Touch-sensitive momentary contact switch with an evaluation circuit detecting a malfunction in an optical sensor

#The present invention relates to a touch-sensitive momentary-contact switch and particularly to such a momentary-contact switch for use in a control device for a household appliance.

#The basic design and the basic principle of such a touch-sensitive momentary-contact switch are known from published, non-prosecuted German patent application DE 40 07 971 A1, for example. The touch-sensitive momentary-contact switch has a transmitter emitting electromagnetic radiation and a receiver receiving electromagnetic radiation, which are disposed downstream of a cover which is at least partially permeable to the electromagnetic radiation. In addition, an evaluation circuit for evaluating a measurement signal produced by the receiver and producing an evaluation signal for further processing is generally provided. One advantageous application of such touch-sensitive momentary-contact switches is their use in control devices for household appliances, for example, such as cookers, glass ceramic hobs, microwave ovens and the like, in which the momentary-contact switch is accommodated behind a cover, such as a glass plate or glass ceramic plate, for simple operation and cleaning.

#One problem of conventional momentary-contact switches of this type is that it is not possible to identify whether the optical sensor, i.e. particularly the transmitter and/or the receiver, in the momentary-contact switch is faulty. This is also a safety risk, for example if the momentary-contact switch becomes faulty only after being successfully switched on and therefore cannot be switched off again. There is therefore a need for a touch-sensitive momentary-contact switch of the type mentioned in the introduction in which it is possible to identify a malfunction in the optical sensor, so that an appropriate reaction to an identified malfunction of this type is finally possible if appropriate.

#FIG. 1 is a diagrammatic, sectional view of a touch-sensitive momentary-contact switch in line with a preferred exemplary embodiment according to the invention;

#FIG. 2 is a simplified circuit diagram of a conventional evaluation circuit;

#FIG. 3 is a simplified circuit diagram of an evaluation circuit for the touch-sensitive momentary-contact switch based on a preferred exemplary embodiment of the present invention;

#Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a mechanical configuration of a touch-sensitive momentary-contact switch 10 according to the invention. The touch-sensitive momentary-contact switch from the invention is an infrared momentary-contact switch for a household appliance, for example, such as a cooker, a microwave oven, a hob, a washing machine, a washer-dryer, a dishwasher or the like, without the invention being limited to electromagnetic radiation in this wavelength range or to these specific applications.

#The touch-sensitive momentary-contact switch 10 has an infrared transmitter 14 and an infrared receiver 16 on a printed circuit board 12. The transmitter 14 and the receiver 16 are surrounded by a masking frame 18 which has two openings 20 and 22 on its top 19. The masking frame 18, formed from an infrared-impermeable material, has feet 24 inserted through holes in the printed circuit board 12 and is mounted on the latter in this way.

#The transmitter 14 and the receiver 16 are positioned in the masking frame 18 such that they are disposed within respective cavities 26 and 28 below the masking openings 20 and 22. In this case, the two cavities 26 and 28 are separated from one another by an infrared-impermeable partition 30. Lying directly on the top 19 of the masking frame 18 is a cover 32 made of a material which is at least partially permeable to infrared, for example a glass ceramic plate on a household cooker.