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What is the principle of the capacitive touch screen?

The capacitive screen is used in many areas as part of the touch terminal. And it has a wide application in the restaurant pos.

Capacitive touch screen is working with the current sensing of body. The capacitive touch screen is a four-layer composite glass screen. The inner surface and the lamination of the glass screen is each coated with a layer of ITO. The most outer layer of the glass screen is a thin silica glass protective layer; the laminated ITO coating is as a work face which leads to four electrodes on the four corners; the inner ITO is as shield to ensure a good working environment.
The princible of capacitive touch screen

When the fingers touch the metal layer, the user and the touch screen surface will form a capacitive coupling capacitance because of the body electric field. For high-frequency current, the capacitance is a direct conductor.

Therefore the finger will absorb a small current from the contact point. The current outflow from the four corners of the four electrodes of touch screen. The current through the four corners is proportional to the distance of fingers from four corners. So the touch point can be got from accurate calculation of the ratio of the four currents.

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