Forums

Decoupling capacitor choice for 4017 decade counter

Started by Unknown November 25, 2012
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.
On Mon, 26 Nov 2012 14:48:29 +1000, David Eather <eather@tpg.com.au> wrote:

> On Mon, 26 Nov 2012 00:22:09 +1000, <orion.osiris@virgin.net> wrote: > >> 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. > > CMOS (4000 series) rarely gives this sort of problem. Put a .1uf ceramic > near the +ve and -ve leads (with an inch or two) that will end that sort > of problem. The other thing that can screw it up is slowly rising clock > signals or noise on the clock signal - if this is the case use a Schmidt > trigger for the 4017 input
On 2012-11-25, orion.osiris@virgin.net <orion.osiris@virgin.net> wrote:
> 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. -- &#9858;&#9859; 100% natural --- news://freenews.netfront.net/ - complaints: news@netfront.net ---
On Sun, 25 Nov 2012 06:22:09 -0800 (PST),
orion.osiris@virgin.net wrote:

>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 www.daqarta.com Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, Pitch Track, Pitch-to-MIDI FREE Signal Generator, DaqMusic generator Science with your sound card!
On Nov 25, 9:22=A0am, orion.osi...@virgin.net wrote:
> Hi all, > > I've been having some problems with a chain of divide-by-ten counters fir=
ing off prematurely and messing up the division. I'm guessing this is a dec= oupling issue (after all, what else could it be, since I'm using a hi-quali= ty filtered power supply that should be well up to the job).
> I seem to recall from somewhere that these chips need larger than usual c=
aps for this purpose. Someone even said 47uF or 100uF for the purpose but t= hat 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. >=20 > Is the circuit on a nice PCB, a rat's nest on copper clad, or plugged >=20 > into white protoboard? As other's have said I think 0.1uF should be >=20 > plenty. >=20 > Maybe you should look at the layout and ground 'issues'???
>=20
I'm inclined to agree. It's always a problem with breadboard, because you c= an'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 inser= tion/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?
On Sun, 25 Nov 2012 06:22:09 -0800, orion.osiris wrote:

> 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.
Are you sure it's decoupling? How long is your clock line, is it terminated, are you using a CA4017 or a 74(mumble)C4017, etc.? If you're using a fast part (i.e. 74ACT4017) and your clock line either has a slow transition or a fast transition and enough wire between the source and the counter for it to ring, then your problem may have nothing to do with decoupling at all. -- My liberal friends think I'm a conservative kook. My conservative friends think I'm a liberal kook. Why am I not happy that they have found common ground? Tim Wescott, Communications, Control, Circuits & Software http://www.wescottdesign.com
On Nov 26, 11:25=A0am, orion.osi...@virgin.net wrote:
> > Do you have a 'scope? =A0You 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? =A0As other's have said I think 0.1uF should be > > > plenty. > > > =A0 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 the= re's no ground plane. Plus the newest piece of breadboard I'm using came fr= om China and the connections just feel like poor quality upon component ins= ertion/removal. I'm rebuilding the thing properly on etched copper clad usi= ng 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.
On Mon, 26 Nov 2012 14:49:05 +1000, David Eather <eather@tpg.com.au> wrote:

> On Mon, 26 Nov 2012 14:48:29 +1000, David Eather <eather@tpg.com.au> > wrote: > >> On Mon, 26 Nov 2012 00:22:09 +1000, <orion.osiris@virgin.net> wrote: >> >>> 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. >> >> CMOS (4000 series) rarely gives this sort of problem. Put a .1uf >> ceramic near the +ve and -ve leads (with an inch or two) that will end >> that sort of problem. The other thing that can screw it up is slowly >> rising clock signals or noise on the clock signal - if this is the case >> use a Schmidt trigger for the 4017 input
And make sure the input is de-bounced
On Tuesday, 27 November 2012 20:07:36 UTC+1, David Eather  wrote:
> On Mon, 26 Nov 2012 14:49:05 +1000, David Eather wrote:
> 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!