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Consider a cushion such as this: Roho air cushion. To make sure one isn't "bottoming out" when sitting on one, usually one would "sit on their hand" and make sure there's about a 1-2cm gap between the boniest part of one's butt and the surface the cushion sits on.

This method has multiple problems (consider a leak for one), and I thought it should be able to be addressed without sitting on ones own hand. I'm considering things like:

  • "capacitive sensing": I'm not sure if this would work on a number of levels: the large distance, the large surface, and the material type of the cushion.
    • For this I've also considered a fine partial mesh "cushion cover" to assist, however ideally there would be no interface at the boundary of the cushion and person.
    • I've also wondered about painting/marking the top of each "cell" of the cushion with some conductive ink or such.
  • "pressure sensing": This could be done in 2 flavors:
    • Pressure sensing the air in the pockets: This is difficult because there's no valve access to each of the chambers (the cushion is divided up in to 4 chambers).
    • Pressure sensing the surface that the cushion rests on: This seems somewhat difficult. It seems like it would require a certain resolution of pressure points to work out when the pressure isn't being distributed evenly and instead is now point-located.
  • Heat: I wonder if making a base that the cushion sits on with a number of temperature sensors in it could determine the closeness of the body part from heat. This seems like it could be influenced immensely by too many variables (clothes, ambient temp, etc.)

What I'm looking for is:

  • Feasibility of certain sensors
  • Form factor of sensors needed (e.g. if capacitive sense was viable, how would I even package it? Can you even buy a big "capacitive sense 'mat'"?)
  • Any other feasible possibilities I haven't thought about.
  • The ability to not be influenced by the environment too much (e.g. ambient conditions, clothing)
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coat the upper and lower inside surfaces of the cushion with something conductive and measure conductivity between them - if current flows the cushion is bottomed out.

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  • \$\begingroup\$ That's a good idea however I'm not really able to edit the inside of the cushion other than perhaps spraying air inside that has a mixture of adhesive conductive material. These cushions are not really something able to be cut open and resealed easily. \$\endgroup\$
    – Clammet
    Jun 7, 2021 at 1:12

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