July 1991 ° £1.50

CGTRONICS

CIENCE AND TECHNOLOGY

Satellites com down to Eart

Electronics wit intelligence

Simple designs for beginners

Practical

Components

Everything abou transistors

Data Sheet

The New Hitachi H8/330

01

(700

Take the Sensible Route!

Boaramaker is a powerful software tool which provides a convenient and fast method of designing printed circuit boards. Engineers worldwide have discovered that it provides an unparalleled price performance advantage over other PC-based and dedicated design systems by integrating sophisticated graphical editors and CAM outputs at an affordable price.

In the new version V2.40, full consideration has been given to allow designers to continue using their existing schematic capture package as a front end to BoardMaker. Even oowerful facilities such as Top Down Modification, Component renumber and Back Annotation have been accomodated to provide overall design integrity between your schematic package and BoardMaker. Equally, powerful

R +7.866, +6.3131N Track 1/86 45° Zoom3gl Layer=1 Width= 3015) Node 1 of 1

Full analogue, digital and SM support - ground and power planes - 45 degree, arced and any angle tracks with full net-based Design Rule Checking.

features are included to ensure that users who do not have Lead nets schematic capture software can still take full advantage of Clear nets BoardMaker’s net capabilities. ae POM acc. BoardMaker V2.40 is a remarkable £295.00 (ex. carriage & nw |

VAT) and includes 3 months FREE software updates and full EEE eae Renunber telephone technical support. ee ee ee

BoardkRouter is a new integrated gridless autoroute module which overcomes the limitations normally associated with autorouting. YOU specify the track width, via size and design rules for individual nets, BoardRouter then routes the board based on these settings in the same way you would route it yourself manually.

Optimized placement by deplaying ratsnest per component. Lines indicate the unrouted nets. This ability allows you to autoroute mixed technology designs (SMD, analogue, digital, power switching etc)in ONE PASS while respecting ALL design rules.

No worrying about whether tracks will fit between pins. If the track widths and clearances allow, BoardRouter will automatically place 1, 2 or even 3 tracks between pins.

You can freely pre-route any tracks manually using BoardMaker prior to autorouting. Whilst autorouting you can pan and zoom to inspect the routes placed, interrupt it, manually modify the layout and resume autorouting.

BoardRouter is priced at £295.00, which includes 3 months FREE software updates and full telephone technical support. BoardMaker and BoardRouter can be bought together for only £495.00. (ex. carriage & VAT)

Tsien (UK) Limited | Don’t just take our word for it. Call us Cambridge Research Laboratories foday for a FREE Evaluation Pack and 181A Huntingdon Road judge for yourself.

Cambridge CB3 ODJ UK Tel 0223 277777

" Voter -3-4-) Sa {S1EN. Fax 0223 277747 ~*~ _ |

All trademarks acknowledged

Cm mmm g <<< July 1991 © Volume 27 No. 7

Due to a lack of communication

petvrear iycolt anil Hlkica ne A Low Hertz Meter... en ee ssosneeeeeeennnnteeessniieesnanieeente 25 H8/330 did not get published as More essential test equipment to build and use.

advertised on the cover last month.

Farlnaiclv- esc itlon hasitesk PE Chronos............. coeeesneenentensaien seseeneensavensnensaeessnensarenan 3/ sorted out and the chip is featured in The final part of the Universal Counter Timer.

the Data Sheet section this month. LOGIC ANAIVSEM oo... eeeecescesecessesscsesessssscescsesuecsuseeeseneees 47

Judging by the number of phone Calls to PE's offices, many readers are missing the PCB service. Unfortunately, this had to be withdrawn for economic reasons - it has since been farmed out to a third party.

As anyone who has done it will tell you, it is quite easy to build your own PCBs and the materials are widely available. To prove the point | set about making a board the results of which can be seen on page 43 to my shame, | have to admit that this is the

A digital code convertor for the workshop.

The Satellite Story oo... cccccssscesscssssssssescssecssesssnsenes 10 The Earth is caught up in an invisible web of telecommunications. Since the launch of TelStar, satellites have played an important role. Neural Networking ........c cece ceecssesecsssesessssesssesscssessssseesees 16 Computers modelled on the human brain may offer startling new processing capabilities.

first PCB | have ever made (degree Innovation and Alienation ..........cccccccsccccssccccesssceeeessseeeeeees 22 level electronics courses are heavy on | Technology affects our values in subtle ways the theory but can be light on the nee

? : Printed Circuit COnStruction .......cccsccssccsecssecseeseessecseeseeseenee. 43

practice).

Kenn Garroch, Editor} Almost all designs use PCBs. Learn how to build them yourselt.

