Diff: HCSR04.cpp

Revision:

0:8871082486ac

Child:

3:9a7899cf5e3a

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/HCSR04.cpp	Sat Dec 05 09:02:35 2015 +0000
@@ -0,0 +1,45 @@
+#include "mbed.h"
+#include "HCSR04.h"
+
+HCSR04::HCSR04(PinName echoPin, PinName triggerPin) : echo(echoPin), trigger(triggerPin) {
+    init();
+}
+
+void HCSR04::init() {
+    /** configure the rising edge to start the timer */
+    echo.rise(this, &HCSR04::startTimer);
+    
+    /** configure the falling edge to stop the timer */
+    echo.fall(this, &HCSR04::stopTimer);
+    
+    distance = -1; // initial distance
+}
+
+void HCSR04::startTimer() {
+    timer.start(); // start the timer
+}
+
+void HCSR04::stopTimer() {
+    timer.stop(); // stop the timer
+}
+
+void HCSR04::startMeasurement() {
+    /** Start the measurement by sending the 10us trigger pulse. */
+    trigger = 1;
+    wait_us(10);
+    trigger = 0;
+    
+    /** Wait for the sensor to finish measurement (generate rise and fall interrupts).
+     *  Minimum wait time is determined by maximum measurement distance of 400 cm.
+     *  t_min = 400 * 58 = 23200 us = 23.2 ms */
+    wait_ms(25); 
+    
+    /** calculate the distance in cm */
+    distance = timer.read() * 1e6 / 58;
+    timer.reset(); // reset the timer to 0 after storing the distance
+}
+
+float HCSR04::getDistance_cm() {
+    startMeasurement();
+    return distance;
+}
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