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Touch pad and display tube circuitry

  • US 4,291,303 A
  • Filed: 08/23/1979
  • Issued: 09/22/1981
  • Est. Priority Date: 08/23/1979
  • Status: Expired due to Term
First Claim
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1. A touch pad circuit comprising:

  • first and second touch pads each having an input and an output, and having a common face plate which permits contaminants located on said face plate to form ohmic and/or dielectric couplings between said touch pads;

    scan pulse generator means for applying touch pad scan pulses to said inputs of said touch pads to cause first and second touch response signals to appear at the outputs of said first and second touch pads, respectively;

    said touch pad scan pulses having a sufficiently fast rise-time that said first and second touch response signals initially pulse to an initial level determined by the capacitance to ground of said first and second touch pads, respectively, and thereafter change their value due to ohmic and/or capacitive coupling between said first and second touch pads caused by contaminants on said common face plate if contaminants of a sufficient amount are located on said face plate; and

    detector circuit means coupled to said touch pads for determining which, if any, of said touch pads is being touched by an operator of said touch pad circuit by examining said initial level of said touch pad response signals.

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