gistfile1.txt

long getDistance() {
  long duration, d1, d2, d3, cm;
  // The sensor is triggered by a HIGH pulse of 10 or more microseconds.
  // Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(80); // was 10
  digitalWrite(trigPin, LOW);
 
  // Read the signal from the sensor: 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.
  
  // get 3 readings, use middle one to avoid noise.
  d1 = pulseIn(echoPin, HIGH);
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(80); // was 10
  digitalWrite(trigPin, LOW);
  d2 = pulseIn(echoPin, HIGH);
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(80); // was 10
  digitalWrite(trigPin, LOW);
  d3 = pulseIn(echoPin, HIGH);
  
  if (d1 < d2 && d2 < d3) {
    duration = d2;
  }
  if (d1 < d3 && d3 < d2) {
    duration = d3;
  }  
  if (d2 < d3 && d3 < d1) {
    duration = d3;
  }
  if (d2 < d1 && d1 < d3) {
    duration = d1;
  }
  if (d3 < d2 && d2 < d1) {
    duration = d2;
  }
  if (d3 < d1 && d1 < d2) {
    duration = d1;
  }
  
  // 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;
}