the electronics magazine with the practical approach · 1989. 7. 8. · the electronics magazine...

THE ELECTRONICS MAGAZINE WITH THE PRACTICAL APPROACHUK £3.20 IR £4.70 (incl. VAT) July/August 1989

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Tracking testerMulti -layer PCBSVideo compressorFloppy disk monitorTest pattern generatorDigital model train (5)Practical filter design (7)RAM extension for BBC "B"

11 11L9 770268 451005

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BBC Micro Computer SystemARCHIMEDES310 basic £695 (al440 basic £2049 la)Please ask for full details on add-ons andsoftwareBBC MASTER SERIES:AMB15 BBC MASTER 128K.. E356ADC06 Turbo (65C102) Card . £115ADF10 Econet Card E49ADJ22 Ref. Manual I E 1 4ADJ23 Ref. Manual Part II £14UPGRADE KITS:1.2 OS ROM £15ONES ROM £19BASIC II ROM (BBC _ £22.50ADFS ROM £261770 DES Kit £49Econet Kit 1B&8+1 E55

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ACORN ADD-ON PRODUCTS:Torch ZEP 100 E229 (a)512 2nd Processor E249 lb)IEEE Interface £265 (b)Teletext Adapter E95 (b)32016 Co Proc E949 la)X25 Gateway £2,175 (a)

Ask for full detads on our tuft range of software

-WORD PROCESSOR ROMs;VIEW 2.1 £35 (dl VIEW 3.0 .. £48 (c)Spellmas-ter E49 (dl VIEW INDEX E12 (dlWORDW1SE E24 (dl WORDWISE÷ £38 (d)

SPELLCHECK IIIWYSIVinG £21 (dl £31 (dlINTERWORD £48 Id) EDWORD II £43 (a)LANGUAGE ROMS:Micro Prolog E62 (el Microtext ... £52 Id)ISO PASCAL £51 (c) LOGOTRON . E55 (c)LOGO E46 (Cl MACRON £33 (dlUSP £39 (dl E43 (dl

Oxford Pascal E36 Ic)COMMUNICATIONS ROMS:TERMULATOR f.25MASTER TERMULATOR E34.75 (dlCOMMSTAR II E28 Id)MODEM MASTER £11 Id)COMMAND £34 (dlUTILITY ROMs:DOTPRINT PLUS for FXJRX compatiblesDOTPRINT DUAL for MX rangeAcorn Graphics Extension Rom £28 IdlMerlin with 57 rase utility commands100 page manual E37.50 Icl

MULTIFORM Z80 2nd Processor for the BBCThis unique 280 2nd Processor running 054.4 wi allow use of almost any standard CP/M soft-ware on the BBC micro. It is supplied with a number of different CM formats and includes atroTrty to configure it to read other formats. This is particularly useful in environments where com-puters with different CP1M formats are used and the data cannot be easily exchanged betweenthem. Mains powered (includes Pocket Wordstar & MS1D0S AM/ ubTrtyl E249MS/DOS Read/Write 1Julny £49 (c)

META Version 3 ASSEMBLERAssembles 17 of the popular processors. Over 70K long program on two toms and a disc andprovides complete Edging and Assembly facenies. It uses appropriate mnemonics for differentprocessors. Fully treatable macros, nestable conditional assembly 11FiELSEENDIF). modularsource code, true local and global labels. 32 bit labels and arithmetic. 30 ways to send objectcode and 50 directives.A powerful editor with many features. Send for detaded leaflet. E145 lb)

BBC DISC DRIVES5.25" Single Drive:1 x 400K 40180T DS: TS400 E80 (Is( PS400 With Ps. E90 (b)5.25" Dual Drive:2 x 400K 40/807 DS: 10800.... £165 tel P0800 with psu E175 la)2 x 400K 401807 OS with psu and built in monitor stand PDBOOP £189 (a)3.5" Drives:1 x 400K 130T DS TS35 1 E69 (b) PS35 1 with psu E95 lb)1 a 400K BOT DS with psu T035 2 (126 (b) P1335 2 with psu E139 (b)

Combo drives (5.25" & 3.5"):P0853 with integral PSU E180 (a) P0853P with integral PSU E205 (al

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

514 DISCS 31/2 DISCS40T SS DD £6.50 id) 40T OS DD. E7.00 (dl 801 SS DD £10.00 (dl80T SS DDE12.00 (dl 80T DS DD £11.00 Id) 80T DS DD £11.75 (d)

DISC ACCESSORIESSingle Disc Cable E6 Id) Dual Disc C -la, E8.50 (dl10 Disc Library Case £1.80 (0 30 Disc Storage Box £6 (c)40 Disc LockaNe Box £8.50 t: 'r.: D:sc Lockable Box £13 (cli11opoielene otiveneao Cleaniria Kit with 20 d::-- -- - - caning kits 511" E14.50 (dl; 314" £16 (dl

BT APPROVED MODEMSMIRACLE TECHNOLOGY WS Range

W34000 V21/23. WS3000 V22 his Professional(Hayes Compatible. Interdgent. Auto Dial/ As V22 and 2400 baud full duplex E495 fa)Auto Answer) E129 (b) WS3000BBC Data Lead EIO (dlWS3000 V21/23 Professional WS2000 V21N23As WS4000 and with BELL standards and Manual Modem E92 fblbattery back up for memory .... £24411:) WS 2000 Auto Dial Card E27WS3000 V22 Professional WS 2000 Auto Answer £27 (d)As WS3000 V21/23 but with 1200 baud fun WS 2000 SKi Kit 15 (dlduplex £379 Ia) WS 2000 User Port Lead E5 (dl

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SPECIAL OFFEREPROMs/RAMS

2764-25 £2.80 (d)27256-25 £6.00 (d)27512-25 £9.00 (d)6264LP-15 £6.00 (d)27128-25 (12.5 Vpp) £4.50 (dl27128-25 (21.0 Vpp) £6.00 (d)

PROJECTS:Junior Computer Kit- £86 (b)Housekeeper kit £58 (b)Elekterminal Kit (1980) £50 WIASCII Keyboard kit £75 (b)J C Books 1, 2, 3, & 4E6.90 lc) eaUniversal Terminal 16502) Kit £75 Ib)Elekterminal Kit (1983) £70 (b)

EPSONLxacio (195 a) TAXAN KP815 (BO col) £155 la)FX800 E295 (a) KP915 (156 coil £275 la)FX1050 £349 (al BROTHER 111120 E349 la)EX800 £399 (a) STAR LC10 £179 fa)EX1000 £530 (al STAR LC10 Colour £225 fatGQ 3500 Kasen £1249 (a) STAR LC24-10 E275 (a)10500 (265 (al JUKI 6100 Palsy Wheel) ..... E295 (a)10850 (80 coil £415 la) INTEGREX (Colour) E529 (a)101050 (136 col) £569 (a) NAT PANASONIC KX P 1081. E145 la)We hold in stock a large variety af plinter attachments, interfaces and consumables.Please write or phone for detais.

PLOTTERSHitachi 672 a D A3 4 col HPGt. £479 (a)Piotmate A4S £379 (a): A3M £549 (a)Roland 880 A3 flat bed 8 col E575 fa)Variety of Plotter pens and accessories in stock. Larger plotters available plaaaFenquire.

ACCESSORIESBUFFALO 32K Buffet for Epson pnnters £75 (di. FX80 plus sheet feeder E129 lb);EPSON Serial Interface: 8143 £30 (b); 8148 with 2K buffer E65 fol.EPSON Paper RoN Holder E17 lb); EX80180÷185 Tractor Attach £37 ltd: RX.FX80Dust Cover £4.50 Id); LX130 Tractor Unit £20 (c); L0800 Tractor Feed £47 ltd.EPSON Ribbons: MX,RXIFX80 £5; MX1RX,EX100 £10 (dl; LXBO £4.50 (di;JUKI: Serial Interface E65 (dl; Tractor Attach. E149 pal: Sheet Feeder E219Ribbon E2.50 (a): Spare Daisy Wheel E14 (dl.BROTHER HR20: Sheet Feed £229; Ribbons Carbon or Nylon £3; Tractor Pei::E116 (a); 2000 Sheets Fanfold with extra fine pert. 9.5" - £13.50; 15" £17.50 (_E3E3C Parallel Lead E6; Serial Lead E6 (dl; IBM Parallel Lead (2m) E12

MONITORSMICROVITEC 14" ROB1431 Standard Resolution £175 (a)1451 Medium F.s.olution E225 (al1441 Hi Res (359 (alMICROVITEC 14" RGBIPAL & Audio1431 AP Standard Resolution E199 (a)1451 AP Medium Resolution E219 la)MICROVITEC 20" RGB/PAL/Autfio2030 CS std Res £380 (a)2040 CS Hi Res £675 (a)Mitsubishi 14" RGB Med Res (88C/I8MI

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TAXAN Supervision 620 £269TAXAN Supervision 625. _ E319TAXAN Supervision 770+

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12" MONOCHROME MONITORS:PHILIPS:

7502 Green Screen E 72 (al7522 Amber Screen E 79 (a)7752 c 851a)Ai Philips /Monitors supplied withswivel stand

BOOKS

LANGUAGES:6502 Assy Lang Prog E19.958086 Book £23.95Acorn BCPL User Guide £15.00Acorn FORTH £7.50Acorn USP £7.50Acorn ISO Pascal Ref Manual ..E10.00Intro to COMAL £10.00Irmo to LOGO £7.50Micro Prolog Ref Manual £10.00Introduction to Turbo Pascal E14.95Prog the Micro with Pascal _...£8.50The UNIX Book £7.50Unix User Guide E19.95Understanding Unix £18.45BBC MICRO GUIDE BOOKS

