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 ...

He’s using an Arduino Uno clone called the Seeduino Lotus, which has easy to use Grove connectors on it for interfacing with their plug-in modules. ... and a solid-state relay (SSR) ...

The finished project will switch 240v so they’ve used a transformer to power the logic circuitry and a solid state relay to handle the load switching, with a Dallas 1820 for temperature data.