I am currently setting up a Pi with the Automation HAT to monitor some security outputs at my home. The signals are 12V based. I was reviewing the schematics for the Automation HAT and I had a few questions.
I see a protection stage with a 20k resistor and 3V3 zener clamp but nothing afterwards. The signals seem to go straight to the IO pins after the zener clamp.
I have been very careful to ensure the 12V supply is switched off before switching off the 5V supply to the Pi. Unfortunately, information regarding the robustness of the GPIO pins on the Pi seems rather scarce. If I switch off the 5V supply to the Pi before removing the 12V to the Automation HAT signal input, could I potentially damage the Pi as the pins will be driven by a voltage without the proper supply?
Has anyone experienced any problems depowering the Pi with signals still attached?