Using an ESP8266 ESP-01 module and an Arduino Pro Mini 3.3V I wirelessly update all outputs from my thermostat to here for data analysis and because it's cool.
This requires a voltage divided rectifier since thermostats run at least 24 VAC RMS.
Nest Thermostat Data Logging
ESP8266 with a ds18b20 temperature sensor mounted in the HVAC plenum right above the air handler.
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