Fullscreen HTML5Med Res (??MB)HTML4

October 1996  1 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” Vol.9, No.10; October 1996 Contents FEATURES 4 An Introduction To Smart Cards A revolutionary new plastic card could soon find its way into your pocket. Here’s a look at how the new “smart” cards work – by Sammy Isreb 25 Snappy: Just Click The Mouse Button For High-Res Video Images WIRED VIDEO TRANSMITTER & RECEIVER – PAGE 12 This new frame grabber plugs into your computer’s parallel port and captures good quality images from any video source – by Greg Swain PROJECTS TO BUILD 12 Send Video Signals Over Twisted Pair Cable Wire your home or business with remote video for entertainment or CCTV security systems – by John Clarke 22 Power Control With A Light Dimmer Use it to dim a table lamp or for low temperature soldering – by Leo Simpson 32 600W DC-DC Converter For Car Hifi Systems Provides high-voltage split supply rails to drive high-power car amplifiers (up to 180W RMS per stereo channel, or 360W RMS total) – by John Clarke POWER CONTROL WITH A LIGHT DIMMER – PAGE 22 53 Infrared Stereo Headphone Link; Pt.2 We complete this project by describing the receiver – by Rick Walters 66 Build A Multimedia Sound System; Pt.1 Get big sound from your computer with this project. It plugs into the motherboard and boosts the output from your soundcard (via special speakers)– by Rick Walters SPECIAL COLUMNS 40 Serviceman’s Log To tip or not to tip: a few tips – by the TV Serviceman 600W DC-DC CONVERTER FOR CAR HIFI SYSTEMS – PAGE 32 75 Satellite Watch What’s available on satellite TV – by Garry Cratt 82 Radio Control Multi-channel radio control transmitter; Pt.8 – by Bob Young 88 Vintage Radio A new life for an old Hotpoint – by John Hill DEPARTMENTS 2 Publisher’s Letter 3 Mailbag 8 Circuit Notebook 65 Order Form 79 Product Showcase 93 Ask Silicon Chip 95 Market Centre 96 Advertising Index MULTIMEDIA AMPLIFIER FOR ENHANCED COMPUTER SOUND – PAGE 66 October 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 Getting onto the Internet can cost big money One of the common enquiries we get from readers is “Are you on the Internet yet? So far, the answer has been “No, not yet.” Naturally, the enquirer is usually disappointed at this reply but when questioned further, as to why they want to know, people generally state that they just like to browse. They don’t really want anything specific via the Internet but they like to have a good look around. For many businesses, the Internet is a huge conundrum. On the one hand, large numbers of business are eagerly jumping onto the bandwagon so that they can grab the kudos of being seen to be innovative and forward-looking. On the other hand, other more cautious firms, ours included, are wondering whether all the effort will produce any worthwhile financial return. I would go further and say that, for some firms, there is risk of a considerable loss via the Internet. I am thinking particularly of copyright. Just recently, the Australian Perform­ing Rights Association has decided to target information service providers and charge them for songs being downloaded on the net. That is likely to result in a protracted legal battle. Once a firm’s intellectual assets are available via the Internet, par­ticularly software, then the chances of any return are virtually nil. The same comment applies to unauthorised material on bulle­tin boards. Unless a business can point to a real return from the very substantial investment required to produce and properly maintain a web site, then the Internet can be guaranteed to be a financial loss. Sure, proponents of the Internet will point to savings on international phone calls and faxes and may even be able to identify some business generated by the Internet but as far as I can determine, very few businesses make any real money from it. They would be better off devoting their scarce resources to the business activity they know best. In fact, I predict that quite a few businesses will see the light and close down their web sites. The same will apply to businesses which have bulletin boards – they will add up all the costs and figure that it is not worthwhile. The obvious excep­tions to this are firms involved in software distribution and service. This is not to say that the Internet will not provide substantial business opportunities in the future. I am sure it will. But at the moment, the Internet is the 1990s equivalent of the CB boom – everybody is talking about it but most of the information on it is pretty trivial. 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 Electronic construction alive & well I was in Australia on business late in March and during a week of vacation that followed I was introduced to your magazine by the people at Altronics in Brisbane. I bought the April 1996 issue – very well done. The USA used to have several magazines like this in wide circulation. In the USA we have become a nation of buy it, plug it in, and use it for a while, then toss it out. Repair is expensive so why not just buy a new one. Construction is for the dedicated amateurs who read “Audio Constructor” or “QST”. It’s nice to see that electronic construction is still alive and well in Austra­lia. D. Gaynor, Woodridge, Illinois, USA. Computer Bits easy to follow Thank you for publishing articles over the last few months about getting better performance from computers (“Computer Bits”). We have found your articles a lot easier to follow than some of the “user’s guides” supplied with our computer and the hints and suggestions regarding upgrades, etc, a lot more down-to-earth and practical than some similar things published elsewhere. We’re looking forward to many more similar articles! D. Terrey, Chatswood, NSW. ESD causes semiconductor failures I have been purchasing SILICON CHIP since the first issue and have always found the content to be of a high standard and thoroughly enjoyable to read. Of particular note would be the Serviceman’s Log section, along with those brilliant drawings. I hope you find the following to be constructive rather than just critical. Your Publisher’s Letter in the August 1996 issue talks of new technology and states that “plastic rules supreme”, all of which is true. I should like to suggest that in light of this “new technology” that you could be paying more attention to handling and mounting issues associated with these devices. I refer to the projects contained within the same issue of the magazine where there is no mention of correct handling procedures for any of the semiconductor devices used nor any reference to the existence of a requirement for special handling procedures. I concede that many home constructors will probably ignore such procedures and few would have the required equipment anyway. This does not alter the fact that these things should always be included in the text of a technical journal. Firstly, I raise the issue of anti-static handling pro­cedures. This is an issue that is largely ignored in many sectors of the electronics industry, yet experience would show that ESD (electrostatic discharge) is responsible for at least 90% of all field failures in electronic products. The statement that ESD control is largely ignored can be verified at almost any TV/video service centre and also at many computer outlets where ESD con­trol procedures are non-existent. Please don’t you follow the same path and ignore this issue like so many others. I conducted a survey of all product failures for Stanilite Communications whilst a production engineer in that company which is where the figure of 90% comes from. The other 10%, by the way, is made up of things such as faulty wave soldering, etc. The extent of ESD damage was enough for Stanilite to authorise a $50,000 plus budget for equipment specifically for ESD control and this at the Perth facility only. Many people assume that only CMOS devices are at risk from static damage when in fact all semiconductors are at risk. Even chip resistors and capacitors can be (and are) damaged in this way. Most static damage does not result in instant catastrophic failure but more insidiously causes degradation of performance ultimately leading to premature failure of a product in the field. Murphy ensures that this happens at the worst possible moment, when the product is least accessible for service and when the end user will have the worse possible view of the suppliers’ quality control. The other 10% of failures mentioned above consist of a significant amount of failures caused by incorrect mounting of power devices, in particular tab-mount plastic devices. It would seem that the single biggest no-no with these devices is that the leads should not be bent at all unless really necessary and bending at or near the lead to plastic (case) junction is strict­ly not allowed. Fig.10 in the 350W amplifier article (August 1996) clearly shows the leads deliberately bent right at the case. Whilst the bending of the leads like this will generally only produce a small percentage of premature failures, some failures will definitely occur and you should not be (perhaps unwittingly) advocating such poor engineering practices. One other item to mention is that Fig.7 in the same 350W amplifier article shows a suggested power supply. While the actual figures for peak current (derived from transformer im­pedance, secondary volts, effective diode resistance and capaci­tor ESR, etc) would seem to make it OK, experience with the common variety of 25A bridge would suggest that some sort of surge limiting would be a distinct advantage. The surge rating of a typical 25A bridge is usually quoted to be around 320A and while most applications do not exceed this rating I have seen too many bridge failures to have a lot of confidence in the quoted 320A figure. D. Woodbridge, SC Kelmscott, WA. October 1996  3 This “Tellcard” is an early European smart card, built by Bull CP8. A 1985 prototype for a electronic travellers cheque card, also developed by Bull CP8. An introduction to smart cards For decades, magnetic stripe cards have been used in a variety of applications involving small amounts of identification data. These magnetic cards have become the norm in applications such as credit and key cards, to name just two. However, they have many drawbacks and will eventually be replaced by a new technology. By SAMMY ISREB The system that will most likely replace magnetic stripe cards is the newer smart card technology. A smart card is similar in appearance to a conventional magnetic card but that is where the similarities end. Unlike a conventional card, a standard smart card contains a CPU (central processing unit) and associat­ ed memory. Because this setup offers read/write capabilities, new information can be added, removed, or processed as needed. An average smart card on the market today contains an 8-bit 5MHz microprocessor, 8K bytes of ROM, 288 bytes of RAM and up to 16K bytes of EEPROM, all fabricated using CMOS technology. 4  Silicon Chip Physically, smart cards have the same dimensions as stan­ dard magnetic stripe cards but have from six to eight gold I/O contacts along the top lefthand corner. These I/O contacts are used in conjunction with a compatible smart card reader to trans­fer data. Hidden under the gold contacts is a single IC, contain­ing the entire CPU and memory contents of the smart card. Possibly the greatest feature of smart cards, apart from their high data storage capabilities, is the fact that they are very secure against unauthorised data reading/writing. On the simplest level, they are much more secure than magnetic stripe cards, as the data is stored inside the card on board an IC and not on the surface where it can easily be read as is the case with magnetic stripe cards. On a more sophisticated level, the fact that a CPU is on­board allows en­ cryption methods to be employed in order to protect sensitive data. And because both the memory and the CPU are on a single IC, it is not possible to “spy” on the data lines that would otherwise be used to connect two or more chips. All these features, along with the fact that most smart cards will destruct when their plastic casing is removed, makes them very secure indeed. The main drawback of smart cards (one that will not be solved in the immediate future) is their relatively high price. A magnetic stripe card can be manufactured for around $1, whereas an average smart card can cost from $15-25. Top-of-the-range cards can cost many times more, however. Until this cost barrier is overcome, magnetic cards will continue to domi­nate the market. Memory cards For some applications that do not require the complexity of a CPU, memory cards are available. These are composed solely of a memory chip, An electronic travellers cheque card from Thomas Cook Financial Services. usually a form of EEPROM or non-volatile RAM. These cards do not have the security of a fully-fledged smart card but are quite adequate for all forms of prepaid value cards, such as telephone or stored value cash cards. Contact or contactless? As already mentioned, most smart cards have a number of power and I/O contacts on their surface that allow interaction with a card reader. The number and arrangement of these contacts varies, depending on the type of card. This setup does have one drawback, however – the card must be inserted into the card reader each time it is used. To solve this problem, contactless smart cards have been developed that can communicate with the card reader by radio. The cards receive power from a 125kHz incident magnetic field A stored value telephone smart card, which began operation in France in 1983. gener­ated by the card reader (along with timing information), which also is used for data transfer at rates up to 19.2Kb/s. Typical contactless smart cards contain an IC which consists of a CPU, ROM, EEPROM and either 128 bytes or 512 bytes of non-vola­tile ferro­ e lectric RAM. A single coil, located inside the card, is used for data transmission, reception and inductive power pickup. Contactless smart cards have a range of about 10cm to 1m, depending on the card and the type of reader being used. Most systems also have the ability to simultaneously accept multiple cards in the reading area without data interference between the units. A less sophisticated version of the contactless smart card does away with the need to obtain its power inductively from the card reader’s Fig.1: block diagram of Hitachi’s H8/3102 Smart Card. magnetic field. Instead, it uses a wafer-thin battery inside the card. This has two disadvantages in that the card is slightly thicker than normal and the card must be re­placed every few years because the battery eventually goes flat. The advantage is extended range – up to 10 metres in some cases. Full or mini-size? Although most smart cards are the same size as standard “credit cards”, mini smart cards have gained popularity in appli­cations where size is critical. These cards are identical in operation to the standard smart cards but are much smaller. They are designed for applications where the card is to be left in a device for long periods of time and where size is crucial, such as in lightweight GSM phones. Uses of smart cards Because of their incredible versatility, smart cards alrea­dy have a wide (and growing) range of applications. In Australia at the current time, probably their largest public use is in the SIM cards for the GSM digital phones. These cards are supplied by the network provider, such as Telstra or Optus, and contain the owner’s account information. By using the card in any digital phone with the same sized slot, the owner can retain his/her phone number and account details, regardless of the phone is being used. In some countries, banks are replacing their magnetic stripe cards with smart cards. However, because of the relatively high cost of smart cards, the transition period will be quite lengthy. In Australia, the infrastructure for such a move is not yet in place. October 1996  5 could get rid of the wad of plastic now found in most people’s wallets. Choosing a system A screen capture from the Smart Card Cyber Show world wide web page. This web site, http://cardshow.com/index.html, is great for those interested in implementing smart cards in their business. However, during the next decade or so, it is quite possible that the switch to smart cards will occur. In some parts of Australia, companies are already trailing various types of stored value smart cards. When these cards are bought, they contain a fixed cash value, which is diminished when purchases are made. When the card is exhausted, it can be “re­charged” at a bank. This type of system may even do away with the need for cash in the future. One of the most exciting possibilities is the development of smart cards that combine a number of applications. Because of their high storage capabilities, it’s possible to make a smart card that’s a bank card, a SIM GSM mobile phone card and a stored value cash card all in one, with a good many other applications thrown in as well. This For those keen business people out there who currently employ magnetic cards for their customers, a switch to a smart card system may not only be feasible but may end up being more profitable in the long run. The first step is to identify which of the advantages of smart cards will make their use worthwhile. It could be their extra security features, their increased memory capacity, or their inbuilt CPU. If smart cards are a likely option, a combination of a smart card system and suitable reader must be found. Searching “smart cards” on the Inter­ net will reveal a list of manufacturers and suppliers who can be contacted to arrange a system that best suits your needs. Alternatively, a Smart Card Cyber Show world wide web page has been set up at web site http:// cardshow.com/index.html. Conclusion Smart cards will be one of the most exciting technologies to watch in the next decade. When fully implemented, they have the chance to make our lives simpler, more efficient and more secure. However, there is still some way to go before smart cards replace magnetic stripe cards. Until then, watch as your magnetic cards start SC disappearing, one by one. TIMELINE OF EARLY SMART CARD DEVELOPMENT 1974: the world’s first memory card developed. This consisted of a chip housed in an epoxy board and was developed by CII-Honeywell Bull. 1980: first Philips smart card developed. Contained two separate ICs: one microcontroller IC and one mem­ory IC. 1975: the first memory card in a “credit card” format, with the chip and its contacts on one side. This card was designed by CII-Honeywell Bull. 1981: first true smart card using a single IC for the microcon­troller and memory, developed by Bull CP8. First smart card cash payment system trials in a small European town. 1977: world leader in smart card technology, Bull CP8, formed from CII-Honeywell Bull. 1983: first smart card payphone system established in France. 1989: Thomas Cook experiments with the use of a smart card as an electronic travellers cheque. ISO standard 7816-3 concerning the electrical characteristics and exchange protocols relating to smart cards set up. 1987: several International Banks consider introducing smart cards. ISO Standard 7816-1 concerning the physical characteris­tics of smart cards set up. 1990 onwards: proliferation of smart card technology begins. However, it is slow to take off in Australia, except for the GSM digital mobile phone area. 1979: first microprocessor card (twochip) designed by Bull CP8. This card used a Motorola 3870 micro­controller and a 2716 EPROM. 6  Silicon Chip 1988: Midland bank introduces smart cards to its customers. ISO Standard 7816-2, concerning the role and position of smart card electrical contacts, is set up. 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. October 1996  7 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. Muting the LM3886 module This circuit can be used with the LM3886 50 watt/channel stereo module described in February 1995 and the LM3876 mono amplifier module described in March 1994. It will allow the modules to be briefly muted at switch-on to avoid turn-on thumps. Because both of these modules are DC coupled throughout, they normally should have no turn-on thumps but this can happen if they are preceded by some AC-coupled preamplifiers. One solution is to use a relay circuit to disconnect the loudspeakers briefly at switch-on. This can be done by the Loudspeaker Protector featured in July 1991. Alternatively, it is possible to use the inbuilt muting feature of the LM3876 and LM3886 chips. Pin 8 is the mute pin and it needs to have a current of at least 0.5mA drawn from it to keep the circuit unmuted. In the amplifier modules referred to above this is achieved with a suitable resistor connected to the negative supply rail via a link on the PC board. This add-on circuit will briefly mute Printer port zero voltage detector This circuit will detect the zero voltage crossing times for the 240VAC 50Hz mains supply 8  Silicon Chip the circuit at switch-on. It works as follows: at switch-on the BC560 PNP transistor has no bias applied and therefore it cannot conduct. After about three seconds, the 100µF capacitor is charged sufficiently via the 82kΩ resistor to bias the transistor on and unmute the LM3886. At switch- and generate an appropriate 50Hz signal to be fed into the parallel printer port of an IBM-compatible computer. The circuit works as follows: the 240VAC mains voltage is off, the 1N4004 diode across the 82kΩ resistor rapidly discharges the 100µF capacitor to mute the chip again and minimise turn-off thump. Note that if signal is passing through the amplifier while it is being muted or un­muted, it will briefly cause distortion. SILICON CHIP fed via the 0.47µF capacitor and 470Ω resistor to a bridge rectifier consisting of diodes D1-D4. The rectified 50Hz is then filtered by a 100µF capacitor and regulated to 16V DC by zener diode ZD1. This DC supply powers the input side of IC1, a 4N28 optocoupler. The 240VAC is also fed via two series 47kΩ resistors to zener diode ZD2 and the 16V clipped signal drives the base of Q1. Transistor Q1 drives the internal LED of IC1 and hence the internal photo­transistor between its pins 4 & 5. The result is a 50Hz signal at pins 10 and 25 of the printer port which is on for every positive half-cycle of the mains waveform. SILICON CHIP 6V motor speed/ direction controller This circuit was designed for use in a hard-wired, remote-control toy car. It has forward, reverse, two pre­­ settable speeds and can be controlled by either +6V logic or switches to the +6V rail. It uses pulse-width modulation for efficient speed control and relay switching for minimum series voltage drops. In the toy car application, two speed/direction controllers are used, one operating a 6VDC motor and reduction box on each rear wheel. The front wheel is a trailing, castor-type wheel mounted under the chassis. I used a 6VDC, 4Ah, SLA battery in the car, to cope with the heavy current demand during takeoff and manoeuvring. The circuit could also be useful in antenna rotator, re­versible fan, model railway and similar applications, with IC1 and IC2 replaced by VR3 and the associated 1kΩ series resistor, if only speed control is required. For speed control, IC3a is an oscillator running at 100Hz. Its output is pulse-width modulated by IC3b. The length of these pulses is determined by whichever speed preset poten­tiometer is currently switched to pin 13. This switching is achieved by IC1, half of a 4013 dual D-type flipflop wired as an RS flipflop and IC2a/IC2b, half of a 4016 quad analog switch. The PWM output of IC3b is buffered by Q1, a 2N3055 which is mounted on a heatsink. The direction is controlled by Q2 & Q3, two BC547 transistors, driving two 6V relays. To ensure that the motor only switches on if one but not both the FWD or REV inputs are brought high, a 4070 XOR gate, IC4a, is used. To operate the circuit, bring FAST or SLOW momentarily high to select the required speed preset, then hold FWD or REV high to run the motor. The motor will slow or stop (depend­ing on load) if “FAST” and “SLOW” are brought high simul­taneous­ly. S. Carroll, Timmsvale, NSW. ($35) THE “HIGH” THAT LASTS IS MADE IN THE U.S.A. Model KSN 1141 The new Powerline series of Motorola’s 2kHz Horn speakers incorporate protection circuitry which allows them to be used safely with amplifiers rated as high as 400 watts. This results in a product that is practically blowout proof. Based upon extensive testing, Motorola is offering a 36 month money back guarantee on this product should it burn out. Frequency Response: 1.8kHz - 30kHz Av. Sens: 92dB <at> 1m/2.83v (1 watt <at> 8Ω) Max. Power Handling Capacity: 400W Max. Temperature: 80°C Typ. Imp: appears as a 0.3µF capacitor Typical Frequency Response MOTOROLA PIEZO TWEETERS AVAILABLE FROM: DICK SMITH, JAYCAR, ALTRONICS AND OTHER GOOD AUDIO OUTLETS. IMPORTING DISTRIBUTOR: Freedman Electronics Pty Ltd, PO Box 3, Rydalmere NSW 2116. Phone: (02) 9638 6666. October 1996  9 Silicon Chip Back Issues Converter; Introduction To Digital Electronics; Simple 6-Metre Amateur Transmitter. December 1990: The CD Green Pen Controversy; 100W DC-DC Converter For Car Amplifiers; Wiper Pulser For Rear Windows; 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers of Servicing Microwave Ovens. September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice. Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2. April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2; The Story Of Amtrak Passenger Services. March 1990: Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC; The Australian VFT Project. May 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; The Burlington Northern Railroad. July 1989: Exhaust Gas Monitor; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; The NSW 86 Class Electrics. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Studio Series 20-Band Stereo Equaliser, Pt.2. October 1989: FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 2-Chip Portable AM Stereo Radio, Pt.2; A Look At Australian Monorails. November 1989: Radfax Decoder For Your PC (Displays Fax, RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive Formats & Options; The Pilbara Iron Ore Railways. December 1989: Digital Voice Board; UHF Remote Switch; Balanced Input & Output Stages; Operating an R/C transmitter; Index to Volume 2. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Phone Patch For Radio Amateurs; Active Antenna Kit; Designing UHF Transmitter Stages; A Look At Very Fast Trains. February 1990: 16-Channel Mixing Desk; High Quality April 1990: Dual Tracking +/-50V Power Supply; Voice-Operated Switch (VOX) With Delayed Audio; 16-Channel Mixing Desk, Pt.3; Active CW Filter; Servicing your Microwave Oven. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protector For Power Supplies; Speed Alarm For Your Car; Fitting A Fax Card To A Computer. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Inverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; A Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateur Radio & TV. April 1991: Steam Sound Simulator For Model Railroads; Remote Controller For Garage Doors, Pt.2; Simple 12/24V Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To Amplifier Design, Pt.2. