Now a days DC motor plays a vital role in most of the industrial areas, it can be seen in most of the electronic devices. They are mainly used for the mechanical movements of physical applications such as rolling the bundle of sheets or CD drives, lifts etc. Many methods evolved to control the revolution of a motor.
DC motors can be controlled either by software or directly by hardware. Software controlling needs computers which are bulky and common man cannot afford for it, so hardware controls are in use. Even in hardware if it is programmable device then it is preferred because it can be modeled according to the requirements of the user.
This circuit controls the speed of the motor on time duration basis. The PWM (Pulse Width modulation) output from the four port pins is given to the H-Bridge circuit which drives the motor. On changing the duty cycle (ON time), we can change the speed. The speeds will automatically vary with time that is from full speed then slow, slower and slower and so on finally after sometime again full speed and the same procedure: