/**

 * Hardware Connections:
 *  Arduino | HC-SR04 
 *  -------------------
 *    5V    |   VCC     
 *    7     |   Trig     
 *    8     |   Echo     
 *    GND   |   GND

 */

// Pins
const int TRIG_PIN = 7;
const int ECHO_PIN = 8;

// Anything over 400 cm (23200 us pulse) is "out of range"
const unsigned int MAX_DIST = 23200;

void setup() {
                pinMode(TRIG_PIN, OUTPUT);
                digitalWrite(TRIG_PIN, LOW);
                Serial.begin(9600);
              }

void loop() {

  unsigned long t1;
  unsigned long t2;
  unsigned long pulse_width;
  float cm;

  
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  while ( digitalRead(ECHO_PIN) == 0 );
                         t1 = micros();
  while ( digitalRead(ECHO_PIN) == 1);
                        t2 = micros();
  
  pulse_width = t2 - t1;
  cm = pulse_width / 58.0;

  if ( pulse_width > MAX_DIST ) {
                                 Serial.print("0");
                                 Serial.print(" ");
                                } else {
                                         Serial.print(int(cm));
                                        Serial.print(" ");
                                        }
  
      
  delay(2000);
}