通过串行口，提示用户输入倒计时时间(0~999秒)；

时间设定完成后提示用户选择控制方式：“倒计时开”还是“倒计时关”；

若用户选择 “倒计时关”，继电器立即吸合，并倒计时直到时间为0时关断继电器；

若用户选择“倒计时开”，继电器暂不吸合，等倒计时时间为0时再吸合继电器；

倒计时时间通过串口送上位机(每秒更新一次)；

倒计时结束时蜂鸣器鸣响2秒作为提示；

-Through the serial port, prompts the user to enter the countdown time (0 ~ 999 seconds)　time is set up prompts the user to select control mode: " Countdown to open"　or " Countdown off"　 if the user selects " Countdown off" , relays immediately suck together, and the countdown until the time is 0:00 off relay　if the user selects " countdown to open"　relay temporarily Pick-up, and so the countdown time is 0:00 and then pull-in relay　countdown time, sent through the serial port bit machine ( updated once per second)　countdown to the end of two seconds when the buzzer sounded as a reminder