2023-12-21, 09:05 AM
found it! Thanks for Your help. I swapped the resistors R3 and R6 because I was a little careless in layouting: the resistors names on the PCB are swapped.
@ironman: The voltage divider for the TX is on the Raspi side... like in your schematics ;-)
@ironman: The voltage divider for the TX is on the Raspi side... like in your schematics ;-)