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 ...

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 ...