Capacitive Keyboard Voltage Correction for Accurate Multi-Key Sensing
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Solution Overview
Problem
Capacitive keyboards struggle to accurately detect the depressed amount of keys, especially when multiple keys are pressed simultaneously, leading to detection failures and reduced accuracy.
Innovation Solution
A capacitive keyboard design featuring intersecting drive and sensing lines with a control circuit that includes a storage unit to store and correct voltages from each key, allowing for precise detection of key depression and amount through voltage analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple keys are depressed simultaneously in a conventional capacitive keyboard, then the keyboard can handle multiple inputs, but the detection accuracy of each key's depressed amount deteriorates due to current diversion through multiple paths
Solution Approach 1:
The sensing process is segmented into multiple sequential phases where only one key column is sensed at a time. The drive circuit selectively activates one drive line at a time, dividing the simultaneous multi-key detection problem into sequential single-column detection tasks, thereby eliminating current path interference between columns
Solution Approach 2:
Before sensing a key column, the corresponding drive line is pre-charged to a predetermined voltage level. This preliminary charging action ensures that when the key is depressed, the capacitance change can be accurately measured without interference from other columns, as the voltage state is already established
2Device complexity
If conventional voltage detection is used without correction, then the detection process is simple, but the detected voltage does not accurately represent the depressed amount when multiple keys are pressed
Solution Approach 1:
The system incorporates feedback by storing the detected voltage in a storage circuit and using it for correction purposes. The correction circuit references the stored voltage to compensate for the voltage drop caused by simultaneous key depressions, feeding back this corrected information to improve measurement accuracy
Solution Approach 2:
The patent replaces direct electrical voltage measurement with a corrected voltage detection mechanism. Instead of relying on raw voltage readings that are affected by multiple current paths, the system uses a correction circuit that substitutes the inaccurate mechanical/electrical measurement with a computationally corrected value
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate detection of key depression and amount, even when multiple keys are pressed, improving input operation accuracy and enabling various input operations with fine movement recognition.
Implementation Method 1
capacitance between the electrodes being changed in accordance with a depressed amount of the operation component
Data Source
AI summary
A capacitive keyboard that can detect a key that has been depressed and the depressed amount thereof with high accuracy is provided. The capacitive keyboard includes a drive circuit 11 that alternatively switches the voltage of each of drive lines M from an L-level to an H-level, a sensing circuit 12 that is connected to each of sensing lines N and that selects one of the sensing lines N to detect the voltage generated in the selected sensing line, and a control circuit 15. The control circuit 15 includes a storage unit 44 including storage areas corresponding to keys, a storage control unit 42 that acquires the voltage generated in the sensing line and that stores the acquired voltage in a storage area corresponding to a key, and a correction unit 43 that corrects, if one of the keys is operated, the voltage generated as a result of an operation of the one of the keys by using voltages stored in storage areas corresponding to other keys. Thus, even if a plurality of keys are depressed at the same time, detection with high accuracy can be realized.