Single wire keyboard encode and decode circuit

Details Single wire keyboard encode and decode circuit Single wire keyboard encode and decode circuit

1995-12-28

1997-04-08

Hofsass, Jeffery

Coded data generation or conversion

Bodily actuated code generator

Including keyboard or keypad

341 26, 341 33, 34087038, H03K 1794

Patent

active

056191960

ABSTRACT:
A circuit for encoding and decoding key input data from a matrix of switches with a single transmission wire. The circuit for encoding and decoding key input data with a single transmission wire includes a control circuit, a charge storage circuit and a keyboard matrix circuit. The keyboard matrix circuit is composed of a group of resistors connected in series. Each resistor is coupled to ground via a manually actuated switch. When one of the switches is actuated or closed the switch provides an electrical path to ground through the resistors that precede the switch and shorts the resistors that follow the switch. When one of the switches is closed the charge stored on the charge storage circuit dissipates through the electrical path to ground provided by the actuated switch, at a rate related to the sum of the resistance preceding the switch. The control circuit, by monitoring the time for a charge stored on the charge storage circuit to dissipate through an actuated switch coupled to ground, determines which switch was actuated.

REFERENCES:
patent: 4015254 (1977-03-01), Strandt
patent: 4817010 (1989-03-01), Dobbins
patent: 4987372 (1991-01-01), Ofori-Tenkorang et al.

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