. These can be bolted direct ontothe PCB, provided that they are -andremain -well insulated from oneanother, as well as from any other parton the board (remember that the heat-sink for IC2 is connected to ground, andthat for IC3 to junction R41 -R43).The phototransistor, Tit, is fitted in aposition that allows the detection of am-bient light only, i.e., the device must not"see" the light emitted by the LED dis-plays. Preset Pt makes it possible to setthe display brightness to personalpreference, and as required for the am-bient light condition.

The display board is simple to build.Commence the construction with fittingthe 8 wire links on it. LEDs Ds. -Dumay be omitted, or fitted purely for

3.5V

Fig. 2. Circuit diagram of the display unit. Fig. 3. Eight miniature resistors may be usedinstead of a 9 -pin SIL resistor network.

54 EE

March 1988decorative purposes. The contrast, andhence the legibility, of the read-out canbe enhanced by means of a red, semi-transparent, display bezel.Check the operation of the on -boardpower supply before fitting the ICs intheir sockets. Set Pi to the centre of itstravel. Verify the presence of +5 V on

pins 26 and 40 of the socket for themicrocontroller, ICI. Evidently, the cir-cuit works only when the microcon-troller Type 8748H contains the correctcontrol program. Ready -programmed8748Hs for this project are availablefrom Elektor Electronics or its agentsunder order number ESS 559.

Fit the ICs, and test the completed cir-cuit by applying power. In the absence oftime and date information from the In-telligent Time Standard, the displaysshould read 00 00 00 (time) and01 01 1900 (date). If this checks out, theboards are ready for fitting into asuitable enclosure.

4

203000000© ii0000008 61000"6:9 JINJR32 -NW--------Drl'OTIfta NM effaintl

{DD CJOD-11111M

1!4//= Ck0:11 rri00-0D

1.0x Ot-

0=11-00

0-1R2 -0 0.1 010,_,,0

0-1.4.1-00

n +"a

0

0 ®ice r}r

0 II

9 9 9AL.)

ADAN

6 6 6

meD QIlma"I° 'EnT

V CI

0204o 1>1 o

(c)

03o444-0

0

r

0

6a

4)

Fig. 4. The printed circuit hoard for the control board in the slate indication unit.

Parts list

CONTROL BOARD. CIRCUIT DIAGRAM: FIG. 1.

Resistors

RI =10KR2=4K7R3= 5K6

incl.=2K2812 . . .R18 incl.;R19...R25 incl.= 3K3 8 -waySIL resistor network

826...R39 incl.=27RR40 = IKO

841=100RR42 = NOR.R43 = 22OR

Pi =25K or 22K preset H

See text.

Capacitors:

Ci=3n3C2;Cio=1y0; 10VCa;C4=33pCs= 2200y; 25 VC6= 22011

C7;C9;C11=100nCo= 10p; 10V

Semiconductors:

Di =1N4148Dz ...Ds incl.= 1N4001Ti =BC547Tz ... Ts incl.=BD676Tto=BC516

Tit = general-purpose phototransistor, e.g.BP103 or TIL81

ICI = programmed 8748H. Elektor Electronicsorder no. ESS 559 (see Readers Servicespage).

IC2=7805ICa=LM317T (T0220 style)IC4;IC5 = ULN2003

Miscellaneous:

Xi = 10 MHz quartz crystal (enclosure:HC25IU).

Heat -sink for 1C2.Heat -sink for !Ca.PCB Type 87104-1 (see Readers Services

page).

EE

March 1988

It is recommended to drill a number ofventilation holes in the top and bottompanel of the enclosure, to keep the tem-perature of the voltage regulators on theheat -sinks within reasonable limits. The

mains transformer plus fuse is preferablyfitted in a separate box. Figure 7 showsa suggestion for making an attractivelooking front panel for the slave indi-cation unit.

Parts list

DISPLAY UNIT. CIRCUIT DIAGRAM: FIG. 2.

Resistors (± 5%):

Rt...R4 incl.= 33R

Semiconductors:

DI ...Ott incl.= LED, 03 mm, redLD1...LD14 incl.= 7750 or 7751 (common

anode LED display)

Miscellaneous:

PCB Type 87104-2 (see Readers Services

Pagel -

Connection to theTime StandardDiodes 132 and D., if present, are re-moved from the PCB in the intelligent

Fig. 5. The printed circuit board for the display unit.

56 EE

March 1988

Time Standard, while CI is replacedwith a wire link. The DCF77 clock sendsits data to the remote indication unit(s)via two wires. Output Tx]) (transinitteddata) on the Intelligent Time Standard isconnected to RXD (received data) on theslave indication unit. The other wire isconnected to ground on both units. Itwas found that an unshielded 2 -wireconnection can have a length of about15 m even when it crosses relativelystrong electromagnetical fields, causedby, for instance, luminescent tubes orelectronic equipment. For distancesgreater than 15 m, reliable data transferis made possible by the use of screenedmicrophone wire. If interference persistsin a system with multiple indicationunits and relatively long connections, itis recommended to insert line buffers atappropriate locations. In some cases itmay also be necessary to ensure someprotection against spurious pulses in-duced on the 2 -wire cable: fit a 5V1 or5V6 zenerdiode across R6 in the In-telligent Time Standard (anode toground).

Time signals

It is possible to drive the slave indicationunit from clock systems other than theIntelligent Time Standard, but only ifthe format of the serial time and date in-formation is brought in accordance withthat discussed in (".The numerical data structure shown inthe example of Fig. 6 is selected when IN-PUT on the Time Standard is activated,and configuration diode DI3 has beenfitted. It should be noted that the slaveindication unit recognizes ASCII inputdata only. Data is organized as two hexa-decimal figures, with two spaces (20n)to separate complete numbers. ASCIIcharacter 3011 (0) is treated as 20H(space) by the slave indication unit,while the Intelligent Time Standard canbe set up to replace leading zeroes by

spaces. The data blocks are displayedstrictly in the order in which they are re-ceived. The carriage return and line feedsequence (CR-LF; ODit-OAn) is used formarking the end of the complete datablock, and for resetting the internalpointers to prepare for reception of thenext data string.With reference to Fig. 6, the LEDs and

displays are controlled by the followingdata blocks:Block 1: LED DI... D7, day of the

week;Block 2: LD7-LDs, day of the month

(1-31);Block 3: LD9-LDio, month (1-12);Block 4: LD13-L114, year (00-99);Block 5: Lth-LD2, hours (0-24);Block 6: LD3-LD4, minutes (0-59);Block 7: LDs-LDo, seconds (0-59).The order in which the data blocks aresent, and their assignment to the dis-plays, is fixed, since the slave indicationunit can not change the format of the re-ceived data.The data speed on the serial link be-tween the time standard and the remoteindication unit is 4,800 bits/s. The struc-ture of the serial data is:

8 databits, no parity, 1 stop bit.

Software

Although the operation of the softwareloaded in the microcontroller is, nor-mally, invisible to the user, it is none theless useful to read the following descrip-tion of its main functions.Broadly speaking, the control program

6

TXD -

DAY IMOKDAY=1)

DAY OF MONTH

PLINTH

'EAR

HOUR

MINUTE

SICOND

-2- -13- - -3- 88- [g 52 - 45 - CR/LF>

= space = 213ngASCII: 20 20 32 20 20 31 33 20 20 20 33 20 20 38 38

20 20 20 38 20 20 35 32 20 20 34 35 20 OD OA

r

LZ1 LD 2

I

I

/NILDS to 11

LOS LOS

I -II

LD t) to

I 1:I I 1CI

I I- ICI

1.1

mft

114

C.1=

1.01_117 I r ITUE TlitEIL-Dt4= LEO

n05E:AY

87104.6

Fig. 6. Data structure and resultin9, time and date indication on the disola) unit.

in the microcontroller 8748H is geared toperform two functions:1. conversion to parallel of the serialdatastream received from the IntelligentTime Standard;2. driving, multiplexing and refreshingthe display unit.The microcontroller used here does nothave an ACIA function (AsynchronousCommunications Interface Adapter), sothat serial -to -parallel conversion (shift-ing in) of received data can only be ef-fected with the aid of timing routines inan interrupt structure. The start bit ineach new dataword causes the first inter-rupt, which is received while the mainprogram works on multiplexing andrefreshing the read-out. Display refreshis automatically corrected as a functionof interrupt handling time. Thanks tothis part of the control software, theread-out is stable and equally brightunder all conditions, while correct pro-cessing of input data is ensured at thesame time. The display routine in thecontrol program is interrupted for 54 psat 208 ps intervals (208 ps is the bitperiod for 4,800 baud). There are 10 in-terrupts per received byte.The displays are multiplexed in pairs(LII-LD7; LD2-LDs; LD3-LD9; and soon) at a frequency of about 125 Hz, andan on -time of about 1 ms. In the absenceof the automatic refresh correction,reception of 10 consecutive databitswould cause an unacceptable delay of540 ps, and hence would give rise to an-noying display flicker. Day of the weekindicators Di... D7 incl. are controlledtogether with LDI3, and only 1 of the 7LEDs can light at a time.The automatic leading zero suppressionfor the tens indication of the day, monthand hour read-out can be disabled by fit-ting jumper E-F instead of D -E.

