There’s so much to love about this project! Lenore and Windell crush it again.
The Evil Mad Scientist Simple Relay Shield is an Arduino add-on that lets you use your Arduino (or shield-compatible clone, such as the Diavolino) to control a single electromechanical relay, for switching loads of up to 24 V DC or 40 V AC, at up to 5 A of current. The relay is an “SPDT” type, meaning that it can be used either as a normally-open or normally-closed relay, so that you can choose to either switch on or switch off your load when the output signal from your Arduino is high. When operated as a normally-open relay, it is capable of handling loads up to 10 A.