Analysis of the Basic Principle and Characteristic of Smart Phone Touch Screen

Touch screen is the input device of computer. Unlike keyboard and mouse, which can realize input, it allows users to choose by touching screen. Computers with touch screens require little storage space, few mobile parts, and can be packaged. Touch screens are more intuitive to use than keyboards and mice, and training costs are low.

All touch screens have three main types of components. A sensor unit that handles user selection; a controller that senses touch and location; and a software device that transmits touch signals to a computer operating system. Touch screen sensors have five technologies: resistance technology, capacitance technology, infrared technology, acoustic technology or near-field imaging technology.

Resistance touch screens usually consist of a flexible top layer film and a layer of glass as the base layer, which is isolated by the insulating point. The inner surface of each layer is coated with transparent metal oxides. The voltage has a difference in each layer of the diaphragm. Pressing the top layer film will form an electrical contact signal between the resistor layers.

Capacitive touch screens are also coated with transparent metal oxides and bonded to a single glass surface. Unlike resistive touch screens, any touch generates signals. Capacitive touch screens require direct touch with fingers or contact with conducting pens. The capacitance of the finger, or the ability to store electric charge, can absorb the current from each corner of the touch screen, and the current flowing through the four electrodes is proportional to the distance from the finger to the four corners, thus obtaining the touch point.

Infrared touch screen based on light interruption technology. Instead of placing a thin film layer in front of the display surface, it sets an outer frame around the display. The outer frame has a light source, or light emitting diode (LED), located on one side of the outer frame, while the light detector or photoelectric sensor on the other side, one by one corresponds to form a cross-vertical infrared grid. When an object touches the display screen, the invisible light is interrupted, and the photoelectric sensor can not accept the signal, thus determining the touch signal.

In the acoustic sensor, the sensor is mounted on the edge of the glass screen to send ultrasonic signals. Ultrasound is reflected through the screen and received by the sensor, and the received signal is weakened. In surface acoustic wave (SAW), light wave passes through the surface of glass; in guided acoustic wave (GAW), sound wave passes through glass.

Near field imaging (NFI) touch screen consists of two thin glass layers with transparent metal oxide coating in the middle. Applying an AC signal to the guide coating generates an electric field on the surface of the screen. When a finger, glove or other conductive iron pen contacts the sensor, the electric field produces disturbance, and the signal is obtained.

With the increasing use of computers as a source of information, touch screen with its easy to use, durable, fast response, space saving and other advantages, makes system designers more and more feel that using touch screen really has considerable advantages. Touch screen has only appeared in the Chinese market for a few years. This new multimedia device has not been touched and understood by many people, including some system designers who are planning to use touch screen. Touch screen is also regarded as an indispensable device. From the popularization process of touch screen in developed countries and the stage of multimedia information industry in China, this concept is still true. It has certain universality. In fact, touch screen is a device that can change multimedia information or control. It gives multimedia system a brand-new look and is an attractive new multimedia interactive device. System designers in developed countries and system designers in China who took the lead in using touch screen have clearly known that touch screen is no longer necessary for computers in various application fields, but essential equipment. It greatly simplifies the use of computers, even those who know nothing about them can still come by hand, making computers show greater charm. It solves the problem that computers can not solve in the public information market.

