系统上电后，发光两级管闪烁，表明控制电路进入工作状态。K1和K2用来设定数码管计时时间，K3命令系统按秒倒计时，当时间到达时继电器被驱动工作，使蜂鸣器动作。-Power system, the LED flashes two tubes that enter the working state control circuit. K1 and K2 used to set the digital time control time, K3 command system by the second countdown, when the time arrived when the relays are driven, so that action buzzer.