说明：  利用单片机控制直流电机，掌握脉宽调制直流调速的方法。通过调节脉冲宽度，改变占空比，从而改变输出，达到改变直流电机转速的目的。
(The DC motor is controlled by single chip microcomputer, and the method of pulse width modulation DC speed regulation is mastered. By adjusting the pulse width and duty cycle, the output can be changed and the speed of DC motor can be changed.)