SERVO MOTOR CONTROL USING PIC16F877A (with 20MHz Crystal Oscillator)

SERVO MOTOR CONTROL USING PIC16F877A

SERVO MOTOR

Servo motors are used to control many things as it offers very precise rotation of 1 degree. For this it uses the feedback from a potentiometer connected.

For controlling the angle it require a pulse of certain duty cycle which can be achieved using the pulse with modulation (PWM) signal.

1. For 0 degree it takes a 800us pulse (us = microseconds)
2. For 90 degree it takes a 1500us pulse
3. For 180 degree it takes a 2200us pulse

Note:- This pulse can vary with different model of servo motor.

We can control is using the PIC16F877A

For this we have to understand the PWM working of the micro-controller.

PIC has overall 3 timers

• TIMER0
• TIMER1
• TIMER2

We will use the TIMER1 for generating the PWM

Register Associated with TIMER1 as a TIMER/COUNTER

TIMER1 Control Register

TIMER1 Block Diagram

The prescaler value is set to 1:1

The Crystal frequency used is 20MHz

You can connect the Bluetooth and send the command to control the angle of the servo motor.

• If the data received is 0 the motor rotates to 0 degree
• If the data received is 1 the motor rotates to 90 degree
• If the data received is 2 the motor rotates to 180 degree

Note:- Compiler or the software used here is MikroC pro for PIC

THE CODE: -

 /*code for generating 800us, 1500us and 2200us pulse for controlling servo motor 0, 90 and 180 degree

  Send the code from the bluetooth to the PIC16F877A for conrolling the angles

  Crystal oscillator connected is 20MHz

  Author:- ASHISH KUMAR       */

char a;             //char for recieving data from bluetooth

unsigned lval=0x60;

unsigned hval=0xF0;

void interrupt(){

  if(TMR1IF_bit){

     PORTB.F0=!PORTB.F0;

     TMR1L=lval;

     TMR1H=hval;

     TMR1IF_bit=0;

  }

  if(PIR1.F5)

 {

    while(PIR1.F5==0);

    a=RCREG;

    if(a=='0'){       //for 800us pulse (0 degree)

      lval=0x60;

      hval=0xF0;

    }

    else if(a=='1'){  //for 1500us pulse (90 degree)

      lval=0xB4;

      hval=0xE2;

    }

    else if(a=='2'){      //for 2200us pulse (180 degree)

      lval=0x08;

      hval=0xD5;

    }

  }

}

void main(){

  OPTION_REG= 0x87;

  TRISB.F0=0x00;

  T1CON.F5=0;

  T1CON.F4=0;

  TMR1L=lval;

  TMR1H=hval;

  TMR1IE_bit=1;

  INTCON.GIE=1;

  INTCON.PEIE=1;

  TMR1ON_bit=1;

  TRISC.F6=0;

  TRISC.F7=1;

  SPBRG=32;

  TXSTA=0x20;

  RCSTA=0x90;

  PIE1.F5=1;

  PIE1.F4=0;

  while(1){

    //write your code

  }

}

SIMULATION OUTPUT: -

Proteus Simulations

   

Pulse Output

800us Pulse

1500us Pulse

2200us Pulse

Get the Code and Simulation (Click Here)