main.cpp

00001 #include "mbed.h"
00002 #include "TextLCD.h"
00003 
00004 float measure();
00005 
00006 int main()
00007 {
00008 
00009     TextLCD lcd(PTE30, PTE29, PTE23, PTE22, PTE21, PTE20); // rs, e, d4-d7
00010     float distance;
00011 
00012     while(1) {
00013         distance = measure();
00014         lcd.cls();
00015         lcd.printf("Distance = %.2f in.", distance);
00016         wait(0.5);
00017     }
00018 }
00019 
00020 // HCSR04 "driver"
00021 float measure()
00022 {
00023     Timer timer;
00024     long time;
00025     DigitalOut trigger(PTB9);
00026     DigitalIn echo(PTB8);
00027 
00028     timer.reset();
00029 
00030     // Ensure HCSR04 is idle.
00031     trigger = 0;
00032     wait (0.060);
00033 
00034     // Trigger the HCSR04.
00035     trigger = 1;
00036     wait_us(10);
00037     trigger = 0;
00038 
00039     // Wait for the HCSR04's measurement cycle to begin.
00040     while (echo == 0)
00041         ;
00042 
00043     // Start measuring.
00044     timer.start();
00045     while (echo == 1)
00046         ;
00047     timer.stop();
00048 
00049     time = timer.read_us();
00050 
00051     if (time > 30000) // Delay at maximum range plus some slop.
00052         return -1.0;   // Didn't receive an echo.
00053     else
00054         return 0.006756 * time;
00055 }