KVR Audio

dimaugh · Post by **dimaugh** » Tue May 05, 2020 9:39 am

Hi there! I've been meaning to build a digital multi ribbon controller for years, but all my previous attempts failed. All I want is 9 ribbons with pressure sensitivity, spaced no more than 25mm apart.

The first I tried were some Softpots glued over force sensors. The problem was, the softpots required a lot of force to be activated, not ideal for fast playing.
Then I tried some graphite with glue, but after a while some of the graphite would wear off and give unconsistent readings.
I also tried some Velostat, but the problem was that pressure would affect the reading too much. I was also using Velostat beneath it as a force sensor, so I thought maybe I could write some algorithm that would compensate for this, but this turned out to be harder than expected since it wasn't linear at all.
Also tried some resistive thread I bought from Plug&Wear, but as it wasn't flat and smooth but rather rough, it wasn't very accurate (similar to buzzing strings in a fretless instrument).

So, the only thing I haven't tried yet is VHS tape. Now, is it durable enough? Will it consistently give the same readings when pressing at the same height a year later, or will it wear off?
Do you know of other reliable alternatives?

Since what I'm after is only a digital controller, I don't have to worry as much about tuning: I can linearize the output with a table of values later.

VariKusBrainZ · Post by **VariKusBrainZ** » Tue May 05, 2020 10:21 am

Are your trying to avoid of the shelf touch strips?

dimaugh · Post by **dimaugh** » Tue May 05, 2020 11:37 am

I only know the Softpot by SpectraSymbol, and as I said above, it's requires too much force (for my taste) to give a reading. Also, they're bit expensive, though trying to build things on your own without the proper tools is sometimes more expensive.

If you know of others that work with a lighter touch, I'd be happy to learn. But they all must be using some relatively cheap material for the resistance.

VariKusBrainZ · Post by **VariKusBrainZ** » Tue May 05, 2020 11:46 am

Cant help sorry, I got mine from icubex on sale years ago. A did a quick Google and found some.

dimaugh · Post by **dimaugh** » Tue May 05, 2020 12:19 pm

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Don't worry, at least now I know the name of another manufacturer, but I can't find their datasheets.

Also, taking a look at the softpot datasheet, it says the actuation force is around 1.5 newtons at room temperature. Not knowing how much that is, I went to take a look on how many newtons we normally apply to press down a guitar string. According to this reddit post, more than 2 newtons:
https://www.reddit.com/r/Guitar/comment ... d_to_push/ (https://www.reddit.com/r/Guitar/comments/3nq382/empirical_measurement_of_force_needed_to_push/)

So why did they feel so "hard" for me? Maybe because I placed them on top of FSRs (https://www.sparkfun.com/products/9674 (https://www.sparkfun.com/products/9674)) instead of a flat hard surface?

Kalamata Kid · Post by **Kalamata Kid** » Tue May 05, 2020 2:37 pm

Try the Kurzweil Expressiomate?
With an overlap it will be at 25 mm center to center.
They can be split in three I believe so you many only need to buy three.

Kalamata Kid · Post by **Kalamata Kid** » Tue May 05, 2020 2:40 pm

Try the Sensel Morph very responsive to velocity and pressure.
https://sensel.com/pages/the-sensel-morph
go their forum where thy make stuff like you request.
https://forum.sensel.com/

If you make one let me know as I would love to try it.

deastman · Post by **deastman** » Tue May 05, 2020 2:46 pm

Kalamata Kid wrote: ↑Tue May 05, 2020 2:40 pm Try the Sensel Morph very responsive to velocity and pressure.
https://sensel.com/pages/the-sensel-morph
go their forum where thy make stuff like you request.
https://forum.sensel.com/

If you make one let me know as I would love to try it.

My thought exactly!

dimaugh · Post by **dimaugh** » Tue May 05, 2020 4:21 pm

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oooh, that Sensel Morph thing looks great and not so expensive!
I'd rather roll my own since I need to adapt it to my own design, but I was wondering how they made something so complex that inexpensive, so I began to snuff around and I kinda found it:
https://dl.acm.org/doi/pdf/10.1145/1520340.1520460 (https://dl.acm.org/doi/pdf/10.1145/1520340.1520460)
(this is not the exact technology they used for the Sensel Morph, though, but a similar one)

It could be summed up as: vertical tracks of copper, a layer of a piezoresistive material (Velostat, or FSR ink) horizontal tracks of copper. The columns are powered one by one, taking readings from each row at each turn. While not being used, the tracks (both columns and rows) are grounded, as you can see in figure 10.

Now, I know how to power the columns one by one with a multiplexer, but how would I ground the rest simultaneously? A multiplexer only allows to access one channel at a time. Of course, I could have a switch for each track, but that seems rather costly.

Kalamata Kid · Post by **Kalamata Kid** » Wed May 06, 2020 12:38 am

^^^
you probably did this already but just in case here it is:
https://www.google.com/search?q=midi+ri ... 4&bih=1218

and HOW TO BUILD A MIDI RIBBON CONTROLLER WITH ARDUINO
http://www.coagula.org/albedo/how-to-bu ... h-arduino/

more
https://www.google.com/imgres?imgurl=ht ... c..i&w=640

Multi ribbon controller