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1. July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power Station. June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers, Pt.2; Active Filter For CW Reception; Tuning In To Satellite TV. August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Generator, Pt.2. July 1991: Loudspeaker Protector For Stereo Amplifiers; 4-Channel Lighting Desk, Pt.2; How To Install Multiple TV Outlets, Pt.2; Tuning In To Satellite TV, Pt.2; The Snowy Mountains Hydro Scheme. September 1990: Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band; the Bose Lifestyle Music system. October 1990: The Dangers of PCBs; Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; NE602 Converter Circuits. November 1990: How To Connect Two TV Sets To One VCR; Egg Timer; Low-Cost Model Train Controller; 1.5V To 9V DC August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder; Tuning In To Satellite TV, Pt.3; Step-By-Step Vintage Radio Repairs. September 1991: Digital Altimeter For Gliders & Ultralights, Ultrasonic switch for mains appliances; The Basics Of A/D & D/A Conversion; Plotting the course of Thunderstorms. October 1991: A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator Mk.II; Magnetic Field Strength Meter; ORDER FORM Please send me a back issue for: ❏ July 1989 ❏ September 1989 ❏ January 1990 ❏ February 1990 ❏ July 1990 ❏ August 1990 ❏ December 1990 ❏ January 1991 ❏ May 1991 ❏ June 1991 ❏ October 1991 ❏ November 1991 ❏ April 1992 ❏ May 1992 ❏ September 1992 ❏ October 1992 ❏ April 1993 ❏ May 1993 ❏ September 1993 ❏ October 1993 ❏ February 1994 ❏ March 1994 ❏ July 1994 ❏ August 1994 ❏ December 1994 ❏ January 1995 ❏ May 1995 ❏ June 1995 ❏ October 1995 ❏ November 1995 ❏ March 1996 ❏ April 1996 ❏ August 1996 ❏ September 1996 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ September 1988 October 1989 March 1990 September 1990 February 1991 July 1991 December 1991 June 1992 January 1993 June 1993 November 1993 April 1994 September 1994 February 1995 July 1995 December 1995 May 1996 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ April 1989 November 1989 April 1990 October 1990 March 1991 August 1991 January 1992 July 1992 February 1993 July 1993 December 1993 May 1994 October 1994 March 1995 August 1995 January 1996 June 1996 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ May 1989 December 1989 June 1990 November 1990 April 1991 September 1991 March 1992 August 1992 March 1993 August 1993 January 1994 June 1994 November 1994 April 1995 September 1995 February 1996 July 1996 Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Signature ____________________________ Card expiry date_____ /______ Name _______________________________ Phone No (___) ____________ PLEASE PRINT Street ________________________________________________________ 10  Silicon Chip Note: all prices include post & packing Australia (by return mail) ............................. $A7 NZ & PNG (airmail) ...................................... $A7 Overseas (airmail) ...................................... $A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details or fax the details to (02) 9979 6503. ✂ Card No. Digital Altimeter For Gliders, Pt.2; Military Applications Of R/C Aircraft. With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1. November 1991: Build A Colour TV Pattern Generator, Pt.1; Junkbox 2-valve receiver; Flashing Alarm Light For Cars; Digital Altimeter For Gliders, Pt.3; A Talking Voltmeter For Your PC, Pt.2. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier With IR Remote Control, Pt.3; Siren Sound Generator; Engine Management, Pt.2; Experiments For Games Cards. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Colour TV Pattern Generator, Pt.2; Index To Volume 4. December 1993: Remote Controller For Garage Doors; LED Stroboscope; 25W Amplifier Module; 1-Chip Melody Generator; Engine Management, Pt.3; Index To Volume 6. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Experiments For Your Games Card. January 1994: 3A 40V Adjustable Power Supply; Switching Regulator For Solar Panels; Printer Status Indicator; Mini Drill Speed Controller; Stepper Motor Controller; Active Filter Design; Engine Management, Pt.4. March 1992: TV Transmitter For VHF VCRs; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Directories; Valve Substitution In Vintage Radios. April 1992: IR Remote Control For Model Railroads; Differential Input Buffer For CROs; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. May 1992: Build A Telephone Intercom; Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; Aligning Vintage Radio Receivers, Pt.2. June 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; Infrared Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; A Look At Hard Disc Drives. July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Multi-Station Headset Intercom, Pt.2. August 1992: An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; 1kW Dummy Load Box For Audio Amplifiers; Troubleshooting Vintage Radio Receivers; MIDI Explained. September 1992: Multi-Sector Home Burglar Alarm; Heavy-Duty 5A Drill speed Controller (see errata Nov. 1992); General-Purpose 3-1/2-Digit LCD Panel Meter; Track Tester For Model Railroads; Build A Relative Field Strength Meter. October 1992: 2kW 24VDC - 240VAC Sinewave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; A Regulated Lead-Acid Battery Charger. January 1993: Flea-Power AM Radio Transmitter; High Intensity LED Flasher For Bicycles; 2kW 24VDC To 240VAC Sinewave Inverter, Pt.4; Speed Controller For Electric Models, Pt.3. February 1993: Three Projects For Model Railroads; Low Fuel Indicator For Cars; Audio Level/VU Meter (LED Readout); An Electronic Cockroach; 2kW 24VDC To 240VAC Sinewave Inverter, Pt.5. March 1993: Solar Charger For 12V Batteries; Alarm-Triggered Security Camera; Reaction Trainer; Audio Mixer for Camcorders; A 24-Hour Sidereal Clock For Astronomers. April 1993: Solar-Powered Electric Fence; Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Converter; Digital Clock With Battery Back-Up. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Alphanumeric LCD Demonstration Board; The Microsoft Windows Sound System; The Story of Aluminium. June 1993: AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; Digital Voltmeter For Cars; Windows-based Logic Analyser. February 1994: 90-Second Message Recorder; 12-240VAC 200W Inverter; 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Engine Management, Pt.5; Airbags - How They Work. March 1994: Intelligent IR Remote Controller; 50W (LM3876) Audio Amplifier Module; Level Crossing Detector For Model Railways; Voice Activated Switch For FM Microphones; Simple LED Chaser; Engine Management, Pt.6. April 1994: Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator; Universal Stereo Preamplifier; Digital Water Tank Gauge; Engine Management, Pt.7. May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Multi-Channel Infrared Remote Control; Dual Electronic Dice; Simple Servo Driver Circuits; Engine Management, Pt.8; Passive Rebroadcasting For TV Signals. June 1994: 200W/350W Mosfet Amplifier Module; A Coolant Level Alarm For Your Car; 80-Metre AM/CW Transmitter For Amateurs; Converting Phono Inputs To Line Inputs; PC-Based Nicad Battery Monitor; Engine Management, Pt.9. July 1994: Build A 4-Bay Bow-Tie UHF Antenna; PreChamp 2-Transistor Preamplifier; Steam Train Whistle & Diesel Horn Simulator; Portable 6V SLA Battery Charger; Electronic Engine Management, Pt.10. August 1994: High-Power Dimmer For Incandescent Lights; Microprocessor-Controlled Morse Keyer; Dual Diversity Tuner For FM Microphones, Pt.1; Build a Nicad Zapper; Engine Management, Pt.11. June 1995: Build A Satellite TV Receiver; Train Detector For Model Railways; 1W Audio Amplifier Trainer; Low-Cost Video Security System; Multi-Channel Radio Control Transmitter For Models, Pt.1; Build A $30 Digital Multimeter. July 1995: Electric Fence Controller; How To Run Two Trains On A Single Track (Plus Level Crossing Lights & Sound Effects); Setting Up A Satellite TV Ground Station; Door Minder; Adding RAM To A Computer. August 1995: Fuel Injector Monitor For Cars; Gain Controlled Microphone Preamp; Audio Lab PC Controlled Test Instrument, Pt.1; Mighty-Mite Powered Loudspeaker; How To Identify IDE Hard Disc Drive Parameters. September 1995: Keypad Combination Lock; The Incredible Vader Voice; Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.1; Jacob’s Ladder Display; The Audio Lab PC Controlled Test Instrument, Pt.2. October 1995: Geiger Counter; 3-Way Bass Reflex Loudspeaker System; Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.2; Fast Charger For Nicad Batteries; Digital Speedometer & Fuel Gauge For Cars, Pt.1. November 1995: Mixture Display For Fuel Injected Cars; CB Transverter For The 80M Amateur Band, Pt.1; PIR Movement Detector; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.1; Digital Speedometer & Fuel Gauge For Cars, Pt.2. December 1995: Engine Immobiliser; 5-Band Equaliser; CB Transverter For The 80M Amateur Band, Pt.2; Subwoofer Controller; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.2; Knock Sensing In Cars; RAM Doubler Reviewed; Index To Volume 8. January 1996: Surround Sound Mixer & Decoder, Pt.1; Magnetic Card Reader; Automatic Sprinkler Controller; IR Remote Control For The Railpower Mk.2; Recharging Nicad Batteries For Long Life. February 1996: Three Remote Controls To Build; Woofer Stopper Mk.2; 10-Minute Kill Switch For Smoke Detectors; Basic Logic Trainer; Surround Sound Mixer & Decoder, Pt.2; Use your PC as a Reaction Timer. September 1994: Automatic Discharger For Nicad Battery Packs; MiniVox Voice Operated Relay; Image Intensified Night Viewer; AM Radio For Weather Beacons; Dual Diversity Tuner For FM Microphones, Pt.2; Engine Management, Pt.12. March 1996: Programmable Electronic Ignition System For Cars; Zener Tester For DMMs; Automatic Level Control For PA Systems; 20ms Delay For Surround Sound Decoders; Multi-Channel Radio Control Transmitter; Pt.2; Cathode Ray Oscilloscopes, Pt.1. October 1994: Dolby Surround Sound - How It Works; Dual Rail Variable Power Supply; Talking Headlight Reminder; Electronic Ballast For Fluorescent Lights; Temperature Controlled Soldering Station; Engine Management, Pt.13. April 1996: Cheap Battery Refills For Mobile Telephones; 125W Power Amplifier Module; Knock Indicator For Leaded Petrol Engines; Multi-Channel Radio Control Transmitter; Pt.3; Cathode Ray Oscilloscopes, Pt.2. November 1994: Dry Cell Battery Rejuvenator; Novel Alphanumeric Clock; 80-Metre DSB Amateur Transmitter; Twin-Cell Nicad Discharger (See May 1993); Anti-Lock Braking Systems; How To Plot Patterns Direct To PC Boards. May 1996: Upgrading The CPU In Your PC; High Voltage Insulation Tester; Knightrider Bi-Directional LED Chaser; Duplex Intercom Using Fibre Optic Cable; Cathode Ray Oscilloscopes, Pt.3. December 1994: Dolby Pro-Logic Surround Sound Decoder, Pt.1; Easy-To-Build Car Burglar Alarm; Three-Spot Low Distortion Sinewave Oscillator; Clifford - A Pesky Electronic Cricket; Cruise Control - How It Works; Remote Control System for Models, Pt.1; Index to Vol.7. June 1996: BassBox CAD Loudspeaker Software Reviewed; Stereo Simulator (uses delay chip); Rope Light Chaser; Low Ohms Tester For Your DMM; Automatic 10A Battery Charger. January 1995: Sun Tracker For Solar Panels; Battery Saver For Torches; Dolby Pro-Logic Surround Sound Decoder, Pt.2; Dual Channel UHF Remote Control; Stereo Microphone Preamplifier;The Latest Trends In Car Sound; Pt.1. July 1993: Single Chip Message Recorder; Light Beam Relay Extender; AM Radio Trainer, Pt.2; Quiz Game Adjudicator; Windows-based Logic Analyser, Pt.2: Antenna Tuners – Why They Are Useful. February 1995: 50-Watt/Channel Stereo Amplifier Module; Digital Effects Unit For Musicians; 6-Channel Thermometer With LCD Readout; Wide Range Electrostatic Loudspeakers, Pt.1; Oil Change Timer For Cars; The Latest Trends In Car Sound; Pt.2; Remote Control System For Models, Pt.2. August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light Array; Microprocessor-Based Sidereal Clock; Southern Cross Z80-Based Computer; A Look At Satellites & Their Orbits. March 1995: 50W/Channel Stereo Amplifier, Pt.1; Subcarrier Decoder For FM Receivers; Wide Range Electrostatic Loudspeakers, Pt.2; IR Illuminator For CCD Cameras; Remote Control System For Models, Pt.3; Simple CW Filter. September 1993: Automatic Nicad Battery Charger/Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Cockroach. April 1995: Build An FM Radio Trainer, Pt.1; Photographic Timer For Darkrooms; Balanced Microphone Preamplifier & Line Filter; 50W/Channel Stereo Amplifier, Pt.2; Wide Range Electrostatic Loudspeakers, Pt.3; 8-Channel Decoder For Radio Remote Control. October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless Microphone For Musicians; Stereo Preamplifier board Goes Flat; Guitar Headphone Amplifier; FM Radio Trainer, Pt.2; Transistor/Mosfet Tester For DMMs; 16-Channel Decoder For Radio Remote Control; Introduction to Satellite TV. May 1995: What To Do When the Battery On Your Mother­ July 1996: Installing a Dual Boot Windows System On Your PC; Build A VGA Digital Oscilloscope, Pt.1; Remote Control Extender For VCRs; 2A SLA Battery Charger; 3-Band Parametric Equaliser; Single Channel 8-bit Data Logger. August 1996: Electronics on the Internet; Customising the Windows Desktop; Introduction to IGBTs; Electronic Starter For Fluores­cent Lamps; VGA Oscilloscope, Pt.2; 350W Amplifier Module; Masthead Amplifier For TV & FM; September 1996: Making Prototypes By Laser; VGA Oscilloscope, Pt.3; Infrared Stereo Headphone Link, Pt.1; High Quality PA Loudspeaker; 3-Band HF Amateur Radio Receiver; Feedback On Pro­grammable Ignition (see March 1996). PLEASE NOTE: November 1987 to August 1988, October 1988 to March 1989, June 1989, August 1989, May 1990, February 1992, November 1992 and December 1992 are now sold out. All other issues are presently in stock. For readers wanting articles from sold-out issues, we can supply photostat copies (or tear sheets) at $7.00 per article (includes p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. A complete index to all articles published to date is available on floppy disc at $10 including packing & postage. October 1996  11 Send video signals over twisted pair cable Use this Video Transmitter and Video Receiver to wire your home or business with remote video for entertainment or for CCTV security systems. By JOHN CLARKE What’s a twisted pair cable? For all intents and purposes, it is equivalent to a pair of telephone wires and you can’t send video over telephone wires, can you? Well, with this new chipset you could, although that is not why we are presenting this arti­cle. With the recent introduction of 12  Silicon Chip low-cost monochrome video cameras, (less than $200 retail) and this project, you can now easily monitor your front door, your swimming pool or any other part of your home that needs watching from a central location. Video signals are normally sent through 75Ω coax cable and for short runs over several tens of metres there is very little loss in signal level. But over long distances the losses in the cable reduce the signal to an unacceptably low level for the receiving equipment. One way of overcoming the signal loss is to modulate it onto a carrier in the UHF or VHF range. Any signal loss in the cable can then be made good by wideband distribution amplifiers. However, at the receiving end, the signal must be demodulated before it can be displayed on a monitor. This approach is well-proven but coax cable and distribution amplifiers are expensive. Wouldn’t it be nice to be able to send video over ordinary twist­ ed wires? Using the video transmitter Fig.1: the general arrangement of the MAX435 & MAX436 ICs. The MAX435 has a differential output while the MAX436 only has a single ended output. These are transconductance amplifiers so the outputs produce a current that’s proportional to the applied differential input voltage. Features • • 1.5km range (expected) Video transmitted over low cost twisted pair • Audio transmitted in stereo over 50m using op amp transmitter • Up to 1.5km range for mono audio using video transmitter and receiver described here, video can be sent over distances up to 1.5km. Transconductance amplifiers The heart of this project is a pair of ICs made by Maxim Integrated Products, the MAX435 and MAX436. These two ICs are classified as high speed, wideband transconductance amplifiers (WTAs) with true differential, high impedance inputs. The unique architecture of these amplifiers provides accurate gain without negative feedback. Without the feedback, the possibility of spurious oscillation is virtually eliminated. Fig.1 shows the general arrangement of the ICs. The MAX435 has a differential output while the MAX436 only has a single ended output. The outputs produce a current that’s proportional to the applied differential input voltage, providing inherent short circuit protection for the outputs. The circuit gain is set by the ratio of the output impedance “RL”, the user connected transconductance network “ZT” and an internally set current gain factor, K. In the case of the MAX­435, the current gain is nomi­ nally 4 (±2.5) and for the MAX436 this figure is 8 (±2.5). Inside the video transmitter. The top view shows the audio board “hinged” back to reveal the video board, which sits on the bottom of the case. The view above shows the audio board in place. The MAX435 has a 275MHz bandwidth and 800V/µs slew rate, while the MAX436 has a 200MHz bandwidth and 850V/µs slew rate. The common mode rejection ratio for both is -53dB at 10MHz and -90dB at DC. While MAX ICs could also be used to transmit audio signals, we have taken a cheaper approach and used dual op amps to produce a balanced October 1996  13 Fig.2: the transmitter circuit takes composite video and provides a balanced output to the twisted pair. The unbalanced audio signals are converted to balanced outputs by the LM833 op amps. audio transmitter and receiver. These produce high quality stereo results over short runs of less than 50m. This will allow you to pipe composite video and stereo audio signals around your house. For many applications though, we envisage that the video transmitter and receiver boards will be all that are required. Transmitter circuit Fig.2 shows the transmitter circuit. Unbalanced video signal is applied to the IN+ input of the MAX435. The inverting input IN- is connected to ground. The transconductance element impedance between pins 3 and 14  Silicon Chip 5 is set at 220Ω, while the output impedance is a nominal 50Ω. The 4.7kΩ resistor sets the supply current for the IC. Supply decoupling for the ±5V rails, pro­vided by the 0.1µF capacitors, is necessary for best performance at the high frequencies involved. Power is derived from a 12VAC plugpack. This is rectified with halfwave rectifier diodes D1 and D2 to supply the ± rails before regulation. The 470µF capacitors filter the raw DC to produce a relatively smooth voltage. REG1 and REG2 regulate the supplies down to ±5V for IC1. Audio input is applied to a single ended to balanced output amplifier comprising IC2a and IC2b for the left channel and IC3a and IC3b for the right. IC2a is a unity gain buffer which is non-inverting. The output at pin 1 is therefore the + output which drives the positive twisted pair line via a 680Ω resistor. IC2b is connected as an inverting amplifier and the resulting output at pin 7 drives the negative twisted pair line via its 680Ω resistor. The 22pF capacitor across the feedback resistor of IC2b prevents high frequency oscillation. The right channel audio amplifier operates similarly to the left channel circuit. Receiver circuit Fig.3 shows the receiver circuit. IC4 is a MAX436 which accepts the Fig.3: the receiver circuit uses a MAX436 to convert the balanced input from the twisted pair to an unbalanced video output. Simi­larly, the balanced audio signals are converted to single-ended signals by op amps IC5 and IC6. balanced input from the twisted pair and produces an unbalanced output. The 51Ω resistors at the IN+ and INinputs at pins 2 and 6 provide the correct loading for the twisted pair line. A 100Ω resistor in series with trimpot VR1 is connected between pins 3 and 2. VR1 sets the gain of IC4, to compensate for losses in the twisted pair line. A second 100Ω resistor from pin 3 is connected in series with a 56pF capacitor and VC1. The capacitance corrects for the loss of high frequency signal through the line. In prac­tice the capacitance is adjusted until the colour burst signal is at its correct level. The 4.7kΩ resistor at pin 11 sets the current for IC4. The power supply circuit is iden- Specifications Video transmitter/receiver pair Frequency response ����������������� typically -3dB at 200MHz Common mode rejection ����������� typically -53dB at 10MHz; -90dB at DC Audio transmitter/receiver pair Signal to noise ratio ������������������ -102dB unweighted (20Hz to 20kHz) with respect to 1V RMS Common mode rejection ����������� -62dB at 50Hz and 1kHz Harmonic distortion ������������������� less than .016% from 20Hz to 20kHz Frequency response ������������������ -0.25dB at 20Hz and 20kHz Clipping level ���������������������������� 1.7V RMS at input Crosstalk ����������������������������������� -80dB (20Hz to 20kHz) with 20m twisted pair along­side video pair October 1996  15 Fig.4: the component overlays and wiring details for the trans­mitter boards. tical to that used in the transmitter. The audio signal is converted from the balanced twisted pair signal to an unbalanced output using op amps IC5a & IC5b for the left channel and IC6a & IC6b for the right channel. The balanced signal is applied to the non-inverting inputs of IC5a and IC5b. The 330Ω resistors tie the inputs to ground and provide a load for the twisted pair line. A .001µF capacitor is included across the input terminals to remove high frequency noise from 16  Silicon Chip the line. Both IC5a and IC5b are set for a gain of two due to the 1kΩ feedback resistors. Signals which are common to each input are rejected at the output and this is due to the feedback for IC5a being connected to the output of IC5b. Difference signals are amplified at the pin 1 output of IC5a. The 100Ω output resistor prevents oscillation in IC5a due to capacitive loading. The right channel audio amplifier operates in exactly the same manner as the left channel audio amplifier. Construction The Video Transmitter and Video Receiver are housed in separate plastic cases measuring 130 x 68 x 42mm. The video transmitter (using the MAX­435) is built onto a PC board measuring 60 x 102mm (coded 023­06961). The audio transmitter PC board (coded 023069623) is piggy-backed onto the video transmitter. The two receiver PC boards (coded PARTS LIST Video transmitter board 1 PC board, code 02306961, 60 x 102mm 1 plastic utility case, 130 x 68 x 42mm 1 self-adhesive front-panel label, 62 x 126mm 1 12VAC 500mA plugpack 1 SPDT toggle switch (S1) 2 3mm screws and nuts 1 DC socket 2 panel-mount RCA sockets 8 PC stakes 1 40mm length of 0.8mm tinned copper wire Semiconductors 1 MAX435CPD high-speed transconductance amplifier (IC1) 1 7805 3-terminal regulator (REG1) 1 7905 3-terminal regulator (REG2) 2 1N4004 1A silicon diodes (D1,D2) Video Receiver board 1 PC board, code 02306962, 60 x 102mm 1 plastic case, 130 x 68 x 42mm 1 front panel label, 62 x 126mm 1 12VAC 500mA plugpack 1 SPDT toggle switch (S2) 2 3mm screws and nuts 1 DC socket 2 panel-mount RCA sockets 8 PC stakes 1 40mm length of 0.8mm tinned copper wire 1 500Ω horizontal trimpot (VR1) Semiconductors 1 MAX436CPD high-speed transconductance amplifier (IC4) 1 7805 3-terminal regulator (REG3) 1 7905 3-terminal regulator (REG4) 2 1N4004 1A diodes (D3,D4) Capacitors 2 470µF 16VW PC electrolytic 2 10µF 16VW PC electrolytic 3 0.1µF ceramic Capacitors 2 470µF 16VW PC electrolytic 2 10µF 16VW PC electrolytic 3 0.1µF ceramic 1 56pF ceramic 1 3-60pF trimmer (optional) Resistors (0.25W 1%) 1 4.7kΩ 1 75Ω 1 220Ω 2 51Ω Resistors (0.25W, 1%) 1 4.7kΩ 1 75Ω 2 100Ω 2 51Ω Audio transmitter board Audio receiver board 1 PC board, code 02306964, 60 x 102mm 4 12mm spacers 4 6mm spacers 4 20mm x 3mm screws 4 3mm nuts 11 PC stakes 1 20mm length of 0.8mm tinned copper wire 1 PC board, code 02306963, 60 x 102mm 4 12mm spacers 4 6mm spacers 4 20mm x 3mm screws 4 3mm nuts 11 PC stakes 1 20mm length of 0.8mm tinned copper wire Semiconductors 2 LM833 op amps (IC2,IC3) Semiconductors 2 TL072 op amps (IC5,IC6) Capacitors 4 10µF 16VW PC electrolytic 2 22pF ceramic Capacitors 4 10µF 16VW PC electrolytic 1 .001mF MKT polyester Resistors (0.25W, 1%) 6 x 10kΩ 2 330Ω 4 680Ω Resistors (0.25W, 1%) 8 x 10kΩ 2 100Ω 4 330Ω 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: ● ● ● ● ● ● 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 October 1996  17 Fig.5: the component overlays and wiring details for the receiver boards. TABLE 1: RESISTOR COLOUR CODES ❏ No. ❏  6 ❏  2 ❏  8 ❏  4 ❏  6 ❏  2 ❏  2 ❏  4 18  Silicon Chip Value 10kΩ 4.7kΩ 1kΩ 680Ω 330Ω 100Ω 75Ω 51Ω 4-Band Code (1%) brown black orange brown yellow violet red brown brown black red brown blue grey brown brown orange orange brown brown brown black brown brown violet green black brown green brown black brown 5-Band Code (1%) brown black black red brown yellow violet black brown brown brown black black brown brown blue grey black black brown orange orange black black brown brown black black black brown violet green black gold brown green brown black gold brown 02306962 and 02306964) are mounted in a similar fashion to the transmitter. On both cases, RCA sockets for video input and output are mounted at the sides of the box while the audio sockets are at one end of the box. The DC socket is mounted at the opposite end while the power switch is attached to the lid. Fig.4 shows the component overlay and wiring details for the transmitter boards while Fig.5 shows the wiring details for the receiver boards. Begin construction by checking each PC board for breaks or shorts in the copper pattern or any undrilled holes. Fix any defects before proceeding further, then insert all the PC stakes. These are located at the signal input and output wiring points and for power supply. Next, solder in all the links and resistors. Table 1 shows the resistor colour codes and it is a good idea to check each resistor value with your multimeter before soldering it into the board. The capacitors can be mounted next, noting that the electrolytic types must be oriented with the correct polarity as shown. Finally, insert the ICs, making sure that each one has the correct orientation. If you do not intend to use stereo audio channels, IC3 on the audio transmitter board and IC6 on the receiver board can be omitted. The voltage regulators are each mounted horizontally on the PC board and secured with a screw and nut. Bend the leads for each component before insertion into the PC board holes. Take care to orient the diodes correctly. Drill holes in the plastic cases for the RCA and DC sockets using the front panel as a guide to their location. A hole is also required in the lid for the power switch on each box. Wire up the PC boards as shown in Fig.4 and Fig.5. In each case, the audio board is stacked on top of the video board and the two are separated by metal spacers. The integral side pillars in each box will need to be removed so that the PC board assembly can fit comfortably within the case. Affix the label to each lid and attach the power switches. Testing The completed units are now ready for testing. Apply power to the transmitter PC boards and check voltages. These two photographs show the completed boards inside the receiver case. The top view shows the video receiver board, while above is the audio board. Fig.6: the top trace of the oscilloscope display shows a PAL colour bar as the video source signal. Note the colour burst at the far lefthand side of the trace. The lower trace shows the received signal after transmission over 20m of twisted pair. The gain has been compensated for signal loss and for video colour burst level. Note the faithful reproduction of the signal. October 1996  19 TRANSFORMERS • TOROIDAL • CONVENTIONAL • POWER • OUTPUT • CURRENT • INVERTER • PLUGPACKS • CHOKES STOCK RANGE TOROIDALS BEST PRICES APPROVED TO AS 3108-1994 SPECIALS DESIGNED & MADE 15VA to 7.5kVA Tortech Pty Ltd These beautifully-made binders will protect your copies of SILICON CHIP. They are made from a dis­tinctive 2-tone green vinyl & will look great on your bookshelf. Price: $A11.95 plus $3 p&p each (NZ $8 p&p). Send your order to: Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. 