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SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings.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: www.altronics.com.au Vol.8, No.2; February 1995 THIS STEREO POWER amplifier module is based on the latest LM3886 monolithic power ICs & delivers 50W/channel into 8-ohm loads. It’s easy to build & has no adjustments – see page 18. FEATURES FEATURES   4 The Latest Trends In Car Sound, Pt.2 by Julian Edgar Sub-woofer design for cars 14 The 1994-95 CESA Sound & Image Awards by Leo Simpson The best hifi & video products in 16 categories PROJECTS PROJECTS TO TO BUILD BUILD 18 50-Watt/Channel Stereo Amplifier Module by Leo Simpson Uses the latest LM3886 monolithic power ICs 26 Digital Effects Unit For Musicians by John Clarke Produces echo, delay, reverb & vibrato effects THIS DIGITAL EFFECTS UNIT can produce a wide range of sound effects, including delay, reverb, echo & vibrato. It is microprocessor controlled & uses the latest in digital delay technology. Details page 26. 40 A 6-Channel Thermometer With LCD Readout by John Western Displays temperatures from 0-50°C 56 Wide Range Electrostatic Loudspeakers by Rob McKinlay New design is available in kit form 72 Build An Oil Change Timer For Your Car by Darren Yates It warns you when the engine hours are up SPECIAL SPECIAL COLUMNS COLUMNS 53 Computer Bits by Darren Yates Adding a CD-ROM drive to your computer 62 Serviceman’s Log by the TV Serviceman The topsy turvy world of remote control KEEP TABS ON the operation of air conditioners, solar heaters, greenhouses, small animal enclosures & fish tanks with this 6-channel thermometer. It has an LCD readout & can track six temperatures within a 10-metre radius. Turn to page 40. 77 Remote Control by Bob Young Building a remote control system for models; Pt.2 82 Vintage Radio by John Hill Restoring a Tasma TRF receiver DEPARTMENTS DEPARTMENTS   2 3   9 38 Publisher’s Letter Mailbag Order Form Circuit Notebook 88 91 94 96 Product Showcase Ask Silicon Chip Market Centre Advertising Index CAN YOU REMEMBER when you last changed your car’s oil. Build this Oil Change Timer & you won’t need to. It beeps a buzzer & flashes a LED when the engine hours are up – see page 72. February 1995  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) PUBLISHER'S LETTER Technical Staff John Clarke, B.E.(Elec.) Robert Flynn When you waste water, you waste electricity too Reader Services Ann Jenkinson By the time you read this, perhaps the drought which has affected so much of eastern Australia will have begun to break. Let us hope so. If you live in the city, the drought probably has not affected you much and you may be sick of hearing about the need to conserve water. But there is another aspect to water usage that you never hear about in the media and that is the huge amount of energy required to bring the water to us. Advertising Enquiries Leo Simpson Phone (02) 979 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 Forgetting for a moment the enormous investment in dams, pipelines and reservoirs, think about all the pumps which are needed to bring the water to your kitchen and bathroom taps. Again, if you live in a major city, the chances are that your water has been pumped though hundreds and maybe even thousands of kilometres of piping. Pumps use a lot of electricity, as anyone who has a swimming pool will be well aware of. 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. As well as the need for pumping and filtering, the water supply needs chlorine added to it to kill bacteria and algae. When you consider the overall consumption of water in Australia, the amount of chlorine required is huge. Where does all that chlorine come from? It is produced by the electrolytic dissocia­tion of common salt, sodium chloride, and again, this consumes lots of electricity. Some of that chlorine injected into the water supply eventually ends up in the upper atmosphere where it plays havoc with the ozone layer. Printing: Macquarie Print, Dubbo, NSW. After you have used the water, most of it goes into the sewers and again it must be pumped to sewage plants for treat­ment. Much of that treatment involves lots of pumps and inevi­tably, it involves further chlorination. After that, the waste water it is pumped into rivers or the sea. So while you don’t think about it, the biggest cost of water is the charge for electricity in processing and transporting it to you and then taking the waste water away. 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) 979 5644. Fax (02) 979 6503. That means that even if Australia had plentiful supplies of water, we should not waste it because so much electricity is required to bring it to us. Most of that electricity will have been generated by coal burning power stations. Inevitably, when you have a glass of water, you are consuming coal, or oil, or natural gas. Think about that next time you turn on a tap. 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 MAILBAG More feedback on bogus RAMS I would like to add a few things to December’s story on the RAM scam originating from Taiwan. (1) I spoke to eight re-sellers and importers. Six sold the bogus SIMMs. None of them knew that the parity chip was not a memory chip. One of the six also sold the genuine SIMMs as AAA grade RAM (the bogus SIMMs as AA grade). None were aware of the scam. One supplier sold only the genuine product and knew of the bogus chips. His business was geared for high reliability users where price was a small concern. This last supplier also sold only the genuine article but was getting killed on price. These suppliers (and I suspect most in Australia) sold the bogus SIMMs as genuine 9-bit SIMMs and purchased them in good faith. The scam’s perpetrators are in Taiwan, not Australia. (2) These SIMMs do work in new computers. They cause prob­lems in older computers where timing requirements are tighter. This is important if you are upgrading an existing computer. (3) Computers can run without a parity bit. Most IBM-com­patible main boards allow the parity to be disabled so they run with 8-bit SIMMs. Bogus SIMMs are 8-bit SIMMs that have been re-worked to look like 9-bit SIMMs. The parity chip is not a memory chip but it is labelled with a legitimate memory chip number; it even has a meaningless access time printed on it. The SIMM manufacturer is therefore engaging in outright fraud. (4) Parity is important in applications where the data has significant real value. A true parity bit would have a 98% chance of catching each memory error and the computer could be repaired with little, if any, data loss and minimal down time. SIMMs with the bogus parity bit will not just fail to find an error. It will attempt to hide it from the user, DOS and the PC. (5) I disagree with your pointers on how to spot a fake. The best method is to use a multimeter and check that the parity chip (the chip closest to pin 30 on the SIMM) is not connected to any data line it should not be (pins 3, 6, 10, 16, 23, 25 on 1Mb and 4Mb 30-pin SIMMs). I have seen the bogus SIMMs made with US, Japanese, Korean and European chips. Just asking for Japanese or US memory won’t help. (6) What can you do? Be kind to your computer supplier; he may not have known. Don’t buy a computer based on price alone. Expect to pay $40-$100 more for good RAM. Ask for the good stuff and check that you’ve got it. As a marketing ploy, maybe they could call the bogus SIMMs eight and a half bit? David Eather, Chermside, Qld. Night viewer works well Many thanks for this interesting project published in the November 1994 issue. I obtained a 25mm kit from Oatley Electron­ics and am most happy with the performance of the completed unit. One small problem I encountered was intermittent flashover between the ends of tubes 2 and 3. This is not too surprising as the spacing is only 5mm or so and the Radiotron Designer’s Handbook suggests that the dielectric strength of this air gap is not more than 5kV. The problem was cured by overfilling the gap with silicone sealant. I potted the two triplers separately in two short lengths of PVC tube with colour-coded input and output leads. I found that my power supply would operate happily down to about 3V, below which the inverter was unable to charge the dump capacitor quickly enough to maintain the EHT so I settled for a 6V supply of four AA cells with a 100Ω series resistor. The current drain is 12.5mA. An apparently completely dark scene appears to be bathed in bright sunshine through the viewer and still makes an impact, even when you know what to expect. Looking at the night sky, I believe I can see stars down to about 10th or 12th magnitude, which is six to eight magnitudes better than with the naked eye in this location. I SILICON CHIP, PO Box 139, Collaroy, NSW 2097. am looking forward to a country trip with a decent dark sky when the performance should be even better. For general viewing, I found the screen image a bit too bright for comfort and there is also a fair amount of random scintillation, even in total darkness. I have therefore added a switch across one of the neons to reduce the EHT when appro­ priate. This still gives adequate sensitivity and reduces the screen brightness and scintillation to a more comfortable level. Incidentally, the current drain increases to 13.5mA on reduced power because the .047µF capacitor is dump­ ed more frequently. A. March, North Turramurra, NSW. Thanks for your feedback on the Night Viewer. We doubt whether the limiting magnitude will improve if you go to a dark sky site because the limit is more likely set by background noise and scintillation of the tube. Your idea of reducing the EHT is probably effective but will also reduce the sensitivity. Dolby surround sound explanation flawed I have read your article in the October 1994 issue entitled “Dolby Surround Sound: How It Works”. I am surprised to see several fundamental mistakes. Firstly, the surround channel is not delayed to provide an echo or reverberation effect in the cinema; quite the opposite in fact. By nature of the matrix system used, some dialogue inevi­tably “bleeds” into the surround channel. When two identical sounds arrive at the listener about 20ms apart, the brain inter­prets the direction of the source of the sound as that of the first arriving sound. By ensuring that the listener hears the surround channel about 20ms later than the front channels, any front to surround crosstalk will not be heard by the listener. If this was not done the listener would hear an echo, as the sound from the nearby surround speakers would reach them before that of the front channels. The exact delay continued on page 89 February 1995  3 Pt.2: Sub-Woofer Design Car Sound In any current state-of-the-art car sound system, a sub-woofer is de rigeur especially amongst those inter­ested in either competition or lots of bass. In Pt.2 this month, we look at some of the trends in sub-woofer design. By JULIAN EDGAR In the past, car sound systems used loudspeakers mounted on the rear parcel shelf as their major bass units, with 6 x 9-inch designs most common. The cone area of a 6 x 9 speaker ap­proaches that of an 8-inch design, but without the packaging difficulties associated with fitting such a large speaker into this sometimes-cramped location. When fitted by the car’s origi­nal manufacturer, 6-inch speakers were most frequently used. Placing the speakers on the rear deck allowed them to use the whole of the boot volume as their enclosure. In fact, with boot volumes of hundreds 4  Silicon Chip of litres, the speakers were effectively being used in infinite baffle form. Since the resonant frequency of high quality 6 x 9-inch loudspeakers is down in the 60Hz range, quite good bass could be developed. Other locations commonly used for speakers have included the front doors, kick panels, dashboard and rear quarter panels. Each of these locations pose major problems in terms of bass response, with the most constraining factor being the lack of volume behind the speaker. A speaker mounted in a very small sealed enclosure will have a high resonant frequency because of the stiffening effect which the small air volume has on the compliance of the cone suspension. Sub-woofers When bass below 60Hz is wanted, it is necessary to match specialised drivers to a detailed enclosure design. Initially, most woofers were mounted in a similar way to the other speakers; ie, mounted on the rear deck and using the full boot volume. However, as woofers in cars increased in size and even more bass performance was demanded by customers, sub-woofer enclosures within the boot space were constructed. The enclosure volumes were usually based on the manufacturer’s recommendation and were usually acoustic suspension (sealed box) designs. In the United States, “sound-off” competitions started becoming popular and these caused a dramatic change in the expec­ tations of the consumer. Part of the competition judging involves the use of a spectrum analyser to measure the in-car frequency response and so the demand for a flat response down to below 32Hz increased. Previously, any bass was deemed to be good but when variations in response of ±3dB or more could be read off the judge’s printout, consumers became far more exacting in their demands. Sub-woofer design Most top-quality car sub-woofer systems are now designed using the computer software package “Term Pro”. This program has been devised specifically for sub-woofer enclosure design in cars and follows on from the very successful “Term One” package. Steve Burgess of the Adelaide car sound company Cartronics took me on a guided tour of the package. In addition to the traditional two designs of loudspeaker enclosure (ie, bass reflex and acoustic suspension), the program also produces bandpass and isobaric designs. In bandpass enclosures, the speaker is mounted on the dividing wall of a two chambered box. Vents may be used in either one or both of the chambers. By contrast, an isobaric design uses two drivers mounted concentrically in close proximity. Generally, the speakers are mounted face-to-face and so are driven out of phase. In Steve’s own Commodore demonstration car, the boot-mount­ed sub-woofer uses a 6th order bandpass ported design, with the central chamber tuned to 100Hz and the outer two chambers to 38Hz. The details of the system are easy to see because the enclosure is constructed entirely of Kenwood’s HQW-300 sub-woofer driver has a maximum power handling of 300 watts RMS. The voice coil diameter is 80mm & the speaker uses a diecast aluminium frame. Claimed frequency re­sponse is 18Hz - 2kHz. transparent polycarbonate! When using the Term Pro software to design a sub-woofer enclosure, the first question that Steve asks of the customer is the type of music that he or she likes to listen to. Although a flat response can be engineered down to almost below audible level, that may not be what the customer wishes to hear. For example, tight, punchy bass of the sort encountered in current “rap-techno” music is best answered by the use of a sealed enclosure. This will also require the use of a power- ful amplifier, as this sort of enclosure provides low efficiency. Other types of music require different enclosure designs – a ported single chamber for classical music, for example. For one cost-no-object system, Steve asked the customer to bring in his 10 favourite CDs. An analysis was then made with a spectrum analyser to determine which bass frequencies were most common in this music. In this case, almost all of the bass mate­rial fell into the 80-120Hz range and a design capable of strong­ly reproducing bass in this area was duly built. Powerful amplifiers are used to drive car sub-woofers. This Earthquake amplifier has an output of 50 watts for each of its four channels, at less than 0.15% THD. February 1995  5 An elaborate 6th order bandpass enclosure is used in this demon­ stration vehicle. The enclosure, which is built into the boot behind the back seat, is made of clear polycarbonate. The whole system (obviously more than just the sub-woofer) took three months to develop and cost $5000. Driver selection The next step, after looking at the type of bass response wanted, is to select the driver. If you have not looked at car woofers recently, the range available is quite staggering. As an example, the “Earthquake” line-up includes a 10-inch unit priced at $239. It boasts a 2.5-inch diameter voice coil, a power han­dling capability of 300 watts, a 1.9kg magnet and a sensitivity of 96dB at 1 watt/1 metre. Most top manufacturers are also quot­ing Thiele/ Small parameters like Qts, Vas and so on. It’s this that allows the software to work so well. The program has the specifications of 612 drivers loaded into it, with space to store the specifications for up to 1000 drivers. Selecting These two photographs show the types of enclosures which the Term Pro software package is capable of designing. 6  Silicon Chip from one of those available, Steve decided to use a top-quality $600 Soundstream unit. Its specifications include a nominal diameter of 10 inches, an Fs (resonant frequen­cy) of 35Hz, a Qts (total Q) of 0.376, a Vas (equivalent com­pliance air volume) of 1.8 cubic feet, and an Xmax (maximum cone excursion) of 0.087 inches (the program can run in either metric or imperial units, with the latter still used most frequently in speaker design). The sensitivity was quoted as 90dB. The program was asked to design an enclosure which would give the flattest frequency response (dubbed the Maximally Flat design). The result was a sealed high-pass enclosure of with an internal volume of 0.71 cubic feet (20 litres). Furthermore, the program predicted that the response would be virtually ruler-flat from 120Hz to 1000Hz – see Fig.1. The predicted low frequency response was -3dB at 66Hz and -10dB at about 38Hz. Next, a ported high-pass enclosure was tried. Given that the program had already recommended a sealed high-­ pass design for the flattest response, improvement in this area obviously could not be expected. However, the -3dB point was substantially low­ered to 40Hz, while the -10dB point now occurred at about 30Hz (meaning that the roll-off was also much steeper) – see Fig.2. This enclosure design required a box volume of 38 litres – almost double the volume of the previous design. Whether or not it could be physically fitted into the vehicle would be another factor in determining the usefulness of this approach. Finally, a purposely mismatched enclosure design was picked. The isobaric 4th order bandpass box substantially reduced the efficiency of the loudspeaker – it was about 7dB down com­pared to the other two designs. A much more powerful amplifier (over Fig.1: the Term Pro enclosure design software was used to design an enclosure which would give the flattest possible response from a specified Soundstream driver. The result was a sealed enclosure with a volume of 0.71 cubic feet. Fig.2: next a ported enclosure was tried. The bass roll-off is now steeper but the -3 dB point has dropped to about 40Hz. Cartronics’ Manager Steve Burgess using the Term Pro software to design a car subwoofer enclosure. February 1995  7 rectangular boxes can be designed. The resulting bass response achieved by designs based on this package and using high-quality drivers is exceptional. Amplifiers & crossovers Fig.3: a deliberately-mismatched isobaric 4th-order bandpass enclosure was also tried. In this case, the speaker efficiency markedly dropped, while there was no improvement in bottom-end response. Fig.4: port design can also be carried out by the software. Here the port diameter has been user-fixed at 50mm, with the program then calculating the length. twice the power rating) would therefore be required to get the same sound pressure level. As well as the loss in efficiency, this system has a steeper bass roll-off than either of the other two proposals. Port design The software can be also used to design the size and length of the port required in vented designs. The internal diameter of the port can be specified by the user, allowing common sizes (2-inch, 3-inch, etc) to be entered, with 8  Silicon Chip the program then calculat­ing the appropriate length of the vent. If the port diameter is too small, then the speed of the air flow back and forth within it can make an audible (chuffing) sound. The predicted port velocity is provided by the program, so that this figure can be kept appropriately low. Finally, the dimensions of the box can be listed. Certain of the box dimensions can be fixed by the user, with the program calculating the others so as to retain the same internal volume. Wedge-shaped as well as Due to the ear’s poor sensitivity to low frequencies and the low efficiencies encountered in some sub-woofer enclosure designs, a separate power amplifier is generally specified to drive the sub-woofer. Fortunately, the omnidirectional nature of bass notes means that only one sub-woofer is required. This also means that a stereo amplifier can be used in bridged mono config­uration to provide the extra power required to drive the sub-woofer. An example of an amplifier that’s suitable for sub-woofer duties is the US-made $500 Earthquake PA2030 which has a mono output of 150 watts into a 4-ohm load, accompanied by a maximum total harmonic distortion (THD) of 0.015%. An alternative ap­proach is to use a 4-channel amplifier, with two channels driving deck-mounted two- or three-way speakers, and the second pair of channels run in bridged mode to drive the sub-woofer. In my own car, for example, a $440 Coustic 45-watt x 4 AMP268 is used, with one pair of channels bridged to give around 90 watts. While these sorts of power outputs initially appear exces­sive (how loud do you want it?), in a moving car which has extra­neous tyre, wind and exhaust noise, the bass notes can be easily lost. Add in low-frequency panel resonances and the power re­quired to drive a sub-woofer to audible levels in a moving car can be quite high. Finally, a crossover network must be employed to prevent unwanted frequencies from being fed to the sub-woofer. For this reason, many amplifiers have a built-in sub-woofer output with a variable crossover point. Indeed, the Coustic amplifier mentioned above has both low and high-pass crossovers built-in, with the low-pass design variable between 32Hz and 400Hz. Either passive crossovers can be used or electronic parametric equali­ sation modules like the Audio Control EQX unit can be employed. As well as having 13 equalisation controls, this unit has a 24dB/octave sub-woofer SC crossover output. 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 February 1995  9 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 Winner of the CD category was the Yamaha CDC-745 5-disc player. This has a number of worthwhile features including “peak search” which finds the highest level signal on a disc & lets you set the correct recording level on your tape deck for copying. The 1994-95 Sound & Image Awards The 1994-95 hifi awards were judged in 16 categories and a total of 243 products were submitted. Two Japanese companies, Yamaha and Pioneer, did very well with several awards each but some awards went to companies that are not well known at all. By LEO SIMPSON The 1994-95 hifi awards, or to give them their full name, the 1994-95 CESA Sound & Image Awards, are a cooperative venture conducted by “Sound & Image” magazine in conjunction with the Consumer Electronics Suppliers Association and have been conduct­ed each year since 1989. Four judges were involved with these latest awards, listed as follows: Greg Borrowman, editor of “Australian Hifi” magazine; Paul Burrows, technical editor of “Sound & Image” magazine; Les Cardilini, lecturer in electronics at the RMIT and for many years a writer for “The Age” newspaper; and Leo Simpson. We don’t have the space to list all the products that were up for judging so this report will concentrate mainly on Arguably the lowest power unit in the amplifier category was the NAD 310, rated at just 20 watts per channel. Our taste is for at least 10dB more. 14  Silicon Chip the winners and runner-up contenders. Nor do I propose to go into how the judging was done except to state that it was a tedious and time-consuming process involving comparison of performance speci­fications, features and prices and, most important, listening tests. Some winners stood out like a beacon in their category while in others it was quite difficult to separate the winner from the runner-up. However, it was eventually done and these are the results. Best amplifier There were 18 entries in this category and they ranged in price from a low $349 for the NAD 310 amplifier to $3977 for the ME 850 power amplifier, an Australian made system built like a battleship and using little or no negative feedback. The NAD310 did not get an award but it must stand out as the one with the lowest power; just 20 watts per channel. The winner was a brand relatively new to the scene, the Grundig Fine Arts model V3, rated at 120 watts per channel into 4Ω loads and priced at $899.00. The V3 stands out because of its value for money, its styl­ing and its easy-to-use remote control. One particular feature that was commended Winner in the amplifier category was the Grundig Fine Arts model V3. It is rated at 120 watts per channel into 4Ω loads & is priced at $899. It has a commendable feature whereby it automatically rotates its volume control to zero in the event of a short circuit across the speakers. Below: winner of the tuner category was the Pioneer F-403 which can store up to 40 stations together with 4-letter names – sounds fairly provocative to us. What would you call the parliament/news station on 630kHz? Definitely the swankiest equipment submitted in the 199495 hifi awards was this Marantz 1020 Slim series system which is teamed with Mordant Short loudspeakers. Consisting of a 45 watt per channel receiver, a CD player and a cassette deck, the system has fully concealed controls which are revealed by motor driven dress-panels which open at the touch of tiny buttons at the sides. FX403, priced at $429. Some of its features include random presets for 40 stations, 4-letter station name memory, RF attenuator, selectable IF bandwidth and three-speed station search. Best cassette deck was found by accident when using the amplifier during listening tests on loudspeakers. As with virtually every amplifier these days, the V3 can withstand momentary shorts across the loudspeaker outputs, without blowing fuses. However, many amplifiers will dissipate a lot of power and many eventually overheat if the short circuit condition is maintained. The Grun­dig V3 ensures against this by rotating its volume control fully anticlockwise when a short is detected. This is a brilliant “common-sense” innovation which is likely to be seen on many other amplifiers in the future. Two entries which were highly commended were the Yamaha AX-380 and Kenwood KA-4060R. Best receiver & tuner There were 12 entries in this category with the winner being the Pioneer SX-303R. Highly commended were the Technics SA-GX170 and the Yamaha RX-385. Eleven tuners were submitted, ranging in price from $1699 for the Audio­ lab 8000T down to $359 for the Technics ST-GT350 (how do they come up with these numbers?). The problem with judging tuners is that many of them have similar performance, operating features and price. In this case, the winner was the Pioneer Another hotly contested category, with 11 entries priced from $499 for the Philips FC-930 to $999 for the Sony TC-K717ES. Many decks had dual transports which does add convenience if you are dubbing but the judges went for the Yamaha KX-580, a single transport deck with maximum Dolby features (ie, Dolby B, C, S & HX Pro), automatic tape tuning and bidirectional intro scan. It sells for $599.00. The Sony TC-K717ES was highly commended. Best CD player In this category the entries fall into single CD players or multi-disc models. The price range for this category was large, ranging from $499 for the Winner of the cassette deck category was the Yamaha KX-580, a single transport deck with maximum Dolby features (ie, Dolby B, C, S & HX Pro), automatic tape tuning & bidirectional intro scan. February 1995  15 Yamaha has been prominent with Dolby Pro-Logic receivers for quite a few years so it was no surprise that it won the home theatre category with the model RXV870, priced at $1599.00. It has three channels rated at 80 watts into 8Ω loads & two rear channels rated at 25 watts. Technics SL-PD867 5-disc player to $3399 for the Quad 67. Included in this range was the JVC-XLMC100 100 disc player priced at $2499. It is a brilliant product which might have fared better if it had been entered in the category for technical innovation. As far as sales are concerned, the multi-play models have much wider acceptance than single disc units and the judges went along with the majority of consumers in plunking for a multi-play model, the Yamaha CDC745 5-disc player. This has a number of worthwhile features including “peak search” which finds the highest level signal on a disc and lets you set the correct recording level on your tape deck for copying. Another worthwhile feature is PlayXchange; when five discs are loaded, the one that is playing is on a separate tray. It will continue to play while the main tray slides out so that the other discs can be replaced. The Yamaha CDC-745 is priced at $599.00. Digital audio product of the year This category includes MiniDisc and DCC products although it is fair to say that none of these has had outstanding success to date – they are just too expensive. Even so, they are brilli­ant examples of large scale integration and the Sharp MDM-11ABK is quite incredible. It is so small that you need to remind yourself that it is a full MiniDisc recorder and it includes a titling facility. It is priced at $1199.00. Loudspeaker of the year As you might expect, the sky is the limit as far as loud­speaker prices are concerned so they are split into In the over 52cm class, which included wide screen sets, the winner was the Hitachi CMT-2998, priced at $2495. This includes surround sound & picture noise reduction. 