LCD touch screen principle

LCD touch screen principle

The first feature of the touch screen: transparency, which directly affects the visual effect of the touch screen. There is a problem of transparency. Infrared technology touch screen and surface acoustic wave touch screen are separated by only a layer of pure glass, and transparency can be regarded as the best. Many touch screens are multi-layered composite films. It is not enough to summarize its visual effects by being transparent. It should include at least four characteristics: transparency, color distortion, reflectivity and clarity, and can be further divided, such as reflective The degree includes the degree of specular reflection and the degree of diffraction reflection, but the diffraction reflection on the surface of our touch screen has not reached the degree of CD disc. For users, these four measures are basically enough.

Resistive touch screen

The screen body of the resistive touch screen is a multilayer composite film, with a layer of glass or plexiglass as the base layer, coated with a transparent conductive layer (ITO film) on the surface, and covered with a hardened surface, smooth and scratch-resistant Plastic layer. Its inner surface is also coated with a layer of ITO, and there are many small (less than one thousandth of an inch) transparent isolation points between the two conductive layers to separate them. Since one of the conductive layers is connected to a 5V uniform voltage field in the Y-axis direction, the voltage of the detection layer changes from zero to non-zero. After the controller detects this connection, it performs A/D conversion and converts the obtained voltage When the value is compared with 5V, the Y-axis coordinate of the touch point can be obtained. Similarly, the X-axis coordinate can be obtained. This is the most basic principle common to all resistive technology touch screens.

The key to resistive touch screens lies in material technology. Commonly used transparent conductive coating materials are: ITO, indium oxide, weak conductors. ITO is the main material used in all resistance technology touch screens and capacitive technology touch screens. In fact, the working surface of resistance and capacitance technology touch screens is ITO coating.

Nickel-gold coating is a nickel-gold coating material with good ductility. Due to frequent touching of the outer conductive layer, the purpose of using a good ductile nickel-gold material is to extend the service life, but the process cost is relatively high. Although the nickel-gold conductive layer has good ductility, it can only be used as a transparent conductor. It is not suitable for the working surface of the resistive touch screen because of its high conductivity and the metal is not easy to be very uniform in thickness. It is not suitable for the voltage distribution layer and can only be used as a probe. Floor.

The base layer of the five-wire resistive technology touch screen adds the voltage fields in both directions to the conductive working surface of the glass through the precision resistance network. We can simply understand that the voltage fields in the two directions are applied to the same working surface in a time-sharing manner. The outer nickel-gold conductive layer is only used as a pure conductor, and the position of the touch point can be measured by the method of detecting the X-axis and Y-axis voltage values of the inner layer ITO contact point after touching. The five-wire resistive touch screen requires four leads in the inner layer of ITO, and only one conductor in the outer layer. There are 5 lead wires in the touch screen.

Capacitive touch screen

The capacitive technology touch screen is a four-layer composite glass screen, The inner surface and the interlayer of the glass screen are each coated with an ITO conductive layer, and the outermost layer is a protective layer of silica glass with a thickness of only 0.0015 mm. The inner layer of ITO is used as a shielding layer to ensure a good working environment, and the sandwich ITO coating is used as a working layer for detection and positioning, and four electrodes are drawn on the four corners or four sides.

Surface acoustic wave touch screen

The touch screen part of the surface acoustic wave touch screen can be a flat, spherical or cylindrical glass plate, which is installed in front of the CRT, LED, LCD or plasma display screen. This glass plate is just a piece of pure strengthened glass, which is different from other types of touch screen technology in that it does not have any film or overlay. The transmitting transducer converts the electrical signal sent by the controller through the touch screen cable into sound wave energy and transmits it to the left surface, and then a set of precision reflection stripes under the glass plate reflects the sound wave energy into an upward uniform surface for transmission, and the sound wave energy passes through On the surface of the screen, the reflection fringe on the upper side gathers into a rightward line and propagates to the X-axis receiving transducer. The receiving transducer converts the returned surface acoustic wave energy into electrical signals. The surface acoustic wave touch screen also has the characteristics of anti-riot, clear and beautiful, fast response speed, and stable performance.