Controlling digital Output with the Arduino

• http://www.arduino.cc/en/Tutorial/Blink

int ledPin =  13;    // LED connected to digital pin 13

void setup() 
{                
  // initialize the digital pin as an output:
  pinMode(ledPin, OUTPUT);     
}

void loop()                   
{
  digitalWrite(ledPin, HIGH);   // set the LED on
  delay(1000);                  // wait for a second
  digitalWrite(ledPin, LOW);    // set the LED off
  delay(1000);                  // wait for a second
}