16  Silicon Chip three price ranges: up to $700; $701 to $2000 and $2001 to the stratosphere. The lowest price range was the most hotly contested, with no less than 21 entries. The winner was the Krix Equinox. In the middle category the winner was the Dynaudio Image 3, Mk II, a very successful speaker designed in Australia. Its stablemate, the Dynaudio Image 7, figured in the closely contested open category ($2001 and up) but it was edged out by the more expensive and considerably larger Mirage M3S1. Home theatre When you look at the whole hifi scene this is the one with the most interest and the most sales. What we’re talking about is full-on stereo receivers with Dolby Pro-Logic decoding, DSP (ie, ambience simulations of theatres, churches, jazz clubs, etc), and five power amplifiers, although oddly, some of the entries were speak­ ers for surround sound. Be that as it may, the winner was the Yamaha RXV870 priced at $1599.00. It has three channels rated at 80 watts into 8Ω loads and two rear channels rated at 25 watts. While many of the contenders in this class offer a lot of electronics for the price, they also impressed the judges for their downright complexity – do average users ever come to grips with all their features? Audio systems These used to be called “rack systems” but now they embrace the full Big, bold & bright, the Pioneer SD-M1407 40-inch rear projec­tion set won the award for best video projection product. It can handle PAL, NTSC & SECAM programs & has hifi stereo sound. CAM) and Teletext. What more could you want? In the over 52cm class, which included wide screen sets, the winner was the Hitachi CMT-2998, priced at $2495. This in­cluded surround sound and picture noise reduction. Video projection units Winner of the hifi VCR category was the JVC HR-J615 machine which includes G-code programming & very flexible editing facilities. gamut from economy to quite elaborate systems which anyone would be proud to own. Some of them are very elegant but they have prices to match. So much so, that there were three price ranges: up to $1000, $1000 to $2000 and over $2000. In the lowest price range the winner was the Denon D-08 while in the mid-range the Kenwood UD-552 got the gong. In the over $2000 class, the Grundig Fine Arts R1 Rack was the clear winner, with the same sort of features that made the V3 model the winner in the ampli­fier category. Also highly commended were the Pioneer XP-840F and the Mar­ antz 1020 Slim series teamed with Mordaunt Short loudspeakers. The Marantz system certainly was one of the most elegantly styled products of the year. Other categories included car audio, portable audio, combo units (ghetto blasters?), video cameras and colour TV sets. The latter was split into 51cm and under, and over 52cm. Even in the smaller class, the sets are packed with features, as evidenced by the winner, the Sanyo CPP3186TX (another of those super numbers again!). Apart from a flat picture tube (pretty standard amongst TV sets), this unit had front mounted inputs, stereo audio/video in/out, SCART connector, multi-system (ie, PAL, NTSC and SEOne of the cheapest products entered in the CESA awards, the original G-Code programmer distributed by Philips took out the award for technical innovation. With home theatre products being the big movers this year, it follows that video projection units would be on the up and up to give the largest of screens. Two contenders stood out: (1) the Pioneer SDM-1407, a rear projection 40-inch set (price $7500) with multi-system reception and a host of features; and (2) the Sanyo PLC-200P LCD video projector (price $7999.00) which was reviewed in the March 1993 issue of SILICON CHIP. The Pioneer set took out the winner’s award because of its large bright picture and the fact that it could also serve duty as a normal set. The Sanyo projec­tor, on the other hand, was highly commend­ed for its technical innovation, absolutely flicker-free picture and a screen size limited only by the room. Video recorders Now you might think of VCRs as being fairly ho-hum products but there has been a lot of development over the last few years and the features now included are quite surprising. Many VCRs now have G-Code included for hassle-free recording. The VCR manufac­ turers have seen the light very quickly on this innovation and there has been a rush to jump on the bandwagon. There were two categories for VCRs, one for mono machines and the other for hifi units. In the result, the machines that won in both categories included G-Code programming. The mono machine was an Akai VSG415EA while the hifi unit was a JVC HR-J615, a machine notable for its flexible editing features. Having mentioned G-Code and its impact on VCR programming, it is only fitting that the original G-Code programmer, the Gemstar VIP-88A, distributed by Philips and reviewed in the April 1994 issue of SILICON CHIP, would win the category for technical innovation. At $125 this product has swept the market. Interest­ ingly, it was by far the cheapest product in its SC category. February 1995  17 A 50 watt per channel stereo amplifier module Want to build a stereo power module which requires few components & no adjustments? This module is the answer. It deliv­ers 50 watts per channel into 8-ohm loads or, with a reduced supply rail, 60 watts per channel into 4-ohm loads, using the LM3886 mono­lithic power IC. By LEO SIMPSON & BOB FLYNN This stereo module came into being for several reasons. First, it supersedes the 50 watt per channel amplifier board which we published in the February 1992 issue of SILICON CHIP. This board was based on the plastic Darlington transistors TIP142 & TIP147 but these are no longer available. Hence, this new module is a drop-in replacement for the 50W/ channel board and has the advantages that it requires no quiescent current adjustment, has better thermal stability and is short-circuit proof. Second, while the 50 watt module based on the LM3876 and featured in the March 1994 issue has been very popular, we wanted to feature the later version of this monolithic IC, the LM3886. This version has the advan18  Silicon Chip tage of being able to deliver slightly higher power into 4Ω loads, provided the supply rails are re­duced. We’ll talk more on this point later. Third, while the abovementioned module was quite popular, it was clear that there was a need for a stereo version, prefer­ably also with provision for ±15V supply rails for a preampli­fier. Performance A look at the performance panel shows that this new module is a very respectable performer, roughly equivalent overall to the now superseded module featured in our February 1992 issue, and subsequently in the March & April 1992 issues, as the Studio Twin 50 amplifier. We are also featuring performance graphs taken with our recently acquired Audio Precision audio test set. Working under the control of a computer, this instrument can take stereo per­formance measurements in a fraction of the time it takes using the old methods. Fig.1 shows the harmonic distortion versus frequency for the module, at 25 watts into an 8Ω load. As you can see, the distortion is below .01% for frequencies below 3kHz. In fact, for much lower powers which is where the amplifier would operate for most of the time on normal program material, the distortion would be around .005% or less. Fig.2 looks to be very similar to Fig.1 but in this case it shows distortion versus frequency at 30 watts into a 4Ω load. As you might expect, the distortion is a little worse over the whole spectrum but is still pretty respectable. Fig.3 depicts the THD (total harmonic distortion plus noise) versus power into an 8Ω load at a frequency of 1kHz. The slow rise in harmonic distortion as the power is reduced below 10 watts is a natural consequence of the increasing noise in the measurement. However, you should not conclude that the amplifier is noisy; far from it. It is very quiet, with an unweighted signal to noise ratio of -107dB with respect to 50 watts. In fact, a few calculations on that noise level will reveal that the THD shown at 100 milliwatts is virtually all noise – the true harmonic distortion would be under .003%. Fig.3 also shows the very rapid rise in THD as the amplifi­er reaches and exceeds the clipping point, just below 50 watts. Fig.4 depicts the separation between channels of the modu­le and, as you can see, this exceeds -80dB over most of the audible spectrum. We should note that this high degree of separation can be easily degraded if the signal connections to the module are not made correctly. In general, you must avoid earth loops at any cost. To do this, the earth of the signal source driving the module must only connect at one point, preferably the earth for the preamp supply. The shielded cables for the stereo signal source must only be earthed at the source, not at the module PC board, even though we have provided earth connections. However, we are getting a little ahead of ourselves. AUDIO PRECISION AMP-THD THD+N(%) vs FREQ(Hz) 5 20 DEC 94 20:43:19 1 0.1 0.010 0.001 20 100 1k 10k 20k Fig.1: harmonic distortion versus frequency at 25 watts into an 8Ω load. AUDIO PRECISION AMP-THD THD+N(%) & THD+N(%) vs FREQ(Hz) 5 21 DEC 94 01:15:02 1 Circuit details Fig.5 shows the circuit details of the module, with just one channel shown. The circuit of each power amplifier is very similar to that of the LM3876 50W module published in the March 1994 issue of SILICON CHIP. The main difference is that the LM3886 has a positive supply connection to pin 5 (O/C on the LM3876). Now let’s just briefly describe the main points of the circuit. The input signal is coupled via a 1µF MKT polyester capacitor and then via an RC network consisting of a series 1kΩ resistor and shunt 220pF capacitor. This is an RF suppression network. The voltage gain of the amplifier is set to 23 by the 22kΩ nega­tive feedback resistor from pin 3 to pin 9, in conjunction with the 1kΩ resistor and 47µF capacitor. The latter capacitor and the 1µF input capacitor sets the low frequency roll-off to about -1dB at 15Hz. The output drives the loudspeaker via an RL network con­sisting of a 10Ω resistor in parallel with an inductance of 0.7µH. This acts in conjunction with the Zobel network 0.1 0.010 0.001 20 100 1k 10k 20k Fig.2: harmonic distortion versus frequency at 30 watts into a 4Ω load. comprising the series 5.6Ω resistor and 0.1µF capacitor to ensure that the amplifier is stable under varying load conditions. Muting We’ve included the optional mute function at pin 8. This is connected via link LK1 and a 39kΩ resistor to the negative supply rail and this disables the muting. To mute the amplifier, a switch should be connected in series with LK1 and when the switch is open the amplifier will mute the signal by 110dB which will be below the noise level. The 22µF capacitor provides a slow turn-on for this feature. Power supply The power supply uses a 50V centre-tapped transformer feed­ing a bridge rectifier and two 4700µF 63VW capacitors. The trans­ former should be rated at 160VA as a minimum; February 1995  19 AUDIO PRECISION THDVSLVL THD+N(%) vs measured LEVEL(W) 20 20 DEC 94 20:00:57 10 1 0.1 0.010 0.001 0.1 1 10 PARTS LIST 1 PC board, code 01102951, 248 x 58mm 2 single sided heatsinks, 72mm high (Altronics Cat. H-0522) 2 TA11B IC mounting kits 8 20mm fuse clips 4 2A M205 20mm fuses (use 3A for 4Ω loads) 2 3-way PC terminal blocks (Altronics Cat P-2035) 13 PC pins 2 15mm tapped standoffs 2 3 x 10mm machine screws 1 1-metre length 0.5mm enamelled copper wire 3 0.25-metre lengths 32 x 0.2mm hook-up wire (three different colours) 100 Fig.3: THD (total harmonic distortion plus noise) versus power into an 8Ω load at a frequency of 1kHz. Semiconductors 2 LM3886 audio power amplifiers (IC1,IC2) 1 KBPC10-04 bridge rectifier 1 LM7815T 3-terminal regulator (REG1) 1 LM7915T 3-terminal regulator (REG2) Capacitors 2 4700µF 50VW electrolytics 4 100µF 63VW electrolytics 2 100µF 16VW electrolytics 2 47µF 63VW electrolytics 4 22µF 16VW electrolytics 2 1µF 63V MKT polyester 6 0.1µF 63V MKT polyester 2 220pF 50V ceramic Resistors (0.25W, 1%) 2 39kΩ 4 330Ω 1W 4 22kΩ 2 10Ω 1W 4 1kΩ 2 5.6Ω 1W Fig.4: separation between channels of the module between 20Hz and 20kHz. anything less and the power output will be degraded. If you plan to drive 4Ω speakers, the transformer should be a 40V centre-tapped unit, again rated at 160VA. Positive and negative 3-terminal regulators have been included to provide ±15V supply rails to a preamplifier board. If you will not be using this feature, these regulators and their asso20  Silicon Chip ciated components should be deleted. If the 3-terminal regulators are not loaded with at least 470Ω each (ie, to draw about 30mA), their input voltage ratings of 35V may be exceeded when the AC mains voltage is high. Construction All of the components for the stereo module except the heatsinks are in- stalled on a PC board measuring 248 x 58mm and coded 01102951. Fig.6 is the component overlay diagram. You will notice that there is a vacant portion of board between the two power amplifiers. This might seem like a mistake at first sight but was in fact necessary to accommodate the mounting centres of the specified heatsinks. The amplifier channel closest to the power supply compon­ents has its supply rails directly connected via the PC board tracks. The other amplifier has its connections made via heavy duty hook-up wire which is twisted to minimise radiation of signal compo- GND INPUT 47uF 22uF 22k SPEAKER 1 100uF SPEAKER GND IC1 3886 100uF +35V 22uF SPEAKER 330  1W +15V -15V 0V 100uF 100uF REG2 47uF 25VAC CT 25VAC the copper pattern thoroughly for any shorts or breaks in the copper tracks. If you find any, they should be fixed, using either a sharp utility knife for shorts or a soldering iron and solder to bridge open circuits. This done, install the PC pins and BR1 REG1 47uF 330  1W nents. These measures are necessary to maximise the separa­tion between channels and also to minimise harmonic distortion when both channels are being driven. Before you begin assembling any components onto the board, check February 1995  21 24 x 0.2 INSULATED WIRE ON COPPER SIDE OF BOARD -35V 4700uF 0V 4700uF F3 Stability �������������������������������������� unconditional +35V F2 Output power ����������������������������� 48 watts per channel into 8Ω; up to 60 watts into 4Ω (see text) Frequency response at 1W ������� 16Hz to 200kHz ±1dB Input sensitivity �������������������������� 870mV RMS (for full power into 8Ω) Harmonic distortion ������������������� <.05% from 20Hz to 20kHz; typically <.005% Signal-to-noise ratio ������������������ 107dB unweighted (20Hz - 20kHz); 109dB A-weighted. Protection ���������������������������������� 2A fuses plus SPiKe(TM); 3A fuses, if driving 4Ω loads. Damping factor �������������������������� >150 (for 8Ω loads) SPEAKER GND 100uF 100uF 0.1 Performance Measurements GND INPUT -35V 47uF 22k 1 Fig.5: the module is based on two LM3886 audio amplifier ICs, although only one channel is shown here. IC1 3886 -15V Fig.6 (below): follow this overlay diagram when installing the parts on the PC board. Note the supply connections via twisted hook-up wire to one channel. OUT 2x33 0  IN REG2 1W -35V 330  1W GND 330  1W CASE 100 16VW 0.1 GND E 0.1 47 63VW +15V 100 16VW 5.6 1W 4700 50VW GND 10 / L1 47 63VW 39k N 4700 50VW 220pF 25V 1k 25V 240VAC 1k T1 L1 : 16T 0.5mm DIAMETER ENAMELLED COPPER WIRE WOUND ON 10  1W RESISTOR BR1 KBPC10-4 +35V REG1 2x33 0  7815 1W OUT IN 22k F1 1A 0.1 -35V 100 63VW 1uF A 11 22 16VW F3 1 F3 2A LK1 F2 0.1 0.1 47 16VW 39k 8W 0.1 5.6 1W 0.1 4 22k 1k 10  1W 3 5.6 1W 7 8 5 10 / L1 9 IC1 LM3886 39k 220pF 1 220pF 22k 10 1k INPUT 1k L1 0.7uH 1k 1 +35V 22k 0.1 100 63VW 1uF F2 2A Fig.7 (left) shows an actual size artwork for the PC board, while Fig.8 (right) shows how the LM3386 IC is insulated from the heatsink using a mica washer and insulating bush. Smear the mating surfaces lightly with heatsink compound before bolting the assembly to­gether. HEATSINK 3mm SCREW links, followed by the resis­tors and capacitors. Make sure that you install the electrolytic capacitors with correct polarity. Next, install the fuse clips and note that there is a trick to this task. The clips have little lugs at one end which stop the fuse from moving longitudinally. If you install the clips the wrong way around, you won’t be able to fit the fuses. Note that the four 330Ω resistors which supply the 3-terminal regulators should not be fitted until after the module has been tested and is to be connected with a preamp, otherwise the input voltage on the regulators could exceed their ratings, as noted above. L1 consists of 16 turns of 0.5mm enamelled copper wire wound onto a 10Ω 1W resistor and soldered at both ends. To wind it, scrape the enamel off the start of the copper wire and solder it to one end of the resistor. Then neatly wind 16 turns onto the resistor body, scrape the enamel off the end of the wire and solder to the other end of the resistor. Finally, install and solder the assembly into the PC board. The positive and negative power supply connections to the second channel should be made with heavy duty hook-up wire (32 x 0.2mm or better) which should be twisted as shown on Fig.6. The 0V connections should be made via the same sort of hook-up wire but underneath the board. Finally, you can install the power ICs. Make sure that the tabs of the devices line up precisely with the back edge of the PC board so that they can be properly secured to the heatsinks. This done, fit 15mm metal standoffs to the board and line up the heat­sinks against the ICs so that the positions of the mounting screws can be marked. After drilling these holes, use standard TO-3P mounting kits to secure 22  Silicon Chip DEVICE MICA WASHER INSULATING BUSH 3mm WASHER 3mm NUT the ICs to the heatsinks – see Fig.8 for the details. Use your multimeter (switched to a high “Ohms” range) to make sure that the IC mounting tabs are isolated from the heat­sinks. The heatsinks we used are supplied by Altronics (Cat H-0522). To mount them into the chassis you could use small L-shaped brackets or, as we did, blind-tap holes into the edge to secure them directly. Testing To test the module, connect the power transformer and apply power. The supply rails will normally be around ±37V depending on the value of the AC mains voltage. Now check the quiescent current in each channel. This can be done in one of two ways. The first is to remove one fuse (while the power is off) and connect your multimeter, switched to an “Amps” range, across the fuse clips. With no input signal and no load, the quiescent current should typically be around 30mA but may range up to 70mA. Alternatively, you can connect a 100Ω 1W resistor across the fuse clips and measure the voltage across it. For a current of 30mA, the voltage across the 100Ω resistor would be 3V DC. The DC voltage at the output of each channel should be within ±15mV of 0V DC. Next connect suitably rated loudspeakers and check that you can get an output. With no signal, both channels should be very quiet. If you touch the input pin on the PC board you should get an audible “blurt” from the loudspeaker. If the circuit isn’t working, check all the audio paths from the input through to the output for continuity. You should also check that the PC pins are well soldered into position, as is link LK1. If LK1 is open circuit, the SC amplifier will be muted. 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 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 $55.95 $59.95 $49.95 $55.95 $55.95 $59.95 $99.00 $140.00 $85.00 $39.95 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 Digital Effects Unit for Musicians This neat Digital Effects Unit can produce a wide range of sound effects to enhance a musical instrument. It can be driven from a guitar or line source (or from both) & uses the latest in digital delay technology. By JOHN CLARKE Adding effects to musical instruments is very popular amongst musicians since they can create their own unique sounds. These effects can vary from the more natural, such as adding auditorium ambience, to the grossly exaggerated where the origi­nal sound becomes unrecognisable. The SILICON CHIP Digital Effects 26  Silicon Chip Unit is based on a micro­processor and provides adjustable echo, delay, reverberation and vibrato effects. It can be used with guitars, electric keyboards and organs, mixing consoles and other sources capable of provid­ing a 50mV to 2V RMS output signal. By connecting this unit into the signal path before the amplifier, you can quickly tailor the sound to your requirements – from adding some interesting reverberation effects to guitar work to pulsating vibrato effects for an electronic keyboard. Alternatively, you can just add in some echo to make a room sound more “alive”, or you can use a combination of effects for some really way-out sounds. These combined effects can be instantly switched in or out of circuit using a single switch (Effects In/Out) on the rear panel. Main features As can be seen from the photos, the unit is housed in a compact case with a sloping front panel. This panel carries a 2-digit LED display that shows either the delay period in millisec­onds or the vibrato rate in Hz. The delay period can be varied from 1-64ms, while the vibrato rate can be varied from 1-20Hz. Immediately to the right of the display are four pushbutton switches, the first of which toggles the display mode between delay and vibrato. Two LED indicators, one above the switch and the other below it, are used to show the current display mode. The next two switches are labelled DOWN and UP and these set both the delay and the vibrato rate, depending on the display mode selected. Pressing a button in delay mode, for example, progressively alters the delay period in discrete 1ms steps. Conversely, if vibrato mode is selected, the display alters in 0.5Hz steps up to 10Hz and then in 1Hz steps up to 20Hz. The fourth pushbutton switch is simply used to toggle the vibrato on or off. A LED indicator above this switch lights when the vibrato is on, while another LED situated immediately above the 7-segment displays flashes at the selected rate (1-20Hz). The remaining controls on the front panel are the Echo switch and the Reverberation and Vibrato Depth potentiometers. These controls have no effect on the LED displays, however. They simply switch the echo in or out and vary the amounts of rever­beration and vibrato. Several controls are also located on the rear panel and these include a Power on/off switch, an Attenuation control and the previously mentioned Effects In/Out switch. Also on the rear panel are a power socket, two signal input sockets (guitar and line) and an output socket. If necessary, both inputs can be used together – the two input signals are simply mixed together before any effects are added. An important point here is that the output signal level remains unchanged when the Effects In/Out switch is operated. This prevents the volume from changing each time the effects are switched in or out. Obtaining sound effects All of the effects are based around the delay function. In practice, this simply involves storing the incoming signal and then replaying it some time later. This delay is adjustable from 1-64ms. Mixing the delayed signal with the original signal gives the echo effect and, when a long delay is select- Main Features ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ Echo, delay, reverberation & vibrato effects Microprocessor controlled delay period & vibrato rate with 2-digit display Digital delay processing Low noise and distortion Delay adjustable from 1-64ms in 1ms steps Vibrato rate adjustable from 1-10Hz in 0.5Hz steps & from 10-20Hz in 1Hz steps User presets to select settings on power-up Input attenuator to prevent signal overload Click-free switching between effects in & effects out No change in signal level between effects in & effects out Specifications Frequency response ��������������������-3dB at 25Hz and 15kHz Signal to noise ratio ����������������������78dB wrt 1V unweighted; 82dB wrt 1V A-weighted Overload capability �����������������������800mV RMS for guitar input (using attenuator); 4.5V RMS for line input (using attenuator) Sensitivity �������������������������������������guitar input 50mV; line input 300mV Distortion ��������������������������������������1% at 1kHz and 300mV output Vibrato sinewave distortion ����������7% at 20Hz (mainly switching noise) Vibrato sinewave level ������������������within 0.6dB from 1Hz to 20Hz Input impedance ���������������������������10kΩ for line input; 47kΩ for guitar input ed, it simulates the effect of a very large hall or outdoor venue. For delay settings of say less than 20ms, we obtain a phase shifting effect. This occurs because the delay time is now simi­lar in magnitude to the period of the input signal. What happens is that the original and delayed signals are added together when they are in phase and are subtracted when they are out of phase. The resulting sound effect is similar to the Doppler shift effect that occurs with a rotating loudspeaker. By contrast, reverberation occurs when the delayed signal is fed back to the input to produce multiple echoes. With a short delay time, the results can be similar to the phase shifting effect described above but the extra multiple echoes make the effect more powerful. The vibrato effect is obtained by continuously varying the delay above and below a preset period at a rate somewhere between 1Hz and 20Hz. This effect can warble a voice or make a normal guitar sound like an Hawaiian guitar. A small amount of vibrato can also improve the phase shifting effect. Digital delay chip One advantage that this Digital Effects Unit has over many other designs is its very low noise and distortion. This has been made possible by basing the design on the M65830P digital delay IC from Mitsubishi – a device designed mainly for use in surround sound decoders. It is a very versatile device and can provide 64 separate delay periods, as selected by a serial code applied to its data pin. The device works by first converting the incoming analog signal to a digital format which is then clocked into a memory. This digital signal is then clocked out at the end of the delay period and converted back to an analog form. In addition, the M65830P also contains several op amps so that input and output filters can be added to the circuit without the need for addi­tional ICs. About the only drawback to using February 1995  27 LINE INPUT 15kHz LP FILTER IC3 MIXER IC1c AMP IC1b GUITAR INPUT ECHO S2 MIXER IC1a ATTENUATION VR1 IN DELAY IC3 15kHz LP FILTER IC3 OUT MIXER IC1d RELAY OUTPUT OSCILLATOR CONTROL INPUT x5.7 REVERBERATION VR2 18Hz LP FILTER IC2 VOLTAGE CONTROLLED OSCILLATOR IC4 VIBRATO LEVEL VR3 PC1-PC3 PC4 DIP SWITCH POWER-ON RESET PD3-5,PD7 PC0 MICROPROCESSOR IC5 (PD0-PD2)(PA0-PA7)(PB0-PB7)(PC7-PC5) LED1 VIBRATO MODULATION LED3 DELAY(ms) S4 DISP1 DISP2 the M65830P is that it is not easy to drive using standard counters and gates. This is because the control signal must be in serial form and must in­clude various identification, sleep and mute codes. This means that some form of programmed device (an EPROM or a microproces­sor) should be used in order to simplify the circuitry involved. We decided to use a microprocessor to do the job because this could also be used to perform a range of other tasks without increasing circuit complexity. In fact, the displays, switches and LEDs are all driven directly driven from the microprocessor lines. The microprocessor is also used to generate the vibrato waveform. Block diagram Fig.1 shows the block diagram of the unit. At the heart of the circuit is IC3, the M65830P digital delay chip mentioned above. To simplify matters, 28  Silicon Chip LED2 S6 DOWN S5 UP S7 VIBRATO ONOFF LED4 VIBRATO RATE(Hz) it is shown with just four connec­tions to the outside world: the signal input and output lines, the oscillator input and the control input (which actually con­sists of three lines). The control lines come from outputs PC1-PC3 on the micro­processor IC5, with the data on PC1 setting the delay number (1-64). Another output from the microprocessor, PC4, is fed to low pass filter stage IC2. Its output in turn is fed via VR3 to voltage controlled oscillator (VCO) stage IC4. By this means, the VCO varies its output frequency accord­ing to the data from PC4 and the setting of VR3. This frequency sets the basic minimum delay period (ie, to 1ms when there is no vibrato). Let’s look now at the signal inputs. The guitar signal is first amplified by 5.7 in IC1b to boost it to line level and then mixed with the line input signal using IC1a. From there, the signal passes via attenuation control VR1 to IC1c Fig.1: block diagram of the Digital Effects Unit. The incoming signals are amplified, mixed & filtered before being fed to a digital delay line based on IC3. Microprocessor IC5 controls the delay line (via PC1PC3) & also provides a control signal (via PC4 & IC2) for IC4 which, in turn, provides the clock signal. where it is mixed with the delayed signal fed back via the reverberation control (VR2). Note that the line level is defined as 285mV. However, signals up to 4.5V RMS can be accommodated by using VR1 to attenuate signals above 1.1V RMS. This attenuation is necessary to prevent signal clipping within IC3. Following IC1c, the mixed signal is applied to the digital delay stage via a 15kHz low-pass filter. This filter keeps un­wanted high frequencies out of the delay line to avoid spurious effects. Note that the op amp used for this lowpass filter stage is actually contained inside IC3. A similar 15kHz low-pass filter stage is also used at the output of the delay line. The filtered output from the delay line is fed to mixer stage IC1d and finally to the output via a set of relay contacts. The relay itself is controlled by the PC0 output of IC5; this keeps the relay contacts open for a few seconds after power is applied to eliminate switch-on “plops”. Echo is added to the output by closing switch S2, so that the signal from IC1c is mixed with the delayed signal inside IC1d. VR2 sets the level of the delayed signal that’s fed back to IC1c and thus controls the reverberation, while VR3 sets the vibrato level (or depth). Vibrato is produced by applying a varying frequency (from the VCO) to the oscillator input of IC3. To provide a natural vibrato sound, this variation should be sinusoidal in nature. This is achieved by first producing a pulse width modulated signal at the PC4 output of IC5 and then filtering it to produce a smooth sine wave. This is then fed through low-pass filter stage IC2 and used to modulate the VCO. If the vibrato effect is switched out, however, IC2’s output sits at a constant level and so the VCO’s output frequency remains fixed. As well as controlling the effects