Patent ID: 6184805
Filing Date: 2001-02-06
Classification: H03M,H04M

Abstract:
An encoding device, for detecting an actuated key of a plurality of keys, the encoding device comprising:a signal generating unit that generates an oscillating signal having a character which corresponds to the actuated key;a signal detecting unit connected to the signal generating unit, said signal detecting unit determines, from the character of the oscillating signal, a final digital value that indicates the actuated key;wherein the signal generating unit comprises a resistance ladder having a plurality of series-connected resistances and having a first connection point upstream of the first resistance in said resistance ladder and having a second connection point downstream of the last resistance in said resistance ladder;wherein the signal generating unit further comprises switches, each switch corresponding to a respective key of said plurality of keys and each switch having a first and a second connection point between which electrical conduction occurs upon actuation of the respective key;wherein the first connection point of each switch is connected to a common point that is common to all said switches and the second connection point of each switch is connected in the resistance ladder such that between two of the resistances in the resistance ladder no more than one of the switches will be connected;wherein the actuated key activates a corresponding switch that creates a first resistance and a second resistance between said common point and said first and second connection point of the resistance ladder, respectively; andwherein the character, of the oscillating signal, has a pulse duration controlled by the first resistance between said common point and said first connection point of the resistance ladder and a pulse space interval controlled by the second resistance between said common point and said second connection point of the resistance ladder, wherein said pulse duration and pulse space correspond to the actuated key.