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FEBRUARY 2023 ISSN 1030-2662 02 9 771030 266001 $ 50* NZ $1290 11 INC GST INC GST THE HISTORY OF COMPUTER MEMORY Soft Starter Active Mains ADVANCED TEST T EEZERS O R D ER YO U R S TO D A Y ! 3-in-1 Advanced 3D Printer This new generation Snapmaker 2.0 includes modules for 3D Printing, Laser Engraving and Cutting, and CNC Carving. Now with faster and quieter operation. MODULAR DESIGN FAST AND EASY TOOLHEAD SWITCHING LARGER WORK AREA TWICE THE SIZE COMPARED TO PREVIOUS MODEL LASER TOOLHEAD 3D PRINTING TOOLHEAD • FASTER & QUIETER OPERATION • FILAMENT RUNOUT AND POWER LOSS RECOVERY CNC TOOLHEAD IMPROVED LINEAR MODULES FOR A STABLE AND FAST WORKING SPEED FROM 2499 $ INTERCHANGEABLE BEDS FOR 3D PRINT, LASER OR CNC CARVING PRINTS UP TO 330MM HIGH! A GREAT PRICE FOR A PRINTER / ENGRAVER / LASER ETCHER PRINT LASER • 5" SMART TOUCHSCREEN • USB & WI-FI CONNECTIVITY ADDITIONAL TOOLS ALSO AVAILABLE. SHOP NOW! CNC Model Comparison 3D Printing Area (W x D x H) Laser Work Area CNC Carving Area (W x D x H) (W x D x H) Heat Bed Temp. A250T TL4620 230x250x235mm 230x250mm 230x250x180mm 100°C max. A350T TL4630 320x350x330mm 320x350mm 320x350x275mm 80°C max. 3D Printing Nozzle Laser Module 0.4mm Dia., 1600mW, 275°C Temp. 450nm, 50-300 microns Class 4 CNC Carving Machine Size (W x D x H) 0.5-6.25mm 405x424x490mm shank, 6,00012,000RPM 495x506x580mm Price $2499 $2899 See it in action at our Castle Hill and Broadway stores, and speak to our Snapmaker experts Shop Jaycar for your 3D Printing needs: • 8 Models of Filament Printers, with over 50 types of filament • 2 Models of Resin Printers, with over 45 types of resin • Massive range of 3D Printer spare parts & accessories • In-stock at over 110 stores or 130 resellers nationwide Order yours today: jaycar.com.au/snapmaker2 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. 1800 022 888 Contents Vol.36, No.02 February 2023 14 Computer Memory, Part 2 Increasingly smaller, faster and larger-capacity memory has been one of the major drivers for technological advances in computers. The last part in the series primarily covers SRAM, DRAM and proposed new technologies. By Dr David Maddison Technology feature 24 Computer Memory Addendum We have compiled some interesting facts about the latest in memory technology that couldn’t make it in to the main series. That includes how images, video and audio are stored on computers and not just text. By Nicholas Vinen Technology feature 52 A 30mm Spark-Gap Tesla Coil Building a full-size Tesla Coil isn’t for the faint of heart, although it can be done if you are careful and know the tricks. Here’s how Flavio Spedalieri built a small-scale Tesla Coil that produces spectacular discharges. By Flavio Spedalieri Educational feature Active Mains Soft Starter Page 33 ADVANCED TEST T EEZERS PAGE 44 The making of a 30mm desktop Spark-Gap Tesla Coil 72 Heart Rate Sensor Module The AD8238-based heart rate monitor module is a low-cost way to monitor the operation of the heart via an Arduino or similar, like an electrocardiogram. It comes with a 3-electrode lead and is available from Jaycar. By Jim Rowe Using electronic modules 33 Active Mains Soft Starter, Part 1 Appliances with high startup current can damage your work, trip your circuit breaker and more. This Soft Starter prevents the high current surge that occurs when the device is first turned on, reducing the ‘kick’ you get. By John Clarke Mains control project 44 Advanced Test Tweezers, Part 1 The Advanced SMD Test Tweezers have numerous features and improvements such as a larger screen and better user-interface. But don’t let the name fool you, as it is not limited to just testing SMD components. By Tim Blythman Test equipment project Page 52 2 Editorial Viewpoint 5 Mailbag 42 Subscriptions 60 Online Shop 70 Product Showcase 86 Serviceman’s Log 96 Circuit Notebook 62 Active Subwoofer, Part 2 In this final article, we show you how to build and install the 180W amplifier, complete the wiring, install the driver and add feet. The completed highfidelity Subwoofer suits just about any hifi system. By Phil Prosser HiFi project 76 Noughts & Crosses, Part 2 We explain how this machine plays noughts & crosses using a game tree, and show you how to build it, including the PCBs and custom case. By Dr Hugo Holden Game project 1. Light with automatic switch-off 2. Automatic mouse clicker 3. Discrete logic frequency comparator 4. Skylight controller 100 Vintage Radio 106 Ask Silicon Chip 111 Market Centre 112 Advertising Index 112 Notes & Errata VE301Wn Dyn Volksemfänger by Ian Batty SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff Jim Rowe – B.A., B.Sc. Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Advertising Enquiries (02) 9939 3295 adverts<at>siliconchip.com.au Regular Contributors Allan Linton-Smith Dave Thompson David Maddison – B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Dr Hugo Holden – B.H.B, MB.ChB., FRANZCO Ian Batty – M.Ed. Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Louis Decrevel loueee.com Founding Editor (retired) Leo Simpson – B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (Australia only) 6 issues (6 months): $65 12 issues (1 year): $120 24 issues (2 years): $230 Online subscription (Worldwide) 6 issues (6 months): $50 12 issues (1 year): $95 24 issues (2 years): $185 For overseas rates, see our website or email silicon<at>siliconchip.com.au Recommended & maximum price only. Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 194, Matraville, NSW 2036. Phone: (02) 9939 3295. ISSN: 1030-2662 Printing and Distribution: Editorial Viewpoint Ripping customers off through service & repair We need legislation to deal with companies’ ongoing assault on servicing and repairing mechanical or electronic devices. Luckily, in Australia, we have strong consumer rights legislation. Despite this, greedy corporations are doing all they can to strip away anything not covered by such legislation. The problems fall under a few categories, including (but not limited to): • No spare parts available for new products, despite the manufacturer having enough parts to make more of the same product. • Purposefully making products difficult to repair, for example, Onewheel electric skateboards that ‘brick’ themselves if the battery is swapped or smartphones that refuse to work if a module is swapped from another identical phone. • Artificially limiting the lifespan of products; planned obsolescence is a huge environmental problem. • Restricting the availability of spare parts and tools. • Limiting the availability of hardware or software required for diagnosis and repair. • Refusing to release schematics and software, even for products that are no longer supported. • Overcharging for proprietary parts. Australian legislation to deal with these assaults on consumers would be a good start. The EU has a strong history of consumer protection, and if they start taking action too, others might follow. Why don’t we just boycott these companies? We should, but a minority of consumers are aware of the situation. The average customer won’t realise they’ve made a mistake until they are already out of pocket. Many competitors will use similar tactics, too, leaving us with few good choices. While I can point at some particularly egregious examples of all the above (and more), this anti-consumer behaviour is an industry-wide trend. Legislation could be drafted to solve these problems without imposing unreasonable burdens on manufacturers. It used to be standard to provide after-sales support such as releasing schematics, making all parts available and devices used to be designed to be repairable (now it’s often the opposite). Some possible solutions to the above points include: • Pay customers compensation or give a full refund if spare parts cannot be provided within a reasonable time frame for products still being sold. • Legislate the availability of spare parts for a certain period after the warranty runs out. • Disallow collusion between companies to prevent the original manufacturers from selling spares to those wishing to repair their devices. For example Apple’s exclusivity deal with Intersil, see: siliconchip.au/link/abiy • If a company stops offering spares, force them to release schematics, CAD drawings and software so others can do so; after all, they’ve effectively abandoned their product at that stage. • Make it mandatory to release all documentation for repairs either when manufacturer support stops, or some reasonable period after the product is released (say, five years), whichever comes first. • Penalties for companies caught charging excessively more for functionally equivalent parts. I realise that a comprehensive legislative solution would be complicated, but that is no reason to avoid trying. The biggest challenge is that the companies often spend large amounts of money to hire lobbyists (who aren’t always truthful), to influence politicians to vote against such measures. by Nicholas Vinen 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Australia's electronics magazine siliconchip.com.au Development tools in one location Thousands of tools from hundreds of trusted manufacturers Choose from our extensive selection au.mouser.com/dev-tools +852-3756-4700 australia<at>mouser.com MAILBAG your feedback Letters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd has the right to edit, reproduce in electronic form, and communicate these letters. This also applies to submissions to “Ask Silicon Chip”, “Circuit Notebook” and “Serviceman’s Log”. RIP Ian Robertson of Engadine, NSW My Dad, Ian Robertson, loved your magazine. He passed away on the 14th of November. Thanks for publishing Dad’s projects over the years. Elizabeth Robertson, Engadine, NSW. Editor’s note: we have two contributors named Ian Robertson, plus a third reader by the same name. The other contributor lives in Belrose, NSW. Modifying test oscillator for a higher output In the Ask Silicon Chip column from October 2022, there was a query about a 2V RMS test oscillator. This made me revisit my sinewave oscillator circuits described in Circuit Notebook (October 2019; siliconchip.au/Article/12027). Circuit 2, with equal-value feedback resistors, seemed perfect for this task. I designed and built one for 1kHz sinewave output using the circuit shown below. I tested it using a 5V USB power supply and a 3.7V Li-ion cell; both worked perfectly. I ran the circuit for a couple of days, and it is very stable. I chose a set of components to satisfy the oscillation conditions and generate a 1kHz sinewave. The Norton op amp (IC1) could be powered from a standard 5V USB supply, but to give a larger output swing, a TM3608 voltage boost module provides a 12V supply rail. The device worked fine with a 3.7V Li-ion battery in place of the USB power supply shown. The TM3608 voltage booster module is very compact and easy to use. Two 1kW multi-turn trimpots are provided for fine-­ tuning. These are adjusted to remove any clipping and achieve very close to 1kHz output. The output signal after trimming is shown in a scope grab. I measured the two combinations of 11kW resistor and 1kW trimpot as 10.96kW + 0.31kW and 10.96kW + 0.14kW. The 10kW attenuator potentiometer allows the output amplitude to be adjusted from zero to 3.4V RMS. To change the target frequency, multiply the resistor and capacitor values in the oscillator by the square root of 1kHz divided by the new desired frequency. Select the nearest standard value for the capacitors and recalculate the resistors by scaling. Mauri Lampi, Glenroy, Vic. On the GPIB (general purpose interface bus) Recently, I have been doing some work with GPIB interfaces. Historically, many peripheral devices used this interface, especially laboratory equipment. I have been working recently with a vintage PET computer that has a GPIB interface, and I wanted to use that to run a printer. After some hunting around, I found an extremely clever GPIB to serial (RS-232) interface. It can convert PETSCII to ASCII. PETSCII was a unique non-­ standard version of ASCII used by Commodore computers. The rare unit I found was made by a company called Taylor-Wilson in the UK in the late 1970s. Due to having no manual or schematics, I had to reverse engineer the whole thing. Here is the story of this interesting machine: siliconchip.au/link/abi3 This project taught me how to build a GPIB interface that could interact with a computer and respond to both primary and secondary addresses. So the basic design can serve many GPIB interface projects. I was surprised to find out that the GPIB is still around, considering its age. I noticed some modern dual-tracking lab power supplies with GPIB, RS-232 and USB interfaces. Since USB came along, RS-232 has become thin on the ground too, and many computers don’t even have an RS-232 port anymore. People have often struggled with RS-232 to get the hookups working (even now). It made a great market for RS-232 breakout boxes. NASA used GPIB interfacing in their electronics labs extensively because they had a lot of National Instruments data acquisition equipment. But probably, that equipment has been retired by now. A circuit and the 1kHz 2V RMS sinewave output that it produces. Australia's electronics magazine February 2023  5 One day, I think it would be a good idea to have a more generalised review article on ‘computer-peripheral equipment interfacing’, explaining how the historical interfaces worked. Still, the go-to method is USB these days, so it might only be of passing value. Another thing about that T-W unit, apart from the GPIB handshakes, is that it also shows how to make and use a very simple and stable baud rate selectable crystal-based UART and line driver system for an RS-232 interface. I’m pretty sure this part of the circuit was borrowed from HP or TI equipment. Unlike the rest of the T-W unit, it was implemented in CMOS, while the rest was TTL. I have seen that exact circuit in the past in some of their gear, but I cannot recall the model. Dr. Hugo Holden, Minyama, Qld. SMD Tweezers add-on for the LC Meter Mk3 I came across these SMD tweezers on eBay: siliconchip. au/link/abiz There is a similar, much cheaper one available from AliExpress at siliconchip.au/link/abj0 I received the eBay ones today and modified them to use with the LC Meter Mk.3. I just had to cut off the multimeter plugs and solder on a BNC connector. Because the wires are extremely thin and fragile, I used several stages to make the connections, as shown in the photo below. I crimped ‘bootlaces’ onto the wires, put heatshrink tubing on, attached them to the BNC connector and covered it all in larger heatshrink tubing. This makes for a secure connection. The cable’s capacitance is 34pF, which is cancelled out by pressing the CAL switch on the LC Meter. It makes measuring SMDs down to M1608/0603 size much easier. Charles Kosina, Mooroolbark, Vic. Great minds think alike The LC Meter Mk3 article (November 2022; siliconchip. au/Article/15543) made an interesting read. It is a very neat compact portable instrument that greatly improves over the original Tektronix T130. I, and I suspect at least a few others, were similarly inspired by the Tektronix articles of June/August 2020 (siliconchip.au/Series/346) and looked into modernising the concept. Using similar techniques, my version measures from <1pF to 40nF and 1µH to 40mH, as my interests do not include VHF coils. One feature of the Tektronix instrument that appealed to me in particular was the very low amplitude test voltage that allowed the measurement of semiconductor devices without driving them into conduction. My test voltage is actively regulated to 0.5V. I trimmed the original display of two decimal places back to one, as even this is optimistic for ±0.5% components over 100pF or so. The problem of ‘reference’ inductors being frequency-­ dependant seems to be primarily due to capacitance between the turns of the winding. As the frequency increases, the distributed capacitance eventually resonates the coil, resulting in it electrically looking like a Q-dependant high-value resistor. I calculated the distributed capacitance of the coil plus strays and added this to the reference capacitor during the calibration process. By adding a second tight-tolerance capacitor and measuring the frequency, the two frequencies and the capacitor values can be used to determine total strays accurately. My reference capacitor is 1200pF ±0.5% and the distributed capacitance of the coil plus tracks and semiconductors worked out to be 89pF. I added that value to the reference capacitance and stored it in non-volatile memory. I have checked a few dozen tight-tolerance silvered mica capacitors between a few hundred pF and 20nF and seen results within ±0.5% of the marked value, with one unit measuring 0.7% high. I considered offering Silicon Chip my design last year, but concluded that my ‘old-­ fashion’ design with a 16×2 LCD plus plugpack power supply and more expensive reference capacitor would not attract much interest. I can provide the maths involved if there is any interest in the distributed capacitance measurements. The photo shown directly below the unit with the top of the case removed. Graham Lill, Lindisfarne, Tas. Praise for LD Electronics Thanks to you and your team for doing Australia proud with a highly-regarded electronics publication worldwide. I would like to express my gratitude to one of your advertisers, LD Electronics. George has been my prime contact within this company. I exclusively use it for all of Left: these SMD tweezers were purchased on eBay and modified for use with the LC Meter Mk3. The cut-in shown at upper right was taken before heatshrink tubing was added. Below: Graham Lill’s LC Meter design, which was inspired by the Tektronix Type T130. 6 Silicon Chip Australia's electronics magazine siliconchip.com.au my PCB needs as I have found them to be second-to-none. In general, most people are driven by price, but to me, it goes much deeper then that. I’m probably an oddity in that I prefer to support local business regardless of price. In saying that, I find that factoring in shipping, ease of contact, fast turn-around, product quality and quality of service, LD Electronics should be highly considered. I’m a bit of an ‘old hat’ in that I use Protel EDA client to produce my PCB designs. LD Electronics accept many different formats. I only have to provide the original design file and George is quite happy to produce the needed files for manufacture. He even picked up a missing trace in one such file, and contacted me to query this discrepancy, which he subsequently fixed. I highly recommend LD Electronics to all of your readers for their PCB manufacturing needs. They won’t be disappointed. Mike Boothroyd, Werrington County, NSW. Misleading power pack capacities I recently bought a power bank from eBay, advertised as a “40000mAh Power Bank, 18W PD USB C Fast Charge Battery Bank Travel work”. No further technical information was provided, but a few references were made to USB. A discharge test on my DC load at 2A showed a capacity of 28Ah (amp-hours), somewhat short of the advertised 40Ah. The supplier promptly answered my query and explained that 40Ah is the capacity of the 3.7V cell pack which makes up the power bank. Of course, this information was nowhere to be found in the advertisement, which stated 40Ah and referred to USB, which I interpreted as 5V. To the supplier’s credit, I was able to return the pack, at their expense, for a full refund. My lesson: always ask for capacity in “Wh” before purchasing a power bank. Erwin Bejsta, Wodonga, Vic. Comments: It is frequently misleading to label a device with an Ah rating without disclosing the voltage range of that measurement. We discussed this in detail on page 6 of the July 2022 issue. As you suggest, it’s always better to have a battery capacity rating in Wh (or kWh or J) rather than Ah, as that is unambiguous. AM interference & DAB+ poor sound quality Have you noticed that when listening to AM radio these days, there is an endless cacophony of switch-mode power supply buzz or power-line-induced noise, making AM an awful listening experience? Why would anyone torture their ears doing so? While talking about radio reception, DAB+ was advertised as rivalling CDs for audio quality, but alas, no. As usual, corporate greed or ‘spectrum exploitation’ has led to crowding of their allotted bandwidth/frequencies with very low bit-rate stations, leading to mediocre audio quality. For some stations, their FM audio sounds better than the equivalent DAB+ ‘cousin’. Similarly, there aren’t many high-definition TV channels because the lure of the advertising dollar by adding more standard-definition channels overrules the provision for more (higher bandwidth) high-definition channels. Streaming is the only way to get a good audio or visual experience, but it comes at a price. Denis McCheane, Allawah, NSW. siliconchip.com.au Australia's electronics magazine February 2023  7 Comment: we have even seen ‘high-definition’ 1080p freeto-air TV programs break up into a horrible blocky mess during certain scenes due to the limited bit-rate allocation. As you say, streaming services are generally able to avoid such problems. Praise for kit & Keith Rippon I had the Multimeter Calibrator (July 2022; siliconchip. au/Article/15377) made by Keith Rippon from the Market Centre advert. He provided good service and prompt delivery and the Calibrator works well. I have just calibrated five meters, and all appear to be within calibration, except one where the resistance range is out by about 1%. I have more meters but checking them is for another day. Thank you for making service gear available in kit form; it is much appreciated. Finally, I have a U1253A meter that does not work with a fresh 9V battery, but when powered on, it plays a brief melody, and all buttons produce a beep when pressed. If any reader wants it for spare parts (including charger, CD, calibration certificate from 2010 and original box) but no leads, they can have it for the cost of postage. Ric Mabury, Melville, WA. Solar power flowing through distribution transformers I am writing in response to George Ramsay’s letter in the December 2022 issue. He believes home-generated solar power cannot be transmitted via the high-voltage transmission network. It can, in fact, be carried via the distribution and substation transformers. In suburban Adelaide, the rooftop solar inverters feed power into the 240/415V street mains. If the total consumer load on a particular phase exceeds the solar feed-in on that phase, the distribution transformer will supply the remainder of the power. However, if solar feed-in exceeds the load, the excess power is fed into the transformer, and a power meter will show negative power. In other words, the solar power is being fed back into the grid via the distribution transformer, which steps up the voltage to 11kV and transmits the excess solar power to the 66kV/11kV substation. Suppose there is still insufficient load on the 11kV feeders. In that case, the excess solar power is stepped up to 66kV to pass to other substations and, ultimately, under ideal solar conditions, from SA to Victoria via the SA-Victoria interconnector. Recently, a storm blew over one of the interconnector steel towers near Tailem Bend and ‘islanded’ SA from the east coast grid for a week, leaving no export option for excess solar power. To prevent supply instability that week, SA Power Networks intermittently cranked the mains up to 260+V AC to force the shutdown of rooftop solar inverters. My solar inverter recorded multiple overvoltage events, and I measured peak voltages of 262V AC. To clarify further, farmhouses and other isolated premises in rural SA have either a two-wire single-phase 11kV/33kV supply or a single-wire 19kV SWER supply, usually followed by a 10kVA stepdown transformer to 230V AC. SAPN (South Australia Power Networks) allows up to 5kW solar export via these transformers. If the resident is not using any or minimal power, the excess solar power of up to 5kW is fed back into the 8 Silicon Chip 11kV/19kV/33kV supply line via the transformer to other consumers on the same line. Once again, if there is still insufficient load, the excess power goes to the substation to be sent to the high-voltage network. While so-called energy experts proclaim that renewable power will bring down the cost of power to the consumer, SA has the highest wind and solar power uptake in Australia. Yet, the price per kW to the consumer is the highest in the nation. I believe this is why I have noticed quite a few new solar rooftop installations within the last few months. As for the argument between distributed and concentrated solar, I have a 5kW system, but I agree with George that large-scale systems are probably more economical. The fact remains that if power weren’t so expensive, many other people and I wouldn’t have bothered with a rooftop solar system. On a mild, sunny day in SA, small-scale solar pushes large-scale solar and wind generation out of the market. In metropolitan Adelaide, the amount of exported rooftop solar power in some suburbs is now being constrained to avoid overloading the 66/11kV substation transformers. It is interesting to compare the price of petrol to electricity. One litre of petrol, mainly imported from overseas and containing 10kW of energy, costs around $1.65 or 16.5¢ per kilowatt. When GST and excise are deducted, the product price is $1.05 per litre or 10.5¢ per kilowatt. Yet I pay 40¢ plus 4¢ GST per kW for locally-produced electricity, primarily produced from renewables. It doesn’t make sense that the cost per kilowatt of renewable electricity is four times the price of a kilowatt of petrol. Andrew Fraser, Para Hills, SA. Comment: traditional, passive transformers are bi-­ directional devices by their nature (referring to the windings as ‘primary’ and ‘secondary’ is just a convention). So we have to agree that there is no reason why power cannot move around the grid from high-production to high-demand areas. Designs that withstood the test of time Earlier this week, I carried out the annual Christmas lights setup at my place. It is not an elaborate setup, but a few basic light strings with the centrepiece being an old Silicon Chip project – the Santa & Rudolph Christmas lights display as published in November 2000 (siliconchip.au/Article/4275). My version is now on display for the 23rd season, enduring nearly 100 weeks’ worth of the harsh elements of western Sydney summers and storms. A couple of years back, I engaged my youngest daughter to repaint the faded areas (unenthusiastically). It wasn’t a great job, and I had to finish it off, but it will do for now. In terms of the electronics and wiring – I have thankfully had no problems. It is not the easiest project to maintain! On the subject of longevity, my very first electronics kit project was the Walkaround Throttle for Model Railroads (April & May 1988; siliconchip.au/Series/267). I was hooked after I chose electronics as a high-school elective subject for years 9 and 10 in 1988-89. A school friend’s father kindly drove us to the Parramatta Jaycar on the corner of Victoria Rd and Church St to purchase our “major projects” to complete during class time. Australia's electronics magazine siliconchip.com.au Power your projects with our extensive range of Arduino® compatible power supply modules, batteries and accessories. A GREAT RANGE AT GREAT PRICES. LED VOLTAGE DISPLAY USB OUTPUT POWER YOUR PROJECT FROM A LOWER VOLTAGE POWER YOUR 5V PROJECT FROM BATTERIES BOOST MODULE Converts 2.5-5VDC from a single Li-Po or two Alkaline cells up to 5VDC. 500mA max. XC4512 ONLY 4 $ 95 DC-DC Boost Module with Display Converts 3-35VDC up to 4-35VDC. 2A max. 2195 $ XC4609 USB OR SOLDER TAB INPUTS EASILY ADJUSTABLE BY MULTI-TURN POTENTIOMETER MAKE YOUR PROJECT BATTERY POWERED RUN ARDUINO BOARDS OFF HIGHER VOLTAGE POWER LITHIUM BATTERY CHARGER MODULE Charges a single Lithium cell from 5VDC. XC4502 ONLY ONLY 4 $ 95 DC VOLTAGE REGULATOR Accepts any voltage from 4.5-35VDC, and outputs any lower voltage from 3-34V. XC4514 ONLY 7 $ 95 Batteries not included SINGLE 18650 BATTERY HOLDER SWITCHED 4XAA BATTERY ENCLOSURE WITH USB PORT PH9205 $3.50 MP3083 $5.95 SWITCHED 4XAA BATTERY ENCLOSURE WITH DC PLUG PH9283 $5.95 3.7V 18650 2600MAH LI-ION BATTERY SB2308 $17.95 Shop at Jaycar for: • Step Up and Step Down DC-DC Converters • Huge range of Batteries and Battery Holders • Great selection of USB and DC Connectors & Leads • Regulated DC Plugpacks & Lab Power Supplies Explore our full range of products to power your projects, in stock on our website, or at over 110 stores or 130 resellers nationwide. jaycar.com.au/powerprojects 1800 022 888 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. I would have paid for it with my tiny income delivering local newspapers and junk mail. If my memory is correct, the kit cost me around $90. It still sees regular use by me and will one day be replaced by DCC equipment. In the 34 years of service of this kit so far, I have had one fault with it. It was an LM324 chip that had failed; after replacing it, I also tidied up the mains wiring to improve its safety. I didn’t have much in the way of tools back when I first built it; for example, I was crimping with pliers instead of a ratcheting crimper. Recently, my NBN connection has been dropping out with increasing frequency each day. I engaged my ISP to fix it, with the pain that brings. However, today, it degraded even more. That motivated me to make basic checks of the cable to the NBN modem, since there is little else that an individual can check. Surprisingly, I found a 90° F-connector to be a dead short across the centre pin to the body. Bypassing that got my household back online. I will check the connection logs to see if there are any further dropouts. The recent History of Silicon Chip series was very Left: the November 2000 Christmas lights display. Below: the damaged 90° F-connector. The Walkaround Throttle for Model Railroads from the April & May 1988 issues of Silicon Chip. 10 Silicon Chip interesting (August & September 2022; siliconchip.au/ Series/385). It reminded me of a work colleague who called into a newsagent to purchase a copy on his way to work a few years ago. My colleague was in a hurry and asked the agent where he might find Silicon Chip magazine. The newsagent was not fluent in English and misunderstood the word “chip”. My colleague was directed to a display of adult magazines that no doubt contained a lot more silicone than silicon! I must thank Leo Simpson and the evolving Silicon Chip team over the years. Silicon Chip magazine has helped me in my initial schooling, understanding how things work, reading about how people fix things, making things and using some of these snippets in my work and hobbies. My interest in trains led me to my interest in electronics and subsequent apprenticeship in telecommunications with the then-second-largest communications network in Australia – the State Rail Authority – in 1992. Although my employment is no longer directly related to my electronics trade skills, I’m still learning and applying the knowledge, particularly with Arduino and similar devices these days. Robert Parnell, St Clair, NSW. Induction Motor Speed Controller modifications I built an ‘analog computer’ to give closed loop torque control of a three-phase induction machine via the 1.5kW Induction Motor Speed Controller (‘IMSC’, April & May 2012; siliconchip.au/Series/25). I built it from an Altronics K6032 kit. The IMSC and analog computer worked really well together with manual torque control and PID control. However, I noticed that when running them together, the motor speed would sometimes have some really annoying chatter. So I did some digging... My analog computer gives a steady output for a steady input voltage (supplied from a linear regulated supply), so it was not responsible for the chatter. When driving the inverter and motor in open-loop mode with a steady voltage and varying the computer’s output up or down, I discovered the motor speed changed neatly in 60 RPM steps and chattered when the analog computer output control voltage approached the IMSC speed step thresholds. So basically, the IMSC generates frequencies in 1Hz steps (I verified this with a current clamp set to its frequency range), and its microcontroller lacks a little hysteresis on its external control input. I then investigated further. The IMSC speed set pot (VR1) also varies the output in 1Hz steps. When set to ramp up to a set speed via the internal control and, given a long ramp time, the motor spins up to the selected speed very smoothly! The specifications for the IMSC state that its “speed control range” is 0.5-50/75Hz in 0.05Hz steps. It looks like the inverter is stepping in 0.05Hz steps when ramping between the discrete 1Hz settings, which isn’t what I expected. I wanted the microcontroller to be set up so that its speed setting increments in 0.05Hz steps, just like it does while ramping. After contacting Silicon Chip for assistance, I was given access to the source code. It took quite a bit of effort and some back-and-forth, but I was eventually Australia's electronics magazine siliconchip.com.au Huge Range of Project Enclosures A hand-picked selection of our plastic and metal type enclosures for projects big or small. SAME GREAT RANGE AT SAME GREAT PRICE. 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Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. jaycar.com.au/enclosures 1800 022 888 able to modify the code to work just as the initially published firmware except without the 1Hz hysteresis in the speed settings. Now, the output frequency and voltage increase and decrease smoothly with the analog control signal. As expected, there is some minor frequency hunting, around ±0.1Hz, which isn’t really a concern for me. I see the benefit in having 1Hz steps, though; as long as the analog commands don’t fall near the thresholds between steps, it works. The IMSC now works really well with the analog torque box. The motor speed is steady with PID control (sometimes with a tiny amount of hunting) and ramps up and down smoothly with manual control. I could get an acceptable full load current curve across speeds without overloading the motor (3A <at> 4% slip). It has been a great learning exercise, tinkering with analog electronics and applying circuit elements learned along the way in the past at TAFE (Advanced Diploma). I have learnt heaps! I did enjoy ‘programming’ the analog computer; it was pretty hands-on. Neil Ross, Glenroy, Vic. Forced upgrades due to incompatibility I enjoyed your “Editorial Viewpoint” in May 2022 issue. However, you didn’t mention anything about the possible need to upgrade when a new version of the operating system is installed (eg, Windows 10 to 11) due to the possible lack of backwards compatibility with some operating systems and programs that run on them. I have been lucky with some of the programs that I’ve 500 been using for many years, obtained from PC Magazine (such as Cross Guesser, Screen Seize, Shot Sender etc) and P Lutus’ arachnoid.com (dbEdit etc). These are all still working on Windows 10 years after they were originally written, although they have to be “authorised” using a system dialog box. The same goes for the Microsoft Office set of programs. I currently have Office 2010 on my desktop (tower) PC and Office 2019 on my recently purchased Windows 10 laptop PC. When using Office 2010, I sometimes get a line just above the spreadsheet and below the edit bar telling me that I am using an outdated version of the program and that it is therefore no longer supported. Do you have any comments on this aspect of the potential need to upgrade to a later version of a program as a result of an OS upgrade due to a lack of backward compatibility? Paul Myers Karabar, NSW. Nicholas responds: You are right that I did not mention that, but I had considered it. If I am forced to upgrade to Windows 11 eventually, the latest version of CorelDraw I have (2022) will work. By the time Windows 12 rolls around, CDR2022 may no longer run. The idea of paying $599/year just for the privilege of running software I already paid for because of an operating system update is not palatable. I use LibreOffice for documents and spreadsheets, which is free, so I don’t have to worry about that. GIMP is the same (images). In fact, besides a couple of key programs like Altium and CorelDraw, pretty much all the software SC I personally use is free and open-source (FOSS). POWER WATTS AMPLIFIER Produce big, clear sound with low noise and distortion with our massive 500W Amplifier. It's robust, includes load line protection and if you use two of them together, you can deliver 1000W into a single 8Ω loudspeaker! PARTS FOR BUILDING: 500W Amplifier PCB Set of hard-to-get parts SC6367 SC6019 $25 + postage $180 + postage SC6019 is a set of the critical parts needed to build one 500W Amplifier module (PCB sold separately; SC6367); see the parts list on the website for what’s included. Most other parts can be purchased from Jaycar or Altronics. 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Jaycar reserves the right to change prices if and when required. > THE HISTORY OF COMPUTER MEMORY > THE SILICON YEARS PART 2 BY DR DAVID MADDISON Last month, we described the memory systems that early computers used, from punched paper cards to magnetic drums and tape, core memory, delay lines, special vacuum tubes, cathode ray tubes and more. As we shall investigate, most of those are now obsolete, replaced with silicon-based memory. HE TURNING POINT T WAS AROU N D 19 65. Very small transistorised memory chips started to become available then; just a couple of bytes at first, then a kilobyte, then a few kilobytes… the rest is history. The two primary technologies that emerged were SRAM and DRAM, but we’ll look into others too, like EPROM, EEPROM, flash, SGRAM and more. Picking up where we left off last month: 1965 Scientific Data Systems and Signetics produced an 8-bit (one-byte) memory device. Later in the year, Ben Agusta and Paul Castrucci developed the SP95, a 16-bit (two-byte) RAM device used in the IBM System/360 Model 95. 1966 Tom Longo at Transitron built the TMC3162 16-bit TTL memory (see Fig.24). This became the first widely produced RAM chip and was also produced by Fairchild (as the 9033), Sylvania (SM-80) and TI (SN7481). You can view the data sheet for the latter at siliconchip.au/link/abhv Honeywell used that chip in their Model 4200 minicomputer. Following that were 64-bit (eightbyte) chips such as the IBM cache memory chip, Fairchild (9035 and 93403) and TI (SN7489); see the data sheet at siliconchip.au/link/abhw 1967 Robert Dennard of IBM filed for US Patent 3,387,286, awarded in Fig.24: the metal mask from the Fairchild 16-bit bipolar TTL RAM IC. Source: Fairchild Camera & Instrument Corporation, www. computerhistory.org/siliconengine/ semiconductor-rams-serve-highspeed-storage-needs/ Fig.25: an illustration from Dennard’s 1968 patent, showing a 9-bit DRAM memory element with nine transistors and nine capacitors. 14 Silicon Chip Australia's electronics magazine siliconchip.com.au Early programs that were run more than once? Fig.26: a labelled silicon die from a 1970s 1024-bit MMI 5300 PROM chip. Source: Ken Shirriff, www.righto.com/2019/07/looking-inside-1970s-promchip-that.html 1968, for a one-transistor DRAM cell (Fig.25). Memory based on this technology displaced magnetic core memory. The differences between DRAM and SRAM (both still in use today, for different applications) will be described later. 1969 the PROM (Programmable Read-only Memory) was invented in 1956 for the US Air Force to keep targeting data in ICBMs. However, the technology was kept secret for over a decade. The PROM is a memory device that can be written only once; after that, the data can no longer be changed (Fig.26). Applications for these devices, which are still used today, include encryption keys, configuration and calibration data in equipment and boot code in computers. It was not initially in the form of an integrated circuit, which wasn’t invented until 1958 (or 1960 for planar devices) – for more details on that, see our articles on IC Fabrication in the June-August 2022 issues (siliconchip. au/Series/382). Programming is done by “blowing” fusible links such as metal links, diodes or breaking down the oxide layer between the gate and substrate in a transistor with a relatively high voltage (eg, 6V) pulse. PROM devices weren’t implemented in CMOS technology until 2001. 1969 Charles Sie published a dissertation on Phase Change Memory (PCM, also known as PRAM), originally conceived by Stanford R. siliconchip.com.au Ovshinsky. A substance such as chalcogenide glass is changed between its crystalline and amorphous (glass-like) phase by applying heat at an appropriate fast or slow rate from a heating element – see Fig.27. Each phase has a different resistivity. PCM has a much higher write performance and comparable read performance to flash memory. There have been many attempts to commercialise PCM devices; despite some product demonstrations and some devices being released onto the market between 2004 and 2014, they have yet to be commercially successful. Intel 3D XPoint memory is an example of PCM. Their “Optane” products It was once related to me by an older colleague that in the very early days, computers were not as reliable, nor did they have the multiple self-checks they do today. Electrical noise could introduce incorrect information, eg, by flipping a bit. It was therefore not uncommon to run science and engineering programs, and presumably others, two or three times to ensure the same answer would be obtained. However, I have found no corroboration of this elsewhere. We would be interested to hear from readers who may have heard of this. were introduced in 2017 and proved reasonably popular among some users, being faster than flash-based SSDs, but Intel discontinued development in 2021. Chalcogenide glass is also used in rewriteable optical media such as CDs and DVDs. 1969 Intel introduced its first product, the 3101 Schottky TTL bipolar 64-bit static random-access memory (SRAM) – see Figs.28 & 29. It could store 64 bits of data or eight 8-bit characters. It was twice as fast as the previous silicon memory products mentioned above (IBM cache, Fairchild 9035 and 93403, TI SN7489) due to its use of schottky diodes. Fig.27: phase change memory structure, with the left-hand cell in a crystalline state and the right-hand cell in an amorphous state. Original source: https://w.wiki/5zxP (GNU FDL) Australia's electronics magazine February 2023  15 D2 O1 D1 WE O2 CS A0 GND Vcc O3 A1 D3 O4 D4 A3 A2 Fig.28: a die photo of Intel’s first product, a 64-bit memory chip from 1969. Source: Ken Shirriff, www.righto.com/2017/07/inside-intels-first-product-3101ram.html Fig.29: two variants of the Intel 3101 IC. Source: Ken Shirriff, “inside Intel’s first product” Its memory capacity was insufficient to compete with the magnetic core memory of the time. Still, it was very fast, so it was useful in CPU registers. 1969 The Intel 3301 1024-bit ROM (read-only memory) was introduced. 1969 IBM produced a 128-bit memory chip for the System/370 Model 145, the first IBM computer to use semiconductor main memory. 1969 Fairchild produced the 4100 (aka 93400) 256-bit memory chip for the Burroughs Illiac IV computer. 1969 The Intel 1101 was introduced. It was a 256-bit SRAM, the first to use MOS (metal oxide semiconductor) technology, leading the way to high-density devices. 1970 Intel introduced the first These devices are easy to recognise as they have a transparent window over the silicon die, usually covered by an opaque sticker. That was to stop accidental erasure by stray light sources such as fluorescent lamps or sunlight. They were used to store the BIOS (built-in operating systems) of early IBM-compatible PCs and many other devices as there was a periodic requirement to update low-level program code or ‘firmware’. At the time, there was no other form of chip-based non-volatile memory, and computer boot processes were time-consuming. Intel founder Gordon Moore said the invention of the EPROM was “as important in the Read/Write Drivers Decode Storage Cells Address Drivers commercially-available DRAM (dynamic random-access memory) IC, the 1103, with one kilobit (1024 bits) of memory – see Figs.30, 31 & 32. This chip was significant because it was sufficiently small and cheap to provide a viable alternative to magnetic core memory. 