Revision 0:ae8d48256ff1, committed 2010-02-11

Comitter:

mshoemaker

Date:

Thu Feb 11 03:47:41 2010 +0000

Commit message:

Changed in this revision

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/PING.cpp	Thu Feb 11 03:47:41 2010 +0000
@@ -0,0 +1,59 @@
+#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();
+}
\ No newline at end of file

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/PING.h	Thu Feb 11 03:47:41 2010 +0000
@@ -0,0 +1,71 @@
+#ifndef MBED_PING_H
+#define MBED_PING_H
+#include "mbed.h"
+
+/* Class: PING
+ *  Abstraction for the PING Ultrasonic range finder
+ *
+ * Example:
+ * > // Print measured distance
+ * >
+ * > #include "mbed.h"
+ * > #include "PING.h"
+ * >
+ * > PING ping(p9);
+ * >
+ * > int main() {
+ * >     while(1) {
+ * >         printf("Measured : %.1f\n", ping.read());
+ * >         wait(0.2);
+ * >     }
+ * > }
+ */
+class PING
+{
+// Public functions
+public:
+   /* Constructor: PING
+    *  Create a PING object, connected to the specified pins
+    *
+    * Variables:
+    *  trigger - Output to trigger the PING
+    */
+   PING(PinName trigger);
+
+   /* Function: read
+    *  A non-blocking function that will return the last measurement
+    *
+    * Variables:
+    *  returns - floating point representation in cm.
+    */
+   float read(void);
+
+   /* Function: read_in
+    *  A non-blocking function that will return the last measurement
+    *
+    * Variables:
+    *  returns - floating point representation in in.
+    */
+   float read_in(void);
+
+   /* Function: operator float
+    *  A short hand way of using the read function
+    *
+    * Example:
+    * > float range = ping.read();
+    * > float range = ping;
+    * >
+    * > if(ping.read() > 0.25) { ... }
+    * > if(ping > 0.25) { ... }
+    */
+   operator float();
+
+private :
+   DigitalInOut _trigger;
+   Timer _timer;
+   Ticker _ticker;
+   void _startRange(void);
+   float _dist;
+};
+
+#endif
\ No newline at end of file