20  Silicon Chip ON + OFF VIDEO TRANSMITTER L R AUDIO IN BALANCED VIDEO OUT Silicon Chip Binders L R BALANCED AUDIO OUT 24/31 Wentworth St, Greenacre 2190 Phone (02) 642 6003 Fax (02) 642 6127 VIDEO IN Fig.7: actual size front panel & PC board artworks for the transmitter. Check your PC boards carefully before installing any of the parts. Connect the nega­tive multimeter lead to GND and touch the positive lead on pins 1, 12 & 14 of IC1 where +5V should be present in each case. Similarly, there should be -5V on pins 7, 8 & 10 of IC1. IC2 and IC3 should have +5V on pin 8 and -5V on pin 4. For the receiver PC boards, there should be +5V on pins 1, 12 & 14 of IC4 and -5V on pins 7, 8 & 10. IC5 and IC6 should have +5V on pin 8 and -5V on pin 4. To transmit video you will require one twisted pair while each audio channel will require a separate twisted pair. Use 75Ω coax cable from your video source to the transmitter and from the receiver to the video input of 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 ON + OFF VIDEO RECEIVER L R BALANCED AUDIO IN VIDEO OUT L R AUDIO OUT OrCAD Capture for Windows… BALANCED VIDEO IN Fig.8: actual size front panel & PC board artworks for the receiver. All PC boards measure 60 x 102mm. your monitor or VCR. Audio connec­ tions should be made using standard shielded audio cable. VR1 on the receiver is adjusted to obtain best black and white levels as seen on the monitor. The 56pF capacitor on IC4 should be satisfactory for twisted pair up to 50m. A larger capacitor value can be used if the colour burst signal is marginal. This can be adjusted until the monitor provides a solid colour pic­ture. Lack of picture sync (rolling) means that there is 50Hz present on the video signal. Either re-route the twisted pair away from mains power wiring or use shielded pair earthed to the GND SC terminals. 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 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. October 1996  21 Power control with a light dimmer By LEO SIMPSON In this article we show you how to wire a standard light dimmer in a plastic case to do low temperature soldering, control an electric blanket or to dim a table lamp. No electronics assem­bly is required, just some drilling of the plastic case and a little wiring. This article was prompted by a reader who wanted to do some low temperature soldering of white metal model railway kits. White metal is an alloy of tin and lead, with small amounts of antimony and copper (typically 19% antimony, 1% copper, 75% lead 22  Silicon Chip and 5% tin). While white metals have long been used in the manu­facture of bearings, they are also used in small castings for model railway locomotives, rolling stock and structures. The reason that white metal is used is that it has a low melting point, typically around 200-250°C. That low melting point means that normal tin-lead solders cannot be used; the casting melts before the solder! There are a variety of low temperature solders available but the one normally used for soldering white metal castings is based on cadmium (tin-lead-cadmium). The most popular is made by Carr’s Modelling Products, a UK company. Carr’s 70 is a solder that melts at 70°C. This cannot be safely handled or worked with using an ordinary soldering iron or even one that is temperature-controlled, for that matter. Why not? Most temperature controlled irons are not designed to op- Fig.1: here's how to wire the dimmer unit to the mains cord and the 3-pin socket. erate reliably with a tip temperature below 200°C. So there is a need to run a soldering iron at much reduced power; sufficient to melt and work the solder but not hot enough to cause heavy metal gases to be evolved or damage the white metal casting. In fact, it is absolutely imperative that solders con­ taining cadmium (or bismuth and antimony) should not be over­heated by the tip of the soldering iron – otherwise you will end up breathing poisonous metal fumes. One way to reduce the power to a standard soldering iron to a low level is to use the 5A heavy duty drill speed controller published in the September & November 1992 issues of SILICON CHIP. That will certainly work but it is rather like using a sledge hammer to crack a walnut. It is also more expensive than the dimmer approach described in this article. Our suggestion is to purchase a low power soldering iron rated at between 15 and 30 watts and use it in conjunction with the dimmer as described here. Use the dimmer at a setting just hot enough to make the solder workable and mark that setting on the dimmer plate so you can repeat it in the future. Second, use the iron only for low temperature work. Do not October 1996  23 55 x 85mm but there are a number of alternatives available. Whichever plastic case you use, it needs to be big enough to accommodate the dimmer panel on its top surface and a surface-mount 3-pin socket at one end. As well as this socket, you will need a 3-core mains flex with moulded 3-pin plug and a cordgrip grommet. You will need to drill holes in one end of the case for the surface mount socket – two 3mm holes for the mounting screws and three 5mm holes for the lead entry. At the other end of the case, you will need to drill and file an elongated hole to take the cordgrip grommet. Finally, you will need to drill two 3mm holes and cut a rectangular hole in the lid so that the dimmer can be mounted. Wiring This view shows the wiring inside the case. Make sure that the mains cord is securely clamped and note that plastic cable ties are used to secure the internal wiring. The Neutral and Earth leads from the mains cord go direct to the socket. use it for normal soldering because if you do, when the iron is hot enough to melt normal solder it will boil off any cadmium residue and you could end up breathing it! Assembly work First, purchase your dimmer. Shop around for it as you will find a wide range of prices. At the time of writing we found dimmer prices to range from $12 at Woolworths to more than $28 at some electrical wholesalers. The one we used is made by HPM (Cat 500A/500VA) and was purchased for $16.60. Other brands of dimmer, made by GAF and Arlec, are cheaper. Second, you will need a suitable plastic box. The one we used came from Altronics and measures 125 x The yellow/green Earth lead from the mains cord is termi­nated directly to the earth terminal of the 3-pin socket. The blue Neutral wire from the mains cord also terminates directly to the Neutral terminal of the 3-pin socket. The brown Active wire from the mains cord goes to one of the switch terminals. The other switch wires goes to the dimmer module. Finally, the second wire from the dimmer module goes to the Active terminal on the 3-pin socket. Fig.1 shows the details. When you have completed the wiring, check it against Fig.1 and then test the dimmer on a table or desk lamp. Don’t forget to screw the lid on the case before you do the test. If everything works as it should, push the plastic screw covers into the dimmer mounting screw holes and SC you are finished. Using A Standard Light Dimmer What they can do: most standard wall-mounting light dimmers are rated at between 300 and 500 watts but there are conditions applied to this rating. Apart from dimming lights, most standard dimmers can be used to control fans and low powered heating appliances such as soldering irons and electric blankets. What they can’t do: because they 24  Silicon Chip have such a modest rating, light dimmers cannot be used to control the speed of a typical power tool or food mixer. If you do attempt to use a light dimmer, it will fail immediately. Most light dimmer manufacturers also warn against dimming lights where the individual lamps have a rating in excess of 150 watts or where the lamp is upright rather than hanging down from the fitting. In both cases, when the lamp fails the broken fila­ment is likely to flail around and come into contact with one of the stem supports. This will cause a brief but very large fault current which often blows the Triac in the dimmer. The good news is that such dimmers can generally be fixed by replacing the Triac with an SC141D. Snappy Just click the mouse button for high-res video images By GREG SWAIN This new technique just has to be the lowest cost way to capture high-quality video images on a PC. It’s called “Snappy” and teamed up with a standard camcorder, it produces images that can rival those from expensive digital cameras costing $6000 or more. A CTUALLY, SNAPPY should be classified as a frame-grabber because that’s what it does – it grabs video frames from a camcorder (or some other video source). But unlike a conventional frame-grabber which plugs into your PC’s mother­ board, Snappy is a compact external device that plugs into the parallel port. This makes for a much more convenient arrangement. You don’t have to pull the cover off your PC and you don’t have any of the installation hassles that can occur with plug-in cards (IRQ settings and the like). It also means that you can easily move the device from one computer to another, should the need arise. In use, Snappy can be teamed with any video source, such as a camcorder, VCR or TV tuner. It’s then simply a matter of click­ing the mouse button to preview a video frame via the proprietary software that comes with the device. This frame can then be captured and saved in a number of standard file formats, includ­ing bmp, pcx, tif, tga and jpg. Image quality The big difference between Snappy and conventional frame grabbers lies in the image quality. Conventional frame grabbers are strictly low-resolution devices and the image quality is limited. By contrast, this new device us claimed to provide video stills at resolutions up to 1500 x 1125 (1,687,500) pixels and in 16.8 million (32-bit) colours. That’s more than twice the resolution from a conventional frame grabber but there are a few other enhancements to the image along the way. In fact, this is claimed to be the world’s highest resolution video grabber. A clever IC The clever part of Snappy is a custom chip hidden inside the hardware. This chip, the HD-1500, was developed by Play Incorporated (USA) and digitally enhances the captured image before it is fed to the PC. Among other things, it provides 8-times oversampling, sets the black level and features adaptive comb filtering and timebase correction. Provided the source material is up to scratch, the result­ing image is sharp and has good colour and contrast. You can get some idea of the quality from the accompanying photographs. These photographs were supplied as jpeg compressed files on a demonstration disc and have not been enhanced in any way. All that we have done is open them in Photoshop, convert the resolution from 72 dpi to 266 dpi, resize them and convert them from RGB to CMYK format. From what we’ve seen, Snappy is perfect as a quick and painless way of capturing good-quality video images. You don’t have to muck about getting film processed and then scanning the resulting images, all of which costs October 1996  25 time and money. Of course, the results aren’t as good as those from a drum scanner or dedi­ cated transparency scanner but then we’re talking horses for courses. The software Fig.1: this is the interface that you get when you boot the Snappy video capture program. Clicking the Preview button brings up a frame grab on the screen. Fig.2: the Snappy software lets you make all sorts of adjustments to the previewed image, including colour, brightness, contrast, picture (gamma) and sharpness. You can also adjust the colour balance. This video grab, from the Snappy demonstration disc, was obtained at a resolution of 1500 x 1125 pixels. 26  Silicon Chip The Snappy software is easy to use, with an intuitive interface – you just click on the action buttons or turn the control knobs. You don’t need fancy hardware to run it either. The specifications are a PC-compatible with a 386 processor or better, 4Mb or RAM, 4Mb of hard disc space and a VGA (640 x 480 or better) video card. The software runs under Windows 3.1, Windows 3.11 and Windows 95 but no mention is made of Windows NT. Fig.1 shows the interface that’s presented when you boot the software. To preview the image, you just click the Preview button. Clicking the Adjust button then brings up the window shown in Fig.2. From there, you can make adjustments (if neces­sary) to various aspects of the image (eg, colour, brightness, contrast picture (gamma) and sharpness). It’s then simply a matter of clicking the Snap button to save the image to the disc in one of the standard formats. One very useful feature of the software is that you can “invert” the image from a negative to a positive. This can be useful if you have a negative colour transparency, for example. The trick is to place the transparency on a lightbox, aim the camera at it and then use the software to produce a positive image. Despite what might seem a rather clumsy technique, the result is still surprisingly good. Of course, you can use the same technique to capture images from a positive transparency but without “inverting” the image. As well as the standard capture software, Snappy also comes with Adobe Photo Deluxe, an easy-to-use image editing program. This will let you add special effects to your images and even add titles. An image distorting program (called Goo) and a morphing program (Griffon Morph) complete the software suite that’s sup­ plied with Snappy. Once again, these are easy to use and you can amuse yourself morphing grandma between her true self and the visage of a bassett hound, if your taste runs to such pastimes! The saved image can also be opened Above & left: provided some care is taken with lighting, Snappy is capable of producing excellent results, as these two photos demonstrate (again from the Snappy demo disc). Snappy is the easiest, most cost-effective way of obtaining video grabs that we've seen. in high-end imaging editing software such as Photoshop or imported into desktop publishing programs. In addition, Snappy boasts a Twain interface which means that an image can be directly acquired through Photo­shop or any other program that supports the Twain standard. Who will use it? Snappy At A Glance • • • Captures images from camcorders, VCRs, laser disc players, etc. • • • • • Preview mode displays image on-screen prior to capturing. • • • Three capture modes: field, frame or multi-frame. Easy to install; plugs into the PC’s parallel port. Custom chip enhances image and provides video resolution up to 1500 x 1125 pixels in 16.8 million colours. User adjustable image processing controls. Twain interface; emulates scanners. Negative mode for grabs of photographic negatives. Saves in one of three resolutions: 1500 x 1125 (5Mb bmp), 640 x 480 (1Mb bmp) and 320 x 240 pixels (250Kb bmp). Dimensions: 64 x 124 x 22mm Comes with Snappy (video capture), Adobe Photo Deluxe, Griffon Morph and Goo (image distorting) software. Just about everyone who needs to capture good-quality images with minimum hassle will want Snappy. To quote a well-worn cliche, the list of applications is endless. This device is perfect for producing catalogs, ad­ vertisements, real estate magazines, school reports, ID cards, newsletters and Internet images, to name just a few. Provided that you have a video camera (or some other suit­able video source), Snappy is the fastest, easiest way to get good quality video grabs into your PC that we’ve seen. The cost won’t break the bank either – the recommended retail price is $449. This price includes the hardware, all the software (Snappy, Adobe Photo Deluxe, Goo and Morph), a video cable, a 9V battery and a manual. For further information, contact the Aus­tralian distributor Star Micronics, Unit A, 107 Asquith St, Silverwater, NSW 2128. Phone (02) 9748 4300. SC October 1996  27 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 600W DC-DC converter for car hifi systems Thinking of fitting high-power audio amplifiers to your car’s stereo system? This 600W DC-DC Converter steps up the battery voltage to provide the high-voltage split supply rails required by the amplifiers. PART 1: By JOHN CLARKE If you like lots of bass and high sound levels in your car then you will want to build this 600W DC-DC Converter. It is used in conjunction with one or more amplifier modules so that up to 360W RMS total (or 180W per stereo channel) can be delivered to the loudspeakers. With that sort of power, and provided your loudspeakers are up to the task, you will have the makings of a really first-class car hifi system. Not 32  Silicon Chip that we are advocating that you use this type of system to blow your brains out or to annoy other motor­ists. That’s not what a high-power car hifi system is used for at all. Instead, it’s used to provide good clean sound with plenty of bass and with plenty in reserve for those high-power tran­sients. What sort of amplifiers can be used with this converter? One that immediately springs to mind is the “Plastic Power” amplifier module described in Features • Output voltag e adjustable • High power ca pability • Fuse protected • Under voltage cutout • Overcurrent p rotection • Fan cooled • Over-temperat ure cutout • Power indicat ors the April 1996 issue of Silicon Chip. This module requires a ±57V supply and is capable of delivering 175W into a 4Ω load or 125W into 8Ω. Two of these modules (for stereo) would provide an excellent hifi amplifier system for your car. That said, the choice of amplifier module is not restricted to any specific type, as we have catered for a wide range of supply options. However, the two modules in a stereo pair must be Fig.1: block diagram of the DC-DC Converter. It uses a switchmode driver stage to produce pulse width modulated (PWM) signals and these are used to drive complementary Mosfet switching stages. These stages in turn drive step-up transformer T1. Its secondary output is then fed to a bridge rectifier and filter capacitor stages to develop the plus and minus DC output rails. capable of operating from a common supply voltage. The amplifiers can be rated for any power, provided that the total power drawn from the DC-DC Converter is less than 600W. This final restriction does not mean that a single 600W amplifier or two 300W amplifiers can be powered by the converter. We must take amplifier efficiency into account and all amplifiers draw more power than they can deliver into a load. In theory, the maximum efficiency of a class B amplifier stage is 78.5% but this does not include the power dissipated by the quiescent current. In practice, the average power amplifier module will be about 60% efficient at full power. This means that only 60% of the power drawn from the converter will be supplied to the load. This in turn sets the maximum amplifier power rating to about 60% of 600W, or 360W total. If two amplifiers are used, then each one should be rated at no more than 180W. Physical arrangement As can be seen from the photos, the 600W DC-DC Converter is quite large. It is built into a two-unit high rack-mounting case and would normally be installed in the boot or, if space permits, under a seat. The unit is fan cooled to keep the components within their heat ratings and this will have some bearing on the final mounting arrangement, as the air vents must be kept free of any restrictions. The only external inputs are from the battery and the igni­tion switch, while the unit provides +V, -V and GND connections to the power amplifiers. Heavy duty cables are used for the battery supply connections and these are a necessity since the unit can draw up to 63A. Heavy duty wiring is also used for the power supply outputs to the amplifier modules. Three front-panel LEDs (Power, Output + and Output -) are used to indicate the status of the converter. The power LED simply indicates when the converter is switched on, either via the ignition or a separate switch. The two remaining LEDs indicate that the plus and minus amplifier supply rails are present. Basic principle The basic principle of the DC-DC converter is really very simple. It works by alternately switching the 12V battery supply to each half of a centre-tapped transformer primary. The result­­ing AC waveform is then stepped up by the transformer secondary and then rectified and filtered to provide the plus and minus supply rails. To achieve high efficiency and reduce the number of bulky components, the circuit operates at a switching frequency of about 22kHz. This high frequency allows us to use a ferrite transformer rather than a bulky ironcored type. The circuit also uses highspeed power Mosfets to switch the transformer and fast recovery diodes for the rectifiers. Power Mosfets were used because they are very fast and have low switching losses. In addition, power Mosfets have a positive temperature coefficient which means that they automatically “throttle” back if the output stage starts to overheat. In addition, the circuit incorporates comprehensive protec­ tion facilities. These include low-voltage cutout, current over­ l oad protection and over-temperature cutout. The low-voltage cutout is a particularly useful feature. In effect, the converter circuit monitors the battery voltage and if it drops below a certain level, the converter switches itself off. This not only saves you from the inconvenience of a flat battery but is also necessary to protect the Mosfets. To explain, a Mosfet is turned on by applying a voltage to its gate. If this voltage is too low, the Mosfet will not fully conduct and this can lead to excessive power dissipation and device failure. The current overload protection circuitry operates at two levels. First, there is a 63A fuse in the supply line which will blow if there is a drastic fault in the converter itself. Second, the circuitry features inbuilt current limiting to provide pro­tection against output short circuits. The accompanying specifications panel shows the performance of the converter. Note that its efficiency is better than 80% at full rated output. Block diagram Fig.1 shows the block diagram of the DC-DC Converter. As mentioned above, it uses a centre-tapped step-up transformer which is driven by Mosfet transistors. The secondary winding is also centre-tapped and is fed to bridge October 1996  33 WHY A CONVERTER IS NEEDED FOR HIGH POWER OK, so why do we need a converter to boost the supply rails for the power amplifier in the first place? Why not simply power the amplifier directly from the 12V battery? To understand this, we need to consider some basic theo­ry. First, we know that the power delivered into a load is the output voltage squared divided by the load resistance (ie, P = V2/R). Now let’s assume that we have a 12V battery which is charged to 14.4V. An amplifier powered from this battery can typically deliver a maximum output of 11V peak-topeak or about 3.9V RMS – see Fig.2. Thus, the maximum power which can be delivered into a 4Ω load from a single-ended configuration is about 3.8W (3.9 x 3.9/4). This can be increased by wiring two power amplifiers in a bridge configuration. If that is done, the output voltage supplied to the load is doubled and so the power output will be four times great­er at about 15W (which is still quite modest). All this assumes that the battery is actually delivering 14.4V. In practice, this only happens if the motor in your car is running and has had time to fully charge the battery. So in practice, the power outputs from single-ended or bridge connected amplifiers will be even less than the above figures. As a result, if we want high power, we need to either reduce the load resistance or increase the supply rails for the amplifier. However, a very low load resistance is impractical because the current in the amplifier output stages becomes exces­sive. This in turn causes high losses in both the amplifier and loudspeaker wiring. The efficient way to increase the power is to increase the voltage, rather than reduce the load impedance. This is because the power is proportional to the square of the voltage and only proportional to the inverse of the load impedance. This “square law” effect means that if we double the voltage, we quadruple the power. By contrast, if we halve the load impedance we only double the power. At the same time as halving the load resistance, we double the current which quadruples the losses. The only practical option is to increase the supply rails and that’s exactly what this DC-DC converter is designed to do. It can deliver supply rail voltages up to ±70V DC, so that you can run really high power amplifier systems (up to 180W per stereo channel). Fig.2: an amplifier powered from a 14.4V rail can typically deliver a maximum output of about 11V p-p or about 3.9V RMS (note: the scope shows a slightly low RMS figure). This means that the maximum power which can be delivered into a 4Ω load from a single-ended configuration is about 3.8W or about 15W from a bridged configuration. 34  Silicon Chip rectifier and filter capacitor stages to develop the plus and minus DC output rails. Mosfets Q3-Q5 drive the top half of the step-up transform­er, while Q8-Q10 drive the bottom half. These in turn are driven by a switchmode circuit which has feedback applied from the DC output. This feedback circuit acts to reduce the width of the pulses applied to the Mosfets if the DC voltage rises above a preset value. Conversely, the pulse width from the driver circuit increas­es if the output voltage falls below the preset value. Note that the two Mosfet driver circuits are switched in antiphase, so that when one half of the winding is conducting, the other is off. The resulting primary drive is stepped-up in the secondary windings. Apart from the voltage feedback which maintains a constant output voltage regardless of load, the switch­ mode driver circuit also detects overcurrent conditions via resistor Rsc. If overcur­rent occurs, the pulse width drive to the Mosfet gates is re­duced. Note that the voltage across Rsc is amplified by over-current amplifier IC3. Circuit details Fig.3 shows the final circuit for the 600W DC-DC Converter. It’s based on a dedicated switchmode IC, the TL494 (IC1). This device contains all the necessary circuitry to gener­ate complementary square wave outputs at pins 9 and 10 and these drive the gates of the Mosfets via buffer stages. The device also contains control circuitry to provide output voltage regulation and low voltage dropout. Fig.4 shows the internal circuitry of the TL494. It is a fixed frequency pulse width modulation (PWM) controller contain­ing a sawtooth oscillator, two error amplifiers and a PWM com­ parator. It also includes a dead­time control comparator, a 5V reference and output control options for push-pull or single ended operation. Fig.3 (left): the final circuit is based on a TL494 dedicated switchmode IC (IC1). It generates complementary PWM signals at pins 9 & 10 and these drive the parallel Mosfet switching devices via buffer stages. IC3 monitors the voltage across RSC to provide current overload protection. October 1996  35 Fig.4: this block diagram shows the internal circuitry of the TL494 PWM controller. It includes a sawtooth oscillator, a PWM comparator, a dead-time control comparator, two error amplifiers and a 5V reference. Emitter followers Q1 & Q2 provide the complementary PWM output signals at pins 9 & 10. The PWM comparator generates the variable width output pulses by comparing the sawtooth oscillator waveforms with the outputs of the two error amplifiers. By virtue of the diode gating system, the error amplifier with the highest output vol­ tage sets the pulse width. Dead-time comparator The dead-time comparator ensures that there is a brief delay before one output goes high after the other has gone low. This means that the outputs at pins 9 and 10 are both low for a short time at the transition points. This so-called “dead-time” is essential since without it the Mosfets driving one half of the step-up transformer would still be switching off while the Mosfets driving the other half were switching on. As a result, the Mosfets would be destroyed as they would effectively create a short circuit across the 12V supply. Fig.5 shows the pin 9 and pin 10 output signals at the maximum duty cycle. Note that each output is high for only 44.7% of the time, indicating that there is 5.3% dead-time. One of the error amplifiers in IC1 is used to provide the under-voltage cutout feature. This is achieved by connecting its pin 2 (inverting) input to the +12V rail via a voltage divider consisting of two 10kΩ resistors. The non-inverting input at pin 1 connects to SPECIFICATIONS Supply voltage ......................................................................... 