Display time of Input pulse on LCD

[Prashant Patel]

Hi..
I want to find out the time of a single pulse input
to the PIC16F877 and display it on LCD. I want to
count it on 16bit counter. I have the example
program: EX_PULSE.c that is given with CCS C PCM
3.202 compiler.

In the code of this file they have used timer0 of 8bit.
I have changed the same code for Timer 1. And apply the
external clock on port B1. When I connect the battery
it is displaying some values on LCD. After that I start
the input signal on port b1 but now this displayed value
does not change. If I apply the signal before to connect
the battery. It does not display anything.

My code is as follows..
---------------------------------------------------------

#include <16F877.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=20000000)

#include <lcd.c>


void wait_for_low_to_high() {

while(input(PIN_B1)) ;/* if it's high, wait for a low */

delay_us(3); /* account for fall time */

while(!input(PIN_B1)); /* wait for signal to go high */
}

void wait_for_low() {

delay_us(3); /* account for rise time */

while(input(PIN_B1)); /* wait for signal to go high */
}

void main() {

// BYTE time;
long time;

set_tris_b(0xFF);

lcd_init();
delay_ms(6);

while(TRUE){

// setup_counters( RTCC_INTERNAL, RTCC_DIV_2 );
setup_timer_1(T1_INTERNAL|T1_DIV_BY_8);


wait_for_low_to_high();
// set_rtcc(0);
set_timer1(0); // start counting


wait_for_low_to_high();

//setup_timer_1(T1_DISABLED);
//time = get_rtcc();
time=get_timer1(); // get the time


printf(lcd_putc,"\fTime = %U ",time); //and print frequency
delay_ms(500);

}
}

------------------------------------
Any help appriciated........

Thanks...
Prashant

[Guest]

Prashant -

What number do you see on the display? What does your input signal look like: how long high, how long low, etc? Can you send and display a constant number on your lcd to narrow it down to an lcd versus input issue? Could just be a wiring/connection issue, but can't tell based on this information....

Thanks!

[Prashant Patel]

Hi..

We are applying square wave input...
Actually I want to display the RPM of the input sinal.
Its range is 0 Hz to 500 Hz. I have tried the simplest
way like below. Now it is working. But if we keep the
same frequency for some seconds then after it does not
change the displayed value on the LCD.
What can be the problem..??
And When we connect the power suppy to the circuit, some
time it is displayed fine and some time it does not displayed
anything on LCD. We can see this time LCD activated.
This method is responding slow.
-------------------------------------------------------------
#include <16F877.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=20000000)

#include <lcd.c>


void main() {

// BYTE time;
int time;
double frpm;

lcd_init();
delay_ms(6);

while(TRUE){

setup_timer_1(T1_EXTERNAL);

set_timer1(0); // start counting
delay_ms(1000);
time=get_timer1(); // get the time

frpm = 60.0*(float)time;

printf(lcd_putc,"\fRPM=%05.0f",frpm);

delay_ms(1000);

}//while(TRUE)
}//main
-------------------------------------------------------------
Thanks...
Prashant