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Order by phone or fax from SILICON CHIP - or use the handy order form inside Vol.9, No.9; September 1996 Contents FEATURES 10 Technology At Work: Making Prototypes By Laser This revolutionary new process uses lasers to produce functional plastic prototypes. Here’s a look at how it works – by Julian Edgar 53 Neville Thiele Awarded IREE Medal Of Honour IREE recognises achievements in TV, audio and loudspeaker design 68 Cathode Ray Oscilloscopes, Pt.5 Digital storage oscilloscopes are rapidly supplanting analog designs. We take a look at how they work – by Bryan Maher EASY TO BUILD HF AMATEUR RADIO RECEIVER – PAGE 28 PROJECTS TO BUILD 16 Build A VGA Digital Oscilloscope; Pt.3 Final article has the construction details – by John Clarke 28 A 3-Band HF Amateur Receiver Build this simple SSB receiver and tune into the 20, 40 & 80-metre amateur radio bands – by Leon Williams 54 Infrared Stereo Headphone Link; Pt.1 Break that annoying wire link between your headphones and your hifi or TV set with this project. This month, we describe the transmitter – by Rick Walters 60 High Quality Loudspeaker For Public Address INFRARED STEREO HEADPHONE LINK – PAGE 54 This high power design features a wide frequency response and is ideal for music and voice in a large listening area – by John Clarke 80 Feedback On The Programmable Ignition System Upgraded software plus hardware tweaks and improvements to enhance engine operation – by Anthony Nixon SPECIAL COLUMNS 40 Serviceman’s Log A bounce with a twist (and a 3-year delay) – by the TV Serviceman 84 Vintage Radio Vintage radio collectors and collecting – by John Hill DEPARTMENTS 2 Publisher’s Letter 3 Mailbag 8 Circuit Notebook 83 Order Form 90 93 95 96 Product Showcase Ask Silicon Chip Market Centre Advertising Index HIGH QUALITY PA LOUDSPEAKER SYSTEM – PAGE 60 September 1996  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Rick Walters Reader Services Ann Jenkinson Advertising Manager Christopher Wilson Phone (02) 9979 5644 Mobile 0419 23 9375 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Julian Edgar, Dip.T.(Sec.), B.Ed John Hill Mike Sheriff, B.Sc, VK2YFK Philip Watson, MIREE, VK2ZPW Bob Young SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $54 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. PUBLISHER'S LETTER V-chip is a sign of a weak society So the politicians have decided that all new TV sets should have V-chips installed. Announced during July as one of the measures in a crackdown on TV and video violence, this must be one of the silliest decisions made by the new Federal government. There is no doubt that we do have a big problem with violence in our society but putting V-chips in TV sets won’t have any effect at all. So how would it work? The V-chip is supposed to sense the presence of violence in the program and stop it being shown on the screen, if the set has been programmed for this action. Just how does the V-chip know that the program contains violence? Because the video signal has a particular code, similar to a Teletext signal, inserted during the blanking intervals. And who puts the codes in? Why the program producers or the TV stations or the video duplicators, that’s who. In other words, there will be a major censorship applied to all programs. Of course, we don’t know how far this violence censorship will go. Will violence be censored from cartoons? Will the Road Runner no longer be able to obliterate the Coyote? After all, it’s pretty violent stuff, isn’t it? And what about TV news? Apart from all the effort which would need to be made to code all programs, the parents must also program their new TV set so that it doesn’t show violence to their kiddies. If you think about how inept most people are when it comes to programming their VCR, and how most children can do it without thinking at age seven, then the possibility of children reprogramming V-chipped sets to show anything is highly likely. But in any case, how long would it take before all the old TV sets without V-chips disappeared from Australian homes? 20 years? 25 years? More than enough for an entire generation to be unaffected by the V-chip measure. No, the V-chip idea is just stupid. At one time, there would have been no argument, in most homes, about whether children could watch a particular program or not? Mum or Dad used the big knob on the front of the set to turn it off! No high technology there. And if the kids gave any backchat they would get a clip over the ear. Oh, I’m sorry, that’s violence, isn’t it? Really, if this idea is to be taken seriously, then most adults have to be classed as incapable of taking responsibility for raising children. Maybe that’s the solution. Maybe people should be “chipped” to stop them having children if they are classed as likely to be incompetent parents. Seem like a silly idea? It’s not as silly as the V-chip. 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 VGA oscilloscope has inadequate bandwidth Why does your VGA Digital Oscilloscope have such a low bandwidth? It’s almost useless. You would not be able to use it on TVs, most certainly not on computers because of their speed etc. So what use is it; it’s like a capacitor tester that came out, buy the kit for $120.00 but you can buy a commercially made unit for $100.00 (in fact, less). I was looking very eagerly forward to this coming event but what a surprise I got. I at least thought it may be 20MHz at the very least. I’m very disappointed with your current effort which is mostly pretty good (on average) up-to-date, yes I know you can buy a 20MHz scope for $300$600 but it is 20MHz not kHz. For the likes of me what good is it? It’s just a toy; excellent idea but could be far better. It can be done even if it were more complex, slower to work and cost a little more - that’s better than this unit. L. Pockley, Hornsby, NSW. Comment: we would love to present a design capable of a 20MHz bandwidth but that would require an absolute minimum sampling rate of 40Ms/s (the Nyquist criterion) and if you are to obtain a reasonably accurate waveform at high frequencies, the sampling rate really needs to be around 100Ms/s. That is not possible in a low cost design with readily available ADCs and RAMs. Sure, ultra-fast ADCs are used in scopes made by Tektronix, Hewlett-Packard and others but they are custom chips which are not available. Add in the fact that commercial digital scopes take hundreds or even thousands of man-years to develop and you can see that expecting a 20MHz bandwidth for our low cost VGA scope is not realistic. As it was, we used the fastest readily available flash ADCs and RAM to come up with an instrument which produces a calibrated screen display. Is there any commercial equivalent of this? Not as far as we know. Windows dual boot article was timely Your article on a Windows dual boot system in the July 1996 issue was very apt for me and your comments re upgrading to Windows 95 are very pertinent. I very recently upgraded my notebook PC and it came with Windows 95. This presented me with a dilemma as my old PC was running Windows for Workgroups 3.11 and all my applications as well. So I had the situation where my old applications had to be copied over and then debugged/modified to work in the new environment! Not a simple task! In some cases, the software had to be reinstalled. I had one application which would not run under Windows 95 and then I saw your article! D. Coutts, No address supplied Does cable TV cause FM interference? Perhaps the time is right to do a story on the EMI potential of the current cable/phone rollout. I have noticed two spots so far. The first one appeared in Sefton Road, Thornleigh, and another in King Road, Hornsby. However both disappeared after a couple of weeks. I have no idea what standards are applicable, but the levels encountered were unacceptable. P. Buchtmann, Hornsby, NSW. Comment: we have heard other reports of interference from cable TV installations. Just as disturbing, though, are reports of quite poor cable TV picture quality. In one case we've seen the cable picture wasn't a patch on the offair signal from a UHF repeater 30km away. Have other readers experience with EMI or poor picture quality from cable TV? Engine immobiliser ratings questioned I recently read the ignition immobiliser in the December 1995 issue of SILICON CHIP and I was surprised that you are still using the Motorola Darlington transistor as you did in your electronic ignition system previously published. In my capacity as an engineer in Telecom Australia (now retired) I am only too well aware of the dangers of using transistors with inadequate voltage safety margins. As a consequence, when I built my electronic ignition unit I chose the Philips BUK 455-600B power Mosfets. I used four of these in parallel to handle the current and reduce the “Rds on” to an acceptable value. As they are packaged in a TO-220 case, I was able to mount them around the sides of the interior of the case with the circuit board mounted centrally. The circuit changes I made are inclusion of 470Ω resistors in the gate circuits of the Mosfets to suppress any tendency to parasitics the output resistor of the MC3334p has been increased to 220Ω. The unit has been thoroughly heat tested and the performance to date has been impeccable. A. Baldock, Kalamunda, WA. Comment: we specified the Motorola MJ10112 because of its proven reliability in ignition applications. It is designed especially for this task and is widely used in aftermarket ignition systems overseas. We also use a chain of zener diodes across the transistor to limit the collector voltage to 300V. We have not heard of one failure of our ignition system designs where the standard car ignition coil has been used. There have been cases of failure where constructors have substituted “sports” coils which draw much higher primary currents. If we were to represent this pro­ ject, we would like to use a Philips TO-220 IGBT which is intended for ignition use. However, ready availability of components is always an important factor and that is why we have used the MJ10012 device in the past. While your approach with Mosfets clearly works, we would be severely criticised by readers and kitset suppliers if we were to specify four Mosfet devices in an ignition system. The resulting kit price would make SC the project unviable. September 1996  3 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 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. Low cost monitor amplifier for 32Ω headphones Most personal "Walkman"-type players use 32Ω headphones with quite respectable quality of reproduction. Several readers have wondered if these 'phones could be used with standard 8Ω amplifer headphone outputs or to monitor, say, line outputs. In the case of 8Ω outputs, most 32Ω 'phones will work perfectly, albeit normally at lower volume. Headphones cannot be used to directly monitor line outputs without some form of amplifier/buffer. The circuit shown here uses the low cost LM833 dual op-amp. The 32Ω load allows an op-amp to be used. Output level should be adequate but if you want more, simply change the value of the 10kΩ feedback resistors between pins 2 and 1, and pins 6 and 7, of the IC to a larger value. No "volume" control is included but if required this could be included with, say, a 10kΩ log pot across each input (pot wipers to the 10µF capacitors). SILICON CHIP Pulse stretcher for printer signals This pulse stretcher was devised because Centronics signals transmitted to a printer over a 7-metre cable occasionally gave erratic results. The problem was traced to losses in the STROBE- signal, which started out as a low-going pulse but arrived misshapen and shortened. This circuit stretches and squares the STROBEsignal. The accompanying timing diagram shows the basic operation. Initially, IN- is high and so pin 4 of IC1c is high. This high charges a 4.7µF capacitor via D1 and a 10kΩ resistor. At the start of a pulse, IN- switches low, the output of IC1a (A) goes high, 8  Silicon Chip and the output of IC1b (B) goes low. IC1a & IC1b form a latch and their outputs remain high and low respectively until a reset signal is applied. This signal is supplied as follows: when IN- goes high again, the output of IC1c goes low and discharges the 4.7µF capacitor via a 1MΩ resistor. This takes about 5ms. At the end of this period, pin 1 of IC1b goes low, and so the B output goes high again and A goes low. IC1d prevents false triggering by providing a small amount of hysteresis to the timing circuit. E. Wormald, Florey ACT. ($25) YOU CAN AFFORD AN INTERNATIONAL SATELLITE TV SYSTEM SATELLITE ENTHUSIASTS STARTER KIT YOUR OWN INTERNATIONAL SYSTEM FROM ONLY: FREE RECEPTION FROM Asiasat II, Gorizont, Palapa, Panamsat, Intelsat HERE'S WHAT YOU GET: ● ● ● ● ● ● Digital display for the geiger counter This circuit uses the 3-Digit Counter Module (SILICON CHIP, Sept. 1990) along with a few extra components to display the amount of radiation picked up by the Geiger Counter (October 1995). When the Geiger Counter starts clicking the reset switch (S1) is pressed briefly. This causes the 3-digit counter module’s display to be set to zero. IC1 and IC2 count the clicks received from the Geiger Counter and divide them by 100. IC3 stops the count after 10 seconds. The 3-digit counter module then displays this value, which is equivalent to millirads/hour. B. Boggs, St. Andrews, NSW. ($30) 400 channel dual input receiver preprogrammed for all viewable satellites 1.8m solid ground mount dish 20°K LNBF 25m coaxial cable easy set up instructions regular customer newsletters BEWARE OF IMITATORS Direct Importer: AV-COMM PTY. LTD. PO BOX 225, Balgowlah NSW 2093 Tel: (02) 9949 7417 / 9948 2667 Fax: (02) 9949 7095 VISIT OUR INTERNET SITE http://www.avcomm.com.au YES GARRY, please send me more information on international band satellite systems. Name: __________________________________ Address: ________________________________ ____________________P'code: __________ Phone: (_______) ________________________ ACN 002 174 478 September 1996  9 Technology at Work Feature Making Prototypes By Laser Story and Photos by Julian Edgar Apart from the "flip top" cranium, this is an absolutely perfect replica of the skull of a real, live person ­– down to the tiniest detail and blemish. No moulds, no artists and, as the magicians say, 10  S C it's all done with mirrors! ilicon hip The skull opposite was crafted by lasers, using information derived from a medical “CAT” scan. It is an example of the amazing work carried on by the South Australian Centre for Manufacturing. What they can produce borders on fantastic – in the truest sense of the word! A key requirement of manufacturing industry is the development of working prototypes, before expensive investment is made in the final machine tools and metal moulds. The South Australia Centre for Manufacturing uses two laser-based machines to develop prototypes in either plastic or laminated paper. Both use carbon dioxide (CO2) lasers and sophisticated drive mechanisms to form the objects, layer by layer. Companies employed in activities as diverse as manufacturing power tools, cars and white goods use the processes, while the Royal Adelaide Hospital Cranio-Facial Unit has also developed skull models using the techniques. The Sinterstation 2000 With a process called Selective Laser Sintering (SLS) the Sinterstation produces prototypes using the heat generated by a CO2 laser to fuse powdered material together, layer by layer. Fig.1 shows a diagram of the SLS process. The object is formed in a chamber heated to approximately 180-190 degrees Celsius - just below the melting The Sinterstation 2000 uses the action of a laser on Nylon powder to produce functional plastic prototypes. point of the Nylon powder usually employed. A thin layer of heat-fusible powder is distributed across the Fig.1: The Selective Laser Sintering process develops 3-dimensional objects by using a laser to fuse powder, one cross-sectional layer at a time. workspace by the action of a roller, with the layer of powder generally 0.1mm thick. The system’s software uses CAD drawings to produce a series of a cross-sectional slices of the component to be built and the heat-generating laser traces these slices, one by one, on successive layers of the powder. The Laminated Object Manufacturing can also be used to produce small parts. This adjustable spanner was formed by the machine, including the adjustment thread formed in situ! September 1996  11 The Selective Laser Sintering process can produce very complex shapes. This is the base of the relay box from the yet-to-be-released Holden VT Commodore. Four of these parts were produced simultaneously, actually standing on their ends. This whistle – incredibly, complete with internal ball ­–­was produced on the SLS machine. movement of the laser is controlled by scanning mirrors, which in turn are controlled by the system’s dedicated PC. The powder on which of the laser falls is heated to the point of sintering, fusing the powder particles and forming a solid mass. The unfused powder remains in place. The working surface then drops by about 0.1mm and the roller distributes another layer of powder across it. The laser traces out the next cross-section of the object, with this sintered layer fusing to the one beneath. And so it goes on with layer after layer being formed. The object is produced at a vertical rate of about 10mm per hour, with the exact rate dependent on the cross-sectional area of the object being formed. When the process is complete the chamber is allowed to cool, the workspace container is removed and the unsintered powder is then brushed away to reveal the part(s). Because of the way in which the part is formed, extremely complex shapes with thin walls can be developed. For example, a referee’s whistle –complete with internal ball – can be made, with the ball developed in situ! As long as there is an opening through which the unsintered powder can be removed, parts can be formed inside other objects. In addition to various grades of Nylon, materials such as poly­carbonate and proprietary casting compounds can be used. The quality of the object’s surface finish is dependent on the thickness of powder layers used and the material used but it is generally slightly rough to the touch. Post-production sanding and waxing can be used to give an extremely smooth finish if required. In addition to the speed of production, the greatest advantage of the process is that the prototypes can be functional. Flexible Nylon hinges and click joins can be incorporated and components with sufficient strength to be tested in actual operating conditions can be produced. Fan blades produced by this technique, for example, can be assessed for flow properties, noise and vibration. The data input required is a 3-dimensional CAD drawing of the object in the form of an industry standard binary STL or IGES 5.1 text file, or Computervision CADDS 5 part database. Factors such as scaling, feed rates of the powder, temperature and so on are adjusted to suit the individual parts being produced. The Sinterstation 2000 cost $600,000 when purchased in 1993 and it has been working almost continuously since then. The manufacturer of the The capability of the SLS process to produce functional prototypes can be seen here. This fan was assessed for flow properties, noise and vibration after it was produced. Part of a rear view mirror adjustment mechanism, produced for a manufacturer of automotive rear vision systems. From this, the moulds for castings can be directly made. 12  Silicon Chip Fig. 2: The Laminated Object Manufacturing uses adhesive-coated paper. The laser cuts out the cross-sectional slices of the object, with a heated roller fusing the paper layers together. machine is DTM Corporation, based in Austin, Texas. The company was formed specifically to commercialise Selective Laser Sintering, with the patent for the SLS process held by the University of Texas. Laminated Object Manufacturing The other prototype manufacturing machine used by the Centre produces objects larger than those made in the Sinterstation 2000. Laminated Object Manufacturing (LOM) can also rapidly produce complex shaped parts by the action of a computer-controlled laser but instead of using plastic powder, adhesive-backed paper is used as the raw material. Fig.2 shows the LOM system. The adhesive-backed paper is fed from a continuous roll across the working surface. A heated roller then passes across the paper, melting the adhesive and bonding the paper to the layer below. In much the same way as the SLS system, the laser then traces that particular cross-section of the object onto the paper - however in this system the laser cuts the paper rather than fusing it. Where there is excess paper the laser crosshatches it, allowing later removal. The build platform then descends and the process is repeated, with the object again being formed layer by layer. Once all the layers have been laminated and cut, the cubes of crosshatched material are removed and the finished object is revealed. The end result has the appearance and characteristics of laminated wood. One of the advantages of the LOM process over other prototype development approaches is that the LOM object can be used in investment casting. Investment casting - once called “lost wax” casting - uses the LOM object as the plug in a mould. There are seven processes in turning a LOM object into a metal casting. Once the LOM object has been made, wax channels to feed molten metal to various parts of the casting are attached to the object. The assembly is then dipped in alternating layers of ceramic slurry and fine sand, until a thick coating has been added. The coated object is fired in a furnace, hardening the ceramic and at the same time burning away the LOM plug, which after all, is made only of paper! The residual ash is removed and then metal is poured into what has now become a mould. The ceramic coating is removed, excess metal from the feed channels cut off and the newly-created metal object is ready for final finishing. The cast object can then be pressed into prototype service, Laminated Object Manufacturing uses the action of a laser to cut out the cross-sectional shape of the part in a sheet of special paper, here cutting out the shape of a transmission bellhousing. Note the smoke released when the laser cuts the paper. Areas of material which will later be removed are crosshatched. Removing the laminated object from its ‘block’ is done by hand, with crosshatched surplus material pulled out. The end result: automotive transmission manufacturer BTR Engineering is using the LOM process to form one-off bellhousing adaptors, allowing the attachment of their transmissions to a variety of engines for testing and evaluation purposes. The bellhousing on the right of the above photo is one cast from the LOM processed prototype on the left. Another example of investment moulding using the LOM process, where LOM objects become the plug for investment casting moulds. The LOM form is burnt away after it is has been coated with a hard ceramic layer. The casting of metals into the resulting mould can then be easily carried out. A close-up of the LOM bellhousing shows the ‘laminated wood’ appearance of the finished prototype. An object like this costs around $8000 and takes 40 hours to produce. September 1996  13 VISIT OUR WEB SITE OUR COMPLETE CATALOGUE IS ON OUR SITE. A “STOP PRESS” SECTION LISTS NEW AND LIMITED PRODUCTS AND SPECIALS. VISIT: https://www.oatleyelectronics.com/ SWITCHED MODE POWER SUPPLY:Compact (50X360X380mm), enclosed in a perforated metal case, 240V AC in, 12V DC/2A and 5VDC/5A out: $17 ...HP POWER SUPPLIES: Compact (120X70X30mm) HP switched mode, power in plastic case, 100-240V AC input, 10.6V/1.32A DC output, slightly soiled: $14 ...LASER MODULE: Very bright (650nM/5mW) focusable module, suit many industrial applications, bright enough for a disco laser light show, good results with the Automatic Laser Light Show: $75 ...AUTOMATIC LASER LIGHT SHOW KIT: 3 motors, mirrors plus PCB and comp. kit, has laser diode reg. cct, could be powered by the above 12V switched mode power supply, produces many different patterns, can be used with the laser module: $70 ...LASER POINTER: Our new metal laser pointer (With keychain) is very bright, with 650nM/5mW diode: $65 ... LEDS SUPER PRICES, INCLUDING A SUPER BRIGHT BLUE!: All the following LEDS are in a 5mm housing ...By far THE BRIGHTEST BLUE EVER OFFERED, superbright at 400mCd: $1.50Ea. or 10 for $10 ... 1C red: 10 for $4 ...300mC green: $1.10Ea. or 10 for $7 .. MAKE WHITE LIGHT BY MIXING THE OUTPUT OF THE PREVIOUS 3 LEDS? ..3Cd Red: $1.10Ea. or 10 for $7 ... 3Cd yellow (Small torch!) also available in 3mm: 10 for $9 ... Superbright flashing LEDS: $1.50 Ea. or 10 for $10 ... PHOTOTRANSISTORS: Enclosed in clear 5mm housing similar to the 5mm LEDS, 30V/3uS/<100nA dark current: $1.30 or 10 for $9 ...CONSTANT VOLTAGE DIODES: 1.52-1.66V <at> 10uA: 10 for $7 ...MASTHEAD AMPLIFIER PLUS PLUGPACK SPECIAL: Our famous MAR-6 based masthead amplifier plus a suitable plupack to power it: $20, Waterproof box: $2.50, bottom box:$2.50 ...17mm MAGNIFIERS: Made in JAPAN by Micro Design these eyepiece style metal enclosed magnifiers will see the grain of most papers, used, limited qty.: $4 Ea. ...HF BALLASTS: Single tube 36W Dimmable high frequency ballasts: $18 Ea. ...12V SLA BATTERY CHARGERS: INTELLIGENT “PLUGPACK” 240V-12V GEL BATTERY CHARGERS, 13.8V / 650mA, proper “switching” design with LED status indicator: $8.80 ...LASER POINTER KIT: A special purchase of some 660nM/5mW laser diode means that we can reduce the price of our Laser Pointer kit, includes everything except the batteries: $29 ...SPECIAL BATTERY AND CHARGER OFFER: When our 7AHr/12V SLA battery ($30) is bought with the SLA battery charger the total price for both is: $33 ...USED BRUSHLESS DC FANS: 4"/12V/0.25A: $8, 24V/6"/17W: $12 ...100,000uF ELECTROLYTIC CAPACITORS: 30V/40Vsurge, used but in exc. cond.:$10 ...12Hr. MECHANICAL TIMERS: 55X48X40mm, 5mm shaft (Knob not supplied), two hours timing per 45deg. rotation, two 25V/16A SPST switches which close at the end of the timing period: $5 ...USED IEC LEADS: Used Australian IEC leads: $2.50 ...STANDARD PIEZO TWEETERS: Square, 85X85mm, 4-40KHz, 35V RMS: $8, Wide dispersion, 67X143mm, 3-30KHz, 35V RMS: $9 ...COMPUTER POWER SUPPLY: Standard large supply as used in large computer towers, +5V/22A, +12V/8.5A, -5V/0.5A, -12V/0.5A, used but in excellent condition, guaranteed: $30 ...MAGNIFIERS: Small eyepiece: $3, 30mm Loupe: $8, 75mm Loupe: $12, 110mm Loupe: $15, a set of one of each of these magnifiers (4): $30 ... NEW NICAD BATTERY BARGAIN: 6 PACK (7.2V) OF 1.2V / 800 mAHr. AA NICAD BATT’s plus 1 X thermal switch, easy to seperate: $4 per pack or 5 packs for $16, FLAT RECTANGULAR 1.2V, 400mAh NI-CAD BATTERIES with thermal switch, easy to seperate, (Each batt: 48x17x6 mm): $4 per pack or 5 packs for $16 ...UV MONEY DETECTOR: Small complete unit with cold cathode UV tube, works from 2 X AA batteries ( Not supplied), Inverter used can dimly light a 4W white fluoro tube: $5Ea. or 5 for $19 ...MISCELLANEOUS USED LENS ASSEMBLIES: Unusual lens assemblies out of industrial equipment: 3 for $22 ...USED PIR MOVEMENT DETECTORS: Commercial quality 10-15M range, used but tested and guaranteed, have O/C transistor (BD139) output and a tamper switch, 12V operation, circuit provided: $10 Ea. or 4 for $32 ...CCD CAMERA WITH BONUS: Tiny (32X32X27mm) CCD camera, 0.1lux, IR responsive (Works in total dark with IR illumination), connects to any standard video input (Eg VCR) or via a modulator to aerial input: $125, BONUS: With each camera you can buy the following at reduced prices: COMMERCIAL UHF TRANSMITTER for $15 (Normally $25), IR ILLUMINATOR KIT with 42 X 880nM LED’s for $25 (Normally $35), REGULATED 10.4V PLUGPACK for $10 (Normally $25) ...PIR CASE FOR CCD CAMERA: Used PIR cases of normal appearance, use to hide the CCD camera, plenty of room inside: $2.50 Ea. or 4 for $8 ...CAMERA-TIME LAPSE VCR RECORDING SYSTEM: Includes PIR movement detector and interface control kit, plus a learning remote control, combination can trigger any VCR to start recording with movement and stop recording a few minutes after the last movement has stops: $90 ...GEIGER COUNTER KIT: Based on a Russian tube, has traditional “click” to indicate each count. Kit includes PCB, all on-board components, a speaker and Yes, the geiger counter tube is included: $30 ...RARE EARTH MAGNETS: Very strong! 