Browse Prior Art Database

Noncontacting Keyboard

IP.com Disclosure Number: IPCOM000091188D
Original Publication Date: 1969-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Farber, AS: AUTHOR

Abstract

The noncontacting keyboard operates on the principle of real time reflectometry. A depressed key introduces a reactive discontinuity into a transmission line that passes under the keys of a typewriter. Such reactive discontinuity determines the time of reflection which is encoded to represent the alphanumeric character of the key. A current source 2, drawing A, produces very narrow high-frequency pulses and, because of its high output impedance, the current source produces substantially no loading effect on transmission line 4. The output impedance of source 2 is at least two orders greater than the characteristic of line 4. A typewriter or keyboard 6 has a set of keys 8 anyone of which, when depressed, creates a discontinuity in line 4.

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Noncontacting Keyboard

The noncontacting keyboard operates on the principle of real time reflectometry. A depressed key introduces a reactive discontinuity into a transmission line that passes under the keys of a typewriter. Such reactive discontinuity determines the time of reflection which is encoded to represent the alphanumeric character of the key. A current source 2, drawing A, produces very narrow high-frequency pulses and, because of its high output impedance, the current source produces substantially no loading effect on transmission line 4. The output impedance of source 2 is at least two orders greater than the characteristic of line 4. A typewriter or keyboard 6 has a set of keys 8 anyone of which, when depressed, creates a discontinuity in line 4. Oscilloscope 10, having a high-frequency response, displays the location of the discontinuity, i.e., the key, causing the reflection as determined from the distance between the input pulse as viewed on oscilloscope 10 and its reflection. In drawing B, line 4 is shown interleaved between keys of the keyboard so that the electrical length between keys is increased.

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