Newsgroups: comp.robotics
Path: brunix!sgiblab!swrinde!cs.utexas.edu!uunet!hobbes!earth.armory.com!rstevew
From: rstevew@armory.com (Richard Steven Walz)
Subject: Re: Preassure sensor (build my own) ???
Organization: The Armory
Date: Sun, 17 Apr 1994 13:32:30 GMT
Message-ID: <CoEoA7.DKt@armory.com>
References: <2oraq8$i6s@zippo.uwasa.fi>
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In article <2oraq8$i6s@zippo.uwasa.fi>,
Anders Nyg}rd <anygard@freeport.uwasa.fi> wrote:
>
>I have heard that one could build ones own preassure sensor
>using a semi-conducting bag. Is this true and if so how do I do?
>
>Thanx in advance...
>
>--&ers (Anders) 
>Stud. Anders Nyg}rd * anygard@freeport.uwasa.fi
-------------------------------
I have not seen this work. All anti-stat bags have to be is a high
resistance, and the ones I've seen are based on carbon impregnated foam
or one could resort to carbon granules in a shallow cup with a diaphragm.
(In other words, a DC use for the carbon microphone!). Another way is to
use the same chips and materials as many IBM and other keyboards use, that
is, to put mylar covered aluminum foil on a plunger with foam backing and
have it press against to semi-circular areas of copper under it. These use
the CD4044 chip pulled up 10K resistors to a selected resistor divider with
the bottom of the branch parallel with a .1uF capacitor, and then through
the switch to 74LS138 with 150 ohm pull ups. The threshold can be set that
way, or you can use the switch as a capacitor in a timing circuit. In this
way you can get either an analog or digital input.
-Steve Walz   rstevew@armory.com

