////////////////////////////////////////////////////////////////////////
//	Sonar.c
//
////////////////////////////////////////////////////////////////////////////

#include <16F876.H>

#fuses   HS,NOPROTECT,NOWDT

#include <CTYPE.H>

#use delay(clock=20000000)

#use rs232(baud=19200, xmit=PIN_C6, rcv=PIN_C7)

#define SONAR_INIT 	PIN_B3
#define SONAR_ECHO	PIN_C1
#define SONAR_BINH	PIN_B5


long time = 0;
long distance = 0;
byte done_read = 0;


void sonar_read() {

	output_high(SONAR_INIT);
	
	// start TIMER1

	set_timer1(0);	

	delay_us(900);		

	//add the blanking signal to here

	output_high(SONAR_BINH);

	// wait for ECHO to go high and get the time

	while(!input(SONAR_ECHO));

	time = get_timer1(); 		

	delay_ms(100);

	output_low(SONAR_INIT);
	output_low(SONAR_BINH);
	
	delay_ms(100);

	done_read = 1;
}


main() {

        setup_timer_1( T1_INTERNAL|T1_DIV_BY_8);

     	printf("\n\r started! \n\r");

	while(TRUE){
		
		distance = 0;

		if (getc() == 's')
			sonar_read();

		if (done_read){	
	
			printf("done read  = 1\r\n");
			printf("time = %lu\n\r", time);
		
			// calculate distance
			distance = (time * 0.276);			//(time * 0.0008)*345;

		      	printf("  Counter value: %lu -- distance: %lu\n\n\r", time, distance);
			done_read =0;
		}
	}
}