charlie@oakhill.UUCP (Charlie Thompson) (10/30/90)
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. Anybody out there ever reverse engineered one? -Charlie
cdl@chiton.ucsd.edu (Carl Lowenstein) (10/31/90)
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. beep beep beep beep -- carl lowenstein marine physical lab u.c. san diego {decvax|ucbvax} !ucsd!mpl!cdl cdl@mpl.ucsd.edu clowenstein@ucsd.edu
murray@sun13.scri.fsu.edu (John Murray) (10/31/90)
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. Silly games to play with your co-workers: Grab a stud-finder, wave it around in the air for a while, then scan across his(*) chest. It'll pick up the sternum just fine. "Whoops! found a stud!" (I said it was silly, didn't I?) (*) I wanted to say "his/her chest" here, but after thinking about it, I realized scanning a female chest with a stud finder might get you slapped.:-/ >-- > carl lowenstein marine physical lab u.c. san diego > {decvax|ucbvax} !ucsd!mpl!cdl cdl@mpl.ucsd.edu > clowenstein@ucsd.edu Disclaimer: Any opinions above have little or nothing to do with reality. John R. Murray | "They call me Mr. Know-it-all, I am so eloquent. murray@vsjrm.scri.fsu.edu | Perfection is my middle name! Supercomputer Research Inst. | ..and whatever rhymes with 'eloquent'." - Primus
phys169@canterbury.ac.nz (10/31/90)
In article <4110@radio.oakhill.UUCP>, charlie@oakhill.UUCP (Charlie Thompson) writes: > How do those electronic stud finders work? They're small metal detectors. There are many ways of making a metal detector, but the best for this job is probably an air-core coil as part of a tuned circuit, where there are 2 tuned circuits, one sensitive to nearby metal (and fingers) in the base circuit, one screened off in the collector circuit. When both are tuned to about the same frequency (because the inductance of one changes when the nail is nearby), the transistor oscillates. This is too over-simplified perhaps, but you probably get the idea. Sensitive ones could use crystals. Mark Aitchison, Physics, University of Canterbury, New Zealand.
DBG@SLACVM.SLAC.STANFORD.EDU (11/01/90)
Several principles are used in various studfinders. The one I find most
effective is based on capacitance, determining the effective dielectric
constant of the wall. With wallboard made of gypsum and cardboard, this
locates the boundaries of wood studs and even shows where double or triple
ones have their edges, quite accurately. This type typically has a flat
body which is slid along the wall, an activating button on the side which
zero's the detector somewhere you hope has no stud, and several LEDs on
the face which form a bargraph. They sell in the US$10-20 range. They
don't work where the wall is filled with foil-backed insulation, as the
foil blocks the electric field effectively.
-- David B. Gustavson, Computation Research Group, SLAC, POB 4349 MS 88,
Stanford, CA 94309 tel (415)926-2863 fax (415)961-3530
-- What the world needs next is a Scalable Coherent Interface!
-- Any opinions expressed are mine and not necessarily those
of SLAC, Stanford University or the Department of Energy.paul@sdd.hp.com (Paul K Johnson) (11/01/90)
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
bill@videovax.tv.tek.com (William K. McFadden) (11/02/90)
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