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Working principle of the capacitive touch screen

Views: 207     Author: Andy     Publish Time: 2023-05-15      Origin: Site


Working principle of the capacitive touch screen

Overview of principles

In order to realize multi-touch control, the capacitor screen increases the electrodes' mutual capacitance. Simply put, the screen is divided into a group of mutual capacitor modules in each area to work independently. Therefore, the capacitive screen can independently detect the touch control situation in each area, and after processing, multi-touch control is simply realized.
Capaciitor technology Touch panel The CTP (Capacity Touch Panel) is operated using the current induction of the human body. The capacitive screen is a four-layer composite glass screen, with the inner surface and interlayer coated with one layer of ITO (nanoindium tin metal oxide). The outermost layer is only 0.0015mm thick, with the interlayer ITO coating as the working face, four angles leading to four electrodes, and the inner layer of ITO as the screen layer to ensure the working environment.
When the user touches the capacitor screen, due to the human electric field, the user's fingers and working face form a coupling capacitor because the working surface has a high frequency signal, so the finger absorbs a small current, the current from the electrode out of the four corners of the screen, and theoretically, through the four electrodes current and the distance to the fingers to the four proportional, the controller, through the precision calculation of the four current ratio, arrives at its destination. It can reach 99% accuracy with a response speed of less than 3 ms.

Projection-type capacitive panel

The projection capacitive touch screen is etched into different ITO conductive line modules on two layers of ITO conductive glass coating. The etched figures on the two modules are perpendicular to each other and can be seen as sliders with continuous changes in the X and Y directions. Since the X and Y architectures are on different surfaces, a capacitor junction is formed at their intersection. One slider can be used as a driver line, and the other slide can be used as a detection line. When the current passes through a wire in the drive line, if there is a change in the external capacitor, it will cause a change in the capacitor node on another layer of wire. The change in capacitance value can be detected by measuring the electronic loop connected to it and then through the A/D controller to the digital signal for the computer to obtain the (X, Y) axis position and then reach the positioning location.
During the operation, the controller successively supplies the current to the drive line, thus forming a specific electric field between each node and the wire. Then scan the sensor line step by step to measure the capacitance between the electrodes to achieve multi-point positioning. When the finger or touch medium is close, the controller quickly changes the capacitor value between the touch node and the wire and then confirms the touch position. This axis is driven by a set of AC signals, and the response through the touch screen is detected by the electrodes on the other axes. Users call this 'cross' sensing, also called projection sensing. The ITO pattern is coated on the X and Y axes of the sensor. When the finger touches the touch screen surface, the capacitance value below the touch point increases according to the distance of the touch point. The continuous scan on the sensor detects changes in the capacitance value, and the control chip calculates the touch point and returns it to the processor.




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