ultrasonic-finder.cpp

00001 #include "mbed.h"
00002 #include "ultrasonic-finder.h"
00003 
00004 static const char CLS[] = "\x1B[2J";        // VT100 erase screen
00005 static const char HOME[] = "\x1B[H";        // VT100 home
00006 static const int delay = 2;
00007 
00008 static const float pulse_line = 4E-5;       // 40 ns
00009 static const int pulse_to_distance = 58;    // 617 / 10.6
00010 
00011 enum
00012 {
00013     DOWN = 0,
00014     UP = 1
00015 };
00016 
00017 int main() 
00018 {
00019     clear_screen();
00020     
00021     Timer timer;
00022     timer.start();
00023     
00024     while (true) 
00025     {
00026         send_pulse(trigger);
00027         while (!echo) {};                  // wait for echo
00028         float pulse = measure_pulse(timer, echo);
00029         show_result(pulse);
00030         wait(delay);
00031     }        
00032 }
00033 
00034 void clear_screen()
00035 {
00036     pc.printf(CLS);      
00037     pc.printf(HOME);               
00038 }
00039 
00040 void send_pulse(DigitalOut& triggerOut)
00041 {
00042     triggerOut = UP;
00043     wait(pulse_line);
00044     triggerOut = DOWN;
00045 }
00046 
00047 float measure_pulse(Timer& timer, const DigitalIn& echoIn)
00048 {
00049     timer.reset();
00050     while (echo) {};
00051     return timer.read_us();
00052 }
00053 
00054 void show_result(float pulse)
00055 {
00056     pc.printf(HOME);    
00057     pc.printf("Pulse length %6.0f uS\n\r", pulse);
00058     pulse /= pulse_to_distance;
00059     pc.printf("\n\rDistance %4.0f cm\n\r", pulse);
00060 }