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SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: https://www.tek.com/ Vol.8, No.7; July 1995 Contents FEATURES 4 Review: Philips’ CDI 210 Interactive CD Player It plays audio & video CDs, CDI discs & photo CDs – by Leo Simpson 8 Review: The Jamo Classic 4 & Classic 8 Two-Way Bass Reflex Loudspeaker Systems Two new high-quality loudspeaker systems from Denmark – by Leo Simpson 16 Review: The Brymen 328 Automotive Multimeter PHILIPS’ CDI 210 INTERACTIVE CD PLAYER – PAGE 4 Affordable diagnostics for electronic engine management systems – by Julian Edgar PROJECTS TO BUILD 20 A Low-Power Electric Fence Controller An automotive ignition coil makes it easy to build – by John Clarke 32 Run Two Trains On A Single track This circuit lets you run two trains on the same track & also includes level crossing lights & sound effects– by Branco Justic 40 Setting Up A Satellite TV Ground Station; Pt.3 Aiming the dish at the desired satellite & tuning in – by Garry Cratt 54 Build A Reliable Door Minder It uses an ingenious pressure sensing method – by Rick Walters LOW-POWER ELECTRIC FENCE CONTROLLER – PAGE 20 76 A Low-Cost MIDI Adaptor For Your PC Or Amiga It’s based on a standard I/O card plus a small add-on board that fits inside a D15 or D25 plug – by George Hansper SPECIAL COLUMNS 68 Serviceman’s Log Well, it looked like that at first – by the TV Serviceman 63 Computer Bits Adding RAM to your computer – by Greg Swain 72 Remote Control Transmitter interference: what can be done about it – by Bob Young 82 Vintage Radio RUN TWO TRAINS ON A SINGLE TRACK – PAGE 32 The 8-valve Apex receiver: a glorified sardine tin – by John Hill DEPARTMENTS 2 Publisher’s Letter 38 Circuit Notebook 53 Bookshelf 88 Product Showcase 92 Ask Silicon Chip 93 Notes & Errata 94 Market Centre 96 Advertising Index ADDING RAM TO YOUR COMPUTER – PAGE 63 July 1995  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Rick Walters Reader Services Ann Jenkinson Advertising Enquiries Leo Simpson Phone (02) 9979 5644 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Marque Crozman, VK2ZLZ Julian Edgar, Dip.T.(Sec.), B.Ed John Hill Jim Lawler, MTETIA Philip Watson, MIREE, VK2ZPW Jim Yalden, VK2YGY Bob Young Photography Stuart Bryce SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $49 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. PUBLISHER'S LETTER Caller ID – now you won't be anonymouse If all goes to plan, Telecomm & Optus will shortly introduce "caller number identification", a system which allows people to identify who is calling them before they answer the phone. The system displays the caller's number of a small LCD screen attached to the phone. Already available in America, it could have been introduced in Australia two years ago but was withdrawn because of concerns about possible breaches of privacy. Well now the system is to get another run and is expected to be submitted to the privacy committe of Austel at about the time this issue goes to press. No doubt there will be bleeding hearts about privacy but as far as I am concerned they've got it wrong. CND will be a boon to people who want privacy – from people who phone. How many times have you been in the middle of a meal and you've had a call from someone doing a marketing survey? How many times have you picked up the phone and answered it, only to have the person on the other end drop the receiver in the cradle? How many people are bothered by nuisance callers whether they be obscene, disgruntled business clients or whatever? Wouldn't it be nice to put a stop to all that? It should stop hoax calls to the police, ambulance and fire brigade too. Some people worried about the way in which Caller ID might be used by business who would enter every caller into a database, Well, what do they think happens now with enquiries to businesses? And it could have the benefit of stopping some forms of fraud. For our part at Silicon Chip, we would prefer to know who is calling us, and being able to record the number, so that we could always call them back if we needed to. You'd be suprised how often people give the wrong address details by mistake. Of course, caller identification is already in use on fax machines and there is no reason it should not be extended to the whole populace. The benefits outweigh the concerns of those who want to retain their anonymity when they are making calls. I should also point out that you will have to pay extra if you want the caller identication system on your phone. Telecom & Optus expect to make money from the service, otherwise they would not want to introduce it. The crucial point about Caller ID is that it is likely to be a blanket system in which every caller has the potential of being identified by the person being phoned, unless he or she informs the telephone company that they want to be out. That means when they ring some people, thye take the risk that they won't be answered. And, further into the future, it could become a condition of doing business over the phone – think about the implications if that. Persons electing to opt out may well be shut out! And while we're on the subject of phones, please note that the numbers of Silicon Chip will change from the 8th of July, as part of the phase number changes that will eventually affect all Australians. Our new phone number is (02) 9979 5644, while the fax number is (02) 9979 5603. Leo Simpson ISSN 1030-2662 WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 2  Silicon Chip HEWLETT PACKARD 334A Distortion Analyser HEWLETT PACKARD 200CD Audio Oscillator • measures distortion 5Hz600kHz • harmonics up to 3MHz • auto nulling mode • high pass filter • high impedance AM detector HEWLETT PACKARD HEWLETT PACKARD 3400A RMS Voltmeter 5328A Universal Counter • voltage range 1mV to 300V full scale 12 ranges • dB range -72dBm to +52dBm • frequency range 10Hz to 10MHz • responds to rms value of input signal • 5Hz to 600kHz • 5 ranges • 10V out • balanced output HEWLETT PACKARD 5340A Microwave Counter • allows frequency measurements to 500MHz • HPIB interface • 100ns time interval • T.I. averaging to 10 ps resolution • channel C <at> 50ohms • single input 10Hz - 18GHz • automatic amplitude discrimination • high sensitivity -35dBm • high AM & FM tolerance • exceptional reliability $1050 $79 $475 $695 $1950 BALLANTINE 6310A Test Oscillator BALLANTINE 3440A Millivoltmeter AWA F240 Distortion & Noise Meter ...................... $425 AWA G231 Low Distortion Oscillator ...................... $595 EATON 2075 Noise Gain Analyser ...................$6500(ex) EUROCARD 6 Slot Frames ........................................ $40 GR 1381 Random Noise Generator ........................ $295 HP 180/HP1810 Sampl CRO to 1GHz ................... $1350 HP 400EL AC Voltmeter .......................................... $195 HP 432A Power Meter C/W Head & Cable .............. $825 HP 652A Test Oscillator .......................................... $375 HP 1222A Oscilloscope DC-15MHz ........................ $410 HP 3406A Broadband Sampling Voltmeter ................................................................ $575 HP 5245L/5253/5255 Elect Counter ....................... $550 HP 5300/5302A Univ Counter to 50MHz ................ $195 HP 5326B Universal Timer/Counter/DVM ............... $295 HP 8005A Pulse Generator 20MHz 3 Channel ........ $350 HP 8405A Vector Voltmeter (with cal. cert.) ......... $1100 HP 8690B/8698/8699 400KHz-4GHz Sweep Osc ............................................................ $2450 MARCONI TF2300A FM/AM Mod Meter 500kHz-1000MHz ................................................... $450 MARCONI TF2500 AF Power/Volt Meter ................. $180 SD 6054B Microwave Freq Counter 20Hz-18GHz ......................................................... $2500 SD 6054C Microwave Freq Counter 1-18GHz ............................................................... $2000 TEKTRONIX 465 Scope DC-100MHz .................... $1190 TEKTRONIX 475 Scope DC-200MHz .................... $1550 TEKTRONIX 7904 Scope DC-500MHz .................. $2800 WAVETEK 143 Function Gen 20MHz ...................... $475 FLUKE 8840A Multimeter RACAL DANA 9500 Universal Timer/Counter • true RMS response to 30mV • frequency coverage 10kHz1.2GHz • measurement from 100µV to 300V • stable measurement • accuracy ±1% full scale to 150MHz • list price elsewhere over $5500 • 2Hz-1MHz frequency range • digital counter with 5 digit LED display • output impedance switch selectable • output terminals fuse protected $350 $795 HEWLETT PACKARD 1740A Oscilloscope RADIO COMMUNICATIONS TEST SETS: IFR500A ............................................................... $8250 IFR1500 .............................................................. $12000 MARCONI 2955A .................................................. $8500 SCHLUMBERGER 4040 ........................................ $7500 TEKTRONIX 475A Oscilloscope TEKTRONIX 7603 Oscilloscope (military) • frequency range to 100MHz • auto trigger • A & B input controls • resolution 0.1Hz to 1MHz • 9-digit LED display • IEEE • high stability timebase • C channel at 50 ohms • fully programmable 5½ digit multimeter • 0 to 1000V DC voltage • 0.005% basic accuracy • high reliability/self test • vacuum fluoro display • current list $1780 $695 $350 TEKTRONIX FG504/TM503 40MHz Function Generator TEKTRONIX CF/CD SERIES CFC250 Frequency Counter: $270 • DC-100MHz bandwidth • 2-channel display mode • trigger - main/delay sweep • coupling AC, DC, LF rej, HF rej $990 • 250MHz bandwidth • 2-channel display mode • trigger - main/delay sweep • coupling AC, DC, LF rej, HF rej • mil spec AN/USM 281-C • triggers to 100MHz • dual trace • dual timebase • large screen $1690 $650 The name that means quality CFG250 2MHz Function Generator $375 • 0.001Hz-40MHz • 3 basic waveforms • built-in attenuator • phase lock mode $1290 CDC250 Universal Counter: $405 NEW EQUIPMENT Affordable Laboratory Instruments PS305 Single Output Supply SSI-2360 60MHz Dual Trace Dual Timebase CRO • 60MHz dual trace, dual trigger • Vertical sens. 1mV/div. • Maximum sweep rate 5ns/div. • Built-in component tester • With delay sweep, single sweep • Two high quality probes $1110 + Tax Frequency Counter 1000MHz High Resolution Microprocessor Design CN3165 • 8 digit LED display • Gate time cont. variable • At least 7 digits/ second readout • Uses reciprocal techniques for low frequency resolution $330 + Tax Function Generator 2/5MHz High Stability FG1617 & FG 1627 • • • • • • Multiple waveforms 1Hz to 10MHz Counter Output 20V open VCF input Var sweep lin/log Pulse output TTL/CMOS FG1617 $340 + Tax FG1627 $390 + Tax PS303D Dual Output Supply • 0-30V & 0-3A • Four output meters • Independent or Tracking modes • Low ripple output $420 + Tax • PS305D Dual Output Supply 0-30V and 0-5A $470 + Tax PS303 Single Output Supply • 0-30V & 0-3A • Two output meters • Constant I/V $265 + Tax Audio Generator AG2601A • 10Hz-1MHz 5 bands • High frequency stability • Sine/Square output $245 + Tax • 0-30V & 0-5A $300 + Tax PS8112 Single Output Supply • 0-60V & 0-5A $490 + Tax Pattern Generator CPG1367A • Colour pattern to test PAL system TV circuit • Dot, cross hatch, vertical, horizontal, raster, colour $275 + Tax MACSERVICE PTY LTD Australia’s Largest Remarketer of Test & Measurement Equipment 20 Fulton Street, Oakleigh Sth, Vic., 3167   Tel: (03) 9562 9500 Fax: (03) 9562 9590 **Illustrations are representative only By LEO SIMPSON The Philips CDI 210 interactive CD player At long last, after a wait of several years, Philips are releasing their interactive CD player onto the Australian market. Billed as the new wave in home entertainment machines, the Phil­ips CDI 210 will play audio and video CDs, CDI discs, and photo-CDs. CD interactive (CDI) players have been available overseas for about two years but it is only now that Philips are releasing a machine onto the Australian consumer market. In the intervening period, a lot of games and other interactive discs (eg, education4  Silicon Chip al) have become available and shortly, many movie titles are also expected to become available. What’s an interactive CD? Essentially, it’s like a CD-ROM. It can take the form of a video game or it might have a more serious purpose; it could be a video book on almost any subject, for example. You place the disc in the machine and you are free to browse through any section of the disc which you can select off the screen, using a remote control. These discs produce full screen, full-motion video as well CD-quality stereo sound. The CDI-210 will play standard audio CDs through your TV set’s stereo speakers, or if connected to your hifi system, through your stereo speakers. CD playing functions can be con­ trolled directly via the remote control and if linked to a TV set, you can also control the functions by pointing the cursor to the on-screen display and This is the opening menu screen. The machine will play audio & video CDs, CDI discs & photo-CDs. “clicking” on the desired function. Viewed from the front, the Philips CDI-210 has very simple styling and even simpler controls on the front panel. These are: On/Off, Open/Close, Play and Stop. All the other functions such as track selection, skip forward and reverse, pause and volume can be accessed only via the remote control. More comprehensive func­tions such as programming, shuffle, repeat and FTS (favourite track selection) are available via the on-screen display. The machine is relatively large, measuring 420mm wide and 95mm high, although at 290mm, it is not as deep as a typical VCR. The supplied remote control doubles as a game control and features a small joystick and four action buttons. This can be used with most games although there are optional wired re- This is an information screen. It can be displayed in one of several different languages. mote controls which are purely games oriented. Connection to a TV set is via a multi-way Euroconnector (SCART plug and socket) and if your set is not so equipped, you will need to feed the CDI machine’s video and stereo outputs into your VCR, via cables fitted with RCA plugs. One feature that is lacking on the CDI-210 is a headphone socket. This is a disadvantage, particularly if your TV set does not have one either, as then you can not enjoy the system without possibly disturbing other members of the household. CD player performance As part of our assessment of the Philips CDI 210, we put it through a full range of performance tests using Technics and Philips test discs and measuring its output with our Audio Preci­sion test set. The accompanying graphs show the frequency re­sponse and total harmonic distortion plots. As can be seen, the frequency response is flat from 20Hz to 20kHz within ±0.1dB while the total harmonic distortion is typically below .02% across the range, at maximum output. The remainder of the perfor­ mance measurements are summarised in the accompanying panel and they too are very respectable. We also found the machine to be an excellent tracker as far as disc defects were concerned and it appears to be more than usually proof against bumps and shocks to the outside of the case. On the other hand, we did feel that the audible noise of the tracking mechanism, a low level but annoying high-pitched squeak, was just a little The rear of the CDI-210 has a Euroconnector for connec­tion to a TV set & RCA sockets for video & stereo outputs. Facing page: the Philips CDI-210 with a small selec­tion of interactive CDs. There is a conventional infrared remote control which has a small joystick & four games buttons & a wired remote games control. July 1995  5 Measured Performance Fig.1: the frequency response of the CDI-210 is very flat. Fig.2: total harmonic distortion versus frequency at maximum output level. too obtrusive, particularly when play­ ing CDs. Video player performance For this review we were supplied with a selection of inter­ active CDs which were either educational or games. All featured full screen, full motion video, as opposed to CD-ROMs which have full motion video but displayed on a small portion of the 6  Silicon Chip comput­ er screen. The video standard used is MPEG-1 which involves considerable compression to restrict the video data. This allows a 1-hour movie to fit onto a standard size CD, an incredible accomplishment when you think about it. Actually, this product is a measure of how blase we have become about technological progress. A few years ago, the concept of a one-hour movie, Channel Separation Signal L to R 100Hz -87dB 1kHz -87.5dB 10kHz -87.5dB 20kHz -84dB Unweighted Signal-To-Noise Ratio (20Hz-20kHz bandwidth) Signal Left With emphasis -89dB Without emphasis -89.5dB Amplitude Linearity 0dB 0dB -1dB -1dB -3db -3db -10dB -10dB -20dB -20dB -30dB -30dB -40dB -40dB -50dB -50dB -60dB -60dB -70dB -70dB -80dB -80dB -90dB -90dB Frequency Accuracy Signal Left 20kHz ±2Hz 20.0008kHz R to L -87.5dB -87.5dB -83.5dB Right -89.5dB -90dB 0dB -1dB -3db -10dB -20dB -30dB -40dB -50dB -60dB -70dB -80dB -90dB Right 20.0008kHz digitally recorded, fitting onto a single-sided 12cm disc was just dream territory. Now it’s here, it works and that’s that. But to us, it’s still amazing stuff. To the eye, the video quality is on a par with that from a standard VHS VCR – certainly better than that from an average rental movie tape but not as good as can be obtained from a really good VHS HQ machine or from an S-VHS recorder. To explain further, the picture quality is essentially noisefree (ie, no snow) but the bandwidth is obviously restricted and the finer details are lost in the fairly coarse quantising process. Lest this assessment seem a little blunt, remember that the comparison with VHS tapes must be put into perspective. While a carefully recorded VHS tape may initially look pretty good, the quality soon begins to suffer with repeated playings and even if it’s just left in the box and not played, it will deteriorate. Video CDs on the other hand, should be very long-lived (no one yet knows how long) provided their playing surfaces or the pro­tective label are not physically damaged. Photo CD Where the CDI 210 really does excel is when it is display­ing still pictures from photo CDs. This medium has yet to really catch on in the consumer market place but as time goes on it is This screen is displayed when playing audio CDs. You can control the playing functions by positioing the cursor & then pressing one of the games buttons. sure to become very popular. Photo CDs have the advantage over ordinary slides and photo prints in that they don’t deteriorate over time and they have the advantage of large screen presenta­tion (via your TV set) without having to set up a slide projector or having to darken the room. The CDI 210 can preview all the pictures stored on a photo CD (something you can’t do easily with slides) and then you can program a slide show. You can determine the order in which the slides are shown, leaving some out if you wish, and you can also rotate them by 90°, to give portrait presentation, if that’s how the photo was taken originally. You can even magnify the central portion of the photo by a factor of two, and because of the very high resolution of the images stored on a photo CD, This is the opening menu screen when a photo CD is fed into the machine. You can preview all slides on a CD (see below) and program a slide show. there is no apparent loss of picture quality. That is something else that cannot be done with a normal slide projector. Truly, until you have seen your photos presented on your TV screen via this medium, you cannot appreciate how good it is. Games/educational software For the brief period for which we had this CDI machine, we were also provided with a small selection of games and education­al software. But while the potential of this medium is apparent, I was not really impressed with any of the games or the software, and nor were my children, who are usually keen to play with any product of this sort. However, it would be unfair to judge the CDI format on this brief encounter. After all, you would This is the slide preview screen, whereby all the images on the photo CD can be paged through. not judge an audio CD player on the basis of just a few discs, par­ticularly as none of the recordings might be the ones you would buy, given a wide choice. When movie titles become plentiful, the attraction of the machine is sure to increase considerably. To sum up, the Philips CDI-210 is another benchmark home entertainment product, in the same way as the CD player was when it was released back in 1982. It represents an enormous step forward in video recording technology but it is likely to be quickly accepted in the Australian marketplace, as it apparently has been overseas. It will be released in Australia in August this year. The price of the CDI 210 interactive CD player had not been set at the time of writing but it was SC expected to be under $1500. An image display from a photo-CD is bright, steady & more convenient to view than via a slide projector. July 1995  7 Jamo's Classic range features rounded styling which makes them appear less boxy. At left is the 2-way Classic-4, at the centre the Classic-6, and at right is the top of the range Classic-8 Jamo Classic series loudspeakers There are any number of compact hifi loudspeakers on the Australian market, but most are presented in boring black & the styling is also uninspiring. That is why it is a pleasant change to review loudspeakers which have good styling as well as excellent sound. By LEO SIMPSON 8  Silicon Chip Jamo is a longtime Danish manufacturer of loudspeakers and in the past they have produced some fairly notable avant-garde designs, some of which have been regarded as classics. Now they have a range of three compact speakers which they have named "Classic". In some ways, the name "classy" would be more apt because they really do look good while still having a conventional box shape. The new styling has been achieved by a subtle rounding of the front of the cabinets so that they look less July 1995  9 ture of these woofers is the central concave voice coil cap which in most speakers is convex. Whether this is a cosmetic feature or is there to improve the per­formance, we don't know and the literature from Jamo is silent on this point. At the rear of the cabinet which is made of 22mm custom wood (MDF – medium density fibre board), the edges are rounded while the rear panel it­self is slightly recessed. The vent for the bass port is flared but this is not a styling feature; it is there to reduce turbulence which would be mani­ fested as audible "chuffing" The cabi­ net measures 210mm wide, 460mm high and 252mm deep. Twin connector panels Fig.1: impedance curve of the Classic-4 loudspeaker system. Fig.1: impedance curve of the Classic-8 loudspeaker system. bulky than they otherwise would. As well, the top of the cabinet features a spe­cial ribbed moulding which is round­ed at the front to again reduce the apparent overall size. Combine the cabinet design with a mahogany ve­ neer finish and you have a most attractive package. We reviewed two speakers in the new Jamo series, the Classic-4 and the Classic-8. The Classic-4 is a two-way 10  Silicon Chip bass reflex system with two woofers and a central 25mm soft dome tweeter with a ferro-fluid cooled voice coil. The Classic-8 employs the same tweeter, a midrange driver and two woofers. Listed as 133mm by the manufac­ turers, the woofers in the Classic-4 have a neoprene rubber roll surround and an effective cone diameter of about 100mm. A most unusual fea- One feature that we have mixed feelings about is the use of twin con­ nector panels which are connected in parallel with gold-plated metal straps. These are incorporated to allow "bi­ wiring" Now whatever interpretation we put on this, we cannot see the point of bi-wiring. After all, if you do use separate amplifiers to drive the bass and mid­range drivers you cannot use an elec­tronic crossover because the existing passive crossover components in the speaker are still in circuit. And if you can't use an electronic crossover, there is no point in using separate amplifiers because there is unlikely to be a reduction in intermodulation which, after all, is the main reason for using electronic crossovers and multiple amplifiers. To add further illogic to this discussion, the larger three-way Classic-8 speakers can only be bi­wired not tri-wired. So while we approve of the large gold plated binding post terminals which will take very thick cables, we don't go along with the bi-wiring fea­ture. The crossover frequency for the Classic-4 is 2.2kHz and its sensitivity is 90dB/W/m. The system is nominally 4W impedance although as the impedance curve of Fig.1 shows, the natural impedance is closer to 6W. The curve shows the conventional double peak of a bass reflex system plus the rise and fall in impedance at around the crossover frequency. Classic-8s While the Classic-4s are intended to be mounted on stands for best per formance, the larger Classic-8s are floor mounting. They have the same rounded styling and measure 225mm wide, 900mm high and 290mm deep. Both systems have overload protection, presumably by means of positive temperature coefficient (PTC) thermistors. The crossover frequencies for the Classic-8s are at 700Hz and 2.5kHz and its sensitivity is the same as the smaller model. Its impedance curve is shown in Fig.2 and again, it could be regarded as a 60 system. not have the reedy quality, probably a beneficial result of the 3-way crosso­ver network. As you would expect, the Classic-8s also have a consider­ ably more extended bass response, down to below 40Hz and this gives a lot of extra weight to orchestral, piano and organ music although it does not make all that much difference to most rock music. Overall though, we were most impressed with the Classic-4s. They give a very well-balanced sound with plenty of punch in the bass and good power handling. The much dearer Classic-8s have more extended bass and a less coloured midrange and more power handling capacity. Both speak­ers will serve very well and with their styling a plus, they are sure to be popular. Both are available in black or mahogany. The Classic-4s are $999 a pair and the Classic-Bs are $1899 a pair. Listening tests Our listening tests embraced a wide range of CDs, involving classical, jazz and rock music. Both gave a very satisfying performance. In more detail, the Classic-4 has quite a smooth re­sponse overall with bass well main­ tained down to below 60Hz. The tweeter tends to be a little prominent in the region of 5kHz to 6kHz and also had a tendency to be slightly "reedy" when sinewaves were being repro­duced. The Classic-8s use the same tweeter as the Classic-4s and it was similarly prominent in the midrange but did Where to buy them All the Classic range have dual recessed terminal panels with gold plated metal straps. Note the flarred bass reflex port to reduce "chaffing". Jamo Classic speakers are on sale at selected hifi retailers. For further in­formation, contact Scan Audio Pty Ltd, 52 Crown Street, Richmond, Vic 3121. Phone (03) 9429 2199. SC SC ANOTHER GREAT DEAL FROM MACSERVICE 100MHz Tektronix 465M Oscilloscope 2-Channel, Delayed Timebase VERTICAL SYSTEM Bandwidth & Rise Time: DC to 100MHz (-3dB) and 3.5ns or less for DC coupling and -15°C to +55°C. Bandwidth Limit Mode: Bandwidth limited to 20MHz. Deflection Factor: 5mV/div to 5V/div in 10 steps (1-2-5 sequence). DC accuracy: ±2% 0-40°C; ±3% -15-0°C, 40-55°C. Uncalibrated, continuously variable between settings, and to at least 12.5V/div. Common-Mode Rejection Ratio: 25:1 to 10MHz; 10:1 from 10-50MHz, 6cm sinewave. (ADD Mode with Ch 2 inverted.) Display Modes: Ch 1, Ch 2 (normal or inverted), alternate, chopped (250kHz rate), added, X-Y. Input R and C: 1MΩ ±2%; approx 20pF. Max Input Voltage: DC or AC coupled ±250VDC + peak AC at 50kHz, derated above 50KHz. HORIZONTAL DEFLECTION Timebase A: 0.5s/div to 0.05µs/div in 22 steps (1-2-5 sequence). X10 mag extends fastest sweep rate to 5ns/div. Timebase B: 50ms/div to 0.05µs/div in 19 steps (1-2-5 sequence). X10 mag extends maximum sweep rate to 5ns/div. Horizontal Display Modes: A, A Intensified by B, B delayed by A, and mixed. CALIBRATED SWEEP DELAY Calibrated Delay Time: Continuous from 0.1µs to at least 5s after the start of the delaying A sweep. Differential Time Measurement Accuracy: for measurements $900 of two or more major dial divisions: +15°C to +35°C 1% + 0.1% of full scale; 0°C to +55°C additional 1% allowed. TRIGGERING A & B A Trigger Modes: Normal Sweep is triggered by an internal vertical amplifier signal, external signal, or internal power line signal. A bright baseline is provided only in presence of trigger signal. Automatic: a bright baseline is displayed in the absence of input signals. Triggering is the same as normal-mode above 40Hz. Single (main time base only). The sweep occurs once with the same triggering as normal. The capability to re-arm the sweep and illuminate the reset lamp is provided. The sweep activates when the next trigger is applied for rearming. A Trigger Holdoff: Increases A sweep holdoff time to at least 10X the TIME/DIV settings, except at 0.2s and 0.5s. Trigger View: View external and internal trigger signals; Ext X1, 100mV/div, Ext -: 10, 1V/div. Level and Slope: Internal, permits triggering at any point on the positive or negative slopes of the displayed waveform. External, permits continuously variable triggering on any level between +1.0V and -1.0V on either slope of the trigger signal. A Sources: Ch 1, Ch 2, NORM (all display modes triggered by the combined waveforms from Ch 1 and 2), LINE, EXT, EXT :-10. B Sources: B starts after delay time; Ch 1, Ch 2, NORM, EXT, EXT :-10. Optional cover for CRT screen – $35 through the vertical system. Continuously variable between steps and to at least 12.5V/div. X Axis Bandwidth: DC to at least 4MHz; Y Axis Bandwidth: DC to 100MHz; X-Y Phase: Less than 3° from DC to 50kHz. DISPLAY CRT: 5-inch, rectangular tube; 8 x 10cm display; P31 phosphor. Graticule: Internal, non-parallax; illuminated. 8 x 10cm markings with horizontal and vertical centerlines further marked in 0.2cm increments. 