Log and Graph 24V Thermostat Events (Optocoupler + Raspberry Pi) using raspberry

There are a lot of Instructables that show how to make a thermostat. But what if you already have a thermostat, and you want to log or monitor when it turns off and on? This Instructable shows how to use an optocoupler to obtain logic-level DC voltages from a common household programmable thermostat that connects …

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