Monitor 24VAC thermostat with MCP23008 Optical Isolated Digital Input

Hardware
1

Could the MCP23008 Optical Isolated Digital Input card be used to determine the on/off state of 24VAC? The purpose is to monitor a household furnace (fan, compressor, heat, air conditioner).

I suspect the internal diodes would result in a string of random 1’s and 0’s if the 24VAC was on, and all zeros if the 24VAC was off.

Thank you.

2

Hi,
Yes, it can be used to detect 24VAC on/off.

Thanks