This module is the master side of the Opentherm Gateway as original designed bij Schelte Bron (https://otgw.tclcode.com/) and to be used as a shield on a arduino based Wemos/Lolin ESP8266 module. In opentherm the master is the thermostat and the slave is the boiler. Therefore this module is to simulate a thermostat in arduino to be able to talk to an opentherm boiler.

There are a few other designs of the opentherm gateway master and slaves already. Mine is not any different and just adds another location from where you can get working opentherm arduino module.

I also have a opentherm slave shield in my Tindie store.

To use with any arduino opentherm library like https://github.com/jpraus/arduino-opentherm and https://github.com/ihormelnyk/opentherm_library

Define D5 as the opentherm master-output and D6 as the opentherm master-input in the library you use. On D7 there is a DS18b20 1-wire dallas temperature sensor so you can use this module also for local temperature measure so it can act as a real thermostat. The module needs only 3.3v and GND (no 5v required for the master shield) for powering it. So to use the module you need to connect GND, 3.3v, D5, D6 and D7 or just install the module on top of the Wemos as a true shield.

This opentherm master shield is also compatible with the Tasmota Opentherm plugin. See pictures how to configure this module in Tasmota. For now you will need to compile Tasmota with Opentherm yourself as Tasmota doesn't include the opentherm module in the production build yet. See the Tasmota Opentherm page how to compile it.

Also you can use the ESPHome-OpenTherm addon which works great also. But make sure you change the pin numbers in the opentherm_component.h file of the addon as described in the readme to reflect the correct pin numbers as mentioned above.

Another usable project is the one from Jeroen88/Metriot. He also sells a similar shield on Tindie intended for the S2 mini. Be sure you modify the defined pins in the code to match the pins of the shield mentioned above if you plan to use his code.