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Touchscreen what is it. Touchscreen in the phone: what is and how it works

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What is a touchscreen

A touchscreen or touch screen is a device that allows you to enter information into a computer by touching its screen with a special pen (stylus) or simply with your fingers. This technology eliminates the need for additional hardware buttons, which increases the usability and can reduce the cost of the entire device.

This method of entering information was invented in the United States in the 70s of the last century. The first computer with a touchscreen was the PLATO IV system, which appeared in 1972. That touchscreen worked on the basis of a grid of infrared rays. Around the same time, Samuel Hirst developed the first touchscreen using resistive technology. And in 1982, the first TV with a resistive touchscreen appeared.

The technology for the manufacture of touch screens has evolved and at the beginning of the 2000s it began to be actively used in the production of mobile devices. First, there were PDAs with a touchscreen, and then, phones, smartphones and tablets. The use of the touchscreen has significantly expanded the capabilities of mobile devices, which has become the impetus for the significant growth of this industry.

Now the touchscreen is used everywhere, it is embedded in phones, smartphones, tablets, laptops, monoblocks, monitors. Also, touch screens are actively used in automotive, medical, industrial and household appliances. In fact, any device that requires input of information can be equipped with such a screen.

Types of touch screens

The general classification of touchscreens that are on the market implies a division into varieties by type and design features. The most used are resistive and capacitive types, which are used in most mobile gadgets. There are also:

  • matrix;
  • infrared;
  • projection-capacitive;
  • optical;
  • DST sensors;
  • wave;
  • induction.

Resistive sensor is considered “the last century” due to imperfect technology

Resistive touch screen

Speaking about what a Touch Screen is, the first thing to mention is resistive screens, which were the first in mass production. Such screens consist of two transparent plates made of plastic, on which the thinnest conductive mesh is applied. A dielectric layer is installed between the plates, which is required to capture pressure on the desired area of ​​the screen by the user.

When the owner of the smartphone performs an action (for example, clicking on the desired area of ​​the screen), the dielectric moves apart in this place, which leads to the contact of the two plates with each other. A current appears, which is registered by a special controller, which determines a specific point of depression on a grid of coordinates. Further, these data are fed to the processing program, which, according to a previously created algorithm, performs the necessary action.

Special electrodes located at the corners of the matrix are responsible for determining the coordinates of the pressure point

Resistive screens are, in turn, divided into two subtypes:

  1. Four-wire sensor. They are made from just one panel, made of glass and a plastic membrane, on which the resistive support of the screen itself is applied. All the free space between glass and plastic is filled with insulators. When you press, the circuit closes, which leads to the appearance of the coordinates of the point of contact.
  2. Five-wire. A distinctive feature of this type is the absence of resistive support of the membrane, the presence of a conductive layer. This ensures greater reliability, since even after the matrix is ​​damaged, it continues to work. The pressure point is tracked by the degree of change in membrane voltage.

FOR YOUR INFORMATION!

There are also eight-wire resistive screens that can improve the accuracy of the processing of pressing, but do not increase the reliability of this type of sensor.

Touchscreen what is it. Touchscreen in the phone: what is and how it worksTouchscreen what is it. Touchscreen in the phone: what is and how it works

The disadvantage of a resistive sensor is the lack of multitouch support

Speaking of resistive touch screens, one should note their low cost, the ability to press with a finger, stylus and even a gloved hand. Among the disadvantages are:

  • low conductivity of light rays;
  • susceptibility to scratches and cracks due to impact;
  • lack of multitouch;
  • short service life, which averages no more than 34 million clicks;
  • the impossibility of implementing the function of sliding across the screen, since the resistive matrix reacts only to pressing.

Capacitive touch screen

The modern type of matrix is ​​the capacitive type of the screen. What it is? The essence of the work of this type is to follow the laws of elementary physics, namely, in the property of an object of greater capacity to conduct alternating current.

