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////////////////////////////////////////////////////////////////////////////////
//
// 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
TMR1L = -14;
T1CON = 0x21; // 1:4 prescale and running
TMR1IF = 0;
trig = 1; // start trigger pulse
while(!TMR1IF); // wait 10uS
trig = 0; // end trigger pulse
TMR1ON = 0; // stop timer
TMR1H = 0; // prepare timer to measure echo pulse
TMR1L = 0;
T1CON = 0x20; // 1:4 prescale but not running yet
TMR1IF = 0;
while(!echo && !TMR1IF); // wait for echo pulse to start (go high)
TMR1ON = 1; // start timer to measure pulse
while(echo && !TMR1IF); // wait for echo pulse to stop (go low)
TMR1ON = 0; // stop timer
return (TMR1H<<8)+TMR1L; // TMR1H:TMR1L contains flight time of the pulse in 0.8uS units
}
void clrscn(void)
{
SEN = 1; // send start bit
while(SEN); // and wait for it to clear
SSPIF = 0;
SSPBUF = 0xc6; // LCD02 I2C address
while(!SSPIF); // wait for interrupt
SSPIF = 0; // then clear it.
SSPBUF = 0; // address of register to write to
while(!SSPIF); //
SSPIF = 0; //
SSPBUF = 12; // clear screen
while(!SSPIF); //
SSPIF = 0; //
SSPBUF = 4; // cursor off
while(!SSPIF); //
SSPIF = 0; //
PEN = 1; // send stop bit
while(PEN); //
}
void cursor(char pos)
{
SEN = 1; // send start bit
while(SEN); // and wait for it to clear
SSPIF = 0;
SSPBUF = 0xc6; // LCD02 I2C address
while(!SSPIF); // wait for interrupt
SSPIF = 0; // then clear it.
SSPBUF = 0; // address of register to write to
while(!SSPIF); //
SSPIF = 0; //
SSPBUF = 2; // set cursor
while(!SSPIF); //
SSPIF = 0; //
SSPBUF = pos; //
while(!SSPIF); //
SSPIF = 0; //
PEN = 1; // send stop bit
while(PEN); //
}
void print(char *p)
{
SEN = 1; // send start bit
while(SEN); // and wait for it to clear
SSPIF = 0;
SSPBUF = 0xc6; // LCD02 I2C address
while(!SSPIF); // wait for interrupt
SSPIF = 0; // then clear it.
SSPBUF = 0; // address of register to write to
while(!SSPIF); //
SSPIF = 0; //
while(*p) {
SSPBUF = *p++; // write the data
while(!SSPIF); //
SSPIF = 0; //
}
PEN = 1; // send stop bit
while(PEN); //
}
void setup(void)
{
unsigned long x;
TRISB = 0xfe; // RB0 (trig) is output
PORTB = 0xfe; // and starts low
TRISC = 0xff;
PORTC = 0xff;
SSPSTAT = 0x80;
SSPCON = 0x38;
SSPCON2 = 0x00;
SSPADD = 50; // SCL = 91khz with 20Mhz Osc
for(x=0; x<300000L; x++); // wait for LCD03 to initialise
}
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