UK £ 1.20USA $ 3.60

IR £1.92(incl. VAT)

EEApril 1986

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*ATTENTION*ALL PRICES ARE

SUBJECT TO CHANGEWITHOUT NOTICE

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MAIL ORDERS TO: 17 BURNLEY ROAD, LONDON NW10 lEDSHOPS AT: 17 BURNLEY ROAD, LONDON NW10

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Orders from Government Depts. & Colleges etc. vselcome

Detailed Price List on requestStock items arc normally by return of pose

important - please mention ELEKTOR ELECTRONICS when contacting advertisers

Printer bufferp. 27

15 Editorial16 News and views47 Letters

ELECTRONICSTECHNOLOGY

64 Computerization boost efficiency in health care66 Sophisticated instruments that regulate

temperature68 Digital colour palette

PROJECTS22 Satellite loudspeakers27 Printer buffer32 Variable dual power supply40 VHF amplifier48 Portable mixer58 Real-time clock

Variable dual PSUp. 32

INFORMATION43 Corrections; 44 Make your own PCBs; 56 Newliterature 73 New Products; 81 Infocard; 82 ReadersServices

GUI E LINES10 Buyers guide; 75 Switchboard; 78 Et 79 Appoint-ments; 84 Classified ads; 84 Index of advertisers

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April 1986VolumeNumber 132ISSN 0268/4519

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April 19864

MI0 TRANSFORMERSFROM illaaWFR

Mit DeDel -

:

MAKER ---_-

WWI:"..0006011.016000 .a., - 77..

4---...,,,,, '

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ft...ASILP Toroidal Transformers are now available through Jaytee Electronic ServicesJaytee. The UK Distributor with the availability andservice to match the quality of the toroidals. 143, Reculver Road, Beltinge,

SWANS iiii II

es104/0.0a1001

AW"0.0M 0_,CL-W , CAE

FOR FREE DATA PACK PLEASE MA Herne Bay, Kent CT6 6PLt"""1WRITE TO OUR SALES DEPT. Telephone: (0227) 375254

TYPE SERIESNO.

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SUPPLIED WITHDUAL PRIMARIESPERMITTING 110V

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important - please mention ELEKTOR ELECTRONICS when contacting advertisers

EE

April 1986

Editor: Len SeymourAdvertisement manager: S BrooksPublished by:Glentop Publishers LimitedStandfast HouseBath PlaceHigh Street, BarnetLondon EN5 lEDTelephone:

Editorial:(01) 441 4139Advertising: 10227) 66106

Telex: 22828A Khmer Group Company

Overseas editions:ElektuurPeter Treckpoelstraat 2-46191 VK Beek - the NetherlandsEditor: P E L KersemakersElektor sariRoute Nationale; Le Seau; B.P. 5359270 Bailieu! -- FranceEditors: D R S Meyer;

C P Raedersdorf

Elektor Verlag GmbHSisterfeld-Straae 25100 Aachen - West GermanyEditor: E J A KrempelsauerElektor EPEKeraiskaki 1416673 Voula - Athens - GreeceEditor: E XanthoulisElektor Electronics PVT Ltd.Chotani Building52 C. Proctor Road. Grant Road (ElBombay 400 007 - IndiaEditor: Surendra lyerElektor JCEVia Rosellini 1220124 Milano - ItalyEditor: D FumagalliFerreira Er Bento Lda.R.D. Estefania, 32-1°1000 Lisboa - PortugalEditor: Jorge GoncalvesIngelek S.A.Av. Alfonso XIII, 141Madrid 16 - SpainEditor: A M FerrerInternational co-ordinatingEt technical manager:K S M WalravenInternational editorial secretariat:M J M Lacroix; G W P WijnenThe circuits are for domestic useonly. The submission of designs orarticles to Elektor Electronics impliespermission to the publishers to alterand translate the text and design,and to use the contents in otherpublications and activities. Thepublishers cannot guarantee toreturn any material submitted tothem. All drawings, photographs,printed circuit boards and articlespublished in Elektor Electronics arecopyright and may not be repro-duced or transmitted in any form orby any means, including photo-copying and recording, in whole orin part without prior written permis-sion of the publishers. Such writtenpermission must also be obtainedbefore any part of these publicationsis stored in a retrieval system of anynature.

Patent protection may exist inrespect of circuits, devices, com-ponents etc. described in thismagazine. The publishers do notaccept responsibility for failing toidentify such patent or other pro-tection.

Distribution:Seymour Press Ltd.. 334 BrixtonRoad, London SW9 7AG.Copyright 1986 Elektuur B.V.

Printed in the Netherlands by NDBZoeterwoude.

IABC

Video in decline?Now the semiconductor markets are beginning to showsigns of a slow revival, it seems to be the turn of videorevenues (and therefore profits) to start declining. Thereason for this is that some forty per cent of householdsin the industrialized world already have a VCR (videocassette recorder).

To retain their share of the consequently decliningmarket, the 20 -odd Japanese (and some other Asian)manufacturers have become engaged in a price warthat is hotting up.

What they are all hoping for is a miraculous expansionof the market, or a new market. But that is pie in the sky,because market observers believe that such an expan-sion or new market will only occur if a technically new,yet lasting and exciting, equipment is introduced.Moreover, such equipment must be relatively inexpensive,easy to operate, and offer a high degree of standard-ization.

The only equipment that seems to meet most of theserequirements is Sony's new 8 mm video system. But sincethis is not compatible with the 100 -odd million half -inchVCRs already in use, it has a long, hard slog ahead of it.

In the mean time, the video market is likely to go ondeclining at an increasing rate. As guarded estimatessuggest that nearly a fifth of Japanese electronics salesconsists of VCRs and their components, some sectors ofthe Japanese industry are in for a leaner time than theyhave experienced for years. The question is: what arethey going to do about it?

EE

April 198616

ItvgS VIEWS NEWS VIEWS NEWS

New marketingmanager forX-TEC

Mark Robson has beenappointed UK MarketingManager of X-Tec Limited',the networking communi-cations company basedin Reading, Berks. Hebrings 13 years' ex-perience in the computerindustry to this newly -created position.

X-Tec Limited, founded in1982. is an all -Britishcompany which manufac-tures and suppliesspecialized communi-cations products for awide variety of networkingrequirements. Principalcustomers include BritishTelecom, the AtomicEnergy Authority, and Im-perial College, London.' 96 Suttons Industrial Park,London Road, EarleyReading, Berk RG6 1AZtelephone (0734) 668161;telex 846727

PCB upswing inwestern EuropeAccording to a recentreport from Frost &Sullivan,' The Printed Cir-cuit Board Market inWestern Europe (,-,--E791), acombination of significantdevelopments and vastly

widening sales within thetelecommunications in-dustry are sending westernEurope's printed -circuitboard's market into a for-midable upswing. Thereport expects total salesin 1990 to reach close to£1800 million, a substantialrise from 1984's total

.market value of just under£1000 million.The report finds the currentlargest areas for use to becomputers andperipherals and telecom-munications, with bothsectors given equalmarket shares of 28 percent. However, the studypredicts that by 1990telecommunications willbe the top end user with amarket share of around 40per cent, almost doublethat of computers andperipherals.As for the product itself,the most striking develop-ment is the rapid growthin the value of the multi -layer market, which is ex-pected to take 50 per centof the market in 1990, ris-ing from 33 per cent in1984. This will be at the ex-pense of double -sidedboards, whose share ispredicted to fall from 49per cent in 1984 to 37 percent in 1990. The most strik-ing fall, however, is that ex-pected of single -sidedboards, which will plum-met from 12 per cent to 8per cent.' 106 Fulton Street,New York, NY 10038; tele-phone 212-233-1080; or104-112 Marylebone Lane,London WIM 5FU, tele-phone 01-935-4433

New vicepresidents forSERT

The Society of Electronicand Radio Technicians(SERT)' announces the ap-pointment of three newVice Presidents of the

society. They are: S L HClarke, B.Sc. (Confab),C.Eng., FIEE, FBCS - Depu-ty Director of the Alvey Pro-gramme; Professor WilliamGosling. B.Sc. (Special),D.Sc., ARCS, C.Eng., FIEE,FIERE - Technical Directorof the Plessey CompanyPLC; and Brigadier G MHutchinson, MA (Confab),RA - Deputy to the Direc-tor General Electrical andMechanical Engineering(Army).

Laurence Clarke held thepost of Assistant TechnicalDirector (Computing andAutomation) at GEC PLCprior to joining the AlveyDirectorate. He is vicechairman of the Controland Computer Board ofthe IEE, and is a visitingprofessor in the ComputerScience Department ofUniversity College London.

William Gosling is a pastPresident and Fellow ofthe Institution of Electronic

and Radio Engineers;Fellow of the Institution ofElectrical Engineers; Fellowof the Institute of Directors;and a Chartered Engineer.An Honorary Fellow ofPlymouth Polytechnic and,currently. visiting professorof CommunicationsEngineering at Southamp-ton University, he is theauthor of seven books onengineering topics andabout fifty papers in scien-tific journals, for one ofwhich he received theClark Maxwell Prize (IERE).

Brigadier Malcolm Hut-chinson joined the Armyin 1958 on a graduatedirect entry commission inthe Royal Electrical andMechanical Engineers. Heattended the Army StaffCourse at Shrivenham andCamberley in 1967 and1968 respectively. He hascommanded a number ofREME units in FederalGermany and the Far East,and has held a number ofWeapons Staff appoint-ments at the Ministry- ofDefence and in the USA,the last of these beingProject Manager in theGuided Weapons andElectronics Directorate ofMoD(PE).

' 5761 Causeway,London SE1 6BL; telephone01-403 2351

EEApril 1986

VIEWS NEWS VIEWS NEWS V:

Korea vs Japanfor share of USmemory marketAccording to The KoreanSemiconductor Industry, anew multi -client study fromProduct Assessment* andBenn ElectronicsPublications**, the muchheralded Korean foray intoworld semiconductormarkets will result in afour -fold increase inKorean overseas sales,from $47 million in 1985 to$203 million in 1986. Thecampaign is aimed pri-marily at the worldmemory market.It is estimated that Koreawill capture up to 7 percent of the US MOSmemory business by theend of the year, largely atthe expense of Japanesevendors, with highly com-petitive pricing tacticsused by both sides: anunwelcome development

for hard pressed US andEuropean producers.Korea currently has twelveindigenous semiconductorproducers, plus the world'slargest sub -contract as-sembly facility, Anam, aswell as seven multi-national assembly fac-tories. This impressiveline-up has taken Korea tothe number three positionin terms of value addedby country, overtakingFederal Germany at theend of 1985 (see Table 1).Whilst the Koreans are in-itially aiming their exportdrive at the memorymarkets, the majorcompanies have a rapidlyexpanding range of prod-ucts and technologiesavailable (see Table 2).* 600 Kingston Road,Raynes Park, London SW2080N; telephone (Of) 5438555; telex 8954575" Chiltern House,146 Midland Road, Luton,Beds LU2 08L; telephone(0582) 417438; telex 827648

Table 1

World Semiconductor ProductionValue Added By Country

US $ Million

Country 1983 1984 1985USA 9,000 11,850 9,010Japan 6,000 8,900 7,600S Korea 510 680 740W Germany 620 720 720UK 420 600 580

Source: The Korean Semiconductor Industry (C) BEP Luton, UK.PRODUCT ASSESSMENT London, UK.

Table 2

Summary of Product Capabilities

Device TypesMOS MemoryMicroprocessorCMOS LogicBipolarCustom MOSCustom BipolarDiscrete Devices

DaewooP

P

P

* Current CapabilityP Planned

Goldstar

P

Hyundai

P

P

P

KEC Samsung

P

Source: The Korean Semiconductor Industry (C) BEP Luton, UK.PRODUCT ASSESSMENT London UK.

$40 millioninvestment inEurope byFactronFactron' has announcedplans to invest over $40million in capital equip-ment for its European op-erations over the nextthree years.Factron is already Europe'spremier supplier of ATEand test automation prod-ucts for the electronicssystems market place, andthe only one of the world'smajor ATE companies withEuropean design andmanufacture. This massiveinvestment will extend Fac-tron's technological leadand further its penetrationin the key market sectorsof telecommunications,computer, office auto-mation, and defence.These investments will bein equipment alone andwill be matched by furthersignificant investments inengineering staff.The largest slice of theinvestment -45 per cent-will fund Computer Inte-grated Manufactur-ing-CIM-engineeringtools.Operations will accountfor 35 per cent of the in-vestment. Extra space willaccommodate state-of-the-art PCB assembly systems,and Factron will par-ticipate in a joint -venture

development of a robot fa-cility for inserting relaysinto PCBs.The existing managementinformation system will beupgraded and com-plemented with acompany -wide networkeddata base which will linkinto the current satellite -based intra-Schlumbergerpacket -switching com-munications system.Applications and salesare seen as providing thevital link with the customer.Factron wil direct 20 percent of its investment intothese areas, with an ag-gressive expansion pro-gramme to increase itsshare, and eventualdomination, of the market.In marketing, the em-phasis will be on joint ven-tures to developcomputerized manage-ment of test and faultdata, automatic PCBhandling, advanced testprogramme generationfacilities, and the develop-ment and evaluation of anew generation of ad-vanced solutions for theelectronics manufacturersof tomorrow.In short, Factron intends tobecome the world leaderin computer -aidedsystems.

F-erndown IndustrialEstate, Wimborne, DorsetBH21 7P/ telephone (0202)893535; telex 41436

EE

April 198618

WS VIEWS NEWS VIEWS NEWS V:

QUAD 306power amplifierQuad ElectroacousticsLimited' was founded in1936 as the AcousticalManufacturing Company.First news in its 50th an-niversary year is the an-nouncement of a newpower amplifier.The QUAD 306 is designedto provide the most ac-curate and realistic musicreproduction in high -quality domestic systems.Power output is more thanadequate for the vast ma-jority of systems (70 wattsinto 8 ohms on music pro-grammes).The QUAD 306 uses ahighly refined anddeveloped version of thefeed forward error correc-tion circuit, which Quadpatented in 1975 andnicknamed current dump-ing. Some of the more ob-vious features of the QUAD306 are separate powersupplies for each channel,derived from separate sec-ondary windings on acommon toroidal trans-former, an absence offuses or relays in thesignal paths, and a signal -plus -noise to noise ratio of110 dR It is fully protectedagainst damage, ac-cidental or otherwise.The QUAD 306, which isnow being delivered toQuad dealers at £229.00incl. VAT, incorporates theexperience gained fromhalf a century of design,development, andmanufacture of poweramplifiers, and the per-formance, design, con-

struction, and reliabilityare the hall marks whichQUAD owners worldwidehave come to recognize.

Huntingdon, Combs PE18708; telephone (0480)

52561; telex 32348

British Telecomseeks todevelopopportunities inIndiaBritish Telecom andMahindra & Mahindra Ltdof Bombay recently signeda memorandum ofunderstanding, wherebythe two companies agreejointly to explore andpossibly develop oppor-tunities in the telecom-munications andinformation technologyfields.British Telecom, one of the.vorld's largest telecom-munications companies,had a turnover last year of£7653 million (Rs 13 423crores), pre-tax profits of£1480 million (Rs 2596crores). and employs astaff of 235 000. It is aworld leader in the appli-cation of latest technologyto provide effective andeconomic telecom-munications.Recent modernization ofnetworks and services inthe UK has involved the in-stallation of major digitalexchanges. the continued

use of satellites, opticalfibres, microwave links,and undersea cables. Itsservices cover the com-plete range of public andprivate telecommuni-cations networks, includ-ing such facilities ashigh-speed text and datatransmission; computer -controlled internationaltelex; car and hand-heldmobile radio telephones:specially designed smallrural exchanges; andmodern cash and creditcard public payphones.Mahindra & Mahindra, es-tablished in 1945, is India'sninth largest companywith a work -force of 14 000.Its activities range frommanufacture of jeeps, lightcommercial vehicles andtractors, to process -controlinstruments. It has twelvesubsidiary and associatecompanies whose manu-facture includes alloysteel, textile machinery,synthetic resins, elevators,and reinforced plastics.The company is movinginto new high-technologyactivities, and will shortlybegin production of elec-tronic private automaticbranch exchanges (PABXs)in collaboration with OKIof Japan for the Indianmarket.The chairman of thecompany, Mr KeshubMahindra, is one of India'sleading industrialists. He ischairman of seven majorcompanies, and a director

on the board of sixteenothers -President of theEmployers' Federation ofIndia, he has served on anumber of governmentcommissions and advisorycommittees.

Scottish dealerwins first StarPorscheMr Michael Fowle of PulseBusiness Systems, Edin-burgh, was recentlypresented with the keys tohis brand new Porsche924S sports car on the StarMicronics' stand at theWhich Computer? show.The photograph shows MsCarina Phillips of PorscheUK and tvir Takahashi ofStar Micronics drawing thewinning key.The competition. whichhas been running sinceSeptember last year, wasbased on sales of printersinto dealerships. An end -user competition for a sec-ond Porsche 924S is cur-rently in progress and thewinner will be announcedat the beginning of thismonth.

Craven House,40 Uxbridge Road, Ealing,London W5 28S; telephone(01) 840 1800; telex 948501

19 EEApril 1986

WS VIEWS NEWS VIEWS NEWS IT:

AIM Cam-bridge = AIMTechnologyFollowing the move to itsnew base at Perry, Combs,AIM Cambridge haschanged its name to AIMTechnology*. The newname and image reflectAIM's main role as a prod-uct and process designconsultancy applying ad-vanced technology andengineering skills. It alsoclears up any confusionnow that the companyhas moved further awayfrom Cambridge itself.The company employsover 50 staff, the majorityof whom are highly skilledin software, electronics,and mechanical engin-eering. It undertakes awide variety of productdesign, consultancy, prob-lem solving, and processdevelopments projects.Among recent projectsthat AIM has been in-volved with are themarket -leading Tempomains time -switch, anelectronic wand, which isused interactively withchildren's quiz books toenhance learning and en-joyment; electronic musicsynthesizers; and a price -shattering OCR reader forthe personal computermarket.The new site, Gaynes Hallat Perry near GrafhamWater, is a Grade II listedGeorgian mansion set in16 acres of parkland. Itprovides 12 000 ft2 ofusable area: twice thespace that AIM had at itsprevious location. The en-tire area has been fittedout to provide purpose -designed electronics, soft-ware, and mechanicaldesign laboratories. Ductshave been fitted aroundeach floor for the instal-lation of fibre optic net-working cables, andspecial computer roomshold the company's VAX -based software design fa-cility.

The photograph shows IanQuayle, managing direc-tor of AIM Technology, infront of the new premises.' Gaynes Hall, West Perry,Huntingdon, Combs PE18OST; telephone (0480)811995; telex 32707

IMO opens PCtraining centreTerm began at IMO Pre-cision Controls' lastJanuary when their newtraining centre was usedfor the first time. Part of a10 000 ft' development atStaples Corner, NW Lon-don, the new suite will be

used to train engineers inthe workings and usage ofIMO's new C -series of com-municating Program-mable Controllers.Courses have been de-signed to acquaintengineers with the exten-sive capabilities of the C -series to ensure that maxi-mim benefit is derivedfrom their implementation.' 1000 North Circular

Rood, Staples Corner, Lon-don NW2 7JP telephone(Of) 452 6444

Surface -mountprototypeserviceFrazer -Nash Electronics*has a productioncapability geared to pro-viding clients with a fa-cility to undertake smallproving runs of pre-

production quantitiesbefore they committhemselves to substantialinvestment in manufactur-ing set-up costs.As an electronics designand developmentcompany, it is vital forFrazer -Nash to remainabreast of newtechnologies so that thecompany may pass onany benefits to clients inthe designs that areundertaken. This has beenthe case with the growthin use of surface -mountdevices-SMDs. Frazer -Nash Electronics has beeninvolved with surface -mount technology-SMT-for over four years and hasbuilt up experience overthis period of the variousproblems associated withthe introduction of smalloutlines-SOs-and SMDsinto existing or newdesigns.The production depart-ment can also call on theexpertise of Frazer-Nash'sdesign and developmentteam to advise clients ofthe pitfalls to avoid in anynew design or to suggestthe most cost-effective wayto rework an existing prod-uct to take full advantageof the benefits of SMT.' Randalls Way,Lea/herhead, Surrey 16.227TX, telephone (0372)379717, telex 946405

EE

April 1986 20

OM VIEWS NEWS VIEWS NEWS V

RegisbrookrestructureRegisbrook Ltd andPulseview Ltd, the sisteropto-electroniccompanies, have beenrestructured into more ef-fective trading units con-trolled by a newcompany, RegisbrookGroup Limited'. Therestructured company hasraised new venture capitalin excess of £1 million tofinance expansion and anincreased stockholding.The re -financing, handledby Venture Link, resulted infunds from a number ofsources, including theForeign and ColonialEnterprise Trust, the WaterAuthorities' Superannu-ation Funds, Equity & Law,and the Venture Link con-trolled M4 Syndicate.The restructuring is in-tended to improve thegroup's potential for suc-cessful trading. Bothcompanies are fore-casting a significant in-crease in business thisyear; several substantialnew orders are already onthe books. Regisbrook willcontinue to expand itsproduct portfolio with newdevelopments in opto-technology, whilePulseview are undertakinga major sales initiativeaimed at capitalizing onthe company's successfuldevelopment of a rangeof advanced new prod-ucts and services.

The photograph shows asmall celebration as acheque for over £1 millionis being signed by Dun-can Fitzwilliams, chairmanof Venture Link, with,seated from left to right,Cathy Williams, ChrisWilliams, and Gary Taylorof Regisbrook. Behindthem stand members ofthe two negotiating teams. Unit 5, Horseshoe Park,Pangbourne, Berks; tele-phone (07357) 4841; telex849013

Private satellitenetworksSatellites are not onlychanging the face ofbroadcasting, they arealso changing that of

Today, majorgrowth is occurring in themarket for private satellitenetworks, and a number ofsatellite systems specifi-cally to service totelecommunications re-quirements of businesshave been developed.Satellite Private BusinessNetwork Terminals in theUS 1985-1995 (01494), anew Frost & Sullivan' studyforecasts that the marketfor private satellites willgrow from $564 million in1984 to S8.35 billion in1995. Annual sales ofprivate satellite network

earth stations, nowestimated at $315 million,are expected to increaseto $1.2 billion by 1995.The 297 -page report in-cludes complete com-petitive information,including market share,discussions of technology,marketing techniques, anda look at how each in-dustry makes use ofsatellite communications. 106 Fulton Street

New York, NY 10038, tele-phone 212-233-1080; or104-112 Mary/ebone Lane,London WM 5FU, tele-phone 01-935-4433

German PCBplant forScot/andFederal German elec-tronics company IsolaWerke AG, of Duren nearAachen, is to set up a £10million plant at Cumber-nauld in Scotland's SiliconGlen. The project willcreate 200 new jobs overthe next five years.Isola, a leading Europeanproducer of printed circuitboard laminates, choseScotland for its firstmanufacturing plants out-side the Federal Republicto get closer to its majorUK customers. It will alsoprovide a base for servic-ing their overseas markets.Isola has an annual turn-over of £77 million, a workforce of 1200, and hasbeen supplying the worldelectronics industry forover 25 years. It is a sub-sidiary of Rutgerswerke AGof Frankfurt, an organicchemical and plasticsgroup, with over 11 000employees and a turnoverin excess of £1000 million.Isola director Dr RainerTillessen said that thecompany intended to in-creasingly serve the UKmarket from the Cumber-nauld base by 1987,

although it also foresawstrong export developmentto the USA and Com-monwealth countries toeventually match the 60per cent export levels nowattained by the DUrenplant.The project representsanother success for LIS-Locate In Scotland, thejoint Industry Departmentfor Scotland and ScottishDevelopment Agency' in-ward investment bureau.* 120 Bothwell StreetGlasgow G2 7JP; tele-phone 041 248 2700

Fifth -generationcomputerA project aimed at thedevelopment of a fifth -generation computer,capable of voice com-munication in severallanguages and simulationof thought, was an-nounced recently by theDepartment of Trade andIndustry.Called Flagship, the pro-ject is the largest elementof the Alvey Programme ofcomputing research, andwill be undertaken by ICL,Plessey, Imperial College,and Manchester University.The five-year Alvey Pro-gramme has a budget of£200 million from theGovernment and £150million from Industry. LPS

EE

April 1986

WS VIEWS NEWS VIEWS NEWS IT:

Plessey GaAscomponentsmarketed byTekelecTowcester-based galliumarsenide componentsmanufacturer PlesseyThree -Five Group Limitedhas announced an agree-ment with Tekelec, aleading frequency -tuningcomponents marketingcompany.Under the agreement,Tekelec is licensed tomarket the full range ofPlessey gallium arsenidecomponents and mono-lithic microwave inte-grated circuits-MMICs-inthe UK.Tekelec Limited wasformed in 1977 as a whollyowned subsidiary ofTekelec-Airtronics SA ofFrance. Since 1977,Tekelec Ltd has grown intoa multi -million pound con-cern, employing a skilled

technical sales force sell-ing Tekelec products inthe USA and Europe. In ad-dition, Tekelec Ltdrepresents in the UK anumber of electronicsmanufacturers.The photograph shows thesigning of the agreementby Alan Price, managingdirector of Three -Five, andJack Siddle, managingdirector of Tekelec Ltd.

