Keyboard encoding system with electronic hysteresis

Details Keyboard encoding system with electronic hysteresis Keyboard encoding system with electronic hysteresis

1975-11-25

1977-07-19

Habecker, Thomas B.

Communications: electrical

Audible indication

Percussion-type sound producer

340365C, G08C 100

Patent

active

040372251

ABSTRACT:
A keyboard encoding system which utilizes electronic hysteresis to prevent undesired key stroke encoding. The output of a capacitive switch matrix is supplied to a sense amplifier which has its sensitivity increased if a particular switch of the switch matrix was closed the last scan cycle. The status of the switches of the switch matrix during the last scan cycle is provided by a shift register having a number of stages equal to the number of switches of the matrix. The sense amplifier includes a comparator which receives an input indicative of the state of a particular matrix switch during the present scan cycle and an input from the shift register indicative of the status of the particular matrix switch the previous scan cycle. If the input from the shift register is high, the sensitivity of the sense amplifier is increased.

REFERENCES:
patent: 3716850 (1973-02-01), Fisher
patent: 3786497 (1974-01-01), Davis
patent: 3918051 (1975-11-01), Bernin

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