circuitry, the micropro­ cessor also drives the LED displays and accepts inputs from the four pushbutton switches (S4-S7). Finally, the PD3, PD4, PD5 & PD7 lines of IC5 connect to a 4-way DIP switch. These switches set the initial configuration of the effects unit at power up and can be configured to suit your requirements – see Table 1. For example, the DIP switches can be set so that the vibra­to function is either on or off at power up and there are options for setting the initial delay and vibrato rate. Circuit details Refer now to Fig.2 for the full circuit details. IC1b, the guitar preamplifier, functions as an inverting stage with a gain of 4.68, as set by the ratio of the 220kΩ and 47kΩ feedback resistors. Its output is fed to mixer stage IC1a which functions with a gain of -1.2 for guitar signals (thus giving an overall gain of 5.7) and -1 for line level signals. Note that the guitar socket shorts the input to ground when no plug is inserted. This is done to reduce hum pickup when this input is unused. The output from IC1a is coupled to VR1 via a 10µF ca­pacitor and then fed to pin 23 of IC3 via IC1c, as described pre­viously. The RC network connected to pins 22 and 23 forms part of PARTS LIST 1 PC board, code 01301951, 141 x 131mm 1 PC board, code 01301952, 41 x 146mm 1 desk console case, 170 x 143 x 31 x 55 (Jaycar Cat. HB6092 or equivalent) 1 front panel label, 168 x 143mm 1 12VAC 300mA plugpack 3 6.5mm mono panel mount sockets with SP switch 1 SPDT toggle switch (S1) 1 SPST rocker switch (S2) 1 DPDT toggle switch (S3) 4 grey momentary click action PC board switches (S4-S7) 1 4-way DIL switch (DIP1) 1 10kΩ 16mm log pot (VR1) 2 10kΩ 16mm linear pots (VR2-3) 1 10kΩ horizontal trimpot (VR4) 1 DC panel mount power socket plus 2.5mm screws & nuts 3 15mm knobs 1 micro U heatsink (18 x 19 x 10mm) plus 3mm screw & nut 1 5V reed relay (RLY1) (Jaycar Cat. SY-4036 or equivalent) 1 40-pin IC socket 4 9mm tapped standoffs 4 3 x 6mm screws 4 3 x 6mm countersunk screws 1 solder lug 1 22 x 34mm piece of 3mm-thick red Perspex 1 4MHz parallel resonant crystal (X1) 2 HDSP-5301 red common anode 7-segment displays (DISP1, DISP2) 4 3mm red LEDs (LED1-LED4) 22 PC stakes 5 cable ties Semiconductors 1 TL074 quad op amp (IC1) 1 LM358 dual op amp (IC2) 1 M65830P single chip digital delay (IC3) 1 ICM7555, LMC555CN or TLC555 CMOS timer (IC4) 1 programmed MC68HC705C8 microprocessor (IC5) 1 7805 5V 1A 3-terminal regulator (REG1) 6 1N4004 1A diodes (D1-D6) 1 BC338 NPN transistor (Q1) 1 BB212 varicap diode (VC1) Wire & cable 1 250mm-length of 6-way rainbow cable (2.54mm separation) 1 60mm-length of twin shielded audio cable 4 300mm-lengths of hook-up wire (red, blue, yellow & green) 1 200mm-length 3-way rainbow cable 1 300mm-length 0.8mm tinned copper wire Miscellaneous Solder, heatsink compound the 15kHz low pass filter shown on the block diagram (Fig.1). This filter prevents frequencies that are greater Capacitors 1 1000µF 25VW PC electrolytic 3 100µF 16VW PC electrolytic 1 47µF 16VW PC electrolytic 1 22µF 25VW PC electrolytic 9 10µF 16VW PC electrolytic 2 1µF 16VW PC electrolytic 2 1µF MKT polyester 1 0.27µF MKT polyester 7 0.1µF MKT polyester 1 0.039µF MKT polyester 2 0.022µF MKT polyester 1 0.01µF ceramic 2 560pF ceramic 2 150pF ceramic 2 33pF ceramic Resistors (0.25W, 1%) 1 4.7MΩ 1 8.2kΩ 2 220kΩ 1 4.7kΩ 3 100kΩ 1 3.3kΩ 2 47kΩ 1 1.8kΩ 4 39kΩ 1 1kΩ 1 27kΩ 1 330Ω 5 22kΩ 1 270Ω 2 18kΩ 1 100Ω 20 10kΩ 1 82Ω Where to get the microprocessor The programmed MC68HC705­C8 microprocessor (IC5) is avail­ able from retailers as part of a complete kit, or can be purchas­ed separately from SILICON CHIP for $45 plus $6 p&p. than half the sampling frequency of the digital delay from causing spurious conversion products which would February 1995  29 10k 10k LINE 285mV 10 10k +16V 13 IC1a TLO74 12 8.2k GUITAR 47k 10 1 10k ATTENUATION VR1 10k LOG 220k 10 14 10 4 2 1 IC1c 3 0.27 15kHz ANTI ALIAS FILTER 10k 9 IC1b 10 +16V 8 18k 23 150pF 39k 22 39k 560pF 100k OUT 82  20 10 11 IN .022 21 100k 100 17 +5V 0.1 MODULATION FILTER 22k 3 22k 22k 22k 1 .039 22k 4.7k 6 IC2a 5 LM358 1 18Hz LP FILTER 1.8k 1 IC2b TP1 10k 2 0.1 0.1 18 270  5 7 1 VC1 VOLTAGE BB212 CONTROLLED OSCILLATOR +5V FREQUENCY SET VR4 10k 3 4 100 16VW 6 A1 A2 10k 2 8 0.1 100k K 8 IC4 7555 7 VIBRATO LEVEL VR3 10k LIN 27k +16V 3.3k 4 0.1 .01 +5V 10k S6 10k 10k 29 PD0 DOWN S5 30 UP S7 PD1 31 PD2 VIBRATO 24 PC4 +5V DIPSW1 POWER S1 DELAY PRESET D1-D4 4x1N4004 V+ VIBRATO PRESET +16V D5 1N4004 12VAC 300mA IN 22 25VW 1000 25VW REG1 7805 GND OUT 10k 10k 10k 10k 4 32 PD3 33 PD4 34 PD5 36 PD7 3 2 1 20 +5V 10 16VW B I GO DIGITAL EFFECTS UNIT 30  Silicon Chip A2 K A1 E VIEWED FROM BELOW C A K 37 +5V 0.1 100 1 24 10k 16 15kHz LP FILTER .022 15 ON 39k IC3 M65830P 14 IN 10k RLY1 560pF 39k 150pF OUT 1 10k 13 OUT 7 9 3 10 11 12 10 7 IC1d 5 100  OUTPUT 47k 220k REVERB VR2 10k LIN 19 OUT TP2 6 IN EFFECTS S3a 10 XIN REQ SCK DATA 2 4 5 6 ECHO S2 18k 47 IN S3b +5V VIBRATO MODULATION LED1 0.1  VIBRATO ON LED2 10k 330 330  25 26 27 PC3 PC2 PC1  V+ 22 23 40 PC5 2 PC6 IRQ 3 D6 1N4004 VPP 1 RESET RLY1 10 PC0 1k 10k 28 B C Q1 BC338 E IC5 MC68HC705C8 +5V 10k DELAY LED3  330  PC7 38 4.7M X1 4MHz 33pF 33pF 39 PA PA PA PA PA PA PA PA 0 7 6 5 4 3 2 1 4 5 6 7 8 9 10 11 PB PB PB PB PB PB PB PB7 0 1 2 3 4 5 6 12 13 14 15 16 17 18 7x 330 8x 330  10 9 7 6 1 2 4 G F A B E D C 5 A DP F B G E C D DISP1 DP HDSP5301 3,8 MSD 21 19 330  DISPLAY S4 VIBRATO RATE (Hz) DELAY (ms) VIBRATO RATE LED4  1 2 4 10 9 7 6 E D C G F A B A F G E B C D DISP2 DP HDSP5301 3,8 LSD +5V Fig.2: IC3 (the digital delay line) forms the heart of the circuit, while microprocessor IC5 provides the control signals & drives the various LED displays. IC5 also controls relay RLY1 to briefly mute the output at switch-on. February 1995  31 RLY1 100k 47k 47k 10uF 10uF 10uF 10k 560pF 0.27 1k 10k 1 10k 1uF 1000uF 560pF 10k 18k 39k REG1 18k Q1 10k 1uF 39k 82  10k 10k TP GND 10uF 39k DIP1 100k 100uF 10k 10uF 10uF 10k D1 D5 10uF IC1 TLO74 10k 10k 10k 10k 100  D2 8.2k 10uF D3 D4 220k 220k D6 39k 22uF 1 2 3 4 150pF 22k IC3 M65830P 22k 10uF 22k 100uF IC5 MC68HC705C8 150pF 0.1 0.1 X1 47uF 22k 100uF 0.1 .022 4.7M 0.1 33PF .022 33pF TP2 1 1 .039 20 22 21 7 8 9 101112 K A 131415161718 S5 20 19 22 21 S7 24 23 Fig.3: mount the parts on the two PC boards as shown here, taking care to ensure that all polarised parts are correctly oriented. Note particularly the orientation of the ICs, the 7-segment LED displays & the four pushbutton switches (S4-S7). An IC socket is recommended for IC5. subsequently be passed to the output. After processing inside IC3, the delayed signal appears at pin 15 and is then fed back into an internal op amp via pin 14. This op amp, together with the associated RC network, forms the 15kHz low-pass output filter depicted on Fig.1. The output signal then reappears at pin 13 of IC3 and is AC-coupled to pin 6 of IC1d via a 1µF capacitor and switch S3a. A 10k 330  K 330  S6 LED4 DISP2 32  Silicon Chip TP1 10k 330  10k 10k 1 1 2 3 4 5 6 10k 23 S4 DISP1 10k LED2 A 330  K K 1 24 4.7k 100k LED3 LED1 A 19 131415161718 VR4 1 0.1 1 2 3 4 5 6 IC2 LM358 27k 0.1 1 7 8 9 101112 1uF 1.8k IC4 7555 0.1 330  1uF 22k VC1 330  330  330  330  330  330  330  330  330  330  330  10k 330  330  330  3.3k 270  .01 IC1d functions as the output mixer stage. It operates with a gain of -1, both for signals from IC3 and for signals fed in from IC1c when the Echo switch (S2) is closed. VR2 sets the reverberation as described previously. It feeds a sample of the delayed output signal to the input of IC1c via S3b, a 10µF capacitor and a 10kΩ resistor. Switches S3a & S3b are used to switch the effects in or out. In the OUT position, the signal from IC1c is fed directly into IC1d and the digital delay circuitry is effectively by­passed. At the same time, the feedback signal from VR2 is switched out to eliminate any reverberation effects that would otherwise occur if VR2 was not set to its minimum position. The 220kΩ resistor connected to pin 7 of IC1d maintains the DC charge on the associated 1µF input coupling capacitor when the effects are switch­ ed out. This eliminates noise when S3a is subsequently switched to the IN position. The muting relay (RLY1) is controlled by the PC0 output of IC5. This output goes high several seconds after power is applied and turns on RLY1 via transistor Q1. Diode D6 protects Q1 by quenching the back-EMF spikes generated when RLY1 switches off. A 4MHz crystal connected between pins 38 & 39 of IC5 sets the clock frequency for IC5. This frequency is internally divided by two, so that the microprocessor actually runs at 2MHz. The 10µF capacitor on pin 1 briefly pulls this input low at switch-on to provide a reset pulse. Power supply The display PC board is mounted on the lid of the case via four 9mm tapped spacers. After mounting, adjust the height of each indicator LED so that it just protrudes through the panel. A small piece of red Perspex provides a window for the two 7-segment LED displays. Following IC1d, the processed signal is coupled to the output socket via a 10µF capacitor, a set of relay contacts and a 100Ω resistor. The latter is there to prevent IC1d from going into oscillation when a long output lead is connected. Vibrato circuitry The vibrato function is toggled on or off using pushbutton switch S7 to pull the PD2 line of the microprocessor low. The resulting PWM signal from PC4 (pin 24) is then AC-coupled to low-pass filter stage IC2a to derive a control signal for the VCO. IC2a’s non-inverting input (and thus its output) is biased to about +5V by IC2b. This latter stage functions with a gain of two and amplifies the voltage fed to its pin 3 input from the wiper of trimpot VR4. As a result, IC2a’s output sits at a con­stant +5V when the vibrato is off and varies in sinusoidal fash­ion about the +5V level when the vibrato is on. This control signal is fed to the cathode (K) of varicap diode VC1 via VR3 (the vibrato level control) and a 100kΩ resis­tor. Note that the +5V bias level, as set by VR4, determines the output frequency of the VCO when the vibrato is off (and when VR3 is set to minimum). VC1 and 7555 timer IC4 make up the VCO. IC4 operates in astable mode and varies its output frequency according to the capacitance of VC1. This capac- itance, in turn, varies according to the control signal from VR3. When the vibrato is off, the control signal remains con­stant and thus the VCO output also remains constant at a nominal 1MHz. Conversely, when the vibrato is on, the control signal varies sinusoidally and so the VCO output varies in similar fashion. This in turn modulates the delay period of the digital delay line to produce a pulsating sound effect. Microprocessor functions Not a lot can be gleaned from the looking at the micropro­cessor circuitry since its operation depends mainly on the soft­ware. Basically, its various I/O (input/output) lines accept inputs from the various switches (S4-S7 and DIPSW1) and drive the various LED indicators and the two 7-segment displays. Depending on the settings programmed into it via these switches, IC5 also controls the digital delay line via its PC1-PC3 outputs as described previously. And, as we have just seen, it also controls the vibrato circuitry via its PC4 output. Outputs PA0-PA7 drive the two 7-segment displays via 330Ω current limiting resistors, while PC5 & PC6 drive the two vibrato LED indicators (LED 1 & LED 2). PC7 controls LED 3 & LED 4 to indicate the display mode –when PC7 is low, LED 3 is on and when PC7 is high LED 4 is on. Power for the circuit is derived from a 12VAC 300mA plug­pack supply. Its output is full-wave rectified using D1D4 and the resulting DC filtered using a 22µF capacitor to provide a nominal 16V rail. This rail supplies RLY1 and is also fed to 3-terminal regulator REG1 via isolating diode D5. A 1000µF capacitor provides further filtering at the output of D5 and the 16V rail at this point is used to power IC1 and IC2. REG1 provides a regulated +5V output and this supplies IC3, IC4, IC5 and the LEDs. When power is switched off, the relay supply falls quickly due to the modest amount of filtering employed. As a result, the relay switches off well before the voltage across the 1000µF capacitor falls by any appreciable amount. This effectively mutes the output and eliminates any nasty switch-off effects. Software Although the software programmed into IC5 is fairly complex, we can describe some of the main features of the program. The program is divided into various subroutines and interrupts and each of these performs a separate function. At power up, the RESET program begins and this sets up the initial conditions for the I/O and monitors the DIP switch set­tings. The Delay period is initially set by the DIP switches on PD3 & PD4, while the Vibrato Rate is initially set to one of two values (either 3.5Hz or 8.5Hz) by the DIP switch on PD5. The DIP switch on PD7 selects whether the Vibrato is ini­ tially on or off. The program then waits for several seconds and then brings PC0 high and updates the delay time in February 1995  33 This view shows how everything fits together inside the plastic case. Note that REG1 is mounted with its leads bent at right angles & is bolted to the PC board along with a small heatsink. The wiring is secured using plastic cable ties. IC3 in a subroutine called UPDTE. The display is then driven by a subrou­tine called SET. The program now monitors switch­ es S4-S7. If one is pressed, it acts according to the function of the switch. This program is called POLL and is the background program that runs continuously until the power is switched off or it is interrupted by an internal interrupt program called TIMER. This interrupt program generates the PWM code for PC4 and LED 1 when Vibrato is selected. When vibrato is off, PC4’s output is a 1kHz square wave. Construction Most of the circuitry is contained on two PC boards: a main board coded 01301951 and a display board coded 01301952. Fig.3 shows the parts layout on these two boards. Before installing any of the parts, check the boards care­fully for shorts and open circuit tracks by comparing The rear panel carries (from left to right) the Effects In/Out switch, the input & output sockets, the Attenuator control, the Power switch & the DC power socket. 34  Silicon Chip them with the published artworks. If all is correct, begin the assembly by installing PC stakes at all external wiring points on the main board, excluding points 1-24. PC stakes should also be installed at TP1, TP2 and TP GND. Next, install the links, resistors, diodes and ICs 1-4, taking care to ensure that the semiconductors are all correctly oriented. Table 3 lists the resistor colour codes but it is also a good idea to check them using a multimeter, as some colours can be difficult to decipher. Note particularly the row of resistors below IC5 – the resistor on the extreme left has a value of 10kΩ, while the rest are all 330Ω. The MKT capacitors can now be installed (see Table 2), followed by the electrolytic types. This done, install RLY1, VC1, Q1, VR4, X1, DIP1 REG1 and a 40-pin socket for IC5. The latter is mounted with its leads bent at right angles and its metal tab fitted with a small heat­sink. Smear the metal tab of the regulator with heatsink compound before bolting the assembly (regulator plus heatsink) to the PC board using a screw and nut. Finally, complete the main board assembly by installing IC5 in its socket. Take care to ensure that it is correctly oriented. By contrast with the main board, the display board carries relatively few components and should only take about 10 minutes to assemble. Begin by installing the resistors, then mount the two 7-segment displays and the pushbutton switches (S4-S7). The displays must be oriented with their decimal points at bottom right, while the flat sides on the switch bodies go towards the bottom of the board – see Fig.3. Push the switches down onto the board as far as they will go before soldering their leads. The four indicator LEDs can now be installed. For the time being, mount them so that they sit about 10mm ▲ Fig.4 (right): figure-8 shielded cable is used for the connections between the two input sockets (Guitar & Line) & the PC board, while the remainder of the wiring shown on this diagram can be run using medium-duty hook-up wire. Points 1-24 of the two PC boards are connected together using four 60mm lengths of 6-way rainbow cable. S3 S1 GUITAR LINE OUTPUT 28 POWER SOCKET 26 VR1 25 TP GND 29 27 MAIN PCB 1 2 3 4 5 6 20 7 8 9 101112 131415161718 19 22 21 25 S2 24 23 VR2 26 VR3 29 28 27 1 2 3 4 5 6 7 8 9 101112 131415161718 20 19 22 21 24 23 SOLDER LUG DISPLAY PCB February 1995  35 Table 1: DIP Switch Settings 1 2 3 4 DIP Switch Vibrato Off on x x x Vibrato On off x x x 3.5Hz Vibrato x on x x 8.5Hz Vibrato x off x x 1ms Delay x x on on 17ms Delay x x on off 33ms Delay x x off on 49ms Delay x x off off TABLE 2: CAPACITOR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Value 1µF 0.27µF 0.1µF 0.039µF 0.022µF 0.01µF 560pF 150pF 33pF IEC 1u 270n 100n 39n 22n 10n 560p 150p 33p EIA 105 274 104 393 223 103 561 151 33 above the surface of the board and secure each LED by just soldering one lead. Do not trim the leads at this stage, as the LEDs are ad­justed for height later on when the display board is attached to the front panel. Take care with the orientation of the LEDs; the anode lead of each LED is the longer of the two (see Fig.2). Refer now to Fig.4 for the wiring details. The first step is to connect points 1-24 of the two PC boards together using four 60mm lengths of 6-way rainbow cable. The main board is then mounted on integral plastic pillars in the base of the case and secured using the small self-tapping screws supplied. The display board mounts on 9mm tapped spacers which are secured to the lid of the case using countersunk screws. Attach the four spacers to the lid, then fit the red Perspex window for the LED displays. This window should be a tight fit into the front panel cutout and can be secured by applying a thin line of epoxy resin around the underside edge. The display board can now be mounted in position. Adjust the height of each indica­tor LED so that it just protrudes through the front panel before soldering the remaining leads. Next, fit the lid to the case and carefully mark out and drill holes in the rear panel for the three 6.5mm sockets, the two switches, the Attenuation pot and the power input socket. The 6.5mm sockets and the switches should be mounted 15mm down from the top edge of the rear panel, while the pot should be mounted half-way down so that its lugs can be soldered directly to the PC stakes on the board immediately below it. The power socket mounts directly below the power switch. The various items of hardware can now be mounted in posi­tion and the wiring completed. Shielded cable is used between the two input sockets and the main PC board, while the remaining wiring is run using medium-duty hook-up wire. Run the wiring along one edge of the main board (see photo) and don’t forget the lead between TP GND and the solder lug on the display board. Once the wiring has been completed, it can be tidied up and secured using a number of cable ties. Testing To test the unit, first connect your multimeter between TP GND on the main board and pin 1 of IC3. This done, set the meter to a low voltage range, apply power and check that the meter reads 5V. The display should initially show two dashes (- -) and then, after a few seconds, a number (the value depends on the DIP switch settings). The Delay LED should be also be lit. Now check that pin 8 of IC4 and pin 2 of IC5 are at +5V. Similarly, check for +16V on pin 4 of IC1 and pin 8 of IC2. If these voltage measurements are OK, check that the LED readout toggles between the Delay and Vibrato Rate modes each time S4 is pressed. If it does, check that the display increments when Up is pressed and decrements when Down is pressed. Check that the display range is 1-64 in Delay mode and 1-20 in Vibrato Rate mode. Now check the operation of the TABLE 3: RESISTOR COLOUR CODES ❏ No. ❏   1 ❏   2 ❏   3 ❏   2 ❏   4 ❏   1 ❏   5 ❏   2 ❏ 20 ❏   1 ❏   1 ❏   1 ❏   1 ❏   1 ❏   1 ❏  1 ❏   1 ❏   1 36  Silicon Chip Value 4.7MΩ 220kΩ 100kΩ 47kΩ 39kΩ 27kΩ 22kΩ 18kΩ 10kΩ 8.2kΩ 4.7kΩ 3.3kΩ 1.8kΩ 1kΩ 330Ω 270Ω 100Ω 82Ω 4-Band Code (1%) yellow violet green brown red red yellow brown brown black yellow brown yellow violet orange brown orange white orange brown red violet orange brown red red orange brown brown grey orange brown brown black orange brown grey red red brown yellow violet red brown orange orange red brown brown grey red brown brown black red brown orange orange brown brown red violet brown brown brown black brown brown grey red black brown 5-Band Code (1%) yellow violet black yellow brown red red black orange brown brown black black orange brown yellow violet black red brown orange white black red brown red violet black red brown red red black red brown brown grey black red brown brown black black red brown grey red black brown brown yellow violet black brown brown orange orange black brown brown brown grey black brown brown brown black black brown brown orange orange black black brown red violet black black brown brown black black black brown grey red black gold brown Fig.5: check your PC boards against these full-size etching patterns before installing any of the parts. Vibrato On/Off switch (S7). When the vibrato is on, its associated LED should light and the Vibrato Modulation LED (LED 1) should flash at the selected rate. Check that the rate at which this LED flashes alters according to the vibrato rate. If you have access to a frequency meter or an oscilloscope, adjust VR4 for a reading of 1MHz at TP2 when the vibrato is off. If this equipment is unavailable, simply adjust VR4 for a voltage reading at TP1 (note: not TP2) of 2.5V. This should provide a clock frequency that’s reasonably close to the mark. The unit can now be given a practical test by connecting the output to an amplifier and feeding a signal into one of the inputs. Check that the Echo On, Reverberation and Vibrato Depth controls all produce the desired effects on the sound and that the Effects In/ Out switch operates correctly. Once you become familiar with the various effects, you can set the DIP switches on the PC board so that your normally selected settings appear at switch on – see Table 1. To see how this works, let’s assume that you want the unit to power up with the following set­tings: (1) vibrato off; (2) vibrato rate = 3.5Hz; and (3) delay = 33ms. In this case, the switch settings would be: DIP1 on; DIP2 on; DIP 3 off; and SC DIP 4 on. February 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. Analog multiplier uses transconductance amp This circuit will generate an output voltage which is the product of two input voltages. The circuit is an adaptation of a circuit published in “General Purpose Linear Devices Databook” by National Semiconductor. Possible applications include power meters, remote volume controls and audio modulators. The circuit is based on the use of a so-called “transcon­ ductance” amplifier. IC1a is one of two such amplifiers in an LM13600 package. The other is not used in this circuit. Two important characteristics of this amplifier are that it generates an output current which is proportional to a differential input voltage and its gain can be controlled by a current into one of its inputs. In operation, an input voltage is applied to IC1a via input A and resistor R1. IC1a converts this input voltage to an output current into load resistor R6. A second input voltage is applied via input B. IC2b and Q1 convert the voltage at B to a current which goes into pin 1 of IC1a. This current controls the voltage-to-current gain (transconductance) of IC1a. R5 and trimpot VR2 provide a bias current into pin 1 to set the quiescent operating gain. Op amp IC2a dynamically adjusts the voltage levels at pins 3 and 4 of IC1a to minimise the effects of temperature changes on input offset voltage. Three-terminal regulator REG1 is connected to generate a constant current (via R7) which is essentially independent of temperature or supply voltage. This current biases the input stage for optimum linearity. The circuit works as follows. Assume that the voltage at input B is zero. The output current from pin 5 of IC1a is propor­tional to the voltage at input A multiplied by the current into pin 1. This current produces a voltage across R6. With trimpots VR1 and VR2 correctly adjusted, the voltage across R6 38  Silicon Chip ADJUST SYMMETRY VR2 10k R5 22k INPUT R4 10k B D1 1N4148 8 6 IC2b 5 TLO72 Q1 BC559 7 REG1 OUT LM317 IN R7 1.2k +12V REG ADJ R3 220  3 INPUT A R1 10k 2 1 IC2a R8 5.6k 3 2 4 4 R2 18k ADJUST ZERO VR1 10k will be equal and opposite to the input voltage at A. Since the load resistor R6 is connected from the output of IC1a to input A, the two voltages cancel and the net output voltage referenced to ground is zero. Now, with a voltage applied to B, the resulting change in current into pin 1 of IC1a will cause the gain to change. The net effect is that the output voltage changes in proportion to the input voltage at A, multiplied by the input voltage at B. Adjustment is best carried out with a signal generator and an oscilloscope. Connect inputs A and B together and apply zero volts to these inputs. Adjust trimpot VR1 for zero output. Now, apply a sinewave signal at, say, 50Hz to the input terminals and adjust the signal amplitude for approximately 200mV peak-to-peak at the output. 11 IC1a LM13600 1 5 OUTPUT 6 R6 10k -12V REG Adjust VR2 for best symmetry of the output wave­form. For optimum linearity in critical applications, the output signal should not exceed 200mV. If larger output voltages are needed, an op amp gain stage should follow the output. In any case, a unity (or higher) gain output buffer (not shown) is recommended to avoid loading the output. The LM13600 includes a couple of Darlington transistors which may be used as unity gain output buffers (emitter followers) in many applications. By connecting an audio signal to one of the input terminals and a DC voltage to the other, this circuit can be used as a remote volume control. Two such circuits can be combined in a stereo system. Alternatively, by replacing the DC voltage by an AC voltage, interesting sound effects might be obtained. 7 G1 CONNECT TO MODIFIED POINT ON MAIN PCB CUT TRACK ON PIN1 IC15 INSERT 10k RESISTOR G1 CONNECTS TO PIN1 7 6 T1 T2 16 9 5 8 IC15 OF TV PATTERN GENERATOR 74HC193 10k +5V G1 8 IC1 74LS145 1 11 10 5 12 9 4 13 7 3 14 6 2 15 1 10k 15 G3 10 G2 (11) NUMBERS IN BRACKETS ARE WIRING PIN NUMBERS ON MAIN PCB 9 11 12 12 10 9 11 1 IC4 4066 4 8 6 13 4 3 5 IC3 74LS04 2 13 14 14 7 1 8 9 (11) 13 3 5 IC2 74LS04 6 5 +5V +5V D7 D5 D3 4 2 1 T1 LINK PIN11 IC10 TO PIN13 IC9 T2 LINK PIN12 IC10 TO PIN12 IC9 T3 LINK PIN11 IC12 TO PIN4 IC12 G3 G2 G1 10 8 2 3 D8 D6 D4 10k 10k T3 (6) (7) D2 D1 8x1N914 D1 (1) (2) (3) +5V 14 16 nect certain lines of the generated data together to produce some of the patterns. Note that, as well as the various connections required to the main board, to links and other points, as (G3) CUT TRACK TO PIN15 INSERT 10k RESISTOR MODIFICATIONS TO MAIN PCB C D THUMBWHEEL SWITCH COM A B 4x10k 10 This circuit addition allows a thumb­­wheel switch to be used to select the patterns in the TV pattern generator circuit fea­tured in the November & December 1991 issues. In essence, the thumb­wheel takes the place of switch S2, the pattern selector in the original circuit. Hence, there are quite a few points where this additional circuit connects into the original circuit. Note that the arrows pointing to numbers in brackets are referring to wiring connection points on the PC board layout diagram on page 69 of the December 1991 issue. In addition to the red and white rasters provided by the original pattern generator design, this modification also provides a green raster which is the most suitable for colour purity adjustments. In all, nine patterns are available at the following thumbwheel settings: 0 checker; 1 crosshatch; 2 dots; 3 white raster; 4 red raster; 5 grey scale; 6 vertical lines; 7 colour bars; 8 horizontal lines; 9 green raster. The thumbwheel switch has four output lines which produce a BCD output. This is decoded by the 74LS145 BCD to decimal decod­ e r/driver, IC1. This device has open collector outputs, hence the need for the 10 10kΩ resistors to the positive supply rail. Five of these decoded outputs are connected to IC2 (a 74LS04 hex inverter) and this drives an array of diodes connected as an OR gate. This drives transistor Q1 to disable colour burst genera­tion for all patterns except colour bars and rasters. IC3 is another 74LS04 hex inverter and this drives IC4, a 4066 quad analog switch which is used to con- 10x10k Thumb wheel selection for pattern generator Q1 BC639 (Edi­tor’s note: while this circuit could be the basis of a DC volume control, its dynamic range, signal to noise ratio and distortion performance would not be adequate for high quality reproduction). By connecting input terminals A and B together, this cir­cuit will generate an output voltage proportional to the square of an input voltage applied to these terminals. This makes the circuit useful for power measurements, or it could be used as the basis for an RMS voltmeter. Herman Nacinovich, Gulgong, NSW. ($30) noted on the dia­gram, a modification is required to the main board and this is shown in the inset diagram involving IC15. Michael Parany, Oakleigh East, Vic. ($50) February 1995  39 The HexTemp is a 6-channel thermometer which allows the observation of temperatures in six locations within a 10 metre radius. It could be used for keeping a check on the operation of air conditioning, solar heaters, greenhouses, small animal enclosures & fish tanks. Build the HexTemp: a 6-channel thermometer By JOHN WESTERN Temperatures on the Hextemp are displayed in the range of 0-50°C with a resolution of 0.2°C; eg, 23.6, 24.8, 34.2, etc. The liquid crystal display (LCD) initially shows all six readings at once but can also be cycled through individual sensors to display the current temperature, together with the maximum and minimum temperatures. In total, there are seven different display screens which can be cycled through using the SEL switch. The maximum and minimum readings for each channel are cleared by pressing the CLR switch when that channel is displayed. If the temperature exceeds 50°C, the display will show ++.+ and if the temperature drops below 0°C, the display will show —.