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MARCH 2024 ISSN 1030-2662 03 The VERY BEST DIY Projects! 9 771030 266001 $ 50* NZ $1390 12 INC GST INC GST Laser Communicator Transmit sound over a laser beam Pico Digital Video Terminal HDMI compatible output and USB keyboard adaptor for devices with USB or serial ports ‘Wii Nunchuck’ RGB Light Driver Control up to four independent RGB strips Review: Arduino for Arduinians 70 Arduino projects to build in this book by John Boxall ...and much more! 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Jaycar reserves the right to change prices if and when required. Contents Vol.37, No.03 March 2024 16 Computer Storage Systems, Pt2 We cover the many modern storage technologies such as hard disk drives (HDD), flash memory and solid-state drives (SSD), as well as future developments like 5D optical, holographic and DNA storage. By Dr David Maddison Computer technology Data Storage Systems 56 Electromechanical Tic-Tac-Toe Due to his fascination with Dick Smith’s original noughts & crosses (tic-tactoe) machine made from telephone exchange parts, Steve decided to make one with a modern twist. This article shows how he did it. By Steve Schultz Noughts & Crosses feature 86 Review: Arduino for Arduinians This 478-page book contains 70 Arduino projects and is aimed at those who already have some experience programming or with Arduino. By Nicholas Vinen Book review Part 2: page 16 Raspberry Pi Pico Digital Video Terminal Page 45 92 Bush MB60 portable radio The Bush model MB60 was released in 1957 and is the first valve-based Bush radio to be described in Silicon Chip. The MB60 is a portable radio that uses the Dx96 series of directly-heated valves. By Ian Batty Vintage Radio 30 Laser Communicator The Laser Communicator allows you to transmit voice or music over a laser beam and is ideal for learning electronics! It might not have many practical uses, but it demonstrates what can be done using simple circuits while serving as a good teaching aid. By Phil Prosser & Zak Wallingford Beginner’s electronics project 45 Pico Digital Video Terminal This project adds the ability to communicate with and control a Micromite, PicoMite or WebMite or similar, using a USB keyboard and HDMI display. It uses multiple Raspberry Pi Picos to do this and is VT100 compatible. By Tim Blythman Computer interface project 66 ‘Nunchuk’ RGB Light Driver Driving up to four independent RGB strips, this strip lighting driver includes a built-in strobe light and is motion-operated(!) using a Wii Nunchuk controller. It can be controlled wired or wirelessly. By Brandon Speedie Lighting controller project 77 Mains Power-Up Sequencer, Pt2 The Mains Power-Up Sequencer has four 10A mains outputs with staggered switching, making it easy to power up several devices together. We cover the construction and setup so you can complete the Mains Sequencer. By John Clarke Power control project Page 66 Wii Nunchuk RGB Light Driver 2 Editorial Viewpoint 5 Mailbag 76 Product Showcase 88 Circuit Notebook 98 Serviceman’s Log 1. Arduino-based water pump monitor 2. Battery Lifesaver with load control 3. Carbon monoxide (CO) monitor 106 Online Shop 108 Ask Silicon Chip 111 Market Centre 112 Advertising Index 112 Notes & Errata 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): $70 12 issues (1 year): $127.50 24 issues (2 years): $240 Online subscription (Worldwide) 6 issues (6 months): $52.50 12 issues (1 year): $100 24 issues (2 years): $190 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 Solid-state drive pitfalls As we increasingly favour solid-state drives (SSDs) over traditional hard drives for their speed and reliability, it’s crucial to understand their limitations. While SSDs have transformed data storage with their efficiency, they are not without pitfalls, particularly regarding long-term data retention. Common wisdom suggests that SSDs are not ideal for archival purposes. Data written to an SSD that’s left unpowered for extended periods is at risk of corruption. Regular usage is essential to avoid data degradation. A less well-known problem occurs even if your SSD is powered up daily, affecting many different brands and models of SSD. It may not affect all of them; some could have mitigation strategies. However, I have experienced it with a couple of different brands. This problem occurs when you write data to an SSD and then don’t access it for a long time (months or years). It happens even if the drive is actively used, as long as that particular data is not touched. When you go to access it again later, it is very slow to read back. While freshly written data may read back at 1000-2000MB/s, after a few months or years, it might only do 50MB/s. Some reports I found from other users said that their drives barely managed 5MB/s! That’s not only a lot slower than the SSD with freshly written data, it’s much slower than even an ancient mechanical drive. After searching the internet, I only found a few reports of this phenomenon, far less than I expected. I attribute this slowdown to voltage drift in the flash cells. For example, SLC flash stores one bit per cell as a voltage level. Over time, that voltage can shift closer to the point that distinguishes a ‘zero’ from a ‘one’, narrowing the margin for error and necessitating slower read speeds to ensure accuracy. Like DRAM, I suspect that the ‘sense amplifiers’ used to convert the analog voltage levels into digital data in a flash chip have a ‘settling time’, and that time will be more extended as the margin between the cell voltage and the threshold narrows. Therefore, the controller will automatically throttle reading back to a slower speed if it detects too many errors. The challenge is more pronounced in more common multi-level cell technologies like MLC, TLC, and QLC. With their finer voltage distinctions, these flash devices are even more susceptible to drift, necessitating extensive error correction if the voltage drifts and, consequently, slower read speeds. I also suspect that when the SSD controller reads back cells with voltages that have drifted significantly, it will be programmed to write that data back to refresh the cells, avoiding data corruption. That will also slow down reading. SSD controllers could be programmed to periodically refresh data in the background, mitigating voltage drift. However, this feature seems lacking in many models, as evidenced by widespread slowdowns. For now, manually refreshing the drives may be a necessary workaround. Software is available to do this automatically, reading back all the data on the drive and rewriting it. It would need to be run periodically, eg, every few months, to avoid slowdowns. I’d like to hear if others have encountered similar problems with their SSDs. Have you noticed a significant slowdown in SSD read speeds over time? Are you aware of any other strategies to counteract this problem? By the way, we’ve added some information on this phenomenon to our article on Computer Storage in this issue as it seemed appropriate, given that it specifically discusses flash memory technology. Still, I thought I would expand on it here, giving the issue more attention. Note on Vintage Radio: you may have noticed that recently, we have been indexing Vintage Radio columns on the Contents page along with other articles instead of in the sidebar. However, nothing has changed in the column itself; it is still ongoing. A question for readers: given that the column often describes nonradio vintage equipment (amplifiers, test equipment etc), should we change its name to just “Vintage”, or perhaps “Vintage Gear”? 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 03 9253 9999 | 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”. The reason DC mains switches were so loud I was very amused by your editorial edition on magazine delivery in the December issue because that magazine, along with the January issue, just arrived today in Germany. Most issues arrive in the middle of the month, so there is still only a month between issues, which is OK by me. In the letter from Marcus Chick in the December issue (page 5), he mentions my problem with the coffee grinder. It was interesting to read his comments on sparking with fridges and washing machines that switched the Neutral conductor. The plugs in Germany are not polarised, yet most devices only switch one wire. It can be Neutral or Active depending on which way around you plug it in. As my coffee grinder has no Earth wire (it’s all plastic), I can only assume that I probably switched the Neutral and somehow caused the Earth leakage circuit breaker to trip and perhaps the interference suppressor cap or whatever produced the spark at the grinder switch. No matter, it is still working perfectly. In Brian Wilson’s memorabilia of 200V DC mains supplies on that same page, which I also remember, he mentions the switches opening and closing with a heavy click. That was normal, as a DC switch must operate quickly to reduce sparking. That was no longer a problem when AC arrived, so the switches became much quieter and smaller. By the way, it was very common for DC switchboards to have fuses in the Active and Neutral lines, so you had twice the number of fuses. The Neutral was probably not Earthed. In the part three article on the History of Electronics by David Maddison, also in the December issue (siliconchip. au/Series/404), he referred to the opening of the COMPAC siliconchip.com.au cable in 1963. I recorded the opening on a Pyrox wire recorder (pictured at lower left). A link to the (excellent quality) recording can be found on the OTVA Member’s Blog at siliconchip.au/link/absf I also recorded the opening of SEACOM (the South East Asia Commonwealth Cable) on 30th March 1967, and a link to that recording can be found on the same website. Many technical aspects are explained in the early part, especially the COMPAC recording. Christopher Ross, Tuebingen, Germany. Capacitor Discharge (CD) Welder Here is a photo (shown below) of our newly completed Capacitor Discharge Spot Welder (March & April 2022 issues; siliconchip.au/Series/379). I used a discarded case that was larger than the one you used in the prototype, so we included the power supply inside it. We also designed 3D-printed mounting hardware to secure the boards and assemblies into the chassis. We purchased a commercial handpiece for the unit from China to finish off the project and 3D printed a shroud assembly for the busbar points at the front of the case. I can share these 3D print patterns for those who want to use them. There are two variants for the ESM backbone mount: one with a spacer for our specific case and one without. We are happy with the result, although we are continuing to experiment with welding copper battery strapping. Ray Ellison, Dover Gardens, SA. 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This is explained in videos from “Right to Repair” advocate Louis Rossman’s at https://youtu.be/RcSnd3cyti0 and Linus Tech Tips at https://youtu.be/WcZbSpTngZI They discuss how an open-source home automation developer was threatened with legal action unless he took down the “integration”, a software plug-in he had developed to control their product with Home Assistant. Home Assistant was covered in detail in my article on Smart Home Automation in the January 2024 issue (siliconchip. au/Article/16082). The developer apparently broke no law, but does not have the legal resources to fight a giant corporation, so is regretfully complying with their request. I recommend against purchasing products from manufacturers that are hostile to third-party and open-source software that can be used to monitor and control their products. It limits the ways you can use your own appliances that you have paid for. There are further details at siliconchip.au/link/absk and siliconchip.au/link/absl Dr David Maddison, Toorak, Vic. Using RCDs with inverters I want to comment on the question about trying to prevent shocks from DC-to-AC inverters with RCDs (Ask Silicon Chip, January 2024, page 100). I think it could help to have an output RCD. Its main benefit would be if more than one appliance were connected to the inverter output and there was leakage to Earth from one of the 230V AC terminals from one of the appliances. That would raise the other terminal above Earth, creating a live conductor, and the usual opportunity for a current pathway between the body and Earth. This is why it is recommended to run only one appliance at a time from an isolation transformer to gain the full isolation benefit. Assuming the insulation is good in the inverter transformer, the output of the inverter will have the same isolation as an isolating transformer when just running one appliance. That is because current cannot flow between the appliance and Earth via a person. Typically, though, people are using inverter outputs to supply multiple appliances at one time, and this creates a hazard if leakage to Earth develops in one appliance from the 230V AC connections to Earth. For instance, say there is an appliance in the basement, which floods, immersing it in water. In the case of equal leakage to Earth from both the 230V connections from the isolated output of an inverter, it raises each of the 230V AC connections alone to 115V AC above Earth. A short, or leakage, inside the inverter from the input to the output, perhaps due to transformer insulation failure or water in there, could raise the battery’s terminal voltage above Earth in a case where the 230V AC terminals had some leakage to Earth too. A high voltage could appear superimposed on the battery terminals above Earth, depending on where the short or leakage was. Touching a battery terminal would 8 Silicon Chip complete the circuit to Earth and the inverter output and you could get a shock this way. The output RCD (if there was one) could possibly not trip if the current was balanced in each arm. However, if an input RCD was also fitted, there should be an unbalanced current that trips it. Any RCD on the input would have to be a type that works with high-level direct current as well as sensing alternating currents. These are called type B RCDs. So, for complete protection, you would want a standard RCD on the inverter output, a type B RCD on the DC/battery side and some testing to see if it can protect from all external leakage to Earth scenarios and internal inverter leakage. This is all to prevent a current flowing via a person to Earth with one hand contacting a terminal on either side of the inverter. Still, it is difficult to protect against every scenario. Dr Hugo Holden, Minyama, Qld. Using hot water as energy storage Regarding the letter published on this topic in the January 2024 issue (page 8), it is erroneous to state that DC electricity to a hot water service will likely cause accelerated tank corrosion. All hot water systems have the heating elements insulated from and enclosed within a submerged watertight metallic housing. Under normal conditions, there should be no issues. However, given the probability of minor defects in the vitreous enamel coating applied to the steel (non-stainless) tank, a suspended magnesium anode is installed to provide cathodic protection of those uncoated areas. In conclusion, it is correct to state that DC electricity is capable of causing accelerated corrosion of steel in an aqueous environment (soil) many times greater than AC under the same conditions, as experienced by DC traction systems. Dick Webster, Port Melbourne, Vic. Comment: while it is true that the resulting accelerated corrosion might not be catastrophic, the lifespan of an offpeak hot water system is often limited by the material in its sacrificial anode. Therefore, applying DC to the element(s) could reduce its lifespan. We had an article on extending the life of such a system by replacing the sacrificial anode in the November 2012 issue (siliconchip.au/Article/417). More on using solar energy for hot water Following up on Brian Day’s letter (January 2024) about the rising cost of running domestic hot water systems, I have a simple solution that bypasses whatever the provider and your smart meter may implement. I have a modest solar system that, by about 10:00am, is generating over 2kW. I changed out the 3.6kW element of the storage hot water system with a 1.8kW element and installed a time switch in the main board set to run the HWS from 10:00am to 3:00pm. The time switch has a manual override option if there’s a need for more hot water. Maintaining my hot water each day takes about 1kWh. It would be nice to have monitoring for exported power so I could switch the HWS element more intelligently, but that’s not available with my existing system. The reduced Australia's electronics magazine siliconchip.com.au Introducing ATEM Mini Pro The compact television studio that lets you create presentation videos and live streams! Now you don’t need to use a webcam for important presentations or workshops. ATEM Mini is a tiny video switcher that’s similar to the professional gear broadcasters use to create television shows! Simply plug in multiple cameras and a computer for your slides, then cut between them at the push of a button! It even has a built in streaming engine for live streaming to YouTube! Live Stream to a Global Audience! Easy to Learn and Use! Includes Free ATEM Software Control Panel There’s never been a solution that’s professional but also easy to use. Simply press ATEM Mini is a full broadcast television switcher, so it has hidden power that’s any of the input buttons on the front panel to cut between video sources. You can unlocked using the free ATEM Software Control app. This means if you want to select from exciting transitions such as dissolve, or more dramatic effects such go further, you can start using features such as chroma keying for green screens, as dip to color, DVE squeeze and DVE push. You can even add a DVE for picture media players for graphics and the multiview for monitoring all cameras on a in picture effects with customized graphics. single monitor. There’s even a professional audio mixer! Use Any Software that Supports a USB Webcam! You can use any video software with ATEM Mini Pro because the USB connection will emulate a webcam! That guarantees full compatibility with any video software and in full resolution 1080HD quality. Imagine giving a presentation on your latest research from a laboratory to software such as Zoom, Microsoft Teams, ATEM Mini Pro has a built in hardware streaming engine for live streaming to a global audience! That means you can live stream lectures or educational workshops direct to scientists all over the world in better video quality with smoother motion. Streaming uses the Ethernet connection to the internet, or you can even connect a smartphone to use mobile data! ATEM Mini Pro $495 Skype or WebEx! www.blackmagicdesign.com/au Learn More! power element and the time switch are what I can do for the moment. It would be nice to see a future with competition for exported power. The current pricing of about 2¢/kWh for export and 50¢/kWh for peak consumption does not look like a fair deal to me. These meters really are smart – for the vendor. Kevin Shackleton, Beverley, WA. We are Australia’s only power semiconductor manufacturer based in Queensland. We offer ASIC designs for OEMs as well as off-theshelf devices for distributors. Here's a small slice of the technologies that we offer at Quest Semiconductors: ● SiC High Voltage Wafers ● SiC Mosfets & Membranes ● SiC Homogeneous SBDs (Schottky barrier diode) ● Solar diodes ● Australian SiC Diode Fabrication and Technology ● IGBTs & TCIGBTs (trench clustered insulated gate bipolar transistor) ● Power Modules ● Sensors and JFETs ● ASICs Quest Semiconductors Pty Ltd Unit 1, 2-8 Focal Avenue, Coolum Beach, QLD 4573 email: sales<at>questsemi.com Tel: +61 (07) 3132 8687 10 Silicon Chip Using PV solar panels for water heating When using photovoltaic (PV) panels to heat water, it’s better to use an MPPT inverter to get the most out of your panels, and you also do not suffer the electrolysis problem! A power diverter or a simple timer to make the water heater only work during the daytime peak is all that’s needed. Use the keep it simple, stupid (KISS) principle. Most heater elements are rated at 3kW, but the average two-person house needs only a 1kW element if you have the smallest solar hot water collector. Two hours of boost per day will keep a 300L storage tank above 60°C as long as it has good insulation. Poorly insulated storage tanks are wasting lots of energy in our system! The 60°C storage myth to kill Legionella bacteria is a waste of energy for hot water storage; the bacteria live in shower heads in the water-air interface, and the tempered water never kills it there as the water is not allowed to get to 60°C! Health requirements for accommodation onboard ships are that the shower heads must be disinfected every three months using bleach or similar, and water from showers and taps must be tested every six months. Also, if people wish to make comments on V2G (vehicle to grid) standards, they are open to submissions. The details of the Standards Australia public comment process are here: AS/NZS 4777.1:2022 Grid connection of energy systems via inverters, Part 1: Installation requirements Comment Start Date: 21/12/2023 Comment End Date: 07/03/2024 siliconchip.au/link/absg AS/NZS 4777.2:2020 and 2:2023 Grid connection of energy systems via inverters, Part 2: Inverter requirements Comment Start Date: 21/12/2023 Comment End Date: 22/02/2024 siliconchip.au/link/absh However, our public standards are hidden behind a paywall! I wish Australia would take the USA’s idea on public documents and make them open. For example, digital nautical charts are free to download from the USA since they are produced/funded by the public tax system. Hiding public information behind paywalls only stops information and knowledge flow! Neil Brewster, Footscray, Vic. More recollections of working at ETI magazine I enjoyed Jonathon Fairall’s reminiscences about things past in the January Mailbag column (page 4). Ah, the Sri Lanka Room! To describe the curries as “spicy” barely does them justice; red hot might be more accurate. 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Jaycar reserves the right to change prices if and when required. March 2024  11 Atomic Potatoes were about the hottest thing on offer, and the curry was indeed red. My favourite was pork vindaloo with green mango, which was a bit milder. I recall going there with people from work, including one young guy who made it clear to everyone several times, that he ate hot (spicy) food and enjoyed it. After his first mouthful, he was pretty quiet for the rest of the evening! I have good memories from there. Phil Denniss, Darlington, NSW. A unique version of the ‘Woofer Stopper’ Thanks for sending me the parts I ordered for the Barking Dog Blaster project. I thought you might like to see my variation on the speaker array. I’m not great at woodworking and had some 100×100 galvanised steel RHS (rectangular hollow section) on hand, so I ended up using that. J. White, Willyung, WA. The Quad 33/303 was innovative but problematic I am writing in response to the Vintage Hifi column on the Quad 303/33 amp/preamp in the January 2024 issue (siliconchip.au/Article/16098). In the 1960s, hifi was the preserve of those who had the resources and time to invest in its study and implementation. At that time, many regarded Quad as the Rolls Royce of British hifi. Hence, there was great interest when the company introduced the 33/303 combo, their first foray into solid-state equipment. The 33/303 pair was innovative in several ways. First, the circuitry of the 303 power amplifier was something new in the still-fledgling move of hifi from valves to transistors. The “Quad triples” were much mentioned in reviews at the time. Secondly, the physical construction was innovative, especially the 33 preamplifier’s use of plug-in circuit boards for subsystems and as a configuration mechanism. Thirdly, their unique and stylish industrial design, built on a trend established with their valve equipment. Some of the innovations were not such good ideas, particularly the plug-in circuit boards. Neither the edge connectors nor the PCB tracks were gold-plated and, over time, these connections developed problems with oxidisation. It was sometimes necessary to wiggle a board to re-­establish good contact. The tape input card had an adjustable sensitivity achieved with a metal bolt screwed into a threaded piece of steel; no gold plating there either. Also problematic was the complex yellow pushbutton switching arrangement that offered flexibility in routing: stereo, mono-left, mono-right, mono both and reverse stereo. The channel switching and input selection buttons eventually suffered from the same contact oxidisation problem, requiring frequent exercising of the buttons to restore correct operation. 12 Silicon Chip Australia's electronics magazine siliconchip.com.au siliconchip.com.au Australia's electronics magazine March 2024  13 One time in the 1980s, when I had our 33 preamplifier serviced, the serviceman recommended partially bypassing the routing buttons as the only way to fix what had become a severe problem. This he did. My father purchased the 33/303 system in 1970. By the 2000s, after I had inherited both units, problems were accumulating. One phono amplifier had stopped working, malfunctions with the buttons had worsened, and the DIN sockets on the rear, also not gold-plated, were temperamental. Rather than attempt to fix what was, by that time, superseded technology, I offered the units for sale on eBay, and an enthusiastic young Asian man picked them up. I suspect the appeal of the Quad was more for the prestige value than the sound quality since I made it clear the equipment was seriously in need of maintenance. Paul Howson, Warwick, Queensland Since 1964 HF/50MHz TRANSCEIVER Quad 303 is not a ‘blameless’ amp design 144, 430/440, 1200 MHz ALL MODE TRANSCEIVER HF/50MHz TRANSCEIVER HF/VHF/UHF ALL MODE TRANSCEIVER www.icom.net.au 14 Silicon Chip Jim Greig has provided an interesting overview of the Quad 303 power amplifier in the January 2024 issue, starting on page 92. However, I fear he might mislead younger readers with the sentence, “The amplifier circuit is broadly similar to a modern ‘blameless’ amplifier circuit in many ways.” The notion of a ‘blameless amplifier’ was introduced by Douglas Self in several articles and in his book, which has come out in several revisions and confusingly changes its name with each revision. One I have here is named “Audio Power Amplifier Design Handbook” [see our review in the March 2010 issue (siliconchip.au/Article/89) – Editor]. This interesting and worthwhile book offers detailed discussion of many amplifier design details. In the book, Self chooses a particular amplifier configuration, then works through every circuit detail to optimise it, particularly concerning distortion and noise. With every sub-circuit optimised, he then suggests that he has an optimal result. He probably chose the word ‘blameless’ rather than ‘optimum’ for two reasons. The first is that it is somewhat unique and identifies his particular design. The second is that he was not in a position to claim that the amplifier could not possibly be improved; instead, he had made all the improvements that he reasonably could. While the optimisation of each sub-circuit might be beyond reproach, the result is not necessarily the best possible according to the criteria he set himself. His result was excellent, and he may be in a position to claim that nobody could hear any improvement in it. I suggest that the term ‘blameless’ be regarded as a Self proprietary term. It is not appropriate to use the term for modern amplifiers of the same general type. The Quad 303 amplifier’s circuit is interesting and stands well without comparison with something so specific and quite different. The input circuit is different; the means of providing a high-impedance load with good headroom for the voltage gain stage is different, and the output buffer is different. All we have left is the general configuration of the circuit. Saying it is essentially a blameless amplifier is a bit like saying cats and dogs are basically the same because they are both mammals with four legs, long ears, a tail etc. Richard Schurmann, Eltham, Vic. 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Jaycar reserves the right to change prices if and when required. Data Storage Systems Part 2: by Dr David Maddison Last month, we covered older storage systems like core memory, magnetic tape, floppy disks and optical discs. This follow-up article will describe modern storage technologies like hard disks, flash memory and SSDs, as well as possible future storage systems like 5D optical, holographic and DNA storage. W hile SSDs have displaced hard disks in many applications, especially for portable computers, mechanical hard disks are still widely used. That’s due to their lower cost and higher storage density, although flash may catch up eventually. Advances in mechanical hard disk storage are still being made, though. We will now look at how both technologies have evolved over time and where they are now. Hard disks/drives Hard disks (or hard drives) store data on internal rotating discs (‘platters’) coated with a thin film of magnetisable material. Movable heads magnetically read and write data on the individual platters (usually on both sides at once). Individual data bits are represented by the magnetisation of tiny magnetic domains (see Fig.31). Modern disk heads ‘fly’ on a thin layer of trapped air just above the platter surface. If the heads ever contact the surface, due to a physical shock or other reasons, it is known as a “head crash”; data loss and head damage can occur. Modern drives try to avoid head crashes by parking the heads in a special zone when the power is off, no data is being accessed or if they detect sudden acceleration. The IBM RAMAC (Random Access Method of Accounting and Control), introduced in 1957, was the first commercial computer with a hard disk drive of about 3.75MB. According to the RAMAC operations manual (siliconchip.au/link/abrw), THE IBM RAMAC is built around a random-access memory device that permits the storage of five million characters of business facts in the machine. In effect, the machine stores the equivalent of 62,500 80-column IBM cards. The Model 350 drive (Fig.32) had 52 platters, of which 50 contained data on 100 surfaces, and a read/write head unit on a moving arm that held two heads. You can see a video of it working at https://youtu.be/aTkL4FQL2FI The Bryant Chucking Grinder Company started developing a disk drive unit in 1959, resulting in the introduction of the 4000-series in 1961 (see Fig.33). It contained 26 horizontally-­ mounted discs 99cm in diameter spinning at 1200 RPM. The 205MB capacity was enormous for the time. You can see their 1965 product brochure at siliconchip.au/link/abrx IBM introduced the Model 1311 disk drive in 1962, which was about the size of a washing machine. It had a removable ‘Disk Pack’ containing five 35.5cm platters with ten recording surfaces that spun at 1500 RPM. The Pack weighed 4.5kg. It stored 2 million characters, equivalent to approximately 25,000 punched cards. In 1973, IBM introduced the “Winchester” disk drive, with 360mm platters, which did not have a removable Table 1: hard drive evolution since 1957 1957 1970 1980 1990 1995 2000 2005 2010 2015 2020 Capacity 3.75MB 29MB 5MB 120MB 4GB 80GB 500GB 3TB 10TB 20TB Volume 900L 768L 2.4L 2.4L 0.39L 0.39L 0.39L 0.39L 0.39L 0.39L Weight 900kg 360kg 2.3kg 2.9kg 1.5kg 0.7kg 0.7kg 0.7kg 0.7kg 0.7kg Access time 600ms 50ms 85ms 28ms 8.5ms 8.5ms 8.5ms 8.5ms 8.5ms 8.5ms $6,000,000 $1,500,000 $7,875.00 $250.00 $2.80 80¢ 8¢ 6¢ 2.5¢ 20kb/cm2 125kb/cm2 2Mb/cm2 50Mb/cm2 2Gb/cm2 13Gb/cm2 97Gb/cm2 128Gb/cm2 180Gb/cm2 7000 11,000 40,000 250,000 500,000 1,000,000 2,000,000 2,500,000 2,500,000 US$/GB $9,200,000 Areal density 309b/cm2 MTBF (hours) 2000 16 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.31: magnetic domains representing data bits on the platter of a 200MB hard disk. Source: https://w. wiki/8XxE (CC BY-SA 3.0). Fig.32: the 3.75MB IBM Model 350 disk drive used in the 1956 IBM RAMAC 305 computer. Source: https://w.wiki/8XxG (CC BY-SA 2.5). Fig.33: the Bryant Chucking Grinder Company Model 2 disk drive, or “disc file” as it was called. Source: www. computerhistory.org/timeline/1959/ Disk Pack. Then, in 1978, IBM introduced the “Piccolo” Model 0680 with smaller 20cm (8in) platters to replace 8in floppies. Over time, hard disks shrank along with floppies, first to 5¼ inches (133mm), then 3.5in (89mm). That final size is still widely used today. At the beginning of the 1980s, hard disks were uncommon for PCs and very expensive, but they reduced in price dramatically toward the end of that decade. Improvements in capacity, density, speed, size, price, reliability and other factors are shown in Table 1. The first hard drives (for mini and mainframe computers) with a standard interface were the Sperry Univac RP01, RP02 and RP03 drives (sold under several names). The RP02 was released in 1969 with a 20MB capacity. The interface design was not made proprietary, resulting in it becoming widely used. Early hard disk interfaces on PCs had a controller card and two cables, one for control and one for data. Popular early defacto standard interfaces were the ST506 and ST412 from Seagate (named after specific hard disk models that used them). ST412 was a refined version of ST506 and was used on the IBM XT. Both used MFM (modified frequency modulation) encoding, but an extended version of ST412, ST412HP, used RLL to give a 50% increase in capacity. I once had a 40MB Miniscribe 3650 hard disk with an MFM controller card, and I swapped the controller for an RLL (Run Length Limited) card, reformatted the disk and achieved a 60MB capacity. Following these interfaces came IDE (Integrated Drive Electronics), also known as Parallel ATA (PATA), which was developed by Western Digital and Compaq and introduced in 1986. It became the ATA-1 standard that virtually all PCs used in the late 1980s and early 1990s. Communication was over a 40-wire ribbon cable with IDC connectors at each end, while power was supplied separately. Enhanced IDE or EIDE was introduced in 1994, closely related to the ATA-2 standard. Further developments of ATA were ATAPI (for devices other than hard drives), ATA-4 with UDMA (Ultra Direct Memory Access), then Ultra ATA variations up to ATAPI8. Later versions of ATA used 80-wire shielded ribbon cables but with the same 40-way IDC connectors. SCSI was a general-purpose interface designed for various devices, including hard disks. It existed concurrently with ATA; it was more flexible, reliable and faster but more expensive to implement, so it was used in higher-end computers such as servers. Current hard drive interfaces include: • Serial ATA (SATA), released in 2003 to replace the IDE/PATA interface, using much thinner cables with fewer conductors. • SAS (Serial Attached SCSI), introduced in 2004, mainly for enterprise computing. It uses cables and connectors similar to SATA. • The M.2 interface is designed for solid-state drives (SSDs). It can utilise a SATA link or the faster PCIe bus (Peripheral Component Interconnect Express) with the NVM Express (NVMe or nonvolatile memory express) communications protocol. • mSATA (mini-SATA) is designed for space-constrained applications for SSDs, but today, M.2 is more likely to be used for such applications. • U.2 (SFF-8639) is designed for enterprise applications where very high performance is required. It uses the PCIe bus and can utilise the NVMe communications protocol. • FC (Fibre Channel) was introduced in the 1990s but has been adapted to SSDs today and is used in enterprise applications. Since 2010, Apple has used proprietary interfaces for their SSDs, while most other consumer-orientated computers have used SATA or M.2. Recently, Seagate developed Multi Actuator technology for their advanced hard disks (see Fig.34). The actuator is the part that moves the hard drive heads. Until now, hard drives had only one actuator to move 2023 2024 2025 22TB 30TB+ 40TB? 0.39L 0.39L 0.39L 0.7kg 0.7kg 0.7kg 8.5ms 8.5ms 8.5ms 2.1¢ ~1.5¢ ~1.2¢ 195Gb/cm2 290Gb/cm2 >350Gb/cm2 2,500,000 2,500,000 ~2,500,000 siliconchip.com.au Australia's electronics magazine An old hard drive legend Massive old ‘washing machine’ hard drives could ‘walk’ around the floor in response to certain head access patterns. There is an unverified legend that once such a drive walked so far that it blocked the only door to the room, and a hole had to be cut in the wall to gain access! March 2024  17 Fig.34: the Seagate Multi Actuator is two independent sets of heads that can double data throughput. all heads simultaneously. That means that all the heads are always over the same track. Seagate uses two actuators so half of the heads can move independently and simultaneously with the other heads, increasing the data throughput. Effectively, the drive acts like two separate drives in one case. You can see how it works in the video at https://i. imgur.com/uZaizwd.mp4 Another advanced technology developed by Seagate is HAMR, or heat-assisted magnetic recording. To make higher data density disks with smaller magnetic domains, materials that are harder to magnetise (and retain magnetisation better) are needed so that small areas remain stable. The heat from a laser in the head assists the magnetisation process. A dot is heated to 450°C, magnetised and then returned to room temperature in one nanosecond! Another recent development is using helium as the gas inside a hard drive. The idea was conceived in the 1970s, but after numerous failed attempts, it was thought to be impossible due to problems with containing the helium. Research resumed in 2009 at Hitachi, which was acquired by Western Digital (WD) in 2013, and Seagate bought WD in 2014. WD now makes about one million helium-filled drives per month – see Fig.35. Seagate also sells them under their own brands, such as Exos and IronWolf Pro. In fact, many hard drives with capacities of at least 8TB sold in the last few years are helium-filled. Helium has around 1/7th the density of air, with much lower viscosity, resulting in much less turbulence and friction inside the drive. That means a much cooler running drive, lower power consumption and less noise. This lesser friction means the drive’s platters can be thinner, allowing for up 18 Silicon Chip to 10 platters instead of 6 in the same size, according to WD. More heads can also be used. Also, since helium-filled drives are completely sealed, atmospheric contaminants can’t enter through the breather port that exists in air-filled drives. Anyone who has worked with helium knows it is notoriously hard to contain, and it will eventually leak out. However, WD says that the helium will remain through the operational lifetime of the drive. Finding a way to hermetically seal the hard drive to keep the helium in was a major challenge during their development. The famous first image of a black hole, or more correctly, its surrounds, was made with the assistance of WD helium-filled hard drives, as it required the acquisition and analysis of 4.5 petabytes of data. Perpendicular recording is a process by which magnetic domains are written in a vertical manner rather than a longitudinal manner. This allows three times the data density of longitudinal writing. Shingled magnetic recording (SMR) is a hard drive technology where data tracks are written slightly overlapping each other, like roof shingles, rather than with gaps between each row, as in earlier drives. This allows higher track density. However, this strategy requires extensive management of the data by firmware within the drive, as whenever a single bit of data needs to be changed, the entire ‘shingle’ has to be rewritten in order due to the overlaps. As far as the computer’s operating system is concerned, though, it appears as a normal drive. SMR drives generally have a high data throughput and reasonable seek performance. Still, the performance will plummet dramatically if many ‘random writes’ are performed without giving the drive time to ‘rest’ (during which it reorganises data and rewrites the shingles). That resulted in WD being sued by customers when they sold SMR hard drives without labelling them as such, as they are unsuitable for certain workloads (siliconchip.au/link/absa). They are mainly used as ‘online backups’ or video recording; applications that involve writing data in large batches. Modern hard drives can be mounted and used in any orientation, including upside-down or sideways, as long as cooling is adequate. That was not necessarily the case for earlier PC hard drives, before ‘flying heads’, as it could affect the head gap and cause data previously written to become unreadable. Then again, with the early washing-machine-sized hard drives, you didn’t have much choice in orientation! The Internet Archive (https:// archive.org/) is a vast free library of information and uses many hard Fig.35: banks of Western Digital HelioSeal hard drives in a data centre. Source: https://documents.westerndigital.com/content/dam/doc-library/en_us/assets/ public/western-digital/collateral/brochure/brochure-helioseal-technology.pdf Australia's electronics magazine siliconchip.com.au disks. As of December 2021, they had 28,000 spinning disks spread across 745 nodes in four data centres. The Wayback Machine internet archive contains 57 petabytes; the book, music and video collections contain 42 petabytes; the amount of unique data is 99 petabytes, and the total storage used is 212 petabytes. Data is held in storage units called petaboxes (https://w.wiki/8Xxe), with 1.4 petabytes per rack. One petabyte is one million gigabytes or 1000 terabytes. Miniature hard drives Kittyhawk was a miniature hard disk introduced by Hewlett Packard in 1992, with a 1.3in (3.3cm) form factor and a capacity of 20MB (later, 40MB). It was discontinued in 1994, being a commercial failure. Microdrive was a miniature 1in (25mm) hard drive format produced by IBM and Hitachi and designed to fit into CompactFlash Type II slots – see Fig.36. They were introduced in 1999 and last produced around 2007. They were used in devices such as cameras, printers, iPods and anywhere else a flash memory card was useful. They provided a higher capacity than flash memory at the time and at a lower cost. In addition to IBM (170MB to 16GB) and Hitachi (512MB to 8GB), the technology was used by the Seagate ST1 (2.5GB to 12GB), GS Magicstor (2.2GB to 6GB), Sony (2GB to 8GB), Western Digital (6GB), Cornice (2GB to 8GB) and Toshiba (2GB and 4GB). Flash memory Flash memory is a form of erasable, nonvolatile memory, usually in the form of NOR flash or NAND flash. Fig.37: both NAND and NOR flash store data using floating-gate Mosfets; the difference is in how the memory cells are addressed. NAND flash has higher density & faster write speeds, while NOR is more reliable and can be read faster. NOR and NAND are types of logic that are formed by the structure of the flash blocks. The NOR function is OR with the output inverted, while NAND is AND with the output inverted. The different layouts are shown in Fig.37. Whichever type of logic is used, the fundamental design is based on floating gate Mosfet memory cells. A charge is kept within highly insulating materials, and the logic inputs are only capacitively coupled to it, so the charge, and thus the memory bit it represents, can be maintained for a very long time, at least ten years (probably much more) with current technology. Toshiba invented Flash memory in 1980 and marketed it from 1987, Fig.36: one of the later Microdrives; this one was produced by Seagate and stored 5GB. It’s the same size as the earlier IBM models, though. The 50 Euro cent coin is the same size as our $1 coin. siliconchip.com.au Australia's electronics magazine although Dawon Kahng and Simon Min Sze invented the floating gate Mosfet at Bell Labs much earlier, in 1967. NOR flash is optimised for random access; individual memory cells can be accessed. NAND flash is optimised for high-density storage and forgoes random data access. Because of its architecture, individual memory cells cannot be accessed, as with NOR. They have to be read and written a block at a time. Because NAND offers a higher data density, it is used in devices like memory cards, USB drives and SSDs that require a large storage capacity. NOR has a lower data density with larger cell sizes, is less prone to data corruption and is used in applications such as code execution in medical devices or mobile phones where high capacity is unnecessary, but reliability is. Because individual cells can be addressed, NOR flash enables fast read times but relatively slow write and erase times due to the large cell size. NAND flash reads are slower because whole data blocks must be read in one go. However, writing and erasing is quicker than with NOR. NAND flash has a lower cost for a given capacity. Flash memory is slower than static RAM or ROM memory. In 2007, Toshiba introduced three-­ dimensional NAND architectures, March 2024  19 Fig.38: the basic structure of 3D NAND flash memory. SGD = drain-end select gate, SGS = select gate line, WL = word line, BL = bit line. Source: Toshiba Corporation. such as the generic 3D architecture shown in Fig.38. 