This module is the slave 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 bases Wemos/Lolin ESP8266 module. In opentherm the master is the thermostat and the slave is the boiler. Therefore this module is to simulate a boiler in arduino to be able to talk to an opentherm thermostat.

There are a few other designs of the opentherm gateway master and slaves already. But my design uses 5v for the 24v boost converter instead of 3.3v so it should be able to provide a bit more power if necessary.

I also have a Opentherm master shield in stock. You can get it here.

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

Define D1 as the opentherm slave-output and D2 as the opentherm slave-input in the library you use. The module is powered directly from the Wemos from the 5v input. This is then boosted to 24v on the shield to be able to work with opentherm. The 3.3v input on the shield is used for the GPIO connections. So you need to connect GND, 5V, 3.3v, D1 and D2 to use this module, or just connect it on top of the Wemos as a true shield.