Loudspeaker Motion Sensor for Low-Power Tap Detection
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Solution Overview
Problem
Existing motion sensors in mobile devices face challenges in accurately detecting user inputs with low power consumption and minimizing false triggers from acoustic sources, especially when trying to replace traditional buttons for device wake-up and operation mode changes.
Innovation Solution
A motion sensor system utilizing dual loudspeakers with a trigger detector module that compares signal responses to determine the presence and location of a motion source, employing reference waveforms and filters to differentiate mechanical from acoustic signals, allowing for low-power operation and reliable detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional buttons or accelerometers are used for motion detection, then device wake-up and input functions are achieved, but power consumption increases and false triggers from acoustic sources occur
Solution Approach 1:
The loudspeaker is designed to serve dual functions: audio output during normal operation and motion sensing during low-power standby mode. The same hardware component performs both audio playback and mechanical vibration detection, eliminating the need for separate always-on motion sensors and reducing overall power consumption.
Solution Approach 2:
The patent replaces traditional mechanical button presses or accelerometer-based motion detection with mechanical vibration sensing through the loudspeaker diaphragm. The loudspeaker's natural mechanical response to vibrations allows it to detect user inputs without requiring active electronic sensing circuits during standby mode.
2Reliability
If a single loudspeaker is used for motion detection, then power consumption is reduced, but detection reliability and accuracy decrease
Solution Approach 1:
Multiple loudspeakers are merged into a single motion sensing system, where their combined mechanical responses are processed by a unified trigger detector. The trigger detector integrates signals from multiple loudspeaker inputs, comparing them to determine if a valid motion event occurred, thereby improving reliability through signal correlation.
Solution Approach 2:
The system uses feedback from multiple loudspeaker inputs to the trigger detector, which continuously monitors and compares signals from each loudspeaker. When the mechanical vibrations detected by multiple loudspeakers correlate with expected tap patterns, the system confirms a valid input, reducing false triggers and improving detection reliability.
3Measurement precision
If the loudspeaker is made highly sensitive to mechanical vibrations, then user input detection improves, but sensitivity to acoustic sources increases causing false triggers
Solution Approach 1:
The detection process is segmented into distinct analysis stages: initial signal acquisition from multiple loudspeakers, correlation analysis of simultaneous vibrations, pattern matching against expected tap signatures, and threshold-based validation. This segmentation allows the system to distinguish between genuine user inputs and acoustic interference by analyzing the temporal and spatial characteristics of vibrations.
Solution Approach 2:
The system dynamically adjusts its detection parameters based on the incoming signals from multiple loudspeakers. The trigger detector continuously evaluates the correlation between signals from different loudspeakers and adapts its response thresholds based on the consistency of detected vibrations across the array, enabling it to maintain high sensitivity while rejecting acoustic false triggers.
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 system effectively detects user inputs with high accuracy and low power consumption, enabling the motion sensor to replace traditional buttons and efficiently switch mobile devices between power modes, with the ability to determine the location of taps and improve detection reliability.
Implementation Method 1
a further loudspeaker mechanically coupled to the loudspeaker
Implementation Method 2
the multi-trigger detector module is operable to compare a signal received on the trigger input with a reference waveform
Implementation Method 3
the trigger detector is further arranged to determine a delay value from a measurement of the delay between a signal received on the trigger input and a signal received on the further trigger input
Data Source
Figure 1~2
Figure 3
Figure 4a~4b
AI summary
Accelerometers are used as motion sensors in mobile devices, such as mobile phones, to detect user inputs such as tapping. A motion sensor for a mobile device is described comprising a loudspeaker for outputting an audio signal, the loudspeaker having a loudspeaker input; a trigger detector having a trigger input coupled to the loudspeaker input, and a trigger output; wherein the trigger detector is operable to output a detection signal on the trigger output in response to a mechanically induced signal on the loudspeaker input due to a motion source. The power consumption of the motion sensor is reduced since the loudspeaker does not require any DC bias to detect a motion source such as a user tapping the motion sensor.