Building traffic light circuit using synchronous digital logic and 555 timer

Discussion in 'Homework Help' started by Kyy, Sep 14, 2015.

  1. Kyy

    Thread Starter New Member

    Sep 13, 2015
    Hi everyone,

    I would appreciate it if you could help me a bit with my assignment.
    I've been trying to figure out how to create a traffic light using logic gates with the SL74HC74 Dual D Flipflop, a 555 timer clock signal and proceeding input logic driving 3 LEDs.
    There are 4 states in total (I've also been assigned certain numbers for the corresponding states):
    U - Unused state (RED, Wait) (10)
    TA - Traffic Active (GREEN, Wait) (00)
    TW - Traffic Warning (YELLOW, Wait) (01)
    TS - Traffic Stopped (RED, Go) (11)
    *With color being for traffic and Wait/Go for pedestrians.

    A switch will be used to set the TA state to TW (active high switch).
    A switch will be used to set the state machine to the U state.
    Inputs will be done with a DIP switch.

    I've been tinkering around trying to create a schematic diagram (using logisim) but to no avail.
    The state diagram and attempted truth table and Boolean algebra is attached below (I apologize for the messy handwriting!).

    As always, thanks for your help!
  2. ericgibbs

    Senior Member

    Jan 29, 2010
    hi K,
    Cleaned up your image, it was hard to read.
    In the UK we would call this a Light Controlled Pedestrian Crossing.
  3. absf

    Senior Member

    Dec 29, 2010
    Resized to 25% of the original so people here are more willing to see it.