Ultrasonic Distance Sensor (HC-SR04)

// Ultrasonic Distance Sensor (HC-SR04)
// Board: Arduino UNO

const int TRIG_PIN = 9;
const int ECHO_PIN = 10;

void setup() {
  Serial.begin(9600);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
}

void loop() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  long duration = pulseIn(ECHO_PIN, HIGH, 30000);
  float distanceCm = duration * 0.0343 / 2.0;

  Serial.print("Distance: ");
  Serial.print(distanceCm);
  Serial.println(" cm");
  delay(500);
}