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I have successfully built the 40V Hybrid Switchmode/Linear Bench Power Supply (April-June 2014 issues; siliconchip.au/Series/241), a really excellent and compact, fully adjustable supply to modernise my workbench. As I was testing it, before enclosing it in the case, I noticed the heat dissipation of the two linear regulators was quite high for an input of 19.5V. This design accepts up to 24V at the input, meaning the dissipation could be higher than in my instance. Based on my finger test, these internal 7805 and LM2940 regulators appear to run above 50°C, and the case has no ventilation. I was pondering the lack of ventilation and whether I should drill holes in the case but concluded that would detract from its looks. I then recalled Advertising Index Altronics........... 9, 31-34, 73, 81, 89 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 Emona Instruments.................. 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Do you have any advice on whether this would introduce any problems or if it would require modifications beyond the 78xx Replacement substitution? (B. R., Eaglemont, Vic) ● Both linear regulators are provided with fairly generous heatsinks and contact with PCB copper, so they should run well within their specifications, even if they get a bit warm. 50-60°C might seem hot, but their maximum junction temperature ratings are 150°C. Still, we understand the desire to reduce power consumption and keep the case cooler. Using thermal paste between the regulator and heatsink, and heatsink and PCB, could reduce the junction temperature, as could using slightly larger heatsinks. However, the same total power would still be dissipated within the case. Your idea of using a switch-mode regulator is a good one. All that the 12V regulator (REG1) powers is a 7555 timer (IC2) driving charge pumps to generate some auxiliary rails (-5V and VBOOST) and 7805 regulator REG2, which delivers the +5V rail. None of those sections should be bothered by the extra noise expected from a step-down/buck regulator, such as the one we published in August 2020. By all means, try the substitution; just verify that the supply doesn’t have any odd behaviour after you swap the regulator over. If it does (which seems unlikely), you might need to add an Errata & Sale Date for the Next Issue Switchmode substitute for warm regulators RC or LC low-pass filter between the output of that regulator module and the rest of the circuitry. You could probably also replace REG2 (7805) with a 5V buck module but we’d be a little more cautious with that one. It drives the panel meters, which should not be a problem, but it also provides a reference voltage for the voltage and current adjusting pots and trimpots. The safest thing to do would be to leave REG2 as a 7805 but disconnect the 5V rails going to the two panel meters and run them from the output of a separate 5V buck converter. We don’t think that would cause any problems and would substantially improve efficiency. Identifying a kit sold by a third party I need your help to find the firmware for a PIC16F84 chip. I purchased a Big Clock kit from Quasar Electronics in England many years ago. The kit was a Big Clock model AS3073. My old but very exact clock suffered damage to the PIC16F84 microcontroller and does not work anymore. I know it will be difficult to find this old program, but I would greatly appreciate it if you could help me. (R. C., via email) ● We can’t find any mention of “Quasar” or “AS3073” in any of our magazines. Perhaps they took one of our designs and turned it into a kit without our knowledge. We have published many clock designs, but the one that seems most likely to be a match is the Big-Digit 12/24-Hour Clock (March 2001 issue; siliconchip.au/Article/4235). The software for that project is here (PCBs are also still available): siliconchip.au/ Shop/6/2171 SC Watering System Controller, August 2023: the original V1.2 version software had two serious faults. It was not driving the correct I/O pins as shown in the circuit diagram, and a calculation error could cause it to water on the wrong day. V1.3 fixes those and adds a new SMTP relay service for sending emails (SMTP2GO), as some users have had difficulty opening a free account with SendGrid. Several minor changes were also made to improve the web pages generated by the firmware. The new firmware is available for free download from our website. If upgrading an existing installation, you can just overwrite the four files in the WebMite’s internal file system, then type RUN “RETIC.BAS” and press Enter. The “settings.dat” file will automatically be upgraded. Next Issue: the December 2023 issue is due on sale in newsagents by Monday, November 27th. Expect postal delivery of subscription copies in Australia between November 24th and December 12th. Australia's electronics magazine siliconchip.com.au