I have a relay that I can activate it with a PIN to GND.
I have connected that relay to a separate power supply, different from the used for the raspberry. As I have read, I can't supply GND using GPIO due to LOW is not the same as GND.
How can I activate that relay that only is activated by GND?
EDIT: Event I would able to supply GND from RPI, the relay doesn't work. In order to work I need to join the GND from external power supply and RPI but this causes false positives in some GPIOs when reading from them