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 ...

Before I start, it is only fair to mention that I have (2022) replaced this entire setup with Loxone miniservers (in the 24x28 in wall boxes) and Loxone wired tree devices (14x14 in wall boxes). This ...