-. The circuit consists of a 68HC11A1 microcontroller, a 16-character by 2line LCD panel, six current to voltage 40  Silicon Chip converters and the power supply. The microcontroller has 256 bytes of RAM, 512 bytes of EEPROM, five I/O ports and an 8-bit 8-channel analog to digital converter, all on the one chip. The LCD has a built-in microprocessor and accepts data and instructions via an 8-bit parallel interface. Circuit description IC5, an LM336 precision voltage reference, is used to pro­vide +5V to pin 52 of IC4, the 68HC11. IC5’s output is also divided by two, buffered by op amp IC2d and fed to the six current to voltage converters. Only two of these are shown on the circuit diagram; ie, IC6 & IC2b and IC11 & IC1a. VR13 allows the output from IC5 to be adjusted for precisely 5V. The temperature sensors IC6 and IC11 (and ICs7-10, not shown on the circuit) are LM334 adjustable current sources, arranged so that their current increases by one microamp (1µA) for each 1°C rise in temperature above absolute zero; at 0°C, the current will be 273µA. To simplify matters, let us on concentrate just on sensor IC6 and its accompanying op amp, IC2b. IC2b is connected as a current to voltage converter so that its output increases by 100mV for every one degree temperature rise above 0°C, as sensed by IC6. Trimpot VR1 is used to set the output of IC2b to 0V at 0°C, while trimpot VR7 is used to cali­brate the sensor against steam; ie, at 100°C. This latter calibration is done as a voltage measurement, as the LCD is over-ranged at this temperature. The output of IC2b is then fed via a 10kΩ resistor to one of the A/D inputs of the 68HC11, in this case, pin 43. Each of the five other temperature sensors is connected in the same way, and the current to voltage converters +12V +5V REF 2.7k +12V 4 13 VR13 10k IC2d 12 LM324 11 10k A IC5 LM336 10k VCC VR7 5k 14 VR1 1k 8.2k 220  IC2b 5 LM324 45 220W 4.7k 2 IC1a 3 LM324 T1 AL7VA IN BR1 12V IN 12V 1000 N IN CASE 470 1 REG1 7812 REG3 7905 GND OUT REG2 7805 PE0 10k 46 RN2/1 4.7k OUT IC3 S8054 OUT 51 VRL 37 12 36 13 35 14 PC0 9 PC1 10 4 PB6 5 6 PC2 11 2 VCC D0 D1 LCD D2 MODULE D3 D4 D5 D6 D7 RS R/W E GND 1 BL -V K RN2/3-7 5x4.7k PC3 12 PC4 13 VCC PC5 14 PC6 15 VCC 17 RESET PA1 0.1 10M 8 X1 8MHz 18pF 18pF Fig.1: the circuit uses six LM334 constant current sources to monitor temperature. These are connected to current to voltage op amp stages which then feed the A/D inputs of the microprocessor. This processes the readings & drives the LCD panel. operating clock for the chip. The LCD panel is connected to ports B & C of the 68HC11, with port B being used as an 8-bit data path and bits 0-2 (three lines) of port C used for the control lines. Port A is used to read in the condition of the SEL and CLR front panel switches. Unused port lines are held high with 4.7Ω pull-up resis­tors in SIL resistor networks RN1 & RN2. The LCD panel is available with or without backlighting. The backlit version should be used for vertical EXTAL XTAL 4.7k 34 S1 S2 33 PA2 32 PA7 27 7 10 4.7k PA0 VCC 0.1 -5V drive pins 44, 45, 46, 47 and 49 of IC4. The 68HC11 is supplied with a reset signal on pin 17 by IC3, an S8054 low voltage detector. When the +5V supply to IC4 drops to +4.6V or below, it is reset by IC3. This is required because a program not executing the correct instructions during power down could accidentally erase the 68HC11’s EEPROM. An 8MHz crystal, X1, is connected to pins 7 & 8 of the 68HC11 and is used to provide the 2MHz internal 11 PB5 PE5 52 VRH IN MULTI CHANNEL THERMOMETER 10 38 A BL +V VO PC7 16 +12V 10 39 PB3 PE4 VCC 10 9 PB7 GND 10 40 IC4 68HC11A1 1 10 GND 8 PB4 PE3 V- OUT 7 41 PB1 PE2 3 42 PB0 PE1 8.2k -5V LM334 GND E 91k +5V REF A V- R V+ VIEWED FROM BELOW 240V AC 49 44 G I O A 47 1 AND 6 OF SIX TEMPERATURE SENSOR CIRCUITS 33  VR14 10k PB2 VR6 1k V+ IC11 LM334 R LM336 10k 43 18 19 V- VR12 5k S8054 7 8.2k -5V 8.2k 1 91k 6 V+ IC6 LM334 R -5V 4.7k RN1/1-7 7x4.7k VCC PD5 25 PD4 24 PD3 23 PD2 22 PD1 21 PD0 20 MOD MOD B VDD A 26 2 3 mounting and is also more useful in low ambient light conditions. The viewing angle of the non-backlit version makes it more suitable for horizontal mounting. A standard linear power supply is used to provide +5V, +12V and -5V to the various circuits. The 7805 voltage regulator requires a small heatsink. The power transformer used is an Arlec AL7VA/24 and it is mounted on the printed circuit board. Software The 68HC11’s contains a machine language program that makes the whole thing work. The program has February 1995  41 The 68HC11 microprocessor is mounted in a 52-pin carrier socket, while 16-way & 3-way pin headers are used to interface the LCD panel & the two switches to the PC board. Make sure that the mains cord is securely anchored & that all polarised components are correctly oriented. routines that convert the voltages to numbers, send the correct information to the LCD, interrogate the switch­es and generally manage things. The A/D converter produces a number from 0 to 255 which represents the analog voltage applied. This number must then be multiplied by a scale factor to produce the desired output. As only 256 different values are produced, it is only possible to display this number of temperatures. Hence, instead of temper­atures being displayed in 0.1 degree steps, for example, the temperature display may skip from 11.2 to 11.4 and not show 11.3. Construction The HexTemp is housed in a folded steel box measuring 110 x 62 x 180mm. The LCD panel and two pushbutton switches are mount­ed at one end while a PC board measuring 150 x 102mm accommodates all of the circuitry except for the six remote sensors. The case will need to be drilled and a cutout made for the LCD panel. This should be done before any work is done on the PC board. Assembly of the PC board is straightforward except for the need to fit a carrier socket for the 68HC11. We suggest that you first fit all the PC pins and wire links, then the resistors and capacitors and then the semiconductors and the 52-pin socket for the microprocessor. Leave the on-board power transformer and the 68HC11 till last. Make sure that you correctly orient the ICs and the polarised capacitors. Note that trimpots VR1 to VR6 are RESISTOR COLOUR CODES ❏ No. ❏   1 ❏   6 ❏   8 ❏ 12 ❏   8 ❏   1 ❏   6 ❏   1 42  Silicon Chip Value 10MΩ 91kΩ 10kΩ 8.2kΩ 4.7kΩ 2.7kΩ 220Ω 33Ω 4-Band Code (1%) brown black blue brown white brown orange brown brown black orange brown grey red red brown yellow violet red brown red violet red brown red red brown brown orange orange black brown 5-Band Code (1%) brown black black green brown white brown black red brown brown black black red brown grey red black brown brown yellow violet black brown brown red violet black brown brown red red black black brown orange orange black gold brown multi-turn types, to take account of the sensitivity of the zeroing adjustment of the op amps. All the other trimpots are horizontal single-turn types since their adjustment is not critical. Header sockets will need to be installed on the PC board for the connections to the two pushbutton switches and to the LCD panel. The 3-core mains flex should be anchored with a cord-grip grommet and the green/yellow Earth wire connected directly to a solder lug at the rear of the case. The Active and Neutral wires are soldered directly to the PC board. Place a layer of insula­tion tape over the AC mains connections on the board. The board is mounted in the case using four 9mm PC standoffs. S1 LCD MODULE 33 10uF 0.1 4.7k 10k 10k RN1 IC5 2.7k VR13 10k 10k 10k IC2 LM324 SENSOR 1 IC3 S8054 IC4 68HC11A1 RN2 10k 1 1 VR7 91k 8.2k 2x 18pF VR1 8.2k VR2 10uF VR9 IC1 LM324 SENSOR 5 8.2k VR6 8.2k 91k 8.2k 4.7k VR12 VR11 POWER TRANSFORMER VR5 GND N N (BLUE) 8.2k Fig.2: the wiring diagram of the HexTemp. Note that the connec­tions to the LCD panel go via header sockets. Trimpots VR1VR6 should be multiturn types. 1000uF 10k 10k 1 SENSOR 6 REG2 470uF 4.7k VR10 REG 1 10uF BR1 4.7k VR3 10uF 91k VR4 91k 4.7k 91k SENSOR 4 REG3 8.2k 8.2k 8.2k 8.2k 8.2k SENSOR 3 10M 1uF 4.7k EARTH LUG ON CASE REAR 2V0VAC A A( BR OW N) VR8 8.2k SENSOR 2 91k 4.7k X1 Testing & calibration When power is applied, the display should show six readings between 00.0 and 50.0. Pressing the SEL switch should step through the seven display screens. The CLR switch should turn the maximum reading to 00.0 and the minimum reading to 50.0. If all seems to work properly then the calibration can be performed. First adjust trimpot VR13 so that the +5V REF line is exactly 5V. Each channel should then be calibrated in the follow­ing manner, as for sensor IC6. Place the sensor in a thermos flask of ice water, with the sensor below the floating ice. Measure the voltage at the output of IC2b and adjust trimpot VR1 to obtain 0V. Next, place the sensor in steam coming from a boiling kettle and adjust VR7 for an 10uF 0.1 PROG CONN VR14 4.7k Sensors The six sensors are each wired with the 220Ω current set­ting resistor soldered between the R and V-pins. The V+ pin is connected to the centre wire of a length of shielded cable, while the V- pin is connected to the shield. Once the connections are made, the sensor leads are protected with a short length of heat-shrink tubing, as shown in the lead photo. Each of the six temperature sensors is connected via its shielded cable to the appropriate PC pins on the board. Before installing the 68HC11 into its socket, do a voltage check on all the socket pins. These should all be at +5V or 0V, apart from the A/D inputs which will depend on the outputs from the op amps. If all is OK, the 68HC11 can be plugged into its socket and the LCD panel can be connected to the board. Check the LCD’s power connections carefully as reverse polarity will de­stroy it! A K GND +5V CON RS R/W E D0 D1 D2 D3 D4 D5 D6 D7 A K GND +5V CON RS R/W E D0 D1 D2 D3 D4 D5 D6 D7 S2 N/ REE ) E (GLLOW YE CORD GRIP GROMMET February 1995  43 PARTS LIST 1 folded metal case, 110 x 62 x 180mm 1 PC board, 150 x 102mm 1 8MHz crystal 1 Arlec AL7VA/24 transformer 1 LCD panel (Altronics Cat Z-7299; backlit version Cat Z-7301) 2 pushbutton SPST switches 1 52-pin PLCC socket 1 3-pin header & plug 1 16-pin header & plug 1 small TO-220 clip-on heatsink 4 PC supports 13 PC pins 4 9mm spacers (for LCD panel) 1 3-core mains cord & moulded 3-pin plug 1 cordgrip grommet to suit mains cord 1 grommet (for sensor cable entry) 2 SIL 7 x 4.7kΩ resistor networks (RN1, RN2) 2 10kΩ trimpots (VR13,14) 6 5kΩ trimpots (VR7-11) 6 1kΩ multi-turn trimpots (VR16) Semiconductors 2 LM324 operational amplifiers (IC1, IC2) 1 S8054 low volt detector (IC3) 1 programmed 68HC11A1 microcontroller (IC4) 1 LM336 5.0V voltage reference (IC5) 6 LM334 constant current sources (IC6,7,8,9,10,11) 1 7812 voltage regulator (REG1) 1 7805 voltage regulator (REG2) 1 7905 voltage regulator (REG3) 1 W04 bridge rectifier (BR1) Capacitors 1 1000µF 25VW PC electrolytic 1 470µF 25VW PC electrolytic 5 10µF 25VW PC electrolytic 1 1µF 25VW PC electrolytic 2 0.1µF MKT polyester 2 18pF ceramic Resistors (0.25W, 1%) 1 10MΩ (5%) 8 4.7kΩ 6 91kΩ 1 2.7kΩ 8 10kΩ 6 220Ω 12 8.2kΩ 1 33Ω Miscellaneous Shielded cable, hook-up wire, heatshrink sleeving, solder. The LCD panel is secured to the front panel of the case on 9mm spacers, as shown here. Note the small clip-on heatsink fitted to 3-terminal regulator REG2 at bottom right. output of +10V at pin 7 of IC2. Some sensors may require the value of the 4.7kΩ resistor to be increased or decreased to obtain the correct calibration value of +10V. Be careful not to short circuit any tracks with the meter probe as applying the +12V or -5V rail to the 68HC11 could damage it. (The A/D inputs are normally protected by the series 10kΩ resistors). When all the sensors are calibrated they can be installed in the required locations. The prototype HexTemp has had sensors positioned up to 10 metres from the control unit and all seems to SC work satisfactorily. 1 2 Where to buy the microprocessor The programmed 68HC11 microprocessor is available only from the author, John Western, who can also provide the printed circuit board. Pricing is as follows: (1) 68HC11 programmed microprocessor, $37.50; (2) PC board, $28.00. Postage & packing $5.00. Send cheque or money order to John Western, 81 Giles Ave­nue, Padbury, WA 6025. Phone (09) 401 2733. 3 °c 4 5 6 . Select . Clear HexTemp Thermometer Fig.3: use this full-size artwork as a drilling template for the front panel. 44  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. 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 COMPUTER BITS BY DARREN YATES Adding a CD-ROM drive to your computer Over the last 12 months, the price of CD-ROMs has plum­meted. For around $300 or less, you can buy & install a high-speed CD-ROM & gain access to a whole new world of software. What’s more, it’s easier to do than you think. Just as the CD (or compact disc) revolutionised the music industry, so is it having the same effect on the computer indus­try. These days, you can’t walk into a computer store without some mention of CD-ROM. And just about every advert that you see for computers makes some mention of either CD-ROM or the current buzzword “multimedia”. What’s “multimedia”? It simply refers to a computer that has a CD-ROM drive, a sound card and a couple of loudspeakers for sound effects. This sort of system enables the integration of high quality sound, animation, text, photographic-quality images and graphics for all sort of applications. And because it’s played back via the computer, it allows for user interaction. CD-ROM advantages So what’s so good about CD-ROM? Well, for starters, it gives you fast access to more information that you could ever imagine. This information can include telephone directories, atlases, dictionaries and even complete encyclopaedias. If you’re in business, you can buy a complete telephone directory for the entire country on CD-ROM, not just for your city or district. It may not sound exciting at first glance but it gives you access to any business phone anywhere in Australia and is much easier to store than 20 or 30 telephone books. Games take on a whole new meaning as well. And if you have a sound card, you get the full range of sound effects – not just beeps and squawks. In fact, some of the latest releases come with complete soundtracks like big-budget movies. Graphics, too, are also improved, with the possibility of moving pictures. With 600-odd megabytes (Mb) on a standard CD-ROM and up to 1.2Gb on a double-speed CD-ROM, there is almost no limit to what you can put on them. CD-ROMs also have the ability to produce CD-quality sound. You can even obtain shareware software which enables you to use your CD-ROM drive to play ordinary music CDs, either through a stereo headphone socket on the front of the drive or via a sound card and loudspeakers. Naturally, this can be done in the back­ground, allowing you to use the computer as normal for other work – like writing articles on how to install CD-ROMs. Another big advantage of CD-ROMs is their ability to store large software programs. Indeed, many software manufacturers, including Microsoft, are beginning to sell software on CD-ROM. For example, Microsoft’s Video for Windows now comes with a CD-ROM containing video images on everything from Space Shuttle launches to music clips to balloon flights. A complete version of CorelDraw 5 is also available on a set of three CDROMs. This not only saves you from having to install the program from multiple discs but also provides you with access to hundreds of fonts (825 in all) and thousands of clipart images. In fact, CorelDraw is really a number of programs all bundled together in the one package. Indeed, many programs are now so large that CD-ROM is really the only sensible way to go. Providing users with 15 or 20 floppy discs to install a program is cumbersome when the job can be done with just one CD-ROM and the manufacturer can include a range of other useful utilities as well. The latest innovation to come from CD-ROMs has been Kodak’s introduction of the Photo CD. When you’ve finished exposing a roll of 35mm colour film, you give it to Kodak who’ll then pro­cess it and give you back a nice new shiny CD-ROM with your photos on it. What’s more, provided it’s a “multi-session” type, you can take the CD-ROM back with your next film and they can load the new frames onto it. This makes it extremely easy to load pictures into desktop publishing programs such as PageMaker and Quark Express. We use this system on occasions for some of the photos that appear in Silicon Chip. Adding a CD-ROM drive Adding a CD-ROM drive to your computer is not that hard to do, although you do have to know what you are doing. About the hardest thing is shopping around for the best price. As a result of competition, prices have February 1995  53 About the only thing missing from this multimedia kit is a pair of speakers (or headphones) to provide the sound effects. Note that the items pictured are about 2.5 years old & some, at least, will have been superseded. fallen like a brick in the last few years. When we first reviewed a CD-ROM system about two and a half years ago, the price was around $1500. Today, stores are tripping over themselves to sell you a complete multimedia system for less than $400. And if you’re looking for a bare-bones CD-ROM system with just the driver card, drive and driver software, you can pick up one for as little as $239. That’s cheaper than a 200Mb hard drive! The basic CD-ROM is the same size as a half-height 5.25-inch floppy drive and is designed to fit into one of the drive bays inside your PC. Basically, you have to mount the drive in posi­ tion, install an adapter card and connect the power supply and interface cables. Before starting work, be sure to unplug the computer from the mains. This done, remove the lid and make a note of where all the existing cables to the drives go, just in case you have to temporarily disconnect some of them. Next, locate a suitable spare 5.25inch bay and unclip its front plastic cover. You may have to do this by applying a modest amount of pressure to the cover from inside the machine. Once the cover has been removed, slide the drive into position from the front of the machine and secure it in the bay using the mounting screws supplied. You will need at least four screws to properly secure the drive. The next job is to install the adapter card into a spare expansion slot on the motherboard. This card is the “go-be54  Silicon Chip tween” for the motherboard and the CD-ROM drive. More often than not, it will be a small 8-bit card but some 16-bit cards are now also starting to appear. Note that both SCSI and IDE adapter cards are available for CD-ROM drives, so make sure that you choose the correct type for your particular drive. In addition, an IDE adapter may be either a proprietary type (ie, it suits only one particular brand) or it may be a generic type, in which case it can be used with one of several different brands. To further complicate matters, some of the very latest CD-ROM drives (eg, the Sony CD-55E) can be used with an IDE hard disc drive adapter card. The drive is simply connected to a spare output connector on the card (provided one is available, that is). Of course, if you buy a complete package, then you don’t have to worry about compatibility problems. If you have a generic adapter card, you may have to change the jumper settings to suit your particular drive. The jumper settings for a Panasonic drive will be different to those for a Sony drive, for example. The literature accompanying the card will show you what jumper settings to use. This done, connect the data cable to the card and then plug it into the mother­board. Be sure to position it so that the other end of the data cable reaches the drive connector. The free end of the data cable can now be plugged into the drive, along with the power supply connection. There will usually be a spare supply cable “floating” around inside the computer. If you don’t have any left, you can obtain supply splitter cables from your local computer store. Note that the plugs and data cable connectors will be polarised, to stop you from making connections the wrong way around. In some machines, you may have difficulty gaining access to the back of the drive due to the proximity of the power supply. This problem can usually be overcome by undoing a few screws so that the front section of the case, including the drive bays, comes free. The connectors can then be plugged into the new drive and the case reassembled. Installing the software OK, that’s the mechanical side of the job done. Before using your new CD-ROM drive though, you have to install the driver software. This is supplied on a floppy disc that comes with the drive. If you didn’t get this disc, then you will have to go back to your computer store because your CD-ROM drive won’t work without it. Loading the software is straightforward, since this can be done automatically; eg, by inserting the disc, logging to the drive and typing INSTALL (or similar). By simply following the instructions on the screen, this will automatically install the correct device drivers and make the necessary alterations to your config.sys and autoexec. bat files. For the vast majority of cases, the automatic installation procedure is the recommended way to go. In some cases, however, you might want to copy the relevant driver file(s) to your hard disc and change the config.sys and autoexec.bat files yourself. If you follow this second route, be sure to create a boot­able floppy disc and backup your existing config.sys and autoex­ec.bat file before altering anything. To create a bootable floppy disc, simply insert a disc in your A: (or B:) drive and type: format A: /s. This formats the disc and copies the MSDOS.SYS and IO.SYS system files across. You can then copy the existing au­ toexec.bat and config.sys files to the disc. This disc is there as an insurance policy, in case you do something Many early CD-ROM drives used a disc caddy to load the CD while in the more recent units, the CD is loaded into a drawer in exactly the same manner as for an audio CD player. A CD-ROM can hold up to 1.2Gb of data. wrong and your computer refuses to boot up after you’ve made changes. If this happens, it’s simply a matter of booting off the floppy and copying the old config.sys and autoexec.bat files to the hard disc. The installation instructions for your CD-ROM will tell you how to modify the config.sys and autoexec. bat files. Let’s take a look at a couple of typical examples, one involving an old Sony CD-ROM drive that we installed in one of our machines and the other a more recent Panasonic drive. In both cases, IDE adapter cards were used. For the Sony drive, the device driver file was called SONY_CDU.SYS and this had to be loaded from config.sys. The line we had to add was: DEVICE = C:\SONY_CDU.SYS /D:SONY001 /B:340 /T:H This tells the computer to load in device driver SONY_CDU.SYS with the following parameters: device name as SONY001; the base address of the CD-ROM as 0340 hex; and the transfer rate as high-speed polling. This last feature determines whether your PC accesses the ROM drive via the standard data transfer mechanism or via direct memory access. This latter method is somewhat faster but relies on the ROM drive being able to go that fast for there to be any benefit. A standard ASCII text editor is used to make the changes to config.sys (eg, the DOS EDIT program). A line was then added to autoexec.bat to load MS-DOS’s MSCDEX.EXE program. The relevant line in this case was: C:\DOS\MSCDEX /D:SONY001 The important thing here is that the device name (ie, what comes after the /D:) must match the name used in the config.sys line. You can basically choose whatever name you want but they must both be the same. This is the way the PC recognises the ROM drive as part of the driver subsystem. Once these changes had been made, the relevant driver file (ie, SONY_CDU.SYS) was copied to the root directory of the C: drive. The computer was then rebooted so that the changes could take effect and give access to the CD-ROM drive On the second computer, similar changes were made to con­fig.sys and autoexec.bat. In this case, however, we had to load a driver file called CDMKE. SYS. The line added to con­fig.sys was: DEVICE=C:\CDMKE.SYS /D:PANASON while the line added to autoexec.bat was: C:\DOS\MSCDEX.EXE /D:PANASON /L:R As before, the name given to the device (ie, PANASON) is the same in both cases. The letters /L:R at the end of the au­toexec.bat line simply designates the CD-ROM as drive R:. If this instruction is left out, then DOS would simply assign the next available letter after the hard drive (eg, D:). Note that the LASTDRIVE= designation in config.sys must come after the assigned drive letter. For example, LASTDRIVE=Z will work OK with the above example, while LASTDRIVE=I will cause problems (since R comes after I). Note also that the above two examples for the Sony and Panasonic drives are given as a guide only. Each installation will be different, depending on the drive model and the type of adapter card used. Unless you know exactly what you are doing, stick with the automatic software installation procedure. Testing To test the new drive, install a CD and check that you can access the drive from the Windows File Manager or by typing R: <ENTER> at the DOS prompt. If you can access the drive OK, it should now be possible to bring up a list of files (type DIR if at the DOS prompt). If DOS returns a “drive not ready” message, it’s possible that you’ve just been a bit impatient. When you install the disc, the drive will take a few seconds to spin up to speed so wait until the green light appears before attempting to access the drive. Finally, note that not all CD-ROM drives are supplied with software that will allow you to play normal music CDs. If this facility is important, check before you buy or make sure that you can obtain the required software by SC some other means. February 1995  55 Build these wide range electrostatic loudspeakers For many years, electrostatic loudspeakers have been very highly regarded but beyond the reach of the do-it-yourself con­structor. Now it is possible, using new materials & a new method. This wide range design is capable of very satisfying performance, equal to the very best of loudspeakers. By ROB McKINLAY This project germinated some years ago after listening to some expensive electrostatic loudspeakers at an upmarket hifi store. The sound quality was superb but the price tag made them unobtainable for most people. The lasting impression of their sound 56  Silicon Chip quality made listening to all but the best box type loud­speakers tedious. My own hifi set up was of very good quality but obviously lacked the clarity and insight of panel speakers. After reading the limited information that was available on ESL design and building some small test panels, I decided that it would be possible to design and build a quality set of ESLs at a much lower price than the commercially available items. As this was to be a completely new design I had the freedom and flexibil­ity to try to eliminate a number of the more tedious construc­tional tasks. The design had to retain the sonic benefits of panel loud­ speakers. It would be a full range design with good bass re­sponse; always a tricky area with ESL panels. They had to be easily made with handyman tools. No special tools or jigs were desired. They had to be made with readily available materials and at an economical price. The ESL III Electrostatic Loudspeaker is a three-panel, full-range Fig.1: the schematic of the ESL III loudspeaker. Each channel of the audio amplifier is coupled to a step-up transformer with a turns ratio of 100:1 & this drives the fixed steel plates which are perforated to allow the sound from the moving diagram to radiate from both sides. The moving diaphragm is a very thin plastic coated with a resistive doping material & this is biased at about 3kV. Note that there are three panels but only one is shown in this diagram. This view shows the various connections to the three panels & the terminal panel. Two wires connect to the audio amplifier while the third connects to a 9V DC plugpack supply. This powers the high frequency DC-DC inverter. The rear view of the ESL III loudspeaker without grille cloth fitted. This clearly shows the three panels, treble in the centre and midrange/bass on either side. Note that the wiring runs at high voltage and would normally be covered by the grille cloth. design, consisting of two bass/mid­ range panels and one upper mid/ treble panel. The three panels of one loud­speaker are arranged in a curvilinear array, ie, the bass panels placed on either side of the treble panel face slightly outward from the speaker centreline. This reduces beaming effects and improves the off-axis stereo image. The design uses a mechanical cross­ over in that, as the frequency roll-off of the bass panel occurs, the treble panel rolls on. This happens over a wide frequency range, resulting in a seamless integration of the bass and treble panels. The advantages of this approach are the elimination of phase anomalies caused by crossover components, greater reliabil­ity, reduction in complexity, better use of available power and most importantly, a reduction in cost. Facing page (top): installed in their custom made enclosures, the ESL III electrostatic speakers are very impressive to look at. They stand 1470mm high, 640mm wide and 150mm deep, with a 700 x 300mm foot­print. You will need a fairly large listening room if they are perform at their best. Design features The overall dimensions of the three panels required to make one loudspeaker are 600 x 1205 x 27mm (W x H x D). At this point it is appropriate to explain briefly how electrostatic loudspeak­ers work. Essentially the speaker is a sand- wich comprised of a move­ able diaphragm suspended between two perforated metal plates. The surface of the diaphragm is made conductive by the application of a highly resistive coating. A negative bias of several thousand volts DC is applied to this coating to provide a polarising force. When operating, one of the plates will become positive in relation to the diaphragm and the other will be negative. The positive plate will attract the negatively charged diaphragm while the negative plate repels the diaphragm. Hence, as the audio signal fluctuates on the two plates, the diaphragm reacts in the manner described above, mimicking the signal. Due to the extremely light weight of the diaphragm and the damping created by the air load, the reproduced signal is faithful to the input signal, with little February 1995  57 a ring of nuts and bolts or bonded together with adhe­sive. Both of these approaches work fine unless you want to open the panel up to make a change to something. The nuts and bolts method is tedious but non-destructive to the diaphragm and air gap spacers. The bonded method can cause damage to the diaphragm or spacers when the joint is broken. I opted for a system that simply clips the two panel halves together. One is able to disassemble the panel in a matter of seconds without damage and reassemble in the same time. This allows access to the diaphragm, which is still held at full tension on one half panel, for service, or to allow experimenta­tion with the node points. Diaphragm tensioning The bottom compartment of the enclosure houses the audio step-up transformer & the DC-DC inverter board. This includes a Cockroft-Walton multiplier, hence the array of high voltage ceramic ca­pacitors. or no distortion as created by conventional cone type speakers. Due to electrostatic loudspeakers being a true dipole, ie, sound radiates equally from both front and rear, a certain amount of low frequency rolloff will take place. This is caused by the cancellation effect of the front and rear sound wave being 180 degrees out of phase with each other. Careful design of the enclosure will reduce these effects. The normal output voltage of a typical power amplifier is not high enough to create the electrostatic field required for normal sound pressure levels so an audio step-up transformer is required. The transformer used in this project has a turns ratio of 1:100; ie 1 volt in produces 100 volts out. This allows effec­tive plate voltages to be reached. Diaphragm nodes Each panel has a series of diaphragm nodes placed in the vertical centreline and scaled in such a way that individual sections of the diaphragm reproduce only the frequencies desired of them. This reduces the inter­ mod­ ulation distortion that would be created by one section of the diaphragm trying to reproduce, say, 20Hz and 20kHz at the same time. Diaphragm bias is provided by a fast recovery diode voltage multiplier driven by an 11kHz oscillator. 