Shakil Seeraji, Enaiyat Ghani Ovy, Tasnim Alam, Ahsan Zamee & Abdur Rahman Al Emon International Journal of Robotics and Automation (IJRA), Volume (2) : Issue (3) : 2011 221 A Flexible Closed Loop PMDC Motor Speed Control System for Precise Positioning Shakil Seeraji shakil.ae@mist.edu.bd Department of Aeronautical Engineering Military Institute of Science and Technology Mirpur Cantonment, Dhaka-1216, Bangladesh Enaiyat Ghani Ovy enaiyat_ovy@yahoo.com Department of Mechanical and Chemical Engineering Islamic University of Technology Board Bazar, Gazipur-1704, BANGLADESH Tasnim Alam rim_mist@yahoo.com Department of Electrical electronic and communication Engineering Military Institute of Science and Technology Mirpur Cantonment, Dhaka-1216, Bangladesh Ahsan Zamee zamee_mist@yahoo.com Department of Electrical electronic and communication Engineering Military Institute of Science and Technology Mirpur Cantonment, Dhaka-1216, Bangladesh Abdur Rahman Al Emon emon1535@gmail.com Department of Electrical electronic and communication Engineering Military Institute of Science and Technology Mirpur Cantonment, Dhaka-1216, Bangladesh Abstract The speed control of DC motor is very significant especially in applications where precision is of great importance. Due to its ease of controllability the DC motor is used in many industrial applications requiring variable speed and load characteristics. So the precise speed control of a DC motor is very crucial in industry. In this case microcontrollers play a vital role for the flexible control of DC motors. This current research work investigates the implementation of an ATmega8L microcontroller for the speed control of DC motor fed by a DC chopper. The chopper is driven by a high frequency PWM signal. Controlling the PWM duty cycle is equivalent to controlling the motor terminal voltage, which in turn adjusts directly the motor speed. H-bridge circuit is implemented for the bi-directional control of the motor. A prototype of permanent magnet DC motor speed control system using the microcontroller is developed and tested. Keywords: ATmega8L Microcontroller, DC Chopper, PWM, Tachogenerator, PMDC Motor, H- Bridge. 1. INTRODUCTION DC motor transforms electrical energy into mechanical energy. They are used to drive devices such as fans, cars, door locks, seat adjust, mirror adjust, anti-lock braking system window lifts, robot arms, hoists etc. So the speed control of a DC motor is essential in this present industrial world. Many significant researches have been found regarding control techniques of the DC motors. From earlier research work, some techniques to control the DC motors are notable to be mentioned. Refai [1] designed a PID controller which was based on MC68B00 microprocessor to