[sdiy] Issue with CD4024 Ripple Counter

David G Dixon dixon at mail.ubc.ca
Sun Sep 19 07:26:50 CEST 2021


The ASR clock circuit is attached to this email.

The two switches are how I am simulating the ON-OFF-(ON) switch.  When
switch "1" is open, then the switch is in the OFF position.  When switch "1"
is closed, then switch "0" represents the momentary switch.  This switch
sends either 0V or 12V through a 1k resistor to the 2.2n debouncing cap.
The signal generator represents a signal plugged into the Clock input jack
(such as an LFO).  This comes in through a 10k resistor.  In this way, the
switch always has priority.  They are both fed through 10k into the
inverting input of the opamp comparator with a 100k resistor to ground to
provide a current path.  The threshold of the comparator is set to a little
less than 2V.  Hence, when the LFO signal rises above this threshold, or
when the momentary switch is pressed, the comparator output is negative.
The diode changes this to about 0V.  When the clock signal is less than
about 2V or the momentary switch is not pressed, then the comparator output
is positive.

The output of the diode goes directly to the 4024 Clock pin.  This will be
either about 10V or about 0V, and the transitions will be about 2
microseconds.  This is dropped to ground through a 100k resistor to provide
a current path.  This then goes through a 10k resistor to a 5.1V zener to
fix the level at 5V, then into a unity gain inverter with a +5V level shift
(-12V through 24k) to give a 5V gate signal for the Gate output jack.  This
signal will have the same polarity as the incoming clock signal, even though
the 4024 advances on the negative edge.  This output can be used to gate an
envelope for a filter, or whatever.

If you see any obvious mistakes, I'd love to know about it.  As I said, this
circuit works perfectly with MC14024B, but CD4024B clocks on the wrong edge.



-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of m
brandenberg
Sent: Saturday, September 18, 2021 12:04 PM
To: 'synth-diy mailing list'
Subject: Re: [sdiy] Issue with CD4024 Ripple Counter

[CAUTION: Non-UBC Email]

On Sat, 18 Sep 2021, David G Dixon via Synth-diy wrote:

> Also, I would remind you that I set up a test rig on breadboard, with 
> similar circuitry (an opamp comparator into a diode), and the 4024s 
> either didn't work or looked real bad (lots of hash) even though the 
> driving waveform is very clean.

Sorry to belabor the point but the 'one diode' mention has made me twitch
twice now.  Is that one diode feeding into a passively pulled up (or down)
input or one diode into a floating node that might be drifting around
metastability?


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