// Define the pin number connected to the TRIG pin of the ultrasonic sensor
const int TRIG_PIN = 13;

// Define the pin number connected to the ECHO pin of the ultrasonic sensor
const int ECHO_PIN = 12;

// Declare variables to store the echo pulse duration and calculated distance
long duration, distance;

void setup() {

  // Start serial communication at 115200 baud rate
  // This is used to display distance values on the Serial Monitor
  Serial.begin(115200);

  // Set TRIG pin as OUTPUT because Arduino sends trigger pulses to the sensor
  pinMode(TRIG_PIN, OUTPUT);

  // Set ECHO pin as INPUT because Arduino receives echo signal from the sensor
  pinMode(ECHO_PIN, INPUT);
}

void loop() {

  // Call the distance calculation function and store the returned value
  distance = getDistanceInCentimeters();

  // Print the distance value on the Serial Monitor
  // String(distance) converts the number into text format
  Serial.println("ULTRASONIC SENSOR Distance = " + String(distance));

  // Delay of 1 second between each reading
  delay(1000);
}

// Function to calculate distance in centimeters
long getDistanceInCentimeters() {

  // Ensure TRIG pin is LOW before sending a pulse
  digitalWrite(TRIG_PIN, LOW);

  // Small delay to stabilize the sensor
  delayMicroseconds(2);

  // Set TRIG pin HIGH to send ultrasonic pulse
  digitalWrite(TRIG_PIN, HIGH);

  // Keep the pulse HIGH for 10 microseconds (required by HC-SR04)
  delayMicroseconds(10);

  // Set TRIG pin LOW to stop the pulse
  digitalWrite(TRIG_PIN, LOW);

  // Measure the time (in microseconds) for which ECHO pin remains HIGH
  // This time represents the sound wave travel time (to object and back)
  duration = pulseIn(ECHO_PIN, HIGH);

  // Calculate distance using speed of sound:
  // Speed of sound = 0.034 cm per microsecond
  // Divide by 2 because sound travels to the object and returns back
  // +1 is added to reduce small measurement errors
  return (duration * 0.034 / 2) + 1;
}