// Define the pin numbers for the ultrasonic sensor
const int echoPin = 3;
const int trigPin = 7;
 
void setup() {
  Serial.begin(9600);                    // Start serial communication with a baud rate of 9600
  pinMode(echoPin, INPUT);               // Set echo pin as input
  pinMode(trigPin, OUTPUT);              // Set trig pin as output
  Serial.println("Ultrasonic sensor:");  // Print a message indicating the ultrasonic sensor is ready
}
 
void loop() {
  float distance = readDistance();       // Call the function to read the sensor data and get the distance
  
  if (distance > 400) {                  // Check if the distance is greater than 400 cm
    Serial.println("Out of Range");      // Print "Out of Range"
  } else {
    Serial.print(distance);              // Print the distance value
    Serial.println(" cm");               // Print " cm" to indicate the unit of measurement
  }
  
  delay(400);                            // Delay for 400 milliseconds before repeating the loop
}
 
// Function to read the sensor data and calculate the distance
float readDistance() {
  digitalWrite(trigPin, LOW);            // Set trig pin to low to ensure a clean pulse
  delayMicroseconds(2);                  // Delay for 2 microseconds
  digitalWrite(trigPin, HIGH);           // Send a 10 microsecond pulse by setting trig pin to high
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);            // Set trig pin back to low
 
  // Measure the pulse width of the echo pin and calculate the distance value
  float pulse_duration = pulseIn(echoPin, HIGH); // Read pulse duration
  float distance = pulse_duration / 58.00;       // Calculate the distance
  
  return distance;                               // Return the calculated distance
}