At points I might do something that might be dangerous because I'm comfortable with some tools or techniques but please always use your common sense and don't try everything you see here.

In this quick Arduino tutorial I will explain how you can control a relay using the Arduino Board, one 1K and one 10K resistors, 1 BC547 transistor, one 6V or 12V relay, one 1N4007 diode and a 12V fan ...

In this project, we are going to build something very simple project, a temperature controlled relay that is used to turn on a dc fan. You can actually change the DC Fan to other electrical devices ...

An Arduino measures the temperature ... ‘on’ position and turning the unit on/off via a relay connected to the 120vac line would work just as well.

You can just leave the power relay on top of the ... it stays on to signal your Arduino. While great with a fan, this programmable switch you’ve created will work with other devices, too.