Touchscreen what is it. Touchscreen in the phone: what is and how it works 

The operation of the capacitive type is based on the rule of the difference in electrical potentials

By its structure, this type of matrix is ​​a glass plate, on the surface of which a layer of resistive material is applied.

FOR YOUR INFORMATION!

In this case, indium oxide and tin oxide alloys are used as the best resistors.

Touchscreen what is it. Touchscreen in the phone: what is and how it works

At the corners of the screen, there are electrodes that apply a small voltage to the entire surface of the matrix. When a person touches a finger, a leak occurs, which is recorded by sensors and transmitted to the processing controller, which calculates the coordinates of the point of pressing. Distinctive features of this type of screens are a long service life, which is more than 200 million clicks, increased transparency, and the ability to not let liquid pass through. But the surface of this sensor still remains vulnerable to mechanical stress, therefore, these types of matrix are used in stationary devices located in a place protected from external factors.

Touchscreen what is it. Touchscreen in the phone: what is and how it works

Most modern mobile devices use projected capacitive sensors.

Projected capacitive sensors

Speaking about what a touch screen is, be sure to note the type of matrix that is used in most modern smartphones and tablet computers. This is a projected capacitive sensor. A design of this type is presented, in addition to the usual panel, with a grid of electrodes, which are applied to the back of the matrix. The available electrodes, together with the human body, form a capacitor, and built-in electronics are required to measure the capacity of the resulting system.

FOR YOUR INFORMATION!

One of the leaders in the production of screens, Samsung, has managed to fit pressure-sensitive electrodes between the sub-pixels, which made it possible to simplify the design and increase transparency.

Touchscreen what is it. Touchscreen in the phone: what is and how it works

Increased transparency, the ability to use thick glass (up to 19 mm) – all this reduces the risk of damage to projection-capacitive screens, so they are installed in devices located in open areas.

Touchscreen what is it. Touchscreen in the phone: what is and how it works

In an infrared sensor, the principle of operation is to interrupt the infrared rays at the point of contact

Matrix and infrared touch screens

Among the varieties of sensors, two not the most common types can be mentioned – matrix and infrared screens. Matrix devices work according to the general principles of resistive designs, but their distinctive feature is simplicity. Vertical conductive strips are applied to the membrane surface, and horizontal stripes are applied to the glass surface. When pressed, the strips touch, and the controller calculates the contact point and determines the coordinates of the point. A significant disadvantage is the impossibility of ensuring high resolution of the sensor due to the simplicity of the design.

The infrared types use a similar principle of intersecting bands, which are infrared rays. When any object touches the screen, the ray grid is interrupted at this point. A similar view is used on devices where high-definition image transmission is required, for example, e-books. The disadvantage of an IR sensor is its susceptibility to contamination.

Touchscreen what is it. Touchscreen in the phone: what is and how it works

Interactive maps use a strain gauge type of sensor

Optical and strain gauge touch screens

The optical type is distinguished by the presence of infrared illumination, which is distributed between the glass and the matrix, and is capable of reflecting up to 100% of light inside itself. When touched with a finger, scattering occurs. The electronics only need to create a scatter pattern to determine the pressure point. This is done in the following ways:

  • installing the camera next to the projector;
  • the introduction of an auxiliary subpixel.

Similar types of screens are used in interactive whiteboards. The strain gauge sensor is sensitive to deformation of the screen surface. This type is distinguished by increased resistance to damage, therefore, these matrices are used on ticket machines, ATMs.

DST technology works on the principle of detecting piezoelectric manifestations inside a glass panel at the touch of a finger

What is the main difference between the display and the touchscreen?

The display is basically a detail with which the image is projected. He is responsible for displaying information, which is directly received by the owner of the device. If the display is damaged, this is reflected in the image: it may be completely or partially absent, black blots with streaks or uneven stripes may be displayed.

