HC-SR04

const int triggerPort = 7;
const int echoPort = 8;

void setup(){
  pinMode(triggerPort, OUTPUT);
  pinMode(echoPort, INPUT);
  Serial.begin(9600);
  Serial.println("Ready.");
}

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

  long duration = pulseIn(echoPort, HIGH);
  long distance = 0.017 * duration;

  Serial.print("Duration: ");
  Serial.print(duration);
  Serial.print(", ");
  Serial.print("distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  delay(100);
}