3D NAND flash allows a much greater capacity in one package. Flash memory has only a finite, although high, number of write cycles as it ‘wears out’. Strategies must be implemented to keep this wear even across all memory cells by ‘wear levelling’ and other techniques within the drive, to delay the inevitable wearing-­ out process as much as possible. With wear levelling, the number of writes to each block is tracked, and when there is a choice, the next block to be written is the one with the lowest number of write cycles so far. To allow this, the controller performs logical-­ to-physical block mapping, allowing it to rearrange currently unallocated blocks at will. Memory cards Flash memory cards are usually based on the flash memory technology described above. There have been many variations over the years, some of which are shown in Fig.39. Table 2 shows how flash chip capacity, cost and speed have changed over time. PC Card (previously PCMCIA, Personal Computer Memory Card International Association) was introduced in 1990 and renamed in 1995. The format was initially designed for memory but later adapted to many other uses, as a convenient way to add peripherals to portable computers. It was superseded in 2003 and replaced with ExpressCard, which became obsolete in 2018 (it was never popular). Linear Flash cards are a PC Card format and are obsolete, but they are still used in various devices and still available for purchase, presumably for military and industrial applications. SRAM is another type of PC Card format memory card that requires a battery to maintain the memory. CompactFlash (CF) is a flash memory card format introduced by SanDisk in 1994. They were initially based on NOR memory but later switched to NAND. The low density of NOR flash is one reason the cards are relatively large. The other reason is that they were designed to be compatible with PCMCIA, using a 50-pin subset of the 68-pin PCMCIA interface. The original CF cards had capacities of 2-15MB at speeds of up to 8.3MB/s (but usually much slower), although the original specification supported capacities up to 128GB. Miniature Card (37 × 45 × 3.5mm) was developed by Intel and first promoted in 1995. It was backed by AMD, Fujitsu and Sharp. It is obsolete, having been available from around 1997. The maximum capacity was 16MB, and it was used in some digital cameras, such as the first HP PhotoSmart and the Intel 971 PC camera kit. SmartMedia Card was introduced by Toshiba in 1995 and discontinued in the early 2000s. One of the intentions of the card was to replace the 3.5in floppy disk; there was even an adaptor to insert them into a 3.5in drive bay. Cards could be written to by a camera, then read in a computer’s floppy drive via an adaptor. Cards from 2MB to 128MB were released. There was no in-built controller chip and therefore no wear levelling to extend the card’s life, so cards often became corrupted or unreadable. It was a popular media in digital cameras at the time, especially with Fuji­ film and Olympus. The Serial Flash Module was introduced in 1996 and discontinued in 2003. Capacities were from 128kB to 4MB; it was renamed to MediaStik in the early 2000s. MultiMediaCard (MMC) was introduced in 1997 by SanDisk and Siemens. SD cards (described below) evolved from MMC; some devices support both SD cards and MMCs. However, MMCs are thinner at 1.4mm compared to SD cards, which are 2.1mm thick, so MMC cards may fit into an SD card slot but not necessarily vice versa. MMC has been released in several varieties and form factors such as RS-MMC, DV-MMC, MMCplus, MMCmobile, MMCmicro, MiCard and eMMC. MMC has lost popularity now, but eMMC, an embedded, non-removable type of memory, is still used for storage in many phones and other devices. Fig.39: a selection of flash memory cards. Source: https://w. wiki/8XxK (CC BY-SA 3.0). 20 Silicon Chip Australia's electronics magazine siliconchip.com.au However, since 2016, when Universal Flash Storage (UFS, see below) was released, it has come to dominate that market. One advantage of MMC over SD is its low cost, and eMMC is cheaper than other forms of embedded storage in phones, such as an NVMe solid-­ state drive. Memory Stick was a proprietary flash memory technology launched by Sony in 1998. Its original format ceased to be available in 2007. Memory Stick PRO-HG Duo HX was released in 2011 and is still available in sizes up to 128GB. They appear to be no longer under active development. There are adaptors to use microSD cards in some devices that require Memory Stick Pro Duo cards (see siliconchip.au/link/abry), but if you are considering buying one, do some research as they have limitations. Sony now makes its own SD cards. USB Flash Drives (‘thumb drives’) are one of the most ubiquitous portable storage devices, often attached to key rings or neck lanyards. These drives originated in 1999 when Amir Ban, Dov Moran and Oron Ogdan of M-­ Systems in Israel filed a patent application entitled “Architecture for a Universal Serial Bus-Based PC Flash Disk” and subsequently were awarded US Patent 6,148,354. Those people are generally recognised as the inventors; there are other claimants, but they did not file for patents. A USB flash drive contains a USB controller and one or more flash memory chips – see Fig.40. SD (Secure Digital) cards are a form of flash memory used (originally) in the form of a postage stamp size module, although much smaller formats are now available. They are primarily used in portable devices like phones and cameras. The format was introduced in 1999 by Panasonic, SanDisk and Toshiba as an improved version of MMC cards. The standards are governed by the SD Association (www.sdcard.org). Formats smaller than the original include miniSD (no longer produced) and microSD (shown opposite). Standard SD cards had a capacity of up to 2GB. SDHC cards were introduced in 2006, ranging from 2GB to 32GB. SDXC cards were introduced in 2010 and have capacities of 32GB to 2TB. We published an article primarily on SD cards (but that also siliconchip.com.au Table 2: flash memory chip evolution since 1990 (per chip) 1990 1995 2000 2005 2010 2015 2020 2023 2MB 16MB 2GB 64GB 256GB 1TB 2TB Read/write 500kB/s speed 2MB/s 5MB/s 25MB/s 100MB/s 250MB/s 1GB/s 2GB/s US$/chip $300.00 $40.00 $20.00 $40.00 $40.00 $100.00 $100.00 $60.00 $20,000 $1,200.00 $20.00 $0.62 $0.40 $0.10 $0.03 Capacity 512kB US$/GB $600,000 mentioned other flash memory cards) in the July 2013 issue (siliconchip.au/ Article/3935). In 2019, SDUC cards were introduced with theoretical capacities of up to 128TB. There are also various speed categories for SD cards, such as Default, High Speed, Ultra High Speed (UHS), UHS-1, UHS-II (with extra pins), UHS-III (also with extra pins) and SD Express. SD Express cards have extra pins to support a PCIe lane and the NVM Express memory access protocol. Some SD cards even have integrated WiFi to automatically offload data wirelessly. The xD-Picture Card was introduced by Fujifilm, Kodak and Olympus in 2002 and discontinued around 2009. The largest capacity released was 2GB. These cards have no ‘flash translation layer’ to emulate a hard disk; the NAND flash hardware is (more or less) accessed directly. It was derived from the SmartMedia card and, like that, has no wear-levelling controller. P2 was a professional memory card format introduced by Panasonic in 2004, available in capacities up to 64GB. They are still listed on the Panasonic website (siliconchip.au/link/ abs6) and are described as having “four SD cards packaged into one” (device). They are packaged into a PC Card (formerly PCMCIA) and were replaced by the compatible MicroP2 (based on SDXC/SDHC). SxS is a flash memory storage card developed by Sony and SanDisk and first announced in 2007, followed by SxS Pro cards in 2011. It is designed for professional video cameras, with an emphasis on high performance and reliability. It is compatible with the ExpressCard/34 interface or USB via an adaptor. Cards from 32GB to 240GB are available from Sony’s website. CFast flash memory cards were introduced in 2009. The format is supported by relatively few cameras; mostly high-end professional cinema cameras from Arri, Atomos, Blackmagic Design and Canon. It is used in still cameras such as the Canon EOS-1D X Mark II and Hasselblad H6D-100C. We have seen CFast 2.0 cards up to 1TB capacity. XQD flash memory cards were developed for high-definition camcorders and cameras. The format was developed by Nikon, SanDisk and Sony and was introduced to the market in 2012. Currently, the cards are available with a capacity of up to 2TB. XQD cards are still available but have been succeeded by CFexpress, which Fig.40: an old 64MB USB flash drive removed from its case. The key components are 1) USB connector, 2) controller, 3) test connectors, 4) NAND flash memory, 5) crystal, 6) LED, 7) writeprotect switch, and 8) space for a second flash chip. Source: https://w. wiki/8XxJ (GNU FDL). Australia's electronics magazine March 2024  21 Fig.41: a comparison of the read/write schemes for eMMC and UFS; LVDS is low-voltage differential signalling. UFS cards are faster because reads and writes can occur simultaneously, and there is command queuing. Fig.42: a comparison of how the electrical interfaces work with SD and UFS cards. is backwards compatible with XQD (for Type B cards). AXS memory cards are a proprietary format for Sony high-resolution digital F55 and F5 cinematography cameras, with a capacity of up to 1TB. They were introduced around 2012. It is not a standard, but we included it in case you wondered what cards are used for certain cinema cameras. Sony SRMemory cards are related to AXS, for use with the Sony SR-R1 portable recorder for HD-SDI (High-­ Definition Serial Digital Interface) cameras. CFexpress is a format for flash memory cards launched by the CompactFlash Association in 2017. They are available in types A, B and C. Type B slots will accept XQD cards. We have seen CFexpress cards with capacities of up to 4TB. Universal Flash Storage (UFS) is a flash storage system designed to be faster, more reliable and use less power than eMMC for internal storage and SD cards for external storage in devices such as cameras, phones and others – see Fig.41. It is intended to replace those two technologies. UFS achieves higher speeds for internal memory than eMMC because UFS has dedicated channels for reading and writing, so reading and writing can occur simultaneously, unlike with eMMC. Also, UFS has command queuing to organise read and write commands in the most efficient manner. According to Samsung, a UFS card is up to 70 times faster than an SD card. UFS memory cards have been designed in a similar form factor to SD cards so that a single slot can accept either a microSD card or a UFS card. It achieves that by placing the contacts for both devices in unique locations, except for the shared power pins; see Fig.42. A UFS card is faster than an SD card in external memory card applications because it has a high-speed serial interface with separate data channels for transmitting and receiving, enabling simultaneous operation. UHS-II and UHS-III SD cards used a similar approach to boost transfer rates, but the UFS serial interface is still faster – see Fig.43. Solid-state drives (SSDs) SSDs are gradually replacing hard disks in applications where a high capacity is not critical, like the boot 22 Silicon Chip Australia's electronics magazine siliconchip.com.au drives of portable and desktop computers. SSDs typically use flash memory for storage. Advantages over traditional hard disks include greater robustness (at least in theory, due to a lack of moving parts), higher speeds, especially for ‘random’ I/O, and silent operation. Most SSDs use NAND flash memory of several possible design types. Flash memory may contain 1, 2, 3, 4 or 5 bits of data per cell. These cells are known as Single-Level Cells (SLC), Double or Multi-Level Cells (DLC/MLC), Triple-Level Cells (TLC), Quad-Level Cells (QLC) or Penta-Level Cells (PLC). As more bits are added per memory cell, there are trade-offs of performance, endurance and reliability. SLCs are the most reliable and fastest, but the most expensive per unit of capacity, so they are suitable for enterprise operations with intensive write operations. The upcoming PLCs offer the lowest cost and highest data density but with the least durability, so they are suitable for large data applications with low-­intensity workloads. SSDs may contain a mix of technologies, eg, some SLC cells for frequently accessed data and many MLC, TLC, QLC or PLC cells for long-term storage. Multi-level cell flash can even ‘emulate’ SLC for faster read/write speeds but lower density, providing a ‘cache’ without needing actual SLC flash. Given the capacities of SSDs and the fact that they are expected to store data long-term, good wear-levelling algorithms are essential. Also relevant to SSDs are the sections above on flash memory, wear-­ levelling, 3D flash technology and hard disk interfaces. While flashbased SSDs can use the same interfaces as mechanical hard disks, the NVMe/M.2 and mSATA interfaces are almost exclusively used for SSDs. Such devices are shown in Fig.44. NVM Express (NVMe or Nonvolatile Memory Host Controller Interface Specification [NVMHCIS]) is an open standard and a logical interface protocol for nonvolatile storage devices, usually attached via PCI Express bus (see https://nvmexpress.org/). It was implemented because existing interfaces like SATA were not fast enough for the latest SSDs. It exploits the parallelism possible in solid-state memory devices and the fact that the SSDs are smaller and thus can be kept closer to the motherboard. This siliconchip.com.au My experience with the longevity of SD cards I had some old SD cards, which I had used in a camera, plus some old USB flash drives. Some had not been used for 10 or 20 years. When I went to read them, I had no problems, suggesting that data should last at least that long. However, it is always wise to have backups and also to “refresh” the cards by putting them in a reader every so often and allowing the card’s internal firmware to correct any fixable defects, plus replace any lost charge on the floating-gate Mosfet transistor used to store bits of data. Note that there’s no guarantee that modern flash memory has the same longevity; it will likely have smaller cell sizes and thus possibly won’t retain data for as long as older flash chips. Fig.43: the physical differences between UFS and microSD cards. They both fit in a combination reader. Source: https://semiconductor.samsung.com/newsevents/tech-blog/ufs-solutions-high-performance-storage-solution/ Australia's electronics magazine March 2024  23 Links and further reading ● ● ● ● ● ● ● ● ● ● Practical applications of the punched card: siliconchip.au/link/abs0 Appletons’ Cyclopaedia of Applied Mechanics: siliconchip.au/link/abs1 The IBM Diskette General Information Manual: siliconchip.au/link/abs2 The IBM 1311 Disk Storage Drive manual: siliconchip.au/link/abs3 IBM 1360 Photo-Digital Storage System manual: siliconchip.au/link/abrv Introduction to IBM Direct Access Storage Device: siliconchip.au/link/ abs4 “1951-1968 Early Computer Magnetic Tape Units”: https://youtu.be/ lEYyZSlQEdg “Debugging the 1959 IBM 729 Vacuum Column Tape Drive”: https://youtu. be/7Lh4CMz_Z6M “Making a bootable OS/8 DecTape for the PDP8/m”: https://youtu.be/ tOWt7LIOVJs “DECTAPE II, TU58, & TEAC MR-30 Transport”: https://youtu.be/jo4qfVl-Y-o specification was introduced in 2011 and last updated in April 2022. Larger devices can use more than the four PCI Express lanes provided by an M.2 connector, such as the large SSD shown in Fig.45. Bit rot One important drawback of the MLC/TLC/QLC/PLC cell structure that is not widely known but that we should mention is the performance degradation over time. Just after data has been written to a flash cell, its voltage should be well within the defined thresholds, so reading it back will be very fast. However, over time (months or years), the voltage will drift due to tiny leakage currents. If the voltage drifts far enough, it could cross one of the boundaries and the data will become corrupted (unless the SSD has built-in error checking and correction; we expect many would). However, even if the voltage doesn’t drift far enough to cause data loss, it can still slow down reading significantly. That’s because the high-speed amplifiers/comparators that read data out of the flash are noisy and imprecise, so they only work properly when the voltage is within a narrow band. Once it drifts outside that band, a slower and more precise method has to be used to determine the stored data. That means that the read speed of an SSD can drop dramatically, from gigabytes per second to just a few megabytes per second, if the particular file hasn’t been touched after a few months or years. In our experience, it isn’t quite so dramatic, dropping to maybe 50MB/s, but that’s still far shy of the expected read performance of an SSD. This seems to affect many makes and models of SSDs and the only complete solution is to periodically (eg, every few months) perform a complete ‘refresh’ of the drive by reading and then rewriting all data. However, most drives and operating systems don’t (yet) do that automatically. There is software available to do it. In our experience, some SSDs will automatically refresh such files when read. So it’s only slow the first time you access a file that was written a while ago. Not all do that, though, and you may be forced to rewrite an older file to fix the slowness. Ideally, the SSD will periodically scan its own data, find blocks that haven’t been touched in a while and refresh them automatically. However, that does not yet seem to be a common feature of SSD controllers. Maybe it will be one day. Exabyte-scale storage CERN (Conseil Européen pour la Recherche Nucléaire or European Council for Nuclear Research) in Switzerland now has a storage capacity of one exabyte of data (or one million terabytes or 1000 petabytes) to store data from experiments at the world’s largest particle accelerator. The data is stored in 111,000 devices, primarily hard disks with an increasing number of SSDs; see Fig.46. Long-term archival storage Spacecraft Voyager 1 and 2 carry a Golden Record, a 12in (30cm) goldplated copper disc containing pictures and sounds of the Earth. It was the first time a library was taken into space. We described the record in our article on Voyager (December 2018; siliconchip. au/Article/11329). The Beresheet Lunar Library was the second attempt to send a library into space. The library comprised data stored in DNA and on nickel disks. The Fig.44 (left): an mSATA SSD is on the left, while an M.2 NVMe SSD is on the right. Source: https://w.wiki/8XxM (CC BY-SA 4.0). Fig.45: an Intel solid-state drive for a desktop computer or server that plugs into a PCI Express 8x slot. M.2 NVMe drives use a similar interface but with fewer lanes on a smaller connector. Source: https://w.wiki/8XxL (CC BY-SA 4.0). 24 Silicon Chip Australia's electronics magazine siliconchip.com.au contents included a 30 million page archive of ‘human history and civilisation’ on a 100mm nanotechnology-­ fabricated device similar to a DVD. It contained 25 discs, each 40 microns thick, see Figs.51 & 52. The first four discs were analog and contained 60,000 images etched from low resolution to increasingly high levels of information up to the nanoscale, made with optical nanolithography. The analog front cover has information visible to the naked eye, plus smaller images and holographic logos. The discs also carry information on many human languages. In total, all the discs carried around 200GB of digitally compressed content. Even though Beresheet crashlanded on the moon, it is thought that the contents of its library remained intact. We had a detailed article on the landing attempt in the November 2018 issue (siliconchip.au/Article/11296). The Arch Mission Foundation (www.archmission.org) is a non-profit organisation aiming to preserve all human knowledge by building data archives. This is so that, in the event of a calamity, it would be much easier to rebuild civilisation (if anyone survives). Lunar Library 1 in the Beresheet Lunar Library was one of their projects. Fig.46: a few of the 111,000 devices that make up one exabyte of storage at CERN. Source: https://home.cern/news/news/computing/exabyte-disk-storage-cern The future of data storage Storage technologies are still evolvingl; the future of data storage technologies includes: In hybrid cloud storage, less frequently accessed data is stored offsite ‘in the cloud’ and more frequently accessed data is stored on the premises. Multi-cloud storage is where multiple cloud storage vendors are utilised to avoid dependency and the risk of being with just one provider. Quantum data storage uses quantum atomic properties such as superposition and entanglement to potentially encrypt and store large amounts of data (see Fig.47). Information is kept in qubits instead of being represented as 0 or 1 bits like in regular memory. A qubit is 0 and 1 simultaneously, vastly increasing the capability of such memory and computer systems. Just 100 qubits could hold more information than all of the world’s hard disks, according to Doug Finke of the Quantum Computing Report. However, such a system is highly susceptible to ‘decoherence’, where siliconchip.com.au Fig.47: a circuit model for Quantum RAM. Original source: https://ncatlab.org/ nlab/show/QRAM Fig.48: the growth of hard drive (HDD), flash and optical data storage (ODS) capacity from 1980 to 2014, with projections to the present. Source: Figure 8 from “Optical storage arrays: A perspective for future big data storage” – siliconchip.au/ link/abs8 (CC BY-NC-ND 3.0). Australia's electronics magazine March 2024  25 would have to consider the size of the coding and decoding equipment in a DNA data storage system. It has been estimated that 1g of DNA molecules could store about 215 petabytes of data (a petabyte is one million gigabytes). The entirety of Wikipedia (16GB in 2019) was turned into synthetic DNA, as described at siliconchip.au/ link/abrz The Beresheet Lunar Library mentioned earlier also contained 10,000 images and 20 books encoded in DNA. Fig.49: two ways data can be stored in DNA, either by sequencing or structure. Source: https://pubs.acs.org/doi/10.1021/acsnano.2c06748 (CC-BY 4.0). the information is destroyed; a significant problem, to say the least! Such memory is called Quantum RAM or qRAM, the quantum equivalent of classic RAM. Also see our article on Quantum Computing in the March 2016 issue (siliconchip.au/Article/9845). Edge storage is where data is stored and processed close to where it is generated rather than, say, in the cloud. The maximum size of hard disks is expected to increase to 100TB by 2025, according to the Storage Technology Consortium (https://idema.org/) – see Fig.48. That figure is from 2014, and the projections to present have already been exceeded. For example, hard disks were projected to have a 1.5TB technical limitation, but that has been far exceeded, and 28TB drives are now available (using shingled magnetic recording and helium filling). A Seagate 32TB hard disk using HAMR (heat-assisted magnetic recording technology) is said to be in production. It should be available to purchase by the time this article is published. Tom’s Hardware claims 40TB+ drives will be on the market by 2025. We doubt that 100TB will be reached by 2025, but it likely will be eventually. Holographic data storage is a future scheme where data is stored in optical media as an interference pattern. According to one estimate, holographic memory has the potential to store 1TB of data in the size of a sugar cube. However, bear in mind that 1TB SD cards are available and occupy less volume than that. For more, see the video “How does holographic storage work?” at https:// youtu.be/4EADwGV5Gv8 DNA Storage (Figs.49 & 50) uses the double-helix-shaped molecule that encodes genetic instructions for virtually all living organisms. Information is encoded as combinations of four so-called nucleobases: cytosine (C), guanine (G), adenine (A) and thymine (T). Information density is exceptionally high since information is stored at the molecular level. DNA is relatively stable (good news for us!) and can last hundreds or thousands of years under the right circumstances. Disadvantages are that reading and writing processes are slow and can be error-prone. To encode DNA with data, bytes or tokens are first converted to a corresponding unique DNA sequence, such as shown in Table 3. The density of DNA storage is hard to give a precise figure for because you 5D optical storage 5D optical storage has been researched as part of Microsoft Project Silica (see Figs.53 & 54). Data is written by the use of a femtosecond laser focused inside a piece of quartz glass, where it causes damage and forms a voxel (volumetric pixel) located within a three-dimensional (X/Y/Z) space also with properties of volume and orientation, which add extra data apart from the spatial position. That leads to the prefix ‘five dimensions’ or ‘5D’, even though it is physically only 3D, as each voxel has five properties. Data is read by a microscope-like device. The technology is read-only (or at least WORM [write once read many]) and is intended for archival storage. Data can be stored for thousands of years, and it is resistant to damage and degradation. Microsoft suggests a capacity of 7TB in a glass platter the size of a DVD. For more information, see the video “Project Silica - Storing Data in Glass” at https://youtu.be/6CzHsibqpIs Keeping data long-term It is important to make sure data in obsolete formats are migrated to more modern formats. In 1985, there was a rumour that US Census data from the 1960s had been lost. The claim was that “The Fig.50: the six steps of DNA data storage. Source: https://pubs.acs.org/doi/10.1021/acsnano.2c06748 (CC-BY 4.0). 26 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.51: the front cover disc of The Lunar Library on the Beresheet lunar lander. Fig.52: a detail of one of the images of the front cover of The Lunar Library. siliconchip.com.au Australia's electronics magazine March 2024  27 Table 3: proposed ASCII to DNA encoding scheme ‘ ‘ ACAT <at> CCAC „ TCCG ! AGGT A TACT a GAGC “ AAAG B TCCT b GTGC # AGAC C TACG c GACG $ AAGC D TGCC d GTAA % AACT E TCTA e GTAC & AGAA F TAGT f GCCT ‘ AATC G TTAA g GCTA ( ATTG H TGGC h GAGT ) AATT I TGTT i GATG * AATG J TTCC j GATT + AAGA K TACT k GGGC , AGAG L TATG l GTTG - AAGC M TAGT m GTGA . ACAC N TGTC n GACT / ACGT O TATT o GCCG 0 CAAA P TTCA p GACA 1 CACC Q TTTA q GACT 2 CCGT R TAGA r GGAT 3 CGAG S TGAG s GGTG 4 CCTT T TAAA t GCTT 5 CCGT U TGAC u GACC 6 CTGT V TGAG v GACT 7 CTCT W TAAC w GCCC 8 CCGT X TCCT x GATC 9 CTCA Y TGAA y GTCG : CTAG Z TAAG z GTGA ; CCGC [ TCAT { GGCT < CACA \ TAAG | GGTG = CATA ] TCCA } GAAC > CTAC ^ TGTT ~ GATG ? CCAG _ TCCG DEL GAGT Fig.53: this 75 × 75 × 2mm piece of glass from Project Silica contains the 1978 Superman movie. It was produced in 2019 and stored 75.6GB. New versions store much more data. Source: https://news.microsoft.com/source/features/ innovation/ignite-project-silica-superman/ Source: “Design and Implementation of a New DNA Based Stream Cipher Algorithm using Python” – siliconchip.au/link/abs9 Fig.54: how a microscope can read Project Silica quartz glass with a green laser. The top view (left circle) shows vertical columns of voxels. The colours represent the different volumes and orientations of each voxel, and the side view (right circle) shows the layers of the voxels, each with a different size and orientation. Source: https://youtu.be/6CzHsibqpIs 1960 Census, for example, was written on tapes for the Univac I, a machine that has been obsolete for more than two decades. Its obsolescence caused much of the census data to be lost.” Fortunately, contrary to popular belief, the data was migrated in that case. Quoting from siliconchip.au/ link/abs7: By 1979 the Census Bureau reported that they had successfully completed copying 640 of the 642 II-A tapes onto 178 industry-compatible tapes. ... a small volume of records from the 1960 census was lost. This occurred because of inadequate inventory control and because of the physical deterioration of a minuscule number of records, not technological obsolescence. From what we have described in these two articles, you can see the huge variety of secondary storage used in the past that has become obsolete while new types continue to be developed. Thus, important data must frequently be migrated from outdated media to new media to preserve it. You must also be aware of the possibility of ‘bit rot’, where data on old media such as floppy disks becomes corrupt over time, a problem the author (and Silicon Chip) has experienced. 28 Silicon Chip Australia's electronics magazine This is especially a problem for modern SSDs; we understand that, in some cases, simply leaving them powered off for a few months can lead to data loss. Most SSDs are not intended to be used for archiving purposes, but rather actively written and read daily or near-daily. Mechanical hard disks also require frequent (eg, monthly) ‘scrubbing’ where the entire disk is read and then rewritten for reliable long-term data storage. That’s because the magnetic domains are so small that untouched areas can eventually lose enough magnetisation to become unreadable. SC siliconchip.com.au Prototyping Accessories GREAT RANGE. GREAT VALUE. In-stock at your conveniently located stores nationwide. 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JUST 4695 $ HG9980 Shop at Jaycar for: • Soldering & Accessories • Components, Cables and Connectors • Magnifiers and Inspection Aids • Tools, Service Aids and Chemicals Explore our full range of prototyping accessories, in stock at over 115 stores, or 130 resellers or on our website. jaycar.com.au/prototyping 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. By Phil Prosser & Zak Wallingford Build your own This project is fun and ideal for people learning electronics, especially kids. It introduces some basic skills, such as soldering, and demonstrates what can be achieved with simple circuits. It is perfect for building with young family members or as a teaching aid for students. T he Laser Communicator is for play; it is not a ‘practical’ device, although you might find uses for it beyond fun and learning, in which case, all power to you! As we all know, everything is better with a laser on it – even sharks! So, what is the Laser Communicator? It allows you to transmit voice or music over a laser beam. That might be across the room, down the corridor or even further! The link is far from hifi and requires you to adjust things to make it work, but it isn’t too hard to set up. During testing and trials, my 10-year-old grandson, Zak, was able to talk over this down our corridor over a distance of about 15 metres. Photo 1: the transmitter box is relatively modest; the screw jack is needed to adjust the elevation of the laser beam. Once your elevation is set, it is easy to nudge the beam azimuth. 30 It would be fair to say that keeping things aligned over this distance was a challenge, as the deflection of our floorboards as we walked on them caused the laser to wobble around a lot at the receiver. We have kept the layout very spread out and used beginner-friendly pads to keep construction straightforward. The hardest part of this project is cutting and drilling the enclosure. We have made the transmitter board so you can use it ‘bare’, but we think the boxed version is better if you can deal with making it. Zak enjoyed drilling the mounting holes but left the larger speaker hole to my more experienced hands. When building this with Zak, we split the PCB construction into two sessions of about an hour each, plus one for drilling and preparing the cases and another for assembly and testing. I made a point of building a unit alongside Zak to demonstrate what he needed to do, and with that guidance, he could undertake the majority of tasks alone. Older constructors may go faster and require less assistance. Let’s start with a caution. This project uses a laser (we could have used an IR LED, but that is nowhere near as fun). We have used a 1mW laser diode and designed the driver so that it cannot deliver more power than that, which ensures this remains a Class 2 laser. This is the same power level as your average laser pointer. The Class 2 laser we are using will cause a “blink reflex”, and people will normally look away. Australia's electronics magazine This Class 2 laser “Would not harm an eye unless a person deliberately stared into the beam. Laser protective eye wear is normally not necessary. A Class 2 laser is not a skin or materials burn hazard.” As a further caution, we have designed this circuit to operate the laser diode at 60% of its standard operating current. This results in the average laser output power being much lower than 1mW, giving us headroom to apply amplitude modulation to the laser output for transmitting the audio signal. Laser beams have very low divergence, and even a 1mW laser can cause visual interference at well over 100m, so never point this toward people or vehicles. If you build this with a youngster, ensure that they fully understand that this is never to be pointed at a person, and supervise them while using it. How does it work? Many things in our day-to-day lives use wirelessly transmitted signals. TVs, radios and mobile phones all use the RF transmission of electrical signals. These systems use radio-­ frequency signals to transmit the data, with antennas at each end (transmitter and receiver). In this project, we transmit the audio information optically using light (the laser) as the carrier. The actual audio is impressed on the light as an amplitude modulation, which means we are changing the intensity of the laser to carry the audio information we want to send. siliconchip.com.au One way to think about it is that it’s a 430THz (terahertz) radio system, although electromagnetic radiation at that frequency certainly behaves a little differently compared to 430MHz or 5GHz! We can amplitude-modulate a laser by changing the current through it, which is a simple way of implementing AM (that’s basically how it’s done for RF). At the receiver end, we need to sense the laser light and somehow turn the amplitude modulation into an electrical signal we can deliver to a speaker (ie, demodulate it). Our approach is to use a photodiode and ignore the DC part of the intensity received by passing it through a series capacitor. The remaining AC part of the intensity is fed to the amplifier. Both the transmitter and receiver are about as simple as we can make them, as this is a learning project. Much more complex approaches are used in a realworld laser communications system, but the spirit of this project is learning and some play. The Laser Communicator comes in two parts: a transmitter and a receiver. Each fits in a standard Jiffy box: UB3 (130 × 67mm) for the transmitter and UB2 (197 × 112mm) for the receiver. The transmitter block diagram is shown in Fig.1, while the receiver block diagram is in Fig.2. The transmitter is shown in Photo 1 and the lead image. This box includes an electret microphone driver, bias generator, voltage-­to-current converter and the laser itself. We have used a fixed bias for the laser diode that sets the current to about 20mA. This has proven sufficient to drive all the laser diodes we tried and keeps using the transmitter simple. The combined bias and audio signal drive our voltage-to-current converter with five transistors implementing an operational amplifier (op amp) with buffer. We selected a Keyes (Altronics Z6370) unit for the laser diode. These are very commonly available as Arduino breakout modules. We have included a screw jack on the base of the box using a 3/16-inch nut and bolt that we found in the shed glued to a PCB offcut (an M5 or M6 nut and bolt/machine screw would also work). This allows fine adjustment of the tilt of the transmitter, which is essential to align it with the receiver over longer distances. siliconchip.com.au Fig.1: the modulator in the transmitter uses a differential amplifier set up as a voltage-to-current converter. Fig.2: the receiver uses a phototransistor driving a LM386 IC amplifier, which in turn drives a 100mm loudspeaker. The receiver is housed in a much larger box, as shown in Photo 2 and the lead image. This box includes the PCB with the phototransistor and amplifier as well as a 100mm loudspeaker. The receiver has a sensitivity control that doubles as a volume control. The illumination level on the receiver will vary greatly over different ranges and depending on how well-aimed the laser is. That means the phototransistor must operate over a wide dynamic range of intensities. We achieve this by making the phototransistor’s load resistance adjustable. This also affects the volume, so there is no need for a separate volume control. Even though we are running the laser at a low power, it is quite intense. We can use this fact to make aiming easier by sticking a piece of white paper over the receiver hole in front of the phototransistor. We put a target on this so we had a clear aim point. The benefits of this are twofold: we can see exactly where to aim, and the paper diffuses the laser light into the inside of the receiver box, which spreads it onto the phototransistor even if the aim is not exact. We found Australia's electronics magazine that to be the best way to make it work even over pretty long ranges. Transmitter circuit details The transmitter circuit is shown in Fig.3. It uses an electret microphone, which converts sound into an electrical voltage. At normal ‘voice levels’, its output signal is a few hundred millivolts. If you want to use a phone or other line-level input to drive this link, you can omit the leftmost 4.7kW resistor and replace the microphone with a 3.5mm jack socket. We are coupling the electret to the differential amplifier via a 100nF capacitor. This fairly low value was selected as younger users tend to talk right into the microphone, which would cause a lot of popping and saturate the laser link if a higher value were used. Caution: Class 2 Laser — Do not stare into the beam. — This power level is safe for unintended exposure for less than 0.25 seconds (250ms). — Never view the laser using telescopic optics. March 2024  31 +9V LASER COMMUNICATOR TRANSMITTER SC Ó2024 S1 POWER IN 1 9V BATTERY +9V +9V 4.7kW 4.7kW 1kW 1kW BC546, BC556 22W 10kW B 220mF 2 0V E ELECTRET MIC 1 Q1 BC556 B CON1 Q3 BC546 100nF C C C 100kW 1 E LASER A 2 K CON3 E 100kW CON2 C B B 2 Q2 BC546 E 1mW l LASER DIODE 22W A D1 1N4148 K A D2 1N4148 D3 1N4148 K A Q4 BC546 C B TP1 E C 10mF B Q5 BC546 E 100mF 56W 1N4148 A 330W K K Fig.3: a handful of discrete components are used to implement an amplitude-modulated laser with direct modulation of the drive current. We made a simple handheld microphone using an empty ballpoint pen case. While basic, this works well, and Zak really enjoyed gluing and shrinking it all together. He also learned that super glue on your fingers is very sticky! More on how we did that later. Photo 2: the receiver box doubles as the speaker baffle. The Post-it note with a target drawn on it is important, as it gives you something to aim at and spreads the laser light, making the link easier to set up (masking tape also works). 