Keyboard entry system

Details Keyboard entry system Keyboard entry system

1981-03-24

1983-08-09

Groody, James J.

Communications: electrical

Audible indication

Percussion-type sound producer

340365C, G06F 302

Patent

active

043981810

ABSTRACT:
A key matrix circuit comprises a plurality of column lines and a plurality of row lines, a plurality of capacitance switches which are respectively arranged at different intersections of the column lines and row lines, and a select switch having a condenser, a movable contact connected to a selected one of the column lines and a plurality of change-over fixed contacts, respectively, connected to different row lines other than the row lines to which the selected column line is connected through the capacitance switches. Each of the fixed contacts is selectively connected to the movable contact and the selected column line is connected to one of the different row lines through the condenser which has an equivalent capacitance to the capacitance switches when operated. A decoder and a multiplexer are respectively connected to the row lines and the column lines of the key matrix circuit. A control circuit scans cyclically the respective conditions of the capacitance switches and the select switch through the decoder and multiplexer. As a result, a simpler circuit and method of operation are obtained.

REFERENCES:
patent: 3921166 (1975-11-01), Volpe

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