// Pins for LEDs
const int redLED = 2;
const int greenLED = 3;
const int yellowLED = 4;

// Pins for HC-SR04
const int trigPin = 9;
const int echoPin = 10;

void setup() {
  // Set up the LED pins as output
  pinMode(redLED, OUTPUT);
  pinMode(greenLED, OUTPUT);
  pinMode(yellowLED, OUTPUT);

  // Set up the HC-SR04 pins
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);

  // Begin serial communication for debugging (optional)
  Serial.begin(9600);
}

void loop() {
  // Measure distance
  long duration, distance;

  // Send a 10 microsecond pulse to trigger pin
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Read the echo pin and calculate distance
  duration = pulseIn(echoPin, HIGH);
  distance = duration * 0.034 / 2;

  // Debugging distance (optional)
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  // Decision based on distance
  if (distance > 250) {
    digitalWrite(redLED, HIGH);
    digitalWrite(greenLED, LOW);
    digitalWrite(yellowLED, LOW);
  } else if (distance > 100 && distance <= 250) {
    digitalWrite(redLED, LOW);
    digitalWrite(greenLED, HIGH);
    digitalWrite(yellowLED, LOW);
  } else if (distance <= 100) {
    digitalWrite(redLED, LOW);
    digitalWrite(greenLED, LOW);
    digitalWrite(yellowLED, HIGH);
  }

  // Small delay to avoid flickering
  delay(100);
}