[sdiy] Searching for a VC Clock schematic ......

[Rykhaard D.A.M.I.A.N.]

On 12/25/05, Magnus Danielson <cfmd at bredband.net> wrote:
>
> From: "Rykhaard D.A.M.I.A.N." <rykhaard at gmail.com>
>
> Hi Ryk,


Hey Magnus. :)

> Well Mag - Harry's gotten me wondering now - with the high speed
> > possibilities. :)  I haven't paid a lot of attention to the 4046 over my
> > building years, as there hadn't been any easily available to me, to play
> with.  But I now DO think that my 1 supplier that stocks CMOS DOES have them
> in stock.  Soooooo. ;)  Time to start looking again, for schematics of stuff
> to do with them. :)
>
> If you toss a TL074 ontop of your 4046, you can get a triangle-wave (as BJ
> demonstrated) and you also got the square-wave output. This is a pretty
> compact triangle/square oscillator which can then be used to create sawtooth
> and sine fairly quickly. You can then get PMed-PWM and non-PMed-PWM as you
> feel comfortable.


Here is one place, where I'm going to be stopping myself from using Quad
opamps:  LFOs.  Due to the comparator being one of them, in an LFO.  The
interruption that it CAN seem to cause in other opamps within the quad, is
quite noticeable. :(
In this case, it'd be acting as a buffer - but I still have concern about
it's possibly effecting the other opamps, with it's buffering the output
from a Schmidt Inverter - who'll ve having fairly sharp edges / quick
changes in voltage.  :-/
With it's main purpose being a Clock, I could still use the Triangle as an
additional LFO of sorts.  It'll almost always be up in the 10,000's and
higher of hertz, due to the 4024 dividers that they'll be running. :)
FM effects could be used from it, as well. :)

> Well here - I was going to put the 3080 in the loop around the 40106 that
> charges / discharges the cap, working with the squarewave output only for
> driving other CMOS devices.  So the output of the 40106, would go into the +
> input of the 3080 (through a 100k/220r divider), and the output of the 3080
> through a diode (to block the negative output) would be connected to the
> Grounded Cap, and the input of the 40106.
>
> Why the diode? Just connect the CA3080 between the same supply lines as
> your 40106 and you don't have a problem. Also, the 40106 already has such a
> diode anyway, two diodes going to each supply line actually.


Hooking up the 3080 between +V/Ground hadn't occurred to me at first. :)
With this though - wouldn't I have to setup 1/2 voltage divider for the
reference point to the - Input of the 3080?  (Here's where I'm stepping
beyond my known theory - as I don't ever build anything that runs on a
'Single Supply'.  :-/
Or - would I just have the 3080 negative input, tied directly to Ground?
I haven't looked at the 40106's internals in my CMOS databook yet.  It HAS
it's own protection from -V's, built in??  That would be very cool, if so.
:D

> (I realized tonight, whilst out socializing - that I'd have to bring the
> > 3080 output back up, about 500 times, after it's 500 times reduction,
> for > the 3080's safety.  So that'll require an opamp between the 3080 and
> the > Cap/40106 input.  There goes chip count up +1 for each clock.)
>
> ? Me no comprendo (OK, there's about all my spanish (except popular
> swear-words then))


Haha.  That's okay. :D  I know how to say 'Hi', and that's about it. :D

I'd figured on using the stand input resistor divider to the 3080.  100k
resistor between input and +input, with a 220r resistor to Ground, from the
+input to Ground. That drops the Input voltage level by 454.5454etc.
So - as with some other circuits that are voltage controlled - I figured
that the output would have to be amplified 454 times, to come back to the
original voltage level coming into it. :)  Hence - an opamp being required
at the output, before the cap. :)

Noooo?  Am I missing something? :D

> Ok.  So from what you've said - my idea SHOULD work. :)  All V inputs to
> the 3080, would then go through an Expo. first and then into the 3080 - and
> possibly - I could get 1V/octave speed control??  :)
>
> Yes? Why not? The CA3080 datasheet even demonstrates an oscillator with
> the range of 1:1000000 and what you are trying to do is basically a variant.
> But I don't think you have heard my message fully: DROP THAT DIODE


Haha!  :D  Understood - now. ;)

(at least mentally). Ah well, there will be one there anyway. You can fully
> resolve that issue by having the 3080 and the 40106 running on the same
> supplies, then the protection diodes will not bias up at all.


That's right!  I never even thought, of the forward voltage drop. :O
But here - I could use an opamp based rectifier, that takes care of the
voltage drop, as WELL as amplifiying the output.  That would take care of
both - even though I apparently don't have to worry about the diode, as the
40106 IS protected.  No?  :)

No, you can drive your 4046 on an expo, it has a current input! ;O)
> Pin 12 is really a current input, which directly hits a current-mirror at
> Vcc. So, your garden varity expo-circuit would fit quite nicely into that
> pin.


As Harry'd said though - not accurate enough, for 1V/octave.  Still though -
with my wishing to keep the circuit as simple as heck, I can toss away the
'1V/Octave' requirement in exchange for simple circuitry. :)

If you have problem reaching higher frequencies with your 40106 you are
> probably running into the 40106 output current limit. Reduce the capacitor
> value to get around that. Oh, you *do* want to isolate your core from your
> load so use one of the inverters as buffer.


Right.  That would drop my Clock count from 6 to 3, but that's ok.  I should
have enough clocks with 3, anyways.  As well as external input.
To keep circuitry down - I could go with 2 clocks, and a buffer each for 2
external inputs.  Hmmmm.  (Still developing this thing, all over the place.
:) )

> It also reminded me - that I can just run the 3080 off of +15/Ground!
> > Thereby - no negative voltages for the CMOS. :D  (Unless I ran it off of
> +/- > 7.5V which I don't wish to bother with. :P )
>
> Exactly! This is what I have been trying to hint. What you could do is to
> run both the 40106 and the CA3080 on +/- 5V or something. That will work too
> and you get a balanced waveform directly. I do recommend this!


I didn't want to go this route, as there'd be extra requirements for
dropping the power supply voltages to both of them, with LM329's (for +/-
6.9V) or 5V regulators.  (A fair bit of wasted current, from the +/- supply,
heating up the voltage regulators.  :-/  )
I'm going to prototype (TODAY, FINALLY!  Haha.) around the +15/Ground PS for
them. :)

> (BIG smile) :D  I do hope you all, have a wonderful day tomorrow (today,
> > yesterday. ;) ) :D
>
> There is only 6 hours between us and already we have problems! ;O)
>
> Cheers,
> Magnus
>

Haha!  Nahhh.  :D  It was meant in, whether you were reading my reply on the
same day (24th), Christmas day (day after), or today (day after Christmas).
;)  LOL

Here's to hoping that you had a wonderful day, on Christmas and received
lots of wonderful stuff. :) :)

--
Take care,
Warmth and Peace,
Ryk

http://deathlehem.bravehost.com/damian.html - D.A.M.I.A.N.;s webpage - Dec
2105 update
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20051226/267fb5a8/attachment.htm>