The main three types of touch screen are resistance technology touch screen, surface acoustic wave technology touch screen and capacitance technology touch screen. Each kind of touch screen has its own advantages and disadvantages. To understand which kind of touch screen is suitable for that occasion, the key is to understand the working principle and characteristics of each kind of touch screen technology. 1. The main part of the resistive touch screen is a resistive film screen which matches the surface of the display very well. This is a multi-layer composite film. It uses a glass or hard plastic plate as the base, and has a transparent conductive layer of metal oxide (ITO indium oxide, transparent conductive resistor) on the surface. It has a hardening treatment on the outer surface and a smooth anti-friction layer on the top. The plastic layer and its inner surface are also coated with an ITO coating. There are many tiny (less than 1/1000 inch) transparent isolation points between them to insulate the two conductive layers. When the finger touches the screen, the two layers of conductive layer have contact at the touch point. The controller detects the contact and calculates the position of (X, Y). Then it operates according to the way of simulating the mouse. This is the basic principle of resistance technology touch screen. Since the resistance screen entered the market, it has occupied the vast market with stable quality, reliable quality and high adaptability of the environment. Especially in the field of industrial control, because of the high requirements for its environment and conditions, it shows the uniqueness of the resistance screen, making its products occupy 90% of the market in the same kind of touch products, and has become the mainstream product in the market. Its greatest feature is not afraid of oil, dust, water. G-Touch's latest fourth-generation resistance technology, touch screen, differs from other resistance screen products in that it uses glass as the base plate, making it more transparent and reflective refractive index more suitable for users. At the same time, the conductive layer on the bottom of uniformly coated glass plate unloads the electrostatic particles adsorbed on the touch screen through the ground wire, which ensures that the touch positioning is more accurate and sensitive, completely eliminating the drift phenomenon caused by excessive charged particles, inaccurate positioning, slow reaction speed, and longer life (physical single point can be used continuously for more than 15 years), and has the ability of maintenance-free. Scratch prevention has also been greatly improved. It is a product of excellent quality and reasonable price.

1. The characteristics of four-wire resistor screen:

High resolution, high speed transmission reaction.

Surface hardness treatment, reduce abrasion, scratch and chemical treatment.

It has smooth surface and fog surface treatment.

Once correction, high stability, never drift. The two transparent metal layers of four-wire resistor analogue technology increase 5V constant voltage for each layer: one vertical direction and one horizontal direction. A total of four cables are required.

2. The characteristics of five-wire resistor screen:

High resolution, high speed transmission reaction.

Surface hardness, reduce abrasion, scratch and chemical treatment.

Thirty million contacts at the same point are still available.

Conductive glass is the medium of base material.

Once correction, high stability, never drift. Five-wire resistor analogue technology adds two-direction voltage to the metal layer nearby through the resistor network. It detects the position of the touching point by detecting both voltage and current. The outer ITO is only a conductor layer and needs five cables.

2. Surface acoustic wave technology Touch screen surface acoustic wave technology is the use of sound waves to transmit on the surface of objects. When an object touches the surface, it hinders the transmission of sound waves. The transducer detects the change and reflects it to the computer, and then simulates the mouse. Surface acoustic wave screen features:

It has high clarity and good transmittance.

High durability, good scratch resistance.

One correction does not drift.

The reaction is sensitive.

Suitable for office, government unit and cleaner environment. Surface acoustic wave screen needs to be maintained regularly, because dust, oil and even beverage liquid contamination on the surface of the screen will block the guide groove on the surface of the touch screen, make the wave can not be transmitted normally, or make the waveform change and the controller can not be recognized normally, thus affecting the normal use of the touch screen, users need to pay strict attention to environmental hygiene.

It is necessary to wipe the surface of the screen regularly in order to keep the screen clean and glossy, and to wipe it thoroughly and thoroughly at regular intervals. 3. Capacitance technology touch screen should work by using human body's electric flu. When the user touches the screen, because of the electric field of the human body, the user and the surface of the touch screen form a coupling capacitor. For the high frequency current, the capacitance is a direct conductor, so the finger sucks a very small current from the contact point. This current flows from the electrodes on the four corners of the touch screen, and the current flowing through the four electrodes is proportional to the distance from the finger to the four corners. The controller calculates the proportion of these four currents accurately to get the position of the touch point.

Characteristic of capacitive touch screen:

Resistance to most environmental pollutants.

The human body becomes part of the circuit, so the drift phenomenon is more serious.

Gloves don't work.

Regular calibration is required.

Not suitable for metal cabinets.

When there are inductances and magnetic inductances outside, the touch screen will fail.