Matrix Keypad Pulse Scanning for Variable Film Resistance
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Solution Overview
Problem
Conventional film keypads using pull-up scan detection face limitations due to resistance value changes in different film materials, requiring adjustments in resistor resistance or Schmitt trigger standards during mass production.
Innovation Solution
A key input apparatus and scanning method that generates a pulse signal and detects its transformation on signal lines, allowing the microcontroller unit to identify switch activation without modifying resistor resistance or Schmitt trigger standards, adapting to different film materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If pull-up scan detection is used with conventional film keypads, then the keypad can detect key presses, but the resistance value changes in different film materials require adjustments in resistor resistance or Schmitt trigger standards
Solution Approach 1:
The patent changes the detection parameter from voltage level (which is affected by resistance variations in different film materials) to pulse signal presence. By injecting a pulse signal and detecting its presence at the output, the system becomes insensitive to resistance value changes in the film material, thereby achieving adaptability across different materials without requiring parameter adjustments.
Solution Approach 2:
The pulse signal detection method serves multiple film material types universally. The same detection circuit and pulse signal injection method work for silver paste membrane, carbon, and other film materials without requiring different resistor values or Schmitt trigger standards, making the detection system universally applicable.
2Reliability
If the resistance of pull up resistor Rpu is increased to accommodate carbon film material, then the voltage level can be detected, but the manufacturing process requires adjustment of resistor resistance values
Solution Approach 1:
The patent changes the detection approach from voltage level detection (which requires matching resistor values to film material resistance) to pulse signal detection. The pulse signal method detects key presses by sensing the presence of the injected pulse at the output, which is independent of the film material's resistance value. This allows fixed resistor values to be used across all film material types during mass production.
3Measurement precision
If the standard of Schmitt trigger is adjusted to detect voltage levels in high resistance film materials, then detection sensitivity improves, but the system requires different trigger standards for different materials
Solution Approach 1:
The patent changes the measurement parameter from voltage level (which requires adjusting Schmitt trigger thresholds for different materials) to pulse signal presence detection. By injecting a known pulse signal and detecting whether it appears at the output, the system achieves consistent detection sensitivity across all film material types without requiring different Schmitt trigger standards.
Data Source
AI summary
A key input includes a keypad device and a micro controller unit. The keypad device has a matrix consisted of first signals lines, second signal lines, and switches located in corners which are formed by the first and the second signal lines, and a plurality of keys corresponding to the switches. The micro controller unit connects the first signal lines and the second lines and provides a pulse to the first signal line. When the switch is turned on by the key, the pulse is translated from the first signal line to the second signal line. Thus, the pulse is directly detected, so as to achieve the fast scanning and low sensitive impedance of carbon membrane efficient.