Scottish boostto UK'selectronicssuccessScotland's electronics ex-pansion last year helpedthe UK to number oneplace in Europe for marketgrowth. The UK has nowpushed its market shareup to almost 20 per cent.This success is partly due

to the growing number ofUS, Japanese, andEuropean companies set-ting up in the UK, particu-larly in Scotland,according to the WestEurope Electronics DataYearbook for 1986, pub-lished by Benn ElectronicsPublications*.Scotland's semiconductorproduction is now 20 percent of total European out-put and contains elevenof the top twenty data pro-cessing companies inEurope.The total value of the WestEuropean market last yearwas estimated to be£64 000 million, up from£60 billion in 1984. It is ex-pected to reach £81.3billion in 1989.European economic ex-pansion is confidentlypredicted to be higherthan in the USA in 1985.Growth rates for FederalGermany and the UK arelikely to be higher thanthe average.Although Europe's balanceof trade in electronicsproducts has worsenedconsiderably since 1979,the UK was one of onlytwo countries to reducethe deficit. In 1983, the UK'sdeficit was £2.73 billion; in1984 it was £2.46 billion;and in 1985 it is estimatedto have fallen further.

Chiltern House,146 Midland Road, Luton,Beds LU2 OBL; telephone(0582) 417438; telex 827648

Surfboards aidsurface -mountprototypingGlobal Specialties* has in-troduced a completelynew concept for buildingprototype circuits withsurface -mount devices.With its Surfboard, thedesigner places a plasticleaded chip carrier-PLCC-into a chip carrier

socket to give him instantbreadboarding access tothe electronics in the chip,without soldering or per-manent connections.The Surfboard provides anumbered breadboardingtie -point for each lead onthe chip carrier. Connec-tion of a particular lead iseffected by inserting stan-dard 22 -gauge hook-upwire into the correspond-ing tie -point.Changes are easily madewithout damage to chipcarriers, PC boards, orcomponents. More thanone surface -mount chipcan be included in aprototype circuit throughthe use of additional Surf-boards connectedthrough breadboarding.Three Surfboard modelsare available to accom-modate 44-, 68-, and84 -pin PLCCs.

Shire Hill Industrial Estate,Saffron Walden, Essex CB113AQ; telephone (0799)21682; telex 817477

Amateur Radio& ElectronicsHobby FairThe Amateur Radio & Elec-tronics Hobby Fair whichwill be held at TheWembley ConferenceCentre, London, on Satur-day 5 and Sunday 6 July,1986, is a major new eventin the Amateur Radio rallycalendar.The two-day fair is ex-pected to be attended bya large number of retailersand manufacturers inamateur radio; RTTY,satellite TV and communi-cations, microwaves, hob-by components.The event is organized byAmateur Radio Promotionsof Woodthorpe House,Clapgate Lane, Birm-ingham B32 3BU; tele-phone (021) 476 8991.

EE 111April 1986

Fig: I. TheDynaudio Type17W75 was usedas the bass andmddle fre-quency driveunit in the proto-type system.Noteworthyaspects of thisunit are thecentre magnetand the PHA(phasehomogenousarea) propylenecone

SATELLITELOUDSPEAKERSFollowing on last monthS Active subwoofer; this articledeals with the satellite loudspeakers that complement thesubwoofer to give complete coverage of the audiospectrum. These satellites are, however; also perfectlysuitable for independent use.

Satellite loudspeakers are not aseparate category of soundreproducing equipment; any loud-speaker whose bass performanceshould be improved could beclassified as a satellite. So-calledbookcase speakers are invariablysatellites, because their modest di-mensions prohibit proper repro-duction of frequencies below about100 Hz.If you are planning a new loud-speaker system, you could do worsethan to opt for a subwoofer-satellitessystem. It is then, of course, bestright from the start to design thesatellites for optimum performancewith the subwoofer and vice versa. Itis on this basis that the presentarticle has come about: the resultsare very satisfactory, indeed.Even those who are not terribly in-terested in the subwoofer will find

that the bass performance of thesatellite speakers (-3 dB point at65 Hz) is perfectly adequate for theirrequirements.Although the design of a loud-speaker enclosure is never an easytask, the one proposed here pre-sents the constructor with relativelyfew difficulties. This is, of course,largely due to there being no needof paying much attention to the bassreproduction. A response down to100 Hz would be perfectly adequate;true, an octave further down wouldbe very nice, but is, in this case, notnecessary.This immediately removes the prob-lem of choosing the right shape andsize of enclosure and deciding howmany "ways" the system should have.The enclosure decided on is a nor-mal closed box. while it was felt thata two-way system would be perfectly

acceptable, provided that thechosen drive units would allow this.The latter aspect also requires lessarithmetic and fewer measurementsthan. e.g.. a three-way system.These considerations have resultedin a very satisfactory practicalrealization, both as regards theenclosure and the number of driveunits. As a bonus, the bass perform-ance measured is considerable bet-ter than that aimed at. In short, theproposed design is compact. easy tobuild, not expensive, and, even with-out a subwoofer. gives an excellentoverall performance.

The drive unitsAs said, the design is based on twodrive units. Since the majority of

111 EEApril 1986

middle -frequency units are notreally satisfactory above about 2000to 2500 Hz, which causes problemsin the choice of tweeter, Dynaudiounits were used for the prototypes.These units did not only meet the re-quirements for the present designbetter than most; they also offer theadvantage of an excellent match withthe subwoofer (which also uses aDynaudio drive unit). The units arethe Type 17W75, a 170 mm bass andmiddle -frequency unit, and the TypeD-28 AF tweeter.The 17W75, shown in Fig. 1. is a driveunit with a relatively large voice coil(75 mm) in hexacoil technique,which, in conjunction with theunusual shape of the one-piececone, gives an ideal transfer of theacceleration force from the coil tothe PHA (phase homogeneous area)cone. Another advantage of the bigvoice coil is the short rise time (fasttransient response) of 50 ps. Very lowdistortion and excellent phasecharacteristics are a result of the totalconcave shape of the cone.The D-28 AF, shown in Fig. 2, is a28 mm soft dome tweeter. The voicecoil is coupled with the aid of ferrofluid. The unit has a noteworthy fasttransient response (short rise time) of12 pS. It offers the great advantage ofhaving been designed specificallyfor use with 6 dB/octave filters: notmany dome tweeters have!

Cross -over filterCross -over filters (or networks) are,

unfortunately, necessary, becausethere is not a drive unit that canreproduce the entire audio rangesatisfactorily. As long as these filtersare not to steep -skirted, they do notcause too much harm, but with in-creasing skirt steepness the flawsthey introduce become more andmore serious. Steep -skirted filtershave particularly bad transientresponse characteristics.The design of a cross -over networkshould therefore be based on6 dB/octave slopes, provided thedrive units used allow this. This is soin the present design as can be seenfrom the diagram in Fig. 3. Strictlyspeaking, this circuit contains onlytwo true filter components: La andC2. The remainder of the compo-nents perform the correcting func-tions that are always necessary forgood filter operation. Network RI -CIserves to counteract the impedanceof the 17W75, which increases withrising frequency. This carefully de-signed network ensures that theoverall impedance of the drive unitremains constant above its reson-ance frequency. Only because ofthis can the filter perform as re-quired.Resistive divider R2 -R3 serves atwofold function. In the first place, itensures level matching of thetweeter, whose efficiency issomewhat higher than that of the17W75. Then, the value of R2 may bevaried between zero ohms and 2.2ohms without the necessity of chang-ing the value of C. A value of 0 ohmscorresponds to a 0.5 dB correctionfor the tweeter, while 2.2 ohms gives

a -1.5 dB correction. Moreover, R3smoothes out a small uneveness inthe tweeter characteristic: its valuemust, therefore, not be changedunder any circumstances.The characteristic in Fig. 4represents the output voltage of thefilter, measured across the two driveunits. Note that the cross -over pointonly appears to be at -5 dB; it is ac-tually at the customary -3 dB. Thecharacteristic of the 17W75 has aslight peak at the cross -over fre-quency, and this has been correctedby a slightly earlier action of thefilter. Acoustically, everything is,therefore, as it should be.Construction of the filter should notgive any difficulties if the PCB (Type86016) shown in Fig. 5 is used. Note,however, that LI should be fastenedwith glue or a brass/nylon bolt: a

Fia. 2. Thetweeter is aDynaudio TypeD-28 AL' whichteas specially de-signed for usewith 6 dB/octavecross -over filters.

Fig. 3. The 6 dB/-octave cross -overnetwork istypified by itssimplicity

L.I

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71,75

teal

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INS4 TS -3

EEApril 1986 24

Sf

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i

i t

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.52tell; etTier

output-H

86016-4

11Es ^rz-'65_

Fig. 4. Character-istic curve of theoutput voltage ofthe cross -overfilter measuredwith the driveunits connected.

Fig. 5. Theprinted -circuitboard for thecross -over net-work (T)re 86016- availablethrough ourReaders'ServiceS).

Parts list

= 0.5 mH air -coredinductor; wire diameter1 mm

= 22 /.4 bipolarelectrolytic or polyester

Cz = 10 µ polyesterRI = 5 Q;5 W112 = 0.47 Q;5 WR3 = 22 Q;5 WDynaudio Type 17W75

drive unitDynaudio Type 0-28 AF

drive unitchip board or plywood,

18 mm thick, asrequired (see Fig. 6)

about 0.25 m2 rubber -

backed floor coveringabout 0.25 rif rock -wool1 variovent; 110 mm;(Dynaudio)

connector terminals asrequired

wood glue, screws, andnails as required

steel fastening would affect the valueof the inductor. Also, observe cor-rect polarity when the drive units areconnected to the board. The PCBmay be conveniently mounted -onspacers- on the bottom lid oragainst the back panel of theenclosure.

The enclosureAccording to the manufacturer'sdata, the 17W75 is best housed in a 10to 15 litre closed box, which hasbeen provided with a so-calledvariovent (acoustic resistance).

Although theoretical considerationspoint to a somewhat larger volume,in practice the manufacturer'srecommendations proved to be cor-rect. In a damped closed box of ex-actly 10 litres volume, the bassperformance of the 17W75 was sur-prisingly good. The difference be-tween a box with, and one without, avariovent is slight. The variovent onlyserves to attenuate the resonancepeak, and this results in a somewhatmore rigid performance at low fre-quencies.Although some photographs accom-panying this article show a beauti-fully styled pentagonal, pyramid -shaped prototype enclosure (cour-tesy Dynaudio), the proposedenclosure has been kept rathersimpler. Note, however, that the pen-tagonal enclosure is available fromDynaudio as a kit: it is acousticallyexcellent, but quite difficult to build.Our own proposal. shown in Fig. 6,offers similar advantages as theDynaudio design: no parallel sidepanels; leaning backwards; upwardtapering front panel; but does notdemand the craft of a furnituremaker.The material is 18 mm fine -chipboard; plywood may, of course, alsobe used, but is rather more expens-ive. The front, back, and side panelshave exactly the same dimensions. Ifthese are sawn very carefully, all fourcan be glued together in one go. Thebottom and top lid must be sawnvery carefully to ensure a good, tightfit onto the leaning vertical panels.The top lid may be glued in place,but the bottom panel is best fittedwith screws and sealing tape so thataccess is possible at a later stage, ifrequired. Next, the holes for thedrive units, the variovent, and theconnector terminals should be cut.The variovent should be glued into

EEApril 1986

Technical characteristics

SystemEnclosureNet volumeCross -over filter

Frequency rangeAmplifier ratingSensitivity

passive; two-wayclosed boxabout 10 litres6 dB/octave; cross -over point at about2500 Hz-3 dB points at 60 Hz and 20 kHz30.100 watts89 dB

place, while the drive units shouldbe screwed on. Afterwards, the gapbetween the rim of the drive unitsand the front panel should be sealedwith suitable tape.The beste place to fit the cross -overfilter is at the back panel betweenthe variovent and the connector ter-minals.Panel resonance is further preventedby gluing strips of rubber -backedfloor covering at the inside of allpanels and then covering these with30 mm thick rock -wool. If thismaterial is amply cut, the strips willbe push-fitt, obviating the need forgluing them into place.The finish of the exterior of theenclosure is left to your own tasteand preference.

PerformanceIt is, of course, easy (and tempting)for a designer to sing his ownpraises, so the performance of thesystem can be gauged from themeasured impedance and fre-quency response characteristicsillustrated in Figures 7 and 8 respect-ively. The smooth impedance curveshould not present any problemsto a good output amplifier. Thefrequency response curve wasmeasured with R2= 0.47 ohms. Whenthis is increased to 2.2 ohms, thecharacteristic shifts down by about2 dB above 2 kHz. Response at lowfrequencies was ascertained byclose -proximity (20 mm) measure -

Fla 6. Construc-tion details of theproposedenclosure. Thematerial may be18 177M plywoodor aood qualitychic board.

EEApril 1986

26

7

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86016.8

Fig 7 Character-istic impedancecurve of thecompletedsatellite system

Fig. 8 Fre-quency responsecurve of thecompletedsatellite system.

ments. The acoustics of the test roomhas such an effect that measure-ments at greater distances give nomeaningful information as to thebehaviour of the system at low fre-quencies. For measurements atmiddle and high frequencies, thetest microphone was placed at adistance of about 2 metres at roughlythe height of the acoustic centre ofthe enclosure.

EEApril 1986

PRINTERBUFFER 1

Whatever speeds their manufacturers claim for them,modern printers still need a lot of precious time tocomplete lengthy listings. This article presents anIntelligent inter -peripheral buffer device with a largememory to be loaded at one swoop by the computer.While the printer buffer patiently feeds the printer, thecomputer is free for the next programming session.

Generally speaking. any peripheralis slow compared with the control-ing computer system. Printers, plot-ters. modems. etc. require computerhandshaking arrangements to allowfor the time they need to completetheir tasks; the computer must in-evitably wait until the peripheraldevice is ready to receive a newcharacter. and this is obviously awaste of (software) time. Indeed,many programmers are forced to goand have a cup of tea while theirever so fast computer feeds theprinter for a quarter of an hour or so.A possible solution to this incon-venience would be to reserve a

large in -computer memory area forbuffer use. from which charactersare sent to the peripheral by meansof a special. usually interrupt -polled.program. It will be self-evident thatthis software -based spooler lays arather high claim on available com-puter memory space and main -taskprocessing speed.This article, however. deals with thehardware approach; it presents a mi-croprocessor based. dedicatedbuffer device with its very own largeRAM memory. I/O. and controllingsoftware. To the computer, thisnovel inter -peripheral will appear asan unusually fast printer which is

loaded via the standard Centronicsoutput port with art appropriate com-mand such as LPRINT, LUST orequivalents. After being loaded. thebuffer independently deals with the

by J M Smeets

Features: 16, 32 or 64 thousand characters holding capacity Start-up text verifies printer operation and connection Space and or form feed cancel modes Single sheet printing and copying

S..itch-selectable default operation Selectable number of lines per page Buffer contents repetition (max. 100 times) Cost effective design

EE

April 198628

Inputinterface

EPROM

CPU

RAMcontrol

dynamicRAM

sys emdisplay

I/O control

outputinterface

commandkeys

0

85114-1

Fig. I. Blockschematicpresentation ofthe micropro-cessor controlledprinter buffer.

printer, while the computer is freefor any other task.Printer buffer input and output is tothe Centronics standard (parallel in-terface), but readers who own aprinter with RS232 (serial) interfacewill find a suitable RS232/Centronicsconverter described in the October1984 issue of Elektor Electronics,page 10-58 ff.Choice of components for the pres-ent design was mainly guided bycommon availability and low cost.Therefore, a configuration with Z80CPU and Type 4164 dynamic RAMswas decided on because these offera simple memory refresh setup, highspeed, and ease of machinelanguage programming.

Block diagramA look at the schematic diagramshown in Fig. 1 reveals that the CPUis clearly the central building blockof the present design. The systemsoftware resides in EPROM, whileprinter characters are mass -stored indynamic RAM. Parallel input andoutput interfacing is to the Cen-tronics standard and uses full hand-shaking with computer and printer.The CPU effects handshaking andcomputer/printer (dis)connection bymeans of an I/O control section. A

set of command keys and a simple,yet effective system display havebeen added for ease of operation.

Buffer memoryAs apparent from the circuit diagramshown in Fig. 2, relatively few partsare required to construct this ver-satile buffer device. A further in-teresting detail is the absence ofZ80 -family LSI support chips; theirapplication in this circuit might haveresulted in an even more compactPCB, but a number of cheap LS-TTLcircuits also work to full satisfaction.The Z80 CPU reads its instructionsfrom a Type 2716 EPROM, starting ataddress 0000 after power -up. As theEPROM has its OE (output enable) in-put connected to CPU address lineA15, it will be evident that read/writeoperations involving RAM memorymust be effected with A15 at highlevel (logic 1). The memory refreshmethod specific to the Type 4164dynamic RAM has been dealt with inthe series of articles on the high-

resolution graphics card; see the Oc-tober 1985 issue of Elektor Elec-tronics. However, since the presentcircuit is based upon a Z80 CPU andhas an EPROM inserted in theavailable 64 Kbyte address area, aslightly unusual refresh arrangement

has been opted for, and this will bereverted to later. For now, it is usefulto know that the Type 4164 dynamicRAM has eight multiplexed addressinputs, Ag...A7 which latch the mostsignificant address byte (MSB) whenRAS (row address strobe) is low, andthe least significant address byte(LSB) when CAS (column addressstrobe) is low. In this way, any bit outof 65 536 (64K) contained in the chipcell -matrix can be selected for aread or write operation. How signalsRAS and CAS are generated in thepresent design is explained below.

RAS timing: CPU signals Ml andMREQ are low during every CPU in-struction fetch cycle; this conditionwill keep the output of bistableNio-N,1, and thus RAS, high. Afterthis fetch cycle, the contents of the Rregister (refresh, this will be revertedto) are placed on /le...Ai, and theCPU starts an execution cycle withMREQ going high, followed by Ml.Only when MREQ goes low againwill bistable Nit -NI, toggle to ac-tivate the RAS lines, which will re-main low until the next CPU fetchcycle.CAS timing: this signal will be active(i.e. logic low) during every CPUread or write cycle with All at highlevel and Ais also high to avoid en-abling the EPROM. Note that RAMmemory WR lines are driven with theinverted CPU RD line to avoid poss-ible fan -out overloading of the Z80WR output.If a mere 32 Kbytes of buffer RAMare required, it is possible to fit onlyIC7...IC19. This implies that everybyte is split into two nibbles by theCPU and stored at two four -bitmemory locations. After power is ap-plied to the circuit, the CPU exam-ines the width of available RAMmemory in order to determine itsmethod of character storage. It iseven possible to install only 16

Kbytes with ICe and IC10 fitted, andbytes will be stored and read as foursequentially placed two-bit units.However, with the price of 64 Kbytedynamic RAMs considerably re-duced over the past few months, itwould seem advisable to install thefull 64 Kbyte at once.

RefreshingsoftwareAs always with microprocessorbased designs, simplified hardwarerequires an extra software effort.However, as long as the additional in-structions do not considerably slowdown system performance, the 'soft-

29 EEApril 1986

5v fl

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PRINTER

ware solution' is often preferred overa corresponding hardware con-figuration, simply because CPU in-structions are free once the thing isrunning properly; it is just as well toget the most out of that instructionset!The Type Z80A microprocessorfeatures an internal memory refreshregister R which is accessiblethrough accumulator A. Duringevery CPU opcode execution cycle,the contents of R are placed on CPUaddress outputs A.. _As to specifyone of 128 rows in the RAM chips forcollective refresh with a RAS pulse;address line A7 is not involved in thisprocess. Therefore, only dynamicRAMs featuring a cell matrix of 128rows and 512 columns may be used

in the present design. After every ex-ecution cycle, R is automatically in-creased by one byte. This software -based refresh using the multiplexedaddress lines eliminates a good dealof hardware whilst opening possi-bilities for ROM -RAM bankswitchingwithin the total addressable area of64 Kbyte. As pointed out above, theonly disadvantage with this methodis the extra number of CPU instruc-tions.Every memory read or write oper-ation is started with placing the up-per eight address bits (mostsignificant byte, MSB) into R. Next, anormal read or write instruction isissued to complete the address withthe lower eight bits (least significantbyte, LSB). Note, however, that MSB

address lines AS, A9, Alo, Au, Ala,and A14 are Vorift care' at that stagebecause R holds the correct M B. Toavoid memory contention problemswith the EPROMs, A11 and Ais mustbe kept high while reading from orwriting to RAM memory.A practical programming examplewill help to shed light on this slightlyodd combination of refresh andselective RAM addressing in a 64Kbyte configuration.Suppose that the byte (i.e. printercharacter) at RAM address 7255hex isto be read into the CPU accumulatorA for transfer to the buffer outputport. The program below shows thatregister pair H -L is used as a RAMaddress pointer with MSB modifiedinto FFhex to avoid enabling the

Fig 2. Circuitdiagram of theprinter buffer.The number ofdynamic RAMSfitted determinesthe bufferholding capacity.

EEApril 1986

30

Fia. 3. ?Yiningdiagram for aread operation inRAM memory

EPROM. The correct MSB 72hez,however, is put into R:

21SSFF3E72ED4F7E

LDLDLOLD

HL ,FFSS

A .72

R.AA.1HL)

set virtual RAM addressload reel MSBfor RAM RP,:

; get byte at $725Sbut 1ts=h1, FFE13M

Figure 3 shows the timing diagramrelevant to this sequence of instruc-tions. It will be noted that rowMSB +1 instead of MSB is selectedbecause R is automatically increasedby one byte after each instructionfetch cycle. However, this flawcauses no problems because it oc-curs both with write and read oper-ations.The proposed addressing methodinterrupts memory refresh cycles, soto avoid loss of data the contents of Rmust be saved in an auxiliary registerand restored after each memoryread or write action. Given the CPUclock speed of 4 MHz, however, theslight increase in actual refresh timeis insignificant.

Buffer I/OCircuit diagram Fig. 2 shows the fol-lowing hardware for processingprinter characters under CPUcontrol: I/O channel selector a single

Type 74LS154 4 -to -16 decoder/demultiplexer IC11 decodes CPU ad-dress lines An... A3 into 16 I/O chan-nel enable signals, 11 of which areused in the buffer circuit. Input interface: the computer that

loads the printer buffer places acharacter on the Da ...D7 inputs andsupplies a strobe pulse STB to indi-cate that data is stable and valid. The

character is clocked into octalbistable IC17 and output Q ofbistable FF1 is set to signal a BUSYcondition to the printer, i.e. the bufferneeds time to process the receivedcharacter. It will be evident thatBUSY will be kept active muchshorter than with a printer connec-ted direct to the computer!An instruction

IN A, (3)will cause I/O decoder output 3 togo low (ICI1), which in turn enablesIC16 to transfer four bits into the CPUaccu. One of these bits, Da,represents the inverted BUSY level; ifit is read as a high level, this impliesthat no strobe pulse has been re-ceived from the computer. When Dais logic low, however, the buffer CPUknows that a new character isavailable in latch IC17, and may becopied into accu with

IN A, (2)and subsequently stored in RAM.The next instructions are

OUT (I), AOUT (0), A

which reset BUSY and supply anACK pulse for the computer respect-ively, in order to prompt it for a newcharacter.It has happened that data processingby the printer buffer is so fast that acomputer supplied STB pulse wasstill present when the bufferdemanded another character, find-ing STB still present, it would enterthe same character twice or eventhree times because the STB pulsefrom the computer was far too long.To prevent this from happening, adifferentiator R -C network may be fit-ted onto the appropriate input con-nector pins; this will be reverted to inthe section on construction. Output interface: the connected

printer supplies an ACK(acknowledge) pulse to indicate thatit is ready to receive a new character

from the printer buffer. This pulsewill clock a low level into bistableFF2 and enters the CPU accu as Dawhen IC15 is enabled with

IN A, (4).Thus, reading Da as low indicatesthat a new character may be got frombuffer memory for transfer to the out-put latch IC15, as effected with

OUT (6), ANext, a strobe pulse is issued on STBwith instruction

OUT (5), Awhich will also set FF2 output highagain to indicate that the characteroutput loop may be started oncemore.

Command keysA number of small momentary push -to -make buttons have been providedto set operation as desired by theuser. There is also a block of DIPswitches inside the buffer housing(61...S5) to set default operation;SI ... S5 may be set to define the totalnumber of lines per page to a maxi-mum of 64 (29. Switch 57 enables theuser to cancel spaces (ASCII 20) inthe printout, while S3 cancels com-puter form feeds, if required. Withthese two switches set, a significantamount of printer paper may besaved with some applications.The TEST/+10 key is used to run achecksum procedure which verifiesEPROM contents; if correct, '99' willappear on the 7 -segment displays.Next, the buffer sends the message'Elektor Printer Buffer' followed bythe entire ASCII character set to theprinter for verification of proper op-eration and buffer connection.The COPY key is depressed to sendthe entire buffer contents to theprinter once more. Before this canhappen, however, the buffer ascer-tains that no more characters are be-ing received from the computer,which is next decoupled from thebuffer as indicated by the dark CC(computer connected) LED insidethe RESET key.The NUMBER key is used to set thenumber of copies to be printed as in-dicated on display. Depressing thiskey will step the indicated number, ifthe user wants to make a fast setting,NUMBER may be kept depressed tostart the auto -increase mode.The RESET key is used to restorecomputer -buffer connection (CCLED lights) and put the buffer in thecharacter load mode.The SPM (single page mode) key isdepressed when the user wishes tostop printing after every form feedcommand issued by the buffer. Thismode is indicated by D3 lighting.

EE

April 1986

The PrC (printer connect) key con-tinues printing after the necessaryuser action has been taken duringSPM mode.The LPM (last page mode) key, usedin conjuction with COPY enables theuser to print a maximum of 100copies of the page just printed (notethat display reads '00' for 100)The OFF key is depressed to resetall internal buffer bistables; also, allabove modes are switched off.As for the hardware associated withthe function keys, refer once more tocircuit diagram Fig. 2. Switch So(TEST/+10) is connected direct tothree -state buffer ICis and read as D3by CPU instruction

IN A, (3) .

Note that this instruction reads statusof BUSY, NUMBER, CC, TEST/+10,and LPM which appear as databitsDa...Di in CPU accu to be separ-ately tested with a further ap-propriate instruction. The NUMBERkey is connected to ICis via Schmitttrigger debouncer circuit Nis -N17which also functions as an auto -repeat device; when NUMBER iskept depressed for some time,oscillation will occur at about 2 Hz tospeed up setting the number ofcopies. Depressing the RESET keyeffects a logic low level at the CPURESET input and also activatesSchmitt trigger bistable N13-14,4

which lights LED Di to indicate a CC(computer connected) condition.Combination C2 -R4 effects computerconnection after buffer power -up;furthermore, the R -C delay timeprevents immediate system restartwhen RESET is accidentallydepressed. Command keys S13. . SI7

are connected to the reset inputs offour set/reset type bistables contain-ed in IC13. All bistables may be setwith the OFF key (S17), while the PrCbistable is also under CPU controlwith

OUT (9), A .

After power -up, capacitor Cs ac-tivates PrC, whereas Cs deactivatesthe remaining three functions.

DisplayTwo 7 -segment displays (LDI-LD2)are driven by two Type 9368 displaydrivers (1C12-IC13) which feature aninternal latch and hexadecimal7 -segment representation (0...F). In-struction

OUT (OA), Aloads the latches and changes thedisplayed value into that of the accucontents.After power -up, the displays indicatethe available amount of RAM -memory; 16, 32, or 64 Kbytes. In case

Fig. 4. Thebuffer powersupply is ahighlyconventionaltype.

818

Fl

8V1A

D6 ... D9= 4 x 1N400187...010=47n 85114.4

a fault exists in the RAM section ofthe circuit, the displays will indicate'OF'. The number of copies isdisplayed after NUMBER has beendepressed, but note that '00' means100 copies.

Power supplyThe power supply of the printerbuffer is shown in Fig. 4; it is highlyconventional and supplies up to700 mA at 5 V. To keep normal dissi-

pation within reasonable limits, thetransformer secondary voltageshould be kept as low as possible. Ifneccessary, ventilation holes may bedrilled at suitable places in thebuffer housing.

The construction will be derailed innext month's issue.

EEA[37;1 19E6

The most frequently used equipment in an electronicslaboratory or workshop is arguably an all-purpose powersupply. Such a unit should not only provide a variablestable output but also be able to withstand theoccasional overload. The supply described here does allthat twice over!

VARIABLE DUALPOWER SUPPLY

Technical characteristics

Output voltageOutput currentOutput rippleCurrent limitInternal resistanceInternal dissipationAmbient temperature

2x0...20 V2x0...1.25 A5 mV peak -to -peak1.3 A0.002 ohms2x8 W25 °C

Anyone with some experience oftesting electronic equipment will ap-preciate the accuracy, stability, andease of control of the present powersupply. This consists of two identicalunits to cater for those situations inwhich two independent outputs arerequired, as. for instance, opampcircuits.

Internal protection circuits preventthe output current exceeding safelimits under overload conditions.Since the whole of the supply ishoused in a standard ABS verobox,great attention has been paid to theproblem of internal heat aeneration,which could be as high as 60 joules.A novel pre -regulation system,which reduces the input to the seriesregulators in a controlled manner, isused to overcome this problem.

Figure 1 illustrates the basic oper-ation of one section of the supply.The smoothing capacitor is chargedvia the bridge rectifier only if the(electronic) switch in the pre -regulator is closed. For a given loadcurrent. this effectively lowers thedirect voltage across the capacitorand, therefore, the dissipation in theseries regulator.The switch is controlled in proper-tion to the load current as will be de-tailed under Circuit descriorion.Figure 1 also shows that each sectionof the supply is provided with athree -digit indication of the value ofoutput voltage or load current.

Circuit description

EEApril 1986

The circuit diagram of each of thetwo sections of the power supply isshown in Fig. 2, which, for conve-nience, has been divided into threeparts: pre -regulator (2a); series regu-lator (2b); and display (2c).Preregulator circuit (Fig. 2a)Basically, this looks very similar to aconventional rectifier -smoothing ca-pacitor circuit; the only differencebeing the semiconductor switch Tiand associated parts. Diodes DI andD2 act as a zero -crossing detector,whose output is applied to thyristorThi. Figures 3 illustrates that Thi isoff at the moment of zero -crossing,which means that switching transis-tor Ti does not conduct. When thevoltage at the anode of Thi rises, Tiwill switch on and connect thebridge rectifier negative supply lineto the negative terminal of smoothingcapacitor C7. When the voltage dropacross R6-117-13, exceeds about 8V, T2will trigger the thyristor, which inturn short-circuits the gate andsource connections of Ti. This tran-sistor then stops conducting, so thatthe smoothing capacitor is discharg-ed via the series regulator and theload, if connected. The gate currentof Thl will drop to zero, but thedevice remains in its triggered state.This chain of events will start all overagain at the next zero -crossing. Thevoltage across C7 is set by PI to avalue which is 8V higher than theoutput voltage.At an output current of 1.25A, the rip-ple across the smoothing capacitorwill be about 5.5V, which means thatthere is a minimum voltage drop of2.5V across the series regulator;enough to work on for the present

antoothingcroseitor

nqulaion

rum

0-I

S6016 -I

design. Components ICI, D4 and Csprovide a separate voltage for thecontrol section of the series regu-lator, because this voltage should befree of ripple.The preregulator offers a con-siderable reduction in dissipation,since the series regulator onlydissipates about 8W at any outputvoltage and the maximum load cur-rent of 1.3A (this supposes a voltagedrop of 6V, a worst case value whichallows for a considerable ripplevoltage). A conventional series -regulated supply dissipates at leastabout 30W under the same load con-ditions (unregulated voltage 28V, out-

put 5V at 1.25A).There is, however, a small disadvan-tage with the proposed method ofvoltage reduction, because it will beobvious that the on -time of thepreregulator MOSFET will decreaseas the output voltage is lowered,since the device is only switched onduring the rising slope of thepulsating voltage; more precisely:on the steeper part of this slope.Since the total charge, Q, containedin a capacitor equals

Q=It [coulombs]where

I = charge current <amperes>;and t = charge time <seconds>,it will be understood that I will haveto increase to obtain the same totalcharge. This implies that the pulseload requirements for the bridgerectifier and power supply trans-former are heavier than usual andthis has been allowed for in the pres-ent design. Rather than roughlycalculating the transformer sec-ondary current from about 1.4 timesthe DC load connected to the recti-fier circuit, a factor 2 should be usedinstead.Series regulator (Fig. 2b).Fig. 2b shows the actual voltageregulation and variable currentlimiting of the output. To enable set-ting the output voltage to OV linearly,the opamp configuration outlined inFig. 4 is used. This is basically a con-ventional differential amplifier withan output voltage

U.= Ma/Rh) Vwhen P<<Iii.

In this setup, Uf and U. need not

Fig. I Blockdiagram of onesupply section.The preregulatorsection serves tokeep the totalpower dissi-pation of theseries regulatortransistor withinreasonablelimits.

EEApril 1986

34

2a b

C

22 V2400..

a v

a v-

131= 8600500013300

1N4001DI

1N4001

C2 C5=4.471,

IC47805

%ID

BUZ 10 (A1

P2 = multavm

4

1 1002x

BC 557B

OS

1N4148

Rld

617 IS

813 TS.

6.4 VI

IC33140

07

on.02

TIP 142

6

BC 5578

CAy CUR RENT

U.,

N4001

880C1000

770025V

LD1 LD3 = 7751

T8 ... T10 = BC 640

BC 640

EFL

P4 ...PG = enuhitum

R23

0 Ell

R24

0C18 MKT

270n

121 14

P5 8

BS 170

G

0 4

7 94M7

1k 10

INT.CAP SJ

HI LSD

NSO

M512

28 IC54.c, 3162 2'

2'2-

1.0 2'GAIN

T10

T

16

5

3

4

6 6

16

2

7

13I 7

P6MIN

10k

C16Neminn

1 On

LD1 1413 I

IC6 od2' 3161 e 9 7

t 15 22: 14 11

2'

c sz. d0 01 0 -0 - OM

R26

LD2 14

R25

9

E010 09

A -.-... V Zs.a Stn b0-0-

LD3 a

ribit

DP

R27

0

O

5.5016-2c

111 EEApril 1986

have the same earth return line. If thewiper of PI is set to point to thepositive reference voltage, will beOV, and the opamp output voltage,theoretically, also at OV. Turning thewiper towards the minus connectionof Ur will result in a higher opampoutput voltage. Provided the opampcan be set to a zero output voltageusing its offset, the voltage settingwill be linear from 0 to (Ra/Rb)Urvolts.The current limiting circuit is ar-ranged around IC3. The voltage dropacross the current sense resistor R12is compared to a preset value pro-vided by PI When the output currentexceeds this user -defined value, IC3toggles (low output level) and thuslowers the voltage at the strobe in-put, pin 8, of IC2; this results in thebase of Ts being held low, and thedevice will act as a constant currentsource. The current limit LED willalso light at this stage.Diodes D4 and Di provide a wiredOR function; therefore, the T3 -T4 cir-cuit is also capable of strobe controlat IC2, and consequently, outputvoltage shutdown. These parts keepthe output voltage low until thepotential across Cs has risen above8V to prevent voltage spikes beinggenerated by the power supply dur-ing its first few milliseconds ofundefined operation after power -up.This preventive measure will be ap-preciated by anyone familiar with thedetrimental effects these spikes haveon TTL integrated circuits.To protect the power supply from ac-cepting a negative voltage, DA hasbeen connected across its outputterminals. A prevention against re-verse current flowing into the regu-lator section is provided by 1:14 fittedwith the preregulator parts. Reversecurrent may occur when the supplyis accidentally connected to a large,charged capacitor or another powerunit with a higher output voltage.Display section (Fig. 2c).There are two identical, separate3 -digit displays for output current orvoltage indication of each supplysection. A Type 3162 A/D converter -multiplexer directly drives a Type3161 7 -segment display driver. Notethat this entire circuit has its ownsupply voltage, obtained from aseparate 8V winding on the powertransformer.Selection of voltage (V) or current (A)is achieved with two -pole toggleswitch S2 and MOSFET T7. In the 'Aposition, section S2b of the switchselects the decimal point on the left-hand display LDI The gate of T7 ispositive in this condition, so that thisdevice will conduct, short-circuiting134 and connecting the HIGH input ofIC5 to point B, which is the right side

of the current sense resistor R12. TheLOW input is connected to C, to theeffect that ICs measures the voltageacross R,2, which is a measure of theoutput current supplied by the pres-ent circuit. The current sense re-sistor has a value to give a voltage of1 mV for every 10 mA of output cur-rent, so that the resolution of the dis-play unit is 10 mA. The 3162 acceptsa maximum input voltage of 999 mV.With S2 set to the 'V' position, thegate and source terminals of T7 areconnected to give a very high drain -to -source resistance. This enablesICs to measure the voltage acrossdivider network R23 -P4 , which isdirectly proportional to the outputvoltage. The network has been di-mensioned to divide the voltage at A

by 100. so that the display resolutionin the 'V' position equals 100 mV. Re-sistor R2 has a high value to providea small offset current for P4 to enablea common zero setting arrangementwith Ps for both the current andvoltage indication.

ConstructionSince the present power supply is ahighly dense unit, as can be beenfrom the photographs with thisarticle, special attention should bepaid to its construction, for someparts are quite difficult to reach oncethe supply has been put together. Itis, therefore, wise to carefully check

3

U pot

U C6

Thl trigpats

lay

T1 off T1 off

T1 on

A K GS.

T1

T I: U

1.14

0,--%I ,----.

%.I

LI .' .ss

.. ; . ,

% ,% ,

, \ /%

%;

86016-3

1t

Fig. 2 The circuitdiagram of eachsection of thedual powersupply unit isdivided in threeparts:preregulator(Fig. 2a), seriesregulator (Fig.2b), and display(Fig. 2c).

Fig: 3TheMOSFET isswitched offwhenever theunregulatedsupply voltage is8 volts higherthan theregulated outputvoltage; thiskeeps thevoltaae acrossthe series regu-lator constant at8 volts.

EE

April 19E636

Um

660164

Fig 4 Thisopamp setupenables the out-put voltage to beset to 0 volts,without the needfor a negativesupply line.

Parts list

Resistors:

131;Re=102

R2;a2';Rs;Re=1k133:R3 =68042

Ra;Re;1110;Rie;

Rio:MA:12i;Rz1';1127;R:e=10k

R6;Re;RERs'=8k2R7',F17. =47k

139;119'=100k

fill:RW=39k1312;1112'=0.14:1W

Rtr;1317'=47k5;1%RicRiii;RIERis' =820kR1s;R1s';

Ris;Rui=182k;1%lizo;f12e=1k;1WRu;R22' =220Q

1123;f123'=82k

R24;112.1"=4M7

R2s;R2e;lits:Rze =82QPI;Pe=100k presetPa;Pi= lk;linear muttitum

P3;P3=1k;linearP4;P4'=1k;multiturn preset

Ps;Ps'= 50k:

muhiturn presetP6;136' =10k;muhiturn preset

Capacitors:

CI;C,"=3,343n

Cl...Ct:C2....C6' =47nCe;Ce;Ca;Ca'=10i440VCr;Cr'=2200u;40VCe;Ci=4701440VCt;Cii;Cis;Cle;

C17;C1e;CA;CA';

Cc;CD=100n.

the completed circuit boards beforeactually mounting them inside theverobox.Track layouts and component mount-ing plans for the preregulator andmain PCBs are shown in Fig. 5b and5a respectively. Note that these PCBshold all parts for the dual powersupply. The large free areas on themain PCB leave sufficient space forthe front -panel mounted multiturnpotentiometers. As shown in thephotographs of the completed unit,the main PCB is mounted vertically, a

little behind the front panel. Notethat this PCB is a double -sided type,but not through -plated, whichnecessitates great care in solderingcomponent leads, because this willhave to be done on both sides of thePCB.However, it is best to start construc-tion with the preregulator PCB: thereare two identical sections on thisconventional board; its completionshould not cause any problems. BothMOSFETs require a U-shaped heat-

sink, bolted direct to the transistor

rirjEE

April 1986

body. Fit soldering pins of suitablediameter into the holes marked1...4., l'...4' and -.Since the main PCB is mounted closeto the front panel, it has holes forcable feedthrouah. Four solderingpins are fitted on the PCB compo-nent side (points 5, 6, 5', 6'), andanother eight (1, 2, 4, 7, 1', 2', 4', 7') atthe soldering side.Because of the high component den-sity on the main PCB. some parts willhave to be fitted vertically, and theymust be soldered at both sides of the

PCB. This method of construction re-quires a certain amount of care andattention, since it is not easy toremove a part mounted in this way. Itis, therefore, strongly recommendedto start completion of the main PCBwith fitting these components. As forthe plastic metal -foil capacitors,make sure to leave a little space be-tween these and the PCB tracks toavoid short-circuits which are diffi-cult to find later. Note that C 5 andC15' are mounted at the solderingside.

0 0 -9

All ICs are preferably mounted insockets; the displays. however. re-quire wire wrap sockets with leadswhich are long enough to bridge thedistance between front panel andmain PCB; the wire wrap leads mayin turn be plugged into conventionalIC sockets on the main PCB. In anycase, the displays should be pressedto the red display window in the frontpanel to ensure maximumbrightness. The LEDs used in thispower supply are mounted in asimilar manner with suitable lengthsof solid wire.When all parts have been fitted ontothe PCBs. the supply wiring may bestarted with reference to Fig. 6.Wires carrying high current must, ofcourse, be of suitable cross-sectionalarea. whereas normal, thin wire issufficient for the connection ofpotentiometers and switches. Ingeneral, keep the wires as short aspossible.Transistors T5 and Ts' are fitted ontoa common heatsink. bolted to therear panel of the verobox. in which arectanaular clearance has beenmade to allow direct thermal contactbetween transistor body and heatsink. Do not forget the two insulatingmica washers and a genereousamount of heat conducting pastewhen fitting the power transistors.The aluminium front panel of theverobox is next drilled and debur-red. To get the holes in the rightplaces. use the template suppliedwith the self-adhesive front panelfoil.Before the PCBs are fitted into thebox, a support bracket will have tobe made from sheet aluminium(2 mm or thicker) - see Fig. 7. Thisbracket serves to hold the trans-former and preregulator PCB. whilstproviding a shield between trans-former and main PCB. since thebracket is connected to the mainsearth line.The verobox enclosure has anumber of guides for PCB mounting,but these will have to be removedwith pliers and a file before the PCBscan be fitted snugly. Remember todrill a number of ventilation holes inthe box, both in the lid and in thebottom plate to assist in cooling thepower transformer, preregulatorFET, bridge rectifiers. and other heatdissipating components inside.The pans DA. CA, and Ca must beconnected direct across the outputterminals, and a 100 nF capacitor.Cc. between the output minus ter-minals. while another 100 nF capaci-tor, Co. must be connected betweenone of these minus terminals and thealuminium front panel.It should be noted that both suppliesoperate completely indepently of

C12;Cle=220,1;10V

CII:C1,'=41;10VC12;C12";Cis:C13'=10p

C,.; C,.' = 820pCIECIs'=470,/;251:Cle;Cia' =270n;h1KT

Semiconductors:

B8005000,3303

Bz;132.=B40C1000

(rectangular type)...

DA; DA' = 1N4001

Ds;Ds;DE.;Ds'=1N4148

DI; DT' = 4V7;

400mW zener

Di'...DI:' =LED red

5mm

Ti;TI'= BUZ10A,iT2... TA: Ti

= BC5576

ilis;Ts'=TIP142Ti-;Tr'=BS170

Te'...T1:'=BC6401C11;1C1';IC.;ICA' = 7E1)5

icz;ic2i;tc,;fc3.=31401C5,1Cs' =3162

ICcICe =3161LD,...LD];

LE),"...LD3' =7751Thl:Thi'=TIC106

Miscellaneous:

FI=500mA slowS, =double pole mainsswitch

Sz; S2' = miniature

double pole toggleswitch

Trt =toroid transformer2 x 22V;2.6A and2 x. ffV;300mA

e.g. ILP 48533

(see note)

heatsink for Is and Ts'ISK08, 5Orriml

heatsinks for Ti and(e.g. SK13 or K13)

strain relief sleeve andgrommet for mainswire

6 off 14 -pip wire wrap

sockets5 insulated terminal

posts

veroboxType 075-014110

soldering pinsPCB 86018-1

PCB 86018-2

note: where a readymade transformer withthe indicated secondarywindings is notavailable, a standard2 x 22V toroid type maybe equipped with twoextra 8V windings bywinding about 65 turns26 SWG copper enam-elled wire around thetorpid core for each 8Voutput at 300mA. Thiscalls for about 30 feetof wire for each 8Vwinding.

EEApril 1986

Fig. 5 These arethe PCBs for thedual powersupply: oneholds twopreregulator sec-tions (Fig 5b),the other (Fig:5a) is a doublesided type forthe regulator anddisplay sectionsof both powersupplies. Notethat identicalparts in the sec-ond unit havebeen markedwith anapostrophe Q.