This option has been included in thedesign to allow the indication unit to beused in applications other than clocksystems (studio timers, score -displays,etc.). With jumper E-F fitted, leadingzeroes are displayed, irrespective ofwhether these are caused by inputcharacter 20H (space) or 30H (0).The software in the .slave indicationrecognizes and processes the SYNC/NOSYNC code transmitted by the In-telligent Time Standard after the twoseconds bytes and subsequent spaces inthe time string (Mode: EXTRA INFOON. SYNC = 42H; NO SYNC = 45H,see Fig. 6 in 9. This code may be usedfor controlling a LED that indicateswhether or not the time standard is syn-chronized to DCF77. Such an indicatorhas not been provided on the slave indi-cation unit, but is readily added by fit-

EEMarch 1988

ting the anode of a LED to CA8, and thecathode to line b2. Th

References:

'" Intelligent time standard. ElektorElectronics January 1988, p. 22 ff.'' Jumbo displays. Elektor ElectronicsJuly/August 1985, p. 7-88 ff.(3) Display intensity control. ElektorElectronics July/August 1987, Supple-ment p. 9.

Note:

The control program in the 8748H (ESS 559) is notpublic domain software: the copyright rests withBator Electronics. Source listings and/or hex -dumps of the program are, therefore, not available.

7

SLAVE UNIT

00

00

0 StTu ... ..

nIELEKTOR 4C-77:> TIME STANDARDELECTRONICS

87104-7

Fig. 7. Suggested front panel Ian -out.

NEW LITERATURE

Practical Digital ElectronicsHandbookby Mike TooleyISBN 1-870775-00-7197 pages - 215 x 136 mmPrice £6.95 (soft cover)As the title of the book suggests, the em-phasis of the work is on the practicalaspects of electronic circuits. Conse-quently, there is hardly any theory to befound in its pages. Quite correctly, Mr.Tooley is saying that the designer of elec-tronic circuits need not know the inter-nal function of ICs, for instance.In a similar manner, logic networks areapproached from a practical angle - noBoolean algebra here.The treatment of microprocessors dealsto some extent with the internal architec-ture, but with these devices that is virtu-ally unavoidable.

The book further deals with semicon-ductor memories, I/O devices, the RS-232C interface, the IEEE -488 generalpurpose instrument bus, and the IEEE -1000 microprocessor bus.A very useful part of the book is an ap-pendix dealing with the necessary toolsand test equipment required for fault-finding, complete with details of anumber of test gear projects.Altogether a very useful book foranyone involved in the design, manufac-ture, or servicing of digital circuits.PC Publishing22 Clifton RoadLONDON N3 2AR

OscilloscopesRevised second editionby Ian HickmanISBN 0-434-90738-3133 pages - 215x135 mmPrice £5.95 (soft cover)

The second edition of this popular bookwas reviewed in the July 1986 issue ofElektor Electronics. This revised editionhas been updated and enlarged to covernew instruments that have been in-troduced since then. Among the new in-struments are the Tektronix 2225 and the11000 Series, the Beckman 9020, theMeguro MO -1255, the Philips M03050,the Crotech 3133, the Nicolet 4094, theGould 4072, and the Hewlett-PackardHP54110D.The book remains well illustrated withdiagrams and photographs and will con-tinue to appeal to everyone who wants toknow about oscilloscopes, from the stu-dent to the graduate, from the hobbyistto the technician.William Heinemann Ltd10 Upper Grosvenor StreetLONDON W1X 9PA

58 EE

March 1988

Audio Amplifier Fault-findingChartby Chas. E. MillerISBN 0-85934-095-3Price 95 pThis chart has been designed to help thereader approach fault rectification andrepair of audio amplifiers in a systematicand logical way.The author has developed the chart bydrawing on many years' experience inrepairing audio and hi-fi systems. Usedcorrectly, the chart should enable theuser to trace many common faultsreasonably quickly.All the user has to do is to select one ofthe faults shown at the top of the chart,and follow the arrows while carrying outthe suggested checks in sequence untilthe fault is cleared.

Measuring 640x450 mm, the chartshould prove of interest to anyone in-volved in the repair or servicing of audiocircuits.Bernard Babani (publishing) LtdThe GrampiansShepherds Bush RoadLONDON W6 7NF

DATABOOKSSoft ,Vagnetic Ferrites is a bi-lingual(Serbo-Croat and English) book thatshould be of interest to anyone involvedin the design of inductors. The 186 -pagepublication is available from ISKRA Ltd Redlands COULSDON CR3 2HT Telephone 01-668 7141.

The ASIC Data Book should be of in-terest to anyone involved with Appli-cation Specific ICs. It is available fromMIETEC UK Easthampstead Road BRACKNELL RG12 1NF Tele-

phone (0344) 53974.

CATALOGUESThe 1988 Babani Books list is availablefree of charge. Just send a 220 x110 mmstamped, addressed envelope to BernardBabani (publishing) Ltd The Gram-pians Shepherds Bush Road LON-DON W6 7NF.

PEOPLE

Chris Cutting (above) has recently beenappointed marketing manager of CirkitDistribution, the well-known Brox-bourne-based electronic product sup-pliers.

Mr. Ron Bull, BSc, CEng, (above) heimmediate past president of The Ma-chine Tool Trades Association, is thenewly elected President of CECIMO, theEuropean Committee for co-operationof the Machine Tool Industries.

The Hawker Siddeley Group has madethe following appointments. Mr. R.P.Hampson becomes chairman of BrushElectrical Machines Ltd.; Mr. B.G.Shoosmith becomes chairman and man-aging director of Crompton ParkinsonLtd.; Mr. W.M.M. Petrie becomes man-aging director of Brush Electrical Ma-chines Ltd.

Printronix have appointed Roy Venables(above) UK Sales Manager in successionto Martin Phillips, who now managesthe company's sales in Scandinavia andthe Benelux.

Mr. David Dey has joined the UK Com-munications Division of British Telecomas Deputy Managing Director. Mr. Deywas until recently Managing Director ofPlessey Telecommunications.

Marconi Radar Systems of Chelmsfordhas appointed John Winstanley director,airspace business, with particularresponsibillity for all the activities of thecompany's airspace control diviion. Atthe same time, the company has ap-pointed Steve Menzies financial director.

Alpha Electronics Ltd have appointedKeith Richens (above) as Technical Di-rector.

Gary Clark (above) has recently been ap-pointed Business Manager of the Tele-communications Products Group atBase Ten Systems.

EE

March 1988

NEW PRODUCTS NEW PRODUCTS NEWAccelerometers for severeenvironmentsBRUEL & KJAER (UK) LTD. have re-cently released two new accelerometersfor use in severe environments.They are Types 8315 and 8317 and bothare constructed on the now well-knownDelta Shear principle.The 8315 is suitable for use at 250 °C,has a frequency range from 0.1 to8100 Hz and weighs 102 grams.

The 8317 is certified as intrinsically safefor explosive areas (Class EEx 11CT6/T5/T4), has a built in line driveamplifier, a frequency range from 0.2 to7500 Hz and weighs 112 grams.Both can be supplied with integral cableif required.Bruel & Kjaer (UK) Ltd 92 UxbridgeRoad HARROW HA3 6BZ. Tele-phone: (01 954) 2366.

New dual -element pyroinfrared detectorsQuantelec has announced a new range ofpyro infrared detectors which arespecially designed for applications suchas burglar alarm systems, positioningunits, automatic light switches and dooropeners.Manufactured by Sentel in WestGermany, the new detectors feature adual element design with parallel op-posed elements which produces a highlevel of common mode rejection. Thismakes the devices ideal for the above ap-plications.

0-*44>

*'vN1W4r4

The detectors use Lithium-Tantalate asthe IR-sensing material so that theresponsivity of the device is independentof the temperature within its operatingtemperature range of -40 to +70 °C.The standard window material is silicon,coated for an optical bandwidth of 7 to14 pm. A range of different filters is alsoavailable including silicon with wide -band AR -coating, quartz, Irtran 2,Calcium Fluoride and narrow band win-dows.Frequency response of the detectors is+6 dB/octave from 0 to 0.3 Hz, flatfrom 0.3 to 0.5 Hz, and -6 dB/octavebeyond 1 Hz. Supply voltage is 3-15 VDC and output impedance is 10 kg2maximum.Quantelec Limited 46 Market Square WITNEY OX8 6AL. Telephone:(0993) 76488. Telex: 837851 SELECT G.

High-performance filtermodulesKemo has developed a new range ofhigh-performance filter modules whichare available with a wide selection ofcharacteristics and in different con-figurations.The standard 1100 Series modules aresupplied in a compact, common-pinout2 -inch square package, but filterassemblies are also available in the formof IBM PC or compatible cards, VMEboards or 32 -channel rack/benchmounting carrier systems.The filtering functions available in the1100 Series cover elliptic, Bessel and But-terworth types, with an emphasis on thepreparation of signals for digital signalprocessing. Both seventh and ninth -order elliptic functions are included,with a wide choice of shape factor.The frequency range of the filter cutofffrequency is from 10 Hz to typically250 kHz, and all filters in the rangeshare a basic common specification withonly small changes between differentresponse and frequency options. Hencedesigners can specify many differentfilters in a complex system without com-patibility problems.Other features of the Kemo 1100 Seriesinclude a deep attenuation floor down to-90 dB, low noise and distortion with awide dynamic range, and close phasematch within batch deliveries.Kemo Limited 9-12 GoodwoodParade Elmers End BECKEN-HAM BR3 3QZ. Telephone: (01 658)3838.

New low-cost card turns a PCinto a fax machinePC users can now use their micros tosend and receive fax messages-thanksto a new, low-cost card available ex stockfrom Dram Electronics.The IC -01B fax card costs £546 and slotsinto the back of any IBM PC or clone.It enables the PC to send text to anyGroup II or Group III fax machine overtelephone lines under CCITT V29 andV27 standards.The card meets T4 and T30 compati-bility. Data rates are as follows; V29:9600/7200/4800 bps; V27 ter: 4800/2400 bps; V21: channel 2 at 300 bps.Data format is synchronous. Power con-sumption is 3.6 W.Built-in software converts data fromASCII to fax format for transmission.The card generates tones up to 4800 Hzand detects tones of 462 Hz, 1100 Hzand 2100 Hz. Dialling is by tone, pulseor voice frequency energy detect.Dram Electronics Ltd. Unit 12Kingston Mill ChestergateSTOCKPORT SK3 OAL. Telephone:(061 429) 0626.

