I'm interested in building a monitoring system for my 4-zone HVAC system, which will require monitoring between 8 and 12 separate 24VAC circuits. Following a suggestion in this question, I plan to use MID400 optocouplers to convert the 24VAC signals to digital, but I'm not sure how to get the 12 separate inputs into the PI.


You could look at the MCP23017 i2c 16 input/output port expander.

It gives you 16 i/o ports and communicates to the Raspberry Pi via I2C so it only takes 2 pins.

  • Looks like a good solution; ordering one (and a batch of MID400s) soon., – TomG Feb 20 '13 at 3:08

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