File content as of revision 0:ae8d48256ff1:

#include "PING.h"
#include "mbed.h"

/*
 * Constructor
 */
PING::PING(PinName trigger) : _trigger(trigger)
{
   // Attach interrupts
   _ticker.attach(this, &PING::_startRange, 0.1);
}

void PING::_startRange()
{
   // send a trigger pulse, 20uS long
   _trigger.output(); // set pin to output trigger pulse
   _trigger = 0; // ensure pin starts low
   wait_us(2); // wait two microseconds
   _trigger = 1; // send trigger pulse by setting pin high
   wait_us(5); // keep sending pulse for 5 microseconds
   _trigger = 0; // set pin low to stop pulse

   _trigger.input();

   // pulseIn
   while (!_trigger); // wait for high
   _timer.reset();
   _timer.start();
   while (_trigger); // wait for low
   _timer.stop();
   _dist = _timer.read_us(); //provides echo time in microseconds
}

// returns distance in meters
// The speed of sound is 340 m/s or 58 microseconds per meter.
// The ping travels out and back, so to find the distance of the
// object we take half of the distance travelled.
float PING::read(void)
{
   // spin until there is a good value
   return (_dist/29/2);
}

// returns distance in inches
// 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
float PING::read_in(void)
{
   // spin until there is a good value
   return (_dist/74/2);
}

PING::operator float()
{
   return read();
}