5 | Connect an LED (if you're using an older board)

The first sketch you will upload to the Arduino board blinks an LED. The Arduino Diecimila (and the original Arduino NG) has a built-in resistor and LED on pin 13. On Arduino NG Rev. C and pre-NG Arduino boards, however, pin 13 does not have a built-in LED. On these boards, you'll need to connect the positive (longer) leg of an LED to pin 13 and the negative (shorter) leg to ground (marked "GND"). The LED will typically be flat on the side with the negative leg. Normally, you also need to use a resistor with the LED, but these boards have a resistor built-in on pin 13. The text of the Arduino getting started guide is licensed under a Creative Commons Attribution-ShareAlike 3.0 License. Code samples in the guide are released into the public domain.