Hello all,

I want to use 8 *unusually long* touch controllers with Pd, via a simple midi-board that I made a couple years ago, and am fishing here for ideas and advice in regard to such controllers/potentiometers.

This is simply about trying to build a more visually-performative/theatrical element into an "instrument", so as to visually sort of amplify the otherwise nearly-invisible-to-the-audience twiddlings of standard linear and rotary pots in a performance. And, the greater potential for "precision" over the greater length would of course be a nice extra.

The catch is that the longest touch pots that I can find online are "membrane pots", up to a maximum length of just 500mm, which is no significant breakthrough length for my purpose (http://www.sparkfun.com/commerce/product_info.php?products_id=8681). And, in any case, these cost about $27 apiece, which should be outrageous by any standards anywhere in the world, and is certainly very much so for me here in India, where a standard pot costs just about 10 cents,.. and $27 could hire me a strong-arm-lad for as long as a week or more!

And so, I wonder whether anyone can guide me on how to simply devise long pots for myself, each say about a meter long.

From an earlier thread that I read on this forum quite sometime ago, I do remember that a length of some sorts of video-tape can serve as the resistance material for a long pot. BUT, that is too fragile a material/coating for me to really bother trying for an instrument that would be meant to be actually playable for a long time, rather than just tried/demonstrated a few times.

I'd be grateful to have any thoughts and guidance on this.

Thanks, and keep well all ~ Shankar

http://www.geocities.com/tpe123/folkurban/synthstick/synthstick.html
This is the videotape idea.
I'm not really sure of another way to do it.

I suppose another way actually, would be to use distance sensors, but then your costs go up again.

Thanks God,

I now remember that it was you I'd read this from earlier too.

But, I see now that the video-tape idea stretches only up to just about a foot.

However, the page did yield this interesting link (http://www.electronicpeasant.com/projects/ribbon/controller.html), which talks of actually fabricating the resistance-strip by rubbing graphite powder into a mylar strip... Which sadly sounds like it would be pretty unstable to me, for long-term use. After all, if the powder can be rubbed in, wouldn't it also rub off?

edit: .........and, check out this lovely paper!! http://recherche.ircam.fr/equipes/temps-reel/nime06/proc/nime2006_230.pdf

Keep well ~ Shankar

How long do you need it??

you could hire the strong-arm lad to watch you move around, as he controlls the fader accordingly.

Haha!

You'll get me thinking now~:o)

But no, I'd like to be able to look to about 1 meter each, so as to clearly have an instrument wherein an audience would be clearly able to see the connection between a performer's touches and strokes and his music, video, or whatever, output.

The best I have heard so far is that the **wire heating-element of a 10W soldering-iron** should have about the right resistance, but that is something I will need to cross town to find here in Delhi, which I cannot do for awhile.

And so, in the meanwhile, does anyone here have any experience with this?

Thanks, and keep well all ~ Shankar

i dont have any experience but ive been looking to do something very similar. so if you do get any solutions, post them here most definately.

well this is all too technical for me, but I have an idea, that just might woik ('work' in a new yoik (york) accent).

Get a knob, put it on it's side, and attach a long stick to it. then you have a giant lever.

... but no greater resolution

Ok so i had a quick look around.
And the longest i've found is the kurzweil, http://www.kurzweilmusicsystems.com/Product.php?product=111
which i will assume you've found.
Its 60cm which is really the just under the vibrating length of strings on a guitar.
the problem is, it looks thick, and at $60US each, thats going to set you back a bit. You could always pull one apart and see how it works.

this guy,
http://www.wiseguysynth.com/larry/ribbon/ribbon.htm
has made a 30" long ribbon control and details it on his site.

i also found this link
http://mypeoplepc.com/members/scottnoanh/birthofasynth/id35.html

now, im going to elaborate a bit on my llight/laser idea.

ok, so here it is simplified, stuck in a piece of wood.

at point A we have a laser, but perhaps a light that disperses more would be of more benefit.

point B is a photoresistor. it can slide up and down its little groove there. The closer it gets, the more light it gets, the less resistance it gives, the higher value gets fed into your I/O board.

D is the laser/light beam. demonstrated in red. the best colour for any laser. but i suppose if you weren't into the sith, you could do green or blue.

point C shows how the little photoresistor can slide up and down, rather than wiring it up, you have two tabs on the bottom of it, which connect to two rails inside the groove, just like how slotcars get their power.

it would be easy enough to create a small cylindrical shield infront of the photoresistor to block out light from other sources.

Im thinking now, that a light other than a laser would be best. that way you get more dispersal of light, and a greater range of data.

Um. I haven't as yet got quite where I wanted to with this.

But, thought that some of you might be interested in what came of the idea for using the wire heating-element of a 15w soldering-iron.