32 Silicon Chip We want to modulate the laser diode amplitude with the audio voltage. Laser diodes need to be driven by a current source, rather like LEDs, which means that we cannot simply connect the microphone to the laser. Furthermore, as shown in Fig.4, laser diodes have a threshold current below which they do not lase, so we need reasonable control over this. We convert the microphone voltage to a laser current using a differential amplifier. The non-inverting input is fed with the microphone voltage imposed on a bias voltage, while the inverting (feedback) input is a voltage derived from the current through the laser diode. The laser current is converted to a feedback voltage by a resistance in series with the laser diode. The five transistors form a differential amplifier as follows. NPN transistors Q4 and Q5 act as a constant current sink, pulling a fixed current from the junction of the emitters of NPN transistors Q2 and Q3. Those two transistors act as the voltage comparator; as their total emitter current is fixed, whenever one conducts less current, the other must conduct more. The one with the higher base voltage of the two will pass more current than the other, as it will have the higher base-emitter voltage (because the emitters are joined). PNP transistor Q1 is the output buffer that drives the laser. Note how the collectors of Q2 and Q3 both connect Australia's electronics magazine to the same +9V rail via 1kW resistors. That means any extra current needed for Q3 (when Q2 is conducting less) will tend to come from the base of Q1, so its base current is related to the difference in the two input voltages. When Q3 conducts more, Q1 switches on harder, and when Q3 conducts less, Q1 starts to cut off. The active current sink comprising Q4 and Q5 is probably unnecessary. Still, this current controls the maximum laser current, and we want to ensure it is consistent as the battery discharges and its terminal voltage drops. The 330W resistor sets the tail current for the differential pair to 1.8mA, so about 0.9mA through each of the two 1kW collector resistors for Q3 & Q4 (although Q3 normally conducts a little more than Q2). The DC bias point for the laser diode is set by the three 1N4148 diodes, which will have a combined forward voltage drop of 1.8V. In the absence of a signal, and as the average of an AC signal, the DC voltage on the base of Q3 is set by this via the 100kW resistor. There is a DC base current for Q3 of about 40μA, so the bases of Q2 and Q3 sit at about 1.4V. A feedback loop is created around Q2 and Q3, with the base of Q2 driven through the 100kW resistor that senses the cathode voltage of the laser diode. The cathode current goes to ground through 22W and 56W resistors. The siliconchip.com.au Fig.4: the laser optical output as a function of input current. Laser diodes do not operate as a laser until they have sufficient current flowing through them, so we need to set a minimum bias current when modulating the power to the laser. feedback loop keeps the base voltages of Q2 and Q3 the same, so the average voltage across these two resistors is 1.4V. Thus, the DC bias current for the laser diode is 18mA (1.4V ÷ [22W + 56W]). All the laser diodes we tested had a threshold current much less than that, so they operated without adjustment in this circuit. If, for some reason, your laser diode is way too dim and everything else in the circuit is correct, the laser bias point can be altered by reducing the value of the 56W resistor. Be very careful doing that, though, as you could create laser intensities that exceed Class 2, which is unacceptable without eye protection. The keen-eyed will note a 100μF capacitor in parallel with the 56W resistor. It increases the system’s AC gain, allowing us to get double service from the voltage-to-current amplifier. It provides about 11dB of extra gain for audio signals. The AC laser current is 45mA/V. The maximum input voltage before clipping is about 500mV peak. Receiver circuit details As shown in Fig.5, the receiver uses a simple phototransistor with a resistive load to detect the incident laser radiation. Because we are amplitude modulating the laser, the output of this detector contains both the DC bias on the laser and the AC content that we have modulated on top. Because the phototransistor acts like a diode that responds only to the intensity of incident light, ignoring the carrier frequency, it also demodulates the signal. The current through the phototransistor develops a voltage across potentiometer VR1. This voltage has a DC component (the average intensity of the laser signal) and an AC component (the modulated audio waveform). If the phototransistor’s load resistance (VR1) is too high, the laser DC bias from the transmitter will saturate it. This will be seen as the voltage on the phototransistor collector increasing until clipping occurs. At high intensities, VR1’s resistance can be reduced to avoid saturation of the photodetector. This allows us to set the receiver’s sensitivity to the intensity of incoming laser light while also acting as a volume control. The 330W resistor is in the circuit so that if VR1 is set to zero, the phototransistor still has a 330W load rather than being shorted across the battery. We have AC-coupled the signal to the input of a venerable LM386 power amplifier, IC1. This is used in pretty much a textbook configuration. We have minimal bypassing on pin 7 as we have battery power, so there should be little rail noise. We have used the gain setting pins (pins 1 and 8) to set a reasonably high gain. If you need to reduce the receiver’s gain, increase the 1kW resistor value. Fig.5: the receiver is straightforward, utilising an old-school LM386 power amplifier driven by a phototransistor. siliconchip.com.au Australia's electronics magazine March 2024  33 ◀ Photo 3: we got some user feedback on the prototype build, resulting in some tweaks to the design and layout to make it more approachable for all builders. I built the two units simultaneously with Zak so he could watch how I did it, but I let him build his own. Photo 4: this shows how the shielded cable is soldered to the electret microphone insert. The screen braid goes to the pad connecting to the mic case. We have specified a 100mm speaker for this project and recommend it be mounted in a UB3 Jiffy box. This is required to achieve decent efficiency and sound output from the receiver. An initial prototype used a much larger hifi speaker, which worked a treat. So if you wish to build a ‘bare’ version of this project, wiring the receiver’s output to a large speaker is a good option. We found that using a tiny 57mm speaker without a box was pretty disappointing, so avoid that. Construction The wide layout and large pads make this an ideal starter project (see Photo 3). The intention was to make it approachable to people of all experiences with a little guidance. We won’t reiterate how to solder, as Silicon Chip has published several guides in the past. The process for the two boards is similar. Fig.6 is the transmitter’s overlay diagram, which shows where each component goes, while Fig.7 is a similar diagram for the receiver. In each case, start with the resistors. Check the values as you go; if you are unsure, use a multimeter to check their values. We used this as a chance to show our youngster how to decode resistors. The transmitter has eleven resistors, while the receiver has only Fig.6: here’s where to solder the components on the transmitter board. For the electrolytic (can-type) capacitors, ensure the longer leads go into the holes marked with + symbols. The transistors have flat faces that are orientated as shown here. 34 Silicon Chip three. Either way, check them against the marked values on the PCB. We start with these as they are the ‘flattest’ parts. Next, install the three diodes on the transmitter board. Make sure they are the right way around, or the transmitter won’t work. We have specified the 1N4148 (a common type, similar to the 1N914 but with lower leakage), but you could use just about any silicon diode. Still, it’s better to stick with the parts that we’ve tested. Next, fit the capacitors. We have ensured that all the electrolytic capacitors face in the same direction, but double-check them as, if they are the Fig.7: similarly, fit the components for the receiver like this. The IC will have a dot or other indicator for pin 1, which has to go at upper left. Like with the transmitter, be careful with the orientation of the electrolytic capacitors and also the phototransistor sensor, Q6. Australia's electronics magazine siliconchip.com.au Fig.8: the transmitter lid drilling is straightforward, with just four 3mm holes to drill in a rectangular pattern for mounting the PCB. The transmitter base needs just two holes drilled, with the larger one sized to suit the laser diode, plus a further three holes in the side. wrong way around, bad things will happen. Follow by soldering in the transistors on the transmitter. Q1 is the PNP type (eg, BC55x), while the remainder are NPN types (BC54x). You can happily use BC556/7/8/9 for the PNP and BC546/7/8/9 for the NPN. The main thing to watch for is that you do not get the two types mixed up. Now mount the LM386. You might need to squeeze the pins in a bit to get it to fit. This is a tough old chip, so don’t be afraid of giving it a squish to get it in. Finally, mount the potentiometer on the receiver PCB, along with all of the screw terminals. Use a logarithmic potentiometer here; a linear pot will work but will be more fiddly to adjust. Now install the laser diode. We bent the middle leg of our Altronics Z6370 out straight; the remaining legs slot straight into the screw terminal. The “S” marked on the module indicates the anode or positive lead, while “−” indicates the cathode or negative. If you have a different laser diode, you can check which is the anode and which is the cathode using a 9V battery with a 4.7kW resistor connected in series (you have one of these for your power LED). The laser will light siliconchip.com.au up when the anode is wired to the positive battery terminal. Don’t forget the resistor, or you could burn it out! Wiring advice We have wiring diagrams over the page, so refer to them once we get to that stage. But first, here is some advice. The flying leads of the battery clips Australia's electronics magazine will form a fair bit of your wiring. Any other power wiring can be done with light-duty hookup wire. The power LED for the receiver comprises a red LED and a 4.7kW current-­ limiting resistor. Make sure that the anode of the diode (longer lead) is wired to the switched 9V input, while the resistor goes from the anode of the LED to the ground pin on the power input. March 2024  35 To make the microphone look neat and for some fun, we put 10mm heatshrink tubing over the whole microphone, down to the cable. If you don’t have a hot air gun to shrink it, many hairdryers are hot enough to work. Housing the boards Fig.9: gluing a nut to the base and threading a screw into it allows you to easily adjust the angle of the case relative to the ground in small increments so you can aim the laser precisely. The microphone input should be made using shielded cable; we used about a metre of Altronics Cat W3010. Jaycar Cat WB1500 should also be suitable. Connect the braided screen to the electret ground. This pin connects to the case of the electret, which is visible on the back of the microphone capsule (see Photo 4). Solder the cables’s inner conductor to the electret’s output (the other pad). The screen of this cable goes to the GROUND terminal of the microphone connector on the transmitter board, while the inner core goes to the MIC terminal. We used an old ballpoint pen case as a handle for the microphone by running the coaxial cable through it, then soldering the electret on top and eventually gluing it in place with super glue. This gave us a simple microphone at minimal cost. Assembly into the cases is optional, but we really recommend it. We are providing drilling diagrams that will allow you to assemble the transmitter and receivers into tidy boxes. For the transmitter, mark and drill the holes in the case lid, as shown in Fig.8. Check the location of your marks by placing the PCB on them before drilling. Next, mark and drill the holes in the base, also shown in Fig.8. That includes holes for the power switch, microphone lead and a zip tie (cable tie) to hold the battery still. Now mark and drill the laser output hole. The laser hole can be anything large enough to ensure you can get the laser out. Run the microphone cable through its hole, mount the switches and terminate the leads on the transmitter board. Use 10mm M3 standoffs, 6mm screws and shakeproof washers to mount the PCB to the top of the case. Make a screw jack base for the transmitter, as shown in Fig.9. Our baseplate was 100mm long and 40mm wide, though anything will do that allows you to adjust the tilt of the transmitter. We glued a nut to our stand so a screw or bolt could be used as a screw jack. Fig.10: there isn’t much to the transmitter wiring, but watch the polarity of both the battery leads and the electret microphone. The laser needs to be screwed to the LASER header. You will need to bend the middle leg out of the way or snip it off with a pair of side cutters. 36 Silicon Chip Australia's electronics magazine siliconchip.com.au Glue the screw jack base to the base of the transmitter box. Sand the ABS plastic so that your glue sticks well. We roughened the base of the case with sandpaper and used Araldite to glue the nut onto the screw jack. Sanding the base gives the Araldite a good surface to adhere to. Make sure you have good ventilation while it cures. Finally, stick rubber feet to the front of the screw jack. We used Altronics H0940 feet. Transmitter wiring There is just a little bit of wiring to do, as per Fig.10. You can use any colour wires you choose, but we recommend red and black for the battery and switch wiring. For the microphone, we ran the coax through the case and tied a knot inside as very low-cost strain relief, ensuring that any enthusiasm from young users does not tear the microphone cable from the terminal on the transmitter board. Receiver case assembly & wiring Mark and drill the holes in the lid, as shown in Fig.12. There are two holes in the main case for the zip tie to secure the battery; see Fig.13. The speaker hole might be fiddly to cut. We used a circle saw for ours. ABS plastic is very soft, so a handsaw will do this job easily. This is one task that is best undertaken by an adult if working with young constructors. More tips for kids from a kid! What was important when assembling the boards? » Working out which part needs to go on the board. » Searching for the numbers on the board and working with an adult to make sure I had the right parts. » Learning to ‘decode’ the resistor codes, to check that an adult had given me the right bits. Some soldering tips, how to do it and tricks for people to know: » Keep the iron’s tip away from people! » Go slow; remember not to rush soldering each joint. » Remember where to put the tip of the iron. Put the soldering iron on one side of the joint and put the solder on the other side. » Also, it’s fun just to melt the solder! Do you have any tips for putting heatshrink tubing on wires? » Don’t point the hot air gun at people or their fingers (and watch your fingers when helping!) » Take your time while doing it so that you shrink the tube fully. » Don’t put the tip of the hot air gun right on top of the heatshrink. There needs to be a gap. Tips on drilling the box » Wear safety glasses for protection, and never turn a drill on with your fingers near the bit. » Put tape where you will drill and mark it with a pen. » Hold the parts tight when you drill them. Keep your hand tightly on the box when drilling small holes in the box. Putting stuff in the box: » Make sure the box is drilled properly with the holes where they belong. Phil helped with this. » Put stuff in spots it can fit, and get some help. » Keep stuff steady when you put a zip tie or nuts and bolts on. Using the communicator: » Don’t put the boxes too far away from each other because it’s harder to line up (it was pretty tricky at 15m apart). » Don’t put the microphone right in your face when talking or put it too far away. » You do not need to shout. » To play music over the link, you play a song of your choice and put the small speaker of the phone or whatever you use against the microphone. This works really well. Are there any other cool things? » Waving your hands in the beam makes some really interesting sounds. » Waving a strainer through the beam makes even crazier sounds. » Putting your hand in the beam totally stops the sound. How to get it all lined up: » First, turn both boxes on. » Look for the dot from the laser. It is bright and you won’t miss it. » Turn the screw to get the laser dot to go up and down until it is at the right height. » Then move the box left and right until the dot is on the paper. You are all set to go! Fig.11: when wiring up the receiver, the speaker’s polarity doesn’t matter, but the battery polarity does, so check it. If you wire the LED incorrectly, it won’t light up. siliconchip.com.au Australia's electronics magazine March 2024  37 Parts List – Laser Communicator (Transmitter) 1 single- or double-sided PCB coded 16102241, 81.5 × 55.5mm 1 UB3 Jiffy box, 130 × 67mm 1 9V battery 1 9V battery clip with flying leads 1 1mW red laser diode module [Altronics Z6370] 1 electret microphone capsule (MIC1) 1 solder tag mini toggle switch (S1) [Altronics S1310, Jaycar ST0554] 3 2-way mini terminal blocks (CON1-CON3) 1 ballpoint pen case (to use as a microphone case) Semiconductors 1 BC556/7/8/9 100mA PNP transistor (Q1) 4 BC546/7/8/9 100mA NPN transistors (Q2-Q5) 3 1N4148 or similar signal diodes (D1-D3) Capacitors 1 220μF 16V radial electrolytic 1 100μF 16V radial electrolytic 1 10μF 16V radial electrolytic 1 100nF 63V MKT Resistors (all 1/4W 1%) 2 100kW 1 10kW 2 4.7kW 2 1kW 1 330W 1 56W 2 22W Hardware 1 M5 or M6 × 40mm panhead machine screw and hex nut 8 M3 × 6mm panhead machine screw 4 M3 × 10mm tapped spacers 8 M3 star washers (toothed type) 2 6mm-tall rubber feet [Altronics H0940, Jaycar HP0816] 1 150mm cable tie 1 1m length of single-core screened cable 2 200mm lengths of light-duty hookup wire (red & black) 1 150mm length of 10mm diameter heatshrink tubing 1 100mm length of 3mm diameter heatshrink tubing 1 100 × 40mm PCB offcut Note how the laser diode is mounted into the screw terminal block, with its third middle lead bent out of the way. You can also see how we used a ballpoint pen case to house the microphone capsule. 38 Silicon Chip Australia's electronics magazine Next, drill the hole for the sensitivity pot and its locating pin, the photodetector hole, the power switch and the LED. Poke the LED through the 5mm hole in the case and use a dab of superglue to hold it in place. Secure the power switch with its washer and nut. A large pair of pliers helps here, but can be fiddly for younger hands. Use 10mm M3 machine screws, M3 flat and shakeproof washers and nuts to secure the speaker. Connect the battery, LED (with series resistor) and speaker to the receiver board, as shown in Fig.11. Testing First, check your wiring and ensure the black battery lead goes into the GND terminal of the power socket on both boards. Turn the transmitter power on, and you should immediately see the laser light up. Measure the voltage at TP1 by setting your DMM into voltage measurement mode, connecting the red probe to TP1 and the black probe to GND. You should get a reading between 0.8V and 1.2V. If the laser is not lit or the voltage on its cathode is out of the specified range, check that the laser has been connected the right way around. Put a meter across the laser diode on the mA range and measure the current. You should get a reading between 14mA and 22mA. Also you should check the voltages across diodes D1-D3. There should be about 0.6V across each. If this is not the case, check that they are the right way around. Then make sure that the 10μF bypass capacitor is the right way around. To verify that the current source is operating, check that the voltage on the base of Q5 (its middle pin) is about 0.6V relative to GND (its emitter) and that the voltage on the base of Q4 (middle pin) is about 1.2V relative to GND. If these are not OK, verify that you have fitted the right transistors and that they are in the right way around. The base-emitter voltages for transistors Q2 and Q3 should be about 0.6V. With the flat side towards you, the base is the middle pin and the emitter is on the right. If they are wrong, check that the transistor types are correct and that they are the right way around. The siliconchip.com.au voltages across the 1kW resistors should be close to 0.8-1V, with the one connected to Q2 being slightly lower than the other. Receiver testing Before switching it on, check your wiring and make sure that the battery is connected the right way around. Switch it on and measure the voltage between pins 4 (lower left) and 6 (one above lower right) of the LM386 IC; the reading should be very close to the battery voltage. If it is lower, check that the LM386 IC is the right way around and check your wiring and the switch. Next, measure the voltage on pin 5 of the LM386 relative to the GND terminal of CON4. This should be around half the battery voltage. If not, check that the electrolytic capacitors in the upper-right corner of the board are the right way around. My LED bench lamp causes substantial buzz when it is close to the phototransistor, and even LED room lights cause buzz at maximum gain. Such buzz indicates that the circuit is working. Try this with a mains-­ powered LED light in your house or lab. If that doesn’t work, check that the photodiode is the right way around. If the above works, move on to the setup stage. Otherwise, as a final test, monitor the voltage on the middle pin of the potentiometer with a voltmeter and turn the sensitivity pot up and down from minimum to maximum. In that case, you should see the DC voltage vary, especially if the phototransistor is illuminated. With the speaker connected, you could inject an audio signal of about 10-100mV at 1kHz (AC-coupled!) into the middle pin of the potentiometer with the volume turned right up. You should hear a loud (possibly distorted) tone from the speaker. Setup To set the system up, switch both the transmitter and receiver on, Figs.12 & 13: the receiver lid drilling (top diagram) is the most complicated of the project, with one large cut-out for the speaker that we made with a hole saw, plus six smaller holes to drill. Shown in the bottom section of the diagram are the locations of two holes that a cable tie passes through to hold the 9V battery in place. siliconchip.com.au Parts List – Laser Communicator (Receiver) 1 single- or double-sided PCB coded 16102242, 80 × 37.5mm 1 UB2 Jiffy box, 197 × 112mm 1 100mm loudspeaker driver [Altronics C0616, Jaycar AS3008] 1 solder tag mini toggle switch (S2) [Altronics S1310, Jaycar ST0554] 1 9V battery 1 9V battery clip with flying leads 2 2-way mini terminal blocks (CON4, CON5) 1 10kW 16mm single-gang logarithmic taper potentiometer (VR1) Semiconductors 1 LM386N 1W audio amp IC, DIP-8 (IC1) [Altronics Z2556, Jaycar ZL3386] 1 BP2334 NPN phototransistor (Q6) [Altronics Z1613, Jaycar ZD1950] 1 red 5mm LED (LED1) Capacitors 2 220μF 16V radial electrolytic 1 10μF 16V radial electrolytic 2 100nF 63V MKT 1 47nF 63V MKT Resistors (all 1/4W 1%) 1 4.7kW 1 1kW 1 330W 1 10W Hardware 4 M3 × 10mm panhead machine screws 4 M3 flat washers 4 M3 star washers (toothed type) 4 M3 hex nuts 4 6mm-tall rubber feet [Altronics H0940, Jaycar HP0816] 1 150mm cable tie 2 200mm lengths of light-duty hookup wire (red & black) 1 100mm length of 3mm diameter heatshrink tubing separated by at least a few metres. Align the laser onto the receiver. We always use this with a piece of paper with a target stuck over the hole for the phototransistor. That makes it so much easier to get a decent link and stops the laser from saturating the phototransistor. To align it, get the laser in the general vicinity of the receiver target, then adjust the screw jack so the laser dot is at the right height. Do this without holding the top of the transmitter, as that will mess up your aim when you let go of the box. Once the elevation of the aim is correct, gently change the laser’s azimuth by nudging the screw jack left or right. Again, don’t try to turn the transmitter by holding the Jiffy box, as everything will move when you let go. Just nudge it. If the sensitivity is high enough, you should hear the receiver go quiet once the aim is good. Adjust the sensitivity from minimum up until you get a clear(ish) link. With the gain right up, you will likely get feedback. Once you get feedback, you can back off the sensitivity on the receiver until you have a clear link. To aid you in this task, it’s a good idea to put something like a radio or smartphone playing music next to the microphone so you have a consistent sound to aim for. If the above are all good and you still can’t get sound from the receiver, switch the transmitter on and point the laser at a wall. Tap the front of the microphone repeatedly with your finger and watch the intensity of the laser spot. It should show brief and slight changes in intensity with each tap. If the variation is not apparent, check that the microphone is wired correctly. If you have an oscilloscope, check the voltage from the electret microphone at the MIC input on the PCB and the base of Q3. The signal should be easily visible on the 100mV/div range. Look for a similar signal on the cathode of the laser; it should be much the same signal as you saw on SC the input. Left: this photo shows how the battery, PCB, switch and speaker are mounted in the Receiver. The PCB is held to the rear of the lid by the potentiometer nut. An individual shot of the PCB is also shown. 40 Silicon Chip Australia's electronics magazine siliconchip.com.au March Power Build It Yourself Electronics Centres® No more eye strain! Ultra-bright long life LED for fantastic clarity (plus no need to change a globe - EVER!). Let “gadget” be your eyes. Identify those impossible to read miniature parts without straining your eyes. Great for collectors, model makers, jewellers etc. SAVERS SAVE $20 Only until March 31st. ONLY... SL4576W 100Ah 109 SAVE $270 Up to 135aH capacity. 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Plus crimp pins. 150pcs total. 90° or straight boxed 2.54mm PCB connectors and plugs in 2, 3, 4 and 5 way. Plus crimp pins. 150pcs total. Mail Orders: mailorder<at>altronics.com.au Victoria Western Australia » Springvale: 891 Princes Hwy » Airport West: 5 Dromana Ave 03 9549 2188 03 9549 2121 » Auburn: 15 Short St 02 8748 5388 » 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 08 9428 2188 08 9428 2166 08 9428 2167 08 9428 2168 08 9428 2169 08 9428 2170 New South Wales Queensland » Virginia: 1870 Sandgate Rd 07 3441 2810 » Prospect: 316 Main Nth Rd 08 8164 3466 South Australia © Altronics 2024. 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 0003 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. The Pico Digital Video Terminal allows you to communicate with and control a Micromite, PicoMite or WebMite with modern, easily obtainable equipment such as USB keyboards and HDMI displays. Raspberry Pi Pico Digital Video Terminal Part 1: by Tim Blythman B oot-to-BASIC computers like the Micromite and PicoMite are an easy way to learn about programming, but they can still leave you tied to a fully-fledged computer as a way to communicate with them. Alternatives like the VGA PicoMite can stand alone but require legacy gear such as a VGA monitor. With this project, you no longer need a PS/2 keyboard or VGA monitor! Put simply, the Pico Digital Video Terminal is an updated version of the ASCII Video Terminal from July 2014 (siliconchip.au/Article/7925). The ASCII Video Terminal allows a microcontroller with a serial interface to connect to a PS/2 keyboard and VGA monitor or composite video display. The Pico Digital Video Terminal does much the same, although it provides more modern interfaces. It also provides a virtual USB-serial port to allow such a microcontroller to easily connect to a serial terminal program such as TeraTerm or minicom. It is modular, allowing some functions to be left off or customised. Instead of a PS/2 keyboard, it uses a USB keyboard. Even wireless USB keyboards are cheap and plentiful these days, so you can easily go wireless. The Terminal also delivers digital siliconchip.com.au video from its HDMI connector, allowing it to be connected to most modern TVs and monitors. There are even compact HDMI displays designed for computers like the Raspberry Pi, which should also work well. The signal is not strictly HDMI-­ compliant but uses a backwards-­ compatible Digital Visual Interface (DVI) set of supported resolutions that are supposed to work with all HDMI-­ compatible displays. We can’t strictly call it HDMI as such; licensing restrictions exist on using the ‘closed’ HDMI standards and trademarks. Regardless, the Terminal has worked successfully with all HDMI-equipped displays we have tried. We considered calling it “I can’t believe it’s not HDMI!” We have also implemented a USB host interface to communicate with the virtual USB-serial device on boards like the Micromite and PicoMite. The Digital Video Terminal features & specifications » » » » » » » » » » » 640×240 pixel monochrome (80×30 character) display option 320×240 pixel colour (53×20 character) display option HDMI socket with DVI-compatible digital video USB-A socket for keyboard (works with wireless keyboards) VT100 terminal compatibility USB-C socket for 5V USB power Three status LEDs Fits in a compact enclosure (105 × 80 × 25mm) Tested with the Micromite, PicoMite and WebMite Turns a development board into a standalone computer Works with other USB-serial capable boards, including: Raspberry Pi Pico/Pico W (including CircuitPython & MicroPython); Arduino Leonardo; CP2102 USBserial converters; and Micromite/Microbridge » Baseline DVI output over HDMI connector » USB host for keyboard » Flexible and modular design Australia's electronics magazine March 2024  45 Parts List – Digital Video Terminal 1 double-sided PCB coded 07112231, 98 × 68mm 1 black double-sided PCB coded 07112232, 99 × 22mm (front panel for H0190 enclosure) OR 1 black double-sided PCB coded 07112233, 99 × 27mm (front panel for H0191 enclosure) 1 ABS instrument case 105 × 80 × 25mm [Hammond RM2005STBK; Multicomp MP004813; Altronics H0190] OR 1 ABS instrument case 105 × 80 × 30mm [Hammond RM2005MTBK; Multicomp MP004811; Altronics H0191] 1 Raspberry Pi Pico programmed with 0711223A.UF2 (MOD1) 1 Raspberry Pi Pico programmed with 0711223B.UF2 (MOD2) 1 Raspberry Pi Pico programmed with 0711223C.UF2 (MOD3) 1 HDMI-compatible socket (CON1) [Stewart SS-53000-001] 2 USB-A through-hole right-angle sockets (CON2, CON3) 1 USB-C power-only SMD socket (CON4) [GCT USB4135 or similar] 3 6mm through-hole tactile switches (S1-S3) 4 2-pin headers (JP1-JP4) 1 4-pin header (LK1) 6 jumper shunts (JP1-JP4, LK1) 6 20-way header pins (optional; for MOD1-MOD3) 6 20-way header sockets (optional; for MOD1-MOD3; will not fit in H0190 enclosure unless low-profile types are used) 4 self-adhesive feet to suit the enclosure (eg, 8mm round) Semiconductors 2 2N7002 SMD N-channel Mosfets, SOT-23 (Q1, Q2) 3 green 3mm through-hole LEDs (LED1-LED3) Resistors (all M2012/0805 size SMD, 1/8W, 1%) 6 10kW 2 5.1kW 3 1kW 8 270W 4 22W The Terminal is a compact device that fits into a small ABS enclosure. The three Pico microcontroller boards communicate with a USB keyboard, provide a virtual USB-serial host interface and deliver a digital video signal. The Pico or Pico H version will work (both are shown here). Short-form kit (SC6917, $65): includes everything except the case. Choose which front panel PCB you want (for Altronics H0190 or H0191). Picos are not supplied pre-programmed. 46 Silicon Chip Australia's electronics magazine Terminal also provides an ‘upstream’ USB-serial device interface that is transparently passed through to the downstream USB-serial device at CON2. This allows these boards to behave as though they were connected directly to a computer, even though the Terminal sits in between. This arrangement enables data from the attached keyboard to be sent to the Micromite or PicoMite. Similarly, data from the Micromite or PicoMite can be displayed on the digital video output, while still being monitored by the computer. The Terminal will also work with many low-cost USB-serial adaptors, allowing it to communicate with a computer. We have verified that those based on the CP2102 chip work. VGA PicoMite comparison You might also be wondering what the Pico Digital Video Terminal offers that the VGA PicoMite does not. The VGA PicoMite (July 2022 issue, siliconchip.au/Article/15382) supports some advanced graphics options that the Terminal does not. Otherwise, using a regular PicoMite or WebMite with this Terminal is similar to working with a VGA PicoMite. The main differences are that you need a PS/2 keyboard and VGA monitor or adaptor to use the VGA Pico­ Mite, while the Digital Video Terminal lets you use a USB keyboard and HDMI monitor. We did recently publish a USB to PS/2 Keyboard Adaptor (January 2024; siliconchip.au/Article/16090) that lets you use a USB keyboard with the VGA PicoMite, but you’re still stuck with needing a VGA monitor or a VGA-toHDMI adaptor. It is possible to combine a VGA PicoMite with the Digital Video Terminal to get a dual-screen PicoMite setup, also allowing you to use a USB keyboard. It could even be a triple screen if you connect an LCD panel to the PicoMite! The Terminal will work with many types of development boards and not just the ‘Mites. Some Arduino boards and even boards that can run versions of the Python language (like MicroPython and CircuitPython) will work with the Terminal. It does not even have to be a separate development board. You can actually build the Terminal with a PicoMite siliconchip.com.au or WebMite embedded onto the main PCB and enclosed in the same compact case! We wouldn’t be surprised if some readers modified our software to create a complete, standalone device that doesn’t need an external board to be connected. We’ll detail some compatible devices later. A word of warning The Pico Digital Video Terminal uses an open-source software library to generate the digital video signal, and this library ‘overclocks’ the RP2040 microcontroller on the Pico to achieve the necessary timings. The original library by Luke Wren can be found at https://github.com/Wren6991/PicoDVI We are using a fork (derivative work) from Adafruit that interfaces the library with the Arduino IDE, available from https://github.com/adafruit/ PicoDVI We are using much the same hardware as Luke used in his prototypes; many other people have also tried this library. It’s impressive that it can generate digital video from a cheap and readily available microcontroller board. Luke notes that the signalling generated by our circuit is probably not wholly compliant with all the DVI and HDMI specifications. Nonetheless, it appears to pass all the critical tests. In the year or so since this library was released, many projects have used this software and custom RP2040 boards have been created for generating digital video. We have yet to hear of anyone who has had problems due to the overclocking or the signalling variances. The RP2040 on our prototype runs at nearly double its specified 133MHz and is barely warm. Every HDMI monitor we have tried has displayed the video correctly. We haven’t tried extreme cases like very long HDMI cables, but we see no reason for that to cause problems. So, this project does some things that are not ‘in spec’, but we and many other people have found it to work well. Connections Fig.1 shows how and where external devices connect to the Terminal and how it is arranged at a block level. Assume that we are using the Terminal with a device like a Micromite, it will connect through USB connector CON2. A complete, standalone system can be made by plugging a USB keyboard into CON3 and connecting a suitable display into CON1. 5V power is provided to USB Type-C connector CON4, feeding all the connected devices. Keys typed on the keyboard are converted to serial sequences by MOD3 and are transferred over the internal serial link to MOD2, which passes them over the CON2 USB connection to the Micromite (or PicoMite etc). The Micromite sends data back to MOD2, from where it is sent to MOD1, which behaves as a terminal display device and delivers video via CON1. With a Micromite, the serial data (from MOD3 to MOD2 and MOD2 to MOD1) takes the form of ASCII characters and VT100-compatible Escape codes. Thus, you can type on the keyboard, and the Micromite will respond as per its programming and display its output on the monitor connected to CON1. The output on CON1 is intended to mimic a terminal program such as TeraTerm. If you connect a computer to the micro-USB socket of MOD2, you can communicate with the Micromite as though it were directly connected to the computer; MOD2 will also transparently pass data between these interfaces. The grey lines show the path of data to and from the Micromite. A USB-serial interface is also provided on MOD3 to allow for the configuration of the keyboard interface properties. Each of MOD1-MOD3 has one LED that can be used to show the status of their respective connected device. Of course, a Micromite is not the only device that can be connected to the Terminal. We will look closer at what devices are compatible with the USB-serial host interface of MOD2, which includes several other development boards. Fig.1: this block diagram shows how the three Picos (MOD1-MOD3) interact and the external interfaces they provide. MOD1 delivers a DVI digital video signal to CON1, MOD2 communicates with the target computer via CON2 and MOD3 interfaces with the USB keyboard at CON3. siliconchip.com.au Australia's electronics magazine March 2024  47 Circuit details Fig.2 shows the detailed circuit of the Pico Digital Video Terminal. MOD1, MOD2 and MOD3 are Raspberry Pi Pico microcontroller boards loaded with different firmware. They each perform one of the main functions of the Pico Digital Video Terminal. We will explain in detail why there are three separate microcontroller boards in the Software section and what the firmware does there, too. The VBUS pins of MOD1-MOD3 are connected together, along with the VBUS pins of CON4, a USB-C socket. The CC1 and CC2 (configuration channel) pins of CON4 are each connected to ground via 5.1kW resistors, which presents the Terminal as a power sink requesting 5V. This is necessary for compatibility with USB-C. Any of MOD1-MOD3 and CON4 can supply 5V to the circuit. Power would typically come from CON4 if the Terminal is not connected to a computer, or MOD2 if it is connected to a computer. MOD1-MOD3 might also be connected to a computer for configuration purposes. Since each Pico provides a distinct 48 Silicon Chip function, we will discuss each in turn before describing how they work together. Note that each Pico has a corresponding connector, switch and LED numbered the same. MOD1 connects to CON1, S1, LED1 and so forth. MOD1 MOD1 is responsible for generating a digital video signal to send to CON1. Its GP12-GP19 (general purpose I/O) pins are each connected to a pin of CON1 via 270W resistors. With the cable impedance of around 50W, each of these pins will sink 10mA when pulled low by the microcontroller or not sink any current when high. The pins are arranged in pairs driven in a complementary fashion, providing the current-mode differential signalling needed. More detail on the TMDS signalling scheme that encodes the video data can be found in the panel titled “DVI-D, HDMI and TMDS standards”. MOD1’s GP9 pin (pin 12) also connects to green LED1 via a 1kW resistor, which is used as a status indicator. S1 is wired between MOD1’s 3V_ EN pin and GND. When pulled low, it shuts off the 3.3V regulator that powers Australia's electronics magazine the RP2040 microcontroller on MOD1, effectively resetting the micro. JP3 and JP4 are wired to GP8 and GP7 (pins 11 & 10), respectively, with the other side grounded. The software applies an internal pullup and can thus check the jumpers’ states by checking the voltage pin levels. The software uses these for configuration. GP10 and GP11 (pins 14 & 15), configured as I2C SDA (data) and SCL (clock), are wired to a 3.3V-to-5V level shifter consisting of Mosfets Q1, Q2 and the associated 10kW resistors. We used a similar scheme in the USB to PS/2 Keyboard Adaptor project mentioned earlier, to interface the 3.3V microcontroller to 5V PS/2 keyboard levels. The operation of this part of the circuit is explained in that article; the design is well-suited to open-drain busses like I2C and PS/2. A low level on either side is propagated to the other side; without a low logic level on either side, the respective pullup resistors maintain the lines at high logic levels. The 5V side of the circuit is connected to the DDC (Display Data Channel) SDA and SCL lines of the CON1 siliconchip.com.au Fig.2: the full circuit shows the eight 270W resistors that limit the current for the TMDS links of the DVI connection to the correct level; around 10mA. The two USB host Picos (MOD2 and MOD3) require only a USB-A socket and a pair of resistors to perform their roles. Most of the remaining circuitry provides communication between the Picos. HDMI connector. This interface can be used to interrogate an I2C EPROM on the display device to check its capabilities. CON1 also provides 5V to the display via JP2. This can power the EPROM on the display device, even when the display is switched off. The display can also connect the 5V back to the HPD (hot plug detect) pin on CON1. The 10kW/10kW divider allows the Pico to safely detect the presence of a connected display at its analog-­ capable GP27 input pin (pin 32). MOD2 and MOD3 The circuitry around MOD2 and MOD3 has been intentionally kept similar to MOD1 to simplify development. We imagine readers will have different ideas for things that can be done with this hardware, in conjunction with different software. Like MOD1, MOD2 and MOD3 have their switches (S2 and S3) wired between the 3V_EN pin and GND. Unlike MOD1, MOD2 and MOD3 have their respective LEDs connected to GP14 (pin 19) via 1kW resistors. These LEDs are otherwise identical status indicators. siliconchip.com.au The remaining circuitry connects USB-A sockets CON2 and CON3 to their respective boards via 22W series resistors. Readers might recognise this from the USB to PS/2 Keyboard Adaptor, which used a similar arrangement to interface the regular GPIO pins GP15 and GP16 (pins 20 & 21) to a USB connector. Jumper JP1 connects MOD3’s GP14 to MOD2’s GP17 pin. This gives MOD2 a second status LED in case MOD3 is not used. Our original design planned to use a single Pico for both USB interfaces; we will revisit that in the Software section. Interconnections Apart from the VBUS and GND lines that are interconnected around the circuit, there are serial data pairs (RX and TX) between each of MOD1, MOD2 and MOD3. The RP2040 has two UART peripherals, so each module has two incoming and two outgoing connections, one to each of the other modules. The following explanation expects two jumper shunts to be fitted to LK1. One is fitted between pins 1 and 2; the second is between pins 3 and 4. Australia's electronics magazine Both MOD2 and MOD3 communicate with MOD1 using their UART0 peripheral on GP0 (pin 1, TX) and GP1 (pin 2, RX). These are crossed over and connected to MOD1 at its UART0 for MOD2 and UART1 for MOD3 (GP4, pin 6, TX and GP5, pin 7, RX). MOD2 and MOD3 connect to each other via their crossed-over UART1 pins; this means that pin 6 (TX) of MOD2 connects to pin 7 (RX) of MOD3 and vice versa. Note how this continues the theme that MOD2 and MOD3 have much the same external connections. An alternative configuration of LK1 involves fitting a single jumper between pins 2 and 3. In this case, data from MOD3 comes into MOD2’s UART0 instead of UART1. You can probably see the spirit of how the Terminal achieves its aims, but of course, the detail is in the software. Software The firmware on all three Pico boards makes good use of the RP2040 PIO (programmable input/output) peripheral. We discussed the PIO peripheral in our review of the Pico March 2024  49 DVI-D, HDMI and TMDS standards DVI (Digital Visual Interface) was a standard developed in the late 1990s as a progression beyond the analog VGA (Video Graphics Array) interface. Part of the motivation was to switch to a digital communication format due to the increasing prevalence of digital displays like LCDs, removing the need to convert to and from an analog signal as required by VGA. Cathode ray tubes are analog in nature, requiring, for example, a ramped analog voltage to perform the horizontal and vertical scanning of the display area. Plasma panels, LCDs and OLEDs are more digital, having discrete pixels rather than a continuous phosphor surface, hence the preference for a digital interface. Our series on Display Technologies (September and October 2022, siliconchip. au/Series/387) has more background on those different technologies. Despite the name, DVI can carry an analog VGA signal, which made it wellsuited to the transition away from VGA. In practice, there were DVI-D (digital), DVI-A (analog) and DVI-I (integrated [digital and analog]) variants of the cables and connectors. DVI can only work if the display adaptor, cable and display all support the same digital or analog variant. For example, a DVI-D Fig.a: HDMI connectors carry many of the same signals as a DVI connectors, although they omit the analog (VGA-compatible) signals; HDMI is purely digital. Pins 1-12 carry the TMDS lines and are sufficient for a working video signal. 