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 Forum index » DIY Hardware and Software » Musical Interfaces
early tests of a DIY pressure playing surface
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otoskope



Joined: Jun 14, 2005
Posts: 26
Location: Sweden
G2 patch files: 1

PostPosted: Sun Jan 31, 2010 3:03 pm    Post subject: early tests of a DIY pressure playing surface Reply with quote  Mark this post and the followings unread

Hi all,

Just want to share this early experiment on a quick-and-dirty DIY pressure sensor playing surface for analog CV signals:

http://www.youtube.com/watch?v=Nh7QJR1VKXI

I will do a proper instruction video or web page soon, but suffice to say that I use 6mm conductive foam, the kind you use to protect ICs from static discharges during transport (actually, this one: http://www.kjell.com/filarkiv/SUPPORTPDF/91-100/98/98216/98216.pdf). It has the interesting property of lowering its resistance when compressed (from very high down to 10-12kOhm, depending on the surface area), so you can simply route control voltages through it. Here I have the +5V in the large foil patch on top, and four patches of aluminium foil underneath, connected to various modulation inputs on the BC16 analog modular (the white round little synth in the background). Essentially, in the configuration in the video, it is a flexible signal splitter of the +5V to four destinations.

I've put the foil patches on plastic sheets so they are changeable, in case I want to test different layouts. The foam will probably get compressed and hence less sensitive after excessive playing, so I want to keep it easily exchangeable, too.

The patches underneath are intentionally placed very close to each other, to force some parameter coupling, just like in acoustic instruments. I will also try a more rigid plastic top sheet to emphasize this effect.

The foam piece cost €3, and I found a HUGE roll of adhesive aluminium tape for €9, so this is cheap stuff. Normal aluminium foil from the kitchen works fine, too, with the help of some glue or double sided adhesive.

There are no other components used but the conductive/resistive foam, the aluminium foil and some cabling. Smoothing the signals with simple LP filtering would probably help, especially for pitch control, but I haven't tried that yet. Would take more thinking...

This was a quick mobile filming of the very first test, apologies for quality of sound and image.

The reasons behind doing this, is to find analogue versions of this:

http://www.youtube.com/watch?v=sVqP6P3t_8U
(I'm the guy at the left side)

This setup uses a quite unusual vector-based mapping technique from sixteen pressure sensors (the TriggerFinger) to synthesis parameters described here: http://www.init.ituniv.se/~palle/publications/Dahlstedt2008_CMMR_DynamicMappingStrategies.pdf

Essentially, I want to be able to play my synths in a very direct way, in a free impro context, be it analogue or digital.

Any feedback welcome!

tjo,
Palle

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Antimon



Joined: Jan 18, 2005
Posts: 4145
Location: Sweden
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PostPosted: Sun Jan 31, 2010 3:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

You're hurting it! Wink

Very cool concept though! I have to check if I have any of that foam around.

/Stefan

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slabman



Joined: Sep 01, 2005
Posts: 102
Location: UK

PostPosted: Mon Feb 01, 2010 4:59 am    Post subject: Very nice Reply with quote  Mark this post and the followings unread

As used on some ARP synths?

I remember reading once about someone making DIY bathroom scales from aluminium foil sheets on both sides of a piece of foam. However, rather than using conductive foam and measuring the resistance, they used ordinary foam and measured the capacitance.

One further thought - Mylar might be robust than foil, or else some conductive fabric.
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otoskope



Joined: Jun 14, 2005
Posts: 26
Location: Sweden
G2 patch files: 1

PostPosted: Mon Feb 01, 2010 6:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for your feedback!

The thing about ordinary foam, measuring capacitance is just great! Difficult on stage, though. Might bring a bathtub on next tour .-) Just mention warm water in the tech rider... Does it work with beer?

Just read about Wheatstone bridges in another thread (http://www.electro-music.com/forum/topic-38612.html), and that seems to be a very clever way to scale the resistances in various ways. I'm more of a programmer than an electronics guy, but I'm happy to learn.

Did ARP use this? Interesting. Didn't know that.

Regarding robustness, the foil I'm using is quite robust. It's a heavy aluminium adhesive tape, that I put under a plastic sheet (cutout from a binder). The plastic prevents the foil from tearing. Maybe the foil will crack after a while, after excessive bending, but it hasn't happened yet.

/Palle

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slabman



Joined: Sep 01, 2005
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PostPosted: Tue Feb 02, 2010 8:28 am    Post subject: Stage performance Reply with quote  Mark this post and the followings unread

otoskope - the technique also works if you stay dry and keep your clothes on, but , hey, you have to keep those audiences happy, right?

Theres' a little bit on the ARP pads here - http://www.synthmuseum.com/arp/arpodyssey01.html

The capacitance technique is probably a bit tricky for what you want. You'd have to find a way to convert it into voltage, eg by controlling a high-frequency oscillator and integrating the output.
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Ricko



Joined: Dec 25, 2007
Posts: 251
Location: Sydney, Australia
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PostPosted: Wed Feb 24, 2010 7:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

I have made some pressure pads using the conductive foam, but I have the foam against the board of a slider potentiometer. The connections are made to the far end of the resistive strip and to the wider strip.

This way you get a kind of ribbon/pressure controller. When you press on the foam, it becomes more conductive in that region, I guess, and bridges between the resistive strip and the wiper strip at the point.

One use I am thinking of for these is to make some little feet for the front of keyboard controller. So the more that you press down on a key, the more the foam is squished: a kind of polyphic aftertouch.

Actually, you can go a little further: use the board from a stereo slider pot. Cut the foam into two lengthwise, but there is no need to insulate the two sides. This gives you a kind of pressure device that it sensitive both to moving your finger up-and-down (depending on the pressure at the vertical position) and side-to-side (depending on the position at the horizontal position).

I have made a row of five of these stereo ones in a block, for five fingers control (10 CV control at once!) but I haven't used them yet: grrrr need to get more modules finished.
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rosch



Joined: Oct 03, 2009
Posts: 164
Location: germany

PostPosted: Thu Mar 04, 2010 12:22 am    Post subject: Reply with quote  Mark this post and the followings unread

interesting!
the use of conducting foam has been described by Thomas Henry in his electronic drum cookbook as a technique to obtain +5V trigger signals.

http://www.lulu.com/product/paperback/the-electronic-drum-cookbook/3167664?productTrackingContext=center_search_results

good idea to generate even cvs from it!
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emdot_ambient



Joined: Nov 22, 2009
Posts: 667
Location: Frederick, MD

PostPosted: Mon Apr 19, 2010 1:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

Antimon wrote:
You're hurting it! Wink

That was my thought. Sounded like a dying duck in a thunderstorm.

I've got 2 ARP Axxe synths with their Proportional Pitch Control (PPC) vibrato and pitch bend pads...I absolutely hate them. First of all they were always very stiff. Even brand new you had to really dig into them to get the right amount of modulation. Secondly, as they've gotten older, they've gotten nothing but stiffer. I'd really like to mod them, rip out the PPC and put in proper mod wheels. Even the pitch bend knob would be better than these.

So far every pressure sensitive idea I've seen for analog synths is unwieldy in real world use. Good sounding ideas...not so good in practice.
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