Patent ID: 8026472
Filing Date: 2011-09-27
Classification: D06F,H03K,H05B

Abstract:
1. A touch-sensitive momentary-contact switch, comprising: a cover being at least partially permeable to electromagnetic radiation; an optical sensor having a transmitter emitting the electromagnetic radiation and a receiver for receiving the electromagnetic radiation and disposed downstream of said cover; and an evaluation circuit for evaluating a measurement signal produced by said receiver and generating an evaluation signal, said evaluation circuit having a device for changing over a measurement range for the evaluation signal, said evaluation circuit taking a detected basic level of the evaluation signal as a basis for assessing that there is a malfunction in said optical sensor if no change in a level of the evaluation signal in said evaluation circuit is detected during a changeover cycle for changing the level of the evaluation signal; said evaluation circuit having a voltage divider circuit formed of a first resistor and a first transistor, said first transistor being controlled by the measurement signal from said receiver, the evaluation signal in said evaluation circuit being tapped off between said first resistor and said first transistor; and said device being a device for altering a voltage divider ratio of said voltage divider circuit.