PRINTERS

No VAT on books; Carriage (e)View 3.0 User Guide E9.00Viewstore £9.00Viewsheet E9.00Wordwise Pius £9.95SOUND & GRAPHICS:Mastering Music £6.95DISC DRIVE SYSTEMS:Advanced Disc User Guide .... £14.95Disc Book E3.50Disc Programming Techniques E7.95Disc Systems E6.95File Handling on the BBC £6.95APPUCAllONS:Interfacing Proj for BBCBBC and Small Business

BBC User Guide Acorn £15.00 PROFESSIONAL SOFTWAREBBC Plus User Guide £15.00Drawing your Own BBC ProgramsE6.95Inside Information E8.95Math Prog in BBC Basic £7.95Toolbox 2 £10.95VIA 6522 Book 450PROGRAMMING/UTIIITYAdvanced Sideways Ram UserGuide E9.95Advanced User Guide IBBCI . £12.50Applied Ass.,12ng on the BBC .E9.95BBC Micro Sideways ROM's RAM sE9.95Guide to the BBC ROM £9.95Beginners Guide to W.P E7.95

£6.95E5.75

Wordstar made easy E16.95Introduction to Wordstar £17.95Wordstar Handbook E11.95dBase-11 for the fest time user E16.95Understanding dBase-111 £22.95Multiplan Made Easy E18.95Muitimate Complete Guide £16.95ABC of LOTUS 123 E17.451.2.3 for Business E16.95Adv Tech in dBase 11,111 E22.95

E17.95MasteringCP. CPA4M Bible £16.50

Introducing CP/M on BBC & Z80 E9.95MSPC DOS Prompt £10.95

PROGRAMMED ROMSPROJECTS

503-N Jnr. Computer Monitor 516 Talking Dice 2716 £ 7.302708 E 4.80 521 CharGen & Video Routine for

504 Disco lights 2708 E 4.80 DOS Junior .. 2732 + 2716 £16.40505 Chess Intelekt . 2 x 2716 £14.60506 J C Tape Monitor _ 2716 E 7.30507-N J C Printer Mon & PME

2716 E 7.30508 J C Bus Control 82S23 E 4.80510 150 MHz Reg Meter 2.82523

£ 9.60514 Dark Room Computer 2716E " 3l

522 CharGen & video; Routine for ex-tended juror 2732 + 2x 2716E24.00523 Char. Generator .. 2732 E 9.00524 Quantisizer 2732 E 9.00525 Universal Term- 2732 E 9.00526 Wind Dir Ind 2716 E 7.30527 Elabytinth 2716E 7.30530 D&sywheei !face 2 2716 E11.00

Please add carriage 50p unlessindicated as follows:

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ELEKTOR ELECTRONICS JULY/AUGUST 1989

CONTENTS July/August 1989Volume 15Number 169

Theme of the month inSeptember w ill he RadioTechniques.

Also in the Septemberissue:

Centronics monitorASIC microcontrollersfrom IntelStereo viewerCommunicationsreceiver front-endfilteringA high-grade powerunitA new generation ofanalogue switchesSimple transmissionline experiments

r::......"JI.C11.11.16.111. le.11132 rurzcar. ursecorso

Pao 6.4e,

Front coverOur front cover thismonth illustrates theteam work required inelectronics design anddevelopment projects.The photograph wastaken in our internationaldesign laboratory in thesouthern Netherlands.

Comment

11 Hacking: fun or evil?

12 Electronics scene

Application Notes

44 Video compression/expansion processorAdvanced Micro Devices

Audio & Hi-fi

14 Bevel arrays

Components

/() LinCMOS circuitsby T. Wigmore

31 Practical filter design (7)by H. Baggot

60 Optical shaft encoder from Sharpby T. Wigmore

Computers

24 Floppy disk monitorby M. Noteris

63 RAM extension for BBC -B computerby P.J. O'Shea

Electrophonics

34 Universal MIDI keyboard interfaceby D. Doepfer

General Interest

48 Multi -layer PCBsby A.J. Kool

49 DC -AC power converterby J. Ruffell

56 The digital model train (5)by T. Wigmore

Intermediate Project

Function generator - final part (3c)by J. Bareford

Science & Technology

5/

38 The versatile cable that tells a taleby Dennis Moralee

Test & Measurement

16 Test pattern generatorby A. Rigby

39 Tracking testeran ELV design

Information

New books 30; Events 33; New products 63; ReadersServices 65

Guide lines

Switchboard 66; Classified ads 74; Buyers' guide 74;Index of advertisers 73

-Test pattern generator - p. 16

Floppy disk monitor - p. 24

DC -AC power converter - p. 49

OUR

Optical shaft encoder - p. 60


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PIEZO ELECTRIC TWEETERS - MOTOROLAJain the Net° revakiton The 14w djranic mass (ro %Oce cot) d a Pere tweeter produces an inprcned transen:response vitri a tower dslortai terel Oen atirary direntic tweeters. As a crossoiv is not reffired these unit cancealt-d- ez cgspeaersysT dip to WO azit (Tore 2p.fiiii-es). FREE EXPLANATORY LEAFLETSSUPPLIED WITH EACH TWEETER TYPE 'A' (KSN2036A) 3' round wirn protective wire

mesh. ideal for bookshelf and medium sized Hi-fiSpeakers Price £4.90 each + 50p P&P.TYPE 'B' (KSN1005A) 33/4' super horn. For generalpurpose speakers. disco and P.A. systems etc. Price£5.99 each + 50p P&P.TYPE 'C' (K SN6016A) 2' x 5' wide dispersion horn. Forquality HA systems and quality discos etc. Price £6.99each + 502 PAP.TYPE 'D' (KSN1025A) 6' wide dispersion horn

type Upper frequency response retained extending down tomci forge (2KHz). &stable for high qualityand puaLly dims. Price £9.99 each + 50p Ps'irmsTYPE 'E' (KSN1038A)3W hem tweeter with attractivesilver Crash trim. Suitable for Hi-fi monitor systems etc.Price £5.99 each + 50p P&P.

TYPE LEVEL CONTROL Combines on a recessed mountingplate. level control and cabinet input jack socket_El5 vilL5min. Price £3.99 + 50p P&P.

STEREO DISCO MIXERSTEREO DISCO MIXER with 2 x 5 band L& Rgraphic equalisers and twin 10 segment LED.Vu Meters. Many outstanding features 5 Inputswith individual faders provId-ng a useful com-bination of the following: -3 Turntables (Wag). 3 4 Line inducing CDplus Mic with tack over switch Headphone Moni-ca. Pan Pot L & R. Master Output controls.Output 775mV_ Size 360v280v sprain. Supply220-240v.

Price £134.99 - £4.00 P&P

A. of A.11. .

I

B. K. ELECTRONICS Dept EUNIT 5, COMET WAY, SOUTHEND-ON-SEA, ESSEX. SS2 6TR

TEL: 0702-527572 FAX: 0702-420243


ELEKTOR ELECTRONICS (Publishing)Editor/publisher Len SeymourTechnical Editor: J BuitingEditorial offices:Down HouseBroomhill RoadLONDON SW18 4JQEnglandTelephone: 01-877 1688 (National)or +44 1877 1688 (International)Telex: 917003 (LPC G)Fax: 01-874 9153 (National)+44 1874 9153 (International)Advertising: PRB Ltd3 Wolseley TerraceCHELTENHAM GL50 1THTelephone: (0242) 510760Fax: (0242) 226626European offices:Postbus 756190 AB BEEK IL)The NetherlandsTelephone: +31 4490 89444Telex: 56617 (elekt nI)Fax: +31 4490 70161Director: M.M.J. Landman

Overseas editions:Elektor sadRoute Nationale; Le Seau; B.P. 5359270 Bailleul - FranceEditors: D R S Meyer;G C P Raedersdorf

Elektor Verlag GmbHSusterfeld-Stralle 255100 Aachen - West GermanyEditor: E J A KrempelsauerElektor EPEKaraiskaki 1416673 Voula - Athens - GreeceEditor. E Xanthou(isElektor Electronics PVT Ltd.Chhotani Building52 C, Proctor Road, Grant Road (E)Bombay 400 007 - IndiaEditor: Surandra lyer

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

Electro-shop35 Naseem PlazaLasbella ChawkKarachi 5 - PakistanManager: Zain AhmedFerreira & Bento Lda.R.D. Estefania, 32-1°1000 Lisboa - PortugalEditor: Jeremias SequeiraIngelek S.A.Plaza RepUblica Ecuador2-28016 Madrid - SpainEditor: A M FerrerElectronic Press ABBox 550514105 Huddinge - SwedenEditor: Bill Cedrum

Distribution:SEYMOUR1270 London RoadLONDON SW16 4DH.

Written and composed on Appleand IBM corporate publishingsystems by Elektor Electronics.Printed in the Netherlands byNOB, Zoeterwoude.

Copyright 1989 Elektuur B.V.

ABC

HACKING: FUN OR EVIL?

There are indications that hacking, the nefarious accessing of computers, isbecoming more widespread. There are many who in their naivity consider thatthis anti -social behaviour is nothing but a bit of fun whose perpetrators do auseful job in testing the security of computer systems. Nothing could be furtherfrom the truth.

A hacker is someone who, without permission, enters your home as it were andgoes through your personal belongings. While doing so, he may, innocently orintentionally, take copies of your computer files. He may destroy or corruptthem. He may unwittingly plant an electronic time bomb that does not go off tillmuch later.