58  Silicon Chip The custom wound audio transformer is rated at 100 watts. This proved to be the most difficult item to source. There are no “off-the-shelf” transformers available with the necessary turns ratio and frequency response to drive these panels. The solution was to have transformers specially wound for the project. After testing about 20 designs, all of which had problems with their high frequency response, we were fortunate enough to obtain a transformer to fit the bill. Each panel consists of two half panels clipped together in a unique manner. One panel half has the diaphragm attached to it, the other half carries the EHT supply rail. When the two halves are clipped together the EHT bias is transferred from the rail to the diaphragm. Each panel can be disassembled in a matter of seconds to effect any repairs or service should it be necessary. Unlike most electrostatic loudspeakers, diaphragm installation or replacement does not require any specialised equipment and can be carried out by a competent handyperson. The design allows experimentation for the more adventurous homebuilder to change the frequency response of the panels. This can done by adding simple resistor networks in series with the panels to create low pass filters. Most conventional electrostatic loud­ speakers are held to­ gether by A satisfactory way of tensioning the diaphragm and attach­ing it to the panel had to be found. Most designs use a tension­ing frame to tighten the diaphragm prior to installing into the panel. Construction of this was likely to take almost as long as the speakers themselves. As an alternative, a diaphragm material was found which had a greater than usual heatshrink rate and was adhesive on one side when heated. This killed two birds with one stone as the adhesive would not creep under full tension and was compatible with the support structure. It simply had to be taped down over the support panel, a heat gun used to activate the adhesive and then tightened by heatshrinking the remainder of the diaphragm. Another area of concern was the conductive coating on the diaphragm. Most commercial designs use a vacuum deposited metallised coating on the diaphragm material. This is difficult to obtain and is very expensive to have made. An alternative to this is to forcefully impregnate the diaphragm with graphite. This works well but can result in areas of diaphragm that are too conductive or not conductive enough. Both of these conditions are detrimental to speaker performance. This approach is also very hard work as considerable time and energy goes into hand rubbing each of the six diaphragms. The design described in this article uses a conductive solution which is mopped onto the diaphragm surface A closer view of the rear of the enclosure, showing the plastic grid structure of the three panels which are held in place by cleats. and cures after a couple of hours. This approach allows the diaphragm to be made conductive only where it is desired, eliminating possible EHT leakage paths. The next aspect of the design was the node point positioning. The final spacing was determined partly by calculation, partly by building numerous small panels and meas­ur­­ing their response, and partly by listen­ ing to the completed full size panels. The positioning of the node points is quite critical to the performance of the speaker. The final design element involved the enclosure and it was found that this had a significant effect on the overall sound of the speaker. It was desirable to raise the panels off the ground so that the centre of the panel was at ear level when seated, due to the centreline symmetrical positioning of the node points. It then became necessary to provide an enclosure that was solid down to floor level to reduce bass cancellation effects. The side cheeks to the enclosure were also found to be critical to bass reproduction. After much experimentation, I decided on the design shown in the photographs. Results The end result was an electrostatic loudspeaker which per­ formed extremely well. So well in fact that some visitors that listened to them wanted to build a pair themselves. This set the plan in motion to provide kits that did not cost an arm and a leg but would still give a performance rivalling commercial models. The kit includes: (1) steel grids that are custom punched specifically for this project and insulated with a high dielec­tric strength powdercoat enam­el; (2) an EHT supply designed by Oatley Electronics and powered from a 9V DC plugpack; (3) custom wound audio transformers; (4) all support panels and air gap spacers cut to size; (5) easy to install diaphragms complete with a spare; and (6) all components required to make a working set of panels. The enclosure is not included but can be purchased ready built. Enclosure drawings are available, at modest cost, for those wishing to make their own. The finished product seriously competes with commercial designs costing much more. They possess clarity and transparency, with very credible bass performance. Soundstaging is excellent with pinpoint centre stage imaging and believable depth. The speakers are available in kit form at $1199 for a pair plus an extra $499 for the two ready-built enclosures. Freight, packaging and insurance charges will vary from state to state. For further information, contact Rob McKinlay, E. R. Audio, 119 Brook­ ton Highway, Roley­stone, WA 6111. Phone (09) 397 6212; fax (09) 496 1546. Next month, we will continue with SC the construction details. February 1995  59 OUR NEW KIT CATALOGUE READY IN FEBRUARY 1995 Poll our (02) 579 3955 or (02) 570 7910 fax numbers for instructions on how to obtain our item/kit list. You can also ask for a copy of these to be sent out with your next order. BITS AND PIECES AT INCREDIBLE PRICES AX526, AX527 and AX 528 ICs: See SC Dec 92, EA Mar 93/94: $3.50 Ea. or 10 for $30. UHF Rx MODULE: Small surface mount receiver module. See SC Dec 92, EA Mar 93/94: $15.ULTRASONIC TRANSDUCERS: 40kHz Tx transducer, 40KHz Rx transducer, plus a 40kHz crystal: $6. PIR COMPONENTS: KC778 IC one chip PIR detector IC with every feature imaginable, plus a PCB mounted Fresnel lens, plus a dual element PIR sensor: $15. UA3730 IC: incredibly versatile combination lock IC plus a keypad to suit: $12. 8 CHANNEL IR REMOTE CONTROL COMPONENTS: Get a range of up to 15M with this combination of an 8 channel IR remote control transmitter IC, IR receiver module, 8 channel IR receiver IC, two resonators to suit : $15. SM7232 IC: Continuous Dimmer/ AC motor controller IC: $4. HIGH POWER IR LEDs: 880nM/30mW/12deg <at> 100mA: 10 for $9. DATA or APPLICATION INFORMATION SHEETS for any of the above are available with the purchase for 60c extra. $10 AM RADIO KIT We are giving away this complete AM radio kit at below the value of the components used. Includes the PCB plus all on-board components, a tuning knob, a speaker and a battery clip (9V battery not provided). See EA Mar 95. A COMPLETE AM RADIO KIT FOR: $10! USED GREEN MONITORS Used but tested 240V-12V operated 11" green monitors. These contain a switched mode mains 12V DC supply. Also contain separate logic boards with lots of ICs, including Eproms. These are easily disconnected, basic hook-up information supplied. $25 OPTICS 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. LARGE LENS ASSEMBLY: Tominon 230mm f4.5 1.7kG symmetrical lens, add an eyepiece ($4) to make a telescope: $40. PAIR OF LARGE LENSES: Two pairs of these are used in the above Tominon lens (0.6kG): $20. LARGE LENS: Out of a night viewer, can easily be pulled apart: $18. ARGON MIRRORS: High reflector and output coupler used to make a Argon tube: $50. 27 MHz TRANSMITTERS These new Australian made transmitters are assembled (PCB and components) and tested. They are Xtal locked on 26.995 MHz and were originally intended for transmitting digital information. Their discrete component design employs many components, including 5 transistors and 8 inductors. Circuit provided. 60  Silicon Chip DYNAMIC MICROPHONES Low impedance dynamic microphones with separate switch wiring, 3.5mm mic plug, 2.5mm switch plug, as used on most cassette recorders: $4 Ea 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: New famous brand 40mW-830nM IR laser diodes, suit medical and other applications: DIGITAL RECORDING MODULES LOW COST 1-2 CHANNEL UHF REMOTE CONTROL $7 Ea. or 4 for $20 Small US designed 12 second digital recording modules. Complete units that include a speaker and a battery: $18.50 PRINTER MECHANISMS Brand new Epson dot matrix printer mechanisms. Overall dimensions are 150x105x70mm. These are complete units and contain many useful parts: 12V DC motor (50mm long-30mm diam.) with built in tachometer, gears, solenoid, magnet, reed switch, dot matrix print head etc: $12 VISIBLE LASER DIODE KIT 5mW/670nM visible laser diode plus collimating lens, plus housing, plus APC driver kit (Sept 94 EA). UNBELIEVABLE PRICE: $35 CD MECHANISMS Brand new compact disc player mechanisms. Include IR laser diode, optics, small conventional DC motor, gears, stepping motor, magnets etc. The whole assembly is priced at less than the value of the collimating lens, which is easy to remove: $8.50 HF ELECTRONIC BALLASTS Brand new “slim line” cased electronic ballasts. They provide instant flicker free starting, extend tube life, reduce power consumption, eliminate flicker during operation (high frequency operation), and are “noise free” in operation. The design of these appears to be similar to the one published in the Oct 94 SILICON CHIP magazine. One of the models even includes a DIMMING OPTION!! Needs external 100K potentiometer or a 0-10V DC source. We have a good but limited stock of these and are offering them at fraction of the cost of the parts used in them! Type A: Designed to power two 32W - 4' tubes, will power two 40W - 4' tubes with no noticeable change in light output, has provision for dimming: $26 Type B: Designed to power two 16W - 18" tubes, will power two 18W - 18" tubes with no noticeable change in light output: $18 WELLER SOLDERING IRON TIPS New soldering iron for low voltage Weller soldering stations and mains operated Weller irons. Mixed popular sizes and temperatures. Specify mains or soldering station type: 5 for $10. PLUGS/SOCKETS 3 pin chassis mounting socket and a matching covered three pin plug. Good quality components that will handle a few amperes at low voltage: $5 for 4 pairs. 40mW IR LASER DIODES $60 Ea Constant current driver kit to suit: $10. 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 FIBRE OPTIC TUBES These US made tubes are from used equipment but in excellent condition. Have 25/40mm diameter, fibre-optically coupled input and output windows. The 25mm tube has an overall diameter of 57mm and is 60mm long. The 40mm tube has an overall diameter of 80mm and is 92mm long. The gain of these is such that they would produce a good image in approximately half moon illumination, when used with suitable “fast” lens, but they can also be IR assisted to see in total darkness. Our HIGH POWER LED IR ILLUMINATOR kit and the IR filter are both suitable for use with these tubes. The superior resolution of these tubes would make them suitable for low light video preamplifiers, wild life observation, and astronomical use. Each of the tubes is supplied with an 9V-EHT power supply kit. INCREDIBLE PRICES: $120 for the 25mm intensifier tube and supply kit. $180 for the 40mm intensifier tube and supply kit. We also have a good supply of the same tubes that may have a blemish which is not in the central viewing area!: !!ON SPECIAL!! $50 for a blemished 25 or 40mm (specify preference) image intensifier tube and supply kit. Matching good quality eyepiece lens only $7 extra! That’s almost a complete night viewer kit for $57. HIGH POWER LED IR ILLUMINATOR This kit includes two PCBs, all on-board components plus casing: switched mode power supply plus 60 high intensity 880nM IR (invisible) LEDs. Variable output power, 6-20VDC input, suitable for illuminating IR responsive CCD cameras, IR night viewers etc. Professional performance at a fraction of the price of the commercial product: COMPLETE KIT PRICE: $60 LASER POINTER SPECIAL A complete 5mW/670nM pointer in a compact plastic case. Uses a more efficient laser diode that results in a battery life of 10 hours. Powered by two AA batteries (supplied). $99 INTENSIFIED NIGHT VIEWER KIT SC Sept 94. See in the dark! Make your own night scope that will produce good vision in sub-starlight illumination! Has superior gain and resolution to all Russian viewers priced at under $1500. We supply a three stage fibre-optically coupled image intensifier tube, EHT power supply kit, and sufficient plastics to make a monocular scope. The three tubes are supplied already wired and bonded together. $290 for the 25mm version $390 for the 40mm version We can also supply the lens (100mm f2: $75) and the eyepiece ($18) which would be everything that is necessary to make an incredible viewer! 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 monolithic 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 monolithic HI-FI amplifier ICs, two PCBs to suit, circuit diagram/layout. Some additional components and a heatsink are required. LIGHT MOTION DETECTORS Small PCB Assembly based on a ULN2232 IC. This device has a built in light detector, filters, timer, narrow angle lens, and even a siren driver circuit that can drive an external 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 GAS LASER SPECIAL We have a good supply of some He-Ne laser heads that were removed from new or near new equipment, and have a power output of 2.5-5mW: very bright! With each head we will supply a 12V universal laser power supply kit for a ridiculous TOTAL PRICE of: $89 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 IR LASER DIODE KIT Brand new 780nM laser diodes (barely visible) mounted in a professional adjustable collimator-heatsink assembly. Each of these assemblies is supplied with a CONSTANT CURRENT DRIVER kit and a suitable PIN DIODE that can serve as a detector, plus some INSTRUCTIONS. Suitable for medical use, perimeter protection, data transmission, IR illumination, etc. responsive tube we ever supplied. The resultant viewer requires low level IR illumination. Basic instructions provided. $140 For the tube, objective lens, eyepiece lens, and the power supply kit. CCD CAMERA SPECIAL 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!!! Can be used in total darkness with infra red illumination. NEW LOW PRICE: $180 NOTE THAT WE CAN SUPPLY A SMALL USED BUT TESTED 5" GREEN MONITOR TO SUIT, FOR AN EXTRA $20!!! These compact units are enclosed in a die cast aluminium housing, but will require a few additional parts to derive the V&H sync signals. Basic hook-up information and the modification circuit/PCB design will be supplied. THE MONITOR IS NOT SOLD SEPARATELY. SOLID STATE “PELTIER EFFECT” COOLER/HEATER $40 These are the major parts needed to make a solid state thermoelectric cooler/heater. We can provide a large 12V-4.5A Peltier effect semiconductor, two thermal cut-out switches, and a 12V DC fan for a total price of: $35 We include a basic diagram/circuit showing how to make a small refrigerator/heater. The major additional items required will be an insulated container such as an old “Esky”, two heatsinks, and a small block of aluminium. We can also provide “just the basics” for this kit: a 5mW/780nM IR LASER DIODE plus a COLLIMATING LENS, plus a CONSTANT CURRENT DRIVER KIT, plus a PIN DIODE. UNBELIEVABLE PRICE: BIGGER LASER We have a good, but LIMITED QUANTITY of some “as new” red 6mW+ laser heads that were removed from new equipment. Head dimensions: 45mm diameter by 380mm long. With each of the heads we will include our 12V universal laser power supply. BARGAIN AT: $45 INFRA RED FILTER 12V-2.5 WATT SOLAR PANEL SPECIAL A very high quality IR filter and a RUBBER lens cover that would fit over most torches including MAGLITEs, and convert them to a good source of IR. The filter material withstands high temperatures and produces an output which would not be visible from a few metres away and in total darkness. Suitable for use with passive and active viewers. The filter and a rubber lens cover is priced at: $20 Ea. or 4 for $60 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, Antenna: Wire antenna - attached, Microphone: Electret condenser, Battery: One 1.5V silver oxide LR44/G13, Battery life: 60 hours, Weight: 15g, Dimensions: 1.3"x0.9"x0.4". $170 6mW+ head/supply. ITEM No. 0225B We can also supply a 240V-12V/4A-5V/4A switched mode power supply to suit for $30. These US made amophorous 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: 305x228mm, Vo-c: 18-20V, Is-c: 250mA. SPECIAL REDUCED PRICE: 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. IR “TANK SET” A set of components that can be used to make a very responsive infra red night viewer. The matching lens tube and eyepiece sets were removed from working military quality tank viewers. We also supply a very small EHT power supply kit that enables the tube to be operated from a small 9V battery. The tube employed is probably the most sensitive IR $15 MINIATURE FM TRANSMITTER $25 REEL TO REEL TAPES New studio quality 13cm-5" “Agfa” (German) 1/4" reel to reel tapes in original box, 180m-600ft: $8 Ea. MORE KITS-ITEMS 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. Magnetic Card Reader: professional assembled and cased unit that will read information from plastic cards, needs low current 12VDC supply-plugpack, $70. Switched Mode Power Supplies: mains in (240V), new assembled units with 12V-4A and 5V-4ADC outputs, $32. Electric Fence Kit: PCB and components, includes prewound transformer, $40. Plasma Ball Kit: PCB and components kit, needs any bulb, $25. Masthead Amplifier Kit: two PCBs plus all on board components: low noise (uses MAR-6 IC), covers VHF-UHF, $18. 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. Brake Light Indicator Kit: 60 LEDs, two PCBs and ten Rs, makes for a very bright 600mm long high intensity Red display, $30. IEC Leads: heavy duty 3 core (10A) 3M LEADS with IEC plug on one end and an European plug at the other, $1.50 Ea. or 10 for $10. IEC Extension Leads: 2M long, IEC plug at one end, IEC socket at other end, $5. Motor Special: these motors can also double up as generators. 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. Green Laser Tubes: Back in stock! The luminous output of these 1-1.5mW GREEN laser diode heads compares with a 5mW red tube!: $490 for a 1-1.5mW green head and a 12V operated universal laser inverter kit. 40 x 2 LCD Display: brand new 40 character by 2 line LCD displays with built in driver circuitry that uses Hitachi ICs, easy to drive “standard” displays, brief information provided, $30 Ea. or 4 for $100. RS232 Interface PCB: brand new PCB assembly, amongst many parts contains two INTERSIL ICL232 ICs: RS232 Tx - Rx ICs, $8. Modular Telephone Cables: 4-way modular curled cable with plugs fitted at each end, also a 4M long 8-way modular flat cable with plugs fitted at each end, one of each for $2. 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. Lenses: a pair of lens assemblies that were removed from brand new laser printers. They contain a total of 4 lenses which by different combinations - placement in a laser beam can diverge, collimate, make a small line, make an ellipse etc., $ 8. 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: $25. 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, $8. FM Transmitter Kit - Mk.II: 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 - Mk.I: 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. Argon-Ion Heads: used Argon-Ion heads with 30-100mW output in the blue-green spectrum, will be back in stock soon, priced at around $400 for the “head” only, power supply circuit and information supplied. Battery Charger: S2 accessory set for Telecom Walkabout “Phones”. Includes cigarette lighter cable, fast rate charger, and desktop stand. Actually charges 6 series connected AA Nicad batteries: $27. Lithium Batteries: Button shaped with pins, 20mm diameter, 3mm thick. A red led connected across one of these will produce light output for over 72 hours (3 days): 4 for $2. Cigarette Lighter Leads: Cigarette lighter plug with 3 metres of heavy duty fig. 8 flex connected. Should suit load currents up to 20A: 5 for $5. Supercaps: 0.047F/5.5V capacitors: 5 for $2. Hour Meter: Non resettable, mains powered (50HZ), WARBURTON FRANKI, 100,000 Hours maximum, 0.01Hr resolution: $15. PCB Mounted Switches: 90 deg. 3A-250V, SPDT: 4 for $2. Cone Tweeters: sealed back dynamic 8ohm tweeters: $5 Ea. AC Power Supply: Mains in, two separate 8.5V/3A outputs, in plastic case with mains power lead/plug and output leads/plugs: $15 Ea. Monitor PCBs: Complete PCB and yoke assembly for high resolution monochrome TV monitors (no tube). Operate from 12V DC, circuit and information provided: $15. OATLEY ELECTRONICS PO Box 89, Oatley, NSW 2223 Phone (02) 579 4985. Fax (02) 570 7910 Bankcard, Master Card, Visa Card & Amex accepted with phone & fax orders. P & P for most mixed orders: Aust. $6; NZ (airmail) $10. February 1995  61 SERVICEMAN'S LOG The topsy turvy world of remote control A popular saying in my boyhood household was that “lazi­ness is no good unless it is well carried out”. It was usually prompted by my tricks that made my chores easier to do; a snipe with the implication that making things easier was cheating in some way. By the standards of those days, the modern TV set, with its remote control unit, must surely represent the ultimate in lazi­ness being well carried out. Be that as it may, they are now a fact of life and, to be fair, they offer more than the opportuni­ty for laziness. For the hospital patient and anyone confined to bed, or the disabled generally, they are a godsend. All of which is leading up to a story about remote control units. I could write innumerable stories about these devices; hardly a day goes by but that one of these turns up on the bench. The faults are mostly routine – routine for remote control units, that is, because they have a pretty hard life. They are left on chairs and sat on, which can be disastrous if it is a hard seat; they are dropped on the floor, which is bad enough in itself, but worse if they are kicked or trodden on; and the kids play “catchings” with them. One that came in recently had fin­ished up in the washing-up water in the kitchen sink. Strangely enough, I was able to salvage that one. The lady of the house scooped it out almost immediately it hit the water and, although some moisture found its way in, it wasn’t flooded. Nevertheless, the lady was very diffident about approaching me, convinced that it would be a write off. I thought so too, until I opened it. To my surprise, it didn’t look so bad, so I gave it a solid spray with dewatering compound, the kind of thing used to dry out wet ignition systems. I left it for a while to dry out, then 62  Silicon Chip gave it a try. And it worked. More importantly, several months later it is still working. So that was one of the happier accidents. Conventional faults The more conventional faults include various battery prob­lems. It’s not so much flat batteries though, because most users fit new batteries immediately there is a problem. However, the battery contacts can give a lot of trouble, mainly due to loss of tension. And there can also be problems where the contacts are soldered to the board pattern. This junction is often weak me­ chanically and, after repeated battery replacements, the joint fails. Then there are the inevitable corrosion problems. Sometimes it is a rogue battery that has leaked but more often it is due to exhausted batteries that have been left in a unit that hasn’t been used for a while. It is usually possible to re-tension the contacts and to clean up corrosion. The latter may mean removing the contacts, scrubbing off the corrosion, and re-tinning them with solder. Fractured joints can sometimes be repaired and sometimes not. And there is some pattern of inherent faults. One that comes to mind seems to suffer more than a fair share of keypad problems. Repairs are seldom satisfactory and they are generally written off. Another problem area concerns the ceramic resonator. In most units, the ceramic resonator is mounted flat on the component side of the board, with its leads bent at 90 degrees and taken through the board to the copper pattern. The weakness here is that, in most cases, the ceramic resonator is supported only by its leads. And, eventually, vibra­tion will take its toll; one of the leads breaks. Fortunately, there is usually enough lead left to salvage the situation, after which a dab of glue to secure the ceramic resonator to the board makes for a better-than-new repair. An unusual fault So much for the general background. The story that started all this is something else again. The fault is so unusual I was tempted to hold back on the solution and offer a prize of a free flight to the Moon for anyone who picked it. Fortunately perhaps, some distant Scottish ancestry caused me to have second thoughts. OK, down to the story. This particular remote control is an NEC model RD-309E and is teamed with an NEC model N3420 TV set. It is owned by one of my a regular customers and the complaint was simple enough and fairly typical: “It doesn’t go”. I checked the batteries (two AA cells) and they were OK but closer examination threw suspicion on the battery contact ten­sion, along the lines already mentioned. It was a simple job to bend the springs to provide adequate contact pressure, then replace the batteries and try it with a test unit I have. No joy; it was still dead. So I opened the case and set it upside down (ie, keypad down) on the bench. As can be seen from the photograph, this reveals the component side of the board, with the IC, the ceramic resonator, a transistor, the IR LED and a few minor components at one end. My first check was at the ceramic resonator. The leads were intact but the ceramic resonator was not secured, so a spot of glue was applied to hold it firm. I then set it up for further testing. I have found that the easiest way to work on most of these units is to leave them upside down on the bench and feed them from a variable power supply via a couple of clip leads. This is often more convenient than trying to use the batteries, which may not be very secure when the case is open. So this was the setup I used for this one. And lo and be­ hold, the thing worked. I pressed a number of keys from under­neath and everything seemed to be OK. The only snag was, I didn’t know what I had done and so I decided to press on and see what happened. I put the whole thing back together again, refitted the batteries, turned it right side up, and checked it again. It was as dead as the proverbial dodo. I pulled it open, hooked it up to the power supply, and checked it again. And it worked. So what was I doing wrong? Seeking inspiration, I carefully turned the whole thing over, checked the front panel, and tried again. Once more, it was dead. It didn’t need many such checks to confirm what I now sus­pected; it would work when upside down but not when right way up. Well, I had no idea what was wrong but I suddenly realised that I had probably been caught out once before with the same symptoms, without realising it. A couple of months before, a customer had brought in exact­ly the same model unit. And, initially, the complaint was the same: “It doesn’t go”. And with good reason it appeared. One of the ceramic reso­nator leads had broken but with enough lead protruding to allow the break to be bridged with a blob of solder. After then gluing the ceramic resonator to February 1995  63 Fig.1: view inside the NEC RD-309E remote control, showing the PC board. The components next to the IC, from left, are: the 47µF electrolytic capacitor, the LED driver transistor, the ceramic resonator & the IR LED. the board, I fully expected the device to work. It did too, when I mocked it up on the bench upside down. I assumed that that was the end of exercise, apart from putting everything back together. As it so happened, pressure of other work caused me to put it to one side at that point, the customer having indicated that he was in no particular hurry. When I did finish the job, about a week later, the thing was dead. Over the next week or so, I tackled it several times in between bigger jobs but without success. Sometimes I could make it work, sometimes I couldn’t. Unfortunately, because of the on-again-offagain approach, I didn’t recognise any pattern; I simply assumed it was one of Murphy’s sick intermittent jokes. When the owner subsequently dropped in to see how I was progressing, I gave him a rundown of the above sequence and advised him that an intermittent fault in one of these devices might be more costly to find and fix that the unit was worth. He thought about it briefly, than decided to write it off, and asked me to get him a new one, which I did. And the old one finished up in the scrap box as a possible source of spare bits (eg, the keypad). But now, alerted by the sequence of events with the unit on the bench, I suddenly realised that the supposed “intermittent” behaviour, could easily have followed an upside down/ right side up sequence, without my realising it. All of which was food for thought but not of much help with the immediate problem. But I was determined to track it down now. I pulled the board out and went over it with a glass, look­ing for dry joints. 