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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
CMOS Sample + Hold Idea
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Tomoroh Hidari



Joined: May 04, 2012
Posts: 39
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PostPosted: Fri Sep 07, 2012 11:30 pm    Post subject: CMOS Sample + Hold Idea
Subject description: first results (pics and sounds)
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hi, i've mentioned this (including some photos) in my Oy a noob (http://electro-music.com/forum/topic-54514.html) threat...
now i finally got myself round to rtf eagle manual/intro and cooked up a sketchy schematic.

the pin in is for an input clock. this goes to the 4040 which drives the 4051 and - at the fastest clock that drives the 4051 also the 4042 flipflop-clock.

the flipflop's 4 ins are fed from the 4 40106 oscs - these can run at pretty much any frequency, though ideally not all at the same...

... now: when the flipflop is strobed it sets its 4 Q outs to the state of the input from the respective 40106 gate (and its notQ to the inverse state).
with these (all together) 8 outputs connected in a somewhat random order to an r/2r network - - and HERE I'm getting insecure about my theory - there should be varying voltages at the different nodes (those leading to the 4051) of the network. (wondering - will I need diodes between the r/2r and the 4051?)

the whole thing is, theoretically cascadable to more 4042s


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Last edited by Tomoroh Hidari on Sun Sep 09, 2012 1:30 pm; edited 1 time in total
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Tomoroh Hidari



Joined: May 04, 2012
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Audio files: 2

PostPosted: Sat Sep 08, 2012 10:26 pm    Post subject: part 2
Subject description: expanded and breadboarded - now the wondering starts
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so, yesterday/today I resumed this idea.
first, i expanded the schematic - (ignore the 2 extra inverters...ic6 and ic7 - i think - just an idea i had!)

so, i breadboarded this with an extra 40106 used for 1 (one) clock - feeding the 4040 and one osc to get a test audio signal. the audio osc. uses a 1mOhm pot in series with a 500k dark-resistance LDR/LED-vactrol fed by the output of the 4051.

got something to work, but also some weirdness - apart from the fact that I soon realized that I needed a walwart psu for this, as my battery was definitely not providing enough current and the circuit started to "fall asleep"... (sorry, English is not my first language and sometimes at past seven in the morning before any sleep the right words do elude me)
- back to the weirdness -
1) the output frequency is rather high, even though the osc uses a 10µf cap and a 1mOhm poti in series with a 500k dark resistance ldr
b) there is a constant modulation on the audio(rate). my suspicion is, that this is mostly from too many chips (and the rather large value caps on the 4 'random' 40106 oscs.) all on one breadboard without (as of yet) much decoupling going on.

anyway, if interested, have a look/listen yourself:
http://soundcloud.com/ivorybunker/cmos-sample-hold-breadboard

- hm, can't seem to find out how to embed a soundcloud player here... so please just follow the link. thx.

i attached both a pic and the eagle file (feel free to use, abuse, tinker...)...
will post pictures of breadboard later.

cheers

- a little update: 1) i re-arranged the circuit. finally found am certain that the "problem" with the 4042* chips is that they are latches (letting the input signal pass) rather than flipflops (which would be set to the respective clock speed - learned the difference the hard way)...
... so for testing out the circuit without too much rearrangement i just connected all the 4042 ins (except clock, etc., of course) to outs from the 4040, so all of them change less frequently then the clock of the 4042 (i.e. q1 from the 4040) and the fastest switch input of the 4051 (again, the clock of the 4042)...

2) i took some photos and recordings of said new circuit (a schematic with the proper cap/pot etc. values could be done, if there's enough interest)...
as you can hear, this one makes much more sense...

2.1 - the first recording is of the circuit as described above... me changing the clock speed and basic freq of the osc.
2.2 - is a recording where the osc. get's gated by the clock with a 1n4448
some interesting sounds in there, especially at fast clock speeds

http://soundcloud.com/ivorybunker/sets/cmos-sample-and-hold-idea

i still feel like there's not all working out as intended but i'm getting there... more tinkering tomorrow

*the reason i'm working with these 4042 is mostly that I got a bunch of them from a cheap german 25pieces of various cmos chips pack... (they're actually from east germany)...


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JingleJoe



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PostPosted: Mon Sep 10, 2012 4:52 am    Post subject: Reply with quote  Mark this post and the followings unread

While you will get different voltages from an R2R ladder like that, that is not the standard way to use an R2R ladder, nor is this really a sample and hold circuit.
I think you may have misunderstood how to use an R2R ladder if you did not intend to use it in an abnormal way (which is fine but makes me suspect that you made a mistake). Care to clarify?

