How it works: touch screen - futureez. Touch screen types

To control modern gadgets, it is no longer necessary to press buttons, just touch the screen. This became possible thanks to the touchscreen (in the environment of experts they simply call it “touch” or “touch panel”), which has become an integral part of smartphones and tablets, including iPhones and iPads. Not surprisingly, due to frequent use, it often fails and becomes a headache for the owner of the device. If you understand what this component is and how it works, you can quickly detect a malfunction and avoid embarrassing situations when contacting a service center.

What is a touchscreen

This term was formed from two English words - touch and screen, which literally translates as "touch screen". The history of its appearance is long and took place in several stages. The world's first finger-operated display was invented and described in his scientific papers by the American E. A. Johnson in 1965. Five years later, Dr. Samuel Hurst, through experiments, developed resistive touch screen, and the physical production of the product began only in 1973.

Currently, urban residents deal with touch panels almost daily: not only smartphones and tablets are equipped with them, but also ATMs, reference terminals and payment acceptance points. touchscreen connects to the display and sensitive to any touch. It can be described as an input device that serves to replace the keyboard.

It is important to know that the touchscreen is only a part of the overall design, responsible only for the sensor. To send an image a display is used, which is a liquid crystal matrix. The unity of these two elements is called the display module, which is practically the main component of any high-tech device.

How the touch panel works

The principle of operation of the touchscreen is simple - any touch on it causes a function or entails certain actions. The physical features of its work directly depend on the type of touch panel. There are seven of them, but the most common today are three of them.

The cheapest in production, resistant to pollution and temperature extremes. Consists of glass panel and plastic membrane between which there are insulators. Any pressing causes the glass to push through the micro-insulator, and the membrane with the panel closes. After that, a special controller reads the changes and converts them into contact coordinates. The weaknesses of this model are low light transmission, short service life and a high risk of damage when dropped.

Capacitive screen

More reliable and durable, but vulnerable to bad weather, water and pollution. It uses a special touch glass coated with a resistive material. An alternating current passes through it, which is supplied by electrodes located at the corners of the screen. That is, when you touch the touchscreen, current leakage occurs, which is fixed by special sensors. They register these changes and pass them to the controller.

Surface acoustic wave sensor

One of the most complex screens. The peculiarity of his work is that in the thickness of the glass there are ultrasonic vibrations. When you press the touchscreen, the waves are absorbed and converted into an electrical signal, which is then transmitted to the controller. The advantage of this technology is a long service life of at least 45 million touches. The main drawback is that the screen is extremely sensitive to pollution and electromagnetic interference.

In addition to this, there are several more varieties of touch panels. These include:

• Projected-capacitive. On the inside of such screens there is a grid of electrodes, which, when pressed, forms a capacitor, the capacitance of which is measured by electronic sensors.
• infrared. Along their edges are light emitters and receivers in the infrared range, when you touch the screen, part of the light overlaps and thereby determines the place of pressing.
• Tansometric. Based on a simple fixation of the screen deformation, they are resistant to damage and are often installed outdoors.
• induction. Inside them there is an inductor and wires, when such a screen is touched with a special tool, the voltage of the existing magnetic field changes.

How to check touchscreen

The touch panel may not work correctly either if the mobile device is physically damaged, or for no apparent reason. The following factors indicate that the problem is in the sensor:

There may be several reasons for such a malfunction:

1. Display dirty. If you do not wipe the sensor in a timely manner with special means, then during operation it is abundantly covered with fingerprints and greasy traces, which can reduce its sensitivity.
2. Violation temperature regime. Too high or low temperatures, as well as their strong drop, is a common cause of touchscreen malfunction.
3. Loop damage. It can peel off the glass in case of mechanical damage, thereby breaking the connection of the latter with the touch coating.
4. Moisture ingress. If there is liquid inside the gadget, then oxidation of the contacts may occur. Sometimes the problem can be solved with a hair dryer.
5. crash software. In this case, you need to reflash the device, this will require a USB cable and the software itself.

