If you have not heard of the sous-vide method of cooking you are not alone. This method uses a low temperature water bath to cook food in airtight plastic bags. Because the temperatures are much lower than normal the cooking time must be much longer and the actual temperature is very critical. The advantage is that the food is heated evenly without overcooking the outside. Since the food is bagged, it also retains moisture.
[Brian] put together a sous-vide control system to automatically maintain the correct temperature of a rice cooker. A temperature control unit was sourced on eBay for about $15. This is not a bad deal considering it has an LED display, control buttons, built-in relay and thermometer input. The control unit is mounted inside a project box with a few other components. The 120 volt AC line comes into the box where the neutral and ground are connected to the control unit and a standard outlet. The hot wire is connected directly to the control unit which determines if the hot wire is or isn’t connected to the outlet by using its built-in relay.
A 3.5 mm headphone jack is also mounted into the project box to make it possible to connect the thermometer. Check out how [Brain] prevents the thermometer from contacting the rice cooker, he mounted it inside a whisk. Keeping the thermometer away from the rice cooker inner surface ensures an accurate temperature reading of the water, not the heating element. Based on the signal received from the thermometer, the control unit determines whether or not to turn on the rice cooker.
Because this project uses a standard outlet as its interface to the cooker, it could be used for anything that is dependent on the ambient temperature. It could turn on an AC unit if it’s too hot or control your 3D Printer’s heated build enclosure.