Browse Prior Art Database

Pulsed Key Encoder Network

IP.com Disclosure Number: IPCOM000076086D
Original Publication Date: 1972-Jan-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Counihan, RG: AUTHOR

Abstract

This is pulsed key encoder network generates a single short pulse per key depression and provides it in coded form to the decode/encode logic of an electronic keyboard. This function is accomplished with a minimum of circuitry and input connections to the decode/encode logic block.

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Pulsed Key Encoder Network

This is pulsed key encoder network generates a single short pulse per key depression and provides it in coded form to the decode/encode logic of an electronic keyboard. This function is accomplished with a minimum of circuitry and input connections to the decode/encode logic block.

Depressing any one key such as K1, generates a pulse through capacitor C which is decoded by diodes D1 and D5. This signal is applied to the decode/encode logic, which may typically be a read-only storage ROS 10. ROS 10 may be a writable logic having a control input. The current generated by closing K1 is limited by current limiting resistor R1. The short discharge time constant (approximately C x R3/2), delivers a microsecond type pulse to ROS 10. This makes it essentially impossible for two key strokes to produce overlapping pulses. The long charging time constant C x R2 insures against key switch bounce effects, while not limiting the fastest typist. Two or more diodes per key provide economical encoding to ROS 10 thus avoiding pin limitations. For example, a two out of thirteen code will allow ninety-one distinct key combinations, and use thirteen inputs to ROS 10 instead of ninety-one. The diodes D2, D3, D4 and D6 as well as R4, are shown as additional circuitry utilized by several of the other keys. The disclosed circuit is readily implemented as an integrated circuit.

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