const int trigPin = 7; 
const int echoPin = 6; 
const int ledPin = 9; 
const int ledPin1 = 10;
const int ledPin2 = 11;
void setup() {   
    Serial.begin(9600);   
    pinMode(trigPin, OUTPUT);   
    pinMode(echoPin, INPUT);   
    pinMode(ledPin, OUTPUT); 
    pinMode(ledPin1, OUTPUT);
    pinMode(ledPin2, OUTPUT);

    }  

void loop() {   
    // Triggering the ultrasonic sensor
    digitalWrite(trigPin, LOW);   
    delayMicroseconds(2);   
    digitalWrite(trigPin, HIGH);   
    delayMicroseconds(10);   
    digitalWrite(trigPin, LOW);    
    // Measuring the echo time
    long duration = pulseIn(echoPin, HIGH);      
    // Calculating the distance (in centimeters)
    float distance_cm = duration * 0.034 / 2;       
    // Set the LED brightness
    if (distance_cm>=101 && distance_cm <200)
    {
      digitalWrite(ledPin, HIGH);
      digitalWrite(ledPin1, LOW);
      digitalWrite(ledPin2, LOW);
    }
    else if (distance_cm>=51 && distance_cm <100)
    {
      digitalWrite(ledPin, HIGH);
      digitalWrite(ledPin1, HIGH);
      digitalWrite(ledPin2, LOW);
    }
    else if (distance_cm>=0 && distance_cm <50)
    {
      digitalWrite(ledPin, HIGH);
      digitalWrite(ledPin1, HIGH);
      digitalWrite(ledPin2, HIGH);
    }
    else
    {
      digitalWrite(ledPin, LOW);
      digitalWrite(ledPin1,LOW);
      digitalWrite(ledPin2, LOW);
    }

    // Display the distance and brightness on the Serial Monitor   
    Serial.print("Distance: ");   
    Serial.print(distance_cm);   
    Serial.print(" cm\n");    
    // Add a small delay between readings
    delay(100); 
    }