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A little help with JK flip flops and counters!

Discussion in 'Electronic Design' started by [email protected], Mar 11, 2006.

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  1. Guest


    I'm currently working on a project for my university course where I'm
    required to design a circuit that will count cars in and out of a car
    park. We have to use components in the LS41 series.

    All I'd like to know is, is there a way to make a (JK flip-flop)
    counter count up or down, or would I need, say, two separate counters
    (One for cars going in, one for cars going out)? I was thinking of
    having two counters (that reset *at some point*) that plug into an
    adder to determine what number of cars are in the car park (This data
    will then goes into an encoder for a LED display). Is there a flaw in
    my logic?

    The ultimate goal of the project is to display a "FULL" sign when there
    are no spaces left, but I have an idea how to do that.

    Also, I'd like to know the purpose of the 'J' and 'K' in a JK
    flip-flop? In all the examples I've seen, they're both set to HIGH and
    left at that.

    Many Thanks
  2. Fred Bloggs

    Fred Bloggs Guest

    I'm currently working on a project for my university course where I'm
    Setting both JK HIGH makes it into a TOGGLE FF and this is the building
    block of a RIPPLE counter where either the Q or /Q of the JK is used as
    the CLOCK of the next stage JK depending on whether the IC
    implementation uses positive or negative clock edge triggering. For the
    parking lot application a single counter can be used as an INTEGRATOR.
    Cars entering increment the counter and cars leaving decrement the
    counter. There must be external control so that when in all 0's state
    further decrement pulses due to cars leaving are locked out, and when in
    all 1's or some other state representing maximum capacity further
    increment pulses are inhibited and the FULL sign is lit. This assumes
    there is an entrance gate. If there is no entrance gate then the counter
    requires OVERFLOW capacity, the FULL sign is lit when the counter
    increments past maximum capacity, increment pulses are never inhibited
    in any state, FULL sign is extinguished when counter decrements below
    maximum capacity.
  3. Guest

    Fred Bloggs,

    Thank you for your prompt reply, but could you expand on what you mean
    by an 'INTEGRATOR'? I've had a look for further explanation and cannot
    find anything!
    Does it take the form of some kind of component that you insert before
    the counter, or is it implemented within it? Thank you for your time, I
    am relatively inexperienced with electronic design and appreciate all
    the help you can give me.

    Also, for clarification - in my initial post I stated I was using
    components in the 'LS41 series'. Clearly I'm talking rubbish! I meant
  4. Tim Wescott

    Tim Wescott Guest

    How To Design With Parts:

    Step 1: Find a data sheet.

    Step 2: Read it.

    Step 3: Think.

    If you find a data sheet of a JK flip flop in the series you're looking
    at (surely you mean 74LS?) you'll see what all the inputs do -- clear,
    J, K, clock and (if it's there) preset.

    Have they troubled to show you Karnaug maps yet? If not do a web search
    (and pardon my spelling) or look in your logic textbook. You should be
    able to go from first principals to design an up/down counter using JK
    flip flops and gates. You should also be able to grab a 74LS series
    data book and find an up/down counter, but that's your problem.


    Tim Wescott
    Wescott Design Services

    Posting from Google? See
  5. Tim Wescott

    Tim Wescott Guest

    Integrator, in this context, means a digital accumulator that simulates
    integration (is in the funny stretched 's', the 'dt' at the end, and all
    the hair lying around that you pulled out trying to solve it).


    Tim Wescott
    Wescott Design Services

    Posting from Google? See
  6. Is that an absolute requirement? 74LS is a rather antique and obsolete
    technology. So is 4000 series CMOS, but it is a hell of a lot easier in
    CMOS than TTL.

    I'm presuming that you are "given" a sensor of some sort with a pulse


    We have to use components in the LS41 series.
  7. Guest

    You don't need two counters. What you need is an up/down counter.
    Google it and you'll find lots of design mostly using JK flip-flops.
    One common place to "steal" a circuit is from a datasheet. Find an
    up/down counter chip in any of the logic family, like the 74HC169 for
    example, and look up the datasheet. You'll usually find a simple
    schematic to explain the operation of the chip.
  8. Fred Bloggs

    Fred Bloggs Guest

    As a general term, integrator means to make many as one. In this case
    the "many" is the entire previous history of increment and decrement
    pulses to the counter and the "one" is the counter state at one
    particular point in time which represents the net count of cars in the lot.
    If you look at the sequence of binary patterns, the up/down RIPPLE
    counter is especially easy to make from JK FFs.
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