1970 The EPROM was invented by Dov Frohman with US patent 3,660,819 awarded in 1972. An erasable programmable read-only memory is a device that can be electrically programmed and retains its memory for many years, but can be erased when needed using ultraviolet light. It is a form of non-volatile memory and retains its data with no power applied. Fig.31: a die photo of the Intel 1103 1-kilobit DRAM. Source: www. cpu-galaxy.at/ cpu/Ram%20 Rom%20Eprom/ RAM/Intel%20 1103%20section. htm Fig.30: the 1972 HP 9830A programmable calculator/computer with optional thermal printer used Intel 1103 1-kilobit memory chips. Source: Hydrargyrum, https://w.wiki/5zxQ (GNU FDL) 16 Silicon Chip Australia's electronics magazine siliconchip.com.au development of the microcomputer industry as the microprocessor itself”. 1971 The Intel 4004 4-bit microprocessor with 2300 transistors was released. This device led to the revolution in microcomputers, creating a huge demand for bigger and better memory. The 4004 was followed by the 8-bit 8008 microprocessor in 1972 and eventually the 8086 in 1978, the predecessor to the x86 architecture that is in widespread use today. 1971 Bill Herndon at Fairchild designed a fast 256-bit TTL memory (the 93410). 1972 The first EPROM was released onto the market, the Intel 1702, with a 2048-bit capacity (see Fig.33). 1972 The EEPROM was invented by Fujio Masuoka of Toshiba, who later created flash memory in 1984. EEPROM or E2PROM (electrically-­ erasable programmable read-only memory) is much like EPROM. It is a form of non-volatile memory, but instead of being erased with UV light, it is erased electrically, making it much simpler to use. In fact, these devices are the precursors of flash memory. EEPROMs are still used in devices such as embedded microcontrollers, phone SIM cards, bank cards, keyless entry systems, security devices and so on. When used in security devices, they usually have some sort of read, write or copy protection. One difference between EEPROMs and flash memory is that an EEPROM requires two transistors per bit for erasure, while flash memory requires only one. Thus, an EEPROM chip of the same capacity is larger than flash memory. However, an EEPROM can erase single bytes, but flash memory must erase entire blocks of data. EEPROMs can usually handle being rewritten more often than flash, so they are more suitable for storing frequently updated data, such as for a vehicle odometer or for remembering the last input selection and volume setting of an amplifier. 1976 The Cray 1 supercomputer was built using 65,000 Fairchild 1024bit RAM chips (type 10415). 1977 The first commercial bubble memory device was released by Texas Instruments in the form of a portable computer terminal that used bubble memory for storage. Bubble memory (Fig.34) is a form of non-volatile memory that uses magnetic material containing magnetised regions called bubbles or domains, each representing one bit of data. The bubbles are arranged in parallel tracks. To read a bubble (one bit of information), the bubble is moved along the track to the edge by a magnetic field, where it is read by a magnetic pickup and then rewritten to the opposite edge. It is somewhat similar to delay line memory, but magnetic domains are used rather than acoustic pulses. Garnet was found to be the best material to use. To form the tracks on a flat piece of garnet, it was necessary to print magnetic guides on the material’s surface in the shape of a “T and bar”, as shown in Fig.35. Otherwise, the domains would drift off in random directions. There were also two orthogonal spiral coils. With out-of-phase sine or triangular waves applied to the coils, they form a rotating magnetic field along the sheet of garnet. Each 360° magnetic field rotation causes each bubble to advance one step. Fig.32: an Intel 1103 SRAM chip. Source: Thomas Nguyen, https://w.wiki/5zxR (CC BY-SA 4.0). Fig.33: an Intel 1702A-6 EPROM. Note the transparent window over the silicon die. This was typically covered to prevent accidental erasure of the contents. Source: Museums Victoria, https://collections.museumsvictoria. com.au/items/1711881 (CC BY 4.0) siliconchip.com.au Fig.34: a bubble memory device with multilayered hybrid control circuitry from a Milstar Communications Satellite, late 1980s or early 1990s. The actual bubble memory element is not visible, but this shows the complexity of the control circuitry. Source: National Air and Space Museum, Washington DC USA, https://airandspace.si.edu/collection-objects/bubble-memory-microelectronichybrid-milstar-communications-satellite/nasm_A19980305001 Australia's electronics magazine February 2023  17 Table 3: desktop computer SIMMs & DIMMs Memory type Introduced Number of pins Typical max capacity Transfer rate (fastest of type) Length (approximate) * SIMM 1983 72 16MB ~250MB/s 107.9mm DIMM 1995 168 128MB 1.066GiB/s (SDR-133) 133.3mm DIMM (DDR) 1998 184 512MB 4.8GiB/s (DDR-600) 133.3mm Rambus RDRAM RIMM 1999 184 512MB 2.4GiB/s (PC1200) 133.3mm DIMM (DDR2) 2003 240 8GB 10GiB/s (DDR2-1250) 133.3mm DIMM (DDR3) 2007 240 16GB 24GiB/s (DDR3-3000) 133.3mm DIMM (DDR4) 2014 288 64GB 35.2GiB/s (DDR4-4400) 133.3mm DIMM (DDR5) 2020 288 512GB 51.2GiB/s (DDR5-6400) 135.0mm * Height is variable depending upon manufacturer, but JEDEC standards specify a maximum height Individual magnetic guides would be first magnetised in one direction, causing the bubbles to move to one end of the guide. Then the field would be reversed, moving the bubble to the other end of the guide, and so on, until the bubble reached the end of the line. Bubbles are created with an electromagnet at one end and a magnetic field detector (pickup) at the other. They are kept appropriately small by permanent magnets above and below the garnet sheet. Electronics Australia published articles on bubble memory in their January 1973 and March 1980 issues. For the details of how the bubbles are constrained and moved, see the video titled “Magnetic Bubble Memory Fundamentals 101-Constraining and Moving Magnetic Bubble Domains” at https://youtu.be/rJ-ysch4-NM Bubble memory once held great hopes, and in the 1970s, it had a storage density similar to hard drives but a higher speed, more like magnetic core memory. It was also more rugged and reliable than hard drives of the time. It was superseded by higher-density hard drives and faster semiconductor memory chips, becoming obsolete by the late 1980s. For further information, see the video titled “Digital Electronics 25 Memory - RAM Controller - Magnetic Bubble Memory” at https://youtu. be/51BslNuGnrs?t=257 You can see live motion video of magnetic bubbles at work in the video “Magnetic Bubble Memory Chip” at https://youtu.be/0rqPmjmQOxw 1978 George Perlegos of Intel developed the type 2816 2KiB EEPROM (2k × 8 bits). You can view a PDF data sheet of a later version, the 2816A, at siliconchip.au/link/abhx 1983 Wang Laboratories released the SIMM (single in-line memory module), which was used in later model IBM PC ATs and the 386, 486, Macintosh Plus, Macintosh II, Quadra, Atari STE and Wang VS computers. 1984 Fujio Masuoka invented flash memory, a form of non-volatile memory used in USB memory sticks, SD cards etc. As mentioned earlier, it is Fig.35: the layout of bubble memory. Note the ‘T and bar’ magnetic structures and the two coils at right angles. There is a permanent magnet above and below the magnetic sheet. Source: Søren Peo Pedersen, https://w.wiki/5zxS (GNU FDL) 18 Silicon Chip Australia's electronics magazine related to EEPROM, which the same person invented. 1985 Toshiba introduced the first flash memory chip (256kbits). 1986 Intel released a 256kbit flash memory using ETOX (EPROM with tunnel oxide) technology, the most common type today. 1986 1Mbit DRAM chips became available, considered a milestone at the time. It represented a transition from planar memory cells to trenched or stacked cells. Its fabrication involved 18 masks. 1993 Samsung released Synchronous DRAM (SDRAM) . 1996 Samsung Electronics introduced a 4MB FeRAM (ferroelectric RAM) chip (invented in 1952, as mentioned last month). The first commercial product to use FeRAM was the Sony PlayStation 2 8MB Memory Card, released in 2000. Its Toshiba microcontroller contained 4kiB of FeRAM. FeRAM’s advantages over flash include reduced power consumption, a larger number of lifetime read/write cycles and faster write times. Disadvantages include lower density, higher cost and lower overall capacity. Its uses include data loggers, implantable medical devices, smart meters and industrial uses to replace battery-backed memory. 1998 The first DDR (double data rate) DRAM was offered for sale. It allowed two transactions per clock cycle, effectively doubling bandwidth. 2003 DDR2 DRAM was released to the market (see Table 3). 2007 DDR3 DRAM was released. 2014   DDR4 DRAM was released. 2019   The Compute Express Link was standardised. CEL is an open standard for CPU-to-memory connections based upon PCI Express (PCIe). siliconchip.com.au 2020 DDR5 DRAM (shown in the lead photo) was released. Most of the latest-generation desktop and laptop computers use this type of RAM; the latest Intel 13th Gen CPUs can use DDR4 or DDR5, while competing AMD Ryzen 7000 CPUs support DDR5 only. SRAM vs DRAM The two main types of RAM in use today are SRAM and DRAM. DRAM (dynamic RAM) has a much higher density than SRAM but tends to be slower and needs to be periodically ‘refreshed’. SRAM uses six transistors per bit, while DRAM only requires one transistor and one capacitor per bit, hence the significant difference in density. Refreshing involves going through the whole RAM, reading each bit and then rewriting it. If this isn’t done periodically, some of the capacitors holding the bit state could discharge, and the information will be corrupted or lost. These days, the memory controller handles refresh, and it occupies well under 1% of the memory’s bandwidth, so it has little impact on performance. SRAM is faster than DRAM but occupies more chip space and is more complicated and expensive to manufacture. SRAM is used in fast cache memory, usually built into the CPU nowadays. The much larger main memory is typically a form of DRAM, which is slower but cheaper and more compact. SDRAM (synchronous DRAM) is a variation of DRAM. The memory device is controlled by an external clock signal (synchronous) via the system bus, meaning there is less wait time and the memory runs faster. In contrast, regular DRAM is asynchronous and not controlled by the system bus speed, so it is slower than SDRAM. EDO RAM (extended data out RAM) is a type of DRAM from the 1980s and 1990s designed to allow improved performance. It was replaced by SDRAM. Memory packaging Many earlier computers from about 1970 used a socketed 16-pin DIP (dual in-line package) memory chip. For example, Burroughs used Fairchild 4100 (aka 93400) 256-bit bipolar TTL RAM chips in their Illiac IV supercomputer; many later computers used the same scheme, up until the original IBM PC XT and early ATs. siliconchip.com.au From the early 1980s, DIP memory chip packages were replaced with the SIMM (single in-line memory module), invented in 1982. A SIMM is a small PCB with an edge connector and one or more memory chips mounted on that PCB (usually in TSSOP SMD packages). These initially had 30 pins on the edge connector, then 32 pins (or 36 pins for parity/ECC [error correction code] versions). From the early 1990s, 72-pin SIMMs were used in PCs with processors such as the Intel 80486, Pentium, Pentium Pro and early Pentium II. After SIMMs came DIMMs (dual in-line memory modules), which were introduced in the mid-1990s. They were developed to solve the problem of Pentium processors having to address two SIMMs in parallel due to the wider address bus of the Pentium. One DIMM effectively combined the circuitry of two SIMMs. DIMMs are still in widespread use and come in many varieties with varying speeds, capacities, number of pins, physical size etc – see Table 3. DIMMs eventually switched from using DRAM ICs in TSSOP packages (with leads on two sides) to BGA packages, with the connections underneath, increasing the board density. DIMMs for laptops are called SO-DIMMs (small outline DIMMs), and there is also the microDIMM for ultra-slim and compact portable computers. The RIMM or Rambus in-line memory module, in varieties such as RDRAM, CDRAM and DRDRAM, was available in the 1990s and early 2000s as an alternative to DIMMs but lost the “standards war” and is now obsolete. Synchronous-link DRAM (SLDRAM) was another alternative to Rambus, now also obsolete. XDR DRAM (eXtreme data rate DRAM) succeeded RDRAM, competing with DDR2 and GDDR4 SDRAM. It was released in 2003 and used in the Sony PlayStation 3. SGRAM (synchronous graphics RAM) is a form of SDRAM for graphics adaptors. Its earliest use was in the 1995 Sony PlayStation. Modern Table 4: other DIMMs Memory type Number of pins Typical max capacity Length (approximate) * DIMM (for printers) 100 512MB 88.9 microDIMM DDR 172 1GB 42.4 microDIMM DDR2 214 1GB 55.0 SODIMM 144 512MB 67.6 SODIMM DDR2 200 2GB 67.6 SODIMM DDR3 204 16GB 67.6 SODIMM DDR4 260 64GB 67.6 SODIMM DDR5 262 128GB 69.6 * Height varies with manufacturer, but JEDEC standards specify a max height Table 5: Graphics memory chips Memory type Introduced Number of pins Typical max capacity Transfer rate (fastest of type) SGRAM 1994 80-100 (TSOPII/QFP) 1MiB 400MB/s DDR SGRAM 1998 128 (BGA) 2MiB 5.6GiB/s GDDR2 2002 84 (BGA) 32MiB 16GiB/s GDDR3 2004 136 (BGA) 64MiB 19.9GB/s GDDR4 2005 78-96 (BGA) 64MiB 17.6GB/s GDDR5 2007 170 (BGA) 1GiB 40-72GB/s GDDR5X 2016 190 (BGA) 1GiB 80-112GiB/s GDDR6 2018 170 (BGA) 2GiB 112-144GiB/s GDDR6X 2020 180 (BGA) 2GiB 152-168GiB/s Australia's electronics magazine February 2023  19 Fig.36: the concept of molecular memory showing the molecule structure (top) and molecules sandwiched between X and Y address buses on conventional silicon (bottom). Original source: www.researchgate.net/figure/Cellstructure-of-a-molecular-memory-device_fig20_265727614 (CC BY 4.0) GDDR SDRAM (graphics double data rate SDRAM) provides fast, high bandwidth memory for graphics processing units or GPUs today. There are multiple generations of this: GDDR, GDDR2, GDDR3, GDDR4, GDDR5, GDDR5X, GDDR6 and GDDR6X. HBM (high-bandwidth memory) is an interface standard for 3D-stacked SDRAM chips. HBM was standardised in late 2013 and has been used in some GPUs and also large-scale CPUs like the Intel Ponte Vecchio (see page 20 of the August 2022 issue). The current version of HBM is HBM2, standardised in early 2016. All DIMM generations have had the option of supporting ‘error correction code’ (ECC). ECC memory has a chip on the memory module to detect and correct errors. It is typically used in mission-critical applications and is more expensive than regular memory for the same speed and capacity. Also, the maximum speed available for ECC memory is usually lower than for nonECC memory. Starting with the latest DDR5 standard, all modules have on-die ECC error correction, but it is not true ECC, which requires a separate chip. Buffered/registered memory Fig.37: how data is recorded and read back in a holographic memory scheme. Original source: https://slideplayer.com/slide/6143717/ 20 Silicon Chip Australia's electronics magazine Buffered memory is intended for servers and high-end workstations, while unbuffered memory is designed for PCs and low-end workstations. With buffered memory, there is a memory address register chip between the memory chips and the system memory controller, reducing the load on the memory controller. Buffered or registered memory (they mean the same thing) is more expensive and more stable than unbuffered memory, Unbuffered memory contains no memory address register, and the memory controller has direct access to the onboard memory chips. Unbuffered memory is also known as conventional or unregistered memory. The main advantage of buffered memory is that, as the CPU/chipset is no longer communicating with the DRAM chips directly, the length of the traces is no longer so critical, so there can be more DIMM sockets, and they can be located further from the CPU socket(s). While a typical desktop or laptop computer using unbuffered DIMMs usually has two or four slots, servers can have 8, 16 or more DIMM siliconchip.com.au slots for huge memory capacities (in the terabytes). Because buffered/registered RAM is usually a bit slower and more expensive, there isn’t much point in using it unless you need a high capacity. Future memory concepts The technologies discussed below are still being researched, but provide an interesting look into what types of memory could be present in the future: Molecular memory In molecular memory, chemical molecules are used as the data storage element. Data is stored as one or more reversible conformations of the molecular structure of certain molecules, as shown in Fig.36. Holographic memory Holographic memory (Fig.37) is a potential data storage medium of the future. In a holographic device, data is stored throughout the device’s volume in the form of an optical interference pattern. More than one datum can be stored in the same volume by being written and read from different angles. Special photosensitive crystals or thick photosensitive optical coatings on discs can be used as the storage medium. In holographic memory multiple bits can be read simultaneously, while in conventional memory only one bit can be read at a time. Racetrack memory Racetrack memory was an experimental concept invented by IBM in 2008. The idea is that the entities that contain the bits of information, magnetic domains, are circulated along a loop of wire (the racetrack) 200nm (200 millionths of a millimetre) across and 100nm thick under the influence Table 6: Comparison of various memory types. SRAM DRAM Flash MRAM FeRAM PRAM Read speed Fastest Medium Fast Fast Fast Slow Write speed Fastest Medium Slow Fast Medium Very slow Scalability Good Limited Limited Good Limited Good Cell density Low High Medium Medium to high Medium High Non-volatile No No Yes Yes Yes Yes Complexity Low Medium Medium Medium Medium Medium Write endurance Infinite Infinite Limited Infinite Limited Limited Table 7: Primary memory capacity of early computers Computer Year Processor EDUC-8 kit (EA, Aug 1974 – Aug 1975) 1974 Logic chips 4 (7400-series) 256b 32kiB Altair 8800 kit (Popular 1975 Electronics, Jan 1975) 8080 16 1kiB 8kiB Commodore PET 1976 6502 16 4kiB or 8kiB 96kiB Tandy TRS-80 1977 Z80 16 4kiB 48kiB Apple ][ 1977 6502 16 4kiB 64kiB Atari 400 and 800 1979 6502 16 4kiB or 8kiB Sinclair ZX80 1980 Z80 16 1kiB 16kiB IBM PC XT 1981 8088 20 16kiB 256kiB+ Commodore 64 1982 6510 16 64kiB 384kiB+ Apple Lisa 1983 68000 24 1MiB 2MiB Amiga 1000 1985 68000 24 256kiB 8.5MiB of an electric field and past read/write devices, as shown in Fig.38. This is somewhat similar to delay line memory (described last month) and magnetic bubble memory but much smaller. If developed, these devices are expected to have a higher density and be faster than flash memory. They would be produced as a ‘universal memory’ device to replace hard disks, DRAM and flash (something that Fig.38: the concept of racetrack memory. The bits of data continuously move on a wire loop past a read/write device as indicated by the meter. Original source: www.nicepng.com/maxp/u2q8e6i1o0r5r5u2/ siliconchip.com.au Australia's electronics magazine Bus width Default RAM Max RAM Intel’s 3D XPoint product Optane did achieve). Skyrmions A skyrmion can be considered a ‘swirl’ of magnetisation that moves through a magnetic material. As it moves, it temporarily changes the magnetic orientation of individual atoms. They are under consideration as memory devices that would be implemented as a form of racetrack memory. Fig.39: a commercial Everspin parallel interface toggle MRAM in a 32-pin SOIC package. It’s available with an 8- or 16-bit interface, 256kb to 32Mb capacity and memory retention of more than 20 years. February 2023  21 Relevant videos and links ● There is a video about making a modern nickel delay line memory to replace a mercury delay line in a replica of an early (1949) computer. It is titled “EDSAC delay line storage - early computer memory” and is at https:// youtu.be/9BA4AyvlKnM ● Comments about Alan Turing’s idea of using gin in a delay line memory unit: siliconchip.au/link/abhy ● A video that goes into some detail about the exact workings of bubble memory is titled “The SBC-85 1-Mbit Magnetic Bubble Memory board for the SBC 85 Single Board Computer” and is at https://youtu.be/yOe-iNIZR0E ● Video titled “What’s a skyrmion?” at https://youtu.be/3s3cmGjxPVc ● Australia’s first hobby home computer, the EDUC-8, was designed by Jim Rowe and published in Electronics Australia in 1974. It was based on two Fairchild 93415 1kbit static RAM chips plus discrete logic ICs. ● There is a modern EDUC-8 emulator; see the video titled “Electronics Australia EDUC-8 Non-microprocessor Kit Computer ROMs” at https://youtu. be/hhGDCakBNZs The emulator supports paper tape or cassette tape storage. Details of this emulator can be viewed at www.teenix.org/educ8.html and also see www.sworld.com.au/steven/educ-8 ● The world’s first mass-produced electronic calculator was the IBM 604. Its input and output were via punched cards, and the original design had up to 40 program steps. See the video titled “Running IBM 604, 1948 computer” at https://youtu.be/n58bu4CMSb8 ● Another interesting video, titled “Magnetic core memory from 40 years ago”, is at https://youtu.be/H98gfQJHZLU It can be considered a reinvigoration of the magnetic bubble memory concept. Spin-Transfer Torque RAM STT-RAM is a proposed technology that manipulates a property of charge carriers such as electrons, called spin, to store information. Magnetoresistive RAM MRAM was developed in the mid1980s and is a commercial product (Fig.39), although it presently occupies only a niche market as its advantages have not surpassed other available products. It is a non-volatile memory, but the hope is that one day it will become a universal memory. In MRAM, memory bits are stored as magnetic domains, as shown in Fig.40. There are two magnetic plates, one a permanent magnet (green) with a set orientation and the other of variable orientation (red). Between these plates, there is a thin insulating layer (blue). To set the variable layer to a particular magnetic polarity and write a bit of information, a current is passed through it via the transistor structure in the base. To read the cell, a current is passed through it. Due to a phenomenon called tunnel magnetoresistance, the resistance of the cell depends on the magnetic orientation of the variable layer. Resistive RAM Fig.40: a simplified version of the MRAM cell structure. Original source: https://w.wiki/5zxT (GNU FDL) RRAM is a proposed type of non-­ volatile memory where a change is bought about in the resistance of a normally-insulating dielectric (insulating) material. A conducting pathway is generated through the insulator using oxygen ions and vacancies from an oxide layer which are analogous to electrons and holes in a semiconductor. The elements are sometimes described as “memristors”. PMC (Programmable Metallisation Cell) memory Fig.41: the structure of an electrochemical cell memory element. Silicon dioxide’s chemical formula is SiO2, while silicon nitride is Si3N4. 22 Silicon Chip Australia's electronics magazine PMC memory, also known as CBRAM or conductive-bridging RAM, relies upon electrochemical reactions to create or dissolve a metal conducting bridge between two electrodes – see Fig.41. PMC memory is non-volatile, has the advantage of radiation hardness in space applications, and has 100 times less energy consumption for write operations than other memory technologies such as flash. 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BY NICHOLAS VINEN HE TOPICS COVERED T IN THIS ARTICLE include how data is stored in memory, more details on the differences between SRAM and DRAM, how DRAM timings vary, the relatively recent development of high-capacity on-CPU DRAM and some of the new features included in the latest DDR5 memory standard. Memory encoding schemes Last month’s first article on Computer Memory described how text could be stored (eg, as ASCII characters). Early computers had so little memory and such limited I/O that numbers and text were realistically the only things they could handle. But of course, these days, computers store and display so much more. Here are some other things that can reside in RAM. each byte can store two decimal digits, 0-9 and 0-9. This is somewhat wasteful as only 100 different values can be stored in a byte rather than 256, but it makes conversion for display easier and ensures correct rounding of dollars and cents etc. For decimal numbers, floating point is the most common storage method. It is similar to numbers in scientific notation, such as 6.02 × 1023 or 1.602 × 10-19. This allows the handling of tiny and huge numbers in the same amount of space. Floating point numbers are usually stored as 32 or 64 bits with one sign bit (positive or negative), an exponent (the power to which 10 is raised) and the mantissa (6.02 or 1.602 in the previous examples). For 32-bit floating point numbers (‘single precision’), the exponent is eight bits and the mantissa is 23 bits. For a 64-bit floating point number (‘double precision’), the exponent is 11 bits and the mantissa is 52 bits. 2. Still Images In the early days of computer graphics, images were typically stored as a grid of numbers. The most basic displays are monochrome and can only turn pixels on or off, so each pixel is allocated a bit and usually 0=off and 1=on. For greyscale images, each pixel is assigned a number, possibly a byte. In that case, 0=black and 255=white with 254 shades of grey in between. Colour images usually require between 16 bits (two bytes) and 32 bits (four bytes) per pixel. Those bits are typically split up into three numbers, one for red intensity, one for green and one for blue. Those three colours are A bitmap (“raster”) image next to a vector version of the same image. Vector images scale better than bitmaps. This is because bitmap images are created via filling individual pixels with a single colour, while vector images are composed of mathematical paths. JPG is an example of a bitmap image format, while SVG is Vector (300% scale) a common vector format. 1. Numbers Whole numbers (integers) are usually stored in binary, with one byte allowing a range of 0-255 or -128 to +127 to be stored. Two bytes (16 bits) can store an integer of 0-65535 or -32768 to +32767, while four bytes (32 bits) can store 0 to about four billion, or negative two billion to positive two billion. Financial systems sometimes use BCD (binary-coded decimal), where Bitmap (300% scale) 24 Australia's electronics magazine Silicon Chip Fixed-point decimal numbers are sometimes used where speed is more critical than precision or range. These are basically integers (whole numbers) with a fixed scaling factor, eg, 1/1000, in which case the integer 1234 represents the decimal 1.234. siliconchip.com.au mixed in varying proportions to create a range of colours. Images intended for printing might use four values: CMYK (cyan, magenta, yellow & black) rather than RGB (red, green & blue). High dynamic range (HDR) images might use even more bits, up to 16 per attribute or 48-64 bits per pixel. Usually (but not always), all the colour information is packed into an integer multiple of the byte size to make reading/writing pixels in the memory buffer easier. For 16-bit RGB colour images, such as those used on small TFTs, the 16 bits are usually allocated 5-6-5, with six for green and five for red and blue. That’s because the human eye can distinguish more shades of green than red or blue. However, the limited number of 16-bit colours often leads to ‘banding’ in gradients such as a blue sky, so 24-bit colour (8-8-8 or better) is preferred. While bitmaps are conceptually simple, the trouble is that they are large. A 4K (3480 × 2160 pixel) image in RGB with HDR (12 bits per attribute) would take 3840 × 2160 × 3(RGB) × 12(bits) = 296.6 million bits or 37.3MB if stored as a bitmap. So images are usually compressed for storage, eg, as PNG (lossless, preserving the original image perfectly) or JPEG (lossy) files. Still, in memory, images are usually kept as bitmaps for fast access. 3. Vector Images Vector images are generally stored as one or more shapes bounded by lines or splines. A spline is an elegant way to define a curve in 2D or 3D space using just a few numbers. For lines, it’s only necessary to know the x & y coordinates of each end of the line, while splines typically have two endpoints and two control points. The coordinates can be integers (whole numbers), floating-point or fixed-point numbers (decimals). Along with the bounding information, there will usually be colour/pattern information, transparency data etc. The characters used in fonts are defined this way, as well as many elements in files such as PDF (portable document format), PS/EPS (PostScript) etc. 4. Audio In memory, audio is usually stored as PCM (pulse-code modulation). This is simply a series of numbers representing the audio signal voltage siliconchip.com.au This image shows the motion vectors (as arrows) from a H.264 encoding of the film Big Buck Bunny (Blender Foundation, Peach Movie Project). Motion vectors are used to describe how one image can be transformed into another. These vectors are used to help compress movie formats, see https://w.wiki/62xT Source: https://trac.ffmpeg.org/wiki/Debug/MacroblocksAndMotionVectors sampled at regular intervals. The number of points per second is known as the sampling rate, while the number of bits allocated to each number is known as the bit depth. CD-quality audio has a 44.1kHz sampling rate and 16 bits per channel (two for stereo). 48kHz is another common sampling rate. Other rates you might see are onehalf, one-quarter, double or four times either value (44.1kHz or 48kHz). A bit depth of less than 16 generally means noisy audio, while lower sampling rates also lower audio quality. 24-bit samples are sometimes used for audio mastering but are not really necessary for consumer audio, even hifi. As with still images, audio files can take up a lot of memory, so they are usually compressed when stored, such as in the FLAC format (lossless) or MP3/AAC (lossy). 5. Video In the most basic sense, a video is just a series of still images (possibly accompanied by audio). Therefore, it can be encoded in the same way as still images but with more than one, which is the idea behind the (quite old) Motion JPEG encoding scheme. The thing is that most video frames are very similar to the last frame, so the amount of memory required is drastically reduced by storing the first frame, then the difference between each subsequent frame. Think of a video camera being panned or zoomed; in the case of panning, a frame will be mostly like the previous frame but shifted slightly. Australia's electronics magazine The distance and direction can be encoded in just a few bytes, compared to kilobytes or megabytes for a whole new frame image. In practice, a complete frame (‘I frame’) is occasionally stored, mainly to prevent image degradation over long periods and allow for seeking in the video. But most frames are stored only as differences, primarily in the form of ‘motion vectors’. Such encoding schemes include the MPEG series: MPEG, MPEG-2 and these days, MPEG-4, which encompasses a wide range of such algorithms. For example, digital TV and BluRays mostly use either MPEG-2 or, more recently, MPEG-4. The audio part of the video is encoded much the same as a regular audio file, usually in chunks between the video frames. Because video data can take up so much space, it is generally stored compressed in this way in both RAM and more permanent storage. A frame buffer is initialised with a bitmap of the first frame. Then, during playback, the motion vectors are applied to that buffer to produce a second buffer containing the next frame image. The process then repeats, alternating between buffers (sometimes more than two). 6. 3D Models 3D models are similar to the vector images described above, only with a third dimension. A three-dimensional ‘mesh’ of points, lines and/or splines describes the shape of an object to be shown on the screen, such as a person, vehicle, building etc. Flat image February 2023  25 in memory similarly to mathematical graphs, allowing the shortest or fastest route to be computed and directions to be generated. SRAM vs DRAM A 3D polygon mesh of a dolphin. Source: https://w.wiki/62xp ‘textures’ are mapped onto the faces of that shape and wrapped around. Lighting effects are applied to make the resulting rendered images look more realistic. Simulated bones can alter the shape of the mesh to produce realistic motion; hair and fur effects can be added on top, and so on, creating a three-dimensional moving image that, these days, can approach photo-­ realistic levels. Much computation is required to turn all that data into high-resolution images in real time, which is why modern graphics processor units (GPUs) are usually the computer’s most powerful (and power-hungry) part. It’s also why GPUs tend to have incredibly fast RAM, sometimes with a total bandwidth exceeding 1000GiB per second! 7. Maps Maps used for purposes such as navigation are effectively also vector data. Streets and intersections are joined and labelled, and ‘metadata’ is added, such as how many lanes are on a given road, which ones can turn, whether a street is one-way etc. They are stored SRAM memories are simple to use. To read a byte/word from an SRAM, the address data is first applied to the chip. Cascaded logic within the SRAM chip activates certain lines within, depending on this address, so only the memory cells at that address are enabled. When the chip’s read-enable line is activated, the data within those cells are fed to the data outputs. After a specific time (usually measured in nanoseconds), it has stabilised and is ready to be accessed by the processor. Writing to an SRAM memory is similar. The address lines are driven to select the address to be written, and at the same time, the data to be written is applied to the data input lines (shared with the data output). When the write-enable line is activated, the selected cells within the SRAM will change their state to match the states of the data inputs. Again, the cycle time is usually measured in nanoseconds. The processor can read and write addresses in any patterns it needs to, and the timings do not change. Reads and writes can proceed at the maximum frequency the chip supports (eg, 100MHz for a 10ns SRAM). Using a DRAM chip is far more complicated. Rather than having just a few timings to consider (like the SRAM’s address and data setup times), a DRAM has dozens of different timings. That’s because, to achieve a high density, the bits in the SRAM chip are arranged in rows and columns, and only one row in a bank can be active at a time. It takes some time to change active rows. To switch rows, first, the old row must be deactivated with a PRECHARGE command (and corresponding tRP delay). Then a new row must be activated with the ACTIVE command, incurring a further delay of tRCS. Then a column can be read or written after a further delay of CL. The tRP, tRCd and tCL delays usually are similar numbers of clock cycles (eg, around 14 cycles for DDR4). There is also typically a longer delay between activating a row and being able to deselect it. So constantly switching between rows to read values scattered throughout the memory is much slower than sequential or random reads within the same row. A few different approaches are used to overcome this. One is to have a highspeed SRAM cache within the processor that stores the most commonly accessed memory locations. That way, cache lines can be rapidly read or written to the main DRAM memory in bursts, taking advantage of the ability to read and write sequential addresses in the DRAM quickly. Also, by having multiple banks within each DIMM, while one bank cannot operate due to row switching delays, data going to/from another bank can pass over the memory interface. So with enough processor cores constantly reading and writing different banks, the interface is never idle. If that seems confusing, don’t worry, it gets a lot more complicated! Modern DRAM has timing parameters that include the following: CAS, RCD, RP, RAS, RC, FAW, RRDS, RRDL and CCDL. That isn’t even a complete list. These timings are stored in a small EEPROM on each DIMM for a range of clock speeds to allow the memory controller to be appropriately configured at boot time. Memory timing commands An example map taken from OpenStreetMap (www.openstreetmap.org/) showing a route (in blue) from Circular Quay to the Sydney Opera House. 26 Silicon Chip Australia's electronics magazine tCL CAS latency tRCD RAS to CAS delay tRP Row precharge time tRAS Row active time For more details, see: https://w. wiki/62vt & siliconchip.au/link/abi2 siliconchip.com.au Despite all this data being available, to achieve the best performance, it’s still necessary for the memory controller to spend some time ‘training’ the RAM (basically, experimenting with different timings until it finds an optimal combination that works). That is why a newly built computer can sometimes take quite some time (tens of seconds) to boot for the first time, or after a BIOS reset. One interesting aspect of DRAM performance to consider is due to the availability of multiple banks and the frequent delays in accessing data within a given bank. Consider a system with many CPU cores running in parallel, accessing DRAM over a shared bus. Some cores will be blocked at any given time, waiting on memory access. However, at the same time, other cores may be accessing data stored in different banks in the DRAM. They can therefore utilise the otherwise idle shared bus to transfer that memory. When those transfers complete, the other banks will likely be ready, and the bus will be handed over to the other cores. Therefore, having many CPU cores not only increases the total processing power available but also leads to better utilisation of the memory bus. This is why sometimes, splitting a task up among many cores can improve performance even when it is primarily limited by memory performance. On-package DRAM Fast on-chip SRAM caches have been around for a long time, at least as far back as 1989, when Intel launched A 2KiB SRAM (Static Random Access Memory) chip used in a NES clone. SRAM is significantly faster, but more costly than DRAM so it’s commonly used in small quantities such as in the L1 and L2 cache of a computer CPU (from a few KiB to a few Mib). Source: https://w.wiki/63EN siliconchip.com.au Table 1 – Apple M1 & M2 RAM configurations Model RAM capacity RAM chip Bus width Data rate M1 8GiB or 16GiB LPDDR4X-4266 128 bit 68.3GB/s M1 Pro 16GiB or 32GiB LPDDR5-6400 256 bit 204.8GB/s M1 Max 32GiB or 64GiB LPDDR5-6400 512 bit 409.6GB/s M1 Ultra 64GiB or 128GiB LPDDR5-6400 1024 bit 819.2GB/s M2 8GiB, 16GiB or 24GiB LPDDR5-6400 128 bit 100GB/s the 80486 processor with 8KiB or 16KiB of internal L1 cache. However, in November 2020, Apple launched their first range of full computers using processors that they designed themselves, dubbed the M1. These processors and their successors, the M2 series, are unique in today’s market because they do not use external DRAM for storage. Instead, they come with a fixed, fairly large amount of DRAM on a separate silicon die integrated into the CPU package – see Table 1. LPDDR is a variant of DDR (double data rate) DRAM, described in the preceding article, optimised for low power consumption. The main disadvantage of doing this is obvious: you cannot expand the RAM on these machines. Also, the chips are quite expensive to fabricate. However, the performance benefits are significant. While the M1 and M2 cores are individually not especially fast by today’s standards, because the onboard RAM has so much bandwidth and so little latency (the delay between making a request and the memory read/write being performed), they punch well above their weight in terms of performance, at least in certain tasks. Unsurprisingly, memory-­intensive tasks benefit the most from this arrangement, eg, database manipulation. Mathematically-intensive tasks benefit too, but not to the same extent. DDR5 advancements The latest computer memory standard, DDR5, is an evolution of the now-mature DDR4 standard that has been around since 2014. Besides manufacturing process improvements allowing higher speeds at lower voltages, the main enhancements to DDR5 are the addition of local voltage regulation and the splitting of the 64-bit data channel into two 32-bit channels with double the maximum burst length. While DDR4 started at 2133MT/s (megatransfers per second), a typical DDR4 DIMM these days is rated at between 3200MT/s and 4000MT/s. DDR5 starts at 3200MT/s, with a typical DIMM being capable of 4800MT/s A Micro M4TC 128kB DRAM (Dynamic Random Access Memory) chip. DRAM typically uses a single capacitor and transistor to store one bit of data rather than multiple transistors for SRAM. DRAM is much cheaper due to a higher density of components per bit, but in turn uses more power than SRAM. Source: https://w.wiki/63EQ Australia's electronics magazine February 2023  27 and some well over 5000MT/s. For DDR4, switch-mode voltage regulator(s) on the motherboard produce the ~1.2V needed for the RAM chips to operate, fed to them via several edge-connector pins. Instead, DDR5 receives a higher voltage (either 5V or 12V) that is stepped down to the required voltage via an onboard regulator that’s usually in the middle of the DIMM. This has several advantages but primarily tighter voltage regulation, especially when there are transients. The baseline operating voltage for DDR5 is 1.1V with a typical maximum of 1.35V, compared to 1.2-1.6V for DDR4. As for splitting the data channel in two, the goal is to reduce latency when memory is being accessed in a ‘scatter-­ gather’ manner rather than sequentially. Importantly, DDR5 DRAM chips have 32 banks compared to the 16 banks of DDR4, meaning that less bank switching is required, so average throughput is improved. The maximum capacity of a DDR5 DIMM is 512GiB, meaning up to 2TiB of RAM in a four-slot system compared to 128GiB per DIMM for DDR4. In short, while DDR5 is a significant upgrade over DDR4 (as demonstrated by benchmarks and performance tests), that is due to several minor improvements rather than any revolutionary upgrades. Older DDR generations As mentioned earlier, DDR4 came out in 2014. Before that, DDR3 ruled the roost for almost a decade, since 2007. DDR4 was also an evolutionary upgrade from DDR3, again mainly due to process improvements. DDR3 modules typically operated at 1.5V compared to the 1.2V of DDR4, so they used quite a bit more power. Compared to the 2133-5000MT/s of DDR4, DDR3 had a much lower throughput at 800-2133MT/s (and rarely up to 3200MT/s). DDR3 DIMMs also topped out at around 16GiB compared to 128GiB for DDR4. DDR4 also SDR DDR QDR 2 signals per clock cycle Double Data Rate A diagram showing how the clock signal differs between SDR, DDR and QDR. Source: https://w.wiki/63sx 4 signals per clock cycle Quad Data Rate clock cycle Silicon Chip doubled the number of banks from 8 to 16. Going back further, it’s much the same story for DDR2 (released in 2003) compared to DD3. DDR2 operated at even higher voltages (starting at around 1.8V), so it was even more power-hungry and slower at 4001066MT/s. DDR2 also topped out at 8GB per DIMM, although this was very rare compared to the typical 2GB per DIMM. DDR2 brought a significant upgrade from the original DDR standard (released in 1998). With DDR2, the memory interface bus is clocked at twice the rate of the DRAM chips themselves, so four sets of data can be transferred per memory clock cycle compared to two for DDR1. DDR1 DIMMs also had fewer pins (184 vs 240). DDR2 also optionally doubled the number of banks from four to eight. DDR1 DIMMs operated at just 200400MT/s and had a maximum capacity of 1GiB per DIMM, limiting most desktop systems to a maximum of 1 signal per clock cycle Single Data Rate 28 Most DDR2-DDR5 memory (DIMM package) will look similar, with the exception of any fancy heatsinks. DDR1 memory in comparison only has 184 pins versus the 240 pins in DDR2-DDR5 memory. This type of memory is typically used in computers and is a form of synchronous DRAM, which have an external clock signal. The photo above shows a set of four DDR3 modules. clock cycle Australia's electronics magazine 4GiB. They ran at a whopping 2.5-2.6V, more than double what DDR5 needs! 