10-14.8VDC Maximum output power .............................................................600W RMS Maximum input current ....................................................... 63A continuous Standby current ................................................300mA (mainly fan current) Output voltage ....................................................................±70V maximum Efficiency at full load ..........................................................................>80% Overcurrent cutout .......................................................... 80A peak approx. Over-temperature cutout .....................................................................80°C Under-voltage cutout ............................................................................ 10V 36  Silicon Chip IC1’s internal reference at pin 14 via a 4.7kΩ resistor. When the voltage at pin 2 drops below 5V (ie, when the battery voltage drops below 10V), the output of the error ampli­fier goes high and the PWM outputs at pins 9 & 10 go low, thus shutting the circuit down. The over-temperature cutout operates in a similar manner. The sensing device is thermal cutout device TH1 and this is mounted on the main heatsink along with the Mosfet output transistors. As shown on Fig.3, it is connected in series between the voltage divider on pin 2 and the positive supply rail. If the heatsink temperature reaches 80°C, TH1 opens and so the circuit shuts down by switching the PWM outputs low as be­fore. Note the 1MΩ resistor between the non-inverting input at pin 1 and the error amplifier output a pin 3. This provides a small amount of hysteresis so that this particular error amplifi­er operates as a comparator. The second error amplifier in IC1 is used to control the output voltage of the converter and provide current limit protec­tion. This amplifier has its inputs at pins 15 and 16. Let’s consider the voltage regulation role first. In this case, the feedback voltage is derived from the positive side of the bridge rectifier and is attenuated using a voltage divider consisting of VR1, a 47kΩ resistor and a 10kΩ resistor to ground. The resulting voltage is then fed via D7 to pin 16 of IC1 and compared to the internal 5V reference which is applied to pin 15 via a 4.7kΩ resistor. Normally, the attenuated feedback voltage should be close to 5V. If this voltage rises (due to an increase in the output voltage), the output of the error amplifier also rises and this reduces the output pulse width. Conversely, if the output falls, the error amplifier output also falls and the pulse width in­creases. The gain of the error amplifier at low frequencies is set by the 1MΩ feedback resistor between pins 3 & 15 and by the 4.7kΩ resistor to pin 14 (VREF). These set the gain to about 213. At higher frequencies, the gain is set to about 9.5 by virtue of the 47kΩ resistor and 0.1µF capacitor in series across the 1MΩ resis­tor. This reduction in gain at the higher frequencies prevents the amplifier responding to hash on the supply rails. The 27kΩ resistor and .001µF capacitor at pins 6 and 5 respectively set the internal oscillator to about 44kHz. This is divided using an internal flipflop to give the resulting complementary output signals at pins 9 & 10, which means that the resultant switching speed of the Mosfets is 22kHz. Pin 4 of IC1 is the dead-time control input. When this input is at the same level as VREF, the output transistors are off. As pin 4 drops to 0V, the dead-time decreases to a minimum. At switch on, the 10µF capacitor between VREF (pin 14) and pin 4 is discharged. This prevents the output transistors in IC1 from switching on. The 10µF capacitor then charges via the 47kΩ resistor and so the duty cycle of the output transistors slowly increases until full control is gained by the error ampli­fier. This effectively provides a “soft start” for the converter. Resistor R1 has been included to provide more dead-time if necessary. It prevents the 10µF capacitor from fully charging to 5V and this increases the minimum dead-time. R1 (1MΩ) is only necessary in those rare circumstances when current limit­ing occurs at full load. This is indicated by a buzzing sound from the transformer. Current limiting The current limiting circuit is based on op amp IC3. This is wired as a non-inverting amplifier with a gain of 101 and is used to monitor the voltage Fig.5: these waveforms show the complementary pulse signals from the TL494 PWM controller at the maximum duty cycle. Note that one output always switches low before the other switches high and that each output is high for only 44.7% of the time, indicating a 5.3% dead-time. Fig.6: these waveforms show the converter performance when there are transient load changes from no-load to almost full load. The con­verter is supplying the power rails to an amplifier which is driving a 4-ohm load at 317W when the signal is on (this corresponds to more than a 500W load on the converter when efficien­cy is taken into account). The middle trace shows the 100Hz tone burst input signal, the top trace is the positive supply rail for the amplifier (20V/div) and the lower trace is the negative supply rail (20V/div). Note the small voltage droop and minimal overshoot when the load is removed. developed across resistor RSC. The output of IC3 in turn drives the pin 16 input of the second error amplifier in IC1 via diode D8. RSC is actually a short length of wire with a value of about 0.7mΩ. It is connected between the commoned Mosfet sources and ground, which means that all the transformer primary current flows through it. October 1996  37 Despite the heavy-duty nature of the circuit, the 600W DC-DC Converter is easy to build since virtually all the parts are installed on a single large PC board. A large heatsink and a fan at one end help keep things cool. As long as the current through RSC remains below 79A, the output of IC3 will have no affect on the operation of the error amplifier. However, if the current attempts to rise above 79A, the output of IC3 will rise above 5.6V and so the voltage applied to pin 16 of IC1 will rise above 5V. As a result, the output of the error amplifier rises and this reduces the output voltage and thus the current. Complementary outputs The complementary PWM outputs at pins 9 & 10 of IC1 come from internal emitter follower transistors. These each drive external 10kΩ load resistors. They also each drive three paral­leled CMOS non-inverting buffer stages (IC2a-c and IC2d-f). These in turn drive transistors Q1 and Q2 on one side of the circuit and Q6 and Q7 on the other side. Thus, when pin 10 goes high, Q1 turns on and drives the paralleled gates of Mosfets Q3-Q5 via a 4.7Ω resistor. Note that each Mosfet gate is connected via a 10Ω “stopper” resistor to minimise any parasitic oscillations which may otherwise occur while the paralleled Mosfets are switching on 38  Silicon Chip and off. When pin 10 subsequently goes low, Q2 switches on and quickly discharges the gate capacitance of Mosfets Q3Q5, thus switching them off. Pin 9 then switches high at the end of the dead-time period and Q6 switches on Q8-Q10 to drive the other half of the transformer primary. Q1, Q2, Q6 & Q7 have been included to ensure that the Mosfets are switched on and off as quickly as possible. This minimises the time that they spend in the linear region where they dissipate high power. Zener diodes ZD2 and ZD3 ensure that the Mosfets are pro­tected against switching spikes generated by the transformer. If the voltage between the drain and gate of any Mosfet rises beyond the zener breakdown voltage plus the gate threshold voltage, that Mosfet switches on to suppress the voltage. Diodes D1 and D2 prev­ent the gate signals from shorting to the drains via the zener diodes. Note the 1Ω resistors connected between the cathodes of ZD2 & ZD3 and the drains of the Mosfets. These prevent large currents from flowing in the PC board tracks. The high-current paths between the drains of the Mosfets and the transformer primary are run using heavy-duty wiring. Note also the six 10µF capacitors between the centre-tap of the transformer primary and the commoned Mosfet sources. These capacitors are there to cancel out the inductance of the leads which carry the heavy currents to the transformer. The transformer, T1, is a relatively small ferrite-cored unit designed to be driven at high frequencies. The primary winding is made up of flat copper sheet with two turns on each side of the centre-tap. The secondary uses conventional enamelled copper wire with the number of turns set to provide the required output voltage. In summary, the power Mosfets in each phase of the circuit alternately switch each side of the transformer primary to ground, so that the transformer is driven in push-pull mode. When Q3-Q5 are on, the 12V supply is across the top half of the prim­ary winding, and when Q8-Q10 are on the supply is across the bottom half. This alternating voltage is stepped up by the transformer secondary and applied to bridge rectifier D3-D6. This produces positive and negative supply rails with respect to the secondary centre tap. These rails are then filtered using four 2200µF capacitors. PARTS LIST 1 PC board, code 05308961, 310 x 214mm 1 2-unit rack case (without rack front panel) 1 front panel label 1 fan heatsink, 214mm long x 69mm wide with fins on one side cut off 1 12V DC fan, 80 x 80 x 24mm 2 Clipsal BP165C18 brass link bars 1 63A (A3 type) cartridge fuse (F1) 1 Neosid 17-745-22 iron powdered ring core (L1) 1 Philips ETD49 transformer assembly with 3F3 cores (T1) (2 cores 4312 020 38041, former 4322 021 33882, 2 clips 4322 021 33922) 3 5mm LED bezels 1 5mm red LED (LED1) 2 5mm green LEDs (LED2, LED3) 6 PC stakes 2 2AG fuse clips 1 1A 2AG fuse (F2) 4 TOP3 insulating washers 4 TO-220 insulating washers 10 insulating bushes 2 6-10mm cable glands 1 80°C cutout switch (TH1) 1 100kΩ horizontal trimpot 1 2-metre length of red 4GA cable (length dependent on installa­tion) 1 2-metre length of black 4GA cable (length dependent on in­stallation) 1 6-metre length of 3.5 sq. mm multi-strand wire (length dependent on installation) 1 55mm length of 3.5 sq. mm multi-strand wire (Rsc) Inductors L1a and L1b limit the peak transient currents in the diodes. Note that L1a and L1b are wound as a compensated choke on a common ferrite core, so that the flux generated by L1a’s winding is cancelled by the flux generated by L1b. This prevents the core from saturating. LEDs 2 and 3 connect across the positive and negative output rails respectively, to indicate that these rails are present. The 6.8kΩ resistors limit the LED current. Voltage regulation is achieved by sampling the positive supply rail and 1 1.5-metre length of 3.3 sq. mm black multi-strand wire (for T1) 1 400mm length of 3.3 sq. mm red multi-strand wire (for T1) 1 1-metre length of 1.78mm dia. solid core insulated wire 1 1.2-metre length of blue hookup wire 1 400mm length of red hookup wire 1 400mm length of green hookup wire 1 2-metre length of red hookup wire for ignition connection (length dependent on installation. 1 1.2-metre length of 1.5mm dia. ENCU (for L1) 1 6-metre length of 1.25mm dia. ENCU (for T1 secondary) 1 150mm length of 0.8mm tinned copper wire 4 large eyelets for 8mm dia. wire with 12mm hole 6 eyelets for 3mm dia. cable and 3mm screws 3 eyelets for 4mm dia. cable and 4mm screws 4 1/8th inch x 9mm long cheesehead screws 10 3mm x 15mm screws 24 3mm x 6mm screws 3 3mm x 9mm screws 13 3mm nuts 6 3mm star washers 4 9mm tapped standoffs 7 15mm tapped standoffs 3 4mm dia. x 15mm screws plus nuts & star washers 2 8mm dia. x 15mm bolts, nuts & washers 1 12mm dia. x 15mm bolt & nut 1 copper strip, 75 x 18 x 0.6mm feeding this back to pin 16 of IC1 via a voltage divider network. The internal error amplifier on this pin then controls the PWM comparator to provide voltage regulation, as described previously. Trimpot VR1 allows the output voltage to be set to the desired value. Power supply The 12V supply from the car battery connects via heavy duty cable and fuse F1 to the centre tap of T1. Because of the high currents involved, there is no on/off switch. 1 copper strip, 295 x 41 x 0.315mm 10 small cable ties Semiconductors 1 TL494 switchmode controller (IC1) 1 4050 CMOS buffer (IC2) 1 LM358 dual op amp (IC3) 2 BC338 NPN transistors (Q1,Q6) 2 BC328 PNP transistors (Q2,Q7) 6 BUK436-100A Mosfets (Q3-Q5, Q8-Q10) 4 1N914, 1N4148 signal diodes (D1,D2,D7,D8) 4 MUR1560 15A 600V fast recovery diodes (D3-D6) 1 16V 1W zener diode (ZD1) 2 47V 400mW zener diode (ZD2,ZD3) Capacitors 4 2200µF 100VW electrolytic (Philips 2222 050 19222) 1 100µF 16VW PC electrolytic 2 10µF 16VW PC electrolytic 6 10µF 100VW MKT polyester (Philips 2222 373 21106) 2 0.47µF MKT polyester 4 0.1µF MKT polyester 1 .0056µF MKT polyester 1 .001µF MKT polyester Resistors (0.25W 1%) 2 1MΩ 3 4.7kΩ 1 470kΩ 1 2.2kΩ 2 47kΩ 7 10Ω 1 27kΩ 2 4.7Ω 6 10kΩ 6 1Ω 4 6.8kΩ 0.5W Miscellaneous Solder, insulating tape, heat­shrink tubing, battery termi­nals Power for the rest of the circuit is supplied via the igni­tion switch (or a separate switch could be used). LED1 indicates the presence of the 12V rail and is supplied via a 2.2kΩ resis­tor. In addition, a 12V fan is wired directly across the supply and this runs continuously whenever power is applied. Finally, a 10Ω resistor and 16V zener diode (ZD1) provide protection against transient voltages for the low current circuitry. That’s all we have space for this month. Next month, we shall give the SC full construction details. October 1996  39 SERVICEMAN'S LOG To tip or not to tip – a few tips Ever wondered what happens to equipment which is written off as not worth repairing? Typically, it would be stripped for any worthwhile spares and what was left would go to the tip. But not always. Yes, sometimes there is the temptation to try to salvage an item, even if obviously uneconomical at a commercial level and there is a risk that the attempt may not be successful. One may spend many hours searching for an elusive – possibly intermittent – fault and not find it. Or, if a fault is found, it may turn out to be a component which, for one reason or another, cannot be replaced. But that’s the risk one has to take. I encountered two such exercises recently which illustrate this situation very clearly. One is from my own bench and one is a colleague’s experience. My own story involves what the makers (Grundig) simply call a receiv- er – Receiver 3000 (GB) – although it would be better described as a tuner/ amplifier combination. It consists of an elaborate stereo amplifier plus an AM/ FM stereo tuner, the latter featuring press-button tuning, as well as continuous tuning and a “Digital Frequency Indication Module”. There are several input sockets to take external signals of various kinds and an appropriate switching system to go with it. It also features both automatic and manual muting systems, and these operate when switching between stations or other signal sources. All-in-all, it is a most attractive unit and this example was in good physical condition. So what was the story behind it? It belonged to a colleague and apparently had had a rather che­quered service history, having previously belonged to someone else. But now, as my colleague summed it up, it didn’t go and he had earmarked it for the tip. When I expressed regret that such a nice unit was to meet such a fate, my colleague responded in­stantly: “take it if you want it – you can send it to the tip as easily as I can” (he is not given to undue optimism). And so I took it. I wasn’t sure what I was going to do with it, assuming I could fix it. For the moment, it was mainly a challenge. A nasty mess At the first opportunity I put it up on the bench but it was dead. I pulled the covers off and this revealed a rather nasty mess. There were three fuses, one of which was obviously the mains fuse while the other two were on the sec­ondary side of the power transformer. All three were blown. In addition, there was a swag components which had been unsoldered. Someone had really gone to town on it. Fig.1: the power supply circuitry in the Grundig 3000. Mains fuse Si.I is at extreme right, while fuses Si.1 and Si.2 are to the left of the transformer. T2 and IC1 are at the extreme left. 40  Silicon Chip I decided the only logical approach was to put everything back and start from taws. I re-soldered all the components, then looked at the fuse situation. The mains fuse, designated as Si.I was marked 2A and the other two were designated as Si.1 and Si.2. Si.1 was marked as 250mA and Si.2 as 1.25A. (No, there weren’t two Si.1s; the mains fuse designation used a capital “I”. Talk about planned confusion!) I replaced the mains fuse and Si.2 and switched on. Splat! Si.2 blew immediately. I realised then that it would be fruitless to go on without a service manual or, at least, a circuit. I rang Southern Cross Electronics, the local agents for Grundig, and asked about a manual. There was some mucking about here. I had to fax a request and they replied a week later quoting $25 for a circuit photostat. I placed an order and it ar­rived after another week. There were 10 A3 sheets in all. Six were circuit diagrams taken from what were originally two large foldout sheets. The rest were parts lists, etc. After dispensing lots of sticky tape and patience, I eventually reconstructed the foldout sheets, each of which turned out to be 1.2 metres long! After all that, I started over again. I tackled the Si.2 fuse circuit first. Si.2 is between a 12V secondary winding and a full-wave bridge rectifier (GL2) which generates a 15V rail. This is then applied to a voltage regulator (IC1) to provide a 5V rail. I suspected IC1 and I was right but in more ways than I expected. First, it was short circuit, which didn’t surprise me. What did surprise me was that it turned out to be a bodgie com­ponent. It was not a 5V regulator at all but, in fact, a 12V unit. Just why this had been changed and by whom remains a mys­tery. It had probably failed because it was the wrong type, par­ticularly as it was working directly into a 5V zener diode (although the zener’s role is something of a mystery in itself). Anyway, I replaced the regulator with the correct type, fitted another fuse and switched on. This time the fuse held and we had a 15V rail and a regulated 5V rail, with no signs of distress. So far, so good. Now to fuse Si.1. This is part of another supply rail which is derived from a 63V transformer winding. This drives bridge rectifier GL1 which in turn drives another voltage regulator based on T2. T2 is not a regulator within itself, however. It is a Darlington pair, housed in a TO-220 flat pack encapsula­tion, and takes its reference from external zener diode D4. This arrangement provides a 55V rail. When I switched on there was an immediate response – R8, a 47Ω 1W resistor in the collector line to T2, began to overheat. T2 was the obvious suspect but an ohmmeter check failed to reveal anything wrong. Nevertheless, I unsoldered it and pulled it out. And there was the fault in full view – the insulating washer between the heatsink (collector) and chassis had punctured. And it was obviously a voltage sensitive breakdown, immune to the low voltage of the ohmmeter. I fitted a new washer and tried again. This time Si.1 held and I had October 1996  41 Serviceman’s Log – continued tran­ sistors form part of the muting circuit. When an appropriate voltage is applied to their bases, they turn on and mute the tuner signals into the amplifier. I confirmed this operation by the simple expedient of shorting the base of each transistor to chassis in turn, whereupon I had normal output from the amplifi­ers. So, the problem was really quite simple – the “muting” voltage (or possibly some other voltage) was being applied to the bases of these transistors and turning them on, even though the muting switch was off. All I had to do was find out what was causing this. Complicated circuits a 55V regulated rail. I had rather hoped that the thing would burst into life now but it didn’t. Granted, some of the LED displays and other lights were now on but the frequency display was dead. A healthy buzz I wasn’t sure of the significance of this but decided to ignore it for the moment and concentrate on getting the sound path working. I pushed a scrap of bare wire into the various amplifier input DIN sockets and, eventually, was rewarded with a healthy buzz from each of the speakers. So, the amplifiers were working – we were making progress. But there was no sign of life from the tuners. Initially, I suspected that the frequency display failure could be a symptom of a major failure in the tuner section, which was rather a nasty thought. But then I noticed something else. If I turned the volume control fully up, I could detect faint sound when I pressed some of the channel selector buttons. So, was the tuner working but unable to pass its signals to the amplifier? After poring over the FM tuner circuit on the other foldout sheet, I pinpointed the stereo outputs as being, initially, at transistors T5 and T6. From there, the signals went to T8 42  Silicon Chip and T9 and from there – on the other sheet – to the switching circuits ahead of the power ampli­fiers. One of the most useful pieces of test gear I have is a small audio amplifier which is equipped with a probe. I use it to trace audio signals and track down losses and distortion. And this quickly confirmed my suspicions; there were strong healthy signals at both T5 and T6 and also at T8 and T9. OK, over to the switching circuits. The tuner stereo sign­als come into the switch bank on terminals 12A1 and 12A3 and emerge on terminals 4A1 and 4A3. From there, they go to the amplifiers via switch position A3/B3 and plug socket SA10. Only they didn’t. The signals were present at the outputs of transistors T8 and T9 but not at the 12A1 and 12A3 switch input terminals. This drew my attention to another part of this circuit. Although the tuner signals are routed through the switches to the amplifiers they also go directly to another pair of transistors, also designated as T8 and T9, just to make it harder. These two transistors are connected between the audio lines and chassis in such a way that, if they are conducting, they pull the audio lines down to chassis. In greater detail, these But what had gone before was merely routine compared with what lay ahead. It was a real round-theworld-for-sixpence job. These circuits are drawn using what I call draughtsmen’s cables; long thick black lines into which individual lines disappear, identified only by a number. One has to follow the line until the number is found, usually on another sheet. And as likely as not, after a small digression into a piece of circuitry, it will go back into the cable on its way back to the first sheet. Believe me, it’s easy to go bonkers trying to trace a circuit like this. Thankfully, I didn’t go bonkers or at least I don’t think I did. I won’t bore readers with all the details of my circuit tracing. In any case, without the circuit, which is much too large to reproduce here, any such description would be meaning­less. I actually lost count of the time I spent on it and as readers will appreciate, there is no way one could ever charge a customer for this work. In summary, I first tracked down the manual mute switch (i1/i2) and backtracked from there to an 8-pole switch which is used to select the FM preset channels. Only seven poles of this switch are used for the actual channel selection – the eighth pole is in the muting circuit I had been tracing. And its func­tion is to momentarily activate the muting function whenever any of the channel selection buttons is pressed, thus masking any clicks, bangs, or crackles, generated in the process. It was here that I struck oil – the switch was faulty. Not only were the muting contacts jammed closed but the whole mechan­ ism was giving trouble. In a sense, I had already been made aware of this. I had noticed that, when a button was pressed, it often took several attempts to get it to lock into position. However, I had previously put this fault to one side, as something to be attended to when the electrical problems were solved. In fact, it was causing one of those problems. As a practical short term solution I removed pin 1 from the plug assembly connecting to this switch, which permanently disa­ b led the muting contacts. I could still mute the system via the aforementioned manual mute switch and the auto-muting, on weak stations and between stations, still functioned correctly. The digital readout Putting the switch problem on hold for the moment, I turned my attention to the only other remaining problem: the Digital Frequency Indication Module. This is in a small metal box and, on removing the covers, I was rewarded with the sight of numerous dry joints – more than I could be bothered to count, in fact. How many more less obvious ones there were I had no idea. To solve the problem, I finished up resoldering every joint but it was worth it. The thing came to life and worked perfectly. And that’s how things now stand. I consider it a pretty good effort, especially as I had done what, apparently, those before me could not. So, what about the switch? Should I repair it? No way; it is made up of numerous tiny pieces, many of them under spring tension. Tackle that lot and there would be bits flying every­ where. What about fitting a new switch? That’s the logical answer but it’s no longer available off the shelf and finding one may be difficult. It was most likely specially designed for this set, which is probably now about 10 years old. The agents are currently checking to see if one can be obtained from the manufacturer. And that’s about the best I can hope for. Scrounged video recorder My second story, from a colleague, is about a device he scored from another colleague – a National NV-180 portable video recorder. Because its fault had proved elusive and so was poten­tially expensive, the customer had written it off and so it had been sitting in a corner of colleague No.2’s shop for about a year. But it left him in a quandary. He wasn’t keen to spend more time on it, yet felt guilty about sending it to the tip. So, when my colleague showed an interest, a deal was struck. My colleague’s interest was understandable. He has a per­sonal interest in video cameras and associated portable recorders. The NV-180 was originally supplied with the models A1, A2 and similar video cameras. Although bulky by modern standards, it was regarded as a major breakthrough in its day, weighing only 2.3kg without the battery. Apart from its portable role, it is an attractive unit in its own right, featuring a large multi-function digital display, slow motion and variable speed stop motion. Its accessories include an AC adaptor, a tuner and a remote control unit. Unfortunately, after a year, the original fault details were rather vague. All that my colleague could find out was that it was something to do with tape speed and a possible faulty capstan motor. As a result, he had to start from scratch. However, before presenting his story, a brief review of the transport control system may help the reader to follow it more readily. In considering the playback mode, it is obvious that the speed of the drum and the capstan – and therefore the tape – must be held constant, at a speed very close to the recording speed. During recording, the speed is controlled by the incoming signal but there is no such reference during replay; the system is on its own. In this mode, it is controlled by an internal reference; eg, a crystal. The capstan motor itself is equipped with a pulse generating device, typically a sensing head (inductive or capaci­tive) mounted close to a rotating wheel or magnet. The resulting pulses are fed to a servo system which com­pares them with the reference (crystal) frequency. This system then generates error correction voltages which hold the speed of the motor constant. A similar system is used to control the drum motor speed. But that is only part of the