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Why projected capacitive touch screen is the best choice?

Why projected capacitive touch screen is the best choice?

2020-06-03

Touch screen technology is the most acceptable computer input method for ordinary people after keyboard, mouse, tablet, and voice input. Nowadays, the latest touch technology is projected capacitive touch screen technology.


The projected capacitive screen can be divided into two types: self-capacitance screen and mutual capacitance screen. The more common mutual capacitance screen is taken as an example. The interior is composed of a driving electrode and a receiving electrode. Current, when the human body touches the capacitive screen, because 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, so that the amount of charge received by the receiving end is reduced Small, and when the finger is closer to the transmitter, the charge decreases more obviously, and finally the point of touch is determined according to the current intensity received by the receiver.



The horizontal and vertical electrode arrays are made of ITO on the glass surface. These horizontal and vertical electrodes respectively form a capacitance with the ground. This capacitance is commonly called self-capacitance, which 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 body, which increases the capacitance of the screen body.


During touch detection, the self-capacitance screen sequentially detects the horizontal and vertical electrode arrays respectively. According to the change of capacitance before and after the touch, the horizontal and vertical coordinates are determined respectively, and then combined into a planar touch coordinate. The self-capacitance scanning method is equivalent to projecting the touch points on the touch screen to the X-axis and Y-axis directions, and then calculating the coordinates in the X-axis and Y-axis directions, respectively, and finally combining the coordinates of the touch points.


If it is a single point of touch, the projections in the X-axis and Y-axis directions are unique, and the combined coordinates are unique. There are two projections in the X and Y directions, respectively, and 4 coordinates are combined. Obviously, only two coordinates are real, and the other two are commonly known as "ghost points". Therefore, the self-capacitance screen cannot achieve true multi-touch.



Mutual capacitance screen is also made of ITO with horizontal electrode and vertical electrode on the glass surface. The difference between it and self-capacitance screen is that the intersection of two groups of electrodes will form a capacitor, that is, these two groups of electrodes form the two poles of the capacitor. When a finger touches the capacitive screen, it 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 horizontal electrodes send out excitation signals in sequence, and all the vertical electrodes receive the signal at the same time, so that 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, the true coordinates of each touch point can be calculated.


The advantage of mutual capacitance screens is that there is less wiring, and the difference between multiple contacts can be recognized and distinguished at the same time. The self-capacitance screen can also sense multiple contacts, but it cannot be distinguished because the signal itself is blurred. In addition, the sensing scheme of the mutual capacitance screen has the advantages of fast speed and low power consumption. Because it can measure all nodes on one drive line at the same time, it can reduce the number of acquisition cycles by 50%. This two-electrode structure has the function of self-shielding external noise, which can improve signal stability at a certain power level.


In any case, the touch position is determined by measuring the distribution of the signal change between the X and Y electrodes, and then using a mathematical algorithm to process these changed signal levels to determine the XY coordinates of the touch point.


TopOneTech Limited is committed to deeply cultivating advanced capacitive touch solutions, with strong research and development capabilities and production capabilities. As the latest touch solution, capacitive technology is well received by the market. 


Projected capacitive touch screen technology has the following 8 advantages:


1. Capacitive touch screen only needs to touch, and does not need pressure to generate signals.

2. Capacitive touch screens only need to be calibrated once or not at all after production, while resistance technology requires regular calibration.

3. The life of the capacitive scheme will be longer because the components in the capacitive touch screen do not need any movement. In a resistive touch screen, the upper ITO film needs to be thin enough to be flexible, so as to bend down and contact the ITO film below.

4. Capacitive technology is superior to resistive technology in optical loss and system power consumption.

5. The choice of capacitive technology or resistive technology mainly depends on the object touching the screen. If it is a finger touch, a capacitive touch screen is a better choice. The capacitive touch screen can also use a stylus, which requires a special stylus to cooperate.

6. The surface capacitive type can be used for large-size touch screens, and the combination is relatively low, but gesture recognition is currently not supported; projected capacitive type is mainly used for small and medium-sized touch screens (large-size technology has also been broken), and it can support gesture recognition.

7. Projected capacitive technology is wear-resistant, has a long service life, and low maintenance costs for users. Therefore, the overall operating costs of manufacturers can be further reduced.

8. Projected capacitive touch screen can support multi-touch technology, and unlike the resistive touch screen is unresponsive and not easy to wear.


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