ABSTRACT
A problem about speed-modulation of DC motor is very important in the field automatic. The requests to the effect after the speed-modulation of the DC motor are different in different fields. Then, different speed-modulation ways are using in different fields. The text will introduce two or three kinds of speed-modulation ways which are used generally. DC motor is used very generally because its speed-modulation effect is very good and its speed-modulation is easily to be realized. PWM theory is used most generally among the speed-modulation ways. The text will introduce the H-PWM way mostly. We will try to do modulation to the DC motor with AT89C51 MCU. The importance of the text is the parts which are composed the system. Another importance is the principles of working about every parts.
Keywords: speed-modulation about DC motor, computer-control, PWM,