LEDs and resistors

LED (right) stands for "Light Emitting Diode".

A diode is an electronics component that only lets electricity flow in one direction. One of its leads is longer than the other: that's the positive lead, the one that goes to your 5v connection. The shorter wire, the negative lead, goes to ground (Gnd).

When you put an LED in a circuit, you need to put a resistor in series with it to limit the current that flows through the LED. Otherwise the LED will burn out right away.

A resistor (left) limits the amount of current flowing through a wire. If you think of the wire as being a pipe electricity flows through, you can think of a resistor as being a narrow part of that pipe, that chokes off the flow.

Resistors don't have positive and negative sides -- you can hook them up in either direction and they work just the same.

Wire up your LED

Let's make sure the LED turns on. We'll use the Arduino just as a 5 volt power source, for now.

Plug your Arduino in to the computer's USB port. A power light should come on.

Wire up your LED as shown at right. Plug the LED into your breadboard, remembering which side is the longer leg (+). You might have to bend the legs a little to get them both to plug in. That's fine.

Connect a wire (a black one if possible) from the LED's - leg to the Arduino's GND. (The Arduino has several GND ports. You can use any of them -- they're all the same.)

Run another wire from the Arduino's 5v to the breadboard. Then connect a resistor from that wire to the LED's + leg.

Your LED should light up!