Half-round, Piezoresistive Fabric, Conductive Heatshrink and Copper Tape

[inline-left:Figure4.jpg]The previous designs are limited by the sizes of floor protecting
disks available. This construction is free
of these size constraints.

A half-round wooden strip is cut to the desired length and two
separate strips of copper tape are employed on the flat length
and the curve. A strip of piezoresistive fabric is trapped and
preloaded under the flat copper tape by a length of ShrinkMate
heat-shrink tubing that is conductive on the inside (http://
methodedevelopment.com). This tubing connects one side of
the fabric to the top conductive strip.
If we ground the upper strip and measure the resistance from
the inner conductor to this ground the sensor is self-shielding.

The half-round configuration works well for the
footswitch application but this technique can be used for
cylinders and other shapes. For example, this grip sensor built
with a larger dowel:
[inline-left:Figure5.jpg]

The inner conductors are strips of separate conductive tape
allowing for separate pressure measurements around the dowel.
By carefully controlling the time of application of the heat gun
the amount of shrink has been controlled to allow the tubing’s
inner conductor to “self connect” to tape on the dowel without
constricting the piezoresistive fabric. This can be clearly seen
on the left of the dowel. These structures are mechanically stable
without adhesives.