Monarco HAT is grounded through Raspberry Pi (via 40 pin header). For complex grounding you should also ground GND output of power supply used to power Monarco HAT and Monarco HAT metal case. Could you please try it?

Cheers,
Tomas

I have done some testing on the two new Monarco I have. I'm not sure what is correct but my findings are.

On an older Monarco I have, there is continuity between the pi and the aluminum case of the Monarco. I do not see any voltage leak on this. I think this is because the HDMI port is pressing against the case, providing a ground link.

On the two new Monarco there is no continuity between the pi and aluminum case. None of the Pi touches the case so it is isolated.

This might be normal, it is just something I have never observed before!

Should the Pi be grounded to the aluminum case?

Cheers

Mike

I have grounded the aluminum case the Monarco HAT comes in. Yet I still have this odd leakage. It's the same Monarco as the one I am having strange Modbus issues with.

Cheers

Mike

do you use grounding which was part of the Monarco HAT package? (ring terminal with screew)

Cheers,
Tomas