10% and 90% for rise time measurements. Australia’s Largest Remarketer of markings Graticule Illumination: variable. Beam Test & Measurement Equipment Finder: Limits the display to within the graticule area and provides a visible 9500; Fax: (03) 9562 9590 display when pushed. X-Y OPERATION Sensitivity: 5mV/div to 5V/div in 10 steps (1-2-5 sequence) MACSERVICE PTY LTD 20 Fulton Street, Oakleigh Sth, Vic., 3167. Tel: (03) 9562 **Illustrations are representative only. Products listed are refurbished unless otherwise stated. July 1995  11 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au Automotive Product Review The Brymen 328 automotive multimeter Electronic engine management systems require special tools for fault diagnosis. Here we take a look at the Brymen BM328 Automotive Meter. It includes a range of useful diagnostic functions, including the ability to measure fuel injector pulse width. By JULIAN EDGAR When woring on an electronically managed car, a multimeter is vital for diagnostics and fault finding. Even the simplest multimeter will be of some use but a more sophisticated unit will add functions which can prove very helpful. Specifically, an automotive multimeter should – in addition to "normal" multimeter functions - have the ability to read pulse width, duty cycle, frequency, engine rpm and temperature. Less exotic – but still useful – is a DC current range which extends up to at least 20A. Meters with these functions have been available for some years but their cost (generally $500 or more) has precluded their use by home-based mechanics. That situ­ ation has now changed following the release of two new automotive multimeters -the Brymen BM323 and Brymen BM328 -at a much lower cost. The Brymen BM323 is the cheapest of the two and includes the following facilities: • DC Volts (200mV-200V); • Resistance (200Q-2MQ); • DC Amps (0-20A, 30 seconds on, 5 minutes off measuring cycle); • Duty cycle (0-100%); • RPM (requires optional inductive pick-up); • Dwell Angle (4, 5, 6 & 8 cylinders). The Brymen BM328, which is the subject of this review, adds the following features to the above list: 16  Silicon Chip Above: testing showed that injector pulse width could only be measured when the fuel injector was actually connected into circuit. Probing the disconnected loom plug gave false readings on this meter, although interestingly this does not occur on a (much more expensive) Vane unit. • • • • • AC Volts (200mV-500V); Temperature (requires optional K-type thermocouple); Pulse Width to 200ms; Dwell Angle (3, 4, 5, 6 & 8 cylinders); Frequency (2kHz-100kHz). Main features The Brymen BM328 Automotive Meter comes in a protective, bright-yellow rubber holster. A set of leads is supplied and these are equipped with screw-on alligator clips in addition to the normal pointed probes. This is useful in that much automotive measuring requires a hands-free fixed attachment to the wiring. A 51-page (but they are very small pages!) instruction manual is also included. At first glance, the BM328 looks like a conventional multimeter. It has a 3.5-digit (1999 count) liquid crystal display (LCD), a large rotary selector switch and the The optional inductive sensor costs $32.95. It clips over a sparkplug lead & allows the engine speed (ie, rpm) to be measured. The Brymen BM328 automotive multimeter is supplied in a soft rubber holster & with leads. At $239, the unit is considerably cheaper than other autoomotive multimeters with comparable functions. usual array of input sockets. Immediately below the LCD are eight pushbuttons and these provide the following func­tions: (1) RPM selection (either 2-stroke or 4-stroke, with 4-stroke default); (2) internal fuse test; (3) maximum read­ing hold; (4) hold for the current display; (5) toggle be­tween triggering on the negative or positive slope when in pulse width or duty cycle modes; (6) trigger level (allows frequency-based functions to be triggered at either 3.1 V or 10.5V; (7) auto power-off disable; and (8) selection of secondary functions shown on the rotary knob display. The maximum hold feature is useful when only the peak value is of interest, with the meter able to be used as a simple data-logger in this mode. An example of where this would be useful in an automotive application is when using the optional K-type thermocouple. Measur­ing the peak inlet air temperature to the engine could be done by locating the meter securely under the bonnet, with the thermocouple located in the intake air duct, and then actually driving the car on the road. Incidentally, the higher this temperature the less dense the combustion air will be – leading to a reduction in potential peak power. The ability to disable the automatic power-off function is useful where engine monitoring is being undertaken for periods longer than 15 minutes. For example, it would normally take at least this long to measure a coolant temperature sensor's output over its full range by starting and then idling the engine. There's nothing more annoying Fig.1: an example of the sort of data that can be measured with the Brymen automotive multimeter. This graph shows the injector duty cycle of a Subaru Liberty RS in a variety of driving conditions. Generally, the injectors are open for less than 10% of the time but at full throttle in the modified car, the duty cycle exceeds 90%. July 1995  17 The probes are supplied with insulated screw-on alligator clips to allow hands-free circuit connections. The instruction book uses a tutorial approach to show how the unit is used to take various measurements. than a meter which constantly switches itself off at the wrong time, particularly when conducting on-road tests. The main rotary selector knob has no less than 30 positions (including OFF). As a result, the markings around the knob are quite small. What's more, the pointer mark­ing does not wrap around the edge of the knob, which means that care must be exercised to ensure that the desired range is indeed selected. A small dab of white paint on the side of the knob would alleviate this prob­lem. Below the range selection knob are the four input jacks. These comprise (from right to left): (1) common, (2) posi­tive input for all functions except current; (3) ground reference for the thermocouple; and (4) current input. Note that banana jacks are used here for the thermocouple instead of the more usual dedicated thermocouple socket. A minor irritation is the unwarranted use of irrelevant inscriptions close to the input sockets. The distractions include legends indicating that the meter has an auto power off function, that it is water resistant, and that it beeps if the jacks are incorrectly placed. All of these are useful features but there's no need to have inscriptions to this effect cluttering the front of the meter! The meter's main selection knob has no less than 30 positions. This, together with the fact that the knob's white line does not wrap around its edge, makes quick selection of specific ranges a little haphazard 18  Silicon Chip Using the meter The instruction manual briefly covers each of the meter's functions and then shows how the meter is used by a series of tutorials. The first, for example, shows how the meter is used to measure the battery voltage and, based on this measurement, describes the conclusions that can be drawn regarding the state of the battery. Other tutorials show how to measure engine rpm, dwell, the voltage across the points (for those with old cars), and so on. The manual is generally clear and well illustrated. One aspect which caused some initial confusion was the measurement of duty cycle and pulse width. These measurements are required when checking fuel injector pulses, for example. There are two important points to note here: (1) the meter is polarity-conscious when meas­uring these parameters; and (2) it will not give a valid reading unless the injector is in the circuit. As an example of the latter point, if an injector plug is removed from the injector and the meter connected to this plug, invalid results will be obtained. This is not the case with some other automotive multimeters. This "problem" is easily overcome by reconnecting the fuel injector, after which the correct reading will be obtained. This also appeared to be the case with the frequency measurement – at least on one test car. To be fair though, the handbook does show the injector connected (and polarity markings are visible) in the diagram for pulse width measurement. The remaining functions of the meter, including the use of the optional inductive pickup for measuring engine rpm, all worked without any initial problems. Considering its relative cheapness, the Brymen BM328 Automotive Meter is a good buy for anyone interested in general tune-up work and fault diagnosis in engine management systems. The unit (Cat. QM-1450) costs $239, while the Brymen BM323 (Cat. QM-1440) costs $159. The optional inductive pick-up (for rpm measurements) costs $32.95 (Cat. QM-1455), while a suitable thermocouple probe is available for just $12.95 (Cat. QM-1282). For further information on the Brymen meters and acSC cessories, contact your nearest Jaycar store. SILICON CHIP BOOK SHOP Newnes Guide to Satellite TV 336 pages, in paperback at $49.95. Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1994 (3rd edition). This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 371 pages, in hard cover at $55.95. Servicing Personal Computers By Michael Tooley. First pub­ lished 1985. 4th edition 1994. Computers are prone to failure from a number of common causes & some that are not so common. This book sets out the principles & practice of computer servicing (including disc drives, printers & monitors), describes some of the latest software diagnostic routines & includes program listings. 387 pages in hard cover at $59.95. The Art of Linear Electronics By John Linsley Hood. Pub­lished 1993. This is a practical handbook from one of the world’s most prolific audio designers, with many of his designs having been published in English technical magazines over the years. A great many practical circuits are featured – a must for anyone inter­ested in audio design. Optoelectronics: An Introduction By J. C. A. Chaimowicz. First published 1989, reprinted 1992. This particular field is about to explode and it is most important for engineers and technicians to bring themselves up to date. The subject is comprehensively covered, starting with optics and then moving into all aspects of fibre optic communications. 361 pages, in paperback at $55.95. Digital Audio & Compact Disc Technology Produced by the Sony Service Centre (Europe). 3rd edition, published 1995. Prepared by Sony’s technical staff, this is the best book on compact disc technology that we have ever come across. It covers digital audio in depth, including PCM adapters, the Video8 PCM format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $55.95. Power Electronics Handbook Components, Circuits & Applica­ tions, by F. F. Mazda. Published 1990. Previously a neglected field, power electronics has come into its own, particularly in the areas of traction and electric vehicles. F. F. Mazda is an acknowledged authority on the subject and he writes mainly on the many uses of thyristors & Triacs in single and three phase circuits. 417 pages, in soft cover at $59.95. Surface Mount Technology By Rudolph Strauss. First pub­ lish-ed 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­ soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Electronics Engineer’s Reference Book Edited by F. F. Mazda. First pub­ lished 1989. 6th edition 1994. This just has to be the best reference book available for electronics engineers. Provides expert coverage of all aspects of electronics in five parts: techniques, physical phenomena, material & components, electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ Return to: Silicon Chip Publications, PO Box 139, Collaroy NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details; or fax to (02) 9979 6503. semicustom electronics & data communications. 63 chapters, in paperback at $140.00. Radio Frequency Transistors Principles & Practical Appli­ cations. By Norm Dye & Helge Granberg. Published 1993. This timely book strips away the mysteries of RF circuit design. Written by two Motorola engineers, it looks at RF transistor fundamentals before moving on to specific design examples; eg, amplifiers, oscillators and pulsed power systems. Also included are chapters on filtering techniques, impedance matching & CAD. 235 pages, in hard cover at $85.00. Newnes Guide to TV & Video Technology By Eugene Trundle. First pub­ lish-ed 1988, reprinted 1990, 1992. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 432 pages, in paperback, at $39.95.  Title Price  Newnes Guide to Satellite TV  Servicing Personal Computers  The Art Of Linear Electronics  Optoelectronics: An Introduction  Digital Audio & Compact Disc Technology  Power Electronics Handbook  Surface Mount Technology  Electronic Engineer's Reference Book  Radio Frequency Transistors  Newnes Guide to TV & Video Technology $55.95 $59.95 $49.95 $55.95 $55.95 $59.95 $99.00 $140.00 $85.00 $39.95 Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ & PNG add $10.00 per book, elsewhere add $15 per book. TOTAL $A July 1995  19 A low-cost electric fence controller Based on an automotive ignition coil, this Electric Fence Controller is ideal for controlling livestock. It’s easy to build and can power fence lines up to 1km long. • • Low cost a nd easy to build Based on an automo ti v e ignition co il • 2mA avera ge c • 12V battery urrent drain operation • Suitable fo r fence run s up to 1km By JOHN CLARKE Electric fences are often used on farms to provide a tempo­rary fenceline or to add security to a fence that is in disre­pair. Their main advantages are: (1) they are relatively cheap (compared to permanent fences); (2) they are easily moved from place to place; and (3) they are very effective when it comes to containing live­stock. Electric fences are also very effective for keeping ani­mals out of restricted areas, such as keeping cattle out of one section in a paddock that has been given over to lucerne. There are many different types of electric fence con­trollers on the market today and each suits a particular purpose. Some can operate fencelines up to 100km long, while others are only suitable for up to 1km lengths. 20  Silicon Chip The main difference between one controller and another is the amount of power which can be delivered to the fence. Of course, the longer the fence the greater the losses incurred along its length. These losses are due to the impedance of the wire, its capacitance to ground and the load on the fence. This load can be provided by a number of factors, including long wet grass, wet insulators and animals contacting the wire. Conse­quently, considerable power is required to overcome these losses and maintain a satisfactory voltage on the fence so that it can still do its job over long distances. On the other hand, the SILICON CHIP Electric Fence Con­ troller is only a low-power unit capable of powering Main Feat ures • • Complies w ith Australia n Standard 3 129.1-199 3 Reverse p olarity prote ction less than 1km of fence. It is designed to operate from a rechargeable 12V battery and this could range from a 1.2Ah (or larger) gel cell battery to a conventional 12V car battery. Ignition coil Because it is only a low-power unit, the circuit is built around an automotive ignition coil. This eliminates the need for complicated inverter circuitry and greatly simplifies the con­struct­ ion. In addition, an ignition coil is cheap compared to a purpose-wound 47  12V D1 1N4004 470 16VW 2.7M 7 1.5k 6 4 B C E B C 8 IC1 7555 2 E L1 IGNITION COIL 6. 8  1W F1 500MA 1 GND Q1 BC327 E 3 2.2k B Q2 MJ10012 C C 100  B 5 0.1 0.68 VIEWED FROM BELOW HT TO FENCE E Fig.1: the circuit uses 7555 timer IC1 to pulse transistors Q1 & Q2 on & off. Q2, in turn, switches the ignition coil which delivers a high-voltage pulse to the fenceline. ZD1 75V 1W ZD2 75V 1W ZD3 75V 1W ELECTRIC FENCE CONTROLLER transformer and this keeps the cost to a minimum. In fact, you don’t even have to purchase a new ignition coil. A second­ hand unit scrounged from a wrecking yard will do the job quite nicely. The circuit has been designed to suit an ignition coil intended for use with a ballast resistor. One problem in building an Electric Fence is coming up with a suitable waterproof enclosure to house the control circuitry. We solved this problem by installing the circuit in a length of 90mm-diameter PVC tubing. End caps were then used to seal the tube from the weather. In addition, one endcap holds the fence terminals while the opposite endcap carries a cordgrip grommet which clamps the twin lead that goes to the battery. The advantages of this type of enclosure are that it is completely weatherproof, is quite cheap compared to other en­closures and can be mounted using standard 90mm clamps. In fact, you may even have some scrap 90mm tubing in your garage which can be pressed into service. All you have to do is purchase a couple of endcaps from your local hardware store and the enclosure is complete. How it works Take a look now at Fig.1 – this shows the complete circuit details for our Electric Fence Controller. Apart from the igni­tion coil, it uses just one IC, a couple of transistors and a handful of other minor components. IC1 is a CMOS 7555 timer wired to operate in astable mode. When power is initially applied, its 0.68µF timing capacitor (on pins 6 and 2) charges via the 1.5kΩ and 2.7MΩ resistors until it reaches 2/3Vcc (ie, 2/3rds the supply voltage). At this point, pin 7 (previously open circuit) goes low and the 0.68µF capacitor discharges via the 1.5kΩ resistor until its reaches 1/3Vcc. Pin 7 now goes open circuit again and so the timing capaci­tor charges once more towards 2/3Vcc. This cycle is repeated indefinitely while ever power is applied to the circuit. IC1’s pin 3 output follows pin 7; ie, it is high while the timing capacitor charges and low while it discharges. As a re­sult, pin 3 alternately goes high for about 1.3 seconds and low for about 0.7ms. This very brief low period is due to the rela­tively low value of the resistor (1.5kΩ) connected between pins 6 and 7 of IC1. Pin 3 of IC1 is used to drive transistors Q1 and Q2. Q2 is an MJ10012 power Darlington transistor, designed specifically as a coil driver in automotive ignition systems. It switches the heavy currents through the coil and so can be regarded as the workhorse of Below: the ignition coil is firmly secured to the PC board using cable ties. Note that you don’t have to buy a new coil – a secondhand coil obtained from a wrecker’s yard will do the job quite nicely. A plastic cap is fitted to Darlington transistor Q2 to help prevent unexpected shocks during testing. July 1995  21 coil. This voltage is about 5kV (across a 1MΩ load) and is applied directly to the fenceline. As a result, a brief (0.7ms) high-tension pulse is applied to the fence approximately every 1.3 seconds. This operation is basically similar to the ignition system in a car, in which the coil primary current is periodically interrupted by a switching transistor or a set of points. In a car, however, the resulting HT voltage is used to fire the selected sparkplug. Despite the fact that Q2 is a very rugged device, it is possible that it could be damaged by excessive backEMF voltages from the coil. To guard against this situation, three 75V 1W zener diodes (D2-D4) have been connected in series across Q2. These limit the collector voltage to 225V which is well within its 500V rating. Note that the circuit is designed to deliver about 5kV by dint of a very brief charging pulse through the coil. In a normal automotive setup the coil would deliver a much higher voltage but this would not be desirable in this case. Electric fences must comply with the Australian Standard (AS 31291981) which sets strict limits on the output voltage, pulse duration and output impedance. PARTS LIST 1 PC board, code 11306951, 171 x 79mm 1 adhesive label, 125 x 50mm (Electric Fence Controller) 1 adhesive plastic label, 85mm diameter (Fence Terminals) 1 adhesive plastic label, 85mm diameter (Input Voltage) 1 230mm length of 90mm diameter PVC tubing 2 90mm diameter end caps 1 12V automotive ignition coil 3 280 x 5mm cable ties 5 PC stakes 2 3AG PC board fuse clips 1 500mA 3AG fuse 2 large binding posts (1 red, 1 black); eg, DSE Cat. P-1731/33 2 5mm ID crimp eyelet terminals 1 TO-3 transistor insulating cap 2 3mm x 6mm-long screws, nuts & star washers 1 red battery clip to suit 1 black battery clip to suit 1 cord grip grommet 1 brass EHT ignition coil connector 1 2-metre length of twin red/ black automotive wire 1 60mm length of red heavy duty hookup wire 1 60mm length of blue heavy the circuit. Q2 also has a high voltage rating (500V) to allow it to withstand the high voltages developed across the ignition coil primary. The circuit works like this. When pin 3 of IC1 is high, PNP transistor Q1 is held off and so Q2 is also held off. Conversely, when pin 3 pulses low, Q1 switches on because base current can now flow via its associated 2.2kΩ resistor. And when duty hookup wire 1 120mm length of green heavy duty hookup wire 1 60mm length of 240VAC insulated wire Semiconductors 1 7555, LMC555CN, TLC555 CMOS timer (IC1) 1 BC327 PNP transistor (Q1) 1 MJ10012 NPN Darlington transistor (Q2) 1 1N4004 silicon diode (D1) 3 75V 1W zener diodes (D2-D4) Capacitors 1 470µF 16VW PC electrolytic 1 0.68µF MKT polyester 1 0.1µF MKT polyester Resistors (0.25W 1%) 1 2.7MΩ 1 100Ω 1 2.2kΩ 1 47Ω 1 1.5kΩ 1 6.8Ω 1W Miscellaneous 1 12V 1.2Ah battery (minimum); 2 x 90mm mounting clamps (to secure the controller to a fence post); 1 x 2-metre long galvanised ground stake; insulators; fence wire (see text). Power supply Power for the circuit is derived from a 12V battery via fuse F1, a 47Ω decoupling resistor and reverse polarity protec­ tion diode D1. The resulting supply line is then filtered using a 470µF electrolytic capacitor to ensure that supply line glitches cannot false-trigger IC1. In addition, a 0.1µF capacitor is connected to pin 5 of IC1 and this filters the trigger point voltage to further guard against false triggering. The primary of the ignition coil is supplied directly from the fuse via a 6.8Ω resistor. This resistor will limit Q1 turns on, Q2 also turns on and current flows through the primary of the ignition coil (L1) via fuse F1 and a 6.8Ω resistor. When pin 3 of IC1 goes high again (ie, after 0.7ms), Q1 and Q2 both turn off and the current through the coil is suddenly interrupted. As a result, the collapsing magnetic field produces a very high voltage across the high tension (HT) secondary wind­ing of the TABLE 1: RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 1 1 1 1 1 22  Silicon Chip Value 2.7MΩ 2.2kΩ 1.5kΩ 100Ω 47Ω 6.8Ω 4-Band Code (1%) red violet green brown red red red brown brown green red brown brown black brown brown yellow violet black brown blue grey gold brown 5-Band Code (1%) red violet black yellow brown red red black brown brown brown green black brown brown brown black black black brown yellow violet black gold brown blue grey black silver brown EHT TO FENCE GND TO GROUND STAKE FENCE TERMINALS Fig.2 (left): install the parts on the PC board as shown in this wiring diagram, making sure that all polarised parts are correctly oriented. The EHT connection to the coil is made using a brass EHT ignition coil connector. Fig.3 (below): check your PC board for defects by comparing it against this full-size etching pattern before installing any of the parts. CABLE TIE IGNITION COIL CABLE TIE CABLE TIE 6. 8  W 47W 100  Q1 IC1 7555 F1 D1 2.7M 1.5k 12V BATTERY POSITIVE Q2 2.2k 0.1 1 0.68 ZD1-ZD3 470uF 12V BATTERY NEGATIVE July 1995  23 Solder the mounting nuts for Q2 to their surrounding copper pads, as shown here. This is necessary to ensure reliable connections for the collector of this transistor. A brass ignition coil connector (soldered to a length of mains-rated cable) plugs into the ignition coil out­put. The connections to the primary terminals are made by terminating the leads using 5mm eyelet connectors. the coil current until fuse F1 blows if Q2 short-circuits between collec­ tor and emitter. F1 also protects the battery in the event of a circuit fault by limiting the maximum current to 500mA. The overall current drain of the circuit is about 2mA, so a fully charged battery should be able to provide many weeks of operation (depending on its size). Note that the overall current consumption has been kept low by specifying a 7555 CMOS timer for IC1 rather than a standard 555 type. A 555 typically draws 10mA compared to about 150µA for a 7555 and so would increase the current consumption by a factor of 6. Construction The control circuit is built on a PC board coded 11306951 and measuring 171 x 79mm. This board, together with the ignition coil mounted on it, fits Two large binding posts are used to terminate the EHT & ground connections from the control circuit. Note that the two end caps should by sealed with silicone sealant to prevent water damage to the circuitry housed inside the plastic conduit. 24  Silicon Chip neatly inside the 90mm plastic conduit. Fig.2 shows the assembly details for the PC board. Begin the assembly by installing PC stakes at the five external wiring points. This done, solder in all the low profile components such as the IC, diodes and resistors. Table 1 lists the resistor colour codes but it is also a good idea to check the resistor values using a digital multimeter before soldering them into position. Take care to ensure that the semiconductors are correctly oriented. In particular, note that D1 (1N4004) faces in the opposite direction to the three zener diodes (ZD1-ZD3). Pin 1 of the IC is adjacent to a notch in one end of the plastic body – see Fig.2. The battery is connected to the circuit via a length of twin red/black automotive wire. Make sure that the battery lead is firmly secured to the end cap using a cord grip grommet. A 12V battery with a minimum rating of 1.2Ah is required to power the fence controller. Fig.4: the circuit can be used to power either single or multiple stands of fence wire, or you can use metallised tape which is specially designed for the job. This is generally white or orange coloured so that it is easily seen. INSULATOR ELECTRIC FENCE CONTROLLER ELECTRIC FENCE HIGH TENSION CLAMPS GROUND POST GALVANISED GROUND STAKE 12V BATTERY Now solder in the capacitors, taking care to ensure that the 470µF electrolytic is oriented as shown. The two transistors are next – push Q1 down onto the board as far as it will comfort­ably go before soldering its leads. Q2 is secured directly to the board (ie, no insulating washer) using 3mm machine screws and nuts. As well as securing Q2 in place, these mounting screws and nuts also connect Q2’s collector (ie, the case) to FENCE TERMINALS + + GROUND HIGH TENSION (TO EARTH STAKE) (TO FENCE) a track on the PC board. To ensure reliable connections, use star washers under the screw heads and solder the nuts to their surrounding copper pads. This done, fit an insulating cap to Q2 – this will prevent any nasty shocks during the testing procedure. The fuse clips can now be installed. Note that these each have a little lug at one end to retain the fuse after it has been installed. These lugs must go to the outside ends, otherwise you will not be able to fit the fuse. The ignition coil is secured to the PC board using three cable ties, after which the leads can be run to its primary terminals. These leads should be terminated using 5mm eyelet connectors to allow for easy connection to the coil. Don’t just crimp the connectors to these leads – solder them as well to ensure long-term reliability. The ground lead can also be installed at this stage. This can be run using a 150mm-length of medium-duty hookup wire. The end caps will need to be drilled for the fence termi­nals and the cord grip grommet to secure the battery leads. The locations of these holes INPUT VOLTAGE 12VDC <at> 2mA AVERAGE (BATTERY ONLY) RED (+) BLACK (-) Fig.5: here are the full-size artworks for the two end caps. These labels should be made from plastic Dynamark® material. July 1995  25 ELECTRIC FENCE CONTROLLER Fig.6: this full-size artwork can be used to make the main identifying label that’s attached to the side of the conduit. can be determined by fitting the two end­cap labels and then using them as drill­ing templates. Large binding posts are used for the two fence terminals (red for the EHT output, black for ground). Mount these in posi­tion, then install the high tension lead. This must be run using a 90mm-length of mains-rated cable. One end is soldered to the EHT binding post, while the other end is attached to a brass ignition coil connector and plugged into the ignition coil out­put. Similarly, connect the ground lead to the ground (black) binding post, then install the twin battery cable (red to posi­ tive, black to negative). The other end of this cable is fitted with large (30A) battery clips. Testing Now for the smoke test. Apply power and check that there is 12V between pins 1 and 8 of IC1. If all is well, you should hear a short click from the coil at 1.3-second intervals. Stay away from the EHT output from the coil and avoid touching the PC board assembly during this test. This FROM NEW N CHIP O SILIC The connections to the battery can be made using heavy-duty clamps, or suitable screw terminals can be used. circuit can deliver a “bite” which is exactly what it is designed to do. If everything works OK, disconnect the battery leads and carefully slide the assembly into its plastic housing. This done, feed the battery cable through the hole in its end cap, secure it using a cordgrip grommet and reconnect the leads to the PC board. The board assembly will be held in position when the end caps are fitted and, generally, this should be sufficient. Howev­er, if you wish the board to be held even more securely, wrap a small amount of foam rubber around the top of the coil so that the assembly is a tight fit within the conduit. Finally, use a suitable silicone sealant (eg, Silastic®) to waterproof all joints around the end caps, the fence terminals and the power cord entry point. Installation Where possible, the controller should be installed inside a building (eg, a shed) so that it is protected from the weather. If used outdoors, it should be mounted on a fixed structure (eg, a fence post) where it is free from the risk of mechanical damage. Use 90mm clamps to secure the controller in position. The controller should be fitted with a separate earth elec­ trode and this should not be connected to any other earthing device. Fig.4 shows a typical installation. Note that all fence wiring should be kept well away from any electrical or telephone cables and from radio and TV antennas. A bare metal conductor can be used for the fence wire. Alternatively, you can used metallised tape which is specially designed for the job. This is available from farm equipment suppliers and is generally white or orange coloured so that it is easily seen. Do not install the unit in any location where people are likely to come into inadvertent contact with it. In addition, any installation should be clearly identified with warning signs posted at intervals not exceeding 90 metres. These signs should carry the words “ELECTRIC FENCE” in block letters no less than 50mm high. SC 20 Electronic Projects For Cars On sale now at selected newsagents Or order your copy from Silicon Chip. Price: $8.95 (plus $3 for postage). Order by phoning (02) 979 5644 & quoting your credit card number; or fax the details to (02) 979 6503; or mail your order with cheque or credit card details to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. 26  Silicon Chip SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd The main board at far left allows two trains to run automatically around a loop of track, each train alternately stopping as it comes to a short isolated section. It also provides LEDs for signalling & for flashing level crossing lights. The smaller board provides various sound effects, including level crossing bells. Run two trains on a small layout Do you have a small model train layout with just a loop of track? Would you like to run two trains on it at the same time? It can be done cheaply and easily with the circuits presented here. As a bonus, you can have level crossing lights and sound effects. By LEO SIMPSON Running a train around a small loop of track is alright for beginners but before too long it becomes boring. However, adding variety is hard unless you extend the layout with points, more track and so on. If that seems like too much of a challenge then consider the circuits presented here. They will enable two trains to safely follow each other around a loop of track. As 32  Silicon Chip a bonus, you can have flashing level crossing lights and the accompanying bell sound effects. Most people with a single loop of track will have probably tried running two trains or two locos on it simultaneously but it doesn’t work well. One loco will eventually catch up with the other and then they will play “push me, pull you” all around the track. A better way of doing it is to divide the loop of track into two sections. Then you place a train or a loco in each section and only have one section energised at a time. That way, one train will proceed around its section until it comes to the end. It will then stop and the other train will proceed around its section until it too comes to the end. Each train will alternate in running and stopping but they will both proceed safely around the track without ever catching up to each other. This applies even if one train or loco is substantially faster than the other. This idea sounds alright in theory but how does the con­trolling circuit know when to switch the power to each alternate section of the track? Well, actually, this simple idea doesn’t work in practice and the loop of track TRAIN DIRECTION TRAIN SIGNALS DETECTOR A TRAIN 1 DETECTOR RELAY TRAIN CONTROLLER DETECTOR B TRAIN SIGNALS Circuit details TRAIN 2 ISOLATED SECTION Fig.1: this diagram shows the principle of operation. There are two infrared detector beams which are broken by the two trains as they pass around the track loop. A relay switches the power on & off to an isolated track section & so one locomotive stops while the other loco proceeds. needs to be sectioned along the lines shown in Fig.1. This depicts a loop of track which has one small isolated section in it. This isolated section need only be long enough to accommodate your longest locomotive. As well as that, two infrared light detector beams are positioned across the track. As a loco breaks one of these light detector beams, it is detected and some logic circui­try operates a relay to energise or de-energise the isolated track section which we’ll call section A. detector beam A. The circuit also provides a simple lighting system to increase the realism. You can have train signals and level crossing lights, as we shall see. Not included in this article is a train speed control cir­cuit. We are assuming that anyone who has a small layout will already have a train control and so this can be employed in the setup described here. tion. Train 1 sets off in pursuit and breaks infrared detector beam B which kills section A again so that when train 1 arrives there, it stops. This sequence continues, with train 1 and train 2 alter­nately stopping at section A while the other one proceeds around the track. On a layout, section A could be a station platform while a level crossing can be positioned near Fig.2 shows the circuit which enables the two trains to run around the loop of track. There are two infrared detector beams, beam A provided by LED1 & Q1, and beam B, provided by LED2 and Q2. When beam A is broken, Q1 will turn off which will turn on transistor Q3. This will pull pin 1 of IC1a low. ICI is a 4011 quad 2-input NAND gate package. Two of the NAND gates, IC1a & IC1b, are connected as an RS flipflop. When Q3 pulls pin 1 low, pin 3 of the flipflop goes high. This will turn on transistor Q5 and energise the relay. Because an RS flipflop is employed, nothing can happen until beam B is broken. This will switch off Q2 and switch on Q4 which causes the RS flipflop to change state. This turns off Q5 and disables the relay. So the RS flipflop is set and reset as beam A and beam B are interrupted and section A is alternately powered or not, to stop the trains. How it works Fig.1 shows train 1 proceeding clockwise around the lefthand section of the loop while train 2 is stopped in section A which has no power applied to it. The rest of the track is permanently powered from the train controller. As train 1 moves around the loop it breaks infrared detec­ tor beam A which causes the relay to apply power to section A. Train 2, which had been stopped in section A, can now proceed and it passes through infrared detector beam B, so the relay removes power from section A. Both trains are now moving and train 1 eventually arrives at the dead section A and stops. Train 2 now continues around and breaks infrared detector beam A. The relay now energises the isolated sec- This close-up shows the locomotive about to break one of the infrared detector beams. Note the optotransistor which has been bent over backwards so that its lens faces the infrared light emitting diode. July 1995  33 VCC A LED3 R1 560  Q1 A K A LED4 Q3 BC548 C B R5 220k C   LED1 C1 .015 R6 68k R2 560  A  LED2 Q2 R10 22k Q4 BC548 C B R8 220k C  C2 .015 R9 68k 14 1 3 2 RELAY 1 K D1 1N4004 SECTION A SPEED CONTROLLER R14 1k E 5 Q6 BC548 C B R12 10k 4 IC1b 6 7 E B VCC E A E K  LED6 Q5 R11 BC548 C 10k B A VCC R4 120k K A  K IC1a 4011 DETECTOR A  LED5 R13 1k E E K  R7 22k R3 120k A C9 0.47 R17 4.7M 13 R21 2.2k R18 2.2M IC1d 11 12 R16 120k  LED7 DETECTOR B 8 IC1c 10 R28 10k 9 A Q7 BC548 R22 10k D6 1N4004 +12V R19 205  ZD1 10V VCC C10 100 8 R15 47k IC2 555 6 0V 2 C3 .001 D2 4 3 5 1 4x1N4148 D3 C5 4.7 D4 E C B Q9 BC548 E C8 4.7 C7 A 4.7 K C VIEWED FROM BELOW E IC1d and IC1c operate as a square wave oscillator with its frequency of opera­tion determined by resistors R17 & R18 together with capacitor C9. The oscillator is enabled whenever pin 12 of IC1d is pulled high. Depending on where you want to put the level crossing lights, pin 12 can be connected to point A or point B (pin 3 or pin 4 of IC1) on the circuit. The complementary outputs of IC1c & IC1d drive transistors Q7 and Q8 and these cause LEDs 7 & 8 to flash B E C4 .01 Fig.2: the train detector board is based on an RS flipflop (IC1a & IC1b) which controls the relay. The RS flipflop is set and reset by the locomotives breaking detector beama A and B. IC2 and the associated voltage multiplier provide a 30V supply for the high voltage relay. 