Capacitive Touch Sensing With Guard Frequency Hopping
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Solution Overview
Problem
Capacitive sensors in human machine interfaces are prone to false positive touch events due to interference from liquids and radio frequency (RF) interference, leading to increased power consumption and latency.
Innovation Solution
Implementing a guard sensor with frequency-hopping for interference detection and a single frequency technique for human input sensors, along with shield electrodes to distinguish between touch and liquid impingement events, and adjusting sensor frequencies to avoid interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If frequency-hopping technique is used for interference detection, then reliability is improved, but use of energy increases and latency increases
Solution Approach 1:
The sensor array is divided into multiple sensor groups, each responsible for detecting specific frequency ranges. This segmentation allows the system to distribute the frequency-hopping detection workload across multiple groups, reducing the energy consumption and latency for each individual group while maintaining overall detection accuracy through coordinated operation of all groups.
Solution Approach 2:
The system performs preliminary frequency detection using a subset of sensor groups before activating all sensors for full detection. This preliminary action identifies obvious interference sources early, allowing the system to avoid exhaustive frequency-hopping detection in all cases, thereby reducing overall power consumption and latency while maintaining reliability when interference is detected.
2Reliability
If frequency-hopping technique is used for interference detection, then reliability is improved, but speed decreases
Solution Approach 1:
The sensor array is divided into multiple sensor groups, each responsible for detecting specific frequency ranges. This segmentation allows parallel detection across different frequency bands, significantly reducing the time required to complete full frequency-sweep detection while maintaining comprehensive interference detection accuracy through coordinated operation of all groups.
Solution Approach 2:
The system implements periodic frequency detection using multiple sensor groups that operate in alternating cycles. Different sensor groups perform detection at different time intervals, allowing the system to maintain high detection reliability across all frequencies while reducing the response time for any single frequency band through overlapping periodic measurements.
3Reliability
If guard sensor is used adjacent to human input sensor, then reliability is improved, but device complexity increases
Solution Approach 1:
The guard sensor and human input sensor are merged into a single integrated sensor element with multiple functional zones. This combining allows the sensor to perform both guard detection (for interference identification) and human input detection (for touch recognition) simultaneously, reducing device complexity by eliminating separate physical components while maintaining reliability through software-based functional differentiation.
Solution Approach 2:
Each sensor element is designed with universal functionality to serve multiple purposes: it can detect human touches, detect liquid interference, and detect RF interference depending on the activation state and signal frequency. This multi-functionality reduces the need for separate dedicated guard sensors and input sensors, simplifying the overall device structure while maintaining high detection reliability across different interference scenarios.
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
Reduces power consumption and latency by effectively distinguishing between touch and interference events, thereby enhancing the reliability and efficiency of capacitive sensors.
Implementation Method 1
Capacitance-sensing devices are, at times, used to replace mechanical buttons, knobs, and other similar mechanical user interface controls
Implementation Method 2
In some embodiments, the controller 125 uses a frequency-hopping technique for sensing signals used with the guard sensor 110 to identify interference sources
Data Source
AI summary
One or more computing devices, systems, and/or methods are provided. In an example, a human machine interface comprises a guard sensor, a human input sensor adjacent the guard sensor, and a controller. The controller is configured to measure a first response of the guard sensor using a first sensing signal having a first frequency, measure a second response of the guard sensor using a second sensing signal having a second frequency, configure a sensor frequency of the human input sensor based on the first response of the guard sensor and the second response of the guard sensor, measure a first response of the human input sensor using the sensor frequency, and identify a touch event on the human input sensor based on the first response of the human input sensor.