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Tune Up Your PC’s Hard Disc Drive SILICON CHIP $5.50* JUNE 1997 NZ $6.50 INCL GST C I M A N Y D 'S A I L A AUSTR E N I Z A G A M S C I ELECTRON SERVICING - VINTAGE RADIO - COMPUTERS - SATELLITE TV - PROJECTS TO BUILD PRINT POST APPROVED - PP255003/01272 Colour TV Pattern Generator This new colour TV pattern generator is programmed from your PC’s printer port. Pt.1 this month tells you how it works. BONUS ! DICK High-current speed controller for 12V & 24V DC motors SMITH ELECTRO PC-programmable thermostat NICS CATALOG Track down faults with our AUST. O NLYJ 1997  1 new signal tracer Stepper motor control circuit ISSN 1030-2662 06 une 9 771030 266001 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings.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 Contents Vol.10, No.6; June 1997 FEATURES   4  Using Robots For Water-Jet Cutting Water-jet cutting is feasible for a wide range of materials. We explain how it works – from ABB 54  Tuning Up Your Hard Disc Drive Your hard disc drive requires regular tune-ups for trouble-free operation. Here’s how to go about it – by Jason Cole 66  Cathode Ray Oscilloscopes; Pt.10 Final chapter looks at diode bridge switches, feedback A/D converters and random equivalent time sampling – by Bryan Maher Build A PC-Programmable Thermostat – Page 10 PROJECTS TO BUILD 10  PC-Controlled Thermometer/Thermostat Simple project plugs into your PC’s printer port and is programmed by clicking a few buttons – by Mark Roberts 14  Colour TV Pattern Generator; Pt.1 Ideal for the service technician, this unit stores its patterns in an on-board ROM which is programmed from a PC – by John Clarke 26  High-Current Speed Controller For 12V/24V Motors Efficient PWM design incorporates soft start circuitry and can control DC motors drawing up to 20A – by Rick Walters High-Current Speed Controller For 12V & 24V Motors – Page 26 40  Build An Audio/RF Signal Tracer Simple signal tracer is ideal for tracing RF and audio signals in radio receivers and audio amplifiers – by Rick Walters 62  Manual Control Circuit For A Stepper Motor Build this circuit and drive a stepper motor in one direction or the other for a fixed time – by Rick Walters SPECIAL COLUMNS 53  Satellite Watch The latest news on satellite TV – by Garry Cratt 57  Serviceman’s Log I don’t like house calls – by the TV Serviceman 74  Radio Control A fail-save module for the throttle servo – by Bob Young Audio & RF Signal Tracer – Page 40 78  Vintage Radio A look at signal tracing, Pt.3 – by John Hill DEPARTMENTS  2  Publisher’s Letter 23  Mailbag 32  Circuit Notebook 37  Order Form 38  Back Issues 86  Product Showcase 90  Ask Silicon Chip 93  Notes & Errata 94  Market Centre 96  Advertising Index Stepper Motor Control Circuit – Page 62 June 1997  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 Brendon Sheridan Phone (03) 9720 9198 Mobile 0416 009 217 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Julian Edgar, Dip.T.(Sec.), B.Ed John Hill Mike Sheriff, B.Sc, VK2YFK Ross Tester Philip Watson, MIREE, VK2ZPW Bob Young Photography Glenn A. Keep 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 Cellular phones & Radio Australia Two topics require comment this month and the first of these concerns cellular phones. There have been recent reports in the media about a possible link between using cellular phones and cancer. Dr Michael Repacholi, from the Royal Adelaide Hospital, and well known in the field, has conducted tests involving mice which were exposed to radiation at 900MHz, the frequency used for cellular phones. Following these tests, there has been an announcement that European Union scientists will spend $35.4 million looking into the interaction been cellular phones and living tissue. These reports will no doubt cause many people a lot of concern, as indeed they should. I am amazed at the amount of time that some people spend glued to a cellular phone. The phone’s antenna radiates directly into your head and while it may not penetrate very deeply according to theory, prolonged exposure can’t be good. We’ve also had reports that some cellular phones can cause some people headaches. At this stage, we have no evidence that these reports are true but it would not surprise us if they were. If you do experience headaches when using a cellular phone, we strongly suggest that you: (1) stop using it; and (2) return it to the retailer where you purchased it. It may just be that the unit is radiating more power than it is supposed to. The second topic worthy of comment is the cutting back of Radio Australia’s operations. There has been a media frenzy over this topic but most of it does not seem very logical. The first point made in defence of Radio Australia is that it is important to Australia’s trade prospects in Asia. I don’t for a minute believe this. In these days of worldwide satellite broadcasts, I can’t imagine too many Asian businessmen being influenced one way or the other about whether to trade with Australia. Second, we are told that for $23 million and 200-odd staff Radio Australia provides 368 hours of programming in nine lan­guages. By comparison with the cost of running the Voice of America, etc, this is regarded as something of a bargain. My reaction to this is why does it cost so much to rehash local news? That is $115,000 spent for each member of the staff. Third, we are told that Radio Australia reaches untold millions throughout Asia and that they rely on our fair and objective reporting of events. Does anyone really believe that? How many people in Australia actually listen to any shortwave radio broadcasts on a regular basis? Very, very few! It can’t be much different in most parts of Asia either as even the smallest villages are able to receive satellite TV services and they do have their own radio stations, after all. This concept of remote villagers hanging on every word of a foreign broadcast might have been true 30 years ago but no longer. Radio Australia might be worth keeping but the reasons raised for keeping it have been pretty weak so far. 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 SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. Using water and its suppliers installed sys­tems to cut floor carpeting and other interior linings. Today, water-jet systems have practically replaced punching and mechani­cal methods for this work. This is because the punching tools needed for complex shapes are highly complicated, making them very expensive. Worst of all, they are completely inflexible and have to be rebuilt every time changes are made to the shapes of the work pieces. For those who haven’t come across it before, the concept of using a jet of water to cut materials is mind-boggling. But with extreme water pressures and abrasives added, water-jet cutting is feasible for a wide range of materials. W ATER-JET CUTTING was first used in 1975, when it was introduced to produce wooden puzzles. It replaced a method in which saws were used to cut out the individual pieces. Besides working with a higher precision, the new method also produced less dust. For many years water-jet technology was used only for mar­ginal applications, for example to cut deep-frozen products and ice-cream. As the versatility of the method was recognised, so-called water-jet job-shops were TOP OF PAGE: Robots used for waterjet cutting have coiled high-pres­sure pipes to provide elastic compensation for changes in angle & twisting of the robot’s wrists. 4  Silicon Chip set up. The technology employed in these shops was almost exclusively two-dimensional, with abrasive being added to the water whenever harder materials had to be cut. Water-jet cutting is most often used to replace traditional punching of materials and not sawing or other cutting methods such as laser or plasma cutting. The main advantage of water-jet cutting is that, unlike punching, it does not require a special tool for each work piece. The first systems for producing parts with three-dimension­al shapes were developed in 1985. Computer-controlled water-jet robots were used first by suppliers to the automotive industry, who employed them to cut roof linings for cars. In the following years, the automotive industry Abrasive water-jets Water-jet technology can be used to cut virtually every material, even steel and aluminium. For example, Crane Fruehauf Ltd. of Norfolk, UK, uses large abrasive water-jet cutting tables to produce the cylindrical containers for road tankers. Due to the high energy of the abrasive water jet, thicker aluminium and steel plates can be cut than with laser or plasma cutters. Unlike laser or plasma cutters, water-jet cutting causes minimal heating. With laser and plasma cutting, the heat devel­oped affects the cut edges, which require further work before the parts can be welded. Also, water-jet cutting is generally insensitive to distur­bances such as vibration caused by other metal-forming processes. With water-jet cutting, Crane Frue­ hauf is able to cut a large variety of different materials. As a rule, the system is used to cut 3mm thick stainless steel and structural steel at a rate of 600mm per minute. More commonly, water-jet technology is used to cut plastics and composites, especially fibre composites, laminated struc­tures, and glass-fibre reinforced and wood-fibre-based com- robots for r-jet cutting Waterjet cutting is used in the manufacture of numerous interior parts of motor vehicles. The result is very clean cut material and no need to make custom punches or jigs. posites. Oscillating cutting methods or conventional machining cannot be used for these materials because they don’t give a clean cut. Much of the interior trim of modern passenger cars can be produced using water-jet cutting, for example the roof, door and boot linings, rear shelves, carpets, instrument panels and bump­ ers. German car maker BMW uses the method for cutting out its instrument panels. This relatively new technology is largely the result of development work carried out by ABB I-R Robotised Waterjet, a joint venture set up by Asea Brown Boveri and Ingersoll-Rand. ABB I-R is the market leader in water-jet cutting equipment for three-dimensional applications and to date the company has in­stalled more than 250 systems worldwide. Water-jets cut with high precision. The main characteris­tics and benefits are summarised below: •  Suitable for cutting composite, textile or fibreglass reinforced materials. •  Minimal heat produced. •  No dust, odours or smoke produced in the workplace. •  Surfaces of the cuts are of a high quality. •  Cutting forces are low. •  Only simple work piece fixtures are needed. •  The tool is always sharp as there is no wear. •   Tool radius can be less than 0.15mm, allowing sharp-edged contours to be cut. Very high water pressures This 3-D water-jet cutting system at Crane Frue­hauf Ltd in the UK is used to cut 3mm thick stainless steel and structural steel at a rate of 600mm/minute. Installed in the cutting box is an electrically driven pump that drives June 1997  5 A water-jet cutting tool consists of: (1) a high pressure pipe; (2) a nozzle made of diamond, sapphire or very hard metals; and (3) a screwed cap. Hard metal nozzles are used when abrasives are added to the water. In this water-jet process, two ABB robots and an automatic shell-lifter are used to cut car head linings in one operation. The finished head lining is then ready for installation in a car. a high-pressure unit. A conventional hydraulic system with a power input of 20-40kW provides the driving force for one or more double-acting pressure boosters which produce the required pressure in the water jet. The working pressure lies between 3,000 and 4,000 bar (equivalent to 43,000 to 58,000 psi), depending on the application. The nozzles are made of sapphire, diamond or very hard metals, with an internal diameter of 0.1-0.5mm, to create a very thin jet. Hard-metal nozzles are needed when abrasives are added to the water. The maximum distance between the nozzle and the surface of the material being cut is about 50mm. After it has cut through the work piece, the jet turns into a spray and imme­diately loses its cutting ability. The particles removed during cutting are washed out with the water and are collected by filters before it drains to the sewer. The amount of water used is quite small – an average of 1.5 litres/minute per nozzle. High noise levels CAD animation allows systems envisaged by a customer to be shown in three dimensions, allowing techni­cal evaluations and the fixing of cycle times. 6  Silicon Chip The process is extremely noisy. For a system pressure of 3500 bar and nozzle diameter of 0.5mm, the velocity of the water-jet is about 800 metres/ second which is about three times the speed of sound. The resulting noise level is somewhere between 110dB(A) and 120dB(A). Because of the risk of physical injury and the high noise levels, the only feasible way to operate water-jet Modified robots ABB robots used for water-jet cutting are modified for wet working conditions. They have specially designed high-pressure piping, including a modification to solve problems caused by the rotation of the robots’ wrists. This involves the pipes being wound in a coil around the axes to provide elastic compensation for changes in angle and twisting of the wrists. As well, the robots are suspended from a gantry. This gives more working space than with floor-mounted robots and ensures that the robots remain relatively dry, since they do not stand in water. CAD animation To speed up the design, construction and installation of customised, robot-based systems, ABB I-R has developed CAD anima­tion of water-jet cutting projects. It enables proposed systems to be shown in detail on a computer screen. The design of the installation, cutting tools and robots are all simulated to allow a detailed evaluation of the overall system. Preliminary studies, such as technical analyses and the determination of collision risk, can be carried out at an early stage. In addition, cycle times can be fixed and the operating times of the individual robots can be harmonised. CAD animation allows the robots to be programmed in paral­lel with the actual construction of the system. CAD animation also enables the robot programs of systems already installed to be easily rewritten for new or modSC ified products. 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______________ Acknowledgement: this article has been adapted from the original which appeared in the January 1997 issue of ABB Review, published by Asea Brown Boveri Ltd. 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). ✂ cutting equip­ment is via robot or numeric control. Water-jet cutting tools in 2D-installations are guided by AC-driven linear units. ABB industrial robots are used in 3D cutting installations to allow optimum control of the water jet. For example, a six-axis robot can manipulate the nozzle in any required direction while ensuring the right cutting angle. The nozzle is moved along either linear or spherically curved paths at high speed and with very good repeatability. June 1997  7 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.dse.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.dse.com.au A PC-controlled thermometer/thermostat Consisting of just a few parts, this simple project plugs into your PC’s printer port and is a fully working digital ther­mometer and thermostat. The accompanying software generates the on-screen display and lets you adjust the thermostat settings. By MARK ROBERTS This little project is ideal for use as a thermostat in an industrial control system and once programmed, it can operate independently of the PC. Alternatively, you could use it to just give a digital readout of the current temperature on your PC’s screen. It’s the software that does all the 10  Silicon Chip hard work here. As well as generating the on-screen display, it displays the current temperature and lets you set the high and low trip points for the thermostat just by clicking a few buttons. We’ll take a closer look at this shortly. By using software control, the hardware requirements are kept to an absolute minimum. In fact, all the parts except for a single IC are housed in the backshell of a DB25 connector. Circuit details Fig.1 shows the circuit details of the Digital Thermometer/Thermostat, together with an optional relay driver circuit. The IC, which forms the heart of the hardware, is a DS1620 Digital Thermometer & Thermostat (IC1) from Dallas Semi­conductor – see Fig.2. This programmable device measures temp­ er­ atures from -55°C to +125°C in 0.5°C increments and has three “alarm” outputs designated THIGH, TLOW and TCOM. In operation, THIGH goes high (ie, switches from logic 0 to logic 1) when the temperature exceeds a user-de- fined upper limit. Conversely, TLOW goes high when the temperature falls below a preset lower limit. The third output, TCOM goes high when the temperature exceeds the upper limit and stays high until the temperature falls below the lower limit. These three outputs can be used to directly control heating and cooling appliances via suitable driver circuitry (eg, relays and optocouplers). Data is read from and written to the DS1620 via a 3-wire serial interface (CLK, DQ & RST). In addition, the user-defined upper and lower trip points are stored by the IC in a nonvola­ tile memory. This means that the IC can be programmed before building it into a control system. Alternatively, the IC can be interfaced to a microprocessor (or left connected to a computer), so that the trip points can be quickly adjusted to suit the process. In this circuit, IC1’s clock and reset inputs (pins 2 & 3) are driven via pins 3 & 9 of the parallel port, respectively. Pin 1 is the data (DQ) input and this is driven by pin 2 of the parallel port via diode D1 and pulldown resistor R1. The outputs from IC1 – T HIGH, TLOW & TCOM – are connected back to pins 11, 12 & 13 of the parallel port, respectively. This allows the software to read the values on these lines and adjust the on-screen display accord- The software lets you set THIGH and TLOW just by clicking the Min and Max buttons. Note that the TLOW indicator (at right) has come on here because the measured temperature is at TLOW. ingly. In addition, each output controls an NPN transistor (eg, BC327) in the suggested relay driver circuit. Transistor Q1 is driven by pin 7 (the THIGH output) of IC1. Normally, THIGH is low and so Q1 and RLY1 are off. However, if the monitored temper- ature exceeds the preset maximum, THIGH switches high and so Q1 turns on and switches on RLY1 to control the process. At the same time, TCOM also goes high and this turns on Q2 and RLY2. If the temperature now drops below Fig.1: the circuit is based on the DS1620 Digital Thermometer/Thermostat IC from Dallas Semiconductor and uses just three components. Also shown here is a suggested thermostat control circuit based on three transistors and three relays. June 1997  11 the preset maximum, THIGH switches low again and Q1 and RLY1 both turn off. However, TCOM remains high until the temperature drops below the preset minimum, as which point it switches low again and Q2 turns off. TLOW now goes high and turns on Q3 and RLY3. In practice, you can use one or more of these outputs to control a fan or a heating appliance to suit your application. For example, you could use the TCOM output to activate a fan when the temperature exceeded THIGH. This fan would then remain on until the temperature dropped below TLOW. It’s up to you how you use the outputs. Construction Fig.3 shows the wiring details for the unit. As can be seen, the two internal components (R1 and D1) are soldered di­rectly to the pins of the DB25 connector, while the IC is con­ nected via eight flying leads. These flying leads are best run to an 8-pin socket, so that the IC can be easily removed after programming. Software The software comes on three floppy discs and runs under Windows 3.1x Windows 95. It’s easy to install – you simply run the Setup.exe file on the first disc (within Windows) and follow the on-screen instructions. The accompanying screen grabs show the control panel that appears when you boot the thermometer/ thermostat program (Therm.exe). As Fig.2: block diagram of the DS-1620 Thermometer/ Thermostat. 12  Silicon Chip Fig.3: the circuit is built by directly wiring it to a DB-25 male connector. Both the THIGH and TCOM indicators come on when the measured temperature reaches THIGH, as shown here. shown, the current temperature is directly displayed (both as a direct readout and on a dial) and you can easily set THIGH and TLOW by clicking the appropriate Min. and Max. buttons. You can also choose an alternative printer port (LPT2). The control panel also shows the status of the outputs. This lets you program the unit and then check that everything is working correctly. Once the unit has been programmed, you can unplug it from the computer and use it in your application. Note that pin 8 of the DS1620 must be connected to the +5V rail when used in the thermostat mode (ie, disconnect pin 8 from the DB25 SC connector). Once it turns on, the TCOM indicator stays on until the measured temperature falls below TLOW. Where To Buy Parts & Software Parts and software for this design are available as fol­lows: (1). DS1620 Thermometer/Thermostat .................................................$12 (2). DS1620 Thermometer/Thermostat with programmed TLOW and THIGH (you specify) ..................................................................$15 (3). Software (read current temperature, TLOW & THIGH only) ............... $15 (4). Software (full read/write version) ....................................................$25 (5). Optional LPT2 interface card for PC ...............................................$15 Please add $5 for postage. Payment by cheque or money order only to: Mr Softmark, PO Box 1609, Hornsby, NSW 2077. Ph/fax (02) 9482 1565. Note: the software associated with this project is copyright to Mr Softmark and may not be copied without permission. PARTS LIST 1 DS-1620 Thermometer/ Programmer software (3-disc set for PCs) 1 DB-25 male connector with backshell 1 8-pin IC socket 1 DS1620 Digital Thermometer/ Thermostat (IC1) 1 1N4184 silicon diode 1 1kΩ 0.25W resistor Optional thermostat 3 5V relays (RLY1-RLY3) 3 BC337 NPN transistors (Q1-Q3) 3 1N4004 silicon diodes (D2-D4) 3 2.2kΩ 0.25W resistors 3 1kΩ 0.25W resistors This close-up view shows how the parts are wired to the DB-25 connector. Note that the final version differs slightly from this early prototype. June 1997  13 Colour TV pattern generator; Pt.1 This versatile colour TV pattern generator stores its patterns in a ROM which is programmed via a computer port. It’s easy to build and you can even customise it to include your own patterns. By JOHN CLARKE This new Colour TV Pattern Generator is a ground-breaking design for SILICON CHIP. It is the first circuit that we have produced that uses an EEPROM which you can program from your own PC. This means that if you don’t like the standard patterns, or have some special requirement, you can modify the software and program 14  Silicon Chip in your own patterns (provided you have Quick Basic). Of course, you don’t have to do this if you don’t want to. We anticipate that several retailers will offer this design as a complete kit of parts and will include a pre-programmed EEPROM. Pre-programmed EEPROMs will also be available from SILICON CHIP, as will the programming software. Basing the design on an EEPROM has a number of advantages. For the first time, it allows us to offer a circle as one of the patterns. Our previous designs have omitted this rather useful feature because it couldn’t be done with conventional logic circuits. The EEPROM approach simplifies the circuit and makes the unit easier to build. Using a pattern generator If you service colour TV sets or want to adjust your own TV set for a first class picture, a pattern generator is a must. It is an essential tool for making convergence and purity adjust­ments, for adjusting picture geometry and for fault finding. These screen images (captured via a PC video frame grabber) show just four of the patterns produced by the pattern generator (the others are red raster, white raster and greyscale). Note that the circle appears stepped because the image is not interlaced. Note also that the colours shown in the colour bar pattern are not true to life, due to limitations in the printing process. This unit can generate seven different patterns: checkerboard, dot, circle/crosshatch, red raster, white raster and colour bars. In addition, you can select between greyscale and colour patterns. We’ll look at each pattern in turn and describe how it’s used. First, the checkerboard pattern provides a useful indica­tion of the low frequency response of the video stages. If the set is functioning correctly, the black/white edges of this pattern will be sharp and straight. Conversely, a set with a poor low-frequency response will show smearing between the black and white areas, along with rounded corners. The dot and crosshatch patterns are useful when making static and dynamic convergence adjustments. On a set with poor static convergence, for example, each dot will actually consist of separate red, green and blue dots rather than a single white dot. Similarly, poor dynamic convergence will cause the lines in the crosshatch pattern to splay into separate red, green and blue lines at the edges of the screen. The crosshatch/circle pattern is also useful when adjusting picture geometry. This involves setting the correct height and width to obtain a perfect circle and minimising pincushion dis­tortion. “Pincushion distortion” refers to the tendency for lines near the edges of the picture to bend inwards or outwards at the centre. The red and white rasters (ie, full red and full white screens) allow purity adjustments, so that the entire screen shows the one colour without irregularities. On sets with purity problems, the white raster may show blotches or red, green or blue. This indicates that it is necessary to degauss (ie, demagnetise) the metalwork inside the picture tube. Eight colour bars – white, yellow, cyan, green, magenta, red, blue and black – make up the colour bar pattern. This pat­tern is ideal when tracking down faults, since any waveforms depicted on a TV set circuit diagram are typically staircases, usually derived using a colour bar pattern as the RF/video source. By comparing the observed waveforms with those depicted on the circuit diagram, it is often possible to locate the faulty section. By turning the colour burst off, we get a greyscale bar pattern ranging from white to black. This is used for checking the greyscale tracking and for brightness and contrast adjustments. Design improvements Our last Colour TV Pattern Generator was published in November 1991. Although it produced nominally the June 1997  15 Main Features •  Produces dot, crosshatch/circle, checkerboard, red raster, white raster, colour bars and greyscale •  Patterns correctly centred on the screen •  Square crosshatch and checkerboard patterns •  Direct video output plus RF video modulator output •  Option for S-video outputs (chrominance and luminance signals) •  Audio input for video modulator (to test sound) •  Patterns and sync stored in ROM with option to customise pat­terns Specifications Number of lines ����������������������������������� 312 (Aust. PAL Standard: 312.5 x 2) Line (H) sync ��������������������������������������� 4.57µs (Aust. PAL Standard: 4.5-4.9µs) Line period ������������������������������������������ 64.087µs (1358ppm fast) (Aust. PAL standard: 64µs) Line (H) blanking ��������������������������������� 12.22µs (Aust. PAL Standard: 11.8-12.3µs) Field (V) sync �������������������������������������� 7 lines (Aust. PAL Standard: 2.5H for preequalis­ing pulses, 2.5H for sync and 2.5H for post-equalising pulses) Field (V) blanking �������������������������������� 25 lines + 12.22µs (Aust. PAL Standard: 25 lines + 11.8-12.3µs) Field frequency ������������������������������������ 50.012Hz (2400ppm fast) (Aust. PAL Standard: 50Hz) Crosshatch pattern ������������������������������ 11 horizontal (1 line high) x 15 vertical lines (305ns wide). Horizontal and vertical lines are located at the screen centre Circle pattern ��������������������������������������� 80% of full vertical screen height, 60% of full horizontal screen. Dot pattern ������������������������������������������ 11 horizontal rows (1 line high) x 15 vertical col­umns (305ns wide). A dot is at the centre of the screen Checkerboard pattern �������������������������� 7 horizontal x 5 vertical squares alternate black and white Colour bar pattern ������������������������������� 8 vertical bars 6.1µs wide with 1.22µs extra width on outside bars Bar colours ������������������������������������������ standard white, yellow, cyan, green, magenta, red, blue and black Colour burst signal ������������������������������ 10 cycles of 4.43361875MHz signal occurring 5.59µs after beginning of H sync <at> 249mV p-p (Aust. PAL Stan­dard: 10 cycles 5.6µs after leading edge of H sync) RGB to YUV encoding ������������������������� Y = 0.299R + 0.587G + 0.114B, U = 0.493 (B-Y), V = 0.877(R-Y) – (to Australian PAL Standard) Chrominance to luminance delay �������� -170ns RF output channel ������������������������������� 0 or 1 Video output impedance ���������������������� 75Ω Video output ���������������������������������������� 