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Home-Made Thermostat

If you've ever looked into automating the temperature control in your home, you will quickly have found out that it's not a cheap prospect. The cheapest network-connected thermostat I could find was $450 US, and that's just a start. So, I decided to build my own thermostat, using an Arduino and some other components.

My thermostat directly controls my HVAC unit, which has a standard four-wire interface. One wire is common, and there is one wire for each of Heat, Cool (A/C), and Fan. I'm using an LM35 to measure the temperature, three relays to connect the HVAC, a nice 20x2 LCD display for status, and some buttons and switches, all mounted into a project box. Since the Arduino has a built-in USB interface, I use that to provide status back to the computer, and allow the computer to issue commands.

Here is the project before assembly, as a mess on my desk:

Once all the kinks were worked out, I assembled it all into this project box:

And here is the final unit, mounted to my wall: I've updated my EventMachine software to support setting the temperature. Now, when I leave my home, the temperature is adjusted so that I don't waste electricity with too much cooling. I've also updated my Touchscreen software to display the current status and allow adjusting of the temperature:

It was a fun project, and saved me about $350!

BONUS

See the source code I wrote for my Arduino here:
Arduino Thermostat Source Code
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