I thought I was all ready to replace a thermostat with an Arduino. I used a multi-meter and bridged some connections to discover the following:
1. bridging 230V (live) with Cool turns on the Aircon outside unit
2. bridging 230V with F2 (brown) turns on internal fan on LOW
Now I would like to insert an Arduino into this circuit, powered from the 230V (using AC to DC module) and not from a battery. The Arduino will control a relay module. Then I realized I do not have a common ground for the Arduino (actually NodeMCU).
The only way to have power run through this circuit is to bridge 230V with either Cool, F1, F2 or F3. I would like to have the Arduino powered on even if the Airco / Fan are not on, since the Arduino should control the relay.
I have two questions:
1. can I use one of the Fan lines as a "common" since it is lower voltage than the live wire?
I assume that in this case there may be some "trickle" of power running from Live to Fan through the AC-DC module. As long as it does not consume a lot of power and does not break the fan I would not care too much. Is this right or am I making a mistake here?
- Are there other options to make this work, without running further wires or using a battery?