Wavelength... ccccccccccccssssccscessssescesesesesseeeessessreeeseeessnnees 5 The great debate over resistor symbols rumbles on plus modificationbs to the PE Tele-Snap.

PIVOT ONS ssanactntssaecicencenantacesttuceeeterntdustetecessenacteneetencastann 6 Microcircuitry, macroeconomics, meters and much more. DECC IRs) 1 :1:) ae 31

Full specifications and diagrams of the new Hitachi H8/330 super powered microcontroller.

Practical COMPONENES.............ceccceesesesseceneesenseeeesteeserseesens 34 The transistor is the key component in modern logic circuit technology.

TOCHINIQUES .....c cece ccccceccccccccessssseeeeeeeeeesseesssnteeeeeneeeeeeeeesens 58 A variety of problems solved by our technical expert, including teperature sensors and guitar pickups.

Barry FOX ......ccecccccccccsseeeeecesseeeessesseeseesessuesesecessueveseseeseas 63

Remote sensing... Charge-Coupled Once again the hydra-like problem of radio spectrum bandwidth

Devices have enormously extended the allocation rears its ugly heads. reach of modern telescopes. IRIS, the

latest IR device, has probed structures

millions of light years away.

Editor: Kenn Garroch Technical Editor: Andrew Armstrong Technical Illustrator: Derek Gooding Advertisement Manager David Bonner Production Manager: Richard Milner Production Assistant: Michael Sullivan Office Manager: Laura Esterman Office Secretary: Wendy Rhodes Publisher: Angelo Zgorelec ¢ Practical Electronics Intra House 193 Uxbridge Road London W12 9RA Tel: 081-743 8888 Fax: 081-743 3062 Telecom Gold: 87: SQQ567 « Advertisements The Publishers of PE take reasonable precautions to ensure that advertisements published in the magazine are genuine, but cannot take any responsibility in respect of statements or claims made by advertisers. The Publishers also cannot accept any liability in respect of goods not being delivered or not working properly. ¢ © Intra Press 1991. Copyright in all drawings, photographs and articles published in PRACTICAL ELECTRONICS is fully protected, and reproduction or imitations in whole or in part are expressly forbidden. All reasonable precautions are taken by PRACTICAL ELECTRONICS to ensure that the advice and data given to readers is reliable. We cannot, however, guarantee it, and we cannot accept legal responsibility for it. Prices quoted are those current as we go to press. All material is accepted for publication on the express understanding that the contributor has the authority to permit us to do so. ¢ Practical Electronics is typeset at Intra Press on Macintosh computers using Quark Xpress. Reproduction by Tetracolour Ltd. Printing by Andover Press, St Ives plc. Distribution by Seymour Press ¢ ISSN 0032-6372 ©

July 1991 Practical Electronics 3

* * ERIES * FRIENDLY SERVICE * LOUDSPEAKERS-19 INCH STEREO RACK AMPLIFIERS LARGE S.A.E., 30p STAMPED FOR CURRENT LIST.

PITTEOTEEWULIMSIEEMTICIIUMES) supplied reaay built and testea OMP VARISPEED TURNTABLE CHASSIS.

OMP POWER AMPLIFIER MODULES Now enjoy a world-wide reputation for quality. reliabiity and MANUAL ARM se STEEL CHASSIS # ELECTRONIC SPEED CON: performance at a realistic price Four models available to suit the needs of the professional and hobby market. |e . Industry TROL 33 & 45 #& VARI PITCH CONTROL #& HIGH TORQUE SERVO Leisure. Instrumental and Hi-Fi etc. When comparing prices. NOTE all models include Toroidal power supply. Integral heat sink DRIVEN DC MOTOR ® TRANSIT SCREWS ® 12 DIE CAST PLATTER & Glass fibre P CB. and Drive circuits to power compatible Vu meter Open and short circurt proot AS NEON STROBE % CALIBRATED BAL WEIGHT % REMOVABLE HEAD

5 Swe F SS $ SHELL #% '- CARTRIDGE FIXINGS % CUELEVER #% POWER 220 240V THOUSANDS OF MODULES PURCHASED BY PROFESSIONAL USERS Ss ——_ SUEUR We seh GG CUPPED a MOTI CUT OUT

OMP100 Mk 11 Bi-Polar Output power 110 watts TEMPLATE PRICE £59.99 + £3.50 P&P. R.M.S. into 4 ohms, Frequency Response 15Hz - 30KHz -3dB, T.H.D.0.01%,S.N.R. 118dB, Sens. for Max. output 500mV at 10K, Size 355 «x 115x65mm. PRICE £33.99 + £3.00 P&P.

