Diff: main.cpp

Revision:

0:ebee649c5b1b

Child:

1:22043b67c31c

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Thu Dec 03 15:43:54 2015 +0000
@@ -0,0 +1,47 @@
+/** Initial test of the ultrasonic sensor HC-SR04  */
+
+#include "mbed.h"
+
+Serial pc(USBTX, USBRX);    // communication with terminal
+InterruptIn echo(p5);       // echo pin
+DigitalOut trigger(p7);     // trigger pin
+Timer timer;                // echo pulsewidth measurement
+
+/** Start the echo pulsewidth measurement */
+void startTimer() {
+    timer.start(); // start the timer
+}
+
+/** Stop the echo pulsewidth measurement */
+void stopTimer() {
+    timer.stop(); // stop the timer
+}
+
+int main() {
+    /** configure the rising edge to start the timer */
+    echo.rise(&startTimer);
+    
+    /** configure the falling edge to stop the timer */
+    echo.fall(&stopTimer);
+    
+    while(1) {
+        /** 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(1); 
+        
+        /** calculate the distance in cm */
+        float distance = timer.read() * 1e6 / 58;
+        timer.reset(); // reset the timer to 0
+        
+        /** Print the result in cm to the terminal with 1 decimal place
+         *  (number 5 after % means that total of 5 digits will be reserved
+         *  for printing the number, including the dot and one decimal place). */
+        pc.printf("Distance: %5.1f cm\r", distance);
+    }
+}
\ No newline at end of file