How to replace the touchscreen on your phone

Before removing the touch screen, turn off your smartphone, remove the battery and SIM card. It is important to remember the disassembly sequence, so that later you can assemble the device back and not damage the internal elements. In some models, a complete disassembly of the case may be required, which requires special knowledge. To replace the touch screen on your phone with your own hands, you need to prepare special equipment in advance, namely:

The touchscreen replacement process itself is as follows:

1. Take off the back cover of the phone;
2. Screwdriver unscrew all bolts along the perimeter of the body;
3. Carefully insert spatula between the body mount and pry;
4. hair dryer warm up the glue, connecting the sensor to the matrix up to a maximum temperature of 80 °C;
5. Attach to display sucker, which will allow you to separate the touchscreen from the matrix;
6. Apply thin layer of glue and install a new touch panel;
7. Carefully press down it and remove the remaining glue;
8. Assemble the device in reverse order.

What is the difference between touchscreen and display

The display is the part of the smartphone that displays the image. It is he who is the conductor of visual information and makes it available to the human eye. The touchscreen is a touch glass, the main purpose of which is to call one or another function. That is, he is only input tool, but no output.

If the phone crashed and a cobweb appeared on it, but the screen continues to work and you can clearly see the picture, then only the sensor needs to be replaced. When the device distorts the image and shows blots, you will have to change the display, which is a more time-consuming and costly procedure.

The screens of modern devices can not only display an image, but also allow you to interact with the device through sensors.

Initially, touch screens were used in some pocket computers, and today touch screens are widely used in mobile devices, players, photo and video cameras, information kiosks, and so on. In addition, each of the listed devices can use one or another type of touch screen. Currently, several types of touch panels have been developed, and, accordingly, each of them has its own advantages and disadvantages. In this article, we will just consider what types of touch screens are, their advantages and disadvantages, which type of touch screen is better.

There are four main types of touch screens: resistive, capacitive, with the definition of surface acoustic waves and infrared . In mobile devices, only two are most widely used: resistive and capacitive . Their main difference is the fact that resistive screens recognize pressure, while capacitive screens recognize touch.

Resistive touch screens

This technology is most widely used among mobile devices due to the simplicity of the technology and low cost of production. The resistive screen is an LCD display on which two transparent plates are superimposed, separated by a dielectric layer. The upper plate is flexible, as the user presses on it, while the lower one is rigidly fixed to the screen. Conductors are deposited on the surfaces facing each other.

Resistive touch screen

The microcontroller applies voltage in series to the electrodes of the top and bottom plates. When the screen is pressed, the flexible upper layer flexes, and its inner conductive surface touches the lower conductive layer, thereby changing the resistance of the entire system. The change in resistance is fixed by the microcontroller and thus the coordinates of the touch point are determined.

Of the advantages of resistive screens, one can note simplicity and low cost, good sensitivity, as well as the ability to press the screen either with a finger or with any object. Of the minuses, it is necessary to note poor light transmission (as a result, you have to use a brighter backlight), poor support for multiple clicks (multi-touch), they cannot determine the pressing force, as well as fairly fast mechanical wear, although compared to the life of the phone, this drawback is not so important, since it's usually quicker for a phone to fail than a touchscreen.

Application: cell phones, PDAs, smartphones, communicators, POS-terminals, TabletPC, medical equipment.

Capacitive touch screens

Capacitive touch screens are divided into two types: surface-capacitive and projected-capacitive . Surface capacitive touch screens are glass, on the surface of which a thin transparent conductive coating is applied, on top of which a protective coating is applied. Along the edges of the glass are printed electrodes that apply a low-voltage alternating voltage to the conductive coating.

Surface capacitive touch screen

When the screen is touched, a current pulse is generated at the contact point, the value of which is proportional to the distance from each corner of the screen to the touch point, so it is quite simple to calculate the coordinates of the touch point for the controller, to compare these currents. Among the advantages of surface-capacitive screens, one can note: good light transmission, short response time and long touch resource. Among the shortcomings: the electrodes placed on the sides are poorly suited for mobile devices, demanding on external temperature, do not support multi-touch, you can touch with your fingers or a special stylus, and cannot determine the pressing force.