7X3mm $2, 10X3mm $4, Torroidal 50mm outer, 35mm inner, 5mm thick: $10 ...IR TESTER: Kit includes a blemished IR converter tube as used in night vision and an EHT power supply kit, excellent for seeing IR sources, price depends on blemishes: $30 / $40 ...ARGON-ION HEADS: Used Argon-Ion heads with 30-100mW output in the blue-green spectrum, power supply circuit provided, size: 350X160X160mm, weight 6Kg, needs 1KW transformer available elsewhere for about $170, head only for: $350 ...DIGITAL RECORDING MODULES: Small digital voice recording modules as used in greeting cards, microphone and a speaker included, 6 sec. recording time: $9 ...WIRED IR REPEATER KIT: Extend the range of existing IR remote controls by up to 15M and/or control equipment in other rooms: $18 ...12V-2.5W SOLAR PANEL KIT: US amorphous glass solar panels, 305X228mm, Vo-c 18-20V, Is/c 200mA: $22 Ea. or 4 for $70 ...MIDI KEYBOARDS: Quality midi keyboard with 49 keys, 2 digit LED display, MIDI out jack, Size: 655115X35mm, computer software included, see review in Feb. 97 EA: $80, 9V DC plugpack: $10, also available is a larger model which has mor features and has touch sensitive response keys: $200 ...STEREO FM TRANSMITTER KIT: 88-108MHz, 6-12V DC supply, 8mA <at> 9V, 25X65mm PCB size, PCB plus all on-board comp’s, plus battery connector and 2 electret mic’s: $25, plastic case to suit: $4 ...WOOFER STOPPER KIT: Stop that dog bark, also works on most animals, refer SC Feb. 96, Kit includes PCB and all on board comp’s, wound transformer, electret mic., and a horn piezo tweeter: $39, extra horn piezo tweeters (drives up to 4) $6 Ea. ...ALCOHOL BREATH TESTER KIT: Based on a thick film alcohol sensor. The kit includes a PCB, all on board comp’s and a meter : $30 ...CENTRAL LOCKING KIT (NEW): A complete central locking kit for a vehicle. The kit is of good quality and actuators are well made, the kit includes 4 actuators, electronic control box, wiring harness, screws, nuts, and other mechanical parts: $60, The actuators only: $9 Ea. ...CODE HOPPING UHF CENTRAL LOCKING KIT PLUS A ONE CHANNEL UHF REMOTE CONTROL: Similar to above but this one is wireless, includes code hoping Tx’s with two buttons (Lock-unlock), an extra relay in the receiver can be used to immobilise the engine, etc., kit includes 4 actuators, control box, two Tx’s, wiring harness, screws, nuts, and other mechanical parts: $109 ...ELECTROCARDIOGRAM PCB + DISK: The software disk and a silk screened and solder masked PCB (PCB size: 105 x 53mm) for the ECG kit published in EA July 95. No further components supplied: $10 ...SECURE IR SWITCH: IR remote controlled switch, both Rx and Tx have Dip switches for coding, kit includes commercial 1 Tx, Rx PCB and parts to operate a relay (not supplied): $22 8A/4KV relay $3 ...FLUORESCENT TAPE: High quality Mitsubishi brand all weather 50mm wide Red reflective tape with self adhesive backing: 3 meters for $5 ...LOW COST IR ILLUMINATOR: Illuminates night viewers or CCD cameras using 42 of our 880nm / 30mW / 12 degrees IR LEDs. Power output is varied using a trimpot., operates from 10 to 15V, current is 5-600mA ...IR LASER DIODE KIT: Barely visible 780nM/5mW (Sharp LT026) laser diode plus constant current driver kit plus collimator lens plus housing plus a suitable detector Pin diode, for medical use, perimeter protection, data transmission, experimentation: $32 ...WIRELESS IR EXTENDER: Converts the output from any IR remote control into a UHF transmission, Tx is self contained and attaches with Velcro strap under the IR transmitter, receiver has 2 IR Led’s and is place near the appliance being controlled, kit includes two PCB’s all components, two plastic boxes, Velcro strap, 9V transmitter battery is not supplied: $35, suitable plugpack for the receiver: $10 ...NEW - LOW COST 2 CHANNEL UHF REMOTE CONTROL: Two channel encoded UHF remote control has a small keyring style assembled transmitter, kit receiver has 5A relay contact output, can be arranged for toggle or momentary operation: $35 for one Tx and one Rx, additional Tx’s $12 Ea. OATLEY ELECTRONICS PO Box 89 Oatley NSW 2223 Phone (02) 9584 3563 Fax (02) 9584 3561 orders by e-mail: branko<at>oatleyelectronics.com major cards with phone and fax orders, P&P typically $6. with any required changes easily made before final tooling is prepared. An example of this approach has been taken by automotive parts manufacturer BTR Engineering, who has used the LOM investment casting process to make unique bell housings so that their transmissions can be test-fitted to various cars. LOM objects can also be used in other casting techniques, involving not just metals but also plastics and silicone rubber. The Laminated Object Manufacturing machine is produced by Helisys, Inc, a Torrance, California-based company. Three-Dimensional Scanning Both the SLS and LOM systems require the input of precise CAD data before development of an object can occur. However, in the case of a prototype developed from modelling clay, for example, no such drawings will exist. A device called a Digibot II scanner is used to develop this data. The Centre’s Digibot II acquires the x, y, z coordinates of complex shaped objects by shining a point of laser light at the object and detecting the reflection of the light with traversing sensors. Trigonometrical calculations are then carried out within the Digibot software to determine the distance from the light source to the point on the object’s surface. Objects containing undercuts, concavities and split contours do not cause the system any problems and because of the non-contact sensing system, even soft objects can be reliably scanned. In addition to the industrial applications of the machine, other uses include the scanning of internal ear models for the custom fitting of hearing aids and the scanning of fragile artefacts or fossils to enable the production of durable replacements for display. The system can produce quite large objects, limited only by the available workspace; up to 460mm in diameter sc and 460mm high. Contact: Jeff Groves, Manager, Advance Manufacturing Facility, South Australian Centre for Manufacturing. Phone: 08 300 1500 Fax: 08 347 1033 Are you frustrated using DOS or non-compliant Windows software? If so then you may be interested in the following schematic design software trade-in offer from OrCAD. Here are 7 good reasons to trade-in your old schematic software tool to OrCAD Capture for Windows… ❶ De-facto standard schematic capture software. OrCAD is the best-selling package with over 180,000 licensed users worldwide. ❷ Easy to use and learn. Capture has an online tutorial and hypertext ‘Help’. ❸ Works on Windows 3.x, Windows 95 and Windows NT. Support for all platforms provided in one box. ❹ True 32-bit application. Faster processing on 32-bit platforms. ❺ Cut, copy and paste between Capture and other Windows compliant software. Developed to comply with Microsoft Foundation Class. ❻ Supports hierarchical designs. Create complex designs in modular form. ❼ Only $799 (Trade-in offer to all registered owners of Protel schematics and selected other schematic capture software tools. Normally $2195). ✄ Please send me more information on OrCAD Capture for Windows. My details are: Name: Company: Address: Phone: Fax: I am using the following brands of software: Schematic Entry: Simulation: PCB Design: (Fax this form to EDA Solutions on 02-9413 4622 or ring and ask for Richard on 02-9413 4611) SC11/96 The Digibot II scanner is used to acquire the 3-dimensional coordinates of complex shaped objects. This data can then be fed into the rapid prototyping machines, allowing copies to be made. Level 3, South Tower 1-5 Railway Street CHATSWOOD NSW 2067 Australia Ph: +61-2-9413 4611 fax: +61-2-9413 4622 email: info<at>eda.com.au Offer for a limited time only. September 1996  15 In this final article, we describe construction of the VGA Oscilloscope, plus testing and operation. This is a relatively straightforward process, with most components mounted on printed circuit boards. By JOHN CLARKE Part 3: Constru ction Build a VGA digital oscilloscope The VGA Oscilloscope is mounted in a plastic instrument case measuring 262 x 189 x 84mm. A Dynamark label measuring 252 x 76mm is fitted to the metal front panel. Most of the components are mounted on five PC boards and these are: the front panel PC board coded 04307961 and measuring 252 x 75mm; the main PC board coded 04307962, measuring 213 x 142mm; the rear timebase board coded 04307963 measuring 252 x 75mm and finally, two memory surface mount PC boards coded 04307964 and measuring 20 x 32mm. Begin by checking the all the PC board patterns against the published artworks. Check for undrilled holes, broken tracks or shorts and fix these before proceeding. Also check that the front and rear boards fit neatly into the slots of the case and file the board 16  Silicon Chip edges to size if they are too large. Memory boards Work can start on the two small memory boards. These, for IC4 and IC10, are intended to be used with the copper side up, suitable for surface mount devices. The board overlay diagrams for both of these ICs are shown in Fig.1. For best results we recommend that pads for the ICs are pretinned using a fine tipped iron. Once the pads are tinned, locate the IC in position, making sure it is oriented correctly and solder the four end pins in place using a minimal amount of solder. Now solder the remaining pins, taking care not to solder any two pins together. Once done, you should check with your multimeter that each pin of the IC does in fact connect to the track, as shown on the published PC artwork. Also check that adjacent pins are not shorted except where the tracks on the overlay show that they are intended to connect. Solder blobs between adjacent pins can be removed with solder wick and a soldering iron. After any repairs have been done, we recommend a thorough final check of the connections. Do not forget to install the 0.1uF capacitor from the copper side. In final assembly, the memory boards are attached to the main PC board using short lengths of tinned copper wire, soldered to the top side of the memory board and to the underside of the main board. Main PC board Now move on to the main PC board. Its component overlay is shown in This photo shows the location of the various front panel controls. The vertical PC board behind the front panel supports all of these controls and associated components. Trimpot VR6 and the PC stakes are installed next. We did not use stakes in the two 4-way locations above IC24 and IC28. Fig.2. Insert all the links, using tinned copper wire, and solder them in place. All the ICs, with the exception of IC4 and IC10, can be inserted. Take care to install the correct type in each place and with the correct orientation. Now insert and solder the diodes and resistors in place. The accompanying resistor table gives the colour codes for each resistor value. It is also good practice to use a digital multimeter to verify each resistor value. The voltage regulators (REG1 & REG2) are mounted horizontally and held in place with a screw and nut. Bend the regulator leads to insert them into the holes provided before installation. Make sure you place the 12V regulator (REG1) in the position closest to the PC board edge. Capacitors can be mounted next. The 1000uF capacitor is placed on its side with the orientation shown. The remaining electrolytic capacitors also must be oriented with the correct polarity. 8-way header pins are installed in the positions adjacent to IC15, and near IC11 and IC12. Finally, insert the trimpots and PC stakes. assembly can proceed in the same order as the main board. Take care to orient the ICs and diodes with the polarity as shown. When installing the transistors, take care to place the BC338s in positions marked Q3, Q6 and Q9. The BC548’s go in positions marked Q4 and Q7 while the BF199 devices are installed at Q5 and Q8. Timebase PC board Two plug-in memory boards are used in the VGA Oscilloscope. The ICs on the boards are surface mount devices and require care when soldering. Fig.1 (above left) shows the PC board layouts and patterns, with a close-up photo of one assembled board at right. The component overlay for the timebase board is shown in Fig.3. Its Front panel board The front panel PC board is shown in Fig.4. Carefully check out the board pattern as before and then install the links, resistors, diodes and capacitors, with the exception of the 0.22uF types. Note that LED1-LED4 are September 1996  17 Fig.2: the parts layout for the main (horizontally mounted) printed circuit board. Solder in all of the wire links first, then proceed with the passive components and finally the diodes, transistors, regulators and finally the ICs. Opposite is the fullsize main printed circuit board pattern. mounted flat to the PC board with the cathode lead (the shortest one) bent sideways to fit into its hole. Do not shorten the leads for LED5. They need to be the full length so LED5 can reach the front panel. VC1-VC3 are mounted on the rear of the PC board for ease of adjustment later on. Before installing any of the pots or rotary switches, cut their shafts to about 12mm long, so that the knobs will fit neatly in place. Switches S2, S5, S4, S6 - S10 and S12 are all soldered directly into the PC board. PC stakes are required to mount the slide switches S1, S3 and S11 and pots VR2, VR4 and VR5. The leads on the pots are bent over to solder to the top of the PC stakes. Soldering in the slide switches S1, S3 and S11 requires a little more patience. The connecting lugs of each switch are inserted between the rows of PC stakes and carefully soldered in place. Check that the pins are connected by testing with a multimeter. Then solder in the 0.22uF capacitors and the PC stakes required for off-board connections. The vertical attenuator switches S2 18  Silicon Chip and S4 will be supplied as single-pole 12-position types and will need to be set to provide eight positions. This is done by rotating the switch fully clockwise and then lifting out the locking washer and repositioning it so that its tab sits in position 4. After this is done for S2 and S4, check that each switch will provide eight positions. Switch S5 needs to be set to 11 positions. In this case the switch is rotated fully anticlockwise and the locking tab placed in position 11. Check that the switch rotates through 11 positions. Before installing any of the boards in the case, it is best to drill the rear panel holes for the VGA lead and for the DC socket. These holes must line up with those on the rear panel PC board. The PC board hole for the socket is made large enough to accom- modate the DC socket pins which will protrude through it when assembly is complete. Fit a grommet into the rear panel for the VGA cord. Pull the VGA cord through the hole and secure it to the PC board using a cord clamp. Then fit the DC socket to the rear panel. The front panel label can be affixed to the metal panel and drilled to accommodate the switches, pots and BNC sockets used for the input connections. The rectangular holes for the three slider switches are filed to shape after they have been drilled out. Then secure the BNC sockets to the front panel, using a star washer, nut and solder lug on each. The socket is connected to the front PC by soldering the centre pin to the PC stake and the earth connection via a short length of tinned copper wire to its GND PC stake. Attach the front panel to the front PC board by securing it with the switch nuts. The pot nuts are not required. Fit all the knobs to the shafts of the pots and switches. Before installing the main board in the case, it is necessary to shorten all the integral standoffs on the base. They should all be drilled off except for those at the outermost four corners. Also cut off the small upright spikes with side cutters. Then attach the main PC board in place, using self tappers into the four remaining integral standoffs. Slide the front and rear panel PC board assemblies into the case slots and the remaining wiring can be done. Wiring Fig.5 shows the wiring between the PC boards. Most of this is done with hookup wire. We used ribbon cable split into strips of four for connecting September 1996  19 20  Silicon Chip Fig.3 (top): the component layout for the timebase PC board, which mounts vertically at the rear of the case. Above is its associated PC board pattern, reproduced full size. September 1996  21 Fig.4 (top) : the component layout for the front panel (vertical) PC board, with its PC board pattern, reproduced full size. The three photographs above are effectively an exploded view of the VGA Digital Oscilloscope, with the front and rear vertically mounted PC boards "folded out" from the main PC board similar to the component overlay diagram on the facing page. Both vertical boards mount in slots in the case with their components towards the front. 22  Silicon Chip Fig.5: the wiring diagram showing how the various boards are interconnected. Use this in conjunction with the photographs on the opposite page along with the circuit diagram in last month's issue. the 8-way pin headers on the main PC board to the rear panel board. Shielded cable is used to connect from the front panel to op amps IC1 and IC7. The VGA cable is terminated onto the rear panel board at the positions indicated. Fig.6 shows the pin-out arrangement for a VGA socket. We September 1996  23 CAPACITOR MARKING CODES ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ Value    IEC Code 0.22µF 220n 0.1µF 100n .047µF 47n .0039µF 3n9 .0015µF 1n5 .001µF 1n0 680pF 680p 560pF 560p 470pF 470p 390pF 390p 150pF 150p 47pF 47p 22pF 22p EIA Code 224 104 473 392 152 102 681 561 471 391 151 47 22 purchased a VGA cable from Dick Smith Electronics and it used white for the line sync, dark brown for frame sync, orange for the blue trace, red for the green trace, light brown for the red trace and purple, light blue, light green, dark green and un-insulated wire for the ground. This may not be the same for your VGA cable so check this carefully with your multimeter. When complete, tidy up all wiring with cable ties. Testing Before applying power, check your wiring carefully for errors. In particular, check that the positive and GND wires from the main PC board connect         RESISTOR COLOUR CODES ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ ❐ No. 1 1 1 1 2 1 2 1 1 2 3 1 2 2 2 3 2 1 2 8 3 1 1 1 5 10 2 1 8 2 1 1 3 Value 10MΩ 3.9MΩ 2.2MΩ 820kΩ 510kΩ 390kΩ 240kΩ 220kΩ 150kΩ 130kΩ 100kΩ 82kΩ 75kΩ 51kΩ 47kΩ 39kΩ 27kΩ 20kΩ 12kΩ 10kΩ 7.5kΩ 6.8kΩ 3.9kΩ 3.3kΩ 2.7kΩ 2.2kΩ 1.8kΩ 1.5kΩ 1kΩ 330Ω 220Ω 120Ω 75Ω 24  Silicon Chip 4-Band Code (1%) brown black blue brown orange white green brown red red green brown grey red yellow brown green brown yellow brown orange white yellow brown red yellow yellow brown red red yellow brown brown green yellow brown brown orange yellow brown brown black yellow brown grey red orange brown violet green orange brown green brown orange brown yellow violet orange brown orange white orange brown red violet orange brown red black orange brown brown red orange brown brown black orange brown violet green red brown blue grey red brown orange white red brown orange orange red brown red violet red brown red red red brown brown grey red brown brown green red brown brown black red brown orange orange brown brown red red brown brown brown red brown brown violet green black brown 5-Band Code (1%) brown black black green brown orange white black yellow brown red red black yellow brown grey red black orange brown green brown black orange brown orange white black orange brown red yellow black orange brown red red black orange brown brown green black orange brown brown orange black orange brown brown black black orange brown grey red black red brown violet green black red brown green brown black red brown yellow violet black red brown orange white black red brown red violet black red brown red black black red brown brown red black red brown brown black black red brown violet green black brown brown blue grey black brown brown orange white black brown brown orange orange black brown brown red violet black brown brown red red black brown brown brown grey black brown brown brown green black brown brown brown black black brown brown orange orange black black brown red red black black brown brown red black black brown violet green black gold brown to the correct points on the front and rear PC board. Reverse polarity on a PC board may cause IC damage! Apply power, check that the LED lights and that the regulators provide an output voltage of +12V from REG1 and +5V from REG2. Now you can check supply on all the ICs. Checking the front panel ICs can be done from the rear of this PC board. IC1, IC2, IC7 & IC8 should have 12V between pins 7 and 4. IC3 & IC9 should have 5V between pins 20 and 8. IC4 & IC10 should have 5V between pins 14 and 28. IC5, IC6, IC11, IC12, IC16, IC17, IC18, IC24 & IC25 should have 5V between pins 8 and 16. IC13, IC20, IC22 & IC28 should have 5V between pins 8 and 1. IC14, IC15, IC19 IC23, IC26, IC27 & IC29 should have 5V between pins 7 and 14. IC21 should have 12V between pins 11 and 8. If all voltages are correct you can test the oscilloscope using a VGA monitor. Turn all power off and connect the VGA lead to your monitor. Apply power to the oscilloscope first, then switch on the monitor. You should obtain at least steady blue vertical graticule lines on the screen. The horizontal graticule lines may not be present. If the graticule is broken up with rolling or with S-shaped patterns, then you have lost vertical or horizontal sync or the ground connections are disconnected. Check wiring to the timebase and main boards for shorts, dry solder joints or discontinuities in tracks. Also recheck the VGA socket connections. Select a timebase other than 50us Fig.6 (above): the standard pin-outs for a VGA socket. . \ \ CH1 SLOPE . . POSITION \ \ - STORE + . TRIGGER LEVEL TIME/DIV . SOURCE . CH2 . . POWER UPDATE . TRIGGERED REALTIME . NORM FAST SLOW VOLTS/DIV AC GND DC . . MAG x1 x2 x4 FREE RUN POSITION VOLTS/DIV AC GND DC . CH2 .5. . .2 (RED) . .1 . . .05 1. 2. 5. . 10 VGA OSCILLOSCOPE 2ms . .1ms . .5ms . . .2ms . . .1ms 50µs 5ms . 10ms . 20ms . 50ms . . .1s .5. . .2 . .1 . . .05 will be seen as many dots in a disjointed arrangement on the screen. When the frequency is adjusted so that the A-D converter operates correctly, the trace will appear normal with all dots following each other. If correct adjustment is not possible, increase the 47pF value at pin 2 and 6 of IC13 to 56pF. The VGA oscilloscope is now ready for use. Note that if GND input is selected, you will also need to switch to Free run triggering to obtain the update straight line on the screen. Any deviation from the straight line is due to noise and least significant digit error in the A-D conversion process. This is normal in a digital oscilloscope. If the timebase selected is too slow for the signal being measured, a phenomenon called “aliasing” will occur. This happens since the sampling rate is not fast enough to obtain half a cycle of the waveform and a trace will be displayed which is of a much lower frequency than the incoming signal. The problem is instantly recognised on the VGA oscilloscope since the waveform cannot be triggered correctly so that it remains steady. In most cases the waveform also shows as an envelope where two traces are evident with one being 180 degrees out of phase to the other. If the oscilloscope is to be used to measure mains voltages take note of these precautions. Set the volts per division switch to 10V. Use only a x10 probe and do not use the earth connection since you may incorrectly attach it to Active. The oscilloscope is earthed via the VGA monitor. If the mains voltage is above 250VAC, the trace will over­ range. To prevent this, the VR1 & VR3 calibration trimpots can be adjusted so that the trace level is reduced. This will uncalibrate SC the volts/division setting. 1. 2. 5. 