2GiB DDR1 DIMMs might have been sold specifically for servers, but it likely would not register as the correct amount of memory in a typical desktop machine. Conclusion DDR DRAM will be used as the primary memory for computers for some time, until something better comes along; nobody knows when or what that will be. QDR (quad data rate) DRAM, which performs four transfers per clock cycle, was briefly tried by Intel in the mid-2000s but never really took off. GDDRX5 video memory chips from 2016 also had an optional QDR mode. DDR performs one transfer on the negative clock edge and one on the positive, while QDR does the same but also performs transfers during the positive and negative plateaus. However, it seems that the added complexity isn’t worthwhile, given that this does nothing to reduce access latency. These days, the best performance seems to come from a combination of highly parallel DRAM, which provides exceptionally high throughputs, with relatively large and very fast local SRAM caches such as AMD’s “Infinity Cache” on its RDNA2 (128MiB cache) and RDNA3 (96MiB to 384MiB cache) graphics processors (GPUs). 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P 7812 39.95 $ Anderson/USB/Car Accessory Panel Handy power connection panel for flush mounting power connections into cabinets or bodywork. Mounting hole size: 126x30mm Monitor your car battery from your phone! Ensure your battery doesn’t go flat with this handy Bluetooth® battery monitor. Provides live feedback on your vehicle or auxiliary battery, plus handy long term stats. The Ultimate Battery Fuel Gauge. Accurately measures battery voltage, current, power, real capacity and run time of your battery (suitable for any type of chemistry and voltages between 8V to 120V). Includes 50A shunt with 2m cable. 1% accuracy. Cut out dimensions: 53.5 x 37.5mm. Order online at altronics.com.au | Sale pricing ends February 28th Make cable runs easy. SAVE $26 SAVE 28% 89 7 $ ea $ PC1392 S 8747C SAVE $15 85 $ D 5118A Through Wire Cat6A Plugs Dual Cat6A J-Boxes Great for office cabling! Easily surface mounted. Punchdown termination. 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Ideal for data/comms installers. Tests both cable length and integrity in both RJ45 UTP data and BNC coaxial cabling. It’s wiremap system detects short circuits, split pairs and cable lengths up to 350m. Powered by USB rechargeable internal battery. Shop with us on eBay | www.ebay.com.au/str/altronicsaustralia SAVE $50 145 $ Q 1344 Great deals on audio visual. Dynalink® F2 Pro Gaming Headset Professional grade UHF true diversity for crisp, clear vocals SAVE $19 49 $ Multi-platform ready! Suits PC, Playstation, Xbox and Switch with included TRRS adaptor. Offers excellent comfort for long gaming sessions with RGB lighting effects (when USB is plugged in). 2m cable. Handy kit to get started in online content creation! SAVE $70 D 0990A 45 A 2696A A 3087C 3 Way 4K UHD HDMI Switch Switch between 3 HDMI sources such as game consoles, Chromecast, media centres etc. Ultra HD 4K ready. SAVE 25% D 0982 16 Channel Wireless Mic Systems The MaonoCaster Lite provides everything you need to get started in podcasting, live streaming, YouTube & Twitch. Get top quality audio from the included XLR cardioid pick up condenser mic, control all your device levels, effects and music using the mixer buttons. Includes mic, mixer console, USB C cable, tripod, windsock, 3 x TRRS jack cables and monitor earphones. Desk mount microphone arm to suit C 0506 $35.95. NEW! SAVE 16% 299 $ C 8867C 1 x Handheld Mic C 8868C 1 x Beltpack Mic All-In-One Mini Audio Studio For Creators C 9042 $ SAVE $80 169 $ A complete wireless microphone system with your choice of handheld or beltpack mic. Offers wireless freedom when on stage. Plugs into existing PA systems for easy connection. Ideal for clubs, & places of worship. Up to 70m range. 389 $ Internet radio, digital radio & audio streaming in one. Wi-Fi Internet Radio System with DAB+, FM & Bluetooth. A stylish, easy to use receiver with access to over 26,000 global internet stations, plus DAB+ digital radio, FM frequencies and bluetooth streaming from your devices. Digital S/PDIF and analogue RCA outputs SAVE $50 109 $ A 1116 Add Bluetooth to your favourite speakers! ® Why buy new bluetooth speakers when you can add this module to existing speakers? 2 x 25W RMS output. Includes power supply. Superb high power USA designed amplifiers! 22 $ SAVE 10% SAVE $100 3.5mm Lapel Mic Ideal for audio recording on smartphones, laptops, vlogging cameras. 3.5mm TRRS or TRS connection. 2m lead. Condenser type. D 0984 SAVE 28% Biema® High Power Music Amplifiers. SAVE $100 549 499 $ High power non-bridgeable design is perfect for DJs, bands, venues using foreground sound reinforcement. 3 pin XLR and 6.35mm inputs. Speakon & binding post outputs. 2 year warranty. A 4157 2x250W $ A 4155 2x150W 35 Send TV sound to your headphones! 49 $ A 1103B Transmits or receives audio via Bluetooth 4.1. Can be powered via USB on your TV (cable included). Includes 3.5mm & RCA cables. aptX low latency - no lip sync issues! $ A 4199 SAVE $80 Electret 3.5mm Lapel Mic Need to record high quality audio for YouTube or live demos? This 6m electret mic offers excellent audio clarity and 3.5mm TRRS or 6.35mm TS connections. 249 Ideal for small businesses or simple multi-zone home audio systems. Switch between up to 4 different audio sources - connect up to 8 speakers. Toslink digital audio input for TV audio. Great for background music use. Also fitted with 6.35mm microphone connection. Western Australia Build It Yourself Electronics Centres Sale Ends February 28th 2023 Phone: 1300 797 007 Fax: 1300 789 777 Mail Orders: mailorder<at>altronics.com.au 25 $ $ Multi-zone Audio Made Easy! 4x30W Zone Amp » Perth: 174 Roe St » Joondalup: 2/182 Winton Rd » Balcatta: 7/58 Erindale Rd » Cannington: 5/1326 Albany Hwy » Midland: 1/212 Gt Eastern Hwy » Myaree: 5A/116 N Lake Rd SAVE 25% Handy HDMI Wallplate P 5970 With easy back to back fly lead connection. Dual cover fascia plate allows you to match your existing decor. Victoria 08 9428 2188 08 9428 2166 08 9428 2167 08 9428 2168 08 9428 2169 08 9428 2170 » Springvale: 891 Princes Hwy » Airport West: 5 Dromana Ave 03 9549 2188 03 9549 2121 New South Wales » Auburn: 15 Short St 02 8748 5388 Queensland » Virginia: 1870 Sandgate Rd 07 3441 2810 South Australia » Prospect: 316 Main Nth Rd 08 8164 3466 Please Note: Resellers have to pay the cost of freight & insurance. Therefore the range of stocked products & prices charged by individual resellers may vary from our catalogue. © Altronics 2022. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. *All smartphone devices pictured in this catalogue are for illustration purposes only. Not included with product. B 0002 Find a local reseller at: altronics.com.au/storelocations/dealers/ Active Mains Soft Starter Part One by John Clarke High startup current appliances can be dangerous, damage your work, cause brownouts or trip out the circuit breaker when power is first applied. This Soft Starter prevents the high surge current, replacing it with a slow current build-up and reducing the ‘kick’ you get from many tools. H ave you ever used a power tool that rips out of your hand when power is first applied? Or do you have a bank of computers or audio equipment (or similar) that you want to power up together from a single power point? When you do so, sometimes the circuit breaker might trip, forcing you to go to the switchboard and reset it. Tools with a motor that are powered from the mains, such as circular saws, drop saws, hand grinders and routers can make a sudden movement Suitable for fixed or portable power tools rated up to 750W ➠ Switch on at GPO or equipment power switch, including triggers ➠ Relay contacts bypass soft start circuitry at completion for minimal power loss ➠ Six startup rate options from half a second to 10 seconds ➠ Indicators for power presence, soft starting and soft start end ➠ 10A continuous rating ➠ Uses trailing edge phase control ➠ Features & Specifications siliconchip.com.au inrush current can be caused by the appliance or appliances using a toroidal transformer or a switch-mode supply that rectifies the mains supply into a large capacitor or capacitor bank. The capacitance represents a near short circuit when power is first applied, causing a massive surge current. This new Active Mains Soft Starter significantly reduces startup current, solving that problem. It’s designed for devices that might be restarted frequently (like power tools), and its Active Soft Starter ➠ Also suits large amplifiers, computers or other equipment with a high inrush current as the torque from the motor startup rotates the tool. This can cause the tool to move dangerously. In the case of a saw, drill or router, it could move the cutting piece off position and possibly damage your work. You might also hear a nasty “splat” from the switch or plug when the equipment is powered up, indicating that it is being worn out by handling the high inrush current. All of that can be solved with a soft starter like this one. As well as large motors, a high Australia's electronics magazine February 2023  33 Fig.1: the mains waveform is a 50Hz sinewave with a positive voltage half the time & a negative voltage the rest of the time. effect will not diminish, nor will it overheat with multiple restarts if used with equipment within its ratings. You can use the Soft Starter with motorised tools up to 750W and appliances with substantial capacitance. Two ways to use it One way to use the Soft Starter is to have the appliance already plugged into the Soft Starter and switched on. You then switch on power at the GPO (general purpose outlet). That is ideal if you want to power up several appliances together from one power point. In this case, the soft start process begins at power-up (if an appliance is connected). Once the soft starting is completed, it supplies the full mains voltage until it is switched off at the power point. The second method of using the Soft Starter is to have it powered up via the power point (GPO), then switch the appliance on and off with its own switch. This method is ideal when using power tools. For both methods, the soft starter detects when the appliance is switched on and off by monitoring its load current. Soft starting only begins when current flow is detected. When the appliance is switched off, current flow ceases, and the power to the tool is also switched off, ready for another soft start. 750W rating We tested the Soft Starter with various loads and power tools and found that it worked well for tools up to 750W. Some parts got uncomfortably hot when used with tools that draw more than that. Also, the ratings of some of the devices used are only sufficient up to that power level. This is less of a concern when switching equipment like computers and amplifiers, as their inrush current periods are short. In that case, you can comfortably connect up to 10A (2.3kW) of equipment to the output. For power tools above the 750W rating, consider building our Refined Full-Wave Motor Speed Controller that incorporates soft starting (April 2021; siliconchip.au/Article/14814). It is rated to handle 10A and therefore should handle any power tool that plugs into a standard GPO. You could leave it set to full speed all the time and just utilise its soft-starting feature. Presentation The Active Soft Starter is housed in a compact plastic case with an IEC mains input connector at one end and a GPO for the appliance. There are three neon indicators on the top. One shows when input power is applied; the second shows the slow voltage rise to the appliance, while the third lights when the soft start period has ended. The neons are very sensitive and light up with a minimal current applied, so they don’t show the full extent of the soft starting. However, they help to show what the device is doing. Soft starting methods The standard method to reduce the surge current is to add resistance in series with the mains supply, reducing the maximum current. We previously published two soft starters using that method, one in April 2012 (siliconchip.au/Article/705) and the other in July 2012 (siliconchip.au/ Article/601). Both utilised negative temperature coefficient (NTC) thermistors. These devices act as a resistor that reduces its resistance as it heats up from the current flow through it. As it starts cold, the resistance is high, so the current is restricted. Then as the thermistor heats up, the resistance drops and allows more current to flow. In both designs, after some time, the thermistor is bypassed by a relay to provide the full mains supply to the appliance. Bypassing the thermistor after the soft start prevents further heating of the thermistor, allowing it to cool down and be ready to provide another soft start when required. Still, if the appliance is powered up repeatedly at close intervals, the thermistor does not have time to cool between uses, so its resistance can be quite low on successive starts. This means that the soft starting is not as effective in such cases. Another consideration is whether the NTC thermistor can survive longterm use conducting current for an appliance that draws significant current at switch-on. If power is switched on at the maximum voltage point in the mains waveform, the initial current can be extremely high, especially if the thermistor is still hot. Over time, that can damage and possibly destroy the device. While our new Soft Starter does use a thermistor, it also includes phase control that initially applies a small portion of the mains waveform. The proportion of the mains waveform applied to the load increases slowly until the full mains cycle is applied. A relay contact then closes to bypass the soft start circuitry. In doing so, it causes very little heating in the thermistor, so repeated starts are not a problem, and the device is very reliable. Also, the phase control always starts at the beginning of the mains cycle, when the mains voltage is close to 0V. The control scheme used is called trailing-edge phase control and differs from the leading-edge phase control Fig.2: traditional leading-edge phase control varies the switch-on point during the mains cycle but always switches off at the zero crossing. So the earlier it switches on, the more power is applied to the load. …continued opposite 34 Silicon Chip Australia's electronics magazine siliconchip.com.au Warning: Mains Voltage The entire circuit of the Active Soft Starter floats at mains potential and could be lethal should you make contact with it. Don’t assume that because we use isolation between different parts of the circuit that some parts are safe to touch – they are not! The isolation between parts of the circuit is to allow for the differing voltage potentials in parts of the circuit rather than for safety. Fig.3: in the Soft Starter circuit, the N-channel Mosfet is connected to a diode bridge, so current always flows from its drain to its source. That way, its parasitic body diode is never forward-biased. The current paths are shown for when the Active conductor is more positive than the Neutral (i1) and for when the Active is negative with respect to Neutral (i2). method that is often used. Leading edge vs trailing edge Fig.1 shows the mains waveform, while Fig.2 shows these two types of power control. Our mains electricity supply (nominally 230V AC) is a sinewave that repeats 50 times per second (ie, at 50Hz). For phase control, power is applied over a portion of each half of the mains cycle. The waveforms labelled “A” in Fig.2 show the situation when there is a small phase angle of the full sinewave applied to the load. In the left-hand waveform, the voltage is applied to the load from late in the waveform until the zero-crossing. However, on the right, the voltage is applied for a short period beginning from 0V, switching off a little while later. Both waveforms apply the same RMS voltage to the load and have the same area under the shaded portion of the sinewave curve. The difference is that one switches on at the end of the half cycle (leading-edge phase control), while the other switches on at the beginning of the cycle (trailing-edge phase control). Leading edge phase control has been used for around 50 years, mainly for dimming incandescent lamps. That is because it can be implemented using a simple circuit based on a Triac, a semiconductor device that switches on when its gate is driven. It can’t be switched off via the gate; instead, it switches itself off when the current flow through it drops to near zero. However, leading-edge phase control is unsuitable for providing soft starting to loads that charge a capacitor. If a voltage is suddenly applied to that type of circuit, it will create a high surge current, regardless of whether the phase angle it is on for is only a small portion of the mains waveform. The solution is to use a trailing edge phase control instead. The switching device now turns on at the mains zero-crossing where there is little or no potential difference between Active and Neutral. The voltage then rises relatively slowly, following the sinewave shape, to charge the capacitance. Current is drawn from the mains in much smaller and more tolerable pulses. Note that a typical circuit that charges capacitors includes a rectifier so that the capacitor is charged with DC voltage. For soft starting, we increase the duration of the waveform applied to the load over time, so the capacitor charges in small increments as the next cycle has a slightly greater phase length and hence a slightly higher peak voltage. The capacitor is ultimately charged, but at a slower rate than if the full supply were applied at power on. By the way, trailing edge control is also used for dimming LED lamps because they are usually powered by a capacitor-input switch-mode power supply (SMPS). If you are interested in learning more about this, Leo Simpson wrote about leading and trailing edge dimmers in July 2017 (siliconchip.au/ Article/10712). The disadvantage of trailing-edge phase control is that a Triac cannot be used. It needs a switching device that can be switched off at any part of the mains waveform. Fig.3 is a simplified version of how we implement trailing-edge phase control. We use a Metal-oxide Semiconductor Field Effect Transistor (Mosfet) and a rectifier bridge. The Mosfet is connected within the diode bridge, so current always flows from its drain terminal to its source. The current paths are shown for when the Active is more positive than the Neutral (i1) and for when the Active is negative with respect to Neutral (i2). The Mosfet circuit allows us to switch mains power to the load on or off at any point in the mains cycle. Results We measured the startup current for a bank of amplifiers that, when switched on normally, would trip the Trailing-edge phase control achieves a similar result, but instead, the load is switched on at the zero crossing and then switched off at some point later in the mains cycle. The later the switch-off, the more power is applied to the load. siliconchip.com.au Australia's electronics magazine February 2023  35 Scope 1: switching on a bank of amplifiers, the current peaks at 138A until the circuit breaker trips after 6ms. Scope 2: with the Soft Starter, the bank of amplifiers can be switched on without tripping the breaker. Scope 3: the 750W angle grinder draws 40A on the first mains cycle, dropping to 6A after half a second. Scope 4: with the Soft Starter, the angle grinder takes four times longer to spin up and no longer kicks. circuit breaker. We also tested it with a 750W angle grinder. For the amplifiers, the startup load is essentially a bank of capacitors that charges up at power-on. When discharged, they effectively form a short circuit, resulting in a huge current flow as power is first applied. This is shown in Scope 1, with each vertical division corresponding to 50A (10A = 1V here). The startup surge current (sometimes called the inrush current) peaks at about 138A before the circuit breaker trips. The time for the circuit breaker to trip is less than a mains half-cycle of 10ms (we measure 6ms to the small negative spike). Scope 2 shows the startup current for the same load with the Active Soft Starter connected, over a longer period (the timebase is now 50ms instead of 5ms). The is much more subdued, with only small peaks to a maximum of around 17A. The amplifier capacitor 36 Silicon Chip banks are fully charged after about 500ms, hence the drop-off in the current spikes. For the 750W angle grinder, the startup current (Scope 3) peaks at nearly 40A in the negative direction and then about 34A in the positive direction, tapering down to about 6A after 450ms. With the Soft Starter connected (Scope 4, again with a longer timebase), a small initial current rises to about 13A peak after 750ms and tapers to about 5A at the two-second mark. The fact that it takes considerably longer to spin up indicates that it has much less of a ‘kick’ to it. Block diagram Block diagram Fig.4 shows how the circuitry is arranged in the Active Soft Starter. Incoming mains Active (A) passes through a fuse and to the mains output for connection to the appliance Australia's electronics magazine while current transformer T1 monitors the current flow. The incoming Neutral (N) does not directly connect to the output, but instead, goes via the soft-start circuitry comprising Mosfet Q1 and bridge rectifier BR1. The relay bypasses this arrangement after the soft-start period. The Active mains wire passes through the centre of the current transformer T1 twice, forming its primary winding. The isolated secondary winding produces a voltage proportional to the Active current. This is rectified using a precision full-wave rectifier and low-pass filtered to give a smoother DC voltage, then fed to the AN1 analog input of microcontroller IC1. The current measurement is used for two purposes. One is to monitor when the appliance is switched on to initiate soft starting. The other is to determine when the appliance is switched siliconchip.com.au Fig.4: a simplified block diagram of the Active Soft Starter. The soft-start circuitry is connected between the incoming and outgoing Neutral; current flow is monitored in the Active wire so that it knows when to activate the soft-starting procedure. RLY1 bypasses the softstart circuitry once the full voltage has been applied to the load for maximum efficiency. off, to reset the circuitry, ready for the next power-on. Microcontroller IC1 controls all the soft starter functions. It monitors the appliance current, controls the gate of Mosfet Q1 and the coil of the relay, monitors the soft start rate setting potentiometer and also monitors the mains waveform zero-crossing timing. The gate drive for the Mosfet needs to be referenced to the negative terminal of the bridge rectifier, which is neither at Neutral nor Active potential. So For IC1 to drive the Mosfet, there needs to be electrical isolation between IC1 and Q1’s gate. This is achieved using an isolated power supply and an isolated gate driver. The isolated supply is produced via the GP4 digital output of IC1 that delivers a 1MHz, 5.5V square wave. That waveform is stepped up and isolated via transformer T2. After rectification and filtering, the result is a DC voltage suitable for driving the gate of Q1. The Mosfet gate is controlled via the GP0 digital output of IC1. This drives an opto-coupler (IC3) containing an infrared LED that is electrically isolated from the opto-coupler’s siliconchip.com.au optically switched transistor. That transistor controls the voltage at the gate of Mosfet Q1. The isolated drive for the relay coil is via an optically-coupled Triac driver (IC4) that connects the lower end of the coil to the output Neutral. The relay has a 230V AC coil with the top end connected to Active and the bottom end connecting to IC4. IC4 has an internal LED that optically triggers the output Triac. It is typically used to drive the gate of a larger Triac, but for our circuit, we are just using it to power the relay coil. The power supply for IC1 is not shown in Fig.4; its supply is derived via a mains-rated capacitor that acts as a current limiter to a zener diode clamp, resulting in the 5.5V supply voltage. The positive side of this supply is referenced to mains Active. Potentiometer VR1 is used for the soft start rate adjustment. It is connected across that 5.5V supply, producing a varying voltage at the microcontroller’s AN2 analog input. Neon indicators NEON1 lights when there is mains Australia's electronics magazine power at the input. NEON2 is connected across the mains output, so it starts dim and reaches full brightness when the soft start period ends. We call this the “run” indicator. Finally, NEON3 lights when the relay is on after the soft start period completes. This is called the soft start “end” indicator. Circuit details The entire circuit is shown in Fig.5. A lot of the circuitry has already been explained by the block diagram. However, several parts of the circuit haven’t been described in any detail. As mentioned earlier, Triac-­output opto-coupler IC4 drives the relay coil. We are using the MOC3042 with zero voltage crossing detection, so its Triac always switches on when the mains supply is at zero voltage. That is not strictly necessary for our circuit, but it does not hurt. Its internal Triac between pins 4 and 6 is guaranteed to trigger, provided there is at least 10mA through the internal infrared LED between pins 1 and 2. We also include a snubber across the Triac terminals, comprising a 22nF February 2023  37 Fig.5: IC1 is the controlling PIC while generating an isolated Mosfet gate voltage supply by feeding a high-frequency square wave into transformer T2. It controls the Mosfet gate across that isolation barrier using opto-coupler IC3, and it monitors the output of the current sense transformer via the full-wave precision rectifier formed by dual op amp IC2. Two transient voltage suppressors and a zener diode protect Mosfet Q1 from voltage spikes. X2-rated mains capacitor and a 150W resistor, connected in series between its pins 4 and 6. This limits the voltage rise time so that the Triac will not switch itself on when power is first applied to the circuit. The 1MW resistor just discharges the capacitor when power is off for safety. The snubber limits sudden voltage rises across the Triac by charging 38 Silicon Chip over time via the 150W resistor. This prevents the voltage from rising faster than 1000V/μs, which is the maximum dV/dt rating for the Triac in IC4, below which it is guaranteed not to switch on by itself. Another precaution against that is connecting pin 4 of the Triac to the Neutral output of the soft-start circuitry rather than directly to the Australia's electronics magazine incoming Neutral. So when power is first applied, there is no voltage across the Triac. As the soft start process begins, the voltage across it rises at a controlled rate. Protecting Mosfet Q1 As well as a snubber for IC4, there is a 220nF/470W snubber across the AC terminals of BR1 to reduce the siliconchip.com.au magnitude of voltage spikes seen by Mosfet Q1. This also has a 1MW bleeder resistor for safety. This snubber also provides a small current flow when an appliance is switched on before the soft starting process has activated. This is enough current to detect and initiate the soft start. Q1 is also protected against over-­ voltage conditions that could destroy the device; it has a 500V maximum drain-source rating. Two transient voltage suppressors (TVS) are used to prevent the voltage from going over that limit. TVS2 is connected directly between the Mosfet’s drain and source and conducts to shunt voltage at the TVS clamp voltage of 400V (255V AC rectified gives ~360V DC). However, this TVS can be damaged if the over-­ voltage spike has too much energy, so a second line of defence is used. A second TVS, TVS3, is connected in series with a 100W resistor between the Mosfet drain and gate. If the drain voltage rises too high, TVS3 conducts and causes the Mosfet gate voltage to rise, so the Mosfet starts to conduct, shunting the voltage spike itself. Zener diode ZD3 prevents the gate voltage from going over 15V in this case, which could otherwise damage it, while the 100W resistor limits the zener current to a safe level. Current detection Current transformer T1 produces an output current from its secondary winding that’s proportional to the current flow through the Active mains wire. The 10kW loading resistor gives about 4V AC output with a current flow of 1A and one turn of the Active mains wire through the current transformer core. We use two turns through the core, giving about 4V AC with 500mA current through the primary. While the input current to output voltage conversion is not very linear using a 10kW loading resistance, we use the high value to improve sensitivity. A 100W loading resistor would be used instead for this current transformer to measure current accurately. That would provide a more linear relationship but only gives 1V AC for a 10A primary current. Current sense voltage rectification Another transient voltage suppressor (TVS1) clamps the output voltage siliconchip.com.au from transformer T1. This limits the current into the following op amp inputs to a safe level. The output from T1 needs to be rectified to give a DC voltage suitable for monitoring by microcontroller IC1. A precision full-wave rectifier is used, made from dual op amp IC2 and associated resistors; note the lack of diodes. The gain of this precision rectifier is 1.5 times. While it may appear impossible to rectify the incoming AC voltage without diodes, it is possible, provided that the op amp has specific characteristics. The op amp needs to be able to operate with an input below its negative supply rail, and the op amp must be able to pull its output close to that negative supply rail. Here, we are using an MCP6272 dual op amp (IC2). One stage (IC2b) is connected as a unity gain buffer, while the other (IC2a) provides the 1.5 times gain. To understand how the rectification works, refer to Fig.6, where A to E correspond to the waveforms at the identically labelled parts of the circuit in Fig.5. That is assuming that our example waveform is present at point A. Sample waveform A is a 2V peak-topeak sinewave. For the negative half of the cycle, the signal applied to the non-inverting pin 5 input of IC2b via the 15kW resistor will cause the voltage at that pin (point B) to be clamped at around -0.3V due to IC2’s internal input protection diode. The output of IC2b (point C) therefore sits at 0V during negative portions of the cycle, since its negative supply rail is at 0V, and it cannot pull its output lower than that. IC2a adjusts its output (point E) so that the voltage at its inverting input pin 2 (point D) matches the voltage at non-inverting input pin 3 (point C). Since the 10kW resistor from point D to ground has no voltage across it, it plays no part in the circuit during the negative portions of the cycle. With the 10kW resistor essentially out of the circuit, IC2a operates as a standard inverting amplifier with both inputs (points C and D) at 0V. Its gain is therefore -30kW divided by 20kW, which equals -1.5 times. So the -1V peak of the waveform is amplified and inverted to produce +1.5V at point E. The way it works for a positive voltage at the input (point A) is more Australia's electronics magazine complicated. Firstly, the voltage at pin 5 (point B) is reduced compared to the 1V peak at the input. This is because of the divider formed by the 15kW and 18kW resistors, so the voltage becomes 0.5454V (1V × 15kW ÷ [15kW + 18kW]). Point C will also peak at 0.5454V since IC2b is working as a unity-gain buffer producing the same voltage at its output as its non-inverting input. Once again, op amp IC2a adjusts the output voltage (point E) so that the voltage at the inverting input at pin 2 (point D) matches the voltage at the non-inverting input, pin 3 (point C). To determine the resulting voltage, we must calculate the currents through the three resistors connecting to the inverting input of IC2a at point D. 1. The current through the 10kW resistor is the waveform D voltage divided by 10kW. This peaks at 54.54μA (0.5454V ÷ 10kW). 2. The current through the 20kW resistor; with 1V peak at the input (point A), there will be 22.73μA ([1V[A] − 0.54V[D]] ÷ 20kW). So we have 22.73μA flowing into the node at point D via the 20kW resistor and 54.54μA flowing away from that node via the 10kW resistor. The extra Fig.6: these waveforms demonstrate how the active precision rectifier used for current monitoring works. They correspond to the expected waveforms at the points marked A-E on the circuit for the condition where there is a 2V peak-to-peak sinewave at point A, corresponding to a resistive load drawing about 88mA RMS. February 2023  39 input (GP3) is filtered with a 4.7nF capacitor, providing a near-zero voltage when the mains voltage is at zero. IC1’s pin 4 input detects when this voltage changes from being positive to zero or negative and vice versa. The voltage at pin 4 is clamped by the internal protection diode to -0.3V during the negative part of the cycle. For positive excursions of the mains waveform, diode D2 clamps the voltage to about 0.6V above the 5.5V supply or close to 6V. This diode is required since the pin 4 input is not protected with a diode to the positive supply. That’s so this input can be used for programming the microcontroller, where the voltage at this pin needs to go above the supply voltage. A sneak peek at the assembled PCB for the Active Mains Soft Starter, with construction details coming next month. current to balance currents at node D needs to come via the 30kW resistor. This is 31.81μA (54.54μA − 22.73μA). Remembering that voltage at point D peaks at 0.54V, the required voltage at point E is 1.5V (31.81μA × 30kW + 0.54V). So the circuit operates as a full-wave rectifier with a gain of 1.5. The degree of precision depends on the op amp parameters and resistor tolerances. The lower the offset voltage of the op amp and the lower the op amp input bias current, the more accurate the fullwave rectification will be, particularly at low signal levels. Fortunately, we are not overly concerned with absolute accuracy here. We just need full-wave rectification of the incoming AC signal from the current transformer. Scope 5 shows the 1V peak sinewave at the input to the full wave rectifier (point A) on channel 1, shown in yellow. Below that is the full-wave rectified waveform at point E, shown in cyan. A 2.2kW resistor and 10μF capacitor filter the rectified waveform to produce a smoothed DC voltage suitable for the IC1 to monitor via its AN1 analog input and internal analog-to-digital converter (ADC). Mains zero-crossing detection IC1 monitors the mains waveform at the mains Neutral via a 330kW 1W resistor. The voltage at its pin 4 digital Scope 5: the input to the active rectifier at point A and the output below (point E). Note the gain. 40 Silicon Chip Mosfet gate drive To drive the Mosfet gate, we need an isolated DC supply and a method of connecting and disconnecting that supply to the gate. As mentioned previously, these voltages need to be galvanically isolated from IC1. The isolated DC supply is generated by applying a 1MHz square wave to the primary winding of high-­ frequency transformer T2 from IC1’s clock output at GP4 (pin 3). This is ¼ the frequency of its internal 4MHz oscillator. The primary has 10 turns, while the secondary has 48, giving a 4.8:1 voltage ratio. Since the primary is a 5.5V peak-topeak square wave, we can expect the secondary to deliver a 26.4V (5.5V × 4.8) peak-to-peak square wave. After half-wave rectification by diode D3, we obtain a 13.2V DC output that is filtered by a 1μF capacitor. 15V zener Scope 6: the isolated Mosftet gate drive signal. It switches on faster than it switches off due to the isolation scheme. Australia's electronics magazine siliconchip.com.au diode ZD2 limits the voltage to a safe level for the Mosfet gate. The Opto-coupled output transistor of IC3 switches the Mosfet gate on or off. It is driven by the pin 7 digital output (GP0) of IC1. When this is high (at 5.5V), it drives the internal infrared LED of IC3 via a 1.5kW current-limiting resistor. The LED then lights and switches on the output transistor within IC3 that connects the 13.2V DC supply to the gate of Q1 via a 47W resistor. When the GP0 output of IC1 goes low (to 0V), IC3’s LED switches off, so the gate of Q1 is pulled to 0V by the 22kW resistor, switching the Mosfet off. Scope 6 shows the gate drive to the Mosfet when driven for 5ms on and 5ms off at 100Hz. When switched on, the gate voltage is initially 14.3V, drooping to 12.3V over the 5ms period. The voltage droop is due to the 1μF capacitor being loaded by the 22kW gate-source resistor. The switch-on rise time is around 43μs and the fall time is 324μs. The fall time is longer due to the 22kW discharge resistor having a higher resistance than the opto-coupler output transistor and 47W resistor that charges the gate up. Power supply Power for microcontroller IC1 and op amp IC2 is derived directly from the mains using a 470nF X2 mainsrated safety capacitor. The circuit operates by transferring charge to a 470μF capacitor via zener diode ZD1 and diode D1. For one polarity of the mains waveform, D1 is reverse-biased and ZD1 is forward-biased, so the charge from the 470nF capacitor is transferred to the 470μF supply filter capacitor. During the other half of the mains waveform, diode D1 is forward-biased and the zener diode clamps to 6.2V between the +5.5V supply rail and the cathode (K) of D1. Since the forward voltage of diode D1 is about 0.7V, the overall voltage across the 470μF capacitor is limited to 5.5V (6.2V − 0.7V). Next month The follow-up article next month will have all the construction details for the Active Mains Soft Starter, along with the testing procedure and usage instructions. SC siliconchip.com.au Parts List – Active Soft Starter 1 double-sided, plated-through PCB coded 10110221, 159 × 109mm ● 1 171 × 121 × 55mm polycarbonate or ABS enclosure [Altronics H0478, Jaycar HB6218] 1 153 × 107mm panel label 1 10A IEC panel-mount mains input socket with integral fuse holder [Altronics P8324, Jaycar PP4004] 1 10A IEC mains power lead 1 mains GPO socket [Altronics P8241, Jaycar PS4094] 1 Talema AX1000 or AC1010 10A current transformer (T1) ● 1 Hongfa HF105F-4/240A1HSTF 30A 240VAC chassis mount relay, 240V AC coil (RLY1) ● 1 SL32 10015 15A 265V AC NTC thermistor (NTC1) ● 3 plastic-bodied mains neon indicators (NEON1-NEON3; optional) [Altronics S4016, Jaycar SL2630] 1 10A M205 fast-blow fuse (F1) 4 2-way 15A 300V screw barrier terminals (CON1-CON4) [Altronics P2101] 1 100kW linear PCB-mount potentiometer (VR1) [Altronics R1948] 1 8-pin DIL IC socket (for IC1) 1 18 × 10 × 6mm ferrite toroid (for T2) [Jaycar LO1230] Hardware & wire 1 1.25m length of 0.25mm diameter enamelled copper winding wire (for T2) 2 4.8mm insulated female spade crimp lugs 1 350mm length of (blue & brown) 7.5A mains-rated wire 1 200mm length of blue 10A mains-rated wire 1 250mm length of brown 10A mains-rated wire 1 150mm length of green/yellow striped 10A mains-rated wire 1 75mm length of 10mm diameter heatshrink tubing 1 20mm length of 5mm diameter (blue, red & green) heatshrink tubing  1 20mm length of 3mm diameter (blue & red) heatshrink tubing  1 20 × 15mm piece of thermal transfer tape [Altronics H7240, Jaycar NM2790] 2 M3 × 10mm Nylon countersunk machine screws 2 M3 × 15mm panhead machine screws 4 M3 × 6mm panhead machine screws 4 M3 hex nuts 17 100mm cable ties  black tubing can be used instead, if preferred. Semiconductors 1 PIC12F617-I/P 8-bit microcontroller programmed with 1011022A.hex, DIP-8 (IC1) ● 1 MCP6272T-E/SN dual rail-to-rail op amp, SOIC-8 (IC2) ● 1 4N28 or 4N25 opto-coupler, DIP-6 (IC3) ● 1 MOC3042M or MOC3043M zero-crossing triggered Triac driver, DIP-6 (IC4) ● 1 SIHS36N50D-GE3 36A 500V N-channel Mosfet, TO-247 (Q1) ● 1 PB5006 45A 600V bridge rectifier (BR1) ● 1 6.2V 1W zener diode (ZD1) [1N4735] ● 2 15V 1W zener diodes (ZD2, ZD3) [1N4742] ● 1 4KE15CA bidirectional TVS, 400W, 12.8V standoff (TVS1) [Jaycar ZR1160] ● 1 1.5KE400CA bidirectional TVS, 1500W, 342V standoff (TVS2) [Jaycar ZR1180] ● 1 4KE400CA bidirectional TVS, 400W, 342V standoff (TVS3) [Jaycar ZR1164] ● 1 1N4004 400V 1A diode (D1) ● 2 1N4148 75V 200mA diodes (D2, D3) ● Capacitors 1 470μF 16V PC electrolytic 1 220nF X2-rated metallised polypropylene (PP) 2 10μF 16V PC electrolytic 4 100nF 63V or 100V MKT polyester 1 1μF 50V multi-layer ceramic 1 22nF X2-rated metallised polypropylene (PP) 1 470nF X2-rated metallised PP 1 4.7nF 63V or 100V MKT polyester Resistors (all 1/2W metal film ±1% unless noted) 3 1MW 1W ±5% 1 15kW 1 330W 1 330kW 1W ±5% 2 10kW 1 150W 1W ±5% 1 30kW 1 2.2kW 1 100W 1 22kW 1 1.5kW 2 47W 1 20kW 1 1kW 5W ±5% wirewound 1 18kW 1 470W 1W ±5% ● these parts are available as part of a set from the Silicon Chip Online Shop, Cat SC6575, for $100 + P&P. All the other parts are available from Jaycar or Altronics. Australia's electronics magazine February 2023  41 Subscribe to JANUARY 2023 ISSN 1030-2662 01 The VERY BEST DIY Projects! 9 771030 266001 $1150* NZ $1290 INC GST INC GST 30 Q Meter for Inductors 40 How to buIld your own MInI-ItX Pc 50 rasPberry PI PIco w backPack 58 HIgH-PerforMance actIve subwoo fer 80 nougHts & crosses PlayIng MacHIne COMPUTER MEMORY Australia’s top electronics magazine THE HISTORY OF EARLY DATA STORAGE Silicon Chip is one of the best DIY electronics magazines in the world. Each month is filled with a variety of projects that you can build yourself, along with features on a wide range of topics from in-depth electronics articles to general tech overviews. 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Specialty Function Display (Count) QM1632 QM1493 XC5078 QM1594 Clamp Meter up to 600A AC/DC Insulation Test up to 4000MΩ LAN Cable Test with pinout indicator Sound, Light, Humidity & Temp 4000 4000 2000 4000 Security Category Cat III 600V Cat III 1000V Cat III 600V/Cat II 1000V Cat IV 600V/Cat III 1000V Voltage 600V AC/DC 750V AC / 1000V DC 600V AC / 600V DC 600V AC / 600V DC 40MΩ 4000MΩ 20MΩ True RMS • Current 600A AC/DC Capacitance 100mF Resistance Frequency • 200mA AC/DC 10A AC/DC 10MHz Temperature 1000°C Non Contact Voltage • Relative Measurement • 40MΩ 100µF 10MHz 750°C • • • Explore our great range of multimeters, in stock on our website, or at over 110 stores or 130 resellers nationwide. • www.jaycar.com.au/specialtydmm 1800 022 888 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. ADVANCED ADVANCED TEST TEST SMD SMD T EEZERS EEZERS Part 1 by Tim Blythman The SMD Test Tweezers and their successor, the Improved SMD Test Tweezers, are both simple but useful tools. We have developed an enhanced version with many more features and other improvements, such as a larger screen and an easier-to-use interface. I f you have not already built an SMD Tweezers kit, you may be wondering what the fuss is about. After publishing our simple design from October 2021 (siliconchip.com. au/Article/15057) and the following refresh in April 2022 (siliconchip.au/ Article/15276), we were left with no doubt that both variants were very popular, with hundreds of kits sold. Both these designs used a tiny 8-pin 8-bit microcontroller run from a single CR2032 coin cell to probe components by applying voltage via a resistor. The original Tweezers measured resistance, capacitance or diode forward voltage and displayed the readings on a tiny OLED screen. The Improved Tweezers used the same hardware but a microcontroller with more flash memory, allowing us to add extra features, such as the ability to flip the display to suit being used in either hand and an expanded capacitance range. Advancements Both those variants of the Tweezers were designed with small size, low cost and simplicity in mind. They both used just about the cheapest microcontroller and smallest display possible. Given their popularity, we had to produce a follow-up, and knew it needed to be good. To be clear, this is not an incremental change over the first two designs, but a vast improvement. You can see from the list of features that the Advanced Tweezers will do much more than its predecessors. One of the things we looked for in a new microcontroller for the Advanced Tweezers was a 12-bit ADC (analog-­ to-digital converter) peripheral. This would provide extra resolution over the 10-bit ADC that is standard on most 8-bit PIC microcontrollers, such as those we used for the previous Tweezers. We reviewed some of the newer 8-pin PICs in the October 2022 issue (siliconchip.au/Article/15505), and have since started using the PIC16F18146 in some projects. However, we chose not to use an 8-bit PIC for our Advanced Tweezers. Instead, we have chosen a 28-pin 16-bit micro, the PIC24FJ256GA702. It also has a 12-bit ADC peripheral, so we still get the improved resolution. It also has some other interesting peripherals that we’ve put to good use. The Advanced SMD Test Tweezers are a bit bigger than the earlier version but only because they incorporate a larger display and extra pushbuttons. They also have new measuring modes, including an oscilloscope, voltmeter, I/V curve plotter and a tone/square wave generator. 