Capacitive Touch Sensor Shielding for Liquid False-Touch Detection
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Solution Overview
Problem
Capacitive touch sensors in control panels often register false touches due to liquids, leading to undesirable actuation and challenges with radiated emissions compliance.
Innovation Solution
A capacitive touch sensor system with a driven shield that monitors raw count data, supplies a driven shield signal when the data exceeds a threshold, and calculates a difference between initial and subsequent data values to distinguish between genuine touches and false triggers, minimizing radiated emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a driven shield signal is supplied to the electrode to prevent false touch detection, then false touch detection is reduced, but radiated emissions increase
Solution Approach 1:
The driven shield signal is supplied only periodically when needed - specifically when raw count data exceeds a first threshold indicating a potential touch event. The controller activates the driven shield temporarily during the measurement window, then disables it afterward. This periodic activation prevents false touches from liquids while limiting radiated emissions to only when necessary for accurate touch detection.
2Reliability
If the driven shield signal is continuously supplied to the electrode, then false touch detection is minimized, but energy consumption increases
Solution Approach 1:
The driven shield operates in a periodic manner rather than continuously. The controller monitors raw count data and only activates the driven shield when the data exceeds a threshold, indicating a potential touch event. This approach maintains reliable false touch prevention during critical measurement periods while minimizing energy consumption during non-critical periods when the shield is disabled.
3Measurement precision
If the driven shield signal is supplied to distinguish genuine touches from false triggers, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The controller uses feedback from raw count data to dynamically control the driven shield. When the raw count data exceeds a first threshold, the controller activates the driven shield and then measures the change in raw count data. This feedback mechanism improves touch detection accuracy by distinguishing genuine touches from false triggers caused by liquids, while the automated feedback loop manages the complexity of the control logic.
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 reduces false touch detection while minimizing radiated emissions, ensuring accurate user input and compliance with radiated emissions standards.
Implementation Method 1
capacitive touch sensors can detect a change in capacitance when the user touches the control panel
Implementation Method 2
water or other liquids splashed or spilled on the control panel may cause capacitive touch sensors of the control panel to register a false touch
Data Source
AI summary
A method of operating a capacitive touch sensor, the capacitive touch sensor including an electrode, includes monitoring raw count data from the capacitive touch sensor and recording a first value of the raw count data when the raw count data exceeds a first threshold. The method also includes supplying a driven shield signal to the electrode after the raw count data exceeds the first threshold and recording a second value of the raw count data while supplying the driven shield signal to the electrode. The method further includes calculating a difference between the first value and the second value and registering a touch when the calculated difference between the first value and the second value is less than a second threshold.