This is the LCD touch screen
March 27, 2022
Due to its advantages of lightness, small footprint, convenience and flexibility, the LCD touch screen has gradually replaced the keyboard and has become a commonly used human-computer interaction tool for embedded systems. Touch screens can be divided into five categories according to their technical principles: vector pressure sensing, resistive, capacitive, infrared, and surface acoustic wave. Among them, resistive touch screens are used more in embedded systems.
With the increasing number of multimedia information inquiries, people talk about touch screens more and more, because touch screens are not only suitable for the national conditions of multimedia information inquiry in China, but also have many advantages such as sturdiness and durability, fast response, space saving, and easy communication. Using this technology, the user can operate the host by lightly touching the icons or characters on the computer display screen with his finger, which makes the human-computer interaction more straightforward. This technology greatly facilitates those who do not understand computer operation. user. As a newest computer input device, touch screen is the most simple, convenient and natural way of human-computer interaction. It gives multimedia a new look and is a very attractive new multimedia interactive device. The application range of touch screen in my country is very wide, mainly for public information query; such as business query of telecommunications bureau, tax bureau, bank, electric power and other departments; information query on urban streets; in addition, it is used in leading office, industrial control, military command, Video games, ordering songs and dishes, multimedia teaching, real estate pre-sale, etc. In the future, the touch screen will also enter the family.
With the increasing use of computers as a source of information, the touch screen is easy to use, durable, fast response, space saving and other advantages, so that more and more system designers feel that the use of touch screen does have considerable advantages. It has only been a few short years since the touch screen appeared in the Chinese market. This new multimedia device has not been touched and understood by many people, including some system designers who are planning to use the touch screen. From the perspective of the popularization process of touch screens in developed countries and the stage that my country's multimedia information industry is in, this concept is also universal to a certain extent. In fact, the touch screen is a device that transforms multimedia information or control. It gives a new look to the multimedia system and is a very attractive new multimedia interactive device. The system designers in developed countries and the system designers who took the lead in using the touch screen in our country already know clearly that the touch screen is no longer a dispensable thing for computers in various application fields, but an indispensable device. It greatly simplifies the use of computers, even people who don't know anything about computers can still use it at their fingertips, making computers more attractive. It solves the problems that computers in the public information market cannot solve. With the development of cities in the direction of informatization and the penetration of computer networks in national life, information inquiries have been realized by touch screens - the display content can be touched in the form of touch.
The working part of a typical touch screen is generally composed of three parts: two transparent resistive conductor layers, an isolation layer between the two conductors, and electrodes. The resistive conductor layer is composed of resistive materials such as indium tin oxide (ITO) coated on the substrate, the upper substrate is made of plastic, and the lower substrate is made of glass. The barrier layer is a viscous insulating liquid material such as Mylar. The electrode is made of materials with excellent electrical conductivity (such as silver powder), and its electrical conductivity is about 1000 times that of ITO.
For the convenience of operation, people use a touch screen instead of a mouse or a keyboard. When working, 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 the information input according to the icon or menu position touched by the finger. The touch screen is composed of a touch detection part and a touch screen controller; the touch detection part is installed in front of the display screen to detect the user's touch position and receive the touch screen controller; the main function of the touch screen controller is to receive touch points 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 commands sent by the CPU and execute them.
To distinguish the touch screen from the technical principle, it can be divided into five basic categories: vector pressure sensing technology touch screen, resistive technology touch screen, capacitive technology touch screen, infrared technology touch screen, surface acoustic wave technology touch screen. Among them, the vector pressure sensing technology touch screen has been withdrawn from the historical stage; the infrared technology touch screen is cheap, but its frame is fragile, easy to produce light interference, and it is distorted in the case of curved surfaces; the capacitive technology touch screen has a reasonable design concept, but its image distortion problem is difficult to obtain The fundamental solution; the positioning of the resistive technology touch screen is accurate, but its price is high, and it is afraid of being scratched and damaged; the surface acoustic wave touch screen solves various defects of the previous touch screen, it is clear and not easy to be damaged, and it is suitable for various occasions. The disadvantage is that the surface of the screen Water droplets and dust can make the touchscreen sluggish or not even work. 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 resistive type, capacitive induction type, infrared type and surface acoustic wave type. Each type of touch screen has its own advantages and disadvantages. To understand which touch screen is suitable for which 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 working principle of resistive touch screen)
This touchscreen utilizes pressure sensing for control. The main part of the resistive touch screen is a resistive film screen that fits well with the display surface. Resistive) conductive layer, covered with a hardened outer surface, smooth anti-scratch plastic layer, its inner surface is also coated with a coating, between them there are many small (less than 1/1000 inch) transparent The isolation point separates and insulates 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 signals are generated in the X and Y directions, which are then sent to the touch screen controller. The controller detects this contact and calculates the (X,Y) position, and then behaves like a simulated mouse. This is the most basic principle of the resistive technology touch screen. The key to resistive touch screens lies in material technology. Commonly used transparent conductive coating materials are:
A. ITO, indium oxide, weak conductor, the characteristic is that when the thickness falls below 1800 angstroms (angstrom = 10-10 meters), it will suddenly become transparent, the light transmittance is 80%, and the light transmittance will be reversed if it is thinner decreased, and increased to 80% at a thickness of 300 angstroms. ITO is the main material used in all resistive technology touch screens and capacitive technology touch screens. In fact, the working surface of resistive and capacitive technology touch screens is the ITO coating.
B. Nickel-gold coating, the outer conductive layer of the five-wire resistance touch screen is made of nickel-gold coating material with good ductility. Due to frequent touches on the outer conductive layer, the purpose of using nickel-gold material with good ductility is to prolong 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 and is not suitable as a working surface of a resistive touch screen, because of its high conductivity, and the metal is not easy to achieve a very uniform thickness, so it is not suitable for a voltage distribution layer, and can only be used as a probe. Floor.