NEW SERIES Il MOS-FET MODULES THOUSANDS PURCHASED OMP/MF 100 Mos-Fet Output power 110 watts R.M.S. MRGLAMMO)W/=5 RUA AOMCLALUN IN SORA CLRMAE CLG BY PROFESSIONAL USERS

into 4 ohms, Frequency Response 1Hz - 100KHz ~3dB, Damping Factor, >300, Slew Rate 45V uS. “sy

T.H.D. Typical 0.002%, Input Sensitivity 500mV, S.N.R. aa Cea eeieieaiu ices amare —125dB. Size 300 x 123 x 60mm.

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STANTON ALS500 GOLDRING G850 PRICE £16.99 + 50p P&P PRICE £6.99 + 50p P&P

& & e& As

OMP/MF200 Mos-Fet Output power 200 watts R.M.S. into 4 ohms, Frequency Response 1Hz 100KHz -3dB, Damping Factor >300, Slew Rate 50V uS, T.H.D. Typical 0.001%, Input Sensitivity 500mV, S.N.R. ~130dB. Size 300 «x 155 x 100mm.

PRICE £62.99 + £3.50 P&P.

NEW MXF SERIES OF POWER AMPLIFIERS ~ THREE MODELS:— MXF200 (100w + 100w) MXF400 (200w + 200w) MXF600 (300w + 300w)

All power ratings R.M.S. into 4 ohms

FEATURES: « Independent power supplies with two Toroidal Transformers * TwinL.E.D. Vu meters * Rotary indended level controls * Illuminated on off switch * XLR connectors * Standard 775mV inputs * Open and short circuit proof * Latest Mos-Fets for stress free power delivery into virtually any load * High slew rate * Very low distortion * Aluminium cases * MXF600 Fan Cooled with D.C. Loudspeaker and Thermal Protection

USED THE WORLD OVER IN CLUBS, PUBS, CINEMAS, DISCOS ETC. SIZES:—- MXF 200 W19" x H3¥2" (2U) x D111"

MXF 400 W19° x H5%" (3U) x D12” MXF 600 W19" x H5%" (3U) x D13" MXF200 £171.35

PRICES: MXF400 £228.85 MXF600 £322.00

SECURICOR DELIVERY £12.00 EACH

OMP LINNET LOUDSPEAKERS OMP SLIDE DIMMER 1K WATT & 2.5K WATT

CONTROLS LOADS UP TO 1KW & 25KW SUITABLE FOR RESISTIVE AND INDUC TIVE LOADS BLACK ANODISED CASE READILY FLUSH MOUNTED THROUGH PANEL CABINFT CUT-OUTS ADVANCED FEATURES INCLUDE :—

; OMP/MF300 Mos-Fet Output power 300 watts R.M.S. into 4 ohms, Frequency Response 1Hz 100KHz -~3dB, Damping Factor >300, Slew Rate 60V uS, T.H.D. Typical 0.0008%, Input Sensitivity 500mV, S.N.R. —130dB. Size 330 x 175 x 100mm.

PRICE £79.99 + £4.50 P&P.

NOTE:— MOS-FET MODULES ARE AVAILABLE IN TWO VERSIONS. STANDARD INPUT SENS 500mV BAND WIDTH 100KHz PEC (PROFESSIONAL EQUIPMENT COMPATABLE; - INPUT SENS 775mV BAND WIDTH SOKHz ORDER STANDARD OR PEC

Vu METER Compatible with our four amplifiers detailed above. A very accurate visual display employing 11 L.E.D. diodes (7 green, 4 red) plus an additional on off indicator Sophisticated logic control circuits for very fast rise and decay times. Tough moulded plastic case. with tinted acrylic front. Size 84 x 27 x 45mm

Bee PRICE £8.50 + 50p P&P.

I

LOUDSPEAKERS a> LARGE SELECTION OF SPECIALIST LOUDSPEAKERS

AVAILABLE, INCLUDING CABINET FITTINGS, SPEAKER THE VERY BEST IN QUALITY AND VALUE

ti Vif!” GRILLES, CROSS-OVERS AND HIGH POWER, HIGH FRE- L mf QUENCY BULLETS AND HORNS, LARGE S.A.E. (30p VM” STAMPED) FOR COMPLETE LIST.

