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Need help on pwm

 
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pokiko



Joined: 27 Jul 2007
Posts: 33

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Need help on pwm
PostPosted: Wed Aug 22, 2007 8:10 am     Reply with quote
i am using pic18f2520 with 20mhz osc and i have to write a program which will drive a full bridge thyristor. The client will enter a set voltage. By triggering the thyristors with suitable pwm, i will force the output to the desired voltage. I am using version 3.212.
The pin configuraion is as follows(This is not code):
Code:



pic_pins        pic pins used as:

RA0..RA5   //to LEDS(not so important)

RC0      SW1
RC1      PWM2
RC2      PW1
RC3      SW2
RC4      SW3
RC5      SW4
RC6      --
RC7      --


RB0      Vout   //analog feedback input for voltage
RB1      Iout   //and current

RB2      RS   //  pins to LCD
RB3      E   //   
RB4      D4   //
RB5      D5   //
RB6      D6   //
RB7      D7   


When i compile it, an error occurs such as "A numeric expression must appear here ". I want to know if a pwm selection, (such below main() ), would be a good approach or would it be better to match a specific voltage value to a specific pwm? Are there any other mistakes? If yes can you help me how can i correct them?

Code:




#include <18F2520.h>
#device  adc=8
#fuses HS,NOWDT,NOPROTECT,BROWNOUT,PUT,NOLVP
#use delay(clock=20000000)

#include "Flex_LCD.c"


#define     BUTON_UP       PIN_C0
#define     BUTON_DOWN     PIN_C3
#define     BUTON_ENTER    PIN_C4
#define     BUTON_BREAK    PIN_C5


/*----------GLOBAL VARIABLES-----------*/

int8     duty_value;     
int16    adc_value;
float    count_adc, LCD_voltage, Error;





//--------- LCD MENU ----------------//
                         

#INT_EXT           

float ext_isr(float volt,float amper)   
   {
          volt=0;


volt_set:     lcd_putc("\f");
              lcd_gotoxy(1,1);
              printf(lcd_putc,"volt set");
              delay_ms(1000);

              lcd_gotoxy(1,1);
              lcd_putc("\fvolt +");
              delay_ms(1000);

              lcd_gotoxy(1,2);
              lcd_putc("volt -");
              delay_ms(1000);

              lcd_gotoxy(1,1);
              printf(lcd_putc, "\f%3.2f", volt);



              if (input(BUTON_UP))
                 {
                  volt+=0.2;
                     if(volt>30)
                        volt=30;
                        printf(lcd_putc, "\fvolt=%3.2f", volt);

                 }


              if (input(BUTON_DOWN))
                  {
                  volt-=0.2;
                     if(volt<0)
                        volt=0;
                        printf(lcd_putc, "\fvolt=%3.2f", volt);
                  }

                    if (input(BUTON_ENTER))
                    return volt;
                    else
                    goto volt_set;
    }



/* ---------------- MAIN PROGRAM -------------------*/


int init_ADC(void);       
//float LCD_menu(float volt,float amper); 


void main()
{




int init_ADC(void)
{
  setup_adc_ports( ALL_ANALOG );
  setup_adc( ADC_CLOCK_DIV_2 );
  set_adc_channel( 12 );            //Sets A_to_D input to channel 12
  set_adc_channel(10);             
  delay_us(10);
}




        lcd_init();       
   set_tris_a(0b00000100);
   set_tris_b(0b00000011);
   set_tris_c(0b00111001);



      delay_ms(10);
      output_low(PIN_C2);                  // Set CCP1 output low
      setup_ccp1(CCP_PWM);                 // Configure CCP1 as a PWM
      output_low(PIN_C1);                  // Setup CCP2 output low
      setup_ccp2(CCP_PWM);                 // Configure CCP2 as a PWM


      setup_timer_2(T2_DIV_BY_1,255,1);   



pwm_calibration:     adc_value = read_ADC();
                     delay_us(10);

                 count_adc=((float)(adc_value/1023))*30;
                 LCD_voltage=ext_isr();
                 Error=LCD_voltage-count_adc;


                 if(Error>0.2)
                   {
                   ++duty_value;
                        if(duty_value>254)
                            duty_value=254;

                           set_pwm1_duty(duty_value);
                           set_pwm2_duty(duty_value);
                           printf(lcd_putc,"\fvolt=%3.2f",voltage);
                           goto pwm_kalibration;
                   }
                 if(Error<-0.2)
                     {--duty_value;
                        if(duty_value<1)
                           duty_value=1;

                           set_pwm1_duty(duty_value);
                           set_pwm2_duty(duty_value);
                           printf(lcd_putc,"\fvolt=%3.2",voltage);
                     }

                 if (Error<0.2 & Error>-0.2)
                       printf(lcd_putc,"\fvolt=%3.2",voltage);

                     goto pwm_calibration;


}
Ttelmah
Guest
PostPosted: Wed Aug 22, 2007 10:02 am     Reply with quote
An ISR, _never_ accepts a value, or returns a value. It must be declared as void (it makes no sense to have it accepting or returning a value, since you do not know _when_ it is going to occur in the main code, and there is nothing 'calling' it, to give it a value, or to have a value returned)...
Then you have 'init_ADC' declared to return an int, but returning nothing.
This routine, is then declared 'inside' main. This is not legal.
You declare an ISR, but never enable the interrupt.

Best Wishes
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