Proximity detection system and oscillator, and method of using same

  • US 5,463,378 A
  • Filed: 12/14/1993
  • Issued: 10/31/1995
  • Est. Priority Date: 01/02/1990
  • Status: Expired due to Term
First Claim
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1. A method of controlling an electrical load, comprising the steps of:

  • (a) providing a conductive medium;

    (b) disposing a sensing means in proximity with said conductive medium, said sensing means possessing a capacitance which varies from a very low capacitance value when said sensing means is in a first proximity to said conductive medium and changing to a substantially higher capacitance value when in a second proximity to said conductive medium;

    (c) providing a dual mode oscillator having an input connected to said sensing means, said dual mode oscillator having an output for providing a control signal to said electrical load and functioning, in a first mode as a phase shift oscillator to generate said control signal at a first duty cycle, and in a second mode as an RC oscillator to generate said control signal at a second duty cycle;

    (d) generating a control signal, at the output of said dual mode oscillator, having a first duty cycle determined by a first capacitance value of said sensing means, to thereby control said electrical load according to the first duty cycle of said control signal;

    (e) varying the capacitance of said sensing means from said first capacitance value to a second capacitance value; and

    (f) changing the duty cycle of said control signal from said first duty cycle to said second duty cycle in response to a change in the capacitance of said sensing means from said first capacitance value to said second capacitance value, to thereby control said electrical load according to said second duty cycle of said control signal.

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