Now a days, automatic control systems are used widely to minimize the human errors and increase the production rate with good quality. So most of the machines used in production stream uses induction motors with variable speeds. Using analog methods we can vary the speed, but they are not accurate because of the tolerance of the devices, and also the circuit is complex.
So by using micro controller we control the speed of a DC motor using MOSFET. By applying a PWM pulse to gate of the MOSFET, the speed of the motor varies. In this system, a micro controller is interfaced with a MOSFET, Liquid Crystal Display and keys to vary the speed. If we press up or down key, micro controller varies the duty cycle of the PWM accordingly so that the average power will vary resulting variations in the speed.
The controller is interfaced with LCD to show approximate speed and set value. A look up table is generated to change the pulse width to achieve different speeds in the assembly program.