Generally speaking, when we operate the touch screen, we must first touch the touch screen installed in the front of the display with a finger or other object, and then the system locates and selects information input according to the position of the icon or menu touched by the finger. The touch screen is composed of a touch detection component and a touch screen controller; the touch detection component is installed in front of the display screen to detect the user's touch position, and then send it to the touch screen controller; and the main function of the touch screen controller is to receive touches from the touch point detection device Information, and convert it into contact coordinates, and then send it to the CPU, it can also receive the command sent by the CPU and execute it. In order to operate the touch screen efficiently, it is necessary for us to first understand the working principles of various types of touch screens:
1. The working principle of resistive touch screen
The working principle of the resistive touch screen is mainly through the principle of pressure sensing to realize the operation and control of the screen content. The screen body of this touch screen is a multi-layer composite film that matches the surface of the display. The first layer is glass or plexiglass. The bottom layer, the second layer is the barrier layer, and the third layer is the surface layer of multi-element resin. The surface is also coated with a transparent conductive layer, and the surface is covered with a hardened, smooth and scratch-resistant plastic layer. The conductive layer and the glass layer sensor on the surface of the multi-element resin are separated by many tiny interlayers; when the current passes through the surface layer and touches the surface layer lightly, it touches the bottom layer, and the controller reads out the corresponding current from the four corners at the same time. And calculate the distance of the finger position. This touch screen uses two highly transparent conductive layers to form a touch screen, and the distance between the two layers is only 2.5 microns. When a finger touches the screen, the two conductive layers that are usually insulated from each other make a contact at the touch point. Because one conductive layer is connected to a 5V uniform voltage field in the Y-axis direction, the voltage of the detection layer changes from zero to zero. Non-zero, after the controller detects this connection, it performs A/D conversion and compares the voltage value obtained with 5V to obtain the Y-axis coordinate of the touch point, and the X-axis coordinate is obtained by the same reason. It is the most basic principle common to all resistive technology touch screens.
2. Surface acoustic wave touch screen
The working principle of surface acoustic wave touch screen is mainly based on the principle that mechanical waves propagate on the surface of a certain medium. This kind of touch screen transmits sound waves through sound wave generators pasted on the surface of the screen, and receives them through sound wave receivers. Acoustic waves are used to transmit signals to the touch screen through an acoustic wave reflector. The acoustic wave generator can send a high-frequency sound wave across the surface of the screen. When a finger touches the screen, the sound wave on the contact is blocked and the received signal is converted into coordinates. Therefore, the coordinate position of the specific touch point is determined. The controller can measure the pressure of the touch screen by how much energy is absorbed by the sound wave, and return the coordinate value that reflects the pressure of the touch at the same time. On the surface of the surface acoustic wave touch screen, the X-direction and Y-direction acoustic wave transmitters and acoustic wave receivers are pasted, and 45-degree stripes of reflected sound waves are engraved around the glass screen. The controller produces a 5.53MHZ signal, which is transmitted to the transmitting transducer through the cable, and the piezoelectric transmitting transducer converts it into ultrasonic energy and emits it. After the two reflections of the reflection fringe, it propagates to the receiving transducer, and is converted into an electric signal to be transmitted to the controller. Since the surface acoustic wave touch screen is composed of a touch screen, a sound wave generator, a reflector and a sound wave receiver, especially the sound wave sensor is not affected by environmental factors such as temperature and humidity, with extremely high resolution, excellent scratch resistance and long life; High light transmittance, can maintain clear and bright image quality; no drift, only need to be corrected once during installation; there is a third axis (ie pressure axis) response, which is most suitable for use in public places.
3. Capacitive touch screen
The capacitive touch screen is a transparent special metal conductive material attached to the glass surface. This kind of inductive touch screen consists of five layers. The first layer is a glass bottom layer, the second layer is a conductive layer, the third layer is a glass sensing layer, the fourth layer is an anti-reflective matte or bright surface layer, and the fifth layer is an anti-noise protective layer. When a finger touches the surface of the capacitive touch screen, the sensing method is that the voltage is connected to the four corners of the glass layer, and the voltage is spread across the glass layer through the electrodes and a constant voltage electric field is established. At the same time, the capacitance of the contact will change. The frequency of the oscillator connected to it changes, and the touch position can be determined to obtain information by measuring the frequency change. Since the capacitance varies with temperature, humidity, or grounding conditions, its stability is poor and it tends to drift. In addition, when the surface layer is touched, current is collected from the four corners of the glass layer, and the controller calculates the distance from the current to the finger position to determine the exact position of the touch.
4. Infrared touch screen
The working principle of this kind of infrared touch screen is relatively simple. You only need to add a light spot distance frame to the display, without coating or connecting to the controller on the surface of the screen, and then arrange infrared emitters on the four sides of the light spot distance frame. With the receiving and sensing components, an infrared detection network is formed on the surface of the screen. When any touch object touches a certain point of the screen, it will block the two infrared rays passing through the position, and the computer can instantly calculate the position of the touch point. The infrared touch screen is not interfered by current, voltage and static electricity, and is suitable for some harsh environmental conditions. Since the infrared touch screen has no capacitive charging and discharging process during operation, the response speed is faster than the capacitive type, but the resolution is lower.