Fig. 6 Wiringplan for the dualpower supply.Keep cablelengths to aminimum anduse heavy gaugewire where highcurrent flows.

cvo

powermemo

preregulator PCB

main PCBEPS 86018-1

EPS 86018-2

0000

TIP 142 TIP 142

T5 :C ri

E

C

O

O52_

P

P

11 1 1.1 r4/1 P2

P2

00

0O

CA

CB

86016-6

L

each other, they do not have any con-nection in common and may,therefore, be connected in parallel,provided they have been set to ex-actly the same output voltage; thisenables the present design to be setup as, for instance, a 5V supply at2.5A.

Setting upThe necessary adjustments may bedivided into two groups: first, thereis the setting of the voltage dropacross the series regulator transistorsTS and T5' (PI, 131'); second, thepresets for calibration of the digitalreadout section (PA; PA'; P5; P5'; PS;Ps').For a speedy and precise cali-bration, use a digital multimeter(DMM), set to the 2A DC range.Turn PI and PI' fully anti -clockwiseto obtain a maximum voltage dropacross the series regulator tran-sistors.Connect the DMM direct to the out-put terminals of the supply to be cali-brated.Now turn the voltage control to a lowoutput voltage.Turn P3 (current limit) fullyclockwise and check if the DMMreads a short-circuit current of about1.25A; when this value needs to becorrected, RI, may be given a differ-ent value.Next, carefully turn P1 clockwise un-til the output current drops to zero.Turn PI once more slightly anti-clockwise to restore current flow,which will correspond to a voltagedrop of 8V across T5.

Since the other power supply is en-tirely identical, the same calibrationprocedure is followed. Note that thesetting of PI is fairly critical, and theoutlined calibration method is bestrepeated several times with bothpower supplies warmed up and ter-minated as indicated.Calibration of the display units isperformed as follows.Set S2 to the A' position and discon-nect the DMM.Set PS to obtain a zero reading (0.00)on the displays.Connect the DMM again and set thesupply to a current of IA on theDMM.Now turn P6 to obtain a reading of1.00A on the relevant display unit.The voltage calibration is also quitestraight forward.Set the supply voltage to give areading of 10.0V on the DMM, switchS2 to 'V', and adjust Pt to obtain thesame voltage indication on thedisplays.

39 EEApril 1986

72mm aluminium V3

T-

. 04

- edge

86016-7

Adjust the other display unit in thesame way.The maximum output voltage may beset to exactly 20.0V by altering thevalues of voltage dividers R1. -R16 andRiale, but note that each of these ismade of two resistors of equal value.

Pl;BL

Fig. 7 This alu-minium supportbracket acts as ashield betweenPCB and powertransformer.

220

197

220

ry

--f-----------1I i I

I

+ I II

-I - - - 4 -iTIA--7-'v17-

=.=._

7

8E05

103.5

485

98

EE

April 198640

RF CIRCUIT DESIGN

Fig. I. Represen-tation of FMband spectrumanalyses showingthat the noisefactor of the pre-amplifier stagedetermines to alarge extent thenumber of sta-tions that can bemade audible inthe FM receiver.

Third in the series, this article discusses aspects of goodVHF preamplifier design, before proposing a practicalcircuit that enables reception of FM broadcast signalshitherto lost in noise

VHF PREAMPLIFIERSome of the important aspects inaerial amplifier design have alreadybeen covered in Elektor Elecuonics,March 1986 issue, along with theprerequisites for successful VHFfilter realization. While the pointsdiscussed in that article remain fullyvalid, the present article aims to lookat the most important technicalcharacteristic of any VHF preampli-fier stage: its noise figure.While many of today's FM tunershave very sophisticated tuning con-trol systems and excellent stereodemodulation, the design of up-to-date RF amplification and first mixersections often deplorably lagsbehind. Since it is certainly not ad-visable to embark upon a completereshuffle of the proprietary RF partsin the receiver front end, an add-onpreamplifier stage of good designmay prove helpful in updating the re-ceiver performance to a con-siderable degree. Moreover, as theabove mentioned article alreadypointed out, a VHF aerial boostershould not be mounted in the re-ceiver, but at the other end of thedownlead coax cable, at the one andonly place where it is effective;direct at the aerial connections(masthead mounting).

NoiseThere are a number of basic con-siderations to go with design andconstruction of an RF preamplifierstage, if this is to operate in the veryhigh frequency (VHF) range, gener-ally referred to as 50...300 MHz. Asection of this band is of special in-terest for this article, namely the FMbroadcast band, which extends from88 to 108 MHz; while being quitecrowded with local stations in mostbuilt-up areas, only few stations maybe received in rural districts. This isdue to the straight line propagationcharacteristics of the RF waves atthese frequencies, which makes itimpossible to receive over -the -

horizon stations, except duringspecial weather conditions.A typical daytime FM -band spec-trum (= survey of signal strengthswithin a certain frequency band)may look very much as sketched inFig. la; there are a number of verystrong transmissions, as well as rela-tively weak and also nearly invisible(i.e. inaudible) ones, sometimes quiteclose to one another. This spectrum

is purely hypothetical, however,since it is a representation of relativesignal strengths at the aerial connec-tions, i.e. without noise caused byany active electronic device. Ob-viously, the spectrum analyser itselfwould feature a certain amount ofself -generated noise, but this hasbeen disregarded for the sake ofclarity. The low noise level Ni inFig. la is, however, present at any

VHF tn.-W1 dr

F 6 dB

- n dB

SI

N.1II-11 II I I I! 1 I I I I I I d11 f2 t3 108

lbRF1(ri Atem

so

N0

as12 13

1CRF signal A

so

Na

aa

111 11

12

iI

FM turd*

II 9 .0000 7G1: Qse

IMHz)

1Ga I ( MHZ)

Ii108 (MHz)

41 EEApril 1986

2BFR 34ABFR 96SBFQ 69

aerialinput p

0o

*Sit tEt t IR4

PI 12V <25mA

C7

to receiverinput

VHF aerial, since this picks up a cer-tain amount of atmospheric noise;the nature of this effect would leadus into theoretical physics, which isbeyond the scope of this article.Spectrum analysis of the preampli-fier output signal (Fig. lb) reveals thatwhile all signals have beenamplified, a certain amount of ad-ditional noise is introduced by theaerial booster, to the effect that somesignals have got lost underneath thenoise threshold No and are,therefore, inaudible in the receiver.Since the amplifier noise output isnot caused by amplification of the at-mospheric noise level Ni (comparethe signal levels of h in Fig. la andlb), level No must needs begenerated by the amplifier itself;clearly, this is an undesirable effect.If we consider the effective signalstrengths of, for instance, the trans-mission at ti in Fig. la as opposed toFig. lb, the total noise factor of theamplifier stage may be defined asthe overall ratio of the outputsignal/noise ratio to the inputsignal/noise ratio, or

F. (So/N0)/(SM) (1)

the noise figure may be calculatedfrom F using

Fel5=10logioF (2)

Clearly, So/No for fi is worse (lower)than the original Si/Ni and this arisesfrom the extra amount of noisegenerated by the amplifier. Werethis device ideal, then

So/No=Si/Ari or F=1, or &is = OdB (3;

Unfortunately, no electronic devicehas been developed as yet for use inthe ideal preamplifier, nor will it everbe developed, due to some basiclaws of physics. However, modernSHF transistors are now readilyavailable with noise figures as low as1.5 dB at 1000 MHz, while GalliumArsenide (Ga-As) FETs have been de-

signed to achieve 2.8 dB at 12 GHz;however, the cost and circuit designcomplexity of these devices putsthem well beyond the reach of theaverage home constructor.The importance of a low preampli-fier noise figure is evident after acomparison of Figures lb and lc;while its signal gain (amplificationfactor) is still ndB, the amplifier ofFig. lc has a noise figure improvedby 4 dB, which enables reception ofsignals that were inaudible with theF=6 dB amplifier of Fig. lb. We may,therefore, establish the general rulethat reception is improved with alower preamplifier noise figure.Thus, designing for low noise shouldbe a high priority issue.So far, only the active device in thepreamplifier has been held respon-sible for the noise addition, but itshould be pointed out that thisdevice can only attain its minimumnoise contribution when supportedby passive components that ensurethermal stability and low signal in-sertion loss at the amplifier input. Itwill stand to reason that anymismatch at the booster input willadversely affect (i.e. increase) thetransistor noise figure as given in themanufacturer's data sheets.No preamplifier stage, however lowits noise figure, will be capable ofreception improvement if the signalsat the target frequency have beenconsiderably attenuated before be-ing applied to the first active device,either by downlead cable losses or asevere mismatch at the booster in-put. As the above mentioned articlepointed out, however, the preampli-fier input necessarily consists of alow -loss filter, which serves the dualfunction of an out -of -band signal at-tenuator and signal source to transis-tor input impedance transformer(source matching). It should be fairlyobvious by now that the actual gainof the booster is far less importantthan its noise figure; if the former issome 10 dB higher than the down -lead cable attenuation, adequate

results are usually obtained; a gain of15...20 dB is common for a single -transistor preamplifier stage.

Practical circuitThe circuit diagram of the presentVHF preamplifier is shown in Fig. 2.The RF signal at the input is passedto the base of Ti by a capaci-tance -tuned, inductive top -coupled,low insertion loss and source match-ing bandpass input filter with a-2 dB bandwidth of 20 MHz (88....108 MHz). This is quite a mouthfulfor a basically simple filter that per-forms the functions outlined above.Note the taps on Li and L2 to obtainimpedance matching of the cableand the transistor respectively. Anyof the listed transistor types may beused in the circuit, but the TypeBFQ69 is preferable because of itsextremely low noise figure. Sincethis transistor has been introducedonly quite recently, however, it mayprove difficult to get hold of.The amplifier is fed by the receiverpower supply over the downleadcoax cable; the parts to the right ofthe dotted line are, therefore,mounted in the FM tuner. Decoup-ling parts Ls and Cr ensure that noRF signal is lost in the power supply.The amplifier bias setting is effectedwith Pt; depending on the transistorin use, this preset may be adjusted tofind the right compromise between

Fig. 2. Circuitdiagram of thelow noise aerialamplifier withreceiver -mounted supplyparts.

EEApril 1986

42

3noise figure

gainnoise figure

F=t lil F nfll14:18) UcE = 10 V; I, = 15 rnA; (48) LICE =10 :1 500 MHz :Zi Zept 148)2.0 2.0 30

Fi1.8Ft1.8

Gassi

BFO 69 BFO 6916 1.6

1.4 1.420

1.2 1.2

1.0 1.0_min.

0.8 0.8

100.6 0.6

0.4 0.4

0.2 0.2

O 0 O200 400 600 800 1000 10 20 30 40 50 O0 0414) 0 (mA)

11c1

UcE = 10 V ; 5001214t ; 2opt

I I

BFQ 69

I I

,at:

10 20 30 40 50 (mA)-orIc 86038.3

Fig. 3. Curvesshowing thecharacteristics ofthe new BFQ69transistor. Notethat the curves inFigures 3b and3c refer to a testfrequency of500MHz and notto the design fre-quency ofpresent pre -ampler.(Siemens)

Fig. 4. This RFdesign is also fit-ted on theuniversal pro-totyping board85000, availablethrough theReadersServices.

optimum noise figure (low current)or maximum amplification with ac-ceptable intermodulation response(high current). For further details onthe bias setting of RF preamplifiertransistors, refer to Elektor Elec-tronics, February 1980 issue. Fig. 3shows three curves relevant to the

novel BFQ69; a collector current of15 mA appears to be suitable for aminimum noise figure of about 1 dB,which will bring the total noise fig-ure of the present design in the1...2 dB range with a Type BFQ69fitted and the filter tuned to optimuminput matching. However, the Types

4

A:101313001:11:1CI CI CI El

130001:10011301:1C1

.13001:1130

rrifirsett-

Pr

C2

earC4 CiL3

LlL2

C6110

BFR34A and BFR96S will also ensurea noise figure that is usually far betterthan the average FM tuner specifi-cation in this respect.The coils and chokes for the presentdesign are wound as follows:Li = 4 turns 20SWG 1 mm) enam-elled wire, close wound on dia.6 mm, tap at 1.5 turns from earth.L2 = identical to Li, but tap at 2.5turns from earth.L3 = 11 turns 20SWG enamelled wireon toroid core Type T50-12 (Amidon).L4; Ls = 4.5 turns 30SWG (¢ 0.3 mm)enamelled wire through 3 x 3 mmferrite bead.For more information on inductorcalculations and specifications, referto last month's issue of Elektor Elec-tronics.

Construction andalignmentThe present amplifier is fitted on theuniversal RF board 85000 as shown inFig. 4; not shown are the bias settingparts, since these are mounted in thereceiver. After completion, the unitmay be tested by tuning the receiverto a weak transmission at about95 MHz and adjusting CI and C2 foroptimum reception. The collectorcurrent setting should be fairly un-critical; its precise effect on theamplifier performance can only bejudged when a very stable and yetsufficiently weak transmission is be-ing received and the input filter hasalready been correctly tuned. Fi-nally, the preamplifier may be fittedin a suitable water-resistant case formasthead mounting, equipped withsuitable coaxial sockets, and fixed tothe aerial mast.

JBJB

43 EEApril 1986

CORRECTIONS/MITT scanner(March 1985, p. 24)In a number of PCBs for thisproject two connections havebeen omitted. Check, therefore,whether there are connectionsbetween IC2 pin 16 and IC3 pin16, and between IC3 pin 3 andIC3 pin 4. If not, make themwith a short length of wire.

Mixer

86012-1

86012-2A

Active subwoofer(March 1986)Owing to a printers' error,

Figures la and lb (p.29) havebeen interchanged.The end of paragraph 2 on p.33should read: (use 68 nF or0.1 pF)

.?MrAcee-gc

86012-2B

BF Circuit Design-2(March 1986)The value of fin Fig. 4b (p.53)should read 65.0 MHz, not65.0 Hz.

MSX Extensions-3(March 1986)The caption to Fig. 5 on p.60should have read: "For slotsignal functions see Infocard121 on page 81 of this issue".Note that further informationon the connector is given inInforcard 122 in this issue

EE

April 198644

MAKE YOUR OWN PCBS

MAKE YOUR OWN PCBS

86012-4

I0

3ww

IS t

Real-time clock 86017

Satellite loudspeakers 86016

vl

EEApril 19E6

46

MAKE YOUR OWN PCBS

EEApril 1986

li

'TERS LETTERS LETTERS LETTERS L

Dear Sir-May I first con-gratulate you on anexcellent magazine. Ihave at present a fullyfunctional 6502 House-keeper and a functionalRugby Receiver. What Irequire though is theEPROM for the Rugbyreceiver in order to beable to combine thesetwo excellent projects. Asfar as I am aware, theEPROM was neveravailable from yourselvesor from Technomatic.Since you have a fullyoperational RugbyHousekeeper, would it bepossible for a copy of theEPROM to be made? Iwould, of course, pay forthe necessary costsincurred.

GEORGE PAVLOUEDGWARE, LONDON

Contrary to your infor-mation, the EPROM isavailable from ourselvesor from Technomaticunder No. 512. Successwith the completion of theproject! Ed.

* * *Dear Sir-I must say in allhonesty that I am not aregular reader of yourmagazine, but a friendhas suggested that youare always very helpfulwith queries. I am anamateur botanist of somestanding, and I urgentlyrequire information, cir-cuits, etc. for a BIO-FEEDBACK machine withaudible and/or visibleoutput for plant experi-ments. If you can help inany way in this matter, Iwould be extremely grate-ful.

G K ALLEN M.Inst.M.NEWHAVEN EAST SUSSEX

I can say in all honestythat I know very littleabout botany andi can-not, therefore, suggest areally suitable circuit for a

810 -FEEDBACK machineNone the les& the follow-ing may be of interest toyou: Electronics and PlantPhysiology (EE, July 1983);pH Meter (EE, March 1985);and House Plant Protector.The last title appears inone of our books, Projectsfor Home and Garden./hope one (or more) ofthese may prove useful toyou. Ed

* *Dear Sir-I am one of yourmagazine's subscribers inIran. I decided to makethe VDU card board (EE,September 1983), butfound that there is no fig-ure of the printed circuitfor this board. Also canyou please supply thecontents of the 2732memory?

S ALI MIRPOURTEHRAN

It is very difficult, if notimpossible, to make thedouble -sided board (withplated -through ho/es) athome, but the completeboard is still availablethrough our Readers' Ser-vices (No. 83082). Similarly,the only way of obtainingthe contents of the 2732memory is to buy thisEPROM (No. 525) throughour Readers' Services Ed.

* *

Dear Sir-Thank you foryour letter of 22 Novemberlast answering my querieson the Wireless Micro-phone project of June1984. Unfortunately, I havecome up against onefurther blockage, namelythe supply of L3 for thereceiver part, rated0.82 pH, for which I cannotfind a supplier. Could youplease advise one?

A J BRADLEYAUGHTON, ORMSKIRKLANCS

Dear Sir-With reference tothe Personal FM(September 1983) I amhaving difficulty in obtain-ing the 0.22 pH coils andL3 (=Toko E526HNA100114). Ihave tried Cricklewoodand Technomatic, butneither of them stock theseitems. Can you help?

M GULAMHUSEINPETERBOROUGH

RF inductors from 0.10 pHto I pH in ten standardvalues are available fromElectroValue (limitedrange) at (0784) 33603 or(061) 432 4945; Maplin(limited range) at (0702)552911; or STC ElectronicServices (full range) at(0279) 26777 CirkilHoldings PLC at (0992)444111 is the soledistributor for Toko in thiscountry and they should,therefore, be able tosupply the E526HNA100114)Ed

* * *

Dear Sir-For some time Ihave been a regularreader of the GermanElektor and have recentlybecome a subscriber toElektor Electronics. I hopeto see construction articlesfor video equipment, e.g.an enhancer with fadefacility, or a converter(Mac D to PAL) for use witha small dish antenna inpreparation for the futureDBS satelite TV transmis-sions.I have already con-structed the video ampli-fier and incorporated asound mixer to take in theoriginal sound from thevideo tape plus twofurther sound inputs: formicrophone and music,and it works first class.Incidentally, I built thevideo colour inverter(October 1984) and Iwould like to hear fromany reader who SUC-CESSFULLY built this projectas in my case I cannot

obtain the change fromcomplementary coloursthrough black/white(where it stays) to normalcolour.I would also like to see aconstruction article for aseparate Mier; I assume itmay be a little tricky, butas many video camerashave such a facility, theremust be a chip in exist-ence to do it.

FRANK CROXSONUHLINGEN-BIRKENDORFBRD

Your suggestions for futurearticles have been passedto our technical boffinswho, hopefully, will comeup with some sort ofanswer in the near future.The idea of the Mac D toPAL converter looks par-ticularly promising as weare already thinkingalong these fines / havesent a copy of your letterto the designer of thevideo colour inverter foradvice on the difficultiesyou are experiencing; assoon as I hear from him /will be in touch again. Inthe mean lime, some otherreaders may come upwith helpful suggestionsEd.

* * *Dear Sir-I am faced withhaving to build a high -quality audio pre -amp.Any designs applicable inElektor Electronics publi-cations? Thanks inadvance.

G ADAMSPOOLE, DORSET

Suitable designs might be:MC/MM Phone Pre -ampli-fier (April 1983) and/orDynamic Pre -amplifier(October 1984). Of the two,the first is probably themore suitable for your pur-poses Ed.

EE

April 192648

PORTABLEMIXER 1

This mixer is not designed for the occasional party, whereone slide control per channel will suffice. Rather, it isintended for the serious electrophonics enthusiast. Andquite naturally, therefore, it has all the facilities such usershave come to expect.

Professional mixers are expected tomeet a long list of special re-quirements: balanced and unbal-anced inputs and outputs; indepen-dent control of each channel for driv-ing special effects equipment andmonitors; automatic setting of inputsensitivity to match the signal level;multiple tone controls per channel;and many more. No wonder that suchmixers are. to put it mildly, pretty ex-pensive. It is. however, possible, to

build one of comparable quality atmuch lower cost. as described in thefollowing pages.

ModularconstructionThe mixer is constructed from fourmodules. A fifth module provides

the power for the entire mixer.The mono input unit is almost cer-tainly the most often used module. Itsinput sensitivity is adjustable be-tween 0 dB and +60 dB. This enablesall sorts of mono signal sources, frommicrophone to keyboard. to be con-nected to this module. The unit isprovided with a three-way tone con-trol; a peak indicator for possibleoverloads; a monitor; a multi -track orPFL (pre -fade listening) control; and

49 EEApril 1986

a panorama control. Balanced inputsare standard, but any of these can bemade unbalanced by connectingone of its terminals to earth.The stereo input unit is intended foruse with a wide variety of signalsources. Its input can be switchedbetween MD (variable -reluctancepick-up), AUX (high-level stereo),and LINE (mono). The latter positionis for use in the event the monomodule is not available. The balancecontrol functions as panorama con-trol when the input is switched toLINE.The headphone -monitor modulecontains a stereo headphone ampli-fier via which each module may bemonitored. Unlike the other mod-ules, this unit is provided with aparametric equalizer instead of athree-way tone control. This is a veryuseful facility, because it enables anytendency to acoustic feedback be-tween the microphone and monitorloudspeaker to be suppressed effec-tively. The main controls and outputterminals of the special effects chan-nel are also fitted on this module.The most important unit is the outputmodule. Apart from the main tonecontrol and other refinements, it hasa stereo LED VU (volume unit) meter.The output is available as a balancedor as an unbalanced signal.

Power supplySince any equipment is only as goodas its power supply, all the supplylines in the present mixer arestabilized twice: once in the powerunit and once in the relevant module.Apart from its mains transformer andon/off switch, the power supply unitshown in Fig. 2 is contained on aseparate printed -circuit board. It issuitable for the supply of up to eight-een modules.Regulators ICI and IC2 hold thesupply voltage, preset with the aid ofR3 -R4, at +18 V. Transistors Ti and T2and associated RC networks ensurea sufficiently slow rise of the supplyvoltage to prevent loudspeakerclicks when the mains is switchedon. Resistor Rs is a voltage -dependent resistor that suppressesnoise present on the mains.Switch S2 enables the mains earth tobe isolated from the case earth,which may be necessary in certaintheatres. If S2 is open, and somethinggoes wrong, neon lamp Lai breaksdown, and the mains fuse blows.The values of resistors R3 and RA canbe ascertained precisely for any in-dividual power unit by replacingthem by two 5 k preset poten-

i136012.1F I

(I)ON

POWER

IED

86012-4F1

tiometers. Adjust these presets untilthe output of the relevant regulator is18.1 V. Switch off, remove the presets,and carefully measure their valueswith an ohmmeter. Fixed resistorswith values so found should then besoldered in the R3 and le positions(this may, of course, entail making upa parallel combination to obtain thecorrect value). Check that the outputvoltages of the regulators are still+18 V.

MIC-LINE moduleAlthough the number of presets maygive the impression of complexity,the circuit in Fig. 3 shows that thiswould be misleading. Operationalamplifiers At, A2, and A3 form an in-strument amplifier that- providesproperly balanced inputs.The sensitivity of the microphone in-put is about 20 dB higher than that ofthe line input.

Fig. I. The frontpanels of (a) theMIC-LINEmodule; (b) thestereo module;and (c) thepower unit.

EE

April 1986 50

2

Fig. 2. Circuitdiagram of thepower unit.

