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 ...
This simple temperature relay circuit can be used to signal a fire or setpoint for temperature monitoring function. You need to adjust P1 so that T1’s base voltage is 0.5V smaller than the emitter ...