[sdiy] Issue with CD4024 Ripple Counter

David G Dixon dixon at mail.ubc.ca
Sat Sep 25 21:02:03 CEST 2021


Hello David,

Thanks for the advice, but no.  My layouts will remain more or less as they are now.  For one thing, I cook all my own boards from one-sided blanks, so a "copper plane" is impossible.  Second, I have a decoupling cap within 0.5" of the counter chip.  I'm sure that's good enough -- also, I've never (ever, in 13 years) had a circuit that benefitted from more decoupling caps, and I've designed lots of circuits.  My standard approach of two 10uF electroytics and two 100nF ceramics at the power connector seems to work well for everything analog.  If I feel I need an extra 100nF cap somewhere, I'll squeeze it in where it is convenient.  The idea that "every chip needs one cap for each supply" is a really good way to waste both caps and PCB real estate.  For audio opamp circuits, extra decoupling caps do exactly nothing.  If you don't believe me, ask Ian Fritz -- this conversation has been had on this very forum, many years ago.  If you need to pepper your PCB with decoupling caps, then there must be something else seriously wrong.

DON'T MISTAKE WHAT I'M SAYING HERE AS ADVICE.  IF YOU BELIEVE YOU NEED 10 DECOUPLING CAPS ON YOUR PCBS, THEN DON'T LET ME DISSUADE YOU.  I WOULDN'T WANT TO BE BLAMED FOR ANY PROBLEMS THAT AROSE AS A RESULT.

As far as using a "plug-board pattern" as a design guide not being good practice, I don't really know what you mean, but remember, I'm using all through-hole components on single-sided boards, so the layout possibilities are not exactly endless.  My basic analog board layout practice has worked extremely well and is exceptionally easy to adapt to just about any circuit, and more or less guarantees the minimum board real estate.  Also, sharp corners are only a concern at RF, based on what I've read -- a lot of this stuff is "mythology" in audio circuits.

Finally, I avoid tantalum caps like the plague.  I don't like things that can explode if you hook up something backwards.


-----Original Message-----
From: rrsounds (null) [mailto:rrsounds at aol.com] 
Sent: Saturday, September 25, 2021 1:30 AM
To: David G Dixon
Cc: synth-diy mailing list
Subject: Re: [sdiy] Issue with CD4024 Ripple Counter

[CAUTION: Non-UBC Email]

Looking at the board layout as posted, I would suggest that 1), there should be a ground plane layer, and if there isn’t, all areas that are not signal or power should be flooded with ground return copper; 2) Low current fast signals don’t need traces to be particularly thick, but they do need to be direct and sharp-turn-free if possible. 3) Using a plug-board pattern as a design guide is not a particularly good practice. And 4) all bypass (0.1µf) caps need to be as close to the chip as possible, with as short as possible connections to power and grounds, and every chip needs at least one cap for each supply.
I also always include a 10µf tantalum across all power supply inputs. 
David Reaves

Sent from my iPad

> On Sep 25, 2021, at 8:39 AM, David G Dixon via Synth-diy <synth-diy at synth-diy.org> wrote:
> 
> Further to my last posting, I think I understand why the CD4024 was 
> used for a 2-bit counter in Ken Stone's original circuit.  Without a 
> schmitt trigger on the clock input, the CD4013 dual D flip flop is 
> absolutely unforgiving in terms of clock inputs.  So far, I haven't 
> been able to get it to work at all with the switch (although it works 
> fine with the signal input).  I figure that if I put a pair of CD40106 
> schmitt triggers in line, then it would be OK, but I don't have room on my board for that.
> 
> Hence, it looks as if I am just going to go with the revised version 
> of my original circuit, with a TL072 comparator and rectified 
> inverter, and CD4024BCN or MC14024B.  After all, it worked perfectly.  
> The only issue was that it didn't work with CD4024BE, but I now 
> believe that this was because the batch from which those chips came 
> from is defective (and don't have functioning schmitt triggers).  I'll 
> follow the suggestion of someone here and replace the rectifier 
> circuit with a diode into a divider into a simple inverter, which saves a diode and doesn't sacrifice output impedance.
> 
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