50 Silicon Chip output will only work with a DVI-D or DVI-I cable and a DVI-D or DVI-I input socket on the monitor. It is the digital variant of DVI signalling that the Terminal implements. However, the connector itself is HDMI due to the ubiquity of displays equipped with HDMI sockets. It is possible to connect a DVI display to the Terminal using nothing more than a passive HDMI-DVI cable or adaptor. HDMI high-definition multimedia interface Similarly to how DVI was backwards-­ compatible with VGA signals, HDMI is also compatible (by design) with a subset of DVI-D. One of the main advantages of HDMI is that the connector can carry digital audio, video, control signals and even data network traffic. The overlapping parts of DVI and HDMI that we are implementing in the Terminal use TMDS (transition minimised differential signalling). We will explain that below. Fig.a shows the pinout of the signals carried by HDMI cables; pins 1-12 have the TMDS signals and their shields. Newer versions of HDMI use higher data rates, compression and encoding schemes. For example, they can also implement different colour spaces, including HDR (high dynamic range), while DVI-compatible signalling uses a straightforward 24-bit RGB colour representation. HDMI adds other data channels between the video source and the sink (or display), and we have added a provision to interface to one of these, although nothing apart from TMDS is necessary for the Terminal to drive a video display. The DDC (display data channel) allows the HDMI source to determine what video formats a sink can accept. Since all HDMI devices must comply with the baseline DVI specification, implementing DDC is unnecessary, as we are not producing a signal beyond the baseline. The DDC used on HDMI is electrically the same as I2C. It is implemented (on the display or sink) as an I2C EPROM with a 7-bit I2C address of 0x50; a host can read this to find the display’s capabilities. We have connected these pins to a pair of I2C pins on MOD1 via a level converter, allowing it to read the sink’s DDC chip. A 5V supply is provided by the HDMI source to power the EPROM, so it can be interrogated even if the device itself is switched off. Internally, the source also connects that 5V back to the HDMI HPD (hot plug detect) Australia's electronics magazine pin, allowing the source to detect when a sink is connected. The sink may also be able to disconnect the HPD pin, for example, when switched on or off. HDMI implements other communication protocols that we have not provided connections for. Some of these protocols are not specified in all versions of the standard, but we’ll note them here for completeness. Consumer Electronics Control (CEC) is a one-wire bidirectional serial bus. It allows connected CEC-capable devices to control other devices. This means, for example, that a single remote control can operate many devices. Audio Return Channel (ARC) allows audio to be sent ‘upstream’. A typical use for this would be when a TV is showing a source that does not come from the receiver (eg, a tuner built into the TV). In that case, the ARC channel can send the audio to the AV receiver to route to its speakers. HDMI Ethernet Channel (HEC) allows Ethernet communications over HDMI cables, but it has been deprecated in the most recent HDMI versions. WiFi has mostly taken over its role of providing internet connectivity. TMDS transition-minimised differential signaling The critical part of both DVI and the baseline HDMI standard is the transition-­ minimised differential signalling that sends the video signal from the source to the sink. It consists of four shielded, twisted pairs of wires, each carrying a differential signal. Differential signals over twisted pairs make the receiver somewhat immune to common-mode noise since a similar signal will be induced in both wires in the pair from an external source. When the difference of the signals is calculated at the sink, the noise effectively cancels out. Also, the available voltage swing is double what it would be with a single line, adding 6dB of headroom to the signals. Of course, HDMI is not the only technology that uses differential signalling. Serial standards such as RS-485 also use differential signalling, as do USB and Ethernet over twisted pairs (eg, 10BASE-T and 100BASE-T). Electrically, the signalling scheme requires that one wire of each pair alternately sinks 10mA (from a 3.3V rail in the video sink by the video source). Which wire siliconchip.com.au sinks the current determines if it is a ‘0’ or ‘1’ being sent. In practice, the Terminal hardware drives its pins high (to 3.3V) or low, achieving the same effect. The cable impedance in series with the 270W resistors allows the right amount of current to flow. This is quite a high-speed signal for a microcontroller to send off-board, and quite a bit more engineering is involved than this simple explanation implies. Still, it should give you an idea of what the Pico needs to do at the hardware level. 8b/10b encoding TMDS uses a coding scheme that reduces the number of transitions that need to occur over the twisted pair, which reduces electromagnetic emissions. The clock differential pair has a 50% duty cycle and operates at a frequency equal to the pixel clock, thus giving two transitions per pixel. PLL (phase-locked loop) hardware at the sink allows the fullspeed bit clock to be recovered without having to be transmitted over the HDMI link. The three other pairs each carry a series of eight-bit data bytes encoded into 10 bit-times (hence 8b/10b encoding), meaning that there is one 24-bit pixel transmitted per pixel clock (see Fig.3 overleaf). Note that other different 8b/10b encoding schemes also exist. Of the 1024 combinations possible with 10 bits, 460 are selected to encode eightbit colour values; this means that some values have more than one encoding. Four further combinations are used to encode control data and are chosen to have a relatively high number of transitions to assist with clock recovery. The four control combinations encode two bits of data. On one of the colour channels (channel 0, blue), these encode the horizontal sync and vertical sync signals. The sync signals are naturally sent outside the times that colour information is transmitted. Channel 1 is allocated to the green component of the video signal, while channel 2 carries the red component. The timing of a baseline (640×480 pixel) digital DVI signal is practically identical to the corresponding VGA signal, but with digital signals instead of analog, so only the digital encoding and decoding steps need to be added (to analog VGA), with no changes in timing. A frame of 640×480 video actually consists of 800 horizontal and 525 vertical pixels. 800×525×60Hz (60 FPS) gives the 25.2MHz pixel clock rate. Fig.b shows how such an analog VGA signal would be encoded and then recovered. Another desirable property is for the running average DC level to be low. The coding scheme helps with this, as it allows 10-bit symbols with a high DC offset to be avoided. In this case, a zero DC offset means a long-term equal number of ‘0’ and ‘1’ bits. The eight-bit values with more than one encoding have 10-bit values with opposite DC offsets, so even long runs of the same eight-bit value can be transmitted with a combination of symbols that result in a low combined DC offset. The remaining codes with only one encoding and the control codes mostly have an equal number of ‘0’ and ‘1’ bits, so they can be transmitted without affecting the DC offset appreciably. The Terminal does not transmit audio, but HDMI allows that to be carried (along with other data) during the sync periods by using control codes to signal the presence of audio data. Fig.b: this shows how the signals found in a VGA analog video signal (on the left) can be encoded to be sent over a fourchannel TMDS link and then back. So, the four-channel TMDS link can be seen as a digitally encoded version of a VGA signal. siliconchip.com.au Australia's electronics magazine March 2024  51 Fig.3: the four differential pairs of a DVI signal look similar to this if seen on an oscilloscope. Note the symmetry and DC balance of all the signals. in December 2021 (siliconchip.au/ Article/15125). It is a specialised processor that implements a few instructions focused on I/O pins. It can easily emulate serial communication peripherals like UART and SPI, or produce PWM signals, including those needed to drive a servo motor. There are two PIO peripherals and each has four state machines. The state machines are the ‘processors’, so up to eight separate emulated peripherals can be created on the RP2040 chip. Each PIO has a memory that can hold 32 instruction words. Each state machine has a four-word deep input FIFO (first-in, first-out) buffer and a similar output FIFO buffer. If only input or output is needed, the two FIFO buffers can be combined into a single eight-word buffer. Being a 32-bit architecture, the words are 32 bits wide. Each state machine also has an input shift register and an output shift register. These take in chunks of data and shift them in or out one or more bits at a time, as is needed for the serial protocols noted earlier. The DVI implementation is a good example of a simple use of the PIO. Each pixel in a DVI video stream consists of 10 bits clocked out very quickly. The nominal pixel clock of a typical baseline 640×480 at 60Hz signal is 25.175MHz; the bit clock is thus 10 times that: 251.75MHz. The PIO operation for DVI video involves passing 10 bits of data at a Making an all-in-one computer Replacing MOD2 with a Pico (or Pico W) programmed with different firmware is possible. This is the reason for link LK1. A shorting block can be fitted between pins 2 and 3 of LK1, and the serial data streams from MOD3 and towards MOD1 are now both connected to UART0 on GP0 and GP1. The following PicoMite BASIC OPTION can be set to use UART0 (on GP0 and GP1) as the console: OPTION SERIAL CONSOLE 0,1,B The default baud rate used by MOD2 and MOD3 is 115,200, which should match the PicoMite’s default. If necessary, it can be changed with another option. OPTION BAUDRATE 115200 The PicoMite is now integrated into a computer with a USB keyboard and digital display interfaces. It’s a bit trickier than usual to access the spare I/O pins. Still, if you were looking to experiment with the BASIC language or perhaps the WiFi interface of the WebMite, it would make a compact machine for those purposes. You could also write your own code to run in place of MOD2, creating a custom computer. There are several projects around that emulate older computer platforms using the Pico. 52 Silicon Chip Australia's electronics magazine time into the PIO’s FIFO, which it then simply clocks out serially at the bit clock rate. The RP2040 also has a direct memory access (DMA) peripheral, which we use to ensure that the PIO is consistently fed data from RAM without requiring the main ARM processor’s attention. The processor simply needs to set data in RAM and arrange for the DMA peripheral to move that into the PIO as needed. The nominal 251.75MHz figure noted earlier dictates the overclocking needed; the Pico is clocked at 252MHz, resulting in a signal that is within VESA tolerances. The DMA and FIFO actually handle data in 20-bit blocks, sending two pixels at a time. In theory, the 32-bit ARM processor could work with blocks of three pixels (or 30 bits), but three does not divide into the 800 pixels that constitute each horizontal scan line (including sync periods). A good amount of data still needs to be generated to feed the PIO. Therefore, one of the two processor cores on the Pico is dedicated to encoding data from an RGB or monochrome frame buffer into the TMDS form that the PIO requires. The other core of the MOD1 Pico listens in on its serial ports and behaves as a VT100 terminal. The VT100 was a ‘dumb terminal’ introduced in 1978. They were standalone hardware devices that allowed numerous users to connect to a large mainframe computer over a simple serial interface. Nowadays, they mainly exist as software emulations by serial terminal programs such as TeraTerm or minicom that can run on a desktop or laptop computer. The VT100 standard allows ‘Escape codes’ to perform functions like moving the cursor around, changing the text colour and clearing the screen. They are called that because they start with the ASCII Escape character (0x1B). Since the various Micromites and PicoMites use the VT100 protocol, this is the most straightforward way to interface with them. This also means that MOD1 (and its associated components) behaves effectively like a dumb display terminal. MOD1 maintains a buffer of characters and their attributes (such as colour or underlining) and manipulates the buffer according to the data that arrives on its serial port. The buffer is then siliconchip.com.au rendered for display and sent to CON1 as a DVI video signal. LED1 is illuminated whenever MOD1 detects a voltage from the HPD pin of CON1, which indicates that a display device is connected. MOD2 MOD2 uses the Adafruit TinyUSB software library to allow it to behave as a USB host to a USB-serial device. The library incorporates the Pico-PIO-USB library, which allows the USB interface to operate on a pair of GPIO pins. We use the PIO peripheral to implement a USB port instead of the RP2040’s dedicated USB peripheral for two main reasons. Firstly, connecting to the GPIO pins is much easier since the internal USB data pins are only available at the Pico’s onboard USB socket or two test pads on the Pico’s underside. Secondly, it gives us two USB ports, allowing the Terminal to transparently connect the Micromite (or whatever is connected via CON2) to a computer, both relaying and intercepting data between the Micromite and the computer. That is most of what MOD2 does. It bridges the link between the device connected at CON2 and a computer connected at MOD2’s micro-USB socket. It can also inject data received from MOD3 as well as exfiltrate data to MOD1, as shown in Fig.1. The LED connected to GP14 is illuminated whenever a compatible device is connected to CON2 and flickers when data is received from MOD3. The Pico-PIO-USB library uses nearly all of the PIO resources, which is the main reason why we need a dedicated Pico for this role and can’t integrate it with either of the others. MOD3 Like MOD2, MOD3 also uses the Adafruit TinyUSB software library to allow it to behave as a USB host, except in this case, it expects a keyboard to be connected. Thus, the circuitry around MOD3 can be much the same as MOD2, but the software is different. The software has much in common with the USB to PS/2 Keyboard Adaptor; that project translates strokes from a USB keyboard into PS/2 scancodes, while MOD3 on the Terminal translates them to serial data and VT100 Escape codes. It also monitors the Number Lock, siliconchip.com.au Silicon Chip kcBBack a Issues $10.00 + post January 1995 to October 2021 $11.50 + post November 2021 to September 2023 $12.50 + post October 2023 onwards All back issues after February 2015 are in stock, while most from January 1995 to December 2014 are available. For a full list of all available issues, visit: siliconchip.com. au/Shop/2 PDF versions are available for all issues at siliconchip.com.au/Shop/12 We also sell photocopies of individual articles for those who don’t have a computer Scroll Lock and Caps Lock keys and changes the state of the keyboard LEDs to suit. The serial data it delivers depends on the state of the Number Lock and Caps Lock keys. MOD3 lights up LED3 whenever it detects a keyboard is connected and flickers it briefly whenever a key is pressed or released. You will see different patterns on LED2 and LED3 during regular operation. Our early prototypes combined MOD2 and MOD3. The Pico-PIO-USB library can support a USB hub so multiple devices can be connected, but it only supports a single hub. Many USB keyboards incorporate a hub, at least internally, so we found that many keyboards did not work when connected through a hub. Since a Pico is much the same price as even the cheapest hub we could find, we opted to simply add another Pico and USB socket. It is a more elegant solution as everything fits neatly into a single enclosure. While MOD2 and MOD3 can only perform the specific role they have been programmed for, the symmetrical arrangement of their external connections means that they can be physically transposed on the PCB with only minor software changes. Hardware notes That is all we can fit into this article, so next month’s second part will describe assembly, testing, configuration and use. We have provided the parts list this month to allow you to collect various components needed for assembly. The design uses a few SMDs, but they are primarily passive parts in M2012 size, so they are not too difficult to solder. The HDMI socket has pins at a 0.5mm pitch, so it is probably the most challenging part to solder. Still, it is not too difficult if you have good flux paste on hand, decent lighting and perhaps a magnifier. There are two case options. One option is to use the 25mm-high Altronics H0190 (or equivalent). This has a corresponding front panel PCB that is coded 07112232. This case is ideal if you plan to permanently solder the Picos to the PCB via pin header strips. An alternative is the 30mm tall H0191, which uses a front panel PCB coded 07112233. This case allows you to fit MOD1-MOD3 using sockets, so they are removable. That might be handy if you are considering using an alternative firmware for MOD2, as described in the panel (“Making an SC all-in-one computer”). Other configurations for advanced users While the Terminal we are describing here is intended to parallel the ASCII Video Terminal in function, the modular nature of this project means that it can be altered to work in various ways. For example, you could build the Terminal with only the parts surrounding MOD1 and use it to deliver a custom video signal to a modern digital display. Fitting just MOD2, its USB socket and surrounding components will give you a USB-serial interceptor device like the one we plan to describe in an upcoming Circuit Notebook. Fitting just MOD3 and its associated components will give you a device with similar capabilities to the USB Keyboard Adaptor for Micros (February 2019; siliconchip.au/Article/11414). However, all of these options require the Pico to be wired up to another device via a serial link to be useful. Australia's electronics magazine March 2024  53 Don't pay 2-3 times as much for similar brand name models when you don't have to. 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ESD means Electro Static Discharge Shop Jaycar for your soldering essentials: • Soldering stations • Electric handheld irons • Gas powered irons • Classic 60/40, lead-free, silver & paste solder options • Multiple desolder braid and tools • Wide range of stands, cleaners and PCB holders Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. By Steve Schultz Electromechanical Noughts & Crosses Machine In his autobiography, Dick Smith described building a machine that could play Noughts & Crosses in 1958 using parts from a telephone exchange. I was fascinated with the idea of such a machine and decided to build my own version of it, with some modern twists! T his article outlines the design of my machine, which uses electromechanical components. It isn’t intended to have the level of detail of a project article, but it should give you a pretty good idea of how I built it and how it works. I was inspired to do this by the competition announced in the October 2021 issue of Silicon Chip (p13) by Dick Smith to design a modern Noughts & Crosses machine. I wanted to see whether I could build a machine using the technology he would have had available to him at the time. Items like PMG stepper switches aren’t readily available anymore, so I would have to 3D-print the mechanical components needed. The result is shown in Photo 1 and in the photo at the end of the article – the shiny dome on top is a bell to announce the winner! My machine includes a display and control board, a register and control board, two stepper switches and a motorised cam switch. The design is loosely based on an article published in 1956 called “Relay Moe plays Tic Tac Toe” – see Photo 2. It is described as consisting of 90 relays, a stepper and a motor that drives a series of cam switches. That article explains the machine’s logic for completing a row of three (or blocking a row of three). However, it doesn’t describe how the machine decides on its moves. I also found a YouTube video at https://youtu.be/SlNxBb_27CA about Photo 1: a top-down view of the completed machine. You can see many of the mechanical components at the top; there are many relays on a PCB under the LED game board. 56 Silicon Chip Australia's electronics magazine a machine invented by Donald Watts Davies (one of the inventors of the packet-switched network). He built it in 1949 using relays and stepper switches – see Photo 3. While Relay Moe used red and green lights to represent noughts and crosses, Davies’ machine appears to project the circle and cross symbols onto a screen. A more compact design Those machines were large and used point-to-point wiring. I minimised the size of my unit and maximised the ease of assembly by using miniature relays, printed circuit boards and ribbon connectors. My first attempt at building such a machine, shown in Photo 4, had a few Photo 2: one of the inspirations for this design was the Relay Moe from 1956, featured in Radio-Electronics. siliconchip.com.au Photo 3 (above): Donald Watts Davies’ 1949 electromechanical Noughts & Crosses playing machine. Photo 4: my first attempt was not so successful, partly because it tended to skip steps, leading to invalid states. shortcomings, including poor reliability. I used solenoids to drive ratchets that rotated multi-pole switches representing the square selected at each turn. The concept worked, but I had problems with the force needed to turn the ratchet and the spring force used to return to the home position. Occasionally, a switch position would be skipped, giving an invalid game. Also, this machine could only play the same game each time – it would always select the top left corner if the machine went first. The new machine has a level of randomness in its first move and in follow-on moves. That makes it more difficult for the player to anticipate the machine’s strategy. It does this by using two stepper switches. One selects the corner squares and the other the edge squares. When a game is started, the stepper switch retains the previously selected square, which is random. The stepper switch will cycle through a random sequence of squares with 11 possible positions (the 12th is home). For example, the corner stepper may step through the following sequence (referring to Fig.1): 1-3-7-9-3-1-7-3-9-13. Hence, each game will be different. In addition, the new machine is designed with a set of rules followed by the motor cam sequence. The original machine was not rulebased but used pre-determined calculations based on previous moves. A set of motorised cam switches effectively cycle through a set of rules in sequence, bypassing the rest of the cycle if a rule matches a condition. For example, one of the key rules is for the machine to select a blocking square if the player has played two squares in a row. siliconchip.com.au In terms of electronics, it mainly uses miniature DPDT relays, diodes, resistors, and capacitors; there are no transistors or integrated circuits. I used LEDs for the display because of their convenience and low power usage, but I could equally have used miniature incandescent lamps. The main display board includes the buttons for the player to select a square, the noughts or cross display, three lights to identify a machine or player win or a draw, and a machinefirst button. If the machine wins, the bell rings four times. I also added a Skill switch with low, medium, and high settings, which changes the rules used. You can see videos of my machine in operation at the following links: • siliconchip.au/link/abrl • siliconchip.au/link/abrm Operating principles The overall architecture of the machine is shown in Fig.2. When a player selects a square, it starts the cam sequence motor, which rotates a series of cams in sequence – see Fig.4. These implement the rules in order. If a decision is made to select a square, the rest of the cam sequence is bypassed. The flow chart, Fig.3, outlines the decision tree for the machine. The flow is shown for the Skill switch on the High setting, in which case the machine implements the “First Player Move” logic in the lower part of the flowchart. If the player has gone first and selected a corner, the machine will attempt to force a draw so the player cannot win. It does this by choosing the centre square and setting the “Corner Bypass” relay. This means that the next machine move will be an edge, and the player must respond with a block, resulting in a drawn game. If the machine has gone first (it will have selected a corner), it will choose the diagonally opposite corner as Fig.1: the numbering scheme for referring to specific squares on the game grid. Fig.2: the basic arrangement of the Electromechanical Noughts & Crosses machine. Australia's electronics magazine March 2024  57 the next move unless the player has already taken that square. The Skill switch is primarily related to the rules for the first move, as the first two moves tend to determine the game’s result. The basic operation of the register and control board depends on combinations of relays to store the current state of the board. 18 relays (nine for the machine and nine for the player) store whether a square has been selected. When a square is selected, the associated relay is activated and self-latches with one set of contacts, so that the relay stays on when the selection is released. This also lights up the nought or cross display for that square. The machine will always try to complete a row of three (to win) or block the player from winning. To do this, a combination of cam switches and ‘branching’ relays determines the next square to select. For example, if the machine has already played squares 1 and 3, square 2 is the winning square. The branching relays are used as AND gates. In this case, square 2 is selected by 1 AND 3. Square 2 would also be a winning square if 5 and 8 had already been selected. So, the logic for choosing square 2 is (1 AND 3) OR (5 AND 8). The cam switches latch such a combination into the Intermediate Memory or “IM” relays. Once the machine’s squares have been latched, another cam will check to see if the player Fig.3: this flowchart shows the steps that the machine uses to play the Noughts & Crosses game. Fig.4: the motor, gear and cam arrangement used to run through the ‘program sequence’ after the player makes a move. Fig.5: the machine uses two 3D-printed stepper switches like the one shown here. One is used to randomly select game board corner squares, and the other is used for edge squares. Photo 5: the 3D-printed stepper switch disc has two bridging contacts that make electrical connections between pairs of pads arranged radially. 58 Silicon Chip Australia's electronics magazine siliconchip.com.au already occupies the winning square and cancel the associated IM relay if so. An uncancelled IM relay can then be used to select the relevant square. Stepper switches Two stepper switches, shown in Fig.5, are used for scanning and selecting free corners or edges. Each stepper switch consists of an electromagnet that attracts an armature. The armature pushes an arm onto a ratchet wheel. The ratchet wheel rotates a set of contacts that effectively form a two-pole, 12-position switch. The A-part of the switch is used to scan for a free square. When a free square is found, the equivalent contact on the B-part of the switch is pulsed and selects that square. Two bridging wipers (see Photo 5) rotate in an anti-clockwise direction by one increment for each movement of the armature. The contacts bridge pairs of pads on the adjacent PCB. If the contact has +24V present, the armature will stop, and a pulse will be passed via the “B Common” line to the relevant B contact. This pulse selects the appropriate square. The control board for the stepper switch has a few relays to latch the scanning action until a free square is found; the free square operates a ‘cancel’ relay that unlatches the scan relay. The stepper switch is self-actuating. When the armature closes, in addition to incrementing the ratchet, it operates a microswitch that opens the coil magnet circuit and the armature returns to its home position. The stepper switch consists of the frame that mounts all the mechanical (including bearings) and electrical components, the electromagnet coil, and two circuit boards: one with the rotary contacts and the other with the control circuitry. Where possible, I have tried to design the components as reusable modules. This is the case for the cam sequence motor unit and the stepper switch modules. All modules are interconnected using ribbon cables and IDC connectors. When designing the stepper switch mode, I kept the following in mind: • It needed sufficient power to operate the armature and rotate the ratchet reliably, between 20 and 40 watts. This dictated the 24V operating voltage. • I made it self-operating so it doesn’t need an external clock/ siliconchip.com.au oscillator to pulse the magnet coil. A microswitch disconnects the magnet when the armature moves to the end of its stroke, with a capacitor to define the operating frequency. • It needed to reliably increment and stop in the correct location. This dictated the final design of the ratchet, which has two profiles: one for the push arm and another for the detent wheel. It also meant that the mechanism needed to be adjustable. I built a special alignment circuit board to drive the stepper switch and used a string of LEDs to confirm the alignment (see Photo 6 and siliconchip.au/ Videos/XvO+alignment). • I also wanted the stepper to be able to be used for “counting” operations. That means it has a ‘home’ position that it can return to. The scan input can then be used to increment the switch. One of the sources I referred to when designing the stepper switch was a 1964 publication, “How to use rotary stepping switches”. The stepper has two inputs: Home and Scan. If the Scan input goes high, the Scan relay is latched and power is supplied to the main magnet coil. The coil attracts the armature, which in turn operates the microswitch when it reaches its limit after pushing the ratchet forward by one position. The microswitch operates the coil release relay, allowing the armature to return to its home position. The hold capacitor keeps the coil release relay latched for a defined period, allowing the frequency of self-actuation to be controlled. In early testing, with no capacitor, the switch would cycle through the 24 contact positions in about a second. With the capacitor, it goes through roughly two steps per second. Each operation of the armature rotates the A and B wiper contacts one increment. If a square is already occupied, that contact will be in a disconnected state, with no voltage present. If a square is free, +24V will be detected on the contact and fed to the A common line. That operates the stop relay, which releases the scan relay, ceasing the scan sequence. The equivalent B-side contact is pulsed with the A common line feed to select the relevant square. Register and control board The nine relays representing whether the machine or player occupies a square are interlocked so that the player cannot select a square if the machine has already occupied it. These are the Machine Memory (MM) and Player Memory (PM) relays. If the player goes first, the motor start relay is latched, and the motordriven cam switches commence their sequence. One of the cams (Cam1) switches the motor stop relay at the end of the sequence. The cam switches drive several actions in sequence. Cam2 checks whether the player has completed a row of three and, if so, operates the player win relay and bypasses the rest of the cycle. The next cam (Cam4) clocks the MM states into the branch relays to determine whether the machine can complete a row of three and therefore win. If, for example, MM1 and Photo 6: one of the stepper switches being calibrated using the purpose-designed adjustment aid PCB. Australia's electronics magazine March 2024  59 Fig.6: this cam disc, Cam1, stops the motor at the end of the cam sequence, so it has a single cam with a short dwell. Fig.7: Cam5 (“Cancel squares occupied by other player”) needs to trigger functions 4, 7, 9 & 11, so it has four lobes with longer dwell than Cam1. MM2 are selected, the branch relays will operate IM3. If the player already occupies square 3, Cam5 will operate the relevant IM cancel relay, clearing IM3. If the IM relay is not cleared, the follow-on cam (Cam6) will select that square. Similarly, the following sequence clocks the PM states into the branch relays, in conjunction with the machine & player swap relays, controlled by Cam3. If the machine can block the player from completing a row of three, it will. Cam7 performs a check to determine whether the machine has managed to complete a row of three and, if so, operates the machine win relay. It also activates Cam12, which has four lobes that ring the bell four times. The cam sequence is summarised in Table 1. Each cam is defined by a few parameters, including the number of lobes, the start and end angle for each lobe, the leading angle, the dwell angle and the trailing angle. For example, for Cam1, the dwell is very short (see Fig.6). We want this cam to operate the motor stop relay but coast to a stop so that the cam switch is ready for the next cycle. However, Cam5 (Fig.7) needs to operate four times during the cycle, with a longer dwell. The cams are mounted on a 7mm hexagonal brass shaft, ensuring an accurate angular relationship between cams. Table 1: Cam Sequence Cam Description 1 2 3 4 5 6 A vital part of the circuitry is associated with bypassing follow-on cam cycle events when an earlier cycle has declared a win for the player or machine, or when the machine has selected a square to play. If a decision is taken to choose a square, we must ensure that only that square is selected and the rest of the sequence is bypassed. These functions are performed by a Bypass Delay relay that, if activated, operates the Bypass Relay. Once activated, the remaining Cam actions are skipped until the end of the cycle. The Player Win Detect and Machine Win Detect functions also trigger the Bypass Relay directly. The first two moves In most Noughts & Crosses games, the outcome is determined by the first two moves. Several relays track and control these two moves, including the ‘Machine Went First’ relay and the ‘Player First Move’ relay. Combined with the Skill switch, they determine how the machine responds to the early player moves using the following rules. If the player goes first and selects a corner, the machine chooses the centre square. If the Skill switch is set to High, it also latches the Corner Bypass relay. The strategy here is that the next machine move will select an edge and force the player into a draw. If the machine selects a corner first, the next move should be to choose the 7 8 9 10 11 12 13 14 15 1 Motor stop 2 Player won 3 PM/MM swap 4 Copy MM into IM register 5 Cancel squares occupied by other 6 Select lowest IM 7 Win if IM still present 8 Clear IM relays 5 Cancel IM relays 4 Copy PM into IM register 5 Cancel squares occupied by other 6 Select lowest IM 8 Clear IM relays 5 Cancel IM relays 9 First move checks 10 Corner check 11 Edge check 60 Silicon Chip Australia's electronics magazine siliconchip.com.au diagonally opposite corner unless the player has already taken that square. The components of this system can be broken into blocks that interact with each other to form the overall system. Machine and Player Square registers Fig.8 shows the arrangement of the machine and player registers for each square. The player selects an available square by pressing the Player Select button. If the machine already occupied the square (MM1 here), the button is isolated from the 24V line and prevented from operating because the MM1.2 contact will be open. If the square is free, the player button operates the player memory relay (PM1), which self-latches. The button also sends a pulse to the cam motor start circuit via an isolating diode. When a square is free, the Square 1 Free output is presented with 24V via the normally-closed contacts of both relays. When the square is occupied, the output is disconnected. If 24V is available on the Square Free line, when the stepper switch is scanning, it will stop and select the free square. If the square is selected, a pulse will be initiated on the MM1 Select line, and the relay will start to switch the MM contacts. That will remove the 24V from the Square Free line, causing the relay to stutter and not reliably latch. The RC network on the Square Free line ensures that this latches reliably without the need for make-beforebreak contacts. Fig.9 shows the part of the circuit that determines the first two moves using two relays. The Player First Move relay represents the first move by the player, whether or not the machine has gone first. This relay is initially unlatched and is latched at the end of the first cam cycle via the Motor Stop signal. It remains latched for the rest of the game. The