Capacitive sensing, solid state touch button system

• US 5,036,321 A
• Filed: 08/31/1989
• Issued: 07/30/1991
• Est. Priority Date: 08/31/1989
• Status: Expired due to Fees

• Current Assignee: Otis Elevator Company (Otis Worldwide Corp.)
• Original Assignee: Otis Elevator Company (Otis Worldwide Corp.)
• Inventors: Youla, Jean, Leach, Robert B., Slabinski, Chester J.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Lau, Yuk H.
• Application Number:
  US07/401,363
• Time in Patent Office: 698 Days
• Field of Search: 341/33, 341/22, 341/24, 341/26, 340/711, 324/684
• US Class Current: 341/33
• CPC Class Codes: H03K 11/00 Transforming types of modulations, e.g. position-modulated pulses into duration-modulated pulses
• CPC Class Codes: H03K 17/14 Modifications for compensating variations of physical values, e.g. of temperature
• CPC Class Codes: H03K 17/962 Capacitive touch switches

Abstract

A solid state touch or control button assembly (10), with no moving button parts and operated by capacitive sensing by monitoring the phase shift of a signal applied to the face of the button, including in a first embodiment (FIGS. 2A & 2B) a auto balancing button and in a second embodiment (FIGS. 3A & 3B) a constant pressure button. If skin or other material comes into contact with the touch surface, the capacitance is changed and sensed, causing the electrical or electronic function controlled by the touch button to be activated (or deactivated, depending on the design, or otherwise altered). LEDs then are activated, providing visual feedback to the button pusher through a light ring (2A) surrounding the button surface (1). False activation of the button by residual impedance and external influences, such as temperature change, cleaner residue build-up and other deposits, are avoided by compensating for them by slowly auto balancing to all such phase shifts, with the rate of auto balance being set to be faster than the rate of change of the steady state phase shift; and, additionally, false activations by noise transients, including those due to EMI, FRI and other environmental fluctuations, are avoided by delaying the activation of the button by an appropriate amount of time, such as, for example, of the order of about one hundred (100 msec.) milliseconds.

Claims

1. A capacitive sensing touch button for controlling a function, said button comprising:

a button surface for receiving a reference signal, said button surface outputting a signal shifted in phase, relative to the reference signal, upon contact of said button surface by a user;

an oscillator, operatively connected to said button surface, to provide the reference signal to said button surface, said oscillator having a predetermined duty cycle;

phase shift to pulse width converter, operatively connected to said button surface and said oscillator, to convert the phase-shifted signal into a pulse width based on the amount of the phase shift relative to the reference signal;

auto-balancing compensation, operatively connected to said phase shift to pulse width converter, including at least two integrators, each having a different time constant, each of said integrators receiving the pulse widths and converting the pulse width into a dc voltage, said auto-balancing compensation outputting either a SET signal or a RESET signal based on the relative dc voltage values produced by said integrators, thereby avoiding false activation of the controlled function due to residual impedence and/or external influences at said button surface; and

delay-on circuitry, operatively connected to said auto-balancing compensation, to receive the signal output therefrom, said delay-on circuitry generating a control signal to control the controlled function provided that said SET signal is present at least a predetermined time period, thereby avoiding false activation of the controlled function due to transient noise.

2. The capacitive sensing touch button of claim 1, wherein:

said auto-balancing compensation includes three integrators, a first integrator having a relatively slow time constant, a third integrator having a relatively fast time constant, and a second integrator having a time constant between the first and second time constants, each of said integrators receiving the pulse width and converting the pulse width into a dc voltage;

said auto-balancing compensation outputting the SET signal when the voltage output from said second integrator is greater than the voltage output from said first integrator; and

said auto-balancing compensation outputting the RESET signal when the voltage output from said third integrator is less than the voltage output from said second integrator.

3. The capacitive sensing touch button of claim 1, said touch button further including electrostatic discharge protection circuitry operatively connected between said button surface and said phase shift to pulse width converter, said protection circuitry comprising:

a spark gap connected between said button surface and a first grounding path;

a resistor having a first terminal connected to said button surface and a second terminal connected to said phase shift to pulse width converter; and

a Zener diode connected between said second terminal of said resistor and a second grounding path, wherein said first and said second grounding paths are separate.

4. A capacitive sensing touch button for controlling a function, said button comprising:

a button surface for receiving a reference signal, said button surface outputting a signal shifted in phase, relative to the reference signal, upon contact of said button surface by a user;

an oscillator to provide the reference signal to said button surface, said oscillator having a predetermined duty cycle;

phase shift to pulse width converter to convert the phase-shifted signal into a pulse width based on the amount of the phase shift relative to the reference signal;

an integrator to convert the pulse width into a dc voltage;

a level detector to output a control signal when the dc voltage is greater than a predetermined threshold voltage; and

a delay/dwell timer to receive said control signal and to control the controlled function provided that said control signal is present at least a predetermined time period, thereby avoiding false activation of the controlled function due to transient noise.

5. The capacitive sensing touch button of claim 4, said touch button further including electrostatic discharge protection circuitry operatively connected between said button surface and said phase shift to pulse width converter, said protection circuitry comprising:

a spark gap connected between said button surface and a first grounding path;

a resistor having a first terminal connected to said button surface and a second terminal connected to said phase shift to pulse width converter; and

a Zener diode connected between said second terminal of said resistor and a second grounding path, wherein said first and said second grounding paths are separate.

6. The capacitive sensing touch button of claim 4, wherein said phase shift to pulse width converter comprises a diode.

7. The capacitive sensing touch button of claim 4 wherein said delay/dwell timer comprises:

a transistor having an emitter operatively connected to said control signal;

a first resistor and first diode in series connection between said emitter and the collector of said transistor, wherein said first diode'"'"'s cathode is connected to said collector;

a second diode having an anode and a cathode operatively connected between said emitter and the base, respectively, of said transistor; and

a comparator having a first input operatively connected to said anode of said first diode, said first input further operatively connected ground via a first capacitor, and a second input operatively connected to an RC network having a predetermined time constant, wherein the output of said comparator controls the controlled function, provided that said control signal is present at least a predetermined time period, wherein said predetermined time period is based on said time constant.