Easy explanation -
Some LM358 have lousy slew rates. The resultant clock to the 4017 is too
slow, resulting in odd behavior. I've found perhaps two such LM358 in my
time, though obviously it appears to be a problem that will keep raising its
head.
Thanks for doing the research. I'll update the project page.
Ken
Ken Stone sasami@... or sasami@...
Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>
Some LM358 have lousy slew rates. The resultant clock to the 4017 is too
slow, resulting in odd behavior. I've found perhaps two such LM358 in my
time, though obviously it appears to be a problem that will keep raising its
head.
Thanks for doing the research. I'll update the project page.
Ken
> I got the main sequencer board soldered up. Powered it up and weird_______________________________________________________________________
>things started happening. Output 3 permanantly on, output 4 never
>turns on, and output seven is skipped (by skipped I mean it jumps
>from out 6 to out 8 with not even a pause on 7). Thought what the...?
>After much head scratching I decided to breadboard the circuit. Just
>the 4017 and half the LM358. No reset or End Out circuitry. Fired it
>up and this time I got nothing on output 2 and output 7 is still
>skipped over. Hmm...I replaced the transistor (bad one) for output 2
>and that problem was fixed. Tried different chips: seven different
>Fairchild CD4017BCN all had the skipping output 7 problem. Out of ten
>Motorola MC14017BCP five worked perfectly. Problem solved, now all 8
>outputs work properly.
> Out of 17 chips I only have five good ones? I found this hard to
>believe, so I re-installed one of the bunk Fairchild chips and
>started swapping out different LM358s. I tried Fairchild and National
>brands, and also LM2904. No change. Then I tried a TL072. Fixed it!
>Then I tried TL082, BA4558,MC33077. All worked. It seemed any split
>supply opamp worked. With the LM358 replaced by a TL082, I started
>swapping out 4017s. Every one of the seventeen 4017s I have worked
>perfectly!
> Can anyone explain this ? I'm just starting to dig into CMOS stuff
>and this really threw me. A nice thing about this discovery is maybe
>I can finally get my Gated Comparator working properly since it
>exhibits the same kind of skipping behavior.
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>See the following URLS for the CGS Modular Synth home page:
>Main: http://www.cgs.synth.net/
>Secondary: http://otherunicorn.0catch.com/synth/
>Yahoo! Groups Links
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Ken Stone sasami@... or sasami@...
Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>