Capacitive Force-Sensing Button Using PCB Traces
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Solution Overview
Problem
Conventional force-sensing buttons in gamepads are costly due to the high expense of force sensing resistors and the inaccuracies and non-linearity of resistive carbon tracks on printed circuit boards, which are difficult to manufacture consistently.
Innovation Solution
A low-cost force-sensing button solution utilizing a conductive-tip actuator and a printed circuit board with a conductive layer and insulating solder resist, forming a capacitor that measures capacitance changes as the actuator deforms, allowing for accurate and linear force sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If force sensing resistors are used for accurate force sensing, then measurement precision is improved, but manufacturing cost increases significantly
Solution Approach 1:
The patent replaces expensive force sensing resistors with a copied functionality implemented through standard PCB traces and a simple conductive tip actuator. The capacitance sensing mechanism copies the force detection function using inexpensive, mass-producible components that can be manufactured through standard PCB fabrication processes, eliminating the need for costly specialized sensors while maintaining measurement capability
Solution Approach 2:
The invention uses extremely low-cost PCB traces and conductive tip actuators that can be easily replaced or reconfigured. These components are so inexpensive that even if they wear or fail, replacement is economically viable. The PCB trace capacitor and simple actuator design eliminates dependence on expensive, delicate force sensing resistors, allowing for a disposable or easily replaceable sensing mechanism
2Ease of manufacture
If resistive carbon tracks are used on PCBs for force sensing, then manufacturing cost is reduced, but measurement precision and linearity deteriorate
Solution Approach 1:
The patent replaces the resistive carbon track mechanical contact system with a capacitive sensing system. Instead of measuring resistance changes through physical contact between a rubber dome and carbon track, the invention measures capacitance changes between PCB traces as the conductive tip actuator approaches them. This substitution eliminates the non-linearity and inaccuracy inherent in resistive carbon tracks while maintaining low manufacturing costs through standard PCB fabrication
Solution Approach 2:
The invention changes the sensing parameter from electrical resistance to electrical capacitance. By measuring capacitance rather than resistance, the system avoids the non-linearity and manufacturing variability problems of resistive carbon tracks. The capacitance between PCB traces changes predictably as the conductive tip actuator approaches, providing a linear and accurate force measurement that can be easily calibrated
3Ease of manufacture
If resistive carbon tracks are used on PCBs, then manufacturing cost is reduced, but manufacturing precision and consistency worsen
Solution Approach 1:
The patent copies the force sensing function using standard PCB copper traces instead of resistive carbon tracks. Since copper trace resistance and dimensions can be precisely controlled through standard PCB fabrication processes, the manufacturing consistency is dramatically improved. The capacitance sensing mechanism uses these precise copper traces to create capacitors with predictable characteristics, eliminating the resistivity variability problem of carbon printing
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 solution provides a cost-effective and accurate force-sensing mechanism with minimal drift after calibration, suitable for consumer products with multiple force-sensing buttons.
Implementation Method 1
forming a capacitor that measures capacitance changes as the actuator deforms
Data Source
AI summary
Disclosed is an apparatus for sensing a force, comprising an actuator having a conductive deformable surface, a substrate having a first conductive trace and a second conductive trace, a housing coupled to the actuator and to the substrate, holding the actuator in proximity to the substrate, and a circuit for measuring a capacitance value.