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Design Example: Resistive Touchscreen
A device engineer is tasked with designing a resistive touchscreen interface for a mobile device. It consists of two conductive layers: a flexible upper layer and a rigid lower layer, separated by a narrow gap.
The resistance between the two layers is high. Upon touching the screen, the two layers make contact at a point called the touchpoint, reducing the resistance between the layers.
To determine the precise touchpoint location, the touchscreen is simplified to a one-dimensional system.
The top layer is characterized by its length, resistivity, and cross-sectional area and is divided into two parts at the touchpoint with resistances proportional to their length.
If a voltage source is connected between the two ends of the top layer, the circuit resembles a voltage divider circuit, and the voltage drop at the touchpoint depends on these two resistances.
Substituting the resistance values and solving the equation gives the relation between the voltage drop at the touchpoint and its position.
At each touchpoint, the voltage is distinct, which helps to pinpoint the location accurately.
1.13:
Design Example: Resistive Touchscreen
A device engineer plays a crucial role in designing user interfaces for mobile devices. One such interface is the resistive touchscreen, which fundamentally consists of two metallic layers: a flexible upper layer and a rigid lower layer, separated by a narrow gap. The high resistance between these two layers is a key characteristic of this design.
When a user touches the screen, the two layers make contact at a specific point known as the touchpoint. This contact reduces the resistance between the layers, effectively changing the electrical properties of the touchscreen at that point.
However, to accurately determine the precise location of the touchpoint, the touchscreen needs to be simplified as a one-dimensional system. The top layer, characterized by its length, resistivity, and cross-sectional area, is conceptually divided into two parts at the touchpoint. The resistances of these two sections are proportional to their lengths.
Connecting a voltage source between the two ends of the top layer transforms the circuit into a voltage divider configuration. The voltage drop at the touchpoint depends on the resistances of the two sections of the top layer.
By substituting the resistance values into the voltage divider equation and solving it, a relationship can be derived between the voltage drop at the touchpoint and its position. This relationship allows the device to calculate the exact location of the touchpoint based on the change in voltage.
This means that each touchpoint corresponds to a distinct voltage, enabling the system to accurately pinpoint the location of the user's touch. This precision is critical for the functionality of the touchscreen interface, ensuring it responds accurately to the user's input.