2Vp-p unloaded, 1Vp-p with 75Ω loading 16  Silicon Chip same patterns as this latest version (but no circle), it did have a few minor drawbacks. First, the patterns were not centred exactly in the middle of the screen, which made convergence adjustments less precise. Second, the crosshatch and checkerboard patterns were not exactly square, which made it harder to check for linearity errors in the picture. Third, it used a Philips TEA­ 2000 colour encoder IC which is now obsolete. These drawbacks have all been overcome in this new design. As mentioned above, the new circuit uses an EEPROM (electrically erasable programmable read only memory) to store all the patterns and generate the sync pulses. This arrangement reduces the IC count from 16 to 11 and correctly centres the patterns on the screen. In addition, the checkerboard, crosshatch and dot patterns are exactly square and a circle has been added, as noted above. The circle allows screen linearity to be checked at a glance and makes for straightforward height/width adjustments. If the circle is looking a little squat, for example, then the height is too low. Conversely, if the circle looks tall and thin, the height needs to be reduced. Most of the signals from the Colour Television Pattern Gen­erator comply with Australian PAL standards. These include the horizontal sync pulse and blanking intervals, and the colour burst and its position. The vertical sync pulse signal does not include the pre- and post-equalising pulses since these are only necessary with an interlaced 625-line signal. Physical arrangement The SILICON CHIP Colour Pattern Generator is housed in a standard plastic instrument case and is powered from a 12VAC mains plugpack. A 5-position rotary switch selects between the checkerboard, dot, crosshatch/circle, red raster and white raster patterns, while a 2-way toggle switch is used to select the colour bar pattern. An adjacent toggle switch selects either the colour and greyscale patterns, while a third toggle is the power on/off switch. Both composite video and RF outputs are provided on the rear panel (RCA sockets) and there is also an audio input socket. The latter allows audio to be fed directly into the RF Fig.1: this block diagram shows the unit in pattern mode. There are three main circuit sections: (1) an oscillator (clock) stage comprising IC6a, IC6b & crystal X1; (2) counters IC2-IC5; and (3) memory IC1 (the EEPROM). The oscillator clocks the counters which in turn drive address lines A0-A15 of the memory IC. The various patterns stored in IC1 appear at the data out­puts (D0-D7). Fig.2: block diagram of the AD722 RGB-to-PAL colour encoder IC. This IC accepts RGB and sync input signals and produces both composite video and S-video (separate chrominance and luminance) signals at its outputs. June 1997  17 (IC10). IC11 detects when the memory has reached the end of one field. It then resets the counters and the pattern starts all over again. Switch S2 selects between the patterns on D0-D3, while S3 and IC8 select between this and the colour bar signal on D4-D6. The selected RGB signal is buffered using IC9 and attenuated to a 0-700mV signal before being fed to the RGB-to-PAL encoder (IC10). IC10 produces a composite video output and a separate luminance signal. Switch S4 selects the composite video output from IC10 for colour video and the luminance output for greyscale video. The resulting signal is then made available as direct video. It is also applied to a video modulator to produce a modulated RF signal on VHF channel 0 or 1. An audio signal can also be applied to the RF modulator if required although this facility is not normally provided in a pattern generator. RGB-to-PAL encoder Fig.3: this is the block diagram of the unit when it is configured to programming mode (by changing some on-board jumper pins). Each address in the mem­ory is programmed by applying the correct level to the data lines (D0-D7) and then applying a short pulse to the E input of IC1 modulator and this can be useful when tracing audio problems in a TV set. In addition, S-video outputs can be added if required by connecting appropriate leads to the luminance and chrominance pins on the PC board. Operating modes Because it is a programmable device, this new pattern gen­ erator can be configured to operate in two modes: (1) programming mode; and (2) pattern generator mode. These two modes are select­ed by means of five jumpers on the PC board. Selecting the programming mode (by moving all the jumpers to the front pins of their 4-pin blocks) allows the EEPROM to be programmed via the PC’s parallel port and an on-board DB25 con­nector. Once programming has been completed, the jumpers are reset so that the unit can function as a pattern generator. The software for programming the EEPROM is written in Quick Basic, which originally came with DOS 5. The data stored in the EEPROM is arranged in lines which directly cor18  Silicon Chip respond to the lines displayed on the TV screen. This means that you can edit an existing pattern line-by-line to produce a custom display, if required. Block diagram Refer now to Fig.1 for a block diagram of the unit (pattern generator mode). It might look complicated but we’ll go through the various stages in turn and explain how it all works. Three main circuit sections are required to produce the requisite patterns: (1) an oscillator (clock) stage comprising IC6a, IC6b & crystal X1; (2) counters IC2-IC5; and (3) memory IC1 (the EEPROM). The oscillator stage clocks the counters which in turn drive the address lines (A0-A15) of the memory IC. The various patterns stored in IC1 appear at the data out­puts (D0-D7). Outputs D0-D3 provide the checker-board, dot, crosshatch/circle and raster signals, while D4-D6 provide the blue, green and red signals for the colour bar sequence. D7 produces the composite sync pulses and these are fed to the RGB-to-PAL encoder stage The RGB-to-PAL encoder is an Analog Devices AD722 16-pin surface mount device. It produces a top-quality PAL video signal from RGB and composite (horizontal and vertical) sync input signals, the latter fed from D7 of IC1. Fig.2 shows the block diagram of the AD722. This IC is rather complicated and, among other things, contains a phase lock loop (PLL) and various filters and delay lines. It requires no external components other than a crystal and a trimmer capacitor to set the colour burst frequency. The RGB inputs to the AD722 are each first passed through on-chip capacitors and clamped to the black level during the blanking interval. These three signals then pass into an analog encoding matrix to create the luminance (Y) and the U and V colour difference signals. After that, the Y signal passes through a 6MHz low-pass Bessel filter which prevents aliasing in the following sampled delay line. This delay line produces a 170ns difference between the luminance and chrominance signals. The delayed signal then passes through a 5MHz low pass filter to remove the sampled delay line artefacts. The U and V signals pass through 1.5MHz low pass filters to prevent Fig.4: this diagram shows the general arrangement of the blanking inter­vals and the visible screen area. The picture is made up of 312 lines which are scanned horizontally, one line at a time, from top to bottom. Note that lines 1-23 at the top of the screen and lines 311-312 at the bottom of the screen are not seen since they are reserved for field blanking aliasing in the following balanced modulator stages where the colour burst signals are injected. Note that the burst injec­ tion to the V signal is alternated between 90° and 270° at half the line rate to comply with the PAL standard. The outputs from the balanced modulators are then summed and fed to a 4.4MHz low-pass filter to remove any artefacts generated in the modulators. The resulting chrominance signal is summed with the lumi­nance output to produce composite video. In addition, the lumi­nance and chromin­ance signals are made available as separate outputs (S-video). The HSYNC and VSYNC inputs accept the sync signals. Either separate horizontal and vertical sync signals can be applied or a composite sync signal (as used in this design) can be applied to just one of these inputs. In either case, the following stages produce a composite sync signal and this is inserted into the luminance signal between the 3-pole low-pass filter and the sampled delay line. All other timing is generated by a 4 x 4.43MHz clock signal which can be derived from a 4.43MHz colour burst crystal or from a 17.734MHz crystal. When a 4.43MHz crystal is used, the IC is configured to multiply the frequency by four using the internal phase lock loop. Programming mode Fig.3 shows the block diagram for the unit when it is con­figured to programming mode. Three regulated supplies are required for programming. The 5V regulator provides most of the power for the ICs, while the 6V supply powers the memory which can be either an EEPROM or a One Time Programmable Read Only Memory (OTPROM). The 12.5V supply is used to provide the programming voltage. Basically, each address in the mem­ ory is programmed by applying the correct level to the data lines (D0-D7) and then applying a short pulse to the E input of IC1. Let’s look at this in greater detail. In practice, the programming process is controlled by the computer and the software which drives the Port A, Port B and Port C lines. There are several lines at work here: (1) the D2 Port C line – this applies the clock signal to the counters (IC2IC5), to increment the address of the memory; (2) the -D1 Port C line – this triggers the program pulse genera­tor IC7; (3) the D4 Port B line – this watches for the end of the program­ming pulse; and (4) the Port A lines – these drive the Data lines (D0-D7) of IC1. When power is first applied, the counters are reset to the first memory address of IC1. Data is then applied June 1997  19 to D0-D7 from Port A, after which D1 of Port C triggers the pulse generator to program the first memory location. At the end of the programming pulse, D4 of Port B signals the computer and the counter is clocked to the next count via D2 Port C and inverter IC6c. The next memory address of IC1 is now accessed and the relevant data again applied to D0-D7 and pro­grammed in. This sequence continues until all the data has been programmed in. EPROM coding Fig.5: this diagram shows, in graphical format, the programming codes for the various patterns which are programmed in via data lines D0-D7 for each line from 1-312. Note that all lines are high during the first 40 locations for line blanking and for lines 311-23 for field blanking. D7 is the sync signal and this is low for 15 locations (4.58µs) and high for the remaining locations in lines 6-310 20  Silicon Chip To understand how the memory is programmed with the pat­ terns, we first need to understand how the picture is displayed on the TV screen. Fig.4 shows the general arrangement of the blanking inter­vals and the visible screen area. The picture from our pattern generator is made up of 312 lines which are scanned horizontally, one line at a time, from top to bottom. Lines 1-23 at the top of the screen and lines 311-312 at the bottom of the screen are not seen since they are reserved for field blanking. This is the period during which the trace returns from the bottom of the screen to recommence at the top. Each line is 64µs wide, with 12µs of this period reserved for line blanking. This means that the visible area on the screen is only 52µs wide by 288 lines high. The visible picture is displayed with a 4:3 width-to-height ratio and this must be taken into account when producing the pattern coding. If this is not done, the circle will look like an ellipse, while the crosshatch and checkerboard squares will be elongated. The memory which contains the pattern codes has a capacity of 64K bytes, which is actually 65,536 bytes. Each of these memory locations is clocked at 3.2768MHz or once every 305.17578ns. If we use 210 memory locations per line, then we have 305.17578ns x 210 or 64.08µs, which is the desired line period. The 12µs line blanking interval takes up 40 memory loca­tions of the 210 total per line, leaving only 170 visible loca­tions. And with 312 lines and 210 memory locations per line, we use 65,520 locations per field which is virtually the capacity of the ROM. The 65,521th location in the memory produces a reset pulse to return the Fig.6: this oscilloscope waveform shows the line sync pulse and the colour burst signal. Note that the 10-cycle colour burst signal occurs 5.6µs after the falling edge of the sync pulse, to comply with the Australian PAL standard. The measured colour burst frequency of 4.443MHz deviates slightly from the true value of 4.433619MHz because of the small number of cycles being measured. Fig.7: these waveforms show the dot pattern (top trace) and the checkerboard pattern (bottom trace). The first dot appears di­rectly after the 12µs blanking interval. Note that the colour burst signal has been turned off here to simplify the presenta­tion of these waveforms. counters to the start of line 1. The frame rate is 305.17578ns x 65,520 = 19.555ms, which equates to 50.01Hz. Although the line and frame rates are not exactly at 64µs and 20ms, they are close enough to these figures not to cause problems. The circle is programmed into memory with its centre at memory location 125 and a horizontal radius June 1997  21 included with the crosshatch pattern. Fig.5 shows the programming codes for the various patterns which are programmed in via data lines D0-D7 for each line from 1-312. These are presented graphically so that it can be seen how each pattern is made. D7 is the sync signal and this is low for 15 locations (4.58µs) and high for the remaining locations in lines 6-310. The signal is continuously low for lines 311-5. The remaining data lines (D6-D0) are for the patterns and these also incorpo­ rate the line and field blanking intervals. As shown, all lines are high during the first 40 locations for line blanking and for lines 311-23 for field blanking. Understanding the patterns Virtually all the parts are mounted on a single PC board so that construction is really easy. The full construction details are in next month’s issue. of 50 locations. This means that the circle crosses the horizontal centre line (line 167) at memory locations 175 (125 + 50) and 75 (125 - 50). Similarly, the circle has a vertical radius of 114 lines. This means that it crosses the vertical centre line at the 125th memory location at lines 53 (167 - 114) and 281 (167 + 114). The remaining points of the circle were calculated using standard trigonometry and the circle coding Some of the patterns are relatively simple, while the others are more complicated. The easiest to understand is the raster which has all lines low for memory locations 41-210. The crosshatch pattern is more complicated. In this case, lines 30, 57, 85 (ie, every 27th line) and so on are always low from memory location 41 onwards, so that we get 10 white horizon­tal lines across the screen. For each remaining line from 24-310, the signal goes low at memory locations 41, 53, 65 and so on (ie, at every 12th memory location) to generate the vertical lines. The dot pattern works in a similar fashion, except in this case all lines are high except for lines 30, 57,85, etc which go low at memory locations 41, 53, 65 and so on to generate the white dots at these locations. The checkerboard coding is quite different, with successive blocks of 24 memory locations programmed high and low for six different groups of lines. The colour bar and greyscale pattern is derived from data lines D4, D5 & D6. Note that the bars are slightly wider at the two outside edges than in the centre of the screen (34 memory locations versus 20 for the others – see D4). This has been done to compensate for the small degree of over­scanning present in all TV sets. Next month Fig.8: the top trace here is the greyscale waveform and this shows the familiar staircase from full white to black in eight steps. The lower trace is the colour bar waveform. Note that the colour burst signals appear to be at a low frequency due to aliasing in the digital sampling process of the scope. 22  Silicon Chip That’s all we have space for this month. Next month, we will give the full circuit and construction details and describe the test procedure. SC MAILBAG Problems with supply of PIP module I am writing to advise you of our difficulty in offering the Picture-in-Picture kit for sale. We are unable to obtain the PIP module from our overseas supplier at the original terms and conditions negotiated at the time the article was being prepared for publication in the April 1997 issue. As a consequence of this, it is no longer financially viable for our company to proceed with the supply of the PIP module. As an alternative, for those customers who are still inter­ested in acquiring a PIP unit, we are prepared to offer a built up unit, with additional features to those offered in the kit design for $385. Our catalog number for this item is T1800 and specifications are included in the current AV-COMM catalog, or can be obtained by calling our Balgowlah office. Garry Cratt, Av-Comm Pty Ltd, Balgowlah, NSW. Errors in NTSC-to-PAL Converter article I came across several errors of fact in the first half of the article “NTSC to PAL Converter” in the May 1997 issue of SILICON CHIP and I feel that these should be pointed out to readers. To begin with, you appear to be confused with the terms frame and field, stating that NTSC uses a 60Hz “frame” rate and that PAL uses a 50Hz “frame” rate. This is quite incorrect. These figures apply only to the “field” rate. The “frame” rate is half of those figures. The reason for the difference is historical. Motion picture film (sound) has always run at 24 frames per second but this speed produces intolerable flicker. The cure for this problem was to screen each frame twice, giving a repetition rate of 48 images per second. Early attempts to run electronic scanning at speed similar to motion pictures were unsuccessful due to the very high line frequency required. The solution was to divide each frame in half and transmit them one after the other. In this way, the line frequency in the American system was reduced to 15,750Hz and in the English/ European system, to 15,625Hz. Thus, each “field” contains only half the picture information and two fields are required to complete one “frame”. Then later in the article you state that the phase of the colour burst in the PAL system “. . . changes by 180° on every alternate line”. I’m afraid that this is quite wrong. For one thing, it is only the red channel that changes phase line by line. The phase of the blue signal remains fixed. The burst phase does in fact change line by line but only by ±45°. This is to provide a means by which the ident circuitry can tell which phase angle should be adopted for the red compon­ent of the following line. The burst provides a reference signal to control the fre­ quency and phase of the chroma sub­ carrier oscillator. It is the output of this oscillator that controls the blue demodulator via a 90° phase shift network and the red demod­ ulator via the ±180° phase switch. To complete the story, it should be noted that the green component of the picture is not transmitted but is derived in the receiver by adding the red and blue together, then subtracting the result from the luminance (black and white) component. I can appreciate that you tried to simplify what is really a very complex subject but simplification is of little value if the result delivers inaccurate information. Indeed, your readers may have been more impressed by the intense signal processing undertaken in this project if they had been given more detailed information. Finally, I would like to make a point referring back to your Editorial in the same issue. If the chips required to operate this project will only be available for perhaps 12 months, what happens after that if one of the chips in the converter fails? Of course, there is every chance that the chips will never fail. But if they do, the owner should be reconciled to tossing out $150 worth of useless NTSC/PAL converter. Jim Lawler, Geilston Bay, Tasmania. Comment: thanks for bringing the errors in the article to our attention. As far as chips failing is concerned, the same draw­back applies to many consumer prod­ ucts nowadays. For example, if the mother­ board in your current Pentium computer fails in 12 months time, what chance is there of having it repaired? Very little, in most cases. To paraphrase your words, there is every chance that your moth­erboard will never fail. But if it does, you would have to be reconciled to tossing out several hundred dollars worth of use­less electronics and buying a new one. June 1997  23 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.dse.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.dse.com.au A high-current motor speed control for 12V & 24V systems This pulse width-modulated 20A speed control can be used for controlling 12V DC motors in cars. Examples are pumps for fuel injection, water/air intercoolers & water injection on modified performance cars. It could also be used for headlight dimming in the daytime & for running 12V motors & pumps in 24V vehicles. Design by RICK WALTERS These days, car manufacturers are coming to realise that running pumps full bore all the time is wasteful of the battery/electrical system and also causes premature wear of the fuel pump. A prime example of this is the pump use to pressurise the fuel rail in fuel injection cars. The pump runs continuously, regardless of the fuel demand, and the excess fuel is bled off to the fuel tank to keep the pressure constant. In the future, most cars will have fuel pumps which are variable speed controlled according to fuel demand. In the meantime, you can do it now with this design, using the car’s map sensor output as a measure of fuel demand. However, the exact method for doing this is beyond the scope of this article. The circuit can control 12V loads up to 20 amps and it uses just two Mosfets to do it. Other possible applications for this PWM circuit are for control of 12V and 24V motors in model locomotives and cars and in control applications in manufacturing. The circuit has excel­lent line and speed regulation and uses just one low-cost IC as well as the two Mosfets. Note: this circuit is not suitable for operating 12V audio equipment in 24V vehicles since its output is pulsed at around 2kHz. As presented, the circuit incorporates a “soft start” fea­ture which is desirable to reduce inrush currents, particularly if the device is used to control 12V incandescent lamps. However, for some pump applications the soft start may not be wanted and so we’ll tell you how to disable it. We are presenting this project as a standalone PC board. If you want to put it in a case it is a simple matter to install it in a suitable plastic box but that will be up to you. The PC board has all components on it except for a diode (D2) and a capacitor which must be wired across the motor being driven. If the circuit is used to control incandescent lamps, the diode and capacitor are not required. Circuit description This small PC board will provide speed control of 12V or 24V motors drawing up to 20A. Not shown on this prototype board is the input protection diode D1 26  Silicon Chip The heart of the circuit shown in Fig.1 is a TL494 pulse width modulation (PWM) controller. It varies the output voltage fed to the motor by rapidly turning Mosfets Q3 & Q4 on and off. Because the Mosfets are Fig.1: the heart of the circuit is a TL494 pulse width modulation (PWM) controller. It varies the output voltage fed to the motor by rapidly turning Mosfets Q3 & Q4 on and off. Note that diode D2 is essential to the circuit operation. being switched fully on or fully off, they dissipate very little power, even when handling cur­rents as high as 20 amps total. This means that they do not get very hot and no heatsink or very small heatsinks (depending on the output current) are required. Note that the TL494 is normally used in switchmode power supply applications but it is suitable for virtually any PWM application. Its block diagram is shown in Fig.2. The chip con­tains the following functions: •  An oscillator, the frequency of which is determined by a capacitor at pin 5 and a resistor at pin 6. •  A stable +5V reference at pin 14. •  A “dead time” comparator with one input driven from the oscillator. •  Two comparators (pins 1, 2, 15 & 16) with their outputs ORed together via diodes (pin 3). •  A PWM comparator with one input from the oscillator and the other from the ORed output of the two comparators. •  A flipflop driven by the dead time and PWM comparators. •  Two 200mA transistors with uncommitted emitters (pins 9 & 10) and collectors (pins 8 & 11), with their bases driven by the outputs of the flipflop. In simple terms, the TL494 operates as follows. Its oscil­lator is set to run at 2kHz and it produces a pulse train at its outputs at this frequency. The width of the pulses is varied (ie, pulse width modulated) and the ratio of the “on” time to the “off” time controls the amount of power fed to the load which in this case is the motor. A fraction of the output voltage is fed to one input of one of the comparators, while the other input is connected to a reference voltage. If the output voltage rises slightly, the comparator input will sense this change and will alter the output onoff ratio and consequently the output vol­tage. This keeps the voltage at the comparator input equal to the reference voltage. This is done by reducing the driving pulse on time, reduc­ing the time the switching device is turned on, thereby bringing the output voltage back to the required level. The converse applies for falling output volt­ages. Now if we refer to the circuit of Fig.1 again, we see that the TL494 is fed via a 7812 12V regulator. This is not strictly essential for the TL494 since it can operate with a supply rang­ing from +7V to +40V. However, it is important that the gate drive to Mosfets Q3 & Q4 does not exceed their specifications and so this condition is met with REG1. In this circuit, the output duty cycle must be able to be controlled over a wide range, from virtually zero up to the maximum of around 90% and so the two internal transistors (C1 pin 8 and C2 pin 11) have their collectors connected to the +12V supply and are used as emitter followers to pull the bases of Q1 & Q2 to +12V. The 2.2kΩ resistor at pins 9 & 10 is the common emitter load and it pulls the bases to ground. Thus, the emitters of Q1 & Q2, together with the gates of Q3 & Q4, swing from 0V to +12V and so the gate drive signal is limited to this voltage. Q1 & Q2 are included for another reason and that is to rapidly charge and discharge the gate capacitances of the Mosfets each time they turn on and off. This improves the switching action of the Mosfets; ie, it speeds up the turn-on and turn-off times and thereby reduces the power dissipation in the Mosfets. Soft start A soft start circuit is incorporated to June 1997  27 Fig.2: functional block diagram of the TL494. This chip is in­tended mainly for switchmode power supplies but we have adapted it to control motors and resistive loads. reduce surge cur­rent into the motor at turn on. When power is first applied, the REF output, pin 14, rapidly charges its associated 10µF capaci­tor, C1. This pulls the INH(hibit), pin 4, high as the 10µF capacitor (C2) between pins 14 and 4 is initially discharged. While pin 4 pin is high there is no output from pins 9 & 10. As cap­ac­itor C2 charges through the 100kΩ resistor the voltage on pin 4 will gradually fall and the output pulse width will increase, giving a smooth rise in the output voltage. In order to control the output voltage precisely, the TL494 monitors both sides of the motor; ie, the input voltage before the 12V regulator (MOTOR +) and the voltage at the Mosfet Drains (MOTOR -). The MOTOR+ voltage is fed via the 20kΩ and 2.2kΩ voltage divider resistors to comparator 1, pin 1. The MOTOR- voltage is attenuated by the 18kΩ and 4.7kΩ resistors and fed through a 47kΩ resistor to pin 2. The voltage tapped off the +5V reference by the speed control, VR1, is also fed through a 47kΩ resistor to pin 2. When the speed control wiper is at minimum setting (ie, 0V), the voltage at the junction of the 18kΩ and 47kΩ resistors will be forced to be twice 28  Silicon Chip that on pin 1 of IC1 (nominally 1.4V for +14V input), as the voltage drop across each 47kΩ resistor will be 1.4V. The voltage at the MOTOR- terminal will be about +14V and so the motor will not run. As VR1 is advanced, the voltage at the MOTOR- terminal will decrease, thereby applying a larger voltage to the motor so it can run. Normally, the reference voltage on pin 1 of IC1 is fixed and referred to the 5V reference at pin 14. In our case this would not be desirable as the output voltage sensed and regulated by IC1 is between the MOTOR- output and ground (across the 4.7kΩ resistor). This means that as we vary the supply voltage, the voltage between MOTOR- and ground will be held constant but the voltage across the motor will vary in a direct relation to the voltage change. By connecting the 20kΩ resistor between the input rail and pin 1 of the TL494 we compensate for this. Protection Reverse polarity protection is provided by diode D1. It is rated at 3A average but has a one-off surge rating of 200A and will blow the fuse if the leads to the battery are reversed. Two essential components to the circuit are not mounted on the PC board but are wired directly across the motor itself: D2 and C3. Diode D2 is the most important as it prevents the genera­tion of excessive voltage spikes, each time the Mosfets turn off. D2 must be a fast recovery diode because of the very fast switch­ing of the Mosfets. The importance of diode D2 and the associated 0.22µF ca­pacitor C3 is demonstrated in the oscilloscope wave­forms of Figs.3, 4, 5 & 6. The waveform in Fig.3 shows the circuit driving a resistive load which could be a heater element or an incandes­ cent lamp. Notice that the waveform is a clean pulse with a duty cycle of about 74%. This gives a voltage of about 8.8V across the load. Now have a look at Fig.4. This shows the circuit set for the same output when driving a motor instead of a resistive load. The scope’s vertical sensitivity has been changed to 20V/ div instead of 5V/div. Notice the enormous spike voltage amounting to almost 80V peak-to-peak, each time the Mosfets turn off. This spike voltage is enough to blow the Mosfets because their Drain-Source voltage rating (VDS) is only 60V. Fig.3: this scope capture shows the waveform across a resistive load which could be a heater element or an incandescent lamp. Notice that the waveform is a clean pulse with a duty cycle of about 74%. This gives a voltage of about 8.8V across the load. Fig.4: this waveform shows the circuit set for the same output as for Fig.3 but driving a motor instead of a resistive load. The scope’s vertical sensitivity has been changed to 20V/div instead of 5V/div. Notice the enormous spike voltage (amounting to almost 80V p-p) each time the Mosfets turn off. This spike voltage is enough to blow the Mosfets because their Drain-Source voltage rating (VDS) is only 60V. Fig.5: this waveform was produced with the same circuit conditions as for Fig.4 but with D2 connected across the motor to clip the voltage spikes. We now see the motor’s back-EMF during the Mosfet off period, showing a value about half of that applied by the control circuit. Fig.6: this scope waveform shows the effect when both diode D2 and the 0.22µF ca­pacitor are fitted to the circuit. Note that the capacitor has a filtering effect which acts to remove most of the hash generated by the motor’s commutator. Fig.5 shows the same circuit conditions but with diode D2 connected across the motor to clip the voltage spikes. We now see the motor’s backEMF during the Mosfet “off” period, showing a value about half of that applied by the control circuit. Finally, Fig.6 shows the effect when both the diode and 0.22µF capacitor are fitted to the circuit. The capacitor has a filtering ef­fect, removing most of the hash generated by the motor’s commuta­tor. The reason that diode D2 and the 0.22µF capacitor C3 are fitted directly across the motor instead of being mounted on the PC board is that this method stops the motor leads from radiating commutator hash which could otherwise interfere with sensitive circuitry elsewhere in the car. The current rating of diode D2 must suit the rating of the motor. It’s not much use connecting a 5A diode across a motor that pulls 20A; it will just blow the diode and then blow the Mosfets. Finally, also not mounted on the PC board is the in-line input fuse F1. This must also match the rating of the motor. PC board assembly The PC board for this design is coded 11106971 and measures 68 x 50mm. It is fairly easy to assemble as it only has a few components on it. Begin by checking the copper pattern against the PC artwork (Fig.8) and repair any defects such as undrilled holes, shorts or open tracks. The component overlay is shown in Fig.7. June 1997  29 Fig.7: the component overlay for the PC board. Fit and solder the resistors, using a cut pigtail from one of them for the one link. This done, fit the IC, REG1 and trimpot VR1, followed by the transistors, capacitors and the Mosfets. If you intend to operate the controller from a 12V battery and don’t intend to draw more than 6A you can use one Mosfet. Provided a small heatsink is fitted you can probably draw up to 10A with one Mosfet. For higher currents, two Mosfets must be used, as shown on the circuit of Fig.1. If you want the full 20A load current, both Mosfets should be fitted with small heatsinks. Testing If you are careful with the assembly, it should work first up. Turn VR1 fully clockwise (minimum speed) and solder a resis­tor of around 100Ω 5W across the motor terminals. If you have a variable power supply, feed 14V to the DC input and ground. If you don’t have a power supply you will have to connect the con­troller directly to a +12V battery. With the negative meter lead connected to the 0V line, you should be able to measure about +12V on pin 16 and +5V on pin 14 of IC1. The voltage on pin 1 of IC1 should be around +1.4V with 14V input and +1.2V with 12V input. If these values are OK proceed with the following tests. If you now connect the meter leads across the 100Ω resistor it should read zero volts. Rotate trimpot VR1 slowly anticlockwise and the voltage should increase up to about 12V when fully rotated. Because IC1 has an internal “dead time” of 10%, the output devices can 30  Silicon Chip Fig.8: actual size artwork for the PC board. only be turned on for 90% of the time and the output voltage will never be the same as the input. For 14V input, the maximum output will be about 12.5V. Be careful not to burn yourself as the 100Ω resistor will become hot at the maximum setting of VR1. Using the speed controller As noted above, the rating of the in-line fuse will depend on the load you plan to drive. Obviously a 20A PARTS LIST 1 PC board, code 11106971, 68 x 50mm 1 5kΩ PC trimpot (VR1) Semiconductors 1 TL494CN switching regulator (IC1) 1 7812 regulator (REG1) 1 BC639 NPN transistor (Q1) 1 BC640 PNP transistor (Q2) 1 or 2 BUK456-60A/B/H N-channel Mosfets (Q3,Q4) Capacitors 2 100µF 50VW PC electrolytic 2 10µF 16VW PC electrolytic (C1,C2) 1 0.22µF 100VW MKT polycarbonate (C3) 2 0.1µF MKT polycarbonate 1 .068µF MKT polycarbonate Resistors (0.25W, 1%) 1 1MΩ 1 10kΩ 1 100kΩ 1 4.7kΩ 2 47kΩ 2 2.2kΩ 1 20kΩ 2 4.7Ω 1 18kΩ 1 100Ω 5W (testing) fuse will not protect a 1A motor. If you don’t want the soft-start facility, it can be disa­bled by omitting capacitor C2. We recommend that the soft-start facility be included for incandescent loads. However, for motor loads, a better approach would be to connect a 1kΩ 1W resistor across the output terminals and then place a switch in series with the motor or whatever load you wish to drive. You then set up the drive voltage you require with trimpot VR1 and use the in-line switch to connect and disconnect the motor. If resistive or incandescent loads are to be driven, D2 and C3 are not necessary but they must be included when driving any motor, regardless of its current rating. D2 must be rated to handle a current at least equal to that drawn by the motor. A suitable cheap diode is the MUR1515 which is rated at 150V 15A and should cover most applications. If you want to run a 20A motor, then use two MUR1515s in parallel. Make sure that they are connected in the right direction across the motor; ie, anodes to the positive supply line. If connected the other way around, you will blow the fuse and perhaps the Mosfets too. C2 should be an MKT poly­ carbonate capacitor with a rating of at least 100VW. The type of FET used depends on the current drawn by the controlled device. The BUK456-60s specified are readily avail­ able and have an “on” resistance of .028Ω. If you want high currents and 24V operation, the MTP60N06 is a more suitable device. It has an “on” resistSC ance of .01Ω. HE-NE LASER TUBE AND SUPPLY Used 5mW/633nm red helium-neon laser tube and our 12V laser power supply kit. Ideal for light shows. Head size: 380 x 45mm (l x dia). ON SPECIAL: $80 NICAD BATTERY BARGAIN 5-PACK (7.2V) of 1.2V/800mA.h AA NICAD BATTERIES plus 1 x thermal switch, easy to separate: $4 per pack or 6 packs for $16, FLAT RECTANGULAR 1.2V, 400mA.h NICAD BATTERIES with thermal switch, easy to separate. (Each batt: 48 x 17 x 6mm): $3 per pack or 5 packs for $10 CHARGER AND DISCHARGER A professional fully assembled and tested fast NICAD battery charger and discharger PCB assembly. The switched mode based unit is mostly surface mounted on a double sided PCB with gold plated-through holes and pads. Employs 6 ICs, 3 power Mosfets, one toroidal inductor and many other components: over 100 in total. The input connector, discharge pushbutton, and the 3 indicator LEDs are also mounted on the PCB: complete assembly! Nominal unregulated input is 13.7V DC and the charging current was measured at 900mA. Appears to employ voltage slope detection for terminating the charge and also has a timer (4060) for absolute charge termination. Probably designed to charge 7.2V AA nicad packs in less than 1 hour. Three trimpots allow some adjustment but we did not investigate. Basic hook-up information provided, unregulated plugpack/ power source is not provided. Incredible pricing: $9 ea. or 3 for $21 MOVING MESSAGE DISPLAY PCB Used complete PCB assembly with bright dot matrix RED LED displays and driver. Circuitry includes twenty 74HC164ICs. Twenty 35-LED displays are arranged in a single line to form a continuous display with a total of 700 pixels (LEDs). Display size is 280 x 18mm and the overall PCB size is 330 x 75mm. Needs external 5V supply. We have not completed the software but do include a simple program on a disc and instructions on how to make the display scroll the number “1” through all the displays when connected to a computer’s parallel port. Limited quantity: $40 machine part. Very quiet operation, made in Japan, overall dimensions 160 x 90 x 90mm, weight 1.2kg, inlet 25mm diameter, outlet 20mm diameter. Other end of motor has shaft: 20mm long, 4mm diameter. It is possible to rewind this motor for lower AC voltage and/or reduced power operation without disassembling the unit. We calculated 5.5 turns per volt: $19 MAINS MOTOR New induction motors that are probably a clothes drier part. Dimensions are 110 diam. x 100mm long, has a mounting bracket, drive shaft has a diameter of 10mm and is 40mm long, total weight is 3.3kg, made in Japan. Power is around 1/4HP, two speeds appear to be possible by selecting correct wires, brief information supplied: $19 CCD CAMERA Tiny (32 x 32 x 27mm) CCD camera, 0.1 lux, IR responsive (works in total dark with IR illumination), connects to any standard video input (eg, VCR) or via a modulator to aerial input: $120, REGULATED 10.4V - 500mA PLUGPACK to suit: $10 (normally $25) KITS FOR CCD CAMERA SECURITY New INTERFACE KIT FOR TIME LAPSE RECORDING: now has relay contact outputs! Can be directly connected to a VCR or via a learning remote control: $25 for PCB and all on-board components, used PIR to suit: $12. ♦ 32mm 10 LED IR ILLUMINATOR: new IR (880nm) LEDs have an output about equal to our old 42 LED IR illum­inator: $18. ♦ 32mm AUDIO PREAMPLIFIER: an $8 kit that produces a ‘line level’ signal from an electret microphone, connect the output to our: ♦ UHF VIDEO TRANSMITTER ($30) or $20 when bought with the camera for a complete Audio-Video link. ♦ 32mm AUDIO AMPLIFIER: an LM380 based $9 audio power amplifier which can directly drive a speaker - needs the 32mm preamplifier. ♦ WHAT IS 32mm? All these boards have a diameter of 32mm so you can house one or more of these kits in a plastic 32mm joiner: inexpensive plumbing part. VERY LARGE 7-SEGMENT DISPLAY Used attractive RED high-output 30mA common cathode display. 57mm high digit in a 70 x 43 x 12mm housing with a grey face. Forward voltage is 2V for the decimal point and 8V for the segments. $6.50 ea. or you can purchase seven of these used but guaranteed displays soldered on one PCB assembly, which we sell for $30 SWITCHMODE POWER SUPPLY Compact (50 x 360 x 380mm), in a perforated metal case, 240V AC in, 12V DC/2A and 5VDC/5A out: $17 LIMITED STOCK SPECIALS ♦ BRIDGE RECTIFIERS: 35A-400V in diecast aluminium: 5 for $15. ♦ TRIACS: Mitsubishi BCR8PM-8L 8A/400V in insulated casing similar to TO220: 10 for $14. ♦ SCHOTTKY DIODES: Motorola MBR745 7.5A/45V TO220: 10 for $18. ♦ DC FAN: small DC motor with 3 blade push on plastic fan: $3. ♦ PLASTIC HANDLES: Robust recessed, for stage speakers and equipment, 10 mounting holes, dimensions 130 x 170 x 50mm: $5. ♦ PLASTIC CORNERS: Robust, dimensions 80 x 80 x 80mm: $1.30. 5mW/650nm VISIBLE LASER POINTER KIT YES, NEW 650nm kit. Very bright! Makes a complete laser pointer that works from 3-4V DC. Includes 650nm/5mW laser diode, new handheld case 125 x 39 x 25mm, adjustable collimator lens, PCB battery holder: (K35) $39 MAGNIFIERS/LOUPES Reviewed SC May ’96, four magnifiers: small jewellers’ eyepiece with plastic lens: $3; twin lens loupes: 50mm $8, 75mm $12, 110mm $15. SPECIAL: Buy set of four magnifiers for total price of $25. MIDI KEYBOARD Quality MIDI keyboard with 49 keys, 2-digit LED display, MIDI out jack, many functions including wheel, transpose. Size: 655 x 115 x 35mm. Computer software included, see review EA Feb. 97: $88 9V DC plugpack: $12 USED PIR MOVEMENT DETECTORS Commercial quality 10-15m range, used but tested and guaranteed, have open collector transistor (BD139) output and a tamper switch, 12V operation, circuit provided: $10 ea. STEPPER MOTOR DRIVER KITS Kit includes a large used 1.8° (200 step/rev) motor and used SAA1042A IC. Can be driven by external or an onboard clock; has a variable frequency clock generator. External switches (not provided) or logic levels from a computer, etc determine CW or CCW rotation, half or full step operation, operation enable/disable, clock speed. PCB and all on-board components kit plus 1 or 2 motors: $18 for single motor driver kit with 1 motor, $28 for twin motor driver kit with 2 motors. INTENSIFIED NIGHT VIEWER KIT Last chance – slightly blemished 3-stage image intensifier tubes as previously advertised. Comes with power supply and eyepiece. 25mm (NO4) $220. 40mm (N05) $260 MOTOR AND PUMP New compact plastic pump with a 240VAC-50Hz-0.8A-91W2650RPM induction motor attached. Probably a washing AUTOMATIC LASER LIGHT SHOW Three motors, mirrors, PCB and component kit. Produces a huge range of amazing patterns: (K83) $77 DISCO LASER LIGHT SHOW PACK The above 5mW/650nm VISIBLE LASER POINTER KIT plus the above AUTOMATIC LASER LIGHT SHOW: $99 for the package! KEYCHAIN LASER POINTER Very bright, very small, 650nm/5mW: $65 12V - 2.5W SOLAR PANEL KIT US amorphous glass solar panels with backing glass: (S12) $22 ea. 4 for $70 8-CHANNEL IR REMOTE Add a remote control to anything with this kit. Has a commercial remote control transmitter. Transmitter kit: (K65T) $20. Receiver: (K65T) $20 4-CHANNEL RELAY KIT Ref SC (Circuit Notebook) Aug. 95. Kit drives any of four relays according to logic level input signal. Either toggle or momentary operation. LED indicators for each relay. 12V coil, 2A contact rating. (K68) $30 WOOFER STOPPER MkII Works on dogs and most animals, ref SC Feb 96. PCB and all on-board components, transformer, electret mic & horn piezo tweeter: (K77) $43, extra tweeters (drives 4): $7 ea. Approved 12V plugpack (PP6) $14 UHF REMOTE TRIGGER Single channel Rx and Tx: (K77T) $40 GEIGER COUNTER KIT Based on a Russian Geiger tube, has traditional ‘click’ to indicate each count. Kit includes PCB, all on-board components, speaker and Geiger tube: (K86) $40 HIGH POWER NEODYMIUM RARE EARTH MAGNETS Very strong. You won’t be able to separate two of these by pulling them directly apart from each other. CYLINDRICAL 7 x 3 mm: (G37) $2.50. CYLINDRICAL 10 x 3 mm: (G38) $5 TOROIDAL 50mm outer, 35mm inner, 5mm thick: (G39) $12. ROD 10mm long, 4mm diameter: (G54) $2.50. WIRELESS IR EXTENDER Converts the output of any IR remote control to UHF. Self-contained transmitter attaches to IR remote. Kit includes two PCBs, all components, two plastic boxes, Velcro strap: (K89) $39. (9V battery not included). Plugpack for Rx (PP10): $11 SOLAR REGULATOR Ref: EA Nov/Dec 94 (intelligent battery charger). Designed to efficiently charge 12-24V batteries from solar panels but can also be used in conjunction with existing simple car battery chargers (such as the common Arlec 4A chargers) to prevent overcharging. Simply turns off the charging current when the battery float voltage is exceeded and turns on when the battery voltage drops a preset amount below the float voltage. Employs a voltage reference IC. Suitable for currents up to 16A and can be easily modified for higher currents (by paralleling MOSFETs and Schottky diodes). The extremely high efficiency is attributed to the very efficient MOSFET switch and a Schottky isolation diode. Has negligible standby current consumption. The PCB is now smaller and we offer a 7.5A or 15A kit. The 7.5A kit has one Schottky diode and the 15A kit has two: $26/$29 (K09) FM TRANSMITTER KIT - MkII Ref: SC Oct 93. Low cost FM transmitter - 100m range, excellent frequency stability, tuning range 88-108MHz, supply voltage 6-12V. Easy to build, has a prewound coil in a shielded metal can. Includes PCB, all on-board components, electret microphone, 9V battery clip: (KIl) $13 FM TRANSMITTER KIT - MkIII Range to 200m. Has a pre-wound RF coil and limited deviation, so needs volume to be set higher on receiver. 6V at about 20mA: (K33) $20 MASTHEAD AMPLIFIER KIT Our famous MAR-6 based masthead amplifier. 2-section PCB (so power supply section can be indoors) and components kit (KO3) $15. Suitable plugpack (PP2): $6. Weatherproof box: (HB4) $2.50. Box for power supply: (HB1) $2.50. (MAR-6 available separately) PC POCKET SAMPLER KIT Ref EA Aug ’96. Data logger/sampler, connects to PC parallel port, samples over a 0-2V or 0-20V range at intervals of one/hour to one/100us. Monitor battery charging, make a 5kHz scope etc! Kit includes on-board components, PCB, plastic box and software (3.5" disk): (K90) $30 KIT OF THE MONTH We are producing many more exciting kits than the magazines can publish! We will try to release at least one new kit every month and give you a detailed description on our WEB SITE. Just ‘click’ onto the KIT OF THE MONTH icon on our WEB SITE. Coming: ♦ laser beam communicator ♦ low cost car alarm ♦ laser fence ♦ new time lapse interface for CCD camera - VCR security ♦ low cost 2-channel UHF remote control with a ready-made transmitter ♦ very effective 10 LED IR illuminator, etc. OATLEY ELECTRONICS PO Box 89, Oatley NSW 2223 Phone (02) 9584 3563 Fax (02) 9584 3561 orders by e-mail: oatley<at>world.net WEB SITE: http://www.ozemail.com.au/~oatley major cards with phone and fax orders, P&P typically $6. June 1997  31 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates. Low-cost telephone intercom The concept behind this design is to be able to connect two rotary or pulse dialing telephones together for a home intercom. It is not to be connected to the public telephone system. Calls are made by dialing a one digit number. The circuit provides for dial tone, ring tone and busy tone features and only allows one call at a time to be made. Referring to the circuit, you can see a DC loop formed by the dial phone (old “800” series), one winding of transformer TX, the LEDs of the two optocouplers and the power supply. When a phone is picked up, this completes the loop and the LEDs inside optocouplers OC3 & OC4 turn on. The two phototransistors inside OC3 & OC4 also turn on, with OC4 32  Silicon Chip pulling pin 13 of IC1 low, enabling it for its decade counting function. Pin 3 of IC1 goes high, enabling a multi­ vibrator consisting of transistors Q1 & Q2 (plus associated components) to produce a “dial tone” for the caller. When the caller dials a number, OC3 acts as a buffer/pulse squarer and feeds the dial pulses into pin 14 of IC1. Pin 3 goes low once one or more pulses are received, turning off the dial tone function until the next call. As soon as pin 3 of IC1 goes low, timer IC2 starts charging up its 10uF capacitor and then begins to produce pulses at pin 3. These pulses turn on the 9V buzzers inside the phone selected during the dialing operation. For example, if we were to dial “4”, then the decade coun­ter’s pin 10 would be high at the end of counting, turning on Q7 and the LED inside OC2. Q7 would then turn on in unison with pulses buffered by Q8, from IC2’s output pin 3. At the same time, the phototransistor inside OC2 would be turning on and off as well, to enable the multivibrator based on Q1 & Q2, this time producing “ring tone” for the caller to hear. When the called party picks up their phone to answer, the switchhook inside the phone disconnects the buzzer, the LED inside OC2 has no path to conduct and the phototransistor no longer enables Q1 & Q2 to produce ring tone. When the caller and the called party both hang up at the completion of the call, OC4 turns off and pin 13 of IC1 goes high, disabling the counter function. This logic high is fed to reset pin 15 of the IC, resetting the counter to pin 3 high. Timer IC2 now stops pulsing, waiting for the next call to be made. A. Hellier, Alice Springs, NT. ($60) Low-loss solar battery charger This solar panel regulator has been designed to minimise forward voltage drop. It uses a relay as the switching element, so the voltage drop across the entire circuit is little more than that across D2. At a current of 200mA, this is about 800mV, resulting in a charging efficiency of around 94%. D2 stops the battery from discharging via the circuit at night. In operation, the relay contacts are normally closed, so the relay consumes no current during charging. The battery begins to charge when the solar panel voltage exceeds that of the bat­tery by about 600mV. At this stage, the current drawn by the Audio signal tracer with inbuilt amplifier This useful circuit can be used to trace signals through any audio device. Transistors Q1 & Q2 act as a pre- circuit is only a few milliamps for IC1, an LM10C op amp with a 200mV voltage reference. IC1 is configured as a comparator with hysteresis. It moni­tors the battery voltage via resistor R8 and VR2, the trip-voltage adjustment pot. When the voltage at pin 3 exceeds the reference at pin 2, the output of IC1 goes high, turning transis­tor Q1 on and energising the relay, which in turn opens the relay contacts. Now the circuit draws about 50mA from the panel (unimport­ant since the battery is fully charged). The battery voltage will now slowly drop and when it hits the lower trip-point, the relay closes, charging the battery and so on. Adjustment is easiest when a bat- amplifier stage with a gain of around 100, as set by the 47kΩ and 470Ω resistors connected to the emitter of Q1. Q2 feeds the volume control VR1 via a 4.7µF ca­pacitor. Q3-Q5 act as a small power amplifier stage with a complementary symmetry tery is connected. Set VR1 at maximum resistance and adjust VR2 for an upper trip-point of about 13.8V. Trim VR1 until no relay chatter is heard on switch­ing, then readjust VR2. The “OVERRIDE” switch prevents the relay from buzzing if the battery is disconnected. It also allows a fused, unregulated solar panel output to be selected. It should be noted that the “OVERRIDE” switch should not be left switched on for more than a few minutes with a battery connected or the battery may over-charge. The circuit and solar panels are protected from reverse battery connection by D3 and fuse F1, the latter selected to match the solar panel output. S. Carroll, Timmsvale, NSW. ($40) output stage. A loudspeaker is shown in the circuit but headphones may be substituted when working in noisy environments. S. Williamson, Hamilton, NZ. ($25) June 1997  33 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 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  GIFT SUBSCRIPTION DETAILS RATES (please tick one) 2 years (24 issues) 1 year (12 issues) Australia (incl. GST)  $A135  $A69.50 Australia with binder(s) (incl. 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Please have your credit card details ready OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail order form to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia June 1997  37 Silicon Chip Back Issues 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. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Low-Cost Inverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages. September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice. 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. 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. 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. May 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; The Burlington Northern Railroad. 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. July 1989: Exhaust Gas Monitor; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; The NSW 86 Class Electrics. 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. 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 Vol. 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: A 16-Channel Mixing Desk; Build A High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2. 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. September 1990: Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band; the Bose Lifestyle Music System; The Care & Feeding Of Battery Packs; How To Make Dynamark Labels. 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; Build An Egg Timer; Low-Cost Model Train Controller; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Build A Simple 6-Metre Amateur Band 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. 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. 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. 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. 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: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator Mk.II; Magnetic Field Strength Meter; Digital Altimeter For Gliders, Pt.2; Military Applications Of R/C Aircraft. November 1991: Build A Colour TV Pattern Generator, Pt.1; A Junkbox 2-Valve Receiver; Flashing Alarm Light For Cars; Digital Altimeter For Gliders, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2; Turn-stile Antenna For Weather Satellite Reception. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Colour TV Pattern Generator, Pt.2; Index To Volume 4. 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Or call (02) 9979 5644 & quote your credit card details or fax the details to (02) 9979 6503.  Card No. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Experiments For Your Games Card. March 1992: TV Transmitter For VHF VCRs; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Directories; A Guide To 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; IR 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. 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. 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. January 1996: Surround Sound Mixer & Decoder, Pt.1; Magnetic Card Reader; Build An Automatic Sprinkler Controller; IR Remote Control For The Railpower Mk.2; Recharging Nicad Batteries For Long Life. 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. 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. 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. March 1996: Programmable Electronic Ignition System; 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. 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. 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. 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. 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. 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. 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. 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; Cathode Ray Oscilloscopes, Pt.4. 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. 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. June 1993: AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; Digital Voltmeter For Cars; Windows-based Logic Analyser. 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. April 1995: Build An FM Radio Trainer, Pt.1; A Photographic Timer For Darkrooms; Balanced Microphone Preamplifier & Line Filter; 50-Watt Per Channel Stereo Amplifier, Pt.2; Wide Range Electrostatic Loudspeakers, Pt.3; An 8-Channel Decoder For Radio Remote Control. August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light Array; Microprocessor-Based Sidereal Clock; Southern Cross Z80Based Computer; A Look At Satellites & Their Orbits. May 1995: What To Do When the Battery On Your PC’s Mother­board Goes Flat; Build A Guitar Headphone Amplifier; FM Radio Trainer, Pt.2; Transistor/Mosfet Tester For DMMs; A 16-Channel Decoder For Radio Remote Control; Introduction to Satellite TV. October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1. 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 1993: Remote Controller For Garage Doors; LED Stroboscope; 25W Amplifier Module; 1-Chip Melody Generator; Engine Management, Pt.3; Index To Volume 6. January 1994: 3A 40V Adjustable Power Supply; Switching Regulator For Solar Panels; Printer Status Indicator; Mini Drill Speed Controller; Stepper Motor Controller; Active Filter Design; Engine Management, Pt.4. February 1994: Build A 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. 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. 