十字路空交通灯工作电路，红黄绿灯交替变化，同时增加一个数码管显示，以时间的倒计时方便提示红绿灯的变化。有行人通过时，需要按动控制开关，延长行人所需要的时间。-Design a Crossroads empty of traffic lights working circuit, so alternating red, yellow, green, and add a digital display, in order to facilitate the prompt change time countdown traffic lights. There are pedestrians, you need to press the control switch, extend the time needed for pedestrians.