10 . Fig.7: the front panel artwork for the VGA Digital Oscilloscope, reproduced full size. CH1 (GREEN) and check that the red and green traces can be moved up and down the screen using the position controls. Note that if the traces are moved above the top of the screen they will produce a slanted two line trace on the lower screen portion. This is a sign of overrange. Signals brought to the bottom of the screen will flatten out to a straight line. Several adjustments are required before the VGA oscilloscope is ready for use. The first is to adjust VR6 to obtain the horizontal graticule lines. You will find that there are several settings for VR6 which will give the horizontal lines. Use the setting which centrally locates the graticule in the screen. Check operation of the VGA oscilloscope by applying a square wave signal to the inputs and adjust the timebase and sensitivity for the best display. Note that you will need to select the Free run and Real time switch positions. To trigger the trace, select the source (CH1 or CH2) the polarity and the Triggered position. Now adjust the trigger level so that the trace is triggered and is updated (as indicated by a momentary loss of display periodically). Use the update selection which best suits your purpose. Check that the MAGnification switch provides an expanded timebase. Adjust the trimmer capacitors VC1 and VC2 for best square wave response. This means that the waveform should be square without overshoot or rolloff at the rising and falling edges. Adjust trimpots VR1 and VR3 for correct vertical calibration. If the peak-to-peak voltage of your signal is not known, measure the voltage of a battery using a multimeter. Then measure it on the VGA oscilloscope with the DC input selected. Now adjust the trimpot for a correct volts per division reading. If the frequency of the oscillator is accurately known, check that the timebase calibration is correct. Now select the 50us timebase and adjust VC3 until the traces stop breaking up. In other words, adjust VC3 to set the maximum frequency before the A-D converters stop operating correctly. Incorrect A-D operation September 1996  25 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. Macservice 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. Macservice Pty Ltd Ideal project for novices... 3 BAND AMATEUR RECEIVER Want to listen in on the most popular HF amateur bands? Perhaps you own a short wave radio but are disappointed with its ability to receive amateur radio signals? This inexpensive and easy to build receiver is just what you need. Short wave listening is a fascinating pastime and you only need a cheap receiver to listen to transmissions from around the world. Most short wave broadcast stations are very powerful and because they use amplitude modulation (AM), a receiver used to tune their signals only requires modest sensitivity and a simple AM detector. Unfortunately it is not this easy to listen to Amateur band transmissions, which are transmitted with much less power and generally use single sideband (SSB). Therefore, receivers used for amateur signals must have high sensitivity and selectivity, and an SSB demodulator. Just as important, amateur bands occupy only a tiny segment of the overall short wave bands. Typical low priced short wave radios, while they may tune over the amateur frequencies, do not have the sensitivity and selectivity to pick up these low level signals and generally cannot resolve SSB transmissions. Of course you can buy receivers that will do a good job receiving both general shortwave and amateur transmission but these are quite expensive and can cost many hundreds, perhaps thousands, of dollars. 80, 40 & 20 metre bands This receiver, while being reason- By LEON WILLIAMS VK2DOB 28  Silicon Chip Fig. 1: The block diagram of the three band receiver. It covers the most popular high frequency amateur bands. ably simple, has adequate sensitivity and selectivity and can receive SSB, CW, RTTY and SSTV signals. It tunes three 500kHz wide sections of the HF spectrum which include the 80, 40 and 20 metre amateur bands. The 80-metre amateur band covers 3.5MHz to 3.8MHz. During the daytime only local signals will be heard, although at night both local and interstate signals can be picked up. The 40-metre band goes from 7MHz to 7.3MHz and is excellent for daytime local and interstate reception and at night it is possible to hear stations from around the world. The 20-metre band, which extends from 14MHz to 14.35MHz, is the best to hear long distance (DX) transmissions from all parts of the world, day and night. This band is affected more by the changes in the ionosphere than the other two bands. Sometimes, only SPECIFICATIONS 80m Band: 3.5 to 4.0MHz 40m Band: 7.0 to 7.5MHz 20m Band: 14.0 to 14.5MHz Power: 12V DC (nom) <at> 250mA maximum – from a regulated supply or high capacity battery (not plug-pack) Antenna: 50Ω impedance Output: 8Ω speaker or headphones signals from certain parts of the world can be heard or even no signals at all and yet at other times the band will be crammed full. With this receiver you can listen to amateur transmissions at almost any time by selecting the band that is best suited to the time of day and the propagation conditions. It was designed to be inexpensive and easy to build, while offering good performance. To this end, the whole receiver is constructed on a single PC board and housed in an inexpensive case. One aim of this design was to eliminate the need to wind coils, as this appears to be quite a challenge for the newcomer to radio construction. Most of the coils used are pre-wound RF chokes; only two coils need to be wound. Power requirements The receiver can be powered from any suitable DC voltage source between 9 and 15V. At 12 volts, the receiver draws 40mA with no signal and about 250mA at full volume. A regulated 12/13.8V power supply capable of about half an amp would be ideal. A diode in the positive supply line protects the receiver from inadvertent reverse polarity connection. Note that most DC plug packs have quite high hum levels and probably won’t be suitable because the hum will make its way into the audio stages. The receiver does not have an internal speaker. This is done for a couple of reasons. The case used is not really big enough and it is likely that there would be some mechanical feedback between the speaker and the oscillator coil. Anyway an external speaker or headphones will provide much better sound than a small internal one. The front panel has the main Tune control with a calibrated dial. The main Tune control does not have a vernier mechanism and so a Fine Tune control is provided to make it easier to accurately tune in signals. Also on the front panel is the volume control and an RF attenuator. The final front panel control is a 3-position band switch. The antenna connection is made via an SO239 socket. The antenna should be one cut for the bands of interest and have an impedance of 50Ω for maximum signal pick-up. If the antenna is simply a long piece of wire, an antenna tuner or matcher will probably improve the performance, especially on the 20m band (see separate panel). Block diagram The overall block diagram of the receiver is shown in Fig.1. The receiver can be divided into two parts: a Direct Conversion receiver tuning from 2 to 2.5MHz, and a switchable 3- band frequency converter. The job of the converter section is to convert or translate the frequency of the signals from the three bands to a common 2 to 2.5MHz Intermediate Frequency band. The direct conversion receiver then converts the Intermediate Frequency signals to audio frequencies, filters and amplifies them. September 1996  29 30  Silicon Chip Signals from the antenna are fed to the RF attenuator, included to reduce the level of very strong signals which could cause the receiver to overload. This is especially true of short wave AM broadcast stations which unfortunately frequent the 40M band at night. The signals from the antenna then pass through the selected bandpass filter and appear at one input to the mixer. The Band switch also activates the relevant crystal oscillator and its output is applied to the second input of the mixer. A 2 to 2.5MHz bandpass filter selects the difference between the signal and oscillator frequencies at the output of the mixer and passes it onto the product detector. A variable frequency oscillator (VFO) is tuned by the main Fine Tune and the Fine Tune controls between 2 and 2.5MHz. The VFO signal is applied to the second input of the Product Detector and audio is recovered at the output. The low level audio is amplified and passed through a 2.3kHz lowpass filter which helps to eliminate adjacent channel interference found on a crowded band. Finally, the audio signal is fed to a power amplifier to drive a loudspeaker or headphones. Mixing The mixer used in this receiver is a double balanced type, meaning that the main outputs are the sum and difference of the two input frequencies. The two input frequencies themselves are largely suppressed. When the receiver is switched to tune the 20m band, 12MHz is injected into the oscillator input of the mixer, while it also receives signals in the range of 14 to 14.5MHz. The output of the mixer contains the sum frequencies between 26 and 26.5MHz and the difference frequencies between 2 and 2.5MHz. The filter connected to the output of the mixer passes only the 2 to 2.5MHz signals. The 14MHz signal has been converted to 2MHz and 14.5MHz to 2.5MHz. When 40m is selected the conversion is similar, where an oscillator frequency of 5MHz is mixed with the 7 to 7.5MHz signals to produce difference frequencies between 2 to 2.5MHz. The operation on the 80m band is slightly different in that the mixing frequency of 6MHz is above the input frequency of 3.5 to 4MHz. This means that this band tunes backwards compared to the other bands. 3.5MHz is converted to 2.5MHz while 4MHz is converted to 2MHz. This is a small price to pay for the simplification it provides. 12, 6 and 5MHz crystals are low cost common items. To make the 80m band tune forwards we would need to use a 1.5MHz mixing frequency which has two problems. Firstly crystals at this frequency are not common and more expensive, and secondly the image frequency lies in the AM broadcast band. This image could not be easily eliminated with the input bandpass filter. Circuit description The circuit diagram for the receiver is shown in Fig.2. Signals from the antenna pass through the variable RF attenuator (VR1) to three bandpass filters. Each filter is a double pole type using capacitive coupling. The inductors are standard prewound RF chokes and are brought to resonance by a parallel combination of a fixed capacitor and a variable trimmer capacitor. The filters are designed with a bandwidth wide enough to suit the Australian amateur frequency allocations. The filters are switched using diode switching and as each band operates the same way we will look at the 20m filter to see how it works. With the band switch in the 20m position, a current of about 3mA flows through each of the 1kΩ resistors, diodes D1 and D2 and the 470Ω resistors. The diodes provide a low impedance path for the RF signals when a few milliamps of DC current flows through them. The other diodes D3, D4, D5 & D6 will be biased off and provide a high impedance to the RF signals, effectively isolating the 40m and 80m filters. Using diodes eliminates the need to switch active signal leads and allows the switch to be located remotely. The only real drawback is some signal attenuation in the diodes. However this can be made up in the rest of the receiver. The output of the selected filter is connected to the primary winding of transformer T1. T1 matches the 50Ω impedance of the bandpass filters to the 3kΩ input impedance of the mixer. T1 also provides conversion from the unbalanced output of the filters to the balanced input of IC1 which is an NE602 mixer. September 1996  31 As you can see from this “opened out” photo, construction is almost entirely on one PC board. Since taking this photograph, we have added the reverse polarity protection diode, D8. The external mixing frequency is injected into pin 6 at around 0.5V peak-to-peak. Each band has its own crystal oscillator, formed with IC3, a 74HC00 and IC4, a 74HC10. This type of oscillator has a number of benefits over standard transistor oscillators. First, as they are made using NAND gates one of the inputs can be used to gate the oscillator on and off without switching power supplies or signal leads. Second, a 3-input NAND gate can be used to combine the oscillators into a single line and the output of the buffer stages will be a 5V logic signal. This means that we can use a simple 32  Silicon Chip voltage divider to provide the needed 0.5V peak-to-peak signal for all the frequencies. IC3a is the 12MHz oscillator with IC3b acting as a buffer stage. The oscillator is adjusted to exactly 12MHz by a trimmer capacitor in series with the crystal. Pin 1 of IC3a and pin 5 of IC3b are normally pulled low by a 10kΩ resistor, disabling the oscillator. When pins 1 and 5 of IC3 are switched to 5V by the band switch the oscillator is enabled. When one input of a NAND gate is low the output is forced to a permanent high state. The 5MHz oscillator uses IC3c and IC3d, while the 6MHz oscillator uses IC4a and IC4b. They both operate in the same way as the 12MHz oscillator. IC4c is the oscillator combiner. Only one oscillator will be operating at a time and the outputs from the other two oscillators will be high. When all the inputs to IC4c are high, pin 6 will be low. When the active oscillator’s output goes low pin 6 will go high. The 5V output signal is reduced to 0.5V by the resistive divider formed with the 1kΩ and 150Ω resistors. The 100pF capacitor across the 150Ω resistor provides some low pass filtering and reduces the level of harmonics. REG2 provides a regulated 5V for IC3, IC4 and the band switching diodes. The output of the mixer stage is applied to a 2 to 2.5MHz band pass filter. The PC board component layout, together with the PC board pattern. Take extra care when placing polarised components, such as electrolytic capacitors and semiconductors, to ensure they go in the right way! This filter is made up of two parts, a high pass filter using L7, two 56pF capacitors and a 150pF capacitor, and a low pass filter using L8, two 47pF capacitors and a 15pF capacitor. The 150pF and 15pF capacitors resonate with the inductors to provide deep notches of attenuation either side of the passband. The 2 to 2.5MHz signal goes to the product detector IC2 on pin 2. IC2 is another NE602 and mixes the input signal with a variable oscillator to produce an audio signal. The variable oscillator is formed with the second half of IC2. The os- cillator appears at pins 6 and 7. L9 is the coil for the oscillator and tuning is accomplished by a BB212 variable capacitance diode CD1. The 330pF capacitors provide the feedback path for the oscillator, while the 68pF capacitor in parallel with L9 acts with CD1 to set the frequency range. September 1996  33 The 330pF and 68pF capacitors are specified as polystyrene types in the parts list. This type of capacitor, while more expensive than ceramic types, offers superior stability in oscillator circuits. The capacitance of CD1 and hence the oscillator frequency is dependent on the voltage which is provided by the tune control. As the voltage on the control pin increases, the capacitance of CD1 decreases and as a result the frequency of the oscillator increases. The Tune control VR2 is a dual gang potentiometer with both gangs in parallel except for a resistor in series with each gang. One gang has a resistor in its positive side while the other gang has a resistor in its earth side. This produces a differential voltage between the wipers and will be constant over the full movement if the resistors have the same value. VR3 is the Fine Tune control and sweeps over the voltage that exists between the two wipers. The wiper of the Fine Tune control provides the tuning voltage for CD1. Note that the 150Ω resistors can be altered to tailor the fine tune range if required. Decreasing the resistors would decrease the fine tune range, and increasing them would increase the range. The resistor values could be made different if more range was required at one end of the tuning range than the other. A 100kΩ resistor and 1µF capacitor isolate CD1 from supply noise that could otherwise modulate the oscillator. A 10kΩ trimpot, VR4, is used in conjunction with the slug in L9 to set the frequency range over which the Tune control operates. The oscillator in IC2 is sensitive to loading on pin 7 and makes it difficult to directly measure the oscillator frequency. To overcome this, a FET buffer stage is used so that a frequency meter can be connected without significantly loading the circuit. Q1 is a MPF102 and its high input impedance, along with the 5.6pF capacitor, provide light coupling to the oscillator. REG1 provides power for the two NE602’s and its output voltage has been increased to 5.6V by the inclusion of a diode in the common lead. This has been done because the NE602 has slightly better performance at this increased voltage. Recovered audio appears at pin 5 of IC2 and any residual RF is filtered out by a .01µF capacitor. The audio stages use an LF347 quad op amp. The first stage, IC5a is configured as a non-inverting amplifier with a gain of around 11 at 1kHz. The non-inverting input is biased to +5.5V by the two 10kΩ resistors connected to pin 3. IC5b and IC5c form a unity gain 4-pole low pass filter with a cutoff frequency of 2.3kHz. IC5d is another non-inverting amplifier and has a gain of around 13 at 1kHz. 470µF and 100µF capacitors provide decoupling for IC5 and help ensure stability and low noise. Both IC5a and IC5d have a tailored frequency response that rolls off the gain for high and low frequencies. The output of IC5d at pin 7 passes to the volume control via a 1µF coupling capacitor. The final audio stage is IC6, an LM386 power amplifier. The 10Ω resistor and the 470µF capacitor on pin 6 provide power supply decoupling. This stage has ample gain and power PARTS LIST 1 1 1 1 1 1 3 1 1 1 1 1 1 1 1 1 2 2 2 2 20 1 1 1 PC board code 06109961, 167mm x 95mm plastic case, 196 x 112 x 60mm (aluminium lid) black binding post red binding post SO239 panel socket, square 6.5mm jack socket 20mm knobs 35mm knob 500Ω linear potentiometer (VR1) 10kΩ dual linear potentiometer (VR2) 50kΩ linear potentiometer (VR3) 10kΩ log potentiometer (VR5) 10kΩ horizontal trimpot (VR4) 2 pole 3 position slide switch (S1) F14 balun former (T1) 5mm coil former assembly (L9) 2.2µH RF inductors (L1,L2) 4.7µH RF inductors (L3,L4) 10µH RF inductors (L5,L6) 100µH RF inductors (L7,L8) PC pins 5MHz crystal (X2) 6MHz crystal (X1) 12MHz crystal (X3) 34  Silicon Chip Semiconductors 7 1N4148 diodes (D1 - D7) 1 1N4004 diode (D8) 1 BB212 dual varicap (CD1) 2 78L05 +5V voltage regulator (REG1, REG2) 2 NE602 balanced mixer (IC1,IC2) 1 74HC00 quad NAND gate (IC3) 1 74HC10 triple NAND gate (IC4) 1 LF347 quad op amp (IC5) 1 LM386 power amp (IC6) 1 MPF102 FET (Q1) Capacitors 3 470µF 25VW electrolytic 2 100µF 16VW electrolytic 2 1µF 16VW electrolytic 17 0.1µF monolithic 1 .047µF greencap (metallised polyester) 1 .015µF greencap 2 .01µF greencap 1 .0047µF greencap 1 .0033µF greencap 2 .001µF ceramic 1 470pF ceramic 3 330pF polystyrene 3 220pF ceramic 4 3 2 1 2 4 2 4 2 2 1 7 2 150pF ceramic 100pF ceramic 68pF ceramic 68pF polystyrene 56pF ceramic 47pF ceramic 33pF ceramic 15pF ceramic 10pF ceramic 5.6pF ceramic 2.7pF ceramic 5-40pF plastic trimmer (VC1-VC4, VC7-VC9) 5-60pF plastic trimmer (VC5-VC6) Resistors (0.25W, 1% or 5%) 3 10MΩ 8 1kΩ 1 1MΩ 6 470Ω 2 100kΩ 3 150Ω 1 47kΩ 2 100Ω 9 10kΩ 2 10Ω 2 4.7kΩ Miscellaneous Screws, nuts, spacers, hook-up wire, 0.4mm & 0.2mm enamelled copper wire, aluminium sheet, white cardboard. output to drive headphones or an external speaker. Construction Start construction by checking that the components with larger pins fit the holes in the PC board. This is especially true for the oscillator coil L9. You may also need to enlarge the holes for the trimmer capacitors and PC pins as well. There is one wire link on the board and this should be installed first. Follow this with the resistors, trimpot and the RF chokes. If you are using one percent resistors, double check the value before you solder them in as it is quite easy to read the wrong value. The 150Ω resistors associated with the main Tune control are actually soldered on the gangs and not on the PC board. The capacitors can be fitted next. Take particular care with the polarity of the electrolytics and the values of the capacitors associated with the bandpass filters. The filters will not work properly if wrong values are used. Note that VC5 and VC6 are 60pF trimmer capacitors while the rest are 40pF. The board has been designed to accommodate common 3 and 2-pin trimmer capacitors. Solder in the PC pins next. These make wiring easier and fault finding simpler, if needed. Install the semiconductors and crystals next, starting with the diodes. Note that IC3 and IC4 are installed upside down with respect to the rest of the IC’s. Coil winding At this stage we need to wind the two coils. Fig.3 gives the details. T1 is wound on a large two hole balun former using 0.4mm wire. The primary winding consists of 3 turns. A turn consists of passing the wire up through one hole and back down the other hole. The secondary winding consists of 23 turns and is wound over the top of the primary winding. The four ends of the windings will be at the same side of the former. You might label the windings so that you do not get the primary and secondary mixed up when you solder them in the PC board. The oscillator coil L9 is wound on a 5mm former which attaches to a 6-pin base and is enclosed in a metal can. The inductance of the coil is varied by an adjustable ferrite slug in the former. Start the coil by gluing the former into the base with a drop of Super glue. The coil requires 80 turns of 0.2mm wire and this needs to be wound in two layers of 40 turns each. Solder one end of the wire onto the start pin as shown in Fig.3 and starting at the base of the former, carefully wind on 40 turns side-by-side, ensuring that the turns are kept firmly in place. When the 40th turn is finished place a tiny drop of Super glue on it and hold the wire until the glue dries. Wind on the next 40 turns proceeding back down the former and solder the end of the wire to the end pin. Put a couple of drops of glue on the coil to keep the winding from moving. When the glue is dry, place the base into the PCB and screw the slug into the former leaving about half the slug outside the former. Place the can over the assembly, passing the slug through the hole in the can. This ensures the former is centrally positioned within RESISTOR COLOUR CODES    No.   Value ❏ 3 10MΩ ❏ 1 1MΩ ❏ 2 100kΩ ❏ 2 47kΩ ❏ 9 10kΩ ❏ 2 4.7kΩ ❏ 8 1kΩ ❏ 6 470Ω ❏ 3 150Ω ❏ 2 100Ω ❏ 2 10Ω 4-Band Code (1%) Brown Black Blue Brown Brown Black Green Brown Brown Black Yellow Brown Yellow Violet Orange Brown Brown Black Orange Brown Yellow Violet Red Brown Brown Black Red Brown Yellow Violet Brown Brown Brown Green Brown Brown Brown Black Black Brown Brown Black Black Brown 5-Band Code (1%) Brown Black Black Green Brown Brown Black Black Yellow Brown Brown Black Black Orange Brown Yellow Violet Brown Red Brown Brown Black Black Red Brown Yellow Violet Brown Brown Brown Brown Black Black Brown Brown Yellow Violet Black Black Brown Brown Green Black Black Brown Brown Black Black Black Brown Brown Black Black Gold Brown CAPACITOR MARKING CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 17 1 1 2 1 1 2 1 2 3 Value     IEC Code    EIA Code 0.1µF 100n 104 .047µF 47n 473 .015µF 15n 153 .01µF 10n 103 .0047µF 4n7 472 .0033µF 3n3 332 .001µF 1n 102 470pF 470p 471 330pF 330p 331 220pF 220p 221 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 4 3 3 2 4 2 4 2 2 1 Value     IEC Code   EIA Code 150pF 150p 151 100pF 100p 101 68pF 68p 68 56pF 56p 56 47pF 47p 47 33pF 33p 33 15pF 15p 15 10pF 10p 10 5.6pF 5p6 5.6 2.7pF 2p7 2.7 September 1996  35 Once you have the PC board finished and the front panel and case drilled, final assembly is quite straightforward. Note the two resistors soldered directly to the Tune potentiometer, VR2. 