S1OV510K250

F1

0

1A

R1 0 VDRR8

Cs

47n250 V-

1

LM337J

Tr 1ILP 11014 D1 ... D4 = 4 x 1N5401

5 CI....04.4x 47 n

11S2,

18e0 GROUND

Loa

LM 317

Cl

-1DI

D3

8

2.1B V

830 mA

C12

100n250 V -

CASE GNO

*sae tart

C2

D2

05

1N4001

C6 CB

Mml4700p 40V

LM

K1

317R2

as.

adj.

R3

00n

Cl C9 R4

immi mos47005. 40V 100,,

41.

BC557B

R

61171

72

BC547B

C13CI-loll25V

C1021.2

C11

25V

C14

R7

0

0

LM337

R5

10p25V

13

0

DO

1N4001B6012-2

-18V

-113V

To keep the overall noise level down,Al and A2 are low -noise types, whileR1 to R13 incl. are high -stability (l%)metal film resistors.Gain control PI, which enables set-ting the gain between 20 dB and60 dB, must be a high -quality type,because it is located in a noise- andscratch -sensitive position.The peak indicator is formed by tran-sistors T1 and Tz . The threshold ofoperation is fixed at 9 Vpp or 3 Vrrrsby voltage divider R14 -R15. Theselevels correspond to a microphoneinput of 3 mNfrins at maximum amplifi-cation. Reservoir capacitor C3 en-sures that short -duration overloadsare also clearly indicated.Coupling capacitor C4 prevents anyDC reaching the potentiometers andconnects the amplified input to thethree-way active (A4) tone control. Ef-fects control P2, of course, precedesthe tone control stage.Potentiometer P6 sets the wantedmonitor output level.Stereo slide potentiometer P7 is thefade control.Since a signal to drive a multi -trackrecorder is also required, slide con-trol P7 -the fader- is a stereo typeto prevent any feedback between

the stereo channel and the multi-track outputs. An alternative to thisarrangement is to provide eachchannel with a PFL (pre -fade listen-ing) facility; C,2 -R26 can then be omit-ted, P- can be a single track control,and S1 and R32 are fitted externally.

Stereo inputmoduleThe stereo input module -seeFig. 7- has no balanced input: in-stead, it is provided with an equaliz-ing pre -amplifier, formed by AI andA2 (Ai' and A2'), for use with variable -reluctance pick-ups.Input selection is effected by Si: pos-ition 1 is for variable -reluctance pick-ups; position 2 for high-level inputs,such as from tape recorders; andposition 3 for mono signals.Position 3 is for use when the MIC-LINE module is not available, or, forinstance, when more equipment is tobe connected than was originallyforeseen. Note, however, that onlyline signal sources can be connec-ted: not microphones. The (un-balanced) signal is then taken from

the right-hand AUX input, andamplified in A2 and A2' by a factor 3.Stereo potentiometer P1 provides amonophone effects signal, but is ar-ranged such that its input and outputresistance are equal, whatever theposition of the wipers.The active tone control is followedby the controls for the monitor out-put (P5), the channel output (Ps), andthe balance (P7). With SI in position 3(LINE), the balance control functionsas panorama control.The pre -fade listening facility is con-structed with (external) componentsRs, Rio, and S2.A multi -track output is not necessaryin this module, because the unit isnormally fed from a multi -track tapemachine.If the MD input is not required, theoperation of AI (AI') can be made lin-ear by omitting CA and Co (C4' andC5'), and replacing RS and R5 (R4' andR5') by Rx (Rx'). The value of thenew resistor may be calculated from

R x =R3 (a-1) [Q]

where a is the amplification of theamplifier. If the amplification is large,R x = R3.

EEApril 1986

Parts list

O

Resistors:

R, =2M2R2 = 220 Q

R3 =3k6'RA =2 leRs= 120 Q

Rs;Fir =47 k

Rs= voltage -dependent

resistor SiemensType S10V-S10k250

(may be available fromElectroValue -telephone 0784 33603

or 061 432 4945)

Capacitors:

C,...Cs =47 nCs =47 n;250 VACCE -,C2= 4700 u;40 V

Cs;C9= 100 n

CIEC,1=222:25 VC12=100 n;250 VACCu:Cu= 10 kr;25 V

Semiconductors:

Di... D4 = 1N5401

Ds; Ds= 1N4001

Ti = BC557B

T2 = BC54713

ICI = LM317TIC2= LUIS/ I

Miscellaneous:

Si =-SPST mains switchsuitable for PCBmounting

Ss=SPST switch= miniature fuse; 1 A;

delayed action;complete with PCBtype carrier

La, = neon bulb withoutbias resistor

La2=neon bulb withbias resistor

Tr, = toroidal mainstransformer; 2x 18 V;0.83 A secondary(e.g. ILP Type 11014)

1(1=13 -pole PCB

connector to DIN41617Heat sinks for IC, andIC?

Front panel foil86012-4F"

PCB Type 86012-4"

* see text available through our

Readers Services

(see p. 82)

Fig. 3. Theprinted -circuitboard for thepower unit.

EE

April 1986

Fig. 4. Circuitdiagram of theMIC-LINEmodule.

Parts list

Resistors:

R1=100REFts =1 le134;RERa:Rs;Riz:

R13 = 10 le

Re= 100 4*R7 =6k8*

RIERti =2k.2*R14=47 kfils:Fils=6k8Rir=1k5RIs;Rzs;Rao;R31;

R32=22 kRacRacRzt;R24= 10 k

R22;R:ERze;R:s=3k3R26; R27 = 100 k

R33 = 1 M

P,=25 k linearpotentiometer

Pr:Ps =25 k logarithmicpotentiometer'

P3 . P5= 100 kfinearpotentiometer'

P7 =10 k log stereo slidepotentiometer 58 mmlong

1% metal film type" with 4 mm spindle

for PCB mounting

Capacitors:

(potycarbonate orpolystyrene unlessotherwise indicated)CI;C2= 15 pC3=2p2:16 V;

electrolytic

C4; C =10 14;40 V;bipolar electrolytic

Cs =47 nCs = 5n6

C7=22 nCa;Cs=4n7Cis= 10 pCia =470 nCls= 220 nCis:Cis= 100 nCie;Ctr= 100 p

= 10 µ;16 V;electrolytic

C20 = 1120 n

Semiconductors:

DI:Dz= 1N4148D3 = LED; red

T1;Tz=BC558BICI =NE5532 or LM833IC2 = LF356 or TL071

IC3 = TL072

IC4=XR4195 (see fig. 6)

Fig. 5. Theprinted -circuitboard for theMIC-LINEmodule.

- 1 i

MIA

lea . -0(.*

Al. A2 - ICI = 111/92. LIA$33/CZ = IS356. 11071

A4.Ar ics , 11072

0

(1),01,,

ICI ICI ICI 7.1

011sv

RIP

1C4

33.

rn

01 0 0 0 0L., _0026 ri0.1R29 [0

CH I-CP(2

0-I R27;Pi"'n_ oiR31

1001R28 IO0 rinnitta 01R30

IC3 0..11=1251-0VVII

C.10

Eck ,4no -I

2 ca44,331-o

1C4CMIVC/

+Anam

ono01

0.10'44-Owls

Foc5(>IR211001R201001F:1240

0-11-° C50--43 FC)C7

oi R231-0

0.1R24 Es

010'5W

CH R6 1-0 oi R11_0 O. R 2 1O1.0

0.i R3 JO -6-oiR 4

7crO_ 4 L:0 0 ti! 0

13

EEApnl 1986

Capacitor C1 (C1') may be adapted tomatch the output impedance of thetape machine used.

ConstructionBefore buying any new components,it is wise to determine how manymodules are required.Prepare the printed -circuit boardsshown in Fig. 5, Fig. 8, and Fig. 9;note that the board in Fig. 8 consistsof two parts, which must beseparated before any componentsare fitted.The dimensions of the front panelsare given in Fig. 10: 10a is that for theMIC-LINE module; 10b that for thestereo module; and 10c that for thepower supply. The overall lengthwill, of course, depend on the casesused. The prototype was built in onealuminium case with compartmentsfor the various modules. The con-struction of this will be described innext month's issue.In the mean time, the completedmodules may be tested by connect-ing their outputs to the TUNER or

5

"0 0" ma*.Lea

LO a

no1.3e,3lOOF101

133.rw

SOW 11.1t

32 AI p. 331 Om

A1 . A2 = IC1 = AlE5522, LA1633A3 . Al = IC2 = TIL1772

Al. AY . ICI liMEM LLAv. AY - ter - non

VS V

15 V

=C.) 1.1") "or1C1 11:7

IC1' Kr

;.%

.0AIrVC

3:3

351.

Miscellaneous:

Si =mini SPST switch3.5 mm insulated stereochassis socket (6.3 mmdia. mounting hole)

XLR Cannon -type 3 -pin

chassis socket13 -pole PCB -type con-

nector to DIN41617Knobs for potentio-meters as required

Front panel foil86012-1P

PCB Type 86012-1'

' available through ourReaders Services

(see p. 82)

Fig. 6. Where aType XR4195voltage regulatoris not available,it may be re-placed by a78L15 and a791,15 connectedas shown here.

Fig 7 Circuitdiagram of thestereo module.

EEApril 1986

Fig. 8. Theprinted -circuitboard for thestereo moduleconsists of twoparts, whichmust be cutapart before anycomponents arefitted.

Parts list

Resistors:

131;RI';RER2' =100 k1:17;R7';RII;RII';RIE

RI3';Fi2t;Rri'= 100 kR3;R3' =390 4*RcRe =16 kRs;Rs'=200 lc'licRe;RERs' =1 MREF110;1320;Rzo';R2r;Rri;

R23:1:123%R24:R21%R26;

Hie = 22 kfilr;R,2'= 47 k11,4;RI4';Ris;Rrs';R16;

1:115';Ri9;Rli'= 10 k

=3k3Rrs;Firr: = 56 kR27;Rn=fik81:179 = k5

R35 = 1 M

P1=25 k linear stereopotentiometer+

122...P4=100 k linearstereo potentiometer

Ps =25 k logarithmicstereo potentiometer+

Ps = 10 k logarithmicstereo slidepotentiometer 58 mmlong

Pr = 10 k linear stereopotentiometer

1% metal film type+ with 4 mm spindle

for PCB mounting

Capacitors:

Ipolycarbonate orpolystyrene unlessotherwise indicated)CI;CI"; =100 n

(see text)Cz;Ci;Ce;C6';Cr:Cr';

Cis;Cle =220 nC3:C3'= 100 ;46.3 V;

bipolair electrolyticCr;C4'=4n7Cs;Cs'= 15 nCECts;Czo;Crs;

C25=100 nCs; Cs' =470 nCo:Cid:Cyr;

= 10 p;40 V:bipolairelectrolytic

Cii;Cti'.47 n=5n6

C.13;CI3'=22 nC14;CIA':C15;Cie;

ClcC15.= 10 pC2 I:C22 = 100 p

C23;Cra =10 p;16 Velectrolytic

C27=2p2;16 Velectrolytic

8b

C1/4".kCC %2) flT4 86°12 620.20

coCkm,/ ° ° e$D41119Th M r+"gt11Lc7)

S7i4&4/ LT7cfj

EEApril 1986

AUX input of a stereo power ampli-fier. and injecting a suitable signalinto the various module inputs. Thecorrect operation of all poten-tiometer controls can then bechecked.

Part 2 of the Farrahle Mixer will ap-pear in the May issue of ElektorElec-tronics.

10

3

25

A

v VVVVVV

313-1F

;5

14

2 2

_5312.2F

4 65

12325

56313-4F

vv v

86012 - 9/10

Fig. 9. This il-lustrates how theboards can bescrewedtogether.

Semiconductors:

D,: D2 = 1N4148

= LED: red

= BC557B

ICI;IC,'=NE5532 orLM833

= TL072

IC3= XR4195 (see fig. 61

Miscellaneous:

Si =3 -pole 3 -position

rotary switchSz = DPST mini switch3.5 mm insulated stereo

chassis socket (6.3 mmdia. mounting hole)

XLR Cannon -type 3 -pinchassis socket

13 -pole PCB -type

connector to DIN41617Knobs for potentio-

meters as requiredFront panel foil86012-2F'

PCB Type 86012-2'

available through ourRe: tiers Services

(see p. 821

Fig. 10. Drillingplans for thefront panals.- (a)the MIC-LINEmodule; (b) thestereo module;and (c) thepower wig

EE

April 198656

NewcataloguesNote that catalogueslisted here may not befree of charge, althoughmost of them are. Further-more, not all businessespublishing a catalogueare prepared to acceptorders from other than pro-fessional or businesscustomers.

Texas ICapplicationsbookThe first volume of a newseries of semiconductordevice applications hand-books, Linear and Inter-face Circuits Applications,dealing with amplifiers,comparators, timers, andvoltage regulators, hasbeen announced by TexasInstruments.After a brief introduction,which explains that thebook will help the user inunderstanding theoperating principles andcharacteristics of the widevariety of devices, comesa useful summary of oper-ational amplifier andcomparator theory.Applications for oper-ational amplifiers andcomparators follow, featur-ing over 20 circuits includ-ing active filters,oscillators, and generators.The operation of each cir-cuit is explained, withclear circuit diagramsand brief derivations ofimportant equations.

This approach makes thebook useful to the studentand amateur as well as tothe professional designengineer. Another attrac-tion is that the selectedcircuit examples have ac-crued from customer in-quiries and relatedlaboratory simulations. Inmany cases there aresolutions to actualcustomer designproblems.Linear and InterfaceCircuits Applications:Volume 1 is available at£6.50 per copy plus £1.50for postage and packingfrom

Texas Instruments LimitedP 0 Box 50Market HarboroughLeicestershire

Threebrochures fromLucas NSFLucas NSF have recentlypublished technicalliterature for three newproduct groups.Subminiature rotary codeswitches. This switch rangegives a wide combinationof coded and sequentialoutputs in a subminiaturepackage. The literaturecontains details of theswitching capabilities, fulldimensions, and mechan-ical and materialsspecifications.Miniature surface -mountelastomeric push -buttons.Two sizes, two shapes, andten colours, plus siliconrubber technology andsurface -mount; full detailsof the Series EAS,M includ-ing dimensional andmechanical parametersare contained in this newpublication.Keylock rotary securityswitches. These newswitches provide econ-

omic and secure accessto high -cost facilities. A six -position key -operatedmechanism gives 1024possible combinations inan economical and com-pact package. The leafletcontains dimensional anddesign specifications aswell as technical data.Lucas NSF LimitedKeighleyWest Yorkshire BD21 5EFTelephone: (0535) 661144Telex: 51270Fax: (0535) 681980

VME-buscapabilitycatalogueBICC-Vero has published auseful 36 -page, full -colourcatalogue detailing itsflexible range for configur-ing VME-bus solutions(VME=Versatile ModuleEurope). The cataloguedetails the complete spec-trum of componentsnecessary for buildingsystems, including ac-cessories, racks, boards,power supplies, systems,and software.A copy of the catalogue isavailable free on requestfrom

B/CC-Vero ElectronicsUnit 5Industrial EstateFlanders RoadHedge EndSouthampton SO3 3LGTelephone: (04892)Telex: 477984

FrequencycontrolcatalogueImproved purchasingmethods and larger stockholdings have enabledIQD to reduce the pricesof many of their standardproducts. The cataloguealso contains several newdevices that will be of in-terest to many engaged in

electronics and com-puters.Extensive stocks, first-classtechnical assistance, andcompetitive prices makeIQD a leading supplier ofcrystals, filters, resonators,oscillators, and other fre-quency control com-ponents.

IQD LimitedNorth StreetCrewkerneSomerset TA18 7ARTelephone: (0460) 74433Telex: 46283Fax: CCITT Group II

Crystals andceramicresonatorsAn illustrated 6 -pagebrochure illustrating theirrange of crystals and cer-amic resonators isavailable from GolledgeElectronics. The companycan also provide crystalsmade to order.

Go//edge ElectronicsMerrioltSomerset TAM 5NSTelephone: (0460) 73718Telex: 46529

New brochurefrom PowerlineA new brochure giving fulltechnical specificationson their Victor range ofpower supplies is nowavailable from PowerlineElectronics. These newunits switch at frequenciesof up to 1 MHz and at zerocurrent and are claimedto produce half the heatand an order ofmagnitude increase inpower density over con-ventional switchedmoderegulation units.

Powerline ElectronicsLimited5 Nimrod WayElgar RoadReadingBerkshire RG2 OEBTelephone: (0734) 868567Telex: 847973

EE

April 1986

GigadiscOptical DiscThe considerable userbenefits of optical datastorage technology overconventional recordingtechniques are explainedin a new 4 -page publi-cation from Thorn -EMIDatatech Limited.The brochure describesthe performance of thenew Gigadisc optical discdrive system, for which thecompany has the sole UKmarketing rights. The laser -based system offers theability to record 2Gigabytes of digital dataon each double -sided 12inch disc. Guaranteedstorage life is over tenyears.The Gigadisc system canbe used with virtually anytype of computer systemand is the first readilyavailable product of itstype with a writelreadcapability.Copies of the brochureare available free on re-quest from

Marketing DepartmentData Products DivisionThorn -EMI DatatechLimitedSpur RoadFellhamMiddlesex TW14 OTDTelephone: (Of) 890 1477Telex: 23995

New mainsfiltersA F Bulgin & CompanyPLC has published a newbrochure illustrating itsbroad range of mains in-let filters.Designed to protect elec-tronic equipment frommains -borne interferenceand to reduce any similaremission the equipmentitself may produce, theBulgin range of mainsfilters incorporates modelssuitable for baseboard,bulkhead, panel, or PCBmounting with currentratings of 1 to 10 amperes.Complying with inter-

national specifications,with approvals eithergained or pending, allBulgin filters, with the ex-ception of PCB mountingversions, are enclosed indrawn steel casings, withprovision for earthing. Allversions are encapsulated.Medical filters PS621 ex-hibit exceptionally low -earth leakage currents ofless than 100 µA, while inall other types leakagecurrents are less than350 A.A F Bulgin & CompanyPLCBypass RoadBarkingEssex IGII OAZTelephone: (Of) 594 5588Telex: 897255

friendlyprogrammerA six -page colourbrochure, Concentratedprogramming, describesthe new ROM 5000D pro-grammer from Micropross,for whom Euro Electronicsis the UK distributor.The 5000D is a completesoftware engineering workstation designed to relievethe user of all tedious ef-fort. It provides the ease ofoperation that is expectedtoday, and programmes,verifies, and tests PALS,PROMS, EPROMs, IFLs, andembedded -memorymicrocomputers.

Euro Electronics LimitedLancaster Gale House319 Pinner RoadHarrow HAf 4HFTelephone: (01) 863 0811Telex: 23848

Comprehensivefuse catalogueNow available from GCAElectronics is the latest132 -page, full colourcatalogue Buss Fuses, acomprehensive guide to

the range of Bussmanfuses, fuseblocks, and ac-cessories.GCA is the fully franchisedUK distributor of the entirerange of Bussmann fusesand keeps an extensiveselection of these devicesin stock.Reference data and appli-cation notes are an inte-gral part of the latestcatalogue and a designobjective was to enablethe engineer to makesummary evaluations andtime -saving pre -purchaseanalysis.

GCA Electronics LimitedUnit 2Great HoseleyOxfordshire OX9 7PFTelephone: (08 446) 8861/2Telex: 837150

Weir 150 -wattpower suppliesWeir Electronics Limitedhas published a new il-lustrated data sheet givinggeneral and technical in-formation on the SMM 150Series of OEM switched -mode power supply units.The series includes fivevariants, all rated at150 watts, and providingeither four or five voltage -regulated outputs. Allmodels include a fullyfloating 5V; 20A main out-put and a -5V; 1A sub-sidiary output.The four -page data sheet,printed in colour through-out with a four-colourphotograph of the powersupply, is available freeon request from

Weir Electronics LimitedDurban RoadBognor RegisSussex P022 9RWTelephone: (0243) 865991Telex: 86543

New EurostylecasesA new brochure fromEnclosure TechnologyLimited outlines thecompany's Eurostyle rangeof 19 inch card frameracks, single or doubleeurocard direct mountingracks, instrument cases,and tower systems. Il-lustrated in colour arevarious configurations ofthe Eurostyle system toshow the adaptability ofthe system.The Eurostyle system hasa unique two-piecemoulded foot that can befitted in different ways toact as a tilt prop for instru-ments, as a retainer forstacked systems, and as astabilizer for tower systems.Eurostyle is a registeredtrade mark of EnclosureTechnology Limited.

Enclosure TechnologyLimitedUnit GSouthampton AirportSouthampton SO2 2HGTelephone: (0703) 614533Telex: 477045

EEApril 1986

.58

Fig. 1 Internalorganization ofthe TypeICM7170 chip, anall-CMOS andmicroprocessorcompatible real-time clock (RTC)controller.

REAL-TIMECLOCKA good many highly interesting computer applicationswill no doubt have been cancelled for lack of aprogrammable time keeping device. This article, however;offers a truly up-to-date RTC extension board to programdates with data!

With the presentation of the univer-sal I/O bus in the May 1985 issue ofElektor Electronics, the peripheralhandling capabilities of the popularC64 computer, as well as other per-sonal micros, have been consider-ably enhanced, since the I/O busboard allows a number of extensionboards to be inserted in a neat andversatile arrangement.The present design enables the userto program real-time software driverswithout the need for critical andcumbersome machine languagewait loops. Time and data can nowbe read from and written to I/O ad-dresses, in the very same manner ascustomary with peripheral controlports; the time updating process isautonomously controlled by a dedi-cated low -power chip: the Type ICM7170 manufactured by Intersil.In order to be useful for manyowners of personal micros currentlyon the market, the present add-onRTC board has been designed tooperate in both 6502- and Z80 -basedsystems equipped with Elektor's

universal I/O bus. However, there isone important restriction for use withthe Z80 processor: since the I/O buswas originally intended for the 65XXseries of microprocessors as used inCommodore machines, no bus lineis left over for the Z80 NMI or INT in-put; this means that the alarm andperiodic interrupt facilities offeredby the RTC chip can not be put touse in conjunction with the Zilog.CPU. None the less, the time andcalendar features of the ICM7170 willalso be fully functional with the Z80.

Inside the RTCchipSince the real-time clock controller(RTC) Type ICM7170 is an all-CMOSdevice with extremely low powerconsumption, it may conveniently beoperated from a back-up battery tokeep the internal oscillator andcounter sections working when the

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computer supply voltage is off, orwhen a mains failure occurs.The main features of the RTC chip inthe proposed circuit may be sum-marized as follows: full compatibility with 8 -bit micro-

processor types that have either afully decoded or multiplexed ad-dress bus; time registers supply binary

coded data to simplify software; faultless RTC register -to -CPU data

transfer thanks to intermediarybuffer section; calendar with automatic leap year

correction; chip switches automatically to

back-up supply; chip access time less than 300 ns; software selection of one of four

crystal frequencies; data buffering after any read of

10 millisecond register (1/100thpart of a second); programmable alarm with mem-

ory function; CPU interrupt requests generated

by alarm section or by one of sixselectable periodic signals; 2µA typical standby current at 3V

and oscillator frequency of32 kHz.

The internal organization of theICM7170 RTC controller is shown inFig. 1. The chip has a low -powerPierce -type CMOS oscillator whichonly requires two external capaci-tors and a quartz crystal to obtain anaccurate frequency standard for thepresent RTC extension board. Oneof the capacitors is an adjustabletype for precise alignment of thecrystal frequency, which is divideddown to 4 kHz by a programmableprescaler section. By virtue of thisprescaler, four crystal frequenciesmay be used with the on -chip oscil-

59 EEApril 1986

Table 1.

