Hello all, This question may have been asked before as it seems like an obvious idea for any maker to want to do but I can't seem to find the answer myself.
I'm looking at doing a smart thermostat project. The brain is probably going to be a raspberry pi but I haven't decided yet if I'm going to just have it set up somewhere as a central server type thing and have an arduino or something handling the thermostat replacement part, or have it actually live in the wall where the thermostat control will be.
But either way my question is still the same, powering the device off the thermostat wiring. My house is newer so I have the common 24v wire already at my thermostat. But 24v is still to much for an arduino or raspberry pi. Also, it's 24v AC and I'll need DC. From what I can gather I need a transformer and to build a rectifier bridge, then use a voltage regulator to get it down to a safe 5v for the controller. But I'm having difficulty figuring out exactly what I can use to do this. All the transformers I can find are kind of huge. I'd be surprised if these small lcds and circuitry in store bought thermostats can handle 24 volts, yet there is no where in them for one of these big transformers.
All the how to build a smart thermostat guides I've been able to find don't really go into detail about powering the controller. The only one that did ran a wall wart for a raspberry pi to a regular 110v outlet. Definitely not something that I want to do, I want it to look good and not have any wires or plugs exposed. Plus the power is there, I just have to figure out how to make it usable lol.
So anyone have any advice? Is there a premade breakout board that would work for what I need to do (convert 24v ac into 5v dc), or can anyone give me some advice on finding a small transformer?
As a side question if anyone happens to have any opinions about this. I plan to have remote temperature sensors all over the house eventually. But initially I'm just going to have one at the thermostat. Can anyone think of a good way to thermally separate the DHT22 (temp / humidity sensor I'm going to use) from the rest of the electronics so that the heat from any transformer or controller doesn't effect the readings?