Wish you'd had the foresight to build the Nest thermostat and get Google's attention? You can't travel back in time, but Spark may give you the next best thing. It just posted a walkthrough showing how to build a smart thermostat of your own. The device centers around both the company's WiFi-equipped Spark Core as well as off-the-shelf displays and sensors from Adafruit, Honeywell and Panasonic. Its software won't compete with anything from Nest, but you can both change the temperature and view historical data from most any modern web browser. More importantly, it's open source -- you can program your own features or simply learn how things tick. While Spark's thermostat won't be an easy DIY project unless you're good with a CNC mill, it's proof that you don't need a vast array of resources to build your own climate controller.