Code for Ultrasonic Sensor HC-SR04 in Arduino

Ultrasonic_Sensor_in_Arduino.ino

#define trigPin 13
#define echoPin 12

void setup() {
  Serial.begin (9600); // Begin the Serial Monitor at 9600 Baud
  pinMode(trigPin, OUTPUT); // Initialize Trigger Pin
  pinMode(echoPin, INPUT); // Initialize Echo Pin
}

void loop() {
  long duration, distance; // Duration varible stores time duration taken by ultrasonic and Distance variable stores distance
  digitalWrite(trigPin, LOW);  // Set Trigger Pin Low
  delayMicroseconds(2); // Delay
  digitalWrite(trigPin, HIGH); // Set Trigger Pin High
  delayMicroseconds(10); // Delay
  digitalWrite(trigPin, LOW); // Set Trigger Pin Low
  duration = pulseIn(echoPin, HIGH); // Set Echo Pin High to set time to variable
  distance = (duration/2) / 29.1; // Convert time into distance
  Serial.print(distance); // Print distance to Serial Monitor
  Serial.println(" cm");
  delay(500);
}