Micro-Controllers are amazing devices, with built in memory, a cpu, and input and output ports, they’re are like a complete compter system on a single chip. The digital output ports can directly control small current devices such as LED’s that require 5 volts or so and only a few tens of mili-watts. But what if you want to use a micro-controller to control a device with larger current requirements, for instance a 100 watt light bulb or a fan. One of my favorite ways to accomplish that is to use a relay. A relay is like an electronically contolled switch. Relays come in many different configurations, but today I will be discussing the new 10 Amp Relay Board available at Roslyn Robot Company. This inexpensive board can be controlled by any 5 volts micro-controller, or even by a small switch with a 5 volt power source, and can control devices with power requirement of up to 10 amps, and 250 volts. It features a built in switching transistor to reduce the current required from the micro-controller to a very low value.
This relay board has two screw down connectors. One for the micro-controller side, and one for the device you want to control. On the device side the terminals are labeled NC, COM. and NO. They stand for Normally Closed, Common, and Normally Open respectively, making this a Single Pole Double Throw switch.
The video below does a great job of explaining the different type of swithces.