#define TRIG_PIN 5
#define ECHO_PIN 18

long readDistance() {
  // Send trigger pulse
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  // Measure echo time
  long duration = pulseIn(ECHO_PIN, HIGH);

  // Convert to centimeters
  return duration * 0.034 / 2;
}

void setup() {
  Serial.begin(115200);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
}

void loop() {
  long distance = readDistance();

  // Show in Serial Monitor
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  delay(200); // 5 readings/sec
}