4 layers234.5 × 81 mm

ZoneTherm
Max-Brants/ZoneTherm
A normal OpenTherm setup is one thermostat talking to one boiler. ZoneTherm sits in the middle of seven of those conversations at once:
239 parts
Boards in 1 GitHub repository, designed in KiCad, that use the PC817XNNIP1B by Sharp Microelectronics (-30℃~+100℃ 1.2V 18us 200mV@20mA,1mA 200mW 50mA 50mA 5kV 6V 80V DC Phototransistor SMD Transistor, Photovoltaic Output Optoisolators ROHS). See how each wires it, with its parts, size, README and files; the PC817XNNIP1B’s symbol, footprint and pinout are on its own page.

Max-Brants/ZoneTherm
A normal OpenTherm setup is one thermostat talking to one boiler. ZoneTherm sits in the middle of seven of those conversations at once: