4-way traffic with down counter design

Discussion in 'The Projects Forum' started by digitaldesign, May 27, 2010.

  1. digitaldesign

    Thread Starter New Member

    May 1, 2010
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    I am trying to make the digital circuit for a 4-way traffic intersection and I am following the circuit below:

    http://www.electronicsforu.com/efylinux/circuit/nov2002/traffic.pdf

    However, as per my understanding, this circuit will change the traffic lighting for any particular road after every second/clock pulse (i.e. green-yellow-red-green in just pulses). However, I want to modify the circuit in the link to keep green on for, say, 9 secs, yellow for 3 secs, and red for 8 secs. Can someone suggest how I should modify the circuit to do this? Also, how would I add a down counter for the traffic light from green to red?

    Please attach circuitry needed if possible. Thanks again.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Check the many mentions here of using an LM555 timer as a clock source. Use one to do your timing intervals.
     
  3. digitaldesign

    Thread Starter New Member

    May 1, 2010
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    The circuit has a 555 timer, but I want to show green and red light for 4 secs each and yellow for 2 secs and show the down count to next light on a 7-segment display. How could I modify the circuit in the link to do this?
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    If you do not need the elaboration of the turning lane and pedestrian signals, you might find this article comes closer to your needs - http://home.cogeco.ca/~rpaisley4/20step.html

    The clock may be applied to a counter like a 74LS190 (straight TTL is very hard to come by, these days. 74 LSxx, 74HC, and 4000 CMOS IC's are easier to find. We don't know where you are, so it's hard to say just how easily some logic families may be to turn up). The next clock after count 0 is AND'ed to do a parallel load to the value you want to count to down to 0 (the '190 will have the U^/D input tied HIGH).

    Adjusting the LM555 frequency to give the desired intervals should not be too hard. Hopefully you have junk box parts to use experimentally.
     
  5. digitaldesign

    Thread Starter New Member

    May 1, 2010
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    Thanks for the idea. Actually I did previously check the diagram in the link: http://home.cogeco.ca/~rpaisley4/20stepTraffic.GIF
    but I don't get where the input to the 74LS145 is coming from? If possible could you describe how this circuit is functioning? thanks again.
     
  6. terokone

    New Member

    May 9, 2010
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    The traffic light was actually a project for me last semester in Digital 2. We built a traffic light system using entirely TTL and it had to have N/S and E/W vehicle detection in the form of a switch. I chose to challenge myself by using a single 7485 comparator and a 74193 counter. By the time the semester ended, I had the light sequence fully working, with one of the two required switches implemented. The 74193 can count either up or down, by the way.

    But anyway, on to your circuit. With the output logic on the bottom of the 20 step traffic page, it almost looks as though the 74145 input is coming from a decade counter, such as a 7490. In the case of this schematic, there's appears to be one decade counter per decoder, with both decoders operating in sink-mode, but I could be wrong on how many counters are really there.
     
    Last edited: May 30, 2010
  7. digitaldesign

    Thread Starter New Member

    May 1, 2010
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    I am trying to implement the circuit in this link: http://www.electronicsforu.com/efylinux/circuit/nov2002/traffic.pdf. However, I just wanted to clarify some confusion:

    1. for adding the various LED outputs, would I first add a 470 ohm resister at the output of the OR gate, then add the LED after the resistor and connect the other LED terminal to the ground?

    Can you please guide in this, as I want to complete this design soon.
     
    Last edited: Jun 6, 2010
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    The '145 decoders are following the counts of two BCD counters.
     
    Last edited: Jun 6, 2010
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