I'm having trouble using one of the GPIO pins. When trying to use BCM 12 (PIN 32 in BOARD mode, name: GPIO26) as an output, I get the warning:
RuntimeWarning: This channel is already in use, continuing anyway.
gpio readall, this pin is not in use and correctly set to out mode. Disabling the warnings didn't help.
This pin is supposed to be the trigger for an ultrasound sensor. My current system uses four of those, with triggers on other pins, and three of them work perfectly. The one on BCM 12, however, does not seem to switch the trigger on. The sensor works fine on other pins, yet I cannot switch to another pin, since all others are used for something else.
Is it possible that BCM 12 is broken or being used by a service I have inadvertently activated? I have double, triple and quadruple checked that it is not a wiring problem.
I am using Raspbian Stretch (the issue is the same on Jessie) on a Raspberry PI 3 B. All packages are up to date, including the firmware. There are four ultrasound sensors connected, a gyro-sensor, a gps-sensor, six ESCs (including motors), and all work fine with said ultrasound sensor being the only exception. For accessing the pins, I use PIGPIOD and python 3.
Can anyone help? Best regards Reto