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Tomoroh Hidari



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PostPosted: Mon Sep 10, 2012 10:16 am    Post subject: Reply with quote  Mark this post and the followings unread

hey jinglejoe,
indeed, I'm using the r/2r in an abnormal way - and possibly in one that does not exactly do what I think it should - but my thinking behind this way was/is that, when sending a signal to some parts of the ladder and others not they should sum up to give different voltages. now if i tap those at different points (somewhat) randomly - that's where the 4051 comes in, I, again, get different outputs...
so what you get is a different voltage each time the master-clock (divided by half once via the 4040) triggers. Pseudo-Sample + Hold would have, admittedly, better.

must admit though that, while being interesting as an experiment (thought and breadboard) I feel that it's - unless I or someone else has an idea to largely improve the circuit - not really worth being built (seeing as there are some rather 'simple' s+h circuits out there anyways). will need to find some other use for those 4042's I guess.

thanks for your feedback in any case,
th

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JingleJoe



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PostPosted: Mon Sep 10, 2012 10:29 am    Post subject: Reply with quote  Mark this post and the followings unread

Tomoroh Hidari wrote:
hey jinglejoe,
indeed, I'm using the r/2r in an abnormal way - and possibly in one that does not exactly do what I think it should - but my thinking behind this way was/is that, when sending a signal to some parts of the ladder and others not they should sum up to give different voltages. now if i tap those at different points (somewhat) randomly - that's where the 4051 comes in, I, again, get different outputs...

so what you get is a different voltage each time the master-clock (divided by half once via the 4040) triggers. Pseudo-Sample + Hold would have, admittedly, better.

You don't need to tap different points to do that; that is what an R2R ladder does, give you different voltages form different binary combinations at it's inputs.
If you measure those points you connected to with a voltmeter or oscilloscope, I think you may find that being connected in that way, they limit the number of different possible voltages but change the weighting towards each end of the ladder.

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Tomoroh Hidari



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PostPosted: Mon Sep 10, 2012 11:58 am    Post subject: Reply with quote  Mark this post and the followings unread

ok, thanks! will try sending just the r/2r output to the led then, see what happens.
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JingleJoe



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PostPosted: Tue Sep 11, 2012 12:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

Why are you sending it to an LED? Laughing try a vco or something else voltage controlled for greater effect Smile

ah but wait, is that a home made vactrol I see there? Wink

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Tomoroh Hidari



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PostPosted: Fri Sep 14, 2012 9:33 am    Post subject: Reply with quote  Mark this post and the followings unread

yes - by Led I meant the one in the vactrol... this (in series with a 500k pot) controls the pitch of a 40106 osc.
you can hear this one on the second two tracks I posted.

I did another test driving the led directly from the r/2r ladder with far less interesting results - i basically changed between two notes.

I had the idea for it from the "fun with seamoss" arpeggiator:
(http://www.milkcrate.com.au/_other/sea-moss/02_arp.gif)
thinking - if rather than just sending in a voltage at different points of the resistor series like done in above schematic - i'll a) send it in at various levels, and rather than just taking the sum at one point, i change the points of where I take it so that


x1 y1
x2 y2
x3 y3
x4 y4
...

(x in = 0 or 1)

so if, say i have 1 on 1+2 and my out is y4 then i should have a different result then when my output is y3, y2, r y1.... (if you listen to the recordings there is quite something along the lines of randomly changing patterns in there - i still feel a bit more (in both, terms of variations and pitch-scale) should be possible... maybe with an emitter follower transistor driving the vactrol led...?!

i decided to still use resistors on the outs of the 4042 (thus ending up with the r/2r) so my ins to the 4051 don't get too high, voltage wise...

in any case this should rather be done with a flipflop rather than with the 4042 (latch) which let's the clock in signal through on clock hi, so you need an input slower than the clock driving the 4042...

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corex



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PostPosted: Fri Sep 14, 2012 11:21 am    Post subject: Reply with quote  Mark this post and the followings unread

I designed a CMOS-based noise generator/sample & hold, and I think it makes sense to share it here. I used a couple CD40106 oscillators to drive an XOR chain as a digital noise source, and then I clock these random bits into a double-buffered shift register. Every 8 bits, I strobe the shift register (pushing the back buffer to the front) and the front side of the shift register outputs bits into an R/2R ladder to convert 8 bits to an analog value. This is buffered and optionally slewed.


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Tomoroh Hidari



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PostPosted: Sat Sep 15, 2012 10:19 am    Post subject: Reply with quote  Mark this post and the followings unread

thank you corex!
I actually hadn't looked at any real Sample & Hold circuits. now i will! Wink
don't have any sort of registers among my chips atm, but see various kinds pop up in quite a variety of circuits... may have to get me some at one point, eventually, i guess.
still wondering what use I could put those 4042s to (in a lunetta environment)...
well, live, learn and occasionally just go back to the schmidt-trigger...Smile

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corex



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PostPosted: Sat Sep 15, 2012 2:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

You can build a shift register with latches:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

You would need two 4042 in place of the 4094.
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Tomoroh Hidari



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PostPosted: Tue Sep 18, 2012 5:57 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks corex... by miraculous means i now also seem to get how shift registers work!

will have to do some experimenting with this new info! thx!

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