34  Silicon Chip Q8 BC548 D5 TRAIN DETECTOR As well as driving the relay, transistor Q5 drives LED3 and LED4 which are in series. Q6, driven from the alternate output of the RS flipflop, drives LEDs 5 & 6 in series. LEDs 3 & 5 are red while LEDs 4 & 6 are green. These are placed on signals situated just before each infrared detector beam, so that when a train goes through the beam, the lights change state (eg, from GO to STOP and vice versa. IC1c and IC1d are arranged to provide a complementary LED flasher. C B E R24 10k C6 4.7 K R23 2.2k C B  LED8 K Q1 C alternately. These can then be used to simulate the flashing lights at level cross­ings. Interestingly, when pin 12 is pulled low, LEDs 7 and 8 will stop flashing but one LED will stay alight, due the high state of pin 10 or 11. To stop both LEDs from lighting when pin 12 is low, transistor Q9 is connected in series with the paralleled emitters of Q7 and Q8. The base of Q9 is connected to pin 12 of IC1 via a 10kΩ resistor. Now, when pin 12 is high, Q9 is on and the LEDs can flash merrily away. But when pin 12 is low, Q9 will be off and so both LEDs 7 & 8 will be dead. The rest of the circuit based around IC2 is there solely to provide a high Q1 BC548 C E +8-15V C1 100 0V R1 2.7k C4 1 B R4 150k 32W 2 C2 0.47 ZD1 5.6V R2 10k TRIGGER 1 4 C5 0.1 7 C 8 Q2 BC548 C3 .015 R5 330  B 9 5 B R3 4.7k COB MODULE E E 10 NO 1 47k LED3,4 LED5,6 205  D6 1k 4.7uF D5 4.7uF Q6 2.7k +12V TRIGGER 0V 10k Q5 .01 +12V D1 10k GND ZD1 RELAY1 1k 120k 10k 10k IC1 4011 22k B 4.7uF D4 IC2 555 NC COM OSC O/P 4.7uF D3 .001 1 A Q4 220k 68k 560  120k GND 22k 68k .015 LED2 0.47 Q3 D2 Q2 220k 560  120k LED1 Fig.4 (left): the LEDs shown here will normally all be mounted on the model train layout. LEDs 7 & 8 are the level crossing lights while the others provide the signalling. Q9 10k 100uF .015 Q8 Q2 SPEAKER Q1 100uF Q3 150k 2.2k Q1 Q7 2.2k There are four PC boards to be assembled for this project: one for the train detector circuit, one for the COB module and two for the infrared light detector beams. We’ll deal with the IR beam boards first. Each board has two components: LED1 (or LED2) and the opto­transistor Q1 (Q2). As can be seen from the photos, the LEDs for these boards have clear lenses and are installed with the longer lead connected to the “A” mark on the board. The optotransistors come in a much smaller rectangular package which has only two leads. Looking at the package with the small lens facing you, the emitter lead is on the left while the 1uF ZD1 LED8 4.7M 2.2M LED7 Construction .015 4.7k The COB circuit is little more than a power supply and a transistor which drives a loudspeaker. The COB module requires a voltage of 5V and this track, or the level crossing bells. It just depends on which of four pins is connected to pin 1. To obtain the level crossing sound, connect pin 1 to pin 7. 10k COB circuit C VIEWED FROM BELOW COB is provided by the simple regulator com­prising a 5.6V zener diode ZD1 and emitter follower transistor Q1. Transistor Q2 provides the trigger facility. If the trigger input is pulled high, transistor Q2 turns on and shorts the zener diode at the base of Q1. This kills the supply from Q1 and so the COB module is silenced. On the other hand, if the trigger input is held low, Q2 is off and the COB module is fed its 5V supply by Q1. Transistor Q3 acts as a buffer stage for the COB module and drives the 32Ω loudspeaker. Depending on when you want the level crossing sound to be produced, the trigger input of the COB circuit can be connected to point A or B on the train detector circuit of Fig.2. While we have yet to mention it, the COB module is capable of a variety of train sounds. You can have a steam train whistle, a locomotive chuffing, a carriage passing over a join in the Q3 C8050 B E voltage source for the relay which is a 48V type. IC2 is a 555 timer connected as a square wave oscillator. Its output drives a voltage multi­plier consisting of diodes D2-D5 and capacitors C5-C8. This produces a DC supply of around 30V which is adequate to drive the relay reliably. But there’s more. As well as the signalling and level crossing lights, this project offers a small module which produc­es the sound of a level crossing. This takes the form of a chip-on-board (COB) module which is effectively a bare integrated circuit die (the chip) on a small PC board and encapsu­lated in a blob of epoxy. The circuit to enable the COB module is shown in Fig.3. C 0.47 COB MODULE Fig.3: the COB module board is little more than a power supply (Q1, ZD1) which is turned on or off by Q2. Q2 is switched by the trigger lead which should be low for sounds to be produced. 0.1 330  Fig.5: the various sounds of the COB module are enabled by connecting a link between the stakes for pin 1 and pins 4, 5, 7 & 8. The connection shown here is for the level crossing bells. July 1995  35 PARTS LIST Train detector 1 PC board (Oatley Electronics) 2 detector beam boards (Oatley Electronics) 1 48V DPST relay Semiconductors 1 4011 quad 2-input NAND gate (IC1) 1 555 timer (IC2) 2 infrared LEDs (LED1,LED2) 2 optotransistors (Q1, Q2) 7 BC548 NPN transistors (Q3-Q9) 2 1N4004 silicon rectifier diodes (D1,D6) 4 1N4148 silicon signal diodes (D2,D3,D4,D5) 1 10V zener diode (ZD1) 4 red LEDs (LED3,5,7,8) 2 green LEDs (LED4,6) Capacitors 1 100µF 16VW electrolytic 4 4.7µF 63VW electrolytic 1 0.47µF monolithic 2 0.15µF ceramic 1 .01µF ceramic 1 .001µF ceramic Resistors (0.25W, 5%) 1 4.7MΩ 2 22kΩ 1 2.2MΩ 5 10kΩ 2 220kΩ 2 1kΩ 3 120kΩ 2 560Ω 2 68kΩ 1 205Ω 2W 1 47kΩ COB sound board 1 PC board (Oatley Electronics) 1 COB module 1 32Ω miniature loudspeaker 5 PC stakes Semiconductors 2 BC548 NPN transistors (Q1, Q2) 1 C8050 NPN transistor (Q3) 1 5.6V zener diode (ZD1) Capacitors 1 100µF 25VW electrolytic 1 1µF 50VW electrolytic 1 0.47µF monolithic 1 0.1µF monolithic 1 .015µF metallised polyester or ceramic Resistors (0.25W, 5%) 1 150kΩ 1 2.7kΩ 1 10kΩ 1 330Ω 1 4.7kΩ 36  Silicon Chip This is the COB module board which is supplied with a miniature 32Ω speaker which produces an adequate sound level. The COB module is butted to the end of the board and the pins soldered. collector lead is on the right; there is no base lead. Insert the optotransistor into the board and solder the leads. If you have soldered the leads correctly, the transistor’s lens will now be facing away from the infrared LED. That means that the transistor body needs to bent over backwards so that the lens faces the LED. Next, we’ll talk about the train detector board. This has two ICs and eight transistors. Its component layout is shown in Fig.4. Install the resistors and wire links first, followed by the small capacitors and diodes. The electrolytic capacitors can then be inserted, followed by the transistors and the ICs. Make sure that all the semiconductors and the electrolytic capacitors are installed the correct way around. If not, they could be destroyed when you first apply power. Finally, the relay can be installed. The LEDs can be wired temporarily into the board but eventually they will be installed on the layout. Note that the LED labelling on the diagram of Fig.4 is different from that shown on the PC board itself. Cur­rent production versions of the board show positions for LED3 & LED4 at diagonal corners. Our diagram shows the correct situation, with LED7 & LED8 mounted in the top lefthand corner of the board, while LEDs 3, 4, 5 & 6 are connected at the bottom righthand corner. LEDs 3 & 4 are connected in series, as are LEDs 5 & 6 and the commoned positive connection goes to the junction of the 10V zener diode ZD1 and the 205Ω resistor. Note that a link is shown on the underside of the board connecting pin 3 of IC1 to pin 12. This enables the level cross­ing lights, as discussed previously. The alternative is to con­nect pin 12 to pin 4 (point B). COB module assembly Another view of the COB module board, showing the five PC stakes which enable a choice of sound effects. The light board mounted at right angles is the COB (chip on board) module. The relevant component layout is shown in Fig.5. The main aspect of this assembly is connecting the COB module to the PC board. The two boards are butted at right angles and the 14 connections SATELLITE SUPPLIES Aussat systems from under $850 SATELLITE RECEIVERS FROM .$280 LNB’s Ku FROM ..............................$229 LNB’s C FROM .................................$330 FEEDHORNS Ku BAND FROM ......$45 FEEDHORNS C.BAND FROM .........$95 DISHES 60m to 3.7m FROM ...........$130 This is the train detector board which provides relay switching to the isolated track section and various LEDs for track signall­ing and level crossing lights. are soldered between them. After that, the remaining work is to install the board components which comprise five resistors, four capacitors, two transistors, the zener diode ZD1 and the PC stakes. Make sure that the semiconductors and the two electrolytic capacitors are correctly oriented. To obtain the level crossing bell sound, connect a lead between two of the PC stakes as shown in Fig.5. Testing Let’s test the train detector board first. You will need to connect the two optocoupler boards first so that the operation of the RS flipflop can be checked. Apply power and check the state of the LEDs. With both detector beams unobstructed, either LEDs 3 & 4 or LEDs 5 & 6 should be on. If LEDs 5 & Where To Buy Kits Both these designs are from Oatley Electronics who own the design copyright.The train detect­ or board kit is available for $20 while the COB sound kit costs just $12. Packaging and postage is $4.00. Send a cheque, money order or credit card authorisation to Oatley Electronics, PO Box 89, Oatley, NSW 2223. Phone (02) 579 4985 or fax (02) 570 7910. 6 are on, LEDs 7 & 8 should be flashing alternately. If LEDs 5 & 6 are on, try interrupting detector beam A by placing your finger between the LED and the opto­ transistor. LEDs 5 & 6 should go out and LEDs 3 & 4 should light and LEDs 7 & 8 should stop flashing. The relay should also be energised at this time. Now interrupt detector beam B in the same way. The circuit should change state again so that LEDs 3 & 4 go out and LEDs 5 & 6 come on, as before. If all of the above occurs, you have a working circuit. Testing the COB board Testing this board is easy. Just apply power and the speak­er should immediately emit the characteristic bells sounds of a level crossing. If it does not, check the 5V rail at the emitter of Q1 and all the connections to the COB module. To turn the sound off, connect a lead from the trigger input to the 8-15V rail. If it doesn’t turn off, check the compon­ ents around transistor Q2. Well, there you have it: a couple of low cost PC boards which will add life and realism to a simple model railway loop layout. Not only that, you could incorporate a similar small loop into a much larger layout and thereby add an automatic section which will run itself and give greater SC visual interest. LOTS OF OTHER ITEMS FROM COAXIAL CABLE, DECODERS, ANGLE METERS, IN-LINE COAX AMPS, PAY-TV DECODER FOR JAPANESE, NTSC TO PAL TRANSCODERS, E-PAL DECODERS, PLUS MANY MORE For a free catalogue, fill in & mail or fax this coupon. ✍     Please send me a free catalog on your satellite systems. Name:____________________________ Street:____________________________ Suburb:_________________________ P/code________Phone_____________ L&M Satellite Supplies 33-35 Wickham Rd, Moorabin 3189 Ph (03) 9553 1763; Fax (03) 9532 2957 July 1995  37 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates. Encoder for surround sound decoders This simple encoder produces the requisite channel informa­tion to select each of the four channels of a surround sound decoder. It is useful for testing surround sound decoders for distortion, noise, frequency response and crosstalk, or for just checking that each channel works. You can also use the encoder for setting up the levels in each output. Table 1 shows what signals are required to generate the channel information for the Left, Centre, Right and Surround outputs. In essence, the circuit consists of a dual op amp and a rotary selector switch. The input signal is attenuated by 3dB with the 33kΩ and 82kΩ voltage divider resistors. Op amp IC1a provides a +3dB gain using the 6.2kΩ feedback resistor between the invert­ ing input and output and 15kΩ resistor from the inverting input to pin 2 of IC1b. Since pin 2 of IC1b is a virtual earth (pin 3 is connected to ground), IC1a acts as a non-inverting amplifier and the resulting 3dB gain restores the output to the original 0dB level. The signal present at pin 6 of IC1a is -3dB since this input follows the non-inverting pin. IC1b inverts the -3dB signal level so that it is 180° out of phase. Finally, double pole switch S1 selects the 0dB, -3dB in-phase and -3dB out-of-phase signals for the Lt and Rt outputs. The switch selections replicate the requirements in the above +15V 33k INPUT 0dB -3dB 5 8 IC1a 6 TL072 82k GND 0dB 7 LEFT CENTRE 6.2k RIGHT -3dB 100  GND 15k 15k +15V RIGHT 2 3 +15V LEFT CENTRE 1 IC1b 10 16VW -15V 4-POINT ENCODER -15V Fig.1: the circuit consists of op amps IC1a & IC1b, plus a double-pole rotary selector switch. IC1a has a gain of 3dB while IC1b operates as an inverter. Table 1 Encoded Channel L Out R Out Left 0dB Off Centre (both in phase -3dB -3dB Off 0dB -3dB -3dB Right Surround (in antiphase) table. The 100Ω resistors isolate the op amp outputs. Power requirements for the circuit are a ±15V supply although lower voltages can be used. The supply rails are decou­pled using 10µF capacitors. A printed circuit board has been produced for this encoder. It is coded 01107951 and measures 85 x 41mm. No special order need be followed when installing the parts on the PC board although it’s best to install the low profile components first and leave the rotary switch until last. Take care with the orientation of IC1 and the two 10µF electrolytic capacitors and use PC stakes to terminate the external wiring. SILICON CHIP 100  -15V 15k IC1 TL072 0V 82k +15V S1 GND Lt GND Rt 1 10uF 15k 100  Fig.2: here’s how the parts are installed on the PC board. Use PC stakes at the external wiring points. 38  Silicon Chip GND -15V 0V 33k 6.2k Rt SURROUND -3dB 180ø 4 10 16VW 100  GND IN 10uF Lt SURROUND Fig.3: this is the full-size etching pattern for the PC board. It measures 85 x 41mm. 8 C E B SPEAKER DRIVER Q3 BC227 B C BUFFER PLASTIC SIDE 12 11 E B 13 10  IC1d 3 10 VIEWED FROM BELOW C 2.2 16VW 47  E E C B 10k 100k 10k 4 5 100k 0.5Hz OSCILLATOR 2 IC1b 100k D2 1N4004 100k COMPARATOR 1M -2.8V 100k 100k 7 6 IC1a LM339 1 100k -11.3V D1 1N4004 1k -12V FROM IGNITION SWITCH 33  0.1 ZD1 16V 1W 100 16VW -4.7V ZD2 4.7V 400mW 6.8k 10k COOLANT LEVEL ALARM FOR POSITIVE EARTH VEHICLES .0047 100k E D4 1N4148 9 8 IC1c 100k 1kHz OSCILLATOR 14 0.1 10k 100k Q1 BD681 C B 10k INDICATOR LAMP D3 1N4148 3.3k 10 16VW 1M GND 100 16VW TO SENSOR The Coolant Alarm featured in the June 1994 issue of SILI­CON CHIP is not suitable for positive earthed vehicles. If used without changes on a positive earthed vehicle, the coolant sensor will form a circuit through the radiator fluid to the positive supply rather than to the nega­tive supply. The alarm will therefore sound whether coolant is present or not. To make it work with positive earthed vehicles, the input comparator sensing has to be changed and its reference voltage needs to be referred to the positive rail rather than to the negative rail. As shown, the coolant sensor is fed via a 100kΩ resistor from the 4.7V zener diode ZD2. The sensor voltage is monitored by the inverting input, pin 6 of comparator IC1a. Pin 7, the non-inverting input, connects to a -2.8V reference provided by the 10kΩ and 6.8kΩ resistors connected across ZD2. Normally, the coolant in the radiator will hold the sensor voltage close to the positive supply. Pin 6 of IC1a will be higher than pin 7 and so IC1a’s output (pin 1) will be low. This inhibits the 0.5Hz oscillator based on IC1b from operating and its output at pin 2 will be low. Transistor Q1 is held off by this low output from IC1b, while diode D3 ensures that Q1 is biased fully off. If coolant is lost from the radiator, the sensor voltage will drop below -2.8V and pin 1 of IC1 will go high and allow the 0.5Hz oscillator to operate. When the pin 2 of IC1b goes high, Q1 turns on and drives the indicator lamp. Note that the lamp is separately powered via D2 from the -12V rail. This prevents the sensor circuit power supply fluctuating every time the lamp switches on and off. The 0.5Hz oscillator formed by IC1b gates a 1kHz oscillator formed IC1c via diode D4. The resulting 0.5Hz bursts of 1kHz signal are then buffered by IC1d and fed to a speaker driver circuit consisting of Q2 and Q3. These two transistors form a simple complementary audio output stage and drive the loudspeaker via a 2.2µF capacitor and a 47Ω resistor. If you want greater volume, decrease the value of the resistor but don’t go lower than 22Ω. SILICON CHIP Q2 BC337 Coolant alarm for positive earth vehicles July 1995  39 Setting up a satellite TV ground station; Pt.3 Setting up a satellite ground station is quite straight­forward – once you have the necessary equipment. The main job involves aiming the dish antenna at the desired satellite. By GARRY CRATT There are many satellites visible from Australia, all with varying power levels and program content. In order to set up a satellite earth station that will provide satisfying results, it is important to carefully consider the available satellites. This will determine the required dish size and operating band. There are also some government restrictions in place, pre­venting overseas broadcasters from offering pay TV services direct to the Australian general 40  Silicon Chip public. This situation should change after 1997 when “deregulation” of the industry takes place. As discussed previously, two frequency bands are used for satellite TV delivery – C band (3.7-4.2GHz) and K band (12.25-12.75GHz). C band (3.7-4.2GHz) is mainly used by international broadcasters, while K band (12.25-12.75GHz) is used for domestic satellite transmissions. The main sources of K-band signals are the Optus B1 and A3 satellites, with occasional teleconferencing carried on Panamsat’s Pas-2 satellite. Generally, the Optus satellites are used as a national delivery system. Among other things, they carry B-MAC transmis­sions such as the ABC, SBS, Queensland Television, Imparja and the Golden West network. These transmissions are designed as a service for remote area viewers and are collectively called HACBSS (Homestead and Community Broadcast Satellite Serv­ice). B-MAC signals can only be received using authorised B-MAC receivers. Without one, no intelligible picture or sound can be received. Unfortunately, the cost of a B-MAC receiver (which will also receive PAL signals) is quite high, at around $2000. The commercial TV networks Table 1: Optus B1 Satellite Channels (K-Band) Transponder Pol. User Mode Decoder Table 2: C-Band Satellite Channels IF (MHz) Audio Intelsat (180°E) 1 V Not Allocated 977 TV NZ; BBC; ITN 964MHz 2 V Not Allocated 1041 TV NZ; ABS 983MHz 3 Lower V Network 9 PAL/NTS Not Required 3 Upper V Network 7 E-PAL 4 Lower V Interchange PAL 4 Upper V Network 10 E-PAL 5 Lower V Network 9 PAL Not Required 5 Upper V Not Allocated 6 Lower V Omnicast FM2 Available 1282 6 Upper V Sky B-MAC Not Available 1308 7 Lower V ABC HACBSS B-MAC Available 1344 7 Upper V SBS HACBSS B-MAC Available 1370.5 8 V Network 9 PAL Not Required 1425 9 H CAA Air to Ground SCPC Scanning Receiver 1009 10 H Pay TV MPEG-2 Available 1996 1073 11 H Pay TV MPEG-2 Available 1996 1137 12 Lower H Network 9 E-PAL 12 Upper H Not Allocated 13 Lower H ABC Interchange PAL Not Required 150.5 13 Upper H ABC Radio Digital Not Available 1276.5 14 Lower H ABC HACBSS B-MAC Available 1313 Gorizont 19 (96.5°E) 14 Upper H SBS HACBSS B-MAC Available 1339 CCTV 4 (China) 1320MHz 15 Lower H QTV RCTS B-MAC Available 1376 AZTV (Turkey) 1425MHz 15 Upper H QTV Data B-MAC Not Available 1402 Network 1 (Russia) 1475MHz also use the Optus satellites to distribute regular programming, using an en­crypt­ion system called E-PAL. Considerable effort is required to unscramble E-PAL and, because the material is subject to copyright, there is little point in expending any effort to decode these signals. In addition, there is a third type of programming known as the “news interchange” service. This material is broad­cast in PAL and is designed to be received by regional TV sta­tions for terrestrial redistribution. It includes entire pro­grams destined for subsequent rebroadcast, news feeds from port­able uplink stations or overseas affiliates, and 30 second “promo” advertisements. There are also many hours of direct un-edited programming which is rebroadcast (after standards conversion) from the Intel­ sat 4GHz service. Typically, services such as CNN, Skynet, BBC World News and many others can be received in the course of a single 24-hour period. Not Required 1094 7.38/7.56 NBC; Network 9 1012MHz 1120 7.38/7.56 RFO Tahiti 1100MHz 1156.5 7.38/7.56 ABC; CNBC; NHK Tokyo 1135MHz 1182.5 7.38/7.56 Worldnet 1178MHz 1219.5 7.38/7.56 CNN 1252MHz NBC/CNBC 1275MHz NBC; ITN; Network 10 1385MHz Occasional Use 1431MHz 1245.5 1188 Panamsat PAS-2 (169°E) 7.38/7.56 1214 6.60/6.60 C-band signals can come from a number of satellites, in­ cluding the “Gorizont” class spacecraft carrying Russian and Chinese language broadcasts, the American Hughes HS-601 satel­lites carrying US and Asian originated programming, and the Rimsat series of spacecraft, leased to countries such as India, New Guinea, and China. Tables 1 and 2 list the available satel­ lites and channels. In the case of Optus K-band satellite reception, a 1.6-metre dish, an LNB (low noise block converter), and a feedhorn are required, along with the satellite receiver. For C-band reception, a 3-metre dish will provide good reception of most of the available international satellites. However, there are some instances where a smaller dish can be used; eg, for dedicated single satellite reception. Aiming the dish Connecting up the system is really no more difficult than connecting the components of a typical hifi system. CNBC (USA) 1035MHz NHK Tokyo (Japan) 1110MHz CNN (USA) 1183MHz MTV 1345MHz Rimsat G2 (142.5°E) EM TV (PNG) 1260MHz ATN (India) 1475MHz However, the dish must be correctly aimed at the satellite in order to receive TV programs. For every location in Australia, there is a different set of “pointing co-ordinates” to aim the dish at a satellite. These dish pointing co-ordinates can be calculated using a commercial software program and most equipment vendors will also calculate them on request. (Note: a dish pointing program for PCs is avail­able from Av-Comm for $15 – Cat. S-1000). Most programs require the satellite longitude, the site latitude and longitude, and the magnetic variation from true north to perform the calculations. Typically, they output the magnetic bearing, the true bearing and the angle of elevation. Fig.1 shows the azimuth and elevation “look angles” for the Optus B1 satellite across Australia. Often, the site latitude, longitude and magnetic variation can be obtained from a local airport. If this source is unavail­able, many general aviation supply outlets carry maps July 1995  41 Copyright Warning Satellite TV reception can be a very satisfying hobby, similar in many ways to shortwave listening. Reception is fortu­ itous and you never know what you may see. However, it is always wise to remember that whatever programming is seen is subject to copyright laws. In particular, readers are warn­ed that the commercial use of such programming invites prosecution unless permission has been obtained from the copyright holder. view of the appropriate part of the sky, unobstructed by buildings, trees or any other objects. There are four critical parameters which must be accurately set, in order to align the dish with the desired satellite and to receive signals: (1) elevation above the horizon; (2) the azi­muth; (3) the focal point; and (4) the LNB (low noise block) polarity. The easiest way to correctly point the dish is to set the elevation first. This can be done using a timber batten, a cheap plastic protractor and a plum bob (eg, a nut tied to a piece of cotton). By affixing the cotton to the centre of the protractor and then holding the protractor against the batten, the angle formed will be equal to the angle of elevation – see Fig.2(a). Fig.1: this diagram shows the azimuth & elevation “look” angles for the Optus B1 satellite which is located in geostationary orbit at 160° longitude. (Aussat Network Designer’s Guide). known as WAC charts (World Aeronautical Charts), which show these details. The magnetic variation for the earth station site is important if a compass is to be used to align the dish. For example, for locations around Sydney, magnetic north is 12.6°E of true north. This means that 12.6° must be subtracted from the true azimuth if using a compass to set the heading. Aiming the dish So having decided on a satellite, assembled the necessary system components and obtained (or calculated) the azimuth and elevation co-ordinates, the dish must be pointed in the correct direction. The dish should have a clear PROTRACTOR LEVEL PLACED MIDWAY UP DISH RIM TIMBER BATTEN ANGLE OF ELEVATION PLUMB BOB (a) ANGLE OF ELEVATION (a) Fig.2: this diagram shows two different methods of measuring the dish elevation. In Fig.2(a), the elevation is measured using a plumb bob & a plastic protractor, while in Fig.2(b) the elevation is measured using a protractor level (eg, from a combination square set). 42  Silicon Chip D Another way of measuring the elevation is with a protractor level (eg, from a combination square set). This is placed on the rim of the dish, as shown in Fig.2(b). The magnetic azimuth bearing (as calculated by the pointing program) can be set using a compass, taking care to ensure that it is kept well away from any stray magnetic metal. Alternative­ ly, if a compass is not available or the magnetic variation is not known, the true azimuth figure can be used, provided that the location of true north is known. To find true north, we need to calculate the midpoint of the day on which the dish is to be set – and we need a sunny day! This is done by first obtaining the times for sunrise and sunset (eg, from a local airport or observatory) and calculating the midpoint of the day. Next, position a pole vertically in the ground. At the calculated midpoint, the shadow cast by the stick will be aligned with true north. It’s then simply a matter of measuring the azimuth angle from true north using an inexpensive protractor and marking out the line of direction (eg, using a pegged string line or a cardboard template). The dish can then be pointed along the marked line. While all the foregoing implies that FOCAL POINT VT The receiver can be tuned to individual transponders during the setting up process by setting the voltage on terminal VT of the tuner module. Table 3 shows the tuning voltages for several transponders on the Optus B1 satellite. the dish must be precisely aimed using these techniques, in practice it is not as complicated as that. All that is required initially is to aim the dish in the general direction of the satellite. A series of “fine-tuning” adjustments can then be made later on, when a picture is visible. Once the dish elevation and azimuth are correctly set, the focal point should be determined. Most manufacturers provide this figure but if not, the focal point can be calculated using the formula F = D2/16C, where D is the diameter of the dish, and C is the depth – see Fig.3. By the way, the depth (C) can easily be measured by stretching a piece of string across the front of the dish and then measuring the distance from the string to the deepest part of the dish. The result indicates the degree of curvature of the dish and determines the location of the feedhorn and LNB. Once the result is known, clamp the feedhorn into position at the correct distance from the centre of the dish. Finally, the polarity of the LNB must be set. In practice, this is done Table 3: Tuning Voltages (Optus B1) Transponder IF (MHz) Format Voltage 3 Lower 1094 PAL 2.95V 4 Lower 1156.5 PAL 3.8V 5 Lower 1219.5 PAL 4.2V 7 Lower 1344 B-MAC 6.8V 8 1425 PAL 7.74V 13 Lower 150.5 PAL 5.16V after a signal is acquired and involves rotating the LNB for best reception of the desired transponder (after the front panel controls have been set). At this stage, some consideration should be given to the routing of the cable from the LNB to the receiver. Among other things, the cable includes a low-loss double-shielded 75-ohm coaxial section which is used to carry the converted block of signals (950-1450MHz) and also to carry the DC supply voltage for the LNB. In addition, the cable has separately insulated conduc­tors for the “Skew Out” connections (where required). The cable should be routed so that C 12281.9 12344.5 F (FOCAL LENGTH) F = D 2/16C Fig.3: the focal point (F) of the dish can be calculated by measuring its depth (C) & its diameter (D) & plugging these values into the formula F = D2/16C. VERTICAL HORIZONTAL 2 1 M 12407.1 12469.7 9 3 10 12270.5 12313.2 12375.8 12532.3 12594.9 12657.5 12720.1 5 6 7 8 4 11 12 13 14 15 12438.4 12501 12563.6 12626.2 12688.8 Fig.4: the transponder layout of the Optus B series spacecraft. Note that adjacent transponders have alternate polarities to minimise interference between them. July 1995  43 +18V 1.5k 680 8 SCAN SPEED VR1 1M 68k 6 IC1 566 7 4 1 100 12VW SCAN RANGE VR2 5k Q1 BC548 150  680  SCAN ON/OFF S1 TUNING VOLTAGE VR3 10k 150  150  D1 1N4148 680  12k TUNING VOLTAGE TO VT 0.1 Fig.5: this scanning circuit produces a triangle waveform which is fed to terminal VT of the tuner module. It allows the entire satellite IF block to be scanned for a signal at a selected rate while the dish is being positioned it can not be tripped over, run over by a lawn mower or subjected to other accidents. If buried underground, it should be run through plastic conduit. This offers good protection and, in the event of a fault, allows the cable to be pulled through and replaced. Final adjustments By far the easiest way to make the final adjustments is to have the receiver and TV set (or video monitor) at the dish site. That way, signals can be directly observed as the dish is aligned. However, before optimising the dish alignment, we must first tune the receiver to a transponder. This can be done simply by setting the correct tuning voltage for that transponder on the tuner module. This is the voltage present on terminal VT in the receiver described last month. Table 3 lists the tuning voltages for a number of transponders. If we study the transponder layout of the Optus B series spacecraft (Fig.4), it can be seen that adjacent transponders have alternate polarities. This is done to minimise interference between transponders and thus maximise frequency usage. For example, transponder 13 is adjacent to transponder 5 and these are horizontally and vertically polarised respectively. By adjusting the receiver tuning to the desired voltage, we can use the corresponding satellite transponder as a beacon to align the dish. For Optus B1, we recommend using transponder 7 – a B-MAC signal –to align the dish. This is a strong transponder and even if the LNB polarity is initially incorrect, will be recognisable as an unscrambled B-MAC signal (see photo). Once a signal is acquired (ie, adjust 44  Silicon Chip The LNB is adjusted by backing off the retaining clamp & rotating the assembly for optimum reception. This video printout shows the typical appearance of an unscrambled B-MAC signal. VR4 until VT reads 6.8V), the dish elevation, azimuth, and LNB polarity and can all be adjusted for best reception. By then tuning a PAL transponder, further visual improvements can be achieved. Note that the LNB is adjusted by undoing its retaining clamp so that the entire assembly can be rotated. Make sure that it remains at the correct focal point during this procedure, however. For reception of other satellites, select a suitable trans­ p onder IF frequency from Table 2. By way of example, a common IF frequency used on Gorizont and