A touchscreen, in fact, is a touch glass that works in a simple way: touching with your finger allows you to perform any functions or perform certain actions. If the touchscreen is faulty, then on its surface it will be immediately noticeable: cracks appear, which are felt under the fingers, the sensor loses its previous sensitivity.

The main difference between the display and the touchscreen on phones or tablets is that in most cases the display is located under the touchscreen. Thus, on the very surface of the device there is a touch glass, and already a display with an image is displayed below.

The design and principle of operation of the capacitive touchscreen

It is glass coated with a transparent resistive material. Usually it is an alloy of tin and indium oxides. In the corners of the glass there are 4 electrodes connected to a ribbon cable connected to the motherboard.

Touchscreen what is it. Touchscreen in the phone: what is and how it works

The closer the finger is to the electrode, the lower the resistance

The module works as follows:

  1. The electrodes supply an alternating or direct voltage of the same value for all angles.
  2. The user touches the glass. When touched, a current leak appears, since the human body is a plate of an uncharged capacitor and begins to fill with a charge from the electrodes.
  3. The closer the finger is to the electrode, the lower the resistance and the greater the current flowing through the electrodes. Sensors measure its values ​​and transmit them to the controller.
  4. The controller calculates the coordinates of the point of pressing and transmits them to the central processor for executing the command given by pressing.

Resistive touchscreen is an outdated technology

There are several systems used to create touch screens. The most common resistive and capacitive technologies are very different.

In old smartphones, it was resistive screens that required the use of stylus (small pointers with which the user gave commands to the phone). The resistive system is glass covered with an elastic film and an electrically conductive layer.

Touchscreen what is it. Touchscreen in the phone: what is and how it works

White space is retained between these two elements. The surface of the display is protected by a special coating that protects the screen from scratches and other mechanical damage. But for better protection, a film is provided (it came with old smartphones).

Resistive touchscreens have a number of disadvantages:

  • the need to press the screen (touching is more convenient);
  • screen calibration resulting from the redistribution of the insulating layer mass;
  • rapid deterioration of the touchscreen quality (cracks, scratches, stains, etc.);
  • short service life, which is explained precisely by the rapid appearance of damage;
  • lack of sliding capability (as on modern smartphones), etc.

Today resistive touchscreens are less and less common. Smartphone manufacturers have abandoned them, they are now mainly used in ATMs and various terminals.

Types and basic principles of work

Touchscreen what is it. Touchscreen in the phone: what is and how it works

  • Smartphones use only two types of sensors – resistive and capacitive. Their main difference from the point of view of a simple user is that the former are activated by pressing, and the latter by touching.
  • A resistive touchscreen is essentially a “sandwich” of a glass panel and two touch membranes superimposed on it. The upper membrane is flexible and the lower membrane is tightly attached to the screen.
  • The inner surfaces of both are treated with a conductive compound. Electrodes (from 4 to 8) are located along the perimeter of the entire system.
  • As soon as the user presses on the screen (stylus or finger), the screen reacts to the touch: the outer film flexes and closes with the inner one. A special sensor detects the closure of the circuit and determines the point of contact.
  • To understand how a screen designed using capacitive technology works, it is enough to recall from a school physics course that the human body is also an electrical conductor.
  • The simplest capacitive touchscreen consists of a glass plate with a resistive layer applied to it and 4 electrodes located at the corners. An alternating voltage is applied from the electrodes to the sensor surface.
  • A finger leaning against the screen becomes a new link in the electronic circuit. A leakage current occurs in the system, which is immediately read by the controller.

Pressure Sensitive Touch Screens – 3D Touch

The forerunner of pressure-sensitive touchscreens is Apple’s proprietary Force Touch technology used in the company’s smartwatches, MacBook, MackBook Pro and Magic Trackpad 2.

After testing interface solutions and various scenarios for using pressure recognition on these devices, Apple began to implement a similar solution in its smartphones. In the iPhone 6s and 6s Plus, the recognition and measurement of pressure became one of the functions of the touchscreen and received the commercial name 3D Touch.

