I bought a nest gen 2 thermostat to play with a open source project that revives old nest thermostats (nolongerevil.com). Since I don’t want to install it into the home, because it will be a toy. I was thinking of building a test rig using a arduino or esp32 to simulate a HVAC and indoor temperature. I’m IT guy, not a HVAC guy, I think this would be a good learning project. Any suggestions?
I used to work as a PQI contractor at Nest, and we actually had test setups like this in the office that were just a circuit breadboard mounted on a plate behind the thermostat. The thermostat doesn't really "communicate" with the HVAC control system at all (all it does is just send ~3V along the circuits based on its current mode), so as long as you have the circuits routed properly on your board, the thermostat will think it's connected to a real system.
The stock firmware doesn't let you go above a certain temp (like 80F or something, I forget the exact limit). But if your custom firmware allows it, the only thing that would realistically happen is that it just runs a 3V circuit to what it thinks is the heater, infinitely, since nothing is actually causing the ambient temperature to raise at all. The ambient temp reading comes from a sensor on the thermostat, itself.
Canonical_Warlock@lemmy.dbzer0.com 14 minutes ago
HVAC-R tech here.
Not sure what you mean about simulating high temps on the thermostat. If you want to trick the thermostat into seeing a higher temp than it is actually at then you would need to find the temp sensor on the thermostat (usually a thermistor) and replace it with something where you can manually control the input like a potentiometer if there was a thermistor there.
If you’re talking about simulating calls from your thermostat to your hvac system, then you can usually do that with just some jumper wires if your hvac system has a built in transformer (almost all new systems do). You just remove the thermostat and jumper the hot wire (R or Rc) to whatever call you want to make.
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