I face the following issue. I connected my RasPi (3b) with an Arduino Uno via RX/TX and a logic level converter. UART comms from the RasPi to the Arduino and vice-versa work fine on minicom and serial monitor. It also works fine from my qt program to the serial monitor, but as soon as I start a Serial.begin(9600,8N1) or Serial.begin(9600) function on the Arduino there seems to be no communication anymore at all between the two. Neither the expected result (toggle an LED, works from serial monitor), nor any blinking of the tx/ex LEDs onboard anymore. Issue occurs no matter if I provide power to the Arduino via USB or the 9v powercable. Any suggestions?

  • Are you saying the USB connection works, but as soon as you try and use pins 0/1 the USB connection breaks? That's logical, since the USB connection uses pins 0/1. There is only one Serial on the Uno, and that is pins 0/1, whether you directly wire them or use the USB port.
    – Majenko
    Mar 7, 2017 at 10:41
  • The funny thing is it works when my raspberry is wired to the Arduino and the Arduino is connected to my Mac on USB to read the serial monitor (there is no connection between the raspberry and the mac) Mar 7, 2017 at 10:44
  • Mac (USB) - Arduino - (Wire TX/RX) Raspberry. Even if I disconnect the Mac (and toggle an LED for example when anything is received on the Arduino) nothing happens... Mar 7, 2017 at 10:46
  • "no external UART comms ...": in those cases, try to see if internal UART comms works first.
    – dannyf
    May 8, 2017 at 23:09

1 Answer 1


Solved. I double crossed the rx/tx connection which made it wrong again... stupidity attacks

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