The working principle of capacitive touch-screen

- Jul 19, 2018-

Principle Overview´╝Ü

Capacitive screen to achieve multi-touch, relying on the increase of mutual capacitance of the electrodes, simply put, is the screen block, in each area set up a group of mutual capacitance modules are independent work, so the capacitive screen can be independently detected in each area of the touch, processing, simple to achieve multi-touch. Capacitive Technology The Touch panel CTP (Capacity touchscreen panel) is used to work with the human body's current induction. Capacitive screen is a four-layer composite glass screen, the inner surface and interlayer of the glass screen are coated with Ito (nano indium tin metal oxide), the outermost layer is only 0.0015mm thick silica Glass protection layer, Interlayer Ito coating as working face, four angle leads to four electrodes, inner Ito is screen layer to ensure working environment. When the user touch the capacitive screen, due to the human electric field, the user's fingers and face form a coupling capacitor, because the work surface has high-frequency signal, so the finger to absorb a very small current, this current from the screen of the four angle of the electrodes in the outflow, Theoretically, the current of four electrodes is proportional to the distance from the fingers to the four corners, and the controller obtains the position by the precise calculation of the four current proportions.

can achieve 99% accuracy, with less than 3ms response speed.

projection Capacitor Panel:

The touch Technology of projection capacitor panel projection capacitive touch screen is a different ITO conductive circuit module etched on two layers of ito conductive glass coating. The etched graphics on the two modules are perpendicular to each other and can be viewed as sliding strips of continuous variation in the X and y directions. Because the X and Y architectures are on different surfaces, a capacitance node is formed at the intersection. A slider can be used as a drive line and another slider as a detection line. When the current passes through a wire in the drive line, if there is a signal of capacitance change in the outside, it will cause the change of capacitance node on another layer of conductor.

The detection capacitance value can be measured by the electronic circuit connected with it, and then by A/D controller into the digital signal to allow the computer to do operational processing to obtain (x,y) axis position, and thus reach the location of the target. Operation, the controller has power supply flow to the drive line, so that each node and wire between the formation of a specific electric field. The capacitance variation between the electrodes is then measured by a row-by-column scanning sensing line, thus achieving multiple positioning. When the finger or the touch medium is approaching, the controller quickly measures the capacitance value between the contact node and the conductor, and then confirms the position of the touch. This axis is driven by an AC signal, and the response through the touchscreen is measured by the electrodes on the other axis. Users call this a ' cross ' induction, or a projection-type sensor.

The sensor is plated with an ITO pattern on the x,y axis, and when the finger touches the touch screen surface, the capacitance below the touch point increases according to the proximity of the touch point, the continuous scan on the sensor detects the change of the capacitance value, the control chip calculates the touch point and returns it to the processor.