36  Silicon Chip the can. Hold the can against the PCB and solder the can pins and then the former pins. Final construction The front panel layout can be seen in the photographs. If you are not building the receiver from a kit with a pre-punched front panel, use the front panel drawing to locate the holes for the front panel controls and drill to suit the potentiometers. The switch requires a rectangular hole and is easily made by drilling a couple of holes first and then filing to shape with a small flat file. The case needs to be drilled to mount the antenna socket on the left hand side and the binding posts and speaker socket on the right hand side. Place the PC board in the bottom of the case to mark the position of the four mounting holes and drill them with a 4mm drill. Mount the controls and switch on the front panel and the binding post and sockets on the case. Place a solder tag under one screw of the antenna connector for the earth connection point. If you are using potentiometers with long shafts, they will need to be cut to length with a hacksaw so that the knobs fit closely to the front panel. (This should be done before they are soldered or mounted). Mount the PC board in the bottom of the case with 3mm screws and nuts and 6mm spacers. All the wiring between the board and controls and sockets is done with hook-up wire. Leave just enough wire between the board and the front panel so that it can be lifted off and turned over to allow access – about 100mm should be enough. The front panel needs to be earthed to avoid hum getting into the Tune control wiring. The best way to do this is to solder short lengths of tinned copper wire (cutoff resistor pigtails are ideal) from the earth lugs of the RF attenuator and volume controls onto their respective metal cases. You will need a good, hot iron to solder to the pot cases and may need to slightly scratch the surface first to ensure the solder "takes". Providing a frequency readout on a receiver is never easy. The modern approach is to use a digital frequency display but these are complex, power hungry, expensive and can cause interference in the receiver sections. This receiver does not have The front panel and dial scale are reproduced actual size, so you can photocopy them and use them as templates for marking your front panel if not working from a kit. September 1996  37 one for all these reasons, although if the receiver is to be used permanently on a desk then a remote digital frequency meter could be attached to the VFO OUT point. This scheme would not give a direct frequency readout, however it would be accurate and the actual frequency could be easily deduced. To keep costs down and make the unit portable, the receiver has an analog dial attached to the main Tune control. It is expected that kit suppliers will provide screened dials but if you are building this receiver from scratch you will need to make your own. There are several ways to do this but the easiest way is to cut an 80mm diameter circle from aluminium, and glue a photocopy of the dial drawing to this. Drill a hole in the centre of the dial large enough to clear the threaded shank of the Tune control (about 12mm). Glue the large tuning knob onto the centre of the dial with suitable adhesive: silicone adhesive proved successful. It is obvious that a little care is needed here so that the knob is centred, otherwise the dial will rotate off centre. When the dial is complete it can be placed on the main Tune control. The marker at the top of the front panel above the dial provides a reference point to read the frequency. Initial testing The front panel should be left unscrewed from the case until all the testing and alignment is finished. Before we apply power, double check the wiring one more time. A minute here could save hours later on, not to mention dollars. Connect a 12V power supply to the binding posts with a multimeter set to measure mA in the positive lead. Plug a speaker into the speaker socket and turn the volume control fully anticlockwise. Turn on the power supply and note the current drawn. The prototypes drew around 40mA with no signal. Obviously no current indicates an open circuit and a much larger current indicates a problem. This could be a wire in the wrong place, a component in the wrong way or a solder bridge on the PC board. If everything appears correct, measure the voltage at the outputs of REG1 and REG2. These should be close to 5.6V and 5V respectively. Check that 38  Silicon Chip The coil (L9) & transformer (T1) are quite simple to make but take care with the start and end of the windings. “ENCU” means enamelled copper wire – small rolls are available from most component suppliers. the voltage between pin 7 of IC5 and the negative supply rail is between +5 and +6V. All the stages of IC5 are direct coupled and any problems with this circuit will probably show up with this check. Turn the volume control to mid position and listen to the speaker. You should be able to hear some hiss, indicating that at least the final audio amplifier is working. At this stage, it may be possible to receive some signals with a suitable antenna but don’t expect too much until alignment is completed. Alignment equipment To properly set up the receiver two pieces of test equipment are required which may not be a part of the average constructor’s workbench . . . yet! You will need a frequency counter capable of reading to 12MHz and an RF signal generator with an output to 15MHz. In addition, a digital multimeter is needed but even novice constructors should have one of these! If you don’t own a digital frequency counter or RF signal generator, think about likely people who could help you out. Most schools would have such equipment in their science or technics areas. Perhaps a local amateur operator could help you out (they’re usually delighted to help beginners get “hooked” on amateur radio!). Look for antennas or towers in local backyards and don’t be afraid to knock on the front door and explain your problem. Take this article with you so the amateur knows what is required. A last resort could be a local technician or service shop. But be warned, these people are trying to earn a living out of electronics and may want to charge you a fee. Frequency setting Ensure that the receiver is powered up for at least 10 minutes before doing this section. This allows the oscillators to stabilise, especially the VFO. Switch the band switch to the 20m position and connect a frequency counter to pin 6 of IC4c. Adjust VC7 until the display reads exactly 12MHz. Switch to 40m and adjust VC8 for exactly 5MHz, and finally switch to 80m and adjust VC9 to show exactly 6MHz. Adjust the Fine Tune control VR3 and trimpot VR4 to halfway. The Fine Tune potentiometer may need rotating so that the pointer on its knob is vertical with the wiper at halfway. Connect the frequency meter to the VFO OUT point and rotate the Tune control almost fully anticlockwise. At the very end of the rotation there is a dead spot and it is not until a few degrees from the end that the potentiometer works properly. Adjust the core of L9 until the frequency counter reads 2MHz. The core of L9 is quite brittle. To avoid damage, use a good quality alignment tool – don't use a screwdriver! Rotate the Tune control almost fully clockwise, again noting the dead spot at the very end of the travel and adjust VR4 until the counter reads 2.5MHz. Go back and forth a couple of times till you are satisfied with the range, as there will be a some interaction between the adjustments. If you use the pre-printed dial or a screened dial from a kit supplier, you should be able to adjust the dial position so that it lines up with the frequencies being received. If not, you will need to mark your own dial - in any case, the following can be done to check the dial positions. Return the Tune control to the 2MHz point and make a mark with a pencil on the dial opposite the line on the front panel. This mark represents the 4MHz point for 80m, the 7MHz point for 40m and the 14MHz point for 20m. Slowly rotate the dial clockwise until the frequency is 10kHz higher and make another mark on the dial. Continue this process until 2.5MHz is reached. This mark represents 3.5MHz, 7.5MHz and 14.5MHz. With an ink pen or rub on lettering go over the marks to make them neat and permanent and at the 100kHz points mark a longer line. The 100kHz points should then be labelled for each band; eg, 4.0, 3.9, 3.8, 3.7, etc. Move the Fine Tune control from end to end and check the frequency shift. If the range is about 5kHz either way no changes need to be made. If you feel the range needs changing refer to the circuit operation section about altering the 150Ω resistors. Filter alignment Connect an RF signal generator to the antenna socket set to 3.6MHz. Switch the receiver band switch to 80m. Connect an oscilloscope or a digital multimeter set to a low AC volts range across the volume control. Move the Tune control until a beat note of around 1kHz is heard in the speaker. Adjust the volume control for a comfortable level. If the receiver is overloaded, giving a distorted tone in the speaker, decrease the output of the signal generator or adjust the RF attenuator until the tone sounds undistorted. Note that the RF attenuator will not completely cut off the input signal due to stray RF coupling around the control. Adjust VC5 and VC6 until a peak is observed in the level of the tone. Select the 40m position and change the generator to 7.1MHz. Move the tune control to give a 1kHz beat note and adjust VC3 and VC4 for maximum audio output. Now switch to 20m and set the generator to 14.2MHz. Move the Tune control to give a 1kHz beat and adjust VC1 and VC2 for maximum audio level. This process gives maximum sensitivity in the middle of the band and should provide a reasonably flat response across the whole range. If instruments are not available, a less precise method is to tune to a station in the middle of each band and adjust the relevant trimmer capacitors for maximum audio from the speaker. Remove all the instruments and screw the front panel to the case. The unit is now ready for use. Connect power, a speaker (or headphones) and SC an antenna and start listening! What about an antenna? For general shortwave listening, the basic rule for antennas ever since the days of Mr Marconi and friends seems to have been “as long and as high as possible”. While technically not quite right, a long, high antenna has been a reasonable choice given the fact that most short wave listeners want to cover frequencies from the broadcast band (around 1MHz) all the way up to 30MHz, and most communications receivers can handle high impedance antennas (which a long wire is). Add to that the fact that most people live in cities or towns and are constrained by their own back yards. For amateur radio it’s a bit more exact, or theoretically should be. To really pull in amateur DX signals, the antenna should be made to suit the band being used - that is, separate antennas for 80, 40 and 20 metres cut so they resonate at the centre of the respective band (or if you are interested in a particular part of the band, at that frequency). You will normally get acceptable performance over the rest of the band. With many variations, there are two basic types of antenna - horizontal and vertical. The horizontal antenna can be a dipole - that is, signal taken from the middle, or it can be a long-wire, with signal taken from the end. Talking generally, a dipole antenna cut to half the wavelength of the frequency of interest will be the better performer, giving good results for signals perpendicular to it - that is, a dipole mounted north/south will have its best reception east/west. Now, what length? The formula for working out the half wavelength (l/2)=150/f, where f is the frequency of interest in MHz. For several reasons which we won’t go into here, the dipoles are cut slightly shorter: dipole length (m) =71.25/f. Therefore a half wave dipole for 3.5MHz (80 metre band) would be 40.7 metres long, with each dipole 20.35 metres. That’s quite a length of antenna, given that the average suburban block is only 45 metres deep! Antennas for the 40 and 20 metre bands are much more manageable. And if you erect an antenna designed for 40m, you can expect at least reasonable performance on 80 and 20m. A dipole can be erected horizontally (supported high at each end), inverted (supported high at the middle with each end supported slightly off the ground), or even sloping (high support one end, low support the other). The last mentioned is often used in suburbia with the antenna supported at one end by a mast on the house and by the back fence at the other! Of course, you could mount a dipole vertically but where are you going to find a forty metre high non-metal pole? (The metal would interfere with the antenna). Strictly speaking, you should use a balun to match the 75Ω impedance of the dipole to the 50Ω impedance of the feedline and receiver. The truth is, especially for receiving, you can usually ignore the mismatch. If you wish to erect a long-wire antenna, theory says that an antenna tuner will be needed for optimum receiver performance. But if you don't have one? Give it a go anyway.You can't do any damage! September 1996  39 SERVICEMAN'S LOG A bounce with a twist No, that’s not a new section in an Olympic Games diving competition. Perhaps I should have called it the bounce that wasn’t. Anyway, we all know what a bounce means in servicing parlance, and that’s the theme. I’ve been talking a lot about bounces in recent notes - and the trauma and acrimony they can cause. Well this story had all the makings of a bounce situation, except for one factor; the time between failures. I wonder what the record is? Anyway, to start at the beginning. The set involved was a General GC187, 43cm colour set of around 1984 vintage and was one of several belonging to a 40  Silicon Chip local motel. It is a rather elementary type of set by modern standards, without any remote control or other up-market gimmicks encountered in later models. The first time I serviced this particular set was back in 1993 and the complaint at that time was that the image was very dark. Because all sorts of funny things - technical things, that is - go on in motels I find it best to view such problems in situ. Damaged antenna outlets, faulty antenna distribution systems, even faulty power points, are all possibilities in such installations. In fact, it didn’t take long to eliminate all these and confirm that yes, the set was faulty. But in spite of having serviced most of these sets in the motel over the years - and some from other customers - I had never seen this symptom before. So it was into the van and back to the workshop. As a general rule, faults of this kind suggest a low or missing voltage around the picture tube and immediate circuitry. My first check was to the picture tube screen (pin 8), which was something over 500V with the screen control as set. I decided that this was a perfectly reasonable figure. The EHT voltage is shown as 22kV and this was, if anything, a fraction high. At a more basic level I checked the supply rails. There are four altogether, +175V off pin 9 of the horizontal output transformer, T602, +127V from the switchmode supply (test point TP601) and two low voltage rails, one at +13.8V and another at +12V. All checked out as specified. That routine completed, it was time to look for something more specific. And the first thing I checked was the collector voltages on the red, green and blue driver transistors, Q201, Q202 and Q203. These are shown as ranging from +105V to +108V but in fact were much higher, over +150V. Which meant, of course, that the picture tube cathodes were similarly too high; around 50V more positive than they should have been. Which is only another way of saying that the respective picture tube grids were 50V more negative than they should have been. No wonder the picture was dark. OK, we were on the track. But why? The fact that this error was occurring on all three drive transistors suggested a common cause and the most likely Fig.1: General GC187. IC301 is at the top, with the sub-brightness and brightness controls below it, and D360 and resistors R624, R640 below again and to the left. One of the drive transistors (red) is at lower right. one would be something associated with the brightness circuit. The three drive transistors are driven from pins 26, 27 and 28 of IC301, described as the video amp/ PAL processor. And the brightness circuit connects to pin 4 of this IC and consists of a sub-brightness control VR304 (10kΩ) and the main brightness control, VR709 (5kΩ). And this leads back to a network, via a diode, D360, consisting of resistors R624 (560kΩ) and R640 (120kΩ) in parallel, connected to the 127V rail. More importantly, the voltage at pin 4, shown as 8.4V, was down significantly. (I can’t remember by exactly how much after all this time but it was significant.) I tried adjusting the sub-brightness and brightness controls but this had only a marginal effect; enough to indicate that they seemed to be working, within the constraints of the fault. I checked diode D360, which was OK, then resistors R624 and R640. And this looked like the answer because R640 had gone high. I replaced it and R624 at the same time, just to be on the safe side. Unfortunately, it wasn’t the real answer; it helped but it didn’t cure the fault. In fact, it made me aware of another fault; the colour was dropping in and out intermittently. I made a few more voltage checks but could find nothing wrong. It was time to check the dynamic aspects of the system; blanking pulses and such like. My first check was on a horizontal pulse to pin 23 of IC301, via a 1kΩ resistor, R327. This was shown as a typical triangular pulse at 3.2Vp-p. And it was; exactly. Next, I checked pin 19. This is shown as a similar pulse at 2.6Vp-p. Only it wasn’t; this waveform was missing completely. Well, I was hot on the trail now, even though it was a rather longish one; all the way back to pin 16 of IC401, the horizontal and vertical oscillator and drive stages. On the way it goes through a 15mH choke, L402 and a couple of resistors. On an impulse, I wiggled the choke. And bingo! Suddenly everything came good; full brightness, normal colour and a first class picture. I didn’t waste time finding out what was wrong with the choke; I reefed it out and fitted a new one. Everything came good again, I let it run for the next couple of days, with no sign of trouble and returned it to the customer. And that was the end of the story. Well, for 1993. But a few weeks ago the motel proprietor was on the phone asking me to have a look at a set. And what was September 1996  41 wrong with it? “Aw, the picture’s gone dark.” And yes, it was the same set, with the same fault, three years later. However, I must confess to stretching things a bit when I imply that this was a “bounce” in the normal servicing sense of the word. The truth is that I was the only one to appreciate the situation. The proprietor had completely forgotten that this was the same set with the same symptoms of three years previously. So there was no aggro of any kind; just a funny feeling on my part as to what might have been. Anyway, down to business. I visited the motel again and yes, at switch-on, the picture was very dark. Instinctively I reached for the brightness control and gave it a tweak. And up came the picture to normal brightness. What was more, the set seemed to be behaving perfectly normally. The brightness control setting was quite reasonable and the range of control was normal. So what did this mean? There was a temptation to assume that it was simply finger trouble on the part of the last user but while I hesitated to accept that, there didn’t seem to be much point in assuming a fault on 42  Silicon Chip such rather flimsy evidence. I suggested that I leave it and for them to keep an eye on it. A couple of weeks went by and they were on the phone again; same problem. I checked it out in situ and yes, it was faulty. So it was into the van and back to the shop again. The only snag was, as soon as I set it up on the bench, it worked perfectly. In short, my worst suspicions were confirmed, it was intermittent. I set it up in “intermittent corner”; the corner of the bench which I reserve for such troublesome devices and let it run all day and every day. This proved only partially successful. The fault did occur on several occasions but by the time I attacked it, it had cured itself. But I did notice a couple of important points. It had a greater tendency to fail when first switched on in the morning and most particularly, when the weather was damp. If not touched, it would come good after about an hour. It was a most frustrating situation; one where one could waste hours of time speculating on likely causes and testing these ideas. In fact I did try a number of ideas. This model is rather notorious for dry joints and I went over all the likely ones and resoldered any which looked at all doubtful. I replaced any electrolytics which looked at all daggy. I went over the work I had done previously. I found nothing positive and in fact, it achieved nothing; the symptoms remained exactly as before. In the meantime, the motel was on my hammer wanting to know when I could finish the job and what it was going to cost. To pacify them, I voiced the only idea had in mind; a fault in the horizontal output transformer (T602) being effected by the damp weather. I quoted them for a replacement – should that prove to be the fault – and of course, it wasn’t cheap. They said they’d think about it. Which at least gave me some breathing space. So I simply let the set run from day to day, hoping for a more definite indication of the fault. And eventually it happened. We had a long bout a very wet weather and I noticed that, instead of a brief burst of the fault at switch-on - which I knew would not stand investigation - it was taking longer and longer for the fault to clear. So, finally, after the fault had remained for several hours, I moved the set out of the corner and tackled it. Thankfully, the fault held and I was able to make a quick check of the four supply rails, screen voltage on the tube and the EHT. All were spot on. Which exposed the fallacy on my faulty transformer theory. Bypassing some of the steps in my previous exercise, I went straight to pin 4 of IC301, fed by the brightness control circuit. Sure enough, the voltage was way down from the stated 8.2V. And incidentally, the fault now seemed to have worsened; it was almost impossible to get any image on the tube. I backtracked to the sub-brightness control, then to the brightness control, still measuring the very low voltage. It was only when I went the other side of the brightness control and measured the voltage applied to it from the 127V rail and the beam limiter circuit of pin 7 of T602, that I found a normal voltage. So it was being applied to the brightness pot but was not appearing on the other side of it. Time to look at the pot itself. Easier said than done, because the control panel had to come out. But sure enough, this was where I Fig.2: Sharp DV-1600X. IC701 is at top left, FB701 below it off pin 4 and C711 to the left of it. Mains power is applied to pins 1 and 3 at extreme right. found it. I had to dismantle the pot to pinpoint it and found that the voltage applied to the lug was not present on the moving arm. And there was no continuity between these two points. The reason? The centre lug of the pot, which ultimately connects to the moving arm, is riveted in place. And under and around this rivet, visible only under the jeweller’s loupe, there was faint evidence of corrosion. The result had been an intermittent break in the lug, under the rivet and effected by temperature and humidity and progressively getting worse. I didn’t have an exact replacement handy and had to put one on order. In the meantime I patched in a 10kΩ pot temporarily. Everything came good immediately. And it stayed that way. The replacement pot eventually arrived, I fitted it, put everything back together and let the set run for a few more days. It never missed a beat and was finally returned to the motel. And that’s my story of a three-year bounce. As I said earlier, it wasn’t a real bounce but the point is it could have been. Had that pot decided to play up a few weeks after the 1993 episode, producing identical symptoms and had it involved a less understanding customer, I would have been hard put to it to convince them it wasn’t the same fault. In fact, I doubt whether they would ever have believed me. So it was a near miss. Well, we must be thankful for small mercies. For a complete change of scene, I have a letter from a Mr. B. L. of Gwynneville, NSW, relating some of his DIY experiences involving faults in his own TV set. This how he tells it. “Daaada!” cried my two year old son - one second he was watching Sesame Street and the next, no more Big Bird. This was the result of a failure in our Sharp DC-1600X TV set; a complete blackout. I have to own up to not being a real serviceman, at least not by trade. However, having graduated last year with a B.E. (Comp.) I felt that, as an engineer, I would have to at least have a look to see if I could do it myself. (Do I hear you groan, “No, not another meddler!”?) Well, after opening the case I discovered the chasm between the basic principles of television transmission and the implementation of those principles. I knew roughly how an image was received, processed and displayed on a CRT but I had no idea where to start looking for faults amongst the myriad of components before me. I decided to invest in a service manual and despite this model’s manual being out of print (it’s about 13 years old), I quickly located one care of High Country Service Data in Cooma NSW. The DV-1600X has a number of service bulletins, mostly relating to the power supply. I checked these items and found a number of apparent faults. R635 (39Ω) in the return path of the horizontal deflection coil measured open circuit. This would explain the symptoms - no sound, no picture. R616 (1.5MΩ) in the protection circuit was also open circuit, which apparently causes shutdown after a period of operation. The power supply IC701’s heatsink appeared to be poorly connected to the copper pattern. I replaced the self tapping screw with a small machine screw, star washer and nut. The horizontal output transistor was similarly modified. I was surprised to find that it was mounted with self tapping screws, soldered to the board and served as a link between tracks. To quote the manual, “Power goes from one track through the metal case of the line output transistor to the next track.” Any bad connections here would spell doom. While I was dabbling with these modifications, I noticed a number of browned-out resistors in the power supply. These were summarily replaced. At this point I wondered how the set ever worked. I fired the set up and found all voltages within specs. and the set operated fine. I was very pleased that I was able to solve this problem without too much drama. My bubble burst about two weeks later. Again it was a complete failure of sound and picture. This time I started out by measuring line voltages and found nothing; not a skerrick of life. I focused on the power supply and September 1996  43 Serviceman’s Log – continued quickly came to the conclusion that IC701 was not operating. Initially, I wondered about the likelihood of a faulty IC but remembered how all too often in my university lab experiments, I mistook my own faulty design, wiring, or measurements for a faulty IC. Then I measured 20V or so at pin 4 of IC701, relative to the negative terminal of the filter capacitor, C711 (10µF, 100V). Well, pin 4 is supposed to connect to this same point, via a device named FB701. Its schematic symbol looks somewhat like a fuse. I had never come across the “FB” monicker before, so I pulled the device out of circuit to examine it more closely. Here was my suspect; I had measured an intermittent 20V across it in circuit, yet a short circuit when free of the printed board. I had a chat with a friendly tech in town, who informed me that it was a ferrite bead used for RF suppression. (Of course, FB.) He suggested replacing it with a link. That was done and all is well some four weeks later - touch wood! I really don’t know if this was the original problem. I wonder if this multiple failure issue crops up often in the serviceman’s world. Well, thanks B.L. for a very interesting story. I particularly liked your comment about the chasm between basic principles and their implementation. Very true B.L. - very true. Also note your comment about the body of the horizontal output transistor forming an electrical path and which, as you suggest, is vital. On the other hand, the mounting of the IC701 heatsink would seem to be less important. As far as I am aware, this is a purely mechanical arrangement which does not involve any electrical circuitry. Regarding the FB701, I am a little concerned at your colleague’s idea of simply eliminating it. It is not clear what form of RF suppression it was supposed to perform or how important this is. However, since the manufacturers chose to fit it - and manufacturers seldom waste money on something which is not necessary - there must have been a reason. It might be advisable to fit a replacement, even at this stage. On a more general note, I would comment that the two main filter capacitors, C711 and C715, are notorious for failure; they dry out due to the heat from IC701. High temperature types are recommended as replacements. And that power supply board is notorious for dry joints. B.L. also raises the matter of connecting mains powered test equipment, such as a CRO, to live, or semilive chassis receivers, such as this one. Unfortunately, this subject is a very complex one, too complex to discuss here. Broadly speaking, each situation has to be assessed individually, using the skill and experience of the technician involved. However, a popular approach is to use a one-to-one 240V isolating transformer, with the secondary floating. The “earthy” arrangement may then be configured in any way required. So, thanks again B.L. for an interesting story – one which has provided an opportunity to discuss a particular set and some of its problems and which may benefit other readers. SC Especially For Model Railway Enthusiasts Available only from Silicon Chip Price: $7.95 (plus $3 for postage). Order by phoning (02) 9979 5644 & quoting your credit card number; or fax the details to (02) 9979 6503; or mail your order with cheque or credit card details to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. 