Manufacturers usually design their products to function normally for a longer time even if they get hot. But sometimes it is better to be sure and better add some extra protection. So if your external hard drive is intensively used then it can get really hot. So adding additional fan wouldn’t hurt. So this project is what it does – cools device when it is needed. It is based on PIC12F675 microcontroller which reads temperature from LM35 temperature sensor and then enables fan depending on temperature.

So this is pretty simple thermostat that controls fan gradually depending on temperature – the hotter the faster fan turns. It is basically done by using a reference table stored in MCU. So this is simple design and can be used for more variety of devices to keep them cooler.