// Define pin numbers
const int trigPin = 9;
const int echoPin = 10;
const int redLED = 2;
const int greenLED = 3;
const int blueLED = 5;
const int yellowLED = 4;

// Define distance ranges (in cm)
const int range1 = 100; // 0-100 cm
const int range2 = 200; // 101-200 cm
const int range3 = 300; // 201-300 cm
const int range4 = 400; // 301-400 cm

void setup() {
  // Initialize serial communication
  Serial.begin(9600);
  
  // Initialize pins
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(redLED, OUTPUT);
  pinMode(greenLED, OUTPUT);
  pinMode(blueLED, OUTPUT);
  pinMode(yellowLED, OUTPUT);
  
  // Turn off all LEDs initially
  digitalWrite(redLED, LOW);
  digitalWrite(greenLED, LOW);
  digitalWrite(blueLED, LOW);
  digitalWrite(yellowLED, LOW);
}

void loop() {
  // Trigger the ultrasonic sensor
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  
  // Read the duration of the echo pulse
  long duration = pulseIn(echoPin, HIGH);
  
  // Calculate the distance (in cm)
  float distance = (duration / 2.0) * 0.0343;
  
  // Print distance to serial monitor (for debugging)
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");
  
  // Turn off all LEDs
  digitalWrite(redLED, LOW);
  digitalWrite(greenLED, LOW);
  digitalWrite(blueLED, LOW);
  digitalWrite(yellowLED, LOW);
  
  // Turn on the appropriate LED based on the distance
  if (distance >= 0 && distance <= range1) {
    digitalWrite(redLED, HIGH);
  } else if (distance > range1 && distance <= range2) {
    digitalWrite(greenLED, HIGH);
  } else if (distance > range2 && distance <= range3) {
    digitalWrite(blueLED, HIGH);
  } else if (distance > range3 && distance <= range4) {
    digitalWrite(yellowLED, HIGH);
  }
  
  // Small delay for stability
  delay(200);
}