main.cpp

00001 #include "mbed.h"
00002  
00003 DigitalOut trigger(p13);
00004 DigitalOut myled(LED1); //monitor trigger
00005 DigitalOut myled2(LED2); //monitor echo
00006 DigitalOut myled3(LED3);
00007 DigitalOut myled4(LED4);
00008 DigitalIn  echo(p14);
00009 int distance = 0;
00010 int correction = 0;
00011 Timer sonar;
00012  
00013 int main()
00014 {
00015     sonar.reset();
00016 // measure actual software polling timer delays
00017 // delay used later in time correction
00018 // start timer
00019     sonar.start();
00020 // min software polling delay to read echo pin
00021     while (echo==2) {};
00022     myled2 = 0;
00023 // stop timer
00024     sonar.stop();
00025 // read timer
00026     correction = sonar.read_us();
00027     printf("Approximate software overhead timer delay is %d uS\n\r",correction);
00028  
00029 //Loop to read Sonar distance values, scale, and print
00030     while(1) {
00031 // trigger sonar to send a ping
00032         trigger = 1;
00033         myled = 1;
00034         myled2 = 0;
00035         sonar.reset();
00036         wait_us(10.0);
00037         trigger = 0;
00038         myled = 0;
00039 //wait for echo high
00040         while (echo==0) {};
00041         myled2=echo;
00042 //echo high, so start timer
00043         sonar.start();
00044 //wait for echo low
00045         while (echo==1) {};
00046 //stop timer and read value
00047         sonar.stop();
00048 //subtract software overhead timer delay and scale to cm
00049         distance = (sonar.read_us()-correction)/58.0;
00050         myled2 = 0;
00051         printf(" %d cm \n\r",distance);
00052         
00053         if (distance<10) {
00054             myled3= 1;
00055         }
00056         if (distance>=10) {
00057             myled4= 1;
00058         }
00059         
00060         
00061 //wait so that any echo(s) return before sending another ping
00062         wait(0.2);
00063         myled3 = myled4 = 0;
00064     }
00065 }