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JK flip-flop as a monostable / static protection

Discussion in 'Electronic Basics' started by Tim Dorrington, Aug 28, 2003.

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  1. Hi - 2 questions that I'm hoping you could help with...

    1) I'm designing a circuit which currently uses half a CMOS 4027 dual
    JK flip-flop. I need to add a monostable circuit to it, so that I get
    a clean pulse (0.5 seconds approx - timing not too important) suitable
    for clocking a counter IC from a push switch. I was going to use a
    NE555 but wonder if there's a way I can use the other half of the 4027
    instead? I assume that the push button will control the clock input,
    and there would need to be some sort of R-C arrangement between the
    output and the J/K inputs...?

    2) If there's a possibility of someone touching a contact linked to a
    CMOS IC's input, is there a simple way of preventing/limiting static
    damage to the IC? The application is a game where the player might
    cause a 2 contacts to touch (one for the IC input, one for the supply

    Thanks for any information,
  2. Of course.
    Why don't you think about it some more? It has sets and resets and
    stuff, with things doing things on a clock signal. Frankly, if you cant
    figure out this one out your tod...jesus wept dude...what about tying
    the jk to a 1, and the output to the reset via an RC...?

    Kevin Aylward
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
  3. I did.
    It gives people a much needed, jolly good kick up the arse. Its been
    done to me many times, and I'm thankful for it. We use to dream of
    getting kicked up the arse when we were young. Sheer luxury it was.

    I must admit the use of the phrase "I'm designing a circuit.." made an
    impact. The reality is that, if someone just knew even the basics enough
    to "design" a circuit, this particular one is a no brainer. It designs
    itself, if you know what the terminals do. I certainly agree that some
    things need more hand holding, but some others don't.

    Kevin Aylward
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
  4. Of course, everyone is a beginner at some point, but even beginners have
    to figure certain things for themselves. In this case, the assumption is
    that the poster knew what a jk does. If so, the solution is truly
    trivial, even for beginners. As I said, sometimes one reasonable hard
    knock is enough to get people thinking for the rest of their lives.

    I would say its standard, and correct, practice for educators to make
    students work a bit rather than be given it all on a plate. I will point
    out that it goes without saying, that yes, sometimes educators can
    expect too much, or not give enough initial background. I just did not
    perceive this to be so in this case here.
    What happened to Robert?
    But a show me the truth, don't pull any punches can do a lot of good.
    Sure, it might be a bit annoying at first, but you dont half remember it
    I think one needs to lighten up a bit. I only said it was good enough
    for the lord Jehovah to eat himself.

    Kevin Aylward
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
  5. Dana Raymond

    Dana Raymond Guest

    I remember a few times when I was just learning about digital electronics
    back in my twenties. The arrogant answers of "Why should I help you with
    this design" for very simple newbie questions stung!

    And, I can honestly say, that I have always tried to help others if I feel I
    can, or at least make an effort. Even when consulting I try to provide
    'value added' at the beginning of the process by being informative - that
    helps a lot of smaller companies figure out if they even need to contract

    As well, I learned while tutoring in HS that I learned a lot myself by just
    covering the material with another, and especially explaining it. Believe
    me, a principal is much more 'yours' if you have to find 3 good analogies to
    explain it.

    And the questions can be fun as well. Try explaining conservation of
    mass/energy to someone who asks "But, WHY doesn't a perpetual motion machine

    If I think that someone is looking for a shortcut due to lazyness then I
    just don't participate. If someone is trying to accomplish something but
    doesn't seem to have even basic knowledge, then I may pull out if the next
    step is I have to do the design for them.

    Just my two cents - not aimed at anyone in particular.

    Dana Frank Raymond
  6. John Jardine

    John Jardine Guest

    I've noticed over the years that peoples 'learning styles' are radically
    different. What's good for one, *completely* fails on another.
    This flip-flop question blew straight by me. To answer it I'd have had to
    dig out a data sheet. I use 'em, regard 'em as boring and find the working
    knowledge 'sticks' for about 5 minutes. If the need arises it's simply a
    case of rummaging a data book and picking something that looks tasty. I have
    though, the luxury of hindsight.
    A neat full answer was provided by Terry P's circuit. From this drawing it
    was simple to backtrack and remind myself of what a JK device does.
    This compares to the time wasting struggle I had years ago, trying to get to
    grips with a description of JK operation as provided by a Texas Instuments
    data book. I look back and even now know it was a piece of s**t.
    Learning would have been much, much, much, faster and pleasurable, if the
    Internet, the newsgroups and the Terry P's had been around at the time.
  7. John Dyson

    John Dyson Guest

    Note that 'lightening up' should include avoiding ANY insults to a
    beginner who just might be still enjoying himself. Please try avoiding
    ruining an interested beginner. Don't take on the attitude that you
    are an educator, but rather a helpful, more experienced individual.

