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From: bill@videovax.tv.tek.com (William K. McFadden)
Newsgroups: sci.electronics
Subject: Re: Electronic Stud Finders
Message-ID: <6119@videovax.tv.tek.com>
Date: 1 Nov 90 23:16:39 GMT
References: <4110@radio.oakhill.UUCP>
Reply-To: bill@videovax.tv.tek.com (William K. McFadden)
Organization: Tektronix TV Measurement Systems, Beaverton OR
Lines: 18

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.

I bought one on sale at Radio Shack recently.  The booklet that came with it
said it detects the density of objects by their capacitance.  Since different
materials have different dielectric constants, the studfinder can detect the
change in capacitance as it passes over a 2 X 4.  If the wall is made of a
similar material, e.g., plywood, the studs are more difficult, but not
impossible, to detect.

I put a scope probe near it and discovered it oscillates at 18 KHz.  I suspect
there's a big plate in it that's connected to the oscillator tank.
-- 
Bill McFadden    Tektronix, Inc.  P.O. Box 500  MS 58-639  Beaverton, OR  97077
bill@videovax.tv.tek.com,     {hplabs,uw-beaver,decvax}!tektronix!videovax!bill
Phone: (503) 627-6920       "The biggest difference between developing a missle
component and a toy is the 'cost constraint.'" -- John Anderson, Engineer, TI