Although Apple did not hide the fact that the new technology only modifies the capacitive sensors we are used to and even showed a diagram that explained in general terms the principle of its operation, details about the device of touch screens with 3D Touch appeared only after the first iPhones of the new generation were disassembled by enthusiasts. …

In order to teach the capacitive touchscreen to recognize pressures and distinguish between multiple degrees of pressure, the Cupertino engineers required a reassembly of the touchscreen sandwich. They made changes to individual parts of it and added another, new layer to the capacitive layer. And, interestingly, in doing so, they were clearly inspired by outdated resistive screens.

The capacitive sensor grid remained unchanged, but it was moved back, closer to the matrix. An additional array of 96 individual sensors was integrated between a set of electrical contacts that monitor the touch point of the display and the protective glass.

His job was not to locate his finger on the iPhone screen. The capacitive touchscreen still coped well with this. These plates are required to detect and measure the degree of bending of the protective glass. Apple specifically for the iPhone ordered Gorilla Glass to design and manufacture a protective coating that would retain its previous strength and, at the same time, be flexible enough to allow the screen to respond to pressure.

On this development, it was possible to finish the material about touch screens, if not for another technology, which was predicted a great future a few years ago.

Wave touch screens

Surprisingly, they don’t use electricity and have nothing to do with light. Surface Acoustic Wave system technology uses surface acoustic waves that propagate along the surface of the screen to determine the point of contact. The ultrasound generated by the piezoelectric elements at the corners is too high for human hearing to pick up. It spreads back and forth, repeatedly bouncing off the edges of the screen. The sound is analyzed for anomalies created by objects touching the screen.

There are not many disadvantages to wave touchscreens. They start to make mistakes after heavily contaminated glass and in conditions of strong noise, but, at the same time, screens with such a sensor do not have additional layers that increase the thickness and affect the image quality. All sensor components are hidden under the display bezel. In addition, wave sensors allow you to accurately calculate the area of ​​contact of the screen with a finger or other object and indirectly calculate the force of pressing the screen using this area.

We are unlikely to encounter this technology in smartphones because of the current fashion for frameless displays, but a few years ago Samsung experimented with the Surface Acoustic Wave system in monoblocs, and panels with acoustic touchscreens are sold as accessories for gaming machines and advertising terminals. now

Safety glass

Touchscreen what is it. Touchscreen in the phone: what is and how it works

The topmost layer of the display that the user interacts with.

The tactile sensations of the user depend on the quality of the glass and the oleophobic coating on it. When working with the iPhone, the finger simply glides over the surface, does not stick with a quick press, and does not rest with a sharp swipe.

Service technicians may suggest replacing the protective glass instead of replacing the entire display. The procedure is not easy, but spare parts are cheaper.

Touchscreen what is it. Touchscreen in the phone: what is and how it works

The glasses of the new iPhone models are very thin, curved around the perimeter and have smooth edges near the Home button and speaker, and in the latest iPhone X it does not have a cutout.

Even the best Chinese glasses are inferior in quality to the original ones, when you replace them, you feel a sharp transition or deepening of the button, often after replacing the sensors on the front surface of the smartphone begin to fail.

Transparent adhesive layer

Touchscreen what is it. Touchscreen in the phone: what is and how it works

The protective glass is glued directly to the matrix. This removes the air gap and reduces the thickness of the display.

A high-quality adhesive layer will not distort colors, will prevent dust from getting under the glass and will reliably hold the top layer even during the most active use.

When replacing the glass, a low-quality adhesive layer may be used, which over time will change its color, distort the picture or allow dust particles to pass through.

The matrix

Touchscreen what is it. Touchscreen in the phone: what is and how it works

Consists of two plates with liquid crystals located on the honey. Under the action of the current, these crystals begin to transmit the corresponding illumination radiation.

