zero crossing detect code

[lindoudaM2]

My code doesn't work well. I have a problem in synchronisation. Help me please.
here is my code
#include <16F877a.h>
#use delay(clock=1000000)
#fuses XT, NOWDT, NOPROTECT, PUT, NOLVP
#define zero_cross pin_B0;


byte x;



void init ()
{

setup_adc_ports(RA0_analog);
setup_adc(adc_clock_div_2);
set_adc_Channel(0);
setup_ccp1(ccp_pwm) ;
setup_timer_2 (T2_Div_by_1,255,1);
setup_timer_1(T1_internal);
enable_interrupts(int_timer1);
set_tris_b(0xff);
output_b(0xff);

}


#int_ext
void ext_isr()
{
if(input (pin_b0) )
ext_int_edge(H_to_L);
else
ext_int_edge(L_to_H);
}


void main()
{
init();
while (1)
{
delay_ms (10);
x=read_adc();
set_pwm1_Duty(x);
delay_ms (10);
}
}

[RF_Developer]

There are a lot of problems with this code.

First, let's put right the formatting:

[asmboy]

the latency and uncertainty of the entire approach may not be suitable - based on what you want to DO .

how little error - and how small a zero deviation can your design tolerate?

an external - latched hardware zero detector may be required .
if you want - say - a low jitter Triac trigger......

[Mike Walne]

Microchip app. note AN521 shows you how to do zero crossing detect.

Mike

[asmboy]

Be warned: the method shown in the APP note can be subject to asymmetric positive and negative half cycles - and is ONLY suitable for low frequencies - ie mains frequencies at best.

I tried and abandoned it for a design some time ago.

Second: selecting a pic with a comparator and using a negative clamped
input provides a less ambiguous way of zero cross detection ( than ADC operation ) and can have low overhead when using the 16f887, comparator #1 or #2 - which are both INTERRUPT capable.

I think you will find that the 887 will be pin for pin interchangeable
in your design and MUCH simpler than what you have been trying to do.

I first used this approach for stable, low jitter zero cross detection several years ago, in a design that works with 50 or 60 Hz line frequencies.