Capacitive sensor circuit

Details Capacitive sensor circuit Capacitive sensor circuit

1994-06-30

1996-03-12

Shoop, Jr., William M.

Electrical transmission or interconnection systems

Switching systems

Condition responsive

361181, H01H 3600

Patent

active

054989140

ABSTRACT:
A capacitive sensor circuit is provided which comprises: a sensor electrode (16) forming a first plate of a sensing capacitor (14) relative to a reference terminal (10), a first (2) and a second (26) inverting Schmitt trigger having the same threshold voltages. A feedback resistor (8) provides feedback from the output (6) to the input (4) of the first trigger (2), which together with the sensing capacitor (14) forms an oscillator whose frequency depends on the magnitude of the sensing capacitor (14). The input (24) of the second trigger (26) is connected to the output of the first trigger (2) via a series resistor (22) and to the reference terminal (10) via a reference capacitor (30). The resistance values of the feedback resistor (8) and the series resistor (22) are equal. A d.c. signal will appear on the output (32) of the second trigger if the capacitance of the sensing capacitor (14) is smaller than the capacitance of the reference capacitor (30) and an a.c. signal in the opposite case.

REFERENCES:
patent: 4850386 (1989-07-01), Bireley
patent: 5238369 (1993-08-01), Farr
patent: 5367198 (1994-11-01), Buergel et al.

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