OpenTherm compatible hardware for home automation. It includes all the hardware needed for OpenTherm communication. Based on the ESP8266, uses the ESP-07S module with external WiFi antenna. Simply connect to OT terminals and power.
You are free to choose the software as there are a few possibilities here:
- Tasmota, more info here: https://tasmota.github.io/docs/OpenTherm/
- build your own local webserver on the ESP using this great library: https://github.com/ihormelnyk/opentherm_library/
For the library use GPIO 14 for IN pin and GPIO 12 as the OUT pin. For Tasmota configure D6 GPIO 12 as OpenTherm TX (203) and D5 GPIO 14 as OpenTherm RX (202).