There is no way of knowing exactly the harm and damage caused to privatecomputer systems, but it is estimated, and in a number of countries adocumented fact, that industrial and commercial losses world-wide amount tothousands of millions of pounds. More seriously, deaths have already occurredowing to the (hopefully inadvertent) changing of medical records by hackersinfiltrating a French hospital computer system. And nobody knows how manycases of blackmail have been, or are being, conducted as the direct result of ahacker's activities.

It is, of course, true that many computer owners to a large extent have onlythemselves to blame. After all, you don't leave your car unlocked parkedanywhere in a big (or even small) town nowadays. Nor do you leave the frontdoor of your home open so that people can just walk in. That is, of course, no

take your car or enter your home, but it does hand themthe opportunity of so doing on a plate. Considering the cost of a computersystem, and the possible losses caused by hacking. the cost and trouble ofmaking the system secure are relatively small.

Many may argue that the laws should be changed to deal with hackers, but thatwill not be the whole answer any more than it is in the case of other kinds ofcrime. Nevertheless, a change in the law is overdue, if only because it will atleast reflect the attitude of the nation to hacking, an activity that is at bestirresponsible, invariably harmful, and often destructive.

UENMER OF ms AUDaCFF CROAATIO1S


Geographical Information System

A low-cost pc -based system, usingvideodisc technology, that opens up geo-graphical information systems to a wholerange of users and applications has beendeveloped by Action Information.

'ActionPlan' is a hybrid system thatplots video pictures and digital datatogether. The system is based on a 1000km by 1000 km grid that allows simple.accurate and speedy placement ofresources and rapid access to sites of inter-est.

At the heart of the system is the rangeof 'Maps in Action' videodiscs that pro-vide background maps with up to 11 levelsof magnification from a scale 1:107 to verydetailed maps with a scale of 1:1250.

UK's Most Powerful Chip

Plessey has produced the first micro -cir-cuit to achieve the performance targets ofa very high performance integrated circuit(mow). The 1.4 pm double -layer metal0.tos chip contains 240,000 transistors, isabout 1.1 cm2, can be clocked at 30 MHzand performs 24 -bit block floating pointarithmetic.

Revolution in Telecoms

British Telecom is progressively imple-menting one of the world's most challeng-ing computer projects to transform its ser-vice to customers. Known as CustomerService Systems (CCS), it is designed todraw together all the main elements of thecustomer services British Telecom pro-vides. It has already been introduced in 13of the 28 operating districts to cover morethan eight million customers. By the endof this year, all 23 million customers willbe able to experience its advantages.

CCS, the world's largest civil comput-ing development, is part of BritishTelecom's £2,300 million -a -year invest-ment programme to improve customer ser-vice and cater for growth. There is nothingcomparable to it anywhere else in theworld. Enquiries from Japan, the United

ELECTRONICS SCENE

States and several countries in westernEurope indicate that it may well prove tobe a significant foreign -currency earner.

Advanced Telecoms forBangladesh Railways

Advanced telecommunications have beenbrought to Bangladesh Railways in Dhakawith the opening of the first phase of a £12million 1700 kilometre optical fibre net-work.

The network, being installed by Tele-phone Cables Ltd (ra.), part of Britain'sGEC Plessey Telecommunicasions Group(GPT), represents the first use of opticalfibre technology in the country. It will beused for both telecommunications andtrain signalling, and also includes a micro-wave radio link across the 25 km wide Ri-ver Jamuna in the north.

BS Approval for Siliconix JFETs

Siliconix has obtained as CECC 50000 ap-proval for two families of dual N -channeljunction field-effect transistors (JFETs), theU430 and U431. These families consist ofiu devices for use op to 100 MHz thathave a low noise figure and guaranteedmatching characteristics.

Transportable Radio AlarmLicensing Simplified

Operators of certain short-range trans-portable radio alarm systems will not needto be licensed individually under theTelecommunications Act since they willbe covered by a class licence granted bythe Department of Trade and Industry. Re-ference copies of this licence may beobtained for £1 from: The Library Officeof Telecommunications Atlantic House Holbom Viaduct London EC1N 2HQ.

BT Takes Lead in Vocational Training

British Telecom has taken a lead in estab-lishing vocational qualifications for thetelecommunications industry. There are atpresent no industry -wide standards ofcompetence.

British Telecom, together with STC Te-lecommunications, GEC Plessey Telecom-munications, Cable & Wireless PLC,Mercury Communications Ltd and

Telephone Rentals PLC, is setting up abody to act as a focus to determine stan-dards of vocational competence through-out the industry.

Data Communications in Europe

According to a report* from Frost & Sul-livan, the forecast for western Europe'sdata communications market looks verygood.

Communications, information and pro-cessing services (oils) still constitute aninfant market in Europe. In 1988, the mar-ket amounted to $1.3 billion, more thanhalf of which in the UK. By 1993, FederalGermany will have gone ahead ($2.5 bil-lion) with the UK second and France third(S2 billion).

COMMUNICATIONS. INFORMATION& PROCESSING SERVICES MARKET

IN EUROPE - 1988

Saw, FCC

...74,41,:eQtr.ra 5477_1J

7=. twat' t' FAce-

* A Strategic Report on European DataCommunications (#E1138)

Bank of Scotland Presents the 1989/90Faraday Lecture

Bank of Scotland has accepted the invita-tion from the Institution of ElectricalEngineers to present the annual FaradayLecture series. It is the first Scottish com-pany - and the first financial institution -to undertake this exercise.

The lecture series, founded by the lEEin 1924, is used as a tribute to the memoryof the scientist Michael Faraday, as ameans of educating the general public ofthe significant strides being made in thearea of Information Technology and tointerest young people in career opportuni-ties.

Recent presenters of the FaradayLecture have been British Telecom, ICL,Ford Motor Company and the BBC. It is


in keeping with the Bank of Scotland'sstance as a leader in the field of innovativebanking that this opportunity has beenaccepted.

sr

V.h4;cfrool Forockry:8y courtesy of kw Dirdor of LS. Royal MorMion

Michael Faraday (1791-1867) pio-neered the use of electricity and in 1831,by his discovery of electromagnetic induc-tion, possibly his greatest achievement, hehad invented the dynamo.

The lecture, entitled 'Electric Cur-rency' and lasting for about an hour, willexamine how electricity has reshaped thepublic's perception of money. It will bepresented by a team of Bank staff atvenues in 20 major cities throughout theUK, starting in Glasgow in September thisyear and finishing in Edinburgh in March1990.

New Metal -coated Optical Fibre AllowsHermetically Sealed Connection

The Electro-optical and Data SystemsGroup of Hughes Aircraft Company hasdeveloped a metal -coated optical fibre thatcan be soldered to provide an hermeticseal resistant to a variety of harsh environ-ments. The fibre, or pigtail, is used to con-nect an optical fibre cable to a packagecontaining a laser or sensor and associatedelectronics as shown in the photographbelow.

ELECTRONICS SCENE

Police Curb Noisy Bikes withNew Device

The ear shattering noise from inadequatelysilenced motorcycles could soon be athing of the past if a recent experimentcontinues to prove successful. Police inDerbyshire are using a hand-held soundlevel meter produced by Lucas CELInstruments to advise bikers if their motor-cycles exceed acceptable noise levels.During roadside checks, the meter is heldhalf a metre from the rear of the exhaust ata 45° angle, and the engine run at half thetotal possible revolutions. If the exhaustnoise exceeds 103 dB (which to most of usis still far too high), the rider is given a'Vehicle Rectification Notice', whichallows him/her seven days to effectrepairs.

Educational Video onNoise in the Workplace

Draft regulations from the Health andSafety Commission on industrial noise,based on the EEC'S 1986 directive, becomelaw on 1 January 1990. By then, employ-ers will need to know the facts about hear-ing damage, assess their own circum-stances, and take the necessary action.Many employers who may consider them-selves safe will find that lower action lev-els than recommended by the current codeof practice will put them in a vulnerableposition.

The importance and urgency of educat-ing employers have prompted noisemeasurement specialist Bruel & Kjaer,Pitman Tutorial College, the BBC and theInstitute of Sound and Vibration Researchto co-operate in producing a video andaccompanying text called 'Noise at Work- Action Now'

Major European Investmentby US Combine

General Signal, a leading world-wideindustrial manufacturer, is opening a newmulti -million dollar centre for semicon-ductor manu factoring technology thataims to be the best equipped facility of itskind in Europe. The centre, which willincorporate General Signal's newEuropean Headquarters for itsSemiconductor Equipment Group, will belocated in southern England.

Sky Television ChoosesGEC Mobile Radio Network

Sky Television has chosen the GECNational One communications network forthe outside broadcast vehicles employedby camera and news trews.

Fibre Optic Telephone Lines BoostPower Supply Market

The change -over of telephone lines tofibre optics will help double the marketfor electronic power supplies in Europesay Frost & Sullivan in a recent report*.

SWITCHED MODE POWER SUPPLIESIN THE EUROPEAN MARKET - 1988

ata_i 1,17 711

Fere9:3 MC.71

Fuhir 11 E.- raze W...31.1

.0: WV.. i.114Ase.s.

Although equipment from computers toTV receivers to X-ray machines needs apower supply, the report singles outtelecommunications as the field of highestgrowth between now and 1993. It actuallypredicts that 18% annual increases willcause power supplies to eclipse computersand computer peripherals as the topdemand area.