64  Silicon Chip The only suspects were the two for a 47µF electrolytic capacitor, which looked a trifle dodgy. I un­ soldered the joints, pulled the capacitor out, checked it (it was spot on) and soldered it back in. This made no difference to the be­haviour. I tried bashing and prodding to try to make it stop when it was in the working position, or to try to make it work when it was the other way up. There was no response either way. What about the ceramic resonator? Was this operating in both positions? With some delicate fiddling I attached the CRO in a manner which I hoped would hold when I turned the device over. Thankfully it did and this confirmed that the ceramic resonator operated in both positions. So what else was left? Not much, it seemed. It had to be a mechanical fault of some kind, but where? I thought about the IC but, without ruling it out completely, put it at the bottom of the list. For one thing, it contains the oscillator circuitry and I knew that this was working. Then I had a wild idea. It wouldn’t be the first time that an IR LED had given trouble, although only as a total failure. But what if...? Well, it was a long shot but it was easy to try; I had spares on hand and it involved only two soldered joints. And believe it or not, that was it. The new LED cured the problem and the unit has now been back with the customer for several weeks, with no sign of trouble. Naturally, as soon as I had proved the point, I could hardly wait to fish out the junked unit and confirm my suspi­cions. And I did; it was an upside down/right side up fault and when I fitted a new LED it came good, just as the other one had. So I now have a spare unit, which will come in handy for testing. But what could possibly be wrong with the LEDs? I dunno please – as they say in the classics. Visual inspection is point­less; both units are totally opaque to visible light and appear black. One of the good ones I fitted is clear but there is little to be seen that would provide a clue. Electrically, the faulty LEDs measure exactly as one would expect them to; ie, like a diode. Nor is there any indication of position sensitivity. Which is about all I can say about it. Not only is the fault almost unbelievable but it has turned up in two units. Well, two that I know of. I wonder if this story rings a bell with any readers. It would be easy to be deceived the first time, just as I was. Food for thought My next story is in a quite different vein. In fact, it is not particularly profound technically but the symptoms, and their possible effect on how the job might have been tackled, provide some food for thought. In particular, the sequence of events demonstrates just how easy it is for there to be a breakdown in communications between customer and serviceman. And while it turned out to be unimport­ant in this case, it emphasises that the risk is always there. And it can prove costly, both in terms of money and reputation. The device was a colour TV set, Palsonic model 345, now about 12 years old. And the same chassis was sold under the Princess label. It belonged to one of my lady customers and was brought in by a friend, who was simply acting as a courier. When I asked if he knew the nature of the complaint, he answered simply, “No picture”. Well, as we all know, that can have a couple of interpreta­tions. If there is a raster on the screen but no image, then there is a fault somewhere in the signal chain, anywhere from the tuner right through to the video amplifier system. If, on the other hand, there is no raster, it is a fair bet that the trouble is somewhere in the horizontal deflection system. So I normally try to clarify this point, using terminology appropriate to the customer (I avoid the word “raster” –it only produces a blank stare). But there was no point in trying to delve further in this case; the good samaritan courier was in no position to help. Oh well, no worries; I’d know as soon as I turned it on. Or so I thought. But when I did turn it on, the result did not really slot into either category, although I had to admit that the customer’s description was not strictly wrong. There was a raster on the screen, and there was evidence of video on the screen too, but there wasn’t a picture because the horizontal scan was out of lock. So much for trying to pick the faulty area from a customer’s description. But that was a minor hiccough; the real question was why was it out of lock. The horizontal hold control (R451, 10kΩ) on these sets is not on the rear apron of the chassis, as in most sets, but towards the front of the chassis. This means that the chassis has to be pulled in order to adjust it but it also means that it is unlikely that anyone has fiddled with it. So I pulled the chassis, located the pot, and gave it tweak. The picture locked up immediately, even though it was only a very small tweak. It gave me the distinct impression that it could have been due to drift in any of the associated resistors, particularly considering the age of the set. And, of course, it was a situation where one might be tempted to make a good show by returning the set to the customer within a couple of hours. But I’m too old to be caught that easily. I let the set run for the rest of the day and planned to do the same the next day too. The set was still running when I pulled the master switch that night and I naturally expected it to come on when I turned the switch back on next morning. But it didn’t, it was dead; no sound, no picture and no raster. My reaction was to wonder whether this was the condition the customer had experienced, when she nominated the fault as “no picture’. Either way, it seemed likely that the set had two faults; the one I had just fixed and the one I was now facing. At first, I suspected a power supply fault but a few quick meter checks tended to rule this out – the HT rail was normal at 112V. However, it was clear that there was no horizontal circuit activity. This prompted a voltage check on the collector of the horizontal February 1995  65 Fig.2: the horizontal & vertical oscillator circuit in the Palso­nic 345 is based on IC301 (top, left). The horizontal output transistor, Q404, is at bottom right, while the driver transis­tor, Q402, is immediately to its left. The horizontal hold con­trol, R451, is below pin 1 of the IC. output transistor (Q404), which was correct at 112V, and also on the collector of the horizontal driver transistor (Q402), which was correct at 42V. Similarly, there was correct voltage on pin 11 of IC301, the horizontal and vertical oscilla­tor generator. Those points cleared, it was necessary to delve a little deeper. I reached for the CRO leads and checked for any horizon­tal signal coming out of the IC at pin 4. There was none. A faulty IC? It could be, of course, but there were other possibilities. One was that some other circuit fault could shut down the horizontal oscillator, particularly involving the x-ray protection (over-voltage) circuit which connects to pin 3. So, before rushing in to replace the IC, I made some more checks. One of these involved the x-ray protection circuit but, as far as I could tell, it had not activated. Another check was at pin 10, which provides the output from the vertical oscillator. And this was quite revealing because it appeared that the vertical oscillator was dead also. And that immediately threw suspicion back on the IC. I made a few more voltage checks around the IC and finally decided that the only logical step was to replace it. They are not particularly expensive and it is no big deal to make the change, the only snag being that I didn’t have one in stock. So it had to be ordered and I put the set aside for a couple of days until it turned up. When it did, I lost no time in fitting it, whereupon the set leapt into life. But, interestingly, the horizontal system was now out of lock again and I had to reset it to what was virtually its original position to restore the lock. And that was it. After a couple of days running on the bench it went back to the customer and it hasn’t missed a beat since. But I did wonder about the faulty IC. Was it two separate faults or two different degrees of the one fault? We can never be sure, of course, but my tip is that it was one fault in some part of the internal circuitry common to both oscillators. At first, its effect was quite mild, being sufficient only to upset the vertical oscillator frequency slightly. Subsequently, it went all the way and shut down both oscillators. It’s all rather academic, anyway. What was more important was that I could easily have been caught out by it. After all, just what did the customer mean when she said “no SC picture”? Protect your valuable issues Silicon Chip Binders These beautifully-made binders will protect your copies of SILICON CHIP. They feature heavy-board covers & are made from a distinctive 2-tone green vinyl. They hold up to 14 issues & will look great on your bookshelf. ★ High quality with heavy board covers ★ Each binder holds up to 14 issues ★ 80mm internal width ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A14.95 each (incl. postage within Australia). NZ & PNG orders please add $A5.00 each for postage. Not available elsewhere. Just fill in & mail the order form in this issue; or fax (02) 979 6503; or phone (02) 979 5644 & quote your credit card number. 66  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 Fit this oil change timer to your car Can’t remember when you last changed your car’s oil? Build this Oil Change Timer & you won’t need to rely on your memory. It beeps a buzzer & flashes a LED after the engine has run for a preset number of hours. By DARREN YATES Keeping your car running in tip-top condition is something that everyone sees as an obvious necessity. However, it’s surprising to think how little time we spend making sure of that fact. Keeping an eye on the oil and water levels is something everyone is used to doing. And if you own a VW Beetle, it’s even easier – scrub one radiator. 72  Silicon Chip But how often do you think of changing the oil? Do you change it every six months or after a set number of kilometres? Or are you like most people and only think about it when the car is put in for other service work? Regular oil changes at the recommended service intervals are vital if engine wear is to be kept to a minimum. In fact, most car manufacturers recommend that the oil be changed every 6000-8000kms (or 5000 miles for us Beetle owners). However, depending on how the car is used, that 8000kms could be chalked up in a couple of months or it may take all year. If you don’t keep track of the kilometres, you have to rely on the 6-month rule and this is only a rough guide at best. So just how do you keep track of the oil change intervals? If you have your oil changed at a garage, a windscreen sticker will serve as the reminder although that’s easily ignored. This electronic reminder is more insistent. It flashes a LED and sounds an (optional) buzzer after the engine has run for a set number of hours. When you think about it, changing D2 1N4004 +5V 0.1 D4 1N4004 RESET S5 10k 3V BACK-UP 0.1 D1 D1 1N914 1N914 11 10M 16 IC1 4060 Q14 Q14 10 3 12 11 16 RST IC3 Q8 13 4040 4 10 Q7 CLK 2 Q6 3 Q5 +16384 +16384 4.7k X1 32.768kHz 39pF 100k 100k 11 RST IC2 4020 3 10 CLK Q14 Q14 16 8 8 E +12V FROM IGNITION SWITCH GND C IN OUT A S3 D7 S1 D8 4x1N914 D9 1N4004 F1 250mA IN 22 25VW K VIEWED FROM BELOW D6 D3 1N914 CHASSIS ZD1 18V 1W REG1 78L05 GND PIEZO BUZZER 1k S2 8 39pF B 10k D5 S4 CHANGE OIL LED1 A  10k B 10k OUT S6 K C Q1 BC548 E +5V 10 16VW OIL CHANGE TIMER Fig.1: the circuit is based on three low-cost CMOS counter ICs (IC1-3). IC1 & IC2 both divide the 32.768kHz clock frequency by 214, while IC3 provides four division ratios ranging from 25 to 28 at its Q5-Q8 outputs. These outputs are then selected by DIP switches S1-S4 to obtain the required timing period. S1 S2 S3 S4 Timer Period 0 0 0 0 Test 1 0 0 0 36 0 1 0 0 73 1 1 0 0 109 0 0 1 0 146 1 0 1 0 182 0 1 1 0 218 1 1 1 0 255 0 0 0 1 291 1 0 0 1 328 Circuit diagram 0 1 0 1 364 Fig.1 shows the circuit diagram for the Oil Change Timer. It uses three low-cost CMOS ICs to do the timing and a single transistor to beep the piezo buzzer and flash the LED. 1 1 0 1 401 0 0 1 1 437 1 0 1 1 473 0 1 1 1 510 coupled to the clock input of IC2, a 4020 14-bit counter IC. The difference between the 4020 and 4060 is that the 4020 doesn’t have an inbuilt oscillator. This IC further divides the frequency by 214, so that the output at its pin 3 is now just 0.00012Hz. This is equivalent to a period of 8192 seconds, or just under 2.3 hours. The output at pin 3 of IC2 then couples into divider stage IC3 which is a 4040 12-stage binary counter. We don’t need all of the stages of division here and only use the Q5-Q8 outputs. These outputs are fed via a 4-way DIP switch to diodes D8-D5 which, together with D3, form a simple but effective 5-input AND gate. D3 is driven directly by the 2Hz signal from IC1. The timing period is set by the DIP switches – see Table 1. Normally, one or more of these DIP switches is closed and so Q1’s base is pulled low by the corresponding outputs of IC3. This means that Q1, LED 1 and the buzzer are all off. At the end of the timing period, the relevant Q outputs of IC3 go high and so their corresponding diodes are now reverse biased. Q1’s base is now alternately pulled high and low at a 2Hz rate due to a 10kΩ pullup resistor and the clock signal driving D3. Thus, Q1 pulses on and off at a 2Hz rate to flash the LED and beep the buzzer. Switch S6 allows the buzzer to be 1 1 1 1 546 February 1995  73 your engine oil after a set number of hours makes a lot of sense. For example, if you spend a lot of your time travelling in the city, your average speed will probably be about 40km/h. Multiply this by 200 hours and you have your 8000kms. On the other hand, if you do a lot of highway driving, then you’ll clock up the kilometres in much less time. That’s why we’ve designed the unit so that you can choose from a number of presettable times from 36 to 546 hours (see Table 1). You should be able to find one that suits your style of driving. The Oil Change Timer uses only common ICs and components, most of which you’ll probably have lying around in your junkbox. It simply connects to your car’s ignition switch and to chassis. It then automatically starts timing whenever the engine is start­ed and backs up the accumulated time when the ignition is switched off using two nicad cells. Let’s look at Fig.1 more closely. IC1 is a 4060 14-bit binary counter with its own inbuilt oscillator. The crystal network on pins 10 and 11 ensures that its frequency is 32.768kHz. IC1 divides this frequency down by 16,384 (214) so that it is just 2Hz at the Q14 output (pin 3). This output from pin 3 is then Table 1: DIP Switch Settings 10k 4.7k 10M 2x39pF S1 IC1 4060 0.1 S2 1 S4 D4 IC3 4040 100k IC2 4020 D2 1k 10uF S3 D3 1 PIEZO BUZZER 1 78L05 22uF 10k 10k X1 10k D8 D7 D6 D5 D1 Q1 D9 12V FROM IGN 0.1 ZD1 S6 S5 3V BACKUP BATTERY K A LED1 Fig.2; make sure that all polarised parts are correctly oriented & note that the positive connection to the ignition switch must be run via a 250mA in-line fuse. The buzzer & switch S6 can be regarded as optional. switched out of circuit after it has sounded, to prevent annoyance. However, the LED continues to flash until the circuit is reset and this is done by pressing S5 to reset counters IC2 and IC3 (ie, when the oil is changed). If all four DIP switches are open, the 2Hz signal from IC1 is fed straight to Q1 which means that the LED flashes (and the buzzer sounds) as soon as power is applied. This is useful for checking that IC1, Q1, LED 1 and the buzzer are all operating correctly. Note also that once the LED starts flashing, it will con­tinue flashing for a period equal to the current time setting (unless the Reset switch is pressed). This means that if you set the unit to 146 hours, for example, the LED will flash for anoth­er 146 hours, or until the reset button is pressed. Power supply Power for the Oil Change Timer is derived from the ignition switch and is fed to a 78L05 3-terminal regulator via fuse F1 and reverse-polarity protection diode D9. ZD1, an 18V 1W zener diode, limits any high voltage spikes that may appear on the line due to the operation of other equipment. The 7805 regulator delivers a +5V rail and this is filtered using a 10µF electrolytic capacitor. This rail then directly powers the buzzer and LED circuitry, while the ICs are powered via isolation diode D2. D4, a 10kΩ resistor and two nicad cells form the battery backup circuit (you could also use two alkaline batteries if you prefer). When the ignition is on, D2 is forward biased and the nicad cells are trickle charged via the 10kΩ resistor. Converse­ly, when the ignition is off, D4 is forward biased and the backup battery provides power to the three ICs. Note that although the minimum operating voltage of CMOS 4000 series ICs is quoted as 3VDC, we’re only using a nominal 2.4V rail here due to the voltage drop across D4. However, we’ve found that a CMOS counter IC will remember its internal count even when the supply rail drops down to as low as 1VDC. At this voltage, you don’t get any output level and they won’t advance the count if you try to clock them. However, the applied voltage is enough to keep the internal flipflops powered up so that they remember their current settings. The other interesting point to note here is that the quies­ cent current is only about 0.2µA. As a result, the voltage devel­oped across D4 is only about 100mV and not the more normal 600mV. This low quiescent current also means that the backup battery will last for the length of its shelf life. To preserve the counts in IC2 and IC3, it is also necessary to disable IC1’s oscillator when the ignition is switched off. This is done using diode D1. When the ignition is on, D1 is reversed biased and the oscillator operates in its normal fash­ion. However, when the ignition is switched RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ No. 1 1 4 1 1 74  Silicon Chip Value 10MΩ 5% 100kΩ 10kΩ 4.7kΩ 1kΩ 4-Band Code (1%) brown black blue gold brown black yellow brown brown black orange brown yellow violet red brown brown black red brown 5-Band Code (1%) not applicable brown black black orange brown brown black black red brown yellow violet black brown brown brown black black brown brown PARTS LIST 1 PC board, code 05102951, 102 x 56mm 1 plastic case, 130 x 68 x 41mm 1 front panel label, 127 x 63mm 1 momentary NO pushbutton switch 1 SPDT toggle switch 1 mini piezo buzzer (7.5mm pin spacing) 1 in-line fuseholder & 250mA fuse 2 AA nicad cells 1 2 x AA cell holder 1 battery snap connector 1 4-way DIP switch 1 32.768kHz watch crystal The batteries can be secured inside the case by wrapping them in foam rubber & then sandwiching them between the board & the lid when the lid is closed. The 4-way DIP switch allows 16 possible settings between 36 hours & 546 hours. In general, the lower settings will be suitable for cars, while the high settings can be used for stationary engines. Semiconductors 1 4060 14-bit counter/oscillator (IC1) 1 4020 14-bit counter (IC2) 1 4040 12-bit counter (IC3) 1 78L05 3-terminal regulator 1 BC548 NPN transistor (Q1) 1 18V 1W zener diode (ZD1) 3 1N4004 diodes (D2,D4,D9) 6 1N914 signal diodes (D1,D3,D5-D8) 1 5mm red LED (LED 1) 4 12mm x 3mm-dia. machine screws plus 8 nuts off, D1 becomes forward biased and pulls pin 11 of IC1 down to 0.6V. This stops the oscillator and so no further clock pulses are produced to clock IC2 and IC3. mounted with its ON position towards diodes D5-D8. The buzzer must be mounted with its positive terminal adjacent to the edge of the PC board –see Fig.2. Capacitors 1 22µF 25VW electrolytic 1 10µF 16VW electrolytic 2 0.1µF 63VW MKT polyester 2 39pF ceramic Construction Final assembly All the components for the Oil Change Timer are installed on a PC board measuring 102 x 57mm and coded 05102951. Before you begin construction, check your etched board carefully against the published pattern to ensure that there are no shorts or breaks in the tracks. If you find any, use a small artwork knife or a touch of your soldering iron where appropriate to fix the problem. Fig.2 shows the layout on the PC board. Begin by installing PC stakes at the eight external wiring points, then mount the remaining parts as shown. Leave the DIP switch and the buzzer until last and take care to ensure that the semiconductors are all correctly oriented. Note that the pins on the 4-way DIP switch can be somewhat flimsy so be careful not to break them. It should be The prototype board was housed in a small plastic case but this can be considered optional. In a practical installation, you might elect to wrap the PC board in foam and hide it behind the dashboard. That way, the LED and the two switches could all be mounted on a small satellite panel situated somewhere on the console. You could even elect to delete the buzzer and toggle switch altogether and just settle on the flashing LED to provide the oil change indication. If you do elect to mount the unit in the specified case, then proceed as follows. First, use the board as a template for marking out and drilling its mounting holes. This done secure the board in position using machine screws and nuts, with an addi­tional nut under each corner serving as a spacer. Resistors (1%, 0.25W) 1 10MΩ 5% 1 4.7kΩ 1 100kΩ 1 1kΩ 4 10kΩ Miscellaneous Light-duty hook-up wire, auto­ motive cable (for power supply connections), automotive connect­ ors, heatshrink tubing. Once the board is in position, drill a 6mm hole in the side of the case adjacent to the buzzer to allow the sound to escape. An additional hole is also required in one end of the case to accept the ignition switch leads. The front panel artwork can now be affixed to the lid and the holes drilled for the warning LED and the two switches. Complete the construction by February 1995  75 OIL CHANGE TIMER OIL WARNING RESET mounting the front panel items and running the wiring as shown in Fig.2. You can use light-duty hook-up wire for this job. Take care with the orientation of the LED; its anode lead is the longer of the two (see Fig.1). Take care also to ensure that the leads to the battery snap connector are wired with the correct polarity. This clips onto a 2-AA cell holder. The ignition leads should be run using medium-duty automotive cable. Before you screw the lid down, connect the circuit to a 12VDC source. This can be either a power supply or a 12V battery. With all of the DIP switches open, the LED and buzzer should start immediately and should pulse on and off at 0.5-second intervals. The supply voltage on pin 16 of each IC should be about 4.4V. Setting the DIP switches Assuming everything works correctly, you can set the DIP switches to give ALARM ON The 4-way DIP switch is used to set the required timing period. Refer to Table 1 for the various settings – there are 16 combinations to choose from. the required number of hours. Table 1 shows the period provided by each combination. In fact, you might want to give yourself a trial period over a few days to arrive at a reasonable average speed. This is easy to do. Just set your odo­ meter to zero and keep a record of your driving periods over the next few days. Fig.4: check your PC board against this full-size etching pattern before mounting any of the parts. 76  Silicon Chip Fig.3 (left): this full-size artwork can be used as a drilling template for the front panel. Alternatively, you can mount the board under the dashboard somewhere & simply mount the switches & the warning LED on a small panel. You can then use the odometer reading and the accumulated period to calculate your average speed. From there, you can then calculate the number of engine hours it will take to cover the required dis­tance. An example will serve to demonstrate this. Let’s say that, over several days, you cover a total distance of 400km in an accumulated time of 12 hours. In that case, your average speed will be 400/12 = 33.3km/h. If we now assume an oil change service interval of 7500km, then the approximate number of engine hours required to cover this distance will be 7500/33.3 = 225.2 hours. If we look now at Table 1, we see that 218 hours is the closest available setting. To obtain this setting, we simply leave S1 & S4 off and set S2 & S3 on. Installation The unit is relatively easy to install, since there are only two external wiring connections. One connection goes to chassis, while the other goes to the switched side of the igni­tion switch. The latter connection is best made at the fuse panel and should be run via a 250mA in-line fuse. Alternatively, you can run this lead to the ignition switch via one of the accessory fuses (eg, for the car radio). Do not leave out the fuse; it is a necessary safety precau­ tion in the event of a short inside the unit. Also, make sure that you install all wiring in a professional manner and use automotive connectors and heatshrink tubing to terminate the leads. Finally, you must press the reset button the first time the unit is powered up, to make sure that the counters start from scratch. After that, the reset button is pressed only when the engine oil is changed. For this reason, you might like to mount the reset button in some inconspicuous location, away SC from prying fingers. REMOTE CONTROL BY BOB YOUNG Building a complete remote control system for models; Pt.2 This month, we present the circuit description of the Silvertone Mk.22 24-channel AM receiver. Although designed pri­marily for the radio control of models, it also lends itself to a myriad of non-modelling applications. The receiver is a “three-PCB” arrangement, with PCB1 for the receiver, PCB2 for the first eight channels in the decoder and PCB3 for the last 16 channels. This month, we are describing the circuit operation, with the construction to follow next month. The design of any electronic device represents a series of compromises which eventually lead to a completed unit. In fact, many of the requirements imposed on the designer are conflicting in nature and we will discuss these conflicts as we go along. Basically, the design requirements for a receiver intended for use in the radio control of models are: small physical size, low cost, out-of-sight range on a low power transmitter (200-600mW), good noise rejection, ability to operate in close physi­ cal proximity to other transmitters (some of which may be only 10-20kHz away), temperature stability, and the ability to operate with one cell in the battery pack short circuited. Quite a number of prototypes were produced during the development of the Mk.22. For those who are curious about the Mk.22 designation, the last production Silvertone receiver was the Mk.14. Mk.15 - Mk.21 were proThis larger-than-life size photo shows the completed receiver assembly. Note the socket for the plugin crystal. The resistors, capacitors & transistors are surface-mounted on the copper side of the board. duced during the development of this unit. The main problems encountered were PCB layout problems causing front end instability, excessive noise, oscillator stability and local oscillator injection levels and coil phasing. You will note that all of these are essentially RF problems. The IF stages were no problem. The resulting receiver is a very useful little unit which gives surprisingly good results considering its simplicity. As my mate Klaus (who provided valuable assistance with this project, including the test flying) pointed out, there is not a lot that can be done with a couple of transistors and IF cans. Sensitivity Receiver sensitivity is approximately 2µV with about 1µV thrown away in the audio slicer. This results in a receiver of approximately 3µV sensitivity. Translated into practical terms, the result is about 600 metres ground range (depending on condi­ tions) and about 1.5km in the air or over water. In R/C modelling, it is important that the transmitter and receiver do not provide excessive performance. This is because many modelling sites are in close proximity to each other and excessive transmitter power or receiver sensitivity can result in inter­field interference. The trick is to provide just enough performance to do the job reliably. The band spacing on this receiver is 20kHz and this spacing can be used with complete safety. In addition, the receiver layout has a very small cross-section and this allows the board to be mounted at right angles to the February 1995  77 C13 2.2 R9 180k R10 2.2k C16 47 B E L5, L6 : TOKO M113CN 2K218 DC L4 : LMC 4100A L2 : LMC 4101A L1 : LMC4102A XTAL1 : 30MHz SERIES MODE 3RD OVERTONE R11 470  E C C VIEWED FROM ABOVE B R2 2.2k S Q3 BFT25 R5 1k E C10 4.7pF 4.7PF C B 30MHz XTAL1 C11 22pF V+ C7 15pF S R3 100k 78  Silicon Chip C9 .01 C12 .01 L3 D1 BFR92A S F F L5 ANTENNA 1 E B ANTENNA 2 C4 10pF 10pF C5 3.3pF C2 10pF 10pF C1 .0047 S F L6 F C3 .001 B R1 680  E E C L4 Q1 BFT25 R4 2.2k C8 .001 B R6 1.5k E R7 2.2k C6 2.2 R8 1M CF1 BFB455 B Q4 BFT25 Q2 BFT25 C Circuit details SILVERTONE MK22 RECEIVER B D2 BAS16 R13 10k L1 L2 direction of travel, even in the most slender of models. A plug-in crystal facility is also provided to allow the crystal to be quickly changed on the field. The machine-wound RF coils suggested