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

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

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