2 layers68.6 × 53.3 mm

Arduino OpenTherm shield
anway0404/Arduino_OpenTherm_shield
Arduino hardware shield to send and receive data from Opentherm devices
54 parts3CERN-OHL-P-2.0
KiCad boards from 2 GitHub repositories tagged “opentherm-slave”, the most starred first; open any of them in PCBKit.

anway0404/Arduino_OpenTherm_shield
Arduino hardware shield to send and receive data from Opentherm devices

michpro/Arduino_OpenTherm_shield
Arduino hardware shield to send and receive data from OpenTherm devices