// Ultrasonic Sensor Example using HC-SR04
// Connections:
// VCC  → 5V
// GND  → GND
// Trig → D9
// Echo → D10

const int trigPin = 9;
const int echoPin = 10;

void setup() {
  // Initialize Serial communication at 9600 baud rate
  Serial.begin(9600);

  // Set trigPin as OUTPUT and echoPin as INPUT
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
}

void loop() {
  long duration;
  int distance;

  // Ensure the trigger pin is low
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);

  // Send a 10-microsecond HIGH pulse to trigger the sensor
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Read the echo pin (returns the sound wave travel time in microseconds)
  duration = pulseIn(echoPin, HIGH);

  // Calculate the distance in cm
  distance = duration * 0.034 / 2;

  // Print the distance to the Serial Monitor
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  // Wait half a second before next reading
  delay(500);
}