The United Kingdom will demonstratea more rapid growth than will France orGermany. The latter is, at present, thelargest market, however, with demand in1988 reaching $698 million, that is, 27%of the total market. The UK market, at$472 million, represented 19% of theEuropean total.

*Switched -mode Power Supplies inEurope (#E1044).


14

BESSEL ARRAYS

Loudspeaker systems that use a relatively large number ofidentical drive units unfortunately provide a highly directional beamof sound. Depending on the alignment of the drive units, frequency

'holes' occur at a number of positions. Arranging the drive unitsin a Bessel array results in even sound distribution. It should

be noted that for the commercial use of the systems describedin this article the permission of the patentee, Philips Export BV,

Eindhoven, the Netherlands, is required

The requirement for frequency -indepen-dent even distribution of sound in largerooms can be met only approximately.Radiation patterns at different frequenciesbut equal magnitude are shown in Fig. 1.From these diagrams, it is clear that thepattern approaches the ideal at low fre-quencies and that the higher the frequencythe more chaotic the distribution. Assu-ming a maximum sound pressure of85 dBm, the sound pressure in the 'eyes'of the 1600 Hz diagram is some 40 dBdown, but only 8 dB at 100 Hz.

This problem is tackled by arranging anumber of drive units in an array. If highpowers are required, further difficulties areencountered, because the individual driveunits then become relatively more expen-sive and less suited for the present pur-pose, since the large cones produce moredistortion. The use of a number of smallerdrive units connected in parallel or seriesalso has disadvantages. One of these isthat the more drive units are used and thehigher the frequency is, the smaller theangle of radiation will become.

The distortion of the radiation patternat higher frequencies is very troublesomeand, for example, does not permit stereoradiation.

The Bessel array developed in thePhilips research laboratories makes it pos-sible to configure a number of identicaldrive units, without additional compo-nents, in a manner where they virtuallybehave as one entity with a higher powerrating.

Bessel functions

The researches at Philips have shownthat a spatially interconnected number ofsmall, identical drive units has a near -spherical radiation pattern if the totalpower applied to them is divided over theindividual units in accordance with aBessel function. Each drive unit, m, isthen powered according to the function:

k k mV (-1) ( p/ 2),( =k=0 k!(m + k)!

For the first drive unit (m = 1), the valueof the function is normalized at 1. With asuitable value for p, the functionsJm+I(p), Jm+2(p).. become whole multi-ples of Jm(p). This mathematical trickobviates fractions for the valency of thedrive units.

The sum of all the functions is 1 andthat is the reason that a number of smallunits in a Bessel array have the same radi-ation pattern as one large one. Strictlyspeaking, this is true only for an infinitearray, but good results are achievedalready when m = 5.

Simple Bessel seriesFig. 2 shows a series layout of five driveunits separated by a distance d and twopossible circuits that satisfy the functionratio of

A:B:C:D:E: = 1:2:2:-2:1.

The normalized power applied to unitsA and E is exactly half supplied to B andC. Unit D, which needs a power of -2, hasits terminals reversed. The two circuits areonly different in their resulting impedance.Assuming that all the drive units are 8 SI,the impedance of the series circuit is 28 SIand that of the parallel circuit is 2.3 Q.

A similar set-up, but for seven driveunits, is shown in Fig. 3. Here, the weight-ing factors are:

A:B:C:D:E:F:G = 1:2:2:0:-2:2:-1.

The factor 0 merely means that unit Dis omitted: in other words, the distancebetween units C and E is 2d.

When nine drive units are considered,some will have the factor 0. Their ratio is:

A:B:C:D:E:F:G:H:I = 1:2:2:0:-2:0:2:-2:1.

itArAPININOWli. _

'4 le Mar-

mlrWillin1111/

laintn73°7, n

11111111WilY1

Fig. 1. Radiation pattern of a drive unit at different frequencies but at constant sound pressure.

Fig. 2. Simple Bessel series with five identicaldrive units. Note the polarity of the units as indicated by the bullets. Distance d is only slightlylarger than the loudspeaker diameter.

If your maths is up to it, you can com-pute higher orders. The procedure is tofirst normalize J i(p), that is, make it 1 andgive a value top.

It is, of course, not necessary to corn-


BESSEL ARRAYS

Fig. 3. A Bessel series with seven weightingneeds only six drive units.

pute the sum to infinity: the terms quicklybecome smaller and, depending on thevalue of p, may be neglected for k> 6.

Array combinationsSimple Bessel series may be combined. Ifa radial pattern in only one direction isrequired, a number of identical arrays maybe combined as shown in Fig. 4. This con-figuration is suitable when the listener(s)is always in a horizontal plane perpendicu-lar to the array surface as, for exam -pie, ina theatre or cinema.

O 000000080O 0000OGGGOO 0®80

Fig. 4. Identical arraysplaced side by sidegive a particularly hori-zontal radiation pat-tern.

Fig. 5. A sphericalradiation pattern re-quires identical rowsand columns.

A different approach is necessary whena semi -spherical pattern is required, forinstance, when the array is suspendedfrom the ceiling, that is, parallel with thefloor. It is then necessary to combine iden-tical arrays both in the rows and thecolumns as shown in Fig. 5. The sameeffect is obtained with the configuration ofFig. 6a, comprising five groups of fivedrive units. The valency of each group isthe same as that of the simple array inFig. 2. Within each group, the valency isdivided in the same way and by the samemethod.

It is, of course, not an easy matter toconfigure 25 drive units in a row. It is,however, amazingly simple to reduce thenumber, because it is possible to rearrange

000000000000000000000000000000

0 0 0 000000000000000000000000000©0

factors Fig. 6. Twenty-five drive units can be combined in a fairly simple manner (a). It is possible byrearranging the weightings (b) to reduce the number of drive units to 11.

the weighting factors of Fig. 6a as shownin Fig. 6b and this results in only 13 fac-tors and 11 drive units. How far the rowsare displaced with respect to one anotherdepends on the number of wanted driveunits, the maximum power at the highestweighting, the maximum weighting ratioand some other factors. The result is, how-ever, always the same.

:1.11000000E00000000000000ocpoompo00000000000000oe@0000

Fig. 7. A seven by seven Bessel array.

The configuration of 49 drive units inFig. 7 is intended to satisfy the aestheticrequirements of interior decorators.

Stereo arrays

In stereo applications, it is not so that twoBessel arrays are required. If from the two

Fig. 8. Layout of the stereo version.

channel outputs a sum signal (L+R) and adifference signal (L-R) are produced,these signals are simply connected to thefive -factor drive unit configuration ofFig. 8. The weighting factor ratio is:

A:B:C:D:E = k(L+R):2( l-k)(L-R)::2k(L+R):-2(1-k)(L-12.):k(L+R).

This ratio coincides with that of themono version (test this by omitting theright-hand channel). The simple factor koffers many possibilities. For example, ifthe amplifier input is preceded by the cir-cuit of Fig. 9, a continuously variable basewidth setting may be realized with the fol-lowing values fork.If k = 0, super stereo results; if k lies be-tween 0 and 0.5, expanded stereo is ob-tained; k = 0.5 gives normal stereo as inFig.8; and k = 1 results in mono opera-tion.

EiC,Oee-19

Fig. 9. Circuit to obtain a continuously variablebase width setting.

It will, no doubt, be of interest to manyreaders that in the above the drive unitsmay be replaced by microphones to yield asupersensitive microphone with a spheri-cal radiation pattern.

Literature: Bessel panels - high -powerspeaker systems with radival sound dis-tribution. Philips Technical Publication091.


16

TEST PATTERN GENERATOR

A. Rigby

A programmable digital pattern generator for all of you who do nothave access to specialized equipment for faultfinding in digital

circuits.

The operation of many digital circuits is,in principle, not simpler or more complexthan that of analogue circuits, but the de-pendency of certain signals on othersgives digital faultfinding a labyrinth ef-fect. Furthermore, it is often impossible toisolate a particular section of the circuitfor a stand-alone test. The omission of asingle control signal, whose function maynot be known at all initially, may cause thewhole circuit to 'stall', making it im-possible to track the cause of the malfunc-tion.

In synchronously operating digital cir-cuits, state changes take place only as aresult of clock signal transitions. Thismakes the operation of this type of circuitrelatively simple to follow, especially if

the clock signal or signals can be gener-ated by external means. By contrast, alevel change at a particular point in anasynchronous digital circuit is taken overby the rest of the circuit. This means thata spurious pulse at any point in the circuitcan easily disrupt the normal operation ofthe entire digital equipment.

A test pattern generator as describedhere enables programmed data to appearin a predefined order at the input of thecircuit under test. An oscilloscope is usedto check whether the circuit gives the cor-rect response to the applied test patterns.

Patterns for testingThe generator is capable of supplying up

to 255 8 -bit test words, or a sequencethereof. The number of test words can beset by the user. A short sequence thereforetakes hardly time to program, and needonly be programmed once. A sequence of,say, five test words simply corresponds tofive bytes loaded into the memory of thetest generator. The remaining 250 mem-ory positions are not used and need not beloaded.

The block diagram in Fig. 1 shows thatthe heart of the circuit is formed by a RAMmemory. Two 8 -way DIL switch blocksserve to program the test words and thelength of the test word sequence. Thememory locations are addressed by acounter, which counts from 0 to 255. Thegenerated address (A) is compared to thepreset length of the sequence (B). When Aand B are equal, output A=B of the wordcomparator is actuated. Depending on theposition of the mode selection switch, thetest pattern is either stopped or repeated.When the switch is set to CONTINUOUS, theoutput signal of the comparator causes theaddress counter to be reset and to startcounting from 0 again. When the modeswitch is set to SINGLE, the oscillator isinhibited, so that the last counter state is'frozen'.