McKENZIE:— INSTRUMENTS, P.A., DISCO, ETC. ALL McKENZIE UNITS 8 OHMS IMPEDENCE

MADE ESPECIALLY TO. SUIT TODAYS NEED FOR’ COM.- PACTNESS WITH HIGH OUTPUT SOUND LEVELS. FINISHED IN HARDWEARING BLACK VYNIDE WITH PROTECTIVE CORNERS

® FULL 65mm SLIDE

8” 100 WATT C8100GPM GEN PURPOSE, LEAD GUITAR, EXCELLENT MID . DISCO ESErORMEC OS ponee te idee’ RES. FREQ, 80Hz FREQ. RESP, TO 14KHz SENS, 99dB PRICE £28.59 + £2.00 P&P. HIGH FREQ HORN FOR FULL | 10” 100 WATT C10100GP GUITAR, VOICE, ORGAN, KEYBOARD, DISCO, EXCELLENJ MID FREQ. RANGE 45H7-20KH? BOTH MONITO' INDICATOR RES. FREQ, 70Hz FREQ, RESP, TO6KHz SENS. 100dB PRICE £34.70 + £2.50 P&P. MODELS 8 OHM. SIZE H18° - W15 * FLASH OVFRRIDF 10” 200 WATT C10200GP GUITAR, KEYBOARD, DISCO. EXCELLENT HIGH POWER MID - 012 BUTTON RES. FREQ, 45Hz FREQ, RESP. TO7KHz SENS. 103dB PRICE £47.48 + £2.50 P&P. | # HIGH & LOW LEVE! 12” 100 WATT C12100GP HIGH POWER GEN, PURPOSE. LEAD GUITAR, DISCO CHOICE OF TWO MODELS * AN PRESETS RES. FREQ, 45Hz FREQ. RESP. TO7KHz. SENS, 98dB PRICE £36.66 + £3.50 P&P. . Fie cue eee 12” 100 WATT C12100TC TWIN CONE) HIGH POWER WIDE RESPONSE, PA. VOICE, DISCO POWER RATINGS QUOTED IN WATTS RMS FOR EACH CABINET 16-85 Bie RES, FREQ, 45Hz FREQ, RESP, TO 14KHz SENS. 100dB PRICE £37.63 + £3.50 P&P. SIZES:— 12” 200 WATT C12200B HIGH POWER BASS. KEYBOARDS. DISCO, PA : 99 PER PAIR Pete aan aee RES. FREQ, 40Hz FREQ, RESP. TO7KHz SENS. 100dB PRICE £64.17 + £3.50 P&P. OMP 12-100 (100W 100dB) PRICE £159.99 PE > SKW H128 - W76 - D79mm 12” 300 WATT C12300GP HIGH POWER B«SS LEAD GUITAR, KEYBOARDS, DISCO, ETC OMP 12-200 (200W 102dB) PRICE £209.99 PER PAIR Siicks...anerensas RES. FREQ, 45Hz FREQ, RESP, TOSKHz SENS, 100dB PRICE £85.79 + £3.50 P&P. 15” 100 WATT C15100BS BASS GUITAR, LOW FREQUENCY. PA. DISCO SECURICOR DEL.:— £12.00 PER PAIR 2.5K WATT £24.99 + 60p P&P RES. FREQ, 40Hz FREQ RESP. TO5KHz SENS, 98dB PRICE £53.70 + £4.00 P&P. 15” 200 WATT C15200BS VERY HIGH POWER BASS PIEZO ELECTRIC TWEETERS-MOTOROLA 15° 250 WATT C16250B8 VERY HIGH POWER BASS. PRICE 73.28 + £4.00 PAP. J PIEZO ELECTRIC TWEETERS MOTOROLA

x Join the Piezo revolution. The low dynamic mass (no voice coil) of a Piezo tweeter produces an improved transient RES. FREQ, 40Hz HORDE eae HIG EOWER Loo EEE OUENey er £80.53 + £4.50 P&P. response with a lower distortion level than ordinary dynamic tweeters As a crossover is not required these units can ee eee Seo ee PRICE £94.12 +£4.50 P&P. | 2€ added to existing speaker systems of up to 100 watts (more if 2 put in series) FREE EXPLANATORY LEAFLETS 18” 400 WATT C18404BS EXTREMELY HIGH POWER, LOW FREQUENCY BASS SHERRIEOWITHEACH TWEETER. ~ VBE “Ai (KSNZ09GA). 6” yolind wilh protective: wile RES. FREQ, 27Hz FREQ. RESP. TO3KHz SENS, 99dB PRICE £167.85 + £5.00 P&P. mech. ideal tor bookchell and caediuch <izad Hich

speakers. Price £4.90 each + 50p P&P

TYPE ‘B’ (KSN1005a) 3'>" super horn. For general purpose speakers, disco and P.A. systems etc. Price £5.00 each + 50p P&P.

TYPE ‘C’ (KSN6016A) 2” « 5" wide dispersion horn. For quality Hi-fi systems and quality discos etc. Price £6.99 each + 50p P&P.

