//This program creates an LED sequence.

#define led1 2                //The first LED is on Arduino pin 2
#define led2 3                //The second LED is on Arduino pin 3

void setup() {
  pinMode(led1, OUTPUT);      //Set the pins controlling the LEDs to outputs
  pinMode(led2, OUTPUT);
}

void loop() {
  digitalWrite(led1, HIGH);   //Turn on the first LED
  delay(500);                 //Pause for half a second (1000ms=1s, 500ms=½s)
  digitalWrite(led2, HIGH);   //Turn on the second LED
  delay(500);                 //Pause for half a second

  digitalWrite(led1, LOW);    //Turn off all LEDs
  digitalWrite(led2, LOW);
  delay(500);                 //Pause for half a second
}