44 Silicon Chip Australia's electronics magazine siliconchip.com.au It isn’t much more expensive than an 8-bit micro, but it is undoubtedly a lot more capable. Importantly, it has much more RAM and flash memory, so we can include many more modes and settings. That extra memory also means that the blocky font used on the earlier Tweezers has been replaced by one that is larger and much more readable. We’ve also used some interesting techniques for probing and sensing. So let’s introduce the various test modes that are available. Modes The earlier Tweezers variants only had a single mode which would try to identify the device under test and display its value. For a resistor or capacitor, it would show resistance or capacitance. For a diode, it would work out the forward voltage and polarity and display both. Dual anti-parallel diodes, such as bi-colour LEDs, would not be detected as they conduct in both directions. The Advanced Tweezers add many more modes, which we will briefly introduce before going into more detail during the usage section of the article (in the second part). Like the older variants, several modes are for characterising components such as resistors, capacitors and diodes. Instead of attempting to identify a device under test, the Advanced Tweezers reports all of its assessments together. This is made possible by using a larger OLED display and removes the possibility of the Tweezers identifying a component incorrectly. There are still dedicated modes for resistors, capacitors and diodes, which each display only one value in a large, clear font, but you need to select them. These modes are especially handy when dealing with surface-mounting capacitors, which typically don’t have any distinguishing markings. The diode mode also provides a low, steady bias current which is only interrupted by the reading cycle. This has the advantage that you know immediately that the LED is working and what colour it is when it lights. Checking the value of hard-to-read surface mounting parts is one of the great advantages of the Tweezers format. It is especially handy for capacitors and LEDs, which often have subtle polarity markings. siliconchip.com.au Features & Specifications ❎ 10 different modes (see modes & options lists) ❎ Runs from a single CR2032 coin cell ❎ Sleep current <1μA ❎ Resistance accuracy ~1% when calibrated ❎ Voltage accuracy ~2% when calibrated ❎ Capacitance accuracy ~5% when calibrated ❎ Adjustable sleep timeout ❎ Adjustable display brightness ❎ Sleep timer can be paused for continuous operation ❎ Display can be rotated to suit left- and right-handed use ❎ Cell voltage displayed in all modes ❎ Auto calibration of some parameters ❎ Works down to 2.4V cell voltage ❎ Standby cell life: equal to shelf life ❎ Operating cell life: typically several hours of use Modes    1    2    3    4    5    6    7    8    9 10 Resistance: 1Ω to 40MΩ, ±1% Capacitance: 10pF to 150μF, ±5%; gives readings up to 2000μF Diode forward voltage: 0-2.4V, ±2% Combined resistance/capacitance/diode display Voltmeter: 0 to ±30V ±2% Oscilloscope: ranges ±30V at up to 25kSa/s Serial UART decoder I/V curve plotter Logic probe Audio tone/square wave generator Oscilloscope options ❎ Voltage ranges: 0-5V, 0-10V, 0-20V, 0-30V, -5 to +5V, -10 to +10V, -20 to +20V, -30 to +30V ❎ Trigger on rising edge, falling edge, both or continuously (auto) ❎ Trigger level settable in 1V intervals ❎ Timebase (per div, 4 divs visible): 1ms, 2ms, 5ms, 10ms, 20ms, 50ms, 100ms, 200ms or 500ms Serial UART decoder options ❎ Baud rate: 110, 1200, 2400, 4800, 9600, 14.4k, 28.8k, 38.4k, 57.6k or 115.2k ❎ 8N, 8O, 8E and 9N data length/parity ❎ 1 or 2 stop bits ❎ active high or active low ❎ text (terminal) or HEX display I/V curve plotter options ❎ six-point sampling, live update, centred on 0V/0mA ❎ vertical scale (per div, four on screen): 1mA, 500μA, 200μA, 100μA or 50μA ❎ horizontal scale (per div, four on screen): 2V, 1V, 500mV, 200mV or 100mV Tone/square wave generator options ❎ frequency: 50Hz, 60Hz, 100Hz, 440Hz or 1kHz ❎ nominal amplitudes (pk-pk): 300mV, 600mV, 3V or 6V ❎ on/off control (defaults to off) Australia's electronics magazine February 2023  45 Fig.1: while the 28-pin microcontroller chip is about twice the physical size of the SOIC-8 parts used for the earlier Tweezers, there are many advantages to having so many available I/O pins. 10 pins are used for probing the tips, giving much more range. Three more I/O pins handle buttons for control and calibration, while the OLED display can be powered down completely using another spare pin. There is now also a digital voltmeter mode, which shows the voltage across the probe tips, up to ±30V. In oscilloscope mode, it can sample at up to 25kSa/s with varying voltage and time scales. It also offers some basic trigger modes. It’s not likely to make your bench ‘scope obsolete, but it could be handy for probing signals in the audio range. The ‘scope mode uses the same ±30V-capable input stage as the voltmeter mode, so it offers the same range. The recent digital oscilloscopes we have reviewed offer a serial decoding utility, and the Advanced Tweezers do too. There is only one input channel, so we can only decode a UART data stream. The Advanced Tweezers can accept and decode a variety of baud rates and data formats. To overcome the limitations of the diode checker only being able to handle single diodes, we have implemented an I/V curve plotting mode. The I/V curve shape will also allow you to categorise many ‘mystery’ components. The logic probe mode can differentiate between a high logic level, a low logic level and a high impedance. It also provides a digital trace so that transient signals and digital waveforms can be seen. Finally, a Tone Generator allows square waves to be delivered at several frequencies and amplitudes. It’s ideal for injecting test signals into The arrangement of the arms and tips is much the same as that for the Improved Tweezers, using the same arm PCBs and gold-plated pins as simple, practical tips. 46 Silicon Chip Australia's electronics magazine audio equipment or a clock signal into a digital IC. If you’re working with audio gear, you might consider having two sets of Advanced Tweezers; one to inject a tone and a second to trace it. The Tweezers also have the great advantage of being battery-operated, allowing them to be used without needing to be referenced to ground. We’ve provided three pushbuttons, giving more control over what the Tweezers are doing and making them easier to work with. This also allows us to add more extensive calibration and configuration options than the earlier variants. Circuit details Fig.1 shows the circuit diagram of the Advanced Tweezers. It has some improvements over the earlier versions that give better accuracy over a wide range of component values and provide better protection to the microcontroller. IC1 is a PIC24FJ256GA702 microcontroller, and its numerous I/O pins allow us to connect to the device under test (DUT) in various ways. However, siliconchip.com.au guaranteeing it draws no current when the Tweezers shut down. We had problems with some apparently faulty 0.49-inch OLEDs drawing too much current in standby mode, so we’re eliminating that possibility with this new design. Measuring resistors & diodes Fig.2: the Advanced Tweezers uses IC1’s internal ADC to measure voltages, using the voltage divider equation to calculate resistances and voltages across diodes. This works much the same as the earlier Tweezers, but with the addition of extra resistances and a 12-bit (instead of 10-bit) ADC to provide more range and accuracy. the design heritage shared with the earlier Tweezers is evident. Like the earlier Tweezers, a coin cell holder (BAT1) provides the nominal 3V supply to the circuit. The three capacitors, and the single 10kW resistor connected to IC1’s pin 1 are essential for any application of this microcontroller. The 10kW resistor pulls up the MCLR pin, allowing normal operation unless a connected programmer/debugger overrides it. This pin and the other pins associated with programming IC1 are connected to CON1 for this purpose. You’ll note that the PGED and PGEC programming pins (pins 4 & 5) are not shared with any other components, making development and debugging much easier. The 100nF capacitors bypass the main chip supply, while the 10µF capacitor bypasses an internal regulator responsible for powering the chip’s processor core. The remaining ten resistors provide the interface between the DUT (connected to the Tweezer tips at CON+ and CON−) and the microcontroller. You might note that there is no direct connection between the tips and the microcontroller; any path is always via at least one resistor. This is another improvement to the design and affords the microcontroller greater protection from the outside world. That’s especially important since we envisage users probing active circuits with the Advanced Tweezers. The 1kW resistors to pins 2 and 26 provide the lowest-resistance path between the microcontroller siliconchip.com.au and external circuitry, so we have protected each of these with a dual schottky diode clamping each to the two supply rails. These shunt excess current away from the I/O pins before any semiconductor junctions within IC1 can conduct current. The three tactile pushbuttons, S1, S2 and S3 also connect to I/O pins on IC1. These pins are normally pulled up weakly to the positive supply internally to the microcontroller, but they go low when the button is pressed so IC1 can sense that. MOD1 is the 0.96-inch (24mm) diagonal OLED display. It is nearly twice as wide and twice as tall as the 0.49-inch (12.5mm) OLED used in the earlier Tweezers, making for a much more legible display packed with more information. Two I/O pins are required for its I2C control interface with the microcontroller. We also use another I/O pin to power the OLED’s VCC pin. That means we can completely disconnect power from the OLED module, Naturally, much of the operation depends on the firmware. Still, before we get to that, we will explain how the microcontroller uses the sensing resistors in different ways to measure various components and voltages. The microcontroller has an internal 1.2V bandgap voltage reference. We measure this using the ADC (with the supply as a reference) and invert the result to calculate the supply voltage. For example, if the 1.2V reference is measured as 40% of the reference voltage, the supply must be 1.2V ÷ 0.4 or 3V. Since the internal bandgap reference can vary by up to 5% from nominal, the exact value of the reference needs to be determined during calibration for improved accuracy. Fig.2 shows the arrangement that is used for probing resistors and diodes. Resistors Ra and Rb could be any two of the 1kW, 10kW and 100kW resistors available, while Rc and Rd have the same options. The micro’s pins can be driven high, low or left floating (in a high-impedance mode). Ra is typically pulled to the supply voltage by driving it high, while Rb is left high-impedance. Similarly, Rd is connected to ground by driving it low, and Rc is also high impedance. Current thus flows from the micro via Ra and into the DUT via CON+, then back to ground via CON− and Rd. Tests are then performed with CON+ pulled low and CON− pulled high to account for reverse-biased diodes. For This view shows the spacing of the OLED module above the main PCB. Note the header pin acting as a reinforcing spacer at one corner of the OLED. This prevents the assembly flexing and causing a short between the two PCBs. Australia's electronics magazine February 2023  47 Screengrabs from part two, showing the Advanced SMD Test Tweezers in operation Screen 5: the AUTO SET tunes three calibration parameters by performing internal measurements with the tips open. It depends on the previous calibration settings being entered and correct. Screen 14: the initial Meter display mode, which can read up to 30V with both negative and positive polarities (with respect to CON+ and CON-). The resolution is 10mV to 9.99V and 0.1V above that. Screen 15: Scope mode is handy, even though there are only 100 horizontal and 48 vertical pixels in the trace area. It samples at up to 25kHz, is suitable for audio use, and has adjustable trigger settings. the following explanations, you can assume that any pins not mentioned are left in a high-impedance state, so they do not affect the calculations. The microcontroller’s ADC (analog to digital converter) peripheral is used to read the voltages on the pins connected via Rb and Rc. With the ADC scaled to use the supply voltage as its reference, the actual value of the supply is not important for resistance calculations. The calculations are made with raw ADC values. For the 12-bit ADC used on the PIC24FJ256GA702, there are 4096 steps, four times as many as with a 10-bit ADC. The calculations make use of the voltage divider equation. Six tests are performed using various combinations of the 1kW, 10kW and 100kW values. These have 2kW, 11kW and 101kW total in series with the device under test for both polarities. The best resolution is when the test and unknown resistors are similar in magnitude, so our algorithm discards invalid results and selects which of the measurements will give the most accurate final value. The two tests with 2kW series resistance are also used for diodes. In this case, the readings are scaled by the previously calculated supply voltage to determine the diode forward voltage. If the DUT voltage is close to the supply voltage, it is assumed that the DUT is not passing current. This will be the case for reverse-biased diodes or when no device is connected. So a diode is only detected if a voltage notably less than the supply voltage is seen in one direction and a voltage close to the supply in the other. In this case, the polarity and voltage are reported. While the CTMU has many applications, what matters to us is that it includes a programmable current source that can be delivered to an ADC pin during sampling. The ‘charge time’ naming comes from the fact that it can be controlled by external triggers and used to measure intervals between those triggers by measuring the amount of charge delivered to a known capacitor. Instead, by delivering a known current over a known interval, we can apply a fixed amount of charge, and with the equations shown in Fig.3, we can measure capacitance. That means we don’t need to resort to complex calculations involving logarithms which are often needed to analyse RC circuits. The 8-bit PIC devices we used for the earlier Tweezers avoided logarithms by using an approximation and limiting the state of charge to regions where the approximation would be most accurate. For this test, Rd is connected to Measuring capacitors Fig.3 shows the different arrangement used to measure the value of capacitors. One of the features of the ADC on this microcontroller is the CTMU or charge time measurement unit. Fig.3: the constant current source of the CTMU peripheral greatly simplifies the measuring of capacitances. It eliminates the need for the processor-intensive logarithmic calculations needed to derive a capacitor value from the time constant of an RC circuit. 48 Silicon Chip Australia's electronics magazine siliconchip.com.au Screen 16: we find the UART Serial Decoder indispensable at times. Like the Scope mode, it is highly configurable in terms of baud rates, bit depth and data polarity. This shows the TXT view. Screen 17: the Serial Decoder also offers a hexadecimal mode, useful for seeing binary data and control codes. Framing or parity errors are shown, which can help to determine the data format. Screen 18: while Diode mode cannot report dual diodes such as bicolour LEDs, the I/V Plotter shows both polarities. The current and voltage scales can be zoomed in for more detail. ground and Ra is connected to the CTMU current source. An initial ADC sample is taken, followed by a second sample after a known interval, with the current source active between the two samples. In both cases, 1kW series resistors are used. This is because the resistors will drop some voltage due to the current flowing, and the 1kW resistors will drop the least voltage. Fortunately, it will be the same for the first and second readings, so it will cancel out. Five different currents can be applied, so we can take multiple readings. To extend the range further, shorter and longer durations are used, giving six readings over different orders of magnitude. Like the resistor measurement, the readings near the middle of the range are chosen. High readings are ignored as the current source tends to saturate as its output nears the supply voltage. That would result in inaccurate readings. Since the voltage is the denominator of the equation, lower values are disregarded because this will diminish the resolution. Higher values lead to closer steps between their respective reciprocals and thus better resolution. The capacitance calculation depends on the supply voltage, CTMU current and time, so the expected accuracy is not as good as for resistance or diode voltage. Still, with calibration, it should be within 5%. Between measurements in the resistor and capacitor modes, the 1kW resistors in each group are pulled low, and the remaining pins are left floating. Apart from minimising current flowing in or out of floating pins, this also serves to discharge any connected capacitor, so it is ready for the next measurement cycle. One exception is in diode mode. In this case, the CON+ terminal is pulled high instead of low to provide a bias to light an attached LED, allowing it to be visually checked. A light-­emitting diode connected in the forward direction will illuminate except for the period when the reading is done, when it will appear to flicker off briefly. Fig.4: the Meter and Scope modes use a set of four fixed resistors to provide a biased divider capable of measuring voltages above and below the Advanced Tweezers’ supply rails. The circuits on the left and right are equivalent. siliconchip.com.au Australia's electronics magazine Scope and meter modes Another arrangement is used for the scope and meter modes that allows them to read voltages outside the Tweezers’ supply rails. Four more 1kW resistors are put into play. Of each pair, one is pulled high at the micro end and the other low. This situation is shown on the left of Fig.4, with the simplified circuit to its right being functionally equivalent. Each tip is thus subjected to a 20:1 voltage divider biased to half the supply voltage. Readings are taken by measuring the difference in the voltage between V1 and V2 and multiplying by 21. With a nominal 3V supply, we can measure up to around 30V (differential) between CON+ and CON−. Biased differential inputs allow positive and negative voltages to be measured. It’s possible for current to flow With three pushbuttons, calibrating and changing modes is much easier than earlier version of the Tweezers. February 2023  49 Screengrabs from part two, showing the Advanced SMD Test Tweezers in operation Screen 19: the Logic Analyser shows whether it detects a high, low or high impedance logic level. A scrolling chart also shows a brief history, making it easier to see transients and repeating patterns. Screen 20: like Scope mode, the Tone Generator is handy at audio frequencies or as a simple clock generator. It can produce square waves at five different frequencies and four different amplitudes. Screen 21: the Auto screen is only one of ten pages but encompasses and surpasses the abilities of its predecessors. It shows resistance, capacitance, diode polarity and forward voltage. through the unused 1kW and 100kW resistors if the applied voltage is greater than the supply voltage. The current through the 1kW resistors is shunted to the supply rails by D1 and D2. The 100kW resistors will conduct much less current, and this will flow through the microcontroller’s internal protection diodes. These unwanted currents dictate the useful upper voltage limits of the scope and meter modes. Voltages beyond those limits could cause damage to the microcontroller. Damage could also occur if excess voltage is applied while the pins are being driven (as for resistor, capacitor and diode modes), since these currents will now flow through the chip’s internal output transistors instead of the external and internal protection diodes. We found that one of our earlier prototypes was running cells flat even when not being used; this was because the damaged microcontroller was drawing excess current in sleep mode. If you find your Tweezers are going through cells excessively, that could be why. So care must be taken only to apply higher voltages in modes when the Tweezers expect it. This was not a concern with the older Tweezers designs, as they did not have any modes to measure externally applied voltages, and were only designed for use with passive devices. Modes that expect digital signals, such as the logic analyser and serial decoder, simply pull CON− to ground via its 1kW resistor. CON+ may be left floating or weakly pulled up or down by the 100kW resistor to detect the difference between high, low and high impedance logic levels. self-contained program that is called upon during the program loop. Each makes the measurements it needs and displays the results. The buttons are checked and flags are set for each mode to process in accordance with its operation. Firmware The firmware program on IC1 is responsible for initialising all the peripherals and the OLED display. It coordinates the measurements, reads the pushbuttons and controls the display as needed. Apart from the main program loop, a timer interrupt is set to fire about three times per second, triggering display updates at a comfortable rate. The code is modular, and each of the individual modes is much like a Power consumption The processor runs at a modest 4MHz instruction clock (down from the maximum possible 16MHz) to minimise power consumption and thus, the load on the coin cell. We could not maintain the desired screen update rate at lower speeds than this. During some of the scope mode’s sample periods, the clock is sped up to 16MHz to allow faster ADC sampling rates. There are also periods where no urgent processing is needed, in which case the DOZE feature is activated. The processing core runs at an even lower fraction of its maximum speed, reducing power usage even further. There is a timer counting off the timer interrupt. When this expires, a routine is called to power off the OLED and put the peripherals and I/O pins The hole at upper left is for a Nylon M2 screw to prevent children from removing the coin cell. While it would be quite difficult for them to remove it anyway, we want to ensure it is safe. 50 Silicon Chip Australia's electronics magazine siliconchip.com.au Screen 22: the Res screen provides the same resistance information as the Auto screen but in a larger font, which is handy for checking and sorting through different resistor values. Screen 23: the Cap screen works similarly, displaying just the measured capacitance in large text. It’s perfect for working out which part is which amongst a pile of unmarked SMD capacitors. Screen 24: the diode screen is similar to the Diode display on the Auto screen but a bias is applied from CON+ to CON− between tests. This lets you quickly check the polarity and operation of LEDs. into a low-power state, after which the processor goes into the lowest-power SLEEP state. By completely powering off the OLED, we avoid any possibility that it is not in its lowest possible power state. The OLED modules we used in the earlier Tweezers have a sleep mode that initially appears quite effective but sometimes had a current draw that crept up higher than expected. Interrupts triggered by a change in the switch states are used to wake up the processor while it is stopped. It resumes by doing much the same as when it first initialises, since the peripherals have all been put into lowpower modes too. The SLEEP mode keeps the RAM contents, so resuming from sleep will retain all the same mode settings and parameters. Our measurements during SLEEP recorded a consistent current draw around 700nA, much lower than the earlier Tweezers variants. At these levels, the cell’s self-discharge is likely to be more significant than the actual circuit current. We also sought to minimise current draw during normal operation; this is typically in the single-digit milliamps, depending on the operating mode. This is critical, as the amount of usable capacity for a coin cell (as measured in mAh) is higher with a lower current draw. So higher consumption not only reduces the time that a given cell capacity can be used, but also tends to reduce that capacity. The internal resistance of a coin cell is of the order 20W, so a current in the milliamps will also reduce the voltage available to the circuit by a noticeable amount, around 0.1V. Apart from its internal controller, the OLED only draws current for lit pixels, so there is the option to adjust the brightness and thus compromise between visibility and power consumption. The OLED is typically the greatest drain on the battery. The OLED dictates the 2.4V minimum voltage as it tends to fade and flicker below that level. The microcontroller will work down to around 2V, but running this low also limits the effective sampling range of the ADC. We initially used a pretty thick font for some of the displays. By changing to a lighter font with thinner strokes, we reduced the current by over 3mA in some modes! We found that the display was perfectly visible indoors at a reduced brightness, so we have set the default brightness to be somewhere in the lower end of its range, prolonging cell life and reducing the voltage drop. You can increase the brightness via the settings if necessary, eg, for use in very brightly lit areas. siliconchip.com.au Next month Because this is a reasonably complicated instrument (at least in terms of its modes and features), we don’t have space in this issue for the full construction, calibration and usage details. That will all be covered in the final article next month. Some screengrabs showing the Tweezers in operaSC tion are shown above. Parts List – Advanced SMD Test Tweezers 1 double-sided main PCB coded 04106221, blue (28 × 36mm) 2 double-sided arm PCBs coded 04106212, blue (100 × 8mm) 3 gold-plated header pins (for tips and OLED support) 1 PIC24FJ256GA702-I/SS microcontroller programmed with 0410622A.HEX (IC1) 1 0.96in 128×64 I2C OLED module, blue/cyan or white (MOD1) 2 BAT54S dual series schottky diodes, SOT-23 (D1, D2) 2 100nF 50V X7R ceramic capacitors, SMD M2012/0805 size 1 10μF 6V X7R ceramic capacitors, SMD M2012/0805 size 2 100kW ⅛W 1% SMD resistors, M2012/0805 size 3 10kW ⅛W 1% SMD resistors, M2012/0805 size 6 1kW ⅛W 1% SMD resistors, M2012/0805 size 3 small SMD two-pin tactile switches (S1-S3) 1 surface-mount 32mm coin cell holder (BAT1) 2 100mm lengths of 10mm diameter clear heatshrink tubing 1 5-pin right-angled header, 2.54mm pitch (CON1; optional, for ICSP) 1 label (optional; see Fig.8 next month) 1 M2 × 6mm Nylon screw 2 M2 Nylon nuts 1 CR2032 or CR2025 lithium coin cell Advanced SMD Test Tweezers Kit (SC6631) The kit includes all the parts listed in the parts list (except coin cell & CON1), with the microcontroller pre-programmed. It is available for $45 + P&P. Australia's electronics magazine February 2023  51 How I made a 30mm desktop Spark-Gap Tesla Coil by Flavio Spedalieri My Solid-State “Flame Discharge” Tesla Coil project from the February 2022 issue (siliconchip.au/Article/15196) worked well but lacked the iconic metal toroid ‘top load’ that most people think of when they hear “Tesla Coil”. So I built an even larger device, that while still quite small, is more traditional! This device generates hazardous voltages! While we are not providing instructions on building or operating a Tesla Coil in this article, we advise caution if you build or operate a similar device. All parts of the Tesla Coil operate at lethal voltages and can deliver enough current to stop a heart or cause serious burns. You can also suffer RF burns if you come close to or contact the discharge terminal, even when no discharge is apparent. Always ensure that you are nowhere near the breakout point when the unit is powered up. Keep all parts of your body (or anyone else’s) clear of it until power has been switched off and the discharge stops. Remember that high voltages can still be present even when no discharge is visible. Electromagnetic interference warning This Tesla Coil is an RF generator. The input power is up to 180W and the spark gaps are broadband RF radiators. During operation, it can cause RF interference over a wide range of frequencies, especially the MF band, including the AM broadcast frequencies, MF amateur band and some mobile phone frequencies. Operation within a Faraday cage is advisable. 52 Silicon Chip Australia's electronics magazine siliconchip.com.au B uilding a full-size Tesla Coil is a significant undertaking. Therefore, in August 2020, when my motivation started to peak, I decided to make a small-scale but traditional Tesla Coil. It is traditional both because it is capped with a metal torus and it uses a spark gap-based oscillator. That oscillator drives the transformer that generates the extremely high voltages (tens of kilovolts) required for breakout. While my February 2022 article explained how to build your own very small Tesla Coil, this article is more of a story describing how I built a somewhat larger Coil. I won’t go back over the theory of Tesla Coils that I presented in the February 2022 issue, but I will quickly recap it to explain how this one differs from that earlier version. A Tesla Coil is a type of resonant transformer invented by Nikola Tesla (patented on the 25th April 1891). It transforms relatively low-voltage AC (a few hundred volts to a few kilovolts) to very high voltages (tens of kilovolts to megavolts) via two LC (inductor-­ capacitor) tuned resonant circuits that are loosely inductively coupled. The primary LC circuit comprises the ‘tank’ capacitor, primary coil (inductor), and a ‘switch’ to complete the circuit. The primary circuit can be switched by several methods; In a ‘classic’ Tesla Coil, a basic spark gap is used (see Fig.1). Other topologies use vacuum tubes while, in modern dual-resonant solid-­ state Tesla Coils (DRSSTCs), solid-state transistors (IGBTs or Mosfets) are employed. That latter configuration is what I used in my February 2022 project. The secondary LC circuit comprises Photo 1: the secondary coil has close to 38 turns per centimetre. the secondary coil (the large central tower that is iconic to a Tesla Coil), and the ‘top load’, which provides the capacitance and a place for the high-voltage breakout to occur. In this case, the capacitor begins to charge when power is applied to the primary circuit. Eventually, the voltage across the capacitor increases to the point that the air in the spark gap breaks down. The energy in the capacitor then discharges across that gap and through the primary coil. The energy then oscillates back and forth between the capacitor and the primary coil at a high frequency that is determined by the capacitor value and the primary coil’s inductance. A Tesla Coil’s ability to generate very high voltages and long arcs (streamers) is due to a process known as resonant voltage rise occurring in the secondary LC circuit. Tesla coils can be scaled up to produce many millions of volts. New design concept My initial idea was to build a small Tesla Coil using an arc lighter or neon sign transformer (6kV/30mA) power supply as the high-voltage source. I had some suitable components at hand, including 3nF 20kV AC rated capacitors, a ‘doorknob’ ceramic capacitor, plenty of 0.25mm diameter enamelled copper wire and a 107mm diameter, 27mm high aluminium toroid. Fig.1: a circuit showing one of the most basic arrangements of a Tesla coil. Fig.2: the output data from the JavaTC software that I used to help me design the Tesla Coil. siliconchip.com.au Australia's electronics magazine In the very early stages of the project, I considered a 50mm diameter secondary coil. However, it would have required so much wire that I would have had to special-order a large spool. My local Jaycar Electronics store had a small spool of 0.25mm diameter enamelled copper wire. Given the available length and the wide range of available diameters of PVC tubes, I spent several hours calculating a secondary form that would allow for around a 4:1 aspect ratio. The final design was a 33.5mm diameter, 132mm high coil of the Jaycar wire on a 30mm PVC former. Winding the secondary I cut a 160mm length of 30mm PVC tube to give approximately 10mm of clearance at each end. I then sanded the PVC and sealed the surface with two coats of UltiMeg 2000 electrical varnish (siliconchip.au/link/abha). I used a hand drill to hold the form and slowly guided the wire onto it, taking ~2.5 hours. During the next few days, I coated and sealed the secondary with several coats of clear varnish. I measured 38 turns per centimetre (Photo 1), very close to the 37.88 calculated (shown in Fig.2), giving close to 500 total turns. I sealed the ends of the secondary form using FR-4 (unclad PCB). The construction techniques I used for the SECONDARY COIL OUTPUT DATA Secondary resonant frequency Angle of secondary Length of winding Turns per unit Space between turns (e/e) Length of wire H/D aspect ratio DC resistance Weight of wire Effec. series inductance (Les) Equiv. energy inductance (Lee) Low frequency inductance (Ldc) Effec. shunt capacitance (Ces) Equiv. energy capacitance (Cee) Low frequency capacitance (Cdc) Topload effective capacitance Skin depth AC resistance Secondary Q 1618.28 90 13.2 37.88 0.00936 52.62 3.94 17.6699 0.024 1.848 1.931 1.879 5.233 5.009 8.014 3.997 0.0562 88.3825 213 kHz deg° cm cm mm m :1 W kg mH mH mH pF pF pF pF mm W February 2023  53 Tesla Coil Specifications Primary ] Capacitor: 3nF, 20kV AC ] Tap: 4.25 turns ] Tap frequency: 1527kHz ] Tap inductance: 2.23μH ] Total inductance: 13.5μH Secondary ] Turns: ~500 ] Resonant frequency without toroid: 2489kHz ] Resonant frequency with toroid: 1708kHz ] DC resistance: 19.2W ] Inductance: 1720μH Toroid ] Major diameter: 107mm ] Minor diameter: 27mm ] Calculated capacitance: 4.62pF ] Calculated breakout: 80.62kV Neon Transformer ] Power supply output: 6kV <at> 30mA (180W) ] Primary resistance: 11W ] Secondary resistance: 12.7kW (6.3kW to centre tap) ] Secondary impedance: 200kW secondary are the same as for much larger (high-performance) coils; no part of the winding can penetrate the former. I terminated the ground end of the winding via a copper tab, while the top of the coil is supported by a Nylon screw that I epoxied to the top plate before sealing the secondary. I finished the ends of the windings with black electrical tape and gave the secondary several more coats of clear varnish. I decided upon a coupling method that would allow the secondary to plug into the overall system, allowing a modular approach and safe storage of the secondary when not in use. The coupling also serves as the electrical ground connecting point at the base of the secondary, as shown in Photo 2. With the secondary complete, I characterised it using an oscilloscope and signal generator. Its DC resistance is 19.2W, while its resonant frequency is 1708kHz with the toroid and 2489kHz without it. At this point, I decided that it was going well enough that I would build a high-quality instrument where the aesthetic aspect was important. I also switched from the idea of using the arc lighter to a neon sign transformer (NST) that I had acquired, rated at 6kV and 30mA (180W). Additional calculations suggested that the resonant capacitor should be 15.9nF, with a larger-than-­ resonant (LTR) capacitor being 240nF. Still, I pressed on with the initially selected 3nF capacitor as I could always increase the capacitance later. Using a neon sign transformer meant that some additional components would be required: a protection filter (‘Terry Filter’), power factor correction (PFC) capacitor and an EMI line filter. Primary construction Photo 2: a coupling was added at the base of the secondary so that it could easily be removed when not in use. It also serves as a ground connection. 54 Silicon Chip The next phase of the project was the design and construction of the primary coil, supports and platforms to mount all the main coil components. Some of the crucial criteria when working with high voltages at high frequencies are sufficient clearances (to minimise arcing and insulation breakdown), selection of appropriate materials suitable for electrical work and fastening techniques. I selected “SwitchPanel Type X” as the main support material for the primary coil. It is a fibre-reinforced impregnated phenolic resin designed Australia's electronics magazine Photo 3: a conical primary (30°) was decided on, with an adjustable platform made from hardwood. for electrical insulation (siliconchip. au/link/abhb). I ordered three sections for the coil supports from Vale Plastics, all 180mm × 180mm, with one panel having a 50mm central hole to allow it to clear the coupling. The primary design took considerable analysis, considering the electrical parameters, size and shape (flat spiral, vertical or conical). Due to the way the primary coil’s electromagnet flux is presented to the secondary coil, I decided on a 30° conical primary (see Photo 3). The field of a conical primary coil is more uniform over the secondary coil’s aspect. At the widest point (outermost turn), the primary width is approximately the same as the secondary height (~140mm). I used a 2.14mm diameter copper capillary tube with an inter-turn (edge-to-edge) spacing of 5mm (7.14mm to the centres), giving a total of 10.5 turns for tuning flexibility. The mounting platform of the primary coil should be adjustable to allow for fine-tuning of the coupling to the secondary. I started building it by making the four support wedges, cut from hardwood. I attached them to the SwitchPanel Standard Soldering Ball Soldering Fig.4: the components for the filter were soldered using a technique called “ball soldering”. This technique helps to minimise corona losses at high voltages. siliconchip.com.au using Loctite two-part epoxy, which has good gap-filling characteristics. No metal screws or nails can be used, so all fixed components are glued or fastened using Nylon fixings. With the coil made and on the supports, I glued the final timber caps in place with more epoxy for better mechanical support and to improve the aesthetics. I also glued the central coupler into place. A copper strip, central brass screw, nut and acorn completed the grounding termination for the secondary. At this point, the primary and secondary were almost complete. Terry Filter and safety gaps Intending to use a neon sign transformer (NST) as the power supply, I made the secondary windings from very fine wire. Typically, enamel wire insulation is not very good at handling the fast, high-voltage transients generated in a Tesla Coil each time the spark gap fires, which can shorten the life of the NST. One method of protecting the transformer’s secondary windings is a lowpass RC filter network known as a Terry Filter (www.hvtesla.com/terry. html) – see Fig.5. I started building one by mounting the main capacitors and MOVs on FR-4 laminate board. I came up with the component layout, marked holes for drilling using a piece of ‘perfboard’ (prototyping PCB) and drilled the 1mm holes by hand. I soldered the components using a special technique called ‘ball soldering’, where the joints are made as smooth and spherical as possible to minimise corona losses at high voltages (see Fig.4). The safety gaps are made from three brass drawer knobs. I sanded each ball with fine wet & dry sandpaper to remove the clear lacquered coating, then drilled and tapped them with M4 threads. I repurposed three aluminium blocks as the supports. I drilled and tapped each block with an M4 thread to mount them onto the FR-4 substrate. The position of the two left/right balls can be adjusted for correct operation of the safety gap (ie, so the air gap will break down at an appropriate voltage). You can see how this arrangement is mounted on the Terry Filter assembly in Photo 4. I made the high-voltage cables that connect to the coil itself using 7.5mm2 siliconchip.com.au Fig.5: the protection filter circuit (Terry Filter) for the Tesla Coil. Photo 4: the safety gap uses three brass knobs mounted to the Terry Filter circuitry (components placed but not yet wired up). The knobs were mounted onto aluminium blocks and set up so that their positions can be adjusted. Australia's electronics magazine February 2023  55 t0 Photo 5: after mounting the Terry Filter onto a plate of SwitchPanel Type X, a test was performed to verify the operation of the safety gaps. OFC stranded power cable with two layers of PTFE tape applied. Heatshrink tubing was added, followed by an additional layer of PTFE tape and a final layer of heatshrink tubing. Readily-available white PTFE (plumbing tape) has a high dielectric strength of around 60-70kV/mm (see siliconchip.au/link/abhc). Common high-density PTFE plumbing tape has a density of about 0.3g/cm3 and a nominal thickness of 0.1mm (siliconchip. au/link/abhd), so it has a dielectric strength of about 6-7kV. I mounted the Terry Filter and safety gaps onto a 150 × 250 × 12mm plate of SwitchPanel Type X. I made the electrical connections to the filter with brass hardware and acorn nuts, while the connection to the Tesla Coil is via the two aluminium blocks on the left and right sides. Photo 5 shows my tests to verify the operation of and adjust the safety spark gaps. Main spark gap & tank circuit With the Terry filter finalised, I moved on to the main spark gap and the layout of the tank circuit components. The performance of a Tesla Coil is determined by the performance of the spark gap, which acts as a momentary switch that completes the circuit between the capacitor and the primary coil. The capacitor’s energy is discharged into the primary coil when the gap conducts. A spark gap is a simple device, but the dynamics of its operation are complex. The distance between the electrodes 56 Silicon Chip t1 t2 Fig.6: the times labelled t1 & t3 are the first and second primary notches – the times when the current in either the primary has fallen to zero and the spark gap can be quenched. t3 t0: gap fires. t0 > t1: primary energy transfers to the secondary. t1: all energy is now stored in the secondary (1st primary notch). t1 > t2: remaining energy in the secondary transfers to the primary. t2: all energy is now stored in the primary (1st secondary notch). t2 > t3: remaining energy in the primary transfers to the secondary. t3: all energy is now stored in the secondary (2nd primary notch). This process repeats until the gap stops conducting (quenches). Once quench occurs, an exponential ringdown will occcur. sets the breakdown voltage of the spark gap. With a static gap, the width would be set at the power supply line voltage (6kV in this case) and would be at the correct setting with the gap firing at the full applied voltage of the transformer. This project utilises a static gap arrangement; however, much larger coils employ rotary spark gaps, giving better control and performance. For a coil of this size, that would be slight overkill. The main spark gap consists of the electrode holders and the actual electrodes. For this project, I have employed 6.35mm diameter parallel-­ faced tungsten rods. Tungsten is a favoured material for spark gaps due to its high melting point and, therefore, resistance to burning and pitting. When the gap fires, the arc ionises and heats the air within it, making it highly conductive. Once the gap conducts, it will continue to conduct even when the capacitor’s voltage has dropped below the initial breakdown voltage. This can allow the energy from the secondary to return to the primary; this energy will be lost as heat, sound and light, reducing the coil’s performance. Extinguishing a conducting spark gap is known as ‘quenching’ and is essential to maximise the energy retained in the secondary. Quenching is the action of the spark gap going open-circuit and ceasing conduction, and can only occur when the current through a conducting gap falls to a certain point. Then, the arc may no longer be sustained, and the Australia's electronics magazine air within the gap cools enough to prevent arc-over as the voltage begins to rise again on the next cycle. The total energy transfer time is the number of half-cycles it takes at the resonant frequency to transfer all the energy from the primary circuit to the secondary (not including losses). Ideally, we would like to trap all the energy within the secondary, as any energy that returns to the primary will contribute to inefficiency and, thus, less energy for the output arcs. The only way to trap the maximum energy within the secondary is to stop the gap conducting