Many years ago I worked for a prosthetic facility in Research and Development. One of the main causes of amputation is from the lack of feeling brought on by the onset of diabetes.
So you don't go down the same path as far as sensors, initially we used the flat laminated sensors. They seem great at first, but any kind of a crease and they are toast. Not to mention they de-laminate very quickly with the sheer forces that happen within your shoe. We had patients that would last a few hours, and some that would last a week.
This led us to develop our own sensor which was an inductive coil that changed inductance as pressure was applied. The coils were constructed on a flexible circuit board much like what was shown earlier in this thread. The coils were of a pancake style and accessed one at a time with the circuit. A neoprene was used as a compressible medium with adhesive aluminum foil on the opposite side of the coil. The neoprene was sandwiched between the coil and the foil.
Note: The foil was two layers of foil with a metal screen sandwiched in between the two layers of foil. This was to help maintain integrity with repeated cycles.
By compressing the neoprene the metal foil would alter the inductance of the coil where it could be read. Each coil was pulsed one at a time with a 1ms pulse. The back emf was captured with a current mirror and fed into a 12-bit ADC to obtain a reading. The returned voltage reading from the ADC was proportional to the inductance value of the coil.
Coil Placement: There were a total of 8 coils ... 4 on the front and 4 on the back. The values were treated deferentially to form two vectors (Front<-->Back) and (Left<-->Right)... i.e. for front ALL four coil values were added together and on the back ALL four coil values were added together and subtracted from the front accumulative value. Likewise for left and right.... the left two coil values on the front were added to the left two coil values on the bottom and subtracted from the sum of the right two front coils and the right two bottom coils. Then finally those two vectors were combined into ONE single vector by applying SINE and COSINE to determine the deg from 0 to 360. As a person applied their weight, they became a "human joystick" as to where they were moving their weight.
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