This system is the example of close loop control system for maintains the speed of stepper motor constant. The speed of stepper motor is sensed and feedback to controller. Controller will compare it with set value and if there is deviation then it will either increase or decrease the speed.In most of the industries the constant speed of motor is required and that should not be fall / exceed beyond specified limit. to get the precise RPM and control stepper motor is the best.The stepper motor is placed on top of laser as shown. The slotted wheel is coupled with the shaft of motor. The wheel is such a big that it can interrupt the laser beam falling on LDR. Now as the motor rotates the slotted wheel also rotates. The beam will fall on LDR only when the slot comes. This will produce one pulse. So every time when slot come in line with LDR and laser, one pulse is produced. Thus the rotation of motor is converted in to pulse that can be counted.