Every garage needs a refrigerator to keep drinks cold during sweaty projects, but Rick Fryar’s Sanyo mini fridge was on the blink. Seemingly at random, it would either run the condenser constantly until everything was frozen, or not run the condenser at all. To get it working again without spending a fortune, Fryar used an Arduino to control the refrigerator.

Old refrigerators and cheap modern refrigerators are very basic electromechanical systems. A thermostat flips at the target temperature, switching power to the condenser. It is similar to a conventional water heater or air conditioner.

But modern refrigerators are often more complicated, replacing that simple electromechanical control with electronic control. That makes additional features possible, but it also makes the fridges harder to repair.

In this case, Fryar decided to forego the Sanyo’s control electronics altogether. He replaced those with an Arduino UNO R4 WiFi board, a DHT11 temperature sensor, and a Kasa smart plug. When the Arduino detects that the refrigerator’s temperature is too high, it updates a PHP webpage that tells the Kasa smart plug to switch on power the condenser. When the temperature is too low, it tells the smart plug to switch off power.

For good measure, Fryar also added temperature data logging. Now he knows exactly how cool his beverages are at any given time.