// Traffic Light Control System using Ultrasonic Sensor (Closed-Loop)

#define TRIG 5   // Ultrasonic sensor trigger pin
#define ECHO 6   // Ultrasonic sensor echo pin

#define RED 9     // Red LED
#define YELLOW 10 // Yellow LED
#define GREEN 11  // Green LED

long duration;
int distance;

void setup() {
  pinMode(TRIG, OUTPUT);
  pinMode(ECHO, INPUT);
  
  pinMode(RED, OUTPUT);
  pinMode(YELLOW, OUTPUT);
  pinMode(GREEN, OUTPUT);
  
  Serial.begin(9600); // For debugging
}

void loop() {
  // Measure distance using ultrasonic sensor
  digitalWrite(TRIG, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG, LOW);
  
  duration = pulseIn(ECHO, HIGH);
  distance = duration * 0.034 / 2; // Convert to cm
  
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  // If vehicle is detected (distance < 10cm), turn Green
  if (distance < 10) {
    digitalWrite(RED, LOW);
    digitalWrite(YELLOW, LOW);
    digitalWrite(GREEN, HIGH);
    delay(10000); // Green for 10 sec
  } 
  else {
    // Normal Traffic Light Sequence
    digitalWrite(RED, HIGH);
    digitalWrite(YELLOW, LOW);
    digitalWrite(GREEN, LOW);
    delay(5000); // Red for 5 sec
    
    digitalWrite(RED, LOW);
    digitalWrite(YELLOW, HIGH);
    digitalWrite(GREEN, LOW);
    delay(2000); // Yellow for 2 sec

    digitalWrite(RED, LOW);
    digitalWrite(YELLOW, LOW);
    digitalWrite(GREEN, HIGH);
    delay(5000); // Green for 5 sec
  }
}