Alan sez, “Spark.io provides instructions for making your own Nest-like ‘smart’ thermostat. Of course it’s entirely open source, with files on github.”
*The Spark Core served as our connected brain.
*
We display the temperature on a few Adafruit 8×8 LED matrices. The interface for the displays is a common I2C bus.*
The primary sensor is a Honeywell HumidIcon temperature and humidity sensor, which shares the I2C bus with the displays.*
For our MVP, we decided a couple LEDs could represent whether the heat and fan were on. In the end the same pins would be connected to relays instead of the LEDs.*
If you want to save energy when a person’s not home, then you need a way to know when they are home so you can err on the side of comfort again. We added a Panasonic PIR motion detector.All in all, it took about an hour to throw together this breadboarded prototype, although we had to order the components a couple of days beforehand. It took another couple of hours to pull together working firmware (see the software section below).
(Thanks,Alan!)