Capacitive touch screen

The capacitive touch screen technology uses the current induction of the human body to work. The capacitive touch screen is a four-layer composite glass screen, The inner surface of the glass screen and the interlayer are each coated with a layer of ITO, The outermost layer is a thin protective layer of silica glass, The sandwich ITO coating is used as the working surface, Four electrodes are drawn on the four corners, The inner ITO is a shielding layer to ensure a good working environment. When the finger touches the metal layer, Due to the electric field of the human body, The user and the touch screen surface form a coupling capacitor, For high-frequency current, Capacitors are direct conductors, Then the finger draws a small current from the contact point. This current flows from the electrodes on the four corners of the touch screen, And the current flowing through these four electrodes is proportional to the distance from the finger to the four corners, The controller accurately calculates the proportions of these four currents, Get the location of the touchpoint.

Capacitive touch screen

Principle Overview
Capacitive screens need to achieve multi-touch, It depends on the electrodes that increase the mutual capacitance, general speaking, Is to divide the screen into blocks, Setting a group of mutual capacitance modules in each area works independently, Therefore, the capacitive screen can independently detect the touch conditions of each area, After processing, Simple realization of multi-touch. [1]
The working principle of capacitive touch screen [2]
Capacitive technology touch panel CTP (Capacity Touch Panel) uses the current induction of the human body to work. The capacitive screen is a four-layer composite glass screen, The inner surface and the interlayer of the glass screen are each coated with a layer of ITO (Nano Indium Tin Oxide), The outermost layer is a protective layer of silica glass with a thickness of only 0.0015mm, The sandwich ITO coating is used as the working surface, Four electrodes are drawn from the four corners, and the inner layer of ITO is the screen layer to ensure the working environment. [3]
When the user touches the capacitive screen, Due to the electric field of the human body, The user’s finger and the working surface form a coupling capacitor, Because there are high-frequency signals on the working surface, So the finger absorbs a very small current, This current flows from the electrodes on the four corners of the screen, And theoretically, the current flowing through the four electrodes is proportional to the distance from the finger to the four corners. The controller accurately calculates the proportions of the four currents, Get the location. Can reach 99% accuracy, It has a response speed of less than 3ms.

Capacitive touch screen

 

Projected Capacitive PanelThe touch technology of the projected capacitive panel The projected capacitive touch screen is to etch different ITO conductive circuit modules on two layers of ITO conductive glass coating. The etched patterns on the two modules are perpendicular to each other, You can think of them as sliders that continuously change in the X and Y directions. Since the X and Y structures are on different surfaces, A capacitor node is formed at the intersection. A slider can be used as a driveline, The other slider is used as a detection line. When the current passes through one of the wires in the driveline, If there is a signal of capacitance change from the outside, Then it will cause the change of the capacitance node on another layer of wire. The change of the detected capacitance value can be measured by the electronic circuit connected to it, Then it is converted into a digital signal by the A/D controller for the computer to perform arithmetic processing to obtain the (X, Y) axis position, And then achieve the purpose of positioning.
When operating, The controller successively supplies current to the driveline, Therefore, a specific electric field is formed between each node and the wire. Then scan the sensing line column by column to measure the capacitance change between its electrodes, So as to achieve multi-point positioning. When a finger or touching medium approaches, The controller quickly detects the change in capacitance between the touch node and the wire, Then confirms the location of the touch. This kind of shaft is driven by a set of AC signals, The response across the touch screen is sensed by electrodes on the other axis.Users call this ‘cross-over’ induction,It can also be called projected induction.The sensor is plated with X,ITO pattern on Y axis,When the finger touches the touch screen surface,The capacitance value below the touch point increases according to the distance of the touch point.Continuous scanning on the sensor detects the change in capacitance value,The control chip calculates the touch point and reports it to the processor.

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