Adafruit forum member [Stephanie] embarked on a mission to replace the thermostat in her home with one that was far more robust and full of electronic goodies.
Her goal was to build a networked thermostat that allowed for 2-way communications between the base station and any other networked device, such as her laptop or iPhone. She wanted to not only be able to monitor her furnace and air conditioning systems remotely, but to control the units from afar as well.
The brains of the thermostat have changed throughout the project, becoming simpler as time went on. It is now controlled with just an ATMega328 mounted to the back of an LCD display with a Wiznet network module where an Adafruit Ethernet shield used to reside. The thermostat shows the current temperature, set temperature, and time on the front mounted LCD, the latter of which is provided by a Chronodot module. It also has an on board LED that can be seen from afar, indicating whether the heat or air conditioning is running,
Right now the thermostat can be controlled at the unit itself, or remotely using a Telnet session. [Stephanie] is currently happy with the setup, but future plans include creating an iPad application to provide a more user-friendly interface.
If you are interested in learning more, or building one yourself, be sure to swing by her blog for a far more in-depth look at the build process.