This PCB is intended to act as an interface between an Arduino/ESP8266 and an OpenTherm-enabled appliance. This is great if you're looking to control a boiler or HVAC system as part of a home automation project.
I created this PCB as part of my homebridge-nodemcu-boiler project which makes use of this PCB to control my boiler via Siri.
The PCB is completely through-hole and is therefore straight forward to assemble. The silkscreen layer indicates which components go where as well as which direction they should face (if that matters for the component).
Please note: there are 5 places on the PCB where two leads from different components must go through the same hole. Whilst this is slightly inconvenient, it was the only way to get the PCB to such a small size. To help you remember, the silkscreen layer should also include small
! marks at holes where this is required.
The PCB has three extra pins available (labelled
SENSOR) where you can optionally solder in a temperature sensor like the TMP36 or a DHT11 module, providing it with
GND (marked with
-) and a data out pin which corresponds to a pin on the header block. This is completely optional and the PCB will function normally even without anything soldered in these holes.
OpenTherm polarity does not matter, so the two OpenTherm wires can go into either of the screw terminals
Pins on the Arduino header are marked just where the optocouplers will go. From top to bottom (with the screw terminal on the left), the pins are:
IN. As mentioned above, the
TMP provides temperature date if you have soldered in your own temperature sensor. If you have not, that is fine, you do not have to use this pin.
The PCB does not power your device, you must do that separately
VCC will work either at 5 or 3.3 volts (so it will work with both the ESP8266/NodeMCU and an Arduino)
The PCB visible in the pictures is the first generation of the board and lacks some silkscreen markings which are mentioned above (which are present in the version provided here)
The dimensions are
|Qty||Value||Device||Package||Parts||Description||MF||MPN||Aliexpress or Ebay link|
|2||PC817||Optocoupler||THT||AliExpress: 50pcs PC817 EL817 817 817C FL817C PS817C DIP Opt...|
|1||2 pin||Screw Terminal||THT||AliExpress: 10Pcs/lot KF301-5.0-2P KF301-3P KF301-4P Pitch 5...|
|1||BC558B||Transistor||THT||AliExpress: 20PCS BC558B BC558 TO-92|
|2||330Ω||Resistor||THT||AliExpress: 1 Pack 300Pcs 10 -1M Ohm 1/4w Resistance 1% Meta...|
|1||220Ω||Resistor||THT||AliExpress: 1 Pack 300Pcs 10 -1M Ohm 1/4w Resistance 1% Meta...|
|1||100Ω||Resistor||THT||AliExpress: 1 Pack 300Pcs 10 -1M Ohm 1/4w Resistance 1% Meta...|
|1||1KΩ||Resistor||THT||AliExpress: 1 Pack 300Pcs 10 -1M Ohm 1/4w Resistance 1% Meta...|
|1||510Ω||Resistor||THT||AliExpress: 1 Pack 300Pcs 10 -1M Ohm 1/4w Resistance 1% Meta...|
|1||4V7||Zener Diode||THT||AliExpress: MCIGICM 1W (3V to 33V) 250 Pcs 25 Values 1W Zene...|
|1||4V3||Zener Diode||THT||AliExpress: MCIGICM 1W (3V to 33V) 250 Pcs 25 Values 1W Zene...|
|1||15V||Zener Diode||THT||AliExpress: MCIGICM 1W (3V to 33V) 250 Pcs 25 Values 1W Zene...|
|4||1N4148||Diode||THT||AliExpress: 1N4001 1N4002 1N4003 1N4004 1N4005 1N4007 1N4148...|
|1||5 pin||Pin Header||THT|