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. March 1995: 50 Watt Per 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. May 1996: Upgrading The CPU In Your PC; Build A High Voltage Insulation Tester; Knightrider Bi-Directional LED Chaser; Simple Duplex Intercom Using Fibre Optic Cable; Cathode Ray Oscilloscopes, Pt.3. 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 (Incl. Lights & Sound); 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 Trans­ verter 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; Index To Volume 8. September 1996: 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); Cathode Ray Oscilloscopes, Pt.5. October 1996: Send Video Signals Over Twisted Pair Cable; Power Control With A Light Dimmer; 600W DC-DC Converter For Car Hifi Systems, Pt.1; Infrared Stereo Headphone Link, Pt.2; Multi-Media Sound System, Pt.1; Multi-Channel Radio Control Transmitter, Pt.8. November 1996: Adding An Extra Parallel Port To Your Computer; 8-Channel Stereo Mixer, Pt.1; Low-Cost Fluorescent Light Inverter; How To Repair Domestic Light Dimmers; Build A Multi-Media Sound System, Pt.2; 600W DC-DC Converter For Car Hifi Systems, Pt.2. December 1996: CD Recorders ­– The Next Add-On For Your PC; Active Filter Cleans Up CW Reception; Fast Clock For Railway Modellers; Laser Pistol & Electronic Target; Build A Sound Level Meter; 8-Channel Stereo Mixer, Pt.2; Index To Volume 9. January 1997: How To Network Your PC; Using An Autotransformer To Save Light Bulbs; Control Panel For Multiple Smoke Alarms, Pt.1; Build A Pink Noise Source (for Sound Level Meter calibration); Computer Controlled Dual Power Supply, Pt.1; Digi-Temp Monitors Eight Temperatures. February 1997: Computer Problems: Sorting Out What’s At Fault; Cathode Ray Oscilloscopes, Pt.6; PC-Controlled Moving Message Display; Computer Controlled Dual Power Supply, Pt.2; Alert-APhone Loud Sounding Alarm; Control Panel For Multiple Smoke Alarms, Pt.2. March 1997: Driving A Computer By Remote Control; Plastic Power PA Amplifier (175W); Signalling & Lighting For Madel Railways; Build A Jumbo LED Clock; Audible Continuity Tester; Cathode Ray Oscilloscopes, Pt.7. April 1997: Avoiding Windows 95 Hassles With Motherboard Upgrades; A Low-Tech Timer With No ICs; Digital Voltmeter For Cars; Loudspeaker Protector For Stereo Amplifiers; Train Controller For Model Railways; Installing A PC-Compatible Floppy Drive In An Amiga 500; A Look At Signal Tracing; Pt.1; Cathode Ray Oscilloscopes, Pt.8. May 1997: Windows 95 – The Hardware Required; Teletext Decoder For PCs; Build An NTSC-PAL Converter; Neon Tube Modulator For Light Systems; Traffic Lights For A Model Intersection; The Spacewriter – It Writes Messages In Thin Air; A Look At Signal Tracing; Pt.2; Cathode Ray Oscilloscopes, Pt.9 PLEASE NOTE: November 1987 to August 1988, October 1988 to March 1989, June 1989, August 1989, May 1990, February 1992, September 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. June 1997  39 A signal tracer for au Ever wanted to trace a signal through an AM radio or amplifier? This simple signal tracer will let you do it. It can trace amplitude modulated RF signals right up to the detector and after that, you switch to audio mode to continue through to the output stages. I F YOU ARE building projects published in SILICON CHIP and other magazines, you probably seldom have a need for a signal tracer. You just wire the projects up and they work first time. Well, mostly they work first time. At those other times you have to fall back on your troubleshooting skills and actually figure out where the trouble lies. Often, you will be able to find faults in circuits just by measuring DC volt­ ages but there will be other times when the DC voltages are correct but the circuit steadfastly refuses to work. Or perhaps you are called upon to do the odd servicing job. Here again, faults can often be found by careful visual inspection, checking voltages and so on. But finally, you will need a signal tracer such as the one featured here. As well as being useful for radio and audio circuits, it can be of use in some digital circuits, as the varying logic level signals will give an audible indication on the low-gain RF position. Features Our new Signal Tracer is housed in compact plastic case with a 3-position toggle switch on either side. On the lefthand side is the power switch which is Off in the centre position; the other positions provide the RF and audio modes. The righthand switch provides three gain settings: hi, med and lo. The Signal Tracer also comes with a black wander lead which clips to the earth or 0V point in the circuit to be traced. And the Signal Tracer has a prod fitted to one end which is touched at each point in the circuit to be checked. The specified case for the project has a battery compart­ ment with a slide-off lid. The small PC board is mounted in the main compartment, together with the switches and a miniature loudspeaker. Circuit description Fig.1 shows the circuit which uses two op amps, an LM318 (IC1) and an LM386 (IC2). IC1 is a wideband op amp which is wired in non-inverting mode with gain switchable by one pole of the switch S1; ie, S1a. This varies the feedback to give the three Fig.1: op amp IC1 works in both RF and audio tracing modes and is switched to provide three gain levels. In the RF mode, diode D1 acts as a detector for AM signals. In the audio mode, the output of IC1 is passed through a 30dB attenuator before being applied to amplifier stage IC2. 40  Silicon Chip udio & RF gain settings (hi, med and low). These correspond to nominal gains of 85 (38.6dB), 10 (20dB) and 2 (6dB), respective­ly. The input impedance of the IC1, as seen by the probe, is around 100kΩ which is quite high and should lead to minimal detun­ing in most RF circuits. By the way, the input coupling capacitor for the probe is rated at 400VW. This will enable it to be safely used for signal tracing in valve radios and amplifiers which may have plate volt­ ages as high as 385V. Now it might seem odd that we are using a fairly common op amp as the input circuit for a signal tracer. After all, it should be good for at least the lower shortwave radio frequen­cies; ie, up to around 10MHz or more. In fact, the LM318 has a typical small signal bandwidth of 15MHz so it is quite appropriate for this application. Unfor­tunately you can’t get something for nothing, especially in electronics. The bandwidth figure of 15MHz means that you can get 15MHz at unity gain. If you want higher gain, the bandwidth will be correspondingly less. Fig.2 shows the frequency response of IC1 from the input to its output at pin 6. The three graphs shows the responses at the high, medium and low settings. The “low gain” graph, corresponding to a nominal gain of two (+6dB) has been normalised to 0dB and as you can see, the gain is usable to well beyond 10MHz. The “medium gain” graph shows an increase of about 14dB above the low gain setting, corresponding to its nominal gain of 20dB. At this setting, the response is usable to beyond 2MHz so the AM broadcast band is well covered. The “high gain” graph shows a further increase of about 18dB and By RICK WALTERS PARTS LIST 1 PC board, code 04106971, 53 x 55mm 1 plastic case, 128 x 68 x 26mm, Altronics H-0342 or equivalent 1 miniature speaker, Altronics C-0606 equivalent 2 2-pole 3-position toggle switches 1 216 9V battery 1 battery clip 2 8-pin IC sockets 1 binding post terminal 1 4mm banana plug Semiconductors 1 LM318 op amp (IC1) 1 LM386 audio power amplifier (IC2) 1 1N914 small signal diode (D1) Capacitors 3 100µF 16VW electrolytic 1 1µF 16VW electrolytic 3 0.1µF MKT polyester or monolithic 1 .047µF 400VW MKT polyester 1 .01µF MKT polyester or ceramic 1 15pF ceramic Resistors (0.25W, 1%) 3 100kΩ 1 120Ω 3 10kΩ 1 56Ω 1 3.3kΩ 1 10Ω 2 1.2kΩ June 1997  41 Fig.2: the frequency response of IC1 from the input to its output at pin 6. The three graphs show the response at the high, medium and low settings. The “low gain” graph, corresponding to a nomi­nal gain of two (+6dB), has been normalised to 0dB and as can be seen, the gain is usable to well beyond 10MHz. once again, there is usable gain over the whole of the broadcast band. Pin 2 of IC1 is biased to half the supply (nominally +4.5V) by a voltage divider consisting of two 10kΩ resistors and a 100µF bypass capacitor. Mode switching While the frequency response curves of Fig.2 don’t show it, IC1’s response extends down to around 200Hz, so it can be used for both RF and audio (AF) signal tracing. In the RF mode, switch S2 selects the output of diode D1, so that the RF signals are “detected” by the diode and filtered by the .01µF capacitor before being feed 42  Silicon Chip to IC2 via a 0.1µF capacitor. Note that the cathode of diode D1 is taken to ground (0V) via a 100kΩ resistor. As the DC voltage at pin 6 of IC1 is around +4.5V this means that this diode is permanently forward biassed and conducting with about 40µA through it. This slight forward bias enables the diode to detect lower signal levels than if it was not biased. An unbiased silicon diode needs a peak signal level of about 0.6V before it begins to conduct. So this measure greatly enhances the circuit operation for RF signal tracing. While we use IC1 at the same gain settings for both RF and AF signal tracing modes, the high gain of the LM318 could easily overload the following audio amplifier (IC2), which itself has significant gain. Therefore, for audio tracing, IC1’s output is fed through a 30dB attenuator (made up of the 100kΩ and the 3.3kΩ resistors) before passing to IC2, an LM386 audio amplifier. This prev­ ents the audio signals, which are normally at a much higher level than RF signals, from overloading the audio amplifier stage. IC2 has its gain switched by the second pole of S1. It has a gain of 20 (+26dB) in the lo position, 38 (+31dB) in the med position and 147 (+43dB) in the hi setting. At the lowest sensitivity the overall audio gain is -2dB (+2 -30 + 26 = -2dB) and at the highest setting it is +51.6dB (+38.6 - 30 + 43 = +51.6dB). This is sufficient to cover all normal input signals. Varying the gain of both ICs lets Fig.3: the wiring details for the signal tracer. Keep all the wiring as short as possible and make sure that the ICs are correctly orientated. RESISTOR COLOUR CODES         No. 3 3 1 2 1 1 1 Value 100kΩ 10kΩ 3.3kΩ 1.2kΩ 120Ω 56Ω 10Ω 4-Band Code (1%) brown black yellow brown brown black orange brown orange orange red brown brown red red brown brown red brown brown green blue black brown brown black black brown 5-Band Code (1%) brown black black orange brown brown black black red brown orange orange black brown brown brown red black brown brown brown red black black brown green blue black gold brown brown black black gold brown June 1997  43 Our prototype used a 4mm banana plug with an old meter probe tip plugged into it. Alternatively, a standard multimeter lead could be used as a test probe, for reaching difficult locations. Fig.5: the full size etching pattern for the PC board. making sure that they have the correct polarity. Solder the 11 wires for the switches as well as the two wires for the speaker into the PC board, leaving each of them around 75mm long. As well, solder the negative battery lead (black) into its pad on the PC board. Drilling the case us boost the audio gain when the RF signal is at a low level and reduce it when the signal is higher. Assembling the PC board The assembly is quite straightforward and the component overlay is shown on the wiring diagram of Fig.3. Begin by checking the PC board for shorted or open circuit tracks and then make any necessary repairs. This done, insert the resistors, diodes and IC sockets, solder them, and cut off the excess leads. If you align all the resistors so the colour bands are in the same direction (horizontally and vertically) it makes it easier to read the values and also makes the finished PC board look better. The same comment applies to the values marked on top of the MKT capacitors which should be fitted next – make them all read in the same direction. Lastly, fit the electrolytics, At the opposite of the case from the battery, drill a 4mm hole on the centrelines and fit a binding post terminal. Next, drill holes for the two switches 16mm down from the top on either side on the centreline (use the label markings as a guide). This done, mount the PC board in the case using the two short screws and complete the wiring as shown in Fig.3. We used a 4mm banana plug with an old meter probe tip in­serted in it as the probe but you could also use a standard multimeter probe for reaching difficult locations. The earth lead consists of a length of wire fitted with a small alligator clip. SILICON CHIP r e c a r T rf off audio hi lo med Testing the signal tracer Fig.4: this is the full size front panel artwork for the signal tracer. 44  Silicon Chip To test the unit, connect the battery, switch to AUD and HI, and place your finger on the probe. You should be greeted with a loud screech. If you live in the city and switch to RF & HI, you should hear one or more AM radio stations if you connect a length of wire to the probe. The reason that you hear several stations (if you hear them at all) is that there is no selectivity and all frequencies are received and are amplified equally. For a good description on how to use a signal tracer, refer to the articles on Vintage Radio in this and last month’s issues of SILICON CHIP. SC SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. 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 SATELLITE WATCH Compiled by GARRY CRATT* In-orbit tests for new Japanese satellite The Japanese satellite JCSAT 4 was launched . successfully on 16th February, 1997. It was originally planned to operate from 124°E but is now located at 141°E for in-orbit testing. JCSAT 4 will be shifted to 150°E to replace JCSAT 1, reported several months ago to have a serious fuel leak. The satellite has 12 C-band and 28 K-band transponders, capable of covering Australia and New Zealand. service can be seen at 1370MHz IF, using an SR of 27500Mbps and an FEC of 3/4. Initial testing indicates a 3.7m dish is the minimum requirement along the east coast of Australia. Optus satellites: Thaicom: Recent political action in Papua New Guinea saw commercial networks scramble for available space on Optus satellites. The A3 satellite, located at 152°E, was utilised by Network 7 on March 24 for SNG out of Port Moresby. This was one of the few occasions that signals have been seen from A3 in recent times. Optus B1 T11U (1152MHz IF) has seen a recent increase in activity, primarily due to the occupation of T5U by SKY New Zealand, causing some SNG links to be moved to this new alloca­tion. April 8th saw initial testing by Sky Network New Zealand on T5U (1250MHz IF). Signals are weak enough to require a 3m dish for noisefree pictures along the east coast. The Video­crypt service commenced testing officially on April 15 and requires a SmartCard. Palapa C2: A new digital service for Malaysia, located on the Palapa C2 satellite, commenced operations over Easter. Called “MEGA” TV, the 7-channel MPEG Myawaddy TV (Burma) is broadcasting through Asiasat on IF 1384MHz. Thaicom 3 was successfully launch­ed on April 17th aboard Ariane V95. The launch was originally scheduled for April 11th but coupling problems between the Ariane body and the Thaicom satellite caused engineers some concern for several days before it was given a clean bill of health. The satellite will be located at 78.5°E, while Thaicom 1 will be moved to 120°E. Intelsat 801: In the April issue’s Satellite Watch, we reported the successful launch of Intelsat 801, destined for the Indian Ocean region. On March 18th, ground controllers working on the satel­ lite testing program inadvertently caused the satellite to enter into an uncontrolled spin and point away from Earth. The satel­ lite has now been brought under control, apparently without damage, and is expected to enter service this month. Asiasat 2: Myawaddy Television has begun digital transmissions on this satellite. With an IF of 1384MHz, the MPEG para­meters for this signal are SR 5080 and FEC 7/8. The service is expected to remain on a permanent basis. Panamsat 2: April 8th saw initial testing of a new analog signal on Pas-2. Apparently broadcast in the Lebanese language, the service ran for several days at 1405MHz IF (horizontal polarisation) before disappearing. The service was delivered into Australia in MPEG format (along with a special version of Rai TV Italy) and is carried on the Optus­vision cable network. April 10th saw the brief appearance Pas-2 of Bloomberg Information TV on 12.590GHz, vertical polarisation. The SC service is broadcast in PAL. * Garry Cratt is Managing Director of AvComm Pty Ltd, suppliers of satellite TV reception systems. Phone (02) 9949 7417. http://www.avcomm.com.au June 1997  53 COMPUTER BITS BY JASON COLE Tuning up your hard disc drive The hard disc drive on your PC requires regular main­tenance for trouble-free Windows 95 operation. The procedure is straightforward but there are some simple rules that must be followed to avoid losing data. With Windows 95 there is one thing you must do: clean your hard disk drive (HDD) on a regular basis. This is known as house cleaning and just like you do at home, you put things away first and then make the place nice and neat. The same goes for the HDD, which needs to be cleaned up on a regular basis. Just how often you should do this is determined by how often the HDD is written to. In addition, there is a strict procedure that must be followed because you can lose data if it is not done correctly. The two programs that you use to clean up your HDD are ScanDisk and Defrag. Let’s take a closer look at these. Fig.1: the hard disc drive (HDD) is checked for errors by running ScanDisk. The standard test will usually suffice but you should occasionally run the thorough test to scan for any disc surface errors. 54  Silicon Chip ScanDisk in Windows 95 is similar to CHKDSK in DOS. Basi­cally, it goes through the HDD and checks all the files against the File Allocation Table (FAT). It then reports any errors that may be there and gives you an opportunity to fix them. ScanDisk is not a particularly powerful program but it is an excellent one to use to ensure the integrity of the data on the HDD. Defrag, which is short for Defrag­ menter, does just that – it defrag­ ments your data. When a drive has been used for some time and a lot of data has been saved and deleted, “holes” appear between the various files that are created on the HDD. That’s because the various files are not necessarily stored on the disc in a contig­uous fashion. What happens is that the Disk Operating System (DOS) always starts looking for space from the beginning of the drive. If it finds that there is already data in the first cluster, it checks the next cluster and so on until it finds space. If your file requires two clusters of drive space and the first available space is only one cluster in length it will write what it can there. It then looks for the next free space to write the remain­ing data and that could be several sectors away. As a result, the file can be split into two or more sepa­rate pieces on the HDD; in other words, it becomes fragmented. And, like the disorder in your home, the longer you leave it, the more defragmented the HDD becomes. Of course, when you access the file, it appears to be all in one piece. That’s because the HDD keeps a record (in the file allocation table) of where all the fragments are. When you access the file, the HDD simply looks for all the fragments so that the file can be reassembled. Fig.2 (left): this is the message that appears if ScanDisk finds no errors on the disc. If errors are found and fixed, it’s wise to run ScanDisk again until it goes through without finding any errors. Fig.3 (below) shows the dialog box that appears when you start the Windows 95 Defrag program. The advantage of this technique is that you can store a lot more data on the HDD. The downside is that if your files are badly defragmented, it takes longer for them to be read from the HDD. In addition, errors are far more likely to occur. By running Defrag, all those fragmented files are moved and written back to the HDD so that they are now in contiguous blocks. Depending on the settings you give the Defrag program, the files can be simply defrag­mented leaving spaces between them, or the files can all be moved to the beginning of the drive, thereby eliminating any “holes” that may have previously been created. But what happens if the drive has an error, such as a file that is given the wrong size in the FAT? If the computer has been told that a file is larger than it actually is, the amount of the oversize may actually overlap an adjacent file. If you run Defrag without first checking for this type of error, the computer will move the oversized file and also take part of the adjacent file with it. The first file may still work but the header of the second may be gone and without it that file cannot be opened. Run ScanDisc first So how can we clean up the HDD and not lose anything? The trick is to correct any disc errors for running ScanDisc first. The procedure is as follows: (1) Click on the Start button, then click Programs, Accessories, System Tools, ScanDisk. A dialog box will appear as shown in Fig.1 (2) If this is the first time you have ever checked your HDD or it hasn’t been done for some time, then make sure you select the “Thorough” option. This not only checks the files and folders for errors but also scans the disk surface for defects. Do not select the “Automatically fix errors” option as it is always best to know what has gone wrong (and to what file) so that you can do something about it. (3) Select the drive to be scanned and click the Start button ScanDisk will now go through your HDD and check for any errors. The Standard test should only take about 20 seconds (depending on the size of the disc and how many files you have). If you chose the Thorough option, however, then get a cup of coffee because it can take over 90 minutes to scan every sector of the HDD for errors. I will not go through all the possible errors that can occur because there are so many of them. However, one of the most common errors is: Lost allocation units found in X chains If you get this message, convert the lost allocation units to files and then have a quick look through them with a text editor to see if they are a part of an important document. These files, by the way, will all have a .chk extension, so they are easy to identify. Going back to our error message, the X chains number tells you how many *.chk files will be made in the root directory. Some of these lost chains can be quite large and I have come across one that was 79Mb in size. However, that was from a system that had a faulty HDD controller. By the way, do not attempt to check your hard disc for errors by running CHKDSK.EXE in a DOS box. If you do, it can pick up open Windows files, such as the Swap File, and show it as an error. CHKDSK.EXE should only be run in DOS itself, while Scan­Disk should be used exclusively in Windows 95 (you can also run Scandisk from DOS). When the scan is completed you should get a message like the one in Fig.2. If you come across an error and elect to fix it, it’s always wise to run ScanDisk again and to keep re-running it until it goes through without finding an error. Defragging the disc Once Scandisk has been run, you can run the Defrag program. This is done by clicking Start, then Programs, Accessories, System Tools, Disk De­ frag­ menter. This will bring up the dialog box shown in Fig.3, allowing you to select the drive to be defrag­ mented. The next dialog box (Fig.4) tells you how badly the disc is fragmented. In this particular case, the reading is only 1% but this figure can be a bit misleading. That’s because it doesn’t really tell you how badly the disc is June 1997  55 Fig.4 (above): this dialog box can be a bit misleading. That’s because it doesn’t really tell you how badly the disc is fragmented at all. Instead, it indicates the degree of file fragmentation which means that there could be lots of “holes” on the disc between the various files. Fig.5 (right): another way to get to ScanDisk and Defrag is to double-click the My Computer icon on the Desktop, then right click on the hard drive of choice and select Proper­ties. You then select the Tools tab to bring up this dialog box. fragmented at all. Instead, it indicates the degree of file fragmentation. This means that while the individual files may be contigu­ous, they can still be all over the place on the disc, with “holes” everywhere between them. And, as explained previously, it is these holes that cause file fragmentation. Clicking the advanced button brings up the Advanced Options dialog box. This lets you select the defrag­mentat­ion method and there is also an option that tells Defrag to scan the disc first for any errors. Clicking OK and then the Start button in the dialog box of Fig.4 sets the Defrag program running and again you can go and make yourself a cup of coffee because the Defrag procedure can take quite some time. Another way to get to Scandisk and Defrag, which is a bit faster, is to double-click the My Computer icon on the Desktop, then right click on the hard drive of choice and select Proper­ties. This brings up a new dialog box, which has several tab options. Selecting the Tools tab brings up the options shown in Fig.5. The Check Now button launches the ScanDisk program, while the Defragment Now button launches the Defrag program. 