A $169 DIY AC controller that saves 450 kWh a month
The parts were fine. The plan wasn't: one small board doesn't have enough pins to run a screen, a network chip, a CO2 sensor, and two infrared emitters at once, and the AC itself spoke a protocol none of the ready-made decoders recognized. Here is the whole DIY smart AC controller build, all $169.70 of it.