[sdiy] Issue with CD4024 Ripple Counter

David G Dixon dixon at mail.ubc.ca
Tue Sep 21 02:48:08 CEST 2021

So, I built the new circuit (I've attached the schematic again here).  Note
that I changed the 100k resistor from the diode to ground to 10k, as this
made the simulation results ever so slightly cleaner at the transitions.
Results: MC14024BCP and CD4024BCN are still clocking as they should.
CD4024BE is still clocking on the wrong edge.
I swapped the diode and the 10k resistor just to see if that would have any
effect -- it didn't.  Also, I like them the way they are because the keep
the levels closer to the opamp output and zero.
I've also attached a scopeshot of the falling edge, taken with the probe
attached to the 4024 CLOCK pin.  As you can see, it is just about the
cleanest transition you could ever hope to see.  If that edge can't clock a
CMOS chip properly, then nothing can.
So, I'm out of ideas.  I could disconnect the 20k resistor to see if the
rectifier is affecting the CLOCK pin, but I honestly cannot see how it
could, given the very low output impedance of the TL072.  The comparator is
more or less completely optimized now, and is performing admirably.
I guess I'll try Tim's simple clocking circuit on breadboard to see if I can
get that to work.  However, I'm not holding out much hope, since I think it
is fair to say that my comparator circuit is generating what looks to be a
more or less perfect clock signal.
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