Diff: HCSR04.cpp

Revision:

0:5461d44a187c

Child:

1:68ad9acbec81

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/HCSR04.cpp	Sun Nov 24 21:45:46 2013 +0000
@@ -0,0 +1,100 @@
+/* File: HCSR04.h
+ * Author: Robert Abad  Copyright (c) 2013
+ *
+ * Desc: driver for HCSR04 Ultrasonic Range Finder.  See header file,
+ *       HCSR04.h, for more details.
+ */
+
+#include "mbed.h"
+#include "HCSR04.h"
+
+#define SPEED_OF_SOUND      (343.2f)    // meters/sec
+
+// HCSR04 TRIGGER pin
+#define SIGNAL_HIGH     (1)
+#define SIGNAL_LOW      (0)
+
+#define TRIGGER_TIME    (10)            // microseconds
+
+
+// Name: HCSR04
+// Desc: HCSR04 constructor
+// Inputs: PinName - pin used for trigger signal
+//         PinName - pin used for echo signal
+// Outputs: none
+//
+HCSR04::HCSR04( PinName pinTrigger, PinName pinEcho ) : 
+trigger(pinTrigger),
+echo(pinEcho),
+measTimeStart_us(0),
+measTimeStop_us(0)
+{
+    echo.rise( this, &HCSR04::ISR_echoRising );
+    echo.fall( this, &HCSR04::ISR_echoFalling );
+    echoTimer.start();
+}
+
+// Name: startMeas
+// Desc: initiates range measurement driving the trigger signal HIGH then sets
+//       a timer to keep trigger HIGH for the duration of TRIGGER_TIME
+// Inputs: none
+// Outputs: none
+//
+void HCSR04::startMeas(void)
+{
+    trigger = SIGNAL_HIGH;
+    echoTimer.reset();
+    triggerTicker.attach_us(this, &HCSR04::triggerTicker_cb, TRIGGER_TIME);
+}
+ 
+// Name: getMeas
+// Desc: returns range measurement in meters
+// Inputs: float & - reference to range measurement
+// Outputs: etHCSR04 - RANGE_MEAS_VALID or RANGE_MEAS_INVALID
+//
+etHCSR04_RANGE_STATUS HCSR04::getMeas(float &rRangeMeters)
+{
+    unsigned long dTime_us;
+    if ( !measTimeStart_us || !measTimeStop_us )
+    {
+        return RANGE_MEAS_INVALID;
+    }
+    
+    dTime_us = measTimeStop_us - measTimeStart_us;
+    rRangeMeters = (float)dTime_us / 1000000. * SPEED_OF_SOUND / 2;
+    measTimeStart_us = 0;
+    measTimeStop_us = 0;
+    return ( RANGE_MEAS_VALID );
+}
+
+// Name: triggerTicker_cb
+// Desc: Timer ticker callback function used to drive trigger signal LOW
+// Inputs: none
+// Outputs: none
+//
+void HCSR04::triggerTicker_cb(void)
+{
+    trigger = SIGNAL_LOW;
+}
+
+
+// Name: ISR_echoRising
+// Desc: ISR for rising edge of HCSR04 ECHO signal
+// Inputs: none
+// Outputs: none
+//
+void HCSR04::ISR_echoRising(void)
+{
+    measTimeStart_us = echoTimer.read_us();
+}
+
+// Name: ISR_echoFalling
+// Desc: ISR for falling edge of HCSR04 ECHO signal
+// Inputs: none
+// Outputs: none
+//
+void HCSR04::ISR_echoFalling(void)
+{
+    measTimeStop_us = echoTimer.read_us();
+}
+