Capacitive Hard-Key Detection to Prevent Accidental Mobile Input
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Solution Overview
Problem
Mobile devices often experience unintended key presses due to accidental actuation while being transported or removed from holsters, leading to frustration and perceived device malfunction.
Innovation Solution
A capacitive sensor system is integrated into the mobile device to distinguish between human touch and object contact by measuring capacitance levels, using a key activation capacitance threshold and secondary confirmation thresholds to determine intended key activations, and intercepting unintended key presses before they activate applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the keyboard is kept unlocked to permit easy access to device features, then ease of operation is improved, but unintended key presses occur during transport or holster insertion/removal
Solution Approach 1:
A capacitive sensor acts as an intermediary between the physical key press and the device's response. The sensor detects whether a key press is accompanied by human body capacitance, serving as a mediator to distinguish intentional from accidental presses during transport or holster insertion/removal
Solution Approach 2:
The patent replaces the purely mechanical key press detection system with an electrostatic sensing system. Instead of relying solely on mechanical switches, the system uses capacitive sensors to detect electrical properties of the object pressing the key, substituting mechanical detection with electrical field-based detection
2Reliability
If a capacitive sensor with high threshold is used to detect human touch, then reliability in detecting intended presses is improved, but object contact may be mistakenly identified as human touch
Solution Approach 1:
The system transitions from a single-dimensional capacitance measurement to a multi-dimensional detection approach by combining capacitance sensing with charge transfer measurement. This additional dimensional information allows for more precise differentiation between human touch and object contact, resolving the threshold discrimination problem
3Reliability
If secondary capacitance sensing is added to confirm key activation, then reliability is improved, but device complexity increases
Solution Approach 1:
The capacitive sensor array serves multiple functions: it detects key press location, measures capacitance values for human touch identification, and provides charge transfer information for confirmation. This multi-functionality reduces the need for separate confirmation sensors, managing complexity while improving reliability
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
Effectively prevents unintended key activations, reducing user frustration and ensuring the mobile device functions correctly by accurately differentiating between intended and unintended key presses.
Implementation Method 1
By measuring a capacitance level at the mobile device keypad, a determination is made to distinguish between a human touch and abutment with an object. A capacitive sensor senses a capacitance level at a location on the keyboard
Data Source
AI summary
A method and device are provided for preventing unintended activation of one or more hard keys on a mobile device. A capacitive sensor senses a capacitance level at a location on the keyboard, to detect whether a hard key is being actuated by a human hand or human skin. If the sensed capacitance level exceeds a key activation capacitance threshold, a key circuit connection is identified as being associated with an intended hard key activation. If the measured capacitance level is within an uncertainty tolerance below the key activation capacitance threshold, a secondary capacitance level is measured at a non-keyboard location. The key circuit connection is identified as being associated with an intended hard key activation when the measured secondary capacitance level exceeds a key activation confirmation threshold. Additional secondary indicators can be obtained based on size and shape capacitance pattern, timing information, and an active application or device state.