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Decoupling capacitor choice for 4017 decade counter

Discussion in 'Electronic Basics' started by [email protected], Nov 25, 2012.

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  1. Guest

    Hi all,

    I've been having some problems with a chain of divide-by-ten counters firing off prematurely and messing up the division. I'm guessing this is a decoupling issue (after all, what else could it be, since I'm using a hi-qualityfiltered power supply that should be well up to the job).
    I seem to recall from somewhere that these chips need larger than usual caps for this purpose. Someone even said 47uF or 100uF for the purpose but that does sound VERY large and we're into electrolytic territory.

    Can anyone offer any advice on the matter?

    TIA.
     
  2. Jasen Betts

    Jasen Betts Guest

    Check the maker's datasheet, 4017 is a pretty common part-number
    and devices from different sources may be subtly different.

    That said, I also would expect 100nf to be plenty.
     
  3. Bob Masta

    Bob Masta Guest

    On Sun, 25 Nov 2012 06:22:09 -0800 (PST),
    This may or may not be relevant to your case, but I used to
    get strange triggering issues with 4013 D-type flip-flops
    Back In The Day. Only seemed to happen on the proto-board,
    not the finished PCB... but of course the whole point of the
    proto-board was development for the PCB... grrr!

    Anyway, I guessed that there was some sort of coupling /
    capacitance issue with the proto-board. (The plastic kind
    with rows and rows of socket holes for chips and component
    leads.) The cure was to put 10K resistors in series with
    each chip's clock pin, apparently (together with chip or
    proto-board C) slowing down the edges just a tad.

    Turned out other guys in the lab had similar problems that
    this worked for, and it became known as the "10K cure".

    Hope this helps!


    Bob Masta

    DAQARTA v7.10
    Data AcQuisition And Real-Time Analysis
    <SNIP>
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    Last edited by a moderator: Oct 12, 2020
  4. Do you have a 'scope? You can look at the power supply rails.
    Is the circuit on a nice PCB, a rat's nest on copper clad, or plugged
    into white protoboard? As other's have said I think 0.1uF should be
    plenty.
    Maybe you should look at the layout and ground 'issues'???

    George H.
     
  5. Guest

    I'm inclined to agree. It's always a problem with breadboard, because you can't get remotely close to zero lead length on the important bits and there's no ground plane. Plus the newest piece of breadboard I'm using came fromChina and the connections just feel like poor quality upon component insertion/removal. I'm rebuilding the thing properly on etched copper clad usingthe tips others have suggested and hope that will clear up the problem. I'll know in a day or so. Anyone else had problems with Chinese breadboard?
     
  6. I rarely use the white protoboard these days. (The last time was a
    chaos circuit with a max frequency of ~2kHz.) Mostly I do the pcb
    directly if it's a circuit I've done before, or a rat's nest on copper
    clad if I'm not sure how something will work.

    George H.
     
  7. Guest

    I'm not using any mechanical switches here; the first 4017 is pulsed by the output from a 555 timer which I believe I'm entitled to assume will be nice and clean. It had better be, anyway, since I don't have a DSO to examine the pulse train in detail!
     
  8. Jasen Betts

    Jasen Betts Guest

    555 + 4017 ia a popular combiation, I've used it myself and the
    internet is full of pages dedicated to it. it should just work.

    the "10k fix" mentioned earlier is worth trying if you're using a
    solderless breadboard.
     
  9. Bob Masta

    Bob Masta Guest

    On Wed, 28 Nov 2012 14:22:00 -0800 (PST),
    Back when 555s were the latest rage, I tried some and found
    that they caused enormous switching spikes. By the time all
    the extra decoupling caps were added, not to mention all the
    parts that the 555 needs to begin with, these chips didn't
    seem worth the trouble. True, they offered pretty good
    timing performance, but it seemed like the vast majority of
    my needs were easily met by simpler (if less precise)
    circuits using a CMOS gate or two and an RC. Or I needed
    high precision (Xtal), or VCO, or something else the 555 was
    just mediocre at (especially considering its big supporting
    parts footprint).

    So I never got into the habit of using them. But I notice
    that people continue to use them like popcorn, so I figure
    maybe they've solved the spike problem? Or maybe not,
    judging by your experience.

    Just for grins, you might want to try one of those CMOS
    Cookbook-type gate-and-RC timers to see if that solves your
    problem.

    Best regards,


    Bob Masta

    DAQARTA v7.10
    Data AcQuisition And Real-Time Analysis
    <SNIP>
    Scope, Spectrum, Spectrogram, Sound Level Meter
    Frequency Counter, Pitch Track, Pitch-to-MIDI
    FREE Signal Generator, DaqMusic generator
    Science with your sound card!
     
    Last edited by a moderator: Oct 12, 2020
  10. whit3rd

    whit3rd Guest

    4000 series CMOS can (if you're using 10-18V power) put enormous spikes on the
    power buss, and the '4017 is a fairly large chip (30 gates, five flip/flops). I'd think
    a 22 uF to 100 uF Al electrolytic capacitor within two inches of the chip should suffice. In
    tantalum, you might be able to go lower. One capacitor for every four
    chips is enough.

    The dominant current requirement of 4000 series CMOS occurs in short times during
    logic transitions; it's ALL spikes, unlike TTL or ECL. At lower voltages, you can use
    smaller capacitance (because of smaller spikes, and slower responses).

    The clock input on '4017 is already a Schmitt trigger type, you needn't add
    a Schmitt gate to obtain that particular advantage.
     
  11. Guest

    OK, thanks for all the tips, guys. All duly noted. Nearly finished transferring the components to CCB with a sprinkling of your suitable, recommended caps around the place. See how we go from here! :)
     
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