Configuring a switch as a relay

If you want to connect a relay of some sort (something that accepts a low/high signal, like a camera control) to a PWM output (the servo outputs), you need to do a few quick things. The actual numbers will vary depending on your FC, but here’s what worked for me with a Matek F405-Wing:

  1. Set the channel you want the relay to trigger on as a controller for the first relay (here I’ll assume you want to control the first relay on channel 11):
    RC11_OPTION=28
  2. Set the pin number for the relay you want to control. This is a bit fuzzy, it depends on your flight controller, but try a few out. This is what worked for me, for S6 on my F405-Wing:
    RELAY_PIN=55
  3. Set a servo to act as a GPIO output. I’m assuming here you want SERVO6, though I’m not quite sure how the servo selection maps to the RELAY_PIN selection above. For me, AUXOUT6 and SERVO6 worked:
    SERVO6_FUNCTION=-1

If you’re amazingly lucky, you should be all set. If not, you need to play with the 50 in the RELAY_PIN parameter and the 6 in the SERVO6_FUNCTION until something works.

Last updated on September 11, 2021. For any questions/feedback, email me at hi@stavros.io.