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 Neville Thiele awarded IREE Medal of Honour On 23rd July 1996, the Institution of Radio and Electronics Engineers Australia made the award of Medal of Honour to A. N. Thiele for his lifelong achievements in the field of electronic engineering. Neville Thiele’s achievements in the field of audio engineering are widely known. He is regarded as a world authority on loudspeaker design and most loudspeakers are now specified with “Thiele-Small parameters” after his collaboration with Richard Small in writing a number of seminal papers. The following is a transcript of the award speech given by Ian Shearman, FIREE, vice-president of IREE Australia. Albert Neville Thiele was born in Brisbane where he grew up and was educated at Brisbane Grammar School. He then commenced working in a bank and studying for Bachelor of Arts at the University of Queensland. He subsequently enlisted for service during the Second World War. He is a professional engineer, having graduated from Sydney University as a Bachelor of Engineering soon after he was released from his wartime army service. Immediately upon graduation he joined EMI Australia. At that time he was appointed to assist with the development of audio products, in53  Silicon Chip cluding amplifiers and loudspeakers. The pride which he demonstrated in the tasks he carried out and the excellent products which were developed for sale brought him to the attention of the management of EMI which sent him to the UK to learn about the design and production of television receivers. He spent some months at the EMI facilities in Hayes, Middlesex. He then returned to EMI Australia to develop and market the HMV range of receivers in time for the launch of television here in 1956. It is worth noting that in the early days of television there were about 25 Australian manufacturers of receivers and HMV soon became one of the most highly regarded brands on the market, for their high quality; Neville’s part in this market position was significant. During this period, Neville carried out research and development of a number of aspects of television receiver design. These were published in the technical press and he became well known for the excellent work in this area of his expertise. One of his other great technical loves is loudspeakers. From his time at EMI during the mid-1950s he has been at the forefront of loudspeaker design and is now a world authority. This has been recognised not all that long ago by the presentation of the Silver Medal by the Audio Engineering Society. The medal is only awarded when there is a recipient identified who is considered sufficiently worthy to receive it. He was instrumental in the development of many innovations for both radio and television. He introduced into Australia some revolutionary ideas, especially in test techniques and other equipment design philosophies which improved the technical quality of the signals. We take these for granted now. With the availability of digital techniques, he was responsible for the initial development of specialised digital audio recording techniques which have been continued to a stage where the ABC is having a product manufactured for local and overseas sale. Neville has also been active in his contribution to his profession. He has been a member of The Institution of Continued on page 59 September 1996  53 Want to listen to headphones without being connected to your TV or CD player? Now you can do it with this infrared stereo link. It takes the stereo signal from any source, converts it to a modulated infrared beam and then converts it back to an audio drive signal for standard headphones. Infrared stereo headphone link PART 1 – THE TRANSMITTER How often have you wanted to watch that “special program” on TV while others have wanted to read, or even worse, sleep. Sure, most modern TV sets have a headphone socket but sitting close to the TV on a cushion or hard chair is not our idea of relaxed viewing. Perhaps you or another member of the household is a little hard of hearing (aurally challenged?) and likes the volume louder than the rest. This new project will also solve this problem. Our new infrared stereo link allows you to relax in your favourite chair and listen to stereo sound at a level that suits you. Individual volume controls allow you set the left to right balance, especially for those who may be a little deaf in one ear. The infrared stereo link consists of By RICK WALTERS 54  Silicon Chip two parts. There is the transmitter unit which is powered from the 240VAC mains and takes the signal from the CD player, TV or whatever. And there is the receiver; it is battery powered and it picks up the IR beam and converts it into an audio drive signal for your headphones. As the receiver is battery operated, it will switch itself off after about half an hour to extend the battery life. If you want to use it for longer periods, you will have to press the ON button every half hour. The transmitter has two infrared LEDs at one end and these should point in the direction of the receiver. Naturally, for best results the receiver’s pickup lens should face the transmitter. For good noise-free reception, the distance between the transmitter and receiver should be no more than about three to four metres. The challenge in producing an infrared circuit like this is that it must have adequate dynamic range, low distortion, good frequency response and adequate separation between channels. Let us state, at the outset, that the quality of reproduction is quite good and most people will judge it perfectly adequate for watching TV. However, it is not as good as CD-sound quality although many people with hearing difficulties will not be concerned with this aspect. The inside story on the infra red stereo transmitter, showing almost all components mounted on a pc board attached to the lid. Note the shrouding around the mains switch – this is essential to prevent you coming into contact with 240V, either directly or through your hifi if a mains wire comes adrift! Transmitter operation Fig.1 shows the circuit of the infrared transmitter. It is essentially a pulse width modulator (PWM) which produces a stream of varying width pulses at 44kHz. The stereo signal is multiplexed into the PWM stream and the left and right channels must be separated by the receiver circuit. Notice that the transmitter can be split into two halves. At the top lefthand corner is the right channel input, feeding into volume control VR1 and then into op amp IC4b. Still on the lefthand side of the circuit but about half way down is the left channel input, feeding into the volume control VR2 and then into op amp IC4c. Let’s concentrate on the right channel to begin with. Op amp IC4b has a gain of 10 at mid-frequencies. IC4b’s output, pin 7, drives a two section low-pass RC filter and then IC4a which has a gain of two. The output of IC4a is fed to the non-inverting input of comparator IC5. The inverting input (pin 3) is driven with a triangle waveform running at 88kHz. This signal comes from pin 1 of IC3a. IC1, a 555-type timer, is wired as a free running oscillator to operate at 176kHz. Its output frequency at pin 3 is divided by two in IC2a, producing symmetrical 88kHz square waves at pins 1 and 2. The signal at pin 1 is fed to IC2b’s clock input, its output being 44kHz square waves at pin 12 and 13. Pulse width modulation The square wave at pin 2 of IC2a is fed to integrator IC3a, which produces a very linear triangular waveform at its output, pin 1. Thus at the input of IC5 we have an audio signal on pin 2 and an 88kHz triangle wave on pin 3. The output of IC5, pin 7 is normally high but will pull down to ground whenever the voltage at pin 3 exceeds that at pin 2. Therefore the output of the comparator will be a train of varying width pulses (Pulse Width Modulation or PWM), the width varying in sympathy with the frequency and volume of the audio. The left audio channel is identical to the right in function. IC4c and IC4d provide the signal gain and IC4d feeds the audio signal to the non-inverting input of comparator IC6. The 88kHz ramp comes from IC3a, as before. The two comparators IC5 and IC6 are open-collector output and they are wired in parallel to a common 1kΩ resistor; when one output goes low it will pull the other low as well. What we wish to do is to transmit the right channel signal for a short period, then transmit the left, then the right etc. This is known as multiplexing. “Wait a minute”, you are thinking, September 1996  55 Fig. 1: the circuit diagram of the transmitter. Quite complex operation is simplified through the use of a number of integrated circuits. “if we chop the audio like this we should only hear half the program.” Luckily, this is not the case. Compact 56  Silicon Chip discs operate on a similar multiplexing principle. If we limit the bandwidth (and thus the slew rate) of the audio signal and sample it at a rate faster than the signal can vary, then no information will be Fig. 2 (left): the component layout and wiring of the transmitter, with its associated PC board pattern shown above. Use this to check your own PC board thoroughly before commencing construction. lost. This is the reason we have low-pass filters in each channel. Multiplexing So, how do we switch between the right and left signals? Fortunately LM311 comparators have a gating pin (pin 6) which allows us to do just that. If this pin is held low, the output at pin 7 will stay high. Thus by applying a square wave signal to pin 6 pin of IC5 we can alternately enable and disable the chip. By feeding the complement (opposite polarity) of the squarewave to pin 6 of IC6, we gate them on alternately, just as we require. The gating signal is 44kHz, as supplied by the Q and Q-bar outputs of IC2b. The commoned output of IC5 and IC6 switches Q1 on when it goes low, turning on LED1 and LED2 which will emit pulses of infrared light of fixed intensity and varying duration. Pilot tone OK, we are now transmitting two audio channels multiplexed in a continuous stream but we will have a problem at the receiving end, for we will not know which channel is which. This is where IC3b comes into the picture. It is configured as a 10Hz square wave oscillator. Its output at pin 7 is fed via a two-section low pass filter to produce a 10Hz sine wave signal. This sine wave is injected at a low level into pin 13 of September 1996  57 PARTS LIST - TRANSMITTER 1 PC board, code 01109961, 106 x 80mm 1 plastic box, 150 x 90 x 50mm, Jaycar HB-6011 or equiv. 1 30V centre-tapped transformer Altronics M-2855 or equiv. 1 DPDT 250VAC miniature toggle switch, Jaycar ST-0552 or equiv. 1 3-core mains core with moulded 3-pin plug 2 chassis-mount RCA sockets 1 TO-220 heatsink (see text) 2 3mm x 15mm machine screws 2 3mm x 12mm countersunk screws 1 3mm x 6mm machine screw 5 3mm nuts 5 3mm star washers 2 6mm spacers 4 12mm square stick-on feet 1 cable clamp, Jaycar HP-0716 or equiv 1 6.5mm crimp lug 1 solder lug 1 100mm cable tie 150mm twin screened cable 100mm green/yellow mains wire Semiconductors 1 555 timer (IC1) 1 4013 dual JK flipflop (IC2) 1 TL072 dual op amp (IC3) 1 TL074 quad op amp (IC4) 2 LM311 comparators (IC5,6) 1 7815 +15V regulator (REG1) 1 7915 -15V regulator (REG2) 1 BC640 PNP 1A transistor (Q1) 2 100mA IR transmitter diodes (LED1,2) Jaycar ZD-1950 or equiv 4 1N4004 1A diodes (D1-D4) Resistors (0.25W 1%) 2 2.2MΩ 6 10kΩ 1 330kΩ 1 5.6kΩ 1 150kΩ 3 4.7kΩ 1 75kΩ 1 3.3kΩ 1 56kΩ 3 1kΩ 3 47kΩ 1 470Ω 4 39kΩ 2 100Ω 1 36kΩ 2 68Ω 2 50kΩ horizontal mounting trimpots (VR1,VR2) IC4d via the 36kΩ resistor and will only appear in the left channel. Thus the left channel will always contain a low level 10Hz sine wave and this becomes the pilot tone used by the receiver to differentiate between the left and right channels. process of high frequency reduction in the receiver is called de-emphasis and again, is standard in FM receivers. A small power transformer and two IC voltage regulators provide the positive and negative 15 volt supplies for the transmitter. High frequency pre-emphasis Putting it together To improve the signal to noise ratio we boost the higher frequencies in the audio signal by increasing the gain of IC4b and IC4c. This is done by the .047µF capacitor in series with the 100Ω resistor. At high frequencies the impedance of the capacitor reduces, thus increasing the gain of the amplifier. Increasing the high frequency signals in this way is called pre-emphasis and it is a standard technique in FM radio transmissions. Then, when the signal is received, the high frequencies are reduced by the same amount as they were boosted in transmission. This reduction in high frequencies also reduces the hiss which is naturally present in high gain circuits and this improves the overall noise performance. The There are three PC boards to be assembled for this project, two in the receiver and one in the transmitter. The transmitter PC board measures 106 x 80mm and is coded 01109961. Before you begin assembling the PC boards, check all three for etching problems, open circuit or bridged tracks and undrilled holes. Fix any defects before proceeding further. Now let’s describe the transmitter assembly. The PC board layout and wiring diagram is shown in Fig.3. Begin assembly of the PC by inserting and soldering the six PC stakes and nine links, followed by the resistors, diodes, trimpots, transistor, capacitors and finally the regulators. The positive regulator (REG1) is fitted with a small heatsink. For our prototype we 58  Silicon Chip Capacitors 2 470µF 25VW electrolytic 1 100µF 25VW electrolytic 5 10µF 25VW electrolytic 1 3.3µF 25VW electrolytic 2 3.3µF 25VW non-polarised (NP) electrolytic 1 0.22µF MKT polyester 4 0.1µF 63VW MKT polyester 1 0.1µF 50VW monolithic 2 .047µF 63VW MKT polyester or ceramic 1 .01µF 63VW MKT polyester or ceramic 1 .0022µF 63VW MKT polyester or ceramic 1 820pF 63VW MKT polyester or ceramic 4 680pF 63VW MKT polyester or ceramic 2 150pF 63VW MKT polyester or ceramic 2 100pF 63VW MKT polyester or ceramic 1 39pF 63VW MKT polyester or ceramic Note: ceramic capacitors must be within ±10% tolerance. used a U-shaped heatsink with the sides straightened out so that it fitted between the two 470µF capacitors. Put a smear of thermal compound on the heatsink before screwing it to the regulator. Finally, insert and solder the ICs checking that their orientation is correct. The same comment about polarity and orientation applies to the diodes, transistor and electrolytic capacitors. The PC board is actually mounted on the lid of the plastic case which is then turned upside down for normal use. The power transformer, power switch and RCA input sockets are mounted in the body of the case, as shown in the photos. The PC board is mounted centrally on the lid of the box, stood off on 6mm spacers. Once you drill the holes make sure you fit the board the correct way, as the mounting holes are not symmetrically placed on the PC pattern. Drill two holes for the RCA sockets on the box centreline 55mm and 70mm from the corner, on the side adjacent to the switch. We made the one on the right (believe it or not) the right RESISTOR COLOUR CODES    No. Value    4-Band Code (1%)    5-Band Code (1%) ❏ 2 2.2M red red green brown red red black yellow brown ❏ 1 330k yellow yellow yellow brown yellow yellow black orange brown ❏ 1 150k brown green yellow brown brown green black orange brown ❏ 1 75k violet green orange brown violet green black red brown ❏ 1 56k green blue orange brown green blue black red brown ❏ 3 47k yellow violet orange brown yellow violet black red brown ❏ 4 39k orange white orange brown orange white black red brown ❏ 1 36k orange blue orange brown orange blue black red brown ❏ 6 10k brown black orange orange brown black black red orange ❏ 1 5.6k green blue red brown green blue black brown brown ❏ 3 4.7k yellow violet red brown yellow violet black brown brown ❏ 1 3.3k orange orange red brown orange orange black brown brown ❏ 3 1k brown black red brown brown black black brown brown ❏ 1 470 yellow violet brown brown yellow violet black black brown ❏ 2 100 brown black brown brown brown black black black brown ❏ 2 68 blue grey black brown blue grey black gold brown channel input and the other one the left input when the box is inverted, as it is when it is in use. The holes for the infrared LEDs are on the end opposite the mains entry, 10mm from the open edge and 15mm either side of the centreline. Once these holes are drilled you can push the two LEDs into their mounting holes on the PC board and adjust them to protrude through the box. When you are satisfied, remove the bolt near them, swing the PC board around and solder them in place. The mains lead is held securely with a cable clamp where it enters the plastic box about 20mm from the bottom and 25mm from the edge. The mains cord is wired directly to a double pole mains switch which is mounted about 40mm to the right of the mains entry point. The mains transformer and metal bush of the mains switch must be earthed. Slip the mains lead earth wire and a 100mm length of green/yellow earth wire into the 6.5mm lug and crimp it securely or solder the wires in it, then slip the lug on the switch, add the star washer and mount the switch. The mains wires and the transformer wires are individually sleeved with 2.5mm heatshrink and soldered to the switch. They must be run through a 50mm length of 20mm heatshrink sleeving before they are soldered. After soldering the four wires slide the sleeves right up over the switch contacts and shrink them, then slide and shrink the large sleeve over the switch. Finally secure a cable tie around this sleeve and tighten it, to anchor the wires CAPACITOR CODES    ❏ ❏ ❏  ❏  ❏  ❏ ❏ ❏ ❏ ❏ Value IEC Code 0.22uF 220n 0.1uF 100n .047uF 47n .01uF 10n .0022uF 2.2n 820pF 820p 680pF 680p 150pF 150p 100pF 100p 39pF 39p EIA Code 224 104 473 103 222 821 681 151 101 39 securely. Should a lead come off the switch it will then be contained and cause no hazard. The switch is wired so that it is ON when the toggle points towards the mains lead. Using countersunk screws, mount the mains transformer about 40mm from the end remote from the mains entry, checking to ensure that it does not foul the PC board components when the lid is fitted. The two orange wires from the transformer are soldered to the bottom stakes adjacent to the power diodes, while the white centre tap lead is soldered to the stake closest to the centre of the PC board. This completes the assembly of the transmitter. Next month we will give the full SC details of the receiver. IREE Medal of Honour to Neville Thiele . . . continued from p53 Radio and Electronics Engineers Australia since 1947 and was elevated to Fellow, in 1969. He has been a Councillor from 1963 to 1973 and from 1982 to the present time. During that period he has held many positions, including that of Vice-President (1972/73), Deputy President (1984/86) and President (1986/87). He has served on the Publications Board and other Boards and Committees and as a Member and Chairman of the Sydney Division of The Institution. He has twice been presented with the Norman W. V. Hayes Medal. He is a Fellow of the Institution of Engineers Australia and of the Audio Engineering Society. During his career he has been a member of the Australian delegations to the CCIR. In addition, Neville has been active for many years in Standards Australia technical committees. Neville is also a prolific author, having published 48 technical papers. While at the ABC he prepared 25 reports on his design and development projects. He has attended 24 conferences at which he has presented at least one technical paper. His personal achievements and his contribution to the affairs of The Institution over many years make him a worthy recipient of the Award of Honour from The Institution of Radio and Electronics Engineers. SC September 1996  59 High Q Public A Loudsp This high quality column speaker will change your perception of Public Address (PA) sound. With a massive 200W By JOHN Public address systems are usually associated with poor quality sound. They often lack any bass below 100Hz and the upper frequency response rarely goes above 10kHz. As for the sound quality in the range from 100Hz to 10kHz, it is usually lacking clarity and is very peaky in its response. A peaky response, particularly in the mid frequency region, can cause acoustic feedback between microphone and loudspeakers. At best, PA speakers with a peaky response will have a tendency to ringing where the system is just on the verge of full        feedback or at worst, no reasonable sound level can be obtained before feedback occurs. Apart from flush-mount ceiling speakers, by far the most common loudspeaker type for indoor public address is the column or line source speaker. This consists of a vertical column of loudspeakers in a box and can be recognised by its long thin shape. These types of speakers have the advantage that the sound is dispersed in a horizontal plane so that levels are consistent throughout the entire Features Quality reproduction for voice Even sound distribution over the whole listening area Complete coverage of audible frequency range Smooth frequency response Good transient response Off-axis response up to 45 degrees High power rating and sensitivity 60  Silicon Chip listening area. Sound dispersion in the vertical plane is much reduced and this minimises reverb­eration from ceiling and floor reflections. A commercial pair of column loudspeakers typically cost around $750. Usually, they each contain four circular or oval shaped drivers all mounted on a loudspeaker box baffle. Commonly, the rear of the box is not sealed so that the dimensions can be made as small as possible. Because of the open back and the use of one driver type to cover the whole frequency range, the bass response is poor and the high frequency range is not covered well either. And while such speakers may be adequate (just) for speech they are usually plain awful with any sort of music program. The design presented here is intended to compete with commercial units in applications where size is not important and high quality sound is preferred. It is ideal for music and speech and the low frequency response makes Quality Address peakers continuous power rating, high efficiency and wide frequency response, it is ideal for music and voice in a large listening area. CLARKE it suitable for electric piano and organ. The prototypes have been installed in a small church. The 2-way loudspeaker system comprises two rows of loudspeakers, one with four 6.5" (165mm) woofers and another with four 1" (25mm) tweeters, all mounted in the one large box. We have specified Philips AD11600/T8 textile dome tweeters and these are relatively inexpensive compared to the more esoteric types with aluminium diaphragm and magnetic fluid damping. They provide a high level distortion-free sound and their typical resonant frequency is quite low at 1300Hz compared to many other tweeters of the same size. Its rated impedance is 8Ω and voice coil resistance is 6.3Ω. Measured Thiele-Small parameters are Qms 3.58; Qes 1.09; Qts 0.84; Re 6.2Ω; Le 1mH and fs 1132Hz. Bass drivers For the bass drivers we have spec- ified the Vifa P17WG-00-08 woofers which have a mineral filled polycone, high damping rubber surround, a smooth overall frequency response and an optimised off-axis response which enables operation up to beyond 4kHz. The resonant frequency is 37Hz which allows for good bass response in a suitable enclosure. Its Thiele-Small parameters are shown in Fig.6 which is a printout of the Bass Box 5.1 enclosure design. We opted for a bass reflex design so that the useable response could be extended to 30Hz; it is actually -10dB down at 30Hz. The -3dB and -6dB points are at 43Hz and 36Hz respectively. The bass reflex design also increases the power rating of the woofer below 100Hz due to the reduced cone excursion enabled by the use of the tuning port. Crossover network The crossover circuit is shown in Fig.1. It is a second order Linkwitz-Riley (Q = 0.5). It has the advantage that it does not cause any horizontal axis Specifications Power rating: Nominal Impedance: Sensitivity: Low Frequency Response: High Frequency Response: Box Size (external): Box capacity (internal) 200W RMS continuous 8Ω 93dB SPL at 1 metre for 2.83V RMS input 3dB down at 42Hz, useable to 30Hz beyond 20kHz 460(w) x 750(h) x 370(d) mm 100 litres September 1996  61 Fig.1: Crossover circuitry for the column loudspeakers comprises 0.82mH inductors and 3.2µF capacitors (total) to form a high pass filter for the tweeters and a low pass stage for the woofers. The tweeters and woofers are connected in series-parallel to provide a system impedance of 8Ω. tilt at the crossover frequency due to different mounting centres between the woofer and tweeter. The Q value of the filter provides ideal damping and transient response, with a 3dB AUDIO PRECISION 100 drop in frequency response at the crossover point. Note that the phase of the tweeters is reversed from the woofers to provide the correct crossover blend IMPEDANCE (OHMS) vs FREQUENCY (Hz) between loudspeakers. This is not a mistake. The crossover frequency has been set at 3.1kHz so that both loudspeakers blend without any abrupt sound level changes and before any marked off axis rolloff by the woofer. This frequency is also more than one octave above tweeter resonance at around 1.3kHz. Each of the woofers is equalised with a shunt RC network consisting of a 12Ω 5W resistor and a 10µF non-polarised (NP) capacitor. This provides a more or less constant impedance load to the low pass filter network and ensures that its attenuation slope is close to the desired 12dB/octave beyond the crossover frequency. Signal to the tweeters is attenuated by a 6dB L-pad which compensates for their higher sensitivity compared to the woofers. The L-pad also helps to maintain an overall 8Ω impedance near the crossover frequency and also increases the power rating of the tweeters. An 8Ω system impedance is obtained by connecting the woofers and tweeters in a series-parallel arrangement. This configuration has two benefits. First, the overall power rating of the loudspeaker system compared to a single driver is increased by a factor of four. Second and more important, the series-parallel connection and mounting the four speakers on a common baffle increases the system efficiency by 6dB. This is equivalent to substituting a 200W amplifier for a 50W unit. The resulting overall efficiency of 93dB/1W/1m is very high for a wide range speaker system. Construction 10 1 10 100 1k Fig.7: measured impedance curve for the prototype column system. 