#define RED  2
#define YELLOW 5
#define GREEN 9

void setup() {
  pinMode(RED, OUTPUT);
  pinMode(YELLOW, OUTPUT);
  pinMode(GREEN, OUTPUT);
}

void loop() {
  digitalWrite(GREEN, HIGH);
  delay(3000);
  digitalWrite(GREEN, LOW);

  // Yellow light ON for 500 milliseconds
  digitalWrite(YELLOW, HIGH);
  delay(500);
  digitalWrite(YELLOW, LOW);

  // Red light ON for 2 seconds
  digitalWrite(RED, HIGH);
  delay(2000);
  digitalWrite(RED, LOW);

  // Cycle repeats after red light is off
  delay(500);
}