Ultrasonic distance measurement

 const int trigPin = 9;

const int echoPin = 8;

// LED pins

const int led40 = 2;

const int led80 = 3;

const int led120 = 4;

const int led160 = 5;

long duration;

int distance;

void setup() {

  pinMode(trigPin, OUTPUT);

  pinMode(echoPin, INPUT);

  pinMode(led40, OUTPUT);

  pinMode(led80, OUTPUT);

  pinMode(led120, OUTPUT);

  pinMode(led160, OUTPUT);

  Serial.begin(9600);

}

void loop() {

  // Trigger pulse

  digitalWrite(trigPin, LOW);

  delayMicroseconds(2);

  digitalWrite(trigPin, HIGH);

  delayMicroseconds(10);

  digitalWrite(trigPin, LOW);

  // Read echo and calculate distance

  duration = pulseIn(echoPin, HIGH);

  distance = duration * 0.034 / 2;

  Serial.print("Distance: ");

  Serial.print(distance);

  Serial.println(" cm");

  // Turn OFF all LEDs first

  digitalWrite(led40, LOW);

  digitalWrite(led80, LOW);

  digitalWrite(led120, LOW);

  digitalWrite(led160, LOW);

  // Turn ON LED based on distance range

  if (distance >= 30 && distance < 50) {

    digitalWrite(led40, HIGH);

  } else if (distance >= 70 && distance < 90) {

    digitalWrite(led80, HIGH);

  } else if (distance >= 110 && distance < 130) {

    digitalWrite(led120, HIGH);

  } else if (distance >= 150 && distance < 170) {

    digitalWrite(led160, HIGH);

  }

  delay(200);

}