Capacitive Sensor Group Scanning for Low-Power Touch Detection
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Solution Overview
Problem
Low power systems with capacitive sensors face high power consumption due to the need for frequent wake-ups to scan multiple sensors, as capacitive sensing only operates in an active mode, necessitating a method to minimize wake-up time for efficient power management.
Innovation Solution
A method involving charging capacitive sensors to a first voltage, transferring electron charge to a sample and hold capacitor, measuring the resulting voltage, and comparing it to a previous measurement to detect capacitance changes, allowing for efficient scanning while minimizing power usage by reducing wake-up time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the system wakes up frequently to scan all capacitive sensors, then the detection of capacitance changes is reliable, but the power consumption increases
Solution Approach 1:
The patent divides the capacitive sensor array into multiple groups or channels. Instead of scanning all sensors in each wake-up cycle, the system scans only one group at a time across multiple cycles. This segmentation allows the microcontroller to spend less time in active mode while still monitoring all sensors comprehensively over time, thereby reducing power consumption while maintaining detection reliability.
Solution Approach 2:
The system implements periodic scanning of different sensor groups across alternating wake-up cycles. By rotating through different groups in a periodic manner, the microcontroller can return to sleep mode sooner each cycle while ensuring all sensors are scanned over the complete periodic cycle. This periodic action pattern reduces average power consumption while maintaining reliable detection capability.
2Reliability
If the system scans all capacitive sensors in each wake-up cycle, then no capacitance change is missed, but the wake-up time increases
Solution Approach 1:
The patent segments the capacitive sensor array into multiple groups that are scanned in different wake-up cycles. During each wake-up, only one group is scanned, significantly reducing the scan time per cycle. Over multiple cycles, all groups are covered, ensuring no capacitance change is missed while minimizing the time spent awake in each individual cycle.
Solution Approach 2:
The system performs preliminary scanning of sensor groups in a predetermined sequence across different cycles. By planning and executing scans in a prearranged pattern, the microcontroller can efficiently manage wake-up durations and return to sleep mode promptly after each group scan, reducing overall wake-up time while maintaining comprehensive monitoring.
3Use of energy by moving object
If the system reduces wake-up time to save power, then power consumption decreases, but the scanning of multiple sensors becomes insufficient
Solution Approach 1:
The patent divides the sensor array into multiple groups and allocates different groups to different wake-up cycles. This segmentation enables the system to scan fewer sensors per cycle (improving power efficiency) while ensuring complete coverage of all sensors over the course of multiple cycles (maintaining productivity).
Solution Approach 2:
The system maintains continuous monitoring of all capacitive sensors by rotating through different groups in successive wake-up cycles. Although each individual cycle scans only a subset of sensors, the continuous rotation across cycles ensures that all sensors are monitored without interruption, maintaining full productivity while reducing per-cycle power consumption.
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 approach enables quick and power-efficient scanning of multiple capacitive sensors, reducing average power consumption by allowing microcontrollers to spend less time in active mode and wake up only when capacitance changes are detected.
Implementation Method 1
charging a plurality of capacitive sensors to a first voltage
Implementation Method 2
electron charge from each of the individually coupled ones of the plurality of capacitive sensors may be transferred to the sample and hold capacitor
Data Source
AI summary
Relative capacitance of a plurality of capacitive sensors may be monitored by using only one ADC conversion. A plurality of capacitive sensors individually charges a sample and hold capacitor. After all of the plurality of capacitive sensors have charged the sample and hold capacitor, a digital conversion of the resulting analog on the sample and hold capacitor is made and stored in a memory. This stored digital collective voltage is compared to a previously stored one and if different then a proximity/touch event may have occurred. Therefore, an entire panel of capacitive sensors may be quickly monitored for a change in the “group” capacitance thereof, or portions of the capacitive sensors may be monitored for a change in the “subgroup” capacitance thereof. By knowing which subgroup of capacitive sensors has changed its collective capacitive value, a more focused and selective capacitive sensor measurement can be made that uses less power.