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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Tunable RnR network
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Stream Operator


Joined: Oct 13, 2007
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PostPosted: Thu Aug 02, 2012 6:28 am    Post subject: Tunable RnR network
Subject description: for use as boolean sequencer aggregator or other uses
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Hey guess what? Today I dreamed up a generalization of the R2R ladder network that has interesting possibilities. It's useful as an aggregator for a boolean sequencer or whenever you have some signals to combine in a somewhat prioritized way.

Take a look at the image below to see how I imagineered a way to chain some potentiometers together into an RnR network, which is a generalization of the R2R network. I say it's a generalization because if you tune it just right, setting each pot to 2/3 of full scale, you get an R2R network. Or you can adjust the pots to different values to emphasize or de-emphasize various bits. To emphasize one bit, crank it's pot to the left (counter-clockwise), and opposite to de-emphasize it.

I wonder if you can make an R3R network and it will actually be a base 3 DAC, and an R4R network for a base 4 DAC - not sure as I have not taken the time to really study it and do the math properly.

Anyway, it's cool - give it a try!

Les


TunableRnRNetwork.jpg
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R2R's crazy cousin: RnR!
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TunableRnRNetwork.jpg



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JingleJoe



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PostPosted: Thu Aug 02, 2012 6:39 am    Post subject: Reply with quote  Mark this post and the followings unread

That's excellent! The schematic made me LOL Laughing, not because it's a tad crude but the idea just looks rather amusing to me Smile however, it will be highly effective, a great idea!
I may even implement it in a control voltage pattern generator I made recently (but in the next version) with an R2R ladder and a 4040.

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Blue Hell
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PostPosted: Thu Aug 02, 2012 7:02 am    Post subject: Reply with quote  Mark this post and the followings unread

Hmm ... but it is possible to short the driving outputs this way Confused
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Inventor
Stream Operator


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PostPosted: Thu Aug 02, 2012 7:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Glad to create some joy there, JingleJoe! Yeah I think it's a really flexible alternative for generating CVs from any group of digital signals including a 4040 binary counter output!

Les

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JingleJoe



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PostPosted: Thu Aug 02, 2012 2:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
Hmm ... but it is possible to short the driving outputs this way Confused

How?
I just pondered it for a few minutes and although slightly drunk I think my trai of thought is straight enough to think straight, that is I think I thought correctly in my thinking qoweuriogsdf ANYWAYS I can't seem to spot any shorts, the inputs will allways have a whole potentiometer of resistance between each other, even if one is turned all the way to the top and the next all the way to the bottom so the wipers are effectively connected, they still have a potentiometer's worth of resistance between each input.
I suppose if you mean between the inputs and the output then that's correct, but one can simply add a buffer or a 1k don't-release-the-magic-blue-smoke resistor Wink

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Blue Hell
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PostPosted: Thu Aug 02, 2012 3:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hmm .. I was a bit too fast there I guess, sorry, undo Laughing
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Stream Operator


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PostPosted: Thu Aug 02, 2012 3:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

Whoah! I gotta agree with JingleJoe here, the incredible guru Blue Hell just stumbled and dropped his golden slide rule for the first time I ever saw. Usually Blue Hell outdoes me in almost all categories of brilliance and understanding but this time he really flubbed the goose beeswax! Had a tough day at work my friend?

Yeah, it looks ok to me in all pot positions, some of them trivial but that's not a flaw, it's a feature! hahahha.

Whatever man.

Les

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PostPosted: Thu Aug 02, 2012 3:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

Tough day .. well yeah I was debugging some stuff that happens once in a blue moon ... while it didn't happen I had a couple of minutes of forum time between tries Laughing

On 2nd thought it seems a nice circuit Cool

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RingMad



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PostPosted: Thu Aug 02, 2012 4:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey Les, where's the datasheet so I can study up on this? Smile

Anyway, a while back I was thinking about tunable R2R's, since I had read somewhere that if you choose different resistances for each "rung", one could tune it to the usual musical scale, say.

Now that I'm done with that major build project, I think I'll try my idea out tomorrow before babbling about it here.

James.
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Stream Operator


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PostPosted: Thu Aug 02, 2012 7:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

RingMad wrote:
Hey Les, where's the datasheet so I can study up on this? Smile
James.


Haha James, I guess that's fair play after i embarassed you like that, lol!

I'd say the datasheet on this one is algebra and Ohm's and Kirchhoff's laws. Just denote each pot's two resistors as R*x and R*(1-x) where x can vary from 0 to 1 and do circuit analysis on say a two-input one for starters. Solve for Vout = f(Vn, Xn, R). It's a good situation for Mathematica or MatLab or the like as you'll probably get a boquoo huge equation out of it symbolically. Then look for the form of the equation or plot slices of it in 2D and 3D.

It would be a good exercise. Or for your musical scale idea, set Vout = kn*vn = f(Vn, Xn, R) and look at the form of the equation, make intelligent guesses for Xn, and see if you can figure it out.

By the way, in case I take a stab at it, what is the musical relationship the bits should have? Some kind of square root of 12 thing I suppose? I forgot that math altogether, refresh my memory and I may go for a solution myself.

Better than a stick in the mud, I say!

Les

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PostPosted: Thu Aug 02, 2012 8:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

Inventor wrote:
By the way, in case I take a stab at it, what is the musical relationship the bits should have? Some kind of square root of 12 thing I suppose? I forgot that math altogether, refresh my memory and I may go for a solution myself.

I really don't know. I think part of the reason I didn't get round to trying it was because I'm not actually interested in the ol' equal temperament convention. If I was any good in math, I'd be more interested in just intonation.
Besides, it's not like my wonky machine is precise enough. I didn't even measure the resistances I used for the R2R's I built, and I don't have %1's either! It's in the key of naught.

I think the thing I read was in this post: http://electro-music.com/forum/topic-33607.html . But there's no math.

James.
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PostPosted: Thu Aug 02, 2012 11:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Speaking of the mathematics of musical scales, have a look at my tumblr post about just that;
http://gda-labs.tumblr.com/post/25218939377/y-2-x-1


I allways thought a chain of resistors with no "branches" like an R2R would give an exponential increse in voltage at the output, or is that logarithmic? I know it's harder to get precisely an exponential increase in a standard chromatic scale but it's entirely possible.

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dougseidel



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PostPosted: Fri Aug 03, 2012 6:53 am    Post subject: Reply with quote  Mark this post and the followings unread

I love that thing Les.
I've been using a similar idea to this tunable R/2R ladder, using LDRs in parallel and/or in series with the resistors in the network. Using various LED and incandescent bulb combinations to control the LDRs. I like the little incandescent flashlight bulbs because they have slow response, and lots of variation in intensity.

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