Capacitive Button Moisture Robustness via Integrator Segmentation
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Solution Overview
Problem
Capacitive touch and proximity sensing systems are prone to false positives due to moisture, such as rain or condensation, which can corrupt sensor measurements and cause incorrect detection of touch or proximity, especially in outdoor applications.
Innovation Solution
The system employs a set of integrators that accumulate and differentiate sensing data with varying levels of low-pass filtering, allowing for the explicit or implicit detection of moisture, and uses a state machine to differentiate between touch or proximity signals and moisture-induced noise, ensuring robust and accurate detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitive sensing is used for touch and proximity detection, then detection sensitivity is improved, but false positives occur due to moisture interference
Solution Approach 1:
The patent segments the sensing data processing into multiple integrators, each accumulating data with different low-pass filtering levels. This segmentation allows the system to analyze both high-frequency (touch) and low-frequency (moisture) components separately, resolving the contradiction between sensitivity and reliability by processing different signal components through dedicated integrators.
Solution Approach 2:
The system dynamically adjusts processing parameters based on environmental conditions. The state machine monitors integrator outputs and adapts the detection algorithm in real-time, switching between touch-detection mode and moisture-compensation mode. This dynamic adaptation allows the system to maintain high sensitivity while automatically compensating for moisture interference.
2Reliability
If low-pass filtering is applied to sensing data, then moisture-induced noise is reduced, but touch detection response time increases
Solution Approach 1:
The patent creates multiple integrators with different low-pass filtering characteristics. Fast integrators use minimal filtering for quick touch response, while slow integrators use strong filtering for moisture rejection. The state machine combines information from both types, achieving both fast response and reliable moisture compensation simultaneously.
Solution Approach 2:
The system applies partial low-pass filtering to some integrators and excessive filtering to others. This partial/excessive action strategy allows the system to get quick initial responses from minimally filtered integrators while using heavily filtered integrators to confirm genuine touches and reject moisture noise.
3Measurement precision
If multiple integrators with different filtering levels are used, then moisture detection accuracy is improved, but system complexity increases
Solution Approach 1:
The patent implements a universal state machine that handles both touch detection and moisture compensation using the same integrator array. The state machine universally processes outputs from all integrators regardless of their filtering levels, adapting its behavior based on the current environmental state. This multi-functionality reduces complexity by using a single control structure for multiple purposes.
Solution Approach 2:
The system changes processing parameters (integrator weights, threshold values, time constants) based on the detected environmental state. When moisture is detected, the state machine adjusts parameters to emphasize slowly varying signals; during dry conditions, it emphasizes rapid changes. This parameter adaptation allows accurate moisture detection without permanently increasing system complexity.
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
The solution effectively distinguishes between touch or proximity events and moisture presence, preventing false positives and ensuring reliable operation in wet conditions, thereby enhancing the reliability of capacitive sensing systems in outdoor environments.
Implementation Method 1
These devices function on the principle of Capacitive Voltage Division (CVD) or charge time measurement technique
Implementation Method 2
compute a first high-pass filtered sequence of a plurality of sensor measurements
Data Source
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AI summary
A method for touch detection includes identifying a high-pass filtered sequence (810, 830) from a plurality of sensor measurements, accumulating (825, 845) a number of samples from a first high-pass filtered sequence into an accumulated value, comparing the first accumulated value against a threshold of accumulated values, and, based upon a determination whether the accumulated value is greater than the threshold of accumulated values, identify whether the sensor has been approached.