[sdiy] Velocity/Position sensing

[Kevin]

Here's the device I saw at the maker faire.

http://cnmat.berkeley.edu/event/2008/07/23/clone_lab_building_sensors_scratch

The person in the picture is Adrian Freed.  His email address and  
other stuff can be found here:

http://cnmat.berkeley.edu/people/adrian_freed

He wrote a paper called "Application of new Fiber and Malleable  
Materials for Agile Development of Augmented Instruments and  
Controllers".  I have a paper copy of it that he was handing out at  
the maker faire.  This paper covers the Tablo as well as a number of  
other sensing techniques.

Here's what it says about the tablo - I just typed this up from the  
printout I have.

====

4.2 The Tablo
The novel controller of Figure 13 exploits recently available  
conductive stretchable fabric and an approximation to the curve known  
as the witch (sic) of Agnesi.

The fabric is stretched in an embroidery hoop and draped over an  
inverted circular bowl.

A piece of conductive plastic cut in a special shape forms a corolla  
on the surface of the bowl.  The tips of each petal are folded inside  
the bowl and tapped with conducting adhesive copper tape.  The micro  
controller board measures the electrical resistances of these petals  
from their tips to a common center established with a conductor at the  
flat of the bowl.  As the conductive stretchable fabric (the "calyx"  
to complete the flower analogy) is displaced towards the bowl, it  
shorts out different lengths of the conductive plastic petal.

The result is a circular array of nearly mass-less displacement  
sensors.  Unlike the Continuum Finger board the gesture-to- 
displacement relationship changes sensitivity according to distance  
from the center of the bowl.  This allows for several different  
playing styles.  One style - similar to hand drum technique - involves  
tapping the fabric surface directly onto the bowl with the fingers of  
one hand and leaning towards the other side of the bowl with the palm.

Another style involves both hands interacting from the outer hoop  
towards and around the base of the bowl.  The latter style affords  
some interesting parameter mappings.  One fruitful approach is to  
divide the circular petal array into two halves and compute the  
direction and amplitude of a pair of vectors by summing contributions  
of sensors accessible to each hand.  An additional third parameter for  
each hand representing the "size" of the gesture is obtained by  
computing the ratio of the arithmetic and geometric means of the  
displacement values.

Two refinements were added recently:  a pressure sensitive  
"aftertouch" using fabric on the base around the bowl, and a presure  
sensing fabric disk at the very center of the controller.


On Sep 30, 2008, at 4:48 PM, Kevin wrote:

> I saw someone doing this at the maker faire in california earlier this
> year.  You may be able to find it on the maker faire website.  If not,
> I will try and find his handouts.
>
> I think he teaches a class at UC Berkeley.
>
> He was using electrically conductive fabric as the surface of the  
> drum 'head'.
>
> On Tue, Sep 30, 2008 at 3:03 AM, Justin Owen  
> <juzowen at googlemail.com> wrote:
>> Hello,
>>
>> I've been asked to look into the idea of designing an electronic  
>> percussion instrument that emulates the surface of a skinned  
>> percussion instrument - i.e. playing different parts of the skin/ 
>> surface will give you a different sound/timbre/etc.
>>
>> Can anyone point me in some directions to start researching a pad/ 
>> surface that could read/sense both velocity/pressure/force and  
>> position - say, some sort of X/Y co-ordinate?
>>
>> At this stage the idea is that the values could be read and  
>> converted into CV information via a microcontroller - but I'm open  
>> to any and all suggestions.
>>
>> I've found a few potential leads - but I thought there might be  
>> some good clues on this list. Thanks in advance.
>>
>> Justin
>>
>>
>>
>>
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