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stepping-motor control with PWM and L293D

 
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spom



Joined: 12 Jul 2007
Posts: 32

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stepping-motor control with PWM and L293D
PostPosted: Tue Dec 04, 2007 5:07 am     Reply with quote
Hi,

I use a Pic 16F818, a no name bipolar stepping-motor with 50 steps, and a L293D(http://www.ortodoxism.ro/datasheets/texasinstruments/l293d.pdf).

I want to generate a PWM signal with the Pic, and then the motor should rotate 50 steps left, and then 50 steps right.

My code looks that way:

Code:

#include <16f818.h>
#use delay(clock=8000000)
#fuses NOWDT,HS,NOPUT,NOPROTECT,NOBROWNOUT,NOLVP

void main()
{

   setup_timer_2(T2_DIV_BY_4, 149, 1);
   setup_ccp1(CCP_PWM);
   set_pwm1_duty(255L);

while(TRUE)
   {
      output_high(PIN_B0);
      output_low(PIN_B1);

     //50 steps and then turn around????
   }
}


I don't know how to handle it that the motor change rotation after 50 steps.
Is the pwm right?

By the way: one inductor is connected to PIN 2 and 7 of the L293D and the other to PIN 10 and 15. Is that right?

Thanks!
Ttelmah
Guest
PostPosted: Tue Dec 04, 2007 5:17 am     Reply with quote
Basically, no.
The PWM, generates a continuous stream of pulses, allowing you to specify the mark space ratio. It does _not_ count pulses.
Almost exactly this question, was asked a while ago. A search should find it. Look for 'PWM stepper', asking the search to find 'all' terms, and you should get a number of threads about this. The simplest way for what you want,will be to ignore PWM completely.

Best Wishes
spom



Joined: 12 Jul 2007
Posts: 32

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PostPosted: Tue Dec 04, 2007 11:25 am     Reply with quote
Thanks!

But I've still had a problem. I connected one inductor with B0 and B1 of the PIC and the second inductor with B6 and B7 of the PIC.

Now my code:
Code:

#include <16f818.h>
#use delay(clock=8000000)
#fuses NOWDT,HS,NOPUT,NOPROTECT,NOBROWNOUT,NOLVP

main()
{
int sequence[8] = {130,129,65,66};

int i=0;
int16 c=0;

   while(1)
   {
      delay_us(2000);
      output_B(sequence[i]);
      i++;

      if (i>3)
      {
         c++;
         i=0;
      }

      if (c==500)
      {
         c=0;
         delay_ms(1000);
      }
   }
}


But it doesn't work! Why?

Thank you for your help!
Ttelmah
Guest
PostPosted: Tue Dec 04, 2007 3:38 pm     Reply with quote
Try reversing one coil. If you have the phase of one coil reversed, it'll just sit and move back/forwards a tiny amount.

Best Wishes
spom



Joined: 12 Jul 2007
Posts: 32

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PostPosted: Sun Dec 09, 2007 6:38 am     Reply with quote
Sorry for my stupid questions again:

I changed my code accorgding to the example EX_STEP.C from CCS C and therefor my pin assignment:

Code:

#include <16f818.h>
#use delay(clock=8000000)
#fuses NOWDT,HS,NOPUT,NOPROTECT,NOBROWNOUT,NOLVP

#BYTE port_b = 6
#define FOUR_PHASE TRUE

#ifdef FOUR_PHASE
BYTE const POSITIONS[4] = {0b0101,
                           0b1001,
                           0b1010,
                           0b0110};
#else
BYTE const POSITIONS[8] = {0b0101,
                           0b0001,
                           0b1001,
                           0b1000,
                           0b1010,
                           0b0010,
                           0b0110,
                           0b0100};
#endif


drive_stepper(BYTE speed, char dir, BYTE steps)
{
   static BYTE stepper_state = 0;
   BYTE i;

   for(i=0; i<steps; ++i) {
     delay_ms(speed);
     set_tris_b(0xf0);
     port_b = POSITIONS[ stepper_state ];
     if(dir!='R')
       stepper_state=(stepper_state+1)&(sizeof(POSITIONS)-1);
     else
       stepper_state=(stepper_state-1)&(sizeof(POSITIONS)-1);
   }
}

main()
{
   BYTE speed, steps;
   char dir;

   while (TRUE)
   {
       speed = 20;
       dir='F';
       steps = 168;

       drive_stepper(speed,dir,steps);
   }
}

But the motor doesn't rotate. I feel an easy movement, but not 7.5°.
The contacts are right as the power supply fall down after switching on. So the motor need current.
Where is the fault?

Thanks!
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