traffic light circuit

  (1) The signal light control circuit consists of an 8-bit one-way shift register to form a twisted ring counter , which counts the unit time and
outputs it through a decoder composed of an inverter to control the east-west, north-south lights respectively, among which the yellow light is flashing Bright.
    (2) The digital display circuit is composed of a presettable reversible 8421BCD code counter 74LS192 coupled with a 74LS48 and LED digital tube.
Setting and counting are controlled by the red and yellow lights of the signal light. When the east-west yellow light is on, set the north-south counter to 28s. When the east-west yellow light is off and the red light
is on, the north-south (green light is on) counter starts counting by 1 from 28s. When reduced to 0, the east-west red light goes out, and the north-south green light goes out,
blocking the second signal count. In the same way, the yellow lights and red lights in the north-south direction control the setting and counting in the east-west direction.
    (3) The basic RS flip-flop (also called dither switch) composed of manual and automatic control NAND gates is used as a manual switch signal, mainly
to facilitate circuit debugging. The automatic control signal is generated by the second signal, and the output of the circuit (composed of 555) is divided by four to form the unit time f.
If you change ￡, you only need to change the frequency division series. If the time is required to be precise, a crystal oscillator can be used to divide the frequency to obtain the seconds signal. The circuit is shown in Figure
16 Book 3.