TYPE ‘D’ (KSN1025A) 2’«6' wide dispersion horn. Upper frequency response retained extending down to mid range (2KHz). Suitable for high quality Hi-fi systems and quality discos. Price £9.99 each + 50p P&P. TYPE ‘E’ (KSN1038A) 3°." horn tweeter with attractive Silver finish trim. Suitable for Hi-fi monitor systems etc. Price £5.99 each + 50p P&P

LEVEL CONTROL Combines on a recessed mounting

EARBENDERS:— HI-FI, STUDIO, IN-CAR, ETC.

ALL EARBENDER UNITS 8 OHMS EXCEPT EB8-50 AND EB10-50 DUAL 4 AND 8 OHM. BASS, SINGLE CONE, HIGH COMPLIANCE, ROLLED FOAM SURROUND

8” 50 WATT EB8-50 DUAL IMPEDENCE, TAPPED 4 8 OHM BASS. HI-FI, IN-CAR

RES, FREQ, 40Hz. FREQ, RESP, TO 7KHz SENS, 97dB PRICE £8.90 + £2.00 P&P. 10” 50 WATT EB10-50 DUAL IMPEDENCE. TAPPED 4 8 OHM BASS. HI-FI, IN-CAR

RES, FREQ, 40HZ. FREQ, RESP, TO 5KHz. SENS, 99dB PRICE £12.00 + £2.50 P&P. 10” 100 WATT EB10-100 BASS, HI-FI, STUDIO

RES, FREQ, 35Hz FREQ, RESP, TO 3KHz. SENS, 96dB PRICE £27.50 + £3.50 P&P. 12” 60 WATT EB12-60 BASS. HI-FI, STUDIO

RES. FREQ, 28Hz FREQ. RESP. TO3KHz SENS. 92dB PRICE £21.00 + £3.00 P&P. 12” 100 WATT EB12-100 BASS. STUDIO. HI-FI, EXCELLENT DISCO

RES, FREQ, 26Hz. FREQ. RESP. TO 3KHz. SENS. 93dB PRICE £32.00 + £3.50 P&P. FULL RANGE TWIN CONE, HIGH COMPLIANCE, ROLLED SURROUND

5%" 60 WATT EBS-60TC (TWIN CONE) HI-FI, MULTI-ARRAY DISCO ETC

RES, FREQ, 63Hz FREQ, RESP, TO 20KHz SENS, 92dB | PRICE £9.99 + £1.50 P&P. 62” 60 WATT EB6-60TC (TWIN CONE) HI-FI, MULTI-ARRAY DISCO ETC Seamer gaye oo + cos Pae JAG SOGKet RES, FREQ, 38Hz FREQ, RESP, TO 20KHz SENS. 94dB PRICE £10.99 + £1.50 P&P. |

8” 60 WATT EB8-60TC (TWIN CONE) HI-FI, MULTI-ARRAY DISCO ETC a

RES. FREQ, 40Hz FREQ. RESP. TO 18KHz. SENS, 89dB PRICE £12.99 + £1.50 P&P. STEREO DISCO MIXER =

eSS SS

10” 60 WATT EB10-60TC (TWIN CONE) HI-FI, MULTI-ARRAY DISCO ETC RES, FREQ, 35Hz. FREQ, RESP, TO 12KHz SENS, 86dB PRICE £16.49 + £2.00 P&P.

TRANSMITTER HOBBY KITS

PROVEN TRANSMITTER DESIGNS INCLUDING GLASS FIBRE PRINTED CIRCUIT BOARD AND HIGH QUALITY COMPONENTS COMPLETE WITH CIRCUIT AND INSTRUCTIONS

STEREO DISCO MIXER with 2 x 5bandL &R graphic equalisers and twin 10 segment L.E.D. Vu Meters. Many outstanding features 5 Inputs with individual faders providing a useful com- bination of the following:—

3 Turntables (Mag). 3 Mics. 4 Line including CD plus Mic with talk over switch Headphone Moni- tor. Pan Pot L. & R. Master Output controls. Output 775mV. Size 360 x 280 x 90mm. Supply RN

3W FM TRANSMITTER 80-108MHz. VARICAP CONTROLLED PROFESSIONAL PER. FORMANCE. RANGE UP TO 3 MILES. SIZE 38 « 123mm. SUPPLY 12V « 0SAMP 220-240v.

PRICE £14.49 + £1.00 P&P 3 watt FM Price £134.99 -— £4.00 P&P FM MICRO TRANSMITTER (BUG) 100-108MHz VARICAP TUNED COMPLETE WITH Transmitter

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4 Practical Electronics July 1991

Wavelengths

If you have any comments, suggestions, subjects you think shouled be aired, write to PE

found the Tele-Snap project in [es May issue of PE interesting

until the software part came into view.

It seems a pity that GW-Basic was used as there are so many good versions of Basic available for the PC these days. However, once I saw Locomotive Basic 2 mentioned, this signalled the Amstrad PC1512 computer.

