Capacitive Touch Switch Scanning Frequency Against Alias Noise
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Solution Overview
Problem
Capacitive touch-sensitive switches in domestic appliances often experience faulty detections due to interference or noise, leading to incorrect switch actuation evaluations.
Innovation Solution
A method to adjust the scanning frequency of capacitive touch-sensitive switches by detecting and avoiding critical alias effects through signal analysis, using a fast Fourier transform to convert amplitude/time graphs into amplitude/frequency graphs and setting the scanning frequency to minimize noise interference, thereby reducing the risk of faulty detections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed scanning frequency is used for the capacitive touch-sensitive switch, then the device operation is simple, but the signal-to-noise ratio is poor and faulty detections occur due to alias effects
Solution Approach 1:
The patent applies preliminary action by determining the optimal scanning frequency in advance through a determination phase before actual switch operation. During this phase, the system evaluates different scanning frequencies and identifies the optimal one that minimizes alias effects and maximizes signal-to-noise ratio. This pre-determined frequency is then used during normal operation, ensuring reliable detection without requiring complex real-time adjustments.
Solution Approach 2:
The patent implements parameter changes by dynamically selecting from multiple available scanning frequencies based on detected alias effects. The system monitors for alias effects in measurement signals and adjusts the scanning frequency parameter accordingly, switching between different frequencies from a predefined set to optimize detection accuracy and eliminate faulty readings caused by interference.
2Reliability
If the scanning frequency is adjusted to avoid alias effects, then the signal-to-noise ratio improves, but the device complexity increases due to frequency selection mechanisms
Solution Approach 1:
The system performs preliminary determination of the optimal scanning frequency before normal operation begins. During this initialization phase, the control unit evaluates different scanning frequencies from a predefined set and identifies the optimal frequency that minimizes alias effects. This pre-determined frequency is stored and used during subsequent switch operations, avoiding the need for complex real-time frequency adjustment mechanisms.
Solution Approach 2:
The patent changes the scanning frequency parameter based on detected alias effects. The control unit monitors measurement signals for alias effects and adjusts the scanning frequency by selecting from multiple available frequencies. This parameter adjustment is performed systematically by comparing signal quality at different frequencies and selecting the optimal one, thereby improving detection reliability without requiring overly complex adjustment mechanisms.
3Measurement precision
If multiple scanning frequencies are tested to find the optimal one, then the detection accuracy improves, but the time required for setup and calibration increases
Solution Approach 1:
The system performs frequency determination as a preliminary action during an initialization phase before normal operation begins. The control unit systematically tests multiple scanning frequencies from a predefined set and identifies the optimal frequency that provides the best signal-to-noise ratio and minimum alias effects. This one-time preliminary determination ensures high measurement precision during subsequent operations without recurring time losses.
Solution Approach 2:
The patent implements periodic action by testing multiple scanning frequencies in a systematic sequence during the determination phase. The control unit cycles through different frequencies from the available set, evaluating each one's performance in terms of alias effect minimization and signal quality. This periodic testing approach efficiently identifies the optimal frequency while minimizing total determination time through structured evaluation.
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 method improves the signal-to-noise ratio and reduces the likelihood of faulty switch actuation detections by selecting an optimal scanning frequency that avoids critical alias effects, enhancing the reliability of capacitive touch-sensitive switches in domestic appliances.
Implementation Method 1
a capacitive sensor element together with the finger of a user forms a capacitance over a touch panel acting as dielectric, which capacitance is variable corresponding to the actuation of the touch-sensitive switch
Implementation Method 2
using a fast Fourier transform to convert amplitude/time graphs into amplitude/frequency graphs
Data Source
AI summary
A method for operating a capacitive touch-sensitive switch having a capacitive sensor element and a sensor circuit includes initially setting a scanning frequency of the capacitive touch-sensitive switch with a good signal-to-noise ratio and then operating the capacitive touch-sensitive switch at a scanning frequency which has been set to detect switch actuation. The process of setting the scanning frequency includes operating the touch-sensitive switch using a first measurement method and at a selected scanning frequency, detecting the measurement signals from the sensor circuit and checking whether the detected measurement signals contain or could contain a critical alias effect. If no critical alias effect and no possibility of a critical alias effect are detected during the check, the scanning frequency can be set as the selection frequency for detection operation of the touch-sensitive switch. A capacitive touch-sensitive switch is also provided.