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It seems like I need to configure the LCD panel, but I can’t get to that via the BackPack’s USB serial port. Using standard Windows serial terminal programs (eg, PuTTY), I can get a basic serial connection at 38400 baud (8-N-1), and when I press a key on my keyboard, the red LED on the BackPack lights up. But there is no reply from the BackPack and no response to any configuration commands. Secondly, at initial power-up, a status page briefly appears before the Frequency Reference main page. After a few seconds, the main page disappears Advertising Index Altronics.................................49-52 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 ElectroneX................................... 13 element14..................................... 7 Emona Instruments.................. IBC Hare & Forbes..........................OBC Jaycar...................... IFC, 11, 15, 39, ..............................71, 78-79, 91, 99 Keith Rippon Kit Assembly....... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.................. 9 and is replaced by the status page. That cycle repeats 4-6 times before the unit finally ‘settles down’ and remains on the main page. I suspect the problem may be caused by the VK2828U7G5LF GPS module trying to get a good fix, but I’m not sure. I’d appreciate any help you can provide for these issues. (D. P., Enon, Ohio, USA) ● You’re on the right track. The red LED that is flashing is driven by IC2 on the BackPack, so it means that data is being received over the USB link. Some touchscreens have a different touch panel orientation, meaning that the ‘factory’ calibration doesn’t work. To access the BASIC console, you need to send a Ctrl-C (from the serial console) to break out of the running program, after which you can issue commands. Running the “GUI CALIBRATE” procedure is all that is needed once you are in the BASIC console. After that, power-cycle the BackPack to restart the main program. The second problem could be either a power issue causing the Micromite processor to reset or perhaps the (poorly calibrated) touch controller sending commands when touches aren’t occurring. The latter should right itself once the touch controller has been calibrated. If that doesn’t fix it, it could be a problem with either the Micromite V2 PCB or the Frequency Reference PCB. A likely candidate on the Micromite Mouser Electronics....................... 4 Oatley Electronics..................... 111 SC GPS Analog Clock................. 58 SC USB Cable Tester.................. 98 SC Vintage Radio PDFs............ 109 Silicon Chip PDFs on USB......... 14 Silicon Chip Shop............ 104-105 Silicon Chip Subscriptions........ 53 Silicon Chip Test Tweezers....... 10 Silicon Chip 500W Amplifier... 107 The Loudspeaker Kit.com.......... 12 Tronixlabs.................................. 111 Wagner Electronics..................... 85 112 Silicon Chip Errata and Next Issue SC Raspberry Pi Pico W............. 77 is the 47µF tantalum/10µF ceramic capacitor that bypasses IC1’s core regulator. If this capacitor has been mixed up with the other capacitors or is somehow faulty, it can definitely cause stability problems. Why no more Mosfet amplifiers? I have noticed that your amplifier module designs almost never use Mosfets. Why is that? They seemed popular in 1980s kits. I have been pondering lately why your amplifier modules never use switch-mode power supplies. They are cheap now and super lightweight. (J. A., via email) ● We don’t design audio amplifiers using Mosfets because they have few advantages in that role. They produce inherently more distortion and are harder to drive. They are arguably more robust, but a properly designed BJT-based amplifier is reliable enough. For more details, see Douglas Self’s Audio Power Amplifier Design Handbook (reviewed in the March 2010 issue; siliconchip.au/Article/89). We have a Class-D amplifier project in this issue (from page 26) that uses a switch-mode power supply. In a linear amplifier, we would be concerned that switching noise might adversely affect the amplifier’s performance. Still, a Class-D amplifier already has a lot of switching noise, so it’s unlikely to matter in that case. SC Secure Remote Mains Switch, July & August 2022: the paragraph at the end of page 84 in the August 2022 issue says to use 10A-rated mains wire; however, some of the wiring can use 7.5A-rated mains wire, as explained later in the article. Capacitor Discharge Welder, March & April 2022: the front panel drilling diagram, Fig.16, on page 109 of the April 2022 issue has two errors. It is shown as 130mm tall, while the base of the case, where the holes are drilled, is only 105mm tall. Also, the distance between the VOLTS and TIME holes is shown as 60mm but incorrectly drawn as 85mm. A revised diagram/template that fixes these errors can be downloaded from siliconchip.au/Shop/6/6306 Programmable Hybrid Lab Supply with WiFi, May & June 2021: the Altronics ESP32 module specified in the parts list may have rows of pins too widely spaced to fit the control PCB. The revised control PCB used in a later project, code 18104212 (siliconchip.com.au/Shop/8/5826) has an extra row of pins to accommodate different module widths. This can be used with the Hybrid Lab Supply project as long as the correct shorting links are bridged (ie, those indicated with arrows on the silkscreen). Next Issue: the May 2023 issue is due on sale in newsagents by Thursday, April 27th. Expect postal delivery of subscription copies in Australia between April 25th and May 12th. Australia's electronics magazine siliconchip.com.au