Weiluntong touch screen - capacitive touch screen component classification introduction

The types of capacitive touch screens are divided into two types: surface capacitive touch screens and projected capacitive touch screens.

Surface capacitive touch screen

Commonly used is the surface capacitive touch screen, which has a simple working principle, low price, and simple circuit design, but it is difficult to achieve multi-touch.

Projected capacitive touch screen

The projected capacitive touch screen has the function of multi-finger touch. These two capacitive touch screens have the advantages of high light transmittance, fast response speed and long life, but the disadvantages are: with the change of temperature and humidity, the capacitance value will change, resulting in poor working stability, and there will often be drift phenomenon, the screen needs to be proofread frequently, and ordinary gloves can not be worn for touch positioning.

The projected capacitive screen can be divided into two types: self-capacitive screen and mutual capacitive screen, the more common mutual capacitance screen is an example, the internal is composed of a driving electrode and a receiving electrode, the driving electrode emits a low-voltage high-frequency signal and projects it to the receiving electrode to form a stable current, when the human body touches the capacitive screen, due to the grounding of the human body, the finger and the capacitive screen form an equivalent capacitance, and the high-frequency signal can flow into the ground wire through this equivalent capacitance, so that the amount of charge received by the receiving end decreases, and when the finger is closer to the transmitter, the charge decreases more obviously, Finally, the point touched is determined according to the current intensity received by the receiving end.

The transverse and longitudinal electrode arrays are made with ITO on the glass surface, and these transverse and longitudinal electrodes form capacitance with the ground respectively, which is commonly referred to as 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 capacitance of the screen, so that the capacitance of the screen will increase.

In touch detection, the transverse and longitudinal electrode arrays are detected sequentially by the capacitive screen, and the transverse coordinates and longitudinal coordinates are determined respectively according to the change of capacitance before and after touching, and then combined into a plane of touch coordinates. The self-capacitive scanning method is equivalent to projecting the touch points on the touch screen to the X and Y axis directions respectively, and then calculating the coordinates in the X and Y directions respectively, and finally combining them into the coordinates of the touch points.

If there are two touches on the touch screen and these 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 there are two projections in the X and Y directions, and 4 coordinates are combined. Obviously, only two coordinates are real, and the other two are commonly known as "ghost points". As a result, self-capacitive screens do not enable true multi-touch.

The difference between the mutual capacitance screen and the self-capacitance screen is that the two groups of electrodes will form a capacitance where they intersect, that is, these two groups of electrodes constitute the two poles of the capacitor respectively. When a finger touches the capacitive screen, it affects the coupling between the two electrodes near the touch point, thus changing the capacitance between the two electrodes. When detecting the size of the mutual capacitance, the transverse electrodes send out an excitation signal in turn, and all the transverse electrodes receive the signal at the same time, so that the capacitance value of the intersection point of all transverse and longitudinal electrodes can be obtained, that is, the capacitance of the two-dimensional plane of the entire touch screen. According to the two-dimensional capacitance change 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, the true coordinates of each touch point can be calculated.

The advantage of the mutual capacitive screen is that there is less wiring, and it can identify and distinguish the difference between multiple contacts at the same time, and the self-capacitive screen can also sense multiple contacts, but because the signal itself is blurred, it cannot be distinguished. In addition, the sensing solution of the mutual capacitive screen has the advantage of high speed and low power consumption, because it can measure all nodes on a drive line at the same time, thus reducing the number of acquisition cycles by 50%. This dual-electrode structure is self-shielding from external noise and improves signal stability at a certain power level.

In any case, the touch position is determined by measuring the distribution of signal changes between the X and Y electrodes, and then these changed signal levels are processed using mathematical algorithms to determine the XY coordinates of the touch point.

Weiluntong touch screen - capacitive touch screen component classification introduction

Weiluntong touch screen - capacitive touch screen component classification introduction

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