56  Silicon Chip There is also a Backup Now option but this requires a tape backup unit to work. more likely to fail than a well-organized volume. Important advice Finally, here’s some fun stuff for Windows 95. Are you sick of the front “splash” screen as you load Windows? If so, this “splash” screen can be easily changed using a graphics utility. The opening “splash” screen is a bitmap file called logo.sys. The bitmap size is 320 x 400 with 256 colours. To change the screen, first backup or rename the existing logo.sys file. This done, grab whatever you want as a “splash”, save it as a bitmap (logo. bmp) and rename the file to logo.sys. Here are the splash screen names: Logo.sys – front splash (located in the root directory); Logos.sys – It’s Now Safe To Turn Off Your Computer (located in the Windows directory); Logow.sys – Please Wait While Your Computer Shuts Down (located in the Windows directory). All three files should be backed up before attempting any changes, otherwise it will be necessary to reinstall Windows if you change your mind and want the originals back again. If the new bitmap is too big or corrupted, the computer should still work but the SC picture will not appear. To sum up, you must follow a strict regime when cleaning up your hard disc. The two main points to remember are these: (1) Do not run Defrag without running ScanDisk first; and (2) Do run Defrag immediately after running ScanDisk. If you run ScanDisk and then do something else, such as opening and saving a file or copying files to the HDD, always run ScanDisk again before running Defrag. This rule should be fol­lowed, no matter how trivial the extra work may have been. After all of this, which may seem a little involved but is really quite easy, your computer will operate a lot better. In some systems you may not notice any real difference but a few will see a significant increase in loading speed and overall performance. In either case, your system will be more reliable. By the way, if you are running DriveSpace to get more room, these processes will take a lot longer. Persevere, however, because a badly organized DriveSpace volume is much Some fun stuff SERVICEMAN'S LOG I don’t like house calls I don’t like making house calls but sometimes they are inevitable. If it’s a large TV set, one usually doesn’t have much choice but if the patient is an old 286 computer, the cost of the call doesn’t make much sense. Some weeks ago, I was called to a house to attend to a Sharp SX-68A7 stereo TV. I was reluctant to go out at the time for three reasons: (1) I was unfamiliar with the set; (2) it had an intermittent sound fault; and (3) someone else had already had a look at it. However, as the owners were semi-retired and didn’t have a car, it was going to be too difficult for them to bring it into the workshop. Besides, they did ask nicely and really I am a great big softy at heart! When I arrived, Mrs Jones made some tea while I extricated the monster from its dark hole in the “entertainment” cabinet. This set is initially a little confusing to operate, even with the instruction book (I often think they ought to have an in­struction book for the instruction book). There are four LED displays on the front, the first three being marked MONO, S/VIDEO and SURROUND. The fourth is unmarked but apparently is the power ON indicator. When I turned it on, only the first and last LEDs were illuminated. However, no matter how hard I tried, I couldn’t get any sound. There was only noise from the loudspeakers, even when the volume was turned fully up. I put a small screwdriver in the RCA audio input socket at the rear, selected AV (audio-visual) and was rewarded with a buzzing noise. Obviously, the output amplifi­er was OK and the fault had to be between that and the IF stage, as the picture was excellent. My guess was that the problem lay in either the muting, AV switching or stereo decoder circuits. I have had a few cases in the past where a TV set muted in the mono mode, so I decided to test this area first. Now most stereo TVs have LED displays that illuminate on stereo or bilingual broadcasts but this TV illumi­nated a LED for mono transmissions, which was rather confusing. Perhaps Sharp thought that as most broadcasts are in stereo, the consumer may need to know when reception was in mono rather than vice versa. In any event, the sound didn’t work in either mode. I removed the large plastic rear shell of the set and tried to get my bearings on the unfamiliar chassis. It is a large flat chassis with three vertically mounted modules on the righthand side. Two of these modules are encased in metal screening which is soldered to the motherboard. Without the service manual, it was very difficult to determine their functions and I couldn’t even find a marked control or test point that might give a clue. I tried tapping them gently with the butt end of a screwdriver but it made no difference. Mr Jones didn’t have much praise for the hapless serviceman who called previously because he “only made it worse”. Before he came he could at least occasionally get some sound and now he didn’t get anything at all. And besides, the previous serviceman “was far too keen to take it to the workshop”. Well, he wasn’t the only one. If it hadn’t been for the fact that it was a 68cm TV with lots of stairs between it and the van, I would have insisted that it go straight to my workshop. What’s more, it was beginning to look as though this was going to be the inevitable course of action. But first, there were a few more things to try. I tuned in to the VCR first but this made no difference. I then I got some AV leads and connected them between the VCR and the TV set. Mrs Jones, who was watching me like a hawk, thought that I was a genius when the sound miraculously appeared but I had to gently deflate her enthusiasm by informing her that it wasn’t really fixed. This would have to be a temporary arrangement while I obtained a service manual so that it could be fixed properly. Even then, there was a good chance that it would have to go the workshop. When the manual eventually came, I was able to work out that module PWB-E to the far right of the chassis was the stereo decoder. This circuit consisted of two ICs (IC351 & IC352) and a transistor (Q351). I enquired as to the trade cost of these parts which came to $55 including freight and tax. The question was, would it be better in the long run to get these parts in now or risk possibly yet another service call and/or a trip to the workshop (ie, would the cost of my labour exceed these parts if it was later found that either was faulty). Unfortunately, the chances of using these chips for another repair if they were bought and kept in stock would be remote. I decided to put the options to the Jones’ and let them make the choice. They decided on ordering in the parts immediate­ly which was just as well because they had to come from Japan. Eventually the parts arrived and, armed with the service manual and an audio probe (a battery powered amplifier to detect audio), I felt reasonably confident I could knock this one off in one hit. Unfortunately, gaining access to the underside of the main chassis PWBA June 1997  57 it rather difficult. As usual, the manufacturer had decided to save vast quantities of money by making sure that the interconnecting leads were as short as possible, thereby making it exceedingly difficult to get the chassis into some sort of serviceable position. This problem is compounded by the light­weight plastic cabinets and chassis used in modern sets – one has to be careful to ensure that the set doesn’t roll onto its face due to the weight of the tube and the remaining front half of the cabinet. Anyway, I finally managed to remove the screen covers from the stereo decoder module and unplug it from the main board. At least I could now work on it in comfort on a table and in good light. A careful examination of the module didn’t reveal any problems so I fitted one of the ICs and plugged it back in. There was still no sound but I quickly realised that I had forgotten to reconnect the flying lead to socket (YA). This time there was some intermittent sound so I got the freezer out and progressive­ly sprayed small areas on the copper side of the board. 58  Silicon Chip It didn’t take long to discover that the sound changed significantly when I hit the area around Q351. I removed the board again and concentrated my search around this component. What I could barely discern was a very faint hairline fracture around the collector pin of the transistor. I resoldered it and plugged the board back in. Success at last – the sound was always there no matter what I did to the board. Before refitting the screen covers I replaced the other IC as well. This wasn’t really necessary of course but was done at Mrs Jones’ insistence, seeing that the new IC “had already been paid for”. This wasn’t as easy as it sounds as it was a 42-pin high-density IC. Anyway, the rest of the reassembly was straightforward and amazingly it all still worked when the set it was snuggled back into its enclosure. Mr and Mrs Jones were both pleased that their pride and joy had been restored and that the bill was less than they had been expecting. The old 286 computer My next house call involved an old 286 computer that would­n’t boot up. Normally, I wouldn’t consider making a house call on this type of equipment as it’s just not cost effective but the customer was very insistent. Mr Smith was a retired engineer in his late sixties and the old 286 computer had been given to him by his son. I tried hard to point out that though his computer was only eight years old it was well and truly obsolete and would probably not be worth the service cost – after all, some people are tossing out their 486s these days! His response was that he only used the machine for letter writing and didn’t really need anything better. Eventually, I agreed to have a look at the machine if only because Mr Smith had been a regular customer of mine for some years. What’s more, he readily agreed to pay for the service call and so I asked for the symptoms. Basically, he had added another lithium back-up battery to the mother­ board when the CMOS settings had been lost but he didn’t know how to reset it. On the surface, it seemed that this should be a simple job, especially as he assured me that you didn’t need to use a back-up disc and he had the original in­ s truction booklets and software. So why couldn’t he do the job himself? This he couldn’t really explain except to say that he just couldn’t do it. When I arrived, Mr Smith showed me into his little “comput­er room” to examine his ailing 286. When we switched it on, his EGA monitor displayed 512KB of RAM. The first error message simply said “keyboard” and then came about six other lines with details of incorrect disc and memory sizes. Finally, it said “press F1” to enter the start-up menu before trying to boot from either drive A or C. The first important thing I noticed was that the machine didn’t respond to the keyboard, except for making a slight noise in the speaker whenever a key was depressed. This, together with the obviously dried-up coffee stains on some of the keys, sug­gested that the keyboard may be faulty. I also noticed that the Num Lock, Caps Lock and Scroll Lock keys didn’t illuminated their respective LEDs. I checked the AT/XT switch which was parked correctly and, as an experiment, put it in the XT position and reset the comput­er (Ctl, Alt, Del didn’t work). Ironically, the three keylocks now worked correctly but that was all. Mr Smith confessed that he had “looked at” the keyboard and had had it apart, which only deepened my suspicions. I still thought that the problem was relatively straight­forward – the keyboard had been ruined by coffee and hence Mr Smith couldn’t enter the CMOS values so that it would boot from the hard drive. It would, however, boot from a floppy disc in the A: drive (despite the error messages) but it still wouldn’t accept commands from the keyboard. Because, this was my last house call for the day and be­cause I was feeling exceptionally charitable, I decided to take his computer and keyboard and test them out at home with my machine. I would then return it on my way to work the next day. The first thing I did at home (after finding an old EGA monitor I had in the garage) was to connect my own keyboard to the 286 and fire it up. You can imagine my amazement when the same “keyboard” error as before came up on screen, along with all the other error messages. I double checked the keyboard by con­ necting his to my computer and it worked perfectly! Well, if it wasn’t the keyboard it had to be the mother­ board inside the computer. Removing the cover, I found that the keyboard DIN socket was located directly under the power supply, so that too had to be removed. Once the power supply was out of the way, I could see that the old nicad battery was still on the motherboard and had leaked acid onto some of the PC tracks. I quickly snipped out the soldered battery and wiped the affected area with CRC-26 to stop further corrosion. The keyboard socket was quite close to the corroded area but I now had to ask myself whether or not I should continue with what could turn out to be a lost cause. The first scenario was to declare the repair uneconomic and return the computer to its owner. However, the owner is an old-age pensioner and obviously wouldn’t be too happy about paying for my service call without a positive result. The alternative scen­ ario was to remove the motherboard, locate the broken track by continuity checks and solder in a jumper – a piece of cake and there was nothing on telly that night anyway. The hardest part was removing the motherboard which had no less than five other boards plugged into it. Having done this, it didn’t take too long to find the offending track from the 5-pin keyboard DIN socket, the only difficulty being that it was a very thin track. I bridged the track with some fine wire, reassembled the computer and anxiously switched it on. Naturally, I was relieved to see it boot up without the keyboard error. In fact, the keyboard was now working and I punched in the correct CMOS values into the setup menus and rebooted. The computer now booted normally, processing the config.sys and autoexec.bat files to finally rest at Mr Smith’s personal menu. Unfortunately, that wasn’t quite the end of the story. This particular 286 came with 1Mb of hardwired RAM chips (640Kb base and 384Kb extended = 1024Kb) but now it could only see 512Kb of base memory and no extended memory. Obviously, it had lost a couple of 256Kb memory banks but by now I had reached the 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 24/31 Wentworth St, Greenacre 2190 Phone (02) 642 6003 Fax (02) 642 6127 P.C.B. Makers ! If you need: •  P.C.B. High Speed Drill •  P.C.B. Guillotine •  P.C.B. Material – Negative or Positive acting •  Light Box – Single or Double Sided – Large or Small •  Etch Tank – Bubble or Circulating – Large or Small •  U.V. Sensitive film for Negatives •  Electronic Components and •  •  Equipment for TAFEs, Colleges and Schools FREE ADVICE ON ANY OF OUR PRODUCTS FROM DEDICATED PEOPLE WITH HANDS-ON EXPERIENCE Prompt and Economical Delivery KALEX 40 Wallis Ave E. Ivanhoe 3079 Ph (03) 9497 3422 FAX (03) 9499 2381 •  ALL MAJOR CREDIT CARDS ACCEPTED June 1997  59 Serviceman’s Log – continued conclu­sion that enough was definitely enough. Mr Smith was delighted to got his 286 back in working order; the missing memory made no difference as he could still run his word processor. In the meantime, I’ve sworn not to even look at a 286 again no matter how simple the problem seems. The work piles up Meanwhile, back at the shop, the work had been piling up with at least four jobs that were relatively urgent. I wondered whether I could polish them all off in one day but it was not to be. Some of the problems were caused by intermittent faults and these are always time consuming. The first set off the rank was an Orion 20J that was com­pletely dead. This is another one of those sets where it is difficult to remove the chassis, mainly because no-one tells you about the concealed clips that lock into the case. It is also impossible to gain access to the PC board without unplugging the loudspeaker lead. Anyway, I measured slightly more 60  Silicon Chip than 273V on the main filter capacitor (C506) and traced this all the way to the power chopper (IC501, pin 3). However, no voltage was found on TP501 which is the main B+ rail (103V). Instead, this registered a dead short to ground. The most likely culprits were the line output transistor Q402 and diode D521 (across the B+ rail), though access to these parts is appalling. I replaced them both and then spent some time patching up the generally poor soldering around the power supply. When I put everything back together again, the set fired up OK and so I put it aside to soak test while I got on with the next job. Who was it that said that pride cometh before a fall? The customer called by the next day on the offchance that the set had been fixed and, when he saw it working, insisted on taking it home. I advised him that I would like to test it a bit longer but, as it was a Friday, he said that he would rather take it home for the weekend and reluctantly I agreed. Guess who was waiting for me at 8.30am on Monday morning with his Orion? Apparently, it had only lasted for half an hour before it died again. Such is life. Stripping it down again, I found that the same zener diode (D521) had gone short circuit. For this to die, the B+ has to rise beyond 130V, so I went back to the power supply and hoicked out all the electros for new 105°C ones. I then reassembled it again without the zener diode but with a meter monitoring the B+ rail and switched it on. The B+ still measured 103V five minutes later so I put the zener back in and left the set on, hoping that it would now stay on. It was not to be –just as my first well-deserved coffee was kicking in, the set died yet again and I was too slow to read the meter before it did. I repeated the whole procedure again and left my coffee to get cold. This time, after only five minutes, the B+ began to rise sharply. I switched the set off and touched the components around the power supply. IC501, an STR58401, was quite hot and because I didn’t have any other clues, I decided to order this in and try again later. The next job was a Sharp CX2168 that had come in with the complaint that it intermittently cut off after a few minutes. Despite having a huge range of service manuals, I didn’t have this one and besides, one cannot afford to purchase a manual for every set that you fix. However, I did have a manual for a CX2048 which didn’t look that different. At least, it used the same power chopper IC which, though not marked on the circuit, was an STR­ 41090 (IC701). The main difference was that the CX2168 was a Teletext set and it also used a relay (RY701) to switch the power on and off. And this was basically what was happening – the relay clicked off after about 10 minutes. I also discovered that the circuit has a miniature slider switch (S1101) which controls the relay driver and leaves the set switched permanently on when the power switch is on. Overriding the relay meant that I could monitor the B+ rail (115V) on the cathode of D732 in the fault condition. But, as happened previously, I wasn’t watching when the fault appeared. In this case, the phone rang after the set had been on for 15 minutes. When I returned, the set was completely dead and like the Orion, zener diode D731 was short circuit. As before, I replaced all the small electros in the power supply and soldered the many dry joints there too. This time, when I switched it on, I doggedly monitored the B+ rail and switched it off when the voltage suddenly began rising after about five minutes. IC701 was hot and as it was the logical suspect, I placed an order for it as well. So far, I hadn’t cleared any of the four sets I had planned to do. The two different ICs arrived a few days later and my hunches proved correct – both sets were still working three days later. Sounding out an NEC The third set I tackled was an NEC N4830 with intermittent no sound. Having fixed a lot of these sets, I felt confident that this would surely be an easy one, especially as wiggling either the aerial or AV socket would make the sound come and go. This set uses a Daewoo C500 chassis and I initially decided on a sweeping rework of the main chassis to eliminate any possi­ble dry joints. Initially, I thought that I had got it in one but after half an hour of soak testing, the same problem re-occurred. I dived back into the set and went for the tuning micropro­cessor, concentrating on sound related functions to resolder. Still no luck. I had saved the IF module until last because – as you’ve probably guessed – it was the most inaccessible! Not only did it and its screen have to be unsoldered from the motherboard, but the screening can also had to be unsoldered before I could get at the PC board. This board appeared to have quite a few suspect joints, so leaving nothing to chance, I reworked all the connections. Unfor­tunately, this model set is difficult to reassemble and by the time it was all back together, I was fairly fuming on how badly the day was going. On the other hand, the set now behaved per­fectly and I pronounced it fixed after three days of thorough soak testing. Another success And so to set No.4, a Hitachi Fujian HFC2125B that was dead. I measured the 278V B+ from the bridge rectifier all the way to the collector of V901 (the supply chopper) but there was nothing on either its base or emitter. Resistors R903 and R904 (82kΩ 1W) in series between the collector and base of V901 were the logical suspects. I whipped in two new ones, after first making sure I had discharged the main filter capacitor (C905) and the set came good. While I was at it, I replaced C920, a 1µF 250V capacitor which often causes the set to lose its memory (due to the -28V rail dropping to about -10V). The set was then put aside to soak test by which time I’d had enough SC for one day. June 1997  61 This photo shows the stepper motor PC board teamed with a small stepper which could be used for a variety of tasks. Note: D3 & a 10µF capacitor have been added since this photograph was taken. This circuit will drive a stepper motor in one direction or the other for a fixed time. It has a variety of applica­ tions & could be used to power a model railway boom gate or give slow motion operation of points. Manual control circuit for a stepper motor By RICK WALTERS Typical stepper motor applications generally involve a drive circuit under the control of a computer or microprocessor. By contrast, this circuit has been produced as a self-contained PC board designed specifically to suit small stepper motors which draw just a few tens of milliamps at 5V. When the actuate button (S1) is pressed, the stepper motor will run in one direction for a fixed time. When the actuate button is pressed again, 62  Silicon Chip the stepper motor will run in the other direction for the same fixed time. You can use two buttons (S2 & S3) to preset the forward and reverse directions of the motor before the actuate button is pressed. While the speed at which the stepper motor runs is fixed, you can set the stepping rate by changing a resistor or capacitor in the circuit. Note, however, that this circuit does not allow an exact number of steps to be specified, just the speed, duration and direction. Model railway application There are still many places in Australia where level cross­ings are controlled by boom gates. Wouldn’t it be nice to have a level crossing with motorised boom gates on a model railway layout? This stepper motor drive circuit could be used to provide the motive power. In practice, the actuate switch (S1) could be a reed switch operated by the model locomotive as it approaches the crossing. This would cause the boom arm to lower. A second reed switch, wired in parallel with the first, is placed after the crossing, so that the locomotive operates it to raise the boom arm. Circuit operation The full circuit of the stepper motor controller is shown in Fig.1. It can be divided into three sections: one controlling the duration of operation, one controlling the speed and direc­tion of stepping, and the third controlling the stepper motor drivers. The first section involves IC1, a 555 timer connected as a monostable. When pushbutton switch S1 is closed, pin 2 of IC1 is pulled to 0V and its output at pin 3 goes high for about 10 seconds. This will turn PNP transistor Q1 off and its collector voltage will fall from +5V to 0V. This has two outcomes. First, D1, which held the 0.1µF capacitor at pins 1 & 2 of Schmitt NAND gate IC5a at +4.4V, is no longer conducting and therefore IC5a works as an oscillator. Its output at pin 3 will be a square wave with a frequency of about 100Hz. This signal is fed to the clock input of a decade counter, IC2. When this input is clocked each of the 10 outputs of IC2 will change from low to high in sequence. The second outcome is that the collector of Q1 – which held IC2 reset via diode D2, IC4a reset at pin 4 and IC4b reset at pin 12 – is no longer high and so these ICs are now enabled and can be clocked. Q1’s collector is also connected to the clock input of IC3a, but as this IC needs a low to high transition to toggle the output, this change has no effect. Bridge drivers Before we describe the logic operations any further, let’s look at the stepper motor drivers. The type of stepper motor specified consists of two centre-tapped windings MA and Fig.1 (right): this motor driver circuit is suitable for driving low current stepper motors. It drives the stepper motor in one direc­tion or the other each time switch S1 is closed. June 1997  63 Fig.2: follow this parts layout diagram when installing the parts on the PC board and be careful not to mix up the transistor types. output high for around 10 seconds, as already noted. During this time IC5a will clock IC2 at 100Hz. This means that the output of IC2, pin 3, will go high for 10ms then low as pin 2 goes high for the same time. Pins 4 and 7 will follow this sequence but when pin 10 goes high it will immediately reset IC2 through D3, causing pin 3 to go high again. Then the sequence will repeat. Each time pin 4 of IC2 goes high, it clocks IC4a and re­verses the direction of the current through MA. IC4b is clocked either by pin 2 or pin 7 of IC2, depending upon the state of the outputs of IC3a. If pin 1 of IC3a is high, gate IC5c is enabled and pin 7 of IC2 will clock IC4b. If pin 2 of IC3a is high, gate IC5b is enabled and pin 2 of IC2 clocks IC4b. In the latter case, IC4b is clocked before IC4a and the motor will step in one direction. If IC3a is toggled then IC4a will be clocked by pin 4 of IC2 before IC4b will be clocked by pin 7. Therefore, as explained previously, the motor will now rotate in the opposite direction. Turn off Fig.3: this is the full-size etching pattern for the PC board. Check your board carefully before installing any parts. MB, the centre taps of which are not used. Each winding is connected across a bridge of four transistors, Q2-Q5 and Q6-Q9. We will first describe how winding MA is driven, as the drive to MB is identical. Assume pin 1 of IC4a is high, and therefore its complement, pin 2, will be low. Pin 1 will turn Q2 off and Q3 on. Pin 2 will turn Q4 on and Q5 off. As both Q3 and Q4 are turned on, current will flow through winding MA from right to left. If IC4a is now clocked, its outputs toggle and so pin 1 goes low and pin 2 64  Silicon Chip goes high. If you trace it out, you will see that Q2 and Q5 are now turned on and the current flow in MA is from left to right. Therefore, by clocking IC4a we reverse the direction of the current in MA. A similar reversal occurs for IC4b and winding MB. To make the motor rotate (in either direction) we have to delay the phase of the current in MA relative to MB. To rotate it in the opposite direction we must delay MB relative to MA. Now that we know what we have to do to run the motor, let’s look at how it happens. When IC1 is triggered it will hold its Ten seconds after switch S1 was closed, the pin 3 output of IC1 will go low and Q1 will turn on again. This resets all the counters and the motor is stopped. At the same time, this low to high transition by Q1’s collector will clock IC3a, thereby ensur­ing the motor will rotate in the opposite direction next time it is powered. At power on, the 0.1µF capacitor connected to pin 6 of IC3a ensures that this pin is briefly pulled high. This sets IC3a so that its pin 1 is high. Thus, the motor will always rotate in the same direction each time the power is first applied. Forward/reverse, up/down Provision has also been made for two switches (UP & DOWN) to change the direction of the motor. These are on the set and reset pins of IC3a. These switches should only be used when the motor is stopped. The motor may not reverse its direction if they are used while it is running, as it depends on the actual phase of the drive waveforms. PC board assembly Begin as usual by checking the PC board against the artwork of Fig.3. Check for undrilled holes, shorts between tracks, especially where the tracks run between the pads on IC4 and IC5, and open circuit tracks. Make any necessary repairs before pro­ceeding. Use the component overlay diagram of Fig.2 as a guide when inserting components into the PC board. Begin the assembly by fitting and soldering the seven links, followed by the resistors and IC sockets, if used. To give the PC board that professional look, make sure that all the resistors have their colour codes running the same way, vertically and horizontally (this also makes them easier to check later on). The MKT and monolithic ceramic capacitors are fitted next and their markings should be similarly aligned. Lastly, fit the two electrolytics, three diodes and nine transistors, making sure that all are correctly orientated. Once you have finished, check your soldering, making sure that all the joints are nice and shiny and that there are no bridged tracks. A dull joint is a sign of potential trouble. Finally, insert and solder the ICs, or plug them into the sockets. Make sure they are inserted correctly. Testing the controller The specified stepper motor’s leads can be removed from the plug by pulling the wire gently while pressing the retaining lug on one side of the socket with a jeweller’s screwdriver or a small nail. Leave the green wires in the plug at this stage. Solder the pins into the PC board with the colours as shown in Fig.2. The motor should turn reasonably freely but when the power is applied the circuit should draw around 50mA and the motor will “lock” and be much harder to turn. Briefly short pin 2 of IC1 to pin 1 and the motor should begin turning. After 10 seconds or so it will stop. If pin 2 is shorted again the motor should run again but in the opposite direction. Once you trigger IC1, the motor will run for about 10 sec­onds in either direction. If you need to run the motor for a longer time, increase the 1MΩ resistor at pin 7 of IC1. The run time is directly proportional to the value of the resistor. Increasing it to 1.2MΩ will run the motor 20% longer. Conversely, if the motor runs for too long, reduce the resistor value. You can also change the speed at which the motor steps by varying the 100kΩ resistor or 0.1µF capacitor at pins 1 & 2 of IC5a although there are limits. If you try to run the stepper too fast it will merely stall. As a guide though, you could double the speed of stepping by halving the 100kΩ resistor between pins 1 & 3 of IC5a. Or if you wish to run the motor at half the speed, double the resistor value between pins 1 & 3 of IC5a. It doesn’t work! The first step is to check your work against the PC board overlay of Fig.3. A tiny solder bridge is all it takes to stop the unit from operating. Next, set your meter to the 10V DC range and connect its negative lead to the DC negative input. Connect its positive lead to D1’s anode. The meter should read 5V ±10% (due to the tolerance on REG1). Momentarily short pin 2 of IC1 to pin 1 and the meter should read 0V for about 10 seconds then return to the previous reading. Check that this occurs at pins 4 and 12 of IC4 and pin 3 of IC3. Each time the anode of D1 goes high it should clock IC3a. Make sure pin 1 of IC3 alternates (+5V or 0V) each time you trigger IC1. While IC1 is triggered, the outputs of IC2 (pins 2, 4 & 7) should be cycling. If you put an analog multi­meter on each pin it should read around 1.3V. A digital meter will jump around PARTS LIST 1 PC board, code 09106971, 76 x 97mm 1 stepper motor, Oatley Electronics M17 or equivalent 1 8-pin IC socket 2 14-pin IC socket 2 16-pin IC socket Semiconductors 1 555 or 7555 timer (IC1) 1 4017 decade counter (IC2) 1 4013 dual-D flipflop (IC3) 1 4027 dual-JK flipflop (IC4) 1 4093 quad NAND Schmitt trigger (IC5) 5 BC558 or BC328 PNP transistors (Q1,Q2,Q4,Q6,Q8) 4 BC548 or BC338 NPN transistors (Q3,Q5,Q7,Q9) 3 1N914 small signal diodes (D1-D3) 1 1N4004 1A diode (D4) Capacitors 1 100µF 16VW PC electrolytic 1 10µF 16VW tantalum or low leakage electrolytic 1 10µF 25VW PC electrolytic 5 0.1µF 100VW MKT polyester or monolithic ceramic 1 .01µF 100VW MKT polyester Resistors (0.25W, 1%) 1 1MΩ 10 10kΩ 2 100kΩ 1 4.7kΩ 1 22kΩ 1 3.3kΩ Miscellaneous Tinned copper wire, red & black hook-up wire, solder with readings