High Precision
Servo Driver Box
Uploaded: 1/14/15

 
 This project will be used
      as a bench test component for setting up servos in other projects,
      including robots, and other moving devices. The knob is read
      with a 10 bit A/D and converted to a .5 to 2.5mS output pulse
      to drive a standard servo with an attachable digital display
      (used for other bench tests as well) for four digit accuracy
      in pulse width settings. This was my first major project written
      entirely in C. :o


      
 Below: Bench
      setup, with servo in small red vice, servo test box and illuminated
      LCD display.

      


      
Below: Accurate
      4 digit readings of pulse width. Essentially, 2mS range in 1024
      steps. 9v batt

      
inside the box.

      


      
Below: Hookup connectors
      for Servo and LCD, a black foam block covers it when not in use.

      


      
Below: 1.508mS
      shown as 1508uS

      


      
Below: Inside the
      box

      


      
Below: Schematic
      of board - 12F675 processor. An xtal is used for running the
      processor at 10Mhz, so it can

      
operate the LCD.

      


      

Code:

//****************************************************************************
//Chris Schur
//Servoboard Knob test box:  12F675
//Date:  1/4/15
//****************************************************************************
/*Description of this Program: This program Will take the push button controlled
servo test board, add a pot and use that instead to vary the pulse output from
.5ms to 2.5ms
*/

//I/O Designations ---------------------------------------------------
// A0 (GPIO0):  (An0) POT INPUT
// A1 (GPIO1):  (An1) LCD & LED OUT
// A2 (GPIO2):  (An2) SERVO PULSE OUTPUT -or- LCD OUT
// A3 (GPIO3):  X (can ONLY be input)
// A4 (GPIO4):  XTAL OUT (An3) 
// A5 (GPIO5):  XTAL IN

//--------------------------------------------------------------------
//Include Files:
#include <12F675.h>  //Normally chip, math, etc.  used is here.
//Directives and Defines:
#device ADC=10  //This directive will only work if put RIGHT HERE first...
#fuses NOPROTECT,NOMCLR
#use delay(crystal=10MHz)
#use fast_io(A)
#use rs232(baud = 9600, xmit=Pin_A1, bits=8, parity=N, INVERT, stream = SERIAL)

//****************************************************************************
//Global Variables:
//******************************************/
   
//Functions/Subroutines, Prototypes:


//****************************************************************************
//-- Main Program
//****************************************************************************
void main(void) {
   // Set TRIS I/O directions, define analog inputs, compartors:
              
        set_tris_A(0b101001);  //sets port directions
        
        //(analog inputs digital by default)
        setup_adc_ports(sAN0);
        setup_adc(ADC_CLOCK_DIV_32);
        set_adc_channel(0);
           
   //Initialize variables and Outputs:  --------------------------------------
   
    int16 result; //0 - 1023 out of ADC
    int16 on_pulse;   //servo high pulse width in uS
    output_low(PIN_A1);   //turn off status led
    
   //----------------------------------------------------------------
//MAIN LOOP:
while (true)  {
    //First read ADC
    result = read_adc();
    
    //calculate pulse width:
    on_pulse = (2*result) +500;    //for a range of .5mS to 2.5mS
    
    //next send pulse to servo output:
    
    output_high(PIN_A2); //servo out = 1    
    delay_us(on_pulse);  //high time
    output_low(PIN_A2);  //turn off pulse    
    
    delay_ms(4);        //space between pulses=20 with lcd serial delays
    fputc(12,SERIAL);    //Clear screen
    delay_ms(1);
    fprintf(SERIAL,"%Lu"on_pulse);
    delay_ms(1);
    fputs(" uS",SERIAL);
    delay_ms(2);
    
   }
   
}
//********* Functions which have prototypes at top of program ****************
   
  






 

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