[sdiy] Issue with CD4024 Ripple Counter
magnus at rubidium.se
Sun Sep 19 22:37:05 CEST 2021
On 2021-09-19 21:18, David G Dixon via Synth-diy wrote:
> Well, the plot thickens...
> I just went out and dug all the CD4024 out of the trash, cleaned them up and
> tested them all in my spanking new prototype with all the bells and
> Here's the result:
> CD4024BCN works perfectly (2 chips tested)
> CD4024BE does not work (3 chips tested) -- it seems to want to clock on both
> edges, erratically.
> I am now willing to concede that there is something in my circuit that is
> preventing the CD4024BE from working -- I just have to hunt down what it is.
> Why the BEs should behave so differently from the BCNs is beyond me -- I
> guess I've got to do a deep dive into the datasheets.
The CD4024B (classic CMOS, buffered) will have their limits for input
low and input high at about 30% of the power from the line they should
be, so for 5 V the low needs to be 0-1.5 V and high needs to be 3.5-5 V.
The CD4024BC has improved noise performance, boasting typical 0-2 V and
3-5 V respectively. Now, the guaranteed values is the same, but the
highlight in the datasheet suggest improvement.
I would look carefully on the clock transition with a fast enough scope.
I suggest you use a fast enough transition and provide good enough
decoupling to deal with the faster transition. Too slow transition
results in false triggers unless you have good enough supression. Yes,
the 4024B should have a schmitt trigger, but that is not always the best
approach to deal with slopes.
As you measure the clock input, make sure there is a small loop area
between probe tip and probe ground-connection at the chip.
> Unfortunately, it is the BE chips that are the most widely available in
> through-hole format ($0.31 at Tayda). I also ordered 100 MC14024 on Ebay,
> as they are now obsolete in through-hole, and therefore no longer available
> via the normal channels. Gawd I hate this part of electronics.
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