If Mr. Becker was using a PC1512 he is correct when he says he cannot use 16 colours from GW- basic, but if he was using an IBM compatible with EGA graphics then my version of GW-Basic will allow the use of 16 colours.

I was an Amstrad PC1512 owner and I quickly got fed up with Basic 2 so I taught myself to program in C, Borland Turbo C in fact, the effort being well worth it I would say. Now to the best part; because I wanted to use the unique 16 colour mode of the Amstrad PC1512 I wrote a graphics library in C which allows the programmer to access the 16 colours just as easily as if using a proper EGA card - the library is available from me at the fully inclusive price of £10.95 and is compatible with Turbo C v1.5 and Turbo C v2.0.

Not content with this I then rewrote the library in Turbo Pascal and this is also available from me for £10.95 and is compatible with Turbo Pascal v4.0, v5.0 and v5.5..

Both disks contain a demo program and several example programs and are available on 5.25in or 3.5in disks, please state size when ordering.

If, like me, you already have an expansion card fitted to your PC which uses address space at 300H then the following modification may be of use.

The PC allocates I/O memory space to a prototype card from 300H to 31FH, its official title is “prototype card I/O map” but this really means the area has not been reserved by IBM for its own use and is available for the user safe in

the knowledge that the computer will not try to access it for any internal use.

As the card already installed in my computer uses I/O addresses 300H to 303H I would need to change the Tele-Snap I/O address to 310H using the following method.

By cutting a few tracks on the PCB and soldering a few links on, the unused gate in IC3 can be used to invert A4 which now makes the base address of the Tele-Snap 310H

If a clearer modification is required then an IC socket can be used for IC1 and a small board made up which plugs into this using a header plug —- an extra 74HC04 would then be required. Douglas Fisher Highfield Braithwaite Workingham Cumbria CA14 4TG

More Squiggles

In May 1991, John Bilson commented that he thought that the ‘squiggle’ resistor was the standard symbol. However, I understand from my GCSE and A level studies that the rectangle was now standard. I remember in the second year I wrote down a squiggle and was told not to do it again!

On the subject of the new design of Practical Electronics, I would like to ask what has become of Space Watch? I have been an intermittent read of the magazine over the past twelve months and the main reason that made me decide to start reading it regularly was the space item that set it apart from other

Letters

magazines. I read with interest the so called ‘science feature’ on superconductors in the May edition. Is this going to be a regular feature, perhaps taking in some of the items from space watch?

Your series named ‘How It Works’ is very good. I like the cut away pictures that have been included. Talking of ‘How It Works’, are you going to publish follow up articles on Nicam Stereo. It seems a pity that ,after showing technical details, this is not backed up with a practical project to show the system, perhaps a small project that would fit into an existing TV?

The article on computer interfacing (April 1991) was illuminating. Here I am typing this letter into my QL with all its slots and plug holes and not a mention in the articles. Am I the only reader with such a computer? I doubt it as it has been described by some people as a good hacking machine or good for experimenting with add on electronics. In addition to having 256k put aside for add-ons, the computer can automatically check for such devices and link in any required extensions to the operating system, if the hardware is accompanied by a small ROM.

Overall I very much like your magazine. I nearly entered the loyalty bonus contest last month but, to my consternation, I find for this and other months that the slip we have to send in is on the other side of some pretty informative articles. Is it not possible to arrange that the slip is with the other adverts, or even on a page of its own?

James Gibson Newbury Berks

Alas, Space Watch is no more but there will be other articles covering similar ground in the future. I'll have to look into the Nicam question nothing is planned at the moment. As for the QL, I'm afraid that there wasn't space, perhaps in a future issue. Turn to page 53 for the solution to your tearing problem. a

July 1991 Practical Electronics 5

Innovations

Telepoint Tax Peril

he new tax on mobile telephones may apply to

telepoint phones as well, because the Treasury is apparently unaware of the difference between telepoint and cellular phones. Telepoint phones are cheaper but can only make outgoing calls and must be in range of a base station, thus cannot be used to annoy customers in restaurants. With only about 5000 subscribers the system is struggling to stay alive. Telepoint operators are keeping their heads down hoping the tax will not be levied on their service.

TV interference

he proposed Channel 5 TV service is liable to

clash with the frequencies used by millions of home video units in the UK. The new service will use two UHF frequencies called channels 35 and 37 these are currently used by radio microphones and airport radar. The channels will be freed for TV use by moving radio mics off the TV waveband and by transferring radar to channel 36.

Unfortunately a lot of domestic video equipment already uses these frequencies, albeit at low power, to connect to the aerial sockets of TV sets, and often suffers from interference as a result. For instance in the area around Heathrow airport, which uses channel 36 radar, many video recorders must be retuned to channel 37 from the usual channel 36 setting.

