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Principle of capacitive touch screen

Time:2023-03-14
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Principle of capacitive touch screen?

To achieve multi touch control on a capacitive screen, it is necessary to add electrodes with mutual capacitance. In short, dividing the screen into blocks and setting a group of mutual capacitance modules in each area is independent. Therefore, the capacitive screen can independently detect the touch situation in each area, and after processing, it can easily achieve multi touch control.

Capacitance Touch Panel (CTP) uses the human body's current sensing to work. The capacitive screen is a four layer composite glass screen. The inner surface and interlayer of the glass screen are coated with a layer of ITO (nano indium tin metal oxide). The outermost layer is a protective layer of silica glass with a thickness of only 0.0015mm. The interlayer ITO coating serves as the working surface, and four electrodes are led out from four corners. The inner layer ITO serves as the screen layer to ensure the working environment.

When a user touches a capacitive screen, due to the electric field of the human body, a coupling capacitance is formed between the user's finger and the working surface. Due to the high-frequency signal connected to the working surface, the finger absorbs a very small current, which flows from the electrodes on the four corners of the screen. In theory, the current flowing through the four electrodes is proportional to the distance from the finger to the four corners. The controller obtains the position through precise calculation of the four current ratios. Can achieve 99% accuracy, with a response speed of less than 3ms.

Touch Control Technology for Projective Capacitor Panels Projective capacitive touch screens are designed to etch different ITO conductive circuit modules onto two layers of ITO conductive glass coatings. The etched patterns on the two modules are perpendicular to each other, and can be viewed as continuously changing sliders in the X and Y directions. Due to the X and Y architectures on different surfaces, a capacitive node is formed at their intersection. One slider can be used as a drive line, and the other slider can be used as a detection line. When current flows through one of the drive wires, if there is a signal of capacitance change outside, it will cause changes in the capacitance nodes on the other layer of wires. The change in the detected capacitance value can be measured through an electronic circuit connected to it, and then converted into a digital signal through an A/D controller for computer processing to obtain the position of the (X, Y) axis, thereby achieving the goal of positioning.

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