But when Arduino uses the power supply from the PC the RX and TX pins flash irregularly when i turn on the ignition.
I didn't add anything between the 0V PC and the vehicle's electrical, just use a USB cable to connect the Arduino with the PC. Can you tell me how to make a good earth? I am a beginner in the electrical.
now i still use arduino pcb board, so still use the voltage regulator from arduino. i tried to use battery as power supply and use usb to ttl to connect it with PC, I only connected tx, rx and ground pins only, but the problem is still there. does adding MOV in VIN solve the problem?