There are three more switches in thecircuit. One of these serves to select eitherthe 'single step' or the 'run' mode. Insingle-step mode, the clock pulse for thecircuit is generated by a push-button,while in run mode it is generated bymeans of a clock generator. Switch oc en-ables the outputs to be switched to high -impedance (three -state). The last switch,marked RUN/FROG causes the WE (writeenable) input of the memory to be con-nected to the clock signal (program), or tothe positive supply voltage (run). In therun mode, the memory is made 'read-only'.

Circuit descriptionThe circuit diagram of Fig. 2 shows howthe previously discussed functions aregiven their practical form. The test gener-ator is composed of only six integratedcircuits.

Since only 256 of the 2,048 memorylocations in RAM IC3 are used, addresslines A8, A9 and Al0 are connected toground. The Type 6116 2Kx8 CMOS staticRAM is used here because it is currently



cheaper and more readily available thanany 256 -byte type.

The counter that drives the eight re-maining address lines of the RAM isformed by IC2, a Type 74HCT393. This8 -bit bistable counts continuously from 0to the value set with switch block Ss. IC4compares the current counter state at in-puts Qn with the preset word at inputs Pn.When the words are equal, output P=Qgoes low. Depending on the position of S4,either the outputs of N3 and N4 areblocked, or the counter is reset. Afterbeing reset, the counter starts at state 0again.

The memory databus is connected toan input buffer with three -state outputs,ICI, and an output buffer, IC,. When thememory is read out, RAM input WE islogic high, and ICI is switched to high -im-pedance mode. The output buffer is trans-parent, and latches the data from thedatabus on the negative edge of the clocksignal. The buffer passes all data appliedto its D inputs as long as input c is logichigh. When c is made logic low, the nega-tive clock pulse transition causes the dataat the D inputs to be latched in the buffer'sinternal registers. The data remains thereand on the outputs, until input c is madehigh again. The or input allows the out-put drivers in the buffer to be switched tohigh -impedance, so that the test generatoris effectively disconnected from the circuitunder test without the need of leads to beunplugged or wires to be removed.

Manual or automatically?As already discussed, the circuit can becontrolled either by a clock generator orwith the aid of the SINGLE STEP switch, Si.R -C network Ri-Ci suppresses bouncepulses generated when the SINGLE STEPbutton is actuated. Schmitt -trigger gate N3gives the switch signal a digital shape andlevel.

Gate N4, capacitor C2 and resistors Piand R3 form an adjustable clock generator.One input of N3 and N4 is connected toswitch S4, which enables the gates to beblocked. When S4 is set to CONTINUOUS,one input of both gates is taken high viaR2, so that the clock oscillator is enabled.The span of potentiometer Pi is fairlylarge at 1:100, allowing the user to set theoptimum test frequency for many types ofdigital circuit.

External push-button Ss, with associ-ated debouncing network R9 -C3, makes itpossible to reset the counter. The enableinputs of ICi and the WE input of IC3 arelogic high as long as S3 is open. The inputbuffer is in high -impedance mode, and IC3behaves as a read-only memory. The cir-cuit is thus set to the 'run' mode.

When S3 is closed, input WE is pulledlow during the active part of the clockpulse, and the input buffer is enabled. Thecircuit is in 'program' mode because thedataword set on S7 is stored into the mem-ory during the rising edge of the clockpulse. The clock signal at the pole of S2 isapplied to the clock input of bistable FFi

Data

Fig. 1. Block diagram of the test pattern generator for digital circuits.

STOP

ar

RI

,s -n,

9

2, IS. .0k

fiCT ,, "r174 .,"A : S n 57547,,,7: 74 ; ":-1- 7 °7';-1-1-7.-.:...°

' E2 /C5 rtz L__.0-07 Al HCT..0

PE511 720 S so 71

EG U -L...1-.1....0 ..; 047 37

3 ,,, 61U.:. tic -.6 C

i SO917 7-0-0

ex.i 1.1.11

vs Ml vz

KI151.16k16v8srirl2assa

1C3

6161

22Z2.1:i2' 4 2 I

A 45J7388g vase,

A FF1 ,] FF2ax a1 13

FF1. FF2 = 1:2=74HCT393

H1.144=106=74HCT132

OS7

v-n9,9 PS

Al lc..4 PsPA

as 74 77A 02 HCT P2

01 666 9,02

mi.

I

15

MEI

T

516S-LSOKT

3

120029 -71

Fig. 2. Circuit diagram of the tester.

ELEXTOR ELECTRONICS JULY/AUGUST 1989

18 TEST AND MEASUREMENT

Fig. 3. Track layout and component mounting plan.

via inverter Output Q4 of FF1 in turnclocks a second bistable, FF2. The bistables(there are actually four in each device) arethus cascaded to form an 8 -bit counter.

SuggestionsThe clock frequency has been chosenrather arbitrarily but will be suitable formost applications. If required, the value ofCa should be adapted to give a differentfrequency. A larger value of Ca results ina lower clock frequency, and a smaller onein a higher clock frequency. It is alsopossible to create a larger frequency rangeby selecting different capacitors by meansof a rotary switch.

Toggle switch S2 may be replaced by athree -position type. In that case, the thirdposition is used for selecting an externalclock source, e.g., one available in the cir-cuit under test.

ConstructionThe compact printed -circuit board de-signed for the tester makes construction amatter of routine. The track layout andcomponent overlay are given in Fig. 3.

Start the construction with the fittingof the ten wire links on the board. Next, fitthe 18 solder terminals and connector 1(2.The HCT ICs are all low-cost types, so thatsockets are not strictly required. Although

Parts list

Resistors (±5%):13-1 = 100k

R2;R3;R4;R6-R17 = 10kRs;1:118 = SIL resistor array 8x10kPi = potentiometer 100k linear

Capacitors:CI :C3-Ca = 100nC2 = 1n0

Semiconductors:ICS = 74HCT541IC2 = 74HCT393IC3 = 6116 or 8416IC4 = 74HCT688ICs = 74HCT563ICS = 74HCT132

Miscellaneous:Si ;Se = SPST push -to -make button.S2;S3;54 = miniature SPDT switch.Ss = miniature SPST switch.S7;S3 = 8 -way DIP switch or hex thumb -wheel -switch.

= 20 -way pin header.PCB Type 890020 (not available ready-made through the Readers Services).

the board allows the fitting of two 8 -wayDIL switch blocks, it is better, in manycases, to use switches that can be mountedon to the enclosure. Hexadecimal thumb -wheel switches are convenient in the prac-tical use of the test generator and are,therefore, suggested as an more ergon-omical and simple -to -connect alternativeto DIP switch blocks.

The power supply is purposely not ac-commodated on the board because a regu-lated 5 V source will nearly always beavailable as part of the circuit under test.The digital test generator draws about30 mA.



Fig. 4. Prototype of the test generatorhoused in a compact enclosure with the wordconfiguration and word number switchesmounted on to the front panel.

1 -,- 19" vIr---

Fig. 5. Bit pattern displayed on a logic ana-lyser.

ProgrammingThe memory has to be loaded with thedesired bit -patterns (test words) beforethe circuit can be used to test a digitalsystem. Fortunately, programming isstraightforward:

Set the number of test words as a hexade-cimal value on Ss (1301-1-FFH).Set S3 to PROGRAM, S2 to STEP and S4 toSINGLE. Set the desired bit pattern on S7.Press srErto store the bit pattern in mem-ory.Set the next bit pattern.

When S4 is set to SINGLE, the circuit will notaccept further data when the number setwith Ss is reached. After loading all bitpatterns, 53 is set to RUN to sequentiallyfeed the data to the circuit under test. De-pending on the position of S2, this feedingout takes place automatically or ma -

RESET WITH DATABYTE PROGRAMMED ON S7

STEP P1 STEP PROG SINGLE OC RESET

OOSC RUN CONT.

PROGRAM (after pressing RESET); INCREMENT WITH STEP KEY

STEP P1 STEP PROG

* [1OSC

U

RUN

SINGLE OC RESET

CONT.

*

STOP PROGRAMMING ; RUN (single)

STEP P1 STEP

* CDOSC

PROG

RUN

SINGLE OC RESET

CONT.

(i)

FROM STEP - MODE TO OSCILLATOR (single)

STEP P1 STEP

OSC

*PROG

RUN

SINGLE

CONT.

OC RESET

FROM SINGLE TO REPEAT PATTERN

STEP P1 STEP PROG

O IOSC

URUN

SINGLE

CONT.

OC RESET

O

55.3023 13

Fig. 6. Overview of the programming and loading operations using the front panel controls.

nually.Timing and level measurements may

start after the digital outputs of the testerhave been connected to relevant points inthe circuit under test. The tester does notprovide a strobe pulse, but this is fairlysimple to implement by programming,say, bit 8 accordingly. In that case, the testword is 7 -bits wide, and the sequentialdata stream has a maximum length of 128samples because the strobe bit musttoggle in between samples.

Finally, one interesting application ofthe test generator should not be left un-mentioned here. It is fairly simple to usethe instrument for driving a D -A (digital -to -analogue) converter. This combinationcreates a simple programmable waveformgenerator.


20

LINCMOS CIRCUITSLinCMOSTv is a process that gives to linear devices a superior

performance over metal -gate CMOS by the use of polysilicon gatesand an optimized 'N well' structure. Equivalents of many

popular operational amplifiers, comparators and timers havealready been available for some time. The major benefits of these

devices are lower power consumption, faster switching andthe ability to operate from very low supply voltages.

