Resistive Sensor Matrix Wake-Up Circuit for Low-Power Key Detection
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Solution Overview
Problem
Conventional sensor matrices in input devices, such as keyboards, face challenges in accurately identifying active sensors when multiple keys are pressed, leading to issues like 'ghosting' or 'phantom keys,' and existing solutions like using diodes increase costs and are not suitable for flexible membrane technologies. Additionally, power consumption is high due to continuous scanning for key presses.
Innovation Solution
A resistive sensor matrix design that uses resistors in series with switches, combined with a wake-up sensing circuit that utilizes GPIO edge interrupts to wake the microprocessor upon sensor activation, reducing power consumption and eliminating the need for periodic scanning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If continuous scanning is used to detect key presses, then responsiveness is improved, but power consumption increases
Solution Approach 1:
The system performs scanning periodically rather than continuously. The microprocessor enters sleep mode between scan cycles, activating only when a key press is detected through the wake-up sensing circuit. This periodic operation maintains responsiveness to key presses while significantly reducing average power consumption.
Solution Approach 2:
The wake-up sensing circuit automatically detects key presses and triggers the microprocessor to wake from sleep mode without requiring continuous monitoring. The system serves itself by using the sensor matrix to generate wake-up signals, eliminating the need for continuous power-intensive scanning while maintaining responsiveness.
2Measurement precision
If diodes are added to prevent ghosting, then sensor identification accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent changes the electrical parameters of the sensor matrix by adding resistors in series with each sensor switch instead of using diodes. This parameter change (adding resistance) allows the sensing circuit to accurately identify active sensors by measuring voltage dividers, preventing ghosting without the complexity and cost of diodes.
Solution Approach 2:
The patent uses inexpensive resistors instead of more complex and costly diodes to solve the ghosting problem. Resistors are simpler, cheaper components that can be easily integrated into flexible membrane technologies, providing the same functional benefit of preventing false sensor readings without increasing device complexity.
3Measurement precision
If resistors are added to each sensor, then sensor identification accuracy is improved, but manufacturing complexity increases
Solution Approach 1:
The resistors serve multiple functions: they create voltage dividers for accurate sensor identification, prevent ghosting effects, and can be integrated into the existing flexible membrane structure. This multi-functionality reduces the need for additional components and simplifies the overall manufacturing process despite adding resistors to each sensor.
Solution Approach 2:
The patent is specifically designed for flexible membrane technologies, where resistors can be printed or deposited directly onto the flexible substrate along with the sensor traces. This integration approach maintains the flexibility and simplicity of membrane manufacturing while adding the necessary resistive elements for accurate sensor detection.
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 allows for accurate identification of active sensors with reduced power consumption, enabling longer sleep times and improved responsiveness by waking only upon sensor activation, thus minimizing power usage and preventing missed key presses.
Implementation Method 1
Each sensor includes a switch in series with a matrix resistor... a voltage-applying mechanism configured to apply a selected voltage to each second conductor of the plurality of second conductors. Each first resistor is connected in series between a first voltage and a first conductor corresponding to the first resistor.
Implementation Method 2
the wake-up sensing circuit is operatively connected to each conductor of the plurality of second conductors... utilizing GPIO edge interrupts to wake the microprocessor upon sensor activation
Data Source
AI summary
Embodiments are disclosed that relate to input devices. In one embodiment, an input device comprises a sensor matrix having first and second pluralities of conductors, a plurality of first resistors, a voltage-applying mechanism configured to apply a selected voltage to each second conductor of the plurality of second conductors, a plurality of sensors, a scanning sensing circuit, and a wake-up sensing circuit. Each first resistor is connected in series between a first voltage and a conductor of the plurality of first conductors. Each sensor includes a switch in series with a matrix resistor, and each sensor is connected to one of the plurality of first conductors and one of the plurality of second conductors. The scanning sensing circuit is connected to each of the plurality of first conductors, and the wake-up sensing circuit is connected to each of the plurality of second conductors.