Machine Went First relay is latched when the player selects the Machine First button, latching the relay and selecting a corner via the Corner Select line. If the machine went first, Cam9 will trigger the Diagonal Select function. Because the machine will have selected a corner on the first move, this operation selects the diagonally opposite corner as the second move if the player has not taken it. If the player has gone first, the machine’s siliconchip.com.au Fig.8: there are nine sets of relays like these. If the player has chosen the square, the Player Memory (PM) relay is latched on, while if the machine has chosen it, the Machine Memory (MM) relay is on. Fig.9: these two relays help the machine to determine the first two moves based on who went first. The move is selected based on the states of the Diagonal Select, Centre Select and Corner Select lines. Fig.10: the logic for square 1 to determine whether to complete a row of three to win the game or to block the player from completing a row of three. Similar logic is used for the other eight squares. first move will be to select the centre square if it is free. Intermediate Memory circuits Fig.10 only shows the logic associated with selecting square 1 to complete a row of three to win, or to block Australia's electronics magazine the player from completing a row of three. However, similar logic applies for the other eight squares. Here, 24V is applied to the positive side of relay IM1 if squares 2 and 3 are occupied by the machine (or 4 and 7, or 5 and 9). March 2024  61 When Cam4 closes, the other side of the IM1 relay is grounded, causing it to operate and self-latch via the IM relay contacts. If square 1 is already occupied by the player (PM1), 24V will be present on the positive side of the IM1Cancel relay. When Cam5 operates, it connects the other side to ground, activating that relay. If square 1 is occupied by the player, the IM1Cancel contacts open, cancelling the IM1 relay and preventing the subsequent selection of that square. Any remaining latched IM relays constitute valid square selections to complete a row of three. Note that more than one IM relay can be operated. To avoid trying to repeat previous moves, the IM Cancel relays also have an input from each associated MM relay. on any of the IM Select lines, the Machine Win relay will operate and self-latch via its first set of contacts. The second set of contacts closing will present 24V to the input of Cam12, which will ring the bell to indicate that the machine won. Machine Win Detect circuit The detection of a Player Win occurs close to the start of the Cam cycle as it is initiated by the player pressing a button. Referring to Fig.12, the branch (B) relays are used to detect the winning This is shown in Fig.11. After Cam6 has operated, selecting the relevant MM relay, it remains closed when Cam7 operates. If 24V is still present Player Win Detect Circuit Photo 7: winding an electromagnet coil with a drill is much less tedious than doing it by hand! I measured the resistance at the end to verify that I had put roughly the right number of turns on. Fig.11: the Machine Win Detect circuit. It is a diode OR circuit based on the state of the nine Intermediate Memory (IM) relays driving a self-latching relay. Fig.12: the Player Win Detect circuit uses the states of the branch (B) relays, combined with diode logic and fed through the Player Memory relay that would be needed to complete a row of three. Photo 8: tapping the iron core support for the electromagnet. Australia's electronics magazine siliconchip.com.au 62 Silicon Chip square in a row of three. For example, if the player already occupied squares 2 and 3, square 1 would be the winning square, and contacts B2.1 and B3.1 would be closed. If the player selects PM1 (the winning square), contact PM1.2 closes, supplying 24V to the input of Cam2. When Cam2 operates, the Player Win relay is latched and the Player Win Light is lit. If squares 5 and 8 were occupied instead, square 2 would be the winning square, and if the player had selected square 2, that would operate the Player Win Relay via PM2.2 when Cam2 closes. Motor Control circuit When the player presses a button associated with a square, in addition to selecting the square, power is connected to the Motor Start relay. This relay self-latches and commences the cam rotation sequence. While the motor is operating, the Player’s Turn light is turned off, indicating that they must wait until the end of the sequence before taking their next turn. Once the cam sequence is completed, Cam1 activates the Motor Stop relay, which unlatches the Motor Start relay. The inertia of the motor coming to a stop means that Cam1 opens, leaving the next cycle ready to start. The motor used is a 12V DC motor with an inbuilt reduction gearhead. It is designed to operate at 36 RPM (one rotation every 1.7 seconds). The desired cycle of about 4 seconds was achieved using a reduction gear in the cam motor assembly. Some technical notes I used FreeCAD to design the mechanical components. It is a parametric CAD package, so it was easy to design the cams (including the cam lobes’ leading, dwell and trailing angles). During development and testing, those parameters needed to be changed frequently. One of the mechanical components I 3D printed was the coil bobbin for the main stepper magnet. After several operations, I noticed that the bobbin had started to melt; the coil consumed roughly 30W. Having prototyped the bobbin using PLA, I ordered Nylon units from a professional 3D printer, as Nylon can handle higher temperatures than PLA. One of the biggest challenges was siliconchip.com.au Photo 9: here you can see the two stepper switches and cam mechanism that are housed in the upper portion of the clear acrylic case, plus the relay board. Australia's electronics magazine March 2024  63 creating an electromagnet with enough force to drive the armature. I needed the armature to be no more than 4mm from the magnet end, which dictated the size of the armature arm, the push arm and the ratchet size. I started with a 12mm diameter core but ended up with a larger 16mm diameter core to increase the cross-­ sectional area and therefore force. I also used a high magnetic permeability iron rod to maximise the magnetic field. Based on the book mentioned earlier, I knew that the magnet needed to consume 20-40W to operate effectively and fast. As the magnetic field is related to the product of the number of turns multiplied by the current (B ~ n × I), I needed to maximise the number of turns while keeping the current at a reasonable level (<2A). I started with a wire diameter of 0.315mm (28AWG) and 1800 turns. This consumed approximately 1.3A. I ended up using a thicker conductor (0.355mm, 27AWG) and 1500 turns on the same-sized core, resulting in a current of 2A and therefore a 26% higher ampere-turn value. I wound the bobbins using an electric drill (Photo 7), feeding the enamelled copper wire from a reel. As I had calculated the turns using the depth and width of the bobbin, I simply filled the bobbin to the outside edge. I then measured the resistance to confirm the approximate number of turns. Photo 8 shows how I tapped the electromagnet’s iron core support. I designed the PCBs using Altium’s CircuitMaker cloud-based software, which is free to use. I chose it because of the vast library of available components, the powerful auto-route function and the general usability of the product. When designing boards such as the rotary select board for the stepper switch, it was essential to dimension and position the pads accurately. I could also create and re-use ‘components’ such as the LED array representing the nought or cross. Initially, I tried to find a commercial multi-segment LED component that could display the nought and the cross. I couldn’t find anything suitable, so I decided to make the display from discrete LEDs on the PCB. Each square has 25 LEDs: 13 red ones for the cross and 12 green for the nought. The 13 LEDs for the cross are split into series strings of six and seven, accounting for the forward voltages of the LEDs. Similarly, for the nought, there are two groups of six. Assembly and enclosure I wanted to give the player the experience of interacting with the machine and seeing and hearing the operation. Therefore, the stepper switches and the cam sequence motor unit are mounted in a clear enclosure at the top of the unit, as shown opposite. When the player selects a square, they can see the motor cam sequence run and the stepper switches operate. LEDs on the main register and control board indicate the current state of the control relays. The display and control panel can be angled up to observe relay operation. The main enclosure is a timber frame that I rebated (using a router) to house the top and bottom panels. The timber frame is made from Tasmanian Oak and varnished. The top panel is a transparent acrylic sheet that supports the display board below via standoffs. I sprayed the bottom surface of the top panel with matte black acrylic paint, with the “windows” for the LEDs masked with adhesive labels. That gives the display squares some depth when viewing. The switch and display labels are self-adhesive “Traffolyte” labels I ordered from a labelling supplier. The bell If the machine wins, a bell is rung four times. It is a modified “Call” bell from Officeworks. A micro-solenoid (visible on the right of Photo 12) operates the striker. When testing the unit with friends, it became clear that the bell was an essential part of the feedback. Initially, the bell only operated when the machine won. I modified the unit to make the bell ring if the player won, making it more engaging and satisfying. Playing a machine that always wins is not much fun. The Skill switch gives the player much better odds of beating SC the machine. Photo 11 (left): this photo was taken towards the end of the extensive testing regime, with the machine fully working but yet to be put into its custom case. Photo 12 (below): I modified a call bell from Officeworks, adding a solenoid to actuate the striker. 64 Silicon Chip Australia's electronics magazine siliconchip.com.au Photo 13: the finished Noughts & Crosses playing machine. The LEDs look a lot brighter in person, you can get an idea of how bright they are from Photo 11 (shown opposite). siliconchip.com.au Australia's electronics magazine March 2024  65 By Brandon Speedie Wii Nunchuk RGB Light Driver Add fun to a party or a professional look to a live performance with this RGB strip lighting driver. It is motion operated through an inexpensive video game controller and includes a built-in strobe light. T he Nintendo Wii is unusual for video game consoles as it uses gestures for control. The input device has buttons like a traditional controller plus a built-in accelerometer. For example, you can hold the controller like a racquet and make a motion to hit a ball for a tennis game. The “Nunchuk” is an attachment for the main Wii controller that includes buttons and a joystick. It is a convenient input device for this project as it communicates via the standard I2C two-wire serial interface, so it can easily be interfaced with a microcontroller. Also, the plug is a perfect fit for a standard 1.6mm-thick PCB, so a connector can be made from the PCB itself, without the need for a proprietary component. There are inexpensive grey-market clones readily available, including UHF wireless versions for cable-free operation. Gestures This project is intended to control four strips of 12V RGB (red/green/ blue) strip lighting, as well as an array of PCB-mounted white LEDs for strobing. Each colour in the RGB strip is independently controlled by pulsewidth modulation (PWM), so we can make any colour or brightnesses we RGB Light Driver Features » Drives up to four independent RGB LED strips » Optional onboard white LED strobe » Functions include variable stripe colour & brightness, strobing, sweeping & fading » Random sequence function » Controlled via a Wii Nunchuk controller (wired or wireless) » Powered from 12V DC 66 Silicon Chip Australia's electronics magazine fancy. Each strip can also be turned on or off as a group, providing further flexibility. The PCB-mounted white LEDs have a simple on/off control to act like a strobe light. We therefore have control of the RGB strip colour, RGB strip brightness, strip on/off and strobe on/off. The controller has two buttons, a joystick, and a three-axis accelerometer, with the axes shown in Fig.1. We therefore have the following inputs: • Joystick X-axis position (8 bits) • Joystick Y-axis position (8 bits) • X-axis (left/right) acceleration (10 bits) • Y-axis (forward/backward) acceleration (10 bits) • Z-axis (up/down) acceleration (10 bits) • C (small) button on/off • Z (big) button on/off The angle of the joystick controls the colour. Right (east) is red, down to the left (southwest) is green, and up to the left (northwest) is blue. Anything between these positions will be a mix of the two nearest colours (see Fig.3). siliconchip.com.au Y X Z a 10% duty cycle (on for 10ms, off for 90ms, repeating at 10Hz). X-axis acceleration triggers a different type of strobing called ‘channel sweep’. If the controller is shaken left and right, individual strips are cycled on and off sequentially. The individual on-time is 100ms, so it takes 400ms to cycle through all four strips. Y-axis acceleration triggers an automatic fade from full brightness to off. A sharp thrust forward starts the effect, which takes around two seconds. The lights will stay off until the joystick is returned to the centre position. Circuit details Fig.1: the Nunchuk remote used to control the LED strips. The acceleration of the joystick Z-axis (up/ down) controls brightness, the X-axis (left/right) triggers the channel sweep and the Y-axis (forward/backwards) triggers the brightness fade. Brightness is derived from a mixture of inputs; firstly, the position of the joystick. When in the centre position, the lights are off. As the joystick is pushed in any direction, the brightness increases until it is pressed fully against a side limit, at which point we have half brightness. The other half of the brightness signal comes from the Z-axis acceleration. By gesturing up and down, the brightness is throttled. The lights can therefore be ‘played’ like a drum to intuitively match the rhythm of music or the tempo of a performance. The Z button also affects brightness. When held down, the Z-axis acceleration is ignored and the brightness is solely controlled by the joystick ‘magnitude’. This can be used to force full brightness instantly, but also for producing a subtle, steady colour without having to hold the controller stationary. The C button controls the strobe. When held down, the strip LEDs are driven on (white) at full brightness, along with the PCB-mounted white LEDs. The flash period is 100ms with siliconchip.com.au The circuit is shown in Fig.2; the brain of the operation is IC2, a Microchip (previously Atmel) ATmega32U4 microcontroller programmed as an Arduino Leonardo. In-circuit serial programming (ICSP) header CON2 and JTAG header CON3 are provided for programming it. The Nunchuk controller connects to PCB card-edge connector (CON102), which supplies 3.3V power to the controller and connects the two I2C communications lines, SDA (data) and SCL (clock). These are connected directly to the dedicated peripheral in the microcontroller. I2C is an open-drain bus, so 4.7kW pullup resistors are provided, although experience suggests there are internal pullups in the Nunchuk, so they are not strictly necessary. Series protection resistors are provided but are usually fitted as 0W links. Higher values could be used to provide some protection to the processor should the Nunchuk ever be extended to a long cable run, but I haven’t found it to be necessary. Footprints for two different external clock sources are provided. I used ceramic resonator X1, but there is also provision for a 5×3.2mm SMD crystal, X2, with the two necessary load capacitors. The microcontroller runs at 16MHz, which is a bit overclocked for 3.3V operation (the data sheet suggests a 4.5-5.5V supply for that clock rate). Still, given that we aren’t using any of the chip’s analog features, it shouldn’t be a problem. USB-C connector CON5 provides an interface for uploading firmware and a generic serial port for debugging etc. Capacitive touch button S1 is made Australia's electronics magazine from a large copper area on the PCB. Pressing the area with a finger cycles through program ‘modes’, to be discussed later. LEDs 8, 9, 12, 17, 21 & 22 are reverse-entry LEDs ‘charlieplexed’ to indicate to the user which mode they are in. Charlieplexing is a technique that we described in some detail in the September 2010 issue (siliconchip.au/ Article/287). It allows multiple LEDs to be driven by a minimal number of pins that can be tri-stated; in this case, only three pins and resistors are required to light any one of six LEDs. The strip LED connectors are fourway header sockets, with pairs connected in parallel. This gives flexibility to suit different strips (for example, to fit male and female connectors) or simply to give more outputs to drive more LED strips. Note that most strips have connectors on both ends, so they can also be extended in series. Strip LEDs are typically constructed with a common anode pin and individual cathode pins for each of the three colours: red, green, and blue. To light a colour, we need to supply +12V DC to the anode and 0V DC to whichever cathode we want to light up at full brightness. On the strip, power flows from the anode terminal through a current-­ limiting resistor and a string of three LEDs in series before exiting the cathode terminal. High-side P-channel Mosfets Q1, Q2, Q3 and Q13 control the +12V drive to the anode terminals. On startup, they are held off courtesy of 4.7kW gate pullup resistors. Logic-level N-channel Mosfets Q4, Q5, Q6 & Q14 are connected to the microcontroller through 470W gate drive resistors. When their gates are driven high (to 3.3V), they conduct and pull the gate of their corresponding high side Mosfet low, which in turn supplies +12V to the strip. The strip cathodes are also connected to six N-channel Mosfets, Q7-Q12. Their gates also connect to the microcontroller through 470W gate resistors. These gates are PWM-driven to provide a full colour palette. PCB-mounted white LEDs101LED136 feature three separate dies in a single package. There are 35 in total, with 17 on one side and 18 on the other, as there is no LED134. The three LEDs in each package are March 2024  67 +12V +12V REG1 ZLDO1117G33TA D1 GS1G K A + GN D 10 m F – VCC (3.3V) VCC (3.3V) OU T IN 22 m F 1 0 0 nF 1 0 0 nF CON1 44 24 2 +3.3V 4 .7 k W C O N102 NUNCHUCK AVcc AVcc Vcc Vcc UVcc TD1/PF7 TD0/PF6 19 18 TMS/PF5 SDA SCL TCK/PF4 0W ADC0/PF0 1 MW CON5 USB-C ADC1/PF1 PD6/ADC9 ADC11/PB4 PD4/ADC8 INT6/AN0/PE6 ADC10/PD7 IC2 ATMega32U4 0W 7 22 W 4 3 22 W 22 LED23 ADC13/PB6 VBUS OC3A/P6 D+ ADC12/PB5 D– PD2/RXD1 PD3/TXD1 PD5/XCK1 SS/PCINT0 470 W PF6 37 38 PF5 39 PF4 X2 16MHz 42 X1 1 6 M Hz 6 5 ALTERNATIVES SCLK XTALI MOSI A re f MISO Ucap RESET UGND /HWB 15 1mF GND 23 GND 470 W 43 K LED17 A K A l K K l A K l A 4.7kW LED12 AUDIO_IN 4 70 W ENABLE1 4 70 W ENABLE2 28 470 W ENABLE3 1 470 W ENABLE4 27 470 W RED1 12 470 W GREEN1 32 470 W BLUE1 30 31 29 470 W RED2 20 470 W GREEN2 21 470 W BLUE2 8 STROBE AUDIO_IN JTAG 2 GND PF6 3 4 VCC PF5 5 6 VTG 7 8 PF7 9 10 C O N3 RST 0W* GND VCC 9 SCK * NOT NORMALLY FITTED 10 MOSI 11 MISO AVR ICSP 13 MISO 1 33 GND 35 LED21 l VCC GND 1 0 0 nF l 40 XTAL2 1MW 17 A A 41 l 16 l LED8 PF4 1 22pF 22pF CLK0/PC7 PF7 XBEE_TX 5.1kW 5.1kW 0C0A/PB7 36 K LED9 470 W 470 W G2 G1 A1 B12 A2 B11 A3 B10 A4 B9 A5 B8 A6 B7 A7 B6 A8 B5 A9 B4 A10 B3 A11 B2 A12 B1 26 25 CAPACITIVE BUTTON 100nF 34 14 4.7kW 0W LED22 MIDI, XBEE_RX 12V IN P U T 470 W 2 VCC SCK 3 4 MOSI 5 6 GND RST 4 .7 k W CON2 MISO 12 CTS 11 GND LED7 A 9 10 8 7 6 5 3 4 l 2 470W LED5 OPTO5 TLP290 MIDI A DTR NC PWM1 RSSI RESET DIO12 DIN VCC DOUT 470W 470W 470W XBEE 3 RF MODULE 1 VCC VCC DIO4 13 14 NC ON 15 16 RTS ASSOC. 18 17 AD3 AD2 20 AD1 AD0 MOD1 19 MOSI l K l 1 4 A LED6 CON7 4 3 K XBEE_TX MIDI IN 2 l K 1 2 5 3 R78 XBEE_RX VCC VCC SC Ó2024 VCC NUNCHUCK LIGHTS CONTROLLER Fig.2: the most important parts of the circuit are microcontroller IC2 and the Mosfets it uses to drive the RGB LED strips (connected via the headers at upper right) plus the white ‘strobe’ LEDs shown on the right. The faded-out components are for future expansion and not needed for the features described here. 68 Silicon Chip Australia's electronics magazine siliconchip.com.au +12V +12V 4.7kW Q4 BSS138 Q1 IRFR9010 S G D D ENABLE1 G 4.7kW Q6 BSS138 S G D D ENABLE2 G S Q3 IRFR9010 4 .7 k W Q5 BSS138 S G D ENABLE3 D G S Q2 IRFR9010 4 .7 k W Q14 BSS138 G D Q 13 IRFR9010 D ENABLE4 G S S S ENABLE2 ENABLE3 RED1 Q8 G G G Q 7 ,Q 8 ,Q 9 , Q10,Q11,Q12: MC U 3 0 N 0 2 Q7 G TO LED138 TO LED134 TO LED139 Q11 S LED1, LED2, LED3 & LED4 D D Q9 D S BLUE1 TO LED4 D D GREEN1 TO LED137 TO LED2 TO LED3 TO LED1 ENABLE4 S G G l l l l l l KB LED134, LED137, LED138,LED139 S RED2 GREEN2 l KG Q 10 S l KR D S A Q 12 l RED2 BLUE2 GREEN2 BLUE2 STROBE l l l l l l l l l VCC A KR R73 KG IC3: LMV324 KB 5 6 1mF IC3b 7 VCC/2 LED101 – LED136 (18 TOTAL) R72 K l A K l A K l A K l A K l A K l A +12V D STROBE 470 W G AUDIO_IN Q 16 MCU30N02 S 4 .7 k W 10 NOTE: FADED COMPONENTS WERE NOT INSTALLED ON PROTOTYPE AND ARE NOT REQUIRED. 9 IC3c 8 LED102 – LED135 (17 TOTAL) R60 K l A K l A K l A K l A K l A K l A D 12 14 R61 K LED18 l LED19 l G 13 Q 15 MCU30N02 S 4 .7 k W 1mF R64 LED20 A A LED15 l K K A A l 470 W +12V +12V VCC VCC K K l R63 A A A l R62 IC3d STROBE LED13 K l LED16 R65 1mF 4 AUDIO_RAW 1 LED14 R81 S1 ELECTRET MIC 2 11 K R80 R79 1mF A l 3 IC3a 1mF LED11 VR100 10kW 1MW CON100 K A l K siliconchip.com.au R70 LED10 CON101 VCC/2 Australia's electronics magazine March 2024  69 wired in series, with the combined LEDs connected in two parallel sets to +12V through 6.2W current limiting resistors. To light them up, N-channel Mosfets Q15 & Q16 are driven into conduction through 470W gate drive resistors by the microcontroller. 4.7kW pull-down resistors ensure the LEDs are off even if the microcontroller is not programmed or running, and therefore has its I/O pins at a high impedance. LDO regulator REG1 (ZLDO1117) creates the 3.3V supply for the microcontroller and Nunchuk from the incoming 12V. REG1 will work with ceramic capacitors, unlike many other linear regulators that need some ESR in their output capacitor to ensure stability, mandating an electrolytic type. Diode D1 provides reverse-­ polarity protection. It is expected that the 12V DC will be supplied by an off-board caged type SMPS or power brick derived from the mains. For four LED strips, 48W (4A) should be plenty, though I used 100W (8.3A) as I had such a supply on hand and it gives me the flexibility to use more strips if I want. I have also directly used 12V DC from a lead-acid battery and solar panel at a music festival where AC mains power was not available. Firmware operation Much of the heavy lifting involved in setting up the I2C peripheral and communicating with the Nunchuk is handled by the ArduinoWirelessNunchuk library. Once the object is set up, all we need to do is call nunchuck. update() to read the controller. The joystick position is stored in 8-bit variables nunchuck.analogX and nunchuck.analogY, giving a range of 0 (left/down) to 255 (up/right). The values sit around 127 if the joystick is centred. These Cartesian coordinates are not that useful to us; what we really want Fig.3: this shows how the ConvertToRGB() function converts the joystick position to a colour in one of six ‘bins’. is an angle (for colour) and a magnitude (for brightness). So the first thing we do is subtract 127 from each reading to give a centre position of 0 and positive numbers for up/right and negative for left/down. Then we convert to polar coordinates using √(x2 + y2) for the distance from the centre and arctangent for the angle: uint8_t magnitude = sqrt( sq(x_normalised) + sq(y_normalised)); int16_t angle = round(atan2( y_normalised, x_normalised) * 180 / 3.14159265); The magnitude is then summed with the z-axis acceleration to give a final brightness figure between 0 and 255. If the Z button is being held down, we double the magnitude value rather than summing it with the Z-axis acceleration. We now have our colour defined in the HSB (hue, saturation, brightness) colour system. Hue is our joystick angle, brightness is our joystick magnitude + z acceleration, and saturation is hard coded to its maximum for the most vibrant colour. We then Table 1 – hue ‘bins’ (b = brightness, h = hue[°] ÷ 60) Bin # Hue range Red (0-255) Green (0-255) Blue (0-255) 0 0-59° b b×h 0 1 60-119° b × (2 – h) b 0 2 120-179° 0 b b × (h – 2) 3 180-239° 0 b × (4 – h) b 4 240-299° b × (h – 4) 0 b 5 300-359° b 0 b × (6 – h) 70 Silicon Chip Australia's electronics magazine convert to the RGB colour space using convertRGB(), which works by segregating the brightness into one of six ‘bins’ based on hue. Each bin is selected as hue(°) ÷ 60 to give a full colour wheel (see Fig.3). With saturation at maximum, the six bins are calculated as per Table 1. These red, green and blue magnitudes are then used to update the PWM outputs. This firmware uses the Arduino’s built-in analogWrite() function, which provides 8-bit resolution at 490Hz. For the strobe, it looks at the status of the boolean (true/false) variable nunchuck.cButton. If true, the c button is being pressed. Variables to control the on and off time of the strobe are loaded with the current time, plus a user-configurable offset: strobe_on = now + STROBE_DUTY; strobe_off = now + STROBE_ DURATION; By default, STROBE_DUTY is 10 milliseconds and STROBE_DURATION is 100 milliseconds, although they can easily be changed to suit the application. If the current time (“now”) is less than strobe_on, the strip LEDs are driven to full brightness on all three colours, giving a bright white. The PCB-mounted white LEDs are also switched on. If the current time is greater than strobe_on, we are in the off period between flashes, so all outputs are driven low. If the present time exceeds strobe_off, the off-period has elapsed, and we need to begin the cycle again. Variables strobe_on and strobe_off are loaded with new values and the flash repeats. Channel sweep works similarly. If the X-axis acceleration (left/right) value is below X_THRESHOLD (default 20), we know the controller is being shaken vigorously. The ‘resting’ value is 512 (around half the 10-bit limit of 1023), so 20 corresponds to a high acceleration in the negative direction of the axis. The time when that threshold is crossed is stored in memory, and the channel sweep starts. The current time is then compared with the previously saved time, and if the difference is more than CHANNEL_SWEEP_PERIOD (default 100ms), we know to cycle to the next LED strip. Channel sweeping works by turning off all but one of the siliconchip.com.au high-side Mosfets that feed the LED strips with +12V. By turning these on or off sequentially, a visually appealing strobing effect is achieved. Similarly, the automatic fade works by checking if the Y-axis acceleration (forward/backward) is below Y_THRESHOLD (default 20). If the controller is thrust forward sharply, this limit will be exceeded and the brightness will subsequently be set to maximum. For the fade program cycle, the brightness is then decremented by FADE_STEP (default 5) until it reaches zero. This achieves a fade from full brightness to black in around two seconds. The lights will stay off until the joystick returns to the centre position, at which point colour_sweep_retrigger is unlatched and normal operation resumes. The firmware also supports an automatic mode. The LED strips will go through a random sequence without user input. The mode is cycled using the capacitive touch button. A square wave is applied to this pad by a pin on the microcontroller. A separate pin senses the voltage on the copper pad. The time it takes to charge and discharge this copper area is proportional to the capacitance of the pad, which changes if a finger touches it. That is sensed in the software as a button touch, which cycles through modes. For more on how that works, see my March 2015 article on an Arduino Touch Shield (siliconchip.au/ Article/8386). The current mode is indicated via the reverse-entry LEDs LED21 & LED22. Only those two are currently driven by the firmware, although six are provided for future expansion. Three pins drive the Charlieplexed LED array. In auto mode, the brightness and hue are randomly generated through Arduino’s built-in pseudo-random number generator function, random(). Once a new random value is calculated, the current brightness and hue will slowly ramp towards those values. When it reaches them, new numbers are generated. This gives a continuously variable LED brightness and colour. Construction Begin by soldering all components to the PCB, referring to the overlay siliconchip.com.au Parts List – RGB Strip Lighting Driver 1 double-sided PCB with black solder mask coded 16103241, 213 × 158mm 1 220 × 160 × 80mm ABS plastic enclosure [Altronics H0313 or H0333] 1 high-current 12V DC power supply 1-4 RGB LED strips [Altronics X3213A or X3328] 1 Wii Nunchuk or compatible controller, wired or wireless 1 16MHz 3-pin SMD ceramic resonator, 3.2 × 1.3mm (X1) [CSTNE16M0V530000R0] 1 2-way 10A+ 5/5.08mm pitch terminal block (CON1) 1 3×2 pin header (CON2; optional, for in-circuit programming of IC2) 1 5×2 pin header (CON3; optional, for JTAG programming/debugging of IC2) 1 Molex 2171790001 16-pin USB Type-C connector (CON5) 4 4-pin right-angle headers, 2.54mm pitch (LED1, LED2, LED138, LED139) Semiconductors 1 ATmega32U4 8-bit micro programmed with 1610324A.HEX, TQFP-44 (IC2) 1 ZLDO1117G33TA 3.3V 1A low-dropout regulator, SOT-223 (REG1) 4 IRFR9010 50V 5.3A P-channel Mosfets, TO-252/DPAK (Q1-Q3, Q13) 4 BSS138 50V 220mA N-channel Mosfets, SOT-23 (Q4-Q6, Q14) 8 MCU30N02 20V 30A N-channel Mosfets, TO-252/DPAK (Q7-Q12, Q15, Q16) 3 green SMD LEDs, M3216/1206/SMA size (LED21-LED23) 35 Cree CLP6B-WKW-CD0E0233 cool white LEDs, PLCC-6 (LED101-LED136) 1 GS1G 400V 1A diode, SMA/DO-214AC (D1) Capacitors (all SMD M2012/0805 size unless noted) 1 22μF 25V X5R M3216/1206 size 1 10μF 50V X5R M3216/1206 size 1 1μF 50V X7R 4 100nF 50V X7R Resistors (all SMD M2012/0805 size 1% unless noted) 1 1MW 2 5.1kW 9 4.7kW 17 470W 2 22W 35 6.2W 1W M6332/2512 [eg, Panasonic ERJ1TRQF6R2U] 4 0W diagrams, Figs.4 & 5. The double-sided board used is coded 16103241 and measures 213 × 158mm. There are components on both sides, although most mount on what will become the underside. Quite a few components are for future expansion and were missing from our prototype, so we suggest you leave them off too. They are shown faded out (transparent) in Figs.4 & 5 and are not in the parts list. As a general rule, start with the lowest profile SMD parts and work up to the larger through-hole components. All can be soldered by hand, but a reflow oven and solder paste can also be used for the SMD components if that is your preference. For those who haven’t tried it, a hot plate also works surprisingly well. It may sound crude, but laying your PCB into a foil-covered pan on the stove is very effective. For many years, I have used a standalone electric hot plate for this purpose, and it has been well worth the $20 investment. Fit all the SMDs on the bottom side first. If soldering by hand, start with IC2 by applying flux paste and then Australia's electronics magazine dragging a tinned chisel tip across the quad flat pack pins. The larger SMD components, such as power Mosfets Q1, Q3 etc and low-dropout regulator REG1, are easiest done next by applying a small amount of solder to the large copper area and leaving the iron to heat the area for several seconds. The component can then be placed using tweezers. Ceramic resonator X1 can be mounted similarly; all three pads can be heated simultaneously. Next, solder all passives. All resistors and capacitors are M2012/0805 size (2.0 × 1.2mm) or larger, so they are manageable by hand. I prefer to first wet one pad with solder, place the component with tweezers, then solder the other pad once the first has set and the component is held in place. Finish the SMD parts by soldering the SOT-23 transistors, diode D1 and the reverse-entry LEDs. Note that the LEDs must face down; they shine through holes in the PCB. Now flip the PCB over and solder the 6-pin PLCC strobe LEDs. This is a challenging component to solder due March 2024  71 Figs.4 & 5: most of the parts are mounted on what will become the underside of the PCB (inside the case). The PCB is attached to the case like a lid, so only the components on the top, including most of the connectors and the capacitive button, are externally accessible. Note how the LEDs all mount on the bottom side but they shine through holes in the board so they’re visible from the top. The 0W resistor (labelled in red) connected to CON3 is only fitted if you want the reset line to also pull down the test reset, for this application it does not need to be fitted. 72 Silicon Chip Australia's electronics magazine siliconchip.com.au This is the side of the board that’s externally visible when mounted in the case. This overlay shows all 35 white LEDs fitted; if you don’t need the strobe to be super bright, you could install a subset of those. I included the 17 evennumbered white LEDs on my prototype and it was bright enough for me. siliconchip.com.au Australia's electronics magazine March 2024  73 to its high thermal mass. If your soldering iron has an adjustable temperature, I recommend you turn it up to at least 400°C, then work your way along the six leads individually. The solder must flow down the leg onto the pad, so apply heat for several seconds to ensure proper wetting. Finish the PCB by soldering the through-hole components: the LED strip headers and screw terminals. If you are planning on modifying the firmware, install USB-C connector CON5. Start with the through-hole pins that hold it in position, then solder the SMD signal pads using the same drag method as for IC2. Power supply We recommend using an external 12V DC ‘brick’ supply since that’s the safest and easiest option. You don’t need to do any mains wiring. All you need to do is wire up its output (with the correct polarity!) to CON1. As we’ve recommended that you fit CON1 on the underside of the board, you can drill a hole in the side of the box and run the wire in through a grommet and directly into the terminals of CON1. You could use a chassis-­mount DC socket and plug, but watch the current ratings of the wiring, socket and plug to ensure they can handle the full output of your supply. While it’s possible to install a mains to 12V DC switch-mode power supply in the base of the box (using a metal baseplate like Altronics’ HA0312A that suits the specified cases), we won’t explain how to do that. You would need to be careful to anchor the mains cable (or use a socket), use mains-rated wiring and plenty of insulation and cable ties to keep it safe. For portable use, one good battery option is to use Makita 12V lithium-­ ion battery packs. They are readily available at hardware stores; you can keep a few charged ones with you while you’re on the go. You can also use them with their power tools! I got the socket from AliExpress for $15 (siliconchip.au/link/abrh), and it works well. Now you can attach the PCB to the top of the enclosure. It takes the place of the enclosure lid in this design and is attached using the screws that come with the case. Finishing it off & using it If you got your microcontroller from the Silicon Chip Online Shop, it will already be programmed. However, if you used a blank chip, you will need to flash the Arduino bootloader onto it via ICSP header CON2 or JTAG header CON3, using a hardware programmer. If you don’t have a hardware programmer, some low-cost options are: • Duinotech ISP Programmer (Jaycar XC4627, $14.95) This is an early prototype, so I had to make some modifications, including rerouting a couple of tracks. The final version of the board presented here won’t require those changes. 