Wide range of enclosures instock at ESS

Available off the shelf from ESS is awide range of West Hyde enclosures.Included in the stock at ESS is thepopular range of Bopla enclosures. Inthe range is the modular electrical/elec-tronics enclosure system Combi-card.ESS Ltd Harrison House HarrisonRoad Swaythling SOUTHAMP-TON SO2 3TL. Telephone: (0703)671166. Telex: 477379 WINSER G. Fax(0703) 331769.

DESIGN ABSTRACTSThe contents of this column are based on information obtained frommanufacturers in the electronics industry, or their representatives,

and do not imply practical experience by Elektor Electronicsor its consultants.

ELECT OMC COMPASSTwo magneto -resistive sensors and a relatively simple measuring

and control circuit form the basis for the design of an all -

electronic direction finder.

Magneto -resistive sensors: .abrief recapThe basic structure of the four magneto-resistive elements in the Wheatstonebridge Type KMZ10A is shown in Fig. 1.The sensor elements are essentiallymeander -shaped, permalloy, tracks withgold stripes. This structure is referred toas a barber's pole for obvious reasons.Inside the plastic encapsulation of theType KMZ10A magneto -resistive sensorfrom Valvo (Philips/Mullard) is a siliconsubstrate that carries four of suchelements connected as the arms of aWheatstone bridge.The KMZ10A makes use of the Gauss-effect, i.e., the property of current -carrying material to change its resistivityin the presence of an external magneticfield. This change is brought about byrotation of the magnetization relative tothe current direction. The degree ofbridge imbalance is used for indicatingthe magnetic field strength, or, more pre-cisely, the variation in magnetic field inthe plane of the permalloy carriers rela-tive to the direction of current.

The Wheatstone bridge is composed oftwo elements whose resistance increases

with measured magnetic field strength,and two elements with exactly the inverseproperty. The bridge is balanced in thequiescent condition because sensorelements of identical property arelocated diagonally on the carrier chip-see Fig. 2.

Designing an electroniccompassThe earth's magnetic field is relativelyweak, so that the final accuracy of anelectronic compass based on magneto -resistive sensors is limited mainly bydrift incurred in the sensor, and offsetvoltages in the instrumentation ampli-fier. Offset voltages and signals causedby magnetic fields can, however, bediscriminated by making use of a prop-erty typical of the the barber's polestructure, namely that the two directionsof magnetization result in two directionsof maximum sensitivity. Thisphenomenon can be exploited in a prac-tical circuit that arranges for the sensorto be fed with a series of positive andnegative magnetic pulses in the x direc-tion. For the KMZ10A, the continouslyreversing field applied should have astrength of 3 kA/m. This value is en -

1

t t

\df\ \A, \.,\ \"\\\\9\\A

-

sured by an inductor winding secureddirect onto the sensor enclosure, or byfitting the sensor inside a small coilformer.Figure 3b shows that the offset voltageremains constant during the periodicmagnetization by the positive andnegative pulses. It is seen that the signalsof interest are rectangular pulses, whichare relatively simple to separate from theoffset voltage. This obviates the need foran auxiliary field, which would degradesensitivity. The full sensitivity of about14 (mV/V)(kA/m) stated for the TypeKNIZIOA is, therefore, available, whilemeasurements of field strengths, ofup to 0.25 kA/m can be carried outwithout running into sensor instabili-ty.iThe proposed principle of alternatingfields for each plane of maximum sensi-tivity is well suited to directionmeasurements in the earth's magneticfield. The construction of an electroniccompass for navigation in or on vesselsand vehicles can be based on twomagneto -resistive sensors positioned atright angles, and fitted in the former ofan inductor that supplies the reversingfield. Temperature compensation for thesensor is not required in most cases,because the relative, rather than absol-

Fig. 1. Barber's pole structure of gold stripes wound on the meander -shaped, permalloy track Fig. 2. Magneto -resistive elements form thethat forms the magnetization -controlled resistance. four arms of a Wheatstone bridge.

EE

March 198861

inductor

Sensor

19.

a)

current pulses

current

N.

b1

magnetization

c)

t

offset voltage

Fig. 3. An external inductor supplies a pulsating and reversing auxiliary magnetic field to thefour sensors in the Wheatstone bridge (a). Elimination of the offset current (b). and pulsediagram (c).

ute, amplitudes of the sensor signals areprocessed and fed to a display unit.Both sensors can be switched by a singleinductor. It was found that a second in-ductor is required for measuring fieldsperpendicular to the x -y plane. Three-sensor arrangements were tested with asingle inductor for the three directions,but gave unsatisfactory results becausethe angles between the magnetic fieldand the x plane were greater than 45°.Details on the construction of a suitableinductor for a 2 -sensor head are given inFig. 4. The inductor should ensure aminimum field strength of about3 kA/m, without causing oscillation orovershoot on the pulse edges. Without asuitable damping resistor, this effectwould lead to changes in the direction ofthe generated magnetic field. The opti-mum pulse length depends on the valueof this resistor in combination with theinductance of the coil. The magneto -resistive sensors used are relatively un-critical in respect of the pulse length, aslong as this is greater than 1 ps.Measuring errors caused by demagnetiz-ation during the pulse time can safely bedisregarded if the pulsating current has alow duty factor. The circuit of Fig. 5supplies 50 ps pulses at an output fre-quency of about 140 Hz (duty factor:0.007). The 140 Hz oscillator shown inthe top left-hand corner clocks a bistableType 4013, which is required to enablesimple AC -coupled measurement of theamplified sensor signals, which areavailable on terminals /A and Lly. The70 Hz signal is first buffered in fourparallel connected CMOS gates, beforeit is applied to two switching transistors,TI -T2, that form the inductor driver.Current pulses of about 50 is are ob-

tained by Cs being charged anddischarged.The output signals of the Wheatstoneelements are passed through couplingcapacitors (C5 -C6) to remove the offsetcomponent, and then raised in low -noiseoperational amplifiers Type NE5535.The circuit is adjusted as follows:1. Set presets Pi and P2 for minimumamplitude of the alternating voltagecomponent in U. and /./).2. Set P3 to achieve equal voltages U.

Fig. 4. Two magnetic field sensors TypeKMZ10A positioned at right angles, and fit-ted in a coil former Type 4322 021 30270(normally part of pot core set P18/11). Theinductor is wound as 100 turns 00.35 mmenamelled copper wire (SWG29). R=0.8 4;L=87 pH; 11'.=8.3 (kA/m)/A.

and U. at an equal magnetic fieldstrength in both sensors (e.g., by rotatingthe head 90° in the earth's magneticfield).

Source:Valvo, Techn ische In form a rioncn861105.

Reference:Magnetic -field sensors. Elektor Elec-tronics May 1986, p. 52.

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TEST & MEASURING EQUIPMENTThe penultimate part of Julian Nolan's review of dual trace

oscilloscopes deals with the Kikusui COS-5042TM and the GrundigM022.

Part 1: dual -trace oscilloscopes (D)

Kikusui COS-5042TMKikusui are a well -established companyproducing a range of test equipment thatincludes signal generators, power sup-plies, FFT analysers, and a variety ofoscilloscopes. Their COS-5000TM rangeof oscilloscopes extends from a 'basic'20 MHz model, the COS-5020TM, tothe 100 MHz COS-5100TM. The COS-5042TM, the top model in Kikusui's40 MHz range, costs £715, excludingVAT. The cheapest single timebase40 MHz scope from Kikusui comes in at£565, excluding VAT. Accessoriesavailable include viewing hoods, trolleys,protective front covers, and a suitablecamera mount. The two probes suppliedwith the 5042 are very similar to thoseprovided with other Japanese scopes.The 5042's small dimensions (288 mm(W) x 150 mm (H) x 370 mm (D))make its use in conjunction with otherinstruments in a confined space particu-larly easy. It is a pity, though, that the5042 is not provided with a swivel stand,something that with an instrument inthis class is normally taken for granted.The one -position stand fitted may beuseful if the instrument is to be stacked.The 5042 weighs 7.5 kg.The 5042 is supplied with a standardIEC style terminated mains lead and canoperate from line voltages ranging from100 to 240 VAC. Facilities provided onthe instrument include a trigger holdoffand 3 input channels, the third channelbeing usable as a trigger view or markerchannel. As usual, both the Z -modulation and CHI output sockets(BNC) are mounted on the rear panelalong with, surprisingly, the CH3 pos-ition control.The two main input channels, CHI andCH2, both have input sensitivities whichrange from 5 mV/div to 5 V/div, extend-able by a x5 switch to 1 mV/div. A vari-able control extends the maximum at-tenuation to approximately 10 V/div. Nouncalibrated indicators are provided forthe Y -amps which could initially lead touser reading errors, but these should bekept to a minimum thanks to the veryclear markings of the variable controls.Input capacitance is reasonable, and cer-

Fig. 19. The Kikusui COS -5042T111 oscillo-scope.

