Ok, here is what i made and it works this way but there is a HUGE problem.
1. I was not able to determine the serial communication with the controller on the thermostat. (Tried detecting the tx/rx traffic, but there was nothing, maybe something enables it, i couldn't figure out)
2. Although it's obvious that this PCB is prepared for some sort of wireless module, i was not able to determine which one or how the main MCU is communicating with it.
3. Great thing is that the thermostat is using bistable/latching relay so it only requires one short pulse from the right side to change the state!3. I was able to trace two lines which are setting the relay, the plan was just to override the thermostat there, and set it to basically never turn ot itself. Even if it does, it will never cause any issues.
4. I have several JDY-08 BLE modules and i was able to set pins at GPIO 01 and GPIO 02 to HIGH/LOW via mobile app/python script
5. BIG PROBLEM IS that by default the wiring at the thermostat controls the relay by setting the certain "side" to LOW and by default both GPIO's that i'm using are set to LOW as the BLE powers up. So the relay starts changing the state very fast.6. For now, i overcome the issue by turning the BLE module on first, setting the GPIOs to HIGH and than putting the batteries for thermostat separately. But i'm worried that the BLE will restart at some point and than i'll have a problem.
7. By looking at this, what would you do in my situation? Is there any other way to change the circuit and control the relay but not damaging the thermostat. I really want to keep it capable of working without BLE module too.
Here is also the docs that i have for the module:
https://amperkot.ru/static/3236/uploads/datasheets/JDY-08.pdfhttps://github.com/kichMan/JDY-08p.s. Since it would probably not be able to do much about the BLE module, should i try some "signal inverting" with a transistors? Is that my only option?