Capacitive Sensing Circuit Water Detection via Charging Time Sampling
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Solution Overview
Problem
Capacitive sensing devices face false touch detection issues when exposed to moisture or water, leading to increased manufacturing costs and reduced functionality due to the need for additional components like guard sensors.
Innovation Solution
A capacitive sensing method and circuit that samples and compares the charging or discharging time of capacitive sensing components to determine if a touch is real, avoiding false triggers by omitting the need for a guard sensor, thus reducing PCB area and MCU pin occupation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a guard sensor is added to detect water coverage, then false touch detection is prevented, but manufacturing cost increases and device complexity increases
Solution Approach 1:
The patent extracts the water detection function from a separate guard sensor and integrates it into the existing capacitive sensing components. By reusing the same sensing capacitors for both touch detection and water detection, the need for additional guard sensors is eliminated, reducing device complexity while maintaining reliability
Solution Approach 2:
The patent makes the existing capacitive sensing components serve multiple functions: they detect both genuine touches and water coverage conditions. The same sensing capacitor and charging circuit are used for dual purposes, eliminating the need for dedicated guard sensors and reducing overall device complexity
2Reliability
If a guard sensor is added to detect water coverage, then false touch detection is prevented, but PCB area and MCU pin occupation increase
Solution Approach 1:
The patent makes the existing capacitive sensing components serve multiple functions: they detect both genuine touches and water coverage conditions. The same sensing capacitor and charging circuit are used for dual purposes, eliminating the need for dedicated guard sensors and reducing overall device complexity
Solution Approach 2:
The patent merges the water detection function with the existing touch sensing function. By combining these functions into a single sensing system, the PCB area and MCU pin occupation required for separate guard sensors are eliminated
3Reliability
If the entire device is locked when water is detected, then false touch detection is prevented, but device functionality is reduced
Solution Approach 1:
The patent divides the sensing device into independent sensing regions, each capable of being individually identified as water-covered. Instead of locking the entire device, only the affected regions are marked as unavailable, allowing other regions to continue functioning normally, thus maintaining device versatility
Solution Approach 2:
The patent applies different states to different regions of the sensing device based on local conditions. Water-covered regions are identified and handled differently from dry regions, allowing the device to maintain functionality in unaffected areas while preventing false touches only where needed
Data Source
AI summary
A sensing method is used for a capacitive sensing device, wherein the capacitive sensing device has a plurality of capacitive sensing components, each of which is charged or discharged by a charging component respectively. The sensing method comprises the steps of: a first sampling step of sampling at least one of charging or discharging time of a capacitive sensing component of the plurality of capacitive sensing components to determine a first sample time for the component sampled, wherein the component sampled and at least one another component of the plurality of capacitive sensing components are charged or discharged simultaneously during the first sampling step; a first comparing step of comparing the first sample time for the component sampled with a reference time; and an outputting step of outputting a trigger signal in the event that the first sample time exceeds the reference time.