#define RED_PIN 2     // Pin connected to Red LED
#define YELLOW_PIN 3  // Pin connected to Yellow LED
#define GREEN_PIN 4   // Pin connected to Green LED

void setup() {
  // Set LED pins as OUTPUT
  pinMode(RED_PIN, OUTPUT);
  pinMode(YELLOW_PIN, OUTPUT);
  pinMode(GREEN_PIN, OUTPUT);
}

void loop() {
  // Turn Red LED on, others off
  digitalWrite(RED_PIN, HIGH);  // Red light on
  digitalWrite(YELLOW_PIN, LOW);  // Yellow light off
  digitalWrite(GREEN_PIN, LOW);  // Green light off
  delay(1000); // Red light on for 3 seconds

  // Turn Yellow LED on, others off
  digitalWrite(RED_PIN, LOW);  // Red light off
  digitalWrite(YELLOW_PIN, HIGH);  // Yellow light on
  digitalWrite(GREEN_PIN, LOW);  // Green light off
  delay(1000); // Yellow light on for 1 second

  // Turn Green LED on, others off
  digitalWrite(RED_PIN, LOW);  // Red light off
  digitalWrite(YELLOW_PIN, LOW);  // Yellow light off
  digitalWrite(GREEN_PIN, HIGH);  // Green light on
  delay(1000); // Green light on for 3 seconds

  // Turn Yellow LED on again, others off (before turning Red)
  digitalWrite(RED_PIN, LOW);  // Red light off
  digitalWrite(YELLOW_PIN, HIGH);  // Yellow light on
  digitalWrite(GREEN_PIN, LOW);  // Green light off
  delay(1000); // Yellow light on for 1 second
}