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How Capacitive Touch displays Work

Views: 207     Author: Reshine     Publish Time: 2023-07-12      Origin: Site


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How Capacitive Touch displays Work

Principle Overview

Multi-touch is made possible by capacitive touch displays, which rely on electrodes to boost mutual capacitance. To put it simply, the screen is divided into blocks, with a group of mutual capacitance modules set up in each area to work independently. This allows the capacitive screen to detect independently each region's contact situation, process it, and then easily implement multi-touch.

Capacitive technology touch panel CTP (Capacity Touch Panel) the use of human current sensing to work. The capacitive screen is a four-layer composite glass screen, the inner surface of the glass screen and sandwich each coated with a layer of ITO (nano indium tin metal oxide), the outermost layer is only 0.0015mm thick silica glass protective layer, sandwich ITO coating for the work surface, four corners lead to four electrodes, the inner ITO for the screen layer to ensure that the working environment.

When the user touches the capacitive screen, due to the human body's electric field, the user's finger and the working surface form a coupling capacitance. Because the work surface is connected to a high-frequency signal, the finger absorbs a very small current, the current from the screen on the four corners of the electrode outflow. And theoretically, the current flowing through the four electrodes is proportional to the distance from the finger to the four corners, and the controller derives the position through the precise calculation of the proportion of the four currents. It can achieve 99% accuracy with a response speed of less than 3ms.

Projected Capacitive Panel

Projected capacitive panel touch technology projected capacitive touch screen is in two layers of ITO conductive glass coating etched on the different ITO conductive line modules. The patterns etched on the two modules are perpendicular to each other and can be thought of as slider bars that change continuously in the X and Y directions. Since the X and Y architectures are on different surfaces, their intersection forms a capacitive node. One of the sliders can be treated as a drive line and the other as a detect line.

When the current passes through one of the wires in the drive line. If there is an external signal of change in capacitance, then it causes a change in the capacitance node on the other layer of wires. Detecting changes in capacitance can be measured through the electronic circuit connected to it, and then converted into digital signals by the A/D controller for the computer to do arithmetic processing to obtain the (X, Y) axis position, and thus achieve the purpose of positioning.

During operation, the controller successively supplies current to the drive wires, thus creating a specific electric field between the nodes and the wires. The sensor lines are then scanned one by one to measure the change in capacitance between the electrodes to achieve multi-point localization. When a finger or touch medium is approached, the controller quickly measures the change in capacitance between the touch node and the wire to confirm the position of the touch.

A set of AC signals power one axis, and electrodes on the other axes detect the response across the touch screen. 'Traversal' sensing—also known as projective sensing—is the term used by users to describe this. The X and Y axes of the sensor are covered with an ITO pattern. When a finger touches the touch screen's surface, the capacitance value beneath the touch point rises following the touch point's proximity. The sensor detects this change in capacitance value through continuous scanning, and the control chip calculates the touch point and sends it back to the processor.

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