Rimsat space­­craft is 1475MHz, while 1105MHz can be used for Intelsat 511 and Pas-2. Scanning circuit For those adventurous enough, the circuit shown in Fig.5 can be built. This is a scanning circuit and was brought to our attention by Herb Miller, a reader from Perth. It uses a 566 voltage controlled oscillator (VCO) based on IC1 and this gener­ates a triangle waveform at its pin 4 output. This in turn drives transistor Q1 which produces a triangular ramp waveform at its collector output and this in turn becomes the tuning voltage for terminal VT of the tuner module. VR1 sets the scanning speed by varying the frequency of the VCO, while VR2 sets the scanning range. Switch S1 allows the scanning function to be switched on or off. When off is selected, the receiver can be manually tuned using VR3. Power for the circuit (+18V) can be derived from the receiver. By fitting an extra 6.5mm socket on the rear panel, the scanning voltage produced by the circuit can be fed to terminal VT of the tuner module via a matching plug. Note that the switch contacts inside the socket must be wired so that, when the plug is inserted, they break the existing connection to VT. The scanning circuit can be built into a separate enclo­sure, or internally wired. When the external scanner is unplugged, the tuning voltage from VR4 is automatically reconnected to the tuner module. Altern­ ative­ ly, if the scanner is built inside the satellite receiver, an additional toggle switch can be added. By using the scanning function, the entire satellite IF block can be scanned for a signal at a selected rate while the dish is being positioned. Once optimum performance has been achieved, the dish can be permanently secured in position. You are now ready to begin exploring the exciting world SC of satellite TV. SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au BOOKSHELF Simplified Design of Linear Power Supplies Simplified Design of Linear Power Supplies, by John D. Lenk. Published 1994 by ButterworthHeinemann. Hard covers, 246 pages, 241 x 160mm, ISBN 0-75069506-4. Price $62.95. The Author says in his preface that “this book has someth­ing for everyone”. The first six chapters cover the basics for all phases of practical design while the last chapter includes over one hundred worked-out design examples including: (1) an adjustable supply using an LM117 (LM317) regulator; (2) a triple output power supply using an LM117 regulator, two LM107 opera­ tional amplifiers and two transistors; and (3) a computer controlled supply using a 7475 latch and an LM338 adjustable regulator. Chapter 1, which covers linear power supply basics, is not a good beginning. It is obviously written for beginners but has errors which could cause confusion, especially if an oscilloscope was used to compare actual waveforms against those shown for the half-wave and full-wave rectifier circuits on pages 2 and 3. The Author shows the output waveforms at the diodes for half-wave and fullwave rectification assuming there is no capacitor but his circuits include electrolytic filter capacitors, which will dramatically change the viewed waveforms. Page 15 shows a diagram of an adjustable shunt regulator. This has a potentiometer between a 4.7 volt zener to ground and a 15 volt source with the caption “0 - 10V regulated” – again, puzzling for the beginner, while the more experienced will re­alise it should read “4.7 to 15V regulated”. Chapter 2 covers heatsinking in linear power supplies. Among the topics discussed in this chapter are heatsink ratings, power dissipation, mounting of components on heatsinks, mounting surface preparation, thermal compounds and the types of heatsinks available for integrated circuits. The majority, if not all of this information would be familiar to the experienced power supply designer. Chapter 3 is titled an introduction to discrete feedback regulators. The author first discusses shunt voltage regulators, including those with outputs both higher and lower than the reference voltage. He then goes on to detail series voltage and current regulators with a worked example for an 8V 4A unit. Details of adding parallel pass transistors to increase the output current are also discussed. Chapter 4 moves on to modern integrated circuit (IC) based regulators and covers the four basic sections: control, bias, DC level shift and output. The circuits for several commercial ICs are shown, with methods of increasing the output current and limiting the maximum current with excessive loads. The Author also shows how to monitor the heatsink temperature and shut down the regulator if the temperature becomes excessive. Chapter 5 is devoted to the basics of IC operational ampli­fiers in discrete linear voltage regulators. The chapter starts with an explanation of the benefits the operational amplifier brings to the designer. A discussion then follows on suitable reference sources and methods of obtaining output volt­ ages higher than the reference voltage. The chapter ends with details of the methods for remote sensing. Chapter 6 is concerned with linear power supply testing. It deals with measur­ ing output and input-output regulation, internal resistance, ripple, transformer phasing and transformer regulation. It also covers the measurement of transient recovery time, drift and temperature coefficient. The chapter finishes by showing methods for the connection of multiple loads to one power supply and two supplies to multiple loads. Again, we noted errors in the dia­grams on pages 90, 91 & 95. Chapter 7 is headed “Linear Supply Design Examples” and occupies over half the book. Disappointingly, it consists of virtually no original material, only reprints of circuits from the major manufacturers’ application notes. Coincidentally, the three design examples listed at the beginning of this review and quite a few others in this chapter were all taken from the Na­tional Semiconductor Linear Applications Handbook, which would surely be in every design engineer’s library. To sum up, a rather disappointing book. While we did not read it from cover to cover, several errors were noted, which should not have appeared. And while circuits from 16 different sup­pliers are included, the reader may be better off buying the application notes of one of the major manufacturers (eg, Nation­al, Motorola or Harris). Our sample copy came from the publish­ ers, Butterworth Heine­ mann Australia, PO Box 5557, West Chats­ wood, NSW 2057. Phone (02) SC 372 5511. (R.J.W.) July 1995  53 Build a reliable Door Minder This project will sense a door opening in a large or small room and will sound a 2-tone chime. It does not have to be anywhere near the doorway as it uses an ingenious method to detect the pressure change caused when the door opens or closes. By RICK WALTERS While the most obvious application of this project would be as a door monitor for shop keepers, it could have applications in offices, workshops, doctors’ and dentists’ waiting rooms, child-minding centres and in the home. It could also be used as a sensor in a burglar alarm. In the past, the classic ways to detect the opening of a door have been a microswitch mounted on the doorway, a pressure switch in a mat on the floor or a light beam relay circuit. The latter method has the advantage that it does not have to be attached to the door and it can be made to work with any type of door, hinged or sliding. The disadvantage of a light beam relay is that it must be near the doorway or an adjacent passageway and it must be carefully set up in the first place, to work correct­ ly. Light beam relays can also be swamped by the Sun or by bright lighting. The Door Minder presented here can be placed anywhere in the room; it does not have to be anywhere near 54  Silicon Chip the doorway. It can even be placed in an adjoining room. How does it work? When a door is closed it can be regarded as a very large piston in a close-fitting rectangular cylinder. When you push a door open, you cause quite a large momentary increase in air pressure in the adjoining room. The Door Minder senses this increase in pressure and sounds a two-tone chime. The Minder can be used on either side of a door because it also senses a momentary drop in pressure. So it works equally well with inward opening or outward opening doors. Nor does the room need to be tightly sealed. Windows can be open, provided they are not really large. Because it senses pressure, the Minder can be placed any­where in the room. It will work in very large rooms too – up to several hundred square metres (say 200 square metres or more). In our offices at SILICON CHIP we have a number of adjoin­ing rooms. Opening the door to one room will trigger the Door Minder in any of the other rooms, even with the windows open. It is highly effective and does not respond at all to wind or to loud noises. What is the pressure sensor? The pressure sensor is nothing more than a cheap electret microphone insert which can be bought for a couple of dollars. The electret microphone is used with an amplifier circuit which only responds to extremely low frequencies. It does not respond to audible sounds at all. The amplifier is used to trig­ger a two-tone oscillator circuit which produces the chime sounds. Another integrated circuit audio amplifier is used to drive a small loudspeaker. And that is virtually all there is to it. Unlike light beam relays, the circuit uses very little power and could be 6 3 .047 8 VR2 4.7k 5 IC3 2 LM386 4 10  10 25VW GND REG1 7808 OUT 33k 0.22 4 .047 220k +8V 5 IC2c 6 .047 13 D5 1N914 4.7M 12 IC2f 56k .047 IC2b 2 3 7 14 0.22 22M 0.22 8.2M 1 IC2a 74C14 D3 1N914 4 IC1b D S VIEWED FROM BELOW G 100 LL 1 MIC 47k VR1 4.7k 3.9M DOOR MINDER I GO 10k 1k D2 +3.3V +3V 150k 5 150k IC1a 3 TL072 2 +3.3V 1 2x1N914 1k D1 15k +3.6V 6 8 7 0.1 0.1 Fig.1 (right): the circuit uses a microphone, a bandpass filter stage (IC1a), a comparator (IC1b), a 2-tone chime generator (IC2) & an audio amplifier (IC3). S 1k G .01 10k 0.22 4.7M 8 9 IC2d 220k Q2 BS170 D 1k S G D4 1N914 .047 11 47k IC2e 10 10k .01 Q1 BS170 D 33k 100 16VW 0.1 +8V The circuitry for the Door Minder comprises the electret microphone insert, a small loudspeaker, three integrated cir­ cuits, two field effect transistors, a 3-terminal regulator and a few resistors, capacitors and diodes. It is powered from a 12V DC plugpack or, as already noted, from batteries. The circuit is shown in Fig.1 To describe how the circuit works, let us start right at the beginning, at the electret insert. This contains an internal field effect transistor (FET) which is connected as a source follower. The DC supply for the internal FET is provided by the 4.7kΩ trimpot VR1 which does double-duty as a sensitivity con­trol. With the wiper of VR1 adjusted up to the +8V supply rail, no signal is fed to the following circuitry; with the wiper adjusted at the extreme opposite setting, maximum signal is fed to the following circuitry. IC1 is a TL072 dual op amp. IC1a is connected as a narrow bandpass filter stage with a gain of about 80. It responds to frequencies within the range of about 0.5Hz to 3Hz. What this effectively means is that IC1 will respond only to brief positive or negative changes in air pressure, as sensed by the electret. Note that the non-inverting input, pin 3 of IC1a (indicated with a + sign), is set at +3.3V by the 15kΩ, 1kΩ and 10kΩ resis­ tors. A 100µF capacitor decouples this input from the supply. This input bias sets pin 1, the output of IC1a, to +3.3V too, which is important as far as the following circuitry is con­cerned. IC1b is connected as a comparator. Pin 6, the inverting input (indicated with a minus sign), is held at +3.6V due to the resistors forming the previously mentioned voltage divider across the 8V supply. Pin 5, the non-inverting input, is held at +3.0V. The output of IC1a is connected to the two inputs of IC1b via two 1N914 IN The circuit 100 16 12V PLUG-PACK run from batteries, if you wanted to. July 1995  55 RESISTOR COLOUR CODES ❏ No ❏  1 ❏  1 ❏  2 ❏  1 ❏  2 ❏  2 ❏  1 ❏  2 ❏  2 ❏  1 ❏  3 ❏  4 ❏  1 Value 22MΩ 8.2MΩ 4.7MΩ 3.9MΩ 220kΩ 150kΩ 56kΩ 47kΩ 33kΩ 15kΩ 10kΩ 1kΩ 10Ω 4-Band Code (1%) red red blue gold (5%) grey red green brown yellow violet green brown orange white green brown red red yellow brown brown green yellow brown green blue orange brown yellow violet orange brown orange orange orange brown brown green orange brown brown black orange brown brown black red brown brown black black brown diodes, D1 & D2. Under quiescent (no-signal) condi­tions neither of the diodes conduct since the voltage across each is only 0.3V between the anode and cathode. Note that the voltage at the inverting input is higher than the non-inverting input by 0.6V and so pin 7 of IC1b is low. When the output of IC1a swings high, due to a pressure decrease sensed by the electret, diode D2 conducts and pulls pin 5 of IC1b higher than pin 6 10k 1k 1k 15k .047 220k 10  10k .01 10k .01 47k Q2 D5 D4 4.7M 0.22 56  Silicon Chip IC3 LM386 56k 8.2M 0.22 1 Q1 33k 0.22 1k MIC 150k 150k .047 1k 100uF 100uF 0.22 2x.047 4.7M 47k VR1 D3 IC1 TL072 1uF 1 220k 22M D2 1 Schmitt triggers 0.22 D1 3.9M VR2 IC2 74C14 10uF 0.1 0.1 100uF and so the output of IC1b goes high. Similarly, when IC1a’s output swings low, diode D1 conducts and pulls pin 6 lower than pin 5 and so pin 7 again goes high. IC2 contains six Schmitt triggers, two of which (e & f) are used as the chime oscillators, while the rest are for time delays. A normal CMOS gate switches at approximately 50% of the supply voltage, whether the input is rising or fall­ing. A Schmitt trigger, on the other hand, has a higher switching level for a rising input than it does for a falling one. Thus, there is a dead band (hysteresis) where the input signal can vary up and down by a fair amount, without changing the output. SPEAKER REG1 7808 5-Band Code (1%) not applicable grey red black yellow brown yellow violet black yellow brown orange white black yellow brown red red black orange brown brown green black orange brown green blue black red brown yellow violet black red brown orange orange black red brown brown green black red brown brown black black red brown brown black black brown brown brown black black gold brown 33k 0.1 12VDC PLUG-PACK Fig.2: install the parts on the PC board as shown here. Make sure that all polarised components are correctly oriented & take care with the supply polarity. PARTS LIST 1 PC board, code 03107951, 105 x 60 mm 1 plastic utility case, 130 x 68 x 44mm 1 57mm 8Ω loudspeaker 1 electret microphone insert 1 12VDC plugpack with DC plug 1 chassis mount socket to match DC plug 2 4.7kΩ miniature vertical trimpots (VR1,VR2) Semiconductors 1 TL072, TL082 dual op amp (IC1) 1 74C14, 40106 hex Schmitt trigger (IC2) 1 LM386 audio amplifier (IC3) 2 BS170 IGFETs (Q1,Q2) 1 7808 3-terminal regulator (REG1) 5 1N914, 1N4148 diodes (D1-D5) The PC board clips into slots in the side of the case, while the loudspeaker is secured using small clamps. Power can come from a 12V DC plugpack. Each time pin 7 of IC1 goes high, it charges the 0.22µF capacitor to about +7.4V and brings IC2, a 74C14 hex Schmitt trigger, into play. This will cause pin 2 of IC2a to go low, pulling pin 9 low via the series .047µF capacitor. Thus pin 8 will go high, charging the 0.22µF capacitor via D4, so that FET Q1 is turned on. The 47kΩ resistor between pins 10 and 11 of IC2e, together with the .047µF capacitor, form an oscillator which runs continu­ously. The signal at pin 10 is a 660Hz square wave. The 10kΩ resistor and .01µF capacitor at the output of IC2e provide a modest degree of filtering to make the waveform more sinusoidal. IC2f is another square wave oscillator and the signal at its pin 12 is 550Hz. When Q1 turns on, the filtered 660Hz signal is fed to its 1kΩ source resistor and then via the 33kΩ resistor to 4.7kΩ trimpot VR2. As the 4.7MΩ resistor on the gate of Q1 discharges the 0.22µF capacitor, the gate voltage of Q1 slowly falls and its resistance increases, thereby reducing the signal. This produces the audible “ding” which gradually fades. When pin 2 of IC2a goes low, as mentioned above, it produc­es a similar sequence to that previously described, pulling pin 3 of IC2b low. After the 8.2MΩ resistor charges the 0.22µF capaci­tor, pin 4 reverts to its low state, momentarily pulling pin 5 of IC2c low, which causes pin 6 to go high. This charges the capaci­ tor at the gate of Q2 to produce the “dong”. The ding-dong out­puts are mixed via the 33kΩ resistors and fed to audio volume control, trimpot VR2. The signal from VR2 feeds IC3, an LM386 audio amplifier which is used to drive the speaker. Time delays One point not mentioned so far is the avoidance of nuisance tripping. Clearly, if people are going in and out of doors fre­quently, the Door Minder circuit would be triggered into ding-donging all the time and that could drive you mad. So to avoid this, once the circuit Capacitors 3 100µF 16VW PC electrolytic 1 10µF 25VW PC electrolytic 1 1µF 16VW low leakage (RBLL) or tantalum electrolytic 4 0.22µF MKT polyester 3 0.1µF MKT polyester or monolithic 5 .047µF MKT polyester 2 .01µF MKT polyester Resistors (0.25W, 5%) 1 22MΩ 2 47kΩ 1 8.2MΩ 2 33kΩ 2 4.7MΩ 1 15kΩ 1 3.9MΩ 3 10kΩ 2 220kΩ 4 1kΩ 2 150kΩ 1 10Ω 1 56kΩ Miscellaneous Hookup wire, solder. has been triggered to produce a “dingdong”, it can’t be triggered again for about seven or eight seconds. This is achieved by the time constant consisting of the 0.22µF capacitor and 22MΩ resistor at pin 1 of IC2a. Once D3 has charged up the 0.22µF capacitor, it takes a significant time to discharge and this prevents re-triggering of the circuit. As mentioned above, power for the circuit is provided by a 12VDC (nominal) plugpack. This is fed to a July 1995  57 label where the crosses are, then place the panel on the lid of the box and mark the holes with a felt pen. The lid can now be drilled. This done, carefully drill the Dynamark® holes one or two sizes smaller, mount the speaker on the lid and affix the label. You also need to drill two holes in the case itself – one for the DC socket and the other to allow changes in air pressure to be sensed by the electret micro­phone. The latter can be drilled in one side of the case, near the microphone. Setting up Fig.3: the PC artwork is reproduced here actual size. + + + + + + + + + + + + + + + + + + + + All the parts, with the exception of the loudspeaker, are mounted on a PC board measuring 105 x 60mm (coded 03107951). This is mounted in the base of a standard zippy box measuring 130 x 68 x 43mm. No special procedure needs to be followed when assembling the board, although it is better if the two links and all the resistors are fitted first. Ensure that all the polarised compon­ents such as the diodes, electrolytic capacitors and ICs are inserted the right way around. This is shown on the component overlay diagram of Fig.2. As can be seen from the photos, we used a socket for IC2. This was done to allow us to check variations in the performance of Schmitt trigger ICs but otherwise a socket is not necessary. Most electret microphone inserts + Construction do not have the their leads labelled but tend to be sold with specifications showing how they are connected. Make sure you obtain this information when purchasing. Ours had an external metal screen with an earth lug which was not connected to either pin. We earthed this lug with a piece of tinned copper wire. The 3-terminal regulator is laid flat on the PC board. When installed in the case, there is adequate clearance between the components and the speaker magnet. If you do have clearance problems, because you use different components, file the PC board where it sits on the guides, to allow it to rest on the bottom of the case. The loudspeaker can be mounted on the front panel, using a silicone or epoxy adhesive, or small clamps and screws. We used the latter. Before doing that though, you will need to drill holes in the lid to let the sound out. Drill small holes in the Dynamark® DOOR MINDER 7808 3-terminal regu­lator which has an output of +8V. Fig.4: this artwork can be used as a drilling template for the loudspeaker grille. 58  Silicon Chip This is easy. Apply power and measure the voltage on the output pin of the 7808 regulator. It should be close to +8V. Check that the same voltage appears at pin 8 of IC1, pin 14 of IC2 and pin 6 of IC3. Now check the voltage at pins 1, 3, 5 and 6 of IC1. They should be close to the values nominated on the circuit of Fig.1. Now set trimpot VR2, near the LM386, fully clockwise (look­ing from the edge of the board) and trimpot VR1, next to the electret microphone, to about half setting and open a door. The chime should sound. Place the Door Minder anywhere convenient and that’s all there is to it. Adjustments Because of the possible spread in Schmitt trigger (IC2) levels, you may have to adjust one or two components. After the “ding”, there should be a short silence, then the “dong”. If they overlap, change the 8.2MΩ resistor on IC2b pin 3 to 10MΩ. Conversely, reduce it if the silent period is too long. If the tone duration is too long, reduce the 4.7MΩ resistors at the gates of Q1 and Q2 or, conversely, increase them for longer chime durations. As mentioned above, the 0.22µF capacitor and 22MΩ resistor at pin 1 of IC2a prevent a double chime as the door is opened and then closed. If you want a longer delay in your situation, in­ crease the capacitor to 0.47µF or even 1µF. Finally, note that when the Door Minder is not chiming, it will produce a low-level buzz. This is normal and is due to radiation of the harmonics of the 550Hz and 660Hz square wave oscillators into the mixing circuit asSC sociated with VR2. ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) TOTAL Australi a $A7.00; NZ $A8.00 (airmail ); Elsewhere $A10 (airmail ). Buy 10 or more and get a 10% discount. Note: Nov 87-Aug 88; Oct 88-Mar 89; June 89; Aug 89; Dec 89; May 90; Aug 91; Feb 92; July 92; Sept 92; NovDec 92; & March 98 are sol d out. All other issues are currently i n stock. $A B INDERS Pl ease send me _______ SILICON CHIP bi nder(s) at $A12.95 + $5.00 p&p each (Australi a only). N ot avail abl e elsewhere. Buy five and get them postage free. $A SUBSCRIPTIONS ❏ New subscription – month to start­­___________________________ ❏ Renewal – Sub. No._______________   ❏ Gift subscription ☞ RATES (please tick one) Australia Australia with binder(s)* NZ & PNG (airmail) Overseas surface mail 2 years (24 issues) 1 year (12 issues) ❏ $A90 ❏ $A49 ❏ $A114 ❏ $A61 ❏ $A135 ❏ $A72 ❏ $A135 ❏ $A72 ❏ $A240 Overseas airmail ❏ $A120 *1 binder with 1-year subscription; 2 binders with 2-year subscription GIFT SUBSCRIPTION DETAILS Month to start__________________ Message_____________________ _____________________________ _____________________________ Gift for: Name_________________________ (PLEASE PRINT) YOUR DETAILS Your Name_________________________________________________ (PLEASE PRINT) Address___________________________________________________ Address______________________ _____________________________ State__________Postcode_______ ______________________________________Postcode___________ Daytime Phone No.____________________Total Price $A __________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ Master Card 9am-5pm Mon-Fri. Please have your credit card details ready ______________________________ Card expiry date________/________ Card No. Phone (02) 9979 5644 Signature OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail coupon to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia July 1995  59 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au COMPUTER BITS BY GREG SWAIN Adding RAM to your computer Do you run graphics-intensive CAD or Windowsbased software on your computer? If the hard disc indicator LED flick­ers constantly, give your system a shot in the arm by adding more RAM. Here’s how to do the job yourself. Although you can run Windows with 2Mb (two megabytes) of RAM (barely), 4Mb is better and 8Mb is a lot better. But even 8Mb of memory is insufficient with some applications. Photoshop, a popular picture editing program, requires a minimum of 10Mb to run properly, for example. Graphics, spreadsheets and drawing programs are particular­ly memory intensive, although they will generally keep working even when system RAM becomes low. This can happen if you are running several applications at once (multi-tasking) or if you are manipulating large spread­sheets or colour images. In this situation, the system frees up RAM by swapping its contents to a specially reserved area called the “swapfile” on your hard disc. In other words, the system treats an area of the hard disc as RAM so that, theoretically, you should have all the RAM you need for the job. There is a drawback to this scheme, however – hard disc access times are many orders of magnitude slower than RAM access times. A fast hard disc will have an average access time of about 10ms, whereas RAM is about 140,000 times faster with access times of 70ns or better. As a result, your system can slow to a snail’s pace when running some memory intensive applications. That’s because you have to wait as the system constantly shuffles data from RAM RAM modules (also known as SIMMs) come in various capacities. Shown here is a 30-pin 1Mb SIMM that carries nine individual memory chips (one for parity checking), although it’s also possible to buy 3-chip types of the same capacity. to the hard disc and back again as required. A sure sign that this is happening is almost continuous hard disc activity, as evidenced by a constantly flickering hard disc LED. Alternatively, you can get “out of memory” error messages when running some applications that require lots of RAM (although this can also occur for other reasons). If this is happening to your system, then it’s time to speed things up by adding more RAM. If you already have 4Mb, then you might like to consider going to 8Mb. If you already have 8Mb, then consider going to 12Mb or even 16Mb. Of course, if your pockets are deep enough, you can go much higher than this – up to the maximum allowable by your motherboard. On older 386 and 486 motherboards, this will generally either be 32Mb or 64Mb, while more recent machines can go as high as 128Mb. Doing it yourself At this stage, you are faced with a choice – you can either take the machine to a dealer and pay to have the memory upgraded or you can save money by doing the job yourself. It’s quite straightforward provided that you have basic mechanical skills and have retained all the documentation for your computer. The first thing to do is to refer to the manual for your system’s mother­ board. Inside, you will find a section on memory installation and there will be a table showing the possible memory configurations. Table 1 is a typical example for a 486 motherboard that supports up to 64Mb but note that your mother­board may differ markedly from this, so check the manual carefully. July 1995  63 TABLE : MEMORY INSTALLATION Bank 0 Bank 1 Bank 2 Bank 3 4 x 256KB Total 1MB 4 x 256KB 4 x 256KB 2MB 4 x 256KB 4 x 256KB 4 x 256KB 4 x 256KB 4 x 256KB 4 x 256KB 4 x 256KB 4 x 1MB 4 x 256KB 4 x 256KB 4 x 1MB 6MB 4 x 256KB 4 x 1MB 4 x 1MB 9MB 4 x 256KB 4 x 256KB 4 x 1MB 3MB 4 x 256KB 4MB 5MB 4 x 1MB 4 x 1MB 10MB 4MB 4 x 1MB 4 x 1MB 8MB 4 x 1MB 4 x 1MB 4 x 1MB 4 x 1MB 4 x 1MB 4 x 1MB 4 x 1MB 4 x 4MB 4 x 1MB 4 x 1MB 4 x 4MB 24MB 4 x 1MB 4 x 4MB 4 x 4MB 36MB 4 x 1MB 4 x 1MB 4 x 4MB 12MB 4 x 1MB 16MB 20MB 4 x 4MB 4 x 1MB 40MB 16MB 4 x 1MB 4 x 4MB 32MB 4 x 1MB 4 x 4MB 4 x 4MB 4 x 1MB 4 x 4MB 4 x 4MB 48MB 4 x 4MB 64MB Adding the extra memory involves pushing the module into its socket at an angle, then pressing it down so that it is held by the spring loaded clips at either end. A notch in one end of the module stops you from plugging them in the wrong way around. In this case, the mother­board has four banks of memory – banks 0, 1, 2 and 3 – and supports three different types of RAM modules or SIMMs (single in-line memory modules): 256Kb, 1Mb and 4Mb. In addition, each bank holds four SIMMs and you must fill each new bank completely with the same type of SIMM. Fig.1 shows the locations of these 64  Silicon Chip memory banks on this particular mother­board. An example will illustrate how this works. Let’s say that this particular motherboard has 4Mb of memory and that this memory consists of 4 x 1Mb SIMMs occupying bank 0. If we want to upgrade the memory to 8Mb, then it’s simply a matter of adding another 4 x 1Mb SIMMs to bank 1. From there, we can go to 12Mb by adding 4 x 1Mb SIMMs to bank 2 and finally to 16Mb by adding 4 x 1Mb SIMMs to bank 3. Note that to get the maximum 64Mb capacity, you would have to install 4 x 4Mb SIMMs in each bank. Another thing that’s obvious from Table 1 is that the SIMMs used in later banks cannot have a lower capacity than those used in earlier banks. This means that if 4Mb SIMMs are used in bank 1, for example, they must also be used in the re­maining two banks. It also means that existing SIMMs will have to be replaced with higher-capacity SIMMs in some cases, in order to achieve the desired total. Note also that some older 386 and 286 motherboards accept only DIL (dual-in-line) memory chips and do not support SIMMs. Once again, check the manual for your motherboard carefully. 72-pin RAM Generally speaking, most 486 (and earlier) machines accept 30-pin SIMMs. However, just to complicate matters, 72-pin SIMMs are also available. These range in size from 2Mb up to 64Mb and are used mainly in later 486 machines and in Pentium machines. As before, consult the manual to find out which type suits your particular motherboard. If this information isn’t listed, then you can easily discover which type your computer uses by removing its cover and inspecting the RAM sockets. If you have a motherboard with 32bit memory access, then it’s possible to expand the memory by plugging in one or more 72-pin SIMMs. The most commonly available sizes are 2Mb, 4Mb, 8Mb, 16Mb and 32Mb, although 64Mb SIMMs are also now becoming avail­able. On the other hand, motherboards with 64-bit memory access will require at least two extra SIMMs for memory expansion. Again, it’s simply a matter of checking the manual for the allow­ able memory configurations. Parity vs. non-parity Unless you know exactly what you are doing, you should always use RAM that includes parity (ie, 9-bit wide RAM). That’s because the original PC specification calls for parity checking and some motherboards can only work with this type of RAM. BANK 0 BANK 2 BANK 1 BANK 3 banks will be designated in screened printing, while for others you will have to check the location of each bank by refer­ring to the manual. The main thing to watch out for is that you plug the extra SIMMs into the next bank in the sequence. For example, if banks 0 and 1 are already occupied, the new SIMMs must be plugged into bank 2. As mentioned previously, a bank cannot be partially filled – it must either be empty or fully occupied. For 30-pin SIMMs, this means adding four extra modules (all the same type) to each new memory bank. To install each SIMM, you simply slide it into its socket at an angle as shown in one of the photos. The module is then pivoted in the socket so that it sits under the spring-loaded retaining clips at either end. Note that there is a polarising notch in one end of the SIMM, to prevent you from plugging it in the wrong way around. CMOS setup Fig.1: the memory bank locations on a typical motherboard. In this case, there are four memory banks & each bank carries four 30-pin SIMMs. Note that each new bank must be completely filled with the same type of memory. On the other hand, many mother­ boards have a facility for disabling parity checking, usually via the BIOS. In these cases, it’s often OK to use non-parity RAM and save a few dollars into the bargain. The proviso here, of course, is that you have to sacrifice the automatic error-checking that parity provides. Our advice is that you stick with the parity RAM when up­grading the memory on a PC, unless money is important to you and you know how to get into the CMOS setup and disable the parity checking (assuming that this can be done). That way, you will be on safe ground. RAM installation This is the easy part – all you have to do is remove the cover of the machine and plug the extra SIMMs into the next available memory bank(s). Before removing the cover screws, be sure to remove the mains plug from the wall to avoid any nasty shocks. Once the cover has been removed, a visual inspection will quickly reveal the location of the existing memory. On some motherboards, the memory When you switch your machine back on again, it will run through its RAM detection procedure and, depending on the BIOS, may come up with a CMOS error message. This particularly applies to AMI BIOS and occurs because the detected memory no longer matches the value stored in the CMOS setup program. Conversely, on some types of BIOS (eg, Award), the extra memory is accommodated automatically and the machine will boot normally. If you do get a CMOS error message, enter the CMOS setup program (just follow the screen prompt to do this), select “Standard CMOS Setup” from the resulting menu, and hit <ENTER>. Your new extended memory value should now be displayed, along with various other settings that are stored here. Assuming all is correct, hit <ESC>, then use the down arrow key to select “Write To CMOS And Exit”, and press <ENTER>. Final­ly, press <Y> to answer “yes” to the question “Save CMOS Settings & Exit?”