Title: Circuit arrangement for a keyboard

Abstract: A circuit arrangement for a keyboard is disclosed, in which the switches of the keyboard are each connected in series with a respective LED to form a switch matrix, the rows of which are connected to a multiplexer and the colums of which are connected to an evaluation device. The LED's serve as decoupling diodes, and furthermore form a diode matrix of an optical indication field by which the commands entered into the keyboard through activation of its switches, or other information, can be made optically visible. Upon activation of a transistor switch, a resistor is switched parallel to a measurement resistor, whereby an LED is lighted at the point of intersection of the activated matrix row and matrix column.

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Inventors: Halder, Mathis (Baar, CH)

Application Number: 015605
Filing Date: 1979-02-23
Publication_date: 1980-11-18
Assignee: LGZ Landis & Gyr Zug AG (Zug, CH)
Primary Class(es): 341/26 340/14.66
Other Classes:
US Patent Ref:

3732389	May, 1973	Kaelin et al.	340/365.
3811025	May, 1974	Bach	340/365.
3990070	Nov, 1976	Spence	340/365.
4065754	Dec, 1977	Miura et al.	340/166.
4077036	Feb, 1978	Avakian et al.	340/365.
4092640	May, 1978	Satoh	340/365.

Other Refs: Other References: "Scanned Optical Keyboard", J. E. Fox, IBM Tech. Dis. Bull'n., vol. 20, No. 9, Feb. 1978, pp. 3615-3616.