// Define the pins for the ultrasonic sensor
const int trigPin = 2;   // Trig pin of the ultrasonic sensor
const int echoPin = 3;   // Echo pin of the ultrasonic sensor

// Define the pins for the LEDs
const int nearLedPin = 13;   // Pin for the LED indicating a near object
const int farLedPin = 12;    // Pin for the LED indicating a far object

// Variables for ultrasonic sensor
long duration;  // To store the time it takes for the sound wave to return
int distance;   // To store the calculated distance in centimeters

void setup() {
  pinMode(trigPin, OUTPUT);    // Set trig pin as output
  pinMode(echoPin, INPUT);     // Set echo pin as input
  pinMode(nearLedPin, OUTPUT); // Set near LED pin as output
  pinMode(farLedPin, OUTPUT);  // Set far LED pin as output
  
  Serial.begin(9600);  // Initialize serial communication for debugging
}

void loop() {
  // Clear the trigger pin
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  
  // Send a 10 microsecond pulse to the trigger pin
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  
  // Measure the duration of the echo pulse
  duration = pulseIn(echoPin, HIGH);
  
  // Calculate the distance in centimeters
  distance = duration * 0.034 / 2 * 10;

  // Print the distance for debugging
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" mm");
  
  // Check the distance and control LEDs accordingly
  if (distance <= 250) {
    digitalWrite(nearLedPin, HIGH); // Turn on the near LED
    digitalWrite(farLedPin, LOW);   // Turn off the far LED
  } else {
    digitalWrite(nearLedPin, LOW);  // Turn off the near LED
    digitalWrite(farLedPin, HIGH);  // Turn on the far LED
  }
  
  delay(100);  // Delay before next reading
}