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 pin is also called the control pin because it is used to control the output of the relay. COM - is connected to the device you intend to connect. NC - terminal is connected to the COM ...