varying between 1.2V and 1.4V. Once you locate the area where the problem exists you will have to check for incorrect component values or solder bridges and the PC board etching SC for shorts or open circuits. RESISTOR COLOUR CODES  No.    1    2    1  10    1    1 Value 1MΩ 100kΩ 22kΩ 10kΩ 4.7kΩ 3.3kΩ 4-Band Code (1%) brown black green brown brown black yellow brown red red orange brown brown black orange brown yellow violet red brown orange orange red brown 5-Band Code (1%) brown black black yellow brown brown black black orange brown red red black red brown brown black black red brown yellow violet black brown brown orange orange black brown brown June 1997  65 Pt.10: More On UHF Sampling Scopes In this concluding chapter in our series on cathode ray oscilloscopes we discuss the diode bridge switches used in UHF sam­pling scopes, accurate feedback A/D converters & random equivalent time sampling. We also look at some of the applications of 50GHz scopes. By BRYAN MAHER Last month, we discussed the broad principles of equivalent time sampling. We saw that UHF sampling scopes dispense with input attenuators and, as a consequence, can only handle a very limited range of signal amplitude. Now let us continue with the circuit techniques used in these UHF scope samplers. Scopes using sequential equivalent time sampling don’t need fast sampling rates because they accumulate sufficient samples over hundreds or thousands of triggers and signal passes. But the faster the sampler runs, the sooner the signal and its changes will appear on the screen. One of the world’s fastest scopes, the Tektronix 11801, has a sampler which runs at up to 200kS/s. This demands an incredibly short sampling interval of only 10 femto­ seconds; ie, 10fs (1fs = one millionth of a nanosecond)! So how does this scope achieve such a short sampling time? We recall from the previous chapter that UHF oscilloscopes use an electronic sampler switch (IC2) right at the input termi­nal, as shown in the block diagram of Fig.1. Periodically, the strobe signal closes IC2 momentarily Fig.1: placing the sampler right at the input terminal allows the use of a lower bandwidth analog amplifier (A2), be­cause the sampler transforms the ultra-high input frequency down to a lower frequency at W. 66  Silicon Chip Fig.2: a 4-diode bridge acts as a sampler switch, because the voltage at B mirrors any voltage applied at A. Early systems used analog feedback. and during that very short sampling interval, the input signal quickly charges holding capacitor C1 through resistor R1. Next, the strobe signal opens IC2 and holds it open for typically 5µs. Capacitor C1 holds the charge, giving the A/D converter ample time to digitise the voltage sample. The result­ant digital word is then stored in RAM. CMOS switching gates are far too slow for this job, because in the “on” condition, they store a considerable charge of elec­trons. These take time to remove, to change the gate to the “off” condition. By contrast, gallium arsenide (GaAs) diodes trap very few electrons while conducting. The less electrons held within the semiconductor, the faster they can be swept out to change from the on condition to the off condition. Diodes as switches How are diodes used as switches? The answer lies in a bridge circuit devised in the 1950s, as shown in Fig.2. The input signal is fed in to point A. For the off condition (which is most of the time), the differential strobe drive X,Y is inactive and all diodes are biased off. They are held nonconducting (ie, reverse-biased) by the positive DC supply V+ applied through resistor R2 to point H and by the negative supply V- applied through R3 to point J. To take a sample, the strobe generator creates a very short negative pulse at X, sufficient to overcome the positive bias at H. Also it produces an equal but positive pulse at Y, enough to overcomes the negative bias at J. Now with J positive and H negative, all diodes slam into full conduction, passing DC current from J to H. But here is the vital idea. Provided all diodes are identi­cal, the forward voltage drops J-A, J-B, A-H, B-H are all equal. So the upward flowing currents force points A and B to be always at the same potential. If no analog signal is applied at A, then, by the circuit balance, A and B will be at zero potential. Now let’s apply some input signal at A. When the strobe drive jolts the diodes into conduction, the diode currents will still force B to have the same voltage as the input signal at A. We say that B mirrors whatever is applied to A. This voltage at B charges holding capacitor C1 through resistor R1. That’s equivalent to a closed switch between A and B, isn’t it? The moment the strobe drive at X and Y ceases, the four diodes instantly become nonconducting. A and B are now complete­ly isolated, equivalent to an open switch. Capacitor C1 holds the sample of the input voltage long enough for the A/D converter to digitise it and store it in RAM. Integrated GaAs diodes In all diode samplers, the diode forward voltage drops should be low and equal. And they must have identical fast switching times. For best results, Gallium Arsenide (GaAs) diodes are integrated on a thin film substrate. This Tektronix TDS820 scope has a passband from DC to 8GHz without the delay line. Maximum sampling rate is 50kS/s on both input channels. The A/D converter digitises all signals into 16,384 decision levels, using 14-bit digital words. This provides increased accuracy in maths calculations and smoother screen traces. Equivalent timebase speeds can be 20ps/div to 2ms/div. June 1997  67 Fig.3: digital feedback raises the sampler efficiency and compen­sates for non-linearities. To keep the large strobe drive signals out of the sample to the A/D converter, the positive and negative pulses at X and Y must be truly differential. They must have exactly the same amplitude (but be opposite in polarity) and must rise and fall precisely together. This is achieved by transformer T1. If the strobe pulses X and Y are exact mirror images of each other, T1 has no effect. But should the positive pulse at Y be smaller than the negative pulse at X, transformer action in T1 will raise the positive and diminish the negative, until they have equal but opposite am­plitudes. Similar action occurs should the pulse timings become unequal. The very short sampling interval (needed to sample ultra high frequencies) reduces the sampler efficiency. That means C1 holds a smaller charge and the lower sample voltage fed to the A/D converter results in errors and noise in its digital output. To raise sampler efficiency, manufacturers first used posi­tive analog feedback, which we show as FB on the righthand side of Fig.2. A feedback amplifier G charges capacitor C2 to a voltage greater than C1. So from point Z the A/D converter was fed by a voltage larger than the sample at B. But this system required critical adjustment and was somewhat nonlinear. Digital sampler feedback Great improvements resulted from the introduction of digi­tal feedback sampling systems in 1987 in the Hewlett Packard HP54120 oscilloscope. In Fig.3, the sampler bridge A-B is fol­lowed by a matched analog amplifier (A2) and a 12-bit A/D convert­er. This produces digital data at N which is fed to microproces­sor M. Software running in this computer dynamically adjusts the feedback loop to increase the system gain and Fig.4: in a two-diode sampler, an integrated GaAs diode pair deposits charges on holding capacitors CN and CP proportional to the analog signal at A. 68  Silicon Chip automatically compensate for sampler non-linearities. This more exact solution, expressed in a longer 14-bit digital word output from the computer at Z, is recorded in the RAM. No adjustments are necessary, as the system is automatically controlled by the software. A positive feedback system is formed by feeding this 14-bit data from Z to a 14-bit D/A converter which converts the output digital data back to an analog signal at P. This is fed back to the sample hold capacitor at W. That raises the efficiency of the sampler, allowing it to be placed right at the scope’s input terminal. This way the scope bandwidth is not diminished by any front end analog amplifiers. Two diode sampler Because two integrated diodes are easier to match than four, Hewlett Packard frequently uses a 2-diode sampling gate as shown in the block diagram of Fig.4. Normally both diodes are biased off by the supply voltage applied through R2 and R3. To take a sample, the differential strobe signal momentari­ly overcomes the back bias, driving the diodes into conduction with their forward impedances equal. In this state, the diodes deposit charges on holding capacitors CN and CP proportional to the voltage of the input analog signal at A. After the strobe pulse has gone, those two capacitors hold the differential sample voltage long enough for the A/D converter to digitise the sample and store the data in the RAM. As before in Fig.2, the equalising transformer T1 keeps the strobe pulses X and Y truly differential. Digital feedback, similar to that in Fig.3, raises Fig.5: the SAR A/D converter (a) generates a 14-bit digital word in IC2. IC4 converts this word back to analog voltage V2 for comparison with the input sample V1 in comparator IC1. IC2 then adjusts that digital word (b) until V1 = V2, within one LSB. June 1997  69 the sampler efficiency and corrects non-linearities. All feedback sampling systems require the input signal to be repetitive. For that reason, they can only be used in equival­ent time scopes and never in real-time oscilloscopes. Feedback A/D converters Fig.6: a delay line allows time for the trigger and strobe elec­tronics to operate so that sequential equivalent time scopes can display signals at or before the trigger point. As we noted in the previous chapter in this series, the sampling rate and bandwidth are related only in real-time scopes but not in equivalent time oscilloscopes which therefore may sample comparatively slowly. The sampling rates are usually between 40kS/s to 200kS/s. This gives them the luxury of more time to digitise the signal. Therefore 14-bit feedback type A/D converters may be used, giving much greater accuracy in maths calculations and smooth­er traces on the screen. Feedback A/D converters use a completely different approach to the digitisation process, compared to the flash converters we saw earlier in this series. But the input analog signal must be repetitive. SAR A/D converters Fig.7: the random sampler (a) free runs continually and the time between the trigger and each sample is recorded. The scope reas­sembles all those samples (b) into a display equivalent to the input signal. 70  Silicon Chip The Successive Approximation Register or SAR A/D converter is one favoured type, which we show in Fig.5(a). The signal sample, after amplification in A2 (in Fig.1), is now called V1. IC2 is the SAR or Successive Approximation Reg­ister, a complex integrated circuit which contains a microproces­sor control section and 14 parallel 1-bit programmable registers, one for each output bit. Bit 1 is the MSB (most sig­nificant bit) and bit 14 is the LSB (least significant bit). CLK is the system clock. In Fig.5(a), the 14-bit output digital word from the SAR goes via 14 parallel lines to an output latch IC3. This digital data also goes around in a feedback loop to a 14-bit D/A converter IC4, which reconverts that data into an analog voltage V2. This feeds into the positive input of comparator IC1. The output of IC1 is at logic 1 level if V2 > V1, or logic 0 if V2 < V1. The aim of a feedback A/D converter is easy to see. The computer within the SAR produces a 14-bit digital word and compares its reconverted equivalent value, V2, with V1 in IC1. As a result of that comparison, on each clock pulse the SAR modifies its 14-bit word to one that will reconvert in IC4 to a new value of V2, which is closer to V1. So, in stepwise fashion, the 14-bit digital word approaches the value which truly repre­sents the sample input V1, as we illustrate in Fig.5(b). Let’s look at just the first three steps in detail. Ini­tially, latch IC3 is disabled, to isolate the converter from the RAM. All 14 output registers are reset to logic 0. When the sampler has captured a sample, it also issues the start command (SC) to IC2. On the first clock pulse, the computer in the SAR (IC2) sets the bit 1 register (the MSB) to logic 1, giving digital word 10000000000000. D/A converter IC4 instantly converts this to V2 = 2.5V, as Fig.5(b) illustrates. Because V2 < V1, IC1’s output will be at logic 0, so bit 1 is accepted as correct. On the second clock pulse, the SAR sets bit 2 to logic 1, giving digital word 11000000000000. That converts in IC4 to V2 = 3.750V which is too large (ie, V2 > V1) – see Fig.5(b). Therefore the SAR resets bit 2 to logic 0, resulting in digital word 10000000000000. The third clock pulse now sets bit 3 to logic 1, producing digital word 10100000000000. IC4 immediately reconverts this to 3.125V, so V2 < V1. Therefore the computer accepts this bit as correct. This action continues, moving down one register at each clock pulse. It sets the next bit to logic 1 and compares the reconverted V2 with V1. That bit remains set to 1, unless the resulting V2 is too large, in which case it’s reset to 0. In this way, V2 approaches V1 in a sequence of successive approximations, as we see in Fig.5(b). After 14 clock pulses, the SAR has created a 14-bit digital word equivalent to the analog sample V1, accurate to within 1 LSB; ie, with an error of less than 5V/214 = 5V/16,384 = 0.000305V. Latch IC3 is then ena­bled, recording that digital word in the RAM. Now the scope accepts another trigger event; a new sample is taken, held, digitised, recorded and the whole process re­peats. From this we see why feedback A/D converters can’t run very fast. And of course, they require a repetitive signal. Delay lines When you trigger the scope inter- Fig.8: a time domain reflectometry (TDR) test (a) for faulty connections at H. Normally the terminated line (b) divides the signal down to 0.5V continuously. But an open circuit (c) at H raises the voltage at X to 1V at time t2. Or (d) a short at H drops the voltage to zero at t2. The product of time difference (t2-t1) and the signal velocity equals twice the distance from X to H. nally from some rising step (ie, the trigger edge part of your signal), you often want to display that section of the input waveform. But sadly, sequential equiv­alent time sampling oscilloscopes cannot directly display that trigger edge (and analog scopes can’t either). The reason is illustrated in Fig.6. All signals suffer a propagation delay of 2-18ns in passing through the trigger takeoff, timebase and strobe generator circuits. So with very fast signals, the rising edge which triggered the scope is gone before the first sample can be taken. To make the rising edge visible, the solution is to take the input signal directly to the trigger takeoff, at point T on Fig.6. The input signal must also be delayed by a few nanoseconds before it enters the sampler diode bridge switch at A. Ordinary 50Ω coaxial cable can provide the required delay, as signals travel in coax lines at about 66% of the speed of light in air; ie, 0.66 x 3 x 108m/s = 200mm/ns. So two metres of coax cable would give a signal delay of about 10 nanoseconds. Scope manufacturers market spe- cial delay cables which provide delays up to 25ns. Some have a spiral inner conductor construc­tion to slow the signal velocity, giving the required delay with a shorter length. Using these, many samples can be taken before, during and after that edge of the signal which initiated the trigger. It’s called displaying pretrigger information. Random equivalent sampling Some oscilloscopes use random, rather than sequential, equivalent time sampling. In this type of scope, the sampling bridge switch free-runs continuously, regardless of whether a trigger event occurs or not. Again we assume that the input signal is repetitive. If a trigger is applied to the scope’s external trigger terminal and it is in sync with the input waveform, then the scope sets about digitising and recording those samples. In Fig.7(a) we show six passes of the input signal, each associated with a separate trigger event T1, T2, T3, etc. On each pass, the scope takes one sample, S1, S2, S3, etc. The signal waveform period might be only 10ps June 1997  71 Eye diagrams are sequential traces of logic pulses. The amount of time jitter in the pulse train is indicated by the degree to which the centre eye is partially closed by fuzzy traces. in reality but triggers and samples are accepted at a much slower pace. This is because the scope must allow maybe 5µs or even 50µs for each A/D conversion. Each sample is digitised and the digital word which repre­ sents its amplitude is recorded in RAM. In addition, the time between each trigger and sample, such as t1 in the first pass, t2 in the second pass, etc, is also measured. The value of this time in picoseconds decides the address in memory in which that sample will be recorded. So each digital word held in RAM represents two pieces of information: the amplitude of the sample and its timing with respect to the trigger. In Fig.7(a) we see just a few samples for clarity. In reality, hundreds or thousands of samples are taken, digitised and recorded. When enough samples are accumulated in the RAM, the display processor assembles them all as many bright dots on the scope screen as we see in Fig.7(b). The vertical coordinate of each represents the amplitude of that sample and the horizontal posi­tion gives its timing with respect to the trigger. The combina­tion displays the equivalent signal waveform. But the free-running sampler is usually not in sync with either the input signal or the trigger. Therefore, sam- ples may be taken anywhere: before, during or after the trigger. Samples taken before the trigger give pretrigger information of the input signal without any need for delay lines. And because the sample timing is random with respect to the input signal phase, this type of scope is insensitive to alias­ing. However, there is a down side to random sam­pling. It’s quite possible for many samples to have the same timing measured from the trigger event. Of all the samples taken, suppose 20 of these occur with the same timing after the trigger. They will all be recorded in the same address in the RAM. So 19 of those samples and digitisations are redundant and a waste of processing time, as they all will represent the same point on the displayed trace. So the scope must take more samples to make up enough for a smooth display. And of course, the input signal must always be repetitive. Applications International telecommunications involves many satellites, each containing 15-50 transpon­ders operating in the Ku 14-12GHz band and relaying 40,000 phone conversations. All float in geostationary orbit 42,000km high above the Earth’s centre. They receive and retransmit strings of serial data generated by many different equipments in many countries. For all these to be compatible, international stan­ dards specify, amongst other things, how much time jitter in pulse trains is acceptable. The Tektronix 11801B 50GHz scope can be expanded to 136 input channels using plug-in sampling heads in bandwidths up to 50GHz and 7ps internal risetime. It supports predefined masks for eye diagram presentation. The SD24 plug-in sampling head produces a step voltage rising in less than 36ps for time domain reflectometry measurements. Equivalent timebase speed can be set to an incredible 1ps/div or it can be slowed down to 5ms/ div, in 1ps steps. 72  Silicon Chip One essential application of UHF scopes is to ensure com­pliance with these specifications. For this, communications engineers and technicians display strings of multiple superim­ posed digital pulses of their systems. They overlay many logic 1 and logic 0 pulses. Inevitably, in real very fast systems, the pulse jitters with respect to the clock and this is displayed as an eye pat­tern on the scope. The more jitter present, the less clear space remains in the “eye” of the diagram. Standard templates are also displayed on the screen. If the eye area within the template remains clear, meaning not too much jitter, then that transmis­sion will be accepted by the satellite. Time domain reflectometry Time Domain Reflectometry (TDR), another important applica­tion of fast sampling scopes, can find circuit faults by measur­ing signal reflection over picoseconds. In Fig.8(a) we see a 1V step signal, from a source A of output impedance RS = 50Ω. This feeds to some integrated circuit B which has an input impedance of RT = 50Ω. The connection from A to B is through a conductor pair which also has a characteristic im­ pedance of 50Ω. We should remember that at Gigahertz frequencies every wire is a transmission line. H may be a soldered joint on a board or a welded junction in leads within an integrated circuit. The 1V step occurs at time t1. Normally the source im­pedance RS and the terminating resistance RT form a voltage divider with a division ratio of 2, so the scope displays a constant 0.5V at point X as shown in Fig.8(b). Now let’s suppose the junction at H is faulty, leaving an open circuit at H. Initially, the 1V step at time t1 must charge up the conductor’s own self-capacitance. The conductor’s 50Ω characteristic impedance forms a voltage divider with the source RS, so at first the potential at X rises to only 0.5V as we see in Fig.8(c). That 0.5V step travels as a signal from X to H, charging up the line as it goes. When it reaches the open circuit at H, the conductor is now charged, so the voltage at H can rise to the full 1V. This new voltage step at H, from 0.5V to 1V, travels as another signal back from H to X, lifting the voltage along the line to 1V as it goes. Eventually it reaches point X at time t2 and only then does the scope display the voltage step up to 1V as shown in Fig.8(c). Signals travel in parallel conductors at velocities between 0.25mm/ ps to 0.29mm/ps. So from the time difference (t2 - t1) we can calculate the distance from X to the open-ended break at H and return. On the other hand, if the fault at H was a short circuit, the display on the scope would be like Fig.8(d). Only extremely fast sampling scopes can measure these picosecond time differ­enc­es. References: (1) HP 5952-0163 and Product Note 54720A-2. (2) Tektronix publications 85W-83061, 85W-8218-0, 85W-8308-0, 55W10416-2. (3) G. Caprara: Encl. of Space Satellites; Eng.trans.Bay. Acknowledgement: thanks to Tektronix Australia and Hewlett Packard Australia and their staffs for data and some of the illustrations. June 1997  73 RADIO CONTROL BY BOB YOUNG A fail-safe module for the throttle servo This month, we present a versatile in-line fail-safe module suitable for all brands of R/C equipment. It will provide preset servo pulses for the throttle in the event that all signal is lost. In this month’s column, we will look at what is probably best described as the first of the projected plug-in modules for the Mk.22 system. It is an in-line fail-safe module. It simply plugs into the line between the receiver and any positive pulse servo. In the event of a loss of signal from the receiver, the fail-safe automatically detects the signal loss and generates an output pulse of the correct voltage and pulse-width. The fail-safe pulse width can be preset via a potentiometer to any point between 1-2ms. It is mainly intended as a throttle fail-safe but could be used for any or all of the servos in a model. In the latter case, you will need a failsafe module for each servo. Particular attention has been paid to compatibility with imported radios as this module fills a very definite market need. The rationale behind a fail-safe throttle module is quite simple. Models travelling at 100km/h or more represent a serious risk to themselves and bystanders if control is lost. As kinetic energy or impact force is proportional to the square of the velocity, it is apparent that any reduction in the speed will reduce the impact. Halve the speed and quarter the impact. Halve it again and you have The fail-safe module is plugged in between the receiver and the servo. You need a fail-safe module for each servo you want to protect. 74  Silicon Chip cut the impact to one sixteenth of the original figure. Here we are talking very worthwhile savings. Motors and radios have much more chance of survival in crashes at greatly reduced speeds. History of fail-safes So a fail-safe throttle is a very good thing. In the past I have discussed PCM radios with their built-in failsafe systems and have stated that fail-safe as a concept was disproved back in 1964 by Phil Kraft. Allow me to elaborate on this contradiction. There are two forms of fail-safe. The first detects signal degradation and locks out all input when the signal falls below a predetermined level. At this point, all the servos run to preset positions, until usable signal levels are once more detected. The second system looks for a complete loss of signal and then, and only then, runs the servos to the preset positions, restoring control upon the receipt of any signal input. Now Phil Kraft’s great discovery, like all great discover­ies, was very simple and self-evident, once it had been made. Phil discovered that a snatch of control was better than no control at all! An occasional snatch of control has saved many an otherwise doomed model. Prior to Kraft’s discovery, all of the pioneer proportional systems were fitted with a lockout fail-safe. As soon as even mild interference was encountered the system went into lockout and control was lost until some nebulous time, the duration of which only the gods knew. Fail-safe very quickly became known as that circuit which neutralised the controls on the way to the crash. Digital propor­ tional systems began to smell a bit off to the astute R/C buff until Kraft realised the flaw in the design approach. His company produced a set which featured no fail-safe and the pilot was left to his own devices to fight his way through the effects of the interference. The effect was magical and the modern digital proportional system was born. The university graduates who designed the first generation PCM systems had either never heard of or had forgotten about Phil Kraft. Apparently, they could not be bothered reading the history of R/C devel­opment and rushed in with full lockout fail-safe systems. The first PCM systems were known as “Programmable Crash Mode” systems by astute R/C buffs and PCM began to smell too. PCM systems still feature fail-safe but at least it can now be activated or deactivated by the operator. Nevertheless, PCM still has a lingering air of decay about it. This is a shame really for the microprocessor has a great affinity for signal processing and error correction and the results should in theory be better than PPM. The Silvertone fail-safe module is, on the other hand, a signal loss detector. The fail-safe action is controlled by a pulse omission detector (POD) or missing pulse detector. This requires a complete absence of signal for a period of 500ms before triggering the fail-safe action. Control is restored immediately upon receipt of the incom­ing signal; no lockout, just good safe practice. Circuit description The circuit shown in Fig.1 is based on a single 4011 quad 2-input NAND gate package and while it looks fairly simple there are number of circuit functions with some NAND gates having more than one function. The first function has already been mentioned and is a POD or “pulse omission detector”. Other branches of electronics would refer to this as a “missing pulse detector. This function is performed by IC1b, diode D3 and capacitors C5a & C5b. Then there is the frame rate generator (an oscillator) involving IC1a & ICd and a monostable involving IC1c. Now let’s go through the circuit op- Fig.1: this circuit is essentially a “pulse omission detector”, otherwise referred to as a “missing pulse detector”. This function is performed by IC1b, diode D3 and capacitors C5a & C5b. If signal is missing, a preset servo signal is generated by the frame rate generator (an oscillator) involving IC1a & ICd and a monostable involving IC1c. eration. A 2-input NAND gate requires both of its inputs to be high for a low output. We use this characteristic to enable or disable oscillators or to gate signal through the circuit. The signal input from TB2 is derived from any normal R/C receiver (positive pulse output) in either AM or FM, PPM or PCM format. TB2 is a normal servo plug and simply plugs into the receiver channel desired. NAND gates IC1b and IC1c provide the normal straight-through path for the positive servo input pulse. As pin 5 of IC1b, is tied high, the gate inverts the positive input pulses and thereby discharges capacitors C5a & C5b via diode D3. This is the “pulse omission detector”. C5a & C5b are charged via the 470kΩ resistor R4 and need to be continually discharged via D3 for normal servo operation to be maintained. Since C5a & C5b are normally kept discharged by diode D3, they also hold pin 13 of IC1d low and thus keep it disabled. The master clock is thus rendered inoperative. IC1c inverts the signal from IC1b and the normal positive-going pulse appears at the signal out pin of TB1. The servo is plugged into this socket. Master clock generator Gates IC1a and IC1d form a free-running multivibrator which generates the frame rate master clock. Kit Availability The fail-safe module is available as follows: Fully assembled module complete with servo leads.........................