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Dynamically Adjustable Capacitive Key Sensing Method

IP.com Disclosure Number: IPCOM000044917D
Original Publication Date: 1983-Jan-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Irwin, JG: AUTHOR

Abstract

This article describes a technique of adjusting the sense amplifier threshold for capacitive key matrix scanning and sensing technique. Capacitive key matrices with microprocessor driven or implemented scanners are known. In addition, such keyboards are known in conjunction with a variable threshold level sensing amplifier that can have the sensing level adjusted in response to an initial threshold value stored in memory in association with the address of a given key whose state of conductance is to be sensed. The present technique maintains a sense amplifier threshold for each key in addressable alterable memory of the microprocessor in a threshold table.

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Dynamically Adjustable Capacitive Key Sensing Method

This article describes a technique of adjusting the sense amplifier threshold for capacitive key matrix scanning and sensing technique. Capacitive key matrices with microprocessor driven or implemented scanners are known. In addition, such keyboards are known in conjunction with a variable threshold level sensing amplifier that can have the sensing level adjusted in response to an initial threshold value stored in memory in association with the address of a given key whose state of conductance is to be sensed. The present technique maintains a sense amplifier threshold for each key in addressable alterable memory of the microprocessor in a threshold table. The threshold table is updated for one key once each scan cycle and a recalibration pointer is maintained to point to one key at a time each scan cycle so that after N scan cycles, where N is the number of keys on a keyboard, each key will have had its threshold measured, adjusted if necessary, and stored in memory for use during scanning.

Initially, the threshold value in the table for each key is set to the highest level that the sense amplifier can achieve. This may result in some keys not being sensed as depressed until they are fully depressed, but will avoid erroneous sensing. During the calibration phase of the microprocessor driven scanning cycle, when a given key is addressed for calibration, the microprocessor will repetitively drive a key location...