/* Ping))) Sensor
   
    This sketch reads a PING))) ultrasonic rangefinder and returns the
    distance to the closest object in range. To do this, it sends a pulse
    to the sensor to initiate a reading, then listens for a pulse 
    to return.  The length of the returning pulse is proportional to 
    the distance of the object from the sensor.
      
    The circuit:
 	* +V connection of the PING))) attached to +5V
 	* GND connection of the PING))) attached to ground
 	* SIG connection of the PING))) attached to digital pin 7

    http://www.arduino.cc/en/Tutorial/Ping
    
    created 3 Nov 2008
    by David A. Mellis
    modified 30 Jun 2009
    by Tom Igoe

  */

 // this constant won't change.  It's the pin number
 // of the sensor's output:
 const int pingPin = 7;

 void setup() {
   // initialize serial communication:
   Serial.begin(9600);
 }

 void loop()
 {
   // establish variables for duration of the ping, 
   // and the distance result in inches and centimeters:
   long duration, inches, cm;

   // The PING))) is triggered by a HIGH pulse of 2 or more microseconds.
   // Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
   pinMode(pingPin, OUTPUT);
   digitalWrite(pingPin, LOW);
   delayMicroseconds(2);
   digitalWrite(pingPin, HIGH);
   delayMicroseconds(5);
   digitalWrite(pingPin, LOW);

   // The same pin is used to read the signal from the PING))): a HIGH
   // pulse whose duration is the time (in microseconds) from the sending
   // of the ping to the reception of its echo off of an object.
   pinMode(pingPin, INPUT);
   duration = pulseIn(pingPin, HIGH);

   // convert the time into a distance
   inches = microsecondsToInches(duration);
   cm = microsecondsToCentimeters(duration);

   Serial.print(inches);
   Serial.print("in, ");
   Serial.print(cm);
   Serial.print("cm");
   Serial.println();

   delay(100);
 }

 long microsecondsToInches(long microseconds)
 {
   // According to Parallax's datasheet for the PING))), there are
   // 73.746 microseconds per inch (i.e. sound travels at 1130 feet per
   // second).  This gives the distance travelled by the ping, outbound
   // and return, so we divide by 2 to get the distance of the obstacle.
   // See: http://www.parallax.com/dl/docs/prod/acc/28015-PING-v1.3.pdf
   return microseconds / 74 / 2;
 }

 long microsecondsToCentimeters(long microseconds)
 {
   // The speed of sound is 340 m/s or 29 microseconds per centimeter.
   // The ping travels out and back, so to find the distance of the
   // object we take half of the distance travelled.
   return microseconds / 29 / 2;
 }