. The new extended memory value is now stored in the CMOS setup and the computer should now complete its boot-up procedure. The only difference now should be the extra memory and that, in turn, should mean slicker performance on those memory-hogSC ging applications. July 1995  65 NICS O R T 2223 LEC 7910 y, NSW EY E OATLBox 89, Oa8t5leFax (02) 5s7a0 C a rd for medical use, perimeter protection, data transmission, IR illumination, etc. $30 AIR COOLED ARGONS i 9 PO Used Argon-Ion heads with 30-100mW 579 4 r C a rd , V e & fax ) 2 0 output in the blue/green spectrum. Priced ( n e e o t n s h : o s a p r h P at around $350 for the “head” only, power de , M ith r d o w r a d d c e supply circuit and information supplied. B a n k x accepte most mix 0. Orders LIMITED SUPPLY. e r 1 o m $ f A ) l & & P mai r i P a ( . s LIGHT MOTION DETECTORS order 4-$10; NZ world.net Small PCB assembly based on a $ <at> . y t e s l t u a ULN2232 IC. This device has a built-in A AIL: o light detector, filters, timer, narrow angle lens, by EM and even a siren driver circuit that can drive an external 2mA ELECTRIC FENCE This extremely efficient design is almost identical to the one published in the current SC. The main difference is that our PCB is much smaller. The kit includes a PCB and ALL ON-BOARD COMPONENTS, USED 12V IGNITION COIL, and even the parts for a high voltage CAPACITIVE VOLTAGE DIVIDER PROBE that flashes a neon lamp for voltages exceeding 2kV. $25 speaker. Will detect humans crossing a narrow corridor at distances up to 3 metres. Much higher ranges are possible if the detector is illuminated by a remote visible or IR light source. Can be used at very low light levels, and even in total darkness: with IR LED. Full information provided. The IC alone is worth $16! OUR SPECIAL PRICE FOR THE ASSEMBLY IS: $5 ea. or 5 for $20 LOW COST PIR KIT These 230mm (1:4.5) lens have never been used. They contain six coated glass lenses, symmetric, housed in a black aluminium case. Scale range is from 1:10 through to 1:1 to 10:1. Applications include high quality image projection at macro scales, and portrait photography in large formats. This PIR movement detector is based on single LSI IC design and features simple construction. Even the lens assembly snaps onto the PCB. Has every imaginable feature: Negligible power consumption, optional/adjustable daylight disable with LDR light detector supplied, 10m range, variable alarm time, disable input, 10A MOSFET output, 10-20V DC operation. Fits into the smallest zippy box! A complete PCB and all on-board components kit is available for only: PROJECTION LENS 40mW IR LASER DIODES TOMINON HIGH POWER LENS $45 Brand new, precision angled projection lens. Overall size is 210 x 136mm. High-impact lexan housing with focal length adjustment lever. When disassembled, this lens assembly yields three 4" diameter lenses (concave, convex-concave, convex-convex). Very limited quantity. $35 $18 New famous brand 40mW-830nm IR laser diodes, suit medical and other applications: $60 ea., constant current driver kit to suit: $10. COLOUR MONITORS A pen style laser rated at 5mW/670nm. Brighter than most pens due to the use of a high quality lens. Has a metal body with a tactile switch and operates from 2 AA batteries (not included). Also suitable for medical uses. German made, used but guaranteed 12" mains powered RGB colour computer monitors. Use bright Toshiba tubes! 9-pin DIN connector for signal inputs, brief information and prewired DIN plug supplied. We should have a circuit/kit available for converting these to an ULTIMATE MUSICOLOUR: a new colour display for every beat of music. Excellent for experimentation!: TOROIDAL TRANSFORMERS LOW COST IR ILLUMINATOR LASER POINTER PEN $75 New 160VA toroidal transformers complete with mounting hardware. 240V primary and 2 x 20V secondary windings. Very limited quantity. $18 HALL EFFECT SWITCH Solid state switch that reacts to the proximity of magnetic fields. Runs at extremely high speeds, up to 100kHz. Operates from 4.5 to 24VDC supply with 10mA sink type digital output. Supplied with a suitable magnet. $2 ea. or 5 for $8 $40 Employs 42 high output 880nm IR LEDs (30mW <at> 100mA ea.) and a 7 transistor adjustable constant current driver circuit. Designed to be powered from 10-14VDC, current depends on power level setting: 5-600mA. The compact PCB is designed to replace the lid on a standard small 82 x 53 x 28mm plastic box. Good for illuminating IR responsive CCD cameras, IR and passive night viewers, and medical use. The complete kit even includes the plastic box and is priced at a low: $40 AC MOTOR HALOGEN TRANSFORMERS Small but very powerful GEARED AC motor. 1 RPM/60Hz/24V/5watt. We supply a circuit diagram that shows how to power this motor from 12V DC: variable speed/full power (bridge output). $10 ea. or 4 for $30 PCB and all on-board components kit for the 12V driver kit: Compact (41x66x30mm) metal boxed electronic transformers. 95%eff. 25kHz. Mains powered & designed to power halogen/incandescent lamps; up to 50W at 12V. Not approved, sold for components/experimentation: MINI PHONO This brand new unit was designed to play small records which are no longer available. The compact self contained unit (140x83x57mm) is housed in a plastic case and includes a motor, speaker and amplifier. Great for a simple workbench audio amplifier that is powered from 2 AA batteries (not included). $8 IR LASER DIODE KIT BRAND NEW 780nm LASER DIODES supplied with a collimating lens and housing assembly, a CONSTANT CURRENT DRIVER kit and a suitable PIN DIODE that can serve as a detector, plus some INSTRUCTIONS. Suitable 66  Silicon Chip Bargain priced: $9 $8 MINIATURE FM TRANSMITTER Not a kit, but a very small ready made self contained FM transmitter enclosed in a small black metal case. It is powered by a single small 1.5V silver oxide battery, and has an inbuilt electret microphone. SPECIFICATIONS: Tuning range 88-108MHz; Wire antenna - attached; Microphone – electret condenser; Battery – one 1.5V silver oxide LR44/G13; Battery life – 60 hours; Weight 15g; Dimensions 1.3" x 0.9" x 0.4". $32 DOT MATRIX LCDs Brand new Hitachi LM215 400 x 128 dot matrix Liquid Crystal Displays in an attractive housing. These have driver ICs fitted but require an external controller. Effective display size is 65 x 235mm. Available at less than 10% of their real value: $25 ea. or 3 for $60 REEL TO REEL TAPES New studio quality 13cm-5" “Agfa” (German) 1/4" reel to reel tapes in original box, 180m-600ft: $8 ea. SMALL PASSIVE NIGHT VIEWER KIT See ELECTRONICS NOW Oct 94. Supplied with a new and completely assembled USSR made scope which was separated from a binocular helmet mounted passive viewer. The EHT power supply is supplied in kit form. The completed scope will work in extremely low light levels! Best value small night vision scope available: $290 POWER SUPPLIES Used but very clean non standard computer power supplies, enclosed in metal casing with perforated ends for air circulation, built in fan, IEC input connector and OFF-ON switch, “flying” DC output leads, overall dimensions: 87 x 130 x 328mm, 110-220V input, +5V/8A, +12V/3A, and -12V/0.25A DC outputs. BARGAIN PRICED: $18 ea. or 4 for $60 ARGON LASER One only large water cooled ARGON laser that outputs 7W of blue-green, or 1W of red (635nM) via an inbuilt Dye laser. Originally intended for medical use, and is supplied with but can be easily separated. Has only done 200 hours of operation! $7990 $215 CCD VIDEO SECURITY SYSTEM Monochrome CCD Camera which is totally assembled on a small PCB and includes an auto iris lens. It can work with illumination of as little as 0.1Lux and it is IR responsive. This new model camera is about half the size of the unit we previously supplied. It is slightly bigger than a box of matches! Can be used in total darkness with Infra Red illumination. NEW LOW PRICE: $180 With every camera purchased we can supply an used but tested and guaranteed 12V DC operated Green computer monitor. We can also supply a simple kit to convert these monitors to accept the signal from the CCD camera: Monitor $25, conversion kit $10. A COMPLETE 12V CCD VIDEO SECURITY SYSTEM FOR $215!! OPTICS USSR LENS 100mm-f2 Pentax screw mount thread, as used for night viewers, has focus adj. but no iris adj.: $60. USSR LENS 58mm-f2 Pentax screw mount lens as used for cameras, has focus and iris adj.: $60. BEAM SPLITTER for 633nM: $45. PRECISION FRONT SURFACE ALUMINIUM MIRRORS 200 x 15 x 3mm: $3, 50 x 72 x 3mm: $3. LINE GENERATING OPTIC makes a line out of a laser beam: $5. LASER DIODE COLLIMATING LENS $4. PORRO 90 deg. PRISM makes a rainbow from white light: $10. PRECISION ROTATING MIRROR ASSEMBLY as used in levelling equipment, needs small motor/belt, plus a laser beam, will draw a line right around a room (360deg.) with a laser beam: $45. ARGON MIRRORS high reflector and output coupler used to make a Argon tube: $50. 27MHz TRANSMITTERS New transmitters are assembled (PCB assy.) and tested. They are XTAL locked on 26.995MHz and were originally intended for transmitting digital information. Their discrete component design employs many components, including 5 transistors and 8 inductors. Circuit provided. A heatsink is provided for the output device. Power output depends on supply voltage and varies from 100mW to a few watts, when operated from 3-12V DC. These are sold for parts/experimentation/educational purposes and should not be connected to an antenna as licensing may be required: $7 ea. or 4 for $20 VISIBLE LASER DIODE KIT A 5mW/670nm visible laser diode plus a collimating lens, plus a housing, plus an APC driver kit (Sept 94 EA) UNBELIEVABLE PRICE: $40 The same kit is also available with a 3mW/650nm laser diode: $65 LOW COST 1-2 CHANNEL UHF REMOTE CONTROL A single channel 304MHz UHF remote control with over 1/2 million code combinations which also makes provision for a second channel expansion. The low cost design includes a complete compact keyring transmitter kit, which includes a case and battery, and a PCB and components kit for the receiver that has 2A relay contact output!. Tx kit $10, Rx kit $20, additional components to convert the receiver to 2 channel operation (extra decoder IC and relay) $6. INCREDIBLE PRICES: COMPLETE 1 CHANNEL TX-RX KIT: $30 COMPLETE 2 CHANNEL TX-RX KIT: $36 ADDITIONAL TRANSMITTERS: $10 3-STAGE NIGHT VIEWER KIT See SC Sept 94. We have accumulated a good number of 40mm three stage fibre optically coupled 3-stage image intensifiers that have minor blemishes. The three tubes are supplied already bonded together: extremely high gain!! We can supply this 3 stage tube plus a power supply kit plus a lens and an eyepiece for a total cost of: $250 That is an almost complete starlight night viewer kit! We can also supply the full SC Sept 94 magazine: $5 VISIBLE LASER DIODE MODULES Industrial quality 5mW/670nm laser diode modules. Overall dimensions: 11mm diameter by 40mm long. Have APC driver built in and need approximately 50mA from 3-6V supply. $60 VIDEO TRANSMITTERS Low power PAL standard UHF TV transmitters. Have audio and video inputs with adjustable levels, a power switch, and a power input socket: 10-14V DC/10mA operation. Enclosed in a small metal box with an attached telescopic antenna. Range is up to 10m with the telescopic antenna supplied, but can be increased to approximately 30m by the use of a small directional UHF antenna. INCREDIBLE PRICING: $25 12V FANS Brand new 80mm 12V-1.6W DC fans. These are IC controlled and have four different approval stamps: $10 ea. or 5 for $40 TDA ICs/TRANSFORMERS We have a limited stock of some 20 Watt TDA1520 HI-FI quality monolythic power amplifier ICs: less than 0.01% THD and TIM distortion, at 10W RMS output! With the transformer we supply we guarantee an output of greater than 20W RMS per channel into an 8ohm load, with both channels driven. We supply a far overrated 240V-28V/80W transformer, two TDA1520 ICs, and two suitable PCBs which also include an optional preamplifier section (only one additional IC), and a circuit and layout diagram. The combination can be used as a high quality HI-FI Stereo/ Guitar/PA amplifier. Only a handful of additional components are required to complete this excellent stereo/twin amplifier! Incredible pricing: $25 For one 240V-28V (80W!) transformer, two TDA1520 monolythic HI-FI amplifier ICs, two PCBs to suit, circuit diagram/layout. Some additional components and a heatsink are required. TWO STEPPER MOTORS PLUS A DRIVER KIT This kit will drive two stepper motors: 4, 5, 6 or 8 eight wire stepper motors from an IBM computer parallel port. Motors require separate power supply. A detailed manual on the COMPUTER CONTROL OF MOTORS plus circuit diagrams/descriptions are provided. We also provide the necessary software on a 5.25" disc. Great “low cost” educational kit. We provide the kit, manual, disc, plus TWO 5V/6 WIRE/7.5 Deg. STEPPER MOTORS FOR A SPECIAL PRICE OF: $42 BIGGER LASER We have a good but LIMITED QUANTITY of some “as new” Helium Neon (red) 6mW+ laser heads that were removed from new equipment. Head dimensions: 45mm diameter by 380mm long. With each of the head we will include our 12V Universal Laser power supply. BARGAIN AT: $170 6mW+ head/supply. ITEM No. 0225B. We also have a limited number of used He-Ne tubes: Used 1-3mW tube plus our 12V Universal Laser power supply: $65 12V-2.5 WATT SOLAR PANEL KITS These US made amorphous glass solar panels only need terminating and weather proofing. We provide terminating clips and a slightly larger sheet of glass. The terminated panel is glued to the backing glass, around the edges only. To make the final weatherproof panel look very attractive some inexpensive plastic “L” angle could also be glued to the edges with some silicone. Very easy to make. Dimensions: 305 x 228mm, Vo-c: 18-20V, Is-c: 250mA. SPECIAL REDUCED PRICE: $20 ea. or 4 for $60 Each panel is provided with a sheet of backing glass, terminating clips, an isolating diode, and the instructions. A very efficient switching regulator kit is available: Suits 12-24V batteries, 0.1-16A panels, $27. Also available is a simple and efficient shunt regulator kit, $5. SOLID STATE “PELTIER EFFECT” DEVICES These can be used to make a solid state thermoelectric cooler-heater. Basic information supplied: 12V-3.4A PELTIER: $25 12V-4.5A PELTIER: $35 We can also provide two thermal cutout switches, and a 12V DC fan to suit either of the above, for an additional price of $10. VEHICLE COMPUTERS Originally designed for bicycles but these suit any moving vehicle that has a rotating wheel! A nine function Computer with speed, average speed, maximum speed, distance, odometer, timer, scan, freeze frame memory, and a clock. Its microprocessor based circuitry can be adapted to work with almost any wheel diameter. Simply divide the wheel diameter in millimetres by 6.8232, and program the resultant figure into the computer. $29.90 MORE KITS MODEL TRAIN CONTROLLER: run two trains on one track without any collisions, uses kit IR LEDs/transistors for detectors (supplied), doubles up as a crossing controller with flashing crossing LEDs. Incredible pricing: $20. TRAIN SOUND GENERATOR: can be used in conjunction with the controller to produce crossing and other sounds, when a train is on a particular part of a track: $12. SINGLE CHANNEL UHF REMOTE CONTROL: SC Dec 92, 1 x Tx plus 1 x Rx: $45, extra Tx $15. 4 CHANNEL UHF REMOTE CONTROL KIT: two transmitters and one receiver: $96. GARAGE/DOOR/GATE REMOTE CONTROL KIT: SC DEC 93: Tx $18, Rx $79. 1.5-9V CONVERTER KIT: $6 ea. or 3 for $15. LASER BEAM COMMUNICATOR KIT: Tx, Rx, plus IR Laser: $60. ELECTRIC FENCE KIT: PCB and components, includes prewound transformer: $40. PLASMA BALL KIT: PCB and components kit, needs any bulb: ON SPECIAL $20. MASTHEAD AMPLIFIER KIT: two PCBs plus all on board components, low noise (uses MAR-6 IC), covers VHF-UHF: $18. BRAKE LIGHT INDICATOR KIT: 60 LEDs, two PCBs and ten Rs, makes for a very bright 600mm long high intensity red display: ON SPECIAL $25. FM TRANSMITTER KIT - MKII: high quality - high stability, suit radio microphones and instruments, 9V operation, the kit includes a PCB and all the on-board components, an electret microphone, and a 9V battery clip: $11. FM TRANSMITTER KIT - MK1: this complete transmitter kit (miniature microphone included) is the size of a “AA” battery, and it is powered by a single “AA” battery. We use a two “AA” battery holder (provided) for the case, and a battery clip (shorted) for the switch. Estimated battery life is over 500 hours!!: $11. PROTECT ANYTHING ALARM KIT: EA May 93, ON SPECIAL, PCB and all on-board components kit: $20. ELECTRIC FENCE KIT: SC Apr 94: ON SPECIAL: $28. ELECTRONIC KEY KIT: EA July 92, 2 keys plus one receiver, ON SPECIAL: $30. MORE ITEMS PRINTER MECHANISMS: brand new Epson dot matrix printer mechanisms, overall dimensions are 150 x 105 x 70mm: $12. CD MECHANISMS: used compact disc player mechanisms that contain optics, small conventional DC motor, gears, magnets etc.: $6 with conventional motor, $4 with linear motor, broken CD mechanisms $2.50. SWITCHED MODE POWER SUPPLIES: mains in (240V), new assembled units with 12V-4A and 5V-4A DC outputs: $32. INDUCTIVE PROXIMITY SWITCHES: detect ferrous and nonferrous metals at close proximity, AC or DC powered types, three wire connection for connecting into circuitry: Two for the supply, and one for switching the load, these also make excellent sensors for rotating shafts etc.: $22 ea. or 6 for $100. IEC EXTENSION LEADS: 2M long, IEC plug at one end, IEC socket at other end: $5. MOTOR SPECIAL: Type M9: 12V, I No load = 0.52A - 15,800 RPM at 12V, 36mm Diam. - 67mm long: $5; Type M14: made for slot cars, 4-8V, I No load = 0.84A at 6V, at max efficiency I = 5.7A - 7500 RPM, 30mm Diam - 57mm long: $5. EPROMS: 27C512, 512K (64K x 8), 150nS Access CMOS EPROMS, removed from new equipment, need to be erased, guaranteed: $4. MODULAR TELEPHONE CABLES: 4 way modular curled cable with plus fitted at each end, also an 4m long 8-way modular flat cable with plugs fitted at each end, one of each for $2. POLYGON SCANNERS: precision motor with 8 sided mirror, plus a matching PCB driver assembly. Will deflect a laser beam and generate a line. Needs a clock pulse and DC supply to operate, information supplied: ON SPECIAL $15. PCB WITH AD7581LN IC: PCB assembly that amongst many other components contains a MAXIM AD7581LN IC: 8 bit, 8 channel memory buffered data acquisition system designed to interface with microprocessors: $29. EHT POWER SUPPLY: out of new laser printers, deliver -600V, -7.5kV and +7kV when powered from a 24V-800mA DC supply, enclosed in a plastic case: $16. MAINS CONTACTOR RELAY: has a 24V-250ohm relay coil, and four separate SPST switch outputs, 2 x 10A and 2 x 20A, new Omron brand, mounting bracket and spade connectors provided: CLEARANCE <at> $5 ea. SUPERCAPS: 0.047F/5.5V capacitors: 5 for $2. PCB MOUNTED SWITCHES: 90 deg. 3A - 250V, SPDT: 4 for $2. 3" CONE TWEETERS: sealed back dynamic 8ohm tweeters: $5 ea. CASED TRANSFORMERS: 230V - 11.7V - 300mA AC - AC Transformers in small plastic case with separate input and leads, each is over 2M long: $6. WELLER SOLDERING IRON TIPS: new tips Weller stations and mains operated Weller irons, mixed popular types, specify mains or station type: 5 for $10. LCD CHARACTER DISPLAYS: standard 16 x 1 displays, 5V operation: $20. NICAD BATTERIES: new Toshiba 7.2V-2.2AHr Nicad battery packs, 2 packs and one 12V intelligent charger (charger may be slightly soiled): $40. STEPPER MOTORS: 6V - 6Wire - 1.8deg. used stepper motors: $4 ea. COMPONENTS HIGH INTENSITY RED LEDs: 550-1000mCd <at> 20mA, 100mA max, 5mm housing: 10 for $4, or 100 for $30. BLUE LEDs: 5mm: $2.50. ELECTRET MICROPHONE INSERTS: high output standard size omnidirectional: 10 for $8. Also some high quality unidirectional electrets that were removed from new equipment: $3 ea. ULTRASONIC TRANSDUCERS: high quality Murata 40kHz transmitter and receiver transducers: $4 pr., 40kHz XTAL to suit: $2. 3.57MHz XTALs: 10 for $6. OP27 OPERATIONAL AMPLIFIERS: super operational amplifier ICs!: $3 ea. ENCODER DECODER ICs: as used in many projects, SC Dec 92, EA Mar 93 and 94, AX526/7/8 ICs: $3.50 ea. UHF Module to suit: $15. DYNAMIC MICROPHONE INSERTS: unidirectional low impedance inserts: $4 ea. HIGH VOLTAGE DISC CERAMICS: 680pF - 3kV: 20 for $4, 0.015uF - 3kV: $2 ea., 1000pF - 15kV: $4 ea. HIGH VOLTAGE DIODES: all are very fast!, 1kV-1A: 10 for $5, 8kV - 20mA: $1.50, 16kV - 20mA: $2 ea. GAS FILED ARRESTORS: 10 for $3. THERMISTORS: 2.5ohm NTC: 10 for $2. TRIACS: 600V - 60A, CLEARANCE: $3 ea. COMPRESSION TRIMMER: 250pF, mica dielectric, new but may be slightly soiled, ceramic base: $1 ea. MORE IR COMPONENTS 880nM/12 deg./30mW <at> 100mA IR LEDs: 10 for $9 880nM/60 deg./30mW <at> 100mA IR LEDs: 10 for $9 940nM/12 deg./16mW <at> 100mA IR LEDs: 10 for $5 IR detector pin diodes: 10 for $10 5mW/780nm laser diode (LTO26): $16 ea. July 1995  67 SERVICEMAN'S LOG Well, it looked like that at first It is probably just as well that neither I nor my col­leagues are medical practitioners. At least if we make a wrong diagnosis, we usually get a second chance & the first error can be corrected. My first story this month is about a video recorder – a Panasonic model NV-SD10A which belongs to the local primary school. This is a fairly recent model, released only a couple of years ago. And while it has nothing to do with the story, it is worth mentioning that it is fitted with the very much upgraded “K” deck. This deck is a considerable improvement on earlier decks which, in most brands, employed some five or six belts, and possibly three motors, to perform all the necessary functions. And as can be imagined, the belts were a common cause of pro­blems. The “K” deck has eliminated most of the belts – it uses only one if my memory is correct – and has proven to be a very reliable unit. But that is by the way. This particular recorder had other problems. According to the teacher who brought it to the shop, it could not be turned on. Well that seemed to be a straightforward enough description, even if a little quaint. I would have simply described it as completely dead. And it was too. I plugged it in while the teacher was there and there was no sign of life of any kind; no clock display or indicator lights and no response to any of the function buttons. All of which was deceptively simple. I imagined a fairly obvious power supply fault, or even just a faulty fuse. So the teacher left it with me adding, as he left, that there was no particular hurry for the machine; they had others that could fill in. Power supply checks It was a day or so before I could get at it, then I went straight to the power supply, which is a switchmode type. A preliminary check revealed nothing obviously wrong. The fuse was intact and mains voltage was reaching the right terminals. Next, I checked the various voltage rails out of the supply (45V, 14V, 12V, 12.3V, 5V, -29V, etc). And they were all present and cor­rect. That put a completely different slant on things. If the power supply was delivering all the necessary voltages, then the failure was in some other section. Fair enough but how would a failure in one section shut the whole thing down, causing it to appear completely dead? The most logical answer was that the fault was somewhere in the management section, possibly in the microprocessor (IC7501) – see Fig.1. This determines and initiates the correct sequence of events for any user command. It also drives the clock and other front-panel displays. Of course, this was simply a broad assumption. Exactly where or how this failure was occurring was what I had to track down. What followed was a long and laborious voltage checking procedure. Fig.1: a section of the microprocessor control circuitry in the National MV-SD10A VCR. IC7502 is at extreme right & its output at pin 3 connects to pin 21 of the microprocessor (IC7501) at top left. The 4.7V shown at pin 3 of IC7502 somehow becomes 4.8V at pin 21 of IC7501. 68  Silicon Chip As far as possible, I tried to confirm that the vari­ous voltages at the power supply were being applied to all the points where they were supposed to be. But, in particular, I concentrated on the voltages applied to the microprocessor. This eventually provided a clue. Pin 21, which is labelled “Reset”, is marked as 4.7V but, in fact, was showing only about 2.4V. Back tracking from there brought me to IC7502, a PST7026. This 3-legged device is similar in appearance to a small signal transistor but is rather more complicated, the circuit diagram showing that it contains a couple of op amps and various other circuit blocks. More to the point is its function. I wasn’t sure of this at the time. All that the circuit indicated was that it is fed from one of the 5V rails – shown as 4.8V at one point and 4.7 at another - and delivers 4.7V to pin 21 of the microprocessor. But obviously, there had to be more to it than that. Its real job is a delay function. At mains (repeat mains) switch-on, it pulls pin 21 low momentarily, before applying the indicated 4.7V. This, apparently, is the “reset” function. Before I go any further, a word about some of the voltages quoted. It is not unusual to find quite silly voltage figures on many circuit diagrams. Usually, the differences are only nominal but I have known them to be quite significant and misleading. It was this kind of mistrust that confused matters later on. Nevertheless, I felt sure that 2.4V in place of 4.7V was too great a difference. And, with very little else in the cir­cuit, the IC seemed the likely culprit. It’s a very inexpensive device costing less than $2, so the easiest thing to do was change it. Unfortunately, I had none in stock, so I placed an order. And that was the next hurdle. They were on back order and it would probably be several weeks before delivery. Well, the teach­er had said there was no hurry, but I contacted him and explained the situation. He was quite understanding and confirmed that there was no great hurry at that time. It was just as well because it was over two months before new stocks arrived. Unfortunately, this is not a rare occurrence; it happens all too often these days. When my order arrived, I lost no time in fitting it. When I switched the machine on, it immediately burst into life. The clock and all other indicators came up correctly and a quick check of all the various functions indicated that they were working perfectly. Problem solved? So that solved that problem. Or did it? Out of curiosity, I went back to the output of the new IC, expecting 4.7V, or something close to it. In fact, it was only about 3.6V. And that was about as awkward a figure as one could imagine. While ob­ viously adequate to allow the set to function, it was less than shown on the circuit. So was the circuit wrong and what was the allowable toler­ance on this voltage, or the spread of the IC tolerance? I had no way of knowing, so I simply let the machine run for the next couple of days. During this time, I made and replayed several test recordings and switched the machine off and on at the mains at regular intervals. It never missed a beat. But I still wasn’t happy and was trying to decide what best to do when the teacher rand to say that their situation had changed somewhat. Some programs that they wanted to record clashed in time and they needed all their machines. Could they have this one back some time in the next week? I explained the situation: that the July 1995  69 SERVICEMAN’S LOG – CTD but, worse than that, I couldn’t find it; there was no sign of it anywhere near its electrolytic mate, adjacent to IC7502. Nor could I see it anywhere else on the board. In the end, I had to resort to tracing the copper pattern on the PC board. And that’s where I found it; a surface mounted type behind the micro­processor (IC7501). I put the meter across it in-situ and measured something over 1kΩ. That wasn’t conclusive, of course, so I pulled it out and switched the machine on. It leapt into life and, more to the point, I now had close to 4.7V on pin 21. Problem solved. I’m not sure of the exact role of this capacitor and the recorder seemed quite happy without it. But, of course, it had to be replaced. I didn’t have a surface mounting 0.1µF capacitor, so I substituted a small disc ceramic type which I’m confident will do just as good a job. Or perhaps even better. No, this wasn’t one of my better efforts but I’m telling the story for the benefit of any reader who encounters a similar problem in this model. Life’s little mysteries machine was working, apparently quite reliably, but that I had some reservations about the job. If he wanted to take it and try it in those circum­stanc­es he was welcome. After all, it might just as well have a trial run at the school as on the bench. The machine returns And so the machine was duly collected. And, as I later learned, it performed faultlessly during their special recording sessions and for a couple of weeks thereafter. Then the teacher was back on the phone again with the news that it was exhibiting exactly the same fault as before. So I told him to bring it back in. He was rather worried about the cost but I assured him that I would stand by the job, as the real fault had not been found. Naturally, I went straight to the output of IC7502 and confirmed what 70  Silicon Chip I feared. It was down to 2.5V again. So what now? I took another look at the circuit. Assuming that the re­ placement IC was not at fault, there appeared to be only two things that could be loading the voltage on pin 21 and pulling it down: (1) a fault in the microprocessor (IC­7501); or (2) one of two small capacitors shown connected to pin 3 of IC7502. I tended to discount IC7501, if only because it performed normally when fed with the correct voltage. And that left the two capacitors – C7511 (a 0.22µF 50V electrolytic) and C7510, shown simply as 0.1µF. Well, if it was going to be one of these, it would be the electrolytic. Wrong again; it took only a few moments to pull it out and fit a replacement. There was no difference. So that left only the 0.1µF as the last hope. I wasn’t very confident My next story comes from a colleague and is another of life’s little mysteries. The problem was eventually solved but with no really satisfactory explanation. This, more or less, is how he told it to me. The set was a National model TC2697 and the customer’s complaint was that the picture rolled occasionally. What a horrible word that “occasionally” is – how does one tackle an “occasional” fault? With difficulty might be the best answer. Anyway, all I could do was set it up and let it run, hoping that when it misbehaved I would see it and gain some insight into the cause. So that’s what I did but trying to keep one eye on it while working on other jobs is a near impossible task. It was a couple of days before there was any hint of trou­ble and then it was only a glimpse out of the corner of the eye. Did that picture roll? I wasn’t sure. But patience paid off; eventually it rolled when I was looking directly at it. It flicked one frame then, a few seconds later, it flicked two more frames. After that, it seemed to settle. I watched it for some time but it was rock steady. This didn’t help very much, except to confirm that the fault was in the set, rather than due to local interference. But I was no closer to even guessing what was causing it. In general terms, of course, I suspected a fault in the vertical deflection system, or a sync fault. Following this latter thought, I checked the hold control behaviour. Weak sync pules will normally make the hold control setting quite dodgy but not in this case; it was locking up solidly. I even contrived to run it on a very weak signal and it still locked up positive­ly. OK, rule that one out. The first real clue came by chance. The workshop happened to be very quiet – I wasn’t running the sound –and I was study­ing a circuit on the bench when I thought I heard a faint splat. At the same time, I thought I glimpsed the picture flick from the corner of my eye. I moved in closer and watched the screen directly. Sure enough, the picture flicked again and there was the splat at the same time. There wasn’t much doubt about it now; I had a problem somewhere in the horizontal output stage and this was triggering the vertical stage. Until now, I hadn’t even taken the back off the set, pre­ferring not to disturb anything until I had seen the fault. Now that I had seen it and had a clue, it was time to look inside. I set up a mirror so that I could watch the screen while looking in the back of the set. It was a good setup but didn’t help much. The picture flicked a couple of times and I could hear the splat but I couldn’t see anything. Naturally, I concentrated around the horizontal output transformer and the ultor cap, but to no avail. And again, I hesitated to disturb anything until I had pinpointed the source. This approach continued for several episodes, without any suc­cess. The next step was born of desperation. I closed all the blinds on the windows, turned out the lights and checked the inside of the set again. I didn’t have to wait long; the picture rolled and I heard the splat. I saw the light from the flash but not the flash itself. I had been watching the ultor cap but it wasn’t there. Anyway, after a few more rolls and splats I finally spotted it and it was quite tiny. It involved the horizontal output transformer but in a very strange way. The transformer is a fairly conven- tional type, consisting of a rectangular ferrite core made in two halves. The windings are on one half and the two halves are glued together and held with a strong steel clip, which sits in a groove in each piece of ferrite. And this spring is floating; it is not at earth or at any other potential. But the layout is such that it is within about a millimetre of an aluminium bracket-cum-heatsink, which is mount­ed on the chassis. This bracket carries the horizontal output transistor. And, by some mechanism, a charge was building up on the clip, eventually becoming strong enough to jump the small gap to the bracket. The set would then behave normally until the charge built up again. By what mechanism this was happening I don’t know. The only explanation that seemed reasonable at the time was that any piece of metal in a strong electric field can acquire a charge from it. I understand that this effect can be quite a problem for power supply linesmen working in the proximity of very high voltage power lines. If this was the explanation, then it seemed reasonable to cure the fault by simply connecting the clip to chassis. And no sooner said than done. I prised up one end off the clip, slipped a short length of copper braid under it, and connected it to chassis. And that fixed it – no more sparks, no more splats and no more rolling. I ran the set for a couple of days, positioned so that I could hear as well as see the fault, and felt confident that it would not occur again. The set was then returned to the customer. Complete failure Which was all very fine – except that, about three months later, the set failed completely. The cause – failure of the horizontal output transformer. Yes, I know, you told me so. Or did you? And, if so, I’d still like an explanation. The obvious one would be that the winding had broken down to the core. OK, but ferrite is supposed to be a non-conductor and, if the suggestion is that it could provide sufficient leak­age at the high voltage involved, then this is a new one on me. Otherwise, I might have decided to replace the transformer in the first place. But could I have justified the cost on the basis of the symptoms described. In hindsight, yes, although a new transformer isn’t cheap. The new one cost over $100 but that was all it cost the customer. I waived any labour charges in the circumstances. After all, fair’s fair. Well, that’s my colleague’s story. I must confess that it’s a new one on me. Doubtless he’ll know better next SC time – and so will I. July 1995  71 REMOTE CONTROL BY BOB YOUNG Minimising transmitter interference This month, we will examine a startling new development which has radically altered the design parameters for the new Mark 22 transmitter. In past issues of SILICON CHIP I have often referred to projects taking on a life of their own, once some heavy duty effort is directed towards them. The Mark 22 project is one of the best examples of this process in action that I have encoun­tered during my long career in R/C manufacturing. It began with me being dragged kicking and screaming by the editor of this magazine once more to the dusty stool in front of my old drawing board. He said he (and his readers) badly needed this R/C project and that my feelings in the matter were of no account. As this argument had raged on for some time, I finally realised that further argument was futile. With that, I reluc­tantly set to work to modernise my old Mark 14 AM system. “That should get him off my back”, I mused. From there I have watched the Mark 22 develop into one of the most versatile R/C systems on the market today. So much so that the model aircraft fraternity have greeted it with a degree of enthusiasm that has taken me completely by surprise. As their enthusiasm has grown so has my own. Each step in the development process A classic scene at an R/C car track. This is much less than the recommended minimum spacing of three metres. How many of these transmitters are interfering badly with each other and possibly causing loss of control? 