Hi all - I got 2 arduino, one nano and one Mega, talking to each other by serial. It's working fine when my laptop is usb-connected to my Mega. But when I unplug the USB cable and power the Mega with a DC adapter 12V, the serial does not seems to work.

Serial1 on mega not working when power by adapter

Topic		Replies	Views
Serial1 Arduino Mega su usb-rs232 adapter Generale	11	1482	May 7, 2021
Garbage serial output when using non-usb power Troubleshooting	3	1900	May 6, 2021
Arduino Mega ADK: Stopped working after using power supply IDE 1.x	1	2341	May 5, 2021
Problem with power supply on arduino mega IDE 1.x	1	501	May 5, 2021
Powering the arduino mega 2560 Motors, Mechanics, Power and CNC	5	2654	May 6, 2021