as soon as the current in the primary circuit reaches zero. Known as the ‘first (primary) notch’, this period is very short, and the amount of energy still within the 1st secondary notch Secondary Envelope 2nd secondary notch Exponential ringdown 3rd primary notch 2nd primary notch 1st primary notch Fig.7: this waveform shows the third notch quenching, meaning the third primary notch is where the gap stopped conducting, followed by the secondary ringdown. siliconchip.com.au Photo 6: a centrifugal blower fan was used on the main spark gap instead of an axial fan, as it provides superior airflow. Photo 7: the spark gap assembly is composed of two electrode holders mounted on a FR-4 substrate. primary is sufficiently high to keep the gap conducting (see Figs.6 & 7). If the gap continues to conduct, the next available opportunity to open the spark gap is at the next point that the current returns to zero (the second primary notch) and so on. Early quenching of the spark gap may be achieved through various methods, including magnetic quenching (siliconchip.au/link/abhe), air blast (siliconchip.au/link/abhf), vacuum (siliconchip.au/link/abhg) or with a rotary spark gap. Using forced air, a vacuum or a rotary gap allows the gap to cool by removing hot, ionised air from it, reducing the chance of the gap re-­ arcing. I decided to use a centrifugal blower fan (drawing 12V <at> 860mA), as such fans generate high-pressure air flows compared to an axial fan (see Photo 6). I was going to use PWM fan speed control but, in testing, it offered little effective control; therefore, I abandoned that idea. Instead, the fan just runs at full speed during operation. I used a copper bus bar to form the support for the capacitor, with a short copper tube to connect it to one side of the gap. One last detail for the coil is the strike rail, which protects the primary coil and primary circuit components from arc strikes, made from a 2.3mm capillary copper tube (Photo 8). The ground rail must present a low impedance path to RF ground, so I made a clip from a copper saddle that is snug fit onto the strike rail. I then added a grounding post to terminate the secondary ground and the strike rail (Photo 9). The strike rail mustn’t form a closed loop, as would otherwise present as a shorted turn. The strike rail supports are made from 9×9×46mm timber sections with a 2.5mm hole drilled through each support. I sanded and stained these before gluing them into place with Loctite epoxy. I then slid the copper tube into place and used heatshrink tubing to cover the open section. Primary tap point Constructing the primary tap connection was a challenge. Early in the project, I drilled four clearance holes with the idea of bringing the tap wire up through the bases. However, this made it difficult to disassemble and reassemble. So instead, I brought up the tap wire from the side, using a clip made from a modified M205 fuse clip, reduced to create a snug fit. I used a length of copper braid to strengthen the clip and provide a better connection. At this point, I had completed much of the Tesla Coil, but was still waiting Main gap & strike rail The main gap is the critical part of the spark gap oscillator. I cut a phenolic resin plinth as the mounting base for both the spark gap assembly and the connections to the capacitor. The gap itself was formed by mounting electrode holders onto two phenolic support blocks, which I then affixed to a strip of FR-4 substrate. I then attached the whole assembly to the phenolic base (see Photo 7). siliconchip.com.au Photo 8: the outermost copper tubing is the strike rail, which was added to protect the primary from arc strikes. Photo 9: after building this, a clip was added to the strike rail to ground it (shown in the photo at right). Australia's electronics magazine February 2023  57 for the high-voltage bleed resistors (10MW, 10kV) for the main capacitor. I searched Digi-Key’s website and found they stock 100MW 10kV 2.5W Maxi-Mox resistors from Ohmite (MOX-1-121006FE). As well as being available, they had the advantage that a 10MW bleeder resistor would have dissipated 7.2W. Increasing to 100MW reduced that below 1W while still discharging the capacitor to a safe level (50V) in 1.5 seconds. Radio frequency (RF) Earthing One of the more overlooked and important areas with any RF system is the provisioning of a suitable low-­ impedance Earth system. Tesla Coils generate heavy RF currents which must be appropriately distributed to Earth. A sound Earthing system is key to a well-performing Coil as the Earth forms the return path for the secondary side of the LC circuit. So I sunk a 19mm diameter, 2.4m-long Earth rod to 1.8m depth, plus a second ‘domestic’ size rod to 1.2m, bonded them together and connected them to the coil via 25mm2 welding cable. Measurements With the Coil essentially complete, I made some measurements to determine the tuning parameters and confirm the resonant frequencies against my calculations. I measured the resonant waveform period as approximately 124μs, corresponding to the total energy transfer time; the first notch came after approximately 8.2μs. Power supply I mounted the neon sign transformer to a 12mm-thick 200 × 300mm base made from SwitchPanel. I added two timber stand-offs to mount the Terry Filter module (Photo 10). I then added the control box, which includes a TE Connectivity 3A EMC-series EFI/RFI line filter to prevent interference from feeding back into the mains. The control box also contains a small mains switchmode power supply (SMPS) to provide 12V <at> 1.2A for the quenching fan. The control box also includes a mains switch, a switch for the fan and a switch to supply power to the transformer, lamps to confirm active power to the circuits and a 2A thermal magnetic circuit breaker (Photo 11). This control box is used with a variac to provide fully adjustable control of the Coil. First tests Following nearly three months of development, I fired it up for a momentary test. I noted a flashover from the end of the primary winding to the strike rail, occurring several times at the same location, causing a tracking burn. I realised this was due to the end of the primary not being smoothed off and sealed. Another overlooked area was that I hadn’t sealed the supports with varnish such as Ultimeg. I repaired the area, smoothed the copper end and applied epoxy resin to seal it. After cleaning up the tracking burns, I also sealed the support. I added more epoxy to all key areas at the primary junction and supports and applied several coats of Ultimeg electrical varnish to the timber supports. I left the primary coil assembly to cure for several days. In hindsight, considering the pulsed nature of the high-voltage present on the primary coil, timber is not the best material to use. A more suitable material would be a phenolic resin; however, it is expensive in small quantities and with suitable dimensions. SwitchPanel Type-X could be used to create the smaller parts, but it would need to be cut from a larger sheet, which would take a great deal of time. With those repairs and improvements completed, I returned to testing, closing down the spark gap to around 3-4mm for the test. The low-power test was successful, with a nice breakout occurring (Photo 12). I then opened the gap to about 5mm and made another run (Photo 13). It was successful, but I noted some random flashover between the final turn of the primary to the strike rail. I obviously needed to improve the insulation between the strike rail and the final turn of the primary coil. I did that by adding more layers of Ultimeg varnish, as well as adding short lengths of clear vinyl tube around crucial points on the strike rail and final primary turn. I let the varnish cure over a week before getting back to testing. I then ran a full power test, applying the full mains voltage to the NST. In doing so, I tweaked the parallel alignment of the spark gap electrodes. The full power test was very successful, with many streamers forming but no arcing at the support points. Photo 10: the neon transformer was mounted to a 12mm thick base made from SwitchPanel. Timber stand-offs were then used to attach the finished Terry Filter above it. Photo 11: the control box for the Tesla Coil. It contains a mains switch, a switch for the fan, another for the transformer, lamps to confirm activity, and more. 58 Silicon Chip Australia's electronics magazine siliconchip.com.au Top-load upgrade I decided to order a larger toroid from a company based in the USA. It took close to two months to arrive. Their customer service left a lot to be desired, so I don’t want to mention the company’s name. The larger toroid has a major diameter of 152mm, a minor diameter of 38.64mm, a calculated capacitance of 6.61pF and a calculated breakout voltage of 114.74kV. The additional capacitance of the larger toroid required re-tapping the primary coil to bring the primary into tune with the lower resonant frequency of the secondary. A further resonant test using an oscilloscope and signal generator on the secondary coil confirmed the new resonant frequency as 1360kHz. I moved the primary tap by one turn to account for the extra load on the secondary, bringing the system back in resonance. The lead photo shows the result of a full-power test with the larger toroid in place. It generated streamers long enough to reach the strike rail; they are equivalent in length to the secondary coil. I conducted another experiment by simply placing the two toroids on the coil, resulting in longer streamers (Photo 14). Re-tuning the coil was not necessary. Photos 12 & 13: on the left is the initial low-power test with a spark gap of 3-4mm, while on the right was another test run with the spark gap at 5mm. Conclusion It was a lot of work, but I am delighted with how this small Tesla Coil turned out. It was interesting to go through the tuning process that Nikola Tesla and other pioneers would have had to figure out. I also learned that it pays to give special attention to insulating everything when working with such high voltages. Tesla was a genius to have come up with such an elegant way of generating extremely high voltages using the very limited technology available at the time. While building a Tesla coil is not for everyone, they are impressive devices and a must-have in any mad scientist’s laboratory! In memory of My Mum (Zina Spedalieri) was amazed when she saw the original article come to print. Sadly, we lost Mum on 2nd of June 2022, It would have been something for her to see the second article come to print. SC siliconchip.com.au Photo 14: placing the newly bought larger toroid on top of the old toroid resulted in larger breakouts. As I was happy with the result, I eventually had the toroids welded together, then cleaned and sanded them to maximise their appearance and performance. Australia's electronics magazine February 2023  59 SILICON CHIP .com.au/shop ONLINESHOP HOW TO ORDER INTERNET (24/7) PAYPAL (24/7) eMAIL (24/7) MAIL (24/7) PHONE – (9-5:00 AET, Mon-Fri) siliconchip.com.au/Shop silicon<at>siliconchip.com.au silicon<at>siliconchip.com.au PO Box 194, MATRAVILLE, NSW 2036 (02) 9939 3295, +612 for international You can also pay by cheque/money order (Orders by mail only) or bank transfer. Make cheques payable to Silicon Chip. 02/23 YES! You can also order or renew your Silicon Chip subscription via any of these methods as well! The best benefit, apart from the magazine? Subscribers get a 10% discount on all orders for parts. 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Just add a signal source, case, power supply and wiring (see page 37, January 2023) $100.00 VGA PICOMITE KIT (CAT SC6417) (JUL 22) DUAL-CHANNEL BREADBOARD PSU MULTIMETER CALIBRATOR KIT (CAT SC6406) (JUL 22) 110dB RF ATTENUATOR SHORT-FORM KIT (CAT SC6420) (JUL 22) BUCK-BOOST LED DRIVER KIT (CAT SC6292) (JUN 22) SPECTRAL SOUND MIDI SYNTH KIT (CAT SC6261) (JUN 22) RASPBERRY PI PICO BACKPACK KIT (CAT SC6075) (MAR 22) 500W AMPLIFIER HARD-TO-GET PARTS (CAT SC6019) (APR 22) HUMMINGBIRD AMPLIFIER (CAT SC6021) (DEC 21) Q METER SHORT-FORM KIT (CAT SC6585) $85.00 $7.50 $10.00 (JAN 23) (DEC 22) Power Supply kit: complete kit with a choice of red + green, yellow + cyan or orange + white knob colours (Cat SC6571; see page 38, Dec22) Display Adaptor kit: complete kit (Cat SC6572; see page 45, Dec22) $40.00 $50.00 DIGITAL BOOST REGULATOR KIT (CAT SC6597) (DEC 22) NEW GPS(/WIFI)-SYNCHRONISED ANALOG CLOCK (SEP & NOV 22) Complete kit that also includes all optional components (see page 87, Dec22) $30.00 GPS-Version Kit: includes everything in the parts list with the VK2828 GPS module (Cat SC6472; see Sep22 p63) $55.00 WiFi-Version Kit: includes everything in the parts list with the D1 Mini module instead (Cat SC6472; D1 Mini is supplied not programmed, see Nov22 p76) $55.00 - VK2828U7G5LF GPS module with antenna and cable (Cat SC3362) $25.00 LC METER MK3 (NOV 22) Short Form Kit: includes the PCB and all non-optional onboard parts, except the case, front panel label and power supply (Cat SC6544) BUCK/BOOST CHARGER ADAPTOR KIT (CAT SC6512) (OCT 22) $65.00 Includes everything in the parts list (see page 64) except the Buck/Boost LED Driver (see adjacent; Cat SC6292) $40.00 $25.00 Partial Kit: includes the PCB, programmed micro, all SMDs, most semiconductors, PPS capacitors and calibration resistors $75.00 - 16x2 alphanumeric LCD with blue backlighting (Cat 5759) $10.00 Complete kit with everything needed to assemble the board, you just require a few external parts such as a power supply, keyboard and monitor $35.00 Complete kit with everything needed to assemble the board Includes the PCB, programmed micro, OLED and all other on-board parts Complete kit with everything needed to assemble the board Complete kit including all programmed PICs (no case or power supply) Complete kit, includes all parts except the optional DS3231 IC $45.00 $75.00 $80.00 $200.00 $80.00 All the parts marked with a red dot in the parts list, including the 12 output transistors, driver transistors, VAS transistors, input pair (2SA1312), BAV21 & UF4003 diodes, TL431 ICs, 75pF capacitor, E96 series resistors and 10kW 1W resistor $180.00 Hard-to-get parts includes: two 0.22W 5W resistors; plus one each of an MJE15034G, MJE15035G, KSC3503DS & 220pF 250V C0G ceramic capacitor *Prices valid for month of magazine issue only. 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Place an order on our website for a quote. $15.00 PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT TUNEABLE HF PREAMPLIFIER 4G REMOTE MONITORING STATION LOW-DISTORTION DDS (SET OF 5 BOARDS) NUTUBE GUITAR DISTORTION / OVERDRIVE PEDAL THERMAL REGULATOR INTERFACE SHIELD ↳ PELTIER DRIVER SHIELD DIY REFLOW OVEN CONTROLLER (SET OF 3 PCBS) 7-BAND MONO EQUALISER ↳ STEREO EQUALISER REFERENCE SIGNAL DISTRIBUTOR H-FIELD TRANSANALYSER CAR ALTIMETER RCL BOX RESISTOR BOARD ↳ CAPACITOR / INDUCTOR BOARD ROADIES’ TEST GENERATOR SMD VERSION ↳ THROUGH-HOLE VERSION COLOUR MAXIMITE 2 PCB (BLUE) ↳ FRONT & REAR PANELS (BLACK) OL’ TIMER II PCB (RED, BLUE OR BLACK) ↳ ACRYLIC CASE PIECES / SPACER (BLACK) IR REMOTE CONTROL ASSISTANT PCB (JAYCAR) ↳ ALTRONICS VERSION USB SUPERCODEC ↳ BALANCED ATTENUATOR SWITCHMODE 78XX REPLACEMENT WIDEBAND DIGITAL RF POWER METER ULTRASONIC CLEANER MAIN PCB ↳ FRONT PANEL NIGHT KEEPER LIGHTHOUSE SHIRT POCKET AUDIO OSCILLATOR ↳ 8-PIN ATtiny PROGRAMMING ADAPTOR D1 MINI LCD WIFI BACKPACK FLEXIBLE DIGITAL LIGHTING CONTROLLER SLAVE ↳ FRONT PANEL (BLACK) LED XMAS ORNAMENTS 30 LED STACKABLE STAR ↳ RGB VERSION (BLACK) DIGITAL LIGHTING MICROMITE MASTER ↳ CP2102 ADAPTOR BATTERY VINTAGE RADIO POWER SUPPLY DUAL BATTERY LIFESAVER DIGITAL LIGHTING CONTROLLER LED SLAVE BK1198 AM/FM/SW RADIO MINIHEART HEARTBEAT SIMULATOR I’M BUSY GO AWAY (DOOR WARNING) BATTERY MULTI LOGGER ELECTRONIC WIND CHIMES ARDUINO 0-14V POWER SUPPLY SHIELD HIGH-CURRENT BATTERY BALANCER (4-LAYERS) MINI ISOLATED SERIAL LINK REFINED FULL-WAVE MOTOR SPEED CONTROLLER DIGITAL FX UNIT PCB (POTENTIOMETER-BASED) ↳ SWITCH-BASED ARDUINO MIDI SHIELD ↳ 8X8 TACTILE PUSHBUTTON SWITCH MATRIX HYBRID LAB POWER SUPPLY CONTROL PCB ↳ REGULATOR PCB VARIAC MAINS VOLTAGE REGULATION ADVANCED GPS COMPUTER PIC PROGRAMMING HELPER 8-PIN PCB ↳ 8/14/20-PIN PCB ARCADE MINI PONG Si473x FM/AM/SW DIGITAL RADIO 20A DC MOTOR SPEED CONTROLLER MODEL RAILWAY LEVEL CROSSING COLOUR MAXIMITE 2 GEN2 (4 LAYERS) BATTERY MANAGER SWITCH MODULE ↳ I/O EXPANDER NANO TV PONG LINEAR MIDI KEYBOARD (8 KEYS) + 2 JOINERS ↳ JOINER ONLY (1pc) TOUCHSCREEN DIGITAL PREAMP ↳ RIBBON CABLE / IR ADAPTOR DATE JAN20 FEB20 FEB20 MAR20 MAR20 MAR20 APR20 APR20 APR20 APR20 MAY20 MAY20 JUN20 JUN20 JUN20 JUN20 JUL20 JUL20 JUL20 JUL20 JUL20 JUL20 AUG20 NOV20 AUG20 AUG20 SEP20 SEP20 SEP20 SEP20 SEP20 OCT20 OCT20 OCT20 NOV20 NOV20 NOV20 NOV20 NOV20 DEC20 DEC20 DEC20 JAN21 JAN21 JAN21 FEB21 FEB21 FEB21 MAR21 MAR21 APR21 APR21 APR21 APR21 APR21 MAY21 MAY21 MAY21 JUN21 JUN21 JUN21 JUN21 JUL21 JUL21 JUL21 AUG21 AUG21 AUG21 AUG21 AUG21 AUG21 SEP21 SEP21 PCB CODE Price 06110191 $2.50 27111191 $5.00 01106192-6 $20.00 01102201 $7.50 21109181 $5.00 21109182 $5.00 01106193/5/6 $12.50 01104201 $7.50 01104202 $7.50 CSE200103 $7.50 06102201 $10.00 05105201 $5.00 04104201 $7.50 04104202 $7.50 01005201 $2.50 01005202 $5.00 07107201 $10.00 SC5500 $10.00 19104201 $5.00 SC5448 $7.50 15005201 $5.00 15005202 $5.00 01106201 $12.50 01106202 $7.50 18105201 $2.50 04106201 $5.00 04105201 $7.50 04105202 $5.00 08110201 $5.00 01110201 $2.50 01110202 $1.50 24106121 $5.00 16110202 $20.00 16110203 $20.00 16111191-9 $3.00 16109201 $12.50 16109202 $12.50 16110201 $5.00 16110204 $2.50 11111201 $7.50 11111202 $2.50 16110205 $5.00 CSE200902A $10.00 01109201 $5.00 16112201 $2.50 11106201 $5.00 23011201 $10.00 18106201 $5.00 14102211 $12.50 24102211 $2.50 10102211 $7.50 01102211 $7.50 01102212 $7.50 23101211 $5.00 23101212 $10.00 18104211 $10.00 18104212 $7.50 10103211 $7.50 05102211 $7.50 24106211 $5.00 24106212 $7.50 08105211 $35.00 CSE210301C $7.50 11006211 $7.50 09108211 $5.00 07108211 $15.00 11104211 $5.00 11104212 $2.50 08105212 $2.50 23101213 $5.00 23101214 $1.00 01103191 $12.50 01103192 $2.50 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT 2-/3-WAY ACTIVE CROSSOVER TELE-COM INTERCOM SMD TEST TWEEZERS (3 PCB SET) USB CABLE TESTER MAIN PCB ↳ FRONT PANEL (GREEN) MODEL RAILWAY CARRIAGE LIGHTS HUMMINGBIRD AMPLIFIER DIGITAL LIGHTING CONTROLLER TRANSLATOR SMD TRAINER 8-LED METRONOME 10-LED METRONOME REMOTE CONTROL RANGE EXTENDER UHF-TO-IR ↳ IR-TO-UHF 6-CHANNEL LOUDSPEAKER PROTECTOR ↳ 4-CHANNEL FAN CONTROLLER & LOUDSPEAKER PROTECTOR SOLID STATE TESLA COIL (SET OF 2 PCBs) REMOTE GATE CONTROLLER DUAL HYBRID POWER SUPPLY SET (2 REGULATORS) ↳ REGULATOR ↳ FRONT PANEL ↳ CPU ↳ LCD ADAPTOR ↳ ACRYLIC LCD BEZEL RASPBERRY PI PICO BACKPACK AMPLIFIER CLIPPING DETECTOR CAPACITOR DISCHARGE WELDER POWER SUPPLY ↳ CONTROL PCB ↳ ENERGY STORAGE MODULE (ESM) PCB 500W AMPLIFIER MODEL RAILWAY SEMAPHORE CONTROL PCB ↳ SIGNAL FLAG (RED) AM-FM DDS SIGNAL GENERATOR SLOT MACHINE HIGH-POWER BUCK-BOOST LED DRIVER ARDUINO PROGRAMMABLE LOAD SPECTRAL SOUND MIDI SYNTHESISER REV. UNIVERSAL BATTERY CHARGE CONTROLLER VGA PICOMITE SECURE REMOTE MAINS SWITCH RECEIVER ↳ TRANSMITTER (1.0MM THICKNESS) MULTIMETER CALIBRATOR 110dB RF ATTENUATOR WIDE-RANGE OHMMETER WiFi PROGRAMMABLE DC LOAD MAIN PCB ↳ DAUGHTER BOARD ↳ CONTROL BOARD MINI LED DRIVER NEW GPS-SYNCHRONISED ANALOG CLOCK BUCK/BOOST CHARGER ADAPTOR 30V 2A BENCH SUPPLY MAIN PCB ↳ FRONT PANEL CONTROL PCB AUTO TRAIN CONTROLLER ↳ TRAIN CHUFF SOUND GENERATOR PIC16F18xxx BREAKOUT BOARD (DIP-VERSION) ↳ SOIC-VERSION AVR64DD32 BREAKOUT BOARD LC METER MK3 ↳ ADAPTOR BOARD DC TRANSIENT SUPPLY FILTER TINY LED ICICLE (WHITE) DUAL-CHANNEL BREADBOARD PSU ↳ DISPLAY BOARD DIGITAL BOOST REGULATOR ACTIVE MONITOR SPEAKERS POWER SUPPLY PICO W BACKPACK Q METER MAIN PCB ↳ FRONT PANEL (BLACK) NOUGHTS & CROSSES COMPUTER GAME BOARD ↳ COMPUTE BOARD DATE OCT21 OCT21 OCT21 NOV21 NOV21 NOV21 DEC21 DEC21 DEC21 JAN22 JAN22 JAN22 JAN22 JAN22 JAN22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 MAR22 MAR22 MAR22 MAR22 MAR22 APR22 APR22 APR22 MAY22 MAY22 JUN22 JUN22 JUN22 JUN22 JUL22 JUL22 JUL22 JUL22 JUL22 AUG22 SEP22 SEP22 SEP22 SEP22 SEP22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 NOV22 NOV22 NOV22 NOV22 DEC22 DEC22 DEC22 DEC22 JAN23 JAN23 JAN23 JAN23 JAN23 PCB CODE 01109211 12110121 04106211/2 04108211 04108212 09109211 01111211 16110206 29106211 23111211 23111212 15109211 15109212 01101221 01101222 01102221 26112211/2 11009121 SC6204 18107211 18107212 01106193 01106196 SC6309 07101221 01112211 29103221 29103222 29103223 01107021 09103221 09103222 CSE211002 08105221 16103221 04105221 01106221 04107192 07107221 10109211 10109212 04107221 CSE211003 04109221 04108221 04108222 18104212 16106221 19109221 14108221 04105221 04105222 09109221 09109222 24110222 24110225 24110223 CSE220503C CSE200603 08108221 16111192 04112221 04112222 24110224 01112221 07101221 CSE220701 CSE220704 08111221 08111222 ACTIVE MAINS SOFT STARTER ADVANCED SMD TEST TWEEZERS SET FEB23 FEB23 10110221 $10.00 04106221/2 $10.00 NEW PCBs Australia's electronics magazine Price $15.00 $30.00 $10.00 $7.50 $5.00 $2.50 $5.00 $5.00 $5.00 $5.00 $7.50 $2.50 $2.50 $7.50 $5.00 $5.00 $7.50 $20.00 $25.00 $7.50 $2.50 $5.00 $2.50 $5.00 $5.00 $2.50 $5.00 $5.00 $5.00 $25.00 $2.50 $2.50 $7.50 $5.00 $5.00 $5.00 $7.50 $7.50 $5.00 $7.50 $2.50 $5.00 $5.00 $7.50 $7.50 $5.00 $10.00 $2.50 $5.00 $5.00 $7.50 $2.50 $2.50 $2.50 $2.50 $2.50 $2.50 $7.50 $2.50 $5.00 $2.50 $5.00 $5.00 $5.00 $10.00 $5.00 $5.00 $5.00 $12.50 $12.50 We also sell the Silicon Chip PDFs on USB, RTV&H USB, Vintage Radio USB and more at siliconchip.com.au/Shop/3 High-Performance Part 2: By Phil Prosser Active Subwoofer For HiFi at Home Last month, we showed the performance of the new ultra-high-fidelity Subwoofer design and provided all the cabinet construction details. In this final article in the series, we’ll finish off the Active Subwoofer by building and installing its internal 180W amplifier, finishing the wiring, installing the driver and adding some feet. A fter building the Ultra-LD Mk.3 or Mk.4 amplifier, most of the remaining work is in making the custom metal bracket, drilling the heatsink and combining the bracket, heatsink, amplifier and power supply into a compact amplification module. It then slots neatly into the 220 × 170mm rectangular cut-out that you would have already made in the rear of the Subwoofer. If you haven’t already built the amplifier module, it’s best to refer to the original article on the module construction. For the Ultra-LD Mk.3, construction details are in the August 2011 issue (siliconchip.au/Article/1129), while the Ultra-LD Mk.4 construction is in September 2015 (siliconchip.au/ Article/8959). There are some subtleties in certain aspects of the construction, such as how to wind and mount the output filter inductor for the best performance. So we strongly recommend you read the relevant article before or during the Ultra-LD Amplifier module construction. However, read the section on amplifier construction below, before you fit the output devices. You will also need to build the Multi-Channel Speaker Protector but with only one relay. You can also leave off the components surrounding the missing relay. For example, you could install RLY2 and leave off everything to the left of diode D2 and the 100kW resistor above it. With those two modules assembled, and the rest of the components gathered, you are ready to start putting it all together. Fabricating the bracket I used a 3mm-thick panel of aluminium as the main plate for the chassis. To that, I mounted a folded bracket made from 1.5mm-thick aluminium for the transformer and an L-shaped panel for the speaker protector. You can see these panels assembled in Photo 11 (note some differences in the cut-out from the final version). All of the plate amplifier parts mount to those panels, mainly the central bracket. What is needed to build an Active Subwoofer Ultra-LD Mk.3 or Mk.4 Amplifier Mk.3 – July-September 2011; siliconchip.au/Series/286 Mk.4 – August-October 2015; siliconchip.au/Series/289 Multi-Channel Speaker Protector (4-CH) January 2022; siliconchip.au/Article/15171 Timber for the case, acoustic wadding, heatsink, wires and other miscellaneous parts (see the parts list) 62 Silicon Chip Australia's electronics magazine I used nutserts to hold those pieces together as they make for an elegant result (they’re basically threaded rivets). However, you can use machine screws and nuts instead. The L-bracket for the Speaker Protector can be made by bending an aluminium sheet by hand in a vise. The larger bracket for the power supply is trickier; if you do not have access to metal folding equipment, I saw some brackets at our local hardware store that would work. Just remember that the transformer is heavy and the mounting needs to consider shock loads such as being dropped. The power supply is straightforward; its circuit diagram is shown in Fig.14. Mains power comes in via CON1 and passes through fuse F1 and power switch S1 to transformer T1 (which may have a single 230V or dual 115V primaries, depending on which transformer you purchase). Its two 40V AC secondaries connect to bridge rectifier BR1 and a capacitor bank, producing ±57V DC rails. As a subwoofer must deliver large amounts of power for extended periods, we have 16mF of energy storage per rail. This reflects the ‘no compromise’ approach to the design. If you only install two 8000μF capacitors, it will still work reasonably well. The 270W 10W resistor is to drop the voltage to a level suitable for powering the Speaker Protector and also to reduce the dissipation in its regulator. Plate amplifier construction I mounted the Ultra-LD amplifier to the main panel and heatsink combined. In other words, the 3mm base plate is between the output devices and the heatsink. You can see the arrangement in Photo 12. Provided your main panel is free of dents and scratches and the heatsink is mounted to this with a good layer of thermal paste, this will make fabrication easier and contribute to the overall heatsinking capacity. To ensure perfect alignment of the baseplate and the heatsink mounting holes to the transistors, I drilled and assembled the heatsink and main panel before building the amplifier and then mounted the transistors to that before soldering them to the PCB. This ensured that the transistors were perfectly aligned to the mounting holes and PCB. Do not use insulators at this point; we will add them later. Once you have soldered the transistors in like this, you can pull everything apart, knowing it will fit perfectly later on. Heatsink drilling Fig.15 shows where to drill the holes Photo 11: The majority of the plate amplifier parts mount on this bracket. Photo 12: The Ultra-LD Mk.4 amplifier attached to the bracket, ready to be wired up. Fig.14: the subwoofer power supply is about as basic as it gets. I used a 300VA transformer, but it is no longer available, and 250VA is adequate. siliconchip.com.au Australia's electronics magazine February 2023  63 Fig.15 (left): the heatsink drilling details. The heatsink used is the same as in the original Ultra-LD Mk.3/4 articles, but the way the heatsink is mounted is different. Fig.16 (below): the rear plate for the amplifier is made from 3mm-thick aluminium cut and drilled, as shown here. It’s a good idea to paint it black when finished. Ensure the rectangular hole for the rocker switch is only as large as it needs to be for the switch to snap in. in the heatsink. My approach was to mark all holes on the main panel first (see Fig.16), then drill and tap the four corner mounting holes into the heatsink and attach it to the main panel with M3 screws. I then drilled 2.5mm holes through both the main panel and heatsink. This guarantees that the transistor mounting holes are perfectly aligned between both panels. 64 Silicon Chip I then took the heatsink off, tapped and deburred the holes in the heatsink, then drilled and deburred the main panel holes to 3.5mm. Details of the main bracket that attaches to the rear panel and holds the amplifier module and power supply are shown in Fig.17. The speaker protector bracket attaches via two of the heatsink Australia's electronics magazine mounting screws. This is fabricated of 1.5mm aluminium sheet folded at 90°; see Fig.18 for the details. I included a small clamp to hold the 270W 10W wirewound resistor to drop the 57V rails by about 15V. It is wired in series with the positive supply to the Speaker Protector module. Once the metalwork is ready, dry-fit everything first and get your assembly siliconchip.com.au Fig.17 (above): and cut fold this support bracket from 1.5mm aluminium and paint it black. It attaches perpendicular to the rear plate. Fig.18 (below): the larger bracket allows the Speaker Protector to be mounted in the space next to the amplifier. The smaller bracket clamps down the 10W resistor needed to drop the supply voltage to the Speaker Protector. Photo 13: the underside of the plate amplifier with everything in place but not wired up yet. siliconchip.com.au Australia's electronics magazine February 2023  65 plan in mind. Use Figs.19-21 and Photos 12-14 to see how everything fits. At this point, temporarily fit the amplifier board, screw the output devices to their mounting positions without insulators and solder the output devices to the PCB. This gets all the holes lined up. Start final assembly with the terminal block, the transformer, Earth screw and diode bridge. Use a small amount of thermal paste under the diode bridge. Install 15mm standoffs for the amplifier module (only in the two corners furthest from the heatsink), making sure you countersink the hole for the screw that goes under the transformer and use a countersunk head screw. Cut a piece of Presspahn or similar and place it under the terminal strip to ensure that if anything shakes loose from the terminal strip, there is insulation surrounding it. Make sure it is mounted far enough away from the rear panel that it won’t interfere with the wiring to the IEC socket. It only needs to be a three-way terminal to Photo 14: A view of the underside of the completed plate amplifier, showing all the wiring. Note though that this version uses a separate fuse holder and a toggle switch; build yours based on the revised design with the fuse holder in the IEC socket. connect the transformer primaries, including joining them in series. Now mount the capacitors. Keep all the negative terminals facing the same way to ensure a tidy build. Then you can finally mount the amplifier module. Flip the module and fit the amplifier using insulating bushes and washers as described in the August 2011 or September 2015 article. Screw this down to the 15mm standoffs you installed earlier, using shakeproof washers under the M3 screws. Next, install the Speaker Protector Fig.19: a view of the underside of the plate amplifier showing the mains wiring. Be sure to keep these wires short, tie them up and insulate all exposed mains junctions. When mounting the transformer, make sure it isn’t too close to the corner or it could interfere with the IEC mains wiring; this configuration should be used rather than what is shown in the photos on the prototype as it keeps all the mains connections away from the lower-voltage side. 66 Silicon Chip Australia's electronics magazine siliconchip.com.au Photo 15: this is how the amplifier side of the module looks after construction and wiring is complete. on its standoffs. Make sure you have connected a 200mm length of lightduty wire to the power input of the Speaker Protector, as this connector will be hard to get to later on. Remember to wire the 270W 10W resistor in series with the power input for the Speaker Protector. This reduces power dissipation in the regulator heatsink on the protector. This is not strictly necessary if you have a single relay installed, provided you use an Altronics H0655 heatsink on the protector, but it doesn’t hurt either. With everything mounted, most of the remaining work is wiring it up, as shown in Fig.19 (mains wiring), Fig.20 (low-voltage supply wiring) and Fig.21 (amplifier module wiring). Use 7.5A mains-rated cable for all power wiring and insulate all mains connections to prevent accidental contact with high voltages. Note that the final design is slightly different than what’s shown in the photos; instead of using a separate fuse-holder, we’re using an IEC input socket with an integral fuseholder and the toggle power switch is replaced by a rocker switch. That simplifies the wiring and also keeps all the mains parts away from the low-voltage side. So follow the diagrams in that respect, not the photos. You can use the following steps to guide you through the wiring. 1 - Install the Earth lug and connect the green/yellow striped Earth wire from a solder lug to the IEC plug mains Earth [we prefer using crimp eye terminals as, if crimped properly, they are more robust than solder joints Fig.20: while similar to Fig.19, this diagram only shows the lower-voltage (~114V DC, so not that low) wiring for the power supply. It’s best to follow this diagram exactly to avoid the possibility of ripple injection in the DC supply to the amplifier module. siliconchip.com.au Australia's electronics magazine February 2023  67 Fig.21: the wiring to the amplifier module, mounted on the opposite side of the bracket to the power supply. – Editor]. You can and should locate the Earth lug right near the IEC socket; we’ve only shown it further away to avoid clutter in the diagram. The Earth screw must connect the Earth lug to the chassis and nothing else. Make sure there is no paint or other layer stopping the Earth lug from making good contact with the chassis; if there is, scrape it away in that area. Connect the second solder lug to a 10nF capacitor and a short green wire from the capacitor to 0V on the capacitor bank. 2 - Cut the transformer secondary wires to appropriate lengths to reach the bridge rectifier AC inputs. Crimp and plug or solder these to the bridge rectifier. 3 - Using heavy-duty red and white wire, connect the bridge’s positive and negative outputs to the capacitor bank. Optionally, use crimp connectors for the bridge. 4 - Covered the exposed metal strip on the IEC socket with neutral-cure silicone sealant. 5 - Using brown mains-rated wire, solder the Active wire to the mains socket, and from there to one pole of the switch, then back to the terminal block. Make similar connections for Neutral using blue mains-rated wire. Use heatshrink tubing to cover all Photo 16: I used a staple gun to attach a double layer of poly wadding I bought at Lincraft. This is required to dampen rear emissions from the driver and reduce resonances. 68 Silicon Chip Australia's electronics magazine exposed junctions. Twist these wires together and use cable ties to secure them, so that nothing can get loose should a connection fail. We do not suggest using spade lugs to connect to the mains socket (except possibly for the Earth) because space is relatively tight due to the proximity of the transformer. Ideally, the wires should be soldered so they extend upwards and over the transformer body to go to the switch. You shouldn’t need to bend the IEC socket lugs to get extra clearance but it could be done if necessary. You could use crimp spade lugs to connect to the switch since it sits just above the transformer. 6 - Connect the transformer primary winding to the switched mains on the terminal strip. Again, tie wrap these securely. If the transformer has two primaries, join the two windings in series via another terminal on the terminal strip (ideally, between the terminals used for the other primary connections). 7 - Now wire up the capacitors using heavy-duty red and black wire. Join all the capacitor grounds together using heavy-duty green wire, and connect them to the transformer centre tap wires. 8 - Next, take 400mm lengths of red, black and green heavy-duty siliconchip.com.au wire and twist them together gently. Connect this to the +57V, -57V and ground terminals of the capacitor bank, respectively. Route this to the power amplifier power input and trim to length. 9 - Use neutral-cure silicone sealant to stick pieces of plastic sleeving over the exposed ±57V connections on the capacitors at this point. This will save you from a potential (no pun intended) 114V DC shock if you slip and come across them. 10 - Connect the +57V rail from the amplifier to the 270W resistor if you need this, and from the other end of the resistor to the positive input of the Speaker Protector. This can be done using light-duty wire. 11 - Connect the amplifier ground to the GND input of the speaker protector. 12 - Connect the amplifier output to the “AMP” input on the speaker protector. The SPKR terminal goes to the positive side of the driver. 13 - The amplifier ground output goes to the negative on the driver. Final assembly Fig.22: this is how the rear of the plate amplifier will look when you’ve finished. Assembly of the Active Subwoofer is very simple as all the work is in the enclosure and amplifier module. Install thick ply wadding on the sides, top and bottom of the enclosure as shown in Photo 16. Do not block the port as, when working hard, a lot of air is moving through it. Connect the amplifier’s output to the driver using heavy-duty speaker wire, being careful to connect the “+” output of the amplifier to the red terminal of the driver. Then install the amplifier module after sticking foam sealing tape around the edge of the hole in the cabinet. Attach the module with eight 16mm screws. Fig.22 and Photo 17 show how it should look when installed in the cabinet. Finally, install the driver with foam tape around the hole using eight 16mm screws. I stuck large felt feet on our active Subwoofer to protect our floor. This thing is not a lightweight piece of kit! Give your new Subwoofer a light workout to verify that everything is working as expected before you move onto the earth-shaking bass! If you’re using the Sub with the active monitor speakers, see the instructions for adjusting the subwoofer level to match the active monitors at the end of the article on building them. SC Photo 17: A rear view of the finished Sub, slightly different from the final version. siliconchip.com.au Australia's electronics magazine February 2023  69 PRODUCT SHOWCASE ams OSRAM LED devices for automotive exterior lighting Mouser Electronics is now stocking the OSLON Black Flat X LED devices from ams OSRAM. Designed for forward lighting applications, including headlamps, night vision, and laser devices, the OSLON LED devices offer high efficiency and excellent thermal conditions. The OSLON Black Flat X LED series of devices have a high focus on system cost, making them a durable, cost-­ effective option for a wide range of lighting solutions. The 3-chip version (KW3 HNL631. TK LEDs) is a high-­performance LED offering 1350 lumens at 1A. They deliver exceptional thermal performance, allowing for smaller heatsinks. They have an extremely high contrast 1:200 design as a result of black case material and TiO2 casting. The 4-chip version (KW4 HPL631. TK) is an ideal replacement for halogen lamps. Offering up to 2115lm at 1A, they are suitable for a range of automotive functions, including headlamps and low-beam and highbeam applications. The devices are housed in a 7.59mm × 3.75mm × 0.5mm package. The 5-chip version (KW5 HQL631. TK) is the most efficient lead-frame device in the OSLON series, delivering exceptional performance in automotive exterior applications, including halogen replacement. The high-­ efficiency LEDs offer up to 2140lm at 1A, and boast an operating temperature range of -40°C to +135°C. To learn more about the ams OSRAM Black Flat X LED devices, visit siliconchip.au/link/abj2 Mouser Electronics Inc. 1000 North Main St, Mansfield TX 76063 USA Phone: (852) 3756 4700 www.mouser.com The results from element14’s Women in Engineering survey element14 launched the second annual Global Women in Engineering survey in June 2022 to help shed light on women’s experiences, career paths, wider challenges and opportunities in the engineering/electronics industry. The global survey is designed to gain direct insight from all members of the industry to understand current barriers to achieving equality and how to diminish discriminatory practices in the workforce. Key insights from the survey included: • 70% of survey respondents said they would intervene when seeing discrimination. However, the seniority of the person exhibiting discriminating behaviour was cited as the biggest obstacle to intervention. A small percentage believed they would not intervene because it is part of their company’s culture. • Women expressed the belief that they were perceived to be less technically capable than men, but this view was not supported by male respondents. • Men cited that woman “missing out on career development opportunities” was an issue. • 25% of survey respondents said they have never experienced sexism in the industry. • Other discrimination challenges cited some women as obstructing other 70 Silicon Chip women in their career progression, although the barrier was not as great as that presented by men. Self-­promotion by women was highlighted as a key issue in this year’s survey. • Genders think similarly about how to address work/life balance. With regards to pay 12% of men are less likely to say they have seen pay differentials, compared to over 40% of female respondents. • Views were similar on the enforcement of policies. However, there was an overall decrease in enthusiasm for inclusion and diversity initiatives. • More than half of the respondents said providing mentorship and development opportunities to women was important. More than 75% of women felt mentorship helped them in their careers. element14’s eight-week global survey was open to everyone working in the electronics/engineering industry. 75% of this year’s survey respondents were from Europe and North America. There was an even distribution of ages, particularly from 25 to 54 years old (at 74%), and 57% of respondents had more than 10 years of experience. element14 72 Ferndell Street, Chester Hill NSW 2162 Phone: 1300 361 005 https://au.element14.com/ Drop-in replacement for crystal oscillators Directly replace traditional quartz crystal oscillators in your most challenging designs with our robust, high-performance DSC1500 family of MEMS oscillators. The DSC1500 family delivers reliability and ruggedness in a small form factor that is ideal for industrial and portable applications. As a direct drop-in replacement for crystal oscillators, these devices also offer excellent jitter and stability with substantially lower power consumption. The DSC1500 family of MEMS Australia's electronics magazine oscillators strikes a unique balance of jitter performance, size and power consumption: 1ps RMS phase jitter with 20mW of power in a 2.0 × 1.6 millimetre package. You can download the DCS1500 data sheet from siliconchip.au/link/ abj1 Microchip Technology Australia Suite 32, 41 Rawson Street, Epping NSW 2121 Phone: (02) 9868 6733 www.microchip.com siliconchip.com.au IPX R ATEX D Keep your electronics operating in Harsh Conditions WATER RESISTANT SWITCH PANELS FOR BOATS OR RVS FROM 7995 $ Marine Switch Panels LOCKING LATCHES FOR EASY ACCESS • IP66 water resistant • Integrated 6-20A circuit breakers • LED illuminated switches • Pre-wired - easy install 4 Way SZ1906 | 6 Way SZ1907 Sealed Diecast Aluminium Boxes • IP65 dust and hoseproof • Internal guide slots • 6 sizes from 64Wx58Dx35Hmm to 222Wx146Dx55Hmm • Flanged versions available HB5030-HB5050 Industrial ABS Enclosures • IP66 weatherproof • Stainless steel hardware • Supports DIN rail components • 2 sizes HB6404-HB6412 FROM 1395 $ Switches for wet & dusty conditions 19 $ FROM 3995 $ STRONG, SAFE & SEALED 95 EA Durable Metal Pushbuttons • IP67 dust & waterproof • 12V LED illuminated (red, green or blue) • DPDT momentary action • SPDT with blue power symbol SP0800-SP0810 FROM 14 $ 95 Illuminated Pushbuttons • IP65 dust & water resistant • Momentary or On/Off • DPDT SP0741-SP0749 Explore our wide range of harsh environment products, in stock on our website, or at over 110 stores or 130 resellers nationwide. Other harsh environment products include: • 15 x Sealed IP65 Polycarbonate Enclosures • 14 x Sealed IP65 ABS Enclosures • 9 x ABS Instrument Cases with Purge Valves • Range of Waterproof Multi-pin Connectors, including Deutsch-type • Range of Sealed Rocker & Toggle Switches • 10 Waterproof Cable Glands jaycar.com.au/iprated 1800 022 888 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. Using Electronic Modules with Jim Rowe Heart Rate Sensor Module This Jaycar XC3784 kit features an Analog Devices AD8232 heart rate monitor front-end IC which forms the ‘heart’ of this module. It provides a low-cost way to monitor the operation of the heart via an Arduino MCU or similar. It comes complete with a matching three-electrode lead; a pack of additional electrode pads is also available. E lectrocardiograms (ECG) are medical tools for measuring and recording the tiny voltages produced on the skin due to heart muscle activity. By attaching two, three or more electrodes or ‘leads’ to the skin of your wrists, ankle or chest, a professional ECG costing upwards of $5000 can record ECG waveforms to allow a GP or cardiac specialist to check your heart’s health. In the October 2015 issue of Silicon Chip, we described an Arduino-based project which allowed you to do all of this using a Windows-based laptop PC (siliconchip.au/Article/9135). The project was not intended for use in medical diagnosis, but simply for use in exploring the way your body works. It can be fun, as well as educational. You can monitor changes to your heart under various conditions, as it is affected by many things, including emotions, mental and physical activity – even breathing. All of these things can have a demonstrable effect on the heart’s ECG waveform. Being able to show this easily, safely and at a low cost is a bonus. To adapt an Arduino Uno module for sampling the low-level signals picked up by ECG electrodes, in 2015, I designed a small ‘front-end shield’ that plugged into the Arduino. It provided a high-gain (1000/2000 times) differential amplifier plus a three-pole low pass filter to reduce the sampler’s susceptibility to 50Hz hum. The Duinotech XC3784 kit comes with everything shown. While it’s called a kit, the module is already assembled. 