Under the terms of the

n

broadcasting Act 1990, franchisees of Channel 5 TV must pay for any modifications to equipment necessary because of interference. Taking into account the numbers of video sets, satellite receivers and game machines involved, the cost is likely to run into many millions of pounds.

Funding Doom?

he annual State of the Universities report from the

6 Practical Electronics July 1991

Committee of Vice- Chancellors and Principals suggests that increases in research grants from industry and medical charities have more than made up for a relative lack of government funding over the past decade. The cash available for each tenured researcher has increased by 35% since 1984, and there are now more researchers doing more research. But since the new funds are often applied to short-term, applied research with a quick payoff - rather

than basic science, which is regarded as_ the government’s respon- sibility - long-term research projects have suffered.

Protectionism

uropean Com- munity policy on support for the

home electronics industry may be in disarray after a recent move by France. When the European Commission, which controls Brussels-based aid to electronics companies, announced a reorientation of funding away from basic research and towards market-lead developments, the French called for an agency modelled on the ESA to support electronics without interference from Brussels and announced £1 billion of support for Bull and Thomson, the computer giants which made record losses last year. The Commission replied that the last attempt at such an agency, the French- sponsored Eureka plan, failed to gain significant support from industry. Furthermore the Commission has promised to investigate the French aid as an unfair subsidy and a distortion of free trade.

A report in The Economist (20-26 April) claims that state subsidies for European computer companies, in the form of grants and large government contracts, have merely enabled manufacturers to survive in the face of superior international competition, and are thus counter- productive.

Instruments

PCB failures can now be tracked down to component level without powering up the boards and without circuit documentation using T3000, a new trouble- shooting instrument for fault-finding on analog or digital printed circuit boards. Designed by Polar and distributed in the UK by Whingate, this portable instrument uses the powerful impedance signature technique to address PCB repair issues.

The T3000 tests a PCB On a component by component basis. It works by applying an AC signal which is both voltage and _ current limited to the component under test and displaying the resulting dynamic “impedence signature” on its built in screen. Different types of component present different forms _ of signature and it is easy to spot when one has failed. This technique easily identifies the vast majority of service-related problems; catastrophic component failures and open or shorts. In its “compare” mode it allows the signature of a good board to be displayed alongside that of the faulty board under test and it is also possible to spot a large proportion of complex parametric failure modes.

The T3000 checks any kind of device technology from discrete resistors, capacitors, inductors, diodes and transistors to analog or digital ICs. It is also possible for non- electronics specialists to operate as it has built in easy to use features such as the autoranger which auto selects the best drive

Innovations

for the device under test. The cost is £2,450 and it is available from Whingate Test Services Ltd 0202 605239.

When measuring far away from any mains power, the new HP 8590B rugged spectrum analyser run from the Hewlett Packard 85901A AC power source could prove useful. It covers a frequency of 9kHz to 1.8GHz and an amplitude range from -115dBm to +30dBm. The new spectrum analyser also has 32 kbytes of nonvolatile program memory and a built in clock/calendar which can be used to stamp time and date information onto test results. Rates are £281 + VAT for one week’s rental which can be obtained from Hewlett Packard Rental Department on 0753 580000.

Testing TVs can sometimes be confusing since it is important to know whether it’s the box or the remote control which is to blame. A remote control tester, now available from Maplin in kit form, checks whether

the remote control unit is transmitting an infra-red carrier or data stream. This tester ignores any ambient infra-red energy, so it can be used in full sunlight. It works by detecting changes in the ambient infra-red level

July 1991 Practical Electronics 7

Innovations

and converts these into visible light by means of an amplifier and red LED. The kit costs £7.10 inc. VAT and is available from Maplin on 0702 554155.

Logic Probes designed for use with TTL, DTL and CMOS IC’s are now available from Maplin for £15.28 (plus postage). Using its memory function to detect the occurrence of single pulses or logic level, the probe can recognise pulses from 30ms up to 500ms. It has 3 coloured LRDs showing high logic level (red), low logic level (green) and pulse(yellow).

Radio buffs are set for an exciting time as with the deregulation of the airwaves as 200 or more new independent local radio station are planned. To enable listeners to take advantage of the variety of stations, the Maplin Radio Rod has been launched. This rod is

Omni-directional and designed to receive national and local

transmissions from any direction in the range 88- 108 MHz. It can be fitted in the loft or on the outside of the house together with a coax plug or coupler. Cost £14.25 inc. VAT (plus postage).

