Capacitive Sensor Switch With Optical Water Suppression
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Solution Overview
Problem
Capacitive sensor switches face false triggering issues due to electrically conductive liquids, which cannot distinguish between a body part and conductive liquids, leading to inaccurate detection.
Innovation Solution
A capacitive proximity sensor combined with an optical sensor and an evaluation circuit that correlates capacitance and light attenuation signals to differentiate between a body part and conductive liquids, using dynamic thresholds and multiple photodiodes to enhance detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitive sensor is used to detect proximity of objects, then detection capability is improved, but false triggering by electrically conductive liquids occurs
Solution Approach 1:
The patent combines a capacitive sensor and an optical sensor into a single sensor switch system. The capacitive sensor detects changes in capacitance when objects approach, while the optical sensor detects light attenuation. By merging these two sensing mechanisms, the system can distinguish between body parts (which cause both capacitance change and light attenuation) and conductive liquids (which cause capacitance change but not light attenuation), thereby resolving the false triggering problem while maintaining detection capability.
Solution Approach 2:
The optical sensor acts as an intermediary verification mechanism. When the capacitive sensor detects a change, the optical sensor provides additional information about whether the detected object is a body part or conductive liquid. This intermediary sensor helps filter out false positives from conductive liquids while maintaining accurate detection of actual body parts.
2Reliability
If an optical sensor is added to differentiate between body parts and conductive liquids, then reliability is improved, but device complexity increases
Solution Approach 1:
The sensor switch housing serves multiple functions: it protects the internal components, provides structural support, and acts as a light guide for the optical sensor. The evaluation circuit also performs multiple tasks including processing signals from both sensors, determining object type, and controlling the output. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity.
Solution Approach 2:
The patent merges the capacitive sensor electrode and optical sensor into a compact integrated structure within the same housing. The evaluation circuit processes both sensor signals together, and the light guide integrates optical pathways with the mechanical structure. This merging approach consolidates multiple functions into fewer components, reducing overall device complexity despite adding optical sensing capability.
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 significantly reduces false triggering by accurately detecting body parts while ignoring conductive liquids, ensuring reliable operation even when the sensor surface is covered with water or other conductive liquids.
Implementation Method 1
the capacitive proximity sensor includes a sensor conductor or sensor electrode, which normally may be a plate or foil of an electrically conductive material forming the active sensor surface... the evaluation circuit configured to evaluate and/or measure the capacitance with respect to ground
Implementation Method 2
The optical sensor of the sensor switch includes at least one photosensor. The photosensor may include at least one of a photodiode, a phototransistor, and an integrated circuit... the photodiode will detect ambient light which may vary depending on the environmental conditions
Data Source
AI summary
A sensor switch with water suppression includes a sensor electrode and a photodiode connected to an evaluation circuit. The evaluation circuit generates a capacitive sensor signal indicative of an electrically-conductive object in the proximity of the sensor switch and an optical sensor signal indicative of an object at least partially opaque or impermeable to light in the proximity of the sensor switch. The capacitive sensor signal and the optical sensor signal are correlated with one another to generate an output signal.