72 Silicon Chip Australia's electronics magazine The heart rate sensor module we’re discussing in this article is basically a much-improved version of the frontend shield in our project, compressed into a single 4mm-square 20-lead SMD chip: the Analog Devices AD8232. This is a very impressive device, as you’ll soon see. This comes on the Duinotech module from Jaycar (Cat XC3784), which combines the AD8232-based module with a colour-coded three-electrode cable and a set of matching adhesive sensor electrode pads. Jaycar currently has this kit for $27.95, with 12 additional electrode pads (Cat XC3785) sold separately for $8.95. Inside the AD8232 Analog Devices describe the AD8232 as a “Heart Rate Monitor Front End”, or an “integrated signal conditioning block for ECG and other biopotential measurement applications”. A simplified version of the circuitry inside the AD8232 is shown in Fig.1. As you can see, it includes an instrumentation amplifier (InstA) to process the incoming low-level ECG signals plus three further op amps: A1, A2 and A3. A1 provides low-pass and high-pass filtering plus additional gain. A3 is used to buffer the half-supply reference voltage, ensuring that the main amplifier InstA can handle the full signal swing. A2 is used to drive the right-leg electrode lead (RLD) with an inverted siliconchip.com.au Fig.1: a simplified block diagram of the AD8232 IC. It’s described as a singlelead ECG front-end and implements various low- and high-pass filters using internal op amps. version of any common-mode signal present in the inputs to the instrumentation amplifier, InstA. This improves the common-mode rejection of the system, giving a significantly cleaner reproduction of the ECG signal. There are also two comparators, C1 and C2, used to provide ‘lead-off’ signals if either of the main electrodes is not in good contact with the skin of the wrists or arms. The result of this complexity inside the AD8232 chip is that when its inputs are connected to electrodes attached to the skin of a human body, and it’s provided with suitable support circuitry, it gives a clean analog ECG output signal. The module circuit Fig.2 shows the full circuit of the AD8232-based module. There’s very little in it apart from the AD8232 chip and a handful of passive components. It all fits on a small PCB measuring 30 × 35mm, including the mini 3.5mm TRS jack socket used to connect the three-electrode lead. Connectors CON1 and CON2 provide alternative connections for the input electrodes, with CON2 being the 3.5mm input jack and CON1 being just a set of three holes in the PCB to receive a 3-pin SIL header. CON3 is a 6-pin SIL header that provides all the power and output connections. As the labels suggest, pins 1 and 2 of CON3 are used for ground and +3.3V power, respectively; pin 3 is the ECG signal output, while pins 4 and 5 provide the ‘lead-off’ error signals. Pin 6 of CON3 is a logic input that allows the AD8232 to be placed in shutdown (standby) mode to save power when ECG readings are not needed. It is normally pulled high by a 10kΩ resistor, so all that is required to place it in standby mode is to pull it low. The rated current drain of the AD8232 chip is less than 250μA in operating mode, dropping to less than 500nA (0.5μA) in shutdown/standby mode. So it is suitable for battery-­ powered portable use. As well as being taken to pin 3 of CON3, the ECG output from pin 10 of IC1 also connects to LED1 via a 1kΩ series resistor. This allows the LED to be used to monitor the heartbeat visually. But if this is not required, the LED can be disabled simply by cutting the PCB track between the two pads of LK1. LED1 is on the module PCB at upper left, in the centre of the printed ‘heart’ symbol. LK1 is visible just to the left of Fig.2: the full circuit of the heart rate monitor module. Apart from IC1 and LED1 the circuit consists of a small number of passive components. The module also features alternative input connectors (CON1 & CON2) for the electrodes. siliconchip.com.au Australia's electronics magazine February 2023  73 the ‘heart’, above the connections for CON3. The latter is fitted underneath the PCB, ready to connect to a breadboard or another PCB. Electrode placement Fig.3 shows two of the suggested placements of the three electrodes with this kind of ECG sensor. On the left, the RA (right arm) electrode is positioned near the right wrist, the LA (left arm) electrode near the left wrist and the RL (right leg) driving electrode is above the right knee. However, another suitable position is just above the right ankle. On the right is another way of achieving much the same result. Here the RA and LA electrodes are placed just above the armpit on each side, while the RL electrode is placed on the abdomen just below the rib cage. Although it’s shown to the right, it can be placed in the centre, just above the navel. Connecting it to an Arduino Fig.3: the typical electrode placements on the human body. Note the orientation of the person is such that their face is facing upward. It’s pretty easy to connect the AD8232 Heart Monitor module to an Arduino like the standard Uno or one of the many compatibles, as shown in Fig.4. The GND and +3.3V pins on CON3 connect to the corresponding pins on the Uno, as shown by the grey and red wires, while the OUTPUT pin connects to the A0 pin of the Uno (blue wire). If you want to try using the LO- and LO+ pins, these can be connected to the Uno’s IO11 and IO10 pins (green and purple wires). And if you envisage wanting to make use of the SDN pin (pin 6) to save power, this can be connected to the Uno’s D8 pin (not shown in Fig.4). It’s also relatively easy to connect the module to an Arduino Nano, as shown in Fig.5. Note that the connections shown in both Fig.4 and Fig.5 are those expected by the sketches I found to put the module to use. Other configurations are possible as long as the software is adapted to match. Firmware and software Fig.4 (above): the connection diagram for the heart rate monitor module to an Arduino Uno or similar. Fig.5: the connection diagram to an Arduino Nano. 74 Silicon Chip Australia's electronics magazine I couldn’t find sketches or PC software on the Jaycar website for use with this module, but after searching the internet, I found references on Sparkfun’s website to a simple sketch called “Heart_Rate_Display.ino”, available to download from: https://github.com/sparkfun/ AD8232_Heart_Rate_Monitor This sketch was written by Casey Kuhns at SparkFun Electronics and seems to have been written originally for the Mini Arduino Pro. It simply sends numeric samples of the ECG signal back to the PC, where they can be displayed as a listing in the Arduino IDE’s Serial Monitor. If you have a recent IDE version (v1.6.6 or later), you can display them as a waveform using the Serial Plotter tool instead. To try out the module and kit with an Arduino Uno, I adapted the Kuhns/ SparkFun sketch to make it work with siliconchip.com.au the Uno. The adapted sketch is called “AD8232_heart_monitor_basic.ino” and is available for download from the Silicon Chip website. Trying it out I connected the Jaycar XC3784 module up to an Arduino Uno, as shown in Fig.4, then connected the Uno to a PC via a USB cable. After that, I started the Arduino IDE (v1.8.19), opened the “AD8232_heart_monitor_basic.ino” sketch, verified and compiled it. After that, I connected the plug on the end of the electrode cable into the 3.5mm jack on the module and fitted the red electrode to my right wrist, the green electrode to my left wrist, and the yellow electrode to my right leg just behind the knee. The next step was to upload the compiled sketch to the Arduino, after which it began running, with the little ‘heartbeat’ LED on the module blinking away cheerfully. When I opened the IDE’s Serial Monitor tool, I was greeted by a scrolling list of numeric samples of my ECG waveform. Of course, it is not easy to deduce much from a scrolling list of numbers, so I closed the Serial Monitor tool and opened up the Serial Plotter tool instead. This gave a waveform that was a lot easier to interpret, although there was a fair bit of noise present. So I tried moving the electrode positions a few times and kept checking the result. The plot shown in Fig.6 is about the best I could get, and as you can see, there’s still a fair bit of noise between the main QRS spikes, almost obscuring the smaller P and T bumps. Your heart & its electrical activity Most people know that your heart is basically a pump that pushes your blood around your body via its blood vessel ‘plumbing’ – the arteries and veins. The typical human adult heart is about the size of a clenched fist and weighs about 300g. It’s located near the centre of your chest and pumps about once per second. The pumping action is triggered mainly by a nerve centre inside the heart, called the sino-atrial or SA node. Each pumping cycle is initiated by a nerve impulse that starts at the SA node and spreads downwards through the heart via preset pathways. The heart comprises millions of bundles of microscopic muscle cells, which contract when triggered. The muscle cells are electrically polarised, like tiny electrolytic capacitors (positive outside, negative inside). As the trigger pulse from the SA node passes through them, they depolarise briefly and contract. So with each beat of the heart, a ‘wave’ of depolarisation sweeps from the top of the heart to the bottom. Weak voltages produced by this wave appear on the outside surface of your skin, and can be picked up using electrodes strapped to your wrists, ankles and the front of your chest. It’s these voltages (about 1mV peak-to-peak) that are captured and recorded as an electrocardiogram or ‘ECG’. The actual shape and amplitude of the ECG waveform depend upon the individual being examined and the positioning of the electrodes, but the general shape is shown in the adjacent graph. The initial ‘P’ wave is due to the heart’s atria (upper input chambers) depolarising, while the relatively larger and narrower ‘QRS complex’ section is due to the much stronger ventricles (lower output chambers) depolarising. Finally, the ‘T’ wave is due to the repolarisation of the ventricles, ready for another cycle. Doctors can evaluate several heart problems by measuring the timing of these wave components and their relative heights. They can also diagnose problems by seeing how wave components change with the various standard electrode and lead connections. Conclusion Although I think some of this noise could be removed by further experimenting with electrode placement, I also gained the impression that some of it was being picked up by the AD8232 module itself and the wiring between it and the Arduino. I suspect that, for the best results, it would be a good idea to place the module and the Arduino inside an Earthed metal box. So the AD8232 module and accompanying electrode kit provide an easy way to check your heart rate. If you get one, I suggest you also get one of the packs of extra electrode pads (Jaycar Cat XC3785), since the pads are only suitable for a single use. SC siliconchip.com.au Fig.6: a heart rate plot taken using the sample software and the Arduino IDE’s built-in Serial Plotter. Australia's electronics magazine February 2023  75 Part Two by Dr Hugo Holden Play your own game of Noughts × Crosses This clever game is built using just discrete logic ICs and an EPROM or EEPROM chip that contains the gameplay data. The first article last month described how the design evolved and how the circuitry works. In this article, we’ll investigate how the gameplay data was generated and then explain how to build it. T he circuit relies on a ‘database’ of moves based on the present state of the playing board and which player started first. Having that information, it performs a ‘look up’ of the EEPROM data to get a number. That number tells the game on which tile to make its next move. So we need the correct data in the EEPROM chip for the machine to play the game correctly and always win or draw, depending on the skill of the human player. How do we go about generating that data? Gameplay decisions Two of my early questions were how many machine responses are required for a game where the human starts first and where the machine starts first. I began by examining the human (X) starting case, ignoring board symmetry and mirror and rotational images. The game has nine different starting possibilities. Let’s say X starts in square 1. Then O has eight remaining squares to choose from. We could limit the response here to taking the central square if X had not taken it initially or, 76 Silicon Chip for the case where X takes the centre square initially, O can take the same initial corner square. The game sequence then depends very much on X’s second move. O’s first response could be called a ‘general start’ because it can be stereotyped as one of two possible squares. After that, we can sort the game sequence into groups of solutions of the form X1,2 and X1,3 through to X1,9, where the first number represents X’s initial move location, and the second number represents X’s second move after the machine’s first response. In the example above, if X’s first move is square 1 (a corner square), there is no game sequence of X1,5 because O’s first response is to take the centre square, so it is no longer an option for X. After O’s initial response, seven squares remain as a choice for X. This means that for each game start-up sequence, seven board patterns occur initially. At this point, it is O’s turn to choose next. Analysis at this point shows that to complete the game, nine Australia's electronics magazine responses are required for each of the initial seven board patterns, to allow for all of the mistakes X could make choosing a square. The nine starting states and seven early board patterns require 63 charts (9 × 7). Each of these 63 charts contains nine data points (or machine responses) to continue the game. The number of responses required by the machine could theoretically be in the order of 569 initial responses in total (9 × 63 + 2). However, once the game has begun, duplicate patterns of Xs and Os appear via different starting sequences. They occur early in the game where two Xs and the one O end up in the same locations; then, the entire group of 9 responses are duplicated. Later in the game, board pattern duplications also occur for the final moves. The required number of computer responses after duplications were deleted for the ‘X starts first’ case turns out to be 285. An example chart is shown in Fig.7, one of 63 supportive charts in the ‘X starts first’ case. I made these by hand siliconchip.com.au Fig.7: one of the many charts I created to calculate the data to load into the EEPROM. They consider every possible move and countermove, and determine which moves are required for the machine to always win or at least draw. siliconchip.com.au Australia's electronics magazine February 2023  77 to examine every possible human move and select appropriate machine responses. The numbers in cyan are the decimal address generated by the game board pattern of X and O playing pieces on the board. I converted these decimal numbers into hexadecimal numbers to program the EEPROM. The numbers in red are the byte values programmed into the EEPROM at those address locations. When the human X starts first, the second player, whether machine or human playing O, is ‘pushed around’ by the playing strategy of X. Many of the responses in this case by the machine O are to prevent being beaten by blocking a winning human move. As mentioned earlier, the starting player has a significant advantage. Consider the human X starting at position 7 (in the chart example above) and making their second move onto square 4. The chart (the upper one and its pathway) is labelled X7,4. Although the human could make their next move differently, onto positions 1, 2, 3, 6, 8 or 9, these are all accounted for in the other X7 charts. X’s initial move generates the decimal address 64. It is then O’s turn, so the computer activates, and it takes the central square. Then X plays square 4 as its second move (in this example of the sequence X7,4). This generates the address 8264 decimal and the machine, in response, takes square 1 because “01” is programmed at that address in the EEPROM. Ignoring the general start moves, there are nine responses from the sequence X7,4, as there are for the sequence X7,1. As can be seen from the charts, there are many opportunities for the human X player to make a mistake where the machine wins, and only one pathway to a draw with the machine. If the human does make a mistake, the machine takes the appropriate square to win. Therefore, most of the data points allow for the many variations of mistakes that the human player can make, so that the machine (which never makes an error) can take advantage of them. In the ‘X starts first case’, there were 28 duplicate charts out of 63, saving 252 responses and leaving just 285. I found that duplications could be increased by settling on a similar gameplay style. Similar data duplications appear later in gameplay for the final responses inside the chart, which match the results in other charts. This further reduces the required number of machine responses. This occurs because game board patterns converge on the same result via different initial playing sequences. Machine starts first When the machine (O) starts first, more charts (72) are required with many more unique machine responses. The number of responses is a little affected by the playing strategy. By starting first, the machine has the advantage and can largely dictate the course of the game, even setting traps where if X makes a poor initial move, they can quickly be in a situation with no way to avoid losing. The game here has been optimised to catch the human out at every opportunity when they make a mistake. Every possible error by the X player has been analysed and responded to. The best the human player can hope for is a draw. Despite that, the same basic principle and strategies apply. It’s just that there are more possibilities, mainly because the machine player chooses a random initial move. There are not as many whole chart duplicates as in the ‘X starts first’; roughly half the number at 15 duplicates. Still, this saves over 100 required machine responses. The total number of machine responses for ‘O starts first’ with my chosen game strategy turned out to be 560, nearly twice the number for ‘X starts first’ (285). Therefore, the total number of unique programmed responses required to ensure both scenarios are supported is 845 with the gameplay strategy used in this design. Case design The two stacked PCBs are somewhat visible through the ‘smoked’ translucent acrylic base. 78 Silicon Chip Australia's electronics magazine Noughts & crosses is such an ancient game and I could imagine people playing it hundreds of years ago with wooden blocks with Xs and Os on them. It’s also commonly played with pen & paper. The problem with board games that use player pieces is that the pieces tend to get lost over time. I decided I wanted a compact game with a quality look, like an elegant product from the 1920s or 1930s, made siliconchip.com.au Fitting the LEDs Getting the LED positions correct is critical. This can be done by feeding the LEDs into their holes and using tape so that they don’t fall out, then temporarily attaching the game board to the top panel. With a game piece or disc in each recess, push the LEDs up so they touch the disc then solder their leads. This ensures that the LED lenses will not prevent the game pieces being placed in their recesses properly. Fig.8: the top side of the game board carries just the 36 blue LEDs and 10 Hall Effect sensors. What is not shown here is that the sensors are spaced about 3.2mm above the top surface of the PCB. I glued phenolic spacers under the TO-92 packages to achieve that, but there are other methods. to last. Popular materials then were plastics such as Bakelite. These sorts of materials are harder to get nowadays, so I decided to build it from 10mm-thick gloss black acrylic panels with white paint-filled engraved markings. I decided on the hinged lid so that the player pieces could be stored inside the game, to reduce the chances of them getting lost. As noted previously, I wanted the game to work without power for two human players. Like some video games, you can choose to play a friend, or the machine if you are on your own. 10mm-thick acrylic has one advantage in that it is relatively easy to tap a coarse thread into it. A good-sized screw for this application is 4-40 UNC. siliconchip.com.au So I tapped long threads, approximately 15mm, into the frame to secure the top & bottom panels. For the initial machine, I used a lightly-tinted 6mm thick see-through bottom panel, so the internal electronics are visible to the observer. The unit can easily be made from any colour combination of 10mm-thick acrylic panels. It could also be made from several other plastic types with variations such as mother of pearl or tortoiseshell patterning. A local plastics company (Sunquest Industries) routed and engraved the acrylic panels for me and added pilot holes. I enlarged and tapped all the required holes with the 4-40 UNC threads. To fit the hinge to the lid, I machined Australia's electronics magazine some 10mm-long, 4mm diameter brass inserts with M2-tapped holes. This is because small-diameter, fine thread pitch screws do not do very well directly into acrylic. You could use pre-made threaded inserts designed for plastic for this task. I drew the PCB designs as images and sent the resulting JPG files to Storm Circuit Technology based in Shenzhen, China. There, Mr Kim Chan converted my images to Gerber files and produced quality PCBs at short notice. I found their service to be excellent. PCB assembly Start by building the two PCBs. The 138 × 166mm game board is coded 08111221, and its overlay diagram is February 2023  79 Fig.9: the resistors, capacitor, ICs, socket strip and wire links are fitted on the underside of the game board. There are five wire links; they can be made using tinned copper wire or component lead off-cuts (if they are long enough) as there is nothing conductive underneath, assuming your board has a solder mask. You might need to change the 1kW resistor value if you aren’t using the A1 version of the Hall Effect sensors. shown in Figs.8 & 9, while the 138 × 124mm compute board is coded 08111222 and is shown in Fig.10. It’s best to start by fitting the components on the underside of the game board, installing the lowest-profile components first (the five wire links and 39 resistors), then the ICs, then the rest. The ICs are all the same type but make sure they are orientated correctly. Nothing else on this side is polarised. Remember to change the 1kW resistor to 510W if you are using the less sensitive (A2) Hall Effect sensors. Now flip it over and solder the 36 blue LEDs with the cathodes (flattened sides in the lenses) facing as shown in Fig.8. EPROM vs EEPROM The only difference between an EPROM and an EEPROM is just how the contents are erased; an EPROM uses UV light through a window on the top of the chip, while an EEPROM is erased by the application of a specific set of electrical signals (“electrically erased”, hence the EE in EEPROM). The data is programmed into both chip types by electric signals, similar to flash memory, a later technology. 80 Silicon Chip Australia's electronics magazine Next, install the Hall Effect sensors with their flat faces away from the PCB and their rounded sides against its surface, bent over as shown. I glued 3.2mm (1/8in) tall phenolic spacers under the bodies of the Hall devices to make sure that they sat at the right height, but they are not definitely required. You could just bend the leads to achieve a 3.2mm gap between the devices and the PCB surface. Assembly of the compute board is straightforward. Start by fitting all the small 1N4148 diodes with the cathode stripes facing as shown in Fig.10, then the resistors, then the larger 1N5819 diode, D1. The next job is to solder all the ICs. You’ll probably want to socket IC1 in siliconchip.com.au Some of the critical items in the parts list can be found on eBay, for example: Hinge screws: siliconchip.au/link/abj3 UNC 4-40 screws for case: siliconchip.au/link/abj4 150mm-long hinge: siliconchip.au/link/abj5 Latches: siliconchip.au/link/abj6 Fig.10: be careful with the orientations of the diodes and ICs when assembling this board as they vary. Also keep in mind that there are different ICs in very similar packages. Once it’s up and running, if something goes wrong, you can probe the test pin points at lower left to get a clue about what it’s doing. They correspond to the EPROM/EEPROM address lines. case it ever needs to be reprogrammed or replaced, but the others don’t need sockets. Take care installing them because there are several different types with the same number of pins, and the orientations vary, with pin 1 being at the top in some cases, and at the bottom in others. Next, bend the leads of REG1 to fit the PCB pads, attach it using a short machine screw and nut, then solder and trim the leads. Follow with header CON2, Mosfet Q1, then the capacitors (all of which are non-polarised) and finally, the piezo buzzer. You can now solder the positive supply wire from your battery or DC socket to the +9V pad next to REG1 via the power switch. Connect the negative supply lead to the pad marked GND. Ensure the supply wiring polarity is correct as there is no reverse protection on the board. The boards can then be plugged together and power applied temporarily to test their function. You can do this by waving the weak magnets over the Hall Effect sensors (especially HS10) with both polarities and checking that the LEDs respond as expected. siliconchip.com.au If it doesn’t work, switch off the power and check for faults like bad solder joints or incorrectly fitted components. If it does, join the two boards using four tapped spacers and eight short machine screws using the predrilled mounting holes. Making the case panels The case is assembled from machined acrylic (MPPA) panels, mainly 10mm-thick black acrylic with some 6mm thick translucent acrylic (the underside panel only). The first step is to prepare these panels. Realistically, you need a CNC mill to make these panels. As I don’t have one, I contacted a local sign-maker, Sunquest Industries. I have used them for some tricky jobs in the past (www. sunquest.com.au). They did a great job making the pieces for me and could likely repeat the job for anyone who wants to build an identical case. Early Noughts & Crosses playing machines This design was inspired by Dick Smith’s challenge in the October 2021 issue (page 13) to design an innovative Noughts & Crosses playing machine. His challenge was based on his creation of a similar electromechanical machine when he was 14 years old (in 1958) that apparently was unbeatable. That was possibly inspired by a machine called “Relay Moe”. Its design was published in the December 1956 issue of Radio-Electronics magazine (also mentioned in Life magazine, March 19, 1956). “Moe” had four playing strategies, but none of them completely precluded the human from beating it. According to the article in Radio-Electronics on Moe, Bell Labs built a similar machine at an earlier date, but that’s all the information they provide on that subject. Another one we found reference to was built by RCA in 1955, the ASTRC-1 – see siliconchip.au/link/abfh Interestingly, both machines depended on timing systems, unlike my design presented here. Australia's electronics magazine February 2023  81 Fig.11: the top panel of the case is somewhat tricky to machine as you need to accurately cut ten recesses in both the top and bottom surfaces, with the underside recesses having smaller recesses within them. Don’t drill too far, or you might break through! You need an end mill for this job, ideally on a CNC mill; a regular drill bit won’t do. 82 Silicon Chip Australia's electronics magazine siliconchip.com.au The most complex panel is the top one, with ten recesses for the player pieces. There are also numerous holes in these recesses for the LEDs to shine through, and recesses on its bottom surface for the Hall Effect devices and the LEDs. Fig.11 shows the drilling details for this panel except for the LED and mounting holes, which have been left off for clarity. Fig.11 also shows the labels on the top panel, which were made by engraving the panel and then filling the recesses with white paint. However, you could attach adhesive labels if you prefer. Fig.12 shows the locations of the LEDs and mounting holes in this panel. Note that some are drilled through while others are drilled partway and tapped. it’s best to use the game board as a template to mark the mounting hole positions to ensure they are accurate. Once you’ve prepared that panel, which is a large portion of the work, move onto the lid, shown in Figs.13 & 14. It has recesses on its underside to allow the pieces to remain on the player board with the lid closed, and optional labelling on the top side. The top edges of the lid were chamfered in my version, which is nice to do but not absolutely required. The details of the side and bottom panels are shown in Figs.15 & 16. The side panels need to be cut to size from 10mm-thick acrylic and one recess made, for either a DC socket or power switch if using a battery. The translucent bottom panel needs ten holes drilled for the screws that hold the case together. Once you’ve drilled all the holes in the top and bottom panels, countersink the ten 3mm holes in each panel and check that the CSK UNC machine screws can be inserted flush with both panels. The tapped holes for attaching the hinges and latches that hold the lid closed are not shown in those figures. That’s because they are best marked and drilled after the case has been assembled, to ensure they are placed accurately. Similarly, the holes in the side panels for the screws that go into the top and bottom panels are not shown as they are made using the top and bottom panels as templates. Making the game pieces The game pieces are made from siliconchip.com.au Fig.12: here are the locations of the holes to drill right through or tap in the top panel, which weren’t shown in Fig.11. There are 36 holes for the LEDs, 10 for the screws that hold the case together and nine to partially drill and then tap on the underside. The complete case without its lid. Note the LED lenses poking through the four holes in each 20mm diameter recess, and the recessed power socket at the front. Australia's electronics magazine February 2023  83 Figs.13 & 14: the lid is a bit simpler to make than the top panel. It just has some artwork on the top and ten circular recesses on the underside, so the game pieces are held inside when the lid is closed. 20mm diameter, 10mm thick pieces of black acrylic with Os and Xs engraved in the top surface and filled with paint. They could be laser-cut or milled from a sheet of 10mm-thick acrylic. It might be possible to make them by hand (eg, using a 20mm hole saw), but that would probably be quite difficult. Once they have been made, drill a recess into the back of each piece deep enough to hold the weak magnets. Glue the magnets in with epoxy, ensuring they are orientated correctly – they need to be reversed on the X pieces compared to the O pieces. To determine the correct orientation, power the unit up and hold a magnet over HS10. If one set of four LEDs lights up, that is the orientation for an X piece; with the X piece held above the magnet, slide the magnet into the recess. If no LEDs light, it is the orientation for an O piece. When you glue the magnets into the pieces, ensure the epoxy surface sits level with the rear of the piece. If it protrudes, the pieces will not fit fully into the recesses, and the lid won’t be able to close. Assembling the case Place the side panels tightly together, place the top panel on top and mark the locations of the holes for 84 Silicon Chip Australia's electronics magazine the ten screws that hold them together. Drill and tap these holes with 4-40 UNC threads. The next job is to mount the PCBs to the rear of the front panel. Screw 4-40 UNC threaded standoffs into the tapped holes on the rear of the front panel, through the game board and some small washers (to act as spacers, giving space for the solder joints on the game board). These are the sort used in computers, available from Jaycar stores. These allow the compute board to be mounted on top of the game board. When installing the game board, ensure that the LEDs all go into their holes (adjust them if necessary). The Hall Effect sensors should slot into their recesses. The standoffs should give enough clearance between the PCB and the front panel so that the solder joints don’t interfere with fitment. You can then attach the four side panels to the top panel, ensuring they fit tightly together, then flip the assembly over, place the rear panel over the opening and mark the ten screw holes like you did for the front panel. siliconchip.com.au Figs.15 & 16: the sides of the case are four rectangles of 10mm thick acrylic with one recess for the DC socket or switch. The bottom panel is a 6mm sheet of translucent acrylic with ten holes drilled through for screws. If you use transparent or translucent acrylic, you’ll be able to see part of the circuit boards inside. Not shown on the bottom panel are holes for mounting feet; we recommend you add them, see the photo. Remove the side panels, then drill and tap those holes for 4-40 UNC. Mark positions for mounting holes for four feet on the base, drill those holes and attach the feet. Mount the DC socket or power switch in the recess in the side panel, then reattach the side panels to the top panel and wire it up. If using a battery, mount that inside the case and wire it up. After checking that it powers up, attach the base. That just leaves the lid. Place the ten pieces in the recesses on the top panel and then lower the lid down on top. It should fit flush – if it doesn’t, figure out why and fix it. Next, hold the hinge centred on the rear of the case so it sits exactly over the seam between the lid and top panel and is centred horizontally. Use tape to hold it in place if necessary and mark out the screw holes (masking tape is best as it doesn’t leave much residue). If in doubt, see the photo to show how it should mount. Similarly, hold the clasps to the front, equidistant from the edges and with the holes halfway between the top and bottom edges of the lid. Mark out siliconchip.com.au the holes in the lid and the front panel. Remove the hinge and clasps, drill the holes to an appropriate depth for the screws and tap the holes. As mentioned earlier, the screws for the hinge are probably too small for you to tap the plastic directly (the screws will pull out and destroy the threads). So instead, drill those holes larger and glue in threaded inserts with epoxy, with threads to suit the hinge screws. You can then attach the hinges and clasps, and the assembly is complete. Conclusion This project is an excellent demonstration of how digital logic can be used to solve a relatively complicated problem. Of course, it could be done with a microcontroller or an FPGA, but this way, you can see exactly how it works. Creating the case from scratch is a considerable amount of work, but I think readers will agree that the result is elegant and suits the game well. The final result is great fun for kids to play with, or as a conversation piece for adults. SC Australia's electronics magazine The lid and one of each of the type of playing pieces. February 2023  85 SERVICEMAN’S LOG Nature abhors a vacuum, and so do I Dave Thompson This month finds me revisiting an old nemesis – our Bissell Air Ram vacuum cleaner. I’m not really an appliance repair guy. I’ve never been asked to look at someone else’s vacuum cleaner, and would likely turn down such an opportunity, but I am willing to have a go at repairing my own. I’ve repaired the Air Ram vacuum cleaner before. It is a battery-powered cordless device with all the hard work done near the floor. This isn’t one of those toy dust busters you buy someone for a Christmas present; it is a relatively heavy-duty, full-sized vacuum cleaner. While ‘dust busters’ typically run from 3.6V (for cheaper models) to 16V (for more expensive models), and some might give you 10 minutes of wheezy dust busting, the Air Ram boasts a blistering 22V lithium-ion battery that lasts for around 40 minutes before it needs recharging. That is enough to do our largeish house in one fell swoop, and at nearly 10 years old, the battery still lasts that long. This machine has done a tremendous amount of work over the years. Not only has it served our domestic needs, but it was also the primary vacuum cleaner I used at our rental place, so it has essentially done double duty for at least half its life. Like all of these types of vacuum cleaners, it has disadvantages – there is no removable flexible hose, for example, so getting spider webs from high corners or scooting down skirting boards or down the sides of chairs will have to be done with something else. Its most significant advantage over traditional ‘hoovers’ is its light weight and manoeuvrability, and the fact that it takes much less effort to push it around. The dust collector and motor assembly are all down in the ‘foot’ of the machine, so dirt only has to be ingested a few centimetres, rather than being 86 Silicon Chip dragged up some long tube to a handle-mounted collection bag (or bin). Ever the best vacuums fail sometimes So, a good unit then, and it has done just fine, but as I mentioned, it failed once before. I wrote about that way back in May 2017 (siliconchip.au/Article/10650), and there is no need to rehash that whole palaver here except to say it jammed due to an incense stick getting caught in the turbine mechanism. Fortunately, there is a built-in overload cut-out in case this happens, so nothing was damaged, but it was a trial to repair. This time, the boss was giving the living room floor a quick vacuum before guests arrived and it just went ‘pfft’ and stopped [ah yes, the dreaded ‘pfft’ – Editor]. The LED battery display on the front still showed four bars – fully charged – but the switch did nothing. No magic smoke came out, but I could detect a faint whiff of that familiar ‘something important has been burnt’ smell. Not a good sign! At least we have another cleaner that we could use, so it wasn’t a show-stopping problem, but it was annoying that something had once again gone wrong with it. I dreaded to think what that was because there was not a lot in there to go wrong except the motor or (and this is a long shot) the switch. Either way, it would need to come apart. All I really remember about the last repair was the faff involved in taking the thing apart. This is the problem when having a go at fixing many devices, remembering how everything worked and went together. This cleaner was no exception. I knew I’d had a bit of a mission getting it apart before and couldn’t recall exactly how I’d done it. I went back and re-read the May 2017 column, and it all came flooding back. I remembered that I had removed many screws and other things that weren’t really necessary to gain access to the workings, so it was handy to have that reference material! It saved me from doing the same thing all over again. As far as appliances go, this machine is extremely well made. I’m not saying it is over-engineered, but – wait a minute, that’s precisely what I am saying! The screws holding it together are all Torx-type splined fasteners, so it is fortunate that I have several bits in my collection that fit them. Plus, some of these screws are buried deep in cavities and wells, which require more than the typical 25mm-long bits we usually use. I have a long-reach bit that came in handy, and because there are a lot of screws Australia's electronics magazine siliconchip.com.au compressor and a soft brush to clean the entire motor assembly, ready to go back in should the repair go well. I checked the switch itself, a reasonably heavy-duty microswitch. It is mounted on its own little circuit board, screwed to the inside of the handle and actuated by a springloaded on/off switch mounted directly above it. Using a multimeter, I soon ruled the switch out as the problem – it seemed to be working as expected. Picking up the problem in this thing, I used a drill to conserve time and my wrists. I poked and prodded and swore a bit (only mildly, the worst word I uttered was ^*<at>#) until I finally got it all apart and on the bench in its main component pieces. The turbine assembly spun easily, so nothing was jammed in it this time. The burnt smell was not apparent now, even up close to the motor, so I was hopeful the motor hadn’t died. If it was dead, that was the end of the cleaner, as parts for this older model are not readily available here. With the fan assembly out, I had clearer access to the internals, though the handle and swivel joint were still to be disassembled – but only if that was required. A dirty job but someone has to do it The problem with vacuum cleaners is they are very dusty, dirty things! The top of my workbench already had piles of dust and clumps of pet hair all over it, and the interior, vents and air gaps in the base unit were all choked with thick dust and hard-packed lint. So the first thing I did was to blow the whole thing out on the driveway using my air compressor. Once I had cleaned it up, I could see what was actually going on. A microswitch sits up by the handle, and wiring runs down the inside of the handle assembly, around the battery cavity and to a very small circuit board mounted near the foot. Another smaller lead runs to the LED assembly at the lower front of the handle, with two thicker wires running from the circuit board down through the footer hinge assembly to the motor. There are no other electronics to speak of other than an overload switch. The motor assembly includes the motor, fan and lots of clear plastic ducting holding it all together. Two heavy contacts are moulded into the plastic housing, and when the assembly is placed back into the foot unit, power is applied via mating contacts connected to the battery and power leads. I used a bench power supply to carefully apply 20V to the motor via these contacts, and to my relief, it spun up quite happily. It certainly is a grunty little motor! Obviously, the problem was elsewhere. I used my air siliconchip.com.au My next step was to ring out the wiring – it is embedded throughout the plastic and cast aluminium handle, emerging right at the flexible joint of the footer unit. It continues, one wire on each side, pressed into channels in the floor of the moulded plastic and cast aluminium main housing. These wires terminate at two prongs pressed onto the motor’s power terminals when the motor assembly is seated and screwed into place. Just before those terminals are two inline inductors with a snubber diode across the connectors. I replaced this diode the last time as it had blown, but a meter showed it still to be intact. However, I soon found a problem trying to ring out the motor power leads. I could only find continuity in the positive side of the power circuit – which meant there must be a break in the negative line