72  Silicon Chip has led smoothly (and not quite effortlessly) to the next logical step, to the point that I now find myself once more at the cutting edge of R/C development here in Australia. However, I have got ahead of myself a little and I must return to the February 1995 issue of SILICON CHIP which featured the new Silvertone frequency keyboard. This keyboard is the latest in a long line which began in 1969 and now incorporates the new frequencies on the 36MHz modelling band. The MAAA (Model Aeronautical Association of Australia) had released these frequencies as a result of the latest range of very elaborate R/C equipment arriving from overseas and I was asked to prepare a new keyboard in anticipation of the operation of 10kHz spacing on the 36MHz band. It was widely believed that this generation of equipment would allow safe operation on 10kHz spacing. Well, the upshot of recent field testing is that the MAAA has decided that 10kHz spacing is definitely NOT SAFE. The new 10kHz frequencies will be used but only at 20kHz spacing. That is startling enough but another problem has come to light because of this close spacing proposal which is potentially more serious and it has been there all along. I am speaking of direct interference between transmitters when they are physically close together and operating on adjacent frequencies. What happens is that if two standard transmitters are oper­ ated close together they both radiate extra signals and these extra signals will be on frequencies which might be being used by other radio control transmitters at the time. So here is the scenario. Two transmitters are being operated close together and they both radiate inter- Fig.1: this frequency spectrum shows two conventional class C R/C transmitters spaced 20kHz apart at 27.175MHz and 27.195MHz. Note the interfering signals spaced 20kHz away at 27.155MHz and 27.215MHz. These signals are only 30dB down on the wanted signals. fering signals at the same frequency as another R/C transmitter on the same field. The result can easily be that the third model loses control and has a crash! No-one has done anything illegal and the poor unwitting victim is left wondering why it happened. Has this happened to you? What we’re talking about is 3rd order intermodulation. This type of interference is generated when two non-linear (class C) transmitters are operated in close proximity of one another. The 3rd order products (P) are generated according to the formula: P = (2F1 - F2)+ (2F2 - F1) Let’s put some actual operating frequencies into this equa­tion. If we have two transmitters operating at 27.195MHz and 27.175MHz (ie, 20kHz apart), they will produce interfer­ ing fre­ quencies at 27.215MHz and 27.155MHz. Note that these interfering signals are “legitimate” frequencies on the same 20kHz spacing. The effect is shown in the frequency spectrum of Fig.1 which is part of a series of tests I did for this article. This photo shows the two operating frequencies as the taller spikes while the unwanted frequencies on either side are only 30dB down. (Note that this and the other spec­tro­­grams shown in this article were taken with unmod­ ulated transmitters to give a clearer re­sult). The power of these interfering frequencies is inversely proportional to the square of the distance between the antennas; so the closer they are, the Fig.2: this frequency spectrum shows a class B transmitter at 27.195MHz and a class C unit at 27.215MHz. Note the lower ampli­tude unwanted signal at 27.175MHz, the result of the improved linearity of the class B transmitter. worse is the interference. This interference can be very powerful and quite capable of shooting down an aircraft. And if the two R/C antennas touch, as they easily can in the excitement of a race, the power of the unwanted products can be almost equal to that of the proper signals. I knew of the problem but had no real concept as to its magni­tude. During these tests I generated enough 3rd order product to lock out PCM receivers and drive them into fail-safe. That is not the end of the problem as there will also be 5th order inter­ modulation products and these are demonstrated in one of the spectrum photos (Fig.4). Hence, as well as the interfering signals noted above, there will also be unwanted signals at 27.235MHz. and 27.135MHz, although their power level will be reduced. This problem is a well understood by RF engineers. When working with multiple transmitters on a single tower, they spend considerable amounts of time minimising 3rd and 5th order inter­modulation products. Why does it happen? When a transmitter is operated close to a second transmit­ter, some of the radiated RF is absorbed by the second transmit­ter’s antenna and its tank circuit. This unwanted RF energy finds its way to the base-emitter junction of the PA transistor which is operating in non-linear class C mode. Because of this, it acts as a mixer and so the unwanted difference frequencies are ampli­ fied and radiated along with the transmitter’s proper signal. The second transmitter affects the first transmitter in exactly the same way, so both transmitters radiate the unwanted frequencies. I must emphasise that this interference problem has always existed but it becomes much worse when the frequency spacing between transmitters is reduced. It is bad enough when a spacing of 20kHz is used and is quite capable of causing crashes. But with 10kHz, the problem would be a great deal worse. How do you stop it? So what measures can be undertaken to eliminate this problem, or at least minimise the risk? First and foremost, the transmitters should be far apart; ideally no closer than three metres between them. Second, any­thing that attenuates the incoming RF will help and so a metal transmitter case is to be preferred. The Mark 22 transmitter will (naturally) feature a metal case. Third, a good way to minimise the problem is use a more linear transmitter circuit. So instead of using the conventional class C transmitter, a move to class B transmitters is very worthwhile and this is demonstrated in the spectrum photos of Figs.2 & 3. Here, one of the transmitters is a class B model and you can see that one of the unwanted signals is greatly reduced. If two class B transmitters are operated close together, the overall radiation of July 1995  73 Fig.3: this test is the same as Fig.2 except that the transmit­ ters have been swapped; class C at 27.195MHz and class B at 27.215MHz. In this case, the lower amplitude unwanted signal is at 27.235MHz. interference signals is reduced even fur­ther. Demonstrate it for yourself Many people express surprise at the thought of a transmit­ter absorbing power and re-radiating it, but it is acting purely as an absorption wave­meter and this can be easily demonstrated, without any need for test gear. If you have two transmitters with RF meters, switch on one and move the other’s antenna in close proximity to it, you will see the meter of the OFF transmitter begin to read RF from the ON transmitter. Move them closer to­gether and you will see the meter on the OFF transmitter register a substantial signal. So you can imagine that when that second transmitter is turned on, all hell breaks loose and the interfer­ence is rife. Here then is an explanation for the completely transient and random nature of some interference. Over the years I have spent hundreds of hours going through sets which have come in with vague complaints of “interference” and all of the sets have checked out perfectly normal and few have ever returned. Was it 3rd order intermodulation? There is no way of knowing but it is highly probable. Having said all of this, I must state also that there is no need for panic. Safe field procedures will eliminate the problem completely and these include separation of each transmitter by a minimum three metres, field testing of suspect transmitters, placing adjacent transmitters at the opposite 74  Silicon Chip Fig.4: taken at a different screen refresh rate, this spectrogram reveals the presence of 5th and higher order interference pro­ducts, as well as the 3rd order signals. end of the flight line and finally if necessary, changing the frequency of suspect systems. Finally, if you see three keys in the keyboard on adja­cent channels and yours is one of them, then be doubly alert as to where the other two transmitters are located while you are flying. Why have 10kHz spacing? The proposed introduction of the 10kHz spacing system was primarily to enable large clubs to increase the amount of activi­ty per hour. Remember here, it is not that anyone particularly wants 60 aircraft in the air at once – nothing is more unpleasant than a crowded sky. The idea is to free up channels so that testing, motor tuning and field adjustments, all activities that tie up frequencies for long periods, may be carried out. Plus, the more frequencies that are available means less frequency clashes and fewer accidents. Proposed transmitter After these tests, I was faced with a dilemma. I have just designed a brand new (class C) RF module and now it is clear that a class B or better still a class AB (linear) PA would minimise the problem and thus make operation on busy fields that much safer. Hence, I have no hesitation in delaying the design to incorporate a vital feature for safe operation. I want the Mark 22 to be as good as I can make it. Thinking about it, I cannot understand why this problem has not been analysed and solved long ago. The Americans obviously understand it for they recommend a minimum of three metres sepa­ration and even go so far as to place boxes on the flight line three metres apart and each pilot must not leave his box. Some American clubs even go to extremes and recommend 10 metres sepa­ration. But even then they can run into problems, as indicated by the landing strip diagram of Fig.5. If we adopt the practise of separating two adjacent trans­mitters by putting them at opposite ends of the flight line, then the aircraft comes much closer to an interfering transmitter and the problem of signal strength ratios begins to become a factor. This is a separate issue to 3rd order interference and is purely related to system bandwidth. Fig.6 shows a simple go/no-go test for determining the safety of operating two R/C systems simultaneously. Here, the signal strength ratios are related to distance and a minimum of 12:1 is called for. To go closer than two metres to the receiver distorts the test due to overload of the receiver. In this regard I recommend that all transmitter antennas be telescoped when entering the pit area. Notice the similarity of this test to the conditions illustrated in Fig.5. Silvertone developed this test in 1969 and it has gained widespread acceptance all over Aust­ra­lia. So it is obvious there are advantages to the linear PA in R/C transmitters. If the 3rd order is eliminated or at least minimised, then operators can be MODEL 1 TRANSMITTER 1 Fig.5: a typical landing field with transmitters spaced three metres apart. This can place interfering transmitters much closer than the control transmitter, as the model comes into land. INTERFERING TRANSMITTER 11 11 TRANSMITTERS SPACED 3 METRES APART LANDING FIELD 30 METRES TRANSMITTER 1 grouped much closer in a much safer pattern, taking into account the signal ratio problem. Interference test procedure For those who wish to conduct a simple field test to deter­mine the safety of operating two R/C systems simultaneously, the following procedure is recommended. (1). Place model 1 on the ground with the antenna parallel to the ground 45ø STATIONARY MODEL CONTROL TRANSMITTER 33 METRES 90ø WALK IN UNTIL INTERFERENCE OBVIOUS RATIO TO BE BETTER THAN 12:1 INTERFERING TRANSMITTER Fig.6: standard interference test (developed by Silvertone) for two adjacent transmitters. and about 30cm above the ground. (If the antenna is closer to the ground, ground effect will distort the results.) If the model features a whip antenna, be sure that it is vertical. (2). Take the control transmitter for the model under test out 33 metres from the model, switch on the Tx, fully extend the antenna and hold it vertical. The angle between the receiver antenna and the transmitter should be 45 degrees. (3). Check the operation of the controls in the model to ascertain that all are working correctly. (4). Take the interfering transmitter out approximately 10 metres but on a line at right-angles to the first transmitter. Fully extend the antenna, switch on the Tx and hold the antenna verti­cal. This ensures that the receiver antenna is evenly polarised and receiving equal field strengths. (5). Take note of the operation of the control surfaces in the model. At these distances there should be no noticeable effect on the controls. (6). Walk towards the model with the interfering transmitter along the 45° line. Keep moving closer until the controls begin to exhibit some signs of interference. Note the distance from the model at which this occurs. The ratio of the two distances of the transmitters from the model should be greater than 12:1. Thus, with the control Tx at 33 metres, there should be no interference with the interfering Tx 2.5 metres away from the model. (7). Repeat the test using model 2 and with the original control transSC mitter as the interfering Tx. July 1995  75 MIDI for a song: a low-cost MIDI ADAPTOR for your PC or Amiga Here’s how to build a low-cost Musical Instrument Digi­tal Interface (MIDI) for your PC using a standard I/O card & little else. You need to build a small PC board inside a D15 or D25 plug & make some modifications to the I/O card. By GEORGE HANSPER A while ago, I was looking for a MIDI (Musical Instrument Digital Interface) for my PC. Although there are numerous sound cards on the market with some sort of MIDI interface, the cheaper ones are all FM-synthesis based (ie, not suitable for music) and the wave-table based ones were all up around $500 or more. At that price, given the rapid rate of obsolescence of computer hardware, it makes better economic sense to buy a stand-alone MIDI sound module for a little extra. What really irked me was that invariably you had to pay another $90 or so to get the MIDI interface, sold as an optional ‘MIDI cable’. This project is my answer. It should cost about $35, plus the cost of a serial I/O card. About another $50 should get you a reasonable high speed serial I/O card, with at least one 16550A UART (Universal Asynchronous Receiver Transmitter) on it (the 16550A is not essential but nice). The bonus is you can still use the extra I/O card for ‘normal’ serial I/O, except that the maximum data rate will now be 250 kilobaud instead of 38.4 kilobaud. Suitable platform Since this MIDI adaptor works from a standard RS232 serial interface, I have tested it on the following hardware platforms and found it to work properly in all cases: • IBM-PC with doctored serial card, running Linux OS • Amiga (using standard hardware and software) • Sun Sparc10 with standard hardware and modified kernel soft­ware. This MIDI adaptor will work with a 9-pin serial port, when used with a normal 9-25 pin serial adaptor. If you have a Sound Blaster equivalent or a Gravis Ultra Sound, this adaptor cannot be used unless a further modification is made. This is because the logic levels for 0 and 1 which appear on the D15 plug are inverted when compared with a normal serial port. I’ll also describe these mods a little later. Performance The performance of this circuit is limited mainly by the delays through the optocoupler. Any delays on the transmit cir­cuit were insignificant in comparison to the delays in the re­ceive circuit. The rise and fall times of the prototypes I made were typically about 5-10µs which is acceptable considering that a single data bit at 31,250 baud is around 30µs long. These three photos show the assembled D15 plug although the connecting cable is yet to be fitted. Above left is the outside of the finished plug, with the three LEDs showing, while at centre is the topside of the PC board. At right is the under­side of the PC board, with four resistors mounted. 76  Silicon Chip TX LED1  1k TX (2) BACK OF SOCKET 330  ZD1 6.8V 1W 4 BACK OF PLUG 1 1 4 2 330  GND (7) 2 5 3 MIDI OUT 3 5 D1 RTS (4) 2x1N4148 D2 DTR (20) 2.2k 4.7k RX (3) Q1 BC549 C 4.7k B A E ON-LINE LED2 8  K GND (7)  7 A IDIOT LED4  2 3 A IC1 6N138 B E C VIEWED FROM BELOW BACK OF SOCKET 220   K 4 K BACK OF PLUG 1 1 4 2 K 2 5 RX LED3 3 MIDI IN 3 5 K D25 SERIAL TO MIDI ADAPTOR Fig.1: the D25 serial to MIDI adaptor employs an optocoupler to avoid the possibility of hum loops in the link-up. As tested with a loop cable, the maximum baud rate for reliable operation varied with each optocoupler. This was as low as 45,454 baud in one prototype and as high as 125000 baud in another. Around 50-60 kilobaud is typical for the maximum baud rate. The Tx and Rx LEDs are a bit faint during normal operation, (hence the preference for high-efficiency LEDs). All in all, they still gave useful indications that things are happening. Given that they are only used during setup and debugging of the MIDI cabling, any more complex LED driving circuitry is not warranted. Circuit operation The hardware required for MIDI is simple: a plain serial interface (along the lines of RS232) but with an optoisolator at the receiving end to prevent hum-loops in amplifiers and other musical equipment. The only thing you need apart from the opto­­­­-i­solator is the right baud rate of 31,250 baud. Most IBM-PC serial cards cannot support 31,250 baud because they have a 1.84MHz reference clock oscillator. Unfortunately, 1.84MHz cannot give a baud rate which is close enough to 31,250, because the UART (Universal Asynchronous Receiver-Transmitter) first divides the clock by 16. This gives us a base-baud rate of 115200 which can then be further divided by a software-controlled divisor to give 57600, 38400, 28800 and so on. The rate of 28800 is close but not close enough (and yes, I tried it). However, all is not lost, because some of the 16450 UARTs and all the newer 16550 UARTs can handle clocks of up to 8MHz. The NS16C552 (which is a dual UART version of the 16550) can handle clock rates of up to 24MHz. This means that all it takes to modify an existing serial I/O card to work with the MIDI baud rate is to replace the crystal oscillator. This is easier than it sounds, because the 16450 and 16550 have an internal oscillator circuit which only requires a crystal and a few discrete components to be added – see Fig.5 for the circuit details. Transmit & receive circuit The transmit circuit consists of a few resistors, a zener diode and an indicator LED, labelled Tx LED1 – see Fig.1. The zener diode is there to limit the effective driving voltage for the MIDI output. The driving voltage on Tx (pin 25 D25) could be anything from 5V to 15V. The desired driving voltage is 5V but the current must always flow through the Tx LED, which has a fairly constant voltage drop of about 2V. Hence the choice of a zener diode around 7V. The same effect could be achieved by putting the Tx LED before the zener diode and using a 5V zener but this would mean that the Tx LED may come on whenever there was a signal on pin 2 of the RS232 port, regardless of whether the cable was connected or not. By placing the Tx LED after the zener, it will only come on when the cable is actually connected and the circuit is complete (and when there is a signal, of course). This gives a good indication about the state of the cable which is the first thing to suspect when things don’t work. The only other noteworthy point is the inclusion of 330Ω resistors in both the ‘driver’ lead and the ‘ground’ lead of the MIDI-out cable. This measure may seem redundant but it adds another level of protection. Let me illustrate, by assuming that instead of two 330Ω resistors, we just have one 680Ω resistor on the ‘driver’ lead (pin 4 of MIDI out) and that the ‘ground’ lead (pin 5 MIDI out) is connected directly to the ground of the computer (via pin 7). If the MIDI-out is plugged into another MIDI-out, then the two driver July 1995  77 BACK OF SOCKET 330  +5V (9) 4 2.2k  8  4.7k GND (4,5) 3 5 IC1 6N138 4 IDIOT LED3  2 3 MIDI OUT BACK OF SOCKET 220  IN (15) 1 4 2 5 330  OUT (12) 6 1 2 TX LED1 +5V (9) BACK OF PLUG 3 5 BACK OF PLUG 1 1  2 5 RX LED2 A Receive circuit 4 2 3 MIDI IN 3 5 K D15 SOUNDBLASTER/GUS TO MIDI ADAPTOR Fig.2: the D15 Sound Blaster serial to MIDI adaptor is essentially the same as Fig.1 except that the +5V supply is directly avail­able at pin 9 of the socket. circuits are at least separated by the (fictitious) 680Ω resistor. If, however, the MIDI-out is plugged into, say, another MIDI-out, with an incorrectly wired cable (eg, reversed), what would happen? Not a problem, you may think, because the resistor on the driver side is still in series with the Tx cir­cuit on both sides. The only difference is that the maximum potential difference across the resistor is now 10V instead of 5V (when both drivers are ‘on’). But there is another connection you should be aware of: the signal ground of your computer is almost certainly connected to ground through the mains plug. Your keyboard or sound-module may also be connected to ground in the same fashion. This would mean that the driver on the other MIDI-out would be connected directly to ground, with the possible addition of hum-loop currents. Of course, the other MIDI-out should be able to survive a short-to-ground like PARTS LIST D25 MIDI Adaptor (preferably with through-hole mounted UARTs) 1 8MHz crystal 1 1MΩ 0.25W resistor 1 1.5kΩ 0.25W resistor 1 39pF ceramic capacitor 1 22pF ceramic capacitor Semiconductors 1 6N138 optocoupler (IC1) 1 BC549 NPN transistor (Q1) 1 6.8V 1W zener diode (ZD1) 2 1N4148 signal diodes (D1,D2) 2 3mm green LEDs (LED1, LED2) 1 3mm red LED (LED4) 1 3mm yellow LED (LED3) Sound Blaster MIDI Interface 1 25-pin female D25 socket 1 shell for D25 connector 1 PC board 2 5-pin 180° DIN plugs 1 3-metre length figure-8 shielded cable Resistors (1%, 0.25W) 2 4.7kΩ   2 330Ω 1 2.2kΩ   1 220Ω 1 1kΩ MIDI Serial Interface 1 high speed serial I/O card 78  Silicon Chip 1 PC board 1 15-pin male D socket 1 shell for D15 connector 2 5-pin DIN plugs 1 3-metre length figure-8 cable Semiconductors 1 6N138 optocoupler (IC1) 1 3mm green LED (LED1) 1 3mm yellow LED (LED3) 1 3mm green LED (LED2) Resistors (1%, 0.25W) 1 4.7kΩ   2 330Ω 1 2.2kΩ   1 220Ω this, but who’s to say what is on the other end? The 330Ω resistor on the ‘ground’ side of the Tx circuit limits the current which may flow through this ground circuit which may be formed by equipment earths and provides a degree of protection for ‘foreign’ equipment. I have used two LED indicators on the receiving side. One (the green LED) indicates that there is data on the line while the other (3mm LED) is an idiot LED to give an immediate indica­tion of a reversed MIDI cable. This LED should be off during normal operation. Power for the receive circuit is obtained by tapping into the CTS and DTR signals from the RS232 interface. The diodes are there to prevent current from flowing from one to the other if one is high and the other is low. I’ve tapped into both CTS and DTR to ensure that we are more likely to get power, since the Rx circuit is useless without it. I’ve also included a power indica­tor LED (labelled ‘OnLine’), so that it is immediately obvious when the receive circuit is getting power. CTS and DTR are ‘high’ during normal operation which is normally the same voltage that Tx is at when it is high. The actual voltage could be anything from 5-15V, but 9-10V seems to be typical. The receive circuit centres around the 6N138 optocoupler. The photo­ transistor has a maximum Vce of 5V, so it is not ac­ceptable to simply connect it in series with a pullup or pulldown resistor across the 5-15V power supply. Instead, the photo­transistor of the optocoupler is connected to a pullup resistor which is connected to the OnLine LED. Although the current through this LED may vary between 2-7mA, the voltage across it remains fairly constant, at around 2V. The resulting signal out of the optocoupler swings from 0V to 2V and is then fed into the transistor, which inverts the signal (again) and gives the cor­rect voltage levels of 0V and 5-15V. In fact, the correct voltages for RS232 are actually -5V to -15V for a low level (logical 1), and +5V to +15V for a high level (logical 0) (and yes, this is the reverse of the usual convention). So in fact, this adaptor does not give Fig.3: these diagrams show the PC pattern, component placement & drilling details for the D25 version of the circuit. the ‘correct’ voltages for RS232 but it works reliably anyway. Assembling the PC board The PC board is a very tight fit inside the D shell as can be seen from the photograph which shows a prototype assembled into a D15 shell. Two circular cutouts need to be filed in the corners to allow clearance for the internal pillars of the D-shell. The board is wedged between the two rows of pins of the D socket. You should make sure that the board and socket assembly will fit into the D shell before soldering any components on the board. Note that the components for the 25pin version are all mounted on the top side of the PC board while for the 15 pin Sound Blaster version, four resistors are mounted on the copper side. Insert and solder all the components, ensuring that the LEDs, IC and diodes and transistor (where applicable) are cor­rectly oriented. You will then need to drill the D-shell to take the LEDs and, to this end, templates are shown in Fig.3 for the 25-pin version and Fig.4 for the 15-pin version. Use a 2.5mm drill and drill from the inside of the D-shell. This means any ‘burrs’ made by the drill entering will not be visible on the outside. Gradu­ally ream out the holes until the LEDs just slide snugly in and out of their holes. I used 5-pin DIN male plugs on the end of the cables, rather than the more traditional MIDI 5-pin DIN female sockets. This meant that I did not need any additional MIDI cables at all; I just plug my MIDI-adaptor straight into my keyboard (1.5-2m for each cable is a sensible length). I also made up a special cable for loop-testing, consisting of two 5-pin DIN line sockets on a short piece of cable. Modifying the serial card The oscillator circuit shown in Fig.5 does not require a special PC board and can be made up on a piece of Veroboard, as shown in Fig.6. In most computer equipment I’ve seen, I noticed that the crystal case is normally connected to ground, so I followed suit. Keep the wires connecting the oscillator circuit to the main board as short as is reasonably possible. Since your serial card may be different to the one I used, you will have to use your own judgement on how to make the necessary modifications to the card. I’ll outline the basic steps: (1). Locate the XIN pin on each of the UARTs. These will probably be connected to each other and to a driver elsewhere on the board. The XOUT pins should be unconnected. (2). Cut the track which connects the XIN pins to the original clock driver. In my case, the driver was an 18.4MHz oscillator which was fed into a divide-by-10 circuit on an 82C11 IC. There should not be any other pins left connected to the isolated XIN pins. (3). Choose one of the two UARTs to drive the new oscillator circuit (I’ll call it the ‘driver UART’). If you have July 1995  79 Fig.4: these diagrams show the PC pattern, component placement & drilling details for the D15 version of the circuit. (b) In the file: “/etc/rc.d/rc.serial: a socketed UART, use it as the driver. (4). Isolate the XIN pin of the driver UART. If you are cutting the track, make the piece of track attached to the driver UART XIN as short as possible. Since I had a socketted IC, I removed the IC from the socket and bent up the XIN pin, so that it became free standing. If your IC is not socketted, it is easier to cut the track to the chosen pin, rather than try to desolder the pin and bend it up. (5). Connect the XOUT pin of the driver UART to the XIN of the other UART. (6). Connect the oscillator circuit to XIN, XOUT and ground of the driver UART. add the lines: Testing the MIDI adaptor echo “Setting cua2,3 baud_base = 500k and divsor = MIDI on EXTB ...” >&2 The MIDI D-shell adaptor can be tested separately by making up a cable with a MIDI socket on each end. This can then be used to connect the MIDI-out to the MIDI-input of the adaptor (assum­ing you’ve put MIDI-plugs on the end of your cables, of course). Do not be concerned if the OnLine LED does not come on when you first Setting Up The Serial Card For Linux (a) In the file: “/etc/rc.d/rc.S” replace the line: # /bin/sh /etc/rc.d/rc.serial with: sleep 20 & TIMEOUT_PID=$! ( /bin/sh /etc/rc.d/rc.serial ; kill $TIMEOUT_PID ) & wait $TIMEOUT_PID ${SETSERIAL} /dev/cua2 baud_base 500000 divisor 16 spd_cust ${SETSERIAL} /dev/cua3 baud_base 500000 divisor 16 spd_cust if [ “`${SETSERIAL} -bg /dev/cua3`” != “” ]; then echo “Setting baud rate EXTB (spd_cust) on /dev/cua3 ...” >&2 stty raw -icanon -echo 38400 < /dev/cua3 fi 80  Silicon Chip es 0x03e8 and 0x02e8). Consult the documentation on your serial card for how to do this. I used IRQs 5 and 7 for the second serial card, since the parallel ports do not need to use interrupts unless you are using them as a network connection. Linux uses polling drivers for the printer ports by default, so this is a safe choice of IRQs. Fig.5: this external oscillator will need to be added to the UART on the serial I/O card in order to achieve the required 31,250 baud rate. Testing the serial card Testing the modified serial card is largely a matter of either it works or it doesn’t. If the oscillator refuses to oscillate, this is evident in that commands like ‘setserial’ and ‘stty’ will hang on the first use. If it doesn’t work, check all your work thoroughly and try varying the value of the capacitors in the oscillator circuit. Try reducing the values first, since there may be some stray capacitance to account for. Also try shortening the wires going to the oscillator circuit, as you may have made these too long. As a last resort, try using a lower frequency crystal, such as 4MHz. Testing the Sound Blaster adaptor (Linux OS) Fig.6: the Veroboard layout of the external oscillator. This is coupled between the XIN and XOUT pins of the UART on the serial I/O card. plug the