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16F684 pwm motor control

 
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daniel123
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16F684 pwm motor control
PostPosted: Wed Jul 29, 2009 7:19 am     Reply with quote
I'm using the pwm module of pic16f684 to control the speed of a DC motor. The only problem is when the duty cycle is zero the motor is still running. Could someone help me.

thank you
Ttelmah
Guest
PostPosted: Wed Jul 29, 2009 7:38 am     Reply with quote
Start by disconnecting the motor, set a duty cycle of zero, and measure what is coming out of the PWM pin. If you have a scope, use this, otherwise, wire up a LED, with a current limiting resistor, and attach this to the pin. Is it off?. If it is, then the problem is in the hardware you are using to drive the motor. Perhaps the transistor is not quite switching off?. If it is on, then simplify the code down to just a routine to setup the timer, and setting the duty cycle to zero. Does this solve the problem?. If not, then the 'odds' are that possibly the PWM output pin itself has been damaged. Classic for doing this, is using a transistor to drive a motor/inductor, without a 'trap' diode across it, or some other circuit to catch flyback. Without this, when the drive switches off, the inductance in the coil (and the generator effect for a motor), can generate a massive voltage, having nowhere to 'go', and eventually finds a route, from the collector to the base of the transistor, then from this into the output of the PIC....

Best Wishes
delifadzli



Joined: 12 Apr 2010
Posts: 27

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PostPosted: Sun Jun 06, 2010 12:43 pm     Reply with quote
Code:
#include <16F877A.h>
#device ADC=10
#fuses HS,NOWDT,NOPROTECT,PUT,BROWNOUT,NOLVP
#use Delay(clock=20000000)

#include "C:\Users\deli\Desktop\satu\brum\Flexlcd2.c"

#define medium   500L
#define slow     100L
#define fast     700L

//#define medium          125L
//#define slow            63L
//#define fast            240L

void main()
{
  int16 temp_adc;
  float temp;
  int16 pwm_duty;




   setup_adc(ADC_CLOCK_DIV_8);
   setup_adc_ports(PIN_A1);
   set_adc_channel(1); //read analog input from channel 1
   output_low(PIN_C2);    // Set CCP1 output low
   setup_ccp1(CCP_PWM);   // Configure CCP1 as a PWM
   setup_timer_2(T2_DIV_BY_4, 249, 1);         // 5khz
   set_pwm1_duty(medium);  // Set for 50% duty cycle

   lcd_init();

   lcd_putc("\fsuhu leni:\n");

   while(1)

   {
    temp_adc = read_adc();

    temp = 5.00*temp_adc*100.00/1023.00;
    lcd_gotoxy(1,2);
    printf(lcd_putc,"%f",temp);
    delay_ms(3000);



     if ((temp_adc < 58) && (input(PIN_B7)==1))

      {
         temp_adc = slow;
      }
      else if ( (temp_adc >= 58) && (temp_adc < 70) && (input(PIN_B7)==1))
      {
         temp_adc = medium;
         }
      else if ((temp_adc >= 70) && (input(PIN_B7)==1))
         temp_adc = fast;

       else
       temp_adc = 0;

    set_pwm1_duty(temp_adc); //Change duty cycle and adjust
        }

}

Isn't in this code...I can produce zero speed--means motor turn off...I also had the same problem....other routine...seems to be ok, just for the turning off the motor- it cause the motor to run at full speed...?? why

input pinb7 just additional pin that i planned to use for another sensor..but in this time i just use a wire....
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