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Patent

Circuit configuration for a capacitive touch switch

TLDR
A circuit configuration for a capacitive touch switch contains at least one sensor circuit with a sensor element which changes its capacitance value when touched, and an evaluation circuit which is supplied with an output signal from the sensor circuit in order to determine whether the capacitive sensor element is actuated or not.
Abstract
A circuit configuration for a capacitive touch switch contains at least one sensor circuit with a capacitive sensor element which changes its capacitance value when touched, and an evaluation circuit which is supplied with an output signal from the sensor circuit in order to determine whether the capacitive sensor element is actuated or not. The at least one sensor circuit has a capacitance which is connected in parallel with the capacitive sensor element, and a capacitance/frequency converter which is connected to the parallel circuit containing the capacitance and the capacitive sensor element and generates, at its output, a frequency signal whose frequency depends on the total capacitance of the parallel circuit containing the capacitance and the capacitive sensor element. The evaluation circuit may thus use a significant change in the frequency of the output signal from the sensor circuit to deduce, in a simple manner, that the capacitive sensor element has been touched.

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Citations
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References
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Patent

Touch sensing device

TL;DR: In this paper, a new type touch sensing device comprises a touch panel with a plurality of transparent touch electrodes, a LC parallel resonant circuit connected to the touch electrode and an oscillation circuit.
Patent

Detection circuit for matrix touch pad

TL;DR: In this paper, a sense circuit responsive to the signals on the sense lines produces a pulse having a width that is proportional to the amplitude of each of the sense signals, and a control circuit measures the width of the pulses produced by the sense circuit and compares each measured pulse width to a reference pulse width.
Patent

Human body detector

TL;DR: In a human body detector, a wave-detection circuit for detecting waves of a resonance voltage is connected to a sensor resonance circuit that varies a constant frequency voltage in accordance with a change in the capacitance of a sensor electrode as mentioned in this paper.
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Touch responsive power control system

TL;DR: In this article, the magnitude of the change in capacitance caused by the human touch is encoded in the form of the number of pulses contained in a pulse train or a series of pulse trains over a selected time period.
Patent

Circuitry for a sensor element

Bernhard Gotz, +1 more
TL;DR: In this article, the authors present a circuit arrangement with a drive circuit for a sensor element of a touch switch which includes a frequency generator, which is used to generate a frequency modulated drive signal.