General

Miniature lamps designed for building into electronic and electrical equipment are now available at quite reasonable prices. The range consists of 3 basic types: signal filament 6- 70V current ratings 20- 200mA; signal neon and green fluorescent lamps 60-220V and current rating 0.3-3.5mA; multi LED lamps in red, green

or yellow 6-48 VDC current rating 10-35mA. The lamps have a life expectancy of between 3000 and 100,000 hours and are available from Electroustic Ltd on 0254 333664.

Ion imbalances in the home can be restored using the new ioniser kit from Maplin. The ioniser called Breeze, produces negative ions electronically to counteract the excessive positive ions generated by electronic apparatus such as TVs. The kit costs £33.67 inc. VAT and is aimed at the experienced constructor as the ioniser generates very high internal voltage and needs to be built with care. For more information contact Vic Sutton of Maplin on 0702 554155.

8 Practical Electronics July 1991

Computers The Oak VGA card from Southern Peripherals, keenly priced at £42, enables users to get graphics display on IBM PC’s AT’s and XTs ata low cost. It claims to have more functions than a standard IBM VGA and as it is fully compatible with the IBM Bios, it is also downwards compatible with MDA, monochrome Hercules, CGA and EGA standards. One of the other key features is that the Oak VGA can be used with a variety of packages including Windows 3.0, Lotus 1-2-3 version 2, Framework II and III, Wordperfect 5.0 and 5.1, Ventura VI.I and Autocad. The card also supports 132 column text mode applications such as Wordstar version 3.3 and 4.2 and Wordperfect version 4.2. The card gas a single ship VGA graphics controller which provides fast host access to video memory, allowing 32bit access to the video RAM.

It operates with a memory configuration of 256kbyte. It can be bought from Southern Peripherals in Hampshire 0256 819 221.

Bigger Bytes are in from Mitsumi with their 3.5 inch floppy disk drives in anticipation of the move to higher capacity 4Mbyte design as the next market standard. This 1 inc high drive is compatible with 1Mbyte, 2DD, 2Mbyte and 2HD media and is powered from signel 5V supplies. It is distributed by Southern Peripherals and enquiries should be directed to their sales office on 0256 819221.

Events

ussex Amateur Radio and Computer Fair is on 14th July at the Brighton Racecourse, Brighton. It starts at 10.30 and purports to bring together the best of computer, amateur radio and component specialists under one roof. Contact: Ron Bray (0273) 415654.

Fourth International 16- Bit Computer Show, 12th- 14th July,The Novotel, London W6. Forum for the latest products and services for the Atari ST, Commodore Amiga and PC. Contact: Tim Collins (081) 549 3444.

Reference Readers may find the Crydom Solid State Relay Handbook at £11.87 a usefully comprehensive reference book. It covers over 233 pages detailing the use and application of devices in the range 0.7A to 90A;120 to 480 AC 4 to 15V DC. Sales enquiries to Alan Coulling, Unitel 0438 321393. a

| mr SQ) Murtifesters

y ¥ 4 \ eo TALKING METER

£79.95 2:16:

[A] Talking Multitester. Press a button on the probe and the meter will call out it’s reading in clear English. The reading is also shown on the units large, easy to read LCD display. Features autoranging, autopolarity, continuity sounder, diode-check and over-range indicators. Measures to 1000 VDC, 750 VAC, 300mA AC/DC, 30 megohms resistance. Requires 4 “AA” batteries.

Digital Multimeter. Full

autorange or manual range

control, selectable by a

switch. Easy to read LCD

display. Ideal for use in the

field, lab, shop, bench or

home. Fold-out stand allows DiC METER you to adjust position for

better visibility or to hang

unit. Features continuity £39 , 95 22-184 check, autopolarity, diode-

check and low battery

indicator. Measures to 1000

VDC, 750 VAC, 200 mA AC/DC,

20 megohms resistance.

Requires 2 “AA” batteries.

andy

ALL THE ACTION AS IT HAPPENS!

InterTAN U.K. Ltd., Tandy Centre, Leamore Lane, Walsall, West Midlands. WS2 7PS Tel: 0922 710000 July 1991 Practical Electronics 9

Satellite Feature

Talking fo

The Skies

Satellite TV, once a dream, is now an accepted part of everyday entertainment. John Brook switches on tunes in and wigs out to find out what it is all about.

s well as being useful for A reviational purposes (they

always point south), TV satellite dishes are bringing more and more news and entertainment into our homes. After getting off on a fairly rocky start, satellite TV is now an established part of the UK entertainment scene.

There are 16 major satellites in geosynchronous or Clarke orbits, visible from the UK. All transmit TV signals in one form or another and represent a colossal investment in the future of communications and direct broadcast TV. Unfortunately, there are a number of different standards in use for encoding the picture as well as a few systems that use scramblers as well.

By far the most common formats