Adrian Freed

This controller demonstrates how most resistive touch screen systems can be modified to provide independent sensing of two positions on the surface. A single pressure measurement is also provided with a third sensing layer. A pair of SlideWide sensors (http://infusionsystems.com) are stuck to each other at right angles.

Illuminated button array music controllers have a long history. I was fortunate to meet the late great, Salvatore Martirano who pioneered the construction of large button array music synthesizers.

This controller with no direct antecedents is made by draping conductive stretchable fabric over a cereal bowl creating a curve similar to the famous one called the witch [sic] of Agnesi. Resistive strips around the bowl are shorted out by the fabric and the varying resistances are measured and sent as OSC messages via USB control software on a host computer - typically resonance model sounds in Max/MSP.

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 taped with conducting-adhesive copper tape or fabric tape. The microcontroller board measures the electrical resistances of these petals from their tip to a common center established with a gold-plated fabric ring 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 each conductive plastic petal.

The result is a circular array of nearly mass-less displacement sensors. The gesture-to-displacement relationship changes according to distance from the center of the bowl (variable “gearing)”. 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.

You may also put it on the ground and use it as multiple foot “pedals”.

A second version increases the number of fabric pressure sensors on the base board from 2 to 16.

An important point about the Tablo is that the drape sensing allows both very delicate light touch to be sensed along with very muscular or fast gestures when the fabric touches the piezoelectric strips. It is very hard with stacked position and pressure sensors to achieve this dynamic range so essential for compelling hand drum gestures.

It has been designed so that all the important sensing nodes are surrounded by grounded fabric to keep the noise down.

The hoop is easily removed so that the only moving part (the stretch fabric) can be replaced or washed.

A single pressure sensor is snuck into the top of the bowl.

There is lots of interesting potential math behind the shape of the bowl: spherical doesn’t work well, a catenary may yield a nice linear relationship between the finger position and sensed value, the “found object” bowl used is very good and almost linear.

You can scale this design up to support multiple people playing it if you can afford the fabric.

You can also build it in a linear/keyboard style instead of "in the round".

Experimental surface sensing for fingerstyle players

A collection of power sources for e-textile and wearables projects.

Piezoresistive fabric is sandwiched by sewn rows of vertical and horizontal pads using a basic sewing machine's custom embroidery pattern.

This wireless variant of Hannah Perner Wilson's fabric tilt sensor uses embroidereded high electrical resistance thread . I designed the tool path to create a resistive track from the patches that can be used as a potential divider . This results in a more continuous estimate of the ball location than is suggsted by the six apparently-discrete patches.

Novel and Forgotten Current-steering Techniques for Resistive Multitouch, Duotouch, and Polytouch Position Sensing with Pressure, Freed, Adrian , NIME 2009, 2009, (2009)

My table at Maker Faire 2007 including my first e-textile work with peizoresistive fabric, and my duotouch pad and floor sensors.

In 2016 I made the video below of a tear-down of those e-textiles with Hannah Perner Wilson.

Our Maker Faire table also include some great interactive demos whipped together by Andy Schmeder.

Michael Zbyszynski dropped in and talked about his Ikea bowl speakers.

It was great that Dan Overholt was nearby demonstrating his e-field sensor array.