tainly acceptable, at 25 pF, although in-put capacitances of 20 pF are becomingincreasingly popular on scopes at andabove this bandwidth. The bandwidth ofboth amplifiers is good, extending up toapproximately 45 MHz (-3 dB) in the5 mV/div to 5 V/div ranges and an ex-cellent 23 MHz (-3 dB) when the x5magnifier is brought into operation. Thex 5 magnifier permits operation in the 2-4-10 sequence against the more usual 1-2-5 sequence, as well as permitting amaximum sensitivity of 1 mV/div. In thex 5 mode, the maximum error is in-creased from 3% to 5%, in commonwith most other scopes of this class. Asis increasingly the case for scopes of thiscomplexity, only one channel is invert-able (CH2) so that in some situationsswapping of probes may be necessary. Aminimal amount of drift is exhibited byboth amplifiers at switch on, enablingaccurate measurements to be carried outduring the warm-up period withouthaving to resort to adjustments of the Ytrace positions after a short period oftime.The third channel is of the same band-width as channels 1 & 2, but its rangesare restricted to 0.1 V/div and 0.5 V/div.These are, however, useful in that by theaddition of a x10 probe they can beused for digital measurements, or as amarker channel. In addition, the chan-nel can also be coupled internally,facilitating its use as a trigger view chan-nel capable of displaying the triggeringwaveform of either CHI or C142. Allthree channels are accurately matched soprobes should be fully interchangeable

between them without any compen-sation adjustments. A 1 kHz 0.5 p -pprobe compensation waveform is pro-vided. The wide variety of operatingmodes provided include the display ofCHI, CH2 or CH3 singly or in any com-bination. Only CHI and CH2, however,can be added. When in add mode, boththe input waveforms can be seen, as wellas the resultant which I found to begenuinely useful. The price paid for thisversatility is in the ease of operation.Push buttons are used in place of themore usual slider type switches for mostof the triggering and mode selectionfunctions. The trigger functions of the5042 are fairly comprehensive and in-clude auto peak -to -peak triggering, trig-ger holdoff ant) an alternate mode. Theauto triggering facility worked well inmost cases, although it did suffer from adistinct lack of sensitivity over the wholebandwidth. Typical sensitivity was twodivisions, which in dual, or triple traceapplications can prove to be inadequate.In this case, it is necessary to switch intomanual trigger control where the sensi-tivity is typically 1.2-1.5 div at 40 MHz,or about div at 10 MHz. The triggerholdoff was successful in stably display-ing a wide range of waveforms and insome ways made up for the lack of sensi-tivity. External sensitivity is good at40 mV (10 MHz) or 150 mV (40 MHz)and its usefulness is extended by a ÷5control, allowing triggering of, forexample, only the wanted signal if a largeamount of noise is present. The effective'lock on' time of the auto trigger circuitwas good with the minimum of delaypresent in most cases. Triggering sourcesinclude the useful alternate triggering fa-cility, as well as line and, of course, CH1,CH2 or CH3 (Ext). Automatic switchingbetween frame and line synchronizationis provided in the TV mode which is sur-prisingly useful, enabling generallyfaster and more efficient operation whenthe scope is operated in this mode.Because of its nature, it did not appearto affect the scope's versatility in anyway. An effective HF reject facility isprovided, although a corresponding LFfacility is not. Triggering facilities for thesecond (B) timebase, are rather limited,

EE

March 198863

TABLE 13

ELECTRICAL CHARACTERISTICSline voltage: - 100,120,220,240 VAC± 10%, externally adjustable. Powerconsumption: 35 WattsLine frequency: 50-60 Hz

MECHANICAL CONSTRUCTIONDimensions: -W 288 mm, H 150 mm.D 370 mmHousing steel sheetWeight: approx. 7.5 kg

Y AMPLIFIER ETC.Operating modes: -CH1 alone, CH2 alone, or CH3 alone.Inversion capability on CH2 only.Any combination of CH1, CH2 or CH3(alternate or chopped (250 kHz))CH1 + CH2Frequency response 0...40 MHz( -3 dB): 20 MHz x 5 Mag.Risetime < 8.8 nsec, (n-5 nsec x 5Mag.)Deflection factor 10 steps:5 mV/div...5 V/div ± 3%, vernier can-trol adjusts min. sensitivity on 5 V/divrange to approx. 10 V/div (fully anti-cw)-CH1 and 2 only.x 5 magnifier extends range to 1 mV/div,

20 MHz bandwidth, ± 5% = total errorInput coupling: AC, DC or Gnd.Input impedance: 1 MQ/25 pF; max inputvoltage 300 (DC + peak AC)Signal Delay time: approx. 20 ns on CRTscreen.

CH3 only specificationsSensitivity: 0.5 V/div or 0.1 V/div ±3%.Input Impedance: 1 MQ/25 pF.Frequency response: 40 MHz.Risetime 8.8 ns.Max input: 100 V (DC + AC peak)

X -Y MODECH1 and 2 Y-axis, and CH3 X-axis in dualchannel mode: single channel CH1 =X,CH2=YBandwidth: DC to 2 MHz 1-3 dB).X -Y phase shift <3° at 100 kHz

SWEEPType: - A; A sweep: Alt; A sweep(intensified for duration of B sweep): B;Delayed sweep: X -Y.A sweep time 0.05 s/div to 0.5 s/div,±3% in 22 ranges, 1-2-5 sequence.Vernier control slows sweep down by upto 3:1B sweep 0.05 s/div to 50 ms/div, ± 3%in 19 ranges, 1-2-5 sequence.Sweep magnification: x 10 ±.5% I ±8%

on 0.05 s/div to 0.2 s/div range)Holdoff; variable up to 10:1Delay modes: trigger delay (Trig);continuous delayDelay jitter: 1/10000

TRIGGERINGTrigger modes: Auto (bright line). Normal,level lock (auto p -p). single -reset.Trigger coupling: AC, DC, HF reject, TVframe and line (auto).Trigger sources: CH1, CH2, Line, Ext. orCH3, Vertical (alternate)Triggering sensitivity: Internal < 1.5 divat 40 MHz, External < 0.15 V p -p at40 MHz, Normal mode

MISCELLANEOUSCRT make: Kikusui, measuring area80 mm x 100 mm; accelerating voltage12 kV, domed -mesh type.Compensation signal for divider probe,amplitude aprox. 0.5 V pp (± 3%); fre-quency 1 kHz.Z modulation sensitivity: 3 V (detectableintensity modulation)Vertical CH1 output: approx 100 mVidivinto 50. Frequency response: 100 Hz to40 MHz except on x 5 (100 Hz to20 MHz).Covered by 1 year warranty.

although perfectly adequate for mostpurposes.The main timebase A, speeds range from50 ns/div to the usual 0.5 s/div, whilethe maximum deflection speed can beincreased 10 times to 5 ns/div. The sec-ond timebase, B, speeds range from50 ms/div to the same 50 ns/div. An un-calibrated indicator is provided for the Avariable sweep control, but not continu-ously variable control is provided on theB timebase. The display/trigger modesA,Alt,B,B trig should as mentionedabove cover most requirements althoughthey are by no means comprehensive.The 5042 offers an 8 trace capability,which consists of CHI, CH2, CH3 andCHI ± CH2 on both timebases. To acertain extent, I found this useful, es-pecially for detailed logic comparisonswhen 3 inputs were being used (6 traces);however, when this was increased to 8traces, vertical measurements of any ac-curacy were not possible, as the screenbecame extremely cramped (1 trace percm). The timebase accuracy was goodacross most of the ranges, but at thefaster timebase speeds it was noticeablethat there was a discrepancy between thetwo speeds which approached the ±5%specified error (10 magnifier was in oper-ation). A channel 1 out BNC socket isprovided on the rear panel giving ap-proximately 50 mV/div into 50.The 12 kV domed -mesh CRT provides asharply defined and bright trace acrossthe vast majority of deflection speeds.The brightness of the tube does, how-ever, limit the maximum magnificationratio of the delayed sweep facility to ap-proximately 1000 times in fairly low am-

bient lighting conditions. A front panelcontrol is provided for B trace intensity,which I found to be useful, especially incases where the delayed sweep facilitywas used at its higher magnificationratios. A photographic bezel is also fit-ted, along with a viewing filter.The 58 -page manual starts by giving ageneral description of the instrument,and goes on to cover operating pro-cedures, application and the specifi-cation in some detail. Although a blockdiagram is provided, no circuit diagramis given, but is available in the servicemanual.Internal construction is centred around anumber of fibre glass PCBs, the ma-jority of which have their print sidefacing outwards for easier servicing.There are, maybe not surprisingly, a

large number of wire links, not all ofwhich are grouped together. This couldin some cases hinder servicing of the in-strument, although I am satisfied that itwill not effect reliability. All boards areremovable, their connections being madeby a number of plugs/sockets. The 5042is based on a steel frame, which gives itthe robustness to operate successfully ina wide variety of environments. In con-trast to many other scopes none of thecontrols extends more than a relativelyshort distance from the instrument andthis should further aid robustness.The COS5042TM offers a very goodperformance combined with a ruggedconstruction, and small size. It doeshave one or two minor drawbacks, suchas its lack of triggering sensitivity and Btimebase facilities, but overall these do

Table 14

CATEGORY Unsatis-factory

Satis-factory Good

VeryGood Excellent

TRIGGER FACILITIESTRIGGER PERFORMANCEDEL'D SWEEP FACILITIESDELT SWEEP PERFORMANCECRT BRIGHTNESSCRT FOCUSSINGY -AMP ATTENUATION RANGEINTERNAL CONSTRUCTIONEXTERNAL CONSTRUCTIONOVERALL SPECIFICATIONOVERALL PERFORMANCEEASE OF USEMANUAL

**

*

*****

***

*

*

64 EE

March 1988

not significantly affect the performanceof the scope. It is likely to appeal tothose users who require real portabilitycoupled with the performance andfeatures it offers. When compared withother scopes in its class, the 5042 comesout particularly well on Y -amp perform-ance and power consumption, which willobviously be of more importance tosome users than others.

