I should have known better
I have been working on a control system using a Seeed Xiao processor with a LoRa radio link (also with an OLED display, SD card and RTC). The system seemed to run but not reliably and was causing some head scratching. Was it my code or was it the hardware ?
After lots of playing with the code I decided it must be hardware. I had run a PCB in Fusion Electronics so all the connections were stable and reliable so what else ? …… Stupidity had persuaded me to power the LoRa modue (RFM9x) from the 3V3 stabilised output provided by the Xiao. Which might be fine when in receive mode but when the LoRa goes over to transmitter it takes a whopping surge of current. This was glitching the system.
All the modules are now powered with 5V via their RAW / VCC power input pins and look after their own 3V3 stabilised rail. Problem solved, system working well. Here is a overview image of the board.
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