story. As well as running at the correct speed, the system must also be in correct phase. The drum must be positioned so that a head, when it meets the tape, exactly engages the beginning of a track. And not just any track. If we are talking about head No.1, then it must engage a track recorded by head No.1. It’s a similar story for head No.2. The way in which this is done is quite straightforward. When a tape is being recorded, square-wave reference pulses, derived from the vertical sync pulses, are recorded every 40ms (alternate field) on a control track on the lower edge of the tape. These are used to provide the aforementioned phase control and also the switching between heads. OK, here’s my colleagues story, as he tells it. Donald Duck sound My mate had been right about there being something wrong with the capstan speed; it was fast, much too fast. As a result, the sound had gone “Don­ ald Duckish” and there were noise bars running up the screen. But I didn’t buy the idea of a capstan motor fault; capstan motors normally either work or they don’t. Perhaps they might run slow but I’ve never ever seen one run fast. The first thing I did was to give the machine a good once over mechanically. This involved a routine clean, belt tension and pinch roller checks, and a check of the pause and search functions. I found nothing wrong. I then checked the main supply rails. There was 5V at pin 13 of IC2505 and 9V at pin 14 of plug FJ24 – exactly as marked. My next step was to check the electrolytic capacitors around the capstan motor drive, mainly C2532, C2533, C2534, C2535. These were checked by simply bridging them with another unit of the same value but this had no effect. It was time to put the CRO to work and check pulses. Unfor­tunately, the compact nature of the device means that servicing it can be difficult. For example, I needed to check the Servo/ Power PC board which mounts hard behind the front panel. In order to gain access to both sides, it is necessary to remove the front panel and then mount the board in a special jig – Service Connector Jig (VFK0275) – which sits it at an angle of 45 de­grees, while maintaining all October 1996  43 Serviceman’s Log – continued connections. Fortunately, I have such a jig. I started by checking for the reference (FG) pulses generated by the capstan motor and the CRO confirmed that these were correct. The FG pulse (FG1) appears at terminal 4 of the capstan motor block and, via an allover-the-place path, finishes up on pin 25 of IC2001 (AN3615K), which is also test point TP2015. I traced the pulses right through to this test point. Next, I checked the internal reference (clock) frequency to which the drum and capstan are locked. This is a 4.43MHz crystal oscillator which applies a 1.2Vp-p signal to pin 26 of IC2001. And as a matter of routine, I also checked the control pulses from the Audio Control Erase (ACE) head, although these are basi­ cally phase rather than speed control pulses. These were present and checked through to pin 9 of IC2001. So, we had FG1 pulses from the capstan, clock frequency pulses from the crystal and control pulses from the control head, all being fed to IC2001. But for some reason, the capstan motor was out of control and running free. What followed was a laborious check of various voltages and waveforms on the Servo/Power PC board. This was at times quite difficult but it eventually lead to pin 4 of IC2001 (test point TP2004) where there should have been a 4.43MHz 50mV p-p waveform. However, this waveform was missing; nor was there any voltage on this pin, shown on the circuit as 3.2V. The upshot of all this was that I concluded that the IC was faulty and ordered a new one on spec. And that was a big mistake. When it arrived I found I’d been billed for $93 – yes $93, for one IC. Move over Mr Kelly. There was worse to come. It was a small IC, with closely spaced pins, and mounting it on the double-sided PC board was not easy. The job took a long time – and achieved absolutely nothing. The fault was there exactly as before. Words failed me – well, in print anyway. The real fault I had to find the real fault now. Taking a closer look at the circuit around the IC, I noted that pin 4 44  Silicon Chip was internally connected to two functions: (1) a playback control amplifier (P.B. CTL AMP); and (2) a tracking mono multivibrator (TRACKING MMV), the latter connecting to pin 13. Pin 13 then goes to the tracking control. It was supposed to be at 0.6V – or higher – but was in fact at 0V. I hadn’t checked this voltage before, due to the difficult access. Nor had I previously checked the tracking control. I checked it now; it wasn’t working. I traced the circuit through to the tracking control (R6562, 100kΩ). This pot is panel-mount­ ed and is connected via a short length of 3-conductor ribbon to connector P205. And the one which ultimately connects to pin 13 was broken where it joined the connector. It wasn’t immediately obvious, however, as it is normally obscured and the other two conductors held the ribbon in place. Of course that was it, although how it happened is a puz­ z le. I can’t imagine any kind of user abuse which would cause it. More likely, I suspect, the unit had originally suffered from a quite different fault. The serviceman had fixed this but had broken the lead in the process. And the resulting symptoms had proved too tricky and confusing for the fault to be traced. In fact, it is not immediately obvious just how the track­ing control circuit upset the speed. But, as far as I can see, the loss of a connection to pin 13 was sufficient to upset the whole capstan servo function within the IC. If only I had checked the tracking control first off. And that’s my colleague’s story. My first reaction is to quote another of my colleagues who, in such situations, was wont to remark, “that’s a decent sort of an oops”. Which it was and I’m glad I didn’t make it. But that’s not to say that I might not have in similar circumstances. The bright side On the bright side, my colleague scored a very nice machine for the price of the IC, plus his labour. Not bad, really and he does have a spare IC in his drawer. But I feel the moral of both stories is obvious; think very carefully before you tackle an undertaking like this. And be prepared for a lot of work – and SC the risk of failure. 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 Last month, we introduced our new Infrared Stereo Headphone Link, which allows you to settle back and enjoy your favourite music, the TV or other audio source without being tied down by a cord. This month, we complete the project with the receiver section. Infrared stereo headphone link PART 2 – THE RECEIVER Fig.1 (page 55) shows the circuit of the infrared stereo receiver. As with the transmitter, it follows some of the circuit techniques used in stereo FM transmission and reception. A photodiode, PD1, detects the IR pulse stream from the transmitter and produces DC current pulses which are fed directly to op amp IC1a, a current-to-voltage converter. IC1a is AC-coupled to op amp IC1b which has a gain of 6.8. The amplified signal is fed to IC2, an LM311 comparator. Its output is an 88kHz 6V peak-to-peak square wave when there is no audio modulation from the transmitter and an 88kHz PWM stream when audio modulation By RICK WALTERS October 1996  53 TL062 for IC1 and a TL064 for IC6 because of their low current consumption, an important factor in a battery operated circuit. The more common TL072 and TL074 types can be used instead but the current consumption is appreciably higher. Left channel identification There are two PC boards in the infrared receiver but only one is visible in this photo. The IR receiver LED is underneath the top board, at the focal point of the lens assembly on the lefthand side. is transmitted. This waveform contains all the audio information that was encoded by the transmitter; all we have to do is decode it. This is done in two steps. First, we recover the signal in mono. To produce the mono signal, all we need to do is to connect a low pass filter at the output of comparator IC2. To produce the stereo left and right channels though, we need to de­ multiplex the audio by switching it to the left and right channels in sequence, using a square wave with the same frequency and phase as the multi­plexing frequency in the transmitter. Phase locked loop This is where the phase locked loop, IC4, comes into the picture. IC4 can be considered to be a square wave oscillator which is “locked” to an incoming reference frequency. Its output frequency will be the same as the transmitter’s but 90° out of phase and the filter components are selected so that it will not follow the modulation. To ensure an exact symmetrical square wave we run IC4 at double the received frequency; ie, at 176kHz. This is divided by two, using flipflop IC3a, to give an 88kHz square wave. This is divided by two again, by flipflop IC3b. In this case, the 18kΩ resistor and 100pF capacitor delay the clock signal to IC3b by 90° to ensure that 54  Silicon Chip its outputs are in phase with the incoming signal. The 44kHz outputs of IC3b, at pins 12 and 13, are used to switch the signal from IC2 to the right and left channels alternately using IC5, an HC4066 CMOS switch. This switching process is called “de­multiplexing” and is the reverse of the multi­­ plexing process in the trans­­mitter. The left and right channel signals appear at pins 1 and 11 of IC5, respectively. As there is a large amount of high frequency noise on the recovered audio signals, heavy filtering is required. To this end, we use a 4-pole filter which gives an attenuation rate of 24dB per octave, above 10kHz. For the right channel the first filter consists of the two 10kΩ resistors and .0012µF and .0018µF capacitors around op amp IC6a. The second filter involves the .0015µF capacitors in a similar configuration around IC7a, Q1 & Q2. There is identical filtering for the left channel, involving op amps IC6b, IC7b, Q3 & Q4. To compensate for the high frequency pre-emphasis which was applied in the transmitter we use the 1kΩ series resistor and the .022µF capacitor across each volume control to attenuate the upper frequency response. This is de-emphasis. By the way, we have specified a To establish which is the left channel we take the signal from the output of the left channel filter, IC6b pin 7, and feed it to two cascaded 10Hz bandpass filters, comprising op amps IC6d and IC6c. The 10Hz signal, if it is present in the left channel, will be amplified, clamped to ground by D1 and then will charge the 0.1µF capacitor at the gate of FET Q5, via D2. This will hold Q5 turned on and its drain will be almost at 0V. If the left channel signal has been switched to the right amplifier there will be no 10Hz signal present in IC6b’s output, thus the 10MΩ resistor will discharge the 0.1µF capacitor on Q5’s gate and the FET will turn off. This will allow the drain of Q5 to rise to the battery voltage (+6V) via the 47kΩ resistor. Because the set input of flipflop IC3b is connected to this point, the flipflop will be held set. This holds pin 13 of IC3b high, switching the input signal permanently to the left amplifier, thus allowing the 10Hz signal to be fed to the bandpass filters. The FET will turn on as described previously and the flipflop will begin to toggle again to give correct de­ multiplex operation. Due to the low frequency of the synchronising signal (10Hz) and consequently, the long time constants in the FET gate circuit, it may switch several times before it gets the phase right. Loss of infrared signal Since the audio signal is sent via an infrared beam, what happens when the beam is interrupted? When the PLL, IC4, is locked to the incoming frequency, the signal at pin 1 is normally high with a brief negative transition every Fig.1 (right): the circuit of the infrared stereo receiver uses seven ICs, four transistors and two FETs. Its operation is explained in the text. October 1996  55 PARTS LIST – RECEIVER 1 PC board, code 01109962, 120 x 60mm 1 PC board, code 01109963, 45 x 42mm 1 plastic box, 130 x 68 x 41mm, Jaycar HB6013 or equivalent 1 lens assembly, Oatley Electronics OLP1 or equiv. 1 pushbutton switch, Jaycar SP0710 or equivalent (S1) 2 AA battery holders, Jaycar PH9202 or equivalent 2 216 snap-on battery connectors 1 3.5mm stereo socket, Jaycar PS0132 or equivalent 1 red knob, Altronics H6001 or equivalent 1 green knob, Altronics H6005 or equivalent 11 PC stakes 2 6PK x 6mm self tapping screws 2 10kΩ 16mm diameter PC mount log pots, Jaycar RP3610 or equiv. (VR1,VR2) Semiconductors 1 TL062 dual op amp (IC1) 1 LM311 comparator (IC2) cycle; when it is not locked this output is low. The resistor and capacitor at pin 1 filter the negative spikes, feeding a steady voltage to pins 12 and 13 of IC5. If this voltage is high, the audio is switched through to IC6a and IC6b but if it is low, the switches are open. Therefore, if the transmitted light source is obstructed for any reason the audio signal to the headphones will be “killed” and there will be no extraneous noises produced. 56  Silicon Chip 1 4013 dual D flipflop (IC3) 1 74HC4046 phase lock loop (IC4) 1 74HC4066 quad CMOS switch (IC5) 1 TL064 quad op amp (IC6) 1 LM833 audio amplifier (IC7) 2 BC337 NPN transistors (Q1,Q3) 2 BC327 PNP transistors (Q2,Q4) 2 BS170 FETs (Q5,Q6) 1 LT536 or equiv. photodiode (PD1) 2 1N914 silicon diodes (D1,2) MKT polyester or ceramic 3 .0012µF 63VW MKT polyester or ceramic 1 .001µF 63VW MKT polyester or ceramic 2 120pF 63VW MKT polyester or ceramic 1 100pF 63VW MKT polyester or ceramic Note: if ceramic capacitors are used, they should be within ±10% tolerance. Capacitors 2 470µF 16VW electrolytic (for 8Ω headphones) 1 330µF 16VW electrolytic 4 100µF 16VW electrolytic 2 4.7µF 16VW electrolytic 2 0.47µF 16VW electrolytic 4 0.15µF 63VW MKT polyester 1 0.1µF 50VW monolithic 6 0.1µF 63VW MKT polyester 2 .022µF 63VW MKT polyester 1 .01µF 63VW MKT polyester 2 .0018µF 63VW MKT polyester or ceramic 4 .0015µF 63VW Resistors (0.25W, 1%) 2 10MΩ 1 18kΩ 2 2.7MΩ 2 12kΩ 3 1.2MΩ 17 10kΩ 1 680kΩ 4 8.2kΩ 1 470kΩ 1 6.8kΩ 1 120kΩ 4 1kΩ 1 100kΩ 1 820Ω 2 68kΩ 1 220Ω 1 47kΩ 2 47Ω 1 39kΩ You will notice in the photos that the end of the receiver case has a tube mounted on it. This is a lens assembly and its job is to focus the received IR radiation onto the photodiode. It gives a significant increase in the distance that the transmitter and receiver can be separated. Miscellaneous Hookup wire, machine screws and nuts, solder. Accordingly, IC7a drives a pair of complementary emitter followers Q1 and Q2, which are connected within the negative feedback loop to keep distortion low. The inputs of the LM833 have to be Below: opening out the top PC board reveals the method of construction, We have used an LM833 dual op with the batteries and lower board amp but this does not have sufficient clearly shown. Use no more wire output to drive all headphones.­ between the boards than is necessary to allow them to come apart. Headphone drive Fig.2: the parts overlay for the two receiver PC boards. It should be followed closely during assembly. In particular, check that all polarised components (semiconductors, diodes and capacitors) are inserted the correct way around. biased to half the supply voltage to ensure a symmetrical output swing. To do this and also to simplify things, the “earthy” ends of the volume pots are taken to this potential; ie, +3V. Automatic switch-off As the receiver is battery operated there will be a tendency to take the headphones off and walk away “for a minute or two” leaving the unit running. When you come back, in a week’s time for example, the batteries could be very flat. To avoid this embarrassment, we have an automatic off switch comprising Mosfet Q6 and a few other components. Hence, there is an ON button but no OFF switch. When the ON button is pressed, the 330µF capacitor connected from gate to source of Q6 is charged to +6V via the 220Ω resistor. This turns Q6 on, applying power to the receiver. The 330µF capacitor will then gradually discharge via the 10MΩ resistor until the voltage is insufficient to keep the FET switched on. At this stage, a few squawks will come through the headphones to alert you to the imminent switch-off. Pushing the ON button again will let you listen for another half hour or so, the idea being to press it at the beginning of each program. modating IC7, Q1, Q2, Q3 & Q4. The larger board, coded 01109962, holds the remainder of the circuitry. Note that neither PC board has holes for mounting screws or pillars. Instead, the headphone drive board is secured in place by soldering two PC stakes at the corners to the metal cases of the volume controls which mount on one end of the plastic case. The main board has the corners cut out to clear the integral pillars of the case. It is neat fit into the case and is sandwiched between the lid and a piece of foam rubber. We’ll cover more of the details as we go. Fig.2 shows the component overlays Case assembly Receiver assembly Now let’s start constructing the receiver. This has the two boards shoe-horned into a plastic case. The smaller board, coded 01109963, is the head­phone driver board, accom- for the two receiver PC boards. Let’s start with the audio amplifier board. First, fit the nine PC stakes, the resistors and the IC into the board and solder them. This done, insert and solder the four MKT capacitors, the four transistors and lastly, the four electrolytics. If you are going to use 32Ω headphones (as supplied with Walkman-type cassette players) all the time, then we suggest fitting 100µF output coupling capacitors to the board. However, if you expect to use conventional 8Ω headphones, you will need to use 470µF output coupling capacitors, otherwise the bass response will be deficient. The larger board has six links which should be fitted first, followed by resistors and diodes, IC sockets (if you use them) and then the capacitors. We don’t recommend using PC stakes in this board except as test points for the left and right audio outputs, as it is more convenient to bring the wires from the copper side of the board to the volume controls and the audio amplifier. The ICs, being CMOS devices, should be plugged into the sockets or soldered in last. The photodiode is mounted on the copper side of the PC board with full lead length. Make sure that the chamfer is on the left side when viewed from the front. The infrared beam is focused on the photodiode by this lens assembly to significantly increase the range. As already noted, the headphone drive board is secured by soldering two corner PC stakes to the cases of the two volume controls. These volume controls must be the 16mm dia­meter type otherwise they will not fit together in the confines of the case. October 1996  57 Fig.3: this wiring diagram shows how the wiring is run from the underside of the larger board to the top of the smaller board. Note that the photodiode, PD1, is soldered to the underside of the larger board. Make sure that this device is oriented correctly. points on the main board. Fig.3 shows the full details of the wiring between the main PC board and the headphone drive board. Follow the wiring diagram of Fig.3 carefully. It is probably easier to solder the wires onto the volume control lugs before you mount them in the case, as you will have easier access to the terminals. Testing As well as drilling holes in one end of the case for the pots, you will need holes in the side for the pushbutton ON switch and the 3.5mm stereo head­phone socket. Finally, you will need to drill holes in the other end of the case to take the lens assembly which was 58  Silicon Chip mentioned above. It is supplied by Oatley Electronics (OLP1). Note that the lens assembly should not be fitted until the transmitter and receiver have been tested. Two double-AA cell holders provide the 6V battery supply. These are wired in series and then to the +6V and 0V If you are very careful with your assembly and check everything closely there is no reason why it won’t work first up. If it doesn’t, you will have to decide which of the units is not functioning properly. If you have access to an oscilloscope this is easily checked out. If no scope is available, testing is a little harder. Starting with the transmitter, normally the first things to measure after you apply power are the rail voltages. In this project, if these check out at +15V and -15V and the regulator tabs don’t burn your finger, it’s a good start. If you have a multimeter with a frequency response to above 100kHz, you will be able to check for the presence of signal at pin 3 of IC1 (176kHz), pins 1, 2, 12 & 13 of IC2 (88kHz, 44kHz), pin 7 of IC5 and IC6, and the collector of Q1 (set the meter to AC volts). If all these points have signals you can feel reasonably sure that there are no problems with the transmitter. RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 2 2 3 1 1 1 1 2 1 1 1 2 17 4 1 4 1 1 2 Value 10MΩ 2.7MΩ 1.2MΩ 680kΩ 470kΩ 120kΩ 100kΩ 68kΩ 47kΩ 39kΩ 18kΩ 12kΩ 10kΩ 8.2kΩ 6.8kΩ 1kΩ 820Ω 220Ω 47Ω The audio can be followed through from the inputs to pin 2 of IC5 or IC6 with high impedance headphones or a signal tracer. If a signal is missing you must check around that area until you find the cause of the trouble. To work on the receiver you must have the transmitter turned on and pointing in the direction of the receiver. Press the ON button on the receiver and measure the battery current. It should be around 17mA. To test for the presence of an 88kHz carrier, set your multimeter to AC volts and check pin 7 of IC2, pin 3 & pin 4 of IC4 and pin 1, pin 12 & pin 13 of IC3. If the sound only comes through the left channel it means that the FET Q5 is turned off. Check the soldering 4-Band Code (1%) brown black blue brown red violet green brown brown red green brown blue grey yellow brown yellow violet yellow brown brown red yellow brown brown black yellow brown blue grey orange brown yellow violet orange brown orange white orange brown brown grey orange brown brown red orange brown brown black orange brown grey red red brown blue grey red brown brown black red brown grey red brown brown red red brown brown yellow violet black brown RESISTOR COLOUR CODES No. ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Value IEC Code EIA Code 0.15uF   150n   154 0.1uF   100n   104 .022uF   22n   223 .0018uF   18n   183 .0015uF   15n   153 .0012uF   12n   123 .001uF   10n   103 120pF   120p   121 100pF   100p   101 around the bandpass filter and also ensure that diodes D1 and D2 are inserted correctly. If you want to install an on/off 5-Band Code (1%) brown black black green brown red violet black yellow brown brown red black yellow brown blue grey black orange brown yellow violet black orange brown brown red black orange brown brown black black orange brown blue grey black red brown yellow violet black red brown orange white black red brown brown grey black red brown brown red black red brown brown black black red brown grey red black brown brown blue grey black brown brown brown black black brown brown grey red black black brown red red black black brown yellow violet black gold brown switch to replace the FET switch, omit Q6, the 330µF capacitor and the 10MΩ and 220Ω resistors. Connect one end of the switch to the battery minus (Q6 source) and the other side of the switch to 0V (Q6 drain). Finally, after testing is complete, the main board can be assembled into the receiver case. Before this is done, the photodiode must have its leads bent so that its face is square in the hole in the end of the case; its face should be flush with the outside surface of the case, as this is the focal point of the lens assembly. The lens assembly can then be secured in position with two self-tapping screws. Finally, fit the lid of the case SC and the job is done. Fig.4: check your PC board against this full-size etching pattern before installing any parts. October 1996  59 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: 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 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 ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) TOTAL Australi a $A7.00; NZ $A8.00 (airmail ); Elsewhere $A10 (airmail ). Buy 10 or more and get a 10% discount. Note: Nov 87-Aug 88; Oct 88-Mar 89; June 89; Aug 89; Dec 89; May 90; Aug 91; Feb 92; July 92; Sept 92; NovDec 92; & March 98 are sol d out. All other issues are currently i n stock. $A B INDERS Pl ease send me _______ SILICON CHIP bi nder(s) at $A12.95 + $5.00 p&p each (Australi a only). N ot avail abl e elsewhere. Buy five and get them postage free. $A SUBSCRIPTIONS  New subscription – month to start­­____________________________  Renewal – Sub. No.________________    Gift subscription  RATES (please tick one) 2 years (24 issues) 1 year (12 issues) Australia (incl. GST)  $A135  $A69.50 Australia with binder(s) (incl. GST)**  $A159  $A83 New Zealand (airmail)  $A145  $A77 Overseas surface mail  $A160  $A85  $A250 Overseas airmail  $A125 **1 binder with 1-year subscription; 2 binders with 2-year subscription YOUR DETAILS Your Name_________________________________________________ GIFT SUBSCRIPTION DETAILS Month to start__________________ Message_____________________ _____________________________ _____________________________ Gift for: Name_________________________ (PLEASE PRINT) Address______________________ _____________________________ (PLEASE PRINT) Address___________________________________________________ State__________Postcode_______ ______________________________________Postcode_____________ Daytime Phone No.____________________Total Price $A __________ Signature  Cheque/Money Order  Bankcard  Visa Card  Master Card ______________________________ Card No. Card expiry date________/________ Phone (02) 9979 5644 9am-5pm Mon-Fri. 