The review model of the KikusuiCOS5042TM was available for a veryshort time only, and it was, therefore,not possible to carry out the review indepth in respect of the more minorpoints.

The Kikusui COS5042TM was suppliedby Telonic Instruments Ltd, Boyn ValleyRoad, Maidenhead, Berkshire SL6 4EG.Tel: (0268) 73933

Fig. 20. SomeKikusui range.Other scopes availableKikusui ranee.

other oscilloscopes in the

under £1500 in the

COS 5020TM-2.2 kV CRT; 1 mV maximumsensitivity; DC -20 MHz bandwidth; alternatechannel triggering ÷ level lock; singletimebase (max sweep 20 ns/div); f.360÷VAT

COS 5021TM-same as 5020 ÷ delayed sweep(2 ps to 5 ms)-£490+VAT

COS 5040TM-12 kV CRT; 1 mV maximumsensitivity; DC -40 MHz bandwidth; alternatechannel triegerine ÷ level lock; singletimebase (max sweep 20 ns/div)-£565+VAT

COS 5041TM-same as 5040+ delayed sweep(2 ps to 5 ms) -1625

COS5042TM-covered in review -f715

COS 5060TM-same as 5042, but 60 MHzbandwidth (a large number of these havebeen bought by British Telecom.)-£820÷VAT

COS 5100TM-Same as 5042 except for100 MHz bandwidth; 18 kV CRT, max sweep2 ns/div-f1145 -VAT

COS 6100A -similar to COS 1500TM, but dif-ferent design ÷ 12 trace capability; 20 kVCRT. -11450

Grundig M022Grundig's M022 oscilloscope is basedon the M020 (reviewed in our January1988 issue), but it has, for instance, asecond timebase and fully automaticcontrol of the main timebase. Because ofthis, the triggering facilities and Yamplifiers will be discussed in detailagain, as they are virtually identical tothose found in the M020. The M022retails at £499, excluding VAT.The M022 is, like the M022, fitted witha non -removable mains lead which is ter-minated in a standard 2 pin IEC typeplug. Layout is similar to the M020,although, as can be seen from the photo-graph, the whole of the top half of thescope is taken up by the timebase andtriggering controls, which include auto-matic timebase selection. The Y ampli-fier controls are mounted on the lowerhalf. All controls are very easy to operateand clearly marked. Both the B timebaseand Y amplifier range selection switcheshave no endstops, which can be inconve-nient if the scope needs to be switchedquickly to one of its end ranges.Automatic triggering is provided on theM022, along with high and low fre-quency coupling. The B timebase is alsotriggerable, although the triggeringthreshold is set by the single trigger levelcontrol, meaning that both timebase aretriggered on the same threshold. In thevast majority of situations this shouldnot be a significant limitation, and paysdividends since it ensures both traces arestable. The B trigger modes are con-tinuous delay and triggered delay, inwhich mode the second timebase caneither be triggered on the rising or fallingslope of a waveform.Triggering of the second timebase is ef-fective across the whole bandwidth andextends to approximately 70 MHz inboth automatic (p -p) and normal trig-gering modes. This is, however, when

Fig. 21. The Grundig M022 oscilloscope.

Fig. 22. Interntil NiVls ut ihr M022.

Fig. 23. Detail of the M022 front panel.

using the soft tuning facility for manualselection of the A timebase sweep speed.When the A timebase was placed inautomatic mode, a maximum reliabletrigger frequency of 35 MHz was ob-tained, this being for the triggering ofboth the automatic facility and thetimebase itself. A trigger holdoff facilityis also provided, which is very effectivein providing accurate triggering on awide variety of waveforms. Its perform-ance was partiCularly good on pulse anddigital waveforms, providing a stabletrace under almost any alteration of thefrequency of the waveform and over avery wide range of timebase speeds (in-cluding automatic). External triggeringis also good with a typical sensitivity of400 mV and a maximum bandwidth ap-proaching 40 MHz, allowing the exter-nal synchronization of most events.Probably the main asset of the M022 isits fully automatic main timebase, whichenables very fast and easy operation ofthe scope when waveforms of a fairlyconstant amplitude, but not frequency,need to be measured. Timebase speedsrange from 220 ms/div to 500 ns/div, or50 ns/div if the x 10 magnifier isbrought into operation, this beingcovered in 18 steps, either by automaticor manual soft tuning via a continuouslyvariable control. Timebase range indi-cation is by 11 green LEDs. This takesinto account the 9 'range' indicators,which are calibrated in the standard 1-2-5 sequence, as well as two scaling LEDs,which indicate whether the ranee in-dicators are calibrated in micro or milliseconds. Auto mode is indicated by asingle red LED, timebase speed stillbeing given by the remaining indicators.When in soft tune mode, the continu-ously variable control !lives a linearresponse: it is very easy to set the desiredtimebase speed. A large amount ofhysterisis is provided between the rangeswitching thresholds, preventing any

EE

March 198865

Table 16

CATEGORY Unsatis-factory

Satis-factory Good

VeryGood Excellent

TRIGGER FACILITIESTRIGGER PERFORMANCEDEL'D SWEEP FACILITIESDEL'D SWEEP PERFORMANCECRT BRIGHTNESSCRT FOCUSINGY -AMP ATTENUATION RANGEINTERNAL CONSTRUCTIONEXTERNAL CONSTRUCTIONOVERALL SPECIFICATIONOVERALL PERFORMANCEEASE OF USEMANUAL

**

*

**

.

***

**

**

. *

Note: Delayed sweep performance and facilities compared to other scopeswith 'coarse' delayed sweep. Also CRT brightness and focusing compared toother 20 kV tubes.

unstable timebase speeds over the con-trol's full range. Overall, I found thatthis enables a very accurate, easy andconvenient way of selecting the sweepspeed, combining the speed of a conven-tional switched timebase speed controlwith the ease of use of a two-way 'up-down' rocker switch, which can be foundin some other scopes with this facility.The LED display also gave a clearer, andin my view easier, to read display thanthe conventional switched system,although it is perhaps not as easy to readas would be a numeric 7 segment display,examples of which can be found onother digital timebase scopes. The auto-matic timebase facility itself is selectedby placing the soft tuning control in afully anticlockwise position. Operationof this was very effective, locking effec-tively onto a wide range of frequenciesand producing a very stable display. Theeffective frequency range (4 cycles div-ision) is 4 Hz to 800 kHz, although ob-viously the actual frequency range iswhat can be expected from a normalanalogue timebase. Timebase switchingoccurs at between two and six cycles/10 divisions, depending on the range,and whether the timebase is being scaledup or down. Switching between theranges is very fast on most sweep speeds,but it was noticeable that there was asmall time delay when changing down insweep speed. This is not, however,clearly noticeable until changing downfrom, for example, 200 ps/div to2 ms/div, when a delay of approximately1 second is present. This increases toabout 3 seconds when switching to200 ms/div, the slowest sweep range.These are 'worst cases' and typicallymay be considerably faster, dependinglargely on the waveform and previousspeed setting. Performance of theautoranging system was good, lockingonto a large range of waveforms, from asinewave to a complex pulse train.

Overall,. I also found the automatictimebase an extremely useful facilitywith few failings, although as a veryminor point it might have been helpfulto have an automatic x10 deflectionspeed facility to increase the maximumspeed under automatic control to50 ns/div in place of the 500 ns/div forhigher frequencies.The second timebase/delayed sweep is ofthe 'coarse' type, in that in most cir-cumstances it is not possible to carry outaccurate timing measurements in situ-ations where a calibrated delay timemultiplier would normally be required.Waveform expansions can, however, becarried out accurately by the secondtimebase. For unstable, or changing, fre-quencies, it is obviously advisable to usethe soft tuning option of the maintimebase, although where this is not thecase, the autorange option can be usedwith good results. The analogue secondtimebase sweep speeds range from2 ms/div to 0.5 µs/div, and can be usedin one of two modes, either intensifyingthe trace to be magnified, or as themagnified sweep. It is worth noting thatin common with most other 'coarse'delayed sweep systems only one timebasecan be displayed at a time, i.e.. either Aor B, and not both, thus giving a maxi-mum of two traces on the screen at anyone time. Jitter is one part in 10,000, andas such is just visible on high magnifi-cation ratios, although it can be kept toa minimum in some situations by usingthe triggered delay facility. The delaytime is variable by a uncalibrated controlover 10 horizontal divisions, and as men-tioned above can either be continuous ortriggered.CRT performance is obviously compar-able to the M020, since the same CRTand drive circuitry are used. Typicalmagnification ratios in normal (artificiallighting) conditions were 1000:1 withoutthe x10 magnifier in operation, or, with

Table 15

ELECTRICAL CHARACTERISTICSLine voltage: 100,220,240 VAC ±-10%; in-ternally adjustable.Line frequency: 45-65 HzPower consumption 35 Watts

MECHANICAL CONSTRUCTIONDimensions: W 375 mm, H 160 mm,D 430 mmHousing: steel sheetWeight: approx. 8.5 kg

Y AMPLIFIER ETC.Operating modes:CH1 alone, CH2 aloneInversion capability on CH1 or CH2Dual CH1, CH2 (alternate or chopped(250 kHz))CH1 + CH2Frequency response: 0...20 MHz (-3 dB).Risetime: = 17.5 ns, (23.4 ns x 5 Mag.)Deflection factor: 12 steps:5 mV/div...20 V/div ±3%, vernier controladjusts max. sensitivity on 5 mV/div range to2 mV/div (fully ccw)Input coupling: AC, DC or Gnd.Input impedance: 1 M4/25 pFMax input voltage 400 (DC +peak AC)

X -Y MODECH1 X-axis and CH2 Y-axis. Less than 3°phase shift at 50 kHzBandwidth DC to 1 MHz (-3 dB).

