SparkFun’s latest tutorial shows you how to work with relays. A relay is an electrically operated switch. In this case, they’re using it to switch a 120V AC outlet. The article carries the standard warnings about how not to kill yourself with AC (plus some non sequitor linking throughout). As an extra precaution, they chose a GFI outlet. You probably know how a relay works, but it’s worth seeing how they implemented it. They use a transistor to prevent overloading the microcontroller’s GPIO pin. The control pin is pulled to ground to keep the relay off. A diode is placed across the relay coil to manage the power flow when it discharges. An indicator LED is included to show when the relay closes. This is a great foundation for an automation project, or maybe you just want to terrorize your cat.