62  Silicon Chip 10k 20k Fig.2 shows the dimensions of the prototype loudspeaker enclosure. The prototype was made from 18mm MDF (medium density fibreboard) and had internal cleats of 12 x 12mm quad at all corners. All cabinet joins were glued (with PVA glue) and screwed. All internal corners of the cabinet were then sealed with a fillet of PVA glue to make sure that it was airtight. The box can be finished with paint or a simulated wood grain material. There are two crossover network PC boards, one for the four tweeters and one for the four woofers. Both measure 120 x 93mm and their codes are 01310961 and 01310962. These Fig.2: dimensions of the prototype enclosure, made from 18mm MDF (medium density fibreboard with internal cleats of 12 x 12mm quad at all corners. The external dimensions will need to be increased if thicker material than 18mm MDF is used. The internal volume is 100 litres. September 1996  63 Fig.3: This overlay diagram shows how to wire up the crossovers. Make sure that the phasing is correct when wiring the loudspeakers. boards will be available from RCS Radio Pty Ltd. Phone (02) 9587 3491. Start assembling the crossover boards by inserting PC stakes at all the external wiring points. Then insert and solder in all the capacitors and resistors. The capacitors are all non-polarised (NP) types so there is 64  Silicon Chip no concern about polarity. Note that these non-polarised capacitors may also be labelled “BP” which stands for “bipolar”. The 0.82mH inductors are secured with a screw, nut and star washers or you can glue them in place. These inductors can be obtained from Jaycar Electronics stores (Cat LF-1320) or from Scan Audio Pty Ltd. Phone (03) 9429 9309. The tweeter crossover board should be wired up with 300mm lengths of hookup wire for both the tweeters and input terminals. Use red for positive (+) and black for negative. The board is Fig.4: manufacturer’s data for frequency response and impedance curves of the Vifa P17WG-00-08 woofer. The three curves for frequency response are for 0 degrees, 30 degrees and 60 degrees off axis. Fig.5: manufacturer’s data for frequency response of the Philips AD11600/T8, measured on axis at a distance of 1m with 1W input power. Note the increased sensitivity compared to the woofer. Shown on the same graph is the impedance. Note the rise in value to the resonance at around 1.2kHz mounted centrally on the tweeter side of the box using self tapping screws. Tie the pairs of red and black leads for each tweeter together with a knot to make sure that they will be connected up correctly later. Similarly, wire up the woofer crossover with 300mm wire lengths for the centre two speakers and 500mm lengths for the outside woofers. Attach this board centrally on the woofer side of the box and tie each pair of the red and black leads together. Attach the terminals for the speaker on the rear of the box and solder the crossover input wires to it. Line the box with Innerbond on all sides except for September 1996  65 PARTS LIST    (for one loudspeaker box) 4 Vifa P17WG-00-08 woofers (Scan Audio Pty Ltd) 4 Philips AD11600/T8 or AD11610/T8 tweeters (Jaycar Electronics or Dick Smith Electronics) 1 woofer crossover PC board coded 01310961, 120 x 93mm 1 tweeter crossover PC board coded 01310962, 120 x 93mm 1 1m length x 910mm Innerbond 2 66mm I.D. ports (76mm long) (Jaycar Cat CX-2682) 2 0.82mH speaker crossover inductors (Jaycar or Scan Audio) 4 10µF 100VW NP electrolytic capacitors 2 2.2µF 100V metallised polyester capacitors 2 1.0µF 100V metallised polyester capacitors 4 12Ω 5W resistors 4 10Ω 5W resistors 4 3.9Ω 5W resistors 20 PC stakes 1 10m length of heavy duty red hookup wire 1 10m length of heavy duty black hookup wire Fig.8: full size artwork for the two crossover network PC boards. Hardware 1 12m length of 12 x 12mm quad section wood 2 1200 x 900 x 18mm MDF panel 1 speaker grille kit (Jaycar Cat CF-2750) or wood frame and four speaker grille clips 1 piece of speaker grille cloth 800 x 500mm 1 loudspeaker terminal posts 1 2m length of speaker sealant 16 self tapping screws to mount woofer 24 self tapping screws to mount tweeter and ports 8 self tapping screws to mount crossovers 2 self tapping screws to mount speaker terminal 66  Silicon Chip the baffle. Pass the speaker wires from the woofer cross­over through the material. Glue the Innerbond to the panel surfaces with PVA to keep the material away from the port holes. Once the glue has dried, the loudspeakers can be connected to the wiring and secured in position. Correct phasing for the loudspeakers is important and is normally indicated on the loudspeaker terminals with a red dot or with a (+) sign on the magnet label. The convention is that a positive voltage applied to the plus terminal will cause the cone to move outward. We used speaker sealant around edge of the woofer mounting holes to ensure that the box is sealed properly. The tweeters have an integral sealing washer. It is a misconception to think that the box need not be sealed properly because it has port holes anyway. To work properly, the ports rely on an airtight box. Any leaks will affect the low frequency response of the loudspeakers, cause extraneous noises and reduce efficiency. Now cut the 66mm I.D. ports to 76mm in length and secure each one to the baffle with four screws. The grille can be constructed using a wooden frame with the cloth secured with tacks or staples. It can be attached with grille clips. Alternatively, you could use a grille kit from Jaycar Electronics. This comprises Fig.6: Predicted low plastic strip mouldings frequency performance for the sides which of the woofer using the BassBox 5.1 CAD are attached to corner software. pieces. The cloth is held using the supplied double sided tape and the whole assembly is secured to the loudspeaker baffle with grille clips. Positioning Used in a hall, column loudspeakers are best mounted one on each side of the hall, forward of the stage area. This positioning will reduce the possibility of acoustic feedback between microphones and loudspeaker. The loudspeakers should be angled downward so that they each point to the centre of the audience area. Some adjustment of the position may be necessary for best results. Alternatives Although the AD11600/T8 has been specified, you can also use the AD11610/T8. The only real difference between these tweeters is that the specified unit has a textile dome while the second version has a polycarbonate dome. An alternative woofer is the more expensive P17WJ-00-08. They are available from Jaycar Electronics or Scan Audio. It has a 70W power rating, a magnesium basket and similar resonant frequency to the WG version. You will have to change the woofer equalisation values from the 10µF and 12Ω values to 6.8µF and 6.8Ω 5W. The ports should be 80mm long each. Also note that the woofer hole cutouts in the loudspeaker baffle will need to be 145.5mm. The loudspeaker can be operated from a 100V line if connected via SC a suitable step-down transformer. September 1996  67 Most readers are familiar with analog oscilloscopes but these are being rapidly supplanted by digital storage oscilloscopes. These can capture and display waveforms with a much wider range of frequencies and they are also better at catching “one-off” glitches and fault conditions. By BRYAN MAHER Until about 1970 there was no satisfactory method of displaying infrequent or once-only events. Yet transient electrical signals and errors, intermittent faults and glitches, are very common in all types of electronic and computer equip­ment. They may occur perhaps once a day or even less, yet they can wreak havoc and no analog oscilloscope can display them. Some deliberate actions, like explosive shots or failure testing of mechanical components, generate (through transducers) once-only signals. We need the ability to find such signals when they occur, to capture them on the screen and to display and analyse them after the event. Analog storage CRO tubes were used 68  Silicon Chip for a decade or so but they had lots of disadvantages. We had to wait until someone thought of digital storage. Basic digital storage scope Then in the late 1960’s some enlightened person combined an analog-to-digital converter and a computer iron core memory with a conventional oscilloscope. From this marriage the Digital Storage Oscilloscope (DSO) was born. The block diagram of Fig.1 illus­trates the basic idea. In modern instruments, the blocks on the left side of Fig.1 constitute the signal acquisition section. There the Sample/Hold unit quickly takes many short samples of the analog signal as it occurs and these samples are immedi- ately digitised in the Analog to Digital converter (ADC). The system stores those digital copies in binary form in a random access memory (RAM). This first part of the operation is illustrated in the functional diagram of Fig.2(a). After the event has passed, you can read out from the memory that captured data and display it on the scope screen as an approximate copy of the original analog signal. That second function is illustrated by Fig.2(b). You can see two important differences between analog and digital oscilloscopes. Firstly, the analog scope can only display the signal while it is occurring. In contrast, the digital storage scope displays a reconstructed copy of the input signal some time after the event has passed. And that data can be held in the memory for as long as required and displayed as many times as you wish. Secondly, the analog scope must display (write or trace) the signal as fast as it occurs. For high frequencies and rapid transients, that requirement demands very expensive cathode ray tubes using electrostatic deflection. By contrast, in the digital scope only the signal acquisition and digital processing sections need to be fast enough to follow the live signal. Those areas include the analog preamplifier, the sample/hold, the ADC and the write to memory functions. Once the data which represents the signal is written to and held in memory, the display section can read out that data and display it on the screen at a conveniently slower pace. Therefore cheaper and slower display tubes using magnetic deflection and raster scan are perfectly adequate. Furthermore, because they can also display continuous waveforms, modern digital storage scopes are now supplanting analog scopes and providing lots of measurement functions as well. Digital scopes are ideal for capturing occasional glitches that would never be seen on an analog scope. This little glitch (circled) on an otherwise normal square waveform could cause untold intermittent problems in digital circuitry. (Yokogawa photo). Sampling Fig.2(a) depicts the taking of 500 Fig.1: in a digital storage oscilloscope the incoming analog signal at left is sampled, converted to a digital code, then stored in memory. Some time later that data is read from the memory, converted to a raster display and shown on the screen. Fig.2: functional diagram of a simple digital scope. The record­ing process (a) converts 500 samples of the analog signal into digital words which are written to the memory. Then that data can be read from memory and displayed as a reconstructed copy (b) of the original signal. September 1996  69 new data are fed into the memory, overwriting the old record. But if the signal never recurs, that first record is all you will ever get, so you keep it in memory as long as you wish. But most importantly - because you have it safely recorded in the memory - you can continue to re-display that waveform for as long as you choose. And many modern digital scopes allow you to print a copy of the screen display as well. Updated display Fig.3: when sampler switch IC1 conducts, capacitor C charges to the instant­ aneous voltage of the analog signal. When IC1 switches off, capacitor C holds that sample voltage while the A/D convert­er encodes it into an 8-bit digital word. Whether the input signal repeats or not, the display is updated, perhaps every 20 milliseconds. This means that the whole record of digital words held in memory is again read, converted to raster format and displayed on the screen, as illustrated in Fig.2(b). This frequent updating (between 30 and 150 screens per second for a simple display) together with the fairly long screen persistence used, gives the appearance of a continuous signal. The sampling, A/D conversion and writing to memory functions should run fast enough to adequately capture every wriggle, spike and harmonic in samples of an input signal at regular slight spread of the electron beam will time intervals. Fig.3 illustrates the merge those dots into a continuous essential components of a sampler, trace. where IC1 is a fast electronic switch. The full set of digital words held in To take each sample, a logic control memory is called one Record, which pulse applied to pin 12 causes IC1 represents all the information you to conduct between pins 10 and 11. know about that analog signal. If the During the few nanoseconds (or less) event repeats, each time the oscillothat IC1 is conducting, the capacitor scope is triggered the sampler and ADC C charges, through resistor R, to the collect a new record of samples. These voltage of the analog signal at that moment. At the end of the control signal pulse, IC1 ceases conducting but capacitor C continues holding that charge. The ADC quickly encodes the voltage value held in capacitor C by generating an equivalent digital word of eight bits. The clock control circuits promptly cause that word to be written to a unique address in memory, as indicated in the functional diagram of Fig.2(a). On each subsequent clock pulse, the instrument repeats the cycle: sample-hold-convert-storein-RAM. This continues until 500 samples are taken and the corresponding 500 digital words are stored in memory. That is sufficient data to reconstruct an approximate copy of the analog signal on the screen. In simple systems this display will be an array of dots, one point Frequency, period and other waveform measurements are an inbuilt feature of for each sample taken, as most digital storage oscilloscopes. This HP 54601 model has four input channels Fig.2(b) indicates. But the and a bandwidth of 100MHz. 70  Silicon Chip a high frequency analog waveform. Otherwise the reconstruction of fast rising or falling edges will be poor. For example, the steep fall at the right hand end of the waveform shown in Fig.2 demands that many samples be taken at a fast rate to record the true wave shape. Sampling Interval is the time between one sample and the next. This is the inverse of Sample Rate, which is also the frequency of the clock pulses. For best resolution and widest bandwidth, the sampling interval should be very short and the process should be repeated at a very fast sample rate. Some modern digital oscilloscopes can take 5,000 million samples each second, or 5 Gigasamples per second, written as 5GS/s. They can fill a 500-point record in the memory in one tenth of a microsecond! The Tektronix TDS320 digital storage oscilloscope has 100MHz effective bandwidth on each of the two input channels. The sampling rate is 500MS/s and the memory holds a record of 1,000 points. The 8-bit vertical resolution in real time mode can be extended to 11 bits with repetitive signals using averaging techniques. Vertical sensitivity extends down to 2mV/div, with an accuracy of 2%. This instrument can capture up to 86 waveforms/sec and make a wide range of automatic measurements. Hard copy output to a printer is a standard facility. Fig.4: in a flash A/D converter, comparators give high or low output depending on whether the analog signal is above or below the DC voltage tapped from the resistor string. IC3000 decodes this data into a digital word. Real oscilloscopes use 255 com­parators and 256 equal resistors to encode the analog sample into an 8-bit word. Real time bandwidth To display one-shot events, digital storage oscilloscopes must operate in Real Time Mode. This means that the samples of the analog signal are displayed on the screen in the same order as they are taken and one trigger event must initiate the total acquisition. These conditions are implied by Fig.2. By a Trigger Event we mean either a voltage change in the analog signal which is sufficient to actuate the oscilloscope trigger circuits or an external signal applied to the scope “Ext Trig” terminal. Real time digital oscilloscopes have two measures of bandwidth. Firstly, the analog bandwidth is the -3dB frequency limit of the analog preamplifier stages. Secondly, the sampling rate also sets an upper frequency limit. In the next chapter we will see why Nyquist’s Rule requires a sampling rate more than twice the frequency of the input signal. So we define the digital real time bandwidth as a frequency less than half the sampling rate. The Effective Real Time Bandwidth is the lower of the quoted analog and digital bandwidths. Flash A/D converters The Flash A/D converter is a very fast circuit which can encode an analog signal as a binary digital word on parallel output lines. For September 1996  71 Fig.5: the 4-bit A/D converter allows only 16 decision levels, which is too coarse a result. Real time scopes use 8-bit systems, giving 256 decision levels, so the steps in the display are fine enough to be acceptable. simplicity, we will look at a 4-bit version, shown in Fig.4, although 8-bit ADCs are standard on digital scopes. These ADCs are referred as “flash” because they are very much faster than the older “successive approximation” types. The circuit shown in Fig.4 can create a 4-bit digital word to represent each positive analog sample which is less than +5V. It is called Unipolar because it accepts only single polarity signals. A 4-bit digital word can represent one of only 16 different voltage levels. So Fig.4 contains (16-1) = 15 analog comparators, IC1 to IC15. A comparator gives a logic high output if the signal at its positive input exceeds the voltage at its negative input. And it gives a logic low output in the opposite condition. The full output from the Sample/ Hold circuit is applied to the positive inputs of all comparators in parallel. In addition, a stable +5V reference source sends a constant current down a series string of sixteen equal resistors, R1 to R16. Each comparator has its negative input connected to the corresponding tap on this string. Decision levels Each resistor develops a voltage drop of +5V/16 = 0.3125V. As Fig.4 shows, the negative input to IC1 is held constantly at +0.3125V; IC2 negative input is at +0.625V, etc..... up to IC15’s negative input, which is held at +4.6875V. These specific values are called the sixteen Decision Levels of this 4-bit circuit. Suppose at some moment that the analog sample (from the sampler in Fig.3) has an amplitude of +0.756V. In Fig.4 this voltage appears at the Because of their very fast sampling rate and inbuilt waveform storage, digital scopes are ideal for viewing irregular and infrequent pulse waveforms. This 150MHz model from Hewlett Pack­ard can view waveforms with risetimes as short as 1.4ns. 72  Silicon Chip positive inputs of all comparators. So in both IC1 and IC2 the positive input voltage exceeds their negative inputs. Therefore the outputs of IC1 and IC2 both go to a logic high level. But all higher comparators, IC3 to IC15, find their +0.756V positive input is less than their various negative inputs. Thus they all give logic low outputs. The outputs of all comparators in Fig.4 feed to 16 digital latches in the assembly IC2000. From thence 16 parallel lines feed to IC3000, the Digital Logic Unit. Here a complex tree structure of logic gates converts the data on the 16 input lines to digital code on four lines, as a 4-bit digital word, which is then written to the memory. We use MSB to mean the Most Significant Bit and LSB to mean the Least Significant Bit, of parallel digital data lines. Table 1 shows the sixteen possible digital words in a 4-bit system produced by the A/D converter illustrated in Fig.4, together with the decision level voltage corresponding to each step. Notice that the difference between the +5V reference and the highest acceptable input, +4.68750V, is equal to the contribution of the LSB, which is +0.3125V. Quantisation noise Imagine, just for a moment, that we constructed a digital storage oscilloscope using 4-bit digital words, generated by the ADC shown in Fig.4. As this circuit has only 15 comparators, it has only 16 voltage decision levels (including zero), as listed in Table 1. The circuit represents each analog value by a quantised number, which is equal to the voltage of the decision level immediately below. So in a 4-bit system, only 16 variations in the input analog voltage are recognisable. Fig.5 shows those sixteen levels. Also depicted in red is an analog input, actually 500 samples, so close together that they look like a continuous signal, which is varying between zero and about 3V. Immediately below this, is its quantised reconstruction which would be displayed on the screen of such a 4-bit oscillo­scope. That lower stepped waveform is the closest approximation our 4-bit system could make to the input signal. Just released from Tektronix, this TDS220 100MHz oscilloscope has two input channels. It has been designed to behave as much as possible like an analog 'scope, to the extent that the actual sampling rate being used at any time is not shown on the screen. The other big change is that it uses an LCD screen instead of a raster-scanned CRT. This makes it very compact – it is only 110mm deep. As you can see, the 4-bit waveform would be awful. Between points g, h, i, j, k & m, the analog signal varies through six different voltage values. But all of these fall between two adjacent decision levels, +1.5625V and +1.875V. Because any analog input can only be represented by the decision level vol­tage immediately below, all those points are called +1.5625V by the ADC. The voltage increment between decision levels is (1/16) 6.3% of screen height, which is obviously much too coarse! When displayed on the screen, you would never know the real value of the input between times g & m. All points in that area would be displayed on the screen as +1.5625V, because they all would result in the same digital word, 0101. This loss of vertical resolution in the display is an error called quantisation noise. This results in a stepped display on any digital scope, in stark contrast to the smooth contin­uous trace on an analog scope. To make these vertical steps or increments so small that the display looks like a smooth continu­ ous trace, we need much more than 16 decision levels. 