adaptor into the computer. The CTS and DTR lines are under software control, and are often kept ‘low’ until the software actually tries to use the serial port. Any ordinary modem driver software, such as ‘Kermit’, can be used to test that the adaptor is working properly. Local echo should be off (off by default anyway). What you type in terminal mode is what you should see on the screen. (Remember that you have to type a ^J to get the cursor to move down the screen). This should work at all speeds up to and including 38,400 (EXTB). It can be useful to use a lower baud rate, in order to give a better indication on the LEDs. Serial card configuration Set up your serial card for COM3 and COM4 operation (ie, base address- It is not possible to use ‘Kermit’ to loop-test this adap­tor as Kermit refuses to recognise the MIDI device file (/ dev/midi) as a tty line. I used ‘seyon’ (another terminal program) instead, which gave a lot of warning messages, but worked anyway. For Linux, on the IBM PC, the operating system supports the ‘customised’ serial port very well. However, there are no appli­cations which you can use off-the-shelf. Given that the source-code is always readily available, this is not necessarily a problem. The major hurdle is that most of the applications writ­ ten for Linux use the /dev/sequencer pseudo-device to generate timing. The obvious solution is to modify the /dev/ sequencer driver to redirect output to a nominated serial port. I have been writing my own application which reads and writes the serial port directly. It uses system-exclusive messag­ es to control my keyboard parameters and this has been quite successful. For the Amiga, using Amiga DOS, the adaptor works with the same hardware as any other interface, so all SC normal MIDI software works. July 1995  81 VINTAGE RADIO By JOHN HILL The 8-valve Apex receiver – a glorified sardine tin In a past Vintage Radio story entitled "Trash or Treasure", mention was made of a 1929 American Apex receiver. This interesting old receiver has some unusual features and posed quite a few challenges during its restoration. This ancient imported receiver is fairly novel in some ways and has a number of firsts associated with it as far as I'm concerned. The Apex is the first metal-cased radio I have found that has an undamaged cabinet. Most steel radio cabinets ended their days as tool boxes. Another first is the large number of valves; no less than eight. Of all the receivers I have restored so far, this old Apex has the highest valve count. Being originally fitted with a 240V transformer is another first, as all the other American receivers I have en­countered have been 110V models. The Apex is also the first radio in my collection with a drum dial, the first mains operated TRF (tuned radio frequency) receiver that I have restored for myself and my first with a push­pull audio output stage. Removing the large cover at one end of the chassis reveals the 240V power transformer (right), two high tension chokes (front) & a large block capacitor for high tension filtering (rear). The power transformer & chokes were OK. 82  Silicon Chip The steel cabinet fad came in dur­ing the late 1920s and went out of fashion a few years later. It wasn't in vogue for very long and was little more than a convenient and inexpen­sive method of housing a budget­priced radio chassis. Personally, I think a bare chassis looks far more impressive than a pressed steel cabi­net. Like other American receivers of late 1920s vintage, the Apex has a very predictable valve line up: an 80 rectifier, five 27s and two 45s in the output. Just about every non-European set of that era would have used those valves. Neutralised circuits Neutralised type 27 valves in a TRF circuit were all the go at the time and the Apex has a metal plate attached to the power transformer cover which boldly states that the set is a "Neutro­ dyne" receiver. However, although labelled as such, I defy anyone to find a neutralising capacitor in any shape or form. What the nameplate says and what the set appears to be are two different things. Some radio manufacturers did some clever things to get around paying Neutrodyne royalties but just what Apex has done is rather a mystery, especially as the set was sold as a Neutrodyne. Perhaps some well-in­ formed Apex expert can give me an answer? Incidentally, the Neutrodyne sys­ tem was developed by Professor Hazeltine to combat the inherent in­stability of triode radio frequency amplifiers. The problem is caused by inter-electrode capacitance between the grid and plate and this capacitance creates positive feedback when both the plate and grid circuits are tuned to the same frequency. The result is uncontrollable oscillation. This oscillation problem can be overcome by introducing an equal and opposite phase voltage into the circuit to counteract the feedback voltage and a small variable capacitor is used to balance the two. It is the feedback voltage that is neutralised, not the inter-electrode capacitance. If the Apex has any neutralising apacitors then they are not at all obvious and have been cunningly concealed. The only small adjustable capacitors to be found are those attached to the 3-gang tuning capacitor and they are the crudest trimmers you ever did see! They are nothing more than tabs that are adjusted by bending them one way or the other. These tabs are connected to the fixed playes and no chassis. The tuning capacitor was completely dismantled in order to clean it & lubricate the spindle bearings. Note the three "bend-a-tab" trimmers along the front. Untuned RF amplifier The Apex circuit has a few interesting oddities, the first being the stage of untuned radio frequency amplification. In this circuit, the aerial goes straight to the grid of the first RF valve. Such a setup could perhaps be described as an untuned aerial coupling device. While offering less gain, it allows the following tuned stages to track, regardless as to whether a long or short aerial is used and whether or not there is an earth connection. Conversely, TRF receivers with a tuned RF stage often had a manual trimmer on the first stage so that that section could be tuned to suit what­ever aerial length was being used. The Apex's untuned RF stage is followed by two stages of tuned RF amplification before the resulting signal is fed into a leaky grid detector. An audio frequency interstage trans­former is then used to couple the de­tector to the first audio amplifier which, in turn, drives the two output valves via a push-pull coupling trans­former with a centre-tapped second­ary winding – see Fig, 1. The output stage is a little unusual (though perhaps not unusual for 1929) in that it uses a centre-tapped choke to feed the high tension to the plates of the output valves. The output trans former does not have a centre-tapped The two wav stalactites descending from this paper capacitor give a good indication of its condition. It was replaced with a modern capacitor of equivalent value. primary as is usually the case. Following the output choke, a normal output transformer is used to cou­ple the signal to the loudspeaker. In this case, the output transformer is housed in the base of the loudspeaker stand. The loudspeaker's field coil winding is wired to a separate lead which connects to a pair of terminals at the back of the chassis marked "Field" Restoration problems As is usually the case with a re­ceiver of this age, there were a few problems with the restoration, the main one being the totally derelict state of the loudspeaker. The old Apex receiver had a number of small paper capacitors throughout the circuit. Once again, the wax that has been pushed out of the ends of this capacitor tells the story as to its condition. All paper capacitors were replaced. July 1995  83 trans­ former) to an 8-inch (200mm) permag speaker mounted on the wall of my den. A 2kW 20W resistor was substituted for the original field coil winding. This component was soldered to the underside of the field coil terminals and can easily be removed when a suitable loudspeaker is found. Any increased hum that may have been caused by this modification is cer­tainly not objectionable. The HT cir­cuit still has two built-in chokes and accompanying filter capacitors. Alignment The 65-year old chassis cleaned up rather well. Note the drum dial with the tuning & volume controls to either side. The push-pull 45s in the audio output stage are the two large valves at the rear of the chassis, adjacent to the transformer cover. Another problem was caused by the removal of the chassis from its cabi­net. Although everything had been disconnected, the chassis would not budge. A bit of "gentle force" released whatever was holding it and out it came. Oh dear! – there on the bottom of the cabinet were several blobs of wax. In the largest of these was embedded a rather important wire – the centre-tap connection of the previously mentioned output choke. As with most early AC-powered receivers, there were numerous cans full of leaky paper capacitors that needed replacing. Other repairs and incidentals included testing the valves, clean­ing and lubricating the tuning capaci­ tor and dial mechanism, and replac­ing the volume control – these OUTPUT VALVES 2x45 DRIVER VALVE 27 in addition to the normal routine cleaning and other minor tidy-up jobs. The main problem at this stage was the damaged centre-tapped output choke. The choke was repaired by subjecting it to major surgery. The outer insulation was cut open with a knife, the centre-tap found and a new leadout wire soldered to it. The wound was then closed with a liberal application of contact adhesive and held together with rubber bands until the incision had fully healed. This simple operation made the choke serviceable once again. Both of the interstage transformers checked out OK but the original loudspeaker was totally wrecked. Because of this, the receiver was temporarily connected (via a suitable output OUTPUT CHOKE OUTPUT TRANSFORMER COUPLING TRANSFORMER TO LOUDSPEAKER FROM DETECTOR HT HT Fig.1: the output stage is unusual in that it uses a centre-tapped choke to feed the high tension to the plates of the output valves. Note that the output transformer does not have a centre-tapped primary as is usually the case. 84  Silicon Chip Alignment of the receiver was not without its problems, mainly because of the rough manufacture of the 3-gang tuning capacitor. The bend-to­ -align trimmers were no problem to adjust but when they were adjusted, the frequency settings were off at the other end of the dial. This alignment problem was rem­ edied by using the trimmers at the high frequency end and bending ca­pacitor plates at the low frequency end. Eventually, the receiver was tracking fairly accurately over the full range of the dial – and the old set performed very well indeed! However, it was later found that the receiver went out of tune a little at the high frequency end of the tuning range when it was installed in its metal cabi­net. This was due, no doubt, to the capacitance effect of such a large area of sheet steel. No wonder the steel cabinet idea was abandoned! Restoration of the cabinet was a relatively simple procedure. The outside of the cabinet had been originally painted a brown colour. "Crinkle Brown" should identify the paint work reasonably well and it seemed to be in keeping with the 1920s trend of crin­kle finishes on metal surfaces. After cleaning, the bare spots were primed with an anti-rust metal primer which was applied quite thickly with a toothbrush. Teasing up the partly dry primer with the toothbrush pro­duced a reasonable crinkle effect which is perhaps a better technique than allowing the paint to dry smooth. While the primed patches were dry­ing, the inside of the cabinet was spray painted to improve its appearance. After that, the primed spots were touched up with brown paint so that they would not show through the fi­nal coat of paint. ELECTRONIC VALVE & TUBE COMPANY VALVE SPECIALS! NEW SOVTEK SHIPMENT A major part of the restoration involved painting the metal cabinet to give it an authentic "Crinkle Brown" appearance. It's no wonder that so many metal radio cabinets ended up as tool boxes. All they needed was a carrying handle at each end. 6L6GC 10.00 5Y3GT 12.00 EL34G 20.00 6V6GT 10.00 6CA7 5881 24.00 18.00 5AR4/GZ34 22.00 12AX7WA/7025 9.00 EL84/6BQ5 10.00 Matching at $1 per valve Prices valid until 31.12.95 Send SSAE for catalogue PO Box 381 Chadstone Centre Vic 3148 Tel/Fax (03) 9571 1160 or mobile 018 557 380 Silicon Chip Binders A bird's-eye view of the Apex receiver with the top cover removed. Although designed as a budget-priced receiver, it performs very well. The top coat was applied sparingly with a short bristled brush and it was put on with a stabbing action rather than a brushing action. The drying paint was worked with the brush un­ til it was almost dry. Doing this pre­vents the paint from filling in the crin­kly surface and also dulls off the sur­face finish. Although the cabinet refurbishing was really only a quick touch-up job, the overall effect was quite pleasing. It looks clean and tidy, is not glossy, and maintains its original crinkle fin­ish. Outwardly, the old Apex looks the genuine article and under the bonnet it is running well on all, eight cylinders, so to speak. However, the restoration cost was fairly high as the two replacement output valves alone cost $100. It would have cost a lot more if some of those interstage transformers had been open circuit. All I need now is an appropriate loudspeaker and the Apex will be a complete outfit. In the meantime, this relic from the past works quite well with my wall-mounted speaker should I wish to demonstrate it or listen to a favourite program. SC These beautifully-made binders will protect your copies of SILICON CHIP. They are made from a dis­tinctive 2-tone green vinyl & will look great on your bookshelf. Price: $A11.95 plus $3 p&p each (NZ $8 p&p). Send your order to: Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. July 1995  85 Silicon Chip v 0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power Station. August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Wave Generator, Pt.2. BACK ISSUES September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice. September 1990: Remote Control Extender For VCRs; Power Supply For Burglar Alarms; Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band. Formats & Options; The Pilbara Iron Ore Railways. April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2; LED Message Board, Pt.2. December 1989: Digital Voice Board (Records Up To Four Separate Messages); UHF Remote Switch; Balanced Input & Output Stages; Data For The LM831 Low Voltage Amplifier IC; Installing A Clock Card In Your Computer; Index to Volume 2. May 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; LED Message Board, Pt.3; All About Electrolytic Cap­acitors. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Speed­ing Up Your PC; Phone Patch For Radio Amateurs; Active Antenna Kit; Speed Controller For Ceiling Fans; Designing UHF Transmitter Stages. June 1989: Touch-Lamp Dimmer (uses Siemens SLB0586); Passive Loop Antenna For AM Rad­ios; Universal Temperature Controller; Understanding CRO Probes; LED Message Board, Pt.4. February 1990: 16-Channel Mixing Desk; High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2. July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor); Extension For The Touch-Lamp Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm. March 1990: 6/12V Charger For Sealed Lead-Acid Batteries; Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Studio Series 20-Band Stereo Equaliser, Pt.2; Auto-Zero Module for Audio Amplifiers (Uses LMC669). October 1989: FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 1Mb Printer Buffer; 2-Chip Portable AM Stereo Radio, Pt.2; Installing A Hard Disc In The PC. November 1989: Radfax Decoder For Your PC (Displays Fax, RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive April 1990: Dual Tracking ±50V Power Supply; Voice-Operated Switch (VOX) With Delayed Audio; Relative Field Strength Meter; 16-Channel Mixing Desk, Pt.3; Active CW Filter For Weak Signal Reception; How To Find Vintage Receivers From The 1920s. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protection Switch For Power Supplies; A Speed Alarm For Your Car; Fitting A Fax Card To A Computer. July 1990: Digital Sine/Square Generator, Pt.1 (Covers October 1990: Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; The Dangers of Polychlorinated Biphenyls; Using The NE602 In Home-Brew Converter Circuits. November 1990: How To Connect Two TV Sets To One VCR; A Really Snazzy Egg Timer; Low-Cost Model Train Controller; Battery Powered Laser Pointer; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Simple 6-Metre Amateur Transmitter. December 1990: DC-DC Converter For Car Amplifiers; The Big Escape – A Game Of Skill; Wiper Pulser For Rear Windows; Versatile 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers When Servicing Microwave Ovens. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Inverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages; Tasmania's Hydroelectric Power System. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; A Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateur Radio & TV. April 1991: Steam Sound Simulator For Model Railroads; Remote Controller For Garage Doors, Pt.2; Simple 12/24V ORDER FORM Please send me a back issue for: ❏ June 1989 ❏ July 1989 ❏ December 1989 ❏ January 1990 ❏ June 1990 ❏ July 1990 ❏ November 1990 ❏ December 1990 ❏ April 1991 ❏ May 1991 ❏ September 1991 ❏ October 1991 ❏ February 1992 ❏ March 1992 ❏ July 1992 ❏ August 1992 ❏ February 1993 ❏ March 1993 ❏ July 1993 ❏ August 1993 ❏ December 1993 ❏ January 1994 ❏ May 1994 ❏ June 1994 ❏ October 1994 ❏ November 1994 ❏ March 1995 ❏ April 1995 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ September 1988 September 1989 February 1990 August 1990 January 1991 June 1991 November 1991 April 1992 September 1992 April 1993 September 1993 February 1994 July 1994 December 1994 May 1995 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ April 1989 October 1989 March 1990 September 1990 February 1991 July 1991 December 1991 May 1992 October 1992 May 1993 October 1993 March 1994 August 1994 January 1995 June 1995 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ May 1989 November 1989 April 1990 October 1990 March 1991 August 1991 January 1992 June 1992 January 1993 June 1993 November 1993 April 1994 September 1994 February 1995 July 1995 Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Signature ____________________________ Card expiry date_____ /______ Name _______________________________ Phone No (___) ____________ PLEASE PRINT Street ________________________________________________________ Suburb/town ________________________________ Postcode ___________ 86  Silicon Chip Note: all prices include post & packing Australia (by return mail) ............................. $A7 NZ & PNG (airmail) ...................................... $A7 Overseas (airmail) ...................................... $A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 979 5644 & quote your credit card details or fax the details to (02) 979 6503. ✂ Card No. Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To Amplifier Design, Pt.2. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1. June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers; Active Filter For CW Reception; Tuning In To Satellite TV, Pt.1. July 1991: Battery Discharge Pacer For Electric Vehicles; Loudspeaker Protector For Stereo Amplifiers; 4-Channel Lighting Desk, Pt.2; How To Install Multiple TV Outlets, Pt.2; Tuning In To Satellite TV, Pt.2. August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder; Tuning In To Satellite TV, Pt.3; Step-By-Step Vintage Radio Repairs. September 1991: Studio 3-55L 3-Way Loudspeaker System; Digital Altimeter For Gliders & Ultralights, Pt.1; The Basics Of A/D & D/A Conversion; Windows 3 Swapfiles, Program Groups & Icons. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator For Model Railways Mk.II; Magnetic Field Strength Meter; Digital Alti­meter For Gliders & Ultralights, Pt.2; Getting To Know The Windows PIF Editor. November 1991: Colour TV Pattern Generator, Pt.1; Battery Charger For Solar Panels; Flashing Alarm Light For Cars; Digital Altimeter For Gliders & Ultralights, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Solid-State Laser Pointer; Colour TV Pattern Generator, Pt.2; Index To Volume 4. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Automatic Controller For Car Headlights; Experiments For Your Games Card; Restoring An AWA Radiolette. February 1992: Compact Digital Voice Recorder; 50-Watt/ Channel Stereo Power Amplifier; 12VDC/240VAC 40-Watt Inverter; Adjustable 0-45V 8A Power Supply, Pt.2; Designing A Speed Controller For Electric Models. March 1992: TV Transmitter For VHF VCRs; Studio Twin Fifty Stereo Amplifier, Pt.1; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Direct­ories; Valve Substitution In Vintage Radios. January 1993: Peerless PSK60/2 2-Way Hifi Loudspeakers; Flea-Power AM Radio Transmitter; High Intensity LED Flasher For Bicycles; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.4; Speed Controller For Electric Models, Pt.3. February 1993: Three Simple Projects For Model Railroads; A Low Fuel Indicator For Cars; Audio Level/VU Meter With LED Readout; Build An Electronic Cockroach; MAL-4 Microcontroller Board, Pt.3; 2kW 24VDC To 240VAC Sine­ wave Inverter, Pt.5. March 1993: Build A Solar Charger For 12V Batteries; Alarm-Triggered Security Camera; Low-Cost Audio Mixer for Camcorders;A 24-Hour Sidereal Clock For Astronomers. April 1993: Solar-Powered Electric Fence; Build An Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Step-Up Voltage Converter; Digital Clock With Battery Back-Up. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Remote Volume Control For Hifi Systems, Pt.1; Alphanumeric LCD Demonstration Board; The Micro­soft Windows Sound System. June 1993: Windows-Based Digital Logic Analyser, Pt.1; Build An AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; Digital Voltmeter For Cars; Remote Volume Control For Hifi Systems, Pt.2 July 1993: Build a Single Chip Message Recorder; Light Beam Relay Extender; AM Radio Trainer, Pt.2; Windows Based Digital Logic Analyser; Pt.2; Quiz Game Adjudicator; Programming The Motorola 68HC705C8 Micro­controller – Lesson 1; Antenna Tuners – Why They Are Useful. August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light Array; A Microprocessor-Based Sidereal Clock; The Southern Cross Z80-based Computer; A Look At Satellites & Their Orbits. September 1993: Automatic Nicad Battery Charger/ Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Cockroach; Servicing An R/C Transmitter, Pt.1. October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1; Programming The Motorola 68HC705C8 Micro­controller – Lesson 2; Servicing An R/C Transmitter, Pt.2. Circuits; Electronic Engine Management, Pt.8; Passive Rebroadcasting For TV Signals. June 1994: 200W/350W Mosfet Amplifier Module; A Coolant Level Alarm For Your Car; An 80-Metre AM/CW Transmitter For Amateurs; Converting Phono Inputs To Line Inputs; A PC-Based Nicad Battery Monitor; Electronic Engine Management, Pt.9 July 1994: SmallTalk – a Tiny Voice Digitiser For The PC; Build A 4-Bay Bow-Tie UHF Antenna; PreChamp 2-Transistor Preamplifier; Steam Train Whistle & Diesel Horn Simulator; Portable 6V SLA Battery Charger; Electronic Engine Management, Pt.10. August 1994: High-Power Dimmer For Incandescent Lights; Microprocessor-Controlled Morse Keyer; Dual Diversity Tuner For FM Microphones, Pt.1; Build a Nicad Zapper; Simple Crystal Checker; Electronic Engine Management, Pt.11. September 1994: Automatic Discharger For Nicad Battery Packs; MiniVox Voice Operated Relay; Image Intensified Night Viewer; AM Radio For Aircraft Weather Beacons; Dual Diversity Tuner For FM Microphones, Pt.2; Electronic Engine Management, Pt.12. October 1994: Dolby Surround Sound – How It Works; Dual Rail Variable Power Supply (±1.25V to ±15V); Talking Headlight Reminder; Electronic Ballast For Fluorescent Lights; Temperature Controlled Soldering Station; Electronic Engine Management, Pt.13. November 1994: Dry Cell Battery Rejuv­enator; A Novel Alphanumeric Clock; 80-Metre DSB Amateur Transmitter; Twin-Cell Nicad Discharger (See May 1993); Anti-Lock Braking Systems; How To Plot Patterns Direct To PC Boards. December 1994: Dolby Pro-Logic Surround Sound Decoder, Pt.1; Easy-To-Build Car Burglar Alarm; Three-Spot Low Distortion Sinewave Oscillator; Clifford – A Pesky Electronic Cricket; Cruise Control – How It Works; Remote Control System for Models, Pt.1; Index to Vol.7. January 1995: Build A Sun Tracker For Solar Panels; Battery Saver For Torches; Dolby Pro-Logic Surround Sound Decoder, Pt.2; Dual Channel UHF Remote Control; Stereo Microphone Preamplifier; The Latest Trends In Car Sound; Pt1. February 1995: 50-Watt/Channel Stereo Amplifier Module; Digital Effects Unit For Musicians; 6-Channel Thermometer With LCD Readout; Wide Range Electrostatic Loudspeakers , Pt.1; Oil Change Timer For Cars; The Latest Trends In Car Sound; Pt2; Remote Control System For Models, Pt.2. April 1992: IR Remote Control For Model Railroads; Differential Input Buffer For CROs; Studio Twin Fifty Stereo Amplifier, Pt.2; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier With IR Remote Control, Pt.3; Siren Sound Generator; Electronic Engine Management, Pt.2; More Experiments For Your Games Card. May 1992: Build A Telephone Intercom; Low-Cost Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; Aligning Vintage Radio Receivers, Pt.2. December 1993: Remote Controller For Garage Doors; Low-Voltage LED Stroboscope; Low-Cost 25W Amplifier Module; Build A 1-Chip Melody Generator; Electronic Engine Management, Pt.3; Index To Volume 6. June 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; Infrared Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; A Look At Hard Disc Drives. January 1994: 3A 40V Adjustable Power Supply; Switching Regulator For Solar Panels; Printer Status Indicator; Mini Drill Speed Controller; Stepper Motor Controller; Active Filter Design For Beginners; Electronic Engine Management, Pt.4. July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Multi-Station Headset Intercom, Pt.2; Electronics Workbench For Home Or Laboratory. February 1994: 90-Second Message Recorder; Compact & Efficient 12-240VAC 200W Inverter; Single Chip 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Electronic Engine Management, Pt.5; Airbags – How They Work. May 1995: Introduction To Satellite TV; CMOS Memory Settings – What To Do When the Battery On Your Mother­ board Goes Flat; Mains Music Transmitter & Receiver; Guitar Headphone Amplifier For Practice Sessions; Build An FM Radio Trainer, Pt.2; Low Cost Transistor & Mosfet Tester For DMMs; 16-Channel Decoder For Radio Remote Control. August 1992: Build An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; Dummy Load Box For Large Audio Amplifiers; Internal Combustion Engines For Model Aircraft; Troubleshooting Vintage Radio Receivers. March 1994: Intelligent IR Remote Controller; Build A 50W Audio Amplifier Module; Level Crossing Detector For Model Railways; Voice Activated Switch For FM Microphones; Simple LED Chaser; Electronic Engine Management, Pt.6. June 1995: Build A Satellite TV Receiver; Train Detector For Model Railways; A 1W Audio Amplifier Trainer; Low-Cost Video Security System; A Multi-Channel Radio Control Transmitter For Models, Pt.1; Build A $30 Digital Multimeter. September 1992: Multi-Sector Home Burglar Alarm; Heavy-Duty 5A Drill speed Controller (see errata Nov. 1992); General-Purpose 3½-Digit LCD Panel Meter; Track Tester For Model Railroads; Build A Relative Field Strength Meter. April 1994: Remote Control Extender For VCRs; Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator; Low-Noise Universal Stereo Preamplifier; Build A Digital Water Tank Gauge; Electronic Engine Management, Pt.7. PLEASE NOTE: all issues from November 1987 to August 1988, plus October 1988, November 1988, December 1988, January, February, March and Aug­ust 1989, May 1990, and November and December 1992 are now sold out. All other issues are presently in stock. For readers wanting articles from sold-out issues, we can supply photostat copies (or tear­sheets) at $7.00 per article (includes. p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. October 1992: 2kW 24VDC To 240VAC Sine­wave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; Electronically Regulated Lead-Acid Battery Charger. May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Multi-Channel Infrared Remote Control; Dual Electronic Dice; Two Simple Servo Driver March 1995: 50W/Channel Stereo Amplifier, Pt.1; Subcarrier Decoder For FM Receivers; Wide Range Electrostatic Loudspeakers, Pt.2; IR Illuminator For CCD Cameras & Night Viewers; Remote Control System For Models, Pt.3; Simple CW Filter. April 1995: Build An FM Radio Trainer, Pt.1; Photographic Timer For Darkrooms; Balanced Microphone Preamplifier & Line Filter; 50W/Channel Stereo Amplifier, Pt.2; Wide Range Electrostatic Loudspeakers, Pt.3; 8-Channel Decoder For Radio Remote Control. July 1995  87 PRODUCT SHOWCASE Tek's new Wavemeter – a scope & multimeter combination While there are a number of combination multimeter/scopes on the market, this new instrument from Tektronix breaks new ground. The Tek Wavemeter looks very similar to a conventional digital multimeter but incorporates an oscilloscope display with a bandwidth of 5MHz. The Tek Wavemeter is just a little bulkier than conventional upmarket digital multimeters and measures 90mm wide, 208mm long and 45mm deep, at its thickest point. The LCD screen is cranked up to make viewing easier and this factor makes it bulkier than it otherwise would be. Designated the THM420, the instrument is a fully autoranging true-RMS 4000 count multimeter with bargraph display. When you consider that it is priced at around the same level as competing upmarket multimeters, the fact that it has a scope display as well is a major achievement. As such, it will be of great interest to technicians and engineers who need to monitor signal characteristics such as noise, glitches or distortion in conjunction with meter measurements. In meter, mode the 3-3/4 digit (4000 count) instrument is capable of meas- uring full scale DC voltages of 400mV, 4V, 40V, 400V and 850V The true­RMS reading AC ranges are similar except that the top range is 600V AC and DC current ranges are 400mA and 8A. A nice feature is the overrange display. Whereas most meters show a leading "1" in the overrange condi­ tion, the THM420 is clearly unam­biguous – it displays "OV.ER". The six resistance ranges are 400W, 4kW, 40kW, 400kW, 4MW and 40MW, while the frequency meter ranges are 100Hz, 1kHz, 10kHz, 100kHz and 1MHz, with the lowest measurable frequency being 10Hz. The continuity and diode test functions are cunningly combined in one switch position. If the resistance be­tween the probes is 300 or less, the internal beeper sounds and if a diode is connected, the voltage drop across it is measured and displayed. The maximum displayed forward voltage is 2.480V and it can supply enough Fig.1: the multimeter display has large numerals & a bargraph to indicate rapid fluctuations in the measurement. Fig.2: this scope display shows a pulse waveform with a vertical sensitivity of 2V/div and a timebase setting of 100µs/div. Meter mode 88  Silicon Chip current to light LEDs (including blue ones). Scope mode The scope display has a central hori­ zontal axis with eight divisions while the vertical axis has four divisions, each division consisting of 16 dots. The vertical bandwidth is DC to 5MHz from 20mV/div to 1V/div and 3MHz for 2V/div and up. The sample rate is 16Ms/s and the resolution is 6 bits. The horizontal sweep time ranges from 100ns/div to 10s/div. Obviously the only waveforms that can be dis­ played are voltage and current. Controls The controls consist of a rotary se­ lector switch and six rectangular push buttons labelled AUTO, DC/AC, ME­TER/SCOPE, RUN/HOLD, PRINT and LIGHT There is also a cluster of five buttons, the centre square one labelled SELECT, surrounded by four triangu­ lar buttons which point up, down, left and right. The rotary selector switch has an OFF position and six function posi­ tions: Volts, Ohms, Diode, Frequency, mA and Amps. The Volts, mA and Amps legends are highlighted with a blue surround, indicating that when these ranges are selected, the scope mode can be enabled. On the con- Fig.3: this display shows an additional horizontal cursor to indicate the trigger point and a central vertical axis. Styled like a conventional digital multimeter, Tek's Wavemeter doubles as a scope with a bandwidth of 5MHz. This can be brought into play when ever the voltage or current ranges are selected. The scope mode is completely automatic and selects the timebase and vertical sensitivity for optimum waveform display. trol buttons, the words SCOPE and SELECT are screened in blue, tying their functions back to the selector switch. It is difficult to describe but simple to use. One unusual feature is the selec­tion of DC or AC for voltage and cur­rent. This is not selected by the rotary switch as is normal, but is carried out by using the DC/AC button, the last selected function being stored when the power is turned off. This mode also sets the input coupling (ie, DC or AC) in SCOPE mode. The AUTO mode of operation comes into play when the Tek Wavemeter is turned on and this is the setting which would be used most often. Should the need arise, this can be overridden by