Relays

The heart of the project is the relay.  A relay is an electrically operated switch.  In this case, I'm using a relay that allows me to use 5V (from the Arduino) to switch 110V (to run the XMas lights).

I picked up my relays from eBay.  Just search for "5V power relay".  I bought a quantity of them for about 50 cents each.  They will switch up to 10 Amps of 125V AC.

 

The relay has five terminals on it.  Two connections energize an electromagnet.  In my relay, it requires 5 Volts.  The other three terminals switch the high voltage.  When the electromagnet is not energized, B and C are connected.  When the electromagnet is energized, the switch is pulled over to connect A and C.

You connect the hot (110V) to terminal C, and then connect either A or B to the hot terminal of the outlet.  I chose to connect B to the outlet.  This way, the switch is "on" (outlet is active) even when the Arduino isn't turned on.  If I were to connect A to the outlet, the outlet would be off unless the Arduino was supplying 5V to the relay.

In my next blog entry, I'll discuss the circuit I used to drive these relays.