Capacitive sensor systems and methods with increased resolution and automatic calibration

  • US 6,940,291 B1
  • Filed: 07/22/2003
  • Issued: 09/06/2005
  • Est. Priority Date: 01/02/2001
  • Status: Active Grant
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First Claim
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1. A capacitive sensing system comprising:

  • a microcontroller, operable to receive electrical power from an electrical power source, and having at least one digital logic input/output (I/O) pin capable of functioning in both an INPUT mode and an OUTPUT mode;

    a conductive sense element in electrical communication with the I/O pin, and a resistance element in electrical communication with the conductive sense element to form an electrical pathway from the conductive sense element to an electrical discharge point;

    wherein the microcontroller is further operable to;

    at a first time, charge the sense element by causing a selected voltage to be placed on the I/O pin by setting the I/O pin to the OUTPUT mode in the high state;

    at a second time, cease placing the selected voltage on the I/O pin;

    thereafter, act the I/O pint to the INPUT mode, which causes the conductive sense element to discharge through the resistance element, and measure voltage at the I/O pin, the voltage at the I/O pin being representative of voltage at the sense element; and

    measure a parametric value required for voltage at the conductive sense element to decline to a value below a threshold value, the parametric value being representative of an effective capacitance formed by at least the conductive sense element and a first object that may be in contact or proximity with the conductive sense element whereby the parametric value is representative of contact or proximity between the sense element and the first object and further wherein;

    the microcontroller is operable to perform digital signal processing on signals derived from the conductive sense element;

    the signal processing includes pattern recognition wherein the microcontroller is operative to implement one or more of a plurality of software applications to perform digital signal processing on signals derived from the conductive sense element to detect one or more selected patterns of contact or proximity between the first object and the conductive sense element; and

    the signal processing comprises the synthesis of at least one virtual sensor capable of detecting one or more of the selected patterns of contact or proximity between the first object and the conductive sense element.

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