somewhere. Measuring from the battery’s positive terminal to the positive motor terminal was fine, but going through the switch, the negative lead was open-circuit. Tracing back from the motor power terminal, I soon discovered why. Buried down in the plastic moulding by the flexible metal foot joint, I spied a break in the wire. The two power wires come down through the handle, split to either side and are held by a variety of clamps and clips before terminating at the motor contacts. At one stress point, right by the joint, one half of the wire simply pulled away when probed with my dental pick. The end showed a bit of burning where the power had arced, but it appeared to be a simple stress fracture because of the location, right beside a metal clamp designed to hold the cable in place. The continual bending of the handle and the foot unit at the joint had work-hardened the wire, and it came apart one strand at a time until it couldn’t take the juice any longer and simply evaporated. That explained the ‘pfft’ and the slight burning smell I detected at the time. The lack of power to the motor explained why the vacuum no longer sucked. So, I had discovered the problem, but that was not the end of the job. These cables are embedded well into this Items Covered This Month • • • • • Nature abhors a vacuum Replacing a Yagi TV antenna An electric toothbrush repair Multiple rotary encoder standards A case of faulty PICs Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz Cartoonist – Louis Decrevel Website: loueee.com Australia's electronics magazine February 2023  87 Left: the broken wire, pulled from between the circular pivot in front and the curved clip behind it. The other end of the broken wire disappears into the joint. Right: a clearer view, but this time of the right-side wire run (which differs from the leftside). This shows the clips, routing and a pinch point similar to where the left-hand wire broke. unit, so to replace it, I’d have to strip everything down to spare parts anyway. There were so many clamps and clips in the line that it wouldn’t be possible to just pull another one through with any great ease. Curses! Now for the hard part Did I mention that this vacuum was over-engineered? Some of the clips holding the cable are custom metal parts, tapped and threaded and form an integral part of the complicated joint mechanism, so all that had to come apart, both sides, to split the two assemblies. Then with that accessible, two screws on the side held the metal wire retaining clip to the hinge. With that loose, I could then pull what remained of the 88 Silicon Chip wire through to the motor terminal end. After loosening several other clips going back the other way, I could pull the old wire through to the switch. What a pain in the posterior! I made sure to tie a bit of Nylon string to the old wire on the handle side because threading a new one by itself down through the assembled and blind-in-places hollow handle would be an absolute nightmare. With the string, I could tie on a new piece of wire and simply drag it back down, easing and pushing it where possible to get it through the tight spots. To do this, I stripped the end of the wire and formed the strands into a kind of low-profile turnbuckle, after which I soldered it up and that allowed me to tie the string to it without having a huge knot in the way. There are probably better ways to do it, but that is how I did it, and the new wire fed through relatively easily. Removing the old broken part of the wire at the motor terminal end was simple; I just desoldered it from the inline filter and unclipped it back through the footer until it came free. I made sure to leave plenty of wire at either end with the new cable and began by soldering it to the switch PCB at the handle end. I left a little slack there (there is plenty of room inside that part of the handle) before beginning the restraining process just below the battery cavity in the handle, where the serious clipping starts. There are several removable clips here that must be loosened to allow the wire to pass through. I had to remove the wheels and the main joint pivot screws to gain access to these clips; getting the wheels off is a mission in itself, as they are mounted on phosphor-bronze bushes retained with a circlip, which of course pinged off the moment I applied my circlip pliers to it. After much blue language and fossicking around the workshop floor (which I noted needed a vacuum!), I recovered the wayward clip and carried on. With the clips loosened and the wire threaded through, I followed all the other plastic retaining channels until the wiring looked like it had in the photos I took before I started all this. I couldn’t just make it look like the other Australia's electronics magazine siliconchip.com.au side because, true to form, both sides were quite different in how the cables went through. There were similarities, but they were not identical. Plus, when I took the whole thing apart, that pulled some of the intact wiring away from its channels anyway, and I had to restore that before refitting the motor assembly on top of it all. There is literally no room in there to do anything different cable-wise. After resoldering the new wire to the existing filter and tightening all the clips and clamps, I was finally ready for reassembly. First, I refitted the wheels, taking special care to keep my fingers over the circlips as I popped them into place – I didn’t want to waste even more time grubbing around the floor. With the wheels on, I could reassemble part of the front roller enclosure, a finicky job requiring three of my two hands. Then I installed the now-gleaming motor and fan assembly. However, it didn’t want to go right home, and after much gnashing of teeth, I realised my new wire was sitting slightly proud of one of the clips. Once that was dealt with, the assembly slotted home and I was able to screw it back into place. At this point, I had enough structure to hold the battery in place and test the system manually. There was no point in going further if I hadn’t actually fixed it! Again, using three hands, I managed to hit the on button and was rewarded with the mighty roar of the Air Ram (they are actually pretty noisy for such a small device!). So, it was going to work. Now it was just the humdrum mechanics of putting all the other plastic and metal parts back on. I oiled and greased where necessary, and soon it was all ready to go. I blew the filters out with my air compressor, which I do periodically anyway, and tested the cleaner on my workshop floor. It worked a treat, and the machine is back in regular use again. A simple enough repair, but a complicated machine to work on! Replacing a 23-element Yagi TV antenna A. L., of Cecil Park, NSW recently refurbished a TV antenna on his rural property, which turned out to be a bit more involved than he initially thought... About six months ago, I needed to replace a 23-element Yagi television antenna that was showing the ravages of time, having been aloft for about 18 years. According to the television receiver, the signal strength wasn’t too good. That was understandable given the condition of the end corner reflector on the antenna array. I had been delaying the replacement as it needed to be mounted atop a flagpole about 7 metres tall, bolted to a substantial concrete plinth. In the days of VHF transmissions, the antenna needed to face NE, toward transmission towers in North Sydney. Later, it was rotated SE toward transmission towers servicing Wollongong with a radiated power of around 50kW. These days, following the introduction of UHF digital transmission, we receive transmissions from a Wollondilly Council RFS site near Picton, which requires the antenna to face 205° (SSW). This directional change places the antenna below a hill and a line of trees. These conditions require a compromise between optimal transmission directional alignment and avoiding the large trees waving in the wind. siliconchip.com.au This phased-array antenna was used as a replacement for the previous Yagi antenna. Australia's electronics magazine February 2023  89 The masthead amplifier in its weatherproof box (left) and the test apparatus for the antenna (right) With that in mind, I chose a phased-array antenna described as “ideal for problem digital reception areas where you may not have direct line of sight to the transmitter”. I also decided to replace the old masthead amplifier with a new one mounted in a waterproof plastic box. I kept the new amplifier in its original “waterproof” housing and mounted the whole lot in the sealed plastic box from an electronic components retailer. I won’t go into the detail of how I lowered and raised the 7m flagpole to make the antenna changes but, even with the help of my wife and several pulleys, wires and a ride-on mower, it was not easy! We achieved directional alignment of the new antenna via a mobile phone conversation with my wife watching the TV screen and relaying the result to me as I rotated the flagpole 100 metres away, using my phone’s compass as a guide. After six months of decent reception, we started getting pixellated images, which I wrote off to very windy conditions. However, it became clear that there was something other than wind causing pixellation and dropout. My first impulse was to ditch the old indoor signal-­ booster amplifier and replace it with another masthead-type amplifier mounted indoors in a cabinet under the TV, followed by a four-way distribution amplifier servicing TVs in other parts of the house. The result was a strong signal level, well over 80dBµV throughout the house according to my Digitech Signal Meter, but now there were black screens. An overloaded TV tuner from excessive amplifier gain will cause that. Fortunately, the second masthead amplifier being used as an indoor signal booster amplifier had a wide-range gain control and backing it off brought the TV picture back. However, we still had pixellated images and intermittent black screens. I was convinced everything relating to amplification and distribution inside the house was OK, so I started investigating the masthead amplifier power supply in the cabinet under the TV. Using my multimeter, I measured a nominal 20mA DC going up to the antenna amplifier atop the flagpole. But over time, I saw a variation in the masthead amplifier current measured by juggling multimeter probes and bits of 90 Silicon Chip wire stuck in F-connectors. I needed a way to monitor the direct current going to the masthead amplifier and the UHF signal strength returning to the TV simultaneously. The test apparatus I came up with is shown opposite. I mounted F-connectors on three sides of a 115 x 90 x 55mm plastic box plus one LED on the fourth side. The F-connectors are screwed to an aluminium bracket/chassis and pass through the clearance holes in the plastic box. The two F-connectors on each long side are labelled “DC & RF”, with one connecting to the antenna amplifier’s DC power source. The second F-connector goes to the coaxial cable going to the antenna masthead amplifier. A DC link is established between the two F-connectors using the AC inputs of a small bridge rectifier. This allows the coax cables to the masthead amplifier and its DC power supply to be connected either way around. The third Fconnector labelled “RF to Meter” is for the RF signal to my Digitech Signal Meter. A 10nF ceramic capacitor is connected between the left “DC & RF” and bottom “RF to Meter” F-connectors, while the second capacitor connects between the right “DC & RF” and bottom “RF to Meter” F-connectors. The capacitors provide RF bypassing for the bridge rectifier and a balanced tap to the signal meter. Using this, I discovered a variation in the antenna amplifier current and signal strength arising from the condition of the buried coaxial cable at the base of the antenna flagpole. When installing the new phased-array antenna six months earlier, I had to rejoin the coaxial cable at the base of the flagpole, which I enclosed in a “sealed” plastic box through plastic cable glands and buried in the ground. On digging up the joiner box, I found it contained a substantial amount of water and, to make matters worse, the shielding braid of the coax was badly corroded for a considerable length. To dig it up and make it good, I might need to replace 90+ metres of very expensive cable, not to mention having to dig a long trench and cross over a creek. Sometimes it pays to sleep on a problem. With the passing of many years since the original installation, I had forgotten that I had laid two coaxial cables. There was a spare! The next day, back at the flagpole, I managed to dig up the spare cable end and found that it was not corroded. I joined the extra cable to the original down cable from the antenna at the base of the pole. Instead of burying the coax join in the ground, I put the F-connector join inside a water-resistant plastic box with gland entry and attached the box to the flagpole, then covered it with an aluminium rain shroud. At last, with the test apparatus in place, I could measure the effect of antenna rotation on signal strength and observe the impact of wind. I started with the antenna bearing at 205° and found good signal strength, but I could see signal strength dropping out with strong wind gusts. After rotating the flag pole towards a gap in the trees, I observed a significant reduction in dropouts. I’m now confident that I have the best compromise of signal strength and dropout. A simple electric toothbrush repair Our own Tim Blythman tried his hand at a simple repair. Not only did he fix the faulty electric toothbrush, he made it better in the process... 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Jaycar reserves the right to change prices if and when required. Photos 1-3 (left-to-right, top-to-bottom): the head of the toothbrush needs to be pushed backwards to open it, with the internals shown in the two horizontal photos. I decided to buy a ‘Dentitex’ electric toothbrush from Aldi on sale for $15. If nothing else, I could pull it apart and make use of its wireless charging circuit. This style of electric toothbrush comes with a small mains-powered base with a small post on top. The toothbrush rests on the post and charges via a pair of coupled coils. After nearly a year of use, I’d been happy enough with it that I hadn’t felt the need to pull it apart to experiment with the charging circuit, until it stopped working one day. It did not turn on when I pressed the power button, although the charge LED would still light up when I placed it on its base. Now that I was interested in actually keeping it going, I had to find a way to get it open without destroying it. I found YouTube videos showing how to open other brands of electric toothbrushes by twisting the head relative to the body as though unscrewing the two parts, but that didn’t work with the Dentitex unit. Still, the twisting motion showed a noticeable seam in that region. Photo 1 shows the bending motion that is required to open this toothbrush. The head of the toothbrush needs to be pushed backwards. It felt like I was about to snap it in two, but the head is simply held in place by locking tabs that come free when pressure is applied. There is also an O-ring that keeps the interior sealed. The mechanism and circuitry then simply slide out of the body, the driveshaft coming away with the head. Photo 2 shows the parts, with the driveshaft section repositioned onto the mechanism to make reassembly easier. Two NiMH cells take up much of the space, while a narrow PCB is the ‘brains’ (Photo 3). The drive motor is in line with the cells behind the PCB. The yellow coil near the batteries is evidently used to receive charging power. Before the failure, I thought the switch seemed a bit sensitive, so I suspected that the switch had failed. I started probing around the switch and Mosfet; I tried shorting the switch terminals, but the motor did not activate. Trying the switch a few times, I got the toothbrush to turn on intermittently, so I looked to see what I was doing that would cause that. Finally, I noticed that the solder 92 Silicon Chip joint for the negative battery tab was not attached to the PCB, as seen in Photo 4. After resoldering that tab, the switch operated reliably; it was definitely the cause of the problems. The presence of a single 0W resistor led me to check and confirm that the PCB is single-sided. That means it is more likely the tab could come loose as there is no through-hole plating to help the solder to adhere (it is an ‘unsupported joint’). I also noted a small gap between the PCB and the cell behind it. This gap meant that any movement of the battery would tend to peel the trace away from the PCB. That might be the reason the joint failed in the first place. Interestingly, the other end of the PCB appears to be fixed in place by a blob of melted plastic fused into a hole on the PCB. A similar arrangement at this end of the PCB might have prevented its failure. To make it more robust long-term, I scraped away the solder mask from around the hole where the tab protrudes, aiming to get a bit more surface area for contact. I then resoldered the joint again, being sure to push the cell firmly against the PCB. This effectively moved the gap to the other side of the PCB, where it could be closed with solder. With no gap, the cell would have less opportunity to move and weaken the joint. A quick test of the button showed that everything was still working, so I gave the area around the seals a bit of a clean and snapped the head back in place. It just slides straight in until the locking tabs seal. The toothbrush now appears to work as good as a new Photos 4 & 5: a solder joint for the negative battery tab was not attached to the PCB. Australia's electronics magazine siliconchip.com.au one, possibly better, as the switch is less sensitive. I think that pushing the button temporarily opened the gap near the battery tab, causing the toothbrush to shut off when it was supposed to be turning on. Rotary encoder signalling standards D. G., of Fremantle, WA discovered the joys of manufacturers using standard parts. However, his joy was shortlived, as he subsequently discovered that multiple competing standards can exist! He still managed to solve it without spending too much money... The Alinco DX-70 is a nice compact transceiver that covers all the HF amateur bands and also the 6m VHF band. Although it was released in the late ‘90s, it can still give a good account of itself on the air. Like most modern compact radios, it has an LCD screen and a comprehensive menu system. There are a few buttons on the front panel and a rotary encoder for tuning and adjusting operating parameters. I acquired one of these units from a deceased estate a few years ago. When I powered it up, it was almost entirely unusable owing to the highly erratic behaviour of the rotary encoder. Rotating it even one ‘click’ would cause unpredictable jumps in the relevant value. Just touching the control caused values to change. A search on the ‘net showed that this was a common fault, but no solutions came up. At the time, I was ignorant about the workings and availability of encoders and imagined that they would be custom items peculiar to each piece of gear. Fortunately, the manual included a parts list, so I Googled the part number and found one supplier in Slovakia who had it listed for €10. I tried to order one, but the company required a minimum order value of €50; that was more than I had paid for the radio! So I put it on the shelf, awaiting inspiration. Two years ago, I saw a post on the ‘net from an amateur who had the same problem. I contacted him to see if we could put an order together from the Slovakian supplier. However, by then, they had no stock and were unlikely to get more. The other amateur ordered a few encoders from China and very kindly offered to send me a couple. When they eventually turned up, I took the front panel off the radio and had a good look at the encoder. The new ones were mechanically almost identical to the original, so I set about replacing it. The board had very thin traces, so it took a lot of patience, solder wick and a solder sucker to remove the old unit, but it all went well. The display was stable on powering the rig up, and the encoder incremented and decremented stably. My joy was short-lived, unfortunately, as I soon realised that for every ‘click’, the value would change by two units! At this point, I received the latest Silicon Chip magazine, which contained an article describing a pocket-size audio oscillator that employed a rotary encoder. The article also included some information on the operation of rotary encoders (Shirt-Pocket Audio Oscillator, September 2020; siliconchip.au/Article/14563). That was very enlightening; I learned that there were two main types of RE – could I have the wrong type? I saw that Jaycar had one in their catalog, so I bought a sample and patched it in parallel with the first replacement, as I did not want to do more work than was necessary on the PCB. To my relief, this encoder worked perfectly! I siliconchip.com.au Australia's electronics magazine February 2023  93 then installed the new one properly, so the Alinco is now working as it should. A case of faulty PICs P. G., of Inglewood, WA found out the hard way that when you repair a device, you’d better make sure the replacement parts are functional... After several years of service, my PICProbe (October 2007; siliconchip.au/Article/2392) had the smoke blown out of it when I inadvertently touched it to a 12V supply point on a circuit board. I built mine as the low-voltage (direct 5V supply) version. I use a PICkit 4 regularly, so I ordered a pack of four PIC10F206 replacement chips. The probe tip connects to the PIC’s GP3 input, which doubles as the Vpp pin for programming. After removing the old chip, I checked the operation of the red and green LEDs to confirm that the MMUN2211 was switching properly – all good. I removed the two external input protection diodes and noted the last two bytes in the new PIC’s flash before downloading. I uploaded PICPROBE.HEX to the chip using MPLAB X IPE. The code was programmed and verified perfectly in the first attempt. But when I tried to use the probe, the output appeared to be locked low, turning on the red LED, indicating a high on the input. This proved to be correct – the input pin GP3 was pulled high. Thinking I might have overheated the chip and internally damaged the input, I tried another fresh PIC with the same result. After removing the first PIC, I closely checked the PIC’s pads, and there was no path between GP3 and Vdd. I used a hot air soldering station, and I am not new to SMDs, so I am confident that I didn’t damage either of these chips. The chips programmed on the first attempt on both occasions, and a manual verification revealed no programming problems. The replacement chips came from an Australian supplier I found on eBay (unsurprisingly now disappeared). I suspect that the chips I got were ‘seconds’ that should have been discarded; possibly, they escaped the factory by the back door – I can’t prove this, but the symptoms point that way. The chips can be programmed, suggesting that 3 of the GPIO pins are operational. The 4th I/O pin, GP2, behaves correctly when toggled by the software. So I think I have 4 I/Os that work. The probe pin, GP3, is pulled high by a current that I measure at 245µA, very close to the “weak pull-up” specification of 250µA. I cannot disable the weak pull-up. When I ground GP3, the software still reads the pin as being at a high level. If I configure GP3 as MCLR, the PIC does not reset/restart when I pull it low. Finally, GP1 sits at a constant 3V regardless of what the software does. So I purchased some PIC10F200s from element14, a vendor I trust, and swapped one in. The PICProbe immediately started working again! There must be a lesson there somewhere regarding purchasing components from unverifiable sources. Also, when I was ordering the replacement PICs, the PIC10F200 was the only option available from element14; the 202, 204 and 206 will not be available for months. Clearly, the world’s carmakers have not resorted to using PIC10F200s in their SC CAN systems! Silicon Chip as PDFs on USB ¯ A treasure trove of Silicon Chip magazines on a 32GB custom-made USB. ¯ Each USB is filled with a set of issues as PDFs – fully searchable and with a separate index – you just need a PDF viewer. ¯ 10% off your order (not including postage cost) if you are currently subscribed to the magazine. ¯ Receive an extra discount If you already own digital copies of the magazine (in the block you are ordering). The USB also comes with its own case EACH BLOCK OF ISSUES COSTS $100 OR PAY $500 FOR ALL SIX (+POSTAGE) NOVEMBER 1987 – DECEMBER 1994 JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 WWW.SILICONCHIP.COM.AU/SHOP/DIGITAL_PDFS Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed 94 Silicon Chip Australia's electronics magazine siliconchip.com.au A selection of our best selling soldering irons and accessories at great Jaycar value! 25W Soldering Iron TS1465 $16.95 Build, repair or service with our Soldering Solutions. We stock a GREAT RANGE of gas and electric soldering irons, solder, service aids and workbench essentials. 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Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. Light with automatic switch-off It is common to have two light switches controlling one light. If they are both in the same position, the light is off, and if they are in different positions, the light is on. That is achieved by wiring the switches up to the light in a clever manner. The circuit shown here is an electronic counterpart of that electrical arrangement, but it also has a timer. This way, even if you forget to switch the light off, it will go off by itself after a certain time. It uses two momentary pushbutton switches connected to the control box via low-voltage wiring. With a press of either button, the light is on for 40 seconds, which should generally be adequate to climb one flight of stairs (for example). The light extinguishes automatically after that. You can change the light’s on-time by varying the value of one resistor. S1 and S2 are both momentary SPDT types, feeding the inputs of their respective debouncing circuits. Each debouncing circuit is a flip-flop 96 Silicon Chip built from two NAND gates, ensuring a clean pulse at the output every time a switch is pressed. Since the two switches are to be located some distance apart, we have used separate NAND gate ICs (CD 4011) for each debouncing circuit. So, every time we press either of the buttons, we get a positive-going pulse at the junction of the cathode of diodes D1 and D2. This pulse triggers the monoshot circuit configured around 555 timer IC3. The triggering occurs on the trailing edge of the pulse. The output of the monoshot goes high for a time calculated as 1.1 × R × C. In this case, R = 3.9MW and C = 10µF, and 1.1 × 3,900,000W × 0.00001F = 42.9s. So, if you increase the value of either component, the on-time will increase and vice versa. This output pulse from the 555 drives the base of NPN transistor Q1 (2N2222), which powers the coil of relay RLY1. Its mains-rated contacts are wired in series with the light. Diode D4 (1N4004) protects Q1 against transients during relay Australia's electronics magazine switch-off. The 10µF capacitor must be a low-leakage type, or it may never charge sufficiently via the 3.9MW resistor to switch off the 555. A CMOS version of the 555 timer is used to provide sufficiently high impedances at inputs pins 6 & 7 for correct operation. The circuit is powered from a 9V DC supply which can be either a plugpack or a battery. The wiring between the relay contacts and mains input/output sockets needs to be fully insulated, with mains-rated wire used and the relay contacts well separated from the rest of the circuit (a chassis-mounting relay is ideal for this). Note that dedicated low-voltage wiring must be used between the switches and the control module. Do not be tempted to use existing mains wiring, even if you disconnect it, as that is a trap for someone who might come along in the future and think it’s OK to reconnect it to the mains. Raj. K. Gorkhali, Hetauda, Nepal ($75). siliconchip.com.au Automatic mouse clicker When programming lots of microcontrollers, we go through the same process many times. We insert the chip in the socket, apply power, switch to the computer, click the Program button, verify it was successful, then go back to the programming board, switch off the power and remove the chip. We thought it’d save a lot of time if we didn’t have to switch between the programming board and the computer; ideally, the computer would click the ‘program’ button for us as soon as power was supplied to the chip. That’s the sort of thing this very simple circuit can do. It takes advantage of the Raspberry Pi Pico’s ability to emulate a mouse. It isn’t just for programming micros; any time you need to click a button on a computer in response to an external stimulus, this circuit could do it. We used the Arduino IDE to produce a program for the Pico that ‘clicks’ the left mouse button when triggered. The trigger is simply an I/O pin configured as an input with an internal pull-up or pull-down. The click is triggered when the pin is pulled low or high (depending on the configuration) and stays that way for 300ms. The Pico waits for the state to reset before getting ready to trigger again. In our case, we use the fact that power is switched to the chip to be programmed as the trigger. The 300ms delay also ensures that the micro’s power stabilises before starting the programming process. The resistor circuit is sufficient for cases where the computer powers the programming rig. You may not need to connect pin 3 if the Pi Pico and programmer are powered from the siliconchip.com.au same computer, as the grounds will be common. The resistor ensures that a voltage mismatch does not cause damage. In this case, use the “POWER_ CLICK_2_RESISTOR.uf2” firmware file. The GP1 pin (pin 2) is set as an input with an internal pull-down. The positive and negative wires are connected to the target chip’s power pins for sensing. The Pico’s USB socket is connected via a USB lead to the computer that needs to be ‘clicked’. This method activates when around 1.5-2V is present on the positive wire. We also tested a version using a 4N25 opto-coupler for more robust isolation. Here, we’ve configured GP1 as an input with an internal pull-up. When sufficient current flows through the 4N25’s LED via the 1kW current-­ limiting resistor, its output transistor turns on, pulling GP1 low. This arrangement triggers at similar voltage levels and should have no trouble dealing with inputs up to 15V. This circuit requires the “POWER_ CLICK_2_OPTO.uf2” firmware file. We don’t recommend using any of these circuits for anything above 15V, and certainly not with mains power. If you don’t need power sensing and just want to trigger a mouse click with a pushbutton or similar switch input, the third switch circuit will also work with the “POWER_CLICK_2_OPTO. uf2” firmware. In this case, the pushbutton pulls the GP1 pin to ground, similarly to the opto-coupler. We’ve included the Arduino code with our downloads for this design. If you are familiar with the Arduino IDE, you can use it to modify and upload the code to the Pico. Australia's electronics magazine Circuit Ideas Wanted Got an interesting original circuit that you have cleverly devised? We will pay good money to feature it in Circuit Notebook. We can pay you by electronic funds transfer, cheque or direct to your PayPal account. Or you can use the funds to purchase anything from the Silicon Chip Online Store. Email your circuit and descriptive text to editor<at> siliconchip.com.au If you don’t have the IDE or want to use the firmware as is, then hold the BOOTSEL button on the Pico while plugging it into the computer. A virtual flash drive (named ‘RPI-RP2’) should appear, and you can upload the firmware by simply copying the appropriate UF2 file to it. If you are using the OPTO version, you can test it by shorting pins 2 and 3 (GP1 and GND) on the Pico, remembering to account for the delay. This should have the same effect as clicking your mouse. Besides the programming rig mentioned above, another possible use for this circuit is a 21st-century update on the Map Reader from March 1989 (siliconchip.au/Article/7516). It used a cheap pocket calculator to count pulses from a photo-interrupter attached to a wheel to measure distances on a map. With our Clicker circuit and the Calculator application in Windows, we could get the same effect by entering “1+” in the calculator and then positioning the mouse pointer over the “=” button. Each click then increments the count. Tim Blythman, Silicon Chip. February 2023  97 Frequency comparator using discrete logic This circuit is a digital system that compares two signals and indicates which has the greater frequency or if they are equal. I aimed to design a circuit for visualisation purposes, comparing two pulse trains that might not have a 50% duty cycle. There may be any phase difference between signals at equal frequencies. In this respect, this design is different from, for example, phase-frequency detectors used in ICs such as the (74HC)4046, MC4044 etc. As their name implies, those detectors respond to the phase difference between both signals, and the logic state of their outputs depends on it. I wanted to avoid using any programmable devices, so I implemented it using flip-flops and logic gates plus some diodes, capacitors and resistors, as shown in Fig.1. It works on the principle that if one signal has a higher frequency than the other, sometimes there will be two edges at that input between edges appearing at the other input. The signals are fed in at F1 and F2. The first part of the circuit on the left, comprising flip-flops IC1a & IC1b (74HC74) and XOR gates IC2a & IC2b (74HC86), functions as a special kind of flip-flop triggered by rising edges at both inputs. The outputs of this part of the circuit (points “a” and “b”) always complement each other (there is no invalid state) and have logic states depending on which of the two inputs received a rising edge last, regardless of the actual logic state of the inputs. It works as follows. If a rising edge arrives at the F1 input, the Q outputs of both IC1a and IC1b take the same logic level, high or low. Due to the input connection arrangement of XOR gate IC2a, its output (point “a”) will go high. As the inputs of IC2b are connected to both Q outputs, its output (point “b”) will simultaneously go low. But when a rising edge is applied to the F2 input, both Q outputs take different logic levels, so point “a” will go high and point “b” will go low. Tying input F1 to F2 and applying a rising edge to them makes points “a” and “b” invert their logic state. The outputs of XOR gates IC2a and IC2b are connected to the D inputs of flip-flops IC3a and IC3b (74HC74). So if, for example, input F1 receives two rising edges without a rising edge arriving at input F2 between them, output Q1 of IC3a will go high. If the Q2 output of the other flip-flop, IC3b, is low, the Q1 output of IC3a will stay high, and IC3b’s Q2 output will remain low. This low level from the Q1 output of IC3a will quickly discharge the 100pF capacitor through diode D1, and a high level will appear at the output of IC4b (74HC00), lighting LED1 while LED2 will remain off. That is the indication that F1’s frequency is higher than F2’s. If the Q2 output of IC3b were also high, NAND gate IC4a would reset both flip-flops. On the arrival of the following two consecutive rising edges at F1, the Q1 output of IC3a goes low again, lighting LED1. If it is input F2 that receives two rising edges instead, the opposite happens and LED2 will be lit, indicating that the frequency at F2 is the highest. If the frequency at F1 is equal to that at F2, both LEDs will show the same logic state (on or off) depending on the phase difference. Diodes D1 & D2, along with their associated resistors and capacitors, plus IC4b and IC4c, convert the negative pulses from IC3a or IC3b into a steady high state (or at least higher duty cycle pulses), improving the brightness of the LEDs. Those two capacitors have low values since, in some cases (mainly when both input frequencies are high), the pulses coming out of IC3a or IC3b can be very narrow. If the capacitors values were not small enough, they would not be completely discharged and the pulses would not reach the LEDs. On the other hand, the resistor values can be high, slowly charging the capacitors to widen the outgoing positive pulses. If low-frequency signals will be applied to both inputs, the RC product should be higher. However, the higher it is, the longer the output will take to settle if the input frequencies change. Fig.1 98 Silicon Chip Australia's electronics magazine siliconchip.com.au In short, the value of these components depends on the frequency span that will be applied to the circuit and the speed desired from it. Some experimentation may be needed. To summarise, if F1 > F2, LED1 will light and LED2 will not. If F1 < F2, LED2 will light and LED1 will not. If F1 ≈ F2, LED1 & LED2 will both be lit, or neither. I found that the difference between F1 and F2 that satisfies the condition F1 ≈ F2 is not constant, neither in absolute terms nor in percentages, but increases with increasing frequency. They must be within about 1% at 500kHz, rising to 2% at 1MHz, 3.5-4% at 2MHz, 5.5-6.75% at 3MHz and 7.5-11% at 4MHz. I primarily intended this circuit to operate between 500kHz and 1.5MHz. Nevertheless, I tested higher frequencies and found that it works correctly as long as both frequencies are below 5MHz, or one is below 30MHz. That maximum could increase if faster devices (such as the 74AC logic subfamily) were used. I did find one circumstance that made it fail. If both frequencies are exactly equal and the rising edges arrive at the inputs with a precise time difference of around 10ns, the output corresponding to the lagging phase input turns on while the other one turns off. That situation is unlikely, and the problem does not arise for smaller or greater time differences. To solve that problem, I designed the add-on circuit shown in Fig.2. The points marked Input 1 and Input 2 are the new signal inputs. This add-on circuit inverts some rising edges, producing a narrow pulse for the falling edges. Thus, if the points “c” and “d” in Fig.1 have different logic states, and if the problem explained above occurs, one of the input signals will have the rising edges changed to falling edges and vice versa. Both outputs will consequently take the same logic state. My testing shows this does not change the maximum simultaneous frequency the circuit can handle, nor the cases where F1 ≈ F2. Ariel G. Benvenuto, Paraná, Argentina. ($100) Skylight controller A massive hail storm destroyed the skylight in our en-suite bedroom last year. I decided to cover up the old skylight and install a solar-powered LED panel skylight I purchased from Bunnings. The results were very impressive. It is very bright, and you would swear it is a real skylight. The drawback (there has to be one) was that during thunderstorms, the skylight would flick on randomly and stay on for about a minute, which is quite annoying when you are trying to sleep. It also came on randomly during the night, even when there was no lightning around. The circuit presented here uses the solar panel as the daytime light sensor and also adds a few seconds of time delay due to the 1000µF capacitor. The 4.7kW resistor discharges the 1000µF capacitor in the absence of daylight and also prevents excessive gate voltage to the Mosfet. The 12V relay was salvaged from an old plasma TV and has a coil resistance of 580W. The series-connected 560W resistor keeps the voltage within the specifications of the relay coil. The relay contacts are connected in series with the LED panel, so it is only switched when there is sufficient daylight. The Mosfet used in this design is overkill, but I had one on hand. I was going to switch the panel directly with the Mosfet but could not get it to work reliably, hence the relay. I used matching plugs from Jaycar to enable me to easily install and remove the device in case of repairs or warranty claims. Geoff Coppa, Toormina, NSW ($65). Fig.2 siliconchip.com.au Australia's electronics magazine February 2023  99 Vintage Radio 1938 VE301Wn Dyn Volksemfänger: the People’s Receiver By Ian Batty Was it only ever a propaganda radio? You will have to decide for yourself. I addressed the historical and political context of radio that came after this one, the DKE38 Kleinempfänger, in the July 2017 issue (siliconchip. au/Article/10728). My reading casts doubt on the common belief that the VE301’s design was purely the result of political pressure. Otto Griessing designed the VE301 at the company Dr Georg Seibt AG. This followed a request by propaganda minister Joseph Goebbels to design a reasonably-priced but high-­ quality broadcast receiver. The cabinet was designed by Cologne’s (Köln’s) Professor of Artistic and Technical Design, Walter Maria Kersting and his students. Costs had to be kept down, but even so, the VE301 cost roughly two weeks’ 100 Silicon Chip salary. Edwin Armstrong’s superhet patent, owned by RCA, was only released for use by other manufacturers in 1930. But superhets required up to eight valves, so they were more expensive to build than simpler regenerative sets. Also, the very complexity that gave the superhet its superior performance was not widely understood and would not be easily supported by existing local repair shops. A previous Armstrong patent, the regenerative receiver, had been widely used for almost a decade and was well understood. It was the design of choice for many experimenters, young and old. With a single radio valve costing several days’ wages, a minimal threevalve set was the obvious choice. Australia's electronics magazine The VE301 was released at the Internationale Funkausstellung (International Radio Exhibition, Berlin) in August 1933. At only 76 Reichsmarks, it was half the price of any competitor. Over 100,000 sold in the first two days. VE301 initial release The VE301 was clearly a result of that 1933 request by Goebbels, but the official ban on foreign broadcasts was not issued until September 1939. While it’s true that the Nazi government progressively forced more and more draconian restrictions on the German people, casting the VE301’s limited reception range as purely the result of its being a propaganda radio is historically inaccurate. That’s reinforced by the absence of siliconchip.com.au A close-up of the slide-rule dial. Note that German and Austrian cities are both listed. the Reichsadler (imperial eagle) on initial VE301 releases, by print articles of the day advising on the construction of antennas, and by a thriving accessories industry. There were stick-on dial charts listing stations all over Europe: London, Oslo, Paris, Prague, Warsaw, Toulouse, Budapest, Stockholm, and Rome among them. And there were add-on dial mechanisms listing international stations. Radiomuseum is a good place to find examples of these (website: www.radiomuseum.org). The Antique Radios website also has an extended discussion – see the references below. The set is built on a steel chassis and the need for mass production did not force compromises on the mechanical design or the quality of electrical components. There are even shallow stampings in the chassis to show valve positions. Different versions The VE301 was issued in various models: AC-only, AC/DC, DC-only and battery. Many battery versions came in timber cases, while the mains versions were in tall Bakelite cabinets. The initial issue featured no overt Nazi symbolism, though it did have a “speaking eagle” below the uncalibrated semicircular dial. The VE301 “German People’s Radio” was to be ‘a radio in every house’. It needed to be cheap enough for people to buy, simple to operate and use technology that technicians and tinkerers could maintain. The initial VE301Wn used a triode in the RF amplifier/demodulator stage, a moving-iron loudspeaker with no speaker transformer and a 3kΩ filter resistor. Altogether, the design made the cheapest possible choices. A minimalist design It was minimal, but was it cheap and nasty? The initial release used a triode RF amplifier/demodulator and a high-impedance moving-iron loudspeaker – both the cheapest possible choices. Component quality was at least equal to comparable radios. My set had some capacitors replaced by a previous repairer, but I only found one resistor sufficiently out of tolerance to need replacement. The VE301 Dyn, released in 1938, upgraded the design to an AF7 pentode RF amp/demodulator