说明：  基于MC51单片机的直流电机PWM调速系统（全套电路图，PCB图）。主要用于需要用单片机来控制直流电机的调速正反转运行
(Dc motor PWM speed regulation system based on MC51 SCM (the complete circuit diagram and PCB diagram). Mainly used in the need to use single chip microcomputer to control the speed of dc motor and reversing operation )