are only suitable for 29MHz but with hand­wound coils, this receiver will tune over the range 27-40MHz. All in all, it’s a very useful little receiver which will satisfy all but the most demanding modellers. Q6 BC848 R12 1k C14 2.2 C C15 .047 V+ Q5 BC848 E C +4.8V TB1 Fig.1 (left): the receiver follows conventional superhet principles & features a crystal controlled local oscillator (Q3 & Xtal1), a double tuned front end feeding a conventional transistor mixer (Q1), two IF stages work­ing at 455kHz (Q2 & Q4), & the transistorised equivalent of an anode bend detector (Q6). The receiver follows conventional superhet principles and features a crystal controlled oscillator, a double tuned front end feeding a conventional transistor mixer, two IF stages work­ ing at 455kHz, and the transistorised equivalent of an anode bend detector. Fig.1 shows the details. The transmitted signal arrives at the antenna and is fed into either the primary or the secondary of coil L5, depending upon the application. Antenna 1 is intended for coax-feed remote antennas, while Antenna 2 is the normal model aircraft antenna (usually one metre of flexible hook-up wire). If signal-to-noise ratio is more important than range in your application, then use Antenna 1, even for the flexible wire antenna. This will result in a much cleaner signal at very low signal strengths but will cost about 6-8dB in gain. Diode D1 acts as a clamp to prevent mixer overload when the transmitter antenna is very close to the receiver antenna. This is a serious problem in model applications, as modellers often need to stand over their models in order to operate them unas­sisted. A common trick is to stand astride a model aircraft, for example, with the tailplane hooked behind the ankles whilst the motor is run up to clear the plug and check the mixture. This will result in a very high signal level at the receiver mixer if precautions are not built into the front end to compensate. earth/antenna and the transmitter antenna, these two signals (which are opposite in phase) can cancel each other out, the nett result being a com­ plete loss of signal and what is known as a glitch. This is a momentary loss of signal which clears itself almost immediately after it occurs. This problem can and does occur in most model receivers and accounts for some of the mysterious little hiccups which occur from time to time. Local oscillator This views shows the completed receiver (right) together with a companion 8-channel decoder unit (to be described next month). The two units can be fitted together inside a small metal case. Thus, D1 clamps the signal to 0.6V maximum. The downside to D1 is that it can introduce intermodulation effects at the mixer. For this reason, D1’s physical characteristics are ex­tremely important, if another transmitter is operated close by and on an adjacent channel. From experience, I know that a 1N4148 diode works well in this application. However, the Mk.22 receiver uses the base-emitter junction of a VHF transistor (BFR92A) for this diode and this also works extremely well. Coil L6 provides additional fre­ quency selectivity and also matches the 1-metre wire antenna into the base of the mixer. Before leaving the antenna coils, there is one very import­ant point to bring to light regarding the earth/antenna relation­ship. Ideally, the signal appears in its strongest form across the antenna and is balanced against a very strong ground connec­tion. In model work and particularly model aircraft work, howev­ er, there is no ground connection and the battery and interwiring have to work as a solid earth. The problem is, this wiring varies from model to model, depending on the size of the model, number of channels, servos and the neatness of the installation. In some cases, signal inversion can take place across coil L5, where the antenna is acting as a counterpoise (earth) and the earth wiring is acting as the antenna. In freak cases, de­pending on the polarisation of the receiver Fig.2: this scope photograph shows the output signal on the collector of detector stage Q6. Transistor Q3 functions as a local oscillator and runs at the carrier frequency plus 455kHz. In Australia, local oscilla­tors run on the high side of the carrier in the 29MHz band, due to possible image problems from the 30MHz band. The opposite is the case on the 36MHz band where the local oscillator runs on the low side of the carrier. Coil L3 forms the tank coil for the local oscillator, while its secondary provides low impedance matching for injecting the oscillator signal into the emitter of Q1 via C12. C7 provides the fine tuning for the crystal frequency. The crystal can be pulled about 1-1.5kHz by adjusting C7 and C10. The values presented on the circuit are for Showa brand crystals and may need some adjust­ment if different brands of crystals are used. Transistor Q1 functions as the mixer and the resulting 455kHz IF signal is derived from the composite signal by L4. C8 damps L4 to prevent ringing if it occurs. It is not fitted with the 4000 series coils provided in the kit but may be required if different brands of coils are used. Q2, L2, Q4 & L1 provide the IF amplification, with R6 acting as the main gain control. Increasing its value will reduce the gain (the value shown on Fig.1 provides near maximum gain). Ceramic resonator CF1 across Q4’s emitter resistor (R11) sharpens the bandpass characteristic of the IF stage by approximately 3dB and is a useful addition. Detection & AGC Q6 acts as the transistorised equivalent of an anode bend detector and provides the recovered audio signal as well as the AGC control voltage. Diode D2 and capacitor C15 rectify and filter out the 455kHz component. The recovered audio will be approx­imately February 1995  79 Frequency Control At Flying Fields The receiver presented in this article is intended for use on the 29MHz band and, in fact, the machine-wound coils recom­ mended will only tune from 27-29MHz. Hand-wound coils will allow the unit to be tuned through the full range of frequencies avail­able to modellers from 27-40MHz. However, its use on modelling frequencies outside the 29MHz band is not recommended for several reasons, as set out below. In addition, non-modelling applica­tions will need to take into account the relevant Department of Transport and Communications regulations. 27MHz Citizens Band (26.95727.282MHz): the original garbage band, cluttered with cosmic noise and thus given over to experimenters from the early days. It was heavily used by modellers for many years until CB traffic made it too dangerous. This band is very busy with CB traffic and now frowned upon by the authorities for modelling use. Two frequencies are given over to children’s toys and “toy” walkie talkies. 29MHz Band (29.72-30.00MHz): a specific modelling band allocated when the CB band became unusable (c. 1975) and the recommended band for this receiver. The frequencies recommended for use in this band are set out in Table 1 Crystals on these frequencies are available from most good hobby shops. This band is used extensively 3V p-p at high signal levels. The slicer in the decoder (to follow) rejects the bottom 1V of the audio output and passes only the clean, high level signal to the audio amplifier. As the signal strength increases, the 80  Silicon Chip Silvertone Keyboards are the recommended method of fre­quency control for all national events sanctioned by the Model Aeronautical Association of Australia (MAAA). Illustrated are the 29MHz board (standing) and the new expanded 36MHz two-board set. The expanded 36MHz band, soon to be released, now features 59 frequencies at 10kHz spacing. Table 1 Channel TX RX 10 29.725 30.18 12 29.745 30.20 14 29.765 30.22 16 29.785 30.24 18 29.805 30.26 20 29.825 30.28 22 29.845 30.30 24 29.865 30.32 26 29.885 30.34 28 29.905 30.36 30 29.925 30.38 32 29.945 30.40 34 29.965 30.42 36 29.985 30.44 by modellers favouring 2-channel equipment (cars and boats) but almost deserted now on flying fields due to the rush to 36MHz. This is a wise choice if you just want to go to the field and fly, free of channel clutter and waiting time. 36MHz band (36.00-36.60MHz): soon to be expanded and opened up for use with a 10kHz frequency voltage at the col­lector of Q6 falls towards ground and the bias supplied to Q1, Q2 & Q4 via R9, R2, R4 & R7 falls, thus reducing the gain of these stages. Capacitor C6 filters out any audio on the AGC line, while R9 & C6 together spacing. The Mk.22 is not recommended for 10kHz spacing and is thus not recommended for use on the 36MHz band. 40MHz band (40.66-40.70MHz): another of the original modelling allocations but now not recommended due to heavy traf­fic from hospital pagers and the like on 40.680MHz. Channel 50 (40.665) and Channel 53 (40.695) are still OK for 10kHz or wider bandwidth receivers in areas free of this traffic. The Silvertone Keyboard pictured above was designed in 1969 to allow the mixing of equipment with various bandwidth characteris­ tics at busy flying fields. It is basically a graphic representa­ tion of the frequency allocation laid out on a 1-inch = 10kHz grid. Each modeller is supplied with a key, the width of which is proportional to the bandwidth of his equipment. Thus, a 10kHz system uses a 1-inch key, while a 20kHz system uses a 2-inch key. To reserve a frequency block in order to fly safely, the correct width key is simply inserted into the appropriate slot in the board, thus reserving the frequencies required. provide the AGC time constant to filter out any flutter caused by rapid variations in signal strength. These can occur due to high speed aircraft flying by the transmitter or through weak signal areas. Finally, Q5 and C16 provide the power supply filtering. In operation, the capacitance of C16 is multiplied by the gain of Q5, thus resulting in a very simple and effective filter. Unusual Use For A Speed Control Unit Substitute at your peril Now a few general notes on the overall design of the re­ceiver. First, substitute values at your own peril. And to those who wish to do their own through-hole layout, the best of luck. Half of the prototypes were rejected because of layout problems. RF circuits are very sensitive to board layout and conse­quently the layout forms a major component in the design. Capacitor C14 is a layout compensation filter and must be mounted in the physical location shown on the component overlay. C13 is there to provide spike suppression on the power rail input. For those still determined to press on, use 2N3646 or BF494 transistors in the RF and IF stages. These will give the best noise and AGC characteristics. The surface mount BFT25 transis­tors used in the unit described here were chosen for the same reason and were selected after trying many types. Let me tell you, these are an expensive transistor but are well worth the money in this application. Also, use a BC847 in the DC and audio stages. Try not to substitute for the IF coils as they are the heart of the system and a change here can create all sorts of havoc. RF coils The only other components which are critical are the RF coils. These may be hand-wound and Neosid make a neat little 4mm coil former which will fit the PC board with only a slight joggle of the mounting pins. Use 12 turns of 28 B&S wire with a 33pF capacitor. The secondary consists of three turns of the same wire. Be sure to follow the start and finish instruction on the schematic. Reduce the capacitor to increase the frequency –there is no need to change the turns. They should tune to 40MHz with about 22pF of capacitance. You can use a 1N4148 diode for D1 but do not substitute anything else. In addition, make sure that you use NPO capacitors on all of the values up to .001µF. The rest of the components One of our readers, Peter Barsden of WA, has sent along some interesting photos of his gyrocopter (no details provided) which is fitted with a pre-rotator. This unit consists of an electric motor (located at the top of the mast) and this spins up the rotor before takeoff to reduce the takeoff distance. The electric motor is controlled by a Speed1B speed control unit fitted with a self- contained pulse generator, as published in Silicon Chip in November & December 1992, January 1993 and April 1993. Peter has purchased six of these units and appears to have convinced his friends that the Speed1B is the way to go. are not that critical. The resistors can all be 1/8W types. Surface mount components Finally, I failed to stress one important point last month on the hand assembly of surface mount components. The manufac­tures do not recommend surface mount components for hand assembly due to the risk of thermal shock cracking the substrate of some of the components. In practise, this can be minimised by heating the pad first and letting the solder flow from the tip of the iron to the component (ie, apply the solder to the tip of the iron and not to the component). Remember also that the iron and the solder (with flux) must be applied simultaneously to the joint. Do not try to transfer solder from the iron to the joint. Also, try to avoid touching the component with the tip of the iron. As you will recall, I suggested soldering one pad of each component first by sliding their ends into molten solder. This minimises the thermal shock. Looked at in this light, it is probably a good idea to immediately solder the second pad of a component after the first (ie, while it is still warm), rather than after all components have been mounted. In practise, I have hand-mounted thousands of these components with no signs of visible damage but do try to be as careful as possible. To recap my previous advice, use a low wattage iron (20W), keep the iron temperature as low as practical and avoid touching the component with the tip of the iron. Next month, we shall continue with details of the SC board assembly and alignment. Acknowledgement I would like to thank everyone at Borundi Electronics for the assistance and cooperation given to me throughout this project. Without the use of their proto­typing PCB facilities, I would have faced great difficulties in completing this design. February 1995  81 VINTAGE RADIO By JOHN HILL Restoring a Tasma TRF receiver I had an interesting & most demanding repair to do recently, involving a 1931 model 65 Tasma console. The old Tasma is a very basic 5-valve TRF (tuned radio frequency) receiver & it was in a woeful state of disrepair. The Tasma belongs to a radio collector mate who bought it sight unseen, except for a photograph which was sent to him from Queensland. What the photograph didn’t show was that the receiver had no valves or loudspeaker and had a totally burnt-out power transformer. On delivery of the Tasma, its new owner was so disheartened with his purchase that he placed it in an auction. However, after a conversation with me about replacement transformers and other parts, the dilapidated Tasma wreck was quickly retrieved from the auction rooms. In due course, the chassis and two electrodynamic loudspeakers (a Jensen and a Rola) found their way onto my work­bench. A Jensen speaker was originally fitted to the Tasma and that make was to be given preference as a replacement over the Rola. Oh, how I wish that I had kept my big mouth shut! On seeing the Tasma for the first time, I soon realized why it had been sent off to the auction rooms. It looked as though it had spent most of its life in a tropical rainforest. I am inclined to think that Queensland weather is not kind to vintage electronics. The burnt-out power transformer was interesting in that it was constructed more like a modern transformer rather than one from the 1930s. As shown in one of the accompanying photographs, each winding is placed side by side instead of one on top of the other, as was usually the case in that era. Rewinding the transformer was considered at one stage but it was more than I could handle, as both the primary and high tension windings were open. And having it rewound professionally would be quite an expensive repair job – probably at least $100. As luck would have it, the owner had a discarded old Hy­pressco chassis which would hopefully supply a suitable power transformer with a 2.5V low tension winding. That too was on my workbench, waiting to be cannibalised for spare parts. Other problems After a complete strip-down & repaint, the derelict Tasma chassis looked as good as new. This particular receiver now works better than ever, following the discovery of a manufactur­ing fault. 82  Silicon Chip A quick check over the Tasma chassis revealed that there were other serious problems apart from the defunct power trans­former. Two of the RF (radio frequency) coils had open primary windings and they would either need repairing or replacing. When you are faced with a rotten job – it’s usually rotten all the way! The 3-gang tuning capacitor had its problems too, with dry rusty bearings and the three sets of moveable plates about 45 degrees out of alignment with each other. In addition, all the paper capacitors were leaky and the large block capacitors used in the high tension filter were particularly bad. Some of the resistors had gone high too and the wirewound high-tension drop­ping resistor had several dead taps on it, This close-up view shows the new power transformer cover. Made from light gauge sheet steel with spot welded seams, it is iden­tical to the original apart from being 10mm higher. indicating either poor connections or a break in the resistance wire. Fin­ally, the tone switch had also been badly strained and wasn’t making contact at any of its four positions. As I said before, rotten all the way! Sorting the transformer When faced with such a job, it is hard to know just where to start. I decided to check out the replacement power transform­er to see if it would work in OK. The Hypressco chassis had its share of problems too. The rectifier socket had a great hole burnt in it and all the valve pin connectors were just dangling on their respective wires underneath. Although the power transformer was a large 2.5V type, it was not the original. There was another set of bolt holes in the chassis that suggested there had been a transplant at some time in the past. Checking out the transformer soon revealed that it had suffered a coronary in one half of the high-tension winding. Repair prospects at that stage of the proceedings did not look very promising. As the transformer was particularly large and robust look­ing, I thought I might try feeding the good half of the winding into a silicon diode bridge rectifier to supply the set’s high tension. In fact, the bridge rectifier setup worked quite well except that it required a sizeable wirewound resistor to reduce the voltage to a level that would work in with a 2kΩ field coil. What’s more, the owner wasn’t really happy about his Tasma being “hot rodded” to such an extent, as he likes things to be reason­ably original. The thought of silicon diodes and large 20W resis­tors did not appeal. The next alternative was to use the half high-tension wind­ ing with the 80 rectifier connected as a half-wave unit. Surpris­ingly, this worked better than expected. It produced the correct voltage and is completely hum free while still using only 10µF electrolytics either side of the field coil. As the set wasn’t working at this stage, all the power transformer tests were done using a test rig that produced a 50mA load. Although the high tension arrangements are not a desirable set up, the receiver has run for prolonged periods of up to four hours without the transformer becoming any hotter than moderately warm. There was another problem yet to be solved regarding the replacement transformer. As the substitute unit is about 10mm higher than the original, the transformer cover would no longer fit. No problems! The local sheetmetal man made up a similar but deeper cover and after a coat of paint no one would ever know the difference. Although some readers may strongly disapprove of all these devious goings on, everything seems to be working well in the power transformer department and once the cover is on it even looks OK. I believe it is better to improvise and have a receiver working than to have it original and either not working or cost­ing a fortune to repair. The Tasma’s original power transformer (left) had many charred windings & was a total write off. Removing & stripping the tuning capacitor (above) was the best way to clean it & lubricate the spindle bearings. February 1995  83 Disaster struck at about fifty turns when the wire broke. A strand of copper wire a mere eighth of a millimetre in diameter is not very strong and coil winding requires a reasonable amount of tension. When winding, one always hopes that the coil does not break or slip out of one’s aching fingers. If either happens, it’s a case of “oh well; start again”! In the end, the outcome was quite successful although re­ winding RF coils is always a tedious job. Other repairs Although the replacement power transformer only had one half of its hightension winding intact, it was still able to supply the Tasma’s needs. Note that this photograph was taken with the experimental bridge rectifier still in place. The two open-circuit RF coils were next. First, a rough sketch was made of the wiring connections so that everything would go back where it should. This is a good precaution to take before unsoldering anything – RF coils or otherwise. The RF coils are identical and they had the same fault. Fortunately, the open primary winding is wound over the top of the secondary which made the repair a good deal easier than if it had been the other way around. The problem was the much dreaded “green spot”. The fine silk-covered wire had several spots of corrosion in it which could be clearly seen as it had come through the silk. The 60 turns of wire were counted before the damaged coil was removed. Not having silk covered wire, I had to compromise. Enamel covered 0.125mm wire is about 0.01 millimetres larger than the wire originally used. It would have to do! The inductance of the primary winding of an RF coil is by no means as critical as the secondary winding which is connected to the tuning capacitor. Variations in the secondary would cause tracking problems when tuning. A turn or two over or under on the primary would make very little difference. There was a lot of wiring that needed to be replaced and the connecting leads from the coils to the valve top caps and tuning capacitor were all rewired. Resistors which had gone high were replaced and the paper capacitors all replaced with modern high-voltage polyester types. The ineffective tone switch mechan­ism was also repaired and a new wirewound volume control fitted. One problem encountered is that the Tasma has a few odd looking original components in it that are a little different from normal. For example, there were a number of square shaped fibre formers bolted to the underside of the chassis (see photo­graph). These little units are either wirewound resistors or radio frequency chokes. The two shown in the photograph are resistors. One is the output valve’s centre tapped filament resistor and this is con­ n ected to the second unit – a 500Ω cathode bias resistor. These square shaped components are not the usual readily identifiable wire­wound, centre-tapped and bias resistors. After checking out the two available loudspeakers, it was not difficult to choose one. As the Jensen had an open field winding, the Rola was the one for the job. The speaker was wired directly to the receiver (no speaker plug and socket), which makes handling the set rather awkward from then on. If it had been mine, I would have been tempted to fit a socket and plug. Early tests These odd looking square components are wirewound resistors. One (right) is the centre-tapped filament resistor (for the directly heated output valve), while the other (left) is the 500Ω cathode bias resistor. 84  Silicon Chip Upon trying out the Tasma, the best that could be said for it was that it was a really poor performer. This was despite that fact that the correct valve types had been fitted: two 24As, a 35, a 45 and an 80, as indi­cated by This microscopic spot of corrosion was sufficient to stop the receiver from working. In fact, the Tasma had two faulty RF coils due to “green spot” corrosion. Note that the primary winding is wound on top of the secondary winding, which made repairs much easier. This photo shows the rewound RF coil, prior to installation in its metal cover. It was hand-wound with enamel-covered wire of a slightly different gauge & this restored it to full working order. the valve location chart inside the cabinet. But there was a very good reason for the weak response. A close examination of the wiring underneath show­ed that the screen grid on one of the 24As had never been connected to the high tension supply. The screen had a bypass capacitor but no screen voltage. Running a wire from an adjoining screen grid connection to the unconnected screen gave a huge improvement to the set’s performance, which improved even further when the trimmers were properly aligned. It would appear as though this particular receiver had been a dismal performer all its life and would have given only medio­cre reception on the strongest of signals. Well that’s about all there is to report on the Tasma repair. There was a lot of time and effort spent getting this one going again, believe me! While some of the repair techniques may be questionable from a purist’s point of view, the nicer alterna­tives would have cost hundreds of dollars. However, outwardly the receiver looks quite acceptable and it is working better now than at any other time SC in its life. February 1995  85 Silicon Chip Switch For Power Supplies; A Speed Alarm For Your Car; Design Factors For Model Aircraft; Fitting A Fax Card To A Computer. July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power Station; Weather Fax Frequencies. BACK ISSUES September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice; Motorola MC34018 Speakerphone IC Data. plays Fax, RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive 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. 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. July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor); Extension For The Touch-Lamp Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Simple DTMF Encoder; 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 (Dis- 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. 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. 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. 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; LowNoise Universal Stereo Preamplifier; Load Protection 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. September 1990: Music On Hold For Your Tele­ phone; Remote Control Extender For VCRs; Power Supply For Burglar Alarms; Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2Metre Band. 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 HomeBrew 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. 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Or call (02) 979 5644 & quote your credit card details or fax the details to (02) 979 6503. ✂ Card No. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateurs & TV. April 1991: Steam Sound Simulator For Model Railroads; Remote Controller For Garage Doors, Pt.2; Simple 12/24V 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; Build A Fax/Modem For Your Computer; 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; Modifying The Windows INI Files. Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Multi-Station Headset Intercom, Pt.2; Electronics Workbench For Home Or Laboratory. 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. 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. 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. 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 Sine­wave Inverter, Pt.5. March 1993: Build A Solar Charger For 12V Batteries; An Alarm-Triggered Security Camera; Low-Cost Audio Mixer for Camcorders; Test Yourself On The Reaction Trainer; 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; A Look At The Digital Compact Cassette. 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. 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. 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 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 Receiver. 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 Micro­ controller – Lesson 1; Antenna Tuners – Why They Are Useful. 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. 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. 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. 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. April 1992: Infrared 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. 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. 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. 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. July 1992: Build A Nicad Battery Discharger; 8-Station 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. December 1993: Remote Controller For Garage Doors; Low-Voltage LED Stroboscope; Low-Cost 25W Amplifier Module; Peripherals For The Southern Cross Computer; Build A 1-Chip Melody Generator; Elec- tronic Engine Management, Pt.3; Index To Volume 6. 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. 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. 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. 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. May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Multi-Channel Infrared Remote Control; Dual Electronic Dice; Two Simple Servo Driver 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; UHF Radio Alarm Pager For Cars & Boats; 80-Metre DSB Amateur Transmitter; Anti-Lock Braking Systems: How They Work; 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;Index to Vol.7. January 1995: 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. PLEASE NOTE: all issues from November 1987 to August 1988, plus October 1988, November 1988, December 1988, January, February, March & 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 (incl. p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. February 1995  87 PRODUCT SHOWCASE Neutrik A2 has digital audio measurement Amber Technology has announc­ ed a digital measurement option for the Neutrik AZ audio test and measurement system. The digital option is available with new in­struments or as a retrofit to all ex­isting AZ systems. When so fitted, an AZ instrument will automatic­ ally detect analog and digital sig­ nals, switching to the appropriate mode. Able to read and write AES/EBU and IEC958 (SPDIF) formats, it provides electrical analysis of the digital bit stream and displays all important status information like sample frequency, user bits, channel status and digital format. Features provided include audio level metering calibrated in dBF (dB full-scale); high performance D/A con­ version providing an analog signal to the analyser section for level, noise, distortion and phase measurements; monitoring of the converted signal on the internal loudspeaker and headphone output; selectable sampling rates; and user-definable status information for the digital generator. Neutrik has also announced enhanced specifications and increased processing speed for the AZ Audio Measurement System. These enhancements include generator and analyser section flatness of ±.05dB (20Hz to 40kHz) and residual THD + Noise <-90dB (0.003%); and an additional IMD signal with 1:1 level ratio for the generator section. In addition, the analyser now handles IMD signals with a 1:1 ratio. Also announced is a free software upgrade for all AZ instruments to V2.0 which includes a revised user's manual at no extra charge. V2.0 includes numerous system improvements. These improvements are as follows: frequency, amplitude, time and table sweeps; load imped­ ance measurement; new remote con­ trol commands for settled measure­ments; and a wide variety of printer drivers Fluke TV/video signal generators Fluke Corporation has announc­ ed the introduction of three new models in its PM 5410 TV signal generator line. The new units in­ corporate BTSC signals for testing MTS Stereo/SAP equipped TV/ video products. Other new features recently added to the line include test pat­ terns for 16 x 9 wide screen televi­sion, Y/C video outputs for S-VHS and Hi-8 recorders, VPS/ PDC for automated video recorder opera­tions and Teletext functions for information delivery systems in use worldwide. The new test functions provide main channel (L+ R), pilot, stereo (L-R) and SAP sound test signals in accordance with BTSC stand­ ards. Available in NTSC M, N and PAL modes, these signals are suit 88  Silicon Chip able for testing frequency response, alignment, total harmonic distor­ tion (THD), channel separation and SAP level adjustment, as well as other aspects of the TV set or video product's stereo/SAP decoder sec­ tion. Where appropriate, signals are compressed in accordance with the BTSC standard to match the condition actually existing in broadcast systems. For further information on the PM 5410 TV signal generator, con­tact Philips Scientific and Indus­ trial, 34 Waterloo Rd, North Ryde, NSW 2113. Phone (02) 888 8222. including HP-DeskJet and LaserJet printers. For futher information on the Neutrik A2 audio test and measurement system, contact Amber Technology, Unit B, 5 Skyline Place, Frenchs Forest, NSW 2086. Phone (02) 975 1211. Siren driver IC from Zetex Zetex has released a new siren driver IC, the ZSD100. A replacement for dual 555 and more elaborate circuits, the chip needs just two timing capacitors, a Darlington tran­ sistor, a piezo transducer and a coupling transformer in or­ der to produce an ear-piercing alarm. The ZSD100 is able to generate a frequency at up to 10kHz and a low frequency sweep signal at up to 10Hz. It also contains divide by two and output driver stages – all that is required for a low cost siren driver for burglar and automotive alarms. Available in 8-pin DIL or surface mount packaging, the ZSD100 will operate at sup­ ply voltages from 4-18V at a current of 10mA, dropping down to 1µA in sleep mode. Maximum power dissipation is 625mW and temperature range is -40 to +125 degrees Celsius. For further information, contact GEC Electronics Division, Unit 1/38 South Street, Rydalmere, NSW 2116. Phone (02) 638 1888. Mailbag – from page 3 to the surround channel is calcu­lated to suit the size of the auditorium. Most cinemas these days use a de­lay of between 60 and 80ms. The "big" sound of cinemas you refer to is more a result of big auditoriums and good subwoofers, not a result of the delayed surround channel. The digital sound systems now in use in many cinemas have no delay to the surround channel, yet we still hear that "big" sound. Dolby digital had absolutely nothing to do with the success of "Jurassic Park". This film was re­leased using the DTS (Digital Thea­tre Systems) format, not Dolby dig­ital. DTS uses a digital sound on a CD-ROM, locked to the film by a timecode track on the edge of the film. There have been many more releases in DTS than in SRD. DTS has been installed in many cin emas across Australia, both independents and the big chains, whereas Dolby digital has been in­stalled in only a handful of cin­emas. G. Warren, Wagga Wagga, NSW. You are right about Jurassic Park and its release in DTS although it was also recorded using Dolby and has now been released on video in Dolby form. February 1995  89 Tiny CCD video cameras Allthing3 Sales & Service has released a new expanded range of CCD video camera modules which includes a tiny "Matchbox" sized camera measuring just 32 x 32 x 23mm, including lens, and weighing only 20 grams. These modules require a 12V DC sup­ply and can be connected to any stand­ard video input on a TV, video moni­tor, VCR, etc. Features include auto-iris-exposure with 1/50 to 10 microsecond exposure, high resolution 320,000 pixel CCD, vertical reset capability for roll free images when switching between cameras, 8-14V DC supply range, 100mA consumption, better than 50dB signal-to-noise ratio, low light and infrared sensitivity, shock & vibration resistance and CCIR PAL 1V compos­ite 75W video output. Complete modules are available with wide angle lenses from 2.94.3mm with a diagonal coverage of 78-110°. Focus is adjustable from a few millimetres to infinity. Also avail­able are modules complete with infra­red light emitting diodes for illumination in total darkness. For servicing existing cameras, modules are avail­ able with standard C & CS lens mounts, to economically upgrade old cameras. Uses for these modules include concealed surveillance, front door monitoring, robotics, digitising, rear vision systems for trucks and buses, alarm systems, CCTV and video intercoms. They are priced from $199. For further information, contact Allthings Sales & Services, PO Box 25, Northlands, WA 6021. Phone (09) 349 9413 or fax (09) 349 9413. Microchine PC board excavation system Those involved in the repair of multilayer PC boards will be interested in this new miniature drilling and milling machine. Called the Pace Microchine, it is intended for the controlled· re­moval of board conformal coatings and copper tracks on outside and intermediate layers. The unit has a handpiece with quiet, low vibra­tion operation and smooth start to selected speeds between 2500 and 10,000rpm. Closed loop tacho­metric feedback maintains drilling and milling speeds under varying loads while torque limiting circuitry helps prevent overload damage. Dynamic braking stops the shaft immediately the finger switch is released. For safe multilayer repair, the convenient "probe brake" feature allows controlled machining to se­lected layer depths without damage. For further infor­ mation on the Pace Microchine, contact Solder Static Pty Ltd, Unit 14/262 Miller Rd, Villa­wood 2163. Phone (02) 725 6211. 90  Silicon Chip 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. How to design a phaser gun game I am trying to construct a light phaser game which is played with two or more people. You have a chest pack and your phaser gun and you shoot the other person using an infrared beam and a receiver which stops or turns off everything then comes back on after a certain period of time. My problems are construction of the infrared beam and re­ ceiver. I brought your “14 Projects for Model Railways” special edition and I tried to relate the IR remote system with this but had no luck because for this you need a fine beam that would only produce a small dot. So if you understand all of that I would like it very much if you could help me please. (M. B., Cowwarr, Vic). • While you could use the circuitry of the infrared train controller as the basis for the game, the infrared diodes are not bright enough and the beam is too diffuse for your application, as you have found. To get a sufficiently fine beam, you will need to use a solid state laser diode and combine this with the modu­lation circuitry of the Queries on the 4-bay bow-tie antenna I am interested in building your 4-Bay Bow-Tie UHF Antenna, as described in the July 1994 issue. We have just moved to Milli­cent in South Australia. The two stations received in the town are from around the Ballarat district and we have a hill range in line with the stations. Looking around the town, 95% of antennas are twin Yagis with boosters. How will the bow-tie compare with twin 10 to 16 element Yagis with a masthead booster? Can the bow-tie be co-phased and could a director element be of benefit? If so, would a director infrared train control. We published a solid state laser pointer in the December 1991 issue which could be suitable for your application. We can supply a photocopy of this article for $7 including postage. Oatley Electronics can supply a kit for this project. You can phone them on (02) 579 4985. Modifying the audio power meter I wish to ask about the Audio Power Meter featured in the April 1993 edition. Is it possible to use this with the 350W Power Amplifier from the June 1994 issue? What changes need to be made to the circuit to allow it to work accurately? If possible, I would like it to be able to register the 350W at the top end of the scale. Also, in the article, you mention it is possible to get two displays, one a moving dot, and one a bargraph display. How do you connect pin 9 to get the bargraph type display? (D. P., Kilsyth, Vic) • It would be much easier to have a full scale reading of 400W rather than 350W. As it turns out, the only change have to be insulated and if it would help, what would the length and distance from the driver element be, also the distance between stacked antennas? (K. C., Millicent, SA). • We assume that your UHF stations are quite distant. If most people are using twin Yagis with a masthead booster it is doubt­ful whether our bow-tie array would be adequate on its own, with or without a booster. You could cophase two bow-tie arrays together but it would make for quite a tall antenna with possibly quite a lot of windage. We would be inclined to take the hint and install an antenna system similar to that used by most of your neighbours. you have to make is adjust the value of 100kΩ trimpot VR1 to 92.46kΩ for an 8Ω system or 62.46kΩ for a 4Ω system. Obviously, as close as you can get with your digital multimeter will do. This will give you a full scale reading of 400W with the bottom LED showing 0.8W instead of 0.2W. To obtain a bargraph display, you’ll need to connect pin 9 to pin 3 of IC1. You will need to take care as this will greatly increase the heat dissipation of the two regulators. You may have to add small TO-220 heatsinks to these devices. TMS 7000 processor wanted I have exhausted all my sources in an attempt to obtain a TMS 7000 Texas Instrument processor. I rang TI’s Australia agent and even they had difficulty recognising their part number. Could you please help me in obtaining this elusive beast? A year or so ago I requested some microprocessor design projects. I am very happy to see SILICON CHIP publish many active processor projects since then. Well done! (Joseph Gold­ burg, 1369 Heatherton Road, Dan­ denong, Vic 3175). BWD oscillator & CRO circuits wanted I am looking for circuit diagrams for a BWD Audio Oscilla­tor Model 120 and BWD Oscilloscope Model 505. I would appreciate any help and will pay any copying costs. (G. Daddy, 459 Avoca Drive, Green Point, NSW 2251). Walkaround throttle gives a jerk I have built the Railpower Walk­ around Throttle for Model Railways and it works well. However, when I switch off the mains there seems to be a surge after about 2-3 seconds which will make the locomotive jump or lurch. It also sounds the overload February 1995  91 Transistor ignition for lawn mowers After reading the letter from P. C. of Dundas, NSW, which appeared in the September 1994 issue, it occurred to me that it might be possible to use a system such as transistor assisted ignition for 2-stroke motors as used in outboards and lawn mow­ers. My idea is that you could use the existing points on the motor as a switch to trigger the transistor assisted system. The only difference is that the system would not need to deliver the same amount of current. This system could then run off a small 12V sealed lead acid battery. Charging could be achieved by using a small 12V motor as a generator with a regulator; this could also double as a starter motor. This system would also be suitable for use in “go-carts”, small boats and even “classy mowers”. Have you published something suitable for this purpose? If so, where can I buy a kit? (H. Z., Kew, Vic). • Your proposal is feasible but is a lot more complex than the ignition systems used on modern 2-strokes. Typically, these have magneto-charged capacitor discharge ignition systems with the points being used to fire an SCR. This system is very reli­able and uses only a few electronic components. It is widespread on outboards, motorcycles and even mowers. We have not published anything on ignition systems for 2-stroke engines and, as far as we know, there are no kits available for this purpose. buzzer briefly – odd? Can you help? (N. W., Gosford, NSW). • Both the switch-off symptoms you describe are normal. They are caused by the momentary transient which occurs when the supply voltage to the op amps falls to a very low value and as a result, they lose control of their output. The simplest was to avoid the slight jerk which may occur with some locos is to provide an additional switch in the output of the controller. You would then switch this off before turning off the mains switch. can protect videos from piracy and duplication. Can you also give me information on how to go about building a device to “override” this protection? Of course, this is only to assist in my understanding of video technology – I’ve only got one VCR! (P. T., Truong, Ipswich, Qld). • We don’t have any information on this subject although we understand it works mainly by truncating the sync signals. We were also under the impression that it is no longer used to any extent. Russian radio circuit wanted OM350 in masthead amplifier lacks gain I have a 1970s Russian Selena Vega B212 radio receiver. It needs knobs and a transformer. Could you please help me get information on this receiver. Wanted particularly are a circuit diagram, knobs and details of the power transformer. (Ian Stanley, PO Box 70, Ormond, Vic 3204). Do masthead amplifiers provide useable gain at Band 5 TV frequencies? My experience with the OM350-based design you de­scribed in August 1991 and another masthead amplifier kit designed around the OM335 suggests that they do not. I, like many people in the Sydney region, desired the opportunity to tune into re­gional UHF band 5 TV channels. To boost the signal and to over­come transmission cable and splitter losses I built both the aforementioned kits, with no apparent improvement in the signal over that without the amplifier/s. Having access to test equipment at my place of employment, I proceeded to sweep the amplifiers through the Video copy protection I was wondering if you could tell me how video copy protec­tion works. At present, I know it has got something to do with the video sync signal but that’s about it. I am curious about how machines such as MacroVision 92  Silicon Chip frequency range up to 500MHz. I found neither masthead amplifier to have anywhere near the stated gain at the upper limits of my generator. In fact, the OM350 kit amplifier was showing no gain at 500MHz, although its full stated gain was available at lower frequencies (around 100MHz). In practice, I have confirmed that a signal fed directly from the antenna produces a slightly grainy but perfectly view­able colour picture on band 5 TV channels. A 4-way splitter and approximately 20 metres of coax reduces this to a barely discern­ible black-and-white image. The addition of the OM350 masthead amplifier prior to the splitter and coax to overcome the inherent signal losses did not restore a viewable picture. Has SILICON CHIP ever confirmed the operation of this kit design at the frequencies required for band 5 UHF reception? After all, these frequencies are almost microwave signals (ap­proximately 750MHz) which is a demanding task for any amplifier. I note that previously two readers have questioned their inabili­ty to make this kit perform as expected. Do commercial designs work any better? (D. N., Baulk­ham Hills, NSW). • It is quite a few years since we have done any work with masthead amplifiers but as far as we know, the OM350 should perform well at band 5 frequencies. The OM350’s performance is characterised up to 860MHz and the recommended PC layout is very simple. Both the designs featured in July 1988 and August 1991 used a similar PC layout but incorporating protection diodes at the input. In our experience, use of the wrong diodes or capacitors can have deleterious results. We have also heard that some OM350s are sourced from Asia and do not perform anywhere near as well as the specifications indicate. Ignition circuit with variable timing I am writing in regard to whether a variable engine timing unit could be designed. Being more mechanically rather than electronically minded, the way I see it being built would be with a frequency counter and a variable delay circuit dependent on the frequency counter and user variable settings. The points would act as the pulse frequency, activating the delay Running a 120V cassette recorder I have recently obtained a Sony 25W CD/radio cassette-corder from the US. My only problem is that it needs a 120VAC 7A power supply. I do though have a 115VAC 0.53A transformer that I can plug the Sony straight into but as you have already guessed, it is no substitute as the tape deck will run at a slower speed. I would like to know if there is a transformer that I can use in place of my existing one or can I pump up the current rating on it by building a circuit for it (if there is such a thing)? (C. R., Winston Hills, NSW). • It should be possible to power your Sony CD/cassette player from your 115VAC transformer without problems, in spite of the fact that our AC mains system is 50Hz instead of 60Hz. These days we would expect that most cassette decks would be run from an internal DC supply and thus are not locked to the frequency of the AC mains supply. Give it a try; you are unlikely to do any damage. On the other hand, if the cassette transport mechanism is lock­ ed to the mains frequency, then you could drive it with an inverter which delivers 60Hz. Unfortunately, we have not designed a project to deliver 110VAC at 60Hz although we did publish a 12V DC to 240VAC 40W inverter in February 1992. This was able to be modified to deliver 60Hz. K ALEX The UV People ETCH TANKS ● Bubble Etch ● Circulating LIGHT BOXES ● Portuvee 4 ● Portuvee 6 ● Dual Level TRIMMER ● Ideal PCB DRILL ● Toyo HiSpeed MATERIALS ● PC Board: Riston, Dynachem ● 3M Label/Panel Stock ● Dynamark: Metal, Plastic ✸ AUSTRALIA’S NO.1 STOCKIST ✸ to the ignition side of the circuit and, depending on the engine speed, vary the amount of advance. In your opinion would a kit of this nature be relatively easy to design and build? (S. B., Casino, NSW). • Such a project would really only be feasible if it contained a microprocessor which would have to be programmed with the characteristics you require. While it is feasible, we do not think we could justify the development cost in view of the rela­tively small number of readers who would want to make this radi­cal modification to their cars. Power amplifier failure For the past five years I have been using the Studio 200 preamplifier and power amplifier combination without any problems whatsoever. Recently, however, I combined the two with an active crossover network and proceeded to destroy the power transistors in both channels of the amplifier. Failure of these components was not instantaneous. There was a gradual degradation in the performance of the system over about a week before the amplifier failed completely, blowing the speaker protection fuses. During this period, I reversed the outputs from the crossover into the power amp on several occa­ sions while attempting to diagnose the problem. This may be the reason for both channels failing. I would appreciate any help you may be able to provide regarding possible reasons for my problem. (P. K., Picnic Point, NSW). • While we cannot be sure, it seems likely that the electronic crossover is the cause of the problem since the combination of the power amplifier and preamplifier had been reliable. In our experience, this preamp/power amplifier combination is very reliable and so we suggest that you have the electronic crossover checked for high frequency instability. If the electronic crossover is oscillating at a supersonic frequency it could cause the power amplifier stages to become very hot and ultimately, to fail. The clue in this is that you said the performance was degraded. Often, one of the symptoms of supersonic oscillation is that the sound does not seem quite right. We suggest you make sure that the electronic crossover is completely fault-free before using it with any system again. Notes & Errata Coolant Level Alarm, June 1994: the circuit on page 21 has an error in that the indicator lamp is connected to the decoupled +12V supply line; ie, after D2. It should go to the +12V line from the ignition switch, as shown correctly on the wiring dia­gram on page 22. K ALEX 40 Wallis Ave, East Ivanhoe 3079. Phone (03) 9497 3422, Fax (03) 9499 2381 TRANSFORMERS • TOROIDAL • CONVENTIONAL • POWER • OUTPUT • CURRENT • INVERTER • PLUGPACKS • CHOKES STOCK RANGE TOROIDALS BEST PRICES APPROVED TO AS 3108-1990 SPECIALS DESIGNED & MADE 15VA to 7.5kVA Tortech Pty Ltd 24/31 Wentworth St, Greenacre 2190 Phone (02) 642 6003 Fax (02) 642 6127 February 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. TINY VIDEO CAMERAS $20 off! This month from $179. Previous buyers get DOUBLE $40 off. MATCHBOX SIZE PCB MODULES from 32 x 32 x 23mm with lens. 16 types. Optional lenses, C lens mounts, cases & technical manuals. ALLTHINGS. Ph/Fax (09) 349 9413 _____________ _____________ _____________ _____________ _____________ VALVES: all types for radio, audio and industrial use. For sale and wanted to buy. SSAE for list. Electronic Valve and Tube Company, PO Box 381, Chad­ stone, Vic 3181. Fax (03) 571 1160. Ph (018) 557 380. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ DUPLICATE TAPE SYSTEM: ex control tower. 10 audio chs. 32 hours recording, auto standby, all manuals, history. Offers. Fairfield (076) 30 0257 A/H. TENDER MILITARY RADIOS, military pamphlets, Yaesu FT102ZD hifi parts, commercial audio genemotors. Catalogue 85c stamp. Hadgraft, 17 Paxton St, Holland Park Qld 4121. AH (07) 397 3751. 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 receiv- Enclosed is my cheque/money order for $­__________ or please debit my RCS RADIO PTY LTD Card No. Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 94  Silicon Chip ✂ ❏ Bankcard   ❏ Visa Card   ❏ Master Card 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 YUGA ENTERPRISE BA, LA, LB, LC, UPA, UPB, UPC, TA, Buy TBA, TDA, TEA, & 2SA, 2SB, 2SC, Sell ese 2SJ, 2SK, SAA, Japan STA, STK, STR, s IC & tors HA, AC, KA, KIA, Transis IX, LM, MN, PA TEL: (65) 741 0300 FAX: (65) 749 1048 705 Sims Drive #03-09 Shun Li Industrial Complex Singapore 1438 Microprocessor For Stereo Preamplifier Now back in stock: the 68HC705-C8P pre-programmed micro­pro­cessor for the Infrared Remote Controlled Stereo Preamplifier (SILICON CHIP, Sept.Oct. 1993). Also suits the Remote Volume Control (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. ing 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. MicaSOFT Electronics and Computing tutor program, written in UK, ideal for TAFE, schools or individual use. Now available in Australia. Send 4 x 45c stamps for demo disk (tell us what size). MicroZed Computers, PO Box 634, Armidale 2350. BINARY CLOCK - OCTOBER 1993: complete documentation supplied, includes introduction to binary, how it works, PLD source list­ings, conversion tables. Kit with PC board and all components $75 plus $5 p&p. Optional Z frame stand (includes spacers and chassis DC connector) $25 plus $5 p&p. Available from Prototype MEMORY & DRIVES PRICES AT DECEMBER, 1994 SIMM (all 70ns) Parity/No Parity 1Mb 30-pin $57/55 4Mb 30-pin $192/185 2Mb 72-pin $130 4Mb 72-pin $230/210 8Mb 72-pin $480/440 16Mb 72-pin $740/670 32Mb 72-pin $1520/1340 Parallax “BASIC STAMP”: 8 I/O pins and proto­ typing area. Program it with a PC, 33 simple instructions. Development kit includes one “BASIC STAMP” ($270). Extra modules ($79.85). Chipset and Resonator to make your own $30.25. STAMP Stretch­ er 16 I/O 1 A/D $91.96. Serial input LCD display $102.85. Scarce com­ponents need­ed for Application notes now in stock. Small items XPress post $5, kit $8. Send four 45c stamps for details. Parallax Distributor and technical support in Australia. MicroZed Computers PO Box 634 (296 Cook’s Rd), ARMIDALE 2350 V (067) 722 777 F (067) 728 987 Credit cards accepted. MAC 8Mb P’BOOK CO-PROCESSORS 387S/DX to 40 $405 $90 LASER PRINTER HP with 2Mb $200 COMPAQ CONTURA 8Mb $550 DRAM DIP 1Mb x 1 256 x 4 70ns 70ns $7.20 $7.20 IBM PS.2 THINKPAD L40/N33 90/95 8Mb 8Mb 4Mb $655 $513 $230 TOSHIBA 3100SX 44/6400 4Mb 4Mb $285 $265 SUN SPARC 10/20 16Mb SPARC 10/20 64Mb $965 $4080 DRIVES – SEAGATE 261Mb 16ms 3yr wty $230 545Mb 14ms 3yr wty $335 1052Mb 9ms 5yr wty $695 Sales tax 21%. Overnight delivery. Credit cards welcome. RING FOR LATEST PRICES 1st Floor, 100 Yarrara Rd, PO Box 382, Pennant Hills, 2120. Tel: (02) 980 6988 Fax: (02) 980 6991 • PELHAM ELECTROSTATIC LOUDSPEAKERS • 3-Panel Full Range Design. Available in kit form or fully assembled. Locally designed & manufactured. • For information brochure, Phone (09) 397 6212 Fax (09) 496 1546 Or write to: E. R. AUDIO, 119 BROOKTON HWY, ROLEYSTONE, WESTERN AUSTRALIA 6111. N.S.W. Ph. (02) 804 6859 S.A. Ph. (08) 332 6513 TAS. Ph. (002) 31 2403 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) 979 5644 & quote your credit card number; or fax the details to (02) 979 6503. Please specify 3.5-inch or 5.25-inch disc. February 1995  95 Microprocessor For Digital Effects Unit Now available from SILICON CHIP: the 68HC705-C8P pre-programmed micro­pro­cessor IC for the Digital Effects Unit described in this 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. Circuit Ideas Wanted Do you have a good circuit idea. 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, NSW 2097. Electronics, 1/29 Stewart St, Parra­ matta, NSW 2124. Phone (02) 890 2960; Fax (02) 630 3148. Pay by cheque, money order, credit card. UNUSUAL BOOKS: Electronic Devices, Fireworks, Locksmithing, Radar 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. DON’S SHORT FORM KITS: PIC­ 16C54-58/71/84 Universal PCB $23; Basic Stamps $65; Serial Driven 18 I/O $70; Parallel Driven 64 I/O $38; Re- SECONTRONICS Advertising Index COMPONENTS, COMPUTERS, ELECTRON TUBES S/H TEST EQUIPMENT, COMPUT­ ER REPAIRS Altronics ..........................IFC,24-25 RECYCLED EPROMS: ALL ARE CLEANED, ERASED AND BLANK TESTED. Av-Comm.....................................85 2716 2732 2764 27128 27256 Avico Electronics.........................59 $1.50 ea or 10 for $12 $1.50 ea or 10 for $12 $2.00 ea or 10 for $16 $3.00 ea or 10 for $26 $3.50 ea or 10 for $32 David Reid Electronics ..............90 TRANSISTORS, ICs, DIODES 2N3440 $0.50 ea or 10 for $4 2N7000 $0.80 ea or 10 for $6 TIP122 $1.20 ea or 10 for $10 74HC04 $0.60 ea or 10 for $5 1N5060 diodes 100/$10 or 1000 for $70 7406 $0.25 ea or 25 for $5 LM380N $2.50 ea or 10 for $20 DAC O8EP $5.00 ea or 10 for $45 VALVES: 12AV7 $4 1B3GT $5 6J6WA $5 QQV07/50 $15 6SG7 $6 1S2 $3 6AS7 $8 3D21 6U8A 6080WA 6X5GT $6 $6 $9 $5 Phone, mail or fax your orders. Credit cards accepted for orders $20 & over. Mail orders to PO Box 2215, Brookside, Qld 4053. Or shop sales at 143 Grays Rd, Enoggera Qld. Hours: Thursday 4pm-9pm; Sat 9am-4pm. Phone (07) 353 4919, Fax (07) 855 1014. lay8 PCB $10-$20; Z80 Dev. $38-$52; 8K-4Mb Print Buff. $38-$52. Promo Disk for all projects $2. Don McKenzie, 29 Ellesmere Crescent, Tullamarine 3043. Phone (03) 338 6286. PRINTED CIRCUIT BOARDS for the hobbyist. For service & enquiries contact: T. A. Mowles (08) 326 5590. Emona Instruments.....................89 E.R. Audio....................................95 Instant PCBs................................95 Jaycar ................................... 45-52 Kalex............................................93 MicroZed Computers...................95 Oatley Electronics.................. 60-61 Pelham........................................95 RCS Radio ..................................94 Rod Irving Electronics .......... 67-71 Secontronics................................96 Silicon Chip Binders....................96 Silicon Chip Bookshop.................23 Silicon Chip Projects Book......OBC WANTED Silicon Chip Wallchart................IBC WANTED: Precission 10-60 American valve tester. Manual required. Ask for Peter. Phone (03) 632 3972. Tortech.........................................77    SILICON CHIP BINDERS These beautifully-made binders will protect your copies of SILICON CHIP. They feature heavy-board covers, are made from a dis­tinctive 2-tone green vinyl & have the SILICON CHIP logo printed in gold-coloured lettering on the spine & cover. To order, just fill in & mail the order form on page 9, or phone or fax your order to: Silicon Chip Publications, PO Box 139, Collaroy Beach, 2097. Phone (02) 979 5644. Fax: (02) 979 6503. 96  Silicon Chip Dick Smith Electronics........... 10-13 Yuga Enterprise...........................95 _________________________________ 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. • H. T. Electronics, 35 Valley View Crescent, Hackham West, SA 5163. Phone (08) 326 5590. Order by phone or fax from SILICON CHIP - or use the handy order form inside