and an electrodynamic speaker with a speaker transformer. The VE301Wn Dyn design, which is what I have, replaced the initial 0-100 semicircular dial with a lettered slide-rule dial and dial cord mechanism. My dial lists cities in Germany and Austria (as you’d expect after the annexation) and, more significantly, cities in what are now Poland and Russia. Editor’s note: At the end of WW2, the Soviet Union annexed East Prussia while much of Pomerania and Silesia became part of Poland. Two Reichsadler symbols flank the dial, and all original components (including the inside of the cabinet) bear that symbol. siliconchip.com.au Opening the rear of the VE301Wn Dyn radio reveals the chassis and electrodynamic speaker (rather than a metal reed type used in the versions from 19337). This later model of Volksemfänger also added an audio output transformer. Australia's electronics magazine February 2023  101 Over twelve years and a variety of models, nine million VE301s were made. 42 manufacturers were involved in pushing out the radios and accessories for the German population. Radiomuseum lists 290 VE301 variants and accessories, so this article cannot cover all possible variations. You can draw basic distinctions from the full type number. VE301B (batterie) is a three-valve battery version, -G (gleichstrom) is the DC version while -W (wechselstrom) is AC only. GW versions were AC/DC, with a barretter (similar to a ballast resistor) in the series heater circuit. Wn (Wechselstrom neu) initially denoted the AF7 RF amplifier/demodulator and revised antenna circuit, but later “W” versions dropped the “n”. Dyn versions use an electrodynamic speaker and the AF7 RF/demodulator. There are inconsistencies, and Radiomuseum is the best single authority. Circuit description I’ve redrawn the whole circuit in Fig.1. My VE301Wn Dyn begins with the dual-wave antenna circuit of L1 to L4. L1 is tapped to allow matching with short or long antennas, with C1 extending the matching capability. L1 is mounted on a swing arm. This allows the user to vary the antenna coupling, substituting for the usual potentiometer-style volume control. Tuned winding L2, in series with feedback winding L4, is used on the 150-350kHz long wave position. L3 shunts L2 for medium wave, reducing the tuned-circuit inductance to cover the range 500-1500kHz. The grid leak resistor-capacitor R1/ C4 combination is in a single casing and sits under the AF7’s shielded grid cap. Its high resistance allows the AF7 grid to drift to a bias of about -0.7V. The screen grid is supplied via R3, bypassed for audio and RF by C7. The anode circuit supplies RF feedback to the antenna circuit via variable capacitor C3. The anode also provides audio, via C6, to output valve V2. The RF amplifier/demodulator stage is decoupled from the main HT supply by resistor R4 and capacitor C5. The output stage, based around V2, uses back-bias developed across R9 and supplied via decoupling components R6/C8 and grid resistor R5. As the RES164 is directly heated by the 4V AC filament supply, R6 is used to balance the average filament voltage to ground, thus reducing mains hum. V2’s screen, unusually, is fed via dropping resistor R7, bypassed by C10. This agrees with the RES164 screen voltage specification of 75V. V2’s anode connects to output transformer T1, then to electrodynamic speaker LS1. T1’s primary is bypassed using anti-resonance capacitor C9. Mains transformer T2 has 220V and 4V AC secondaries. Rectifier V3, an RGN1064, has its filament supplied from an extension of the HV secondary. It’s an unusual configuration but avoids the need for high-voltage insulation between the HV and filament windings. This does commit the design to halfwave rectification and the resulting need for better supply filtering, but the low HT drain of only 24mA eases the task. It is unusual to see a valve rectifier’s anode connected to supply ground (via back-bias resistor R9). Still, the circuit works perfectly well, with the rectified DC supplied from the other end of T2’s HV winding. Supply filtering is by the combination of filter capacitors C11/C12 and the field winding of electrodynamic Fig.1: the redrawn circuit diagram for the VE301Wn Dyn radio. As there were many different versions of this radio produced, many circuits found online will have small changes compared to this one. 102 Silicon Chip Australia's electronics magazine siliconchip.com.au Most of the rubber-covered wiring on the set was in good condition, but some sections had lost insulation and were promptly replaced. The AF7 wears a shielded “top hat” over its grid cap connection. The grid leak resistor and capacitor are housed underneath the shield. speaker LS1. Finally, R8 adds to the HT current drain of the two valves, ensuring enough magnetising current for the loudspeaker’s field coil. Regeneration Edwin Armstrong showed that controlled regeneration could greatly improve receiver performance. As detailed below, full regeneration in the VE301 Wn increases sensitivity by some 40 times. It’s easy to understand that regeneration increases gain, and feedback calculations can either derive gain from feedback if the feedback factor is known, or derive the feedback factor if the gain is known. But it might not be so obvious why bandwidth varies so greatly. We’re familiar with negative feedback’s effect on bandwidth – it generally increases it. Thus, it makes sense that positive feedback should reduce bandwidth. In the regenerative tuned circuit, feedback does this by reducing the effective circuit resistance, increasing tuned-circuit Q. Q can be calculated either as 2πf × L ÷ R or as (1 ÷ R) × √L ÷ C. The second formula is preferred as it indicates that a tuned circuit with a high L/C ratio will have a higher Q. Q can also be measured as fc ÷ ∆f, where fc is the resonant frequency, and ∆f is the bandwidth between half-power points. Measured bandwidths of ±400Hz (maximum regeneration) and ±4.15kHz (zero regeneration) at 1400kHz gave calculated Q factors of 750 and 66, respectively. Circuit resistances came out to 1.5W and 17W, respectively. The ratio of the measured Q values (approx 11.3:1) conforms to the calculated resistance ratio of 1:11.3. We can also determine the relationship between gain and bandwidth by assuming that the gain-bandwidth product is constant; increased gain gives reduced bandwidth. In summary, along with the general stability problem, the regenerative circuit suffers from reduced bandwidth with increasing feedback. The VE301 also suffers from dial calibration errors. Tuning to 600kHz with maximum regeneration, the set drifts about 40kHz high as regeneration is adjusted to zero. The close antenna-grid circuit coupling also affects dial calibration. Restoration I auctioned this set off at an HRSA auction to a fellow HRSA member. He was kind enough to let me borrow it to check out this classic radio. The first problem was the mains cord. It was not anchored, and the Active wire had broken clear of the mains switch connection. Fortunately, I observed my own advice to never This Volksemfänger was designed with multiple models to suit batteries and AC or DC mains. For example, this set has a wire on the power transformer to select between 110V, 150V and 220V mains operation. Some other manufacturers would provide 125V or 130V instead of 150V for the primary tap. Be sure to check the circuit diagram for your set. siliconchip.com.au Australia's electronics magazine February 2023  103 turn anything on until I’d checked the power supply. A cordgrip clamp fixed the problem – these grip the cord securely, insulate it from the chassis penetration and prevent twisting. The set had been worked on, with both electrolytics and many of the fixed capacitors replaced. Much of the rubber-covered wiring was still good after some eighty years, but I replaced the sections that had lost insulation. The original regeneration capacitor was missing and a potentiometer had replaced it in the feedback circuit. On testing, this arrangement worked well enough. I did alter the pot’s connections to give more predictable control. The resulting changes to the circuit are shown in Fig.2. This is an example of a set where you either demand complete authenticity and try to salvage components from a wreck, or accept some compromise and create a working radio. Valve V1 and rectifier V3 both tested weak, while V2 had been substituted with a Russian valve for which I’ve been unable to find data. As this had a “loctal” base, an adaptor to the European 5-pin base had been fitted. V3 had been bypassed with a 1N4004 silicon diode. The HT drain is low, so I accepted that the original RGN1064 would work well enough and removed the 1N4004. On test, with just the RGN1064, the main HT measured 234V – close enough! The AF7 and the substituted RES164 were more of a problem. I was able to buy a pair of NOS AF7s online and Using clip leads for testing has the advantage that you don’t have to reach into the chassis to make measurements and it’s harder to slip and short something! they tested perfectly. The RES164 is one of the “Miniwatt-class” of output pentodes such as the B443, with 4V/150mA filaments. I couldn’t get a suitable replacement in time, so the substitute stayed in place. The tuning capacitor’s outer plates have the ‘petalled’ form that allows exact tracking adjustment. These had been mangled, preventing the capacitor from fully rotating. Some inner plates were also distorted and shorting, but I easily straightened them up and restored correct operation. The hum-balancing pot in the output stage filament circuit was intermittent. It had also been twisted through 360° at some stage, badly bunching up Fig.2: the radio’s regeneration circuit was modified with a potentiometer replacing the original (failed) regeneration capacitor. This modification would have been easier than fixing or finding a substitute. 104 Silicon Chip Australia's electronics magazine the heater circuit wiring and other connections. The pot has a fragile resistance deposition that cannot withstand extensive rubbing from the moving contact. If you find one of these pots in good condition, resist the temptation to adjust it unless really necessary. A similar pot is found in the DKE38, but that one is used to set the bias, not for hum reduction as some online sites mistakenly assert. I substituted the VE301’s faulty pot with a miniature version. How good is it? It’s a three-valver with just two signal valves. The AF7 pentode operates as a conventional regenerative gridleak demodulator, while the RES164 is the output valve. On test, I was able to get the standard 50mW output for an input of 400µV at 600kHz and 1400kHz, 1200µV at 155kHz and 200µV at 350kHz. These were achieved just below the point of regeneration and are the maximum possible figures. For the reasons described earlier, these sensitivities gave extreme -3dB bandwidth restrictions of ±250Hz at 600kHz (really!), and ±400Hz at 1400kHz. A practical regeneration setting, needing about 2mV input for 50mW out, gave bandwidths of about ±1kHz at 600kHz and ±1.8kHz at 1400kHz. Signal-to-noise ratios exceeded 20dB for all measurements. With full regeneration, -40dB skirt selectivity was ±25kHz at 600kHz and ±86kHz at 1400kHz. siliconchip.com.au Experience with the DKE38 led me to expect a significant change in the AF7’s anode/screen voltages. They did rise a bit, but less than expected. The result is that the VE301 gives a pretty constant output for most signals, as though it had an AGC function. Regenerative gain Going back to my maximum sensitivity of 400µV for 50mW out and then cutting regeneration completely, I needed around 15mV to get 50mW output again. That implies that regeneration supplies an extra stage gain approaching 40. The DKE38 Kleinempfänger’s best sensitivity of around 600µV suggests that regenerative demodulators give comparable RF performance just before the point of oscillation. Any major improvement would need extra RF gain before the demodulator, or extra audio gain after it. Buying another I picked up another VE301Wn (AC operation, moving-iron speaker, triode RF amplifier/demodulator) online for about half what most were asking. It was described as “working”. It will be interesting to see what some folks think “working” really means. Special handling The VE301Wn Dyn radio is a fairly simple set, with sparse few parts located on the top and underside of the chassis. Many of the capacitors had been previously replaced; only one resistor ended up needing to be changed. On air, with about 10 metres of antenna thrown over the carport, 774 ABC Melbourne rocked in with minimum regeneration and the antenna coupling backed off. With some adjustments, I could easily pick up all metropolitan stations. Given the optimum sensitivity of 400µV, would I be able to pull in 3WV at 594kHz? Yes and no. Tuning to that frequency, I still had a strong signal from Radio National at 621kHz. Adding a signal generator on its CW setting, I could hear a heterodyne at 594kHz, but could not make out the broadcast. The VE301’s skirt sensitivity was siliconchip.com.au just not good enough to sufficiently reject the 621kHz signal in favour of 3WV at 594kHz. Among the many accessories marketed for the VE301 were several passive antenna tuners/preselectors and a powered RF preamplifier. Either of these would have improved the separation of closely-spaced stations. What about strong signals? Starting with 400µV, giving 50mW output, I cranked up the signal generator. The output reached the VE301’s maximum of 0.5W at 2mV of signal and did not rise much as I got to 100mV on the signal generator. Australia's electronics magazine P-base valves such as the AF7 seat into the socket by sliding down past leaf springs. When seated, the valve’s Bakelite base does not extend very far upwards past the chassis/socket rim, so it’s tempting to remove a valve by grasping the envelope. Don’t do this. Take the time to grasp the top rim of the valve base. You may need to rock the valve side-to-side to get it moving, and be careful – it might suddenly release with the risk of smashing the envelope against other parts of the radio, the case, or other things on your bench. I should register a new acronym, TNMTAM (they’re not making them anymore) and just use that from now on. Acknowledgements Thank you to Herbert Detlefsen of the HRSA for the loan of this historic radio. For more on this series of radios, see the extended discussion: siliconchip. au/link/abgf For the relevant Radiomuseum page, visit siliconchip.au/link/abgg SC February 2023  105 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. Send your email to silicon<at>siliconchip.com.au Questions about the Breadboard PSU I am curious to know what oscilloscope you used for the three scope grabs Scopes 1 to 3, on page 35 of the December 2022 issue. While all digital oscilloscopes can precisely measure time on the X-axis, it is customary for the calibration divisions to be at round figures, usually in 1-2-5-10 intervals. For the calibration points to be at odd values, with three significant figures, is most unusual. I hope I never have to use such an oscilloscope since it makes reading the time values at various points very difficult (unless using measurement cursors). I am also curious to know if Tim Blythman is left-handed. I would, as a right-handed person, have designed the Breadboard PSU and Display to be at the left side of the breadboard, out of the way of my right hand making changes to the components on the breadboard. As pictured on page 40, the display would be upside-down for 90% of the population wanting clear access to the breadboard. (R. S., Kogarah, NSW) ● The scope grabs were made using a PicoScope USB scope and the PicoScope 6 PC software. The X-axis time values are relative to the trigger point. Tim Blythman is right-handed. He advises that he unplugs the Breadboard PSU from the breadboard to make changes to the design. Thus, it is on his right while using the PSU, giving convenient access to the settings, and the breadboard is open to both hands to make changes to the circuit. item that comes up on the website is item 1416715, a 100-400mm stepper motor module. (K. M., Margas, Tas) ● Graham P. Jackman responds: I checked the Banggood website and the actuator I used seems to be missing now. However, eBay has similar units available from China, such as: siliconchip.au/link/abiv siliconchip.au/link/abiw siliconchip.au/link/abix The last item is a bare mechanism to which you could add a motor. Others are also available if you search. The main disadvantages are longer delivery times. IKEA clock opens a can of worms Do you know why the New GPSSychronised Analog Clock driver does not work with my two IKEA TJALLA sweep clocks (September 2022 issue; siliconchip.au/Article/15466)? The article mentions that these clocks are suitable. I am sending some oscilloscope traces that show their waveforms. (G. K., Macgregor, Qld) ● Geoff Graham responds: You seem to have uncovered a “can of worms”. I tested a TJALLA clock, and here is the waveform it generated (shown below). It does not match your waveform, nor does it match the waveform generated by my circuit. This is very strange as I know of several TJALLA clocks that are running fine with the New GPS Clock Driver. Unfortunately, I cannot purchase another to double-check because IKEA is no longer selling the TJALLA clock. The best solution would be to make the pulse width programmable, but it was very difficult to do that, as there was very little free flash left in the microcontroller. Still, I managed to do so and by the time this issue is published, testing should be finished and the revised firmware (v1.2) will be available. With the new firmware, when you select a sweep movement, it will prompt you with an additional question: “Pulse Width?”. You will have three choices: Normal Pulse (50%), Wide Pulse (75%) or Extra Wide (100%). It will not necessarily be obvious which setting to use, so a short ‘README’ file will be included with the firmware to explain the choices and give some guidance. In the meantime, please recheck the output of your TJALLA clocks. The fact that it does not match my measured waveform is rather confusing Sourcing screw drive for traverser In the Circuit Notebook entry “Traverser for photography” (December 2022; siliconchip.au/Article/15592), the part number given for the screwdriven platform and stepper motor on banggood.com was 1416716. Is that the correct part number? The only similar 106 Silicon Chip Australia's electronics magazine siliconchip.com.au and implies that IKEA can change their clock designs on the fly. GPS Analog Clock has low output voltage I bought a GPS-Synchronised Analog Clock kit from you recently. Initially, I had a problem with IC3 (MCP16251), which did not produce the required voltage (4V) for the GPS module. You sent me a replacement IC which fixed that problem. Now the problem is that the circuit is not producing the required 1.5V to the clock’s coil. I thought IC2 (MCP6041) was also faulty, but the problem remains after replacing it. The circuit produces 4V, but when the LED goes off, the voltage drops gradually from 4V to 0.1V. Is that normal? Could there be a problem with the PIC16LF1455? (G. P., Quakers Hill, NSW) ● Yes, it is normal for the 4V supply voltage to the GPS module to drop to near zero after the LED turns off. That’s because power for the GPS module is only provided when the module is active. Once a satellite lock has occurred and the time is known, it is powered down. We doubt the PIC is faulty, although that is not impossible. How are you measuring the voltage across the clock motor’s coil? If you are using an ordinary multimeter, it will always read low (or even zero) because the voltage is pulsed. The only reliable way to measure the output is with an oscilloscope. Have you tried the circuit with a clock movement? What happens when you do? To help further, we need to know the exact configuration and detailed sequence of events when it is connected to the clock movement and the batteries are inserted. Are you using a sweep or stepping movement? Does the clock try to run? Do you get the correct sequences of flashes on the LED etc? With a detailed description, we may be able to help further. Bench Supply output voltage will not adjust I have built the 30V 2A Bench Power Supply from the October & November 2022 issues (siliconchip. au/Series/389). It was working fine after I finished building it, but I wanted to see if I could put some load on it. I had it set at 5V and 0.2A, then started to raise the amps. I’m not sure what happened next but now I can’t adjust the voltage. It is stuck at 24.8-25V and cannot be changed using VR1. (J. T., Werrington, NSW) ● First, check if potentiometer VR1 has its wiring connected to the potentiometer terminals. A wire might have become disconnected. If that is OK, check op amp IC1. Verify that its pin 4 supply is at about -8V and that pin 8 is at about 24V, both with respect to a 0V point on the PCB (eg, V- at CON2). Compare the voltage at pin 3 of IC1 with the output at pin 1. They should be at a very similar voltage, within a few millivolts. If using a socket for IC1, ensure it is inserted correctly without any IC leads bent up under the socket. If Q1 was not attached to the heatsink when you put a load on the supply, it could have overheated and gone short-circuit, resulting in the output voltage staying at around 25V. Check that there is no short circuit between its collector and emitter leads (middle & right) with the supply off. GPS-Synchronised Analog Clock with long battery life ➡ Convert an ordinary wall clock into a highlyaccurate time keeping device (within seconds). ➡ Nearly eight years of battery life with a pair of C cells! ➡ Automatically adjusts for daylight saving time. ➡ Track time with a VK2828U7G5LF GPS or D1 Mini WiFi module (select one as an option with the kit; D1 Mini requires programming). ➡ Learn how to build it from the article in the September 2022 issue of Silicon Chip (siliconchip. au/Article/15466). Check out the article in the November 2022 issue for how to use the D1 Mini WiFi module with the Driver (siliconchip.au/Article/15550). Complete kit available from $55 + postage (batteries & clock not included) siliconchip.com.au/Shop/20/6472 – Catalog SC6472 siliconchip.com.au Australia's electronics magazine February 2023  107 If you need more help, send us back more information, such as the results of the above checks. Increasing VGA PicoMite resolution Would it be feasible to use a second Raspberry Pi Pico as a video coprocessor for the VGA PicoMite (July 2022; siliconchip.au/Article/15382)? Two VGA PicoMite boards could be joined via the 40-pin interface using long-pin headers into a socket. Some pins may need to be isolated between the two boards by using short pins (or no pins) to avoid hardware conflicts. The MMBasic code would need to be modified to send video drawing instructions to the video coprocessor, freeing up the RAM used by the video buffer. Since the code on the coprocessor would be relatively simple, this should free up lots of RAM and allow for a resolution like 1440 × 900 pixels. If the coprocessor used a Pico W, it could also act as a WiFi coprocessor, communicating with the MMBasic board via the same 40-pin interface. This would be neater than having an ESP8266 or ESP32 board connected by a cable. If there is sufficient RAM space on the coprocessor, it might be possible to have more colours and/or multiple brightness levels, although this would require a new version of the board(s). I am a software person, so I am curious to know whether the communication between the two boards would be fast enough for my ideas to work. (P. B., Turramurra, NSW) ● Geoff Graham responds: those are interesting ideas and I will discuss them with the others on the team, but I cannot see us implementing them. The main reason is that the VGA PicoMite was intended as a super simple computer; with just a few components, you could have something that worked. Adding a second Pico with interconnect issues is a lot more complexity just for a higher video resolution. Using SC200 Amp with Active Subwoofer In the articles on the Active Monitor Speakers and associated Active Subwoofer (November 2022 to February 2023; siliconchip.au/Series/390), you 108 Silicon Chip have specified the Ultra-LD Mk.3 or Mk.4 amplifier for driving the Subwoofer. Wouldn’t the SC200 Amplifier module suit this project just as well? (January-March 2017; siliconchip.au/ Series/308). As stated in Fig.9 of the SC200 article, “The frequency response of the SC200 is almost ruler flat over the range of 10Hz-100KHz and should result in greatly extended bass.” (C. H., Evanston, SA) ● Phil Prosser replies: I had to choose one or two amplifier options to keep the design from becoming too complicated, and the Ultra-LD Mk.3 & Mk.4 seemed the best options. However, you are right; the SC200 would work well too. Any good high-power amplifier that can deliver close to 200W into 4W will work. Given the price of the drivers, I encourage people to invest in a good amplifier. If substituting the SC200, you will need to make some alterations to the heatsink drilling, but that is all part of the fun. The design of the amplifier module, which includes the power supply and amplifier, can be changed in a few different ways. Besides swapping the amplifier module, it’s also possible to reduce the transformer voltage to 35V AC or even 30V AC. That will reduce the maximum output from the Subwoofer, but it will not affect the sound quality. It will affect the maximum SPL generated, though. Charging a battery with a load I built the Buck/Boost LED Driver (June 2022; siliconchip.au/Article/ 15340) and want to add the Battery Charger (October 2022; siliconchip. au/Article/15510). I want to use it in my car to charge an auxiliary battery. Is it OK to have the load (a fridge) connected during charging? (P. C., Balgal Beach, Qld) ● We assume you are referring to the Multi-Stage Buck/Boost Charger add-on and not the article on using the Buck/Boost LED Driver as a float charger in the same issue. That is a good question, and the answer applies to pretty much any multi-stage charger. It is sometimes possible to get away with using a multi-stage charger to charge a battery while there is a load on it. However, it is not ideal because the charger cannot distinguish Australia's electronics magazine between the load current and the current going into the battery to charge it. As a result, the charger will likely be forced into bulk charging mode whenever the fridge is running. That could result in the battery being overcharged. It might be possible to compensate for that by changing the various charging parameters, as the MultiStage Buck/Boost Charger Adaptor is very configurable. However, with a load always connected, it won’t be easy to pick a combination of settings that are both safe and optimal, especially with a load that may vary in its current draw. Our suggested solution is to set it up so that the fridge runs directly from the vehicle’s battery and alternator while the vehicle is running and from the auxiliary battery when it is off. That way, the fridge does not put a load on the auxiliary battery during charging, and the charger can operate unhindered. That should be easy to arrange with a suitably rated double-throw relay, with the coil connected to the switched ignition line. That should also be a more efficient arrangement, as less current passes through the Charger. The fridge will probably not be adversely affected by the brief (<10ms) drop-out in power during switching, but if it is, should help to add a low-ESR capacitor bank from the relay common terminal to ground to filter it. By the way, while this is not related to charging, you should have a lowvoltage cutout for the battery to prevent the fridge from over-discharging it, such as our Battery Lifesaver (September 2013 issue; siliconchip.au/ Article/4360). Any other transistor options for 500W Amp? I’ve just ordered two PCBs for the 500W Amplifier (April-June 2022; siliconchip.au/Series/380) as I need an amp that can easily drive nominally 4W speakers (dropping below 3W). My system is active, and this amp will drive only woofers from 80Hz to just above 400Hz, but no more than 500Hz. I already have amps to drive mid- and high-frequency speakers. I want to build this amplifier using components I already have to minimise costs (I have retired, so every dollar counts). My toroidal transformers are 1kVA 52+52V types; I’ll use two siliconchip.com.au bridges with each transformer, one for each secondary winding, so the power supply voltage will be about ±74V. I plan to use NJW1302/3281 power transistors as I have enough to match them. I prefer to use 0.33W 5W low-­ inductance emitter resistors instead of 0.47W as I have plenty of these, and with matched output transistors, lower emitter resistor values should be acceptable. Lower values here would also somewhat lower distortion and output impedance. NJW1302/3281 transistors have lower safe operating areas (SOA), so I should change some resistor values in the protection circuit. Base resistors might also be needed for the output transistors as NJWs have 30MHz bandwidth. I’d appreciate any comments or suggestions to help me build this amp using my stock of components. I’d also appreciate it if you published the formulas used to calculate the protection circuit component values. If the specified transistors are discontinued, it might be necessary to find substitutes and develop new protection resistor values to suit them. (J. P., Wanneroo, WA) ● Based upon the Safe Operating Area (SOA) curves for the NJW1302/3281 transistors, you will need nine devices on each side to ensure the SOA is not compromised when using reactive loads such as a 4W loudspeaker. We considered those devices for the original design (along with several others) but rejected them due to the requirement of nine devices per side, which we considered unreasonable. We chose the MJW21195/MJW21196 devices because they have an approximately 1.5 times higher SOA rating, allowing us to use just six per side. The temperature derating of 1.43W/°C is the same for the NJW1302/3281 and MJW21195/MJW21196 transistors. If you use six on each side of the NJW1302/3281 transistors, the amplifier would be prone to failure unless the load line protection is changed to prevent transistor damage. In this case, the amplifier would also have severe distortion due to signal limiting when used with 4W speakers. It might not be possible to make the load line protection work with 0.33W resistors. For the design as published, the 0.47W resistances were necessary to ensure sufficient voltage at the required current(s) to switch on the load line protection transistors. With nine NJW1302/3281 transistors, you will need emitter resistors of at least 0.75W for the load line protection to work. Recalculation of the load line protection values involves multiple calculations based on the dual-slope load line protection method as described in the paper “The Safe Operating Area (SOA) Protection of Linear Audio Power Amplifiers” by Michael Kiwanuka, B.Sc. (Hons) EE. We provided a link to that paper on page 35 of the April 2022 issue (siliconchip.au/link/abc4). The dualslope calculations begin on page 35 of that PDF. Base resistors for the NJW1302/3281 transistors may be necessary if the amplifier tends to oscillate, but they were not required in our original design. A value between 10W and 100W should be sufficient. To summarise, if we could have used cheaper parts to achieve the goal of 500W into 4W with SOA protection and low distortion, we would have done so. The output transistors and emitter resistors were deliberately VGA PicoMite Build this amazingly capable ‘boot to BASIC’ computer, based on a Raspberry Pi Pico. It has a 16-colour VGA output, a PS/2 keyboard input, runs programs from an SD card and can be quickly built Blocks is a BASIC game that runs on the VGA PicoMite $35 + Postage ∎ Complete Kit (SC6417) ∎ siliconchip.com.au/Shop/20/6417 The circuit and assembly instructions were published in the July 2022 issue: siliconchip.au/Article/15367 This kit comes with everything shown (assembly required). You will need a USB power supply, PS/2-capable keyboard, VGA monitor and optional SD card. siliconchip.com.au Australia's electronics magazine February 2023  109 selected; we don’t think there is any way to change those parts without compromising the performance in some way. We have an article on building a 500W Class-D amplifier coming up within the next few months. It will be considerably cheaper to build than the linear version discussed, as well as being more compact and efficient. However, its distortion and noise figures are not as good (although probably good enough for subwoofer use). Finally, regarding your concern over the MJW21195/MJW21196 being discontinued, that could happen. We try to stockpile critical devices like these when they are about to be discontinued if there is no suitable replacement. If supplies do dry up, we’d have to revise the design completely, as we aren’t aware of any parts that can act as drop-in replacements. Bass Block driver is no longer available I want to build the Bass Block subwoofer from the January 2021 issue (siliconchip.au/Article/14710), but the specified Altronics C3055 woofer is no longer available. Is there a suitable substitute? (P. B., Maryborough, Qld) ● Nicholas Dunand replies: The closest equivalent driver I can find is the SB Acoustics SB16PFCR25-8, available from Wagner Electronics for a reasonable price ($46.50 and in stock at the time of writing). However, the design needs some slight adjustments to get the best performance out of this new driver. Without spending a lot of time investigating all possibilities, a reasonable option is to expand the volume of the 15L part of the enclosure to 20L (eg, by lengthening the enclosure from 396mm to 483mm) and eliminate the tube from the 63mm port, leave it as a 63mm hole in the box. The predicted transfer function is shown below, and it seems reasonable. The iPad software mentioned in the original article is free, so potential constructors can experiment with the design with this new driver option. They might be able to find a better configuration. Getting parts for LowNoise Stereo Preamp I want to build the Low-Noise Stereo Preamp featured in your March & April 2019 issues (siliconchip. au/Series/333). Can you still supply the PIC16F88-I/P programmed with 0111111A.HEX and the 4MHz crystal? I cannot find any reference to the above in your shop. Also, how can I add a balance control to the circuit? (C. J., Samson, WA) ● Yes, the programmed PIC is available. Go to siliconchip.au/Shop/ ?article=1216 and scroll down to the PIC16F88 (Cat SC0886). You can purchase the 4MHz crystal from Jaycar (Cat RQ5274) or Altronics (Cat V1219A). As far as adding a balance control, the simplest method is to disconnect the ground connections of VR1 (eg, by cutting the PCB tracks) and wire them to either end of the track of an added linear pot. Connect its wiper to the ground that VR1 was previously wired to. When centred, the signal level in each channel will be the same. If the control operates backwards, swap its wiper connections. This added potentiometer’s value depends on the volume control pot’s value and the required balance range. A 5kW linear potentiometer should be sufficient when using the specified 20kW volume control potentiometer. Parts for the Hearing Loop Level Meter I am interested in building the Hearing Loop Level Meter from November & December 2010 (siliconchip.au/ Series/15). Are the parts still available from Jaycar etc? Does the circuit use a computer chip? I do not have any way to program one. (J. B., Blackwood, SA) ● Most parts are easily obtained. The circuit board and panel artwork are available online (siliconchip.au/ Shop/?article=345). The only troublesome part is the LM3915. Jaycar has some in stock but only at some stores; see: www.jaycar.com.au/p/ZL3915 There is no computer chip required. Note that we sell programmed chips in our Online Shop for virtually all the projects we publish that require them (see siliconchip.au/Shop/9). Repairing Active Loop Antenna I built the Active Loop Antenna project (October 2007; siliconchip. au/Article/2398) from an Oatley Electronics kit back in the day, but it was trashed when we moved. I am trying to build another one. The loop is finished and I have a PCB that I designed myself, but I need help sourcing a suitable tuning diode. The original SR1060 is not available. Can you suggest a readily available substitute? I have searched element14, RS, Jaycar, Altronics and the internet without results. (P. C., Balgal Beach, Qld) ● The recommended replacement was the KDV149 (two in parallel). You can view the data sheet of the KDV149 at siliconchip.au/link/abho You should be able to get a couple of samples from Kynix at siliconchip. au/link/abhp Circuit for driving a VU meter Have you previously published a driver circuit for the old-style analog audio VU meters such as Altronics Cat Q0490 “VU Meter With Backlight”? (J. A., via email) ● You can use the rectifier and filter circuits for the signal applied to the continued on page 112 110 Silicon Chip Australia's electronics magazine siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip KIT ASSEMBLY & REPAIR FOR SALE DAVE THOMPSON (the Serviceman from Silicon Chip) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, New Zealand, but service available Australia/NZ wide. Email dave<at>davethompson.co.nz LEDsales KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com LEDs and accessories for the DIY enthusiast LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware – www.ledsales.com.au VISIT THE NEW TRONIXLABS parts clearance store for real savings on new parts at clearance prices, with flat rate express delivery Australia-wide – go to https://tronixlabs.com Lazer Security PCB PRODUCTION PCB MANUFACTURE: single to multilayer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au For Quality That Counts... QUALITY COMPONENTS + MORE The parts clearance sale continues, but stock is limited, this month check out the freebies – go to lazer.com.au FOR SALE OATLEY ELECTRONICS www.oatleyelectronics.com CHECK OUT OUR “BULK BUYS” WITH FREE POSTAGE: * 7 X 5M 12V rolls of white/green/blue LED strips for $29 * 10 X 0.5M 12V LED bars for $50 Both include postage. Add any or as many other items for no more than an extra $8 P+P. www.oatleyelectronics.com Phone: 0428600036 ASSORTED BOOKS FOR $5 EACH Electronics and other related subjects – condition varies. Some of the books may have already been sold. See all books at: siliconchip.com.au/link/aawx Email for a quote (bulk discount available), state the number directly below the photo when referring to a book: silicon<at>siliconchip.com.au BUSINESS FOR SALE Well known Australian electronics company for a bargain price. GENUINE BUYERS ONLY Phone: 0410600330 ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone Glyn (02) 9939 3295 or 0431 792 293. 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 Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia's electronics magazine February 2023  111 microcontroller in the VU/Peak Meter with LCD Bargraphs (May 2007 issue; siliconchip.au/Article/2232). Lapel Mic Adaptor SNR & PCB query I am curious about the signal-tonoise ratio for the Lapel Mic Adaptor described in the January 2004 issue (siliconchip.au/Article/3330). Sadly, you do not have the PCB in your inventory, but I understand you can’t have everything in stock. (P. S., Mount Pleasant, SA) ● The signal-to-noise ratio (SNR) was not measured for the published specification as it depends on the noise from the electret lapel microphone itself. That information can be found in the electret microphone manufacturer data. We expect the circuitry to provide an SNR of at least 100dB with respect to 1V RMS output. When tested at the time it was published, the noise was not audible and was better or at least comparable to a Advertising Index Altronics.................................29-32 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 Emona Instruments.................. IBC Jaycar........................ IFC, 9, 11, 13, ............................. 23, 43, 71, 91, 95 Keith Rippon Kit Assembly....... 111 Lazer Security........................... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.............OBC Mouser Electronics....................... 4 good-quality commercial radio microphone system. The SNR could be improved to as much as 114dB with respect to 1V output by using an NE5532 op amp instead of the TL072. We could add this PCB to our Online Shop if you want to order some. There are two versions of the PCB. If you are interested, please tell us which one you want and how many and we can estimate the cost. In most cases, as long as we have the artwork on file and the rights to it, we can get PCBs made for pre-2010 projects. We already stock PCBs for pretty much all post-2010 projects (it is now available SC6627). Variac won’t filter generator output I have a 2.5kW petrol generator that I use to power an older refrigerator, lights etc if there is a blackout. I don’t use it for computers, TVs and other electronic appliances as I suspect these might be damaged by voltage spikes and harmonics from the generator. Is there a straightforward way to filter the generator’s output to enable it to be used with electronic items? I thought of using a 2kW variac since it is basically a large inductor with resistance, but I need some advice on whether this will work and be safe. On another subject, I recall reading Jim Rowe’s articles in Electronics Australia many years ago describing how he built a home computer. This was long before IBM developed the PC architecture, so components such as memory, communication systems, software, processors etc couldn’t be bought off the shelf. If I remember correctly, he was the first person in the world to complete a working home computer, or was narrowly beaten by an American. It might interest readers to hear Jim’s recollections of his achievement and the challenges he faced. (I. P., Fullarton, SA) ● The autotransformer probably will provide little filtering, especially at its full voltage setting. A commercially-­ available line filter will remove some of the RF hash, and a surge-­protected power board can reduce voltage spikes. Concerning the computer, it was just about the first published home constructor article for a computer but was beaten by a month. The computer was called the EDUC-8, and a scan of its 80-page manual is still available to purchase at siliconchip.au/ Shop/3/1816 Help with a power supply kit from AEM I assembled a power supply from a kit many years ago. As I was an Electronics Australia subscriber at the time, I assume it was one of theirs. The only information I have on it is that it is labelled “VERSATILE LAB SUPPLY” and “AEM2521” on the front panel. It is a 30V supply with an ammeter and an inbuilt crowbar circuit inbuilt. I have no idea where I purchased the kit. Do you have any information on this supply? (O. A., Boort, Vic) ● The AEM2521 is from Australian Electronics Monthly magazine. Unfortunately, we do not own the rights to that magazine, so we cannot provide copies of articles. The National Library or your state library would have a copy; the main challenge is figuring out the month of publication; we suspect that the project was published in the July & August 1988 issues. As far as we know, Dick Smith Electronics sold the kit for the AEM2521 supply. SC Oatley Electronics..................... 111 Silicon Chip 500W Amplifier..... 12 Silicon Chip PDFs on USB......... 94 Silicon Chip Shop.................60-61 Silicon Chip Subscriptions........ 42 Silicon Chip VGA PicoMite...... 109 The Loudspeaker Kit.com.......... 93 Tronixlabs.................................. 111 Wagner Electronics....................... 7 112 Silicon Chip Errata and Next Issue SC GPS Analog Clock............... 107 Bass Block subwoofer, January 2021: the specified Altronics C3055 driver is no longer available. The SB Acoustics SB16PFCR25-8 is a suitable substitute available from Wagner Electronics for $46.50 at the time of writing. See the February 2023 Ask Silicon Chip column for advice on tweaking the design to suit this new woofer. High-Performance Active Subwoofer, December 2022: in the parts list, two 3.7-4mm crimp eye terminals are required, not one, and the 377 × 140 × 1.5mm aluminium sheet listed is slightly too small. It needs to be at least 377 × 150mm. Next Issue: the March 2022 issue is due on sale in newsagents by Monday, February 27th. Expect postal delivery of subscription copies in Australia between February 24th and March 15th. Australia's electronics magazine siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes NEW 200MHz $649! New Product! 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