If I have an external board which has 2 pins, ground and pin16 which I want to short (as would a mechanical switch) from the Pi, can I link grounds from the Pi to the external board and use the fact that pins 2 & 3 have pull up resistors on them, then send them low and that will effectively short the 2 pins on the external board?

The external board has this diagram:

enter image description here

COM is described Comun (-) .. Its in Spanish where Comun is Common in English.

And I would like to replace the switch show on pin 16 with a Pi:

enter image description here

Some other bits that I imagine are important.

Voltage on pin 16 when not connected = 12V

Current between pin 16 and Com when shorted 1mA (as well as I can measure it)

  • Please draw a circuit diagram. Commented Jan 30, 2022 at 17:57

1 Answer 1


You CAN NOT use a Pi (or indeed ANY computer) to close a switch.

GPIO can output 3.3V or 0V.

You need to use a relay or similar although a transistor can often do the job.

Connecting a Pi to an unknown circuit is likely to result in a dead Pi. If the pin has 12V on it damage is almost inevitable.

  • 1
    Can't say clearer than that. Thank you!
    – S Waye
    Commented Jan 30, 2022 at 22:07

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