    A beginner will get enough of the 'arrogant educator' attitudes in their

    For lightening up, yes, please do so...

  8. I, for one, would like to thank all the people who take time to read and
    respond to these (mostly beginning) questions. Even a little 'kick'
    sometimes gets my marbles rolling in the right direction.

    Bob Monsen

  9. Just to say thanks to Terry for the circuit - I'll give it a go as
    soon as I can.

    To Kevin... I'm sure it's frustrating when it appears that people
    don't make an effort to solve their problems. What I posted was
    polite, to the *basics* newsgroup only (no such thing as a 'stupid'
    question, I thought), was for a solution that has evaded me one way or
    another after a reasonable time messing about with the circuit... and
    I'm not a student asking for help with their homework. I'm not sure I
    would have come up with Terry's solution - I'm only a hobbyist and am
    just trying my best to understand a subject I find enjoyable. The
    nearest I'd managed to get was a debounced bistable circuit. That
    said, you tried to point me in the right direction, and I'm grateful
    for that at least - it *was* the bit with the passive components that
    tripped me up. I just think a little more patience would be more
    helpful - especially in this particular newsgroup.

    Thanks again folks.
  10. I've been playing guitar since I was 11. If I teach myself a new tune,
    it sticks. If I read it from music, I forget it by the next day.

    If we go back to what I actually posted, prior to terry I might add,
    what could have given the most satisfaction in finalising the result?
    Wow....I suppose I must be missing something. It was introduced to me as
    a clocked RS bistable, with the exception that 11 toggles it. What more
    is there to know.

    We have one of two options, ether everyone's normal and I'm a genius,

    I look back and even now
    Well, out of around 10,000 posts, I don't think there that many where
    I'm too abrupt.

    Kevin Aylward
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
  11. I started as a hobbyist. I agree that at the very beginning, even the
    most basics need to be taught clearly such that the student can get a
    feel of what's going on.

    In your case, you stated that you were using a JK. I took the assumption
    that you would therefore know what it does. i.e. a clocked set reset
    bistable, with the addition that j=k=1 toggles it. This level of
    knowledge would imply to me that you also were aware of RC time

    What I will say is this. I taught myself amplifier design by studying in
    detail other amplifiers. Armed with only the basics, I reinvented for
    myself why such and such was the way it was. I don't believe that I am
    special in this way. I would say I understand amplifier design in much
    greater detail than those that simple learned by simple route.
    It depends on what day it is.

    I also think that if you had had a bit more patience you would have came
    to the solution on your own.

    Kevin Aylward
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
  12. John Jardine

    John Jardine Guest

    Neat but unfair analogy. By random strumming(?) you, (or even I) may be
    fortunate to come across a unique chord or pleasing sequence of notes.
    Electronics stuff needs a shed load of fixed ground rules to be learnt and
    applied before anything good can even begin to start to happen.
    (Point noted about precedence). The most satisfying outcome would be that
    'flash of understanding' based on a *analysing a good example of the craft*.
    You did actually answer Tim's question but it was cryptic to the point of
    impenetrability. It read as if an irritable half of you was struggling to
    take control of the helpful half.
    Yes, my Texan nightmare was actually a 7470 ... but ... the revealing
    statement is, "It was introduced to me". This implies the possibility of a
    question being raised and some expert human feedback given in response. Tim
    has not that luxury.
    I think the rest of us are but easily damaged mortals.
    In the couple of years of reading your posts I've taken on board a lot of
    interesting stuff and a new slant on things. I've got to 'know' your
    writing style and yes!, of the posts I've read, only a few I might regard
    as unreasonably abrupt.
    A K.A. post is a K.A. post. Myself, I take it as I find it and will look at
    what's in there. Just the same as talking to a mate down the pub.
    That's just my view though.
    OTOH, many people may be unaware of the person and from the writing style,
    induct elements (wholly without reason of course ;-) of pedantry? or
    arrogance? or intransigence? or bloody mindedness? or even helpfulness!.
    (Y'know ... the stuff we mortals all suffer from but won't admit to!)

    Does Tim know of these things?.
    Will he unfairly have marked you down as a twat? (and by logical default,
    the rest of us poor sodding plebs ;-).
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