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Stud detector using a magnetically actuated switch with magnetic biasing

  • US 4,310,797 A
  • Filed: 06/21/1979
  • Issued: 01/12/1982
  • Est. Priority Date: 09/21/1978
  • Status: Expired due to Term
First Claim
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1. An apparatus for indicating the presence of ferrous fasteners beneath a wall covering, the apparatus comprising:

  • magnetic actuated switch means having a substantially planar wall engaging surface, first and second terminals, and which normally is in a state in which current cannot pass between the first and second terminals and which switches to a state which allows current to pass between the first and second terminals when the wall engaging surface is held near a ferrous substance, the magnetic actuated switch means comprising;

    a compartment having side walls and first and second ends, the first end being located proximate the wall engaging surface;

    a first contact connected to the first terminal, the first contact being positioned within the compartment;

    a second leaf spring contact connected to the second terminal, the second leaf spring contact being positioned within the compartment and having a free end for contacting the first contact;

    a permanent magnet arranged to permit sliding movement within the compartment, the permanent magnet, when positioned proximate the first end causing the free end of the second leaf spring contact to make electrical contact with the first contact, thereby allowing current to pass between the first and second terminals, and when positioned proximate the second end permitting the free end of the second leaf contact to assume a position spaced from the first contact thereby preventing current from passing between the first and second terminals, wherein the first contact and the second leaf spring contact are positioned between the first end and the permanent magnet; and

    ferrous metal bias means on an opposite side of the second end of the compartment from the permanent magnet, wherein magnetic attraction between the magnet and the ferrous metal bias means normally biases the permanent magnet to a position proximate the second end, and wherein magnetic attraction between the permanent magnet and a ferrous substance proximate the wall engaging surface causes the permanent magnet to slide to a position proximate the first end;

    light source means; and

    power source means conductively connected in series with the magnetic actuated switch means and the light source means whereby the light source means is energized when the substantially planar wall engaging surface is held near a ferrous substance.

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