8-bit flash ADC To achieve that aim most digital oscilloscopes use an 8-bit A/D con- TABLE 1 STEP V (Analog) Binary Word 0 0.0000 0000 1 0.3125 0001 2 0.6250 0010 3 0.9375 0011 4 1.2500 0100 5 1.5625 0101 6 1.8750 0110 7 2.1875 0111 8 2.5000 1000 9 2.8125 1001 10 3.1250 1010 11 3.4375 1011 12 3.7500 1100 13 4.0625 1101 14 4.3750 1110 15 4.6875 1111 Table 1: the 4 Bit Natural Binary Code; Reference = +5.00V. September 1996  73 Fig.6: the summing op amp IC2 translates all analog samples from their (-5V to +5V) range, up to new (0V to +10V) range, by inverting them and adding +5V. These are now accepted by the flash A/D converter and encoded to offset binary code. SAMPLE VOLTAGE DIGITAL WORD At A At C Output at F +5.0000 ZERO 0000000 +4.9609375 +0.0390625 0000001 +3.8671875 +1.1328125 00011101 +2.500 +2.50 01000000 ZERO +5.00 10000000 -1.6406250 +6.6406250 10101010 -2.500 +7.50 11000000 -4.9609375 +9.9609375 11111111 Table 2: Offset Binary Code verter for standard real time operation. The circuit is identical to that shown in Fig.4, except that it provides 256 voltage decision levels and contains 255 (256-1) linear com­parators. The series resistor string consists of 256 precision real-value resistors. Despite the resulting increase in cost, complexity and size of the converter, this larger 8-bit system is necessary to achieve adequate vertical resolution. The voltage increment between decision levels is 1/256 or 0.4% of the screen height, so the slight steppiness in the trace is much more acceptable. In this 8-bit version of Fig.4, IC2000 now contains 256 digital latches. These are joined by 256 parallel lines to IC3000, which contains about 3200 transistors in an enormous tree structure. This converts signals on 256 parallel lines to an 8-bit digital word on 8 parallel output lines, which feed to the RAM. 74  Silicon Chip Critical large scale integration (LSI) techniques are needed to manufacture such A/D converters and maintain accuracy. Bipolar A/D conversion Flash A/D converters are all called unipolar, because they respond only to positive signals. This means that they cannot directly accept bipolar analog samples, which range through negative and positive values. To fix that problem, we translate (ie, lift up) the samples of the analog signal into an all-posi­tive range. Fig.6 shows one form of voltage translator which we insert into Fig.1 between points A and C. It consists of an inverting summing op amp IC2, placed between the bipolar analog sample signal at A and the unipolar A/D converter at C. The op amp gain is equal to -1 from either input A or B to the point C. The -5V DC reference voltage at B, when inverted in IC2, adds +5V DC to all signals which are applied at the point A. Signals at A may be between -5V and +5V. As Fig.6 illustrates, that whole range is simultaneously inverted and lifted up by +5V. It is linearly translated to a new signal range, between 0V and +10V. For example, a +5V signal at A is inverted to -5V and has +5V added, to become 0V at C. Or a -5V signal at A is inverted to +5V and has +5V added, so is translated to +10V at C. Then, to cope with these higher signal voltages, the reference voltage in the 8-bit flash A/D converter is set at +10V. With this signal translation before A/D conversion, the system can encode bipolar analog samples. It produces 8-bit digital words in the Offset Binary Code. Table 2 shows a few of the 256 entries in this code. Using a +10V reference, the increment between decision levels is 10V/256 = 0.0390625V. Other codes exist which could also be used. Reconstructed display Fig.2(b) illustrates the reading of data from memory and its conversion and display on the screen, in a simple system. Each digital word of 8 bits is called one byte and occupies one memory address. Two separate pieces of information are associated with each word stored in memory. Firstly, the address of each word in memory corresponds to the horizontal coordinate (ie, sample number 1 ..... sample number 500) of that point on the waveform. And secondly the digital value of each word held in memory indicates the vertical coordinate of the corresponding point on the screen. This is the best approximation the digital system can make of the voltage of that sample of analog input. In the next chapter we will describe the intricacies of raster display, where a simple presentation consists of a set of 500 points on the screen, like those shown in Fig.2(b). Because the display consists of 500 points, the smallest horizontal increment is 0.2% of screen width. The width spread of the light spot merges the 500 discrete points into a continuous trace. SC 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. Please feel free to visit the advertiser’s website: 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. Please feel free to visit the advertiser’s website: 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 Feedback on the Programmable Ignition System By ANTHONY NIXON The programmable ignition system featured in the March 1996 issue has created quite a lot of interest from motoring enthusiasts. Now the designer has some follow-up information to enhance its operation. Since the original article was published in the March 1996 issue, a reluctor version of the circuit was published in the Circuit Notebook pages of the May 1996 issue. Apart from that, I have come across some problems which may affect the processor due to electrical noise finding its way back into the inputs. This causes the micro to operate in an erratic manner and upsets the engine operation. Fig.1 shows suggested modifications to give better electrical isola80  Silicon Chip tion between the ignition circuit and the Programmable Ignition board. “Method 1”, shown at the top of Fig.1. shows the use of 4N28 optocouplers for the three connections to the PIC microprocessor. “Method 2” employs zener diode clamping to prevent any serious voltage transients which may otherwise affect the micro. The software has been upgraded and now allows the user to program a two-stage advance curve instead of the original single stage curve. This is shown graphically in Fig.2 while the effect on an 8-cylinder car is shown in Fig.3. The new software allows the user to switch between the two data settings while the engine is running. Also the Rev Limit feature has been changed and it now misses every second spark instead of retarding the timing. The main concern with users was the fact that you could set the advance for one data set, say 20 degrees, but you could not program more advance into the Fig. 1: two methods of minimising noise in the microprocessor circuitry. Fig. 2: with new programming the system now allows the use of a twostage advance curve. Fig. 3: the timing diagrams for the two-stage advance curve on an 8-cylinder engine. September 1996  81 Fig. 4 (above): connecting the Knock Sensor (SILICON CHIP April 1996) may be done using an LM311 comparator. It connects to the Vacuum Advance input on the microprocessor. Fig. 5 (right): a rotor button with a “lagging” tail piece added. This can prevent misfiring problems caused by the rotor button being at the wrong position relative to the relevant spark lead post. second data set, say 30 degrees. This was due to the fact that the timing was retarded from the advance point as set by the distributor. At low revs, the software retards the timing by 45 degrees and will give advance to that set by the user as the RPM rises. In this way, more advance can be programmed for the other data set. This is needed to correctly set up timing for a change from petrol to gas, for example. This upgrade is available for the cost of return postage to anyone who has purchased either the micro direct from myself, or to those that have bought a kit from Jaycar which may have the original micro supplied. The upgrade also includes documentation. There have also been enquiries about using the Knock Sensor (published in the April 1996 issue of SILICON CHIP) in conjunction with the Programmable Ignition. Fig.4 shows how the knock sensor is connected to the Vacuum Advance input to the micro. The vacuum advance mechanism is left connected to the distributor as normal. The filtered output from the knock sensor is fed to an LM311 comparator. When this voltage goes higher than that preset on the inverting input pin 3, the output at pin 7 will go high. When the micro detects this high, it will retard the ignition by an amount set by the user. In effect it works in the opposite manner to which it was intended. As the output of the LM311 comparator is open collector, it provides com82  Silicon Chip patibility between the 8V circuitry of the Knock Sensor and the 5V supply of the Programmable Ignition board. Note: this circuit arrangement has not been tested on a vehicle). Modified rotor button Having address­­ed all of the problems that have been presented so far, one still remained, which I also had trouble with at times on my vehicle. The engine was misfiring especially while starting. I finally traced it to the shape of the brass contact on top of the rotor button. From my observations, the relative firing position of the rotor button to the spark lead posts in the rotor cap does not change even when the timing is retarded or advanced by the normal action of the advance springs. It does change though, when the vacuum advance mechanism is functioning. When the ignition is controlled by the micro, it has the same effect as changing the timing the way that the vacuum advance mechanism does, ie, it also alters the relative position of the rotor button to the spark lead post. As the micro is capable of delaying the spark by 22.5 degrees on the distributor shaft, the rotor may rotate past the correct spark lead post and send the spark on to the next one, thereby causing the engine to misfire. To counter this, I made up a new brass top for the rotor button with a “lagging” tail piece added and I also trimmed off the leading tip. This is shown in Fig.5. This diagram can only be used as a guide as each vehicle has a different distributor setup. I had to look at a few of the newer types of rotor button available and some of these also had a “lagging” edge. These are used with factory electronic ignition systems that still employ distributors. I have designed a new board which incorporates the method 2 protection mode mentioned previously. It also allows Jaycar keypads and LED displays to be used directly and has provision for the optical timing module. The board dimensions are still the same. SC ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) 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. TOTAL $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) 2 years (24 issues) 1 year (12 issues) Australia (incl. GST)  $A135  $A69.50 Australia with binder(s) (incl. 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Please have your credit card details ready OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail order form to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia September 1996  83 VINTAGE RADIO By JOHN HILL Vintage radio collectors and collecting Collecting vintage radio receivers can be a very rewarding hobby but to get the most satisfaction and value it is a good idea to have every receiver in your collection in working order. That way, if you want to sell it, it will bring a good price. Way back in 1987 I tried to sell the idea of having vintage radio stories in a modern electronics magazine but with only limited success. I reckoned that the subject of valve radio restoration could have been covered reasonably well with a series of about 10 articles but the powers that be allowed me only two. However, those two stories produced a surprising reader response and suddenly, valve radios and their restoration took on a new meaning. The stories sparked off quite a lot of interest, for no other reason than that they The photographs this month are mainly of the more unusual items that some collectors prize. Shown are 3L0 window posters advertising the week’s program highlights. The posters were displayed in radio shop windows during the early days of broadcasting. (1933?) 84  Silicon Chip appeared at the right time. Radio collecting was just starting to kick off in the mid 1980s and the collecting and restoring of old receivers has grown in the past decade to a stage where many businesses have been successfully established to cater for the needs of an ever increasing number of collectors. Now, both here and abroad, vintage radio columns are a regular item in some electronics magazines and are read by many thousands of radio collectors and other interested readers. I have had a number of people write to me just to say that they enjoy my column, even though they are not collectors themselves. So it would appear that the continuing interest in valve technology extends well beyond those who are directly involved in maintaining it. However, many Vintage Radio readers are interested to some degree in collecting old radios and collectors are the subject of this month’s column. I have met many collectors over the past few years and they are a strange lot if you stand back and take a close look - with some being stranger than others! Thank goodness I have been able to retain my sanity and not let my collecting enthusiasm take control. Who am I kidding?! Radio collectors fit into many categories. Some are totally obsessed by their hobby, as though some kind of narcotic drug has taken over, while others can either take it or leave it as the mood finds them. I guess I fit somewhere in between. I first became interested in radio when I was a kid in short pants. Although I was very interested at the time, lack of money curbed my enthusiasm and I never progressed past the crystal set and simple regenerative receiver stage. My latent radio interests were reawakened with the advent of the “Technicraft” series of kit radios that appeared in the mid 1980s. These sets were the “Unidyne”, “Reinartz Two”, “Super Crystal Set” etc. Putting together a few vintage style kits really grabbed my attention at a stage when I was looking for a new hobby. So vintage radio came along at the right time. From the Technicraft kits I graduated to the real thing when I was given a 1939 5-valve console model Radiola. After restoring that receiver I was hooked and just had to find another and go through the whole process again. Before I realised it, I had become a collector of old radio receivers. Collecting valve radios is one thing, getting them working again is another matter. While some collectors do not care if their radios work or not, most like to restore them or have them restored, to work­ ing order, which can be a difficult task at times. Regarding the previously mentioned Radiola, about all that was required to fix it was the replacement of a faulty capacitor and the refurbishing of the timber cabinet. The set was in really good condition and needed very little doing to it. Even the dial lights lit up. Alas I was soon to find out that other receivers had entirely different problems and more of them. Some of these faults were incredibly hard to locate, believe me. It took several years before I came to grips with most of the common valve This old transmitter once powered 3SH Swan Hill. Once again, it is an item that takes up a lot of space. Collectors of large equipment such as this 5kW AWA transmitter are faced with storage problems normal collectors never experience. To give some idea of size, the windows in the doors are about eye height. This transmitter was once used by 3TR Sale and was donated to the Maryborough Creative Arts and Science museum by the Bendigo TAFE College. Transporting it was no easy job. radio faults. Then, as now, I considered the fun part of collecting old radios to be the repair aspect. There is nothing quite like the satisfaction one experiences when some old wreck of a receiver bursts into life after being dead for many decades. Once a restoration has been completed and the receiver goes on the shelf, it means very little to me from that point on, apart from the memory of getting it going. I guess that is where I may differ from most other collectors. Everyone sees vintage radio differently. Naturally the repairing of a receiver is not everything. I enjoy the scrounging, bartering, trading, etc and I also like to listen to some of my receivers from time to time. But the really rewarding part of it all is getting them September 1996  85 An attractive display of EverReady batteries from the Dick Howarth collection. working again and that is why I like to collect valve receivers. In my opinion, a lot of collectors are not really collectors; they are hoarders. This type of person often goes to a great deal of trouble and expense to obtain something but does nothing constructive with it once he brings it home. I have been to see a number of collections only to find that you stand in an obstructed doorway and have various items pointed out at the far end of the room. Whether a rare piece or common, they all share the same fate and gradually deteriorate because of inadequate care and improper storage. Mice, cockroaches, dust and dampness all take their toll over the years and a good collectable item eventually becomes a wreck. I visited a place in Melbourne some time ago where every room in the house was stacked to the ceiling with “collectables” of many types. There were narrow, maze-like passages through the rubble and although the windows were unlocked no intruder would ever be able to get in. This guy had even filled his bedroom and bathroom with junk to such an extent he was forced to sleep on the floor in the passage with his dog and took a shovel out the back when he wanted to go to the toilet. Believe me - it’s true! And where did all this hoarding get him? He died an unhappy and friendless man. As he could not take his treasures with him, his sister sold me a car full of unrestored radios for about $200. The radios were like the cameras, TV sets, clocks, watches, car parts and dusty books. They were all in poor condition through sheer neglect. A true collector will try to restore and preserve the things he collects while the hoarder’s collection slowly deteriorates because he can’t be bothered to even throw a dust cover over something old in order to protect it. Unfortunately, there are a few Also from the Dick Howarth collection is this display of miscellaneous bits and pieces from yesteryear. Some of the more interesting items at the back are a Willard wet rectifier, an Edison battery and a Leclanche cell. 86  Silicon Chip hoarders in the vintage radio movement. Having the best part of my collection restored and on public display pleases me greatly. There is little satisfaction to be gained from cluttering up one’s home with collectable items, regardless of what they might be. When collecting takes over your life, it’s time to seek help! The following description would cover most radio collectors. They pick up a few sets at affordable prices, keep the good ones and turn the others over for a small profit which helps finance their hobby. There is nothing wrong with such an attitude, for buying, selling and trading is a good way to operate. It also involves other collectors and gives them the opportunity to buy or trade what others may not want. At least this approach keeps things in circulation and most of those involved get something out of it. A collector I met just recently has built up his entire collection from his local tip. Over a period of years he has been able to gather together quite a few reasonable receivers (mainly 40s and 50s mantel types) plus a considerable collection of valves and other very usable radio components which have been stripped from chassis that were also deposited at the tip face. Someone’s rubbish is another’s treasure! On the other hand there are other collectors who only want the very best and nothing else will do. No 50s plastics, no 40s Bakelites, no battery sets or portables, only those gems of receivers from the late 20s, early 30s era. This type of collector thinks nothing of spending $1,000 or more on a particular receiver. Needless to say such a collection requires a lot of money to put together. Whether that cost will be returned when the time comes to sell remains to be seen, because there are very few up-market buyers. There is a radio collector of my acquaintance who some may not regard as a collector at all simply because he has only a few commercially made receivers. This guy prefers to build his own: they can be simple battery regenerative sets, perhaps a 4 or 5-valve superhet or maybe a mono or stereo amplifier with a push-pull output. He likes to build a variety of valve equipment. The author is pleased that the majority of his collection is restored and on public display. This is part of that collection. When building one of his creations, the first step is to draw up a circuit, which usually combines the good features of many circuits. Once the circuit is finalised, the next step is a plan of what parts go where. This usually takes the form of a full scale detailed component wiring diagram. He then knocks up a chassis of suitable size and builds his own special creation. What’s more, they look good and work really well too. In my opinion it is this type of collector/experimenter that gets the most out of vintage radio. They obtain really good value for their money and that that’s how a hobby should be. Other collectors prefer to tinker with more unusual items such as military equipment and communications receivers, while some collect transmitters and even radar installations. To find the necessary storage space is, no doubt, a problem of some magnitude for any collector with a passion for the big stuff. Although a keen collector myself, I try to maintain a balance in my collection and do not concentrate on any particular make, model or era. I collect only those radios that appeal to me and come my way at what I consider to be reasonable prices. I have receivers from the 1920s, 30s, This professional video equipment became redundant and unwanted with the advent of aggregation. Again, difficult equipment to store because of its size. September 1996  87 Most collectors will settle for more realistic items such as this STC mantel radio with its timber cabinet. Somehow it is a little more appealing than several tonnes of transmitter. SATELLITE TV EQUIPMENT     Receivers  Feeds Positioners  LNBs  Actuators Dishes And much much more! C-Band Systems from $1495 Ask us for a catalog! B&M ELECTRONICS 469 Light Street, Daniella WA 6062 Phone/Fax: (09) 275 7750 Mobile: 041 99 0 55 00 RESURRECTION RADIO VALVE EQUIPMENT SPECIALISTS VINTAGE RADIO ✰ Circuits ✰ Valves ✰ All Parts ✰ Books Fully restored radios for sale ALL TYPES AND BRANDS OF AUDIO VALVES IN STOCK 40s and 50s. There are consoles, table models, mantel models, portables and even some early transistor radios. There are a few novelty items too, such as home-made receivers and crystal sets, plus a few interesting old valves, although nothing in the way of a comprehensive valve collection. Perhaps one of the driving forces behind my radio collecting is this Vintage Radio column. Originally I saw it as a series of about ten articles, so unless I pursue my hobby fairly intensely, I will find it difficult to maintain a variety of subject matter to write about. Believe me, it is not easy coming up with a suitable story plus photographs each month. It takes a considerable amount of time and effort! The writing aspect of my vintage radio activities is actually a secondary hobby in itself, which also includes another of my interests; photography. So radio collecting for me is a threefold affair - radio, writing and photography, all rolled into one big hobby. How people can spend their time watching TV every evening is beyond my understanding, especially when there are so many more interesting things to be done. Doing something yourself is much better than watching others doing things on the magic screen. So if your radio collecting is in the doldrums and focused on a narrow spectrum, then it may be time to diversify a little, broaden your horizons and try something different. The various aspects of vintage radio are many. SC Send SSAE for Catalogue Visit Our Showroom At: 242 Chapel Street (PO Box 2029), PRAHRAN, VIC 3181. Tel (03) 9510 4486   Fax (03) 9529 5639 88  Silicon Chip Many collectors favour receivers from the 1930s era. This one was made by Eclipse Radio back in the days when big was beautiful. It is a 7-valve superhet. 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.oatleyelectronics.com/ PRODUCT SHOWCASE Tektronix digital scope has LCD screen In a move that will galvanise the opposition, Tektronix has released two new digital oscilloscopes which are priced at about half the cost of comparable scopes. Both are very light and compact and use an LCD screen. If you have recently purchased a medium priced digital scope, the chances are that you will initially be annoyed when you see the prices for these new Tektronix models. Called the TDS 200 series, the new line-up is the 100MHz TDS 220 and the 60MHz TDS 210. Both have a maximum sampling rate of one gigasamples per second (1GS/s), two input channels, wide range dual timebase and host of other features previously only seen on scopes costing more than five thousand dollars. Apart from the low price and wide bandwidth, the overwhelm­ ing feature of these new scopes is that they really don’t look or drive like digital scopes at all; they have an “analog” feel about them. The controls are laid out in a similar way to those on an analog scope and the screen display does not indicate the sampling rate in use, in contrast to the display on most digital scopes. 90  Silicon Chip The biggest giveaway that the TDS 200 series are, in fact, digital scopes, is the high contrast backlit liquid crystal display instead of the usual CRT. It measures 115 x 86mm, about the same as for a conventional analog scope. The fact that no CRT is used means that Tektronix have been able to house the new scopes in a very shallow case. At first sight, the frontal dimen­sions are about normal but the depth is minimal. Overall dimen­sions are 305mm wide, 151mm high and only 110mm deep. Weight is a mere 2.9kg. Unlike a typical analog scope though, the TDS 200 series have Auto Setup – just press the button and the scope sets the vertical gain, timebase, triggering and coupling conditions to give a stable display on the screen. As well, they have automatic measurements for period, frequency, RMS, mean and peak-to-peak waveform values. Waveforms can be stored as well and also down-loaded to a printer or computer via the optional Centronics parallel port or the combined GPIB/ RS232 and parallel port interfaces. And while most digital scopes have multi-layer menus to help you use all their features, they are not a big help if you don’t have English as your first language. As well as English, the TDS 200 series has on-screen menus in German, Spanish, French, Chinese (simpli­fied and traditional), Japanese, Korean and Portuguese. Available from 1st September, the TDS 210 60MHz model is priced at $1395 plus sales tax while the TDS 220 100MHz scope is $1995 plus sales tax. We plan to review the TDS 220 in the coming months. For further information, contact Tektronix Australia Pty Ltd, 80 Waterloo Road, North Ryde, NSW 2113. Phone (02) 888 7066. Release 7.0 of OrCAD Capture for Windows OrCAD has introduced Release 7.0 of OrCAD Capture for Wind­ows. This third major release of Capture, which runs under Wind­ows 3.x, Windows 95 and Windows NT, includes new functions and enhanced performance. OrCAD Capture takes full advantage of all versions of the 32-bit Windows operating system and a Visual Basic for applica­ tions (VBA)-compatible macro language is included. Using the macro language, users can customise Capture’s schematic editor and reduce multi-step tasks to a single command. Capture now supports DXF output, including export of files to AutoCAD and compatible programs. Wiring processes are streamlined with the new “smart drag”, “sketcha-wire” and manual junctioning features. “Smart drag” stretches the wires orthogonally when wires, components or blocks of components are moved, eliminating manual wire editing. With “sketch-a-wire” the user moves the Kenwood AC-3 Surround Sound Receiver AUDIO MODULES broadcast quality Kenwood Electronics Australia Pty Ltd has announced their Dolby AC-3 surround sound receiver, the model KR-V990D. Dolby AC-3 refers to the compression technology that is used in Dolby SR-D and Dolby surround digital films. AC-3 delivers six separate channels: left, centre and right front channels, left and right surround channels and the subwoof­ er channel. In addition to offering AC-3, the KR-V990D features Dolby Pro-Logic, Dolby 3 stereo, and DSP Logic. The amplifier has 100W front left, centre and right channels, 70 watts for the two surround channels and a subwoofer output. In addition, there are line outputs for all six channels for connection to auxiliary equipment. Kenwood’s GUI (Graphical User Interface) allows on-screen indications that the user can select and activate via the remote control. The remote control unit lets the user move a tiny “hand” around the screen, in much the same way as the mouse does on a computer, enabling any function to be selected. The KR-V990D has a recommended retail price $2299, a 24-month warranty and is available at selected Kenwood dealers. In these days when all instruments seem to be digital, it is refreshing to come across one with an analog scale, as in the case of this new insulation tester made by Hung Chang, the model BassBox ® Design low frequency loudspeaker enclos­ures fast and accurately with BassBox® software. Uses both Thiele-Small and Electro-Mechanical parameters with equal ease. Includes X. Over 2.03 passive cross­over design program. mouse to instantly bring up a ghosted image of the wire. OrCAD Capture now includes schematic macros and primitives for devices from all the major silicon vendors including Actel, Altera, AMD (through MINC), Lattice and Xilinx. Designs can now be directly exported from Capture into Xilinx’s place-and-route tools without the use of an additional interface. The new Auto­block feature generates a hierarchical symbol from a schematic and “autoport” takes that hierarchical symbol and automatically generates the ports on the underlying sheet. For