While giving good ± supply rail perfor-mance, with a total voltage not exceeding16 V, the input and output are optimizedfor single supply operation. This isachieved with an input common moderange that included GND (-VDD withsupplies) and an output range that pullsdown to within a few millivolts of GND(with a load connected to GND). TheTLC27x range are specified to work withsupply voltage down to 3 V and will thusoperate with the supplies that are commo-ny available for Tri. and tiCMOS. For maxi-mum dynamic range, single rail operationwith 16 V supplies should be used. Forlow power and battery operation, theTLC25x range are specified to operatewith 1 V total supply voltage.

High bias mode gives a wider band-width (2.3 MHz) and faster slew rate(4.5 V/I.ts) than standard bipolar opamps(especially single -supply devices) for thesame order of supply current. Theenhanced bandwidth gives an increase inthe open -loop to closed -loop gain ratio ata particular frequency improving accuracyof, for example, filter circuits, or allowinghigher frequency operation. Slew rateenhancement gives a wider large -signalbandwidth and generally allows the imple-mentation of faster circuits.

Medium bias mode gives standardbipolar opamp performance at roughly atenth of the supply current.

The main advantage of the low biasmode is the low power consumption withsufficient bandwidth and slew rate forbasic sensor interface and audio applica-tions.

Low bias and offset currents allow cir-cuit simplification through the eliminationof bias current balancing resistors, higherimpedance circuits for greater accuracy(for instance, smaller, higher tolerancecapacitors) and circuit current definedonly by feedback components. Anotheradvantage is insignificant noise due to biascurrent (shot noise): noise is dominated bynoise voltage and resistor noise-seeFig 3.

P2 R2

--

HJPa

R5

N5

Ct

NI 112

DIV VCRNI

v2D

P12

Pit

:411 -

Pt

N6

R7

N7

b4-

NII

NI2

NIB

NI3

OFFSET OFFSETNI (42

OND 2ASSELECT

890039 - 12

Fig. 1. Circuit diagram of a typical LinCMOS operational amplifier.

TECHNOLOGY BIPOLAR' BIFET'LinCMOS (bias levels)

LOW MEDIUM HIGH

Vc, MAX REC 1.'15 ±15 16 16 16V, MIN REC ±5 :5 1 1 1Vcc SPECFD =15 ±15 10 10" 10"V, mV 1-10 3-20 2-10 2-10 2-10.V, oV:degC 5-20' 10 0.7 2 5I. 2-750nA 5p-2nA 1-300pA 1-300pA 1-300pAI a 20-800nA 30p-10nA 1-600pA 1-600pA 1-600pAV,a V =13 or ±12 -0.2 to 9 -0.2 to 9 -0.2 to 9

Vcc-1.5V. IN 10kabms 24-26 or 24-77 0-7.8 0-7.8 0-7.8

Vcc-1.5 RI- IM RL.-1004 RI -10kAv, V/mV 15-200 15-200 20-500 15-280 7.5-40CMRR dB 70-90 70-76 70-88 70-88 65-82Icc 0.5-3.3mA 1.4-2.8mA 10-40µA 150-400µ4 1-2.2mAB, MHz 0.7-1 3 0.1 0.7 2.3SR VipS 0.5 13 0.04 0.6 4.5en nVii-iz

(a lkhzin pA-L Hz

(a 1khz

22'

0 55*

18

0.01

70

0.013'

38

0.013'

30

0.013'

1) bipolar: pA741 / MC1458 / LM3242) biFET: TL080-series

typical value (not specified)- TLC25X types are also specified at 1V 890039-11

LinCMOS is a trade mark of Texas Instruments. Table. 1. Comparison between bipolar. BIFET and LinCMOS operational amplifiers.

E L E KTOR ELECTRONICS JULY/AUGUST 1989

LINCMOS CIRCUITS

0 SUPPLY CURRENTvsBIAS SELECT PIN VOLTAGE

O SUPPLY CURRENTvsFREE TEMPERATURE

10.000

1000

Vo Vto . 0.2 VDDNo loadTA - 7.5C

10.000

1. 1000H.

VDD 16v

4 VO

1.1.. 100 - 100

VDD . 1.4 V 00 10

10.1 1 10

V8 -Bias Satact Pin Vottap -V

100

DEVICE FEATURESTiaacia at VDD 5 V. TA - :

DLLS-SELECT NODEwar

1 Nati isaaaum LowPO 3375 525 50 sWSR 16 04 I 003 VimVA 26 32 I 66 nVN%al 17 05 I 009 lab

AVD 23 170 I 480 V veN

8.o Varsess

VDD 10 VVic 0VVo 2VNo load

Alediamilias Winton:

Lorrain Vaniom

10 20 30 40 50 63 70 50

TA -Fns -Ai Tampaca,re - C

010.000

a 1000

3100

0 0

SUPPLY CURRENTvs

SUPPLY VOLTAGE

V0 - vic 0 2 VDDNo toad

TA 2 -PC

0 2 4 6 11 10 12 14 16 18 20

VDD-Supply Voltage -V

Parameter Bias Low Medium High

Offset voltage drift tTypl 0.1pVimonth 0.1pVimonth 0.1pV/month

Offset temp coef (Typ) 0.7pWC 211110T WPC

890039 - 13

Fig. 2. The voltage at the bias -select pin of a LinCMOS operational amplifier influences the characteristics of the device.

Operational amplifiers

The operational amplifier is the mostpopular of all Lincmos circuits. In fact, thefirst devices available in the new technolo-gy were the now well-known opampsType TLC251/271 (single), TLC252/272(dual), and TLC254/274 (quad). These areintended as replacements for the standardTypes 741/3140, MC1458/CA3240, andLM324.

A close examination of the TLC271reveals that the opamp, apart from theusual inputs, output and supply connec-

tions, has a so-called bias -select pin. Thevoltage at this pin determines the currentdrawn by the device-see Fig. 2. In thelow -bias mode (bias -select pin connectedto the +ve supply voltage), the current isonly (typically) 10 µA. The price to bepaid for this low current is a poor slew rateof only 0.04 V/µs and a unity -gain band-width of a mere 100 kHz.

The speed is determined largely by thedevice's internal capacitances. When thesupply current is small, the charge and dis-charge currents through these capacitanceswill assume a larger importance, whence

110

100

so

80

15 70>

a 60

50

2 40C?.zcr

20

Equivalent input noise Vs. frequency for High (H).Medium (M) & Low (L) bias modes.

10

010

L

M

H

100 1kFrequency Hz

10k

Fig. 3. Equivalent input noise voltage vs frequency for high (H), medium (M)and low (L) bias modes.

the lack of speed. However, there are anumber of applications in which the lowslew rate is of no importance

In the medium -bias mode, the currentis about 15 times higher, but the slew rateand unity -gain bandwidth are correspond-ingly better: 0.6 V/µs and 0.7 MHz res-pectively). These values are comparable tothose of, for instance, a standard 741. Notehowever that the latter draws a current of1.7 mA.

In the high -bias mode, the current risesto 1 mA, but for that you get a very fastopamp with a slew rate of 4.5 Vita and a

lb

10

5

Maximum output voltage Vogt Vs. output current lowith V Dp as parameter

miliiIIIIIII1111111111111111111111E-iiiiiimE111111111111111

v 1111 MIIIMICINE111I.11111

thr

11111111M1NIIIIIIE11111111111111111101111111111111111111S1111111nommitiimmill1111111111111111111111

MIIIIIIIIMII11111111111.111111v- III1111111111111111111111111111111M11111M111111111111111111111M111111MIN111111111111111111111O11111111111111simemousinI1111111111111111111MIIIIIIIIMII111111111:111111=1111

M11111111111111111MINIIEMIIIIIII1011 00u lm

Output Currant to - A10m

890039-14

100m

Fig. 4. Maximum output voltage Vom vs output current 10 at various supplyvoltages.

ELF KTOR ELECTRONICS JULY/AUGUST 1969

COMPONENTS

unity -gain bandwidth of 2.3 MHz.The dual versions TLC252/272 and the

quad Type TLC254/274 are not providedwith bias -select pins (for which they haveno space in any case). In these versions,the bias mode is permanently set internal-ly. The type number indicates which biasmode the device provides. For instance, aTLC27L2 is a low -bias type; a TLC272 isa high -bias version; and the TLC272M2 isa medium -bias type.

Power supply and loadAs mentioned briefly already, to obtain

maximum dynamic range, Lincmos op -amps are optimized for single -rail opera-tion from supplies not exceeding 16 V.

The output voltage vs output currentcharacteristic for loads connected to earthis given in Fig. 4. An open -circuit output,or one with the load connected to earth,can be pulled to within a few millivolts of0 V. The output can only be pulled to the+ve supply level if the load is connected tothe +ve rail or an external pull-up resistoris added. Such a resistor has, however, thedisadvantage of resulting in a relativelylarge power consumption at low outputvoltages. Also, the open -loop amplifica-tion drops sharply when the output voltagegets close to the +ve supply voltage. Thisis caused by N5-see Fig. 1-switchingoff.

When relatively heavy loads are used,it should be noted that the sinking ratemay exceed the sourcing rate; in otherwords, that the output current is greaterthan can be provided. If, therefore, largeoutput currents are required without addi-tional components, it is recommended thatthe load is connected to the +ve supply railas shown in Fig. 5b.

