Capacitive Proximity Sensing Circuit for Moisture-Resistant Detection
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Solution Overview
Problem
Capacitive sensors in vehicles often falsely detect human presence due to moisture or rain, leading to inappropriate triggering of vehicle functions, as the presence of water can increase the capacitance value beyond the threshold, similar to a human presence.
Innovation Solution
A capacitive proximity sensor with a detection circuit and microcontroller that employs a dual acquisition phase process, where the sensor alternates between charging and discharging the detection capacitor and transferring charge to a storage capacitor, calculating the difference between two averages of voltage values to determine a detection parameter, which helps differentiate between human presence and moisture interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitive sensor uses a simple threshold-based detection method, then the device complexity is low and ease of operation is high, but measurement precision deteriorates due to false detections caused by moisture or rain
Solution Approach 1:
The patent applies preliminary action by performing an initialization phase before the acquisition phase. During initialization, the detection capacitor is charged to a known voltage (Vcc/2) to establish a baseline state. This preliminary setup allows the subsequent acquisition phase to accurately detect changes in capacitance caused by human presence, while compensating for environmental factors like moisture. The initialization ensures that the detection system starts from a known state, improving measurement precision without requiring complex real-time correction circuits.
Solution Approach 2:
The patent implements periodic action through dual acquisition phases (first and second acquisition phases) that are repeatedly executed. Each acquisition phase involves periodic charging and discharging of the detection capacitor, followed by measurement. The microcontroller alternates between these phases multiple times and compares the results, allowing it to distinguish between transient effects (moisture) and genuine human presence. This periodic measurement approach improves detection accuracy while keeping the circuit relatively simple.
2Reliability
If the sensor increases the number of measurements and iterations to improve detection reliability, then measurement precision improves, but loss of time increases due to multiple acquisition cycles
Solution Approach 1:
By performing initialization before acquisition, the system prepares the detection capacitor in advance with a known voltage state. This preliminary action ensures that each measurement cycle starts from a consistent baseline, allowing for more reliable detection results without requiring excessive measurement iterations. The pre-established baseline reduces the number of repeated measurements needed to achieve reliable detection, thus minimizing time loss while improving reliability.
Solution Approach 2:
The patent employs a differential measurement approach where the microcontroller compares results from two acquisition phases. By skipping intermediate verification steps and directly comparing the differential result against a threshold, the system rapidly determines human presence. This method rushes through the detection process by focusing on the critical comparison step rather than performing multiple sequential verification measurements, thereby maintaining high reliability while reducing overall detection time.
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
This method effectively eliminates the influence of moisture on sensor measurements, preventing false detections and ensuring accurate human presence detection in various weather conditions.
Implementation Method 1
a capacitive proximity sensor comprising a detection circuit provided with a detection capacitor
Implementation Method 2
the proximity of a human body part increases the electrostatic field and therefore the capacitance value of a capacitor device
Data Source
AI summary
A capacitive proximity sensor including a detection circuit, including a detection capacitor, a storage capacitor and switches, a DC voltage generator and a microcontroller which is configured to control the switches and to: obtain a voltage value across the terminals of the storage capacitor and across the terminals of the detection capacitor; calculate a first average defined by the average of the voltage values which are obtained at the end of each iteration of a first acquisition phase and a second average defined by the average of the voltage values at the end of each iteration of a second acquisition phase; and detect a human presence when the difference between the first average and the second average is above a predefined detection threshold.