SWEEPOperating Modesi; A; timebase A only: Aintens. B; A brightened in range B, remainderblanked: B; timebase B onlyA Sweep Time: 0.5 ps/div to 0.2 s/div, ± 3%in 18 ranges, 1-2-5 sequence. Vernier controlslows sweep down by up to 2.5:1;B sweep: 0.5 ps/div to 20 ms/div. ± 3% in12 ranges, 1-2-5 sequence.Range Selection: A -automatic or manual(potentiometer): B -switchedSweep magnification: x 10 ±5% total errorHoldoff: variable up to 10:1Delay modes: Trigger Delay (slopeswitcheable); Continuous delayDelay jitter: 1/10000

TRIGGERINGTrigger modes: Auto (p -p), NormalTrigger coupling: AC,DC,HF reject, LF reject.TV frame and line(auto).Trigger sources: CH1, CH2, Line, Ext.Triggering sensitivity: Internal 1 div at20 MHz, External '0.5 V p -p at 20 MHz,Normal mode

MISCELLANEOUSCRT -make: Valvo, measuring area 80 mm x100 mm, accelerating voltage 2 kVCompensation signal for divider probe; ampli-tude approx. 1 Vpp (±3%), frequency 1 kHz.Z modulation Sensitivity: 3 V (completeblanking)Covered by 1 year warranty.

this, approximately 100:1. For a 2 kVtube these figures are certainly aboveaverage, especially as the traces at thesespeeds were fairly well defined. Zmodulation is provided as standard onthe M022 and exhibited a very good sen-

66 EE

March 1988sitivity of +2 V for total blanking of atrace at maximum brightness. Negativevoltages have no effect however, so thetrace cannot be intensified by an externalvoltage.

Internal construction, like that of theM020, is based on two PCBs; the lowerone, housing the Y -amplifiers, powersupply, etc., is almost identical to thatused in the M020. The upper board isentirely different, however, and housesall the components for both timebases,as well as the trigger circuitry. BothPCBs are of fibre glass construction andscreened with both component identifi-cation numbers, and, where appropriate,their functions. The PCBs are held inplace by a steel chassis which should beextremely rugged under a very widerange of operating and environmentalconditions. The outer casing is also steel;the absence of ventilation slots makesthe M022 externally resilient to a rangeof conditions compatible with those out-lined above.The manual is very similar to that sup-plied with the M020, the main differ-

ence being a very brief explanation ofdelayed sweep operation

CONCLUSIONThe Grundig M022 represents a con-siderable advance in terms of timebasetechnology for an oscilloscope in itsprice range. I found the automatictimebase facility genuinely useful,making the measurement of a widerange of waveforms significantly easierand faster. The second timebase providesa good range of sweep speeds and thusexpansion ratios, although its use indelayed sweep applications is limited insome situations by the 'lack of a cali-brated sweep delay and delay line fortriggered operation, and, of course, the2 kV CRT. These featues, however, can-not really be expected in this price range,especially when the high grade of con-struction and additional features aretaken into consideration. This, alongwith the automatic timebase, shouldmake the scope ideal for service work,particularly in the TV area as the TVtriggering was very effective in both

horizontal and vertical modes. To sumup the Grundig M022 is unique in itsprice range in having in fully automatictimebase. The advantage of this over aconventional analogue system obviouslydepends on the application, but from myown experiences I have found it wellworth while. This, coupled with the sec-ond timebase, should make the scope agood choice where ease of use and ver-satility are among the main re-quirements, such as in a servicing oreducational environment.

The Grundig M022 was supplied byElectronic Brokers Ltd., 140-146Camden Street, London, NW1 3YP. Tel:01-267 7070

Other scopes available under £1500 in theGrundig range.

M053Dual trace 50 MHz bandwidth. Fullautoranging timebase with digital readout;trigger holdoff; TV line and field (1 or 2)triggering: 11 kV CRT; calibrated delayedsweep facility.

NEWS

New photoelectric switchesscan up to 8 metresFeaturing a unique design that offers themaximum possible component inte-gration, the Sensick P reflex and prox-imity photoelectric switches from STCMercator have an operational range ofup to 8 m (reflex) and 0.3 m (proximity).Insensitive to ambient light, the WL(reflex) and WT (proximity) series offervariable user -adjustable time delays,operate with both AC and DC, and havea new plug-in system for easy instal-lation and servicing.

Sealed to either IP65 or IP67, thedevices have a voltage range of 10 to240 V AC or DC, and offer reverse po-larity protection, interference pulse sup-pression, and short-circuit protectedoutputs.Further details from STC Mercator South Denes GREAT YARMOUTHNR30 3PX.

1300 nm detector with fibrepigtailA long wavelength optical detector, the13PD100-F, which has a 50/125multimode fibre pigtail, and is producedby Telcom, is now available from HeroElectronics.The 13PD100-F is a p-i-n photodiodewith a photosensitive area of nearly8,000 um2. It has a responsivity of notless than 0.7 A/W at 1300 nm, rise andfall times of not more than 1 ns, and adark current of not more than 10 nA.The device is suitable for use as a fastresponse detector in fibre optic systems,in data links, in optical sensing equip-ment, and in communications networks.Further information from Hero Elec-tronics Ltd Dunstable Street AMPT-HILL MK45 2JS.

Long -life photosensorThe light-sensitive TFA 1001 Wphotosensor incorporates an integratedphotodiode and amplifier in a trans-parent miniature case with 6 leads. Thiscomponent, intended for many appli-cations (ranging from TV cameras tomedical test strip analysis) operates at aconstant sensitivity (5 pA/lx) over awide range of light intensity. For thetransparent case compund, Siemens isusing a new material with improved op-tical and thermal resistance. The tem-perature range now extends to 85 °C (theprevious limit was 70 °C) and the lowerlimit has been improved from 0 to-20 °C. The TFA 1001 W is thus alsosuitable for equipment with a 'particu-larly long life such as cameras.With the TFA 1001 W, the output cur-

rent rises linearly from 0.25 pA to25 mA (typical values) between 0.05 lxand 5000 Lx. The output signals are,therefore, directly proportional to the il-luminance. This simplifies the electronicevaluation circuitry for controlling, forexample, the aperture and exposure of acamera.Further information from Siemens Ltd Siemens House Windmill RoadSUNBURY-ON-THAMES TW16 8HS.

New photo sensors fromOrion-EurosemOrion-Eurosem has available a widerange of photo sensitive devices, includ-ing infra -red LEDs, photo detectors, in-terrupters, reflective sensors, and fibreoptic devices.Manufactured by Toshiba Semiconduc-tors, the devices are suitable for use in allapplications requiring photo sensitivecontrol, including end -of -tape detection,fire alarms, smoke detection, TV remotecontrols, photoelectric switches, and soforth.Further information from Orion-EurosemLtd Sunley House Oxford Road AYLESBURY HP19 3EQ.

EE

March 198867

New Maplin store in BristolMaplin Electronics, the well-knownretail distributor of electronic products,has opened a new shop at 302 GloucesterRoad, close to Bristol City Centre.Established 15 years ago, Maplin has be-come the UK's largest retail distributorof electronic products, employing a staffof nearly two hundred.The company's mail order activitities oc-cupy a custom -designed 40,000 ft2 com-plex in Southend-on-Sea. Supportingthis operation are six retail stores locatedin Birmingham, Bristol, London, Man-chester, Southampton, and Westcliff-on-Sea.In addition to a wide range of electronicproducts, from aerials to semiconduc-tors and tools and test gear, Maplin alsosupplies a range of training kits whichhave become very popular within boththe industry and educational establish-ments.Since its introduction in 1985, M.P.S.(Maplin Professional Supplies), a servicespecially designed to meet the needs ofprofessional, trade, industry, and edu-cation customers, has grown substan-tially. Apart from the Bristol shop,Maplin addresses are:Mail Order: P.O. Box 3, Rayleigh, Essex SS6 SLR.Telephone: Sales (0702) 554161: Enquiries (702)552911.Sutton New Road, Erdington, Birmingham. Tele-phone: 021-384 8411.159-161 King Street, Hammersmith, London, W6.Telephone: 01-748 0926.8 Oxford Road, Manchester. Telephone: 061-2360281.46-48 Bevois Valley Road, Southampton. Tele-phone: 0703 225831.282-284 London Road, Westcliff-on-Sea, Essex.Telephone: 0702-554000.

New sensor systems develop-ment facilityERA Technology has formed a specialgroup - the Sensor Systems ProgrammeOffice - in response to industry's needfor the development of short rangeremote sensing systems suitable for awide range of applications.The new group has a design capabilitycovering a variety of sensors includingelectromagnetic, acoustic, optical andinfra -red.Projects are currently being undertakenin such areas as offshore drilling, civilengineering, process measurement, non-destructive testing and inspection,defence and robotics. Systems based onshort-range radar have been developedand much of the design work involvesthe use of radio frequency techniques.Acoustic, magnetic and infra -red devicesare also under consideration for multi -sensor systems used for surveillance andnavigation.Further information from ERA Tech-nology Ltd Cleeve Road LEATHER -HEAD KT22 7SA.

Micro miniature pressureprobesEntran's EP1-050 and EP1-060 pressuretransducers measure static and dynamicpressure where very small size is of primeimportance and access is difficult. Ap-plications include wind tunnel and flighttesting, engine test stand work, modelstudies, and bio-engineering research.Three standard mounting configurationsand probes, each using a 50 mil(1.27 mm) external diameter diffuseddiaphragm, are available for measuringpressures from 0 to 2 p.s.i. (0 to 0.13 bar)to 0 to 300 p.s.i. (0 to 20 bar) with out-puts up to 125 mV and resonant fre-

quencies to 1.7 MHz.Additionally, barrel -shaped andthreaded probes with or without protec-tive screens and with custom diameter/length options are available.Further information from Entran Ltd 5Albert Road CROWTHORNE RG117LT.