more information, call EDA Solutions, (02) 9413 4611, fax (02) 9413 4622 or email to richard<at>eda.com.au. Insulation tester has analog meter Manufactured in Australia Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 476-5854 Fx (02) 476-3231 $299.00 Plus $6.00 postage. Pay by cheque, Bankcard, Mastercard, Visacard. EARTHQUAKE AUDIO PH: (02) 9948 3771 FAX: (02) 9948 8040 PO BOX 226 BALGOWLAH NSW 2093 The HC-2500I measures insulation resistance up to 200 me­gohms and has an internal test voltage of 500V DC. As well, it will measure AC voltages up to 450V. It is powered by a single 1.5V AA cell. The HC-2500I is available from Altronics in Perth or their resellers at $95 (Cat Q-1240). HC-2500I. The analog meter is useful when a device breaks down intermittently, which would probably not be revealed on a tester with a digital readout. Computer power supplies For most computers, when the power supply fails it is more economical to replace than repair it but suppliers will only sell a power supply together September 1996  91 with the case; the original case must be junked as well as the supply. To remedy this, Computronics is now stocking a range of computer power supplies. These can replace a faulty unit or upgrade a lower powered unit. Currently stocked are 200W and 250W models in two case sizes, supplied with mounting screws and flying leads to allow quick reconnection. All models are UL-approved. For further information, contact Computronics International Pty Ltd, 31 Kensington Street, East Perth, WA 6004. Phone (09) 221 2121; fax (09) 325 6686. UHF wireless microphone system The Beyer U600 series wireless microphone system has fre­ quency synthesised operation with the capability for up to 64 channels within one TV channel and up to 15 channels simultane­ously. Since the transmitter has an ident code, called the Chan­nel Grip facility, the receiver is locked and excludes all other signals. The TS600 UHF beltpack trans- mitter can be switched through 16 frequencies and operates from 794822MHz and 854-862MHz. Oper­ating from a 9V battery, it is claimed to provide full transmis­sion power for up to 12 hours. A warning LED illuminates when one hour of battery life remains and the battery condition is trans­ mitted to the matching NE600 receiver. A comprehensive range of head and lavalier microphones can be connected, via a 4-pin Lemo plug. The TS600 measures 80 x 54 x 20mm and weighs 157 grams. The matching NE600 receiver is a dual diversity system. Its operating frequency can be selected from the front panel or via an ex­tern­al computer which can monitor t r a n s­m i t t e r and receiv­e r parameters as well as battery life. For further information, contact Amber Technology, Unit B, 5 Skyline Place, Frenchs Forest, NSW 2086. Phone (02) 9975 1211; fax (02) 9975 1368. KITS-R-US PO Box 314 Blackwood SA 5051 Ph 018 806794 TRANSMITTER KITS •• FMTX1 $49: a simple to build 2.5 watt free running CD level input, FM band runs from 12-24VDC. FMTX2B $49: the best transmitter on the market, FM-Band XTAL locked on 100MHz. CD level input 3 stage design, very stable up to 30mW RF output. •• FMTX2A $49: a universal digital stereo encoder for use on either of our transmitters. XTAL locked. FMTX5 $99: both FMTX2A & FMTX2B on one PCB. •connector FMTX10 $599: a complete FMTX5 built and tested, enclosed in a quality case with plugpack, DIN input for audio and a 1/2mtr internal antenna, also available in 1U rack mount with balanced cannon input sockets, dual VU meter and BNC RF $1299. Ideal for cable FM or broadcast transmission over distances of up to 300 mtrs, i.e. drive-in theatres, sports arenas, football grounds up to 50mW RF out. FMTX10B $2599: same as rack mount version but also includes dual SCA coder with 67 & 92kHz subcarriers. • AUDIO •soldDIGI-125 Audio Power Amp: this has been the most popular kit of all time with some 24,000 PCBs being since 1987. Easy to build, small in size, high power, clever design, uses KISS principle. Manufacturing rights available with full technical support and PCB CAD artwork available to companies for a small royalty. 200 Watt Kit $29, PCB only $4.95. AEM 35 Watt Single Chip Audio Power Amp $19.95: this is an ideal amp for the beginner to construct; uses an LM1875 chip and a few parts on a 1 inch square PCB. Low Distortion Balanced Line Audio Oscillator Kit $69: designed to pump out line up tone around studio complexes at 400Hz or any other audio frequency you wish to us. Maximum output +21dBm. MONO Audio DA Amp Kit, 15 splits: $69. Universal BALUN Balanced Line Converter Kit $69: converts what you have to what you want, unbalanced to balanced or vice versa. Adjustable gain. Stereo. • • •• COMPUTERS •to Max I/O Card for PCs Kit $169: originally published in Silicon Chip, this is a real low cost way to interface the outside world from your PC, 7 relays, 8 TTL inputs, ADC & DAC, stepper motor drive/open collector 1 amp outputs. Sample software in basic supplied on disk. •onlyIBM3 chips PC 8255 24 Line I/O Card Kit $69, PCB $39: described in ETI, this board is easy to construct with and a double sided plated through hole PCB. Any of the 24 lines can be used as an input or output. Good value. •• Professional 19" Rack Mount PC Case: $999. All-In-One 486SLC-33 CPU Board $799: includes dual serial, games, printer floppy & IDE hard disk drive interface, up to 4Mb RAM 1/2 size card. •PC104 PC104 486SLC CPU Board with 2Mb RAM included: 2 serial, printer, floppy & IDE hard disk $999; VGA card $399. KIT WARRANTY – CHECK THIS OUT!!! If your kit does not work, provided good workmanship has been applied in assembly and all original parts have been correctly assembled, we will repair your kit FREE if returned within 14 days of purchase. Your only cost is postage both ways. Now, that’s a WARRANTY! KITS-R-US sell the entire range of designs by Graham Dicker. The designer has not extended his agreement with the previous distributor, PC Computers, in Adelaide. All products can be purchased with Visa/Bankcard by phone and shipped overnight via Australia EXPRESS POST for $6.80 per order. You can speak to the designer Mon-Fri direct from 6-7pm or place orders 24 hours a day on: PH 018 80 6794; FAX 08 270 3175. 92  Silicon Chip Flexible ferrite film Siemens Ltd has released a flexible film which is a com­posite of plastic and ferrite. Called FPC (flexible polymer composite), the new material could be used to produce cores that would be impractical with conventional ferrite powders. Alterna­tively, the ferrite film could be used for shielding applications to reduce EMC effects in equipment. As well, FPC could be used for flexible coils, flat coils or coil-onchip devices. FPC can be punched and can be made up as a self-adhesive film. The standard film is 80mm wide, 0.2mm thick and is supplied by the metre. For further information, contact Advanced Information Pro­ducts, Siemens Ltd. Phone (03) 9420 7716; fax (03) 9420 7275. 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. 6V operation for UHF remote control In the December 1992 issue you described a UHF remote transmitter that used a SAW resonator circuit. The unit uses a 12V DC battery. However, I would like to use a 6V battery to power the unit in another application. Would you or one of the team please advise on what changes are needed to get the unit to work on the 6V supply. (S. W., Perth, WA). • The UHF transmitter should work on 6V but the range can be expected to be greatly reduced. We suggest that you eliminate the series LED and change the 6.8kΩ resistor to 3.3kΩ. Burp charger for nicads wanted In the January 1996 issue of SILICON CHIP, an article de­ scribed a commercial nicad charger which was designed to “burp-charge” nicads. As I understand the article, the nicads were pulse-charged for a period, discharged at a high current for a brief period, then the voltage measured. The charger then detect­ed the delta-V to end the fast charge. Would it be possible to modify the Ignition system has reluctor I have built three High Energy Ignition kits published by SILICON CHIP in 1988, for me and two for friends. The last one was working for six months on a Holden but on trying it with a Ford V8, with a Mallory distributor, the unit would not work. I checked all components: resistors, diodes, capacitors and transistors, except the MC­ 3334P and MJ10012, which I was not able to test. I purchased a new MJ10012 but the test on an analog meter showed the same value. How can Fast Nicad Charger fea­ tured in the May 1994 issue of SILICON CHIP to do the same thing? Perhaps this could be achieved by removing L1 and adding extra circuitry to detect when each positive charge pulse has ended, and then give a brief high current discharge. I understand that the maximum charge cycle of IC1 (TEA1100) is 70% so there should be sufficient time period for a discharge pulse. I guess the only limiting factor is when the delta-V is measured, as there would have to be sufficient time between the discharge pulse and delta-V measurement. (M. B., Kew, Vic.) • It should be possible to modify the TEA1000 circuit to do “burp charging” but we are reluctant to do any work in this direction as this process has patent protection, as we understand it. Surge current in vacuum cleaner My house has a 12V DC system for lighting and TV. When using smaller power tools I use a 600 watt inverter. Whilst in theory I should be able to run a vacuum cleaner of 1000W for a short period of about 10 minutes, in I test MC3334P? Would you please give me a clue to be able to have it working. (R. J., Springwood, Qld). • It appears likely that the Mallory distributor you are using does not have points but has a toothed reluctor wheel and inter­nal coil to generate timing pulses. The circuit described in the May 1988 issue is not suitable for reluctor distributors. In­stead, you should be using the version described in the May 1990 issue. The best way to test the MC3334P and MJ10012 is to install them in the original circuit and test it in a car with a points distributor. practice it will not start because the starting current is too high. Is there some simple way of getting a 1000W tool started and being able to use it for a limited period before the thermal overload of the inverter shuts it off? The September 1992 issue of SILICON CHIP has a motor speed controller. Would this device be the answer? (R. O., Wittenoom, WA). • As you have found, the initial surge current of the motor is far too high to allow a 600W inverter to handle it. Nor is there any practical way of getting the motor up to speed that we can think of. You cannot use a normal speed control because this places all the load current on positive half cycles of the wave­form and this would be an even more difficult load for an invert­er to drive. While it sounds corny, in your position we would be in­clined to use a push-type carpet sweeper. Isolation transformer is dangerous I am building an isolation transformer from two primary coils salvaged from a couple of discarded microwave ovens. The problem is that there is a loud humming noise. The transformer has a laminated iron core in the shapes of E and I. The two coils are separated by spacers. Before dismantling the step-up transformers, I had a quick test and they were noiseless. What do I have to do to reduce this humming noise please. (B. M., Darwin, NT). • We strongly suggest you take the whole mess and put it in the garbage bin before you kill yourself! Microwave oven trans­formers are extremely dangerous at the best of times. We have published at least one story in the past about the death of a serviceman, who presumably knew what he was doing when servicing a microwave oven. To be more specific, we don’t know what you’ve done wrong to cause the transformer to make a loud humming September 1996  93 Pulse power in train controllers A few months ago, I purchased “14 Model Railway Projects” which is a most interesting publication. The kit my son is assem­bling is from the final article, the “Diesel Sound Simulator”. We have controllers of both the “pulse” and “fully rectified wave­form” types. What are the effects of running an engine with the “pulse” circuit or a “rectified wave form” type? I have found the waveform type produces better results than the pulse type. The pulse type is a Hornby R921 putting out 12V DC at 4VA and the waveform type is a Bachmann 6607A putting out 17DC at 0.6 amps (7VA, although I don’t know how that maths works. 17 x 0.6 = 10.2). Is amperage the key? It seems from your articles that 3A is a good value. This figure contrasts signifi­ cantly with the 0.6A maximum used by a local model railway at­ traction (Mike Scott’s Trainworld). noise. It could be any one of a number of faults such as loose laminations, shorted turns, anti-phase primary connections or who knows what. Please, please, give it all up as a bad job before you kill yourself or someone else. By the way, your letter had no address on it but was post­marked “Darwin Mail Centre”. Normally we do not feature letters in SILICON CHIP where no address is supplied but in your case we have made an exception. We hope you get a chance to read this! Millivoltmeter drive modification I am interested in constructing your AC Millivoltmeter as described in the August & September 1988 issues. I have a SIFAM meter movement from an old hybrid AC millivoltmeter which has its scale calibrated precisely as in your design. Because this is a very high quality movement I would like to incorporate it into your 1988 design. The question is, can the circuit be 94  Silicon Chip He seems to be able to happi­ ly double-head a very long train (two Lima class 31s). (J. H., Auckland, NZ). • We are not sure about the question you are asking. As de­scribed in the article, the Diesel Sound Simulator circuit can be made to work with both pulse or rectified (waveform) controllers. However, once set up to work with a particular controller, it will not necessarily work well with other controllers. As far as pulse and waveform controllers are concerned, most so-called “pulse” controllers do not use the same system of pulse width modulation at about 200Hz as used in the SILICON CHIP controller design. As such, they do not perform as well as our design and generally not as well or as reliably as simpler recti­fied waveform designs. Most locos with can motors draw currents of less than 1A but others require a lot more and if smoke and lighting circuits are added, plus double-heading, then a much higher current is re­quired. of IC7b. The accompanying circuit shows the general scheme and you will prob­ably need to increase the 6.2kΩ resistor at pin 3 of IC7b to provide the appropriate zero offset to the meter. We must emphasise that we have not tried either of these ideas but one or the other should be workable. A 300V range can be included by using a 12-position switch and by splitting the 1.1Ω resistor at the bottom of the existing input voltage divider. The two new resistors would be 0.75Ω and 0.35Ω. More on battery capacity meters I have a suggestion in reply to the request in “Ask SILICON CHIP” July 1996 for a battery capacity meter. I too am a regular RC model aircraft flier and have been using the following method to determine nicad battery capacity for several years with suc­ cess. If your nicad battery discharger has a LED to indicate that discharge is taking place, it is a simple matter to connect a single-cell crystal clock in parallel with the LED. If you set the hands on 12.00, the clock will begin ticking when the dis­charge button is pressed and stop ticking when the LED goes out. It is then just a simple calculation to work out the battery capacity. For example, if the discharge rate is 200mA and the clock reads 2.00 (two hours), then the capacity = 2 x 200 = 400mA.h. (R. H., Kingston, Tas). Notes & Errata modified to accommodate a 5mA meter instead of the 100µA movement specified and if so how? I had thought that a simple transistor current amplifier would do the trick, perhaps even a PNP/NPN push-pull pair but I have not been able to find any data on such an idea. I would also like to include a 300V range. (J. L., Yate, UK). • As far as we can tell, the circuit should be able to drive a 6mA meter movement without problems although the calibration trimpot VR4 will need to be reduced to 200Ω or 250Ω. If you find that the LM833 cannot do the job, you will need an emitter follower to boost the output current Stereo Simulator, June 1996: pin 7 of the M65830P (IC2) is shown connected to both +5V and GND on the circuit diagram on page 16; it should only be connected to +5V. The PC board overlay diagram on page 19 is correct. 16V 15A Power Supply, Circuit Notebook, July 1996: there are number of mistakes and omissions in the circuit on page 17. First, the 56kΩ resistor from the collector of Q4 should go to the +25V line instead of to the base of Q1. Second, D4 should be a LED. The designer has also suggested that the 100µF capacitor across the output terminals be increased to 220µF and a 1kΩ resistor be connected across the 10kΩ potentiometer VR3 (Voltage SC Max). MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. FOR SALE SATELLITE DISHES: international reception of Intelsat, Panamsat, Gori­ zont,Rimsat. Warehouse Sale – 4.6m dish & pole $1499; LNB $50; Feed $75. All accessories available. Videosat, 2/28 Salisbury Rd, Hornsby. Phone (02) 482 3100 8.30-5.00 M-F. MicroZed has range of PIC chips OTP and /JW versions available. PIC 16C84/04 one off price $9.76 inc S/T. C COMPILERS: Dunfield compilers are now even better value. Everything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC16, 8051/2, 8080/85, 8086 or 8096: $140.00 each. Macro Cross Assemblers for these CPUs + 6800/01/03/05 and 6502: $140 for the set. Debug monitors: $70 for 6 CPUs. All compilers, XASMs and monitors: $400. 8051/52 or 80C320 simulator (fast): $70. NEW: Disassemblers for 12 CPUs only $75. Demo disk: FREE. All prices + $5 p&p. GRANTRONICS PTY LTD, PO Box 275, Wentworthville 2145. Ph/Fax (02) 631 1236 or Internet: lgrant<at>mpx.com.au. EDUCATIONAL ELECTRONIC KITS: Best prices. Easy to build. Full details. Latest technology. LESSON PLANS FOR TEACHERS – see our web page. Send $2 stamp for catalog and price list to: DIY Electronics, 22 McGregor St, Num­ urkah, Vic. 3636. Ph/fax (058) 62 1915. Or Email laurie.c<at>cnl.com.au and let us send details. Go WWW:http://www.cnl. com.au/~laurie.c or BBS (058) 62 3303. Download details free any­time. MicroZed Minilog kit $25 incl S/t, pgms on disk, all parts, except BS2. See SC July 1996. EASY PIC’n Beginners Book to using MicroChip PIC chips $50, Basic Compiler to clone Basic Stamps into cheap PIC16C84’s $135, CCS C Compiler CLASSIFIED ADVERTISING RATES 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 on a separate sheet of paper, fill out the form below & 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) 9979 6503. ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. ✂ Enclosed is my cheque/money order for $­__________ or please debit my $145, heaps of other PIC stuff, Programmers from $20, Real Time Clock, A-D. Ring or fax for FREE promo disk. WEB search on Dontronics, PO Box 595, Tullamarine 3043. Phone 03 9338 6286. Fax 03 9338 2935. MICROCRAFT PRESENTS: Dunfield (DDS) products are now available exstock at a new low price; please ask for our catalogue. Micro C, the affordable “C” compiler for embedded applications. Versions for 8051/52, 8086, 8096, 68HC08, 6809, 68HC11 or 68HC16 $139.95 each + $3 p&h • Now on special is the SDK, a package of ALL the DDS “C” compilers for $399 + $6 p&h • EMILY52 is a PC based 8051/52 high speed simulator $69.95 + $3 p&h • DDS demo disks $7 + $3 p&h • VHS VIDEO from the USA (PAL) “CNC X-Y-Z using car alter­nators” (uses car alternators as cheap power stepper motors!) $49.95 + $6 p&h (includes diagrams) • Device programming EPROMs/PALs etc from $1.50 • Fixed price electronic design and PCB layout • Credit cards accepted • All goods sent certified mail • Call Bob for more de­tails. MICROCRAFT, PO Box 514, Concord NSW 2137. Phone (02) 744 5440 or fax (02) 744 9280. PRIVATE TUTORIALS in Electrical/ Electronic Trades and Industrial Electronics Advance Certificate. Computer Programming in ‘C’ and Pascal and ASM. Phone (02) 610 2137 after 5pm. Ask for Stelios. RCS RADIO PTY LTD Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 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 September 1996  95 5V Reg. CPU with 8 or 16 I/O 20mA (conditional) EPROM stores your program and data Stamp I or Stamp II Your next project will be easy, fast and satisfying with a development kit from Program in BASIC with your PC Your application, Switches, LEDs, LCD, Motors, Thermistor, Position Sensor, Humidity, Temp, Motor, other computers, etc MicroZed Computers Av-Comm.......................................9 PO Box 634, ARMIDALE 2350 (296 Cook’s Rd) Ph (067) 722 777 – may time out to Mobile 014 036 775 Fax (067) 728 987    (Credit Cards OK) B & M Electronics........................88 Specialising in easy-to-get-going hard/software kits. Other gear available. Other CPU systems, support modules etc Send 2 x 45c stamps for information package STOP PRESS Stamp kits now have a compiler for 16C58 MEMORY * DRIVES * MODEMS SPECIAL! (Ex Tax) 1Mbx9 – 70ns $24 30-pin Simms INFRA-RED SALE: IR Responsive CCD Camera Module $149; IR LEDs 50mW 940nm 10 for $6; IR Detector Module with amplifier, filter, demodulator, etc. $9.40; IR Photorelay Sensor $84; PIR Sensor Module $19; IR Illuminator Kit uses 36 LEDs $25. Free postage. M. Pearen, 135 Smiths Road, Caboolture, Qld 4510. MicroZed has Micro Engineering Labs PBASIC Compiler for $120 + $5.00 post. Put Stamp programs into raw PIC chips. RAIN BRAIN 8-STATION SPRINKLER KIT: Z8 smart temp sensor, LED display, RS232 to PC. Uses 1 to 8 DALLAS DS1820. Call Mantis Micro Products, 38 Garnet Street, Niddrie, 3042. P/F/A (03) 9337 1917. mantismp<at>c031.aone.net.au MicroZed has MICROCHIP NEW PICSTART kits also Programmers from Parallax and Micro. Eng. Lab. 68HC705 Development System: Oztechnics, PO Box 38, Illawong NSW 2234. Phone (02) 9541 0310. Fax (02) 9541 0734. http://www.oz­technics.com.au/ MicroZed has the gear to make development easy and fast. KITS KITS KITS: control up to 4 relays via telephone line $91.15, PIC16C84 programmer $49.70, PC printer port relay board (incl. software) $68.50, Codepad/Simple burglar alarm $78.65, Z80 Single Board Computer $152.40. Many 96  Silicon Chip Advertising Index SIMMS (Parity/No Parity) 4Mb 30 PIN-70 $54 $83 4Mb 72 PIN-70 $60 $46 8Mb 72 PIN-70 $108 $84 16Mb 72 PIN-70 $198 $172 32Mb 72 PIN-70 $388 $352 EDO SIMMS 8Mb (1Mbx32) – 60ns $89 16Mb (2Mbx32) – 60ns $177 32Mb (4Mbx32) – 60ns $357 MAC MEMORY 8Mb P’BOOK 190 $240 VIDEO MEMORY 256K x 16 70ns (SOJ) $17 LASER PRINTER MEMORY 2Mb UPGRADE $150 CO-PROCESSORS 80387 DX to 40MHz $100 COMPAQ 8Mb CONTURA AERO $239 All other models available $Call TOSHIBA PORTEGE/SATELLITE 8Mb / 16Mb EDO $211/ $395 All other models available $Call IDE HARD DRIVES: SEAGATE 1080Mb EIDE 10.5ms 3yr $280 1620Mb EIDE 14ms 3yr $361 2113Mb EIDE 10.5ms 3yr $413 MODEMS: BANKSIA / SPIRIT 28,800 BANKSIA V.34 $360* 28,800 SPIRIT V.34/V.FC $350* *Plus 14% sales tax on modems Ex Tax Pricing – Delivery $8. Pricing as at 18/7/96. Phone for latest. Car Projects Book....................OBC Dick Smith Electronics............... 4-7 Earthquake Audio........................91 EDA Solutions.............................15 Harbuch Electronics....................91 Instant PCBs................................96 Jaycar ................................... 45-52 Kits-R-US.....................................92 Sales Tax On Modems 14%. Everything Else 22%. Credit Cards Welcome. We Also Buy And Trade-In Memory. PELHAM Memory Pty Ltd Suite 6, 2 Hillcrest Rd, Ph: (02) 9980 6988 Pennant Hills, 2120. Fax: (02) 9980 6991 Email: pelham1<at>ozemail.com.au Macservice............................ 26-27 MicroZed Computers...................96 other kits. FREE catalog. Credit cards accepted. Ozitronics, 24 Ballandry Crescent, Greensborough 3088. (03) 9434 3806 ozitronics<at>c031.aone.net.au http://www.hk.super.net/-diykit/oz.html DATAMAN EPROM PROGRAMMERS: World’s leading programmers. S4 hand­ held, on-screen editor, EPROM emulation, EPROMS/EEPROM/Flash up to 8Mbits. Dataman-48 up to 48pin DIL. Call or email for details. DIGITAL GRAPHICS P/L, PO Box 281, North Ryde 2113. (02) 9888 3105. dgriffo<at>ozemail.com.au http://www.ozemail.com.au/~dgriffo COMPUTER PARTS: 6-month warranty. HDD MFM used 40Mb $45, 20Mb $30; AT 1:1 cont w cables new $39. Floppy disks 65% clip/100 new 360K $20, 720K $60, 1.2M $55, 1.44M $75. Freight to 5kg $10. ACE Tel (07) 3878 4076. POB 609, Kenmore 4069. WANTED NEEDED: two new heads for National RS7555S. Offer. R. Jollin, 131 Hall Road, Springwood 4127. Model Railway Projects Book......44 Oatley Electronics...................14,89 Pelham........................................96 RCS Radio ..................................95 Resurrection Radio......................88 Rod Irving Electronics .......... 75-79 Silicon Chip Wallchart................IFC Zoom.........................................IBC _________________________________ 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. R AUSTRALIA’S BEST AUTO TECH MAGAZINE It’s a great mag... but could you be disappointed? If you’re looking for a magazine just filled with lots of beautiful cars, you could be disappointed. Sure, ZOOM has plenty of outstanding pictorials of superb cars, but it’s much more than that. If you’re looking for a magazine just filled with “how to” features, you could be disappointed. Sure, ZOOM has probably more “how to” features than any other car magazine, but it’s much more than that. If you’re looking for a magazine just filled with technical descriptions in layman’s language, you could be disappointed. Sure, ZOOM tells it in language you can understand . . . but it’s much more than that. If you’re looking for a magazine just filled with no-punches-pulled product comparisons, you could be disappointed . Sure, ZOOM has Australia’s best car-related comparisons . . . but it’s much more than that If you’re looking for a magazine just filled with car sound that you can afford, you could be disappointed. Sure, ZOOM has car hifi that will make your hair stand on end for low $$$$ . . . but it’s much more than that. If you’re looking for a magazine just filled with great products, ideas and sources for bits and pieces you’d only dreamed about, you could be disappointed. Sure, ZOOM has all these . . . but it’s much more than that. But if you’re looking for one magazine that has all this and much, much more crammed between the covers every issue, there is no way you’re going to be disappointed with ZOOM. Look for the June/July 1998 issue in your newsagent From the publishers of “SILICON CHIP”