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.

Tinkerers take note, because Arduino has launched its new Esplora controller, which just so happens to be customizable and open source. The Esplora is derived… ...

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).