Ultrasonic SRF05 with PIC 16F877a or similar

////////////////////////////////////////////////////////////////////////////////
//
//     PIC16F877 + SRF05 + LCD03 example
//     Written October 2005 by Gerald Coe, using HITECH PIC16 compiler
// 
//		 Performs ranging using just a single pin on the PIC16F877 (RB0)
//
//		 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 <htc.h>
#include <stdio.h>
	 
__CONFIG(0x3b32);								// configuration register - see PIC data sheet for details		

#define TrgEch			RB0
#define TrgDir			TRISB0

void clrscn(void);							// prototypes
void cursor(char pos);
void print(char *p);
void setup(void);
unsigned int get_srf05(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,"SRF05 Ranger Test");		// text, printed into our buffer
	print(s);									// send it to the LCD03

	while(1) {									// loop forever
		range = get_srf05();					// get range from srf05 (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 srf05 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_srf05(void)
{
	TMR1H = 0xff;								// prepare timer for 10uS pulse
	TMR1L = -14;
	T1CON = 0x21;								// 1:4 prescale and running
	TMR1IF = 0;
	TrgDir = 0;									// make trigger/echo pin an output	
	TrgEch = 1;									// start trigger pulse
	while(!TMR1IF);							// wait 10uS
	TrgEch = 0;									// end trigger pulse
	TMR1ON = 0;									// stop timer
	TrgDir = 1;									// make trigger/echo pin an input
		
	TMR1H = 0;									// prepare timer to measure echo pulse
	TMR1L = 0;	
	T1CON = 0x20;								// 1:4 prescale but not running yet
	TMR1IF = 0;
	while(!TrgEch && !TMR1IF);				// wait for echo pulse to start (go high)
	TMR1ON = 1;									// start timer to measure pulse
	while(TrgEch && !TMR1IF);				// wait for echo pulse to stop (go low)
	TMR1ON = 0;									// stop timer
	TrgDir = 0;									// make trigger/echo pin an output again	
	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;

	PORTB = 0xfe;						// RB0 (trig) is output
	TRISB = 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		
}