$47.50 Complete kit with PC board and servo leads....................................$32.50 PC board only.....................................................................................$5.50 When ordering, purchasers should nominate the R/C system they are using. Postage & packing for the above kits is $3.00. Payment may be made by Bankcard, cheque or money order to Silver­tone Electronics. Send orders to Silvertone Electronics, PO Box 580, Riverwood, NSW, 2210. Phone/fax (02) 9533 3517. June 1997  75 Fig.2 (left): the component overlay diagram for the PC board. Most of the parts are surface mount types. Note: board shown approximately 170% actual size. Right: this larger than life-size view shows one of the prototype fail-safe modules. Normally it would be fitted with heatshrink sleeving before being installed in the model. This is set by resistors R6 & R7 and capacitor C3 to approximately 20ms. If the incoming pulse at TB2 disappears, capacitors C5a & C5b charge via R4 and pin 13 of IC1d goes high. This allows the master clock to start running. IC1c, VR1, R5 and C4 form a halfshot or monostable pulse generator. This generates a positive pulse which may be set anywhere between 1 - 2ms with VR1. Thus with no input at TB2, the output of IC1b will be high and IC1c’s output will be the internal generated signal. This is a perfectly normal positive servo driving pulse with a width between 1-2ms, set by VR1. Diode D1 serves a triple purpose. First, it protects against reverse voltage on the supply rail. Second, it serves to drop the supply rail to the IC by 0.6V. This is a very important point when using some imported receivers. These receivers can have an output pulse as low as 2.5V which means that the 4011 may not switch reliably because the input pulse never reaches half rail. The 0.6V across D1 eliminates this possibility. Third, it can serve to isolate a backup battery, a point we will examine later. This version is known as Mode 1 and is the preferred op­tion. It is simple to build and simple to install and operate. The kit is all surface mount and comes with the PC board and all the components. The component overlay for the PC board is shown in Fig.2. If you have not assembled a surface mount PC board before, I suggest that you refer to the article on “Working with Surface Mount Components” in the January 1995 issue of SILICON CHIP. When you have assembled the board, just plug it into the servo lead, set the desired fail safe point on the servo and go and have fun. Other versions The above version is simple and uncomplicated. At least, the design was simple before the “what if?” Fig.3: this diagram illustrates a modification which has been made to the Silvertone keyboard to cope with the problem of paired slots. It involves the use of an additional key. 76  Silicon Chip brigade got hold of it! As is my usual practice with any new design, I give prototypes to various people for testing and evaluation and such was the case with the prototype fail-safe modules. No sooner had the first prototypes gone out than the phone rang and the wail went thus. “It doesn’t work if the battery falls out of the model!” I had no sooner put the phone down and the next wail came in: “what happens if the battery shorts out to the car chassis and the car catches on fire and the battery goes flat?” Looking back on the whole affair, I guess it serves me right for calling it a fail-safe module. I should have given it another name like throttle shut-off or something equally simplis­tic. Now we come to the messy bit. To begin I must say that no circuit designer can protect people against their own stupidity. Batteries should not short out to the car chassis or leads become disconnected. Correct installation requires leads to be taped and batteries and receivers to be wrapped in foam. However, cells do fail and batteries do go flat so the criticism does have some validity. The solution was the provision of points P1 and P2 on the board. This lets diode D1 serve its third purpose, which is to act as an isolation diode for a second battery. In this case, the positive lead of TB1 is taken to P2. Thus, if a “Y” or dual socket lead is plugged into the servo socket, the servo uses one socket and a second 4.8V battery pack (any capacity) is plugged into the spare socket. This calls for another switch harness to stop the second pack going flat when the set is not in use. Diode D2 was added for the same reasons as D1. Again it’s simple and easy to manage. Using a standard receiver pack, multiple fail-safes (for other channels) could be run in parallel with no problems. This ar­rangement is known as Mode 2. The “what if?” brigade were aghast at this solution! Anoth­er battery and another switch! All that weight and two switches to switch on and off. What if you forget to charge the battery or switch the switch? Here we come to the main objection to these people. They expect others to look after them and will not face the conse­quences of their own actions. How did they think I was going to move the servo when the main receiver battery has fallen out of the model or caught fire or disappeared in a puff of smoke? By now the reader has begun to realise that there is no end to this game but I had to have one more try just out of cussed­ness. In this case, the solution is to add R1 & C2 and change the back-up battery to a 3-cell button pack of anywhere between 50-500mA.h capacity. As there is not enough vol­tage to tolerate the diode voltage drop through diode D2, the positive servo socket lead must be taken directly to P1. This is known as Mode 3. Now the back-up battery charges automatically from the main receiver battery at a rate set by R1. This rate can be very low and I have found 3-5mA quite adequate. I cannot do anything about the second on/off switch which incidentally should go into the servo lead in this mode. This allows the Rx battery to charge the back-up battery without the drain from the servo. Just switch the Rx on a few minutes before the fail-safe. However, there are a few catches to this system too. As I said there is no end to this game once you start. The smaller the battery, the less number of servo actions possible before the battery goes flat. As all throttle movements come from the back-up battery it is possible to exhaust this battery and leave yourself without a throttle. Actually, the battery recovers quickly and 20-30 seconds is usually enough to get another servo movement. If the back-up battery is too large it will take too much power from the main battery to charge it, so compromise is the order of the day. A 100mA.h button cell pack is a good compro­mise. There is one more problem in that the servo current drain will also influence the number of movements available. A rough servo with a poor motor will require a larger current than a good servo. “But what if . . . ?” I rapidly became tired of this game. I recommend the Mode 1 version of this fail-safe. No, it won’t save the model if it is attacked by a cruise missile or a demented sparrow hawk but it will give you extra insurance against total loss of a model if there is a serious loss of signal. SC Feedback On Previous Articles The February 1997 article evoked an unusually large amount of comment, most of which was favourable. However, some people (mostly trade) still refuse to believe that transmitter intermod­ulation presents a real problem and have commissioned further testing by independent organisations which is fine by me. The series of articles presented in February, March and May 1997 will stand or fall on their own merit in light of further testing. On another level, Wal Gill from Coff’s Harbour (NSW) sent down a worthwhile suggestion for an added safety feature for the keyboard described in the February issue of SILICON CHIP. Wal found my description of the function of the paired slots (601-614) a little ambiguous so he suggested making available a spe­cial key with the window moved 14mm higher for use in the paired slots. These keys are to be reserved for the exclusive use of the 646-659 frequencies. An additional row of numbers from 646-659 should be printed on the keyboard 14mm above row 601-630 which coincides with the existing key window. Thus, when a normal key is inserted in 608 for example, the number 608 appears in the window. If, howev­er, a special key carrying the number 651 is inserted, then the figure 606 is masked off and the correct number (651) appears in the window, thereby eliminating the ambiguity. Fig.3 illustrates the concept. Well done Wal. I love constructive stuff like this. Com­plain about the shortcomings and then present the solution. The modified keys will be available by the time this column appears in print. Another reader, Renee Jackson from Deniliquin, NSW, has sent in the story of her latest creation along with the pictures. The model is a “363” Delta with modified control surfaces and a cockpit and fairing added. It is powered by a “rather tired” O.S. 40H motor. The model is fitted with a Mk.22 Tx and Rx with Hitec servos and a prototype Silvertone fail-safe module on the throt­tle. The Tx setup is for “delta-mix” on elevons with a standard rudder and throttle. I am told that it flies a gentle as a lamb, with a very docile stall, and is quite forgiving to fly. Nice to see someone using some of the more advanced features of the Mk.22 to full advantage. Another reader, Anthony Mott of Black­burn (Vic), is using one of the very advanced (or more unusual) features of the Mk.22 system. Anthony is building a submersible with a twisted pair umbilical cord in place of the RF modules. To date he is success­fully running with 40 metres of cable with no problems. So as you can see, the Mk.22 has found its place in the R/C field. The hard-wired encoder/decoder feature is a big hit with the non-modelling fraternity. Mk.22 encoder/decoder modules have found their way into a myriad of control systems in a wide varie­ty of forms. This model from Renee Jackson of Deniliquin, NSW, is a “363” Delta with modified control surfaces and a cockpit and fairing added. It is powered by an O.S. 40H motor and is controlled by a Silvertone Mk.22 Tx and Rx, with Hitec servos and a prototype Silvertone fail-safe module on the throttle. June 1997  77 VINTAGE RADIO By JOHN HILL A look at signal tracing, Pt.3 Last month, we looked at the tuned signal tracer and described how it is used to troubleshoot a typical superhet valve radio circuit. This month, we look at the untuned signal tracer and describe how it is used. A signal tracer has the ability to intercept both RF and AF signals at many test points throughout a receiver. It can give an indication of stage gain, locate distortion and quickly lead the repairer to the trouble spot where the signal either stops or falters. And where the problem is intermittent, the ability to trace a signal is sometimes the only way to track down such a fault. The intermittent fault is the bane of every serviceman. It would be easy to write a whole article on this subject but a brief summary must suffice. The word intermittent tells most of the story. An intermit­tent fault – be it total loss of signal, a drop in level, distor­ tion, instability, or any combination of these – can appear quite spontaneously, for no obvious reason. And then it will often disappear just as mysteriously. Often, it will be due to a faulty connect­ion somewhere. Inside an old paper capacitor is a common location This simple untuned signal tracer was constructed by the author from a couple of kits for about $30. Note that it uses separate audio and RF probes whereas the unit described in this month’s SILICON CHIP uses a single probe for both jobs. 78  Silicon Chip but it can be in almost any component in the chassis or simply due to a poor solder joint. Another characteristic of intermittent faults is that they are often quite sensitive to movement (mechanical shock), temper­ature and/or sudden electrical changes. Switching the set off and on again will often cure an intermittent fault, for example, if only temporarily. In some cases, the fault is extremely sensitive to even the slightest changes. In this situation, touching a meter prod on almost any part of the circuit can cure the fault. The same applies to a signal tracer probe; connect the probe to troubleshoot the circuit and the fault will vanish. Indeed, this type of fault can be very frustrating. The only practical solution is to get in first. You connect the tracer probe while the set’s behaviour is normal, set the level as appropriate and wait. And the logical spot to start is close to the middle of the set, near the detector or first audio stage. When the fault occurs, the direction to follow will be obvious. Shifting the probe will probably cure the fault, in which case you simply wait for the next failure. It may take some time but your patience will eventually be rewarded and you will be able to track down the location of the fault. Generally, the more facilities there are on the tracer, the better are your chances of finding the fault quickly. Unfor­tunately, there are not many signal tracers like the Healing Dynamic Signalizer described in last month’s story. They were mainly bought by service technicians, which is another way of saying that there may not be many around today for vintage radio enthusiasts to find and use. The old Healing Dynamic Signal- izer is a fairly good tracer and is particularly useful because of its ability to accurately tune a wide range of frequencies. The untuned tracer There is another type of signal tracer that is quite useful and that is the untuned tracer. Whereas the tuned type can home in on any chosen radio frequency, the untuned tracer simply accepts a much broader range of frequencies. Reduced to its simplest form, a signal tracer would consist of a pair of high impedance headphones and a small mica capacitor to block high DC voltages. This sort of device could be used to troubleshoot audio circuits by tapping in at various points along the signal chain. Such a simple device would have definite limi­tations, however. Most signals would be either too low to hear or too high for the headphones to handle, so a tracer of this type really isn’t of much use. The simple tracer just described can be made a little more versatile by adding a diode to the probe. It could then be used to detect radio frequency RF) signals in radio circuits. Once again, some receiver test points may not produce enough energy to make audible sounds in the headphones, while others may be too high for comfort. The low input impedance of such a tracer would also load RF circuits and detune them, thereby giving misleading results. However, during the early days of radio, the few signal tracers in use would have mostly been simple home-made devices, just as described above. Another type was constructed in much the same way as a 1-valve headphone receiver, with the probe connect­ing to the grid of the valve via a small coupling capacitor. While this arrangement would provide some amplification, it was still very crude and had many limitations. To sum up, such simple signal tracers are frustrating to work with and leave much to be desired because of their inade­quate design. A radio frequency (RF) generator can be used in conjunction with a signal tracer to identify the frequency of an unknown IF trans­former. You simply couple the signal generator to the primary winding of the IF transformer and the tracer to the secondary. The signal generator is then adjusted for maximum response from the tracer and the frequency read directly from the dial. This photo shows the generator’s dial set on 455kHz, a common IF. would be the minimum specifications for a simple signal tracer. Building such an outfit is relatively easy, especially if one builds a transistorised version rather than the tradi- Using an untuned tracer Design requirements To be really useful, a signal tracer must have an RF probe that does not unduly load the circuit to which it is connected. It should also have amplifying stages (both RF and AF), a gain control and a loudspeaker. These tional valve type. I recently had a go at making a unit from a couple of kits (an RF probe kit and a low-power amplifier kit) and a reasonably effective tracer was produced for about $30. However, as an adjunct to this series on signal tracing, S ILICON CHIP has developed a complete signal tracer and the design is in this month’s issue. This untuned unit is based on a couple of low-cost ICs and is suitable for tracing both RF and audio signals in old valve receivers. It is also suitable for tracing signals in modern circuitry. The controls simply consist of two 3-position switches. One is a sensitivity switch, while the other selects between Audio, RF and Off. The probe plugs directly into a banana socket on one end of the case and you can use a short probe as shown in the article, or a probe at the end of a wire lead. The construction details for this simple untuned signal tracer are given in this month’s SILICON CHIP. It can trace both audio and RF signals in valve and solid state circuits. An untuned signal tracer is used in much the same way as a tuned tracer, as described last month. And although a simple untuned tracer can be used with a signal generator, a radio station usually makes a much more convenient signal source. For this reason, it is necessary to connect an aerial to the receiver to obtain suitable signals. In addition, the receiv­er must be tuned to a station if a signal is to be traced through the June 1997  79 These IF transformers have tuned frequencies which vary from 175kHz to 460kHz. An untuned signal tracer and an RF signal generator can accurately sort them out. set. In fact, it’s a good idea to have a few dry runs with muted working receivers to find the best test points. Although a tuned tracer can follow a signal from the aerial terminal on, one cannot expect that sort of a performance from an untuned tracer. In my locality, a 5kW transmitter just a few kilometres away dominates the scene. The receiver under test may be tuned to another station but when an RF probe connected to an untuned tracer is placed anywhere in the aerial coil circuit, the local station overrides the tuned signal. If the strong local station is used as the tuned signal, the probe will pick it up no matter where it placed. This is one disadvantage of the untuned tracer – unlike the tuned type, it is not selective. In most locations, however, our simple tracer would not be so overpowered and should pick up the tuned station at the con­trol grid of the converter valve. In fact, if this section of the receiver is working, then quite a few stations should be heard at this test point. It is only a matter of tuning them in on the receiver. The next test position is at the plate of the converter valve. The signal should be much stronger here, due to the gain through that particular stage. Misleading results If a tuned tracer is being used it can also be tuned to the receiver’s intermediate frequency (IF) and this too should be present at the converter plate. This check indicates that the local oscillator is functioning but this is something that an untuned tracer cannot do. If the oscillator is out of Old pen cases are ideal for making audio and RF probes. The unit at top uses a case from a “Texta” marking pen, while the unit at bottom is from an old ballpoint pen. 80  Silicon Chip action, it will not be apparent until the probe is moved to the secondary of the first IF transformer where the signal will stop. This could easily lead you to believe that the IF trans­former was defective, whereas it could be the local oscillator that was at fault. For this reason, a thorough check of both circuit sections would be required. As one can see, the untuned signal tracer has its draw­backs. But this little quirk only applies to superhets. Any regenerative or TRF receiver would be straightforward to test. Moving on, the signal should be heard at the control grid of the IF amplifier valve and it should be louder again at the plate connection. The tracer should then be able to follow the signal through the second IF transformer to the detector. As mentioned last month, a noticeable loss of volume through the first IF transformer is normal and is caused by the loading effect of the RF probe. Once the signal has been traced to the detector, the tracer is switched to the Audio position. Remember that the audio signal first goes to the volume control and if this control is fully backed off it will go no further. In fact, the receiver’s volume control is a convenient way of controlling tracer overload while probing the audio test points. The valve control grids and plate connections are the obvi­ous places to probe the audio stages. After checking a few work­ ing receivers it doesn’t take long to get the feel of things and develop a systematic routine. Identifying IF transformers Provided you have an RF signal generator, a signal tracer can also be used to identify the frequency of an unknown IF transformer. To do this, you couple the signal generator to the primary winding of the IF transformer and the tracer to the secondary. The signal generator is then adjusted for maximum response from the tracer, at which point the frequency can be read directly from the generator’s dial. And that brings us to the end of this 3-part series on signal tracing. If you build the tracer described in this issue, just remember that it is a relatively simple test instrument and has its limitations. However, provided that it is used correctly, it is a very SC useful troubleshooting tool. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. PRODUCT SHOWCASE Non-contact temperature meter Macservice has just announced the release of the QuickTemp, a pocket size non-contact temperature sensor. This device can safely and accurately measure the temperature of moving objects, dangerous materials and electrical components. All materials emit infrared energy. The QuickTemp uses special optics to gather this energy from a target surface and focus it onto a custom detector. The temperature measurement is shown on a 3-digit LCD. Using it is simple – just point it at the object to be measured, press the membrane switch below the LCD window and the temperature is displayed within one second. The reading is held for six seconds after the button is no longer pressed. The tem­perature range is from -18°C to 315°C. Resolution is 1°C and accu­racy is ±2% of reading or ±2°C, which ever is greater. Because it measures temperature without physically touching objects, the infrared sensor has advantages over conventional contact temperature sensors such as thermocouples or therm­ist­ors. Any contamination due to touch is eliminated and where objects are operating at high voltages, it offers safety and convenience. The unit is powered by a 9V battery. In use, it requires a minimum target diameter of 25mm and a minimum measurement dis­tance of 75mm; ie, the distance/target ratio is 3:1. However, it will still give useful indication at much closer proximity. We tried out the QuickTemp in our laboratory and compared its reading with thermocouple test setup accurate to within ±1°C. When measuring objects in close proximity, at around 10mm, the QuickTemp indicated about 2°C higher than actual. But when the distance was extended out to 75mm, giving a target area of 25mm, the indicated temperature was within 1°C of the actual value. But even though the readings at close proximity were a little high, we would regard it as very useful for measuring the temperatures of semiconductors mounted on heatsinks where other methods are inconvenient. The QuickTemp is available at $245 from Macservice Pty Ltd, 20 Fulton St, Oakleigh South, Vic 3167. Phone (03) 9562 9500; fax (03) 9562 9590 12VDC to 230VAC 1500W inverter This 12V switchmode inverter will deliver up to 1500 watts for 25 minutes or up to 1700 watts for 10 minutes. Its continu­ous output rating is 1200 watts and it can deliver short term surges up to 2500 watts. The output waveform is a modified square wave. The unit will operate from 10-15VDC and emits a low battery alarm at 10.7V. Conversion efficiency is listed at 85-90% depending on load and the no-load current drain is 600mA. With such a high surge output, the inverter can be used to drive power tools, refrigerators and freezers, vacuum cleaners, food mixers and blenders, VCRs, TVs and computers. It will have a wide 86  Silicon Chip range of applications at remote farm and home sites, on boats, in recreational vehicles, caravans, and so on. When used at high power outputs from a vehicle, it would be wise to have the motor running to continually charge the battery. For example, when delivering 1500W at 85% conversion efficiency, the current drain will be around 147A at 12V! Only a very large battery system can sustain this current for more than a short period. The unit measures 425 x 240 x 77mm and weighs 3.6kg. Its recommended retail price is $995 from Altronics, 174 Roe St, Perth, WA 6000. Phone 1 800 999 007 Jaytech digital clamp meter Digital clamp meters used to be quite expensive and many still are but this Jaytech QM-1560 is quite affordable. It is compact unit with a 31/2-digit display and will measure AC voltage up to 500V and AC current up to 400A. Its voltage accura­cy is ±1% while the current accuracy is claimed as ±2%. To measure current, you press the clamp open and place it around the circuit conductor to be measured. To measure voltage, you use conventional meter leads which plug into the end of the meter. The meter leads are supplied. The QM-1560 is powered by two LR44 button cells which give a claimed life of 100 hours. Available from all Jaycar Electronics stores and resellers, the Jaytech QM-1560 sells for $79.50. It comes complete with a vinyl carrying case. New Electronics Workbench EDA The new version of Electronics Workbench EDA from Emona Instruments has analog, digital and mixed analog/ digital SPICE simulation plus a full suite of analysers and over 8000 devices. Electronics Workbench EDA’s simulation engine is based on Berke­ley SPICE 3. Claimed to be the easiest interface to learn and use, users can be working productively in 20 minutes. Windows support also means users can cut-and-paste schematics and graphs to word processors to create reports. Other features include a custom­is­able parts bin, automatic reference de­ signation, easy-to-edit model parameters and component values, industry standard ANSI and DIN symbols and easy output of materials lists and hierarchical schematics. SPICE simulators are used to verify that analog and mixed-signal circuits will yield the expected outputs. A schematic netlist file and circuit input values are fed to the SPICE soft­ware which simulates the circuit’s behaviour. Voltage and current levels can then be observed at any circuit node as they change with frequency and time. For more information, call Emona Instruments on (02) 9519 3933 or fax them on (02) 9550 1378. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. June 1997  87 Versatile touch pad for PCs VersaPad, a new computer touch pad, has been released in Australia by BJE Enterprises. VersaPad offers precise cursor control via fingertip or stylus, one-touch pan and scroll cap­ ability, a toolbar and on-the-fly signature and graphics capture. For added convenience, VersaPad provides dedicated pan and scroll bars for “one touch” screen control. These variable-pressure controls can be operated by any of three methods: (1) by applying pressure to the arrows at the ends of the bar – slight pressure to scroll or pan slowly and heavier 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. 