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Advertising Index Altronics.................................11-18 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 Emona Instruments.................. IBC Hare & Forbes..........................OBC Jaycar.............................. IFC,53-60 Keith Rippon Kit Assembly....... 111 Lazer Security........................... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.................. 5 Mouser Electronics....................... 7 Ocean Controls............................. 9 PMD Way................................... 111 SC USB Cable Tester.................. 75 Silicon Chip Pico BackPack...... 42 Silicon Chip Subscriptions........ 97 Silicon Chip Shop............ 106-107 The Loudspeaker Kit.com.......... 89 Tronixlabs.................................. 111 Wagner Electronics....................... 8 Starter we designed that used that type of power supply, and it explained how it worked. Fundamentally, they are pretty simple. At a fixed frequency (50Hz for our mains supply), the impedance of a capacitor is inversely proportional to its value. So with a capacitor connected in series with the supply, the current drawn depends on the capacitor value; double the value, and you roughly double the current that the device draws. The capacitor applies the mains voltage waveform to a bridge rectifier, with its output voltage being clamped by a zener diode or similar to produce a DC rail. Since the capacitor limits the current being fed in, the zener is not destroyed and the desired supply voltage is achieved. So the capacitor value is chosen based on how much current the circuit will consume; making it larger than necessary will just waste power, and if it's too small, the desired supply voltage will not be achieved. So any significant drop in capacitance is likely to stop the device from working. The only solution is to replace that capacitor. Unfortunately, it is not uncommon for X2 capacitors to lose capacitance over time. Money and space pressure sometimes cause manufacturers to choose capacitors that are physically too small to be reliable. Also, by the nature of the way X2 safety capacitors are designed, being exposed to voltage spikes (eg, caused by nearby lightning) will often cause them to lose capacitance. Question about an old project I can’t find anything on your website about the PCB used in the September 1992 LCD Readout. I have the used PCB here for testing; the code on it is 00921. I’d love to make a spare as this unit has become well worn. Mostly I use it for testing displays before fitting them to other equipment. Is this PCB pattern available? I have been subscribed since the early 1980s. I may be able to find the magazine in my attic storage, it would take some time, and it’s hot up there. (J. P., Shailer Park, Qld) ● 00921 does not look like a Silicon Chip PCB code as our codes are usually eight digits long. We can’t find any projects in September 1992 called “LCD Readout”, but there is a General-Purpose 3 1/2Digit Panel Meter project (siliconchip.com.au/Article/5520) that uses an LCD screen. Presumably, that is the one you are referring to. Its PCB code is 04110921, similar to the code you provided. We don’t sell many PCBs from that long ago (as there is virtually no demand), nor do we have any CAD or other computer files for that designs before about 1995. The pattern was published in the article on page 85. It looks like it was made with tape, not on a computer, which is likely why we don’t have any files from back then. We have scanned the PCB pattern, cleaned it up, and added the image to our website’s PCB Patterns download section (siliconchip.com.au/ Shop/10/6329). SC Notes & Errata Dual Hybrid Power Supply part two, March 2022: in Fig.11 on page 85, the metal sheet for the heatsink folds up where shown, not down. Also, the hole in the heatsink should be drilled 25mm from the left edge, not 30mm. Note that link LK1 on the control board, shown in Fig.13 on page 86, needs the shorting block in the upper RDO position, not the lower SDO4 position. Finally, instead of the 15μF tantalum capacitors specified, non-polarised 15μF 50V X7R M5750/2220 ceramics can be used. We supply those in the kits as they are superior to the tantalum caps in virtually every way. Remote Control Range Extender, January 2022: if needed, the optional pull-down resistor at pin 1 of the IC1 (PIC10LF322) on the transmitter should be 1kW rather than 100kW as originally specified. This lower value ensures the resistor is reliably detected and the internal pull-up is always disabled. Programmable Hybrid Lab Supply with WiFi, May & June 2021: on p74 of the June issue, Fig.7 shows the copper layers swapped and thus the SMD components are shown placed on the wrong side of the board and mirrored. The actual locations of some of these parts can be seen in the photo at the bottom of p75 of the same issue, and the diagram has been corrected in the June 2021 online issue. This means that two 1.8kW resistors are under the ESP-32 module. The June 2022 issue is due on sale in newsagents by Thursday 26th of May. Expect postal delivery of subscription copies in Australia between May 24th and June 10th. 112 Silicon Chip Australia's electronics magazine siliconchip.com.au