使用PIC单片机的超声波测距仪C程序

////////////////////////////////////////////////////////////////////////////////
//
//     PIC16F877 + HC-SR04 + LCD03 example
//     Written October 2008 , using HITECH PIC16 compiler
// 
//  Note - assumes a 20MHz crystal, which is 5MHz timer clock
//  A 1:4 prescaler is used to give a 1.25MHz timer count (0.8uS per tick)
//
//     This code is Freeware - Use it for any purpose you like.
//
///////////////////////////////////////////////////////////////////////////////


#include <pic.h>
#include <stdio.h>
 
__CONFIG(0x3b32);

#define trig RB0
#define echo RB1

void clrscn(void); // prototypes
void cursor(char pos);
void print(char *p);
void setup(void);
unsigned int get_srf04(void);

char s[21]; // buffer used to hold text to print

void main(void)

{
unsigned int range;

setup(); // sets up the PIC16F877 I2C port
clrscn(); // clears the LCD03 disply
cursor(2); // sets cursor to 1st row of LCD03
sprintf(s,"SRF04 Ranger Test"); // text, printed into our buffer
print(s); // send it to the LCD03

while(1) { // loop forever
range = get_srf04(); // get range from srf04 (round trip flight time in 0.8uS units)
cursor(24); // sets cursor to 2nd row of LCD03
sprintf(s,"Range = %dcm  ", range/72); // convert to cm
print(s); // send it to the LCD03
cursor(44); // sets cursor to 3rd row of LCD03
sprintf(s,"Range = %dinch  ", range/185); // convert to inches
print(s); // send it to the LCD03

TMR1H = 0; // 52mS delay - this is so that the SRF04 ranging is not too rapid
TMR1L = 0; // and the previous pulse has faded away before we start the next one
T1CON = 0x21; // 1:4 prescale and running
TMR1IF = 0;
while(!TMR1IF); // wait for delay time
TMR1ON = 0; // stop timer
}
}

unsigned int get_srf04(void)
{
TMR1H = 0xff; // prepare timer for 10uS pulse