I'm powering a GSM shield with a 10 volts battery. Arduino Mega is powered through USB. Doing like this, the communications between both through the serial port 1 is OK.
However, when I also power Arduino with the 10 volts battery through Vin, the serial comunication stops to work. I've used another trafo (in order to try it with and independent power supply) but the result is the same. No communication.
Communication between PC and Arduino though USB to debug my code is always fine.
¿Does anyone know why this is happening?
Have you connected the 0v ( gnd) points together
Yes, all GND are connected together.
I've also tried to power Arduino Mega with a USB Charger and serial communication between Arduino and GSM shield doesn't work too. It's strange... it only works when Arduino is powered through USB connected to a PC.
Does anyone see the problem?
Using jack to power arduino doesn't work either.
I don't know what else to do...