Capacitive touch screen touch principle - Hitech

Capacitive touch screen provides you with a fast man-machine interface so that it can be used all over the world, and its capacitive touch screen with low power consumption, long service life and smooth operation performance is well received by the market, and various capacitive touch screen products emerge in endlessly. With the advancement of the process and mass production, the cost decreased, and the resistive touch screen was gradually replaced.

Capacitive touch screen touch principle - Hitech

Capacitive touch screen touch principle - Hitech

The surface capacitive touch screen only uses a single layer of ITO, and when the finger touches the surface of the touch screen, a certain amount of charge will move to the human body. In order to recover these lost charges, the four corners of the screen are compensated for the charge, and the amount of charge made up in each direction is proportional to the distance of the touch point, so that the orientation of the touch point can be estimated.

Surface capacitive ITO coatings generally require linearized metal electrodes around the perimeter of the screen to reduce the effect of corner/edge effects on the electric field. There may also be an ITO shield underneath the ITO coating to block out noise. The appearance capacitive touch screen needs to be calibrated at least once before it can be used normally.

Inductive capacitive touch screens are able to penetrate thicker overlays than exterior capacitive touch screens without the need for calibration. Inductive capacitive requires etching different ITO modules in two layers of ITO coating, taking into account factors such as the total impedance of the modules, the impedance of the connecting lines between the modules, and the parasitic capacitance generated at the intersection of the two layers of ITO modules. In addition, in order to detect the touch of a finger, the area of the ITO module must be smaller than the area of the finger, and the length of the diagonal line is generally controlled at 4 mm to 6 mm when using a diamond drawing.

The green and blue ITO modules are located on a double-layer ITO coating, and they can be seen as sliders with continuous changes in the x and y directions, which require separate scanning of the ITO modules in different x and y directions to obtain the orientation of the touch point and the touch track. Between the two layers of ITO coating is PET or glass insulating layer, the latter has good light transmittance, can accept greater pressure, has a high yield, and can be directly plated on the surface of the LCD with a special process, but it is heavier. The thinner the barrier layer, the better the light transmittance, but the greater the parasitic capacitance between the two layers of ITO.

The touch orientation detected by the inductive capacitive touch screen corresponds to the intersection point where the maximum capacitance change value is induced, and the bearing amount is calculated by weighting the signal amount of the different ITO modules on the x-axis or y-axis, and the touch point or track is displayed on the LCD under the touch screen.

When there are two fingers touching (the red two dots), there are two maximums for each axis. At this moment, there will be two possible combinations, and the system will not be able to accurately locate and discriminate. This is what we generally call a mirror point (a blue two-dotted ground).

In addition, there is a liquid crystal screen underneath the touch screen, which is also conductive on the outside, so it generates parasitic capacitance with the nearby ITO-coated ITO module. In order to reduce the effect of parasitic capacitance, it is generally required to leave a certain layer of air between these two layers.

Capacitive touch screen touch principle - Hitech

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