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Decoupling capacitor choice for 4017 decade counter

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.
 
J

Jasen Betts

Jan 1, 1970
0
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-quality filtered 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?

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.
 
B

Bob Masta

Jan 1, 1970
0
On Sun, 25 Nov 2012 06:22:09 -0800 (PST),
Hi all,

I've been having some problems with a chain of divide-by-ten counters firin=
g off prematurely and messing up the division. I'm guessing this is a decou=
pling issue (after all, what else could it be, since I'm using a hi-quality=
filtered power supply that should be well up to the job).
I seem to recall from somewhere that these chips need larger than usual cap=
s for this purpose. Someone even said 47uF or 100uF for the purpose but tha=
t does sound VERY large and we're into electrolytic territory.

Can anyone offer any advice on the matter?

TIA.

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
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Frequency Counter, Pitch Track, Pitch-to-MIDI
FREE Signal Generator, DaqMusic generator
Science with your sound card!
 
Last edited by a moderator:
G

George Herold

Jan 1, 1970
0
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-quality filtered 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.

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.
 
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'???
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?
 
G

George Herold

Jan 1, 1970
0
I'm inclined to agree. It's always a problem with breadboard, because youcan'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 from China and the connections just feel like poor quality upon component insertion/removal. I'm rebuilding the thing properly on etched copper clad using the 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?

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.
 
And make sure the input is de-bounced

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!
 
J

Jasen Betts

Jan 1, 1970
0
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!

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.
 
B

Bob Masta

Jan 1, 1970
0
On Wed, 28 Nov 2012 14:22:00 -0800 (PST),
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!

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:
W

whit3rd

Jan 1, 1970
0
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...
I seem to recall from somewhere that these chips need larger than usual caps for this purpose. Someone even said 47uF or 100uF

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.
 
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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