Custom node RAK3172 - todos

Hi all,

I am currently designing a custom node based on the RAK3172 bare module. This question might sound vague, but are there to-dos or rules I have to pay extra attention to?
One example: this one on VREF


Hi @pico ,

This is something we can probably create and add on our documentation. However, some practices like the link you shared is specific to certain applications.

I will share some points that I think are generic (*some of the ideas here are already in the RAK3172 documentation:

  1. Bypass capacitors near the supply line.
  2. Removal of ground plane in all layers on the RF pinout (if non-IPEX variant).
  3. Make provision on BOOT pin for connection to VDD. This is needed for device recovery via STM32WL UART bootloader.
  4. Reserve UART2 for firmware update and use UART1 for external peripheral/modules (even AT commands).
  5. Make headers or provision for in-circuit external debugger tools like ST-link.
  6. Make reset pin accessible and add bypass capacitor.
  7. Consider to make the footprint compatible with RAK11720 (it has additional two pins for BLE - pins 33 and 34). In case you’ll need BLE in the future.
  8. Do not use pin 27 (PB12). It is internally connected to a resistor.
  9. ESD protection on RF trace if ESD exposure is possible with antenna handling.
  10. Remember that RF pinout is only available on non-IPEX variant. If your RAK3172 has IPEX connector, the RF pinout is floating and not connected internally.

Great! Thanks for the guidance.
I’ll be happy to contribute to document.

So the BOOT pin can float or is it pulled down?

Normally it is pulled down. Then you have to pull it up if you will recover a bricked STM32WL chip using UART bootloader of STM32.

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