Communication with Arduino

Good evening!
Due to programming work on Pixracer, I have a problem: I need to give an arduino a (short) electrical signal. I saw there is the possibility of using UART. So I connected UART (arduino–>Pixracer) and GNDs.
Afterwards, I took the code of the documentations:
Pixracer should send a signal: hal.uartB->begin(57600); hal.uartB->write(10) bzw. hal.uartB->printf(“text”);
So is there anything wrong? Which uart have I to use for my reasons?
And finally the code in arduino, adapted from:
Is there everything correct? I get no signal; I despair!!! :sob:
Thanks for all who take their time to answer my questions getting on your nerves!! :slight_smile:

Take a look at this. MAVLink and Arduino: step by step