Component classification of Capacitive touch screen

- Jul 19, 2018-

Capacitive touch screen types are divided into surface capacitive touch screen and projection capacitive touch screen two kinds.

Surface type Capacitive touch screen:

Commonly used is the surface capacitive touch screen, its working principle is simple, low price, design circuit simple, but difficult to achieve multi-touch control.

Projector Capacitive touch screen: 

The projector Capacitive touch screen has the function of multiple finger touch control.

Both of these capacitive touch screens have high transmittance, quick reaction speed, long life and other advantages, the disadvantage is: with the temperature, humidity changes, capacitance value will change, resulting in poor work stability, often drift phenomenon, the need to regularly proofread the screen, and can not wear ordinary gloves to touch positioning. The projection capacitance screen can be divided into two types: self-capacitance screen and mutual capacitive screen, the more common mutual capacitance screen for example, the internal by the driving electrode and the receiving electrode, the driving electrode issued low voltage high-frequency signal projection to the receiving electrode to form a stable current, when the human body contact with the capacitive screen, because the human body grounding, the finger and the capacitance screen on the formation of an equivalent capacitor, The high-frequency signal can flow through this equivalent capacitor to the ground, so that the receiving end receives less charge, and when the finger is closer to the transmitter, the more obvious the charge decreases, and finally, according to the receiving end of the current intensity to determine the touch point.  On the glass surface, Ito is made into a transverse and longitudinal electrode array, and these transverse and longitudinal electrodes form the capacitance, which is usually called the self capacitance, that is, the capacitance of the electrode to the ground. When the finger touches the capacitive screen, the capacitance of the finger will be superimposed on the panel capacitance to increase the power capacity of the screen body. In the touch detection, the capacitance screen in turn to detect the horizontal and longitudinal electrode array, according to the change of the capacitance before and after the touch, respectively determine the horizontal and longitudinal coordinates, and then combined into the plane of the touch coordinates. Self-capacitance scanning means that the touch point on the touchscreen is projected to the X and Y axes respectively, then the coordinates are computed in the direction of the X and Y axes, and finally the coordinates of the touch point are combined. If it is a single point of touch, then projections in both the X and Y axes are unique, the combination of coordinates is unique if there are two touch points on the touchscreen and the two points are not in the same x direction or the same y direction, then there are two projections in the X and y directions, then 4 coordinates are combined. Obviously, only two coordinates are true, the other two are commonly known as "ghost points." Therefore, the self capacitive screen can not achieve real multi-touch.The mutual capacitance screen is also on the glass surface with Ito to make transverse electrode and longitudinal electrode, it is different from the capacitance screen, the two sets of electrodes will be the intersection of the capacitance, that is, the two groups of electrodes constitute the capacitance of the poles. When the finger touches the capacitive screen, it affects the coupling between the two electrodes near the touch point, thus altering the capacitance between the two electrodes. When detecting the mutual capacitance, the transverse electrode emits the excitation signal in turn, all the electrodes in the longitudinal direction receive the signal at the same time, so the capacitance value of all transverse and longitudinal electrode junctions can be obtained, that is, the capacitance size of the two-dimensional plane of the whole touch screen. According to the two dimensional capacitance variation data of the touch screen, the coordinates of each touch point can be calculated. Therefore, even if there are multiple touch points on the screen, you can calculate the real coordinates of each touch point.The advantages of the mutual capacitance screen is less wiring, but also can identify and distinguish between multiple contacts, since the capacitive screen can also detect multiple contacts, but because the signal itself blurred, it can not be differentiated. In addition, the capacitive screen's induction scheme also has the advantage of fast and low power consumption, because it can measure all the nodes on a drive line at the same time, so it can reduce the number of collection cycles by 50%. The dual-electrode structure has the function of self shielding external noise, and can improve the signal stability at certain power level.In any case, the touch position is determined by measuring the distribution of the signal changes between the x electrode and the y electrode, and then the mathematical algorithm is used to process the altered signal levels to determine the XY coordinates of the touch point.