Dynamic Updating of Key-Sensing Thresholds
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-04
Microprocessor-based keyboard scanners and control mechanisms are known to employ variable threshold level sensing amplifiers to determine when a given key in a key matrix has been depressed. For example, U.S. Patent 4,305,135 shows a typical example. In capacitive keyboard matrices, small dust or debris particles may lodge themselves beneath the capacitive coupling plate on top of the capacitive circuitboard and reduce the amount of capacitive coupling by increasing the space between the coupling plate and the capacitive circuit elements on the circuitboard. Extremely small electrical signals are encountered under the best of circumstances; hence, the occurrence of contamination can sometimes result in inability to sense a truly depressed key.