LED Traffic light Circuit

Discussion in 'The Projects Forum' started by daskywalker, Mar 29, 2010.

  1. daskywalker

    Thread Starter New Member

    Mar 28, 2010
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    So for my final project I decided to build this circuit:
    http://www.bowdenshobbycircuits.info/page10.htm#traffic.gif

    I was just wondering whether there are any substitutes for the CMOS 4017 decade counter...
    I also tried to understand how this circuit works but with little success. So far I only understand that the 47k resistor changes the cycle time since it affects the discharge time of the 10uF capacitor...anybody can explain why the LED alternates between the two sets of LEDs and how it manages to have the yellow light shorter than the green and red?
     
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    The 4017 (in some variation) is fairly unique as it acts as both a counter and decoder; each clock pulse in to it steps the active output along one of it's output pins.

    That should also tell you how & why the LED timing works..

    It is possible to build something to do the same job, using two or three other ICs..
    4017s are cheap and common, with many suppliers. Stick to that.
     
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  3. John P

    AAC Fanatic!

    Oct 14, 2008
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    Basically, the 4107 counts through 10 different states. The diode networks cause these outputs to work in groups, so they act as if each element of the group has the same effect, but in fact the various components are sequential, and each take the same length of time. The numbers of states in each group are 4, 1, 4, 1 (making 10 in all). That means you get 4 state times showing green, 1 showing yellow, then 4 states of green and one of yellow for the other direction, then it starts again. By wiring the LEDs in series, when north-south traffic is seeing green or yellow, east-west is seeing red. It's simple and quite ingenious.

    Yes, the timing (same for all states) is set by the 10K, 47K and 10uF components on the left.
     
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  4. daskywalker

    Thread Starter New Member

    Mar 28, 2010
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    Many thanks for the replies. Now I got a little follow up question. I was looking for the components online at newark.com and each chip seemed to have different manufacturing numbers and stuff which kind of confused me. Can anyone comfirm that NTE4017B and CD4017BM are the same thing?
     
  5. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    Yep, they are the same basic chip.

    The 4000 series are made by many companies and each make has it's own prefix, but generally they are interchangeable.

    The suffix letter can signify the package type; normal through-hole pins or surface mount. You need to check that when you are ordering and make sure you don't get a surface mount chip my mistake - they are rather difficult to work with..
     
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  6. daskywalker

    Thread Starter New Member

    Mar 28, 2010
    13
    0
    yep I was told to look for DIP chips, which fits our provided mini breadboards. :)
     
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