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Digital counter small question

  1. Dec 12, 2009 #1
    hi there...
    I wanted to ask about a way to cascade or let's say connect two sets of 4-bit flipflop JK counters together..
    I want to create a circuit that is an up-down counter from 0 to 99..but as it is known, its difficult to use 8 inputs ofcourse.. so the best way is to have two sets of 4 jk flipflops..the first set will be connected to a 7seg and will count up and down, while the other one will not count up or down unless the first one has finished 10 counts..I hope u get what I mean..
    the problem is that I didnt know how to connect the first circuit with the other one, in order for the first one to trigger the second one..do u guys have any idea how can I apply this? thanx a looot in advance :)
     
  2. jcsd
  3. Dec 13, 2009 #2

    vk6kro

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    The output of the 4th JK counter (X3 in the diagram below) falls when it clocks over from 9 to 0.
    You can use this falling pulse to clock the next set of flip flops. You could invert it if the counter needed a rising edge.

    You would wire the 1st 4 JKs as a BCD counter so that it divided by 10 but gave outputs from each stage as powers of 2.
    So the 1st stage would give a 0 or a 1 and this would be worth 0 or 1.
    But if the next stage gives a 1 it is worth 2. The next stage's 1 is worth 4 and the last one is worth 8.

    So, 1 0 0 1 is worth 9.
    Note the values from 10 to 15 cannot occur as this is a BCD counter.


    deccount.gif

    This would only count up as shown.


    However, to do what you want, you could just get a 74LS192 chip or the 4510 which can count up or down, and already give BCD out.

    If counting down wasn't important, you could get a 4518 which already has two BCD counters in the one chip, or the 40110 which already has 7 segment drivers in the counter chip. These only count up though.
     

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    Last edited: Dec 13, 2009
  4. Dec 13, 2009 #3
    You can easily design any such counter using the K-mapping tutorial given in the instruction section of this site.

    KM
     
  5. Dec 19, 2009 #4
    Thanx guys that was a lot of help :) I really appreciate it..
    but now I am having a problem connecting the two IC's.. I hope I figure it out..
     
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