PIC Servo Controller

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Code

#include <18f4520.h>   
#device ADC=10                 // set ADC to 10 bit accuracy
#fuses HS,NOLVP,NOWDT,NOPROTECT
#use delay(clock=40000000)
#use rs232(baud=19200, UART1)  // hardware uart much better; uses  RC6/TX and RC7/RX 

#define PanTorqueMax 650       // 650 corresponds to 100% duty cycle for driving the motor full on in one dirction
#define PanTorqueMin -650      // -650 corresponds to 0% duty cylce for driving the motor full on in the other direction
#define pGain 0                // This is the Proportional coefficient, adjust this first
#define iGain 0                // This is the Integral coefficient, adjust this second
#define dGain 0                // This is the Derivative coefficient, adjust this last

signed int32 rise,fall,pulse_width;
int32 msecs=0;
signed int32 PanTarget = 0;
signed int32 PanActual = 0;
signed int32 PanError, PanErrorLastTime=0, PanIntegral, PanDerivative, PanTorque=0;
int16 value;
int i=0;

#int_ccp1                      // This is the CCP capture interrupt, this allows you to use one pin (CCP1) to capture both
                               // the rising edge and falling edge of the servo PWM signal, which leaves the other CCP pin
                               // open for drving the servo motor
void isr()
{
   if (i==0) {output_high(PIN_A1);
              rise = CCP_1;
              setup_ccp1(CCP_CAPTURE_FE);
              i=1;}
   else if (i==1) {output_low(PIN_A1);
                   fall = CCP_1;
                   pulse_width = fall - rise;
                   setup_ccp1(CCP_CAPTURE_RE);
                   i=0;}
}

 
#INT_TIMER2                    // designates that this is the routine to call when timer2 overflows
void Timer2isr() {
   msecs++;                    // keep track of time
     
   if ((msecs & 7) == 0) {     // servo routine every 8ms is plenty.  125x/sec
      output_high(PIN_B0);
      PanTarget=pulse_width;
      PanActual=read_adc();
      PanActual=25*PanActual;
      
      PanError = PanTarget - PanActual;      // position error
      PanIntegral += PanError;
      PanDerivative = PanError - PanErrorLastTime;
      PanErrorLastTime = PanError;
      
      PanTorque = pGain * PanError + iGain * PanIntegral + dGain * PanDerivative;     
      TorqueShifted=PanTorque>>16;
      if (PanTorque < PanTorqueMin) PanTorque = PanTorqueMin;
      if (PanTorque > PanTorqueMax) PanTorque = PanTorqueMax;
      
      if (PanActual<PanTarget){
         output_low(PIN_C0);
         set_pwm2_duty(PanTorque);       
      }
      else if (PanActual>PanTarget){
         output_high(PIN_C0);
         set_pwm2_duty(650 + PanTorque);
      }
      
      output_low(PIN_B0);
   }
}
      
     

void main() {

   setup_timer_2(T2_DIV_BY_4, 156, 16);        // clock at 16KHz, interrupt every 4*25nS * 4 * 156 * 16 = 1.0mS
   setup_timer_1(T1_INTERNAL);  //start timer 1
   
   setup_adc_ports(AN0);               // Enable analog inputs; This will read the ADC on pin AN0
   setup_adc(ADC_CLOCK_INTERNAL);      
   
   setup_ccp2(CCP_PWM);                // PWM output on CCP1/RC2, pin 17
   setup_ccp1(CCP_CAPTURE_RE);
   
   enable_interrupts(INT_CCP1);  
   enable_interrupts(INT_TIMER2);
   enable_interrupts(GLOBAL);
   
   //set_pwm2_duty(value);             // h-bridge for pan motor from CCP2 (pin 16, RC1) to C0 (pin 16)
   //output_high(PIN_C3);
 
   
   while (TRUE) {          

      //This is useful for debugging using the RS-232 serial communication

      printf("pulse width: %Lu     Target: %Ld         Actual: %Ld        Torque: %Ld \r\n", pulse_width,PanTarget,PanActual,PanTorque);
 
      

   }
}



Circuit

Servo Drive and Control Circuit
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