1. Classification of Touch Screen:

Touch screen is divided into capacitive touch screen, surface acoustic wave touch screen, infrared touch screen, resistive touch screen.

2. The Working Principle of Touch Screen:

Capacitive Touch Screen

Capacitive touch screen is a transparent layer of special metal conductive material on the surface of the glass, this induction touch screen has five layers. The first layer is the bottom layer of glass, the second layer for the conductive layer, the third layer of glass induction layer, the fourth layer of anti-reflective matte or bright surface layer, the fifth layer of anti-noise protection layer. When the finger touches the surface of the capacitive touch screen, the induction method for the voltage connected to the four corners of the glass layer, through the electrodes will be scattered in the glass layer and establish nothing to change the voltage electric field, while the capacitance of the contact will change, making the oscillator frequency connected to it changes, by measuring the frequency change can determine the touch position to obtain information. Because the capacitance varies with temperature, humidity or grounding conditions, so its stability is poor and often produces drift. In addition when the surface layer is touched, the current from the four corners of the glass layer gathered, the controller calculates the distance of the current to the location of the finger, so as to determine the exact location of the touch.

Surface Acoustic Wave Touch Screen

Surface acoustic wave touch screen works mainly based on the principle of mechanical wave propagation on the surface of a medium, the touch screen through the acoustic wave generator pasted on the screen surface at three corners of the acoustic wave emission work, through the acoustic wave receiver to receive acoustic waves, and then through the acoustic wave reflector is responsible for transmitting signals to the touch screen, where the acoustic wave generator can send a high-frequency acoustic waves across the screen surface, when the finger Touch the screen, the contacts on the sound waves that are blocked, the received signal is converted into coordinate values, thereby determining the coordinate location of the specific touch point, where the controller through the amount of acoustic energy absorption, you can measure the size of the touch screen pressure, while returning the coordinate value of the size of the response touch pressure. On the surface of the surface acoustic wave touch screen, the X-direction and Y-direction acoustic wave transmitter and acoustic wave receiver are pasted, and around the glass screen, 45-degree stripes of reflected acoustic waves are inscribed. The controller produces 5.53MHZ signal, which is transmitted to the transmitting transducer through the cable, and the piezoelectric transmitting transducer converts it into ultrasonic energy and sends it out. After two reflections of the reflective stripe, it propagates to the receiving transducer and converts it into an electrical signal to the controller. As the surface acoustic wave touch screen is composed of touch screen, acoustic wave generator, reflector and acoustic wave receiver, especially the acoustic wave sensor is not affected by temperature, humidity and other environmental factors, extremely high resolution, excellent scratch resistance, long life; high light transmission rate, can maintain a clear and translucent image quality; no drift, only need to install when - a correction; there is a third axis response, the most suitable for public places to use.

Infrared Touch Screen

The working principle of this infrared touch screen is relatively simple, just add the light point distance frame on the display, no need to add a coating on the surface of the screen or connected to the controller, and then arranged on all sides of the light point distance frame infrared transmitting and receiving sensing elements on the screen surface, forming an infrared detection network, any touch object touching the screen at a certain point, it will block the horizontal and vertical two infrared rays passing through the location, the computer Then you can instantly calculate the location of the touch point. Infrared touch screen is not subject to current, voltage and static interference, suitable for certain harsh environmental conditions. As infrared touch screen in the work without capacitive charging and discharging process, the response speed is faster than capacitive, but the resolution is lower.

Resistive Touch Screen

Resistive touch screen works mainly through the principle of pressure sensing to achieve the operation and control of the screen content, this touch screen body part is a multi-layer composite film with the display surface is very compatible, including the first layer of glass or plexiglass bottom layer, the second layer for the spacer, the third layer of multi-resin surface, the surface is also coated with a transparent conductive layer, covered with a layer of the outer surface of the hardened treatment The third layer is a polyresin surface layer, which is also coated with a transparent conductive layer and covered with a plastic layer with a hardened outer surface, smooth and scratch-resistant. The conductive layer and the glass layer on the surface of the multi-lipid surface of the sensor is separated by many tiny partitions;

The current passes through the surface layer, and when the touch surface layer is pressed down, it touches the bottom layer, and the controller simultaneously reads the proportional current from the four corners and calculates the distance of the finger position. This touch screen utilizes two highly transparent conductive layers to form the touch screen, the distance between the two layers is only 2.5 microns. When the finger touches the screen, the usual mutual insulation of the two conductive layers in the location of the touch point has a contact, because one of the conductive layer connected to the Y-axis direction of the 5V uniform voltage field, making the detection layer of the voltage from zero to non-zero, the controller detects this connection, A/D conversion, and the voltage value obtained compared with 5V, you can get the Y-axis coordinates of the touch point, the same reason that the X-axis coordinates, which is the most basic principle common to all resistive technology touch screen.