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Component classification of Capacitive touch-screen



The type of capacitive touch screen is divided into two types: surface capacitive touch screen and projective capacitive touch screen.

1. Surface Capacitive touch-screen:

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

2. Projected Capacitive touch screen: The projected Capacitive touch screen has a multi-finger touch function.

These two capacitive touch screen have high transmittance, fast reaction speed, long life and other advantages, the disadvantage is: with temperature, humidity changes, capacitance value will change, resulting in poor stability, often drift phenomenon, need to constantly proofread the screen, and can not wear ordinary gloves touch positioning. Projection capacitive screen can be divided into two types of self-capacitive screen and mutual capacitive screen, the more common mutual capacitance screen for example, the internal drive electrode and the receiving electrode composition, the driving electrode emits low voltage high-frequency signal projection to the receiving electrode to form a stable current, when the human body in contact with the capacitive screen, the finger and capacitive screen formed an equivalent capacitance The high-frequency signal can flow through this equivalent capacitance to the ground, so that the receiving end of the charge amount is reduced, and when the closer the finger to the transmitter, the more obvious the charge decrease, and finally according to the receiving end of the current intensity to determine the touch point. a transverse and longitudinal electrode array is made with Ito on the glass surface, and these transverse and longitudinal electrodes form the capacitance, which is usually referred to as self-capacitance, which 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 screen body capacitance to increase the capacity of the screen. In the touch detection, the self-capacitive screen in turn detects the transverse and longitudinal electrode arrays, respectively, according to the change of capacitance before and after the touch, determine the horizontal and vertical coordinates, and then combined into a planar touch coordinates. The self-capacitance scanning method is equivalent to projecting the touch points on the touchscreen to the x-axis and y-axis respectively, then calculating the coordinates in the x-axis and y-axis respectively, and finally combining the coordinates of the touch points. [5] If it is a single touch, the x-axis and y-axis projections are unique, the combined coordinates are unique if there is a two-point touch on the touchscreen and the two points are not in the same X-direction or the same y-direction, there are two projections in the X and Y direction respectively, the combination of 4 coordinates. Obviously, only two coordinates are true, the other two are commonly known as "ghost points". Therefore, the self-capacitive screen cannot achieve true multi-touch. [5] Mutual capacitive screen is also used in the glass surface with Ito to make transverse electrodes and longitudinal electrodes, which differs from the self-capacitive screen is that the two groups of electrodes cross the place will be formed capacitance, that is, the two groups of electrodes constitute a capacitance of the Poles respectively. 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 the mutual capacitance is detected, the transverse electrodes emit an excitation signal in turn, and all the electrodes in the longitudinal direction receive the signal simultaneously, so that the capacitance of all transverse and longitudinal electrode junctions can be obtained, that is, the capacitance of the two-dimensional plane of the whole touch screen. The coordinates of each touch point can be calculated according to the two-dimensional capacitance variation data of the touchscreen. As a result, even with multiple touch points on the screen, you can calculate the true coordinates of each touch point. [5] The advantages of the mutual capacitive screen is less wiring, but also to identify and distinguish between multiple contacts between the difference, self-capacitive screen can also be sensing a plurality of contacts, but because the signal itself is blurred, it can not be differentiated. In addition, the sensing scheme of the mutual capacitive screen also has the advantage of fast speed and low power consumption, because it can measure all the nodes on a driving line simultaneously, so it can reduce the number of acquisition cycles by 50%. This double-electrode structure has the function of self-shielding external noise, which can improve signal stability at a certain power level.

[5] In any case, the touch position is determined by measuring the amount of signal change between the X-electrode and the Y-electrode, and then using the mathematical algorithm to process these changed signal levels to determine the touch point xy coordinates.