[moved] creating 50hz PWM using PIC16f877 on ccs c for Thyristor Firing

[ABHI9868715910]

Hi,

Hello Everyone this forum has been instrumental in my design work on FPGA/8051 and now PIC.

But Im stuck in a strange situation where iam required to read the status of External Interrupt and on every rising pulse I have to create a PWM of 50hz using Timer 0 to fire a thyristor.

Let me explain the circuit a little bit

Im reading the output from a zero crossing detector on PIN_B0 which is a square wave of 50HZ.
According to this signal I want to trigger my thryistor for Half wave configuration.
Im generating PWM using interrupt on timer1 and increasing the PWM using keys.

More over,if iam varying the "pwm_tm" value the whole PWM frequency is varying.

Please suggest!!

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#include <main_timer0.h>
 
#define PWM_TIMER    20480     // duty cycle 
#define PWM_OUT      PIN_C1
#define PWM_OUT1     PIN_C2
#define  Up    PIN_A5
#define  Down  PIN_A4
#define  max   PIN_A3
#define  off   PIN_A2
 
 
int1  pwm_so ;
int16 pwm_tm ;
#INT_EXT
void  EXT_isr()
{
clear_interrupt(INT_EXT);
}
 
 
 
#INT_TIMER1
void wave_timer() {
{
clear_interrupt(INT_TIMER1);
 
if (pwm_so) {
      // OFF 
      output_high(PWM_OUT); 
      output_high(PWM_OUT1); 
      
      set_timer1(56536-pwm_tm);
   }
   else { 
      // ON 
      output_low(PWM_OUT); 
      output_low(PWM_OUT1);
      set_timer1(56536-pwm_tm); 
   } 
   pwm_so = ~pwm_so; 
} 
 
}
 
 
void main()
{  setup_timer_1(T1_INTERNAL|T1_DIV_BY_1);   // setup interrupts
   enable_interrupts(INT_TIMER1);
   enable_interrupts(GLOBAL);  
   enable_interrupts(INT_EXT);
   ext_int_edge(H_TO_L);
   
   
  pwm_tm=4000;//24536-19hz //4536-100hz
  
   while(TRUE)
   {
 
{   
   if(!input(Up))
  {
   pwm_tm+=1000;
  output_d(0X02);
           }
else if(!input(down))
  {
     pwm_tm-=1000;
     output_d(0X04);
     }
else if(!input(max))
  {
     pwm_tm=0;
     output_d(0X06);
     }
else if(!input(off))
  {
     pwm_tm=4000;
     output_d(0X08);
     }
 
 delay_ms(500); // 0.5 second delay to release the selected button
 
  
  }while(input(up) && input(down)  && input(max)  && input(off));
 
  }
   
   }

---

 

[ud23]

 set_timer1(56536-pwm_tm);

you are changing the timer value so it obvious that change frequency not duty cycle.You can use CCP module to generate the PWM.


look above for example

 

[paulfjujo]

hello,


i think 50Hz frequency for PWM control is outside of spec of CCP module...
or decrease the FOSC ...

or you simply can use timers .. to built your commande.