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Discussion in 'Electronics Homework Help' started by azuz, Apr 23, 2012.

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  1. azuz


    Apr 23, 2012
    Hi Guys,

    I study at the University and found in the Internet this useful site and I need your help....
    I need u to guide me to design a counter circuit (counts from 0 to 14 using flip flop)
    In General

    Thanks in advanced
  2. GreenGiant


    Feb 9, 2012
    What type of flip flops?

    my personal preference is J/K flip flops

    that coupled with some other logic gates (a few AND's and an OR or two)

    and a 555 timer with some resistors and you have yourself a counter

    Though if this is for homework I think you should have posted it in the Homework section, I also don't want to draw it completely out for you as its for school

  3. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Here the workings of counters are explained.There is even a figure using JK-flipflops - just what you need.

    Without further circuitry, a binary counter will count powers of 2 (2, 4, 8, 16, ...).
    Since you want to count only from 0 to 14, you will have to devise a circuit that will make the counter go from 14->0 (instead of 14->15), You need to detect the counter state 14 and will have to use this detector signal to control the JK-inputs of the flipflops such that on the next active clock edge the flipflops all will reset to 0.

    Hint: An obvious solution would be to detect the counter state 15 and use this signal to reset all flipflops asynchronously. However, this approach has several drawbacks and is therefore not recommended:
    1) the state 15 shows for a short period of time at the outputs of the counter. This may confuse other logic.
    2) If the flipflops behave drastically different, not all flipflops may be reset (assume one especially fast flipflop going to 0, then the state is no longer 15, the reset signal is cleared and some especially slow flipflops may not be reset in that time).
    3) Mixing asynchronous and synchronous operation may lead to so called hazards or races, both conditions that can wreack havoc in the following logic stages.

  4. azuz


    Apr 23, 2012
    Thanks Mr.Harald...

    could u draw that circuit for me which count from 0 to 16 or 8 through Logic Works?

  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Also take a look at twisted ring counters (a la the 4017). They have 2n states where n is the number of flip-flops.

    I mention them because they have an interesting property of having only a single transition per clock cycle (i.e. only one flip-flop changes state on each clock cycle)
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    neither do I have the time nor Logic Works to draw this circuit. It is not the way this forum is supposed to operate. We are not doing youre homework, you're supposed to solve the problem yourself. We give guidance and advice.

    Start with a 1 bit counter using 1 JK-flipflop. It will count 0 - 1 - 0 - 1 ...
    How would you realize that with one JK-flipflop?

    Now add a second stage to build a 2 bit counter that will count 00 - 01 - 10 - 11 - 00 - ...
    How do you have to connect the JK-flipflop of the second stage to the first flipflop to achieve this function?

    From there it is easy to extned to any number of stages.

    If you present your solution as a schematic diagram, I'll be happy to check it.

  7. azuz


    Apr 23, 2012
    I am the one who is really sorry
    i thought this forum is for share knowledge not to keep it:) Prof.Harald​
  8. davenn

    davenn Moderator

    Sep 5, 2009
    we do share knowledge , but in the homework section we are here to help you , NOT do the project for you. which is what you were wanting.
    We have lives and jobs too, we dont have 100's of spare hours to completely design other peoples projects for them, instead we expect them to do some work for themselves and we will check their progress :)
    You will find this the guideline on any electronics forum

    Read the guidelines of the homework section, so you understand its purpose :)

    Last edited: Apr 25, 2012
  9. azuz


    Apr 23, 2012
    C the attached file.

    and give me ur guidance.....

    Attached Files:

  10. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    This circuit doesn't make sense.
    You connected the clock to the reset inputs (plus you left the leftmost Tand C inputs open). Thus the flipflops will be reset with every clock and essentially do nothing.

    Look again at my earlier advice:
    Start simple and consider the case of the 1 Bit counter (not very useful but a good starting point). How would you make it toggle between 1 and 0 at each clock? Hint: The toggle function is hidden in the name of the T-flipflop. Where or how do you have to connect the inputs T, Clk, Reset?
    Once that works, What is the condition for the T-flipflop to count? From that you find out how to connect the output of the first flipflop to a second stage.
    Post your solution and I'll have a look at it.

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