74 Silicon Chip Australia's electronics magazine siliconchip.com.au • Pololu USB AVR Programmer v2.1 (Core Electronics [CE] POLOLU-3172, $26.05) • SparkFun Tiny AVR Programmer (CE PGM-11801, $33.32) • SparkFun Pocket AVR Programmer (CE PGM-09825, $33.25) • USBasp USBISP AVR Programmer (CE 018-USB-AVR-ISP, $10.95) If you have a spare Arduino, you can repurpose it as a hardware programmer using the “Arduino ISP” project – see siliconchip.au/link/abri Make sure the Leonardo is selected in Tools → Board and select your programmer from Tools → Programmer. You may also need to select the serial port for the programmer. Then use Tools → Burn Bootloader to turn the blank chip into a Leonardo. Our article on repairing an Uno goes into more detail on ISP programming the processor on an Arduino board (March 2020 issue; siliconchip.au/ Article/12566). Once flashed, the microcontroller should automatically appear as a virtual serial port when plugged into a computer via the onboard USB port. If not, drivers can be manually downloaded and installed from the Arduino website (siliconchip.au/link/abrj). Once you have that working, the firmware can then be uploaded via the USB port using the Arduino IDE. You should now have a functioning product. Plug your Nunchuk controller into the PCB, ensuring the connector is orientated correctly (notch facing up) – see Fig.6. Plug in your RGB LED strip(s), and you should be ready to perform! A bit of practice is required to get familiar with the controls, but before long, it begins to feel natural. Once comfortable with the basics, you will find yourself combining multiple controls to give a more compelling experience. Experience suggests the Z button works well with the channel sweep, Fig.6: the correct orientation for the Nunchuk controller plugged into the PCB connector. Note how the notch is facing up. and sparing use of the C (small) button in combination with the Z-axis acceleration to add interest. A final word of advice: much like the rest or pause in music, sometimes periods of darkness can add emphasis. SC Less is more! I only fitted the white strobe LEDs on one side of the board, but you will get a brighter strobe if you add them on both sides. The board name was also changed to a slightly less ‘silly’ one during development. siliconchip.com.au Australia's electronics magazine March 2024  75 PRODUCT SHOWCASE Mouser Electronics opens new Customer Service Center in Australia Mouser Electronics is pleased to announce the opening of a new Customer Service Center in Melbourne to support its growing number of customers across Australia and New Zealand. Australia is the world’s 53rd largest country and home to a growing number of tech companies and start-ups. The country is considered a world leader in silicon-based quantum computing. Mouser’s new Customer Service Center in Melbourne will have a team of members onsite to personally assist with orders and respond to customer calls, all in the local language, time zone, and currency. This will be Mouser’s 12th office in the APAC region. Mouser’s other APAC locations include Hong Kong, Shanghai, India (Bangalore and Pune), Republic of Korea, Malaysia, Philippines, Singapore, Taiwan, Thailand and Vietnam. The Melbourne office will be Mouser’s 28th service center location worldwide. To view all of Mouser’s global office locations, visit www.mouser.com/ Contact/GlobalBranches/ Mouser’s customers can expect 100% certified, genuine products that are fully traceable from each of its manufacturer partners. To help speed customers’ designs, Mouser hosts an extensive online library of technical resources, including a Technical Resource Center, product data sheets, reference designs, application notes, engineering tools and more. Engineers can stay abreast of today’s exciting product, technology and application news through Mouser’s complimentary e-newsletter. Learn about emerging technologies, product trends and more by signing up today at https://sub.info.mouser.com/ subscriber Mouser Electronics Unit 1/15 Howleys Road Notting Hill VIC 3168 Phone: (03) 9253 9999 www.mouser.com Royal Ohm SP series resistors available from TME Royal Ohm, a Thailand-based company, is one of the leading manufacturers of resistors. Its products are available from TME: www.tme.com/au/en/ linecard/p,royal-ohm_145/ Resistors are among the cornerstones of modern electronics. These small but vitally important components are used throughout virtually every electronic circuit. Choosing the right value and power of the resistor is one of the challenges for today’s electronics designers, as incorrectly selected components can result in a device failure in the future. (SMD) power resistors. Royal Ohm’s SMD power resistors are an interesting alternative to classic components that can dissipate greater amounts of energy. In the TME catalog, you will find models rated at 2W, 3W, 4W, 5W & 6W. The components are available in the classic resistance variants from 0W to 10MW, and in various package sizes: 2010, 2512, 2817, 4320, and 4527. The resistors are designed to operate at temperatures from -55°C to 155°C with a tolerance of ±1% or ±5%. SMD power resistors (SP series) Widespread miniaturisation has extended to include not only integrated circuits, but also surface-mounted Classic SMD resistors Apart from the SP series, Royal Ohm supplies classic surface-­mounted (SMD) resistors. They are available in a wide 76 Silicon Chip Australia's electronics magazine range of resistance values (from 0W to 10MW) in 01005 packages (in the metric standard, this size is described as 0402) with a 31.25mW power rating. These low-power resistors are also designed to operate at temperatures from -55°C to 155°C, and their tolerance can also be ±1% or ±5%. Royal Ohm is a manufacturer with a wide range of resistors that will easily meet the requirements of even very demanding industrial applications. The TME catalog includes an extensive range of through-hole, SMD and many other resistors. TME Group ul. Ustronna 41 93-350 Łódź Poland www.tme.com siliconchip.com.au Part 2 of John Clarke’s Mains Power-Up Sequencer This Sequencer solves problems that can occur when switching on multiple mains-powered devices, like circuit breakers tripping or loud thumps from speakers. It can also be used as a master/slave power-saving solution. The Sequencer can handle up to four devices but multiple units can be chained to handle 8, 12 or more. T he Sequencer can switch on one to four (or more) devices in sequence, with an adjustable delay between each power-on. It can also switch them off in sequence, either in the same order as they were switched on or in the reverse order. It can be configured to start to switch on the devices in one of three ways: immediately when power is applied to it, when the appliance plugged into the first outlet starts to draw power (in which case the first outlet is always on), or when a separate, isolated mains supply comes online. That last feature can join multiple Sequencers to control more than four devices. It can even allow you to switch on devices in sequence across multiple mains phases (eg, if you have a big lab full of equipment). In last month’s first article, we described all its features and how the circuit works. Now we pick up where we left off and move on to building it, followed by testing and configuration. Construction Most of the Mains Power-Up Sequencer’s parts are assembled onto a double-sided PCB coded 10108231 that measures 203 × 134mm. The completed assembly is housed in an ABS or polycarbonate plastic IP65 sealed enclosure measuring 222 × 146 × 55mm. siliconchip.com.au Figs.5 & 6 show where all the components go on the circuit board. You will not fill the entire PCB with components when building the Mains Power-Up Sequencer. Typically, you would only install the Current Detection section or the Mains Input Detection section, but not both. Or you could decide not to use either, in which case none of those parts are needed. The parts list last month separated out the parts for the optional sections. The OUT1 channel must always be installed, but note that there are a couple of component value changes in that section depending on whether Current Detection is installed. Additionally, if Current Detection is not used, the two pads for CON7 must be connected using a short length of 10A mains-rated wire. Before construction, you will need to decide on how many outlets you will install. The PCB is initially set for four outlets with the RA0 and RA1 pins Warning: Mains Voltage All circuitry within the Mains Sequencer operates at Line (mains) voltages. It would be an electrocution hazard if built incorrectly or used with the lid open. Only build this if you are fully experienced in building mains projects. Australia's electronics magazine on IC9 tied to the 0V supply by short tracks on the underside of the PCB. To change this, the bottom layer tracks right next to the RA0 and/or RA1 pads will need to be cut (eg, using a sharp hobby knife) and then those pad(s) soldered to the small adjacent pads on the top layer that connect to +5.1V. Refer to Table 1 to see which need to be changed for one, two or three outlets. If you can’t get the solder to reach across the gap, use a short length of component lead offcut. Ensure you’ve properly isolated the pads before soldering them to those top pads, or you could short out the 5.1V supply (which will prevent the unit from working but shouldn’t blow anything up). Circuit sections The Mains Power-Up Sequencer PCB screen printing separates the four mains output circuitry sections (OUT1 to OUT4) using lines to delineate each channel. The Current Detection and Mains Input Detection sections are also marked on the screen printing and in Fig.5, so it is easy to see where the components associated with each section are located. Before construction, decide which sections you need using the information above. You can then start by installing the smaller ¼W resistors. March 2024  77 They have colour-coded bands indicating the values (shown in the parts list last month), but it’s best to use a digital multimeter (DMM) to check each resistor before soldering it in place. Zener diodes ZD1 and ZD2 (if used) and TVS1 (if used) can also be installed now, taking care to orientate the zener diodes correctly. TVS1 can go in either way around. Mount the ICs now, including the opto-couplers, taking care to get the correct IC in each place and with the proper orientation. We used sockets for IC9 and IC10, although you could solder them directly to the PCB, assuming that IC9 has already been programmed. The opto-couplers (IC1-IC8 and IC11) are not all the same, so don’t get them mixed up. Note that on the PCB, pin 5 of the IL410/4108 and the IL420/4208 have only a tiny pad for an increased separation distance between the internal Triac pins located at pins 4 and 6. Those pins are not connected to the rest of the circuit but you can solder them if you want to. The Triacs can be mounted now. There are a few different ways to do this. One is to smear a thin layer of flux paste onto the large pad, then position the device on the PCB and solder one of the small leads. Check its alignment and, if it’s OK, solder the other one. Otherwise, reheat the initial joint and nudge it into position first. Finally, turn up your iron and feed solder slowly into the large tab, as Table 1 – number of outlets RA1 (pin 18) RA0 (pin 19) # outlets 0V (bot) GND (bot) 4 (default) 0V (bot) 5.1V (top) 3 5.1V (top) GND (bot) 2 5.1V (top) 5.1V (top) 1 it will take a while to melt. Once it gets hot enough, solder all along the exposed portion of the tab. The flux paste underneath will pull solder under the tab and solder it to the circuit board. Alternatively, it is possible to tin both the pad and the tab of the device, clamp them together while heating the tab and feeding in more solder to reflow them together, then solder the two smaller pins. Bridge rectifiers BR1 (and BR2 if used) can now be mounted. These components must be correctly orientated with the + lead inserted into the position marked with a + and seated close to the PCB before soldering. The 1W resistors can be fitted now. Ensure the correct values are used and note that for the OUT1 channel, R1 is 470W 1W when the Current Detection components are installed or 330W 1W when the Current Detection circuitry is not installed. There are 1MW resistors under the relays that are inserted from the underside of the PCB, as shown in Fig.6. Solder these in place Before soldering the inductors, they should be secured to the PCB using cable ties. 78 Silicon Chip Australia's electronics magazine and cut the leads flush with the top of the PCB. Then mount the 1kW 5W resistor with a gap of about 1mm from the PCB, to allow air to circulate. Next, fit the capacitors, of which there are three types: the mains X2-rated capacitors, electrolytic capacitors, and MKT polyester types. The electrolytic capacitors need to be orientated correctly since they are polarised, while the others can be installed either way around. For the OUT1 channel, C1 is 220nF X2 when the Current Detection components are installed or 10nF X2 when they are not installed. We have provided for the different sizes and lead spacing on the PCB. Next, install potentiometer VR1 and the three toggle switches S1-S3. Then, mount the current transformer, T1, if used. Winding inductors L1-L4 It’s much easier to mount inductors L1 to L4 before the relays. These are wound using a 500mm length of 1.25mm diameter enamelled copper wire, with 10 turns evenly spread around the powdered iron toroid. Strip the insulation back by 1mm at each end of the wire using a sharp craft knife, insert the wire ends into the holes allocated and solder them in place from the top side of the PCB. Each inductor is supported using a 200mm-long cable tie that loops through the toroid and then through the slotted holes in the PCB. It’s best to tighten and trim the cable ties before soldering the leads. Make sure the solder adheres to the bare copper; it won’t make electrical contact if you haven’t fully stripped back the enamel. The relays can now be mounted, followed by the sockets for the two-way terminal blocks. They must be inserted so the plug-in screw connectors are orientated correctly, with the screw head access positioned toward the top edge of the PCB (left side, as shown in Fig.5). The easiest way to ensure this is to plug the screw terminals into the sockets before inserting them into the PCB. The LEDs are mounted above the PCB, with the leads bent by 90° 4mm siliconchip.com.au Fig.5: the PCB is divided into sections by lines. All components outside the boxed sections should be fitted, along with the OUT1 section and however many other outputs you need. Depending on how you plan to use it, you can also add either the Mains Input Detection (‘daisy-chain’) components or the Current Detection components (including T1), but not both. Fig.6: the only components you need to fit on the underside of the PCB are these four 1MW resistors underneath the relays. You can omit those from any output sections that are not being populated. This diagram is shown at 70% of actual size. from the rear of the LED, so they sit horizontally. First, cover each lead with a 20mm length of 1mm diameter heatshrink tubing. Then shrink the tubing with a hot air gun and bend the leads, ensuring that the anode (longer lead) will be orientated correctly with the LEDs bent (anodes facing to the top in Fig.5). The LEDs stand 20mm above the siliconchip.com.au PCB when measured from the top surface of the PCB to the LED centreline. Case preparation Before attaching the PCB, the IEC connector cutouts must be made in the side of the enclosure. You will also need to drill holes in the lid for the GPO sockets and in the enclosure side for the LED indicators. The Australia's electronics magazine required holes are shown in Fig.7. It can be downloaded as a PDF from our website at 100% scale and printed at actual size to use as a template. Don’t make the holes in the lid just yet as there are some options there, which we’ll get to shortly. Additionally, the two plastic standoffs (not the ones with brass tapped inserts) that would be beneath the March 2024  79 Fig.7: here are where the holes/ cutouts are made in the case. The Mains Detect Input IEC socket hole and the adjacent screw holes are only needed if you’re using that feature. If you aren’t planning to fit the GPOs to the lid, don’t make any holes in the lid; you can mount the grommets on the opposite side of the case to the LEDs. OUT4 components on the PCB need to be shortened using a large drill to allow clearance for soldered joints under the PCB. Wiring You can install the mains outlets in one of two ways. One way (as in our prototype) is to use surface-mounting GPOs on the lid of the enclosure, as shown in Fig.8. Alternatively, you can use inline mains sockets and mains leads (possibly cut from extension cords), held in place using cord grip grommets on the side of the enclosure, as shown in Fig.9. In this case, the Earth wires are attached to an M4 bolt on the side of the enclosure. We provide cutout positions for the GPO sockets in Fig.7 since they need to be positioned on the lid so they don’t foul PCB components underneath. We haven’t provided drilling details for the alternative method using the cord grip grommets as the positioning is not so critical. However, the cutout shape for cordgrip grommets is important as it needs to be made so the grommet fits snugly when the cord is captured, so the lead cannot be pulled out from the grommet. The cutout shape is essentially an elongated circular hole. Cable glands could be used instead of cordgrip grommets. In that case, it is essential to secure the gland nut so that the mains cable cannot be pulled out. This can be done by coating the gland threads with superglue before tightening the nut to secure the mains cable lead. The LEDs are inserted into 16kV-rated bezels mounted on the side of the case to prevent shock hazards; how to mount the bezels is shown in the inset photo. The switches and potentiometers are used to adjust the sequencing settings. 80 Silicon Chip Australia's electronics magazine siliconchip.com.au COVER EXPOSED ACTIVE BUSBAR WITH NEUTRAL CURE SILICONE OUT1 OUT4 N CURRENT DETECT MASTER CON7 1MW 1W OUTPUT2 OUTPUT3 N A N A N A OUTPUT4 CON4 N A + + COIL COIL COIL RLY4 RT334730 RLY3 RT334730 RLY2 RT334730 RLY1 RT334730 (DAISY CHAIN OUT) CON3 CON2 CON1 COIL ~ OUTPUT1 B R1 W04 – ~ 1MW 1W CON6 A 1kW 5W IEC CONNECTOR OUT3 OUT2 MAINS IN 470nF X2 10kW 15kW CON8 18kW MCP6272 IC10 470W 1W** TRIAC2 330W 1W 10nF X2 330W 1W 10nF X2 Cable tie L2 300W TRIAC3 330W 1W 10nF X2 330W 1W 10nF X2 Cable tie L3 300W TRIAC4 330W 1W 10nF X2 330W 1W Cable tie L4 300W 10nF X2 330W 1W **220nF X2 IC4 IC5 IC6 IC7 IC8 IL4208 IL4108 IL4208 IL4108 IL4208 + ~ SWITCH OFF SWITCH ON – ~ 680W A OUT3 OUT2 S3 100nF A LED4 A OUT1 S1 VR1 10kW START RATE UP DELAY NO DELAY LED3 LED1 A POWER LED2 LED5 1kW 1W 100nF 10mF 10mF CURRENT/DAISY CHAIN DETECT NON-DETECT IC9 PIC16F1459 TP 5.1V 10kW IC11 4N25 1.5kW 100kW 10kW 4.7kW ZD2 12V 22nF X2 BR2 W04 RA1 RA0 TP 0V SILICON CHIP 680W 680W 230V AC 750W IC3 IL4108 750W IC2 IL4208 750W IC1 IL4108 680W 10mF 10mF ALL PARTS AT 750W CAUTION! 1MW 1W COVER ANY EXPOSED TERMINALS WITH HEATSHRINK 10nF X2 TRIAC1 300W 1kW 1W 10kW IF CURRENT DETECT NOT USED 1kW 1W 30kW L4 L3 L2 1kW 1W 20kW 2.2kW L1 **10nF X2 & Cable tie L1 330W 1W CURRENT DETECTION COMPONENTS P4KE15A IEC CONNECTOR TVS1 1kW 1W NYLON SCREWS SHOULD BE USED T1 AC1010 1000mF CON5 CON9 A S2 OUT4 COVER LED LEADS IN HEATSHRINK TUBING (SHOWN HERE AT 50% FULL SIZE) Fig.8: the wiring for the GPO version, which is what we built. Use 10A mainsrated wire with the correct colours for all connections, although the optional Mains Detect Input wiring can use 10A or 7.5A mains-rated wire. Don’t skip the cable ties as they have an important safety function. OUT2 OUT1 NOTE: USE 10A MAINS WIRE EXCEPT FOR CON8 TO CON9, WHERE 7.5A WIRE CAN BE USED. OUT3 OUT4 CORD GRIP CLAMPS M4 SCREW WITH M4 NUT & STAR LOCKWASHER CRIMP EYELETS COVER EXPOSED ACTIVE BUSBAR WITH NEUTRAL CURE SILICONE MAINS IN A N CURRENT DETECT MASTER 1kW 5W CON7 OUTPUT2 OUTPUT3 N A N A OUTPUT4 CON4 N A + + COIL COIL COIL RLY4 RT334730 RLY3 RT334730 RLY2 RT334730 RLY1 RT334730 (DAISY CHAIN OUT) CON3 CON2 CON1 N COIL – ~ OUTPUT1 A BR1 W04 ~ 1MW 1W IEC CONNECTOR 1MW 1W CON6 470nF X2 ZD1 5.1V 10kW MCP6272 IC10 10nF X2 330W 1W 330W 1W TRIAC3 300W 330W 1W 10nF X2 330W 1W 10nF X2 330W 1W Cable tie L4 TRIAC4 300W 330W 1W 10nF X2 330W 1W **220nF X2 IC8 IL4108 IL4208 IL4108 IL4208 IL4108 IL4208 IL4108 IL4208 230V AC NO DELAY A OUT3 A OUT4 ~ + – ~ S3 100nF A OUT2 SWITCH OFF SWITCH ON S1 LED4 A OUT1 LED3 LED1 A POWER CURRENT/DAISY CHAIN DETECT NON-DETECT IC9 PIC16F1459 LED2 LED5 1kW 1W (SHOWN HERE AT 50% FULL SIZE) 100nF 10mF 10mF TP 5.1V 10kW 1.5kW 10kW 100kW 4.7kW ZD2 12V 22nF X2 BR2 W04 RA1 RA0 TP 0V SILICON CHIP IC11 4N25 680W IC7 750W IC6 680W IC5 750W IC4 680W IC3 750W IC2 680W 10mF 10mF ALL PARTS AT IC1 750W CAUTION! 1MW 1W COVER ANY EXPOSED TERMINALS WITH HEATSHRINK 470W 1W** TRIAC2 300W 10nF X2 Cable tie L3 1kW 1W 18kW TRIAC1 300W 10nF X2 Cable tie L2 1kW 1W 15kW CON8 IF CURRENT DETECT NOT USED L4 L3 L2 10nF X2 1kW 1W 30kW 10kW L1 **10nF X2 & Cable tie L1 330W 1W CURRENT DETECTION COMPONENTS 20kW 2.2kW P4KE15A IEC CONNECTOR TVS1 1kW 1W NYLON SCREWS SHOULD BE USED T1 AC1010 1000mF CON5 CON9 siliconchip.com.au NOTES: USE 10A MAINS WIRE EXCEPT FOR CON8 TO CON9, WHERE 7.5A WIRE CAN BE USED. ALSO EARTH LEAD SHOULD BE ONE CONTINUOUS LENGTH WITH INSULATION REMOVED AT EACH GPO EARTH CONNECTION. ZD1 5.1V The large cutouts for the mains GPO sockets and IEC connectors can be made by drilling a series of small holes around the inside perimeter, knocking out the centre piece and filing the outline to a smooth finish. Other methods include using a speed bore drill to remove most of the inner area and then filing the rest to the shape required. Once the drilling and filing are complete, install the IEC connector(s). The PCB can then be placed inside the case, and the LEDs inserted into the bezels as you drop the PCB into the enclosure. Then secure the PCB to the base of the enclosure with 6mm-long M3 machine screws into the case’s integral brass inserts. We specify Cliplite bezels specifically since they cover the LEDs and are rated to withstand 16kV, so they protect against a possible shock hazard should the LEDs fail. Using exposed LEDs at mains potential could be an electric shock hazard. Most 5mm LEDs don’t specify the insulation capability of the package between the LED dome and the LED die inside. So use the bezels specified to ensure safety. The IEC connector must be secured using countersunk 10mm Nylon M3 screws, although you can use metal nuts. The Nylon screws are essential as they avoid the possibility of the screws becoming live (at mains voltage) should a mains wire inside the enclosure come adrift and contact a screw holding the IEC connector. Before attaching the mains GPO outlets and LED indicators, you can download and print out the front panel label shown in Fig.10. Details on making a front panel label are at siliconchip.au/ Help/FrontPanels The download includes two versions of the front panel. One front panel version does not have labelling for the Mains Detect Input IEC connector if you haven’t installed it. All wiring must be run as shown in either Fig.8 or Fig.9, using mainsrated cable. Be sure to use 10A wire (7.5A is OK for the Mains Detect Input wiring). The brown wire must be used for the Active wiring, blue for Neutral and green/yellow striped for the Earth wiring. Note again that if you are not installing the Current Detection, then the two pads for CON7 need to be joined using 10A mains wire (ideally brown). S2 VR1 10kW START RATE UP DELAY COVER LED LEADS IN HEATSHRINK TUBING Fig.9: the wiring for the non-GPO version is similar to that shown in Fig.8 but the Earth wires are terminated slightly differently. The output cables can be made either by connecting mains flex to individual line sockets, or by cutting the plug ends off 10A extension cords. Australia's electronics magazine March 2024  81 For the lid-mounted GPOs, the Earth wire from the IEC socket must go straight to the first GPO Earth terminal, then to the second and so on as a single length of wire. To do that, strip the insulation off a single piece of wire at each connection point. Take great care when making the connections to the mains sockets (GPOs). In particular, be sure to run the leads to their correct terminals. The GPO sockets will have the A, N and E clearly labelled, although Active might be marked with an L (Live) instead of an A. Do the screws up tightly so the leads are held securely. Similarly, ensure that the wires to the two-way screw terminals are firmly secured. For the version without GPOs, the Earths are connected to crimp eyelets that are then all attached to the M4 Earth bolt, which is secured to the case using a star washer and nut. Be sure to insulate all the Active and Neutral connections on the IEC connectors with heatshrink tubing for safety, and cable tie the wires as shown to prevent any broken wires from coming adrift. Use 5mm diameter heatshrink for the wires to the IEC connector. Secure the Active and Neutral leads together using cable ties. Also, use neutral-cure silicone sealant (eg, roof & gutter silicone) to cover the Active bus piece that connects the Active pin to the fuse at the rear of the IEC connector. That bus is live, and there is no need to leave it exposed. Testing Always attach the lid using at least two screws at diagonally opposite locations before switching on the power. All the circuitry is operating at mains potential, so do not touch the components unless the power is off and the IEC power leads have been disconnected for at least ten seconds. Before applying power, check your wiring carefully and ensure all mains connections are covered in heatshrink tubing and the wiring is cable tied. Then install the 10A fuse inside CON5’s fuse holder and verify that IC9 is plugged into its socket and correctly orientated. If you have installed the Mains Input Detection circuitry, insert the 1A fuse into CON8. VR1 can initially be set to mid-travel for a nominal 10-second sequence interval. If set fully anti-clockwise, VR1 gives a 100ms sequence delay Fig.10: the lid label indicates which inputs and outputs have which function, while the side label shows what each LED means. There’s another version of the label that you can download from our website without the text for the Mains Detect Input if you aren’t using that feature. 82 Silicon Chip Australia's electronics magazine siliconchip.com.au period while near full-clockwise (about 10° away) gives a 22 second sequence interval. Set switch S1 to the left (open) position to disable Current Detection. Set S2 to the right for a startup delay and S3 to the left so VR1 sets the on-­ sequence period. Remember the earlier advice to unplug the unit before opening the lid and adjusting any settings. Also note that settings like the periods are only stored at power-up. Making adjustments while the power is on won’t do anything. On power-up, check that the power LED lights and that the OUT1 LED lights after about ten seconds, followed by OUT2 after another ten seconds. The remaining LEDs should light after similar periods. You can test the off-sequencing if you have installed the Current Detection or Mains Input Detection circuitry. To do this, unplug the unit, open the lid and move S1 to the right (closed) position. Reinstall the lid and power it back on. If using Mains Input Detection, plug CON8 into the mains and the startup sequence should begin. Disconnect or switch off that supply and the LEDs should switch off in sequence, starting with the last output and finishing with OUT1. The default delay for the off-sequence is two seconds. Alternatively, if using the Current Detection circuitry instead, plug an appliance into OUT1 and switch it on to trigger the on-sequence, then unplug it or switch it off to trigger the off-sequence. Again, the off-sequence should start with the last output and finish with OUT1. We have installed surfacemounting GPO sockets on the interior of the lid. An alternative method is shown in Fig.9. Exposed terminals should be covered with heatshrink tubing, while the active busbar on the IEC connected must be covered with neutral cure silicone for safety. Settings Two lots of settings can be made. First, there are the on-sequence and off-sequence periods, set using VR1. The on-sequence period is set with switch S3 in the left position and is only stored at the instant that power is switched on. To set the off-sequence rate, you also use VR1, but place S3 in the right-hand position before powering it up. Each value is stored in flash memory, so it is recalled at power up, allowing you to set these two periods independently. For these settings, VR1 can be adjusted from fully anti-clockwise to siliconchip.com.au Australia's electronics magazine March 2024  83 Ideal Bridge Rectifiers Choose from six Ideal Diode Bridge Rectifier kits to build: siliconchip. com.au/Shop/?article=16043 28mm spade (SC6850, $30) Compatible with KBPC3504 10A continuous (20A peak), 72V Connectors: 6.3mm spade lugs, 18mm tall IC1 package: MSOP-12 (SMD) Mosfets: TK6R9P08QM,RQ (DPAK) 21mm square pin (SC6851, $30) Compatible with PB1004 10A continuous (20A peak), 72V Connectors: solder pins on a 14mm grid (can be bent to a 13mm grid) IC1 package: MSOP-12 Mosfets: TK6R9P08QM,RQ 5mm pitch SIL (SC6852, $30) Compatible with KBL604 10A continuous (20A peak), 72V Connectors: solder pins at 5mm pitch IC1 package: MSOP-12 Mosfets: TK6R9P08QM,RQ mini SOT-23 (SC6853, $25) Width of W02/W04 2A continuous, 40V Connectors: solder pins 5mm apart at either end IC1 package: MSOP-12 Mosfets: SI2318DS-GE3 (SOT-23) D2PAK standalone (SC6854, $35) 20A continuous, 72V Connectors: 5mm screw terminals at each end IC1 package: MSOP-12 Mosfets: IPB057N06NATMA1 (D2PAK) TO-220 standalone (SC6855, $45) 40A continuous, 72V Connectors: 6.3mm spade lugs, 18mm tall IC1 package: DIP-8 Mosfets: TK5R3E08QM,S1X (TO-220) See our article in the December 2023 issue for more details: siliconchip.au/Article/16043 84 Silicon Chip The finished Mains Power-Up Sequencer built to include the Mains Input Detection and with the panel label that includes the Mains Detect Input label. An alternative label can be used that does not have the mains detection labelling if this feature isn’t used. about 10° short of fully clockwise. That gives a range of 100ms (anticlockwise) to about 22s (near clockwise). The other settings are made with VR1 set fully clockwise, which causes the Sequencer to enter another mode. It does two things in this position. One is to measure the voltage from the precision rectifier when no appliance is connected to OUT1. This is the offset voltage from the op amp circuit, which is usually a few millivolts. This value is stored and subtracted from any future Current Detection measurements. If you are not using the Current Detection, it still happens but won’t affect anything. The other function of this mode is setting the off-sequence direction. With the power off and the unit unplugged from the wall, rotate VR1 fully clockwise. No appliance should be plugged into the sequencer GPO (OUT1) outlet or any mains power applied to the Mains Detect Input (if used). If switch S3 is set to the right, you will set the off-sequence to forward, meaning that OUT1 switches off first. If S3 is placed to the left, it sets the reverse off-sequence direction, so the last outlet switches off first. The initial setting of the programmed microcontroller is this reverse off-sequence. After a few seconds in this mode, the Sequencer can be unplugged. After that, remove the lid and rotate VR1 back from fully clockwise to the desired period for the sequence rate, depending on the position of S3. This is important as, if VR1 is left set at the fully clockwise position, the Sequencer will not run to switch on any outlets. Table 2 summarises the functions of switches S1, S2, S3 and potentiometer VR1. Settings are only changed at SC power-up. Table 2 – power-up settings Switch Left (open) Right (closed) S1 No Mains/Current Mains/Current Detection Detection enabled S2 No initial delay Delay before on and off sequences S3 VR1 sets on-rate VR1 sets off-rate 100ms to 22s (from full anti-clockwise to 10° less than clockwise) S3 Reverse off-sequence Forward off-sequence Fully clockwise (also stores full wave rectifier offset) Australia's electronics magazine VR1 siliconchip.com.au Keep your electronics safe with our HUGE RANGE of Low Voltage Circuit Protection SAME GREAT RANGE AT SAME GREAT PRICE. 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Jaycar reserves the right to change prices if and when required. JUST 34 95 $ Arduino for Arduinians by John Boxall 478 pages, paperback / digital ISBN 9781 7185 02789 Price: $95 RRP (paperback) $30 ~ 40 (digital) This book, subtitled “70 projects for the experienced programmer”, is aimed at those who are familiar with Arduino programming and want to learn some more advanced techniques. It doesn’t assume much electronics knowledge outside of programming, so it would be suitable for those who have dabbled in software but not much hardware. Book Review By Nicholas Vinen T his 478-page book is split into 24 chapters. Each chapter covers several projects, which may share some of the same hardware but demonstrate different principles. Each project demonstrates a particular technique, allowing you to build it yourself and experiment with it. You could also use the book as a reference to draw from when writing your own Arduino programs or designing hardware to interface to an Arduino module. Many of the chapters and techniques are things you will have seen in Silicon Chip magazine, although the book goes into much more detail on how the software works. Examples of techniques he describes that we’ve used recently include (these are not necessarily the exact chapter titles): • Chapter 5: Controlling LEDs with Charlieplexing • Chapter 11: Emulating USB mouses and keyboards • Chapter 13: Interfacing with PS/2 Keyboards • Chapter 14: Bluetooth serial communications using an HC-05 module • Chapter 21: Retrieving the current time from an Internet Time Server (NTP) • Chapter 24: Capturing images with an ESP32-CAM module He also shows how to ‘hack’ a commercial UHF remote-­controlled mains switch so it can be controlled by an Arduino. That is similar to how our November 2014 Programmable Mains Timer works. 86 Silicon Chip So, if you found the projects in which we used those techniques interesting and want to know more about how they work and how to implement them yourself, this book could be for you. Of course, the book covers more topics than just the ones I listed above. John starts with some fairly basic but useful demonstrations, such as how to sense multiple button presses using a single analog input (12 buttons in his demonstration), how to quickly change the state of multiple digital output pins at once, how to drive a seven-segment display and so on. Guided by an expert craftsman with over 30 years of experience, you’ll build 70 awesome Arduino projects and emerge a true Arduinian ready to invent your own complex creations. He explains concepts as basic as a voltage divider; as I implied earlier, the book seems aimed at those with some software experience but little hardware experience. Of course, if you already know those concepts, you can skip those sections. There’s still plenty of valuable demonstration code. More advanced concepts are covered later in the book, such as driving a graphical OLED display, creating a WiFi web server with an ESP32 module, having the Arduino control its own power supply, transferring data to and from USB flash drives, reducing Australia's electronics magazine siliconchip.com.au power consumption for battery-powered projects, interfacing with vehicle electronics via CAN bus, logging data to Google Sheets and more. I learned some things by reading this book. For example, I didn’t know about the TCA9548A I2C multiplexer, which seems like a handy little chip. I would also find it useful as a reference; for example, I could figure out how to read files from a USB flash drive if I had to, but it would save me time and effort to simply follow John Boxall’s examples in Chapter 12. One thing to note is that the photos throughout the book showing modules, components and his assembled PCBs are all in monochrome. The contrast is decent, so the subjects are readily visible. Still, it’s a pity that the ebook version doesn’t have colour photos, as the choice of monochrome was likely due to the cost of printing the physical edition. Building the projects Many of the projects are based on connecting prebuilt modules to the Arduino, which can usually be done quite easily with jumper wires or a breadboard. He provides some suggestions on places to buy those modules. Most of them are common and widely available. He also shows suitable breadboard layouts in many cases (where the circuits aren’t too complicated). Along the way, build fun and useful devices like: • A camera-enabled circuit to stream videos • An MP3 player to listen to audio • A CAN bus circuit which gathers speed and engine data from your car • A web server using an ESP32 board • A PS/2 keyboard In contrast, seven chapters require you to wire up many components to the Arduino (sometimes, the same circuit is used for multiple projects). He explains that you can wire those up manually on breadboard or protoboard, but as that would be a lot of work, he helpfully supplies PCB designs for seven of the more complex circuits. Interestingly, rather than sell the PCBs as we do for our projects, he has made the Gerber files for each design available, which are basically PCB blueprints. At the start of the book, he explains how to view those files and upload them to manufacturers to get the boards professionally made. He also suggests three possible manufacturers (including one of our advertisers, PCBWay). That is helpful if you have never used commercial PCB manufacturers before; the book goes into a fair bit of detail on how to get the boards made. However, to make things easier for readers of this book, John has agreed to let us sell a pack of the PCBs required to build the projects in his book (see the links at the end of this review). Conclusion I like the idea of this book because there are many people out there who are interested in tinkering with Arduino, perhaps coming from a background in computers or software, but who are relatively inexperienced when it comes to building actual hardware. It is ideal for people like that because of the way it explains the hardware concepts at a basic level and provides concrete examples. Also, despite going into some pretty advanced topics, the code is easy to understand, to the credit of both John and the Arduino developers. If you have some experience with Arduino but would not consider yourself an advanced Arduino programmer, this book is worth reading. Even relative beginners to Arduino should be able to get something out of it, as long as they are confident and willing to learn quickly and hone their skills. You can preview an entire chapter of the book (Chapter 8: Controlling High-Power Shift Registers) at https://nostarch.com/ arduino-arduinians A ZIP file at the bottom of that web page contains all the sample sketches and PCB design Gerber files. The book is available from numerous retailers for a bit over $60 for the printed edition ($95 RRP) or $30-40 for the ebook version (depending on platform etc). To order a copy or for more information, see www.penguin.com.au/books/ arduino-for-arduinians-9781718502789 Probably the best place to order the ebook version is the publisher’s website at https://nostarch.com/arduinoarduinians Similar books by John Boxall include Arduino Workshop (now in its second edition) and AVR Workshop. You can also find them via both the Penguin and No Starch web pages linked above. You can order the PCBs for building the projects in Arduino for Arduinians from our website at the following links: 1. Pack of six PCBs for Projects 3, 13, 14, 18, 19 and 26 for $20 + P&P: siliconchip.au/Shop/8/6903 2. The PCB for Project 27 for $7.50 each + P&P: siliconchip. au/Shop/8/6904 Note that P&P is per order, so you can order the six-PCB pack and one or more of the Project 27 PCB at the same time (and SC anything else from our Shop) and save on postage. Raspberry Pi Pico W BackPack The new Raspberry Pi Pico W provides WiFi functionality, adding to the long list of features. This easy-to-build device includes a 3.5-inch touchscreen LCD and is programmable in BASIC, C or MicroPython, making it a good general-purpose controller. This kit comes with everything needed to build a Pico W BackPack module, including components for the optional microSD card, IR receiver and stereo audio output. $85 + Postage ∎ Complete Kit (SC6625) siliconchip.com.au/Shop/20/6625 The circuit and assembly instructions were published in the January 2023 issue: siliconchip.au/Article/15616 siliconchip.com.au Australia's electronics magazine March 2024  87 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. Arduino-based water pump monitor This circuit forms a device to monitor a water pump. At my place, the pump is a little distance from the house, so you cannot hear whether it’s running or not. I had the misfortune of getting a bit of debris in the pump’s non-return valve, which allowed the water to flow backward, causing the pump to turn on and off every few minutes, significantly reducing the pump’s life. Also, if the pipes spring a leak somewhere after the pump, it could be weeks before you find your tank empty, not to mention all that power usage. This design monitors the pump current to determine when the motor starts, then logs the number of pump cycles and the time in seconds that the pump was on. Every hour, the data is transferred from one line of the display 88 Silicon Chip to the next, with the last entry eventually dropping off. A little OLED screen (128×64 pixels) displays the data in three columns. The first row of the first column shows the data for the present hour, while the remaining part of the first column shows the past 13 hours. The second column displays the number of pump cycles per hour, and the third column shows the time the pump was on that hour. So it’s easy to see what happened in the last 14 hours. For example, if the pump was running while you were sleeping, there must be a problem. The circuit uses a current transformer (CT1) to monitor the current through the Active wire feeding the pump. Its output is fed into a preamplifier, a precision rectifier, a differential Australia's electronics magazine amplifier and then a DC gain amplifier. This analog DC voltage is then fed into an Arduino Nano board, which also drives the OLED display. In my case, I am using an SPI interface simply because that’s the type of display I had on hand. The software could be modified to use the common I2C-type OLED display instead. I made CT1 from an HY2 powdered iron core wound with 100 turns of enamelled copper wire and potted it in a small plastic former. One of the 230V wires going to the pump must pass through the centre of CT1. The value of R1 is selected to get at least 1V at the A0 input of the Arduino Nano when the pump is on. VR1 is used to make fine adjustments in this voltage. You could start with, say, 100W for R1 and then increase siliconchip.com.au the value in steps if there isn’t enough voltage at A0. Be careful to avoid making the value of R1 too high, as we don’t want the transformer output voltage to exceed 5V; that could damage IC1. The Arduino sketch is available for download from siliconchip.com.au/ Shop/6/372 Alfred Hirzel, Oratia, New Zealand. ($80) Editor’s note: premade split core current transformers are available for around $12, including delivery, from various suppliers on eBay. Search for “split core transformer”; a 20A type should be sufficient. Battery Lifesaver with load control The Battery Lifesaver circuits from the September 2013 issue (siliconchip.au/Article/4360) and December 2020 issue (siliconchip. au/Article/14673) are useful in most simple setups. However, on some occasions, more ‘smart’ features are needed. This circuit helps fill the gap. In simple terms, it acts as a ‘battery lifesaver’ with a ‘load control’ function using inputs from other external devices. The idea is that a battery and charger/power supply provide power to one or more loads, with the battery voltage maintained in float condition while mains or solar power is available. The key features of this circuit include: • Low power consumption from the battery when the loads are isolated. • Firmware-configurable battery voltage switching thresholds. • An early warning output to signal that load isolation is imminent. • Independent and configurable switching control of two loads by external devices. • A watchdog timer function that is resettable by an external device. At the heart of the circuit is a PICAXE-14M2 microcontroller. It has an analog-to-digital converter (ADC) that is easily configurable to perform the battery lifesaver function. It also has adequate input/output capability for load control inputs and a warning output signal. The circuit has a very modest power consumption of 1.4mA when the battery is on float charge with the loads connected. When the charger is off, the battery has discharged and the loads are isolated, the power consumption drops to around 400μA. The 400μA figure is achieved in several ways. Firstly, a low quiescent current 5V regulator, the LP2950-ACZ5.0, powers the 14M2. Secondly, the 14M2 has a low-power sleep mode that is used once the loads are isolated from the battery. Thirdly, with the loads isolated, the resistive divider network used to feed the 14M2 ADC input is isolated from the battery, saving around 325μA at 12V. When the battery voltage is low, the divider is only enabled now and then to check the battery voltage. If it has recovered sufficiently, the micro comes out of sleep mode. The dual load switching is achieved using IRF4905 P-channel power Mosfets driven by 14M2 output pins via 2N7000 N-channel small-signal Mosfets. The Mosfet arrangement is commonly called a high-side switch as it switches the positive battery voltage to the loads. The IRF4905 was selected for its low on-resistance (RDSon) of 20mW. A load current of 5A causes less than half a watt of dissipation in one of the IRF4905s, so no heatsinks are required unless the load current is somewhat higher than that. continued on page 90 The three LOAD1 outputs are connected in parallel, as are two LOAD2 outputs. You can vary the number of outputs as required. siliconchip.com.au Australia's electronics magazine March 2024  89 The circuit accepts several inputs to control the connected loads. Active-low inputs RB1 and RB2 control LOAD1 and LOAD2 individually. With the firmware provided, a falling edge on RB1 causes LOAD1 to be power cycled while LOAD2 is unaffected. Similarly, a falling edge on RB2 causes LOAD2 to be power cycled while LOAD1 is unaffected. WDOG is an active-low input that causes a 14M2 firmware watchdog timer to be reset without affecting LOAD1 or LOAD2. In the provided firmware, the watchdog timeout is set to 28,800 seconds (eight hours). If a watchdog reset is not received within that time, both loads are power cycled. EXT_TIMER is an optically isolated input originally intended for a commercial mains power timer and plugpack combination to perform a Circuit Ideas Wanted 90 Silicon Chip brute force power cycle of either or both loads. Each of the inputs, RB1, RB2, WDOG and EXT_TIMER, can be separately configured to affect LOAD1, LOAD2 or both by defining a control mask value in the 14M2 firmware. WARNING is an open-drain, active-low output that signals upstream devices of an imminent load isolation event due to low battery voltage. The WARNING flag is asserted 10 