I needed a way to measure the temperature of our furnace's smoke. I wanted an insight into how pure our wood was and how optimal our furnace parameters are set. I also wanted a way to easily automate shutting off some valves after our furnace stopped burning to prevent condensation buildup and thermal losses. So I started writing this simple code to send temperature measured by a K-type thermocouple and translated by the MAX6675 TC converter over on MQTT, where I can read it with Home Assistant and create some NodeRED flows for the valves. The PCB is still being built, so I have no idea whether or not its functional. It should work electrically, but I haven't designed many boards before, so I could be missing something perfectly obvious to experienced designers. The main idea behind adding a battery to the project, was to enable a simple backup incase power is lost, but I just decided to use is as a portable or powered sensor, so I can experiment with shutting off the ESP and waking it up, as well as testing how long a battery lasts. I might not even use the battery in the final installation of my sensor, as I haven't made a proper power changeover circuit which would funciton without a mechanical removal of a jack.