Multiplexed Capacitive Button Sensor With Reduced I/O Pinout
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Solution Overview
Problem
Multiple-capacitive-sensor controllers require multiple I/O ports for both capacitive sensing and LED driving, leading to inefficiencies in system area and cost, as each function necessitates a separate port.
Innovation Solution
A control circuit that enables sharing of a single I/O port for both capacitive sensing and LED driving by selectively disabling and enabling the respective circuits, using a bias driver to maintain voltage equality during capacitive sensing, and employing PWM for LED brightness control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate I/O ports are used for capacitive sensing and LED driving, then each function can be independently controlled, but the number of I/O ports increases leading to larger system area and higher cost
Solution Approach 1:
The patent implements multi-functionality by enabling each I/O port to serve dual purposes: capacitive sensing and LED driving. The controller alternates between sensing mode and LED drive mode on a per-port basis, allowing a single I/O port to perform both functions sequentially. This reduces the total number of I/O ports required from N (for N capacitive inputs + N LED drivers) to approximately N/2, directly addressing the contradiction between independent function control and device complexity.
Solution Approach 2:
The patent employs periodic action through time-division multiplexing, where each I/O port alternates between capacitive sensing mode and LED driving mode in periodic cycles. During each period, the port is dedicated to one function, then switches to the other function in the next period. This periodic switching enables a single port to handle multiple functions sequentially, resolving the contradiction by reducing port count while maintaining independent control capability through precise timing management.
2Adaptability or versatility
If more I/O ports are provided for both sensing and LED functions, then system functionality is enhanced, but system area and manufacturing cost increase
Solution Approach 1:
The patent applies multi-functionality to reduce manufacturing cost by making each I/O port universal. Instead of requiring separate dedicated ports for capacitive sensing and LED driving, each port can be configured to perform either function based on timing control. This reduces the total port count required in the controller, directly lowering manufacturing complexity and cost while preserving full system functionality through time-division multiplexing of the universal ports.
3Reliability
If multiple separate circuits are used for capacitive sensing and LED driving, then each circuit can be optimized independently, but the overall system current consumption increases
Solution Approach 1:
The patent reduces system current consumption through periodic action and time-division multiplexing. Instead of having multiple circuits operating simultaneously with continuous current draw, the system activates only one function per I/O port at a time in periodic cycles. The capacitive sensing circuit operates during sensing periods while LED driving is inactive, and vice versa. This temporal separation eliminates redundant simultaneous operations, reducing overall current consumption while maintaining the ability to independently optimize each circuit's performance during its active period.
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 the number of I/O ports required, improves noise immunity, and decreases system current consumption by allowing 5 capacitive inputs and 5 LED drivers to be managed with only 6 I/O ports, while maintaining effective user input detection and LED control.
Implementation Method 1
The input/output circuit includes a capacitive sense circuit that is configured to measure a change in capacitance when an object approaches the touch sensor device
Implementation Method 2
The input/output circuit also includes an LED driver circuit configured to drive the first electrode of the LED
Data Source
AI summary
A capacitive touch sensor and LED driver device achieves a reduction in pin count by multiplexing LED drive functionality and capacitive sense functionality on each input/output pin. A control circuit switches between LED drive mode and capacitive sense mode at a frequency of approximately 200 Hz, although other switching frequencies can be used. A bias driver functions as a current sink for LEDs in LED drive mode and can also be used to drive a bias voltage to the LEDs during capacitive sense mode to improve noise immunity.