seconds before the 14M2 disconnects the loads in the firmware provided. Modifying the code allows you to set the ADC threshold values, all the various timing values and load control settings to suit a specific application. For best accuracy, the 14M2 ADC input should be calibrated. The best way to do this is with a bench power supply and digital volt meter. During operation, the firmware logs data over the serial port, including ADC values, which can be viewed on the PICAXE editor terminal. The ADC is set to use an internal reference of 4.096V and 10-bit sampling, so the highest ADC reading of 1023 corresponds to 4.096V. Simply adjust the bench supply upwards until the ADC value just reaches 1023. For the circuit shown, this should be around 15.1V. The ADC values for the LOAD OFF and LOAD ON points are then the desired voltages multiplied by 1023 and divided by the final bench supply voltage. The firmware includes comments to assist in understanding the various commands and subroutine functions. It can be downloaded from siliconchip.au/Shop/6/270 David Worboys, Baulkham Hills, NSW. ($100) 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, including PCBs and components, back issues, subscriptions or whatever. Email your circuit and descriptive text to editor<at>siliconchip.com.au Australia's electronics magazine siliconchip.com.au Ultra-low-power carbon monoxide (CO) monitor Each year, thousands of deaths are reported in many countries due to accidental carbon monoxide (CO) poisoning. However, this gas is easily detectable and measurable. There is an abundance of commercial devices dedicated to this task and also several DIY prototypes for tinkerers, including my brother’s Minimalist CO Detector (Circuit Notebook, June 2023 issue; siliconchip.au/Article/15827). This compact, low-power embedded device periodically measures the concentration of carbon monoxide gas (CO), in parts per million (ppm). The measurement period and alarm changes depending on the last CO concentration measured: • <15ppm: every minute • 15-25ppm: every 30s • 25-35ppm: every 15s (1 beep) • 35-50ppm: every 5s (2 beeps) • 50ppm+: every second (3 beeps) It uses an ultra-low-power and precise CO sensor, the Figaro TGS-5042. Unlike the popular MQ-7, which is siliconchip.com.au power-hungry and sensitive to other gases, this sensor doesn’t contain a heater resistor and is very simple to calibrate. The TGS-5042 comes with a sticker indicating its sensitivity to CO in nA/ppm, which is linear! CO sensors with similar characteristics to the TGS-5042 are the TGS5141 (more compact), TGS-5342 (more expensive) and ME2-CO (cheaper, from Winsen). A current-to-voltage preamplifier is necessary, as shown in the sensor data sheet. I used the MCP6141 instead of the recommended AD708, as it has very similar characteristics, but with a far lower quiescent current of 0.6µA typical, against 4.5mA for the AD708! I am using a Nokia 5110 LCD screen to keep power consumption as low as possible. It is very popular, well-­supported and has a meagre power budget. It consumes a typical current of just 1.5µA when put in deep-sleep mode. One could consider using a small ePaper display; while more expensive, Australia's electronics magazine they can show text and graphics even when unpowered. Microcontroller IC1 is a PIC16F1829 8-bit enhanced mid-range XLP (eXtreme Low Power) model from Microchip. It takes a measurement, re-adjusts the periodicity if the measurement differs from the previous one, then goes into deep sleep mode (20μA <at> 3V). The software can be downloaded from: siliconchip.com. au/Shop/6/374 The display is kept in deep sleep mode by default, unless pushbutton S1 is pressed or the alarm is activated. The alarm circuit uses a tapped power inductor that provides a loud sound from the piezo despite the 3V supply. This prototype is powered by a Li-ion cell that can be recharged via the USB port. The USB/serial adaptor also allows the CO level to be monitored from a computer, as does the optional Bluetooth transceiver, but wirelessly. Mohammed Salim Benabadji, Oran, Algeria. ($120) March 2024  91 Vintage Radio The Bush MB60 portable radio By Ian Batty We have previously described two Bush transistor radios: the early (1957) TR82C in the September 2013 issue and the VTR103 (1961) in August 2021. The MB60, also released in 1957, is the first valve-based Bush radio to grace these pages. T he Graham Amplion Company, founded in 1894, was well-known for loudspeakers from the early 1920s until their closure in 1932. The Bush radio company took over the remains of Amplion in 1932, deriving their name from their Shepherd’s Bush (London) facility. Initially trading as a subsidiary of the Gaumont British Picture Corporation, Bush became a subsidiary of the Rank Organisation. Bush was a major manufacturer of radios and merged with Murphy Radio in 1962. While their corporate history has been a roller-coaster, their products were among the best from England. Bush launched their popular DAC90A and DAC10 radios in 1950, followed by their distinctive TV22 television. David Ogle (MBE DSC) was a British industrial and car designer who founded Ogle Design in 1954. After the war, he studied industrial design at the Central School of Art and Design in London. He subsequently 92 Silicon Chip joined Murphy Radio, leaving Murphy in 1948 to join Bush Radio. While at Bush, he was responsible for the iconic design of the MB60 portable radio. The MB60 set a benchmark for style, well-matched by performance and sound quality. Valve lineup The MB60 uses Dx96-series directly heated valves. Released in 1940/41, the RMA/RETMA 1R5, 1T4, 1S5/1U5 and 1S4/3S4/3V4 series established the all-glass design that would continue almost until the end of receiving valve evolution, followed only by the short-lived Nuvistor and all-­ ceramic types. The initial release featured 1.4V filaments drawing 50mA (100mA for the 1S4/3S4/3V4 output pentodes). These appeared in the Mullard-Philips system as Dx91~93 releases. At 50mA per valve, a four-valve portable set would demand 250mA from the A battery. A compact set using a single ‘A’ cell Australia's electronics magazine would get less than ten hours of filament battery life. The Dx96 series halved the filament current consumption while giving near-identical performance, making portables more practical. The DK96 pentagrid converter differs from the familiar DK91/1R5. It’s the classic pentagrid, providing a committed oscillator anode. By comparison, the 1R5 inherited the dual screengrid design from the octal 6SA7. The DF96 pentode, DAF96 diode-pentode and DL96 power pentode use the same electrode structures as their predecessors, the 1T4, 1S5/1U5 and 1S4/3S4/3V4. Circuit details My redrawn (and hopefully clarified) circuit is shown in Fig.1. I am using the Bush’s own service manual circuit as my reference, as the Wireless and Electrical Trader 1403 version is impractical. I have preserved the component numbering but their strict siliconchip.com.au Fig.1: the circuit diagram for the Bush MB60. Note the extra IF amplifier (DF96, V3), making this set very sensitive. first-to-last numbering order has been upset by my aim of making the circuit more understandable. The MB60’s dual-band design (long wave and medium wave/broadcast band) is accommodated by a ferrite rod antenna with two windings, and an oscillator coil with just one. This design was reused in the follow-on TR82 that was mentioned in the introduction. The circuit parallels the ferrite rod’s two tuned windings for medium-­ wave reception. This gives a lower inductance than either winding by itself, allowing the antenna section of the tuning gang (VC1) to tune over 526~1605kHz for the medium wave/ broadcast band. Bush advises against adjusting the antenna coils for low-end alignment, so this is done by adjusting the oscillator coil for maximum sensitivity at 600kHz. Top-end alignment is performed using trimmer TC3. Revised antenna coupling The initial release’s antenna input/ car radio socket connects to the top of the tuned circuit via a 5.6pF capacitor. As noted below, this is not highly effective, and can put the antenna circuit off-resonance. The second issue of the MB60 uses the accepted design of a dedicated primary winding, as shown in Fig.2. The converter operates with zero bias and is gain-controlled from the AGC circuit via grid resistor R2. The oscillator section uses a secondary-­ tuned Armstrong circuit formed by transformer L4/L3. As the DK96 is a 6A8-style pentagrid, its oscillator anode (pin 3) is supplied from HT via resistor R5. Feedback is coupled to L4 via capacitor C13, while L4 couples inductively to the local oscillator (LO) coil’s tuned primary, L3. 515pF padder C11 ensures tracking between the antenna and oscillator circuits for medium-wave reception. L4/ L3 is slug-tuned to allow adjustment at the bottom end of the medium wave band. Trimmer TC4 provides top-end alignment, while the LO is tuned by the oscillator section of the gang, VC2. For long-wave tuning, the antenna circuit uses only the L1 winding on the ferrite rod, with L2 switched out of circuit. L1 alone, tuned by tuning capacitor VC1, now shunted by capacitor C3 (160pF) and the two trimcaps (TC1/ TC2), restricts the antenna circuit’s siliconchip.com.au Australia's electronics magazine March 2024  93 Fig.2: the dedicated primary winding of the revised MB60. tuning range to only 158~280kHz. A local oscillator’s tuning inductance is usually changed for different bands by switching in a different coil set, as changing tappings on one coil would modify the feedback ratio and affect the converter’s injection voltage. This is undesirable, as pentagrids must have a defined minimum injection voltage for optimal conversion gain. Instead, the MB60 switches extra capacitances into the circuit. C9 (450pF) is connected across tuned secondary winding L3, restricting the LO tuning range to around 630~750kHz. As C9 has a fixed value, low-end alignment and correct tracking rely on the adjustment of L4/L3’s ferrite core, which was set during the medium wave alignment. The LO’s top-end frequency is restricted by 33pF capacitor C10 and adjusted by trimcaps TC5/TC6. The converter drives the first intermediate frequency (IF) transformer IFT1’s primary. As with the other two IF transformers (IFTs), it has an untapped, inductance-tuned primary and secondary. The first IF amplifier operates with zero bias, with gain control via the first IFT primary. The second IF amplifier is similar, driving the third IF transformer, IFT3. Both stages get their screen supply via 33kW resistor R7, bypassed by 40nF capacitor C15. The secondary of IFT3 drives the DAF96’s demodulator/AGC diode. Demodulated audio develops across 500kW volume pot VR1, with the IF signal filtered out by 68pF capacitor C18 and 27kW resistor R10. The automatic gain control (AGC) signal is picked off via 2.7MW resistor R9, with filtering and voltage division by 40nF capacitor C16 and 2.7MW resistor R8. All controlled stages are fed with the same AGC voltage. The audio signal is conveyed to the first audio pentode section of the DAF96. This operates with low screen and anode voltages, as is common. The low anode current – which reduces the valve’s transconductance and thus its voltage gain – is compensated for by the high value of the 1MW anode load resistor, R13. The valve gets contact potential bias due to the action of 10MW grid resistor R12, allowing the grid to ‘drift’ weakly negative. The amplified audio signal is fed to the DL96 output valve’s grid via 3nF capacitor C24 and 330kW grid stopper R17. The DL96 gets about -5V bias via 1.8MW grid resistor R16 from the backbias developed across 560W resistor R18, filtered by 50μF capacitor C26. The DL96 valve drives the speaker via output transformer T1. The output transformer’s natural resonance is damped by 3nF capacitor C28. This is shunted by the tone control network of 10nF capacitor C27 and 100kW tone potentiometer VR2. Audio feedback is picked off from the loudspeaker and returned to the bottom end of 500kW volume control potentiometer VR1 via 10kW resistor R15, 40nF capacitor C23, 100nF capacitor C22 and 1kW resistor R11. My set is powered by a combined 1.5V/90V battery pack or from the mains. The later issue used two parallel D cells for the LT supply and a separate 90V B battery for HT. Mains transformer T2, with a multi-tapped primary, supplies full-wave rectifier MR2a/MR2b. After filtering by two-section pi low-pass filter C35/ R21/C34/R20/C33, it delivers about 1.35V to the filaments. The filament voltage from the mains supply is stabilised by shunt regulator MR2c. As the HT supply needs to deliver a lot less current, it is half-wave rectified by MR1 and filtered by C32/R19/C31. Mains/battery switching, via switch poles S2a/b/c/d, is performed by inserting or removing the mains plug. A quick glance had me puzzled. Was part of the battery HT+ wiring really going via the mains transformer primary’s wiring? Sure enough, it does, but only when the power plug is removed and S2 changes over to the battery position. This unusual connection effectively turns the set off via the On/Off switch in volume pot VR1: it cuts the mains input when on AC power and the HT supply when on battery. For battery operation, the LT supply is switched by S3a. Cleaning it up I got this set from a fellow HRSA member, happy to close the loop on Above: the controls for the Bush MB60 are located on the top of the cabinet. Right: a close-up showing the underside of the IF transformers with the added ceramic capacitors circled. Their values are in Table 1 shown opposite. 94 Silicon Chip Australia's electronics magazine siliconchip.com.au this line of distinctively designed English radios. It had been made to work, then smashed in transit. My friend and I divided the job – he would repair the case, and I would do the electronics. On receipt, it was working, but I reckoned it was a bit ‘deaf’ for a set with two IF stages. I recalled the Astor Aladdin (described in August 2016; siliconchip.au/Article/10049), which used a similar lineup. That set had only four valves but used two in the IF strip and employed one as a reflex stage for the first audio amplifier. Given the improvements in valve and component design, the MB60 should have been at least as good. The audio checked out OK, so it was on to the RF/IF section. All the IF transformer slugs were coated with white paint. A bit of gentle heating showed that I wouldn’t be able to soften it and free the slugs, a trick I had used on the Astor APN. What to do? At the converter grid, the IF responded best at 472kHz. So why did I get the best performance at 467kHz on the first IF grid and at 478kHz on the second IF? The bandwidth was wide enough to drive a truck through, confirming that, whatever the true intermediate frequency should have been, the various IF-tuned circuits disagreed. Also, it needed 20μV at the converter grid for 50mW of output, much worse than I expected. Believing that the manufacturer’s specification of 470kHz could be fiddled with a bit, I got a handful of 1~10pF trimmers, popped one across each tuned winding, and adjusted them for maximum gain. The final intermediate frequency of about 460kHz was lower than the specification, but the gain came up pretty well – see Table 1. A bit too well, in fact. I had been ready for IF oscillation with the trimcaps bodies hanging out of the circuit wiring, but expected that the feedback would be absent once I popped in small, fixed ceramics. It was stable but still a bit ‘chirpy’, so I dropped a 470kW resistor across the second IF primary. That did reduce the sensitivity at the converter grid from 6μV to 12μV, but the improved stability was preferable to instability. I then checked the antenna/LO alignment and found that the set working about as I expected. Having lived on a farm for around fifteen years, I reckon I know ‘agricultural’ when I see it. The LO coil looks like the designers forgot it, then just Table 1 – added capacitors IFT # Primary 1 Secondary 10pF 2 4.7pF 5.6pF 3 12pF 8.2pF threw it down, bolted it in place and told the assemblers to finish the set. Performance It is very good; more than just a standout example of 1960s design. For the standard 50mW output, it needed 60μV/m at 600kHz and 32μV/m at 1400kHz with signal+noise to noise (S+N:N) figures of 10dB and 11dB. For the standard 20dB S+N:N, the field strengths were 200μV/m and 150μV/m. Bandwidth for -3dB was under ±1kHz, implying some residual regeneration in the IF section. For -60dB, it was ±22kHz. Audio bandwidth, from volume control to speaker for -3dB was 140Hz to 10kHz, antenna to speaker about 130~1200Hz. Turning the Tone control to full cut brought the top end down to around 1kHz. The AGC was effective, needing a +40dB rise of input to give a +6dB increase in output. It would not overload even at 200mV/m field strength. The set went into clipping at 80mW, The front view of the Bush MB60 chassis which shows the ferrite rod antenna, permanent-magnet loudspeaker and controls. Nearly all the discrete components are mounted on this side. siliconchip.com.au Australia's electronics magazine March 2024  95 Tone Volume Bandchange A labelled photograph of the rear side of the chassis. In the service manual, they recommend an Ever Battery/Mains Ready type B147 Switch battery. Antenna socket 1st IF 1st IFT Oscillator coil Converter Output Transformer HT Rectifier 2nd IFT LT Rectifier 2nd IF 3rd IFT HT Filtering LT Filtering Demod/1st Audio Audio Out with 10% total harmonic distortion (THD). At 50mW, the THD was 7%, and 3% at 10mW out. Versions As noted above, the first release used capacitive coupling from the external antenna socket, while the follow-on used the conventional primary winding on the ferrite rod. The MB60 seems to have been released in just one colour scheme: a Mains Transformer grey case with a red perimeter band. There’s a moulded depression at the lower right of the rear cover in all three models. The VTR103 used it for the Tape Recorder output connector, but it was blank in the TR82. It was originally placed for the MB60’s mains connector plug. Mystery solved! Special handling Like the follow-on TR82 and This is a portable set running from 90/1.5V; you can see the battery plug and lead lying in the bottom of the cabinet. The cabinet was designed by David Ogle, who also designed the Ogle SX1000 car. 96 Silicon Chip Australia's electronics magazine Mains Socket VTR103, the tuning knob is a push fit. See the TR82 article (September 2013; siliconchip.au/Article/4404) for advice on safe removal. That said, I found finger pressure was adequate to withdraw the knob. Radiomuseum offers two online schematics (siliconchip.au/link/abrc). The Wireless & Electrical Trader 1403 version (like for the TR82 and VTR103) is difficult to understand: all switches are broken out into individual make/ break contacts. That demands that you get out a pencil and try to work out what is on (or off) for each band according to the description near the end of the article. It also takes some work to realise that mains voltage cannot connect through to the HT+ line. Pity the poor service technician. The other schematic, titled “Radio Servicing” is an extract from the Bush Radio Service Instructions MB60. This circuit is an improvement, except for the confusing power supply wiring. The manual contains extensive details and modification notes. I recommend the complete Bush original, which you can download from ElektroTanya (siliconchip.au/ link/abrb). They provide free original manuals, many from European equipment not hosted elsewhere. If you do visit them, consider uploading material they don’t have, or maybe just a donation. Radios like these come up on eBay, but you’ll also find them at auctions run by the Historical Radio Society of Australia (HRSA). 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However, nowadays, we all too often hear tales of a 'smart' TV that lasts less than two years or an expensive kitchen appliance that fails after just over a year (sometimes sooner!). Most of us have experienced this. My wife has had several of those trendy fitness watches that are all the rage now. She has had two in the past few years, and both failed either physically (the flimsy straps or case breaking) or electronically (the screen failing). Those things are not cheap to buy, yet they are cheaply manufactured. There are no spares for them other than third-party products from sites like AliExpress, so essentially, they are throwaway items. Being old-school, I’ve been wearing my Tag Heuer Professional watch every day for 30 years now, and it still looks like the day I bought it. It is definitely not a throwaway item, and while it has been regularly serviced, spare parts are still available from the maker if need be (the bezel detent spring has been replaced twice). My wife now has a Garmin smartwatch, which seems to do what it says on the tin. It also appears very well-made and is as robust as those devices need to be. So, companies can do it if they want to. I feel that because 98 Silicon Chip so much of technology is here today, gone tomorrow, the manufacturers just don’t expect anything they produce to last long enough before it is essentially redundant, so they don’t care that much about repairability or even providing spare parts. In my bread-and-butter trade, computer service and repair, a particular computer brand (that always reminds me of brown sauce) became a joke for its high failure rates. So much so that my customers commented, on many occasions, that the company must have built a timer into the machines because they always seemed to fail just outside their warranty period. I’m not claiming that this company was the only one whose computers failed – that happened across the board. Honestly, their failure rates were more likely tied to mechanical hard drive reliability (or lack thereof) than a secret motherboard timer, but I’m not entirely discounting that conspiracy theory! Of course, we all know nothing is made to last these days. Everything has become consumable because technology marches on at an alarming rate. Last year’s $10,000 OLED TV is today’s $1500 bargain bin special, replaced by some new QDLED, 4XLED or ZZYZXLED models (I might have made some of those up). Moore’s Law (the idea that the number of transistors on a chip doubles roughly every 18 months) might seem naïve now, but as a product of his time, it is still valid. The increasing complexity and reduced cost of integrated circuits have greatly impacted how and what we buy and what is being created in those massive factories overseas. Despite the bad things that come from it, the beauty of all this technology and manufacturing is that relatively inexpensive consumer electronics are widely available for anyone in all but the farthest-flung reaches of the planet, even New Zealand! One of the first truly ‘consumable’ items many of us experienced was the venerable computer printer. Early printers were made like old English cars. Solid, heavy, noisy and mostly reliable. Later printers were flimsy, but at least they produced good-quality prints when they worked. However, the printer companies eventually realised they could sell the printers for less, often below cost, and make up for it by charging a King’s ransom for the ink (and sometimes other consumables). I once worked out that for a typical $100 printer, an average customer would shell out $2000 for ink over its lifetime. No wonder all those ‘refill your own ink’ businesses Australia's electronics magazine siliconchip.com.au Items Covered This Month • • • • • • A device with one foot in the grave A quick fix for a failed start capacitor Cleaning a dirty preamplifier Fixing a muffled woofer The old days of TV antennas Simple troubleshooting 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 flourished under that business model. At one point, printer ink was the most valuable product on earth by weight! Many people would buy a new printer rather than shell out for expensive cartridges. Because consumers who wanted decent colour printers had few options at the time other than ink-jet or bubble-jet printers, we all printed millions of pages with them and fed several booming industries. The problem with them is that when a 50¢ plastic piece of hardware fails, we can’t buy spare parts to repair it. Manufacturers soon decided they didn’t want capital tied up with spare parts sitting on shelves, and they’d rather us buy a whole new printer. That’s what the consumable business model became. The printer itself became the consumable and that is still the case today. It was a boon for the manufacturers, but making printers a throwaway item sure created a lot of waste! Now it is also the same with mobile phones, tablets, laptops, fridges; anything with a shelf life of less than a couple of years. Even if made available, parts are expensive and often impractical to source. It is great that the Right To Repair movement exists, but they have only made a small dent in the problem so far. If the parts aren’t readily available, we still have to take the hit and chuck the item away. There is certainly a wealth of gadgets and tools out there designed to keep us buying more. One such device is a foot sander. I don’t know the actual name of it, but you’ve likely seen these things for sale at pharmacies and big box stores. They are designed to remove dead skin from feet and prevent corns and other maladies. A motor and gearbox assembly spin the replaceable abrasive roller, and it’s used very much like a palm sander, except for feet. They are usually battery-powered and come with a charger and rechargeable batteries hard-wired inside. Some are marketed under brand names, but many are just generic and sold cheaply. Again, they have consumables to keep the cash rolling in, in the form of abrasive sanding rollers that wear out all too quickly. A cynic might think these could be made of sterner stuff and last a lifetime, but where’s the profit in that? My wife has one, of course, and it has done some work. We found a Chinese source for the rollers, so we didn’t have to pay the exorbitant prices at the local outlets. These replacements might not be quite as high quality, but considering their low cost, they work well. She went to use it the other day and had it charging as siliconchip.com.au usual. When she picked it up, it was smoking hot! She called me in, and she was right; the thing was almost too hot to hold. Not only that, it also wouldn’t turn on. Flick the switch, nada. Something was evidently wrong inside there, which meant I was duty-bound as a Serviceman to open it up and have a look as soon as possible. This is a simple device, but was it simple to open? No, it was not! Only three small PK screws held it together, but it seemed to be like one of those puzzles where nothing will come apart until some magic happens. I could separate the case slightly and see the batteries inside, but pulling the abrasive wheel end apart seemed impossible. The roller itself just popped out, but the rest of it seemed to be either glued or clipped together in a way I couldn’t figure out. A central piece needed to be removed, but it appeared to be nailed in there; I couldn’t move it at all. There were no hidden screws under a sticker or anything like that. In situations like this, the urge is to use more salt and pepper and make something move, but I thought I would break something if I did that. It seemed impossible, so I did what anyone would do and walked away to ponder the problem. A fresh set of eyes might be the answer. I returned the next day, and fresh eyes didn’t help; I was just as perplexed. I poked and prodded to no avail and, in the end, just decided to use brute force where I thought it should come apart. I figured that if it broke, I’d repair it or just get a new one; this ‘simple little job’ had turned into a real mission. Thankfully, it did come apart in the way I thought it would, and it appeared to have been made purposely that way due to the clips inside it. I was fortunate not to break any off, and I got it apart without damage. It took a lot of blue language and struggling, though; this is the curse of The Serviceman! I wonder why someone would design something like that – after all, it isn’t like they were trying to prevent me from repairing it. Or were they? Australia's electronics magazine March 2024  99 Either way, I could see the problem right away. One of the internal AA cells had vented and dumped a gloopy mess all over the PCB. I could deal with that. I had a couple of commercial, high-quality NiCad cells that I could use to replace both. The heat appeared to have been generated by a half-watt resistor in the charging circuit. It had been mounted standing clear of the board, so this was obviously by design. The board was a little scorched underneath, but I desoldered and pulled one leg and used my LCR meter to measure it, and it was still within 5% of its marked value, so I just resoldered it back in and left it. The batteries were a different story. The blown one measured about 0.1V, while the other was 1.1V. That was understandable as it hadn’t been charged, but I was going to replace them both anyway. They were connected to the PCB by the usual nickel straps many batteries come with these days. These are typically spot-welded on and are rolled to form a solderable connector. Desoldering them from the board is easy; getting them off the board was a different story! I don’t know what the military-spec construction adhesive they’d glued these cells to the board with was, but it was as hard as nails, and I feared I would have to cut the batteries off with a Dremel or similar rotary cutting tool. The board itself was single-sided, so nothing special, but it was only half a millimetre thick and very flimsy. That seems to be the modern way. This meant that if I went Arnold Schwarzenegger on the batteries with a pry bar (screwdriver), the board would break beneath it. I loaded a new blade into one of my hobby knives and set about trying to cut the dead batteries off the board. This is the sort of job horror stories are made of; super-tough glue, 100 Silicon Chip poor access and a hyper-sharp blade are a recipe for disaster. As a long-time aeromodeller, I have been using these knives since I was a boy and have many of the distinctive straight-line scars on my fingers and hands to prove it! Luckily, this time, with decades of cautionary experience, I was OK. Still, one has to be constantly careful with tools like this. A moment’s lapse in concentration can really ruin someone’s day! The batteries did have a shrink-wrapped coating on them, so I was able to cut the cells free from that and at least get the bulk of them out of the way. But that left the cement and the jackets still stuck on the board. I trimmed what I could of the leftovers and tried sitting the new cells in the same position. That worked, but it wasn’t ideal. There was no way I could remove that glue from the board without damaging anything, so I just mounted the new cells on the remains of the old glue and used a spot of gel cyanoacrylate adhesive to hold them in place. I have a small spot-welder for this type of battery work and used that and nickel strips to connect the new NiCads together. These batteries have a much higher capacity than the old, dead ones. While the charging circuit might not be optimal for them, they would trickle charge without too much bother. Also, the runtime of the repaired unit would be about twice as long as before. Now all I had to do was reassemble it and I’d be finished. Well, that was easier said than done. Trying to manipulate the three main parts back together was like trying to herd cats into a bath. I know how it came apart, but using brute force doesn’t work as well when trying to get it back together as it did when getting it apart. It felt as if doing the same thing in reverse was definitely going to break something. The designer of this thing must have worked for Reginald Perrin’s company, Bastards Inc! I spent a good while sweating and coercing it back together. I can’t imagine how those poor sweat-shop workers making these things cope with it. I suppose they have their tricks and methods (perhaps even a jig), but this was such a frustrating gadget to work on. Given its relatively low price and throwaway vibe, it seemed increasingly ridiculous for me to even bother with it in the first place. Still, that’s what a good Serviceman does. If it can be fixed, it should be fixed. I wonder if, in the future, there will be any servicemen (or women) left who will even attempt to make things right when they see something broken. I’d like to think there will be, but time will tell. I managed to coerce the parts back together and screwed the PKs back in. After inserting the replaceable abrasive wheel, I switched it on and was rewarded with a fast-­ spinning roller. I would be very careful about getting this thing anywhere near my skin, but I guess that’s the beauty industry for you! My wife was grateful to have it back, and after a few months, it is performing well and charging correctly. While this was a ‘throwaway’ item, I feel that we should be repairing as many of these types of gadgets as possible because the e-waste we humankind are generating is appalling. I would be all in favour of making things to last again, or at least making them repairable, with traditional spare parts business models returning. I don’t think much good can come of just making things to throw away, especially with toxic electronics and batteries onboard. Australia's electronics magazine siliconchip.com.au A quick dryer repair G. D., of Mill Park, Vic fixed a machine with a common fault, but the exact way it failed was a bit surprising... A few weeks ago, my daughter called to say her clothes dryer would not start. She had just finished one load, and the machine just made a humming noise when she tried to start the second. I called in the next day and sure enough, a humming noise was all it would do, so off came the back cover. The problem was immediately very obvious. It was a failed start capacitor, but the failure mode was something that I had not seen before (photo below) – it looked like it had grown a tumour! A trip to a local supplier provided a replacement, although not in the same package format. Once installed, the machine worked as it should. rest of the PCB looked acceptable, evidently having been made on a different assembly line. Not being able to identify the unit meant I didn’t have a circuit diagram. Still, it appeared to be a straightforward audio preamp with RIAA correction circuitry switched in or out. I cleaned and tinned the switch terminals, checked the switch, replaced the missing tracks with wires and reassembled it all to give it a try. Success! Everything was working as expected. In the end, an easy fix for a bad job. Fixing the muffled woofer T. T., of Bribie Island, Qld, had a friend ask him to look at his audio preamplifier, which he said was crackling and sometimes wouldn’t work at all... I agreed, and when I received the preamp, I found that it was housed in a small plastic enclosure with RCA sockets marked “Aux”, “Phono” and “Output” on the back. On the front was a switch for selecting “Aux” or “Phono”. There was no brand name or model number visible anywhere, which made me suspicious, but he assured me that although he had bought it many years ago, it had been from a reputable shop in Sydney, and it had worked fine when he bought it. Opening the case revealed a PCB supported only by being soldered to the switch terminals. When I say soldered, that was a stretch of the imagination! It looked as if coffee or some sticky, brown cold drink had been spilled onto the PCB while the factory worker attempted to do the soldering (see the photo at lower right). Three of the six switch terminals had only vestiges of solder on them, and the copper of the corresponding PCB tracks and pads was badly corroded and lifting from the board. The copper pads were just touching the switch terminals here and there. Quality control in that factory must have been on holiday that day! I had to scrub the dried residue from the board, which did away with the lifted and corroded copper tracks. The P. M., of Christchurch, New Zealand recently came across some bouncing speakers. That is, after he fixed them and they were put back into service, they came back again... A local music venue has two powered speakers for its main PA system. One failed and was delivered to my door. The problem was that the woofer was no longer woofing. I am familiar with these units, so I dismantled the amplifier module after confirming that the problem was with the amplifier and not the speaker driver. This module is not dissimilar to the one used in the 500W Class-D Mono Amplifier (April 2023; siliconchip. au/Article/15730). It uses two IRF4227 Mosfets driven by an IRS20957 driver IC to deliver approximately 500W. A common problem with these units is the output inductor that filters the switching frequency from the output. This component works hard, as all the output current flows through it. The manufacturer has supplied an uprated coil to be used as a replacement. I fitted a new inductor and tested the amplifier, and all was well. After reassembly, the speaker was returned to the customer. A few weeks later, the other speaker from the venue turned up at my door. This time, the woofer was cutting out intermittently. After a few checks, I replaced the output inductor and could not get the fault to occur again. The speaker was returned, but a few days later, it boomeranged. Once again, I could not get it to fault, but I had an idea. I had a dead module from a previous repair of another unit. At that time, I could get a replacement module from the supplier, but this time, when I checked, they didn’t have any more. So I would repair my dead module and swap it for the troublesome one. The very obviously failed start capacitor from a clothes dryer. This PCB from a preamplifier had little to no solder left on the terminals of one of its switches. The case of the sticky preamp siliconchip.com.au Australia's electronics magazine March 2024  101 I figured the older one had died because of the output inductor, so I first replaced that and then the shorted Mosfets, and to be sure, the driver IC as well. But when I fitted it to the speaker, it refused to work. I was running out of ideas, so I asked the supplier if I could send my module to him to see if he could repair it. He agreed but reported that it worked perfectly when it got to him. Like the speaker, I was baffled, and asked if he had any suggestions. He asked if I had checked the low-side bias supply that comes from the separate power supply board. This supply is roughly 12V, sitting on top of the main negative rail, and is used to switch the low-side Mosfet. It comes from a separate winding on the switch-mode transformer and is regulated by a 7812. Apparently, it is not uncommon for the legs of the regulator to fracture due to vibration from the speaker. I checked the regulator and found it was solid, but the pins on the transformer had fractured solder joints. A quick touch-up and the speaker was back in business. A couple of months later, one of the speakers was back, this time with a different fault. After running for a while, it would start to make a fizzing noise from the high-­frequency horn. These speakers are bi-amped, so they have a separate amplifier driving the horn. I only heard the fault a couple of times, but it disappeared each time I got near it. I decided that the only way to narrow down the problem was to get the other speaker and swap modules between them. The electronics in these include a preamp board and a DSP board, which handles the crossover and equalisation. I swapped both from one speaker to the other, but the fault remained with the original. I swapped the amplifier boards and let both run on test. Of course, neither of them faulted. I accidentally left them running all night; the next morning, one was not working at all. It was not the one that had the fault originally, so the failure was with the amplifier board. I swapped the board for my repaired one to save time, and all was well again. The HF amplifier on the board consists of a high-power 102 Silicon Chip The repaired amplifier module from the powered speakers. Class-D IC (TDA8954TH) mounted under the board in contact with the heatsink, plus a few other components. I suspect that IC was the cause of the noise, and it eventually failed completely. As it is an SMD device with 24 pins, I was in no hurry to replace it. Maybe next time. The old days of TV antennas S. G., of Bracknell, Tasmania was a bit shocked when he had to deal with a very messy TV installation... This happened many years ago, well before digital television; I guess it was around 1985. I was working as a contractor installing television antennas when SBS Melbourne was transferring from channel 0 to UHF channel 28. Work was coming in fast, and it was all techs ‘to the pump’ for the upgrade as many people still wanted to watch SBS. Many installations needed a total rewire, replacing the old 300W cable with newer 75W cable to all outlets due to 300W cable being very lossy at UHF (477MHz for channel 28). Some jobs were easy (one antenna to one television), while others needed much more work. Depending on the job, we would be there from an hour to maybe a whole day for bigger sites. This job was one where I thought I would be in and out real quick. How wrong I was! The customer was one of Melbourne’s big hotels/motels, with a basic MATV system that serviced the main bar, sports bar and ladies’ lounge, with another feed over to the motel part of their complex. Thankfully, the whole system was wired in what looked like good-quality coaxial cable. The problem was that none of the televisions around the hotel or the motel had much reception; what could be received was very poor quality, varying from channel to channel and television to television. It was a real mess. Where to start? First, I measured the signal at the main distribution amplifier (a KingRay DW40). This turned up trumps; I found very little signal. So, up on the roof (flat, thank goodness) to find the big VHF antenna. Looking Australia's electronics magazine siliconchip.com.au Refresh your workbench with our GREAT RANGE of essentials at the BEST VALUE. 