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 October 1996  65 Get big sound from your computer with this . . . Multimedia Sound System Most computer sound systems are wimpy little boxes with poor quality sound. This system is compact, has plenty of power and produces high quality wide range sound with oodles of bass. Design by RICK WALTERS 66  Silicon Chip Let’s face it, while today’s computers may be superfast, with millions of colours on their monitors and connected to the whole world via the Internet, their sound quality is strictly yesterday’s fodder. Not only are the amplifiers on sound cards puny by comparison to any home music system, most Multimedia speakers are just a joke – you could get better quality out of an old 6 x 9-inch car radio speaker! So what do you want from your Left: the neat speakers flanking this monitor are only part of our new Multimedia Sound System. The other part is the power amplifier and electronic crossover board (above) which plugs into a spare slot in your computer. It puts out better sound than you have ever heard from a computer. Multimedia sound system? For a start, if you are into games, you want the sound effects to be at least halfway realistic. If you’ve just blown up the robber kingdom with a 5-megaton bomb, the sound effect should be a little more notable than a sneeze from a guinea pig. And if you’ve just crashed out of the Monte Carlo rally, you expect to hear a little more than a few coins rattling inside a drink can. Well, don’t you? We certainly do. And if you are listening to CDs or sound tracks via your CD-ROM player, you have every right to expect clean wide-range sound, every bit as good as from a home music system with a CD player. Our new Multimedia Sound System will deliver the goods. It has decent power output, high quality low distortion amplifiers and decent loudspeakers which cover the full audio spectrum from 50Hz to 20kHz. They will blow existing commercial computer sound systems and speakers into the weeds! Total power output of the audio amplifier system is in excess of 20 watts, distortion is less than 0.2% and signal to noise ratio is better than 65dB with respect to full power. And as the photos show, you don’t need a massive amount of electronics to get this power. It all fits on a standard half-size card which slips into any vacant slot in your PC. There is no power supply required because the card makes use of the 12V supply inside the computer. Apart from slotting the amplifier PC board into your com­puter, there is no other modification required to your machine. You will need to connect cables from your computer’s sound card to the amplifier PC board and there are also the connecting cables to the two speakers. But once you have the amplifier and speakers connected, your computer will function exactly Performance Output power �������������������������������1.5 watts per channel into 8Ω (tweeter); 9 watts per channel into 4Ω (woofer) Frequency response ��������������������-4dB at 20Hz and -0.2dB at 50kHz (see Fig.3 & Fig.4) Input sensitivity ����������������������������32mV for tweeter amplifier; 40mV for woofer amplifier Harmonic distortion ���������������������0.2% (see text) Signal-to-noise ratio ��������������������65dB with respect to 1.5 watts (tweeter); 59dB with respect to 8 watts (woofer) October 1996  67 AUDIO PRECISION SCTHD-W THD+N(%) vs measured 10 LEVEL(W) 20 AUG 96 15:22:48 1 0.1 0.1 1 3 Fig.1: power output of the tweeter drive amplifier. Maximum power is about 1.5 watts before clipping. Note that the true harmonic distortion is less than 0.2%. AUDIO PRECISION SCFREQRE AMPL(dBr) vs FREQ(Hz) 15.000 20 AUG 96 14:11:44 10.000 5.0000 0.0 -5.000 -10.00 -15.00 3k 10k 50k Fig.2: this graph shows the frequency response of the tweeter amplifier, over the range from 3-50kHz. as it did before, except that you will have big sound to match. Nor is there any need for massive loudspeaker boxes that would dwarf your computer system. While they are bigger than typical Multimedia speakers, they are still quite compact – the volume of each enclosure is a mere five litres. So they will sit quite comfortably on either side of your computer 68  Silicon Chip monitor. Naturally, the woof­ers and tweeters in the enclosures have full magnetic shielding so there will be no adverse effects on your monitor. Power amplifier features As already noted, the power amplifiers for this new Multi­media system are all on one PC board which is the size of the standard half-size card for a PC-compatible computer. On board are three Philips TDA1519A stereo amplifier ICs which are specif­i cally designed for use in car radios. Why three ICs? We’ll tell you about that later. Only four connections are made via the PC board edge con­nector to the computer’s motherboard: two for the earth or 0V connection and two for the +12V and -12V supply rails. There are two 9-pin female D sockets on the metal mounting bracket, together with a 3.5mm stereo jack socket and two screw­driver-adjustable multi-turn volume controls. These are set when you first connect the system up but after that they are not touched – you will normally set the volume by using your mouse and on-screen controls. The 9-pin D sockets are used for making the loudspeaker connections. The two enclosures each have a 5-inch woofer and a 1-inch tweeter. The enclosures are ported, to give an extended bass response down to 50Hz. Each loudspeaker is connected to the amplifier PC board via a 4-way cable; two wires for the woofer and two for the tweeter. There are no crossover networks inside the loudspeaker enclosures since the tweeters and woofers are separately powered. Now let’s have a look at the electronics on the amplifier card. Fig.5 shows the circuit of the whole Multimedia Sound System. Both channels are shown. If you look at the righthand side of the diagram you will see that each tweeter is driven by its own power amplifier while each woofer is driven by two power amplifiers in “bridge” mode. In effect, this doubles the power delivered to the woofer and makes best use of the power available from the 12V supply in the computer. There are several reasons for this unusual amplifier setup. First, the specified tweeter is an 8Ω type and has an efficiency of 94dB at 1 watt and 1 metre (usually expressed as 94dB/1W/1m). By contrast, the woofer is a 4Ω type and has an efficiency of only 86dB. In other words, the tweeter is twice as efficient. Therefore, we need to deliver four times as much power to the woofer as to the tweeter. This is why the woofer is driven in bridge mode. Using a 12V supply rail, the TDA­ 1519 can typically deliver a maximum of 1.5 watts into an 8Ω load before clipping, from each channel. This is AUDIO PRECISION SCFREQRE AMPL(dBr) vs FREQ(Hz) 15.000 20 AUG 96 14:05:54 10.000 5.0000 0.0 is loafing along, using the regulated 12V supply in the computer. That is just as well, because we have mounted the three TDA1519As on quite small heatsinks, bearing in mind that most of the time they will be delivering little or no power at all. And just in case the chips do get too hot, they are thermally pro­tected and will shut down safely if the going gets too tough. By the way, they are also protected against short-circuited outputs. Performance graphs -5.000 -10.00 -15.00 20 100 1k 5k Fig.3: frequency response of the woofer amplifier from 20Hz to 5kHz. Note the 3dB boost in the region of 35Hz. AUDIO PRECISION SCTHD-W THD+N(%) vs measured 10 LEVEL(W) 20 AUG 96 13:27:36 1 0.1 0.2 1 10 20 Fig.4: power output of the woofer amplifier. Maximum power from the bridged amplifiers is about 9 watts before clipping. what the tweeters get. In bridge mode, the two amplifiers in the TDA1519A are driven out of phase so that their output voltages add across the speaker. Under this condition, the TDA1519A can deliver 9 watts. In practice, this gives a safety margin – we don’t need to drive the woofers at a power level six times that of the tweeter but it is good to have a little in hand. By the way, if you come across the specs for the TDA1519A you will see that it is rated for a maximum power output of 22 watts in bridge mode into a 4Ω load. However, this is for a supply of 14.4V and a harmonic distortion level of 10% – hardly what you would regard as hifi specs. By comparison, under our design conditions the chip The performance of the Multimedia Sound System is summar­ised in the accompanying panel and we have included a number of graphs which need a little explanation. Fig.1 shows the power output of the tweeter drive amplifier and as you can see, it delivers about 1.5 watts before clipping, at which point the harmonic distortion suddenly rises. The minimum distortion on this graph is 0.4%, which is double what we claimed above for this parameter. What the graph doesn’t show is that the distor­tion measured is mostly due to the 54kHz hash superimposed on the computer’s power supply. This is completely inaudible and does not affect the sound quality; as stated above, the true harmonic distortion is less than 0.2%. Fig.2 shows the frequency response of the tweeter amplifi­er, over the range from 3kHz to 50kHz. Similarly, Fig.3 shows the frequency response of the woofer amplifier from 20Hz to 5kHz. Note the 3dB boost in the region of 35Hz. Fig.4 shows the power output of the woofer amplifier and the above remarks about power supply hash also apply here. The power supply hash also affects the signal-to-noise ratio, so while we have quoted a figure of -65dB for the tweeter amplifier and -59dB for the woofer amplifi­er, the true figures are considerably better. In any case, there is little point in having signal-to-noise ratio figures much in excess of -60dB in a Multimedia sound system since the computer itself generates so much noise from its fan and disc drives. Now let’s have a closer look at the circuit details shown in Fig.5. At the lefthand side of the circuit are the stereo inputs, at the jack socket SK1. These are fed via 2.2µF non-polarised October 1996  69 70  Silicon Chip Fig.5: the two tweeters are driven from single power amplifiers (IC5), while each woofer is driven in bridge mode by a pair of power amplifiers. IC1 and IC2 provide slight bass boost and the electronic crossover at 3.5kHz. The amplifier board is the same size as a typical half-size PC card and plugs directly into a slot on the motherboard. The edge connector makes contact with the ±12V rails of the computer and the 0V line. (NP) capacitors to the 10kΩ multiturn trimpots, VR1 & VR2. Now let’s talk about the left channel only, since both channels are identical. VR1 feeds an op amp buffer, IC1d, and then the signal is split into two paths. The first is via a bass boost stage involving op amp IC1a. This is really a high pass filter which gives a 3dB boost to frequencies in the region from 35Hz to 50Hz. Following the bass boost stage, the signal is fed to a low pass filter employing op amp IC2d. This is a Linkwitz-Riley filter which rolls off signals above 3.5kHz and drives a voltage divider comprising resistors R1 & R2. These are used to adjust the drive signal to the amplifier stage so that the woofer signal level can match that of the tweeter. The equivalent resistors in the right channel are R3 & R4. The Linkwitz-Riley filter configu­ration is used here because it gives the flattest response from the two speakers in the crossover region. Woofer drive The signal is then coupled via a 2.2µF capacitor to the inputs of bridged amplifiers IC3a & IC3b, the TDA1519A. Note that the signal drives the non-inverting input of IC3a (pin 1) and the inverting input of IC3b (pin 9). Note also that pin 3 is the inverting input of IC3a and the non-inverting input of IC3b (internally con­nected). This automatically gives the condition whereby the outputs of the two amplifiers are out of phase; ie, when the output at pin 4 is swinging positive, the output at pin 6 is swinging negative. This means that the total voltage across the speaker is the sum of the two amplifier outputs. Hence This shot shows how the audio cables from a sound card are plugged into the power amplifier PC board. The two female D sockets for the four-way cables to the speaker boxes. the output power delivered to the speaker is about four times what it would be if a single amplifier was employed. As both inputs of IC3 are biased to the same DC potential (half the 12V supply), there is negligible DC voltage across the 4Ω woofer and so no large coupling capacitor is required. Howev­er, Zobel networks, consisting of a 4.7Ω resistor and 0.1µF, are used at the output of each amplifier to ensure stability at high frequencies. Tweeter drive Going back the buffer stage IC1d, it also feeds a Linkwitz-Riley high-pass filter based on op amp IC2a. This rolls off frequencies below 3.5kHz. The output of IC2a feeds one power amplifier, IC5a. As the output voltage at pin 4 of IC5a is close to +6V the tweeter must be AC-coupled and a 100µF electrolytic capacitor is used to do this. A Zobel network is also connected at the out­put. Due to phase inversion in the filter (IC2a) at the crosso­ver frequency, the tweeter polarity must be the reverse of the woofer. This is why the positive terminal of the tweeter is grounded. On the right channel tweeter, you will notice that the tweeter connection is different. In this case, the positive terminal is driven by the output of October 1996  71 Fig.6: this is the component layout for the PC board. Note the two long jumpers underneath the board. Fig.7 (right): this diagram shows the dimensions of the two heatsink brackets. IC5b and the negative terminal is grounded. The reason for this is that because of the internal connection of the amplifier inputs at pin 3, IC5a must be driven via its inverting input at pin 9. Therefore it inverts the signal and the tweeter connections must therefore be reversed. This reversing of tweeter connections is automatically taken care of by the PC board and so each speaker box is wired identically via its respective cable and 9-pin D connector. Note that IC1 and IC2, the two TL074 quad op amps, are powered from the ±12V rails of the computer whereas the power amplifiers, IC3, IC4 and 72  Silicon Chip IC5, are powered only from the +12V rail. The -12V rail in the computer cannot deliver lots of current but IC1 and IC2 will typically draw a total of less than 20mA. PC board assembly Fig.8: this diagram shows the details of the heatsink mounting for the TDA1519As. Be very careful when bending the legs of the IC at right angles that you do not stress the leads where they come out of the IC body. Enough of how it works, lets get into making it work. The PC board assembly is reasonably straightforward. Before mounting any components, check the board carefully for any defects such as shorted or broken copper tracks or undrilled holes. You can check the pattern against the artwork shown in Fig.10. Fig.6 shows the component layout PARTS LIST Amplifier PC board 1 PC board, code 01110961, 145 x 108mm 1 PC-mounting bracket (see Fig.9) 2 9-pin “D” females PC mounting socket 2 9-pin “D” male plugs 2 9-pin “D” backshells 1 3.5mm miniature PC mount stereo socket 1 3.5mm miniature stereo plug 2 14-pin IC sockets (optional) 1 PC mounting bracket (with holes for D-sockets, etc) 2 10kΩ multiturn potentiometers Bourns 3006P (or equivalent) Semiconductors 2 TL074 quad op amps (IC1,IC2) 3 TDA1519A dual power amplifiers (IC3,IC4,IC5) Capacitors 4 470µF 16VW electrolytic 9 100µF 16VW electrolytic 2 2.2µF 50VW non polarised (NP) electrolytic 2 2.2µF 50VW electrolytic 12 0.1µF 63VW MKT polyester 7 0.1µF 50VW monolithic ceramic 8 .01µF 63VW MKT polyester Resistors (0.25W, 1%) 2 150kΩ 2 1.5kΩ 2 22kΩ 4 100Ω 2 10kΩ 6 4.7Ω 8 4.7kΩ Fig.9: details of the PC board mounting bracket. for the PC board. Fit and solder the wire links first and don’t forget the two long jump­ers, made from insulated hookup wire, which install on the copper side of the PC board. These connect the outputs of IC5 to the respective D sockets. Leave the link marked “Power” off the board for the moment. This is connected during the testing procedure. The next step is to fit the resistors, small capacitors, trim­pots and 3.5mm jack socket. Note that the 0.1µF monolithic ceramic capacitors are used for supply filtering, so they are the ones adjacent to the 100µF electrolytics. The 0.1µF MKTs are specified in the signal parts of the circuit. The small electrolytic capacitors are next, followed by the larger ones and then the female D sockets. The two TL074s can be soldered in or if you prefer, plugged into sockets. The heatsinks for the power amplifiers are made from 3mm thick aluminium angle, 20 x 12mm. The heatsink for IC5 is 30mm long and the one for IC4 & IC5 together is 55mm long. Fig.7 shows the drill­ing details. The nine leads of each TDA1591A need to be bent at right angles before soldering into the board. With each TDA1519A facing you and the type number visible, bend the leads down at right angles, 8mm from each IC body. Note: do not put any stress on Miscellaneous 1 55mm length 20 x 12 x 3 aluminium angle 1 30mm length 20 x 12 x 3 aluminium angle 22 3mm x 20mm bolt 22 3mm nut 30 3mm flat washer 6 2.5mm x 12mm screws 6 2.5mm nuts 6 2.5mm spring washer 6 2.5mm flat washer 3 TO3 mica washers the leads where they come out of the IC body. To avoid stressing the leads, hold them with long-nose pliers when bending each one. This done, apply a smear of heatsink compound to October 1996  73 Fig.10: check your PC board against this full size etching pattern before installing any of the parts. the metal mount­ing surface of each IC and mount it on its heatsink – see Fig.8. Testing To test the amplifier board, you will need a power supply capable of delivering ±12V at several amps. We strongly sug­gest that you do not just build the amplifier board and plug it into your computer. If there is a fault on the board you could damage your computer’s power supply. Three PC stakes are provided on the PC board for supply connections. They can be seen near the edge connector, on Fig.6. Connect the power supply to the PC stakes and then use The enclosures have an internal volume of only five litres but that, combined with a spot of low down bass boost, is enough for them to put out good bass down to below 50Hz. We’ll describe their construction next month. 74  Silicon Chip your multimeter to measure voltages around the circuit. The principal voltages should be as follows: • IC1 & IC2 – pins 1, 2, 3, 5, 6, 7, 8, 9, 10, 12, 13 & 14, 0V; pin 4 +12V; pin 11 -12V. • IC3, IC4 & IC5 – pins 2 & 5, 0V; pins 1, 3, 4, 6 & 9, +6V; pin 8, floating; pin 7, +12V. For some of the pins of IC1 and IC2, designated as 0V, your multimeter may actually measure a few tens of milli­volts above or below 0V. That is normal. The current drain at this stage should be between 15 and 20mA, or thereabouts. This is the current drawn by IC1 and IC2. The current drain of the power amplifiers is negligible at this stage since we have not connected pin 8, the MUTE pin, to +12V. If all the voltage checks so far are correct, you can now install the link marked “Power” on the board. This enables the power amplifiers. When power is applied the total current drain should be around 140-160mA, with no signal applied. Well, that is as far as we can take it this month. Next month, we will describe how to build the speakers and give the parameters of the BassSC Box design. SATELLITE WATCH Compiled by GARRY CRATT* PALAPA C1 to C2M CHANGE­OVER: The change ­­over from Palapa C1 to the Palapa C2M satel­lite at the end of June has done little to solve the reception problems being experienced by enthusiasts in Australia and New Zealand. There has been virtually no change in the receive level of transponders of either polarity on the new C2 satellite, meaning that those wishing to receive this satellite in the eastern states of Australia will need a 3.7m dish for good re­sults. GORIZONT 19/27 - 96.5°E longitude: Early indications (at August 31st) show that this satellite was replaced on August 20 by Gorizont 27. This new satellite runs a lower power level over Australia, requiring users to upgrade to a larger dish, perhaps up to 3.7m. The degree of inclination of this satellite is much less compared to Gorizont 19. OPT 1 continues to be the sole source of programming available, on IF 1475MHz. ASIASAT 2 - 100.5°E longitude: The two new Chinese stations re­ported in the August issue of Satellite Watch have now been identified as Henan TV (IF 1430MHz) and Guangdong Satellite TV (IF 1310MHz). In addition, MTB from Mongolia appears at IF 1470MHz each night around 7pm AEST. TVSN, otherwise known as “The Value Channel”, appeared on this satellite during August, on IF 1485MHz, supplementing their service on Panamsat PAS-2. Meanwhile, a trickle of MPEG decoders continues to arrive in this country from South Africa. Available for around $1600 and originally supplied for the “Multichoice” pay TV service in South Africa, these decoders work well on the European Bouquet of channels broadcast on AS2. GORIZONT 42 - 142.5°E longitude: Global TV’s adult channel “21 Plus” has not yet commenced operations despite a July 1st start being advertised. Industry reports indicate that Global’s con­tract was not in place at deadline and startup has hence been delayed. Meanwhile, Filipino channel RPN (primarily English language programming) has a 90-day contract to operate using the same transponder from 2200-1600UTC daily. Broadcasts are currently in NTSC. Its IF is 1375MHz. The screen grab is from TVSN (The Value Channel), which appeared on Asiasat2 during August on IF 1485MHz. Other broadcasters on this satellite continue normal opera­tions: EM TV at 1265MHz and Asia Music/Zee Education at 1470MHz. APSTAR 1A - 131°E longitude: Launched successfully on July 3rd aboard a Long March launch vehicle from China, this bird may be parked permanently at 131°E longitude, despite having no authori­sation from the ITU to do so. This is a similar situation to the one occurring after the launch of Apstar 1 several years ago. In that instance, Apstar 1 was parked initially at 131°E degrees, much to the horror of operators of satellites at both 132°E and 130°E. Finally, they negotiated the orbital “slot” of 138°E with Rimsat. It seems this time, the Chinese owners of the satellite plan another “brute force” orbital intrusion. OPTUS B3 - 156°E longitude: This satellite carries the Galaxy pay TV service on transponders 10 and 11 in MPEG2. New to market, Panasat MPEG IRDs can be used to receive Galaxy MPEG transmis­ s ions sent without conditional access, such as “The Value Chan­nel” and the Galaxy “Preview” channel. PANAMSAT PAS2 - 169°E longitude: Normally inactive on K band other than for special events, this satellite carried the Network 7 feed from the Olympic games at Atlanta during July. C band activ­ity continues as follows: 1115MHz NHK Japan, 1183MHz CNNI, 1405MHz The Value Channel, 1057MHz NBC digital service. The NBC digital service requires an MPEG IRD and whilst operating at present with no conditional access, this situation may change in the future. SC *Garry Cratt is Managing Director of Av-Comm Pty Ltd, suppliers of satellite TV reception systems. October 1996  75 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au PRODUCT SHOWCASE Dick Smith Electronics opens new Powerhouse retail store Dick Smith Electronics has opened a vast new electronics retail store in Bankstown, Sydney. It is six to eight times larger than the average DSE store, with a floor space of 2000 square metres. Since it represents a new concept for Dick Smith Electronics, it has been named the "PowerHouse". It has been designed to focus on the convergence of electronics technology. Not only does the new store devote a much larger area to conventional electronics parts and semiconductors, the PowerHouse new store has a much wider range of products than ever before. As well as a large area devoted to computers and software, printers, multimedia sound systems and other peripherals, it has a large display of TV sets, a car radio and amplifier display and a range of camcorders, each working with a standard monitor. This camcorder display alone is better than virtually any electronics retailer in Australia. There is also an amateur radio shack, a hifi sound lounge, a theatre surround sound lounge, and a Telstra kiosk selling mobile phones and other services such as Easycall and Foxtel. You can have mobile hands-free kits and car radios fitted at the store as well. For those curious about the Internet and the World Wide Web, there is an Internet bar with several machines permanently connected. And if you are upgrading your computer with memory, drives or new cards, there is an on-site technical service centre where this can be done while you wait. The PowerHouse will also have regular clinics for electronics enthusiasts and this will demonstrate the building of current kits and also trouble-shoot kits which have been built by customers. This could be a great service to constructors. A really impressive aspect of the PowerHouse is the large number of working product displays. For example, they have a large selection of multimedia sound systems, all of which can be demonstrated and selected by a touch screen. Anything else? Well, they have a large range of audio CDs in stock, a big 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. $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 October 1996  79 STEPDOWN TRANSFORMERS 60VA to 3KVA encased toroids Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 9476-5854 Fx (02) 9476-3231 range of printer consumables such as paper and ribbons. We visited the PowerHouse just after it had opened and it was difficult to comprehend the range and scale of products on display. It is certain to establish a benchmark for all electronics retailing in Australia. Dick Smith Electronics' PowerHouse is located at the Christies Home KITS-R-US RF Products FMTX1 Kit $49 Single transistor 2.5 Watt Tx free running 12v-24V DC. FM band 88-108MHz. 500mV RMS audio sensitivity. FMTX2A Kit $49 A digital stereo coder using discrete components. XTAL locked subcarrier. Compatible with all our transmitters. FMTX2B Kit $49 3 stage XTAL locked 100MHz FM band 30mW output. Aust pre-emphasis. Quality specs. Optional 50mW upgrade $5. FMTX5 Kit $98 Both a FMTX2A & FMTX2B on 1 PCB. Pwt & audio routed. FME500 Kit $499 Broadcast specs. PLL 0.5 to 1 watt output narrowcast TX kit. Frequency set with Dip Switch. 220 Linear Amp Kit $499 2-15 watt output linear amp for FM band 50mW input. Simple design uses hybrid. SG1 Kit $399 Broadcast quality FM stereo coder. Uses op amps with selectable pre-emphasis. Other linear amps and kits available for broadcasters. 80  Silicon Chip Centre, Cnr Chapel Street & Canterbury Road, Bankstown, NSW 2200. It is open seven days a week. Meters for light & colour measurements 800V Mosfets have low on-resistance Emona Instruments have available the Tektronix LumaColor photometers. Two photometers and their eight interchangeable heads form the TekLumaColor family. Each head transforms the handheld into a different precision photometer, radiometer or colourimeter. Each combination automatically displays the appropriate units on a large, backlit LCD screen. Designed for on site as well as production use, the TekLumaColors are manufactured with a rugged exterior to protect from shock and vibration. They can operate for 30 hours on a 9V battery or connect to an optional AC power supply. An RS-232 port allows the user to automate testing and data recording. The J18 TekLumaColor II is designed primarily for testing, calibrating and adjusting colour displays. With Its J1810 chromaticity head, the TekLumaColor II updates colour and comparison readings twice each second. The unit stores ten reference settings IXYS Corporation have expanded their line of power Mosfets with the introduction of five new high voltage devices. They have a minimum blocking voltage (BVdss) of 800V and are fabricated using the company's HiPerFET process. This process guarantees a high avalanche energy rating and a faster switching intrinsic rectifier, providing higher reliability while reducing component cost in power switching circuits. The new devices range in current from 8A to 27A and offer some of the industry's lowest on-resistance (Rds(on)) and highest current ratings in their respective packages. For example, the 15A IXFH15N80 offers the industry's lowest Rds(on) in a TO-247 package at 0.6#. For further information, contact GEC Electronics Division, Unit 1, 38 South Street, Rydalmere NSW 2116. Phone (02) 9638 1888; fax (02) 9638 1798. PO Box 314 Blackwood SA 5051 Ph 0414 323099 Fax 088 270 3175 AWA FM721 FM-Tx board $19 Modify them as a 1 watt op Narrowcast Tx. Lots of good RF bits on PCB. AWA FM721 FM-Rx board $10 The complementary receiver for the above Tx. Full circuits provided for Rx or Tx. Xtals have been disabled. MAX Kit for PCs $169 Talk to the real world from a PC. 7 relays, ADC, DAC 8 TTL inputs & stepper driver with sample basic programs. ETI 1623 kit for PCs $69 24 lines as inputs or outputs DS-PTH-PCB and all parts. Easy to build, low cost. ETI DIGI-200 Watt Amp Kit $39 200W/2 125W/4 70W/8 from ±33 volt supply. 27,000 built since 1987. Easy to build. ROLA Digital Audio Software Call for full information about our range of digital cart players & multitrack recorders. ALL POSTAGE $6.80 Per Order FREE Steam Boat For every order over $100 re­ceive FREE a PUTT-PUTT steam boat kit. Available separately for $19.95, this is one of the greatest educational toys ever sold. Portable data acquisition system National Instruments has announced a high-resolution, portable data acquisition box that communicates through the parallel port with PC compatible computers. The DAQPad-MIO16XE-50 features a 16-bit ADC with a 20ks/s sampling rate, 16 single-ended or eight differential inputs and enhanced timing and triggering capabilities, programmable gain up to 100, two 12-bit DACs with voltage outputs, one constant current source for powering resistance temperature detectors (RTDs), eight lines of TTL-compatible I/O and two 24-bit up/down counter/ timers for timing I/O. It is compatible with the Enhanced Parallel Port (EPP) standard defined by IEEE 1284 as well as the original Centronics or standard parallel ports (SPP). As well, it has a second parallel port connector for a pass-through connection to a printer. It can be powered from an AC plugpack, an optional BP-1 rechargeable battery pack or any 9-42VDC source. For more information, contact National Instruments Australia, PO Box 466, Ringwood Vic 3134. Phone (03) 9879 5166; fax (03) 9879 6277. and is calibrated at D6500 for accurate white light readings. It offers RS-232 control, analog output capabilities and RGB bar graphs for easy calibration. For applications where real-time colour isn't critical, the J17 TekLumaColor is a unit that shares many of the family's features, including auto-range, auto-zero, hold, colour coordinate conversions and US to Metric conversions. The family of eight heads provides measurements for luminance, illuminance, chromaticity, irradiance, luminous intensity and radiant intensity. Measurement applications range through CRT displays, flat panel and projection displays, photographic equipment, infrared LEDs and lasers and coloured LEDs. For more information, contact Emona Instruments on (02) 9519 3933 or fax on (02) 9550 1378. PC board touch-up pen Now available is a range of marker pens intended for touching up PCBs before they are etched. Available in blue or red, the ink resists etchants such as ferric chloride and ammoniated alkali (eg, ammonium persulphate). Ink marks can be erased with a cloth or Q-tip moistened with napthas or chlorinated solvents. For further information, contact Australian Warehouse Solutions Pty Ltd, PO Box 146, Roseville 2069. Phone (02) 9417 7550; fax (02) 9417 7953. 