[sdiy] crazy CMOS behavior

[Peter Grenader]

It depends on how much this circuits is based on the Serge!

The TBK is supposed to do random (it's actually quasi random) and it's
sounds like you might have that dialed in.

If yours doesn't include this function (intentionally preloading the preset
inputs with async. numbers), make sure you've grounded the preset inputs to
the 4516.  If you haven't you might be catching crap which is creating false
logic conditions and sending the counter all willy-nilly.

Also, look for grass. Turn your scope intensity up, stick it in X-Y mode so
there's no sweep and look at every pin to see if there are any tiny blips on
any of the pins you arn't causing intentionally.  Finding these through this
process is the easy part.  The hard part is getting rid of them!  First
thing to try is hanging caps in all the usual places.

Now, if it's pseudo-random you're after:

I made a 4516 counter based sequencer a few months back and was having
simular problems until I put an r/c at the base of the trannies that lead to
the clock, reset, random select and direction inputs, much like you mention
here.  I got this tip from an engineer here at work, Rich Walburn, who used
to work for Moog.  He actually designed Keith Emerson's Programmer module.

Turns out, my circuit is really simular to the TBK as far as it's method of
achieving quasi-randomness and it was an accident - I didn't see this
circuit until I was well into the design of my own.  You may remember I
posted a note here about the best way to achieve this.

I boiled down to two methods: feeding the preset inputs with four different
white noise sources, all of which went through comparitors and a latch
before hitting the 4516 and...

Running something lese which is producing 4 bit binary into the preset ins
of the 'master' 4516.

I elected the latter because there was less wiring involved and I was
running very low of vectorboard space!   I ran a second 4516 counter via a
555 at about 40Khz.  Put that output throug a latch which was bieng gated by
the same clock that was running the sequencer and I get quasi-random out.

It works OK.  there are patterns which come and go from the two assync
clocks (the one rtunning the sequencer and the one going off the 555), but
all in all, I'm pleased.

I also use a 4516/4051 pair, but almost all sequencers which aren't micro p
based use those.




on 10/2/02 11:30 AM, mark verbos at a0284520 at addcom.de wrote:

> I have built a sequencer based on the 4516 counter. The clock input is
> stolen from the Serge TKB schematic that is on music machines. That is,
> trough a cap to an NPN then a CMOS inverter then to the counter. When I
> clock it, with anything, it jumps all over the place with no real sense
> or pattern. Could this be related to the step length not being right?
> How does it work for the actual Serge? It's not the chips, I have
> switched them all out and it does the same tihng. Am I just missing
> something not grounded or something?
> 
> thanks for any ideas, I'm going nuts here.
> 
> mark
>