Table 2.

Table 3.

Notes

Table 4.

COMMAND REGISTER ADDRESS 110001b, 11h) WRITE-ONLY

D7 D6 D5 I D4 I D3 D2 D1 DO

n -a I n a Test I Int. I Run I 12/24 Freq. I Freq.

D1 DOCRYSTAL

FREQUENCYD2

24/12 HOURFORMAT

D3 RUN/STOP D4INTERRUPT

ENABLED5 TEST BIT

0 0 32.768kHz 0 12 hour mode 0 Stop 0Interruptdisabled

0NormalMode

0 1 1.048576MHz 1 24 hour mode 1 Run 1 interrupt enable 1 Test Mode1 0 2.097152MHz.

1 1 4.194304MHz

ADRESSFUNCTION DATA

VALUEA4 A3 A2 Al AO HEX D7 D6 05 D4 D3 D2 131 DO

0 0 0 0 0 00 Counter -1/1C0 seconds - - - - - - - - 0-990 0 0 0 1 01 Counter -hours

12 Hour Mode0 0 0 1 0 02 Counter -minutes0 0 0 1 1 03 Counter -seconds0 0 1 0 0 04 Counter -month0 0 1 0 1 05 Counter -date0 0 1 1 0 06 Counter -year0 0 1 1 1 07 Counter -day of week - - - - - - - - 0-60 1 0 0 0 08 RAM -1/100 seconds M - - - - - - - 0-990 1 0 0 1 09 RAM -hours

12 hour Mode M - - - - - - 1-120 1 0 1 0 OA RAM -minutes0 1 0 1 1 OB RAM -seconds0 1 1 0 0 OC RAM -month M - - - - - - - 1-120 1 1 0 1 OD RAM -date M - - - - - - - 1-310 1 1 1 0 OE RAMyear0 1 1 1 1 OF Ram -day of week

1 0 0 0 0 10Interrupt Statusand Mask Register

1 0 0 0 1 11 Command register - - - - - - - -

+ = not present in interrupt -mask register, MSB in interrupt -status register.- = not used.* = AM/PM in 12 -hour indication mode; (AM = 0, PM = 1).M = alarm time is compared with corresponding counter time when this bit is

programmed low (0)Note that addresses 10010 up to and including 11111 (i.e. 12hex... Max) are not used bythe RTC chip.

INTERRUPT MASK REGISTER ADDRESS 11000013, 10h) WRITE -ONLY07 1 D6 I 135 134 D3 D2 I 01 I DO

n/a Day I Hour I MM. I Sec. I 1110 sec. I VICO sec. I Alarm

INTERRUPT STATUS REGISTER ADDRESS (10000b. 10h) READ-ONLYD7 D6 I D5 I D4 I D3 D2

IDl DO

Int. Day I Hour I MM. If Sec. 1/10 sec. I 1/100 sec. Alarm

lator. 4.194304 MHz, 2.097152 MHz,1.048576 MHz, or 32.786 kHz. As canbe seen from Tables 1 and 2, twobits, Da and DI in the RTC commandregister at address llhex (100012) sel-ect the appropriate prescale divisorfor the crystal in use. Databit D2allows selection between 12- or24 -hour mode operation.The 4 kHz signal is next divideddown to 100 Hz for use as a centralclock input to the ripple counterstages. The time and calendar dataare available from eight sequentiallyarranged and programmable coun-ter sections: 10 milliseconds, se-conds, minutes, hours, day of theweek, date, month, and year. The in-

formation is binary coded and basi-cally consists of eight bits persection, as can be seen from Table 3.However, since a maximum indi-cation of 31 is sufficient for the datecounter, 59 for the seconds counter,and so on, eight bits are never re-quired (28 = 256); the unused onesare kept logic low (0) during a read,while they are not observed ('don'tcare') in the case of a write operation.Also inside the chip is a 51 -bit RAMmemory area to hold the alarm timeand date as programmed by theuser; these registers are loaded inexactly the same way as the updatedcounter sections. When set to thealarm mode, the RTC chip will gen-

erate an interrupt request signalwhen the current (updated) timematches the preprogrammed alarmtime, i.e. the updated counter sec-tions are constantly compared on abyte -by -byte basis to their RAMcounterparts after every counterstep. If a certain counter section is tobe ignored in this continuous com-parison, the user may set the M(mask) bit in the relevant RAM byte,which will prevent an interrupt frombeing generated if the updatedcounter contents match those of thecorresponding alarm register.The RTC chip interrupt request out-put may be programmed to supplyany one of the following periodic

Table I. RTCcommandregisterorganization.

Table 2. Pro-gramming func-tions of bitsD. . D5 in thecommandregister at ad-dress 11/2

Table 3. Addressorganization forthe RTC countersections andtheir RAMcounterparts.

Table 4.Organization ofthe internal RTCinterrupt maskand interruptstatus registers ataddress 10±,.

EE

April 1986

2

Fig 2 By virtueof the hiahnumber of func-tional sectionscontained in ICAthe final circuitof the RTC exten-sion board isfairly simple.Note that it is notpossible to usethe RTC chip in-terrupt facilitiesin Z80 -basedsystems, sincethis would re-quire an ad-ditional bus line.

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digital signals: 100 Hz. 10 Hz,I pulse/second. 1 pulse/minute.1 pulse/hour, or 1 pulse/day. Provi-sion has been made for both simul-taneous and independent interruptoperation of the alarm and periodicsignal circuitry.Both the alarm and periodic inter-rupts are under the control of theinterrupt -mask reaister (IMR) andinterrupt -status register (ISR), the bitassignments of which are shown inTable 4. Selection of the desired in-terrupt signal is effected by settingthe relevant bit in the IMR. Byreading ISR, the CPU is informedabout the nature of the interrupt re-quest; ISR is automatically clearedby the falling edge of the CPU readpulse.Whatever the source of the interruptrequest signal, it may or may not bepassed to the 6502 IRQ line depend-ing on the logic level of the interrupt

enable bit in the RTC commandregister (see Table 1). This bit con-trols an on -chip output FET whichhas its drain connected to the INTterminal (pin 12) and its source tothe INTERRUPT -SOURCE terminal(pin 11). This arrangement allows theINT output to be used in an existingWIRED -OR interrupt request busconfiguration, together with otherdevices that may supply interrupts tothe CPU. Ii an interrupt is generatedby the RTC chip, the INT output willbe at near interrupt -source potential,since the FET is switched on intern-ally; this may occur both in the stand-by and in the power -down (batteryback-up) mode.If, as in the proposed circuit, theRTC supply voltage is connected tothe Vdd and Vss terminals. and theinterrupt -source connection also toVES, the INT output can only be ac-tive (i.e. logic low with respect to

Vi. -s) in the presence of a sufficientlyhigh chip supply voltage; that is,when the computer has beenswitched on (RTC fully operational).In case the user wishes to pass inter-rupts in the power -down mode only.pin 11 should be connected to thenegative terminal of the battery at theVbackup pin. This arrangement maybe useful to activate a computerwake-up circuit after a predeter-mined time has elapsed sincesystem power -down.When the voltage between theViirf,-.,p and VSE terminals dropsbelow 1 V, the RTC chip switches tothe power -down mode with only theinternal clock and interrupt sectionsactive; all other functions are dis-abled to ensure minimum powerconsumption from the back-up bat-tery. Chip terminals A,i... A.,D2 ...Dr. ALE, WR, RD, and CS areinternally connected to IL,: with a

ID EEApnl 1986

single 50 kQ resistor. In case a bat-tery back-up supply voltage can bedispensed with, Vda may be connec-ted to Vbackup.

Practical circuitThe proposed circuit of the real-timeclock extension board for the univer-sal I/O bus is shown in Fig. 2. Notethat very few components are re-quired to make a functional unit withthe ICM7170 RTC chip in a 6502- orZ80 -based system. To select be-tween these two types of micropro-cessor, the user need merely fit theappropriate wire links; connection tothe I/O bus is through a standard21 -way PCB connector.The ready-made PCB for this projectis fitted with the necessary parts asshown in the mounting plan of Fig. 3.Note that the battery is an integralpart of the completed RTC board; itmay be charged from the computer+5V supply by means of DI and 111.Since it was considered a waste ofavailable I/O address space to re-serve 17 memory locations or I/Ochannels for the RTC registers, ICIand IC2 latch the RTC registernumber which must be supplied as adatabyte with a POKE or OUT in-struction to an address within the slotthat has a 0 for address line Az; thecontents of the RTC chip registersare next read from or written to anaddress within the same slot with Ao

high (I). Since every slot offers fourI/O addresses (see the article on theuniversal bus, Elektor Electronics,May 1985), both the latch and theRTC chip appear two times withinthe slot occupied by the present ex-tension board. Finally, Z80 program-mers are referred to the first articlein the series on MSX extensions inthe January 1986 issue of ElektorElectronics to find details onmodification of the universal I/O busas required for this CPU.

Setting upAs can be seen from Table 1, thereal-time clock may be stopped andstarted by programming bit D3 in thecommand register; this bit controlsthe 100 Hz clock input to the countersections. To stop the clock in orderto synchronize it with an availabletime standard, D3 must be set low (0).The desired start time for the RTC isnext loaded into the time registers,the correct data is also supplied, andthe RTC may be started at the de-sired time by setting D3 again (I).To enable the CPU to read glitch -freearid therefore absolutely stable timedata from the RTC chip, time registerdata are passed through a buffer sec-tion before being transferred to theCPU databus during a read cycle.However, this buffer is only loadedwhen the 10 ms register is read, andprogrammers are advised to start any

time reading from the RTC chip witha read of this latching register to en-sure that time data are stable and ac-curate.The command register comprises aTEST bit (D5) to apply the internal100 Hz signal to the seconds counter;this will cause the clock to run a hun-dred times faster than normal, whichmay be useful for test purposes.It will be evident that the accuracyof the present RTC board dependssolely on crystal stability and correctfrequency setting of the oscillator.Outlined below is a preferred align-ment method using a period countersuch as the one featured in ElektorElectronics, January 1985. To preventthe RTC INT output from actuallygenerating an interrupt pulse in thecomputer during the alignmentsession, temporarily disconnect thewire at pin 12 of ICIFirst, write all zeros to the IMR. Next,load the command register withdecimal values 24 or 28 (18 or IChexadecimal respectively) to run theclock in either the 12- or 24 -hourmode with interrupts enabled. Nowset D3 in the IMR to generateperiodic interrupts with a frequencyof 1 Hz. Adjust capacitor C2 for an in-dication of exactly 1.000 second onthe period counter which should beconnected to the RTC chip INT out-put (pin 12). For this measurement,the period counter should be set totrigger on the falling edge of thedigital input signal. Reset ISR by

Fig. 3 Compo-nent mountingplan for the RTCextension.Note the on-board .NiCd bat-tery and the glrelinks to accom-modate eitherthe 5502 or theZ80 processor inthe host com-puter.

Parts list

Resistors:

117=21(2

R2= 10k

Capacitors:

CI =18pC2 = 10-33p trimmerC3 -,C4= 100n

Semiconductors:

D1=1N4148ICI:IC2=74HC(T1/LS1731C3=ICM7170 (IntersillIC, = 74HC(T)/LSOO

ICs=74HCIT1/LS10

Miscellaneous:

X1=32.768 kHz quartzcrystal (subminiature

type)21 -way DIN41617connector, angledconnections

NiCd battery 2.4V ortwo 1.2V cellsconnected in series

PCB 86017

EEApril 1986

62

Listing 1. Theessentials ofMSX real-timeclock program-ming. Althoughthe present RTChardware doesnot support inter-rupts with theZ80, provisionhas been madeto set the RTCalarm function.For this purpose,the subroutinesat lines 1000 andOM maybe called withN=8 andU$= 'ALARM"Note that theregister latch isat OUT 113, theRTC proper atINP/OUT 112.

5 CLS:FRINT-**** MSX REAL-TIME CLOCK ****"7 OUT 113,17:OUT 112,4:REM STOP CLOCK9 REM GO GET TIME&DATE INFO10 N=0:US="SYNCHRO":60SUB 100020 CLS: PRINT "SET ";UWDATE =";A(N-1-5);"--;A(N+47;--";A(N+5)30 PRINT 'SET ";US; -TIME =";A(N+1);":";A(N-1-2);":";A(Ni-3);"+":10*A(N)40 PRINT "IF CORRECT PRESS [Yr:INPUT OS:IF QS="Y- OR 0$="y" THEN GOSO GOTO 755 REM GO LOAD RTC60 N=0:605118 2000

CLS:PRINT"HIT ANY EEY TO START CLOCK75 IF INKEYS="' THEN 60T0 75

70

SO CLS64 REM READY TO START CLOCK65 OUT 113:17:OUT 112.1290 OUT 113,0:A=INP(112):REM 10MS LATCH100 OUT 113,3:S=INP(112)110 OUT 113,2:M=INP(112)120 OUT 113,1:H=INP(112)130 LOCATE0,0:PRINT"TIME=";H":":MC:";S140 IF iNKEYS="- THEN 60TO 90150 END:REM OPTION HERE FOR RETURN1000 REM GET TIME AND -DATE1010 INPUT'YEAR = 19";A(N+6)1020 INPUT'MONTH = (1-12)';A(N+4)1030 INPUT"DATE = 1-31 r;A(N-1-5)

1040 INPUT"DAY OF THE WEEK = (0-6)";A(N-1-7)1050 INPUT "HOURS = (0-23)-;A(N+1)1060 INPUT 'MINUTES = (0-59)-;A(14+2)1070 INPUT 'SECONDS = (0-59)-iA(N+3)1080 INPUT -10 MILLI -SECONDS = (0-5y) ";A(N)1090 RETURN2000 REM LOAD RTC REGISTERS2005 FOR N=N TO N-1-72010 OUT 113,N:REM POINT LATCH2020 OUT 112,A(N):REM LOAD RTC2030 NEXT N2040 RETURN

reading it; this will also deactivatethe INT output (logic 1). The outlinedmethod should be programmed asan instruction loop to obtain maxi-mum clock accuracy.Where a period counter is notreadily available, use may be madeof another time reference signal withknown accuracy, such as the BBCtime signals on radio and TV. Ob-viously, this method costs more timeand requires a good deal of patiencebefore the target accuracy isreached.

RTC programmingHardware needs software supportand vice versa. To complete thisarticle, two sample programs are of-fered to guide in further program-ming explorations, which will, nodoubt, lead to more complex andsophisticated time -keeping softwareonce the basics of RTC control havebeen mastered.

Programmers should be well awareof the essential difference in I/Omapping between the Commodoretype of computer and Z80 -basedmicros, such as the MSX series. Gen-erally speaking, the former usememory locations for I/O bytetransfer, the latter have 256 I/O chan-nels available which are under con-trol of IN and OUT instructions,whereas the 65)a -based computerswork with PEERS and POKES for thispurpose. However, the basic methodof RTC control remains the same forboth computer types: first the inter-nal RTC register is specified with anappropriate instruction, then datamay be read from or written to thatregister by addressing the RTCproper.MSX users may key in the program ofListing 1 which displays a digitalclock in the top left-hand corner ofthe screen. Obviously, the screenformatting and graphics features ofthis computer type allow the user to'brush up' this little program to his

heart's content. Note that line 100

reads the 10 ms register before theactual time reading is performed in aloop. Experienced programmersmay have a go at writing a routinethat prints time and date on everyprinter sheet prior to a listing or anyother draft copy. Note that, once theclock has been synchronized, timedisplay is simply effected withGOTO 90. However, some provisionwill have to be made to exit the timedisplay loop and resume the mainprogram.The sample program listed for theCommodore 64 and 128 model com-puters is somewhat lengthier thanthe MSX version, and, therefore, of-fers more programming functions;among these are selection of videopolarity and word -based input ofdays and months - see Listing 2.

HS:GS

63 EEApril 1986

10 REM COMMODORE 64 REAL-TIME CLOCK CONTROL *20 DIM AS(12),B$(7)30 RESTORE40 FOR 0=1 TO 12:READ A$(Q):NEXT 050 DATA "JANUARY","FEBRUARY","MARCH","APRIL","MAY","JUNE","JULY","AUGUST"60 DATA "SEPTEMBER","OCTOBER","NOVEMBER","DECEMBER"70 FOR 0=1 TO 7: READ B$(0): NEXT 080 DATA "MONDAY","TUESDAY","WEDNESDAY","THURSDAY","FRIDAY","SATURDAY","SUNDAY"90 PRINT CHR$(147):PRINT:PRINT"--COMM0D0RE 64 REAL-TIME CLOCK CONTROL--"100 PRINT:PRINT:PRINT:110 INPUT"CLOCK SETTING (YYN)";V$120 IF VS="N" THEN 365130 PRINTCHR$(147)140 REM CLOCK SETTING150 INPUT ' ENTER HOURS ";H:PRINT:PRINT160 INPUT ' ENTER MINUTES ";M:PRINT:PRINT170 INPUT ENTER SECONDS ";S:PRINT:PRINT180 INPUT " ENTER MONTH ';MS:PRINT:PRINT190 FOR 0=1 TO 12: IF M$=A$(Q) THEN R=C200 NEXT 0210 INPUT ' ENTER DATE ";D:PRINT:PRINT220 INPUT ' ENTER YEAR ";F:PRINT:PRINT230 F1=INT(E/100):F2=INT(F1/10):F3=F1-10*F2:Y=F-F1,100240 INPUT ' ENTER DAY OF THE WEEK ";WS:PRINT:PRINT250 FOR 0=1 TO 7:iF W$-8$(0) THEN E=Q260 NEXT 0270 INPUT " PRINT MODE (NORMAL/REVERSE) ";P$: IF P.S="R' THEN C=128280 POKE 56832,17:POKE 56833,4:REM 24 HOURS -MODE SELECT290 POKE 56832,1:POKE 56833,H:REM SET HOUR300 POKE 56832.2:POVE 56833,M:REM SET MINUTES310 POKE 56832,3:POKE 56833,S:REM SET SECONDS320 POKE 56832,4:POKE 56833,R:REM SET MONTH330 POKE 56632,5:POKE 56833,D:REM SET DATE340 POKE 56832,6:POKE 56833,Y:REM SET YEAR350 POKE 56832,7:POKE 56833,E:REM SET DAY OF THE WEEK360 POKE 56832,17:POKE 56833,12:REM ACTIVATE CLOCK365 PRINT CHRS(147)370 POKE 56832,0:REM PUT TIME IN LATCH380 POKE 56232,1:H=FEEK(56933):REM READ HOUR390 POKE 56832,2:M=PEEK(56833):REM READ MINUTES400 POKE 56832,3:S=PEEK(56833):REM READ SECONDS410 DH=INT(H/10):UH-H-DH10+C:DH=OH+C:REM PRINT HELP HOURS420 DM=INT(11110):UM=M-DM*10+C:DM=DM+C:REM PRINT HELP MINUTES430 DS=INT(S/10):US=S-DS*10+C:135=0S+C:REM PRINT HELP SECONDS440 POKE 56832,4:R=PEEK(56833):REM READ MONTH450 POKE 56832,5:D=PEEK(56833):REM READ DATE460 OD=INT(D/10):00=0-DD*10:REM PRINT HELP DATE470 POKE 56832,6:Y=PEEK(56833):REM READ YEAR480 DY=INT(Y/10):UY=Y-DY*10:REM PRINT HELP YEAR490 POKE 56832,7:E=PEEK(56833):REM READ DAY OF THE WEEK500 KL-54272:REM PRINT TIME WITH COLOUR HELP510 POKE1051,0H+48:POKE1051+KL,14520 POKE1052,UH+48:POKE1052+KL,14530 POKE1053,58*C:POKE1053+KL,14540 POKE1054,0M+48:POKE1054+KL,14550 POKE1055,UM+48:POKE1055+KL,14560 POKE1056,58+C:POKE1056+KL,14570 POKE1057,0S+48:POKE1057+FL,14580 POKE1058,US+48:POKE1058+KL,14590 PRINT:PRINT TAB(27);13$(E)600 POKE1171,00+48:POKE1171+KL,14610 POKE1172,U0+48:POKE1172+KL,14620 PRINTTA8(30);AS(R)630 PRINT "";:REM CURSOR 3 LINES UP640 POKE1211,49:POKE1211+KL,14650 P0KE1212,57:POKE1212+KL,14660 POKE1213,DY+48:POKE1213+KL,14670 POKE1214,UY+48:POKE1214+KL.14680 GOTO 370

Listing 2. Com-modore 64 and128 users mayenter this BASICprogram, in-tended as aguide to furtherexperiments withthe real-timeclock board asdescribed in thisarticle.Note the PEEKand POKE in-structions to ac-cess the RTCregisters at lo-cations 56832,0(R7V) and56833w (latch).

EE

April 198664

COMPUTERS ANDHEALTH CARE

by Helena Buswell

When a 38 year old Scot-tish housewife made anappointment to visit herdoctor at the local healthcentre, she was unawareof the role that computerswere about to play in herlife.Mrs Ann Robertson (not herreal name) had stomachpains, and, like mostpeople, was nervous whenshe tried to describe hercondition.Dr Michael Ryan hadbefore him a summarylisting his patient's detailsproduced by the healthcentre's own computerready for Mrs Robertson'svisit. He could see at aglance her age, numberof children, occupation,height, weight, bloodpressure, previous and cur-rent health problems, andother demographic datarelevant to her generalhealth.Almost all of the 56 millionpopulation is registeredwith one of about 50 000general practioners (GPs),contracted to work withinthe National Health Ser-vice (NHS). Each GP has alist of several thousandpeople, and for each andevery one he has casenotes - most going backto that person's birth.At health centres likeHowden, near Livingston incentral Scotland, thesedetails have been trans-ferred to new computersystems, which produce asummary sheet ready foreach patient's con-sultation.

Further testsIn Mrs Robertson's case,Dr Ryan decided to sendher to the area hospital -Bangour General Hospital- for further tests. Her ap-pointment there hadalready been computergenerated, and, when she

arrived, more details wereentered into the computersystem by the receptionist.As Mrs Robertson hadbeen a patient at thehospital some yearsbefore, the computer auto-matically alerted thehospital staff, and herearlier case notes wereproduced.Bangour uses the de Dom-bal system for diagnosingabdominal conditions.Developed by Tim deDombal, a consultantsurgeon at Leeds GeneralHospital, this computer -based diagnostic systemassesses the chances ofdifferent causes of acuteabdominal pain with avery high degree of accu-racy. The system is nowused in many Britishhospitals, and, with fewerunnecessary exploratoryoperations of the abdo-men, more patients aresent home from casualtywards and both lives andmoney are saved.The system is also used insubmarines of both the USNavy and the Royal Navy.Dr Ryan says: "in these sortof conditions, with longperiods at sea, acute ab-dominal complaints arethe most critical todiagnose correctly. Afterall, apart from heart at-tacks, they are the mostlikely to kill you:'A comparable system in

use at Glasgow has adyspepsia program thatobtains data on symptomsby directly interviewingthe patient. Where directcomputer interviewing isalso used, the patient isoften more relaxed andforthcoming, talkingdirectly to a machine,rather than to another per-son. The de Dombal inter-view has already beentranslated into Swedishand Dutch, and is beingtested in other clinics hereand overseas.

