Help with debugging...compass on Matek M8Q-5883 stopped working when I added new hardware

Just wondering if anyone has any experience debugging I2C issues. I had a plane that I maidened without any telemetry radio or FPV gear, and the compass worked fine.

I added a Holybro 915MHz SiK radio, a Foxeer Toothless 2 FPV cam, and a Rush Tank Ultimate Plus VTX, and now when I power on it shows the compass as “missing” most times. I couldn’t sort it out, so I ended up just disabling the compass for my next flights, but I’d like to get it back.

I had used the full length of the wires that came with the GPS, plus another inch and a bit. Is this an issue with cable length or just electrical interference? Is there any setting I can adjust in ArduPlane to improve things or do I need to start using shielding or something?

If it’s intermittent then I would suggest you look at a wiring issue.

Hi @cbf123

I2C wires are prone to be “antenna’s” for noise. You added a few components at once which could be the source of the problem. Remove them individually just to identify the “bad guy”. The SiK-radio or the powerful VTX would be my first guess. In this cases distance between the components can make a difference.

If you have a scope available, you could check the I2C signals with and without the VTX or the modem running.

Good luck!!!