Application: information kiosks in secure premises, in some ATMs.

Projected capacitive touch screens are glass with horizontal leading lines of conductive material and vertical defining lines of conductive material deposited on it, separated by a dielectric layer.

Projected capacitive touch screen

Such a screen works as follows: a voltage is sequentially applied to each of the electrodes in a conductive material by a microcontroller and the amplitude of the resulting current pulse is measured. As the finger approaches the screen, the capacitance of the electrodes under the finger changes, and thus the controller determines the place of touch, that is, the touch coordinates are intersecting electrodes with increased capacitance.

The advantage of projected capacitive touch screens is fast response to touch, multi-touch support, more accurate coordinates than resistive screens, and pressure detection. Therefore, these screens are more used in devices such as iPhone and iPad. It is also worth noting the greater reliability of these screens and, as a result, a longer service life. Among the shortcomings, it can be noted that on such screens you can only touch with your fingers (it is very inconvenient to draw or write by hand with your fingers) or with a special stylus.

Application: payment terminals, ATMs, electronic kiosks on the streets, touchpads of laptops, iPhone, iPad, communicators and so on.

Touch screens SAW (surface acoustic waves)

The composition and principle of operation of this type of screens is as follows: piezoelectric elements are placed at the corners of the screen, which convert the electrical signal applied to them into ultrasonic waves and direct these waves along the surface of the screen. Reflectors are distributed along the edges of one side of the screen, which distribute ultrasonic waves across the entire screen. Sensors are located on the opposite edges of the screen from the reflectors, which focus the ultrasonic waves and transmit them further to the transducer, which in turn converts the ultrasonic wave back into an electrical signal. Thus, for the controller, the screen is represented as a digital matrix, each value of which corresponds to a certain point on the screen surface. When a finger touches the screen at any point, waves are absorbed, and as a result, the overall pattern of propagation of ultrasonic waves changes and, as a result, the transducer produces a weaker electrical signal, which is compared with the digital matrix of the screen stored in memory, and thus the coordinates of touching the screen are calculated.

Touch screen SAW

Of the advantages, one can note high transparency, since the screen does not contain conductive surfaces, durability (up to 50 million touches), as well as SAW touch screens, allow you to determine not only the coordinates of pressing, but also the pressing force.

Among the shortcomings, one can note a lower accuracy of determining coordinates than capacitive ones, that is, drawing on such screens will not work. A big disadvantage is malfunctions when exposed to acoustic noise, vibrations or when the screen is dirty, i.e. any dirt on the screen blocks its work. Also, these screens work correctly only with objects that absorb acoustic waves.

Application A: SAW touch screens are mainly in security information kiosks, educational institutions, gaming machines and so on.

Infrared touch screens

The device and principle of operation of infrared touch screens is quite simple. Along two adjacent sides of the touch screen are LEDs that emit infrared rays. And on the opposite side of the screen are phototransistors that receive infrared rays. Thus, the entire screen is covered with an invisible grid of intersecting infrared rays, and if you touch the screen with your finger, the rays overlap and do not fall on the phototransistors, which is immediately registered by the controller, and thus the coordinates of the touch are determined.

Infrared touch screen

Application A: Infrared touch screens are mainly used in information kiosks, vending machines, medical equipment, etc.

Of the advantages, one can note the high transparency of the screen, durability, simplicity and maintainability of the circuit. Among the shortcomings: they are afraid of dirt (therefore they are used only indoors), they cannot determine the pressing force, the average accuracy of determining coordinates.

P.S. So, we have considered the main types of the most common sensor technologies (although there are also less common ones, such as optical, strain gauge, induction, and so on). Of all these technologies, resistive and capacitive are the most widely used in mobile devices, as they have a high accuracy in determining the touch point. Of these, projected-capacitive touch screens have the best characteristics.

