[sdiy] Issue with CD4024 Ripple Counter

Roman Sowa modular at go2.pl
Mon Sep 27 13:01:32 CEST 2021


That sounds patronizing a bit when general guidelines found in beginer's 
PCB design course book are directed towards anybody with some design 
experience.

1. no there should not be a ground plane, this is not high speed 
circuit, and it's home etched PCB. Anybody made 4-layer PCB at home so 
far? Also, ground pour is more like a fashion thing today, not 
engineering. I've seen so many poorly made PCBs, totally filled with 
careless automatic ground pour that could work as high frequency 
resonators, not to mention absurd 5 mils gap (sometimes less) from 
traces. Current return path is important, and ground pour does not 
assure proper path just because it is there.

2. they are not that fast, it's CMOS 4000 logic driven by TL072, that's 
low speed.

3. if I understand correctly the term "plug-board-pattern", this pattern 
was in use since 100-mils spacing DIP ICs went into general use so 
probably for last 60 years?. Nothing wrong with that, it looks neat. 
Again, this is nothing high speed to plan parts placement too hard.

4. yes, I agree, that 100n cap decoupling the 4024 was too far, so it 
could be even skipped with not much effect. I already pointed that to 
David when I was patronizing (I hope it didn't sound like that then)

I'm making popcorn, this may be interesting debate

Roman


W dniu 2021-09-25 o 10:30, rrsounds (null) via Synth-diy pisze:
> 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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