Measuring Distance

Arduino-Measuring Distance using PING:
             Ultrasonic sensors provide a measurement of the time it takes for sound to bounce off an object and return to the sensor. The “ping” sound pulse is generated when the pingPin level goes HIGH for two microseconds. The sensor will then generate a pulse that terminates when the sound returns. The width of the pulse is proportional to the distance the sound traveled and the sketch then uses the pulseIn function to measure that duration. The speed of sound is 340 meters per second, which is 29 microseconds per centimeter. The formula for the distance of the round trip is: RoundTrip = microseconds / 29.So, the formula for the one-way distance in centimeters is: microseconds / 29 / 2.

This recipe uses the popular Parallax PING))) ultrasonic distance sensor to measure the distance of an object ranging from 2 cm to around 3 m. It displays the distance on the Serial Monitor and flashes an LED faster as objects get closer.

/* Ping)) Sensor

 * prints distance and changes LED flash rate

* depending on distance from the Ping))) sensor

*/

const int pingPin = 5;

const int ledPin = 13; // pin connected to LED

void setup()

{

Serial.begin(9600);

pinMode(ledPin, OUTPUT);

}

void loop()

{

int cm = ping(pingPin) ;

Serial.println(cm);

digitalWrite(ledPin, HIGH);

delay(cm * 10 ); // each centimeter adds 10 milliseconds delay

digitalWrite(ledPin, LOW);

delay( cm * 10);

}

// following code based on http://www.arduino.cc/en/Tutorial/Ping

// returns the distance in cm

int ping(int pingPin)

{

// establish variables for duration of the ping,

// and the distance result in inches and centimeters:

long duration, 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);

pinMode(pingPin, INPUT);

duration = pulseIn(pingPin, HIGH);

// convert the time into a distance

cm = microsecondsToCentimeters(duration);

return cm ;

}

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;

}