Capacitive touch screen classification

Capacitive screen principle
There are two types of capacitive touch screens: surface capacitive touch screens and projected capacitive touch screens.Surface capacitive touch screen
The surface type capacitive touch screen is commonly used,Its working principle is simple, the price is low, and the designed circuit is simple,But it is difficult to achieve multi-touch.

Capacitive touch screen classification

Projected capacitive touch screen
The projected capacitive touch screen has a multi-finger touch function.Both capacitive touch screens have the advantages of high light transmittance, fast response, and long life.The disadvantage is: as temperature and humidity change,The capacitance value will change,Lead to poor work stability,There is often drift phenomenon,Need to proofread the screen frequently,And do not wear ordinary gloves for touch positioning.
Projected capacitive screens can be divided into two types: self-capacitive screens and mutual-capacitive screens.Take the more common mutual capacitance screen as an example,The inside is composed of driving electrodes and receiving electrodes,The driving electrode sends out 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,Since the human body is grounded,The finger and the capacitive screen form an equivalent capacitance,And high-frequency signals can flow into the ground through this equivalent capacitance,such,The amount of charge received by the receiving end decreases,And when the finger gets closer to the transmitter,The more obvious the charge reduction,Finally, the touched point is determined according to the current intensity received by the receiving end.
Use ITO on the glass surface to make horizontal and vertical electrode arrays,These horizontal and vertical electrodes respectively form a capacitance with the ground,This capacitor is commonly referred to as self-capacitance,That is the capacitance of the electrode to ground.When the finger touches the capacitive screen,The capacitance of the finger will be superimposed on the capacitance of the screen, increasing the capacitance of the screen.

Capacitive touch screen classification

During touch detection,The self-capacitance screen detects the horizontal and vertical electrode arrays in turn,According to the change of capacitance before and after touch,Determine the horizontal and vertical coordinates respectively,Then combine the touch coordinates of the plane.The self-capacitance scanning method is equivalent to projecting the touch points on the touch screen to the X-axis and Y-axis directions respectively.Then calculate the coordinates in the X-axis and Y-axis directions respectively,Finally, the coordinates of the touch point are combined.If it is a single touch,Then the projections in the X-axis and Y-axis directions are unique,The combined coordinates are also unique. If there are two touches on the touch screen 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 real,The other two are commonly known as “ghost spots”.therefore,Self-capacitive screens cannot achieve true multi-touch.
The mutual capacitance screen also uses ITO to make horizontal electrodes and vertical electrodes on the glass surface.The difference between it and the self-capacitive screen is that,A capacitance will be formed where the two sets of electrodes cross,That is, these two groups of electrodes respectively constitute the two poles of the capacitor.When the finger touches the capacitive screen,Affects the coupling between the two electrodes near the touch point,Thereby changing the capacitance between the two electrodes.When detecting the mutual capacitance,The lateral electrodes send out excitation signals in turn,All longitudinal electrodes receive signals at the same time,In this way, the capacitance value of the intersection of all horizontal and vertical 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,It can also calculate the true coordinates of each touch point.

Capacitive touch screen classification

The advantage of the mutual capacitance screen is that there is less wiring,And it can identify and distinguish the differences between multiple contacts at the same time,The self-capacitance screen can also sense multiple contacts,However, due to the blurring of the signal itself,It cannot be distinguished.In addition,The sensing solution of the mutual capacitance screen also has the advantages of fast speed and low power consumption.Because it can measure all nodes on a drive line at the same time,Therefore, the number of acquisition cycles can be reduced by 50%.This two-electrode structure has the function of self-shielding external noise,The signal stability can be improved at a certain power level.
Under any condition,The touch position is determined by measuring the distribution of the signal change between the X electrode and the Y electrode.Then mathematical algorithms are used to process these changed signal levels,To determine the XY coordinates of the touch point.

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