pressing the up or down arrows to manually select the required range. Unfortunately, in the American manner, the UP and DOWN buttons work in the opposite manner to that ex­pected, the UP button decrementing the Ohms ranges. In SCOPE mode the centre button, SELECT, as the name implies, allows manual selection of trigger, scale and position with successive presses. TRIGGER allows the up and down ar­rows to move a dotted cursor up or down about the reference for positive or negative triggering. With SCALE selected, the up and down arrows change input ranges while the left and right arrows control the timebase speed. POSITION, as its name suggests, al­ lows the up and down arrows to move the trace about the horizontal axis, similar to the Y shift control on a conventional oscilloscope. The left and right arrows move the Y axis from the lefthand side to the centre, and to the righthand side, allowing the pre­and post-trigger waveform to be viewed, just as you can with most digital sampling scopes. We found the THM420 Wavemeter intuitively simple to use. Without using an instruction manual, the ranges are easily selected and a few minutes spent with a function generator and "pressing buttons" will soon give a good working knowledge of the capabilities of the unit. Reading the manual gives an in­sight into functions and capabilities that are not obvious. For example, if the right arrow is held down when the unit is turned on, the auto power off mode is disabled. The auto power off mode is 10 minutes but it is good to be able to turn it off when signals have to be monitored for long periods without touching the control settings. Battery life from the six internal alkaline AA cells is relatively short, at around 10 hours. However, the bat­tery pack clips off the back readily and appears to have provision for re­charging if nicads were employed. A companion printer will be available, which will receive data via an infrared light beam (945nm) from the Wavemeter. It is claimed that the two units will communicate over a distance of one metre The THM420 Wavemeter comes complete with test leads and batteries. A soft carrying case is available as an option. While we did not have the review instrument in our laboratory for long, we feel that its great measurement capabilities combined with ease of use will make it a landmark product that it is sure to be a winner. It is priced at $865 plus tax. For further information, contact Tektronix Australia Pty Ltd, 80 Waterloo Road, North Ryde NSW 2113. Phone (02) 888 7066 or fax (02) 888 0125. Digital video encoder for NTSC & PAL The new Philips SAA7185 digital video encoder is MPEG-compatible and is intended for use in computers, video servers, video CD players and video games. It encodes digital YUV data into an NTSC or PAL CBVS and S-video to be displayed on consumer TV sets or recorded on VCRs. The SAA7185 is an economical solution requiring no licence payments to Macrovision Inc because it does not contain Macrovision's anti-taping cir­cuitry. The SAA7185 is a programmable 5V CMOS device controlled via an July 1995  89 New range of D back shells with multiple cable entry Amtron has released a new series of "D" subminiature back shells for use in the electronics and communications industries. Currently, 9, 15 & 25-way versions are available, while 37 & 50-way versions will be available later this year. All back shells are offered with or without RF shielding. The major feature of this new product is the number of cable entry points available. The 9-way version has two entries, the others have three, which are 60°, straight and 90° The shielded backshell has been tested to MIL STD 285. Each backshell comes with a set of different diameter grommets to suit various cable sizes. For further information, contact Amtron Australia Pty Ltd, 687 Gardeners Rd, Mascot, NSW 2020. Phone (02) 317 5511. KITS-R-US PO Box 314 Blackwood SA 5051 Ph 018 806794 TRANSMITTER KITS $49: a simple to build 2.5 watt free running CD level input, FM band runs from 12-24VDC. •• FMTX1 FMTX2B $49: the best transmitter on the market, FM-Band XTAL locked on 100MHz. CD level input 3 stage design, very stable up to 30mW RF output. $49: a universal digital stereo encoder for use on either of our transmitters. XTAL locked. •• FMTX2A FMTX5 $99: both FMTX2A & FMTX2B on one PCB. FMTX10 $599: a complete FMTX5 built and tested, enclosed in a quality case with plugpack, DIN input •connector for audio and a 1/2mtr internal antenna, also available in 1U rack mount with balanced cannon input sockets, dual VU meter and BNC RF $1299. Ideal for cable FM or broadcast transmission over distances of up to 300 mtrs, i.e. drive-in theatres, sports arenas, football grounds up to 50mW RF out. FMTX10B $2599: same as rack mount version but also includes dual SCA coder with 67 & 92KHz subcarriers. • AUDIO Audio Power Amp: this has been the most popular kit of all time with some 24,000 PCBs being •soldDIGI-125 since 1987. Easy to build, small in size, high power, clever design, uses KISS principle. Manufacturing rights available with full technical support and PCB CAD artwork available to companies for a small royalty. 200 Watt Kit $29, PCB only $4.95. AEM 35 Watt Single Chip Audio Power Amp $19.95: this is an ideal amp for the beginner to construct; uses an LM1875 chip and a few parts on a 1 inch square PCB. Low Distortion Balanced Line Audio Oscillator Kit $69: designed to pump out line up tone around studio complexes at 400Hz or any other audio frequency you wish to us. Maximum output +21dBm. MONO Audio DA Amp Kit, 15 splits: $69. Universal BALUN Balanced Line Converter Kit $69: converts what you have to what you want, unbalanced to balanced or vice versa. Adjustable gain. Stereo. • • •• COMPUTERS I/O Card for PCs Kit $169: originally published in Silicon Chip, this is a real low cost way to interface •to Max the outside world from your PC, 7 relays, 8 TTL inputs, ADC & DAC, stepper motor drive/open collector 1 amp outputs. Sample software in basic supplied on disk. PC 8255 24 Line I/O Card Kit $69, PCB $39: described in ETI, this board is easy to construct with •onlyIBM3 chips and a double sided plated through hole PCB. Any of the 24 lines can be used as an input or output. Good value. 19" Rack Mount PC Case: $999. •• Professional All-In-One 486SLC-33 CPU Board $799: includes dual serial, games, printer floppy & IDE hard disk drive interface, up to 4mb RAM 1/2 size card. PC104 486SLC CPU Board with 2Mb RAM included: 2 serial, printer, floppy & IDE hard disk $999; VGA •PC104 card $399. KIT WARRANTY – CHECK THIS OUT!!! If your kit does not work, provided good workmanship has been applied in assembly and all original parts have been correctly assembled, we will repair your kit FREE if returned within 14 days of purchase. Your only cost is postage both ways. Now, that’s a WARRANTY! KITS-R-US sell the entire range of designs by Graham Dicker. The designer has not extended his agreement with the previous distributor, PC Computers, in Adelaide. All products can be purchased with Visa/Bankcard by phone and shipped overnight via Australia EXPRESS POST for $6.80 per order. You can speak to the designer Mon-Fri direct from 6-7pm or place orders 24 hours a day on: PH 018 80 6794; FAX 08 270 3175. 90  Silicon Chip I2C serial interface or via an 8-bit microprocessor port. It can be syn­chronised as master or slave to external de­ vices. The SAA-7185 also pro­vides an 8-colour on-screen display and "line 21" closed caption encoding. For more information, contact Philips Components, 34 Waterloo Rd, North Ryde, NSW 2113. Phone (02) 805 4479 or fax (02) 805 4466. Video intercom for the home has optional solenoid door release For those who want to see and hear who is ringing their doorbell Dick Smith Electronics now has the answer – the Look-C Door Vision intercom. This unit has a CCD video camera which is mounted outside the front door. When the visitor presses the call button, a chime is triggered while their image is dis­played on a monitor inside the home. The system in­cludes a 2-way intercom so that the householder can talk to, as well as see, the visitor. The CCD camera includes infrared LEDs for illumina­ tion at night, providing an extra degree of security since the caller does not see the light. The camera has auto iris so that it adjusts automatically to a wide range of lighting conditions. An optional solenoid door release is available to com­ plete the package which may be professionally installed or installed by the do-it-yourself owner. The system is available from all Dick Smith Electronics stores at $599. (Cat L-5800). Surplus display module from Oatley Electronics The Hitachi LM215XB, a 480 x 128 dot liquid crystal display (LCD) module, is now available from Oatley Elec­ tronics. This brand new unit, which costs $25, comes complete with an attractive housing, a mating connector and data sheet. The module is 270 x 110 x 11.5mm and needs a 5V positive supply and a negative supply of around lOV to operate. For further details on this LCD module contact Oatley Electronics, PO Box 89, Oatley, NSW 2223. Phone (02) 579 4985 or fax (02) 570 7910. AUDIO TRANSFORMERS SILICON CHIP SOFTWARE Stereo TV sets with multi-system compatability ORDER FORM Akai has announced three multi-system stereo colour TVs which comprise the 68cm CTK-2976 and CTK-2877A models, and the 59cm CTK-2577A set. All models offer audio outputs for connection to home stereo systems and all are compatible with up to 23 TV and VCR playback systems, including NTSC, SECAM and several PAL formats. All three models feature program memory, auto search tuning, infrared remote control, dark tint tube, on-screen menu display and a sleep function, which turns the power off after a preset time. The CTK-2976 (RRP $1399), CTK2877A ($1499) and the CTK-2577A ($1299) are covered by a 12-month warranty and are available at selected Akai dealers and department stores. For further information on these colour TV sets, contact Akai on (02) SC 763 6300. PRICE ❏ Floppy Index (incl. file viewer): $A7 ❏ Notes & Errata (incl. file viewer): $A7 ❏ Alphanumeric LCD Demo Board Software (May 1993): $A7 ❏ Stepper Motor Controller Software (January 1994): $A7 ❏ Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7 ❏ Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7 ❏ Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7 ❏ Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7 ❏ I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7 POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5 Disc size required:    ❏ 3.5-inch disc   ❏ 5.25-inch disc TOTAL $A Enclosed is my cheque/money order for $­A__________ or please debit my Bankcard   ❏ Visa Card   ❏ MasterCard ❏ Card No. Signature­­­­­­­­­­­­_______________________________ Card expiry date______/______ Name ___________________________________________________________ PLEASE PRINT Street ___________________________________________________________ Suburb/town ________________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). ✂ Manufactured in Australia Comprehensive data available Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 476-5854 Fx (02) 476-3231 Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. July 1995  91 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. Capacitor shortages – but substitutes OK I have been trying to track down the 2.2µF 16VW electroly­ tic capacitors specified in the parts list for the Lightning Distance Meter described in the March 1995 issue. I can’t find them in Dick Smith’s or Jaycar’s catalogs and 1N4002 silicon diodes seem to be off their lists as well though these are used in many of your projects. Where do you get them? I would like to know more about the magneto resistor, a semiconductor device made from a polycrystalline compound, which alters its resistance according to the strength of the magnetic field in which it is placed. Also, I don’t know if you have seen them or not, but some gas servicemen carry around a device which when switched on and placed near a gas source (eg, LPG gas bottle or gas heater con­nections) checks for leaks and emits a warning sound – much better than relying on soapy water to check for leaks. I was wondering whether you could build one as a project? (G. L., Laidley, Qld). • 2.2µF 16VW electrolytics do seem to be hard to obtain but you can substitute higher voltage capacitors without any prob­ lems; eg, 35VW or 63VW. The same comment can be made about the 1N4002 diodes – substitute the higher Speed indicator for train controller I recently purchased a copy of “14 Model Railway Projects” and I have started building the infrared remote controlled throt­tle and will be building the walkaround throttle version for a friend. He would, however, like a speed indicator incorporated. Firstly, could you advise how the meter would be wired in circuit and, secondly, would I be able to use an MU-45 0-5A meter that I already have 92  Silicon Chip rated 1N4004s. We have heard of magneto resistors or more particularly, magneto­resist­ ance. This refers to the phenomenon of a magnetic material carrying current in the presence of a magnetic field – the resistivity of the material increases when the field is parallel to the current flow and decreases when it is at right angles. However, we have not come across any components of this type. We featured an exhaust gas monitor project using a gas sensor in the July 1989 issue. While the original kit is no longer available, various gas sensors are available from RS Components in Melbourne. Soldering iron kit doesn’t work I am writing in regards to the soldering iron kit featured in the October 1994 issue. My problem is that my kit doesn’t work. While reading the instructions over and over again and checking for correct voltages and the components, I have found by accident that if I earth out a LED test light and touch the probe to the gate of Triac 1 (BT139600) the soldering iron barrel works but it cannot be controlled by the temperature control. I have also noticed that the print says that a 4.7MΩ resis­tor is connected on hand, instead of a 1mA meter move­ment? Any advice you could give would be gratefully received. (J. H., St Marys, Tas). • A speed meter can be wired into the circuit quite simply. Just connect a 1mA meter and 2kΩ trimpot in series between pin 1 of IC1c and the 0V line. IC1c is the buffer for the speed control pot. You can’t really use an ammeter movement to do this job unless you can remove the inbuilt shunt which is a heavy piece of wire between the two meter terminals. between pins 5 and 6 of IC1a and so on. The diagram shows that a 4.7MΩ resistor is connected between pins 5 and 7. I have also replaced the Triac (BT139600), the opto-coupled Triac (MOC3021) and even the op amp (LM324) with new components and still it doesn’t work. Would you please help me to work out what the problem might be? I would also like to know if it is possible to get my alarm clock radio to turn on my stereo unit. The alarm clock works but the radio has malfunctioned. It is a separate appliance to the stereo unit. Would it be possible to connect the two appliances using a Triac and an opto-coupled Triac? (I. M., Schofields, NSW). • The way to solve your problem with the temperature con­troller is to isolate the malfunction to a particular stage. For example, you have already indicated that the Triac can be made to turn on. Next, by shorting the collector and emitter of Q1, you should be able to get LED2 to turn on and also to turn on the Triac. If this happens, then IC2 is OK. Next, rotate VR1 so that pin 5 of IC1 is at +3V. Pin 6 should be well below this and pin 7 should be high (ie, +7V or higher) and so Q1, LED2 and the Triac should turn on. If this all checks out, then you only have to check the thermistor and the stage involving IC1a. Having said all that, we expect that the most likely cause is a soldering fault, as this is the most common problem with do-it-yourself projects. In principle, you could get your clock radio to turn on your stereo system, however, without knowing the details we cannot recommend a particular circuit as there are several diffi­culties to be resolved. First, clock radios are usually very tightly packed and making internal connections can be quite difficult. Second, the Triac will be switching an inductive load which is mainly comprised of the transformer in the power supply of your stereo system. To enable the Triac to switch reliably, it will need a snubber RC circuit connected across it. Without knowing the characteristics of the transformers (or transformers, if more than one unit is involved) we cannot come up with a suitable snubber circuit. Recording video signals on an audio machine Although I have been involved in electronics and computers for a number of years now, I have never yet examined or read about the encoding used for video signals. When I say “video signals”, I am referring to the signal emerging from the “video out” socket on most VCRs. My question is: can this video signal be recorded onto and retrieved from normal audio tape? Obviously, if this was possible it would be a novel and revolutionary way of storing video images. My first thought is that maybe the video signal is too high a frequency to be recorded on audio tape and that the distortion and background noise on the resulting signal would be too great to recreate the original signal. I hope you can prove me wrong, as this would be a great experiment, even if extra circuitry would have to be added to the tape recorder/player involved. If it were possible, video could be recorded on one track and audio on the other. On another matter, maybe you could clear up a problem I am having with a colour monitor I recently acquired. The screen is of the Apple brand and is marked “colour composite monitor”. The video input socket (there is only one socket apart from the mains cord on the whole monitor) is the RCA type, corresponding with the aforementioned “video out” of my VCR. Logically, I thought that just maybe the two signals were compatible, so I connected the screen to the “video out” of my VCR. I then activated the VCR, set the internal tuner to a strong television channel and up came a remarkably clear picture on the monitor in question, except for one minor blemish: no colour! The VCR is not at fault and all adjustments on the exterior of the monitor have been tried. Could you shed some light on the subject? The monitor is not known to be good, so it could well be an internal fault. Unfortunately, I do not have a colour computer video card with the corresponding RCA connections (al- NTSC playback on a PAL TV I am writing to ask for your assistance on a matter which has annoyed me for quite a while. I have a VCR which can do “NTSC playback on PAL TV”. The only catch is that my television is not a multisystem set and, even though I can see a colour picture, the vertical hold is off. That’s OK as long as there is an adjustment for the vertical hold. Unfortunately, my television doesn’t have one. I have heard from somewhere (can’t recall where) that it’s because the tape is outputting 60Hz and our PAL sets only seem to enjoy 50Hz. Is this true? If so, how can I build a device that can convert it to 50Hz – could you send me schematics? If this is not true, then why is it that colour is present and the vertical hold goes off line? I know that when using a “true” NTSC machine, no colour is repro­duced though I have a monochrome card that works just fine with the monitor). Any response would be gratefully received. (A. M., Northbridge, NSW). • Trying to record video signals with an audio recorder is doomed to failure since the bandwidth of typical video signals is at least 4MHz, with the colour intercarrier at 4.49MHz, while most audio recorders are flat out trying to get to 20kHz. We doubt whether even the best audio recorders would be good enough and stable enough to accurately record the line sync signals at 15.625kHz. Even if they were, the resulting recording would only store the lowest of video signals (ie, below 20kHz) and the result would be an extremely blurred grey picture. It has never occurred to us to try it but that’s what we assume the result would be. As far as your computer monitor is concerned, it is likely to be using an American video standard; ie, NTSC. If you had a VCR with NTSC outputs, no doubt it would produce a fine colour picture. However, the Australian video standard is PAL, based on an original German standard and this is incompatible with NTSC composite video signals, as far as colour is concerned. by the TV. It seems that the VCRs that can play back “NTSC ON PAL TV” only decode the colour portion, not whatever is put­ting the vertical hold off. I would greatly appreciate your help on this matter. (P. T., Indooroopilly, Qld). • As you suspect, the reason you cannot obtain a locked pic­ture on your PAL set is that it requires a TV signal with a 50Hz frame rate, not 60Hz as is produced by your VCR when playing NTSC tapes. There is no way that this problem can be solved other than by adjusting the vertical hold control on your TV set. If your set does not have such a control, it may be possible for a local TV serviceman to add this facility to your set and if so, this would be the cheapest solution to your problem. A TV standards converter will not help in this regard since the output signal from your VCR is a mixture of PAL and NTSC; ie, PAL with a 60Hz frame rate. Notes & Errata Mains Music Transmitter & Receiver, May 1995: a number of errors have appeared on the circuit and wiring diagrams for the receiver. C4 is shown as 330pF on the circuit and .0033µF on the wiring diagram; 330pF is correct. C17 is shown as .0047µF on the circuit and .015µF on the wiring diagram; .015µF is cor­rect. C25 is shown as .0047µF on the circuit but not marked on the wiring diagram; the correct value is .0033µF. C28 is shown incorrectly polarised on the wiring diagram but is correct on the circuit. The cathode of diode D2 is shown connected to the junction of C11 and R9 on the circuit but incorrectly shown on the wiring diagram as connected to the wiper of trimpot VR2. To correct this, the track section connecting D2 to the wiper of VR2 should be cut and then linked to the junction of C11 and R9. The circuit board will work as presented but will not mute fully when no carrier signal is present. CTOAN Electronics has advised that all PC boards supplied in the future for this design will be correct. SC July 1995  93 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. CLASSIFIED ADVERTISING RATES FOR SALE Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50 cents for each additional word. Display ads (casual rate): $25 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. To run your classified ad, print it clearly in the space below or on a separate sheet of paper, fill out the form & send it with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy, NSW 2097. Or fax the details to (02) 979 6503. WEATHER FAX programs for IBM XT/ ATs *** “RADFAX2” $35 is a high resolution, shortwave weather fax, Morse & Rtty receiving program. Suitable for CGA, EGA, VGA and Hercules cards. Needs SSB HF radio & Radfax decoder. *** “SATFAX” $45 is a NOAA, Meteor & GMS weather satellite picture receiving program. Needs EGA or VGA plus “WEATHER FAX” PC card. *** “MAXISAT” $75 is similar to SATFAX but needs 2Mb expanded memory (EMS 3.6 or 4.0) and 1024 x 768 SVGA card. All programs are on 5.25-inch or 3.5-inch disks (state which) & include documentation. Add $3 postage. Only from M. Delahunty, 42 Villiers St, New Farm, Qld 4005. Phone (07) 358 2785. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ CHEAP HEATSHRINK TUBING: Australian made, red, black, blue, white, clear, 2.4mm/$1.10pm, 3.2/$1.30, 4.8/$1.70, 6.4/$2.10, 9.5/$2.30, 12.7/$2.70, 19/$3.70, 25.4/$5.10. P&P $3.00 up to 10 metres. Free data sheet. DOMCOR DISTRIBUTORS, 67 King Road, Beechboro, WA 6063. CHEAP PIC STARTERS KIT $89: At last! a complete starter kit for the fantastic PIC16Cxx chips. Includes a REAL programmer for ALL of the PIC family, 16C84 EEPROM chip, 10,000x Re­programmable without UV erasure! Assembler, simulator, full 16C84 data, appli­cation notes! quality software inter- Enclosed is my cheque/money order for $­__________ or please debit my RCS RADIO PTY LTD Card No. ✂ ❏ Bankcard   ❏ Visa Card   ❏ Master Card Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 94  Silicon Chip RCS Radio Pty Ltd is the only company that manufactures and sells every PC board and front panel published in SILICON CHIP, ETI and EA. RCS Radio Pty Ltd, 651 Forest Rd, Bexley 2207. Phone (02) 587 3491 HEATSINKS GREG BALL ELECTRONICS UNIT 8, 9-11 ABEL STREET, PENRITH PH: (047) 31 5661 FAX: (047) 31 5982 face, BBS support and more! Everything you need! Send cheque or money order to NEWFOUND ELECTRONICS, 14 Maitland Street, Geelong West 3218. Ph (052) 241833. STAMP TO PIC Source Disc/Book $89, PIC16C84 Programmer PCB $20, EEPROM CPU $15. Stamp Kit $65, Stamp/PIC 16 I/O Expansion Chip (A/D Option) $20. A $2 coin for my Promo Disk. Covers all items. Don McKenzie, 29 Ellesmere Crescent, Tullamarine 3043. Phone (03) 9338 6286. SATELLITE DISHES: International reception of Intelsat, Panamsat, Gorizont, Rimsat. Warehouse Sale - 4.6m Dish & Pole $1499, LNB $50, Feed $75. All accessories available. VIDEOSAT, 2/28 Salis­bury Road, Hornsby. (02) 482 3100 8.30-5.00 M-F. YOUR UNUSUAL PARTS source: UCN5804B, DS1620, DS1202, DS­ 2401, DS1215, DS1232, UGN3503U, UDN2998W, UDN2993B, MAX038, MAX691, ISD2590, IR LEDs, PCB mounted switches, latest remote control decoder chip, & more. With data sheets. DIY Electronics, tel/fax: (058) 62 1915. 68705 DEVELOPMENT SYSTEM: In Circuit Simulator/Emulator and programmer board. Supports 68705 and 68HC705 series of Motorola micro controllers. Oztechnics, PO Box 38, Illawong, NSW 2234. Phone (02) 541 0310. Fax (02) 541 0734. Email oztec<at> ozemail.com.au. C COMPILERS: everything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC16, 8051/52, 8080/85, 8086 or 8096: $150.00 each. Macro Cross Assemblers for these CPUs + 6800/01/03/05 and 6502: $150 for the set. Debug monitors: $75 for 6 CPUs. All compilers, XASMs and monitors: $450. 8051/52 or 80C320 simulator (fast): $75. Demo disk: $5. Network Software: use serial, parallel, Arcnet or Ethernet to share files and MEMORY & DRIVES Parallax Basic Stamp EX. TAX PRICES AT MAY, 1995 SIMM (all 70ns) Parity/No Parity 1Mb 30-pin $64/58 4Mb 30-pin $220/200 2Mb 72-pin $148/135 4Mb 72-pin $250/232 8Mb 72-pin $489/478 16Mb 72-pin $850/755 32Mb 72-pin $1650/1580 MAC 8Mb P’BOOK CO-PROCESSORS 387S/DX to 40 $405 $90 LASER PRINTER HP with 2Mb $200 COMPAQ CONTURA 8Mb $630 DRAM DIP 1Mb x 1 70ns DIP $7.80 256 x 4 70ns DIP $8.40 256 x 16 70ns DIP $48.00 IBM PS.2 THINKPAD L40/N33 8Mb 4Mb $650 $300 TOSHIBA 3100SX 2100/50 4Mb 8Mb $275 $590 SUN SPARC 5 32Mb SPARC 10/20 64Mb $1870 $3870 DRIVES – SEAGATE 545Mb 14ms 3yr wty $280 1052Mb 12ms 3yr wty $535 2148Mb 9ms 5yr wty $1470 Sales tax 21%. Overnight delivery. Credit cards welcome. Ring for latest prices. We buy & trade RAM. PELHAM Tel: (02) 980 6988 Fax: (02) 980 6991 Shop 6, 2 Hillcrest Rd, Pennant Hills, 2120. printers on your PCs. DOS and Windows compatible. $105 per net­work. All prices + postage. GRANTRONICS, PO Box 275, Wentworth­ville 2145. Ph/Fax (02) 631 1236. TENDER MILITARY/AMATEUR RADIO, audio/phone parts, Morse keys, radio manuals, general. Hadgraft, 17 Paxton Street, Holland Park 4121. (07) 397 3751. SATELLITE EQUIPMENT from SATELLITE PROFESSIONAL. We only sell quality equipment but unlike everyone else, we sell at prices you can afford. Dishes 65cm from $130, LNBs from BS1-IC Only 35 x 10mm with 8 20mA I/O pins Get your circuit development done fast. BASIC STAMP and other gear available. (1) Programming Package for STAMPS; (2) BS1-IC; (3) Proto boards; (4) Chip sets; (5) LCD backpack; (6) Stamp Stretcher; (7) 8K Data EEPROM kit; (8) Scarce components for Parallax app. notes; (9) PIC Source Book; (10) PIC Hobby kit; (11) Weather station equipment. Also (12) 68HC11 development kit. Send 5 x 45c postage stamps for information package and prices for all products. MicroZed Computers PO Box 634 (296 Cook’s Rd), Armidale 2350 V (067) 722 777 F (067) 728 987 Credit cards accepted. $150, receivers from $299. Some of the brands we carry are Chaparrel, Drake, Pace, KTI, Gardiner. Phone or fax Satellite Professionals today on (03) 803 0215. NEW SPRINKLER CONTROLLER KITS: RAIN BRAIN version uses ‘C8 and switch mode supply. Features galore!! Contact Mantis Micro Pro­ducts, 38 Garnet St, Niddrie 3042. Phone/fax (03) 337 1917. UNUSUAL BOOKS: Electronic Devices, Fireworks, Locksmithing, Radar SILICON CHIP FLOPPY INDEX WITH FILE VIEWER Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. Price $7.00 each + $3 p&p. Send your order to: Silicon Chip Publications, PO Box 139, Collaroy 2097; or phone (02) 9979 5644 & quote your credit card number; or fax the details to (02) 9979 6503. Please specify 3.5-inch or 5.25-inch disc. July 1995  95 Microprocessor For Digital Effects Unit Microprocessor For Stereo Preamplifier Advertising Index Now available from SILICON CHIP: the 68HC705-C8P pre-programmed micro­pro­cessor IC for the Digital Effects Unit described in the Feb­ruary 1995 issue. Price: $45 + $6 p+p Payment by cheque, money order or credit card to: Silicon Chip Pub­lica­ tions, PO Box 139, Collaroy, NSW 2097. Phone (02) 979 5644; Fax (02) 979 6503. Now back in stock: the 68HC705-C8P pre-programmed micro­pro­cessor for the Infrared Remote Controlled Stereo Preamplifier (SILICON CHIP, Sept.Oct. 1993). This device also suits the Remote Volume Control published in May & June, 1993. Price: $45 + $6 p+p Payment by cheque, money order or credit card to: Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. Phone (02) 9795644; Fax (02) 979 6503. Altronics ................................ 60-62 Invisibility, Surveillance, Self-Protection, Unusual Chem­ istry and more. For a complete catalog, send 95 cents in stamps to Vector Press, Dept S, PO Box 434, Brighton, SA 5048. Car Projects Book....................OBC Defence Force Recruiting..............9 Dick Smith Electronics........... 12-15 Electronic Valve & Tube Co..........85 Greg Ball Electronics...................95 Harbuch Electronics....................91 Instant PCBs................................96 Jaycar ................................... 45-52 Kits-R-US.....................................90 MicroZed has MicaSOFT Tutor Program. For demo send 4 x 45c to MicroZed (see display advert p.95 for address). I’VE GOT 80 EPROM Emulator PCBs left. Normal Price $30, now $10! 8031’s $2. P&P $5. This PCB can be used for 8051 devel­ opment projects too. See EA Jan/Feb 92. Tantau Australia, PO Av-Comm.....................................81 L & M Satellite Supplies...............37 Macservice...............................3,11 Box 1232, Lane Cove 2066. AH (02) 878 4715. PRINTED CIRCUIT BOARDS for the hobbyist. For service & enquiries contact: T. A. Mowles (08) 326 5590. WANTED: YOUR CIRCUIT & DESIGN IDEAS Do you have a good idea languishing in the ol’ brain cells. If so, why not sketch it out, write a brief description of its operation & send it to us. Provided your idea is workable & original, we’ll publish it in Circuit Notebook & you’ll make some money. We’ll pay up to $60 for a really good circuit but don’t make them too big please. Send your idea to: Silicon Chip Publications, PO Box 139, Collaroy Beach, NSW 2097; or fax your idea to (02) 9970 6503 MicroZed Computers...................95 Oatley Electronics.................. 66-67 Pelham........................................95 Railway Projects Book...............IBC RCS Radio ..................................94 Rod Irving Electronics .......... 27-31 Silicon Chip Back Issues.............96 Silicon Chip Binders....................96 Silicon Chip Bookshop.................19 Silicon Chip Order Form..............59 SILICON CHIP BINDERS These binders will protect your copies of SILICON CHIP. ★ Heavy board covers with 2-tone green vinyl covering ★ Each binder holds up to 14 issues ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A14.95 each (incl. postage in Aust). NZ & PNG orders please add $A5 each for p&p). To order, just fill in & mail the order form in this issue to: Silicon Chip Publications, PO Box 139, Collaroy 2097; Or phone (02) 9979 5644 & quote your credit card details or fax (02) 9979 6503. 96  Silicon Chip Silicon Chip Software..................91 Tektronix....................................IFC _________________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 587 3491. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. • HT Electronics, Shop 4, 8 Roberts Rd, Hackham West, SA 5163. Phone (08) 326 5567. Especially For Model Railway Enthusiasts Order Direct From SILICON CHIP Order today by phoning (02) 9979 5644 & quoting your credit card number; or fill in the form below & fax it to (02) 9979 6503; or mail the form to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. This book has 14 model railway projects for you to build, including pulse power throttle controllers, a level crossing detector with matching lights & sound effects, & diesel sound & steam sound simulators. If you are a model railway enthusiast, then this collection of projects from SILICON CHIP is a must. Price: $7.95 plus $3 p&p Yes! Please send me _______ copies of 14 Model Railway Projects Enclosed is my cheque/money order for $­_________ or please debit my  Bankcard    Visa Card    Master Card Card No. Signature­­­­­­­­­­­­_________________________ Card expiry date_____/_____ Name _________________________Phone No (____)_____________ PLEASE PRINT Street ___________________________________________________ Suburb/town __________________________ Postcode____________