Where I actually started, and it isn't the thermostat Before telling the story, I need to say who did it, or none of it will make sense. I'm a senior software engineer. I can design systems, read a spec, debug ugly problems. About hardware I knew close to nothing . The only program I had ever written for an ESP32 was a loop that blinked some LEDs to a beat: a digitalWrite() inside a delay() , and the satisfaction of someone who has just invented fire. I had never soldered anything ...