Arduino relay circuit and Arduino relay code:
In this video we’ll learn how to use a SainSmart 4-Channel 5V relay module with an Arduino. We also discuss the SainSmart relay board’s capability, its use of optocouplers for optoisolation, and how to hook up the Arduino relay circuit. We use the Arduino to switch a light on and off, demonstrating the relay’s ability to control high voltage loads with an Arduino.

Where you can buy the tools and materials:
[✓] Arduino Uno http://amzn.to/2zqDqXE
[✓] SainSmart 4-Channel Relay Module http://amzn.to/2xUvJN7
[✓] YwRobot Breadboard Power Supply Module http://amzn.to/2yDuwsb
[✓] 9V Power Adapter http://amzn.to/2yDSF1F
[✓] Extension Cord http://amzn.to/2xVKxuC
[✓] Breadboards http://amzn.to/2yDvapn
[✓] Jumper wires http://amzn.to/2zpiT5E
[✓] Light seen in the video http://amzn.to/2zrgTto

Links:

More on Optocouplers
http://searchnetworking.techtarget.co...
http://www.futureelectronics.com/en/o...

More on Wiring Relays:
http://www.how-to-wire-it.com/how-to-...
https://electronics.stackexchange.com...
http://www.dummies.com/programming/el...
https://www.hunker.com/12536777/how-t...