用单 片 机实现pwm控制小车的前进后退调速系统，使得学习单片机增加兴趣-MCU control with pwm speed control system car' s forward and back

控制小车用pwm方式来控制小车的转速，小车的步进电机需要用直流电机控制，因为单片机产生的电流小-Control pwm to control the car with the car' s speed, the car of the stepper motor DC motor control needed because the current generated by small SCM