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.emona.com.au/ Stop and direction arrow kits for cars Oatley Electronics has two simple kits for cars. One is a Stop sign while the other is a direction arrow, both made using an array of high intensity LEDs on a PC board. These are connected in parallel with the brake and direction indicator lamps of your car and would normally be mounted inside the rear window, on the parcel shelf. The complete Stop sign kit is $30 while the direction arrow kits are $15 each. For further information, contact Oatley Electronics, PO Box 89, Oatley, NSW 2223. Phone (02) 9579 4985; fax (02) 9570 7910. October 1996  81 RADIO CONTROL BY BOB YOUNG Multi-channel radio control transmitter; Pt.8 This month we will deal with the more complex programming functions which can be provided in this very advanced R/C transmitter. But first, let’s get this month’s grizzles, whinges and additions out of the way. In Pt.6 (July, 1996), which dealt with the construction of the transmitter case, Fig.2 showed the wiring arrangements for the various control elements. In this drawing set, mention is made of the connecting cable for these functions being a blue/white/ blue 3-core ribbon cable. As these leads are intended for reversing, the blue/white/ blue was to indicate that polarity was not important on these connectors. The b/w/b also matched the transmitter interior which is all in blue and white and it added to the internal appearance. The cable was ordered weeks before that article was written and the order clearly stated blue/white/blue. Months passed and still no cable. The July issue came out, still no cable. Finally, the big day arrived. The delivery docket stated b/w/b, the invoice stated b/w/b but it appears the production people decided that red/white/blue would look much better. As I was desperate for cable by this time I had no alternative but to use the r/w/b ribbon and to my amazement, the production people were absolutely correct. The finished transmitter did look much better, especially since I had increased the cable length after looking at the July issue photos. The leads now run neatly around the sides of the case. From now on, all leads will be red/white/blue as dictated by the cable manufacturers. This has one advantage in that it removes the need to paint a dot on one side of the connector (recommended in the July issue), as it is now very easy to determine visually if the lead is normal or reversed. All jokes aside, this business of quality control is driving me nearly insane. Almost without exception, every major component has been returned due to lack of quality or correctness. My heart is in my mouth every time I open a new batch of components. From powder coating to pots, I have sent back more components than I have accepted. Under these conditions, delivery promises mean nothing, and even now I am still struggling to get the project running smoothly with regards to deliveries. However, I digress. The wiring in those July photos looked totally disorganised. By increasing the lead length, it is now possible to run the leads right around the outside of the case (see photo). This was mentioned in the July issue but not highlighted. The lengths shown in Fig.2 of the July issue were the corrected, longer values. The addition of the frequency interlock key, as described in the text, eliminates the possibility of two transmitters operating on the same channel. 82  Silicon Chip Fig.1: the frequency interlock key, developed by the Author, cuts off the power to the transmitter while it is plugged into the charging socket. When the transmitter is in use, the key is removed and hangs on a key board in the club. Another nice touch added to the kits is the inclusion of self-adhesive cable clamps which stick to the case sides and secure all the cables neatly. These are made out of the large headed split-pin type paper clips, available at any stationers. The legs are clipped in length and covered in heatshrink and the heads stuck to the case side with double-sided foam tape. They sit flat against the wall, can hold a large number of cables and are dead easy to open and close, in order to add and remove cables; in other words, the ideal cable clamp. Also, since the July issue, I have found a source of components for crimp connectors which allows me to crimp my own leads. These feature a housing similar in size to the Futaba servo connector housing but less the polarising flange. These are fitted with high contact pressure, gold-plated pins. All kits will henceforth use these connectors which will be pre-crimped. These connectors are of a higher quality and are less fiddly to assemble than the original solder connectors. They also have one large flat face which is ideal for a self-adhesive numbering label. A sheet of self-adhesive numbers is now included in all kits as an aid in identifying the leads. The following list gives the lead numbers in production transmitters: The view inside the case from the rear. The operating channel is set by the plug-in crystal near the centre top of the photo. The interconnecting wiring is now laid around the perimeter of the case for a much neater appearance. 1. Throttle pot 2. Aileron pot 3. Elevator pot 4. Rudder pot 5. Switch 1 (outside left) 6. Aux 1 pot (left) 7. Switch 2 (inside left) 8. Switch 3 (inside right) 9. Aux 2. Pot (right) 10. Switch 4 (outside right) Please note that these numbers are not meant to correspond with those given in the channel allocation table in the August issue. As I have no idea which switch you will use for what application, I cannot possibly match these numbers to the channels. They are only a guide to identifying the leads. Frequency interlock There is one correction for the August article. It stated that the charge plug must be a 2.5mm non-shorting jack. This should read “3.5mm non-shorting”. In the kit will be found two 3.5mm jack plugs. One is for the charger while the other should be fitted to the frequency key as shown in Fig.1. This plug/key combination forms the basis of the Silvertone Frequency Interlock system. Under the rules of operation for the Silvertone Keyboard frequency control system, each transmitter has its own individual key which is inserted into the Keyboard to reserve the frequency and bandwidth required for the transmitter. The only person allowed to insert or remove a key in order to reserve a frequency is the operator of the transmitter on that frequency. Thus, the logical position for the key at all other times is for it to be plugged into the transmitter, thereby rendering it inoperative. The plug/key combination performs this function. When it is inserted into With the back of the case on, the channel-setting crystal is instantly obvious. Only one transmitter may use this channel, for obvious reasons. October 1996  83 Fig.2 (left): detail of the mixing inputs and outputs. Any channel may be mixed with any other and multiple mixes are possible. Fig.3: this diagram shows how the various micro-shunts (shorting links) must be placed across TB10 if the configuration module is not used. the charge socket located on the bottom right of the transmitter control panel, the +9.6V line is open circuited, thereby rendering the transmitter inoperable even if the switch is left on. When the operator wishes to switch on, he takes his transmitter to the Keyboard and checks to see if his frequency is clear. If it is, he then removes his key from the charge socket and inserts it into the Keyboard. Thus, we now have a true frequency interlock system. If the key is in the Keyboard, the transmitter is cleared for transmission. At all other times, the key is in the charge/interlock socket on the transmitter so that the latter is inoperative. Bingo, no more inadvertent shoot downs by transmitters accidentally left on in the transmitter pound! There is an interesting sidelight to this story. When Silvertone invented and patented this system in 1969, the importers went berserk for the simple reason they would have had to pay a royalty on every transmitter sold in this country, had the system been officially adopted in Australia. They kept the system out of official use with a particularly vindictive campaign until about two years after the patent had expired. Then the very people who so vehemently campaigned against the system were the very first to start manufacturing and selling it when the coast was clear. Today the system is known as the Australian National Frequency Con84  Silicon Chip trol System and is approved for use by the MAAA at all national contests, although the frequency interlock aspect of the system is never mentioned. However, every Silvertone transmitter produced since 1969 has featured frequency interlock. Simple mixing programming This explanation will concentrate on the basic principles involved rather than covering every possible combination of mixing. Once the principles have been mastered, the rest falls into place quite easily. Four simple mixers are built into the standard Mk.22 encoder module. Two are inverting and two are non-inverting. These are located at the top righthand corner of the module and consist of a quad op-amp IC (LM324), four mix volume pots, and a double row 8-pin header plug. Fig.2 shows these controls in detail. In radio control parlance, a mixer is essentially a variable gain buffer amplifier, necessary to prevent reverse mixing when the channel inputs and outputs are connected together. Thus, a mixing amplifier is necessary for each mixing function. The input of the mixer is connected to the output of the control channel and the output of the mixer is connected to the input of the mixed channel. If you are confused by this explanation, you may like to refer back to the article on mixing in the December 1995 issue. Mixers 1 & 2 are inverting while mixers 3 & 4 are non-inverting. A non-inverting mixer will give the same direction of rotation in the mixed channel as the primary control channel. An inverting mixer will give the opposite (reverse) direction of rotation in the mixed channel to the primary. Any channel may be mixed with any other channel and multiple channel mixing is possible. Referring to Fig.3 (repeated from page 73 of the August 1996 issue), the pins numbered 1-8 carry all control input data to multiplexer IC5, including dual rate switching. The pins identified by letters are the outputs from the control stick potentiometers via the gain control pot wipers (see the circuit diagram in March 1996) and are used in certain complex mixing functions. When discussing mixing, the primary control channel from which the mix data is to be derived is considered to be the output channel. The mixer inputs and outputs may be found on the Mix Input/Output connectors TB27 and TB28, located at the extreme top right corner of the encoder module. Fig.2 shows these inputs and outputs in detail. Note that there are four pins for each mixer: an input, an output and two for the mix IN/OUT switch. Fig.4 shows the details of the mixing patch cord used to connect the mixer inputs/ outputs to the pins on TB10. One patch cord is required for each Fig 4: the mixing patch cord used to connect the mixer inputs/outputs to the pins on TB10. One patch cord is required for each mixing function. mixing function. The 2-wire, 2-pin socket connects to the appropriate mixer input/output pair with blue to mix/in and white to mix/out. The split leads go to TB10. The blue 2-pin connector is connected to the primary control (channel output) and the white 2-pin connector to the mixed channel (channel input). Two pins of the 3-pin socket on any toggle switch are connected to the switch pin pair. This provides front panel switching for mix in/out. The sense of the toggle switch (UP/OFF) is determined by which two pins are used (centre/left, centre/right). If remote switching of the mixer is not required, then the toggle switch may be replaced with a micro-shunt across the two pins. One switch or micro-shunt is required for each mixing function. Servo throw That completes the description of the basic components in the mixing circuits. Before proceeding any further, there is a very important point to bear in mind when setting up mixing functions. Each mixer input has an additive effect on servo throw and this must be taken into account when setting mix ratios. Failure to observe this may result in the servo being driven into its internal end stops with attendant gear damage. The Mk.22 has automatic compensation built in but it is still possible to drive the servo into over-travel if the mix ratios are set too high. Therefore, be sure to check the final servo travel with the full extremes of mixing applied, as servo travel varies with the brand of servo used. To illustrate the point being made in the above warning, let us examine the mixing process for a delta aircraft featuring elevons (Delta mix). Such an aircraft uses two control surfaces, one on each wing, and each control surface performs two functions: aileron and elevator control – hence the name “elevon”. Fig.5 shows the control sequence in detail. To bank such an aircraft, one control surface goes up and the other goes down, thereby imparting a rolling motion to the aircraft. To raise or lower the nose (pitch control), both control surfaces go up or down, respectively. Complications arise when one wants to bank and climb at the same time. If full throw on the aileron servo gives the desired rate of roll, what Fig. 5: the control sequence for each of a variety of movements in an aircraft fitted with elevons. Elevon controls are very complex to set up correctly. Step-by-step instructions are included in the text. happens when we then apply full up elevator to impart a climbing motion to the aircraft? If we are turning left, then some “up” mixed into the right elevon (which is down in a left roll) is easily accommodated. However, there is no more travel available in the left servo which is already full up. To apply an additional pulse width variation will only drive the servo hard into the end stops and possibly strip the gears. Therefore, the controls must be mechanically arranged so that 50% differential servo travel (one up, one down) gives the maximum rate of roll and 50% common servo travel (both up or both down) gives the maximum pitch angle. If this is done, then we may apply full pitch and roll commands simultaneously. Oddly enough, at this point only one servo actually moves and it goes to full travel. The two commands on the opposing servo cancel each other out and the servo remains in neutral. Elevon controls are very complex to set up correctly, especially when you start to consider the reflex and unequal differential angles which must be taken into account for the correct aerodynamic conditions October 1996  85 Fig. 6: this revised diagram shows the configuration module socket (TB10) in the centre of the encoder PC board. This socket was inadvertently left off the diagram published on page 73 of the August 1996 issue. required by “tail-less” aircraft. So let us move towards this complex programming task cautiously and one step at a time. Simple 2-channel mixing Such applications as Coupled Aileron/Rudder, Flap with elevator compensation and Main Rotor/Tail Rotor mixing all come under the heading of simple mixing applications and may be accomplished with the use of the simple programming patch cord and the on-board mixers. Dedicated, complex mixing utilises the configuration module and these mixing functions will form the basis of later articles. Coupled aileron/rudder with dual rate mixing In this program mode, the Aileron and Rudder controls will be coupled with an adjustable ratio of mix which will change proportionally to the dual rate ratio. To program for coupled Aileron/ Rudder, we are going to take some output from the Aileron channel and feed it into the input of the Rudder channel via one of the on-board mixers and the mix select connectors TB27 and TB28. Both the output and input programming pins are located on TB10, the configuration port connector (Fig.3). At this point, it is necessary to establish whether an inverting or non-inverting mixer is required for your application. Such details as the direction of rotation of the servos and the placement of the control linkages will all play a part here. If the complexity of working it out in your head proves too much, just whack the 2-pin connector onto a non-inverting mixer and if the rudder moves the wrong way, plonk it onto an inverting mixer; very scientific! The procedure is as follows: (1). Replace the micro-shunt from pin 2 of TB10 with the Blue socket. Next remove the micro-shunt from the rudder input on TB10 (pin 4) and replace it with the White socket. (2). Connect the 2-pin socket of the patch cord to the appropriate MIX IN­PUT/OUTPUT connectors on TB27 and TB28, with the Blue lead to “IN” and the White to “OUT”. A close-up view of the frequency interlock key. It plugs into the charging socket on the transmitter when the latter is not being used. 86  Silicon Chip (3). If remote switching of MIX IN/ OUT is required, connect two pins of the appropriate toggle switch to the “Switch” pin pair, checking the sense of operation as you go. If permanent mixing is required then place a micro-shunt across the “switch” pin pair. (4). Adjust the dual rate ratio using the Aileron channel ATV potentiometer in the usual manner and set the ratio of mix using the mix control pot associated with the mixer you have chosen. You are now programmed for Coupled Aileron/Rudder with dual rate mixing. Coupled aileron/rudder without dual rate mixing In some cases, it may be desirable to change the dual rate without changing the mix ratio. In this case, replace Steps 2 and 5 in the above with the following: (2). Connect one pin of the Blue socket to pin A on TB10, leaving the other to float free. Next, replace the micro-shunt on pin 4 with the White socket. (5). Set the ratio of mix using the appropriate mixer potentiometer. Having mastered the basics of simple mixing, and it really is simple once you get the hang of it, the same principles apply to all 24 channels in the Mk.22 transmitter. Any channel can be mixed with any other channel and even multiple channel mixing is possible using the same principles. Let us now look at the more complex task of programming for elevons. In SILICON CHIP SOFTWARE Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. ORDER FORM PRICE ❏ Floppy Index (incl. file viewer): $A7 ❏ Notes & Errata (incl. file viewer): $A7 ❏ Alphanumeric LCD Demo Board Software (May 1993): $A7 ❏ Stepper Motor Controller Software (January 1994): $A7 ❏ Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7 ❏ Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7 ❏ Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7 ❏ Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7 ❏ I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7 POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5 Disc size required:    ❏ 3.5-inch disc   ❏ 5.25-inch disc TOTAL $A Enclosed is my cheque/money order for $­A__________ or please debit my Bankcard   ❏ Visa Card   ❏ MasterCard ❏ Card No. Signature­­­­­­­­­­­­_______________________________ Card expiry date______/______ Name ___________________________________________________________ PLEASE PRINT Street ___________________________________________________________ Suburb/town ________________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). ✂ ✂ this application we begin to confront the concept of channel allocation which really is at the heart of complex mixing. Referring back to our earlier discussion on elevons and comparing it now with the channel allocation table, we find that there are no Aileron or Elevator channels, at least in the sense that we normally understand them. Instead, we are confronted with a left elevon servo and a right elevon servo, both of which respond to Aileron and Elevator commands. Where do we go from here? We still have an Aileron stick on the transmitter as well as an Elevator stick. If we allocate one to left Elevon and the other to right Elevon, I hate to think what would happen. I do not think humans would be too good at manually mixing these controls. The answer is quite simple really. We will use cross-coupled simple mixing in which we will mix channel 2 into channel 3 and channel 3 into channel 2. We will also allocate the Aileron control stick to Channel 2 and the Elevator Control stick to channel 3. Thus, the Aileron stick reverts to its normal action, as does the Elevator stick. So the programming sequence for servos of the same rotation is as follows: (1). Set both the channel 2 and channel 3 vary/normal headers to the vary position. (2). Take two patch cords and connect one to an inverting mixer and the other to a non-inverting mixer on TB27 and TB28. (3). Connect the Blue lead from the non-inverting mixer to pin E on TB10 and the Blue lead from the inverting mixer to pin A on TB10. (4). Remove the micro-shunts from TB10 pins 2 & 3 and replace them with the White socket from the non-inverting mixer to pin 2 and the White socket from the inverting mixer to pin 3. (5). Fit micro-shunts to the appropriate “switch” positions on TB27 and TB28. (6). Use both channel 2 and 3 ATV pots and both mixer volume pots to achieve perfect balance between the movement on both servos. Remember here that Aileron will send the servos in opposite directions (differential), while Elevator will send the servos in the same direction SC (common). October 1996  87 VINTAGE RADIO By JOHN HILL A new life for an old Hotpoint My first commercial radio was a 1940s 4-valve AWA Radi­ola. Recently, I had the chance to restore an almost identical model and that’s what this month’s story is about. So how did an old Hotpoint get into the act? I have mentioned before my early interest in radio and how my spare time as a lad was spent building crystal sets and simple regenerative receivers. This was an exciting time of my life and I have fond memories of those distant days. But although this period spanned many years, it came to a very abrupt end. My tinkering with home-made radios finished the day my father bought me a new receiver for my bedroom. Actually, I think my mother was the main instigator behind this move because she had tired of the perpetual mess that graced the top of a chest of drawers. For years, this area had been strewn with a variety of radios, mountains of batteries, including a smelly rechargeable lead-acid B battery, and other miscellaneous accessories such as headphones, with their long dangling cords. From my mother’s viewpoint, that was untidiness of the worst kind and it had to go! However, in order to remove the junk without fuss or ill feeling, there had to be a satisfactory replacement. Enter one new radio in the form of a late 1940s 4-valve AWA Radiola mantel model with a brown Bakelite cabinet. It must have been Mum’s idea because it wasn’t even Christ­mas or my birthday – it just happened! The little Radiola was in regular use for about 10 years up until the time I left home for the big smoke. Sometime after that it strangely disappeared. Presumably it developed some terminal complaint and was gently laid to rest. At the time I never bothered to ask what happened to it. Now that I would like to know, no-one can remember. Different styles The Hotpoint receiver after restoration. This particu­lar model with the ovalshaped Bakelite dial escutcheon (part of the cabinet moulding) survives better than the model with the separate moulded plastic escutcheon. 88  Silicon Chip My old Radiola had a cabinet style that was not as common as a similar and slightly larger model of that era. As a result, I had, for quite a while, been looking for one to add to my collection – not that postwar 4-valve Radiolas are highly sought after collectables. I just wanted one the same as the one I had back in the 1950s for sentimental reasons. Just why there were two distinct cabinet styles is someth­ing of a mystery. However, the smaller one had an oval shaped dial while the other had a rectangular dial. Otherwise they were much the same inside and the dial shape was about the only no­ticeable difference between models. It was the oval version that I was seeking. This cabinet style is far more durable than the rectangular model. The reason for this difference is that the oval dial has a Bakelite escut­cheon whereas the other is white plastic. The latter warps and cracks with age and, after 40 years or so, is inclined to fall to pieces. Many other Radiolas of similar vintage have the same lousy plastic in their speaker grilles and these too can look terri­ble due to the distortion that takes place over the years. When it comes to plastics, some are far more stable than others. Bakelite vs. plastic Before going further, let’s briefly digress and examine the differences between Bakelite and plastic, just to clarify that last paragraph. Although they are both plastics, Bakelite is a thermosetting plastic which is very stable and holds its form extremely well, even over time spans exceeding 60 years. Thermoplastics, on the other hand, have quite different characteristics and many early thermoplastics virtually self-destruct after 40 years or so. However, thermoplastics can be re-melted and recycled, wher­eas thermosetting plastics cannot! From a collector’s point of view, I’m not particularly interested in restoring any receiver that has a badly deteriorat­ed cabinet due to the use of poor quality plastics. A restoration job should result in a receiver that both looks and performs as new (or close to it). If the cabinet or cabinet fittings have cracked or warped out of shape, then the set is not worth restor­ing. Well, that’s how I see the situation! A Radiola with the rectangular dial escutcheon. This 4-valve model is unusual in that it is a dual-wave receiver. Very few 4-valve sets have a shortwave band. The Hotpoint substitute Anyway, the little 4-valve Radiola I was seeking finally came my way in the form of a Hotpoint! This was, in fact, exactly the same as a Radiola but marketed under another name. Both sets were made by AWA and there were sometimes minor cabinet differ­ences to distinguish the two but not in this instance. Unfortunately, the Hotpoint had a white cabinet with nu­merous cracks which showed up as black lines. Although the set was working, it was in terrible condition with an intermittent contact in the on/off switch and crackles in both the volume and tone controls. But for the miserable sum of $10, it was worth buying, even if it wasn’t a Radiola in a Bakelite cabinet. The old Hotpoint receiver used a couple of unusual valve types: an N78 (6BJ5) and a 6AR7 GT. Note the shield on the 6AR7, a peculiar characteristic of this Australian-designed and manufactured valve. What I didn’t realise at the time was that there was a suitable Bakelite cabinet stowed away in the shed, which I had completely forgotten about. I have no recollection as to where it came from or how it was acquired. The Radiola cabinet was discov­ered quite by accident while I was looking for a valve tester which, I might add, could not be found. No doubt it will be unearthed while I am looking for something else some other time. So it was only a matter of combining the Hotpoint chassis with the Radiola cabinet and I would have a working model of my original little 4-valve radio. Cleaning up The Bakelite cabinet had seen better October 1996  89 A rear view of Hotpoint chassis. This chassis uses a 5-inch (125mm) permag speaker whereas many radios of this era still used electrodynamic speakers. The chassis cleaned up quite well. days. The dirty front half looked so different to the reasonably clean back half that I initially assumed they may not have been a matched pair. To explain, each batch of Bakelite has its own colour char­ acteristics and an unmatched pair of cabinet halves can stand out like a neon sign. Fortunately, this was not the case because when the cabinet was washed and polished, the two pieces blended together perfectly. The Radiola dial had been cracked in two places and this meant that the Hotpoint dial had to be used. Because there ap­pears to be no difference between the Radiola and the Hotpoint radios, I guess I can tolerate a name change. Valve types This 7-pin miniature valve socket is fitted to a chassis that has obviously been designed for octal valves. The other 4-valve chassis uses an octal 6V6GT in this position. 