88  Silicon Chip touch speeding up the action; (2) by placing a finger or (stylus) on a specific portion of the bar to pan or scroll to that position in the document; or (3) by sliding your fingertip along the bar to pan or scroll in that direction. VersaPad is available through selected retail outlets. It has a suggested list price of $99.00 and includes the VersaPad touch pad (serial and PS/2 connector), VersaPad Windows 95 soft­ware, User’s Guide and a limited lifetime warranty. For more information, call BJE Enterprises Pty Ltd at (02) 9858 5611, or visit Interlink’s web page at http:// www.interlin­kelec.com Single-chip DC/DC converter Philips has introduced a low-voltage DC/DC converter with a peak output power of 8W and a conversion efficiency greater than 95%. Targeted for use in cordless and cellular tele­ phones, where battery power is at a premium, this new single-chip DC/ DC con­verter will allow considerable extension of standby and talk times with the available batteries, even 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. when they are approach­ing complete discharge. The TEA1204t can be used to up-convert the output of a 2 or 3-cell NiCd/NiMH battery pack or a single cell Li-Ion battery pack to 3.3V or 5V, or it can be used to down-convert the output of a 4-cell NiCd/NiMH or single-cell Li-Ion battery pack to 3.6V or 3.3V. These output voltages cover the power supply require­ ments of virtually all mobile phones. For more information, contact Philips Components, 34 Water­loo Rd, North Ryde, NSW 2113. Additional in- Magnetoresistive sensor has flipping coils Philips’ latest magnetoresistive sensor has coils integrat­ed into its package to compensate for temperature drift and sensor offset. By eliminating the need for external coils, the KMZ51 sensor simplifies system design in applications requiring the measurement of weak magnetic fields. The integrated coils have an excellent magnetic coupling factor, so the KMZ51 also has very low power consumption, allow­ ing it to operate from a 5V supply. Even operating at this low supply voltage, the sensor requires no DCDC up-converter to provide sufficient coil current, as required by some sensors with integrated coils under the same conditions. The KMZ51 is the first device in a new family and is suited for electronic compasses, earth magnetic field compensation circuits, traffic detection units and applications such as virtu­al reality glasses. For more information contact Philips Components, 34 Water­loo Rd, North Ryde NSW 2113 or access the Philips web page at: http:/www.semiconductors.philips.com BassBox® formation can be obtained by accessing the Philips web site at http://www. semiconductors.philips.com EMC filters up to 2500A A new family of AC line filers for frequency converters in electrical drives has been added to the range of Siemens Mat­sushita Components. The filters are designed for use in 3-phase systems and are available as standard filters for rated voltages up to 690V and rated currents up to 2500A. In modern electrical drives, 3-phase motors are con­ trolled by frequency converters. This has the advantage that the speed of the motor can be precisely controlled, allowing for smooth acceleration and deceleration. The disadvantage is that rapid switching operations at high currents with steep signal edges produce high electro­ magnetic interference. Such high-frequency interference can be suppressed with EMC filters designed specifically for converter applications. The flagship of the new three-conductor filter family from Siemens Matsushita has been developed specifically for 690V IT industrial supply systems and is suitable for current loads of up to 3 x 2500A. For such a high connected load the filter is quite compact, measuring 650 x 320 x 220mm and weighing 105kg. This new filter has a high attenuation of 85dB, a volume resistance of only 15µΩ, a leakage current of less than 6mA and a power loss of 280W. For further information, contact Advanced Information Pro­ducts, Siemens Ltd. Phone (03) 9420 7716; fax (03) 9420 7275. 13.8-inch colour LCD monitor Click Electronics has released the PD-50 range of colour LCD monitors. There are two inherently low radiation models in the range, the PD-50F with a 13.8-inch (viewable) TFT display and the PD-50N with a 13.8-inch (viewable) DSTN display. The PD-50F TFT monitor has a maximum resolution of 1024 x 768 pixels with 262,000 colours, a brightness of 200 Cd/m2 and a contrast ratio of 300:1 (typical). The PD-50N DSTN monitor has the same maximum resolution and brightness, 4096 colours and a contrast ratio of 20:1 (typical). The monitors have on/off, brightness and contrast controls, and an operating temperature range of 0-40°C. For further information, contact Click Electronics, 29 Bachell Ave, Lidcombe, NSW 2141. Phone (02) 9649 4155; fax (02) 9649 4206. email: SC comgiant<at>ca.com.au 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) 9949 8071 FAX: (02) 9949 8073 PO BOX 226 BALGOWLAH NSW 2093 TOROIDAL POWER TRANSFORMERS Manufactured in Australia Comprehensive data available Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 9476-5854 Fx (02) 9476-3231 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. June 1997  89 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. CW filter is too sharp I recently constructed the “Active CW Filter For Weak Signal Reception” from the April 1990 issue of SILICON CHIP. Could you please advise how I can make the bandpass wider? The slightest movement of the receiver tuning knob or the slightest shift in frequency of the receiver or the incoming signal and the Morse signal is gone. I have tried different values of capacitor on pin 2 of the LM567 as recommended in the write-up without any success. I have also constructed the “Active Filter for CW” featured in the June 1991 issue and I have found it to be quite good as it has a wider tuning range but I prefer the previous circuit as it completely eliminates the noisy background. I realise that there is a great difference in the filtering circuitry of the two circuits and I cannot expect the June 1991 circuit to operate as well. I am a radio amateur trying to pass the Morse Code exam. As you probably know, the reception on 80m is very IGBTs for automotive ignition I have investigated the availability of a Philips IGBT for an automotive ignition system. In fact, I have already designed and produced a PC board for the purpose. One comment I would like to make is that the IGBT voltage drop is 3.5V, which must be taken into account to ensure that the correct current through the coil is maintained. I have some “Big O gauge” locomotives which have inter­nal traction batteries. Therefore they have to be controlled by some “wireless” link. I have designed a simple speed control system 90  Silicon Chip noisy, the signal being down in the noise. (J. C., Reynella, SA).   There is little that can be done to increase the bandwidth of the phase locked loop IC in the May 1990 circuit. At the maximum, the best bandwidth that could be expected for a 1.2kHz centre frequency is about 170Hz instead of 130Hz as it is now. However a difference of 40Hz or so in the bandwidth is negligible when you consider the shift in frequency which would be brought about by even the slightest shift in receiver tuning. There you have the advantage and the disadvantage of the PLL circuit; it completely eliminates the noise because it gener­ates a fresh tone but it is very narrow in bandwidth and so is finicky to use. We published a later design for an active filter unit in the December 1996 issue. It does have adjustable bandwidth but it will not cancel noise completely, as does the May 1990 design. Headphone Amplifier as described in the May 1995 issue of SILICON CHIP but I’d like to add a single bass-treble pot or two pots (treble and bass). Could you send me the appropriate modifications? I’m hoping it would not be too difficult. Otherwise, this unit seems ideal for my preamp needs. (T. F., Malanda, Qld). Unfortunately, there is no easy way of adding a bass and treble control to this circuit, without the use of another cir­cuit board and at least a couple of transistors. About the only tone control which could be practically added to the circuit is a passive “treble cut” control which would involve the addition of a potentiometer and a capacitor. However, we doubt whether it would do any more than the existing passive tone controls on most solid-body guitars. Tone controls for guitar headphone amplifier I built the LED Digital Tachometer that was published in the August 1991 issue of SILICON CHIP. It ran well to begin with but later I had random problems which eventually I traced to a poor earth connection. It is now in a different vehicle. Before reinstalling the unit, I set it up to calibrate it and all went well so I left it running for about an hour. When I came back it was dead. I was now out of my depth so I took it to my kit supplier who had a repair person. What they tell me now is that the unit won’t work for more than an hour or two before transis­tor Q1 blows or fails. It was replaced a number of times and everything checked out but the same result. It’s dead. I need more help, please. I’m spoiled with this unit – it’s far better than the dial type. I also built the Intelligent Charger for Gel Cells de­ scribed in the July 1989 issue of SILICON CHIP. I use it for charging a “Sonnerschein” gel battery to run a camcorder. After a few months this battery • I would like to build the Guitar which requires just one byte of RS232 serial information to be sent whenever a speed change is required. I would welcome suggestions for a wireless link transmitter and receiver design with a range of two metres that I can use for this pro­ject. (R. B., Kalamunda, WA).   Your comment regarding the voltage drop for the IGBT is a cause for concern. We would expect the voltage drop to be around 2V rather than 3.5V. A high voltage drop will lead to quite high dissipation in the IGBT and could be critical if the battery voltage is low. For your wireless link we suggest the single channel UHF transmitter featured in the February 1996 issue of SILICON CHIP. • • LED digital tachometer failure started self-discharging quite quickly. Sonnerschein replaced the battery but they sug­gested my charger could be improved. As I can follow directions for simple circuits but not really know what I’m doing or able to do calculations, I need your help. With the aid of a digital multimeter I have the following figures. When the battery is dis­charged for the camcorder (5.9V) the charger delivers 490mA at 6.2-6.3V. This rises to 7.3-7.4V on float. That is when the battery is charged. Sonnerschein suggest the charging voltage should be 6.9V. Can you suggest what I need to do, because we are on the road a lot? I run this charger off the vehicle 12V battery when stand­ing, not when the alternator is running. I did put a flag heat­sink on Q1. (K. C., Balgownie, NSW).   If Q1 is failing in such a short time it suggests that it has the wrong value collector resistor (should be 18kΩ) or the input resistors (33kΩ + 10kΩ) are incorrect and too low in value. Check also that diode D1 is connected the right way around or is not open circuit. As far as your charger is concerned, if the battery voltage is 7.3 to 7.4V when on float then it is fully charged. If it was 6.9V, it would not be fully charged. Checking a faulty LCD I am writing regarding the letter entitled “faulty display in DMM” from M. E., Tokoroa, NZ, published on page 91 of the April 1997 issue. In the circumstances described by M. E., I would make the following diagnostic tests before exchanging the LCD. (1) Clean all display contacts (the LCD, conductive rubber and contact fields on the PCB) with alcohol. When cleaning the LCD, do not wet it excessively and immediately dry it, as alcohol may dissolve glue and destroy the display (use cotton bud only spar­ingly wetted). (2) After reassembling, connect pin 37 to the +U supply – this is the “Display Test” function of the 7106. Then the LCD should show “1888”. Do not use this function longer than absolutely neces­sary; • Woofer stopper is ultrasonic I purchased a kit for the Woofer Stopper Mk.II described in the February 1996 issue. It came with a pre­ wound transformer. When I assembled the kit and connected 12V power, the red LED came on and when I made a noise the green LED came on and after 10 seconds it went off. I connected the horn and put a .0022µF capacitor across pins of 1 & 2 of IC5. There was no sound and the green LED stayed on but you could hear a click through the horn every 10 seconds. I checked the +12V on all the ICs. They were OK. I also connected a 0.47µF capacitor between base and emit­ter of transistor Q3, as advised in the Notes & Errata featured in the December 1996 issue. I checked the current on standby. It was 20mA on standby and when activated it was 320mA. I changed IC1 and IC6 but it made no difference. I checked the voltage at the output. It varied from 8V to 9V on the 20VAC meter range. Can you help me to find the fault? (W. C., Waverley, Tas).   From your description, we would assume that the Woofer Stopper circuit is working properly since it draws the extra current when triggered. The 8-9V on your AC meter also suggests that it is operating. Remember that it is ultrasonic and you won’t normally hear it. If you want be able to hear the sound, try doubling the value of the .0022µF capacitor across pins 1 & 2 of IC5. This will reduce the frequency to well below 10kHz. The extra capacitor between base and emitter of Q3 is to prevent the clicking sound during the sound burst which occurs every second or so. It will not have an effect on the initial turn-on click as the speakers are initially turned on after triggering. We should point out that our Notes & Errata suggested using a 47µF capacitor, not a value of 0.47µF. • Washing electric blankets This is more of a housekeeping question than an electron­ics topic but I thought I’d ask you anyway. Can you wash an electric blanket? I understand the display then is driven by DC and will be destroyed after prolonged use this way. (3) Those having access to a frequency counter may read the internal clock frequency of the 7106 on pin 38 as faulty resis­tors or capacitors are not unknown. Those having no frequency counter but having a square wave oscillator may disconnect R & C components from pins 38 & 39 and then feed, say 40kHz, between pins 37 & 40 of 7106 (set p-p output voltage of the oscillator to slightly below supply voltage of 7106). I would normally expect that with this fault at every power-on a different value would be displayed and the reading would not change until power-off. I hope that the above procedures are helpful, not only for M. E. but to everyone else having similar troubles. (M. F., Warszawa, Poland). the manufacturers recommend against this but then they would, wouldn’t they? They want to sell more electric blankets! (E. J., Parramatta, NSW).   We contacted the manufacturers of Linda electric blankets for their opinion on this subject. Their BLU range of electric blankets, recommended for use in nursing homes, can be handwashed, which means that even the controls can be immersed in water. They emphasise that any washing of the BLU range must be done by hand, not in a washing machine. All other models of Linda electric blankets can be spot cleaned in the case of soiling or spillage but they will not countenance hand washing. As a matter of coincidence, one of our staff members re­cently had a electric blanket which needed washing otherwise it would have to be thrown out. It was made by Linda but was not from the BLU range. His approach was as follows. First, he removed the cover plates which anchor and protect the connections to the electric blanket wiring. The connections themselves are shrouded in clear plastic but do not appear to be waterproof. That done, he carefully handwashed and rinsed the blanket in cold • June 1997  91 Shunting a microammeter Is it possible to make a 50µA - 50µA centre zero meter to read milliamps? If so, could you inform me of the procedure? (D. B., Port Macquarie, NSW).   The answer is yes and yes. The procedure for converting a meter that reads in microamps to one that reads milliamps or even amps involves adding a shunt resistor to the meter movement. In essence, a shunt resistor is connected in parallel with the meter’s coil to “shunt” away most of the current from the deli­cate coil itself. To work out what value shunt you need, you need to know the basic sensitivity of the meter. Most 50µA meter movements for example, have a resistance of 2kΩ and by using Ohm’s Law we can work out that they will have 100mV across them when 50µA is passing through the coil. By extension, we say the meter move­ ment’s sensitivity is 20kΩ/volt. 20kΩ/volt is the same as 2kΩ/100mV. A further piece of information is that the 100mV across the meter at full scale deflection is the “burden voltage”. You’ll need to know that when calculating the shunt resistor for your particular application. Even if you don’t know the sen- • water. It was laid out to dry on a flat surface (a tram­poline) but not in the sun. Shrinkage is to be avoided at all costs. Care must be taken to make sure that the plastic shrouded connections and the heat controllers do not get wet or that water does not run down the leads into the controllers. When the blanket was fully dry, and it takes quite a while because of their two-layer construction, the connections had partly pulled out of the blanket which was now rucked up in several places. Judicious pulling of the blanket this way and that pulled the connections back into place so that the anchor plates could be re-attached. The blanket was then left a further couple of days to dry, just to make sure that there was no moisture in the controllers. 92  Silicon Chip sitivity of a meter movement, you can easily measure it by connecting in series with a high value resistor to a (say) 12V supply. If the resistor value is 100kΩ, the current passing through the meter will be close to 12µA. What does the meter read? 12? Good – now reduce the value of the resistor until you get a full scale deflection of the pointer. You can work out the exact value of the current by measur­ ing the voltage across the series resistor with your multimeter and then using Ohm’s Law to make the calculation. You can also use your multi­meter to measure the burden voltage. So say you have worked out that your centre zero meter has a 100mV across it when it is passing 50µA. You can use that information to work out the shunt resistor. If you want it to read 5mA at full scale deflection (FSD), you need a resistor which will pass 5mA (or to be really precise, 5mA - 50µA = 4.95mA) with 100mV across it. Using the equation R = V/1, the result is 20Ω. If you wanted 50mA instead of 5mA, the shunt resistor would be 2Ω. That broadly explains the principle of shunting a meter. If readers want a more detailed article on this subject, please write and tell us. Higher capacity speed control I was interested in the train controller featured in the April 1997 issue of SILICON CHIP. How about a version to run the high efficiency well-built 24V DC motors obtainable for almost nix from photocopiers, etc? They are many possible uses: coil winders, power feeds for small milling machines, lathes, robot­ics. Keep up the supply of articles on interfacing PCs with various hardware. I have every issue since you started and I still think you do a great job. (I. S., Camberwell, Vic).   It is relatively easy to modify the circuit to make it suitable for 24V motors but you would have to mount the transis­tors on much more substan- • tial heatsinks to ensure adequate heat dissipation. A better approach would be to build a modified version of our earlier Rail­ power controller, as published in the April & May 1988 issues of SILICON CHIP. This switch­mode design could be modified simply by changing the 12V transformer to one with an 18V secondary and changing the filter capacitors to 35VW rating. Alternatively, have a look at the 24V 20A speed controller featured in this issue. Notes & Errata Bridged Amplifier Loudspeaker Protector, April 1997: a reader has pointed out that this version of the loudspeaker protector cannot be used in some bridged amplifiers in cars. This applies mainly to lower-powered bridged amplifiers which do not use a DC-DC inverter and which have the loudspeaker outputs floating at half the DC supply, around +7V. It also applies to some inverter-driven bridge amplifiers which have a single DC rail. In these cases, the amplifier outputs may be floating at around +25V DC above chassis, for example. Therefore, before you consider building the Loudspeaker Protector for installation with bridged amplifiers in cars, you should measure the DC voltage at both sides of the speaker out­puts with respect to chassis. If the outputs are floating at a DC voltage above chassis (eg, +7V), the Loudspeaker Protector will not be suitable as it would be permanently latched off. Note also that the parts list specifies a value of 100µF for C1 whereas it should be 220µF, as on the circuit diagrams. The additional 100µF capacitor for the built-in version should be rated at 75VW or 100VW not 63VW, where the amplifier supply rail is between 66V and 75V. Extra Fast Nicad Charger, October 1995: the lengths of the 0.8mm wires specified for the primary and secondary windings of transformer T1 are incorrect, although the number of turns and the turns ratio are correct. The length of the quadrifilar primary wires should be 1.7 metres before termination, while the two secondary wires (bifilar) should be SC 3.5 metres. 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 Price $55.95 $39.95 $59.95 $49.95 $55.95 $59.95 $120.00 $85.00 $99.00 $52.95 Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ & PNG add $10.00 per book, elsewhere add $15 per book. TOTAL $A June June 1997  93 1997  93 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. CLASSIFIED ADVERTISING RATES FOR SALE Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50 cents for each additional word. Display ads (casual rate): $25 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. C COMPILERS: Ever ything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC12, 68HC16, 8051/52, 8080/85, 8086 or 8096: $140.00 each. Macro Cross Assemblers for these CPUs + 6800/01/03/05 and 6502: $140.00 for the set. Debug monitors: $70 for 6 CPUs. All compilers inc ‘HC12, XASMs and monitors: $480. 8051/52 or 80C320 Simulator (fast): $70. Disassemblers for 12 CPUs only $75. Try the new C-FLEA Virtual Machine for small CPUs, build a “C-Stamp”. Demo disk: FREE. All prices + $5 p&p. GRAN­ T RONICS PTY LTD, PO Box 275, Wentworthville 2145. Ph/Fax (02) 9631 1236 or Internet: http://www.mpx.com.au/~lgrant. To run your classified ad, print it clearly on a separate sheet of paper, fill out the form below & send it with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy, NSW 2097. Or fax the details to (02) 9979 6503. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________  Bankcard    Visa Card    Master Card Card No. ✂ Enclosed is my cheque/money order for $­__________ or please debit my Signature­­­­­­­­­­­­__________________________  Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 94  Silicon Chip HOMEMADE GENERATORS: how to instructions. Eight pages free text and colour photos on the Internet at: http://www.onekw.co.nz/ !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! WARNING ! WARNING ! WARNING ! WARNING ! VIDEO CAMERA MODULES Beware of HIGHER prices for a similar Camera! BUY A BETTER CAMERA AT A LOWER PRICE! CHOOSE from..... 380, 420 & 460 TVL Resolution. Low Light & IR Sensitive 0.05 lux. TEENY WEENY 28 mm x 28 mm PCBs. ELEVEN Board Lenses. FOUR Pinhole Lenses. IR Cut/Pass & Polarising Filters. 845+ nm 74 mW IR LEDs. Ancillary Equipment. BEFORE & AFTER-SALES SERVICE, HELP & ADVICE! Before you Buy! Ask for our Detailed, Illustrated Price List with Application Notes. Also available CCTV Technical, Design & Reference Manuals & Inter-Active CD ROM. Allthings Sales & Services 08 9349 9413, fax 08 9344 5905. PCBs MADE, ONE OR MANY. Low prices, hobbyists welcome. Sesame Electronics (02) 9554 9760. Fax: 9718 4762. Email: skybus<at>zip.com.au MICROCRAFT IS NOW ON THE WEB: 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 • 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) • Fixed price electronic design and PCB layout • Credit cards accepted • All goods sent registered mail • Call Bob for more de­ t ails. MICRO­CRAFT, PO Box 514, Concord NSW 2137. Phone (02) 9744 5440 or fax (02) 9744 9280. http://www.micro.com.au email sales<at>micro.com.au $79 ! VIDEO CAMERA MODULES ! $79 ONLY! $79 !!!!! ONLY! $79 !!!!! Complete with 3.6 mm Board or 5 mm Pinhole Lens, Low Light & Infra Red Sensitive, Tiny 32 x 32 mm PCB. Cat No MOD-BW 506 ONLY! $79!!!!! Allthings Sales & Services 08 9349 9413, fax 08 9344 5905. CAR/RALLY COMPUTER KIT: including fuel sensor & speed sensor. 68HC05 & HC11 DEVELOPMENT SYSTEMS: Oztechnics, PO Box 38, Illawong NSW 2234. Phone (02) 9541 0310. Fax (02) 9541 0734. http://www.oz­technics.com.au/ Video Audio TX/RX Modules UP TO 100 M RANGE, 915-928 MHz band, $80 pair, with Interface PCBs $99. Allthings Sales & Services 08 9349 9413, fax 08 9344 5905. Microprocessor For Digital Effects Unit This is the 68HC705-C8P pro­ gramm­ed micro­pro­cessor IC for the Digital Effects Unit (see Feb­. 1995). Price: $45 + $6 p+p Payment by cheque, money order or credit card to: Silicon Chip Pub­ lica­ tions, PO Box 139 Collaroy 2097. Phone (02) 9979 5644; Fax (02) 9979 6503. MicroZed Computers PO Box 634, ARMIDALE 2350 (296 Cook’s Rd) Ph (067) 722777 – may time out to Mobile 014 036775 Fax (067) 728987    (Credit Cards OK) http://www.microzed.com.au/~microzed BASIC STAMPS & PIC Tools With third party supporting products, all in stock Easy to learn, easy to use sophisticated CPU based controllers Credit cards OK   Send two 45c stamps for info MEMORY * MEMORY * MEMORY LIFETIME WARRANTY!! 651 Forest Rd, Bexley 2207 makes all the project PCBs published in SILICON CHIP and other Australian magazines Tel +61 2 9587 3491 Fax 9587 5385 E-mail rcsradio<at>cia.com.au RAIN BRAIN AND DIGI-TEMP KITS: 8-station controller and 8-chan­ n el, RS232 digital thermometer uses the incredible DS1820 sensor. Call Mantis Micro Products, 38 Garnet St, Niddrie, 3042. P/F/A (03) 9337 1917. http://www.home.aone.net.au/mantismp SIMMS (Parity/No Parity) 4Mb 30 PIN-70 $50 $38 4Mb 72 PIN-70 $53 $36 8Mb 72 PIN-70 $94 $70 16Mb 72 PIN-70 $160 $125 32Mb 72 PIN-70 $298 $285 EDO SIMMS (60ns) 4Mb/8Mb $36/70 16Mb/32Mb $128/252 64Mb/128Mb $1066/2112 DIMMS 8Mb/16Mb - 168 PIN $70/144 32Mb/64Mb - 168 PIN $306/570 SYNCHRONOUS (SDRAM) 168 PIN - 16Mb $144 168 PIN - 32Mb $281 168 PIN - 64Mb $676 LASER PRINTER MEMORY 4Mb HP 4&5 8Mb HP 4 & 5 All other models available COMPAQ 16Mb ARMADA 1100 All other models available TOSHIBA 16Mb Tecra 500/610 Sat All other models available IBM 16Mb T.Pad 755, 360 EDO All other models available $42 $83 $Call $215 $Call $218 $Call $244 $Call ALSO AVAILABLE: ACER, DELL, GATEWAY 2000, AST, CANON, NEC, ZENITH & MANY MORE Ex Tax Pricing – Delivery $8. Pricing as at 05/05/97. Phone for latest. Sales Tax 22%. Credit Cards Welcome. We Also Buy And Trade-In Memory. PELHAM PTY LTD Suite 6, 2 Hillcrest Rd, Ph: (02) 9980 6988 Pennant Hills, 2120. Fax: (02) 9980 6991 Email: pelham1<at>ozemail.com.au TV 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) 9482 3100 8.30-5.00 M-F SILICON CHIP FLOPPY INDEX WITH FILE VIEWER Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. Price $7.00 each + $3 p&p. Send your order to: Silicon Chip Publications, PO Box 139, Collaroy 2097; or phone (02) 979 5644 & quote your credit card number; or fax the details to (02) 979 6503. Please specify 3.5-inch or 5.25-inch disc. June 1997  95 * THE TINIEST * VIDEO CAMERA MODULE PCB 28 x 28 mm, IR & Low light sensitive, with Pinhole Lens. 08 9349 9413. SILICON CHIP FOR SALE. First 110 from Vol 1 No 1. $220 job lot. Roberts, 116 Lamonerie Street, Toongabbie NSW 2146. Phone (02) 9631 5584. INFRA RED ILLUMINATORS 240 vac Auto on/off in Aluminium Housing with Adj Bracket $149. PCB with LEDs $79. PCB with LEDs AND Auto Control PCB $99. DIY LED & PCB Kits: 50 LED 52mm Round Lamp $50. 88 LED $72. 180 LED $113. Variations include up to 210 LED 34 watt. Allthings Sales & Services 08 9349 9413, fax 08 9344 5905. MicroZed have STAMP VER 1.8 handbook $30 + $p&p. Has 80 pages. BS1 -> BS2 conversion data. Circuit Ideas Wanted Do you have a good circuit idea. If so, why not sketch it out, write a brief description of its operation & send it to us. Provided your idea is workable & original, we’ll publish it in Circuit Notebook & you’ll make some money. We’ll pay up to $60 for a really good circuit but don’t make them too big please. Send your idea to: Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. Advertising Index Altronics................................. 34-36 Av-Comm.....................................21 Dick Smith Electronics..... 8-9,24-25 Earthquake Audio........................89 Emona.........................................73 Freedman Electronics..................89 Harbuch Electronics....................89 Instant PCBs................................95 Jaycar ............................IFC, 45-52 Kalex............................................59 Kits-R-US.....................................88 14 Model Railway Projects Shop soiled but HALF PRICE! Our stocks of this book are now limited. All we have left are newsagents’ returns which means that they may be slightly shop soiled or have minor cover blemishes. Otherwise, they're undamaged and in good condition. SPECIAL CLEARANCE PRICE: $3.95 + $3 P&P (Aust. & NZ) Macservice....................................3 MicroZed Computers...................95 Model Railways Book..................96 Oatley Electronics........................31 Pelham.........................................95 RCS Radio...................................95 Rod Irving Electronics .......... 81-85 Silicon Chip Back Issues....... 38-39 Silicon Chip Bookshop.................93 Silicon Chip Binders................OBC Silicon Chip Software....................7 This book will not be reprinted Silicon Chip Wallchart..............OBC Yes! Please send me _____ copies of 14 Model Railway Projects at the special price of $A3.95 + $A3 p&p (p&p outside Aust. & NZ $A6). Enclosed is my cheque/money order for $­A__________ or please debit my Telstra..........................................87 ❏ Bankcard   ❏  Visa Card   ❏ MasterCard Zoom Magazine.........................IBC _____________________________ Card No. Signature­­­­­­­­­­­­___________________________  Card expiry date______/______ Name Street Tortech.........................................59 ______________________________________________________ PLEASE PRINT ______________________________________________________ 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). 96  Silicon Chip PC Boards Printed circuit boards for SILICON CHIP projects are made by: •  RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 9587 3491. •  Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730.