5-Wire Resistive Touch Screen Pressure Measurement Circuit
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Solution Overview
Problem
Conventional 5-wire touch screens cannot accurately measure touch pressure or force, limiting their capability to support 3-dimensional applications and signature verification, and are prone to errors due to mechanical vibrations and electromagnetic interference.
Innovation Solution
A 5-wire touch screen system that includes a wiper layer and a resistive layer with corner contacts, where the touch pressure generates a resistive contact area with a resistance inversely proportional to the touch intensity, allowing for the measurement of x, y coordinates, and z-coordinate touch pressure using analog to digital conversion and multiplexing circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional 5-wire touch screen measurement methods are used, then the device structure remains simple, but the measurement precision of touch pressure is insufficient
Solution Approach 1:
The measurement process is segmented into distinct phases: first measuring the baseline resistance without touch pressure, then measuring the resistance with touch pressure applied. This segmentation allows the system to calculate touch pressure by comparing the two measurements, improving precision without requiring a completely new complex measurement architecture.
Solution Approach 2:
The system performs a preliminary measurement of the resistive layer resistance before the actual touch pressure measurement. This preliminary action establishes a baseline value that is stored and later used for comparison, enabling accurate touch pressure calculation while maintaining the simplicity of the original 5-wire configuration.
2Reliability
If conventional touch screen measurement is used, then the device operates quickly, but the reliability of touch pressure measurement is poor due to vibrations and electromagnetic interference
Solution Approach 1:
The system takes preliminary measurements before actual touch events to establish baseline values, and uses comparison logic to distinguish real touch pressure from false signals caused by vibrations or electromagnetic interference. This preliminary anti-action approach filters out unreliable measurements while maintaining operational speed.
Solution Approach 2:
The measurement system uses feedback by comparing the measured resistance value against the stored baseline resistance value. This feedback mechanism allows the system to identify and reject measurements that deviate significantly from expected values, thereby improving reliability without substantially increasing measurement time.
3Adaptability or versatility
If basic 5-wire touch screen functionality is maintained, then the device complexity remains low, but the adaptability for 3-dimensional applications and signature verification is limited
Solution Approach 1:
The enhanced measurement system maintains compatibility with the standard 5-wire touch screen interface while adding touch pressure measurement capability. This universal approach allows the same hardware to support both basic touch location detection and advanced applications like signature verification and 3D interactions, increasing adaptability without requiring separate dedicated systems.
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
Enables accurate measurement of touch pressure, improving signature verification and distinguishing real touches from vibrations and electromagnetic interference, supporting 3-dimensional applications by converting analog touch voltages to digital representations.
Implementation Method 1
a touch on the wiper layer (11) presses a small portion (31) of the wiper layer (11) against the resistive layer (16) to form a resistive contact area (30) having a touch resistance (RZ) between the wiper layer (11) and the resistive layer (16), the touch resistance (RZ) being inversely proportional to an intensity (Ptouch) of the touch
Data Source
AI summary
A 5-wire touch screen system includes a touch screen (10) including a wiper (11) and a resistive layer (16) aligned with the wiper and first (UL), second (UR), third (LR), and fourth (LL) resistive layer contacts, wherein a touch on the screen presses a small portion of the wiper against the resistive layer, producing a touch resistance (RZ) between them at a touch point on the resistive layer. The wiper and various contacts are selectively coupled to first (VDD) and second (GND) reference voltages, respectively, to generate an analog touch voltage (VZ) at the touch point. The wiper and various contacts are selectively coupled to an analog input (56) and a reference voltage input of an ADC (48) for converting the touch voltage (VZ) to a digital representation. Analog voltages (VX) and (VY) at the touch point are converted to corresponding digital representations by the ADC.