This is how the IPS-matrix works, which is used in all iPhone models except the new iPhone X. The system itself was slightly modified by Apple specialists, and later called Retina marketers.

Backlight

Touchscreen what is it. Touchscreen in the phone: what is and how it works

The light source that is located behind the matrix. It is responsible for backlighting the crystals so that the image becomes bright and clear. By themselves, the crystals do not glow, but only pass the illumination light through themselves.

Features of different types of touchscreens

The cheapest touchscreens, but, at the same time, the least clearly transmitting the image are resistive touchscreens. In addition, they are the most vulnerable, because absolutely any sharp object can seriously damage a rather delicate resistive “film”.
The next type, i.e. wave touchscreens are the most expensive among their kind. At the same time, the resistive design, most likely, refers, after all, to the past, the capacitive design to the present, and the wave design to the future. It is clear that the future is absolutely unknown to no one and, accordingly, at the present time, one can only assume which technology has great prospects for its use in the future.
For a resistive system of touchscreens, it does not really matter whether the user touches the device’s screen with the rubber tip of the stylus or just with his finger. It is enough that there is a contact between the two layers. At the same time, the capacitive screen recognizes only touches with some conductive objects. Often, users of modern devices work with them with their own fingers. In this respect, the screens of the wave structure are closer to resistive ones. It is possible to give a command with almost any object – in this case, you just need to avoid using heavy or too small objects, for example, the shaft of a ballpoint pen will not work for this.

Capacitive screen device. Digital present

In touchscreens of this design, the glass base is covered with a layer that plays the role of a receptacle-storage of electric charge. By touching, the user releases some of the electrical charge at a certain point. This reduction is determined by microcircuits located in each corner of the screen. The computer calculates the difference in electrical potential between different parts of the screen, and the touch information in full detail is immediately transferred to the touchscreen driver.

An important advantage of capacitive touchscreens is the ability of this type of screen to retain almost 90% of the original display brightness. In resistive screens, only about 75% of the original light is retained. For this reason, images on a capacitive screen appear much sharper than on a resistive touchscreen.

Wave touch displays. Bright future

At the ends of the X and Y axes, the grid of the glass screen is located along the transducer. One of them is transmitting, and the second is receiving. On the glass base are also reflectors that “reflect” the electrical signal transmitted from one transducer to another.

The transducer-receiver “knows” exactly whether the pressure has taken place and at what point it happened, since by touching the user introduces an interruption in the acoustic wave. The wave display glass is devoid of metal coating, which allows you to retain 100% of the original light. Due to its such a nice feature, the wave screen is the best choice for users working in fine graphic details. Indeed, both resistive and capacitive touchscreens are not ideal in terms of image clarity. The coating traps light and distorts the picture.

Types of touchscreens

There are two types of touch screens:

  1. Resistive.
  2. Capacitive.

Touchscreen what is it. Touchscreen in the phone: what is and how it works

Resistive touch screens respond to finger, stylus, and other objects. Input of information is available when using ordinary gloves. At the same time, it is required to offer a certain effort to enter the information. Often, too much pressure will damage the input surface and cause scratches, and sometimes even damage the display itself.

The capacitive touchscreen reacts only to finger pressure, as well as other objects that can simulate the touch of a person’s finger: stylus, gloves, etc. Therefore, the cost of accessories capable of working with such touchscreens is much higher. For that, the process of entering data is much easier, just a light touch. The reaction and responsiveness are several times higher in comparison with the resistive type, which provides comfortable conditions for navigating in menus or games.

Output

The touchscreen makes it much easier to enter information on some devices. Touching with your finger is much easier and faster than typing with the mouse cursor or searching for the desired keys on the keyboard. Also, this design helps to save space in certain devices. At the same time, the production technology remains costly in terms of money, which hinders the mass production of touchscreen notebooks and monitors.

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Post source: lastici.ru

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