Article View: sci.electronics
Article #8073Re: Electronic Stud Finders
From: Paul K Johnson
Date: Wed, 31 Oct 1990 22:31
Date: Wed, 31 Oct 1990 22:31
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In article <533@chiton.ucsd.edu> cdl@chiton (Carl Lowenstein) writes:
>In article <4110@radio.oakhill.UUCP> charlie@oakhill.UUCP (Charlie Thompson) writes:
>>How do those electronic stud finders work? They seem
>>to be able to distinguish fingers from thin air as well.
>>They are apparently electrostatic or capactive from what
>>I can tell.
>
>They are acoustic. Sonar, so to speak.
>
Egads, no smileys!?!??!?!??!???!!!??
They measure the dielectric constant of the volume immediately below the
sensor. This is easily done by measuring the capacitance between two
metal plates. The dielectric constant of air is far different from
wood, and the fact that there is some drywall in the way just offsets
the two measurements and otherwise doesn't interfere.
paul johnson
Internet: paul@sdd.hp.com
UUCP : {hplabs|hpfcla|ucsd}!hp-sdd!paul
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!zaphod.mps.ohio-state.edu!sdd.hp.com!paul From: paul@sdd.hp.com (Paul K Johnson) Newsgroups: sci.electronics Subject: Re: Electronic Stud Finders Message-ID: <1990Oct31.223138.26355@sdd.hp.com> Date: 31 Oct 90 22:31:38 GMT References: <4110@radio.oakhill.UUCP> <533@chiton.ucsd.edu> Organization: Hewlett-Packard, San Diego Division Lines: 21