Floor Protector and Force Sensing Resistor (FSR)

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The foot/switch interface is provided by a soft but “grippy”
toroidal ring of molded rubber embedded in a hard PVC disk.
These disks are sold as “floor protectors” for furniture. A flat
ring of polyurethane foam with a peel-off adhesive is on the
opposite face of the disk. This foam provides the restoring force
for the “switch” which is implemented with an Interlink Force
Sensing Resistor (FSR).

A screw provides the necessary
adhesion to resist kicks of the foot and also preloads the FSR.
Although not generally a good idea, punching a hole at the
center of the FSR (with an office hole punch) provides a clear
path for the screw to reach the wooden substrate below.

Dust is
prevented from entering the gap between the interdigitated
conductor layer and the piezoresistive film layer by the foam.

This sensor works adequately but the tension adjustment is
delicate as the FSR saturates easily at the range of forces a foot
can easily apply.