Position Sensing Trip and Rubber Door Threshhold

To create multiple foot switches we can simply tile out arrays
of the previously described devices. There is a better, faster
way with the additional convenience that the switch functions
are built into a single strip that is constructed quickly in a few
steps. Instead of employing the principal of piezoresistivity
change we employ a printed-resistor position-sensing strip such
as the SlideLong (http://infusionsystems.com) or a Softpot
(http://spectrasymbol.com).
[inline-left:Figure8bis.jpg]
These position-sensing strips
were originally designed for finger touch interaction. To protect
the sensor strip and provide tactile feedback we attach it to the
base of a length of rubber door threshold. This is molded with
corrugations that grip the sole of the foot well and a curved
surface above the sensor. The flat sensor stays where it is put
on smooth flooring and carpets.

Unfortunately the lateral sensitivity region of position sensing
strips is narrow and the top of the door threshold may simply
collapse and not activate it. The solution is to fill the gap above
the sensor with a lightweight flexible incompressible material.
Two lengths of nylon rope worked well in the prototype.
[inline-left:Figure8.jpg]

This device was designed to roll up and fit into a guitar case.
The electronics is configured to measure the positions of up to
two concurrent depressions of the strip. Instead of using
the well-known potential divider method we ground the
“wiper” contact and measure the two end point resistances to
this ground node to estimate the position of the outer most
touch point pair. This idea was patented in 1972 for duophonic
analog synthesizer keyboards (USPO3665089).