当输入引脚接收到一个低信号时，输出为高电平，延时30S.如果一直有信号，则灯不熄。直到检测到输入端为高时，延时一段时间后熄灯(When the input pin receives a low signal, the output is high level, delay 30S. If there is always a signal, the lamp will not go out. The lights go off after a period of time when the input terminal is high)