Interfacing Servo Motor with 8051 using Keil C

Interfacing Servo Motor with 8051 using Keil C

A servo motor uses servo mechanism, which is a closed loop mechanism that uses position feedback to control the precise angular position of the shaft. Stepper Motors, which is an open loop system can also be used for precise angular control. But Servo Motors are preferred in angular motion applications such as robotic arm. Moreover controlling of servo motors are very simple, easy and needs no extra hardware like stepper motor. Usually hobby circuit servo motors have three wires. Two of them are red and black which is used to give power to the motor and the third wire is used to provide control signal for angular position. It uses Pulse Width Modulated (PWM) waves as control signals. The angle of rotation is determined by the width of the pulse at the control pin. The servo motor used here is having angle of rotation from 0 to 180 degrees. We can control the exact angular position by varying the pulse between 1ms to 2ms. Before using this in your application, please refer the datasheet of your servo for angle and pulse width informations.

Controlling Angular Position of Servo Motor using Pulse Width Modulation

Controlling Angular Position of Servo Motor using Pulse Width Modulation

Circuit Diagram

Interfacing Servo Motor with 8051 - Circuit Diagram

Interfacing Servo Motor with 8051 – Circuit Diagram

8MHz crystal is used to provide the required clock for 8051 microcontroller and 22pF capacitors are used to stabilize the operation of crystal. 10KΩ resistor and 10μF capacitor is used to provide the required Power On Reset (POR) to the microcontroller. Control of Servo Motor is connected to first pin of Port 2.

Keil C Code

#include <intrins.h>

sbit motor_pin = P2^0;
void Delay(unsigned int);
void Delay_servo(unsigned int);
void main()
  motor_pin = 0;

    //Turn to 0 degree
    motor_pin = 1;
    motor_pin = 0;


    //Turn to 90 degree

    //Turn to 180 degree


void Delay(unsigned int ms)
  unsigned long int us = ms*1000;

void Delay_servo(unsigned int us)

Download Here

You can download Keil C files and Proteus files here…

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Comments (23)

  • Rohan

    _nop_ wat is it

    October 25, 2013 at 2:46 am
  • Ligo George

    It is an instruction to “do nothing”… It simply waste time for 1 clock cycle…

    October 25, 2013 at 8:44 pm
  • Thiago Isac

    Which the compiler you used?

    I use Sdcc, but it does not work with your code.

    July 16, 2014 at 12:54 am
  • Ligo George

    Keil C

    July 16, 2014 at 7:23 am

    how to control the position sir

    July 16, 2014 at 9:43 am
  • Ligo George

    Just adjust the pulse width.. position will be updated accordingly..

    July 17, 2014 at 10:31 am

    Hello sir..
    sir i want coding of servo motor in assembly language that servo motor rotate in clockwise as well as anti-clockwise.
    please guide me sir.
    i will be thankul to you…

    November 26, 2014 at 1:09 am
  • Ligo George

    Sorry, we haven’t assembly language code.

    November 28, 2014 at 7:40 pm
  • dheeraj

    hello sir
    is it possible to contrl the pulse width externaly…..? if yes ….how?

    January 31, 2015 at 1:26 am
  • Ligo George

    Yes, ofcourse..
    You may use switches or potentiometer to provide input signals..

    February 9, 2015 at 8:26 pm
  • shardul

    by pulse width do you mean the values of “xx” in delay_servo(xx)??

    May 5, 2015 at 4:10 pm
  • Ligo George

    You can change the pulse width by changing the delay.

    May 6, 2015 at 10:29 am
  • Hồng Đàm Thu

    Hi sir! how to calculate the value xx?

    October 31, 2015 at 10:28 am
  • Ligo George

    It will vary depending on the servo you are using. Best method is to use trial and error.

    November 21, 2015 at 1:53 pm
  • Rahul Tiwari

    can you please explain delay calculation behind the figures 50 ,82 and 110
    i mean what is the formula behind it

    April 7, 2016 at 7:29 pm
  • Ligo George

    That is calculated by trial and error.

    April 15, 2016 at 8:14 am
  • Vishnu Satheesan Kallarakkal

    i tried this code in Tower Pro M G 90S micro servo and 89s52 controller,sadly my servo become very hot and now its not working,i tried the same thing on another servo…i lost that one tooo.. 🙁 plz help

    June 10, 2016 at 12:51 pm
  • Ligo George

    Are you sure those connection were correct ? It won’t damage the servo even if you provide wrong signals from the microcontroller. Most probably you given motor power supply to the signal input terminal.

    August 27, 2016 at 12:21 pm
  • makarand max

    very good article, cleared all my concepts of controlling the servo by using PWM .The simulation worked very well on proteus. Now i hope i can control this hobby servos with industrial PLC.

    November 6, 2016 at 10:18 pm
  • Ligo George

    Thanks for the feedback.

    November 27, 2016 at 2:32 pm
  • Cyril Joy

    Can this program work on AT89S52

    March 14, 2017 at 2:43 pm
  • __GK__

    This code will work for at89s51?

    March 28, 2017 at 5:44 pm
  • vinnakota ratish raj

    how do we upload this code to the microcontroller

    October 1, 2018 at 3:00 pm

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