1. the wire is thinner and far more fragile than a human hair, and (un)fortunately not too long.

2. I wrapped this spirally around an insulated rod about 2-3mm thick, with 2-3mm gaps between each spiral, yielding a full sweep-length of just about 30cm. Be careful if you try this. I lost about a quarter of the wire-length in my first try, because the spirals obviously have to be tight enough so as to not move when the wand is swept over the contact. In fact, I'd probably first put something like a cloth surface to the rod if I do this again, so as to better hold the spirals in place (i.e. sans adhesive)

3. to test it, I have so far used just the small audio circuit that you see in the attached pic (since I obviously don't want to start with breaking upon my midi-controller~:o)

4. the range isn't very much in comparison to a 10k pot

5. and so, I put in two sweeps, in series ~ one is of the course the wand itself (relatively "fine"), which is independently "played" by sweeping it back and forth over a contact, and the second sweep is a linear pot in the handle (relatively "coarse"), which can be separately controlled at the same time with one's thumb

6. in playing it, the sweep of the wand is obviously not entirely "smooth", on account of the gaps between the wire spirals. But one can overcome this to some degree by using a broad contact, so that 2-3 spirals always touch it simultaneously

7. in use with a midi controller, I envisage that the performer would play a set of wands over a single wide horizontal contact,.. somewhat like cooking seekh-kebabs!

And so, just in case this is anything new, I suggest we call it either the "MuSeekh" (Seekh = Kabab skewer/stick), or the "MusiCrop" (from riding-crop)

Wot say?

.. and keep well all ~ Shankar

edit: sorry ~ couldn't figure out how to post the image inline.

http://www.pdpatchrepo.info/hurleur/MuSeekh-05-small.JPG

Shankar;

1. You could use any resistive element as a voltage divider, magnetic tape, resistive wire... I've been thinking of getting a tub of that 'magnetic paint' they sell in craft stores here; it is just iron mixed with a binder. I'm guessing if you add the right amount of graphite tho the paint, you can mask a surface, paint a few coats, and you are golden.

2. The overall resistance, or length of the physical object will not affect resolution, as long as your are using the midi standard. The resolution depends on the ADC. Midi constant control messages will give you 127 steps. To increase resolution, some other platform(arduino, etc...) and 'language(osc, serial) is needed.

3. How about a linear encoder? Google rotary encoders to see how they work... Ok? Now, fabricate a meter long strip of plastic or whatever with holes evenly spaced along it. Get a few IR gap detectors, also called slot detectors, basically an IR emitter/receptor pair. Glue two of these side by side so that your strip can go between both of them. Mount your "shuttle" (the slot detectors) so that you can move it up and down the strip. Hook these guys to two DIGITAL pins on an arduino(or anything else) and use some example code from the ardiuno playground. Basically, each time the detector goes HIGH, you increment or decrement a counter variable by 1. The direction is determined by which of your two detectors goes HIGH first. The benifits of this are: Your "resolution' is unlimited, it is determined by the number of holes in the strip and the spacing. It is much 'cheaper' in terms of cpu load, because it uses no ADC.

This may help explain what I am getting at: (scroll down)

http://todbot.com/blog/2008/06/17/get-on-the-blinkm-bus-with-a-blinkm-cylon/

Thank you Nestor,

That is pretty fascinating stuff. Almost had me reach out for the nearest mouse,.. to disassemble it.

However, it is sadly not what I am looking, especially in regard to the (missing) option of being able to do a direct on-off at various selected points of the sweep.

In the case of the wand for example, that is achieved by simply making or breaking contact at any desired point along the length (*firmly*, so as to avoid crackle). And, holding the value can be achieved by simply leaving the wand in place, as long as desired.

Basically, the idea of a simple resistive material now suits this line of thinking just fine for me. And, since what I am therefore now after is the *ideal* such material for my own particular intended purpose, I really wish I had the shopping choices for possible raw materials that you seem to have wherever you are (I'm in Delhi/India)

I should perhaps also mention here that the wand was essentially just a testing-matrix for me, and not really what I was looking for as an end result. And so, I shared it here because I do think that what it has "accidentally" become is a very funky possible interface for some sorts of performers to use, in some sorts of performances,~:o)

Meanwhile, that's the second time I have come across the term "voltage-divider" in this context over the past couple of weeks. But, what I have not properly understood so far, in regard to adapting something like this to take the place of standard pots in a controller is ~ where's the equivalent of the 3rd contact of a standard pot in this matrix (e.g. -0v)?

I ask because, from my limited knowledge, I suspect that that's where the ADC takes the resolution from.

Any explanations/ideas?

