How does a resistive touch screen work?
Simply put, the core principle of resistive touch screens is "pressure sensing". It determines the position of th...
Simply put, the core principle of resistive touch screens is "pressure sensing". It determines the position of the touch point by detecting the voltage changes on the screen surface caused by pressing.
The working process can be decomposed into the following key parts and steps:
1、 Basic structure (core consisting of two layers of thin film)
A resistive screen is usually composed of four (or five) tightly adhered thin films, arranged from the outside to the inside as follows:
Outer layer: a hard, scratch resistant plastic or glass protective layer.
Upper ITO conductive layer: a flexible plastic film (usually polyester film) coated with transparent conductive indium tin oxide (ITO). This is a bendable layer.
Lower ITO conductive layer: another layer coated with ITO on a hard substrate (usually glass or hard plastic). This layer is rigid.
Support pad (isolation point): Between the two ITO conductive layers, there are many small transparent isolation points (Spacer Dots) evenly distributed, ensuring that the two layers are separated and non-conductive when not touched.
Bottom layer: the back panel of the screen.
Key point: The conductive surfaces of these two layers of ITO film (the side with ITO coating) are placed relative to each other, with a small gap in between.
2. Working principle (taking four wire resistor as an example)
When the screen is not touched, the two layers of ITO are insulated. Once touched, the workflow is as follows:
Step 1: Press contact
When you press the screen with your fingers, stylus, or any hard object, the upper flexible film will bend, forcing the upper ITO conductive layer to make contact with the lower ITO conductive layer at the pressing point, and the circuit will conduct at that point.
Step 2: Coordinate measurement (performed in two steps)
The controller needs to measure the X and Y coordinates of the touch point separately. This is achieved by alternately applying voltage gradients (voltage linearly changing from one end to the other) to two layers of ITO thin films.
Measure X coordinate:
The controller applies a fixed voltage difference (e.g. 5V on the left and 0V on the right) to the left and right electrodes of the lower ITO layer, creating a horizontal voltage gradient field that uniformly varies from left to right across the entire lower ITO layer.
Meanwhile, the upper ITO layer is used as a voltage probe (with electrodes suspended for measurement purposes only).
When two layers make contact at a touch point, the upper ITO layer can detect the corresponding voltage value of that point in the lower voltage gradient field.
The controller measures this voltage value and can accurately calculate the corresponding X-coordinate of the point through an analog-to-digital converter (ADC).
Measure Y coordinate:
Next, the controller switches the circuit.
Apply a fixed voltage difference (e.g. 5V at the upper end and 0V at the lower end) to the upper and lower electrodes of the ITO layer, forming a vertical voltage gradient field from top to bottom.
At this point, use the lower ITO layer as a voltage probe.
At the same touch point, the lower ITO layer detects the corresponding voltage value of the point in the upper voltage gradient field.
The controller measures this voltage value to calculate the Y coordinate.
Step 3: Data Processing
The controller sends the measured X and Y coordinate data to the main processor of the device (such as the CPU of a computer or mobile phone), and the operating system and software perform corresponding operations such as clicking and dragging based on it.
The entire measurement process is completed in milliseconds, so users feel that it is an instant response.
3.Main features (advantages and disadvantages)
Advantages:
Low cost: The manufacturing process is relatively simple.
Strong adaptability: It can be operated with any object (fingers, gloves, stylus, nails) without relying on the conductivity of the human body.
Good anti-interference ability: not affected by dust, water vapor, or oil stains (as long as no pressure is generated).
High precision: suitable for scenarios that require precise clicking or writing (such as early PDAs, industrial equipment).
Disadvantages:
Poor light transmittance: The multi-layer structure results in a light transmittance of usually only 75% -85%, and the screen appears somewhat dark.
Not scratch resistant: The surface is a soft plastic film that is easily scratched by sharp objects.
Not supporting multi touch: Traditional resistive screens can only detect one touch point at a time. Although there are two improved supports, they are rare.
Requires certain pressure: the film needs to be deformed, making it impossible to achieve the smooth operation experience of a capacitive screen.
Limited lifespan: Repeated bending of flexible films may lead to fatigue damage.
4. Typical application scenarios
Due to the above characteristics, resistive screens are commonly used in environments that require high reliability, low cost, or require glove operation:
Early PDAs, smartphones (such as Windows Mobile phones), MP4 players.
Industrial control equipment, medical instruments, industrial computers.
Supermarket POS machines, bank ATM machines (partially).
Handwritten input devices, low-end navigation systems.
summary
A resistive touch screen is like a precise "pressure switch+coordinate ruler" system. It contacts two layers of conductive films through physical pressing, and then calculates their position coordinates by measuring the voltage value at the contact point. Although capacitive touch screens have been replaced by more advanced and better experience in the consumer electronics field (mobile phones, tablets), resistive screens still occupy a place in specific industrial and commercial fields due to their reliability and adaptability.
