Diff: PING.cpp

Revision:

0:02a23e3031ee

diff -r 000000000000 -r 02a23e3031ee PING.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/PING.cpp	Mon Sep 24 15:52:56 2012 +0000
@@ -0,0 +1,91 @@
+#include "PING.h"
+#include "mbed.h"
+
+/*
+ * Constructor
+ */
+PING::PING(PinName trigger) : _trigger(trigger)
+{
+   // Attach interrupts
+   _ticker.attach(this, &PING::_startRange, 0.1);
+   _invalidctr = 0 ;
+}
+
+void PING::_startRange()
+{
+   int invalid ;
+   invalid = 0 ;
+
+   // 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
+   _timer.reset();
+   _timer.start();
+   while (!_trigger) {
+    if (_timer.read_us() > 10000) { // invalid thre
+        invalid = 1;
+        break ;
+    }
+   } // wait for high
+   if (invalid == 0) 
+   {
+    _timer.stop();
+    _timer.reset();
+    _timer.start();
+    while (_trigger) {
+     if (_timer.read_us() > 10000) 
+     { // invalid thre
+            invalid = 1 ;
+            break ;
+     }
+    } // wait for low
+    _timer.stop();
+   }
+   if (invalid == 0) {
+        _dist = _timer.read_us(); //provides echo time in microseconds
+        _invalidctr = 0 ;
+   } else {
+        _invalidctr++ ;
+        if (_invalidctr > 5) { // Invalid (none) thre
+            _dist = 0.0 ;
+            _invalidctr = 0 ;
+        }
+   }
+}
+
+// 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
+
+// 2012.9.25 : Add check echo timeout detection
+
+float PING::read_in(void)
+{
+   // spin until there is a good value
+   return (_dist/74/2);
+}
+
+PING::operator float()
+{
+   return read();
+}
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