Testing the Board
What if the very first example, "blink an LED," didn't work? Wouldn't that be a bit depressing? Let's figure out what to do.
Before you start blaming your project, you should make sure that a few things are in order, as airline pilots do when they go through a checklist to make sure that the airplane will be flying properly before takeoff:
Plug your Arduino into a USB plug on your computer.
Make sure the computer is on (yes, it sounds silly, but it has happened). If the green light marked PWR turns on, this means that the computer is powering the board. If the LED seems very faint, something is wrong with the power: try a different USB cable and inspect the computer's USB port and the Arduino's USB plug to see whether there is any damage. If all else fails, try a different USB port on your computer or a different computer entirely.
If the Arduino is brand new, the yellow LED marked L will start blinking in a bit of a nervous pattern; this is the test program that was loaded at the factory to test the board.
If you have been using an external power supply and are using an old Arduino (Extreme, NG, or Diecimila), make sure that the power supply is plugged in and that the jumper marked SV1 is connecting the two pins that are nearest to the external power supply connector.
Note
When you are having trouble with other sketches and need to confirm that the board is functioning, open the first "blink an LED" example in the Arduino IDE and upload it to the board. The on-board ...
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