The main types of touch screen differences and functions
The main type of touch screen
According to the working principle of the touch screen and the medium for transmitting information, we divide the touch screen into four types, which are resistance type, capacitance induction type, infrared type and surface acoustic wave type. Each type of touch screen has its own advantages and disadvantages, to understand the kind of touch screen suitable for the occasion, the key is to understand the working principle and characteristics of each type of touch screen technology. The following is a brief introduction to the various types of touch screens mentioned above:
1, resistive touch screen
The touch screen uses pressure sensing for control. The main part of the resistance touch screen is a resistance film screen that is very compatible with the surface of the display, which is a multi-layer composite film, which takes a layer of glass or hard plastic plate as the base layer, and the surface is coated with a layer of transparent metal oxide (transparent conductive resistance) conductive layer. It is then covered with an outer, hardened, smooth, anti-rub plastic layer, and its inner surface is also coated with a coating, and between them there are many small (less than 1/1000 inch) transparent isolation points separating the two conductive layers. When the finger touches the screen, the two conductive layers are in contact at the touch point, the resistance changes, and the signal is generated in the X and Y directions, and then sent to the touch screen controller. The controller detects this contact and calculates the position of (X, Y), then operates in a manner that simulates a mouse. This is the most basic principle of resistive technology touch screen. The key to the resistive touch screen is material technology, and the commonly used transparent conductive coating materials are:
A, ITO, indium oxide, weak conductor, characteristic is that when the thickness drops below 1800 angms (angms =10-10 meters), it will suddenly become transparent, and the light transmittance is 80%, and then the light transmittance decreases, and rises to 80% when the thickness is 300 angms. ITO is the main material used by all resistive technology touch screens and capacitive technology touch screens, in fact, the working surface of resistive and capacitive technology touch screens is ITO coating.
B, nickel gold coating, the outer conductive layer of the five-wire resistance touch screen uses a malleable nickel gold coating material, the outer conductive layer due to frequent touch, the use of malleable nickel gold material is intended to extend the service life, but the process cost is relatively high. Although the nickel gold conductive layer is good in ductility, it can only be used as a transparent conductor, and is not suitable for use as the working surface of the resistance touch screen, because it has high conductivity, and the metal is not easy to achieve a very uniform thickness, it is not suitable for voltage distribution layer, and can only be used as a probe layer.
1.1 Four-wire resistance screen
The two transparent metal layers of the four-wire resistance analog technology operate with a constant voltage of 5V in each layer: one vertical and one horizontal. A total of four cables are required. Features: High resolution, high speed transmission response. Surface hardness treatment, reduce scrapes, scratches and chemical treatment. With smooth surface and fog surface treatment. One correction, high stability, never drift.
1.2 Five-wire resistance screen
The base layer of the five-wire resistance technology touch screen adds the voltage field in two directions to the conductive working surface of the glass through the precision resistance network, we can simply understand that the voltage field in two directions is added to the same working surface, and the outer nickel gold conductive layer is only used as a pure conductor. The position of the touch point is measured by measuring the voltage values of X and Y axis of the inner ITO contact point. The inner ITO of the five-wire resistance touch screen needs four leads, the outer ITO is only one conductor, and the touch screen has a total of five leads. Features: High resolution, high-speed transmission response. High surface hardness, reduce scrapes, scratches and chemical treatment. The same point contact 30 million times can still be used. Conductive glass is the medium of the substrate. One correction, high stability, never drift. The five-wire resistive touch screen has the disadvantages of high price and high environmental requirements
1.3 Limitations of resistive screens
Whether it is a four-wire resistive touch screen or a five-wire resistive touch screen, they are a completely isolated working environment for the outside world, not afraid of dust and water vapor, it can be touched with any object, can be used to write and draw, more suitable for industrial control fields and limited people in the office. The common disadvantage of the resistive touch screen is that the outer layer of the composite film is made of plastic material, and people who do not know that too much force or touch with a sharp instrument may scratch the entire touch screen and lead to scrap. However, within the limit, the scratch will only hurt the outer conductive layer, and the scratch of the outer conductive layer is not relevant for the five-wire resistance touch screen, and it is fatal for the four-wire resistance touch screen.
2, capacitive touch screen
2.1 Capacitive technology touch screen
Is the use of the human body’s current induction to work. The capacitive touch screen is a four-layer composite glass screen, the inner surface of the glass screen and the interlayer are coated with a layer of ITO, the outermost layer is a thin layer of silica glass protective layer, the interlayer ITO coating as the working surface, four electrodes are drawn from the four corners, and the inner ITO layer is the shielding layer to ensure a good working environment. When the finger touches the metal layer, due to the human electric field, the user and the touch screen surface form a coupling capacitor, for high frequency current, the capacitor is a direct conductor, so the finger draws a small current from the contact point. The current flows from the electrodes on the four corners of the touch screen, and the current flowing through the four electrodes is proportional to the distance between the fingers and the four corners, and the controller obtains the position of the touch point through the accurate calculation of the ratio of the four currents.