Keep well all ~ Shankar

[edit] ps. I don't have an Auduino board, but do sometimes wish I did

a voltage divider is simply two resistors in series: like this:

R1 V1 R2
V+ ----wwww---•----wwww----- GND

The Voltage at V1 is 'divided' by the resistors, and is proportional to the value of the two resistors; if R1=R2 then V1 = 1/2 of V+. The diagram of a potentiometer reveals how it is constructed. Here's one wired as a divider:

V1
|
R1 V R2
V+ ----wwwwwwwwwwww----- GND

The guts of a pot are simply a piece of resistive material, and a conducive 'wiper' which you move with the knob when you turn it. AS the wiper moves, the value for R1 and R2 change proportionally, and so goes the voltage at V1. The middle tab on a pot is the wiper. If the other two tabs are wired as V+ and GND respectively, you can tap the divided voltage at the center tab. A ribbon controller is basically the same exact thing as a pot, except the 'wiper' is a piece of conductive mylar overlaying a resistive tape, but not touching; when one touches the mylar, it makes contact. In a stylophone, the wand is the 'wiper'.

Helpful?

Yes Nestor, very helpful indeed. Particularly that little tailender mention of the stylophone.

Thank you.

As it happens, one approach I was thinking of was in fact stringing together a line of resistors, which I may still try to do, since one would then be able to work with very robust contacts. And I see from your explanation that I jut need to link up the tip of my wand for the third contact.

At the same time though, I am finding that my wand and tester-circuit actually amount to a most excellent and quite versatile *audio* instrument in itself, with even just a bit of signal-processing at the output end.

In fact, since CeC 2009 is now really *impending*, I think I'm going to leave this at that for now, and perhaps look again towards actually implementing my original idea sometime after we're done with that (http://www.theaea.org/cec_cac/cec09/index.htm)

But, yes, I'd love to keep up the conversation here to arrive at some final resolution of what might be the ideal (i.e. easily-available and adequately robust) material to use in making a loooong touch-pot/ribbon-controller.

Thanks again, and keep well all ~ Shankar

[edit] I have attached an example file of what one can do with the MuSeekh, in the output section of this forum, for anyone who might like to check it out: http://puredata.hurleur.com/sujet-2391-just-example

Keep in mind though that I have played with the device for not more than perhaps 1-2 hours so far, so, please do excuse the ineptness

ARe you making a wizard's staff?

Shankar,
Yes, it would be great to continue the discussion. I am going to get some of that magnet paint and test it's resistance. Otherwise, Maybe I'll experience with mixing powdered graphite into regular latex paint. I'll keep everyone posted. Also, I like the idea of the series of many resistors. you could even set different scales by playing with the values of the different resistors. Or, how about a matrix of resistors?

Sunji~:o), Yes, it seems to have accidentally become the beginnings of a potential magic wand. But, that's because it is essentially just the opposite of collateral damage, deriving as it does from the opposite of destructive practices ~ i.e. *white* magic ~ LoL

Nestor ~ hey!, Thanks for thinking to check out some alternative approaches to the resistive length. Meanwhile, in regard to the resistors idea, I suspect that the Stylophone uses independent oscillators for each key because, if one were to go in series, so as to drive through a single osc, then the resistor values will have to sequentially reduce/increase quite precisely.... sort of like the fret-spaces of a guitar.

.... I think.

[edit: BTW ~ although I love this so far, it is obviously not what I was originally targeting to make, because I want to have at least 8 controllers, that can be simultaneously played with one's fingers over vast sweeps]

Keep well all ~ Shankar

ShankarBaba;
How's the progress on this going? any closer to your 1m length?

I'd love to see some more pictures too to see how this works.

Hi God,

Sorry for the slow response ~ was on a wireless modem for a month, instead of broadband, and somehow just couldn't get here via that route.

But, no, I have not worked on my wand any further, since CeC 2009 is really-really impending,... and looking very nice too (http://www.theaea.org/cec_cac/cec09/index.htm). Yes, I do plan to use the wand in my performance, as an audio controller, mainly just to share the lovely simplicity with folks.

H-o-w-e-v-e-r, my friend Dhananjay Gadre has very kindly been exploring an alternative approach for us, and has come up with an interesting LED-based controller.

To quote him here:

Uses a Tiny861 and has 10 LEDs for sensing/display. The white LEDs are always ON and just provide uniform illumination...

The output is a 10-bit PWM, filtered to provide analog voltage between minimum (0) and maximum (4V) in 10 steps

Pictures of the circuit board are on my flickr account: http://flickr.com/photos/gadre

Knowing Dhananjay, I'm sure he will post a DIY page when he is fully done with development, so, will post that too in time.

Keep well all ~ Shankar

@ShankarBaba said:

Sunji~:o), Yes, it seems to have accidentally become the beginnings of a potential magic wand.

Hahaha.... get it?! POTENTIAL magic wand?