[sdiy] Issue with CD4024 Ripple Counter
mbryant at futurehorizons.com
Mon Sep 27 16:21:01 CEST 2021
I totally agree that ground planes and ground pours have to be done properly (definitely no floating islands) but that aren't there for correct operation of your circuit, or for fashion, but to try to ensure your produce passes FCC part 15B and all the other country or region-specific EMC/EMI regulations that apply to digital products. Using CD4xxx's makes it a digital product, even if they are just driven from an on/off switch.
Despite some silly stories one sees, these standards are not optional for low volume products, only for a total run of six units where the units can be given away, but not sold. Thus if you made say a VCO for your own synth and made seven of the modules then it still needs to pass the regulations even if you keep all seven units for your own use. In most of the world you can test yourself and self-certify once you have the results, but for the FCC regs you have to use a qualified test lab which gets expensive so don't build more than six of any module even for your own use :-)
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Roman Sowa
Sent: 27 September 2021 12:02
To: synth-diy mailing list
Subject: Re: [sdiy] Issue with CD4024 Ripple Counter
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
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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