Frequency compensationIn low -power applications, the current

will be determined largely by the resis-tances in the feedback loop and by theload. The value of these resistance will.therefore, be normally quite high. As faras DC signals are concerned, that presentsno problems. When AC signals areinvolved, however, more account must betaken of input and other stray capacitances(CstTay in Fig. 6) than in conventionalopamp circuits. To obtain a sufficientlywide bandwidth, it may in some cases benecessary to use a compensating capacitoras shown in Fig. 6 to reduce the feedbackat high frequencies.

ComparatorsA number of comparators available in

Lincmos technology are shown in Table 2.The TLC372 and TLC393 are pin -compat-ible replacement of, for instance, doublecomparator Type LM393. Quad compara-tor Type LM339 may be replaced by theTLC339 or TLC374.

As with opamps, the current consump-tion of Lincstos comparators is substan-tially lower than that of bipolar equiva-lents, while the input current is very low(typically 5 pA). There is not much differ-ence in the input offsett voltages.

The outputs of most comparators are ofthe open -drain type, enabling logic func-tions to be produced by interlinking them.Normally. a pull-up resistor will also berequired. but not with the TLC3702 andTLC3704, since these have totem poleoutputs.

Unlike some opamps, comparators donot offer a choice of three bias modes. Thebias mode is inherent in the type. Forinstance, the TLC393 draws 22 I.LA (typi-cal) compared with the 0.8 mA drawn byan LM393, but it is slightly slower (2.5 Lisagains 1.3 tts). A TLC372 has a higherpower consumption. but is much faster(650 Rs)

COMPARATORS Table 2

INPUT

OFFSET

VOLTAGE

IatV)

INPUT

OFFSET

CURRENT

(MA)

INPUT 81AS

CURRENT AT

25°C(pA)

RESPONSE

TIME

luS)

SUPPLY

CURRENT

(MI

SUPPLY VOLTAGE

RANGE

IN9

OUTPUT

TYPE

Min MuDualTLC372 12.0 1 5 0.65 750 3 16 Open DrainTLC393 10 1 5 2.10 50 3 16 Open DrainTLC3702 10 1 5 2.30 50 3 16 Totem PoIe

QuadTLC374 12.0 1 5 0.65 1000 3 16 Open DrainTLC339 10 1 5 2.10 100 3 16 Open DrainTLC3704 10 1 5 2.30 100 3 16 Totem Pole'

Totem Pole Outputs are HCMOS and TTL compatible 890039-21

Table 2. Some LinCMCS comparators and their main parameters.

D1, D2 = 1N4148 89,7.039 17

Fig. 5. Circuit adaptations for obtaining a largeroutput current in a load connected (a) to earth.(b) to the +ve supply rail, and (c) symmetrically.

R2mommmm

Cst:ai

890039.18

Fig. 6. Input and other stray capacitances maybe countered by a compensating capacitor.

KTOR ELECTRONICS JULY/AUGUST 1989

TIMERS

LINCMOS CIRCUITS

Table 3

single

dual

quad

OPA bl PS

ov-rserin [er-et. [GTO

.CUT1 el -I OS 0/10

1 OJT

I PI.VDD

2 24 .2 2.2 OUT

7073 we seemvco

) cur0.73FT

21102 CUT

2at -21)2.

.OUT

.21-IM.G1.0

34.1 -SCUT

TLC251TLC271

TLC252TLC272

TLC254TLC274

COMPARATORS

dual tcow

dual 2 3 our

01511. 22 od-}c°"P

COVP 1 OUTCOUP 12OUT

V00

quad c°"1.,-. 2

CO.1,12

C.0412 13 OUTCOMP II OUT4113

CO2.

II. COUP.

TLC393TLC372TLC3702

TLC339TLC374TLC3704

TIMERS

cuDLTICour C

essarC

Ll2 71 a

DSC-.attazsCD11

singleTLC551TLC555

21/12121

dual t

DSO.11.1215

COUPRESET

OUTTRIG

41.13

T.0 TLC5522 TLC556

840039 - 19

Fig. 7. Pinouts of the various LinCMOS circuitsdiscussed in this article.

Examiner for hard -diskcomputer memories

Dissatisfaction with the availableequipment led Servo Computer Servicesto develop its own system for examiningthe disks and disk -packs in computers.

The 'Disk Pack and Cartridge Inspec-tor' can use either an existing disk driveor its own disk -drive spindle to test awayfrom the drive. Highly accurate spindlesare needed for this as the flatness of thedisk surface needs to be within ±0.5x10`6metre (2x10-' inch) accuracy. In addition.such measurement is made on most diskwithout physical contact, so an opticalmethod is used.

Hard disks often contain very valuablecompany information and the surfacequality is very important. The Servo In-spector uses a variety of light sources as

SUPPLY

CURRENT

IHA)

POWER

DISSIPATION

WW1

SUPPLY

RANGE

09

MAX

FREQUENCY

(MHZ)

MAX

TIMINGPERIOD

MAX

TIMING

ERROR

OUTPUT

CURRENT

(mA)

Min MuSingleTLC551 350 1 1 18 2_1 Hours 3% +10/-100TLC555 350 1 2(31* 18 2.1 Hours 3% +10/-100

DualTLC552 1000 2 1 18 2.1 Hours 3% + 10/-100TLC556 1000 2 Mr 18 2 1 Hours 3% - 10'-100

'Indicates for industrial Temp Range 890039-22

Table 3. A variety of LinCMOS timers and their main parameters.

It should be noted that Texas Instru-ments is not consistent in their recommen-dations on maximum supply voltage volt-age. In some data sheets they mention16 V and in others, 18 V. It is. perhaps,wise to be on the safe side and stick to16 V.

TimersAs might be expected, there are equiv-

alent Lincmos ics for the renowned 555series of timers. In fact. there are four: theTLC555 (single) and TLC556 (dual) toreplace the standard (LM/NE)555 and 556for supply voltages from 2 V to 18 V andthe TLC551 and TLC552 for operationfrom low voltages (down to I V).

Apart from the much reduced powerconsumption, the great benefit Lincmostimers offer is the greatly extended fre-quency range. The maximum frequency isabout ten times higher than that of a stan-dard 555 (2.1 MHz against 200 kHz),because the saturation normal transistorshave to cope with has no or negligible

well as mirrors and lenses to carry thisout.

The equipment has been designed to beused quickly and easily, to be reliable andrugged enough to be carried around by aservice engineer. It fits easily into a com-pact case, suitable for air transport.

Servo Computer Services 2-10 SheffieldRoad Dronfield SHEl-HELD S18 6GG Telephone (0246) 410375.

Versatile computer keyboardA robust, easy -to -use keyboard,

designed as a teaching aid for pupils andteachers with no technical computerknowledge, is available from Star Micro -terminals.

The 'Concept Keyboard' will interface

effect in the new technology. Even at rela-tively low frequencies (from 20 kHz tosome hundreds of kHz), the TLC555 has amajor advantage in that the frequency canbe defined much more precisely by exter-nal components. Note that the frequencyrange is extended also at its lower end.

Since the input impedance and inputleakage current are much smaller than in abipolar 555, the Itc networks that are con-nected to these timers can have a muchhigher value. This makes realization ofvery long time delays (up to hours)possi-ble.

with most computers in common use andhas already been used extensively inschools for work on a wide range of sub-jects.

It uses a touch -sensitive membrane thatis sensitive over the entire matrix area.Each touch cell produces an 8 -bit outputcode and individual cells can be groupedto form large response areas. An EPROMoption allows selective non -responseareas.

Outside the educational field, theConcept keyboard has applications inword processing, banking, informationmanagement. robotics, stock control, etc.

Star Microterminals Ltd Moorside Road Winnal Industrial Estate WINCHESTER S023 7RX Telephone (0962) 843332.


24

FLOPPY DISK MONITORM. Noteris

It often happens that PC users are left completely unaware of what isactually happening to the floppy disk inserted in the machine. Is themachine reading, attempting to read, or writing, and if so, to which

track? This simple monitor circuit for IBM PCs provides the answersby making the control signals of the disk drives visible.

The drive select LED on a floppy diskdrive does just what it is supposed to do:indicate drive activity. Many PC usershave, therefore, no idea whether thefloppy disk they have just inserted is readfrom or written to. Clearly, this is an un-acceptable situation in this day and age ofdata security and a few bits on a diskdetermining access to files that representmany hours of work. While the present

circuit can not restore data on a corruptedfloppy disk, it helps to prevent the mostserious of mishaps because you witnesshow they come about!

The principleThe floppy disk monitor works on thesimple principle of visually indicating thestatus of the various control signals used

for the floppy disk drives in a PC. Practi-cally all user manuals supplied with PCsgive a disk -drive wiring diagram that in-dicates the signals Drive Select (DSO toDS2, and, in some cases, DS3), Read Data,Write Enable, Step, Direction andTrack 0.

The movement of the head in the diskdrive is fairly simple to monitor by clock-ing a counter with the Step pulses, drivingthe up/down input of the same counterwith the Direction signal, and driving itsreset input with the Track 0 signal. Thevisual indication function is assumed by aType 4543 IC that decodes BCD data sup-plied by a counter Type 4510. The 4543 iscapable of supplying the required 20 mAsegment current for a Type 7760 LED dis-play, of which two show the current tracknumber.

Since the maximum number of trackssupported by the floppy disk monitor is80 (0-79), two counter/display circuitsare cascaded by driving the CARRY INinput of the decade driver with the CARRYOUT signal of the unit driver.

Signals Read Data and Write Enableare visualized with the aid of the decimalpoints on the LED displays. These indica-tions are referred to as DPR (decimal pointread), and DPW (decimal point write) in thisarticle.