90  Silicon Chip Repairs to the receiver were relatively straightforward and started off well when all four valves tested OK. The valves used were: 6BE6 frequency converter, 6AR7 IF amplifier and detector, N78 (6BJ5) audio output, and a 5Y3 rectifier. The valve complement in the Rad­ iola 4 varies quite a bit. The other receiver shown in one of the accompanying photographs uses a 6A8, 6AR7, 6V6 and 6X5. There receivers were made at a time when manufacturers often had to use whatever components were available, not necessarily what they wanted to use. Getting back to the Hotpoint valve line up, the 6AR7 is an odd type in that it is an Australian-designed and made valve used only in locally made SATELLITE TV EQUIPMENT     Front view of Hotpoint chassis. The loudspeaker sits directly behind the dial. Note that the dial setup uses approximately two metres of dial cord. 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 The UV People ETCH TANKS ● Bubble Etch ● Circulating Shown here are the volume control (left) and the combined tone control and on/ off switch (right). Both potentiometers were repaired by cleaning the resistance track and repositioning the wiper arm. The switch responded to a flush-out with a non-lubricating cleaning fluid. equipment. It usually tests poorly for some reason or other but this one was OK. An EBF35 will work in its place if a 6AR7 is unobtainable. The N78 is also an unusual output valve as far as domestic radio receivers are concerned. The only receivers I have encoun­tered that use this valve have been these early postwar Radi­ olas. Should a substitute valve be required, a 6AQ5 with a re­wired socket and grid bias modification should do the trick. Grid bias Speaking of grid bias, it is worth noting that many 4-valve receivers are under biased. In fact, the output valve’s bias voltage is often at about half the recommended value, even taking into account the lower plate voltages at which some of these small receivers work. If the bias is changed in order to produce the correct voltage, there is a noticeable drop in output volume. Presumably, the output valve is deliberately under biased to raise the output level of the receiver. One must remember that a 4-valve receiver is really only a 3-valve receiver (plus recti­fier) and needs every bit of encouragement LIGHT BOXES ● Portuvee 4 ● Portuvee 6 ● Dual Level TRIMMER ● Ideal PCB DRILL ● Toyo HiSpeed MATERIALS ● PC Board: Riston, Dynachem ● 3M Label/Panel Stock ● Dynamark: Metal, Plastic ✸ AUSTRALIA’S NO.1 STOCKIST ✸ 40 Wallis Ave, East Ivanhoe 3079. Phone (03) 9497 3422, Fax (03) 9499 2381 October 1996  91 In the case of the little Hotpoint, a hollow had been worn through the resistance track on the tone control. This control was combined with an on/off switch and had turned the set on and off many thousands of times during its 45-year life span. This problem was eliminated by simply bending the wiper arm away from the damaged area and onto an unused portion of the track. New capacitors When the text refers to poor quality thermoplastics, it really means poor quality. Shown here is a Radiola plastic escutcheon that has badly distorted with age. A Bakelite escutcheon, on the other hand, would have held its shape, even over a long period of time. in the performance de­partment it can get. Under-biasing the output valve helps to give a bit more gain on those weaker signals –even at the expense of valve life and sound fidelity, which apparently doesn’t amount to much anyway. Problem areas The worst problem areas of the receiver were the volume control and the combined tone control and on/off switch. These components were very worn and highly suspect, especially the on/off switch which was making such poor contact the dial lights were flickering in unison. None of these controls was replaced. Instead, they were all repaired and they came up quite OK. Many volume and tone control potentiometers can be restored to good working order simply by cleaning the resistance track. However, this can be a fairly temporary repair if the track is worn. A better repair results if the wiper arm is bent away from its original contact path and is placed on a previously unused part of the track. Such a simple modification can give a worn potentiometer a completely new lease of life. Faulty on/off switches also respond well to a cleanup and a flush-out with a non-lubricating contact solvent is a good starting point. An ohmmeter set to the 1-ohm range will quickly indicate the condition of the switch contacts. Any measurable resistance in a switch must eventually cause trouble. It is also a good idea to turn old receivers on and off at the power point, as a 40-50 year old switch deserves a rest. On cannot expect them to keep working forever. Any potentiometer combined with an on/off switch will also benefit from switching at the power point, as this will reduce the wear on the track that would otherwise occur each time the switch was used. These replacement control knobs were so tight that the flats on the control shafts had to be filed down so that they could be fitted. 92  Silicon Chip Replacing all of the paper capacitors with more modern varieties raised the high tension voltage by 20V. The electrolyt­ ics were the originals and seemed OK but they were replaced anyway. After applying some Silastic® silicone rubber compound to the thin outer rim of the loudspeaker, it was time to find three control knobs. Finding them was not a problem but getting them to fit the control shafts was another matter. They were so tight that breaking them was a distinct possibility. This problem was solved by filing the flats on the control shafts. They can now be fitted and removed without risk of break­ing. So there it is: a quick and relative­-ly easy restoration of a humble 4-valve receiver, with a few repair hints thrown in for good measure. From my point of view, it was a satisfying project because I could relate to that particular model receiver. Of course, it would have been better if the set had been 100% Radiola. But I guess a mix of Radiola and Hotpoint isn’t a bad compromise, especially when they were both made in the SC same factory. This view shows the replacement loudspeaker cloth around the dial escutcheon. Even the dial light windows were removed and cleaned during the restoration process. 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. Drill speed controller has limitations I recently purchased a 5A Heavy Duty Drill Speed Con­troller kit, as described in the September & November 1992 issues of SILICON CHIP. Although called a Drill Speed Controller, your article does indicate that it is suitable on all “brush type” motors. It also indicates that the incorporation of the Silicon Bilateral Switch has improved the previous circuit which had the problem of “not being particularly good at very low speed set­tings”. I purchased the kit for a specific purpose usage – I have a 5-inch Makita angle grinder (9800 RPM) and I wanted to reduce its speed to about 1000-2000 RPM for use as a buffing machine for polishing cars. The problem with the controller seems to be twofold. At low speeds it seems to make the motor of the machine click on and off, causing an unacceptable jarring of the motor (I am sure it could­n’t be doing the machine any good!) and, at low speeds, the power of the machine is so reduced that it is not practical to use. To overcome these problems I have Stopping stray cats at night This is a cry for help! I built your May 1993 Woofer Stop­ per with great success, not for dogs, but for cats. It was a pleasure to watch them go like greyhounds when the Woofer Stopper was aimed at them. Now that they have the message they don’t come near our garden during the day. Instead, they’ve got crafty and come during the night and there’s nothing I can do to stop them, and this is where the cry for help comes in. I would like to build your Woofer Stopper Mk.II but before I do I would like your to increase the speed of the motor so that it spins smoothly to a speed that unfortunately causes burning of the paintwork (the reason a normal angle grin­ der cannot be used for buffing paint). The technician at the shop where I bought the kit checked my completed speed controller and he felt that I had successfully constructed the kit – he felt that the problems I have outlined above are inherent in the device. I would appreciate your comments on whether these are typi­cal problems or whether they can be fixed. If they cannot then perhaps you should state on the advertising literature that it is unsuitable for use on angle grinders. (R. K., Lismore, NSW). • It is true that the circuit will work with most universal “brush type” motors but we would not go so far as to say that it will work with “all”. In general, these motors should not be used at such a low speed that their inbuilt fan becomes ineffective because no cooling is then available. It is not possible to say how long a particular motor can be used at low speeds but if the case becomes noticeably warm, it would be prudent to stop work to allow it to cool down again. We should also note that all universal motors, when run with this type of speed control and at very low speeds, will have very little useful power output. Your Makita angle grinder is designed to run at a very high speed at which it develops consid­erable power but it is to be expected that if you want to run it at below 2000 RPM, its power output will be feeble. Running a polishing disc actually requires quite a lot of power and even the average 3/8-inch electric drill is really not up to the task – they tend to quickly overheat. Your symptom of jarring at very low speeds is also normal. When a universal motor is running at a very low speed it develops very little back-EMF and so these types of speed control are subject to “cogging”. Just how bad this cogging is will depend on the amount of iron in the field and armature cores. Normally, the higher the operating speed of the motor, the smaller will be the amount of iron and correspondingly, the cogging will be worse. The only cure is to run the motor at not such a low speed set­ting. advice on how to bypass the nine minute timer so that I can switch it on with the toggle switch for a whole night. (J. G., Maylands, WA). • Disabling the 9-minute timer in the original Woofer Stopper can be done by removing Mosfet Q8 and connecting a shorting link between its Drain and Source connections on the board. Alterna­ tively, just remove Q3 and Q8 will be turned on permanently. In the Woofer Stopper Mk.II, the timer is presettable for time intervals of five seconds to 160 seconds. If you wish to build it without the timer, omit IC3 and IC4 and connect pin 4 of IC5 permanently high. I am writing in regard to the Engine Immobiliser kit that appeared in the December 1995 issue of SILICON CHIP. I construct­ed the circuit and the test voltages were all close to what they should be. I then installed the immobiliser into a 1993 model Mitsubishi Magna and it worked as it should. However, one day I accidentally left the ignition on while the Immobiliser was switched on and, after about five minutes, I could smell someth­ ing burning and quickly switched everything off. After inspection of the Immobiliser, I found that the high voltage transistor had overheated to an extent that the plastic case had partially melted. Surprisingly, it still worked. Even though this was an accident, Car engine immobiliser melt-down October 1996  93 Low Voltage Rails for Plastic Power Amplifier I am about to start the “Plastic Power Amplifier” featured in the April 1996 issue of SILICON CHIP and would be obliged if you would let me know the following: (1) Would it be OK to use trannies I have, which are 300VA toroi­dals, giving a 40 volt rail, without compromising the circuit? (2) If OK, I guess the setting of the quiescent would remain the same? (3) Approximately what output would I have – 100 watts? (4) Do you use only off-the-shelf devices and parts; eg, matched pairs, o/p devices? Many thanks for your previous articles. I hope the Plastic Power amplifier is as good as my SILICON the same thing would happen if a car thief was to leave the wires connected after trying unsuccessfully to steal my car. I would then return to the carpark and find nothing but a pile of molten metal! I am confid­ent that the circuit was constructed and installed correctly. It operates fine over any period of time when the key is in acces­sory position. However, when the ignition is on, +12V is present at the coil connection and the circuit overheats. Could this be a design fault? If so, how could it be recti­fied? (T. V., North Adelaide, SA). • We think that your unit may be malfunctioning. When transis­tor Q1 is turned on, the current through the coil should be no more than about four or five amps, as determined by the coil resistance and its associated ballast, if it has one. Hence, the transistor should only be dissipating about 6 or 7W, when it is turned on. However, the transistor is only turned on for about 0.7 seconds in 2.9 seconds (0.7s on, 2.2s off) or 24% of the time. Therefore, even if the circuit is powered up continuously, the power transistor should only dissipate less than 2W. This will make it hot but is not likely to be enough to melt the plastic case or your car! It should be possible to check for correct operation of the Immobiliser with it out of the car. Connect a 1kΩ resistor bet­ween the collector of Q1 and the +12V supply and then apply 94  Silicon Chip CHIP amplifier using boards SC111287 (Decem­ber 1987) which more than compares with a Tandberg amplifier I had (to me anyway). (H. M., Balga, WA). • You can run the amplifier with 40V rails; the quiescent current setting would be the same. However, the power output would be markedly reduced, to around 50W into an 8Ω load or 100W into 4Ω loads. We have not bothered to use matched output devices in our circuits because they are generally not readily available. Howev­er, the use of matched pairs can produce a slight reduction in the harmonic distortion of an amplifier. power. Use your multimeter to measure the voltage between collec­tor and emitter of Q1. It should be +12V (or close to it) for 2.2 seconds, then close to 1V for 0.7 seconds, and so on. If it does not follow this sequence, check the operation of Q2 and the 555. Zener diode tester has incorrect transformer I purchased a zener diode test kit from Dick Smith Elec­tronics and have noted a couple of changes to the original cir­cuit as published in the March 1996 of your magazine: (1) T1 has prewound secondary winding with 136 turns and not 40 as per circuit. The primary winding was 18 turns and not 20 as per circuit and this was for the constructor to wind. The transformer in your article was stated to be a 2:1 step up transformer, thus the windings on the supplied transformer made it, by my calcula­tions, to be a 7.5:1 step-up transformer. (2) ZD1 was a 75V 5W diode not 56V 3W as in the March 1996 circuit. I decided to construct the circuit as supplied and on com­pletion the output voltage measured 470V instead of 112V. I checked and double checked with no change to my test results, so I decided to rewind the transformer with 36 turns to the second­ary and 18 turns to the primary, as I felt this would make it a 2:1 step up, and also be more in line with the original circuit. The output voltage now read 141V. As ZD1 is higher than original specs, the higher voltage output of 141V is probably acceptable. On testing known value zener diodes, the circuit appears to be measuring correctly. Could you please advise me of the implications of changing the ratio of turns on windings as I have done with my circuit. (G. M., Seven Hills, NSW). • We are aware that Dick Smith Electronics has been supplying a different transformer. However, the zener diode should still be 56V as specified, in order to be certain that the various versions of MTP3055 which may be used will not break down. The turns ratio for the transformer does not need to be precisely 2:1 since the circuit has current feedback from the Source of Q1 and this controls the overall level of power deliv­ered to the zener diode under test. However, the turns ratio should still be in the region of 2:1 for correct operation, given that zener diode ZD1 is 56V. Accordingly, with the 136 turn secondary, the primary winding should be somewhere between 60 and 70 turns. Alternatively, as you have found, the transformer can be wound with lesser turns on the primary and secondary and with a ratio of 2:1. We have advised Dick Smith Electronics to this effect. Making Clifford work in daylight I built your Mini Electronic Cricket (Clifford) as de­scribed in the December 1994 issue of SILICON CHIP. I would like to know how to reverse the LDR so it comes on in the light. (I. B., Strathpine, SA). • It should be possible to make the circuit operate in ambient light by swapping the positions of the LDR and the associated 47kΩ resistor. Notes & Errata Fluorescent Lamp Starter, August 1996: the circuit diagram on page 16 shows D1-D4 as 1N4004 diodes. They should be 1N4007 1000V types, as specified in the parts list. 2-Amp SLA Battery Charger, July 1996: the wiring diagram on page 57 has reversed polarity signs on the output cable crocodile clips. The cable coming from the lefthand side of the SC PC board should be positive. MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. FOR SALE LARGE VALVE AMPLIFIER: Make an offer. Greg Wolfe, Warne Street, Bombala. Phone (064) 58 3663. CUSTOM CIRCUIT BOARDS: For all your single and double-sided prototypes. Prompt service, competitive rates. Phone (03) 6228 2600. KITS KITS KITS: EPROM Emulator 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 in the space below or 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. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ $103.70. PIC 16C84 programmer $49.70. Programmable Codepad $78.65. Two Station Intercom $29.50. Logic probe $15.45. Peltier module $32.55. Stereo 3W amplifier module $16.65. Many more. FREE catalog. Mastercard/Visa. Ozitronics (03) 94343806. email: ozitronics<at>c031.aone.net.au 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. C COMPILERS: Dunfield compilers are now even better value. Everything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC16, 8051/52, 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) 9631 1236 or Internet: http://www.mpx.com.au/~lgrant EASY PIC’n Beginners Book to using MicroChip PIC chips $50, Basic Compiler to clone Basic Stamps into cheap ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. ✂ Enclosed is my cheque/money order for $­__________ or please debit my 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 October 1996  95 Your next project will be easy, fast and satisfying with a development kit from MicroZed Computers Scott Edwards Electronics Microchip OPTO 22 NEW Micro Micro Engineering Labs (PICBASIC) MICROMINT PicStic DOMINO BLACKJACK PO Box 634, ARMIDALE 2350 (296 Cook’s Rd) Advertising Index Altronics................................. 76-78 Ph (067) 722 777 – may time out to Mobile 014 036 775 Fax (067) 728 987    (Credit Cards OK) Av-Comm.....................................17 http://www.microzed.com.au B & M Electronics........................91 Specialising in easy-to-get-going hard/software kits. Send 2 x 45c stamps for information package Stamp kits now have a compiler for 16C58 Dick Smith Electronics........... 28-31 Earthquake Audio........................79 EDA Solutions.............................21 MEMORY * MEMORY * MEMORY SPECIAL! (Ex Tax) 1Mbx9 – 70ns $18 30-pin Simms PIC16C84’s $135, CCS C Compiler $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. SIMMS (Parity/No Parity) 4Mb 30 PIN-70 $47 $63 4Mb 72 PIN-70 $50 $42 8Mb 72 PIN-70 $90 $67 16Mb 72 PIN-70 $167 $143 32Mb 72 PIN-70 $355 $284 EDO SIMMS 8Mb (1Mbx32) – 60ns $76 16Mb (2Mbx32) – 60ns $144 32Mb (4Mbx32) – 60ns $290 MAC MEMORY 8Mb P’BOOK 190 $147 8Mb DOCK DUO $249 16Mb P’BOOK $257 MicroZed Web page always under construction. http://www.microzed.com.au KIT CONSTRUCTION: Electronic and speaker kits assembled at rea­sonable prices. Money back guarantee. Phone (014) 93 1227. 96  Silicon Chip Emona.........................................81 Freedman Electronics....................9 Harbuch Electronics....................79 Instant PCBs................................96 Jaycar ................................... 45-52 Kalex............................................91 Ex Tax Pricing – Delivery $8. Pricing as at 28/8/96. Phone for latest. Sales Tax 22%. Credit Cards Welcome. We Also Buy And Trade-In Memory. PELHAM Memory Pty Ltd MICROCRAFT PRESENTS: Dunfield (DDS) products are now available ex-stock 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. LASER PRINTER MEMORY 2Mb UPGRADE $150 COMPAQ 8Mb CONTURA AERO $147 All other models available $Call TOSHIBA 8Mb Portege/ Sat EDO $135 16Mb Portege/ Sat EDO $235 16Mb Tecra 500/610 Sat $298 All other models available $Call CACHE 256K PIPELINE BURST $25 256K 7200/8500 $100 VIDEO MEMORY 256K x 16 70ns (SOJ) $17 1Mb 7200/7500/9500 $83 SO DIMMS 8Mb/16Mb $108/227 Suite 6, 2 Hillcrest Rd, Ph: (02) 9980 6988 Pennant Hills, 2120. Fax: (02) 9980 6991 Email: pelham1<at>ozemail.com.au Kits-R-US.....................................80 MicroZed Computers...................96 Oatley Electronics..........................7 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 Pelham........................................96 RCS Radio ..................................95 Rod Irving Electronics .......... 60-64 Silicon Chip Bookshop...............IBC MicroZed has MICROCHIP NEW PICSTART kits also Programmers from Parallax and Micro. Eng. Lab. Silicon Chip Software..................87 68HC705 Development System: Oztechnics, PO Box 38, Illawong NSW 2234. Phone (02) 9541 0310. Fax (02) 9541 0734. http://www.oz­technics.com.au/ Silicon Chip Wallchart..............OBC WANTED WANTED: Circuit of Silver SS171. Box 535 Geraldton, WA 6531. Tel (099) 21 2176. SWAP MEET VINTAGE RADIO SWAP MEET: Sunday October 20th 1996. Glenroy Tech School Hall, Melbourne, Victoria. Mel­ way Ref Map 16.K.2. Admis­ sion $3. Inquiries (054) 49 3207. Silicon Chip Back Issues.............10 Tortech.........................................20 Zoom Magazine.........................IFC _________________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 587 3491. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, semicustom electronics & data communications. 63 chapters, in hard cover at $120.00. Silicon Chip Bookshop Radio Frequency Transistors Newnes Guide to Satellite TV Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1994 (3rd edition). This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 371 pages, in hard cover at $55.95. Guide to TV & Video Technology By Eugene Trundle. First pub­lish-­ ed 1988. Second edition 1996. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 382 pages, in paperback, at $39.95. Servicing Personal Computers By Michael Tooley. First published 1985. 4th edition 1994. Computers are prone to failure from a number of common causes & some that are not so common. This book sets out the principles & practice of computer servicing (including disc drives, printers & monitors), describes some of the latest software diagnostic routines & includes program listings. 387 pages in hard cover at $59.95. format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $55.95. The Art of Linear Electronics By John Linsley Hood. Pub­lished 1993. This is a practical handbook from one of the world’s most prolific audio designers, with many of his designs having been published in English technical magazines over the years. A great many practical circuits are featured – a must for anyone inter­ested in audio design. 336 pages, in paperback at $49.95. Components, Circuits & Applica­ tions, by F. F. Mazda. Published 1990. Previously a neglected field, power electronics has come into its own, particularly in the areas of traction and electric vehicles. F. F. Mazda is an acknowledged authority on the subject and he writes mainly on the many uses of thyristors & Triacs in single and three phase circuits. 417 pages, in soft cover at $59.95. Digital Audio & Compact Disc Technology Electronics Engineer’s Reference Book Hard cove Produced by the Sony Service Centre (Europe). 3rd edition, published 1995. Prepared by Sony’s technical staff, this is the best book on compact disc technology that we have ever come across. It covers digital audio in depth, including PCM adapters, the Video8 PCM Power Electronics Handbook Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order r Edited by F. F. Mazda. version now available First published 1989. 6th edition. This just has to be the best refer­ ence book available for electronics engineers. Provides expert coverage of all aspects of electronics in five parts: techniques, physical phenomena, material & components, ❏ Bankcard ❏ Visa Card ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ Return to: Silicon Chip Publications, PO Box 139, Collaroy NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details; or fax to (02) 9979 6503. Principles & Practical Applications. By Norm Dye & Helge Granberg. Published 1993. This book strips away the mysteries of RF circuit design. Written by two Motorola engineers, it looks at RF transistor fundamentals before moving on to specific design examples; eg, amplifiers, oscillators and pulsed power systems. Also included are chapters on filtering, impedance matching & CAD. 235 pages, in hard cover at $85.00. Surface Mount Technology By Rudolph Strauss. First pub­ lished 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­ soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Audio Electronics By John Linsley Hood. Pub­lished 1995. This book is for anyone involved in designing, adapting and using analog and digital audio equipment. Covers tape recording, tuners & radio receivers, preamplifiers, voltage amplifiers, power amplifiers, the compact disc & digital audio, test & measurement, loudspeaker crossover systems and power supplies. 351 pages, in soft cover at $52.95.   Title  Newnes Guide to Satellite TV  Guide to TV & Video Technology  Servicing Personal Computers  The Art Of Linear Electronics  Digital Audio & Compact Disc Technology  Power Electronics Handbook  Electronic Engineer's Reference Book  Radio Frequency Transistors  Surface Mount Technology  Audio Electronics Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ & PNG add $10.00 per book, elsewhere add $15 per book. TOTAL $A Price $55.95 $39.95 $59.95 $49.95 $55.95 $59.95 $120.00 $85.00 $99.00 $52.95