Communications: electrical – Audible indication – Percussion-type sound producer
Patent
1985-06-27
1987-11-03
Caldwell, Sr., John W.
Communications: electrical
Audible indication
Percussion-type sound producer
340365R, 340365S, H04L 300
Patent
active
047046015
ABSTRACT:
A keyboard having a plurality of selectively operable matrix element key switches, each having an actuated and an unactuated state. The state of each switch is sequentially determined by applying one of two input signals to the input of each switch. The output of the switch is integrated and compared to a predetermined value to determine whether the switch is to be recognized as actuated or not actuated. If during a particular sequence the integrated output exceeds the predetermined value (so that the switch is recognized as actuated), the second input signal is applied to the switch during the next sequence. Because the second input signal has different parameters from the first input signal, whether by a greater number of pulses or greater amplitude pulses, then if the key switch is still depressed, the integrated signal produced by the second input signal exceeds the predetermined value by a greater amount than during the prior sequence. This has the effect of eliminating false multiple key recognition caused by noise signals. In addition, it provides separate travelpoints of the key switch for recognition of actuation and release.
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Rowe, Jr.-"Dynamic Updating of Key-Sensing Thresholds"-IBM Technical Disclosure Bulletin-vol. 29, No. 4A, Sep./84-pp. 2012-2018.
Buckman T. W.
Caldwell Sr. John W.
Fatahi-Yar Mahmoud
Illinois Tool Works Inc.
Mondul D. D.
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