Capacitive Touch Sensor AC Line Synchronization
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Solution Overview
Problem
Capacitive touch sensors using DC power face significant noise interference from AC power sources, particularly high-amplitude, low-frequency noise, which affects measurement accuracy in systems employing half-wave demodulation techniques.
Innovation Solution
A touch sensing system that generates a trigger signal synchronized with the AC power cycle, allowing measurements to be taken at a consistent phase, reducing noise interference by converting AC power to DC and using a digital controller to initiate scans only when the trigger signal reaches a predetermined value, thereby minimizing the impact of AC noise on sensor operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If AC power is used to power DC touch sensors, then the device can operate from standard AC power sources, but high-amplitude low-frequency noise from the AC power source interferes with sensor measurements
Solution Approach 1:
The patent converts the harmful AC noise into a useful synchronization signal. By detecting the AC power line frequency and using it to trigger sensor scans at specific phases, the system transforms the previously harmful noise source into a beneficial timing reference that enables consistent measurement conditions and actually reduces the impact of noise on measurements.
2Productivity
If sensor scans are performed continuously, then measurement data is collected frequently, but measurements taken at different AC cycles experience varying noise levels reducing accuracy
Solution Approach 1:
The patent implements periodic scanning synchronized to the AC power cycle. Instead of continuous or random scanning, the system performs sensor measurements at regular intervals triggered by the AC frequency, ensuring all measurements occur at the same phase of the AC cycle. This periodic approach maintains high measurement frequency while ensuring consistent noise conditions across all measurements.
Solution Approach 2:
The system performs preliminary detection of the AC power line frequency and phase before initiating sensor scans. By first identifying the AC cycle position and then triggering scans at the optimal phase, the system prepares the measurement process in advance to ensure consistent timing and minimize noise impact, rather than performing measurements without prior synchronization.
Data Source
AI summary
A method includes powering multiple touch sensors using DC power derived from an AC power signal; monitoring the AC power signal and producing from the AC power signal a trigger signal that occurs repeatedly at a predetermined point in a cycle of the AC power signal; and initiating a scan of the touch sensors when the trigger signal occurs during each cycle of the AC power signal.