Design of 5-wire resistive touch screen structure
Structural design of 5-wire resistive touch screen This is a significant improvement to the four wire design, with the core being the separation of the driving layer and sensing layer, greatly enhancing durability and accuracy
Previously, we introduced the structural design of a 4-wire resistive touch screen. Today, we will provide a detailed analysis of the structural design of a 5-wire resistive touch screen. It is a significant improvement over the four wire design, with the core being the separation of the driving and sensing layers, which greatly enhances durability and accuracy.
Core design philosophy
Unlike the four wire type (where both layers are uniform resistive films), the five wire type adopts an asymmetric structure of "one layer for driving and one layer for detection":
Bottom layer: A complete and uniform ITO resistance layer serves as the voltage gradient field (driving layer).
Top layer: A uniform ITO conductive layer (rather than a resistive layer) serves as a pure voltage probe (sensing layer).
This design moves all the easily worn electrodes and precision resistor networks onto a bottom substrate that is not easily bent, while the top layer only performs simple detection functions, thus solving the problem of fatigue fracture of four wire top ITO.
Detailed structural decomposition
1. Bottom substrate
Material: Typically made of glass or hard, flat PET, providing stable mechanical support.
Coating: A uniformly coated ITO resistive film on the surface.
Key feature: Print a silver paste electrode (A, B, C, D) at each corner of the ITO layer. These are the four wires in the "Five Lines". These four electrodes are used to establish a uniform voltage gradient field on the ITO layer.
2. Top layer film
Material: Flexible PET film.
Coating: Apply a uniform ITO conductive film on the bottom surface. Note that the ITO here is processed to have excellent conductivity and extremely low resistance (square resistance is usually<100 Ω/□), and it does not generate voltage drop itself, only used to "detect" the voltage at a certain point in the bottom layer.
Key feature: The top layer itself does not have electrodes. Connect to the controller only at the edge through a single lead (usually a contact on a flexible circuit). This lead is the fifth wire in the "five wires" and the only sensing wire.
3. Isolation point
Similar to the four wire pattern, evenly distributed on the bottom ITO surface, used to isolate two layers when there is no touch.
4. Adhesive border
Also used for sealing and fixing two layers, leaving a channel for five electrode leads.
5. Top covering film
Hard wear-resistant coating, used for protection.
Working principle (part-time drive)
All driving and measurement switches of the five wire type are performed on the four corner electrodes at the bottom layer, while the top layer always maintains a "listening" state.
Phase 1: Measure the X coordinate
Establish an X-direction electric field: Apply a reference voltage (VCC) to the upper left corner (A) and upper right corner (B) electrodes of the bottom layer, while grounding the lower left corner (C) and lower right corner (D) electrodes (0V).
Forming a voltage gradient: At this point, a horizontal linear voltage gradient will be formed on the underlying ITO from left to right (with high A/B terminals and low C/D terminals).
Detection voltage: When the top conductive film is touched and pressed to make contact with the bottom layer, the top conductive film detects the instantaneous voltage value (Vx) at the contact point to the bottom layer at that point.
Calculate X-coordinate: The controller measures the voltage Vx returned by the top sensing line (fifth line), which is proportional to the X-coordinate of the touch point.
Phase 2: Measure the Y coordinate
Establish Y-direction electric field: switch electrode excitation. Apply reference voltage to the upper left corner (A) and lower left corner (C) electrodes of the bottom layer, while grounding the upper right corner (B) and lower right corner (D) electrodes.
Forming a voltage gradient: At this point, a vertical linear voltage gradient is formed on the bottom ITO layer from top to bottom (with high A/C terminals and low B/D terminals).
Detecting voltage: Similarly, through the contact point, the top layer detects the instantaneous voltage value (Vy) at that point.
Calculate Y coordinate: The controller measures the voltage Vy returned by the top-level sensing line again, which is proportional to the Y coordinate of the touch point.
Loop: The controller switches between X and Y measurements at high speed (usually hundreds of times per second) to continuously obtain the coordinates of the touch point.
Core advantages and disadvantages of structural design
Advantages (compared to the four line model):
Extremely high durability (core advantage):
The top ITO layer is a low resistance conductive layer without electrode leads, and is not easily broken by repeated bending.
All precision resistors and electrodes are on a sturdy substrate that is not affected by mechanical stress.
The lifespan can reach over 35 million cycles, far exceeding the one million cycles of the four wire type.
Higher accuracy and linearity:
The voltage gradient is established by four corner electrodes together, resulting in better uniformity of the electric field throughout the entire effective area, and much better edge linearity than the four wire bilateral electrodes.
No need for frequent software calibration like the four wire model.
Better stability:
The top layer is only responsible for detection, and its own resistance changes have minimal impact on the measurement results. Even if the top ITO has uneven resistance due to scratches, as long as it can still conduct electricity, it will not affect accuracy (because the measurement is voltage, not current).
Lower sensitivity to environmental changes (temperature, humidity).
Disadvantages:
Higher cost:
The controller chip is more complex and needs to handle the switching of the four corner electrodes.
The manufacturing process requires higher standards.
Still single touch: The physical structure determines that it can only report the voltage of one contact point and cannot recognize true multi touch.
Still requires some pressure: the essence is still resistive technology.
One wire becomes a single point of failure: If the only top-level sensing wire or contact point is damaged, the entire touch screen will fail (while a damaged wire in a four wire configuration may only cause one coordinate axis to fail).
Comparison of structural diagrams (textual description)
Five line structure:
|-----------------------------------|
| Hard wear-resistant coating |
|-----------------------------------|
| Top PET film |
|-----------------------------------|
| **Low resistance ITO conductive layer * * (only used as a probe) | <---**Connect only through one lead wire (5th wire)**|-----------------------------------|
|-----------------------------------|
| **Uniform ITO resistance layer * * (voltage gradient field) | <--- **The key! The four corners (A, B, C, D) have four electrodes**|-----------------------------------|
| Glass/hard PET substrate (stable platform) |
|-----------------------------------|
Summary and Application
The five wire resistive touch screen solves the fatal weaknesses of short lifespan and poor linearity of the four wire design by physically separating the driving (bottom four wires) and sensing (top one wire) functions, while maintaining all the universal advantages of the resistive screen (anti-interference, touchable to any object).
The essence of its structural design lies in solidifying vulnerable components and simplifying moving parts.
Therefore, it is widely used in situations that require extremely high reliability, durability, and accuracy, such as:
Industrial control system (factory workshop)
Medical equipment (often requiring disinfection and wiping)
Public Information Query Machine (Kiosk)
High end POS terminal
Car navigation system (early and some specific applications)
It is a pinnacle of the development of resistive touch screen technology, and was the preferred choice for high-performance touch applications before the popularization of capacitive screens.
Industrial touch screen：https://www.idtdisplay.com/products/industrial_touch_screen/
TFT LCD:https://www.idtdisplay.com/products/AUO_LCD_Displays/
