Electronic data input keyboard comprising keys provided with con

Details Electronic data input keyboard comprising keys provided with con Electronic data input keyboard comprising keys provided with con

1985-04-08

1987-11-24

Caldwell, Sr., John W.

Communications: electrical

Audible indication

Percussion-type sound producer

340365E, G06F 302

Patent

active

047092289

ABSTRACT:
In matrix keyboards whose keys are provided with conductive contacts and are arranged at respective crosspoints of conductors, a diode is connected in series with each key contact in order to allow for n-key rollover, i.e. the simultaneous actuation of several keys in an arbitrary configuration. For many technical realizations of the key contacts, for example in the form of electrically conductive materials provided on plastics foils by silkscreening, the series connection of a diode with each contact element is not simply possible. In accordance with the invention it is proposed to connect an ohmic resistor, which can also be provided by means of a silkscreening process, in series with each key contact and to connect the interrogated matrix conductors to a point of low impedance. Thus, current control is used to a high degree in order to ensure that no signal voltage which is capable of exerting an effect via other actuated keys can appear on the interrogated conductor. The point of low impedance is effectively formed by the inverting input of an operational amplifier which is fed back by means of a resistor.

REFERENCES:
patent: 3676697 (1972-07-01), Davenport
patent: 4374384 (1983-02-01), Moates
patent: 4502039 (1985-02-01), Vercesi et al.
patent: 4614937 (1986-09-01), Poujois
Joseph E. Jesson, "Smart Keyboards Help Eliminate Entry Errors" Computer Design/Oct. 1982, pp. 137, 138, 140 and 142.
"Varicap Compensation of Output Amplifiers", IBM Tech. Discl. Bulletin, vol. 27, No. 11, Apr. 1985.

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