PossibleappendicitisMrs Robertson, however,was asked a series ofstructured questions by thehospital doctor, and heranswers keyed into thecomputer. The computer'sdiagnosis showed a 90 percent chance of appen-dicitis, with lesser chancesof constipation orgynaecological abnor-malities.Admitted to hospital,Mrs Robertson's subsequentoperation and stay werelogged from start to finishon the hospital's computer.Her files, both at thehealth centre andBangour, were updated.Howden Health Centre isone of 50 to have recentlyinstalled computer systems

A VDU and keyboard gives hospital staff instant to infor-mation.

in Scotland with the helpof the Scottish Home andHealth Department. TheGPs buy their own Britishbuilt Apricot computers,but the software and itsdevelopment and main-tenance are provided freeby an NHS computerteam. Dr Ryan, who ischairman of the project'ssteering committee, says:"We except many morepractices to install com-puters in the near future."Some of the practicesalready using computersare in Scotland's mostisolated communities -the outlying islands. Aswell as holding patientrecords, the computers areused for repeat prescrip-tions, and for monitoringcontinuous conditions likehypertension, diabetes,and thyroid problems.Under the overall directionof the Department ofHealth & Social Security,health care in England isprovided by regionalhealth authorities, whichin turn are divided intoadministrative districts. Thelogistics of running suchan enormous enterpriseare formidable, and it is

this, as much as anything,that has encouraged theintroduction of computersat all levels.

ManagementinformationThe NHS is introducingnew management infor-mation systems in the nexttwo to three years, andtheir success will relyheavily on the use of com-puters. However, computersare not new to the healthservice. Some were in-stalled nearly 20 yearsago, and with this wealthof experience, the NHS isnow marketing a range ofsoftware in other countries.Milton Keynes GeneralHospital is typical of those

65 EEApril 1986

opened in recent years.The new town of MiltonKeynes has a populationof 145 000 - expected toreach 220 000 by the year2000. The hospital wasplanned in three phases.Phase one began in 1978as a community (mainlygeriatric) hospital. Phasetwo, with 400 beds, wasopened in 1984, when thecomputer system was in-stalled. The last phase isscheduled for 1990, givingspace for more beds anda mental health unit.The computer system isbased on three interlinkedminicomputers - in theevent of breakdown ormaintenance the systemcan run on one - and100 terminals around thehospital, half of whichhave a printer attached.Terminals are also on-lineat outlying clinics. Andunder a pilot scheme, oneGP in an outlying district ison-line to a clinic ter-minal.A computer system is usedfor patient identification;record management;patient location and log-ging; bed. clinic, andwaiting list management;and management infor-mation. Each ward has aterminal, as do the casu-alty, pathology, andradiology departments.A busy hospital has muchin common with a largehotel in the comings andgoings, catering, clean-ing, general maintenance,and payment of wages.Patients have to be bookedin and out in the sameway as hotel guests. Sur-prising as it may seem,bed management is apermanent problem. AtMilton Keynes, tight com-puter control is kept onthe occupancy of beds,where and when beds areavailable for waiting listpatients (there are alwaysbeds kept for emerg-encies), patient movementfrom ward to ward, and soon. A computer check ismaintained 24 hours aday so that all authorizedpersonnel can see at aglance which beds areoccupied, and who thepatients are. Before com-puterization, it could take

hours for an accurate bedcheck to be made.

Wider healthcontextAlthough computerizedbed management hasbeen -developed tofacilitate the smooth run-ning of hospitals, the ac-cumalated data can pro-vide vital information in awider health context. AtMilton Keynes, a potentialminor epidemic wasaverted after a patient,who had entered hospitalfor routine treatment anda two week stay, wasdiscovered to have activetuberculosis. From com-puter data, all his con-tacts from severals wards- staff, patients (most ofwhom had already beendischarged), and evenvisitors - were located inless than 24 hours. Aspecial clinic was set upfor screening and im-munization the same day.Payroll systems wereamong the first computerapplications introducedby British healthauthorities. The WestMidland Regional HealthAuthority uses OMR (Op-tical Mark Reading) formsand readers to process acomplicated payroll for102 000 people working ina widespread area. As afurther complication,about 52 per cent aremonthly salaried, with therest being paid weekly."People fail to realize thatevery sort of trade andprofession - from surgeonto carpenter - isemployed by the NHS,"says computer operationsmanager Peter Owen. "Wehave one of the most com-plex payroll structures inthe country. At least oncea month some 200 000OMR documents are be-ing processed."The East Anglia RegionalHealth Authority coversCambridgeshire, Norfolk,and Suffolk, and has apopulation of two million.The eight major hospitals,and many of the smallerones, have computersystems dealing with ad-

ministration, in -patientsand out -patients, radi-ology, and pathology.Pathology statistics help toanalyse the incidence ofmedical conditions, pro-viding valuable leads tolinks between such par-ameters as occupations,social conditions, and theoccurence of illness.As with all regionalauthorities, East Angliawrites its own software. Arecently developed cater-ing program at Peter-borough General Hospitalhas simplified patientmenu orders, and hasdrastically cut costs.Around the area's healthcommunity centres, allchild health immunizationprogrammes are alsocomputerized.International ComputersLtd (ICL) has emerged asone of the leading sup-pliers of computer equip-ment to the NHS. Formedin 1968, ICL operates inover 70 countries andemploys 21 000 peopleworldwide. It has col-laborative agreementswith Fujitsu of Japan; PERQSystems of the UnitedStates of America, andMitel of Canada, and alsohas a joint research in-stitute in Munich with Bullof France and Siemens ofWest Germany.

PatientadministrationICL has recently formedthe ICL Health SystemsBusiness Unit. It includesthe 100 strong team thathas been working on theICI Patient AdministrationSystem already ordered byabout ten healthauthorities. The companyalso runs seminars for NHSpersonnel and ICL usergroups.An idea of the scale ofICUs health computersystems, and of thephenomenal growth ofNHS computerization, isevident in just a shortselection of recent in-stallations.An ICL supplies infor-mation system being in-stalled for the GrampianHealth Board in Scotland

will handle 6500 stockitems, ranging from staffuniforms and cleaningmaterial to surgicalneedles and sutures.The Brighton Health Auth-ority is installing two newnetworks for district infor-mation, replacing andupgrading older hard-ware. Brighton will also beone of the first districts toinstall an obstetrics soft-ware package developedat St Mary's Hospital inLondon, where thePrincess of Wales had herchildren. Obstetrics com-puter systems have helpedreduce perinatal deathrates.Tender letting controlsystems have been in-stalled by seven healthauthorities to help with theadministration of thetendering process, includ-ing the monitoring of suc-cessful contractors.

Real-timesystemsA new real-time patientadministration system isbeing used by the WestGlamorgan and Gwyneddhealth authorities. Suppliesinformation systems havebeen installed by all thedistricts under thesouthwest London RegionalHealth Authority, and bysix districts of the OxfordHealth Authority.Apart from systems basedon orthodox computerhardware, British scientistshave developed ad-vanced computer basedtechnology for thespecialized diagnosis andtreatment of a range of ill-nesses. The NationalHospital for NervousDiseases in London, forexample, is to have aprototype expert systemcalled BRAINS designed togive powerful aid in theanalysis of brain scans.The main goals of a teamfrom University College,London, LeicesterPolytechnic, and thehospital were to give theradiologist a tool for fastand efficient study of thescan image, and to re-duce unnecessary scans.The team decided to

EE

April 198666

make use of the statisticalmethods that had grownup in epidemiology in thelast 25 years.A statistical database of900 scans has been en-tered into the system byMr du Boulay, the team's

radiologist. The databasetook five years to collect,covers 22 different forms ofcerebral disease, and canbe extended.The system allows less ex-perienced radiologists toaccess sample scans of

diseases and comparethem with the scan of thepatient being examined.To get advice from thesystem, the radiologist isrequired to describe theposition and appearanceof damaged tissue, and

indicate the presence orabsence of other signs.Based on this information,the system gives a shortlistof disease probabilities,and indicates whichsymptom leads to itsprediction. LPS

ELECTRONICS ANDTEMPERATURE CONTROL

by Vic Wyman

Temperature control isoften the key to efficientand economic industrialproduction. In many pro-cess plants, for example,the temperature mayneed to be held withinnarrow bounds if the pro-cess is to be a success.And the close control ofthe temperature of pro-duction processes and offactory environments canoften lop a large chunkfrom a company's annualenergy bill.A growing number of con-trol equipment suppliersrecognize that simplyknowing a temperature isof little use. What isneeded is the ability tomonitor how temperatureis changing and adjust itaccordingly. Thesedemands are being in-creasingly satisfied aselectronics expands theoptions of equipmentdesigners and allows lowcost solutions to pastproblems.

MicroprocessorbasedA good example of thegreat flexibility availablewith the latest temperaturecontrollers is the micropro-cessor based digital unitfrom Control & Readoutol,designated the 451. Thegeneral purpose 451 isaimed particularly atmachine makers andusers in the food, plastics,oven and furnace in-dustries, and accepts arange of inputs.But as well as being a

proportional, integral orderivative (PID), three termor onbff control unit with arange of common fea-tures, the 451 is easilyreconfigured to changethe basic functions. Themeasurement range, con-trol algorithm and limitmode, as well as PIDterms, output cycle timeand limit setting, can bechanged as often aswanted.Because of this, any 451can serve as the spare forother units, cuffing thenumber of controllers heldin stock and minimizingthe cash tied up in spares.The 451 can take inputsfrom K, J and S sensorsover the respective tem-perature ranges 60 to1200 °C, 60 to 600 °C, and60 to 1600 °C, as well asfrom Pt100 sensors over-200 to + 400 °C and 4 to20 mA;10 to 50 mV or zeroto 20 mA;0 to 50 mVsignals. The controllerworks on supplies of115'230 V at 50'60 Hz.

Hidden buttonFor commissioning, an in-ternal security switch isactuated and a hiddenbutton on the front paneloperated together with thenormal controls. Thisallows the 451 to bematched to the processneeds.Any reconfiguration re-quires the entry of aspecial code after the ac-tuation of an internalsecurity switch. As anexample of how input andoutput control functionscan be altered, the unitcould be changed from

thermocouple input withonbff control to a resist-ance thermometer sensinginstrument with PID control.A non-volatile memory re-tains the configuration formore than ten years, evenwithout power.For slow and controlledheating of large structures,the 451 has a soft start orcontrolled ramp function,with a digitally set rate of0.1 to 50 °CI minute.An automatic manual op-tion also allows such pro-cesses as mixing to bestarted manually and thenswitched to automaticcontrol. The device has5 A relay or logic outputs.

Self -tuningadjustmentAnother digital indicatingtemperature controller isthe 810 unit, which, themanufacturer, Eurotherm(21,claims, has carved out aniche for itself in industryonly a short while after itsintroduction. The devicewon an award from theDesign Council in 1984. Toexpand the market further,the company has in-troduced a self -tuningcontrol adjustment aimedmainly at the plastics ex-trusion and continuous fur-nace markets. The newfeature is intended to cutout long, involved manualadjustment.The 810 is a three term,microprocessor based in-strument with a highdegree of control accu-racy and easy front paneladjustment of all 15 mainparameters. It features anew, self -tuning algorithm

for such equipment as ex-truder barrel and diezones, where there is amaximum rate of tempera-ture change under fullpower of about one unit/second, requiring only300 bytes of code space.The three easily setoperating modes provideself -tuning on start-up aslong as the measuredvalue is well below thedesired set -point, and self -tuning at set -point if theloop is over -damped orunder -damped. In thethird mode, self -tuning canbe initiated manually dur-ing operation.There is a high or devi-ation alarm and three set -point and alarm rangesfrom zero to 500 zero to1000 'C and zero to1500 C. The operator canoverride all the par-ameters available fromthe 810's scroll push-buttons.

Set -pointchanged withtimeThe flexibility of the latestcontrol equipment is il-lustrated by the possibleuses claimed by Gultont33for its West 2050 program-mable controller. The PID,microprocessor based unitis said to be suitable forthe heat treatment ofmetals, kiln control, en-vironmental chambersand cabinets, food andchemical processing, resinmanufacture, textile dye-ing and autoclaves, aswell as other uses whereset -point must be

67 EEApril 1986

changed with time.The 2050, from the Gultongroup's control and in-strumentation division, isbased on the establishedWest Opus 70 temperatureand process controller. Ithas the same mechanicalconstruction and is in ametal case with splash -proof and dust -proof mem-brane front panels.The programmer controlsa measured value througha set -point profile whichcan change with timethrough up to four stages,each with a ramp and adwell segment adjustableup to 99 hours 59 minutes.Rate or time programmingcan also be adopted forthe ramps.The 2050 can handle ther-mocouple, resistance ther-mometer, direct currentlinear, and voltage andcurrent inputs. Outputforms include relay, logicfor solid state relay, directcurrent linear, voltage andcurrent. thyristor pulse, andvalve motor drive.

Integral lock -outThe manufacturer claims a0.25% accuracy and thePID control has an integrallock -out. Typically, controlparameters can be re-tained without power forfive years, according toGulton.The 2050's optional extrasinclude an RS422 serial in-terface, a digital (event)output, a remote pro-gramme start, andguaranteed soak times.Preliminary trials of FGHControls14) furnace tem-perature controller, knownas the thermal head ratiosystem, suggest typicalfuel cost savings of 15 percent. Aimed at such sec-tors as the aluminium in-dustry, with medium sizedand large furnaces, thesystem is claimed to im-prove the efficiency ofheat treatment and to be

simply controlled by non-specialist workers.Present control methodsfor furnace temperaturestypically involve regu-lating the furnace at-mosphere and letting theload warm to this tern-

perature, or controlling theload at a chosen tem-perature and probablysuffering from high at-mosphere temperaturesand high load skin tem-peratures.

ThermocouplesTo eliminate the need forthis wasteful system, FGHhas come up with a twoinstrument and two ther-mocouple design. Thethermocouples monitorload and atmospheretemperatures.One instrument comparesthe load temperature witha load set -point andgenerates a further set -point, which is fed to thesecond instrument. Thesecond set -point is com-pared with measured at-mosphere temperaturewhich it maintains.To avoid dangerously highatmosphere temperatures,the user can include afurther set -point in the at-mosphere controller instru-ment, operating as anupper clamp. A range ofcontrol components canbe coupled to the system.FGH can also supplysuitable thermocouples,and up to three can beused to sense load tem-perature. In this case, anadditional control unitselects the highest tem-perature and switches thisthrough to the ratio system.

A similar set of three ther-mocouples can be usedfor atmosphere tempera-ture sensing.

Factory heatingTemperature control canalso be applied profitablyto the heating system of afactory or other plant. Arecent addition to theenergy managementequipment made byGent(5) is the micropro-cessor based 6202 tem-perature controller.This unit, which is easy toprogram with a 25 buttonkeyboard, can be used asa stand-alone energymanagement device orcan form part of a morecomprehensive controlsystem. It is suitable forboth existing and newheating installations.The 6202 can control up toeight zones, three boilers,a main system pump, ahot water circuit andalarms, with up to 14digital outputs. The unitaccepts signals from up to24 dedicated analogueinputs.Gent sees as a particularadvantage the ability ofthe 6202 to control energyuse in any of three ways.The first, a pulsed powermode, links a zone directto a boiler and pump op-eration. By monitoring out-side and zone tempera-tures, the unit calculates

The 6202 energy manaaement unit from Gent can pro-duce major cost savinas when applied to factory tempera-ture control.

the input power eachzone needs to maintainthe desired space tem-perature. By monitoringthe system flow tempera-ture, the controller alsodetermines the period thezone valve needs to bepulsed open.

Three wayvalveThe modulating valvemode calls for each zoneto be controlled by athree way valve and zonecircuit pump, with a corre-sponding zone flow tem-perature sensor. The valveis modulated in line withthe outside and spacetemperatures.The third mode,designated onloff, is for awide range of energy con-suming plant such as oiland gas fired air heaters,electric heaters, lighting,and pumps. Independentzone operation allows timeand temperature or time -only control.The 6202 can also be pro-grammed with 99 con-secutive shut -downs up tosix days in advance, andthere is a back-up batteryto retain programs for upto 72 hours. The user canalso select parameters tobe coupled to alarm out-puts, and an RS232I422 in-terface can be used toconnect the unit to remotecomputer equipment. LPS

1. Control & Readout Ltd.Woods Way, Goring -by -Sea, Worthing,West Sussex, BN12 4TH.

2 Eurotherm Ltd, FaradayClose, Worthing,West Sussex, BNI3 3PL.

3. Gulton Ltd, West Division,The Hyde, Brighton,East Sussex, BN2 4J1I.

4. FGH Controls Ltd,Burymead Road, Hitchin,Hertfordshire, SG5 1R1:

5 Genl Ltd, Temple Road,Leicester; LE5 4,1f:

EE

April 1986

While many users of graphics terminals arecontent with the colour features of their 8- or16 -colour systems, the era of true multi -colour

image production on a digital basis has recentlybeen heralded with the availability of colourpalette chips which offer up to 4096 possiblecolours to put the older systems in the shade.

DIGITAL COLOURPALETTE

For a number of centuries,artists have used palettesto obtain a certain targetcolour by mixing a limitednumber of basic colours;the mixing process is onethat requires skill and pre-cision since any ad-ditional spot of paint mayspoil the desired colournuance. Today's elec-tronics industry offers thedigital equivalent of thewooden palette in theform of a chip that incor-porates a number ofregisters for target colourdefinition; the objectcolour is 'mixed' by pro-gramming the relevantcolour index code beforethe register contents areconverted to analogueRGB levels.This article examines twoof these devices as offeredby different LSI manufac-turers: Texas Instrumentsand Thomson. However,before discussing the tech-nical characteristics ofeach of the palette chips,their general method ofoperation in a RGB videosystem must be sketched.

Principle ofoperationGraphics terminals andgraphics cards such asthe one featured in ElektorElectronics, issues fromSeptember 1985 onwards,generally provide three or

four output bits togenerate eight or sixteenpossible colour shades ona RGB monitor. In a con-figuration with a palettechip, these bits are 'in-tercepted' and used toaddress (specify) eight orsixteen registers that holda higher number of colourdefinition bits. for exampletwelve; obviously, the morecolour bits, the morecolour shades withinreach of the programmer.The register contents arepassed to three digital -to -analogue converter (DAC)sections in the chip. Thethree analogue voltagesat the chip output ter-minals then represent thecolour shade asprogrammed in the ad-dressed palette register.Thus, starting from onlyfour bits (RGBI) to specifyone of sixteen pixel colourshades, the palette chipexpands the total number

of available shades to4096 if it contains sixteen12 -bit registers for this pur-pose. This may appear ahuge number at first sight,but it should be noted thatonly 16 of 4096 colournuances may be used atone time.It will be readilyunderstood that theessence of the matter liesin the method and timingarrangement relevant tomodification. i.e. readingand reloading of thecolour conversion registersin the palette chip.Clearly, the faster theregister contents can bechanged. the more colournuances will be simul-taneously visible on thescreen.To illustrate the possibilitiesoffered by a palette chip,consider a RGBI systemwith four output bits usedto address the 16 -by -12register array in the

palette. Suppose that it is

only allowed to modify theregister contents duringthe vertical scan retracetime (field or raster blank-ing). The screen is empty,the background is, say.red; this implies that thefour input bits are pro-grammed to address butone of the paletteregisters. which is loadedwith a 12 -bit code thatspecifies red. If nothing isdone about the registercontents. the image willsimply remain red. How-ever, if the colour indexcode is incremented byone during every fieldblanking pulse (20 ms). therange of 256 shades of redwill be passed from paleto dark (fully saturated) inabout five seconds. with-out any trace of picturedisturbance. Likewise. onehalf of the screen may bepale red and the otherhalf dark blue. If the rel-

Fig. I. The basic principleof digital palette chips restson the use of RGBI pixel in-formation to selectregisters which hold ahigher number of colourdefinition bits for conver-sion in DAC sections.

evant colour conversionregisters are simul-taneously incremented(red) and decremented(blue), an interesting andattractive effect is ob-tained on the screen.As already pointed out,palette register reloadingshould, ideally, be poss-ible as frequent as poss-ible, since the rate ofaccess determines thetotal number of colourshades simultaneously vis-ible to the human eye;happily, the palette chipsexamined below offer ahigh flexibility in thisrespect; both accept thehorizontal blanking pulseas a timing signal forregister access, despitethe fact that the actualnew register contents areobtained quite differently,as will become evidentfrom the detailed descrip-tions below.

TMS34070Texas Instruments offer avideo palette chip to thedesign outlines given inthe functional blockdiagram of Fig. 2. Ident-ified as TMS34070, the chipfeatures a 16 -by -14 registerarray; each register mayhold 12 colour conversionbits and two auxiliary bitsfor special functions. Theregister outputs aremultiplexed before being

applied to three on -chipDACs which supply the rel-evant voltage levels to theanalogue inputs of an RGBmonitor. At the left of thediagram are two 4 -to -16decoders for addressingthe registers in the array.The internal configurationis completed with thenecessary timing and con-trol sections.Addressing the colourconversion registers in theTMS34070 palette chip iseffected by a ratherpeculiar method. Asalready explained, everypixel has a four -bit codein the relevant location invideo memory (bit map).By virtue of its internaltiming, the TMS34070 iscapable of loading thefour -bit colour codes of apair of adjacent pixels atits DA3...DA0 andDB3 ...DBO inputs, clockedby CLKOUT, which isDOTCLK divided by two.Two -to -one multiplexingand digital -to -analogueconversion is performed atDOTCLK frequency; seeFigures 3a and 3b for the

method of the inputclocking process. The evenpixel is output as ananalogue voltage atter 6CLKOUT periods, the ad-jacent odd pixel half aperiod later. Palette inputsDA3...DA0 and DB3 ...DBOalso give access to theregister array to effectdefinition of colour shade;

loading requires two suc-cessive CLKOUT periods asshown in Fig. 3b; duringthe first clock period, fourred bits and two auxiliarybits are loaded, the nextclock cycle loads the bitsfor blue and green.At this point, it isnecessary to establish theorigin of the colour indexbits which form the con-tents of the 16 conversionregisters. As visible in theblock schematic of thechip, the Texas palettedoes not feature a micro-processor interface, andcan, therefore, not obtainthe register data from anyarea in the computermemory. Instead, theTMS34070 gets its registerdata from a dedicated256 -bit area located in thepixel bit map. These bitsare loaded as outlinedabove, immediately afterthe MODE input of thechip is pulled logic low.The user is free to applyeither the system raster orline blanking pulse to thisinput; the raster loadmode implies that theTMS34070 loads its registersduring the last blankedscan line, just before thepicture scan spot lightsagain in the upper lefthand corner of the screen;the transfer of the 256 bitstakes 32 clock cycles. Theline load method, if used,requires the same amountof cycles, but the horizon -

2a DIGITAL

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16-by -14 register file

TIE515P

XAT R15 G15 815

control and timing

14

DATER DUMP CLKOUTMODE DOTCLK

ANALOGUE

p.

repeat bit

85044-2e

I XAT

I BLANK

1

EEApril 1986

tal (line) blanking intervalis used to allow for the bittransfer to take placebefore the scanning spotbecomes visible again atthe beginning (left) of thenext lower line on thescreen. Irrespective of themode selected, the 16registers are loaded witha video memory resident,but invisible, block of 256bits during the MODE =low interval, starting withregister 0 and ending withnumber 15 (OFhex). Notethat two bits are 'don'tcare' for every registerload, since only 14 bitsare required to fill anyregister; 4 red, 4 blue, 4green, and two auxiliary.Also note that the 256 -bitregister area in the pixelbit map is not visible onthe screen, because this isarranged to 'disappearfrom sight' by the blankingpulse.

