/*
 * Wiring: Ultrasonic Sensor -> Arduino:
  * --- VCC -> 5VDC
   * --- TRIG -> Pin 9
    * --- ECHO -> Pin 8
     * --- GND -> GND
      */

      int trigPin = 9;    // TRIG pin
      int echoPin = 8;    // ECHO pin

      float duration_us, distance_cm;

      void setup() {
        // begin serial port
          Serial.begin(9600);

            // configure the trigger pin to output mode
              pinMode(trigPin, OUTPUT);
                // configure the echo pin to input mode
                  pinMode(echoPin, INPUT);
                  }

                  void loop() {
                    // generate 10-microsecond pulse to TRIG pin
                      digitalWrite(trigPin, HIGH);
                        delayMicroseconds(10);
                          digitalWrite(trigPin, LOW);

                            // measure duration of pulse from ECHO pin
                              duration_us = pulseIn(echoPin, HIGH);

                                // calculate the distance
                                  distance_cm = 0.017 * duration_us;

                                    // print the value to Serial Monitor
                                      Serial.print("distance: ");
                                        Serial.print(distance_cm);
                                          Serial.println(" cm");

                                            delay(500);
                                            }