// Define pins for ultrasonic sensor
const int trigPin = 6; // Trigger pin
const int echoPin = 5; // Echo pin

// Define pins for LEDs
const int greenLed = 2;
const int yellowLed = 3;
const int redLed = 4;

// Variables to store distance and duration
long duration;
int distance;

void setup() {
  Serial.begin(9600); // Initialize serial communication
  pinMode(trigPin, OUTPUT); // Set trigger pin as output
  pinMode(echoPin, INPUT); // Set echo pin as input
  
  // Set LED pins as output
  pinMode(greenLed, OUTPUT);
  pinMode(yellowLed, OUTPUT);
  pinMode(redLed, OUTPUT);
}

void loop() {
  // Clear trigger pin
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  
  // Send a 10us pulse to trigger pin to start ranging
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  
  // Measure the duration of pulse from echo pin
  duration = pulseIn(echoPin, HIGH);
  
  // Calculate distance in cm
  distance = duration * 0.034 / 2; // Speed of sound in air is 343 m/s (34.3 cm/ms), divide by 2 because sound travels to the object and back
  
  // Print distance to serial monitor
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");
  
  // Turn on appropriate LED based on distance
  if (distance < 20) { // If distance is less than 20 cm
    digitalWrite(greenLed, LOW);
    digitalWrite(yellowLed, LOW);
    digitalWrite(redLed, HIGH); // Turn on red LED
  } else if (distance >= 20 && distance < 50) { // If distance is between 20 cm and 50 cm
    digitalWrite(greenLed, LOW);
    digitalWrite(yellowLed, HIGH); // Turn on yellow LED
    digitalWrite(redLed, LOW);
  } else { // If distance is greater than or equal to 50 cm
    digitalWrite(greenLed, HIGH); // Turn on green LED
    digitalWrite(yellowLed, LOW);
    digitalWrite(redLed, LOW);
  }
  
  // Delay before next reading
  delay(1000); // Adjust delay according to your requirement
}