The reason I am learning to program PICs was originally to make a car anti
theft device.  For that device I needed a switch that could be placed under
the carpet (and even the padding) of the car.  I found a product called Tape
switch that was perfect http://www.tapeswitch.com/ .
You purchase the switch part in rolls and cut to the length needed then
(with PVC glue) glue on the wire lead end and the terminating end.   They
also sell premade lengths.  Pressure upon any portion of the tape makes a
connection (normally open contact switch).  The tape is flexible and
available with sticky back so it can be used on most any surface without
affixing geminately.  And no I don't work for them, I just thought it to be
the perfect solution for the project. If placed on the seat and maybe also
on the back (giving 2 sensing sources) if the person fell or was removed
from the seat the switch would break and start whatever program .  I am a
mechanical engineer and usually have the problem of over designing a
project, but this would make this project ultra simple.  Dare I say it, it
may not even need a PIC.  Maybe just a 555 to wait X time then turn on
something.
----- Original Message -----
From: Peter L. Peres <plp@ACTCOM.CO.IL>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, April 02, 2001 12:15 PM
Subject: Re: [EE] Pressure/Mass sensor pad/mats


> I don't think that the cushion can be made to work reliably. I think that
> you should investigate a non-intrusive addition to the $8000 wheelchair,
> like a pair of strain gages (the glue-on kind) attached on some convenient
> structural elements in the chair, near the wheel bearings. This will
> indicate strain (i.e. weight) on each rear wheel. The analog circuitry
> required to read the gages can be built for $20 to $50 in parts (Burr
> Brown, Linear Tech, Analog Devices etc all have gage amplifiers). You
> could trigger on low weight or imbalance (chair tilted at a serious angle
> with you in it, or you hanging out of chair sideways while inconscious
> or hurt), and high weight (front wheel(s) not touching ground).
>
> hope this helps,
>
> Peter
>
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>

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