They used an Arduino to control the temperature and a motor shield to power the peltier plate. It kind of worked but they discovered it was difficult to assess the physical state of the chocolate.

The build uses the osPID Open Source PID controller we saw last week that comes with inputs for a thermocouple and pair of relays capable of switching a hot plate or immersion heater.

I can find regular temperature switches (if temp >80, then turn on), but that won't help if its warmer outside than inside (often the case in the first half of the day).