I'm currently trying to create an interface between my Arduino-compatible (NodeMCU) and my OpenTherm boiler. OpenTherm is a protocol used by some boilers (mainly in Europe) which allows for the control of boiler temperature and other things like the boiler state; this is usually done by a stand-alone OpenTherm-compatible thermostat wired into the boiler. The protocol allows you to send and receive information from the boiler. However, the protocol operates on AC, and at a much higher voltage than an Arduino, thus, an OpenTherm to TTL levels adapter is needed
I've found myself upon this tutorial which seems to be the only one available relating exactly to what I am trying to accomplish. The writer of the article has made an Arduino Library which allows for the Arduino to communicate directly with OpenTherm via this circuit:
X2 are the Opentherm wires (doesn't matter which); the
OUT go directly into the Arduino's GPIOs. Finally, the
VCC goes to Arduino 3.3 or 5v and the
GND to Arduino ground.
Whilst the circuit does function perfectly, I felt that this was slightly overcomplicated as it involved numerous different components like multiple diodes. This would require the purchasing of a wide range of components which is not desired. As a result, I did some more digging and found myself upon this question on the forum. Whilst the question is not the same as mine, the top answer notes that:
• any of these parts will the same or better job.
What was linked was optotriacs. The answer also states that:
That circuit provides a DC current shunt to an AC rectified source and series load from a 24Vac furnace transformer. All it has to drive is a logic driver to activate the furnace, the same way a reed relay might work.
Now, whilst it does seem that the original poster of the question asked for more clarity on how exactly the optotriacs could be used in this situation, I feel the person answering does not give a sufficient enough answer for the skill level of the person asking.
Similarly, I am not super skilled with electronics and found the explanation of the proposed solution rather lacking. As a result, I am asking this question.
My question is: How can the above circuit be replaced with a simpler solution? Is all that circuitry required to allow the communication from 5v DC to 24v AC and back? The answer linked above mentions optotriacs, how could they be used in this situation to simplify the circuit?
P.S. The NodeMCUs logic voltage is 3.3V