Keyboard Scanning Circuit Ghost Key Elimination
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Solution Overview
Problem
Existing keyboard scanning circuits suffer from ghost keys due to the crisscrossing of scanning and sensing lines, leading to inaccurate key registration and signal precision issues.
Innovation Solution
A keyboard scanning circuit design featuring a microprocessor, M scanning lines, and N sensing lines with switching elements at intersections, where each sensing line has a common node extended to M transmission lines, allowing the microprocessor to output different scanning signals and determine the state of switching elements to prevent ghost keys by using a scanning confirmation line and a sensing confirmation line.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a crisscrossed scanning matrix is used in the keyboard scanning circuit, then the keyboard can detect key presses through scanning lines and sensing lines, but ghost keys are inevitable due to signal interference at intersection points
Solution Approach 1:
The patent segments the scanning matrix into isolated scanning regions by introducing transmission lines that connect sensing lines to multiple scanning lines. Each switching element is assigned to a specific scanning region, allowing independent scanning and confirmation operations that prevent signal interference between adjacent keys, thereby eliminating ghost keys while maintaining reliable key detection
Solution Approach 2:
The patent implements a two-stage scanning process: a preliminary scanning phase that identifies potential key presses, followed by a confirmation phase that verifies the key state by reversing scanning directions. This preliminary action followed by verification ensures that ghost keys are detected and eliminated before final key registration, improving detection reliability
2Reliability
If diodes are added to each key to prevent ghost keys, then ghost key prevention is achieved, but the hardware complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts the ghost key prevention function from the key level and implements it at the scanning circuit level through transmission lines and direction-controlled switching elements. This eliminates the need for adding diodes to each key, maintaining simple key construction while achieving ghost key prevention through the scanning mechanism itself
Solution Approach 2:
The transmission lines serve multiple functions: they connect sensing lines to multiple scanning lines, enable isolation of scanning regions, facilitate bidirectional scanning for confirmation, and allow single-key scanning even when multiple keys are physically pressed. This multi-functionality achieves ghost key prevention without requiring additional components at each key location
3Productivity
If the I/O capability of the microprocessor is enhanced to augment the scanning matrix, then the scanning capability is improved, but the cost and complexity of the microprocessor increase
Solution Approach 1:
The patent introduces transmission lines as intermediary elements between sensing lines and scanning lines. These transmission lines act as mediators that enable a single microprocessor I/O pin to control multiple scanning regions sequentially, augmenting the effective scanning capability without requiring enhanced microprocessor I/O capabilities
Solution Approach 2:
The patent implements periodic scanning cycles where the microprocessor alternates between scanning different regions and confirming key states by reversing directions. This periodic action allows the microprocessor to systematically scan the entire matrix using standard I/O capabilities, improving scanning productivity without requiring faster or more numerous I/O pins
Data Source
AI summary
A keyboard scanning circuit includes a plurality of switching elements, M scanning lines and N sensing lines. Each of the sensing lines has a common node extended to M transmission lines. A switching element is coupled where one of the transmission lines and one of the scanning lines intersects. Two scanning lines correspondingly coupled through two switching elements to two transmission lines extended from one sensing line are different from each other.