Capacity responsive control circuit
DCFirst Claim
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1. A capacity responsive circuit for providing a control output signal in response to a person'"'"'s proximity to a sensing element comprising:
- an oscillator for providing periodic output signals therefrom;
a relatively high impedance element coupled to said oscillator;
an amplifier circuit having an input coupled to the output of said oscillator through said relatively high input impedance and an output terminal, said amplifier including an automatic level control circuit having a selected response time for controlling the switching threshold of said amplifier to a predetermined level;
switch circuit coupled to said amplifier output and responsive to changes in the output signals therefrom for changing state;
a sensing element coupled to the input of said amplifier circuit for coupling a body'"'"'s capacitance t said amplifier input for varying the signal voltage applied to said amplifier from said oscillator and affecting a change in output state of said switch circuit in response to transient body capacitance coupled to said sensing element for a time period generally corresponding to the response time of said automatic level control circuit; and
an initializing circuit coupled between said oscillator and said amplifier circuit for establishing an initial D.C. voltage level for said automatic level control circuit.
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Abstract
A capacitive detecting circuit for detecting transient capacitive changes such as that of a person moving into proximity of a sensing element. A sensing element is coupled to a threshold level controlled amplifier supplied with relatively high frequency signals from an oscillator through a high input impedance. A detector circuit is coupled to the amplifier output to detect D.C. variations in the level control loop caused by transient capacitive changes and provide a control output signal representative of such change.
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17 Claims
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1. A capacity responsive circuit for providing a control output signal in response to a person'"'"'s proximity to a sensing element comprising:
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an oscillator for providing periodic output signals therefrom; a relatively high impedance element coupled to said oscillator; an amplifier circuit having an input coupled to the output of said oscillator through said relatively high input impedance and an output terminal, said amplifier including an automatic level control circuit having a selected response time for controlling the switching threshold of said amplifier to a predetermined level; switch circuit coupled to said amplifier output and responsive to changes in the output signals therefrom for changing state; a sensing element coupled to the input of said amplifier circuit for coupling a body'"'"'s capacitance t said amplifier input for varying the signal voltage applied to said amplifier from said oscillator and affecting a change in output state of said switch circuit in response to transient body capacitance coupled to said sensing element for a time period generally corresponding to the response time of said automatic level control circuit; and an initializing circuit coupled between said oscillator and said amplifier circuit for establishing an initial D.C. voltage level for said automatic level control circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A capacitive sensitive circuit for providing a control output signal in response to a change in capacity at a sensing element comprising:
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an oscillator for providing periodic output signals therefrom; a threshold level controlled amplifier circuit having an input coupled to the output of said oscillator by a relatively high impedance and an output terminal for providing output signals thereat; a detector circuit coupled to said amplifier for establishing a quiescent D.C. voltage level corresponding to a steady state environmental capacity field; and a sensing element coupled to the input of said amplifier circuit for coupling a capacitance to be detected to said amplifier input for momentarily lowering the D.C. voltage level in response to a transient capacitance coupled to said sensing element; a switch circuit coupled to said detector and responsive to changes in the D.C. voltage level therefrom to provide a control output signal representative of a detected change in capacity at said sensing element; and a clamping circuit coupled between said oscillator and said amplifier circuit for initializing a predetermined D.C. voltage level for said level controlled amplifier. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17)
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Specification