Capacitive Touch Sensing via RC Filtering for Noise Immunity
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Solution Overview
Problem
Conventional capacitive touch detection methods are sensitive to noise and external electrical interference, generate broadband electromagnetic radiation, and require complex components like touch controllers, leading to high costs and false-positive detections.
Innovation Solution
A capacitive touch detection device using an RC filter with a touch electrode and an ohmic resistor generates a periodic signal, which is filtered and evaluated for deviations, allowing for reliable detection with simple components and reduced electromagnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional CVD method with current integration is used for capacitive touch detection, then touch detection function is achieved, but the system becomes sensitive to noise and external electrical interference
Solution Approach 1:
The patent replaces the conventional CVD method using current integration with a voltage-based measurement approach. Instead of measuring current to detect capacitance changes, the system applies a voltage step signal and measures the voltage response across the touch electrode, fundamentally changing the measurement principle from current-based to voltage-based detection.
Solution Approach 2:
The patent changes the signal type from continuous current integration to discrete voltage step signals with specific rise times. By controlling the voltage signal characteristics (rise time, amplitude) and measuring the resulting voltage response, the system achieves noise immunity through parameter optimization rather than complex signal processing.
2Object-affected harmful factors
If current integration method is used during charging and discharging of sensor capacitance, then capacitive touch detection is achieved, but broadband electromagnetic radiation is generated on long leads
Solution Approach 1:
The patent eliminates the need for current sources and current integration by using voltage step signals and measuring voltage responses. This substitution of the measurement principle removes the primary source of broadband electromagnetic radiation generated by fast current edges, while maintaining capacitance measurement capability through voltage-based detection.
Solution Approach 2:
The patent employs periodic voltage step signals with controlled rise times to excite the capacitive sensor. By using repeated, periodic excitation signals rather than single sharp current edges, the system achieves stable measurements while limiting electromagnetic radiation through consistent, predictable signal characteristics.
3Measurement precision
If touch controllers with dedicated current drivers are used, then accurate capacitive touch detection is achieved, but system cost increases
Solution Approach 1:
The patent enables microcontrollers without dedicated touch controller hardware to perform accurate capacitive touch detection by using general-purpose I/O pins configured for voltage measurement. The same microcontroller that controls other system functions can also detect touch events, eliminating the need for separate touch controller ICs and reducing overall system cost.
Solution Approach 2:
The system uses the microcontroller's built-in ADC and timer resources to perform capacitance measurement without requiring external touch controller hardware. The microcontroller generates the voltage step signals and measures its own output through the touch electrode circuit, making the system self-sufficient and eliminating additional component costs.
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 achieves high detection sensitivity, effective noise suppression, and low electromagnetic radiation, enabling the use of cost-effective components and minimizing false-positive detections.
Implementation Method 1
the ohmic resistance and the capacitance of the touch electrode form an RC filter with respect to the signal generated by the signal generator and supplied to the touch electrode
Implementation Method 2
at least one touch electrode (2) with a capacitance (C) for detecting a change in capacitance when an object, in particular a finger, approaches the touch electrode (2)
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
The invention relates to an apparatus (1) for capacitive touch detection, having at least one touch electrode (2, 2', 2", 2'", 2.1, 2.2, 22) with a capacitor (C) for capturing a change in capacitance when an object (3) approaches the touch electrode (2, 2', 2", 2'", 2.1, 2.2, 22), a signal generator (4) for generating at least one predetermined periodic signal (5) with a predetermined frequency and phase, which signal is electrically supplied to the touch electrode (2, 2', 2", 2'", 2.1, 2.2, 22), and an electronic computing unit (6). The signal generator (4) is electrically coupled to the touch electrode (2, 2', 2", 2'", 2.1, 2.2, 22) by means of a non-reactive resistor (R) in such a manner that the resistor (R) and the capacitor (C) of the touch electrode (2, 2', 2", 2'", 2.1, 2.2, 22) form an RC filter for the signal (5) supplied to the touch electrode (2, 2', 2", 2'", 2.1, 2.2, 22), wherein the computing unit (6) is configured to receive the signal (7) filtered by the RC filter and to evaluate a deviation of the filtered signal (7) from the generated signal (5). The invention furthermore relates to a method for capacitive touch detection and to a steering wheel (20) for a motor vehicle having at least one heating conductor (22) forming an electrical resistance heating system and an apparatus (1) for capacitive touch detection having a touch electrode (22), wherein the heating conductor (22) forms the touch electrode (22) of the apparatus (1).