The circuitThe circuit diagram shown in Fig. 1 maycause some readers to wonder why two

monitors all floppy disk drives availablefor PC/XT. PC/AT and compatible PCs:51/4 -inch, 31/2 -inch, single/double sided,double or quadruple density

static display of head position (currenttrack number)

read and/or write indication for selecteddrive

read indicator shows data flow resultingfrom pulses induced in the head by themagnetic carrier

monitors two floppy disk drives simulta-neously


FLOPPY DISK MONITOR

track 0

drive select 0drive select 1drive select 2

read datadirection

step ;pilewrite enable

5V

KI

200--0 10OO

12

5V

7

Cl

100n

RCe.s CentA

10 aMMV1

CLR11

a

2

11

17

2

0 $13

2Y12A1

2A2 2Y2

2A4 102 2Y4

1A1 IY16 taa 74 1Y4e bk3HCT iya

,A2 240 ty2

2A3 2Y3

to 2G

93

18

5V

OAS

12

14

18

5

J3R

0 OPR0/13

0 DPW

5"

R2[1O

14

O

O

OO

3018

2024

01

02

03

ii

if

if

515

Rs

13

5

2

0

0 52a

MMVI = 1/21C1= 74HCT123

2_44 2Y'2n1 2Y1" 1C3 3Y21.53 1Y.

1A 1 74 IY,A2HCT iy21A3 240 iy 3

2A3

a

=1E1

I RIO

912

5V

16V

MUM

3 I .

ii

IS

lola

2am, 5V

5V

5V

C4

100Play

RS All

102 103100n

10

R

0 CARLl."21

0 0?;-?0 CLY.

Fig. 1. Circuit diagram of the driver section of the floppy disk monitor. Shown inset is the pinning of the cable socket for powering disk drives.

Type 74HCT240 bus buffers are used. Thesix signals used for controlling all diskdrives in a PC are carried in parallel be-tween the disk controller board and thedisk drives, so that the signals for the ac-tuated drive must be selected before theycan be directed to the associated indicatorcircuit. This directing of control signals isaccomplished with the aid of the driveselect lines, DSO, DS1 and DS2, which en-able the bus buffers depending on the po-sition of switches Si and Sz.

Since all control signals involved areactive low, they are inverted by the74HCT240s to enable driving the displayunits. A number of bus buffer inputs areconnected to outputs to make sure theyare properly terminated.

With Si in the position indicated in the

circuit diagram, signal Drive Select 2 en-ables bus buffer 1C2 with a low level atinputs TG and 2G. Pull-up and pull -downresistors are fitted on the output lines ofthe bus buffers since these are switched tohigh -impedance when the device is dis-abled via the TG and 2G inputs. Outputlines R (reset) and U/D (up/down) arepulled low, and CLK (clock) is pulled high.

The Track 0 signal guarantees that thedisplays are always correctly reset to zero,which is useful when, for one reason oranother, the counter loses track of the steppulses. Monostable multivibrator MMVIshapes the Track 0 signal supplied by aslotted optocoupler in the disk drive. Thearm on which the head is mounted inter-rupts a light beam when it is in the ex-treme outer position with the head(s) over

track 0 of the disk. The monostable leng-thens the track 0 signal to about 1.5 ms tomake sure that the display counter isproperly reset even with drives that usethe fastest step rate, 3 ms. Edge -triggeringis used to cope with tolerance on thetrack 0 detection circuit and associatedmechanical parts. In certain disk drives,the signal is still active even when thehead is half way between tracks 0 and 1.

R -C network R12. -C2 resets the countercircuits to zero at power -on by supplyinga brief 'high' pulse via line x.

More about drive selectionAlthough the cable from the disk control-ler board has four drive select wires, DSO-DS3, the practical number of floppy disk


DI

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11

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FLOPPY DISK MONITOR

drives supported in IBM PCs and com-patible machines is usually limited to two.This is because each floppy disk drive re-quires two signals, one to control themotor, and one to control the actual selec-tion of the drive. Thus, the motor indrive A is energized under the control ofa low level on line DSO, while the driveproper is enabled under the control of alow level on line DS2.

It should be noted that the above func-tions of DSO and DS2 are the other wayaround on some PC compatibles of FarEastern make. The floppy disk monitorsolves a potential problem arising fromthis oddity by virtue of rotary switches Stand S2.

Another noteworthy point is that sig-nal Write Enable is fed to the display unit.The use of Write Data would appear morelogical at first. The background to the useof Write Enable is that some disk control-ler boards, for instance, those of WesternDigital, generate clock pulses on the WriteData line except when actually writing tothe disk drive. This clock pulse stream cannot be used by the display circuits, andwould cause these to light the wRrrE indi-cation (DRW) continuously.

Counter and display moduleThe counter/display circuit is based on anearlier design published in Ref. 1. Fig-ure 2 gives the circuit diagram. The mo-dule is composed of four identicalcombinations of a synchronous BCDcounter Type CD4510, a latching BCD -to -7 segment display driver Type CD4543,and a common -cathode LED display Type7760. Cascading is achieved by connecting

Parts list

DRIVER BOARD

Resistors (%):R1;R2= 33012R3-R11 = 15kR12= 10k

Capacitors:C1;C3 = 100nC2= 1110: 16 V; radialCe = 100p: 16 V

Semiconductors:Di-Ds = LED; red; 3 mmlei = 74HCT123IC2;1C3 = 74HCT240

Miscellaneous:Si ;S2 = two -pole, three-way rotary switch.Kt = 34 -way pin header.PCB Type 890078 (see Readers Servicespage).


Fig. 3. Track layout and component mounting plan of the driver board.

28 COMPUTFRS

Parts list

COUNTER'DISPLAY BOARD

Resistors (7_5%/:R. --R5= 2200

Semiconductors:ICI = 4543IC_ = 4510LD1 = 7760

Miscellaneous:PCB Type 85019 (see Readers Servicespage; 4 off required for two display units).

the CARRY OUT (CO) output of each of thetwo units counters to the CARRY IN (CI)input of the associated decade counter.The functions of the U/D (up/down), andR (reset), Ph, BI, PE and to are covered inRef. 1.

ConstructionThe driver circuit of the floppy disk moni-tor is built on the printed -circuit boardshown in Fig. 3, and the counter/displaymodule on that shown in Fig. 4. Neitherboard should present any difficulty inpopulating.

Start the construction of the driverboard by fitting the 12 insulated wirelinks. Continue with the resistors, ofwhich most are fitted upright, the capaci-tors, the soldering terminals, IC sockets,and, finally, the 34 -way pin header, in thatorder.

nnNO OMB S111111.11111 OMB MP OMB

IMO MilL_

Fig. 4. Track layout and component mounting plan of the counter display board.

Each display board accommodates twodisplays and two driver circuits. Theready-made printed -circuit board must,therefore, be cut into three along the twodotted lines printed at the componentside.

The fitting of the parts is carried out asusual. The interconnection between thetwo control boards to the display circuitrequires further detailing, however. Tak-ing one pair of displays as an example, theconstruction is started by populating thedisplay board, and then the associatedcontrol circuit. Resistors Ri through Rs aremounted between the control board andthe display board, and give the completeassembly the required rigidity.

Proceed with connecting paired pointsPh/COM, R, 0, U/D, PE, Clk, + and LD. The cooutput of the units display driver is con-nected to the cr input of the decade dis-play driver, as shown in the circuit

diagram of Fig. 2 (note the mirrored posi-tion of the displays in this drawing).

The completed counter/display unitsare connected to the driver circuit via the6 signal lines and the 2 supply lines. In thestandard version of the floppy disk moni-tor, there are two counter/display unitsand one driver unit.

The remaining connections are thosefor the LEDs and the rotary switches. In-stall the wiring as shown in the circuitdiagram.

Power supplyThe circuit is conveniently powered fromthe 5 V rail provided by the computer'spower supply. Tire prototype of thefloppy disk monitor is a stand-alone unitthat is powered via a small socket as usedon portable cassette recorders. The PC isfitted with a similar socket, and the twounits are interconnected by a 30 cm long2 -wire supply cable.

If the circuit is installed permanently inthe PC, the ground and +5 V connectionsmay be made at appropriate points on themotherboard. Another, more practical,solution is shown in Fig. 7. A cable shouldbe made to enable the supply voltage to betaken from one of the disk drives.

CablesThe floppy disk monitor is connected tothe disk controller board via a home-madeflat ribbon cable. This cable is crucial tothe operation of the circuit and is, there-fore, drawn in Fig. 5.

The job is almost done if the right partsare to hand: 50 cm or so of flat -ribboncable, two 34 -way IDC (insulation displace-ment) sockets, and one 34 -way IDCheader. The sockets and the header maybe types with or without a strain reliefclip. The two sockets are mounted at thecable ends, and the IDC header at about15 cm from one of the sockets. Do nottwist the cable in between the header andFig. 5. The home-made 34 -way flat -ribbon cable.


FLOPPY DISK MONITOR 29

tzt-Jio-14

Fig. 6. Interconnection between the floppy disk drive, the monitor and the disk controller card in the PC.

the sockets: use the coloured wire in thecable to mark pin 1 of the connectors.

The existing cable between the floppydisk drives and the controller board mustbe disconnected at the side of the control-ler board. Figure 6 illustrates how the soc-kets at the ends of the previouslydescribed cable are connected to the diskcontroller board and the floppy diskmonitor. The free end of t

the electronics magazine with the practical approach · 1989. 7. 8. · the electronics magazine...

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