Auxiliary bitfunctionsIn addition to the threecolour definition nibbles,each colour conversionregister in the TMS34070palette chip may hold twoauxiliary bits, the functionof which will be briefly ex-amined in the followinglines.Whenever a register is ad-dressed, the logic level of

Fig. 2. Internal structureand pin layout of the TypeTMS34070 video palettechip from Texas Instru-ments. Note the absence ofa microprocessor interface'7"DCf1017

EEApril 1986

its XAT (external auxiliary)bit is output at the corre-sponding palette terminal,which may be useful tosupply control informationfor devices external to theTMS34070. A typical use ofthe XAT funtion could bethe selection of an exter-nal RGB source connectedto an analogue multi-plexer output circuit inorder to obtain videooverlay effects. Furtherdetails of this interestingoption will be given in thesection on the Thomsonchip, later in this article.The REP (repeat) bit has afunction internal to thepalette chip; when set, itrepeats the colour infor-mation last clocked intothe palette chip. Thisfeature may be put into ef-fect as follows: first, thescreen is cleared andgiven a colour which hasan index code with theREP bit set. Next, thedesired polygon outlinesare drawn and it will beobserved that the definedscreen areas will be auto-matically coloured (Fig. 4).Any time the register withREP high is addressed, thepreviously loaded colourindex is repeated, over-riding a new latch oper-ation at the DA3...DA0and DB3...DBO inputs. So,rather than constantly ad-dressing a register to ob-tain an even colouredscreen area, the REP bitmay be programmed toeffect fast polygon fillingat the time of picturevisualization on thescreen. Needless to saythat this method offers in-teresting possibilities forreal-time video animationon an effective basis.

EF9369

70

As shown in Fig. 5a, the in-ternal configuration of thispalette chip by Thomsonis roughly indentical tothat of the TMS34070. The16 -by -12+1 register array isreffered to as the colourlookup table, CLUT. The M(marker) bit has basicallythe same function as theXAT bit in the TI chip.Unlike the TMS34070, theEF9369 has a micropro-

3aeven odd

oren I odd COLOUR PLANE 0

rid. memory

even odd COLOUR PLANE 1PLANE 2COLOUR

3frten pixels odd pixels

COLOUR PLANE

video palette chip

oddpixels

13138

DB1

18 MHz,

eh It eg DB2

DB3 RED 0even

pixel&

TMS GRN34070

}RGB0 VIDEO75 n

18 MHzDAB

BLUDA1\ 7 0DA2

shrft register DA3

18 MHzCL KOUT

XATEXTERNAL

CRT timing OATEN BLANKB.BLANK

10' FUNCTIONS

DOTCLK MODE

36 MHz

36 MHzoscillator

86044-3a

3brase

LSB LSB

MSB

LSB

XAT REP RED GREEN BLUEDA3 DA2 DA1 DAB D83 DB2 081 DB/

loaded outing first dock cycle

DA3 DA2 DA1 DAB DB3 DB2 081 088

4 fowled second

cessor interface and con-trol section; registeraddressing and loadingare likewise effected dur-ing the line or rasterblanking periods. The 9369palette chip may be usedto enhance the colourcapabilities of existinggraphics- or semi -graphicsterminals, and the chipmay even add colour toan alphanumerical ter-minal, if the interface is setup properly. All that the9369 requires are four in-put bits to address thepalette registers, and acentral clock pulse tolatch pixel data. The man-ner in which the registersare addressed and theircontents visualized isessentially the same asoutlined for the Texas chip.Loading the colour index

4

1

1

212 1

1 . . .. . . . . 1 .....1...2 ...... 1 . . . .1 . . 2 ........ 1 . . .1 . . . 2 ...... 1 . . . .

1 . 3 . . 2 . . . . 3 . . 1 . .

1.3 1

1 1 1 1 1 1 1 2 1 1 1 1 1 1 1 11 1 1 1 1 1 2 2 2 1 1 1 1 1 1 1

1 1 1 1 1 2 2 2 2 2 1 1 1 1 1 1

1 1 1 1 2 2 2 2 2 2 2 1 1 1 1 1

1 1 1 2 2 2 2 2 2 2 2 2 1 1 1 1

1 1 1 1 2 2 2 2 2 2 2 1 1 1 1 1

1 1 3 3 3 2 2 2 2 2 3 3 3 1 1 1

1 1 3 3 3 3 2 2 2 3 3 3 3 1 1 1

11331332333331111 1 3 3 3 3 3 3 3 3 3 3 3 1 1 1

Fig. 3a. The TMS34070 maylatch the four -bit codes oftwo adjacent pixels, andconvert them sequentiallyinto an RGB signal atDOTCLK frequency.

Fig 3h Timing diagram il-lustrating a TMS34070register load cycle.

Fig 4. In Fig 4a, all pixelson the screen are black(colour while the REPbit for this colour has beenset. Fig 4b shows how theoutlines of an object aredrawn in colours 1, 2, and3, all of which have REPreset. Fig. 9c shows theresult; all pixels defined asblack automatically colourlike the preceding pixel.

bits into CLUT, however, dif-fers widely from themethod specific to theTMS34070.

MicroprocessorInterfacingThanks to the interfacesection incorporated inthe EF9369, CLUT may beread and loaded via theµP bus; the register file willappear as an indirectlyaccessed 32 -byte table.Every one of the 16registers No. Nis (No... Norhexadecimal) comprises13 bits, which are dividedas 8 bits at an even ad-dress (red and green, CAand CB), four (blue, CC) inthe LS (least significant)nibble of the next odd ad-dress, and the M -bit in theLS bit position of the MSnibble at this odd address(see Fig. 6).The 9369 can be used withboth multiplexed and non -multiplexed 1.4P bus struc-tures; to select the relevantmode, the SMI (selectmode interface) terminalis tied low or high. In thelatter case, the chip maybe incorporated in systemswith CPU types such asthe 6800, 6808, 6502, or68008 which have a non -multiplexed address bus.A smart feature offered bythe Thomson palette chipin this mode is its auto -

EEApril 1986

Fig. 5. Internal structureand pin -layout of the TypeEF9369 palette from Thorn -son Semiconductors.

Fig. 6. Organization of thecolour lookup table (CLLTI,in the EF9369. The addressregister is automatically in-cremented after every dataregister access.

C

vooc Csv Ccc C

,7

C

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AC, raz;

LADA E

v .4\3ar3Ill /2

PI

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3 Al

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, 3 ADP

.ts3 ADS

6RegisterIndex

GLUT byte address 16 -register CLUT

7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0

0a

a

x

x

xx

0 0

0 0

0

0

0

0

0

I

G3 G2 GI GO R3

83

R2

B2

RIB1

RI80v IA

1a

x

a

x

a

x

e a

0 0

0

0

1

1

0I. G3 G2 G I G II R3

83

R2

B2

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110

BO./5":, Z.A.:, kl

7

151

xx

x

a

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I 1

1 1

1

1

1

1

0

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83

R2

82

RI81

Re

80" ArA M

address -increment capa-bility, which will be brieflyexamined below.The 9369 is memory -mapped at two addresses:one to hold the registernumber, the other to passregister data for read orwrite operations. If the ASterminal of the chip iswired to address bus lineAo, this will result in the fol-lowing addressingmethod:Ao = 0 : address holds

read-write datafromrfor specifiedregister;

Ao = 1 : address holdsregister number(write only).

To access a specific colourconversion register, it is firstnecessary to write its arraynumber (0..1510, 0 ..0Fhe.)to an AS=Ao=1 addresswithin the 10 block, fol-lowed by a read or writeoperation, whichever re-quired, involving anAS=Ao= 0 address within

the same block. Each ac-cess to the data registercauses the addressregister to be automati-cally incremented modulo32, which obviates theneed for the programmerto explicitly address thenext register before ac-cessing it. Obviously, thisclever auto -point methodenables the register arrayto be loaded efficientlyand fast: instead of some60 cycles, a mere 33 arenow required to load theentire array with a 'look -uptable and data downloadloop' programmed inmachine language andtriggered off during thepicture blanking interval.

Towards apracticalcircuitThe 9369 palette chipmerely requires a

terminal -generated four -bitpixel data stream at itsPo. . . P3 inputs, a dot clocksignal for the DOTCLOCKinput, and a pictureblanking pulse (BLK) todetermine the size of thedisplay window on thescreen. Pixel codes arelatched into the colour in-dex register at the risingedge of the DOTCLOCKpulse; the index register, inturn, addresses the rel-evant colour conversionregister in CLUT, and thecontents of the red, green,and blue register sectionsare passed to the threeoutput DACs, while thelogic level of the M bit ispassed straight to the chipterminal with the samename. After having beenbuffered, the RGB signalsare applied to the inputsof an RGB monitor withanalogue inputs.How RGB signal bufferingmay be put into practiceis shown in Fig. 7; either

EE

April 1986

Pia .7 Application of theEF9369 palette chip incombination with theElektor high -resolutiongraphics card.

Fig 8. The XAT or M bitallows interesting videooverlay applications to berealized swth an analoguemultiplexer such as the7),pe TEA5114 connectedas indicated.

three simple emitterfollower stages or aspecial chip, the TypeTEA5114, are connected tothe 9369 RGB outputs. Theformer has been wired tofunction as a wide -bandvideo buffer section in theproposed circuit, but Fig. 8shows a configuration inwhich a similar video out-put multiplexer devicemay be used to obtainvideo overlay effects incombination with thepalette XAT (M) signal.Returning to Fig. 7, how-ever, it can be seen thatthe high -resolutiongraphics card featured inE/ektor Electronics(September 1985 -March1986) is eminently suitedfor further colourenhancement with the ad-dition of the Thomsonpalette chip and a fewother odds and ends. Theaddress decoder sectionis local to the palettehardware and uses theE17X 10 block signalavailable on the main

7

AlA2

A3

..P bus

0

5V

16 .1

00

2

RSV 0AB 0

DO 001 002 0D3 00.. 0D5 0D6 0D7 0

'1T

A® Gl47B V6

c vsLS va

138 vni4c

5-0U7713 VITO

2

07 EI7E E17F

El7C El7D010 E17A E1./8Oil E178

D- E176 ...E177013 E174 E1754,14

8172 E173

01-5 6178 E171

05V

3 111191 018

2021

22

8

11

12

14

15

16

17

o g .9 aos p 17,

8.'4 7'CA

DO

301A132

133304305 DEAD7RP !

C

EF9369 cc

81K

3.100 n

5

6

4

281 24125)26

4

6

12V

0

14

12 V

108F

TEA5114

15 LEI

16 *

3 *

on.ecigtio RGB monitoror SCART TVsal

R

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23

GRAPHICS CARD L

B

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B

-S

graphics card (pin 7 ofIC2). The 741S138 3 -to -8decoder locates the 9369data register at E170 andthe address register atE171. If, for instance, a byte04 is written into the ad-dress register at E171, thefirst byte of the third colourconversion register maybe accessed at E170; ifdata 62hex are written tothis location, and next19hex to the same address,the following colour com-bination is selected(remember that the ad-dress register has been in-cremented automatically):red index : 2hex = 18%;green index : ones A 43%;blue index : 9nex = 62%;M -bit = 1.This mix results in a shadeof cyan. Since the M -bithas been set for thiscolour, the analoguemultiplexer shown in Fig. 8will pass the palette RGBsignals to the monitor atleast every time a pixel ofthis shade of cyan is ap-plied to the palette chip;

the RGB signals suppliedby the external videosource will not be passedin that case. In this way, ahigh -resolution overlay ef-fect may be produced,e.g. coloured bold lettersor other signs illustratingcamera -recorded stills.So far, an importantaspect of the palette andexternal video combi-nation has been leftunmentioned; it involves

the necessary clock -signalsynchronization betweenthese video sources topreclude trouble with pic-ture instability andundesirable colour inter-ference; the problem andthe method of tackling itwill be reverted to in afurther article on the sub-ject of up-to-date colourapplications. DM

8

VIDEOMEMORY

(4 bits

Per pixel) CLOCK

B/AT

palette R

G

R

EXTERNAL GVIDEO

to analogue

RGB monitor

e".

860448

-111 EE

April 1986

RFI suppressiondevicesNow available fromSwissinco UK Ltd is a widerange of RFI suppressiondevices. Products include2- and 4- terminalcapacitors; filters invarious sizes and styles; RFIsuppression chokes withopen and toroidal coresin both moulded and un-moulded versions; andspark suppression devices.VDE approved, the BVseries of suppressioncapacitors has a ratedvoltage of 250V and arated current of 4A. Typedependent, the rated ca-pacity is 0.024 to 0.2The BV series of chokes isavailable in iron -core, VHF,and thyristor versions. Ithas a rated current of 0.5to 10A and, type depen-dent, a voltage specifi-cation of 380, 440, or 250V.Certain types have VDEapproval.Also supplied is the F11,F12, F22, and F33 series ofsuppression filters. Featuresinclude a 250V rated

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Smart socketcures electronicamnesiaA new memory retentionsocket for RAMs from MSComponents eliminatesloss of data due to powerfailure.Two lithium batteries builtinto the socket providedual redundancy back-upin the case of systempower failure. A trans-parent and automaticswitching circuitry sensesthe loss of power when itoccurs and selects

whichever of the Iwo bat-teries has the highestpotential to supplymemory retention voltage.If both of the batteries fallbelow 2 volts, a batterystatus warning is initiated.The smart socket acceptseither 28 -pin 8Kx8 or24 -pin 2Kx8 CMOS staticRAMs and provides a'write protect' signal atswitch over to preventgarbled data. Memorychips used with the socketshould have a standbycurrent of less than 1 pA;typical types include theToshiba TC5564PL andTC5517BPL.

MS Components LimitedZephyr HouseWaring StreetWest NorwoodLondon SE27 9LH.Telephone: 09 670 4466Telex: 892425 (3430:1)

Plastic casesfor instrumen-tation purposesBICC-VERO Electronics nowoffer the Apollo range ofplastic cases in light and

mid grey colour combi-nations for portable ordesktop instrumentationapplications.The Apollo range com-prises six sizes for singlePCB mounting up to casesthat may hold severalboards; all types comecomplete with self-adhesive pads which,together with the pre -marked grid moulded intothe case, offer a simple,yet effective means forboard mounting. Alterna-tively, the cases accept astick -on pad with a self -tapping boss for moresecure board installation.The front and rear panelsmay be clipped on in achoice of positions andways, allowing the user toconceal or display con-nections or controls asdesired.BICC-VERO ElectronicsLimitedIndustrial EstateChandlers FordHampshire S05 3ZR.Telephone (04215) 60211Telex 47551 (3430:8:F)

EEApril 1986

74

Mini printer forportable/compactequipmentEpson OEM Division's newM-180 series miniatureshuttle printers combinehigh print quality andspeed with low powerconsumption. The newrange includes the M-180,181, 182, and 183 printers.The basic 24 -column M-180provides a print speed of1.5 lines per second (LPS)and 144 dots per line(DPL). The M-181 will give30 columns, 1.3 LPS and180 DPL; the M-182 36columns, 1.1 LPS and218 DPL; the M-183 42columns, 0.9 LPS and252 DPL. The paper widthis the same for all types at57.5 mm, and power con-sumption is low at 200 mA(typ) from a 5V supply,which makes battery oper-ation feasible.The printers can operatein text and graphicsmode; a compact controlboard, the BA -180 and

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(3430:3:F)

Top class letterquality printerStar Micronics haverecently introduced a newdot matrix printer, theNB -15. Fitted with a 24 -pinhead, it is capable of pro-ducing draft copy at 300cps and letter qualityprint-outs at 100 cps. In ad-dition to the standardASCII set with internationalalternatives in both draftand letter quality, up totwo additional fontmodules may be in use atany one time, giving aremarkable degree offlexibility.Standard features of the

new LB -15 include bothtractor and automaticsingle sheet feed, easilyaccessible DIP switchesand comprehensive frontpanel controls, full IBMcharacter set includingstandard block graphiccharacters, 16 Kbyte buffer,and easily interchange-able interfaces.Priced at around £950, theLB -15 is claimed to besignificantly betterequipped than com-petitive products, since it

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Single -boardcontrollerNew from J.P. Designs isthe Gimini 2 hand heldcontroller, ideally suitedfor real time applicationssuch as lathe control,robotics, etc, where userinteraction may be re-quired.At the heart of the systemis a Type 6502 micropro-cessor operating at 1 MHz,with up to 8 Kbytes ofstatic RAM (2K provided),

EPROM.A 6522 VIA provides 16 10lines, two 16 -bit intervaltimers and a serial shiftregister. A further eight in-puts and outputs are pro-vided for keyboard orsystem interfacing.A 6551 ACIA provides anasynchronous serial portallowing all standardbaud rates to be used.Also on the board are areal-time clock chip anda 16 -character LCD dis-play which allows user in-teraction and system statusmonitoring.The card comes with apowerful monitor programand a full documentationpackage; the price of theunit is £199.95 + VAT.J.P. Designs37 Oyster RowCambridge CBS 8LJ.Telephone: (0223) 322234

(3430:6:F)

87 EEApril 1986

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This Must be ONE OF THE YEAR'S BEST BUYSSupplied BRAND NEW and BOXED. complete with DATA and 90 day guarantee

SUPPLIED BELOW ACTUAL COST- ONLY £149.00

DECCA 80 16" COLOUR monitor. RGB input.Little or hardly used manufacturer's surplus enables us to offer this specialconverted DECCA RGB Colour Video TV Monitor at a super low price of only£99.00. a price for a colour monitor as yet unheard off' Our own interface, safetymodification and special 16" high definition PIL tube, coupled with the tried andtested DECCA 80 series TV chassis gives 80 column definition and picturequality found only on monitors costing 3 TIMES OUR PRICE In fact WEGUARANTEE you will be delighted with this product, the quality for the price,has to be seen to be believed Supplied complete and ready to plug direct to aBBC MICRO computer or any other system with a TTL RGB output Otherfeatures are internal speaker. Modular construction auto degaussing circuit,Attractive TEAK CASE, compact dimensions only 52cm W x 34 H a 24 D. 90 dayguarantee. Although used units are supplied in EXCELLENT condition, ONLY£99.00 + Carr.DECCA 80, 16 COLOUR monitor. Compositve video input Same as abovemodel but fitted with Composite Video input and audio amp for COMPUTERVCR or AUDIO VISUAL use ONLY £99.00 + Cam.REDIFFUSION MARK 3, 20" Colour monitor. Fitted with standard 75 ohn-composite video input and sound amp. This large screen colour display is ideafor shoPs, schools, clubs and other AUDIO VISUAL applicaticns Suomi' ed in ASNEW or little used condition ONLY £145.00 + Carr.BUDGET RANGE EX EQUIPMENT MONOCHROME viaeomonitorsAll units are fully cased and set for 240v standard working with composite videoinputs Units are pre tested and set up for 80 column use on BBC micro etc Evenwhen MINOR screen burns exist- normal data displays are unaffected12" KGM 320.1 B/W high bandwidth input, will display up to 132 x 25 lines

T?28fiEE f4 SCREEN version of KGM 320-1 Only£39.959 KG IA 324 GREEN SCREEN fully cased very compact unit Only £55.009 HITACHI VM-906E/K Black and White screen £49.95

Carriage and insurance on all monitors £10.00

a C. POWER SUPPLY S CIALSGOULD OF443 enciosed compact supply with regu'ated outputs of-i-5v .:-; 5 5a +12v 0 0.5a, -12v 0.1a and -23v "."` 0.02a Dim 18 x 1 1 x 6 crn i a 0 or240v input BRAND NEW only £14.95GOULD G6 -40A 5v 40 anw switch mode supply NEW £130.00GREENDALE 19A-BOE Switch mode 60 watt open PCB with a kitty regulated DCoutput of 5v .F.._ 6 amps, and three semi retated outputs of +12V, -12V +15V Fupto 1amp Dim only 11 an a 20 cm .5.5 cm Sunilar to RS 591-994 110 Or 240v AC inputTESTED ex equipment Only £24.95AC -DC Linear PSU for DISK drive and SYSTEM applications Constructed on a ruggedALLOY chassis to continuously Supply fully regulated DC outputs of +5V CE. 3 amps -5VC4 0.6 amps and +24v O 5 amps Short circuit and overvoltage protected 110 or 240 VAC input Dim 28a 12.5 x 7 cm NEW £49.95.

Carriage on PSUs E.3.00

SPECIAL 300 SAUD MODEM OFFEiAnother GIGANTIC purchase of these EX BRITISH TELECOM. BRA DNEW or little used 2B data modems allows US to make the FINALREDUCTION, and for YOU to loin the exciting world of datacommunications at an UNHEARD OF PRICE OF ONLY £29.95. Made tothe highest POST OFFICE APPROVED spec at a cost of hundreds ofpounds each, the 2B has all the standard requirements for data base.business or hobby communications. All this and more!! 300 baud hill duple. r CALL ANSWER and AUTO modes Full remote control `- Standard RS232 swat intenace CCITT tone standards .NON ONLVn Built in test switching Supplied with full data -7 E29.95

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240w Mains operation Modular construction -) A 1 year full guarantee Direct isolated connection -' y, Just 2 wires to comms line

BT 600 Jack plug and cable £2.25 Carriage and Ins £10.00

CI I c FI fiei

VDU TERMINALSStandard VDU data entry terminals at give awayrincev,OUME OVT108. Current product state of the artterminal with detachable keybOard 12- greenscreen. 2 page RAM. TVI 925 emulation 25x60.Crock, Sony' el and till base, Printer port Functionkeys etc BRAND NEW and BOXED AT ALMOSTHALF PRICE Only £425.000.1510 - EX RENTAL 280 controlled 15green screen 24 a 80 display. graphics. cursoraddressing printer port etc Very good conditionTESTED complete with manual only £225.00.ADDS 520 - Dumb terminal used. 12 tew screenR5232 interface and printer port TESTED.ONLY £125.00

Carriage on terminals £10.00100-s of other terminals in stock

CALL for more details

All prices quoted are for U.K Mainland paid cash with order in Pounds Sterling PLUS VAT Minimum order value .

Minimum Credit Card orderE10.00. Minimum BONA FIDE account orders from Government Depts_Schools.Universitiesandestablished comparuzsE20.00_ Where post and packing not indicated please ADD £1.00 + VAT. Warehouse open Mon -Fri9.30-530. Sat 10.30-5.30. We reserve the right to change prices and specifications without notice. Trade, Bulk and Export

-CL.LL 1 1\1_11 I II- -I- Telephone 01-679 4414 Telex 894502 Data 01-679 1888r 1_l CrTri A/ rt: 32 Biggin Way, Upper Norwood, London SE19 3XF

important - please mention ELEKTOR ELECTRONICS when contacting advertisers

Lowest possible prices?Top quality components?

Fast reliable service?Large range?

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Pick up a copy of our new 1986 catalogue from any branch ofW.H. Smith for just £1.45.Or post this coupon now, to receive your copy by post for just£1.45 + 40p p & p. If you live outside the U.K. send £2.50 or11 International Reply Coupons. I enclose £1.85.

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MAPLIN ELECTRONIC SUPPLIES LTD.0:r...er: P.O. Box 3. Rape on. Essex SS5 SLR.

Telephone: Southend (0702) 552911

SHOPS BIRMINGHAM Lynton Square. Perry Barr. Tel:021-356 7292. LONDON 159-161 King Street. Hammersmith, W6.

Telephone: 01-748 0926. MANCHESTER 8 Oxford Road, Tel: 061-236 0281. SOUTHAMPTON 46-48 Bemis Valley Road, Tel: 0703 225831. SOUTHEND 282-284 London Rd. West:MI-on-Sea, Essex.

Telephone: 0702.554000Shorts closed all day Monday.