说明：  单刀双掷处接单片机I/O口，通过单片机输出高低电平导通三级管来驱动nmos管，使得直流电机电路导通或者断开来实现直流电机开关
(Single pole double throw is connected with I / O port of single chip microcomputer, and NMOS is driven by high and low level on-off three-stage transistor of single chip microcomputer output, which makes DC motor circuit on or off to realize DC motor switch)