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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/workbench March 2024  103 1800 022 888 closely at it, I found the balun’s plastic cover was not installed properly and had become dislodged, sliding down the coaxial cable, allowing water into it. After a quick talk with the manager, it was decided to replace the antenna with a combination UHF/VHF antenna and replace the water-damaged coaxial cable as required. The antenna was mounted above the main office, with the coaxial cable running through the roof and down an internal wall. Having done that, I finally had a solid signal to feed into the distribution amplifier. Readjusting the gain and slope controls at the test point on the amplifier brought all of the televisions into working condition, with no crosstalk or inter-channel interference. I went around the hotel, checking the televisions as I went; the main bar still had reception problems. The Teletext wasn’t working very well; it was important as the public in the bar would want to see the sports results. The bar had sixteen 26-inch televisions, all tuned to different Teletext pages. They were all sitting on a heavyduty shelf behind the main bar. After a bit of cable tracing (wires were going everywhere, including PA and phone/ intercom cables), I found that all these TV sets were fed from one coax cable via a series of splitters. It looked like the system had grown over the years, but the splitters were all of the wrong types, and someone had used a couple of 300W four-way splitters and had made a real mess of the job. I had to rewire the lot with the correct 75W splitters. Some sets had the old-style tomb balun, with the coaxial cable direct to the screw terminals of the balun. All the televisions were fed from a single coaxial cable, which I traced back to the wall, expecting to find a wall outlet, but no! All I found was a 75W Belling-Lee line plug and socket. I needed to pull it apart to measure the signal coming from the amplifier and adjust for the signal level. The next thing I remember was getting a strong electric shock through one arm, across my chest and through my other arm. It nearly knocked me off my ladder! Sitting down, I had a short break to think about what had happened, and that’s when the penny dropped. All 16 sets were of the same manufacturer and model and likely would have been powered from a switch-mode supply. The antenna input socket would have a couple of capacitors to isolate the input antenna socket from the chassis, which usually sat at around half the mains supply voltage. I had 16 in parallel, each putting a small current into the antenna cable. In total, it was enough to pack a wallop! After fixing and replacing the coaxial cable, installing proper splitters, an isolated wall outlet, and tidying up the cabling, I was greeted with a first-class signal, no more Teletext dropouts, and a happy manager. I also installed an AC/DC isolator at the head end, and to the main feed that went to the motel wing. I ran into a similar situation later, when I was working in Mildura for a local television repair centre around 15 years ago. A customer from one of the outlying cattle stations on the other side of Wentworth called me to say her television reception had failed. The next day, I loaded up the Songbird An easy-to-build project that is perfect as a gift. SC6633 ($30 plus $12 postage*): Songbird Kit * flat rate postage Australia-wide Choose from one of four colours for the PCB (purple, green, yellow or red). The kit includes nearly all parts, plus the piezo buzzer, 3D-printed piezo mount and switched battery box (base/stand not included). See the May 2023 issue for details: siliconchip.au/Article/15785 104 Silicon Chip Australia's electronics magazine siliconchip.com.au work van with what I thought I would need: new antennas, masthead amplifiers, cable, masts, guy wires and sundries. It took me just over an hour to get to the farm gate and a further 15 minutes to the farmhouse. The television reception was woeful. The customer had several televisions around the house (four in all). The main one was a little 20in Sanyo set that had stood the test of time. Turning the set on, I was greeted with a screen full of snow. I was about to check the aerial connection when I realised that the socket on the set had failed at some point, and the customer had removed it and spliced the cable from the antenna directly to the cable from the tuner. This set (like many others) has capacitors built into the antenna socket to isolate the chassis from the antenna system. Most televisions of the era had the chassis at half mains potential. I told the customer to wait to use the television until it was repaired; it was taken back to the workshop and fixed later. The rest of the antenna system checked out OK, and the reception was restored once the masthead amplifier had been replaced. Don’t overamplify troubleshooting J. N., of Mt Manganui, New Zealand reminds us that sometimes looking for faults in the most obvious places first is the best strategy... As I am known to take a challenge with regard to repairs, a friend asked me if I could look at his Fender AmpCan 15W guitar amplifier that kept cutting out intermittently. I said yes, but no guarantees. After he delivered it, I put it through its paces with my own guitar and, sure enough, it was annoyingly intermittent (the worst faults are when they are intermittently intermittent)! Firstly, I dismantled the unit and discovered that it had an internal 12V SLA battery and could also be powered from a suitable charger. The owner lost the charger and had been trying to run the amplifier from a 15V DC power supply. I found and downloaded a copy of its circuit, wiring diagram and user’s manual. They allowed me to discover that the charger could charge the battery and power the unit separately, but not both. The external power passed through an L7815CV 15V regulator and a diode to the battery, then onto an isolating main switch. I established that the battery positive terminal was the point where the power was being lost. I immediately suspected the L7815CV voltage regulator; however, on removing it and bench testing it, it proved good! So the following diode must be faulty. After isolating the diode, I found it was not so. Where to now? Re-soldering, of course! To identify any faulty solder joint, I resoldered each point separately. And there it was, the last spot after the diode output from the voltage regulator. It just goes to show that I could have saved a lot of time by applying the simplest remedy first! Luckily, the battery was still usable. I had a used 15V 2.1A battery charger that allowed battery operation. To ensure safety for the L7815CV, I relocated it onto the large heatsink for the amplifier, as the original charger rating was only 400mA. The owner is very happy with the repair, especially as he can now use the unit cordless. SC siliconchip.com.au Australia's electronics magazine March 2024  105 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. 03/24 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. PRE-PROGRAMMED MICROS For a complete list, go to siliconchip.com.au/Shop/9 $10 MICROS $15 MICROS 24LC32A-I/SN ATmega328P Digital FX Unit (Apr21) Si473x FM/AM/SW Digital Radio (Jul21), 110dB RF Attenuator (Jul22) Basic RF Signal Generator (Jun23) ATmega328P-AUR RGB Stackable LED Christmas Star (Nov20) ATtiny45-20PU 2m VHF CW/FM Test Generator (Oct23) ATtiny85V-10PU Shirt Pocket Audio Oscillator (Sep20) PIC10LF322-I/OT Range Extender IR-to-UHF (Jan22) PIC12F1572-I/SN LED Christmas Ornaments (Nov20; versions), Nano TV Pong (Aug21) PIC12F617-I/P Active Mains Soft Starter (Feb23), Model Railway Uncoupler (Jul23) PIC12F617-I/SN Model Railway Carriage Lights (Nov21) PIC12F675-I/P Train Chuff Sound Generator (Oct22) PIC16F1455-I/P Auto Train Controller (Oct22), GPS Disciplined Oscillator (May23) Railway Points Controller Transmitter / Receiver (2 versions; Feb24) PIC16LF1455-I/P New GPS-Synchronised Analog Clock (Sep22) PIC16F1459-I/P Cooling Fan Controller (Feb22), Remote Mains Switch (RX, Jul22) K-Type Thermostat (Nov23), Secure Remote Switch (RX, Dec23) Mains Power-Up Sequencer (Feb24) PIC16F1459-I/SO Multimeter Calibrator (Jul22), Buck/Boost Charger Adaptor (Oct22) PIC16F15214-I/SN Tiny LED Icicle (Nov22), Digital Volume Control Pot (SMD; Mar23) Silicon Chirp Cricket (Apr23) PIC16F15214-I/P Digital Volume Control Pot (through-hole; Mar23) PIC16F15224-I/SL Multi-Channel Volume Control (OLED Module; Dec23) PIC16F1705-I/P Digital Lighting Controller Translator (Dec21) PIC16F18146-I/SO Volume Control (Control Module, Dec23), Coin Cell Emulator (Dec23) PIC16LF15323-I/SL Remote Mains Switch (TX, Jul22), Secure Remote Switch (TX, Dec23) W27C020 Noughts & Crosses Computer (Jan23) ATSAML10E16A-AUT PIC16F18877-I/P PIC16F18877-I/PT High-Current Battery Balancer (Mar21) USB Cable Tester (Nov21) Dual-Channel Breadboard PSU Display Adaptor (Dec22) Wideband Fuel Mixture Display (WFMD; Apr23) PIC16F88-I/P Battery Charge Controller (Jun22), Railway Semaphore (Apr22) PIC24FJ256GA702-I/SS Ohmmeter (Aug22), Advanced SMD Test Tweezers (Feb23) PIC32MM0256GPM028-I/SS Super Digital Sound Effects (Aug18) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) Advanced GPS Computer (Jun21), Touchscreen Digital Preamp (Sep21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) $20 MICROS ATmega32U4 Wii Nunchuk RGB Light Driver (Mar24) ATmega644PA-AU AM-FM DDS Signal Generator (May22) $25 MICROS dsPIC33FJ64MC802-E/SP PIC32MX470F512H-I/PT PIC32MX470F512H-120/PT PIC32MX470F512L-120/PT 1.5kW Induction Motor Speed Controller (Aug13) Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) Micromite Explore 100 (Sep16) $30 MICROS PIC32MX695F512H-80I/PT Touchscreen Audio Recorder (Jun14) PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) KITS, SPECIALISED COMPONENTS ETC PICO DIGITAL VIDEO TERMINAL (CAT SC6917) (MAR 24) MAINS POWER-UP SEQUENCER (FEB 24) Short-form kit: includes everything except the case; choice of front panel PCB for Altronics H0190 or H0191. Picos are not programmed (see page 46, Mar24) $65.00 Hard-to-get parts: includes the PCB, programmed micro, all other semiconductors and the Fresnel lens bezels (SC6871) $95.00 Current detection add-on: includes the AC-1010 current transformer, (P)4KE15CA TVS and MCP6272-E/P op amp (SC6902) $20.00 MICROPHONE PREAMPLIFIER KIT (CAT SC6784) (FEB 24) Includes the standard PCB (01110231) plus all onboard parts, as well as the switches and mounting hardware. All that’s needed is a case, XLR connectors, bezel LED and wiring (see page 35, Feb24) USB TO PS/2 KEYBOARD & MOUSE ADAPTOR - VGA PicoMite Version Kit: see page 52, January 2024 (SC6861) - ps2x2pico Version Kit: see page 52, January 2024 (SC6864) - 6-pin mini-DIN to mini-DIN cable, ~1m long. Two cables are required if adapting both the keyboard and mouse (SC6869) (JAN 24) (DEC 23) MULTI-CHANNEL VOLUME CONTROL (DEC 23) - Kit: Contains all parts and the optional 5-pin header (see page 77, Dec23) - 1.3in blue OLED (SC5026) SECURE REMOTE SWITCH (DEC 23) - Receiver short-form kit: see page 43, December 2023 (SC6835) - Discrete transmitter complete kit: see page 43, December 2023 (SC6836) - Module transmitter short-form kit: see page 43, December 2023 (SC6837) IDEAL DIODE BRIDGE RECTIFIER - 28mm square spade: see page 35, December 2023 (SC6850) - 21mm square pin: see page 35, December 2023 (SC6851) - 5mm pitch SIL: see page 35, December 2023 (SC6852) $30.00 $32.50 $10.00 COIN CELL EMULATOR (CAT SC6823) - Control Module kit: see page 68, December 2023 (SC6793) - Volume Module kit: see page 69, December 2023 (SC6794) - OLED Module kit: see page 69, December 2023 (SC6795) - 0.96in SSD1306 cyan OLED (SC6176) $70.00 (DEC 23) $30.00 $15.00 $50.00 $55.00 $25.00 $10.00 $35.00 $20.00 $15.00 $30.00 $30.00 $30.00 siliconchip.com.au/Shop/ - Mini SOT-23: see page 35, December 2023 (SC683) - D2PAK SMD: see page 35, December 2023 (SC6854) - TO-220 through-hole: see page 35, December 2023 (SC6855) $25.00 $35.00 $45.00 MODEM / ROUTER WATCHDOG (CAT SC6827) (NOV 23) PICO AUDIO ANALYSER SHORT-FORM KIT (CAT SC6772) (NOV 23) K-TYPE THERMOMETER / THERMOSTAT (CAT SC6809) (NOV 23) PIC PROGRAMMING ADAPTOR KIT (CAT SC6774) (SEP 23) CALIBRATED MEASUREMENT MICROPHONE (AUG 23) Short-form kit: includes all non-optional parts, plus a 12V relay and unprogrammed Pi Pico. Does not include a case (see page 71, Nov23) $35.00 Includes most parts, unprogrammed Pi Pico and OLED screen. The case, battery, chassis connectors and wires are not included (see page 41, Nov23) $50.00 Short-form kit: includes most parts except the case, LCD, thermocouple probe, cable gland and switches S4 & S5. A 10A relay is included (see page 58, Nov23) $75.00 Includes all parts, except the optional USB supply (see page 71, Sept23) SMD version kit: includes the PCB and all onboard components except the XLR socket. You also need one ECM set (see below) (Cat SC6755) Through-hole version kit: same as the SMD kit (Cat SC6756) Calibrated ECM set: includes the mic capsule and compensation components; see pages 71 & 73, August 2023 issue, for the ECM options (Cat SC6760-5) DYNAMIC RFID/NFC TAG (JUL 23) RECIPROCAL FREQUENCY COUNTER KIT (CAT SC6633) (JUL 23) BASIC RF SIGNAL GENERATOR (JUN 23) SONGBIRD KIT (CAT SC6633) (MAY 23) DUAL RF AMPLIFIER KIT (CAT SC6592) (MAY 23) Smaller (purple PCB) kit: includes PCB, tag IC and passive parts (Cat SC6747) Larger (black PCB) kit: includes PCB, tag IC and passive parts (Cat SC6748) $55.00 $22.50 $25.00 $12.50 $5.00 $7.50 Includes all parts, except the case, TCXO and AA cells (see page 57, July 2023) $60.00 Kit: includes everything but the case, battery and optional pot (Cat SC6656) Includes all parts required, except the base/stand (see page 86, May 2023) Includes the PCB and all onboard parts (see page 34, May 2023) *Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # Overseas? Place an order on our website for a quote. $100.00 $30.00 $25.00 PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT LINEAR MIDI KEYBOARD (8 KEYS) + 2 JOINERS ↳ JOINER ONLY (1pc) TOUCHSCREEN DIGITAL PREAMP ↳ RIBBON CABLE / IR ADAPTOR 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 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 ACTIVE MAINS SOFT STARTER DATE AUG21 AUG21 SEP21 SEP21 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 NOV22 NOV22 NOV22 NOV22 DEC22 DEC22 DEC22 DEC22 JAN23 JAN23 JAN23 JAN23 JAN23 FEB23 PCB CODE 23101213 23101214 01103191 01103192 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 09109221 09109222 24110222 24110225 24110223 CSE220503C CSE200603 08108221 16111192 04112221 04112222 24110224 01112221 07101221 CSE220701 CSE220704 08111221 08111222 10110221 Price $5.00 $1.00 $12.50 $2.50 $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 $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 $10.00 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT ADVANCED SMD TEST TWEEZERS SET DIGITAL VOLUME CONTROL POT (SMD VERSION) ↳ THROUGH-HOLE VERSION MODEL RAILWAY TURNTABLE CONTROL PCB ↳ CONTACT PCB (GOLD-PLATED) WIDEBAND FUEL MIXTURE DISPLAY (BLUE) TEST BENCH SWISS ARMY KNIFE (BLUE) SILICON CHIRP CRICKET GPS DISCIPLINED OSCILLATOR SONGBIRD (RED, GREEN, PURPLE or YELLOW) DUAL RF AMPLIFIER (GREEN or BLUE) LOUDSPEAKER TESTING JIG BASIC RF SIGNAL GENERATOR (AD9834) ↳ FRONT PANEL V6295 VIBRATOR REPLACEMENT PCB SET DYNAMIC RFID / NFC TAG (SMALL, PURPLE) ↳ NFC TAG (LARGE, BLACK) RECIPROCAL FREQUENCY COUNTER MAIN PCB ↳ FRONT PANEL (BLACK) PI PICO-BASED THERMAL CAMERA MODEL RAILWAY UNCOUPLER MOSFET VIBRATOR REPLACEMENT CALIBRATED MEASUREMENT MICROPHONE (SMD) ↳ THROUGH-HOLE VERSION ARDUINO ESR METER (STANDALONE VERSION) ↳ COMBINED VERSION WITH LC METER WATERING SYSTEM CONTROLLER SALAD BOWL SPEAKER CROSSOVER PIC PROGRAMMING ADAPTOR REVISED 30V 2A BENCH SUPPLY MAIN PCB ↳ FRONT PANEL CONTROL PCB ↳ VOLTAGE INVERTER / DOUBLER 2M VHF CW/FM TEST GENERATOR TQFP-32 PROGRAMMING ADAPTOR ↳ TQFP-44 ↳ TQFP-48 ↳ TQFP-64 K-TYPE THERMOMETER / THERMOSTAT (SET; RED) PICO AUDIO ANALYSER (BLACK) MODEM / ROUTER WATCHDOG (BLUE) DISCRETE MICROAMP LED FLASHER MAGNETIC LEVITATION DEMONSTRATION MULTI-CHANNEL VOLUME CONTROL: VOLUME PCB ↳ CONTROL PCB ↳ OLED PCB SECURE REMOTE SWITCH RECEIVER ↳ TRANSMITTER (MODULE VERSION) ↳ TRANSMITTER (DISCRETE VERSION COIN CELL EMULATOR (BLACK) IDEAL BRIDGE RECTIFIER, 28mm SQUARE SPADE ↳ 21mm SQUARE PIN ↳ 5mm PITCH SIL ↳ MINI SOT-23 ↳ STANDALONE D2PAK SMD ↳ STANDALONE TO-220 (70μm COPPER) RASPBERRY PI CLOCK RADIO MAIN PCB ↳ DISPLAY PCB KEYBOARD ADAPTOR (VGA PICOMITE) ↳ PS2X2PICO VERSION MAINS POWER-UP SEQUENCER MICROPHONE PREAMPLIFIER ↳ EMBEDDED VERSION RAILWAY POINTS CONTROLLER TRANSMITTER ↳ RECEIVER DATE FEB23 MAR23 MAR23 MAR23 MAR23 APR23 APR23 APR23 MAY23 MAY23 MAY23 JUN23 JUN23 JUN23 JUN23 JUL23 JUL23 JUL23 JUL23 JUL23 JUL23 JUL23 AUG23 AUG23 AUG23 AUG23 AUG23 SEP23 SEP23 SEP23 OCT22 SEP23 OCT23 OCT23 OCT23 OCT23 OCT23 NOV23 NOV23 NOV23 NOV23 NOV23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 JAN24 JAN24 JAN24 JAN24 FEB24 FEB24 FEB24 FEB24 FEB24 PCB CODE 04106221/2 01101231 01101232 09103231 09103232 05104231 04110221 08101231 04103231 08103231 CSE220602A 04106231 CSE221001 CSE220902B 18105231/2 06101231 06101232 CSE230101C CSE230102 04105231 09105231 18106231 01108231 01108232 04106181 04106182 15110231 01109231 24105231 04105223 04105222 04107222 06107231 24108231 24108232 24108233 24108234 04108231/2 04107231 10111231 SC6868 SC6866 01111221 01111222 01111223 10109231 10109232 10109233 18101231 18101241 18101242 18101243 18101244 18101245 18101246 19101241 19101242 07111231 07111232 10108231 01110231 01110232 09101241 09101242 Price $10.00 $2.50 $5.00 $5.00 $10.00 $10.00 $10.00 $5.00 $5.00 $4.00 $2.50 $12.50 $5.00 $5.00 $5.00 $1.50 $4.00 $5.00 $5.00 $5.00 $2.50 $2.50 $2.50 $2.50 $5.00 $7.50 $12.50 $10.00 $5.00 $10.00 $2.50 $2.50 $5.00 $5.00 $5.00 $5.00 $5.00 $10.00 $5.00 $2.50 $2.50 $5.00 $5.00 $5.00 $3.00 $5.00 $2.50 $2.50 $5.00 $2.00 $2.00 $2.00 $1.00 $3.00 $5.00 $12.50 $7.50 $2.50 $2.50 $12.50 $7.50 $7.50 $5.00 $2.50 LASER COMMUNICATOR TRANSMITTER ↳ RECEIVER PICO DIGITAL VIDEO TERMINAL ↳ FRONT PANEL FOR ALTRONICS H0190 (BLACK) ↳ FRONT PANEL FOR ALTRONICS H0191 (BLACK) WII NUNCHUK RGB LIGHT DRIVER (BLACK) ARDUINO FOR ARDUINIANS (PACK OF SIX) ↳ PROJECT 27 MAR24 MAR24 MAR24 MAR24 MAR24 MAR24 MAR24 MAR24 16102241 16102242 07112231 07112232 07112233 16103241 SC6903 SC6904 $5.00 $2.50 $5.00 $2.50 $2.50 $20.00 $20.00 $7.50 NEW PCBs We also sell the Silicon Chip PDFs on USB, RTV&H USB, Vintage Radio USB and more at siliconchip.com.au/Shop/3 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 Using Keyboard Adaptor with Maximite Could the USB to PS/2 Keyboard Adaptor (January 2024; siliconchip. au/Article/16090) be used with the Colour Maximite Computer (CMM1; September-October 2012; siliconchip. au/Series/22) to replace the PS/2 keyboard? (R. M., Melville, WA) ● Yes, the original Colour Maximite from 2012 should work fine with either of the USB to PS/2 Keyboard Adaptors, although we have not explicitly tested them with the older Maximites. The VGA PicoMite version from July 2022 is the better option if building a new computer (siliconchip.au/ Article/15382). Still, anything that expects a PS/2 keyboard should work with the Adaptors published in the January issue. Can bridge rectifiers be paralleled? Is it possible to parallel two bridge rectifiers to increase the power handling? Can you decrease the losses by using diodes with lower forward voltages? The diodes sometimes have capacitors across them – what purpose do they serve? (F. C., Maroubra, NSW) ● When you need a higher current rating for a diode or a bridge rectifier, it is customary to use a single part with a higher current or power dissipation rating. That is because simply paralleling diodes does not ensure even current sharing between them. Further, silicon diodes have a negative temperature coefficient, so the hotter diode will carry more current, exacerbating any mismatch in paralleled parts. There would be some current sharing, but you cannot safely assess how much, so we do not recommend it. You could add current-sharing resistors that will reduce the current sharing imbalance. Still, the resulting voltage drop would probably be at least 100mV, and you would be much better off selecting beefier diodes. 108 Silicon Chip Two ‘mainstream’ diode types are used for power rectification: standard silicon rectifiers (SSRs) and schottky diodes. These have various benefits. Schottky diodes have about half the forward voltage drop of silicon diodes (0.3-0.5V rather than 0.6-1.0V, depending on size and current). This is a big deal and, in many applications, schottky diodes are the norm. A good example is a switch-mode flyback circuit, where the diode is usually a schottky type. Indeed, most low-voltage DC/DC converters use schottky diodes for efficiency. Schottky diodes are not used everywhere because of their limited reverse voltage handling. It is common to see a silicon diode with a peak inverse voltage (PIV) rating well above 100V and often 1000V or higher. On the other hand, schottky diodes are typically rated in the tens of volts, and rarely above 120V. Similarly, the reverse leakage (how well the diode blocks reverse current) is much better for SSR than schottky diodes. So you can’t always substitute a schottky diode for an SSR. Also remember that even a forward voltage drop of just 0.3-0.5V can still lead to significant dissipation at high currents. Capacitors are sometimes placed across diodes in bridges to reduce electrical noise from hard switching. These serve a very different function to how the diode handles current. The bottom line is that all conventional bridge rectifiers dissipate a lot of power at high currents. At 10A, even a beefy schottky diode has a forward voltage drop of 0.4V or more, so with two of these conducting in a bridge, you have a dissipation of 8W (0.4V × 2 × 10A). The Active Bridge Rectifier from the December 2023 issue (siliconchip. au/Article/16043) will outperform a standard bridge rectifier as long as the resulting voltage is under 72V (up to ±72V with two). It does this by using an active circuit and Mosfets. In the same case as above, the result is a Australia's electronics magazine voltage drop of just 25mV per Mosfet, ie, 0.5W (0.025V × 2 × 10A). Soft starting an induction motor Thanks for the great articles and projects in the Silicon Chip magazine. Also, the comments provided by your readers, the questions you have responded to and the Circuit Notebook all combine to keep one’s mind active and foster the creative juices. Could the February and March 2023 Active Soft Starter (siliconchip.au/ Series/395) be modified to control an induction motor? I want to reduce the inrush current of a house water pump powered by a small inverter. (G. I., Tumby Bay, SA) ● That soft starter (and most similar designs) is not suitable for soft-­ starting all but the smallest induction motors (eg, those used in domestic fans) because their speed is primarily dependent upon the drive frequency. Any type of voltage control without altering the frequency can cause the motor to draw considerable current, behave erratically and possibly overheat. At startup, the current drawn by an induction motor is very high since the rotor is at a low speed and the rotor inductance is low. You may be able to soft-start the pump motor for brief periods using that circuit, provided the startup period is set relatively short to avoid the motor overheating. In that case, no modifications should be required. The high current draw by the motor at startup could mean that the Mosfet’s current rating needs to be increased. If you try it and the Mosfet fails, consider using a similar device with a higher current rating. The best way to soft-start an induction motor is using a variable speed drive (VSD) with a slow initial speed ramp, like our Induction Motor Speed Controller from the April & May 2012 issues (siliconchip.au/Series/25). It is more expensive to build, and some siliconchip.com.au parts are becoming hard to obtain, but we believe it is still possible to make it. It was designed to control the speed of a pool pump, so it seems ideal for your application, even if its ratings are overkill. Note that there are important updates to that design in the December 2012 and August 2013 issues; the PCBs that are available now incorporate those improvements. Adding new fonts to the Pico BackPack I bought the Pico BackPack kit (March 2022 issue; siliconchip.au/ Article/15236) to use as a Pico trial in stages and have found it pretty good. I used it for some software development, adding the sections I needed without drama. As a shortcut, I replaced Mosfet Q1 with a short link on the drain-source PCB pads, and audio wasn’t required, so I left that out completely. It has been very useful and is a good project. The demo software (Arduino example) seems grimly determined not to change fonts! Do you have any suggestions on how to do that? (S. W. O., Sydney, NSW) ● As you have found, the demo software for the Pico BackPack was intended to provide a useful but quite basic overview of the features of the BackPack and LCD. We’re not sure how you have tried to change the fonts (only one font file is included with the demo software), but it would be along the following lines. First, download a font file from www.rinkydinkelectronics.com/r_ fonts.php This website is mentioned in the “Arial_round_16x24.c” file that’s part of the download package. There are warnings on that page that the fonts will only work with specific libraries, but the format is quite simple, and we have designed our code (including most projects that work with these sorts of LCD panels) to work with these font files. Make sure to choose a full alphanumeric font with 95 characters. You may have to make some minor changes to the downloaded file; you can compare our modified Arial_ round_16x24.c to the one that can be downloaded. The main changes are the architecture “#defines” near the start and the “#include” guards at the top and bottom. Add the font file to the Arduino sketch folder and add an #include reference in the main sketch file. See the showarray() function calls for how the font is used. If you want to use the font for the button controls, you will probably have to add an #include reference and change the BUTTON_FONT #define in the file “LCD.h”. If you only want to use one single (but different) font, you can probably get away with simply replacing the font data between the braces {} in the “Arial_round_16x24.c” file with the equivalent data from the font file you downloaded. Micromite BackPack V1 with Digital Preamp I intend to build the Touchscreen Digital Preamp with Tone Control from the September & October 2021 issues (siliconchip.au/Series/370). I have already built a Micromite BackPack V1. Can this version be used to control the Preamp? I note it has the same processor and PIC Programming Adaptor Our kit includes everything required to build the Programming Adaptor, including the Raspberry Pi Pico. The parts for the optional USB power supply are not included. Use the Adaptor with an in-circuit programmer such as the Microchip PICkit or Snap to directly program DIP microcontrollers. Supports most newer 8-bit PICs and most 16-bit & 32-bit PICs with 8-40 pins. Tested PICs include: 16F15213/4, 16F15323, 16F18146, 16F18857, 16F18877, 16(L)F1455, 16F1459, 16F1709, dsPIC33FJ256GP802, PIC24FJ256GA702, PIC32MX170F256B and PIC32MX270F256B Learn how to build it from the article in the September 2023 issue of Silicon Chip (siliconchip.au/Article/15943). And see our article in the October 2023 issue about different TFQP adaptors that can be used with the Programmer (siliconchip.au/Article/15977). Complete kit available from $55 + postage siliconchip.com.au/Shop/20/6774 – Catalog SC6774 siliconchip.com.au Australia's electronics magazine March 2024  109 LCD screen as the version 2. (D. H., Mapleton, Qld) ● In short, yes, you can. The two major differences between the LCD BackPack V1 and V2 are: 1. The BackPack V1 lacks the Microbridge that provides the USB interface, which makes programming and communications easier. That shouldn’t affect its operation in the Preamp. 2. The BackPack V1 only has manual backlight brightness adjustment, so the digital brightness controls won’t do anything. That should actually be beneficial for sound quality, though, as it avoids switching noise. CLASSiC DAC error codes After great success building the SMD Trainer (December 2021 issue; siliconchip.au/Article/15127) and Improved SMD Tweezers (April 2022; siliconchip.au/Article/15276), I set about building your ‘CLASSiC DAC’ design from the February to May 2013 issues (siliconchip.au/Series/63). It is a fascinating mix of technologies, and it is also clear that a great deal of effort and thought went into its design. The use of screen-printed PCB material for the front and rear panels is brilliant and makes for a professional appearance. Congratulations! Incidentally, I had the same 7915 regulator problem mentioned in the articles. I purchased the PCB, front and rear panels, programmed microcontroller and “hard to get” parts from the Silicon Chip shop. I hope you can help me with a problem I have encountered: Upon powering up the DAC, the green sampling rate LEDs flash in sequence, from 44.1kHz to 192kHz, then back to 48kHz. As far as I can tell, the 44.1kHz LED does not flash again. Then, the right-most blue S/PDIF LED (LED7) starts flashing at about one flash a second. There is no further activity. I assume from this behaviour that the microcontroller is apparently running through a check routine before entering its normal control loop, but a problem has been detected. Unfortunately, I do not know what sort of problem this behaviour indicates. Can you shed any light on what this condition signifies? Perhaps you have a list of such condition indications from back then that you could send me, because I don’t think this will be the only problem I encounter with getting it all working. I have scanned the Silicon Chip issues from 2013 onward, hoping to find a list of such conditions, in vain. Using the Watering System Controller with an Apple device I have just completed your Watering System Controller presented in the August 2023 issue of Silicon Chip magazine (siliconchip.au/Article/15899). I built it for my son for Christmas. It works a treat with my Android phone and Windows laptop, but not with any of my son’s Apple devices. It goes to the home page OK and displays the “Run Now” buttons in blue. It is the same for save buttons in configuration screens. This behaviour (blue buttons) is after the controller has been configured using my Android phone. But buttons only appear blue when the controller is accessed by an Apple device. When any of those blue buttons are pressed, the application presents a blank screen, and nothing happens. Can we set something in the Apple devices for this to work? Also, all the browsers tried on the Apple devices show the home page as insecure. Android devices do the same but allow you to use the controller as designed. I’m wondering if anyone else has experienced this behaviour. (E. H., Trafalgar, Vic) ● Geoff Graham responds: I have heard that some people have had trouble with Safari on Apple devices. The solution is to use the Chrome, Edge or Firefox browser, which you can install on Apple hardware. It seems that not all browsers are created equal. I carefully selected HTML/Java constructs that were supposed to be universal and tested the code on Chrome and Microsoft Edge. But I have since heard of other browsers that do not work, including Safari on an iPhone. Unfortunately, I don’t have an Apple platform to test with Safari and Apple no longer supports Safari for Windows. I will have to sit down and review all the HTML/ Java constructs and see what can be done, but that does not sound very positive. If you can install Chrome, Edge or Firefox on the Apple devices, that would be the best short-term solution. In the meantime, I will do some head scratching. 110 Silicon Chip Australia's electronics magazine I should say that all the SMD ICs are immaculately soldered in (I would say that, of course); they have been checked many times under bright lighting with 40x magnification. I can’t find a fault, so I need some pointers on where to look. I know from servicing OCR machines and magnetic tape drives (showing my age there) that most digital electronics just works, unless there is a physical problem or a chip failure, so I expected the CLASSiC DAC also to ‘just work’. Any help would be greatly appreciated. (D. J., Umina Beach, NSW) ● You are right that after the microcontroller is powered up and after it does the LED chaser (to show that it is alive and the LEDs are all working), it runs some tests before regular operation. Those tests are to verify that it can communicate with the three critical chips (PLL1708, CS8416 & CS4398) and that they return valid IDs, indicating that they are present and (presumably) working. Regrettably, we forgot to include the error code flashing information in the original articles. We did touch on it before, in Ask Silicon Chip, June 2015 (page 91). In brief, if it halts with LED5 flashing, that indicates a problem with the CS4398. If LED6 is flashing, there is a problem with the CS8416. Finally, if LED7 flashes, that indicates a problem with the PLL1708 chip. Please check the soldering on the PLL1708 IC again. Also check pins 46 & 62 of microcontroller IC5. If the soldering is good, there is something else wrong with it; perhaps the chip is faulty, or there is a problem with the 27MHz crystal or bypass capacitors. If you can’t find anything wrong with it, try carefully probing the VCC and GND pins to check that each has the correct voltage applied. If all else fails, apply a little flux paste along both sides of the chip and heat some solder braid on top of each set of pins, pressing down gently with your iron until the solder reflows. That could clear up a hidden bridge or fix a dry solder joint. Give the board a clean, power the unit back up, and, fingers crossed, that will have fixed it. If not, you may need to replace the PLL1708 chip. It can be removed relatively easily with a low-cost hot air rework station or, if you don’t want to buy one, by adding enough solder to continued on page 112 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 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 SALE LEDs and accessories for the DIY enthusiast LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware. For a full list of the parts we sell, please visit www.ledsales.com.au PMD WAY offers (almost) everything for the electronics enthusiast – with full warranty, technical support and free delivery worldwide. Visit pmdway.com to get started. SILICON CHIP MAGAZINE GIVEAWAY ASSORTED BOOKS FOR $5 EACH Electronics and other related subjects – condition varies. Most of the remaining books are data sheets. Some of the books may already have been sold. See the photos (updated once again 31/01/2024): siliconchip.au/link/ absm Email for a quote (bulk discount available), state the number directly below the photo when referring to a book: silicon<at>siliconchip.com.au I have subscribed to the Silicon Chip magazine for many years and have kept every copy received , however, due to moving to smaller premises, I am now unable to store these magazines. I have magazines going back to April 2001. I would like to donate these free to anybody willing to collect and give them a good home. Stephen Cooper stephenjcooper<at>hotmail.com Mobile: 04 1042 0860 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 (02) 9939 3295. 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 March 2024  111 Advertising Index Altronics.................................41-44 Blackmagic Design....................... 9 Dave Thompson........................ 111 DigiKey Electronics....................... 3 Emona Instruments.................. IBC Hare & Forbes............................ 6-7 Icom Australia............................. 14 Jaycar.......................IFC, 11, 15, 29 ............................54-55, 85, 97, 103 Keith Rippon Kit Assembly....... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology....... OBC, 13 Mouser Electronics....................... 4 PMD Way................................... 111 Quest Semiconductors............... 10 Silicon Chip Back Issues........... 53 SC Ideal Bridge Rectifiers........... 84 SC Pico W BackPack.................. 87 SC Programming Adaptor........ 109 Silicon Chip Shop............ 106-107 Silicon Chip Songbird.............. 104 The Loudspeaker Kit.com.......... 12 Wagner Electronics................... 105 Notes and Errata Mains Power-Up Sequencer, February & March 2024: in the Fig.3 circuit diagram (February, p52), fuse F1 should be rated at 10A, not 1A. Also scope grabs 1 & 2 show the current drawn by three amplifiers in parallel, not one. Ideal Diode Bridge Rectifiers, December 2023: 1.5mm diameter wire is too large for the SOT-23 version PCB pads; use 0.7-1.0mm diameter wire or lead off-cuts. GPS-Disciplined Oscillator, May 2023: some PCBs we sold had manufacturing errors with the four pins of REF5 (plus one nearby) shorted to the ground plane. If you have one, you can either drill those holes out slightly larger to break the connection to the plane and solder the wire link on the top, or contact us for a replacement board. Next Issue: the April 2024 issue is due on sale in newsagents by Thursday, March 28th. Expect postal delivery of subscription copies in Australia between March 27th and April 12th. 112 Silicon Chip bridge all the pins on each side, then alternately heating them while gently pulling up on the chip with tweezers. Either way, you will need to use flux paste and solder wick (pressed down firmly) to clean off all the remaining solder before placing a new chip. socket that is affecting operation. Also check the continuity for the tracks that you cleaned. While you’re at it, verify that the silicone insulating washers for Q1, Q2, D1 and D2 are insulating the device tabs from the rear panel/heatsink. Fixing Multi-purpose Fast Battery Charger FM antenna recommendations I built a Dick Smith K-3216 battery charger kit many years ago and have not used it in a while. I needed to recharge a 6V car battery with the charger this month, but it had stopped working. I found that the output fuse had blown, so I replaced it with another, which fused at switch-on. I took the cover off the unit to find that some sort of mould or corrosion had spread over one corner of the circuit board. The residue was on both sides of the circuit board, over the main switching inductor and between the rear panel and the instrument case. It appeared to follow the circuit tracks and parts soldered to the board; however, there was none around the electrolytic capacitors. They looked like new. It was hard-attached to the circuit board and components; I had to scrape it off with a flat-bladed screwdriver and wire brush. I then used WD40 to remove it from large components soldered to the board. The case was cleaned with steel wool and washed. When dry, I put it back together and followed the testing procedure in the article. All tests passed bar one: the measured output voltage should be around 10V on the 6V battery selection. My reading was 23V, no matter what settings were selected. What should I do to get the 10V on the output terminals? (K. W., Manly, Qld) ● That kit appears to be for the Multi-purpose Fast Battery Charger from the February and March 1998 issues (siliconchip.au/Series/144). The incorrect output voltage is likely due to a problem with transistor Q1; it seems it is continuously switched on. That could be due to a fault in it or transistor Q3. Check that Q1 and Q3 read open-­ circuit between the collector and emitter when the power is off. If you find a short circuit between the collector and emitter of either or both transistors, you will need to replace them. There could also be residue in IC1’s I wish to build or erect an FM antenna for the tuner in my hifi receiver. I noticed that Silicon Chip had an article in the March 1998 issue, but as it turned out, I have every issue from April 1998 (plus August 1997), so I just missed out. Is there a later article or an alternative to this antenna? Being a Yagi design and therefore directional, where can I source the information regarding the location of the FM broadcast transmission sites? I assume they’ll all be in approximately the same location here in Newcastle. Also, the transmission polarity appears horizontal, but car antennas are vertical. Do they transmit in both polarities? Any help would be greatly appreciated. (T. C., Newcastle, NSW) ● Yagi antennas are the best for FM radio. Cars mainly use vertical antennas because that is the only practical solution. Typically, FM transmission antennas provide both vertical and horizontal polarisation. That makes the transmission suitable for mobile use (eg, in cars) and for fixed antennas (with a horizontal orientation). If the transmission is purely horizontal or vertical, a receiving antenna will have more signal pickup when placed in the same plane as the transmission. However, there will still be reception if the receiving antenna is mainly in the orthogonal plane. We published a more recent FM antenna design in the October 2015 issue (siliconchip.au/Article/9137). Transmission antenna locations can be found at siliconchip.au/link/abse If you need one, you could get a copy of the March 1998 issue. While we have sold out of printed back issues of that month, you can can get access to view or download a PDF copy from siliconchip.au/Shop/12/3277 or order a photocopy of an article in that issue from siliconchip.au/Shop/2/265 It can also be obtained as part of our PDFs on USB (siliconchip.au/Shop/ digital_pdfs). SC 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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