Interconnect plug forproximity sensor systemINIO's Microchange, developed jointlyby IMO/OMRON and the Brad Har-rison Corporation, provides users withplug-in rather than hard -wired detectiondevices. This means that upon failure orreplacement of either the cable or thedetector only one element needs to bedisposed of rather than both. Sincenearly 50% of maintenance problemsexperience by proximity switch usersemanate from the cable rather than fromthe device itself, this could lead to con-siderable cost savings.Further information from IMO Ltd 1000 North Circular Road Staples Corner LONDON \W2 7JP.

Modular positioning systemA new modular positioning system fromLambda uses 5 -phase stepper motorsthat can be controlled manually, exter-nally, or by computer. The 5 -phase step-per motors provide a high basic resol-ution, smooth operation, and excellent

dynamic properties. They offer anumber of advantages over 4 -phasetypes, such as improved equidistance ofthe stepping angle and high stiffness ofmagnetic snap -in positions. These inturn guarantee high positioning accuracyduring load movement.The controller provides fine resolutioncontrol - 1,000 steps/rev - and is idealfor use with 3 -axis positioners. Steppingfrequency capability extends from 30 Hzto 15 kHz.IEEE -488 and RS232 interfaces, andsuitable MS-DOS software, are op-tionally available to allow complete con-trol over the system from a computerkeyboard.Further information from LambdaPhotometric.s Ltd Lambda House Bat -ford Mill HARPENDEN AL5 5BZ.

Micro lable thermometer stripThermographics' Micro Lable is an ir-reversible four -level thermometer stripthat can be applied to any surface whosetemperature requires to be measured.Changing from silver white to black onreaching a set temperature, the strip canbe used with products requiring war-ranty protection from abuse.

II 1 111111111111----- w gCa - -

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Isa =41- iiEach 10 x 3 mm strip can indicate fourlevels of temperature, and the strips areavailable in nine groups with tempera-tures ranging from 40 °C to 224 °C.Response is not greater than 1 second.Micro Lable is of particular interest inelectrical and electronics fields, but canobviously be used anywhere to monitorheat generation.Further information from Thermo -graphics Measurements Ltd Bank House Neston Road Burton SOUTH WIR-

RAL L64 5TA.

68 EE

March 1088

A WORD ill'sTHE ME

THE AND MAKESURENifENT

By David Simpson, National Physical Laboratory, Teddington, London

Though electronic sensors are now widely used for laboratory measurements, manyinstruments, especially the more accurate ones, still have to be read by someone. Ahand-held computer terminal developed at the National Physical Laboratory helps

observers to record readings from instruments faster and more reliably. When numbers arekeyed into it, a speech synthesizer dictates them back to confirm that data have been

entered as intended. It also warns against improbable readings.

Each year the National PhysicalLaboratory calibrates several thousandscientific instruments for customers whouse them industrially to measure a widerange of parameters. Although there is agrowing tendency to incorporate ana-logue or digital electrical outputs thatenable readings to be recorded automati-cally by a computer, few of the instru-ments have such a facility. Vernier -scalebarometers, dial -gauge proving -rings(for measuring force) and mercury -in -glass thermometers are good examples.Moreover, the interfaces of those sent infor checking which are electricical innature are often not immediately com-patible with the calibration laboratory'scomputer. So it is still quite normal formany observations to be made by eyeand written down.Most metrologists believe that obser-vations made by eye are, as a rule,recorded more easily by jotting themdown on paper than by using a keyboardthat calls for extra concentration toavoid mistakes. They generally prefer towrite their observations and transferthem to a computer later, when the datainput can be carefully compared withtheir observation book.The speaking computer terminal seemeda logical device to develop because aportable numeric keyboard that wouldaudibly confirm what key had beenpunched would enable direct input ofvisual observations into a computerwithout calling for special concentrationto detect keying errors. If you think"three" when you key and the terminalsays "four" it is very unlikely themistake will get past.

General design criteriaTo optimize the terminal's usefulness tometrologists, who use a range of tech-niques in widely differing environments,a number of design features were con-sidered: the synthesizer should be crisp,clear, have a local accent and, apartfrom speaking numbers from zero tonine, should be able to say things rel-evant to metrology such as "out of

Base station includingspeech synthesiser

IEEE488 or RS232C interface

16 -characterdisplay

Keyboard

Loudspeaker

Interconnections of the NPL *stem.

range", "measurement error", "prob-lem with reading six" and so on. Theterminal should be small enough to beheld in the hand, so that the user cantake it many metres from one instrumentto another during a calibration; it shouldhave a clear and bright display capableof displaying alpha -numeric promptswhich may be easily read under a varietyof lighting conditions; a simple keyboardemploying high -quality switches; becapable of transmitting non -numeric`special function' (or `soft -key) charactercodes to the laboratory computer forcontrol purposes (typically to mean"yes", "no", "abort", or "repeat lastreading"), and communication with thelaboratory computer should be via anIEEE 488-1978 interface. The hand unitshould be cordless to avoid problemswith trailing cables.The terminal was built in collaborationwith Peter Rush, of Triangle Digital Ser-vices, Walthamstow, London. Its finalform complied with all but the lastdesign consideration, that is cordless op-

eration. While this would have beeneasier for users, it was thought impracti-cal for two reasons. Firstly, neither radionor infra -red communication could eas-ily provide the degree of integrity re-quired; some measurements need to betaken near sources of electrical inter-ference or in Faraday cages, and line -of -sight communication between the ter-minal and its 'base -station' (linked to thelaboratory computer) could not alwaysbe guaranteed. Secondly, the power re-quired to provide a bright display ruledout the use of batteries. It was thereforedecided to accept a thin cable linking theterminal with its base -station.We settled on a hand unit that has abright 16 -character display, a loud-speaker, and a high -quality keyboard. Inaddition to the digit keys there aredecimal and minus signs and fourediting keys, two special function keysand a "send" introduction. A key -shiftof the numeric keys gives ten otherspecial function keys.The terminal's cable, which may be up to

30 metres long, links the unit to the base -station containing the speech syn-thesizer, a power supply and both IEEE488-1978 and RS232C interfaces forcommunication with the laboratorycomputer. The synthesizer has avocabulary of 70 discrete words selectedspecifically for metrological purposes. Itmay be actuated by the terminal'skeyboard, to speak digits, or by thelaboratory computer to speak any wordsfrom its vocabulary.

Optimum characteristicsThe essence of the device is its ability tospeak the value of numeric input data,and we had to experiment to find opti-mum synthesizer operating character-istics. Firstly it was programmed tospeak only after a complete number hadbeen entered. That is, typing "123<send>" evoked "one two three". Sec-ondly, "123 <send>" called up "Onehundred and twenty-three". Thoughsomewhat novel, this format was notfound to be very helpful when takingreadings. A third mode is the one weadopted, in which digits are spoken im-mediately numeric keys are touched. Toenable the synthesizer to keep up with arapid sequence of key operations, itspeaks digits quickly and, under veryfast operation, truncates them to avoid adelay between pressing the key and start-ing to speak. For example, very rapid en-try of, say "678" would cause "Sisev-eight" to be spoken, but that is quite in-telligible.When the unit is in typical use, a pro-gram running on a laboratory computersends a visual prompt to the terminal,reminding the metrologist standing nearthe instruments he is calibrating whatmeasurement to take next. He keys in hisobservation, which is audibly confirmedas he does so. If it is correct, he sends itto the laboratory computer which pro-cesses the information and usually re-sponds with the next prompt. The com-puter can trigger a short verbal opinionif it recognises the number to be anunreasonable one.The terminal handles visual prompts in

Using the terminal in the laboratory.

Reading No.

23

4

Bridge Reading

0.58843839404341

When an instrument with, say, a six figureresolution has to be read repeatedly withchanges in only the less significant digits, thelaboratory instrument can send a promptthat allows just the last part of the number tobe added. This is the electronic equivalent ofentering readings in a laboratory observationbook.

two different ways: the first, most usualway, simply allows the prompt to disap-pear from the display as soon as numerickeys are pressed; the second allowsnumbers to be added' to the end of aprompt and is used when many similarobservations have to be made. Forexample, an instrument with six -figureresolution may have to be read repeat-edly with changes only in the last fewdigits. After receiving the first reading inthe normal way, the laboratory com-puter can send a partially numeric visualprompt such as "Bridge? 0.5884", (sim-

EE

March 1988ultaneously speaking it if required), en-abling just the last digits of the numberto be added to the right-hand side.

69

Quick and reliableThe first NPL speaking computer ter-minal was built over three years ago andeight are now in service. They provide aquick and reliable means of recordingdata from instruments that do not givean automated read-out. They are helpingus in many ways, from precisionweighing to the calibration of mercurybarometers, vacuum gauges, line stan-dards and radiation dosimeters.Most users prefer the terminal in itsspeaking -digit mode but some choose toenter numbers silently and have the fullnumber dictated back after it has beenentered. But both ways have been foundto cut the concentration needed andmake the process of entering numbersless tiring. Other benefits of the ter-minal have become apparent. On -the-spot prompting during calibration worknot only helps the experienced metrol-ogist but assists with the training of newstaff: recording numbers directly into thelaboratory computer with audible con-firmation is quicker than writing themdown and then typing them into akeyboard, later cross-checking a com-puter print-out with the observationbook; results, comments or instructionsmay be dictated to the operator while heis concentrating, for example, on makingobservations through a microscopeeyepiece; spoken warnings attract moreattention than visual ones and providemuch better diagnostics than a bleep.For example, if the user's concentrationfails and a gross mistake comes up suchas typing in 1000 mbar instead of 20°C,a spoken "Really?" requesting the dataagain points out the mistake much fasterthan a display can do. Cross-checkinglists of data is easier when one list isspoken.

