This evening after a session of DarkMatter great progress was made on the SonoffMQTT project. This project aims to replace the firmware on a Sonoff with custom firmware so that it is accessible via MQTT instead of the supplied eWeLink. Having it available on MQTT means it will plug directly into Home Assistant and will be cointrollable from there. After soldering some headers into the board, I was able to power it externally (not mains) and flash it using Arduino IDE.

Flashing Sonoff with custom firmware. To do this you have to externally power the Sonoff with 3.3v via the header. This, however, does not allow you to operate the relay because the coil is on the 5v relay.

A pretty productive day. The code has now been refactored to accept simple non-json type commands on specific topics ie <uuid>/relay/0/set. This allows the relays to work with the "switch" function in Home Assistant.

After some refactoring of the dual relay board code, it's now reporting temperature, humidity on MQTT topics. This means it will work correctly with Home Assistant.