What is the principle and working of touch screen?

The classification and working principle of touch screens. Nowadays, touch screen technology is widely used in daily life, from computers to mobile terminals, as well as in various shopping malls, hospitals, libraries, stations, and other places. The touch screens used in different scenarios and devices are also different, and the working principle of different touch screens is also different, So next, let's take everyone to understand the classification of touch screens and the working principles of touch screens.

Classification of touch screens:
The touch screen is divided into capacitive touch screen, surface acoustic wave touch screen, infrared touch screen and resistive touch screen

The working principle of the touch screen:
1. Working principle of capacitive touch screen
A capacitive touch screen is a special metal conductive material that is transparent and coated on the surface of glass. This inductive touch screen consists of five layers. The first layer is the bottom layer of glass, the second layer is the conductive layer, the third layer is the glass sensing layer, the fourth layer is the anti reflection fog or bright surface layer, and the fifth layer is the anti noise protection layer. When a finger touches the surface of a capacitive touch screen, the sensing method is to connect the voltage to the four corners of the glass layer, and spread the voltage through the electrodes to establish an unchanged voltage electric field. At the same time, the capacitance of the contacts will change, causing the frequency of the oscillator connected to it to change. By measuring the frequency change, the position of the touch mode can be determined to obtain information. Due to the variation of capacitance with temperature, humidity, or grounding conditions, its stability is poor and often leads to drift. In addition, when the surface layer is touched, the current converges from the four corners of the glass layer, and the controller calculates the distance between the current and the position of the finger to determine the accurate position of the touch.

2. Working principle of surface acoustic wave touch screen
The working principle of the surface acoustic wave touch screen is mainly based on the principle of mechanical wave propagating on the surface of a certain medium. This and the touch screen transmit sound waves through acoustic generators pasted at three corners of the screen surface, receive sound waves through acoustic receivers, and send time signals to the touch screen through acoustic reflectors, where the acoustic generator can send a high-frequency sound wave across the screen surface, When the finger touches the screen, the sound waves on the contact are blocked, converting the received signal into coordinate values to determine the specific coordinate position of the touch point. The controller can measure the magnitude of the touch screen pressure by absorbing the energy of the sound waves, and return the coordinate value reflecting the magnitude of the touch pressure. On the surface of the surface acoustic wave touch screen, acoustic wave transmitters and receivers in X and Y directions are pasted. Around the glass screen, there are 45 degree stripes reflecting acoustic waves. The controller produces a 5.53MHZ signal, which is transmitted through a cable to the transmitting transducer, which converts it into ultrasonic energy and emits it. After two reflections of the reflection stripes, it propagates to the receiving transducer and is converted into an electrical signal specifically for the controller. Because the surface acoustic wave touch screen is composed of touch screen, acoustic generator, reflector and acoustic receiver, especially the acoustic sensor is not affected by temperature, humidity and other environmental factors, with high resolution, excellent scratch resistance and long service life; High light transmittance, able to maintain clear and bright image quality: no shifting, only one correction is required during installation; There is a third axis (i.e. pressure axis) response, which is most suitable for use in public places.

3. Working principle of infrared touch screen
The working principle of this infrared touch screen is relatively simple. It only needs to add a light point distance frame on the display, without the need for coating or connecting controllers on the screen surface. Then, infrared emission and reception sensing elements are arranged on the four sides of the light point distance frame, forming an infrared detection network on the screen surface. When any touch object touches a certain point on the screen, it will block the horizontal and vertical infrared rays passing through that position, The computer can immediately calculate the position of the touch points. The infrared touch screen is not affected by current, voltage, and static electricity, and is suitable for certain harsh environmental conditions. Due to the fact that infrared touch screens do not have a capacitor charging and discharging process during operation, their response speed is faster than that of capacitive touch screens, but their resolution is lower.

4. The working principle of resistive touch screen
The working principle of a resistive touch screen is mainly achieved through the principle of pressure sensing to operate and control the screen content. This type of touch screen body is a multi-layer composite film that is very compatible with the display surface. The first layer is a glass or organic glass bottom layer, the second layer is a partition layer, and the third layer is a multi resin surface layer. The surface is also coated with a transparent conductive layer, which is then covered with an outer surface that has been hardened Smooth and scratch resistant plastic layer. The conductive layer and glass layer sensors on the surface of the polyunsaturated fatty acid are separated by many small compartments:
When the current passes through the surface layer and lightly touches the surface layer, it contacts the bottom layer. The controller simultaneously reads the corresponding current from the four corners and calculates the distance between the finger positions. This type of touch screen utilizes two highly transparent conductive layers to form a touch screen, with a distance of only 2.5 micrometers between the two layers. When touching the screen with fingers, the two conductive layers that are usually insulated from each other make a contact at the touch point. As 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 compares the obtained voltage value with 5V to obtain the Y-axis coordinates of the touch point, and similarly, the X-axis coordinates are obtained, This is the most fundamental principle shared by all resistive technology touch screens.