The NPL speaking computer terminal is nowavailable from Triangle Digital Services,Walthamstow, London.

New decade capacitanceboxThe new CB610 has 6 decades ofcapacitance from 10 pF to 11.11111 pi:with an accuracy of ±1% ±2 pF. Driftis < ±0.3% ±1 pF in 1 year below50 nF and < ±1% above 50 nF. The dis-sipation factor is <0.002 at 1 MHz from30 pF to 1 nF, <0.001 at 1 kHz on 1 nFto 50 nF and <0.01 on 50 nF to 11 #F.Maximum input is 250 Vdc, 160 Vac and1 A at HE These compact boxes have di-mensions of 190 x 110 x 90 mm andweigh 550 g.The decade capacitors are selected fromcomponents with stable dielectrics and

the switches have silver plated self -wiping contacts with low losses up to1 MHz. The minimum control setting of10 pF includes the residual capacitanceso the controls indicate total capacitance

at all settings. The capacitors are iso-lated from the case and an RFI screen isjoined to a separate terminal that islinked to the adjacent capacitor terminalduring calibration.Level! Electronics Limited MoxonStreet BARNET EN5 5SD. Tele-phone: (01 449) 5028.

70 EE

March 1988

READERS SERVICES READERS SERVICESPARTS & BOOKS

All orders must be sent BY POST toour Brentford office using the appro-priate form opposite. Please note thatwe can not deal with PERSONALCALLERS, as no stock is carried at theeditorial offices. The postal address isgiven at the back of the form.All prices shown are net and customersin the UK should add VAT whereshown. ALL customers must addpostage and packing charges for ordersup to £15.00 as follows: UK, £1.00;Europe, £1.50; other countries, £2.00(surface mail) or £3.00 (airmail). Fororders over £15.00, but not exceeding£50.00. these p&p charges should bedoubled. For orders over 150.00 invalue. p&p charges will be advised.Software is also available fromTECHNOMATIC LIMITED (for address,see inside front cover).In Sweden, printed -circuit boardsshould be ordered fromELECTRONIC PRESSBox 63S-182 11 DanderydTelephone: 08-753 03 05

SUBSCRIPTIONSSubscriptions car, ce pia:toedanywhere in the world: they may beordered on the appropriate form op-posite.

LETTERS

Letters of a general nature, or express-ing an opinion, or concerning a matterof common interest in the field of elec-tronics, should be addressed to TheEditor. Their publico: n in Elektor Elec-tronics is at the Ms :,: :in of the Editor.

PAST ARTICLES

A limited number of past issues can besupplied at the current cover price pluspostage & packing as detailed above Ifpast issues are no longer available.photo copies of the relevant article canalways be provided at a price of £1.00per article plus postage and packing asdetailed above

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COMPONENTS

Components for projects appearing inElektor Electronics are usually availablefrom appropriate advertisers. If difficult-ies in supply of components are en-visaged, a source will normally beadvised in the article.

BOOKS

The following books are currentlyavailable: these may be orderedfrom certain electronics retailersor bookshops. or direct from ourBrentford office.

301 Circuits302 Circuits303 Circuits

£6.25E6.25£7.95

BINDERS

Elektor Electronics binder T. .... £2.95

FRONT PANELS

No. Price VAT1E1 1£1

Indoor unit for sat&Tire TV reception 86082-F 3.50 0.53

Top -of -the -range 86111-F1 5.60 0.84preamplifier 86111-F2 4.45 0.67

Intelligent timestandard 86124-F 15.70 3.71

Digital sine -wavegenerator 87001-F 5.45 0.82

Autoranging DNIM 87099-F 2.80 0.42Frequency meter 87286-F 10.75 1.61

SOFTWARE

Software in IEIPROMs

ATP -controlled frequency

No. Price VAT(Cl 1E1

meter 1 x 2732 531 9.00 1.35X -Y plotter1 2732programmable timer

532 9.00 1.35

1 - 2732 535 9.00 1.35GHz pre -scaler1 x 2732automate yourmodel railway

536N 9.00 1.35

1 2716marine computer

537 7.30 1.10

1 x 2716 538 7.30 1.10Jumbo clock2 x 2716 539 14.60 2.20Graphics card2 = 825123printer buffer

543 9.60 1.44

1 x 2716 545 7.30 1.10MSX EPROMmer1 a 27128 552UK 7.30 1.10Intelligent time standard1 x 2764 553 10.00 1.50EPROM emulator1 x 8748H 558-A15.00 2.25Slave indication unit

for I.T.S. 559 15.00 2.25

PRINTED CIRCUITS

Readers who wish to make their ownPCBs (for private end personal use only)may in many. but not e9, cases receivethe relevant drawings free of charge byordering these on the order form oppositeand enclosing a stamped addressedenvelope (preferably 9.6 In or230r 150 mm).

Price VAT1E1 ILI

APRIL 1987valve preampifier-2 87006-2 12.52 1.85

Facsirr a -:erface:ea

- MAY 1987Capacitance meterMetal detector

No.

8703864071

8604286069

Price VAT1E1 lE1

8.83 1.327.26 1.09

5.15 0.564.25 0.64

M101 signal distribution 87012 7.40 1.11Spot sine wave

generator 87036-1 net avaistie

JUNE 1987Intercom for motorcyclists 87024 6.85 1.03

Spot site wavegenerator 2 87036-2 rot ealoit=

Autoranging 0MM 87099 6.55 0.98JULY/AUGUST 1987Wien bsinte °sr:dater 87441 2.15 0.32Duty fa::: a a . ser 87448 5.85 0.88Digit : -= a ..rent=kW, 87468 6.50 0.98

32K ROM 87500 4.00 0.60Headoh, , .:-ropfifer 87512 9.00 1.35Halogen lamp [anent!" 87452 rot avalahte7 -digit code lock 87463 rut avatatteSEPTEMBER 1987Surface.mount stereo

FM receiver 87023 3.20 0.4816 Kbyte CMOS RAMfor C64 87082 4.10 0.62

Active phase -linearfilter 87109 15.00 225

EPROM emulator 87136 17.50 2.63OCTOBER 1987IEEE interface 87054 Not availableS58 adapter 87145 Not available14 -bit 0-A converter 87160 9.00 1.35RecorcingIplaybacl..amplifier 87486 riot available

Low -noise microphone=Wier 87058 3.45 0.52

NOVEMBER 19875513 Receiver for 80 mand 20 m 87051 14.75 2.21

BASIC computer 97192 20.25 3.04Dimmer for inductiveloads 87181 6.00 0.90

IR Transceiver 87179 Not availableDECEMBER 1987Digital motor drives forRC models 87098 4.50 0.68

Frequency meter 87286-A 12.50 1.88LCD VU meter 87505 6.75 1.01

87520 6.75 1.01

JANUARY 1988DCF77 Receiver andFrequency Standard 86124-A 8.70 1.31

87105 Nor avalsbreStereo limiter 87168 7.25 1.09Light -powered

thermometer 87188 6.75 1.01Switch -made P50 880001 5.00 0.75FEBRUARY 1988Intelligent timestandard 86124.2 7.15 1.07

Infra -red headphones 87640 6.10 0.92Preece-ler for frequencymeter '980005 9.25 1.39

MARCH 1988Infra -red detector for=arm systems 87067 4.55 0.69

5?... 87104-1 10.50 1.5887104-2 10.50 1_58

87259 16.00 2.40'Lev 880041 6.50 0.98

880042 5.00 0.75

880067 5.00 0.75

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Advertisements' ArticlesJanuary 1988 17 Dec. 1987 9 Nov. 1987 26 Oct. 1987 HF & VHF TechniquesFebruary ;988 14 Jan_ 1988 4 Dec. 1987 20 Nov. 1987 TelecommunicationsMarch 1906 18 Feb. 1988 15 Jan_ 1988 28 Dec. 1987 SensorsApril 1988 17 Mar. 1988 12 Feb. 1988 29 Jan. 1988 ElectrophonicsMay 1988 14 Apr. 1988 11 Mar. 1988 26 Feb. 1988 Artificial IntelligenceJune 1988 12 May 1988 8 Apr. 1988 25 Mar. 1988 Electronics & ArtJulyiAugust 1988 16 June 1988 13 May 1988 29 Apr. 1988 Amateur Radio & TVSeptember 1988 18 Aug. 1988 15 Juty 1988 1 July 1988 Computers & MicroprocessorsOctober 1988 15 Sep. 1988 12 Aug. 1988 29 July 1988 Power suppF.esNovember 1988 20 Oct. 1988 16 Sep. 1988 2 Sep. 1988 OptoelectronicsDecember 1988 r 17 Nov. 1988 14 Oct. 1988 30 Sep. 1988 Computer.aided test & measurementJanuary 1989 15 Dec. 1988 11 Nov. 1988 28 Oct. 1988 Audio & Hi4iFebruary 1989 19 Jan. 1989 5 Dec. 1988 21 Nov. 1988 TV & videoMarch 1989 16 Feb. 1989 13 Jan. 1989 30 Dec. 1988 Knowledge -based systemsApril 1989 16 Mar. 1989 10 Feb. 1989 27 Jan. 1989 TelecommunicationsMay 1989 20 Apr_ 1989 17 Mar. 1989 3 Mar. 1989 Robotics

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March 1988

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