The text was prepared based on materials from open sources by Methodologists Karabin A.S., L.V. Gavrik, S.V. Usachyov

Today, no one is surprised by a touch screen phone. Manual control has become fashionable, but few people think about what happens when you touch the display. I'll cover how the most common types of touch screens work. The convenience and productivity of working with digital technology depend primarily on the information input devices used, with the help of which a person controls the equipment and downloads data. The most massive and versatile tool is the keyboard, which has now become widespread. However, it is not always convenient to use it. For example, the dimensions of mobile phones do not allow large keys to be installed, as a result of which the speed of entering information is reduced. This problem was solved by using touch screens. In just a few years, they revolutionized the market and began to take root everywhere - from mobile phones and e-books to monitors and printers.

The beginning of the sensory boom

Buying new smartphone, on the body of which there is not a single button or joystick, you hardly think about how you will control it. From the user's point of view, there is nothing complicated in this: it is enough to touch the icon on the screen with your finger, which will lead to the performance of some action - opening a window for entering a telephone number, SMS or address book. Meanwhile, 20 years ago, one could only dream of such opportunities.

The touch screen was invented in the USA in the second half of the 1960s, but until the early 1990s it was mainly used in medical and industrial equipment to replace traditional input devices, the use of which is fraught with difficulties under certain operating conditions. As the size of computers decreased and the appearance of PDAs, the question arose of improving their control systems. In 1998, the first handheld with a touch screen and an input and handwriting recognition system appeared. Apple Newton MessagePad, and soon communicators with touchscreens.

In 2006, almost all major manufacturers started producing smartphones with touch screens, and after the advent of Apple iPhone in 2007, the real touch boom began - displays of this type appeared in printers, e-readers, various types of computers, etc. What happens when you touch the touch screen, and how does the device “know” exactly where you clicked?

How a Resistive Touch Screen Works

Over the 40-year history of touch screens, several types of these input devices have been developed, based on different physical principles that are used to determine the location of a touch. Currently, the most widely used two types of displays - resistive and capacitive. In addition, there are screens that can register several clicks at the same time ( Multitouch) or just one.

Screens made using resistive technology consist of two main parts - a flexible upper and a rigid lower layer. Various plastic or polyester films can be used as the first, and the second is made of glass. On the inner sides of both surfaces, layers of a flexible membrane and a resistive (having electrical resistance) material that conducts electric current are deposited. The space between them is filled with a dielectric.

Along the edges of each layer there are thin metal plates - electrodes. In the back layer with resistive material, they are located vertically, and in the front - horizontally. In the first case, a constant voltage is applied to them, and an electric current flows from one electrode to another. This results in a voltage drop proportional to the length of the screen section.

When you touch the touch screen, the front layer flexes and interacts with the back, which allows the controller to determine the voltage on it and calculate the coordinates with it. touch points horizontally (x-axis). To reduce the influence of the resistance of the front resistive layer, the electrodes located in it are grounded. Then the reverse operation is performed: voltage is applied to the electrodes of the front layer, and those located in the rear layer are grounded - this way it is possible to calculate the coordinate of the touch point along the vertical (Y axis). This is how a four-wire (named after the number of electrodes) resistive touch screen works.

In addition to four-wire, there are also five- and eight-wire touch screens. The latter have a similar principle of operation, but higher positioning accuracy.

The principle of operation and design of five-wire resistive touch screens are somewhat different from those described above. The front resistive layer is replaced by a conductive layer and is used solely to read the voltage value on the rear resistive layer. Four electrodes are built into it at the corners of the screen, the fifth electrode is the output of the front conductive layer. Initially, all four electrodes of the back layer are energized, and on the front layer it is zero. As soon as such a touch screen is touched, the upper and lower layers are connected at a certain point, and the controller detects the change in voltage on the front layer. So he determines that the screen has been touched. Next, the two electrodes in the back layer are grounded, the coordinate of the touch point along the X axis is calculated, and then the other two electrodes are grounded, and the coordinate of the touch point along the Y axis is calculated.

Working principle of capacitive touch screen

The principle of operation of capacitive touch screens is based on the ability of the human body to conduct electric current, which indicates the presence of electrical capacitance. In the simplest case, such a screen consists of a solid glass substrate on which a layer of resistive material is deposited. Four electrodes are placed at its corners. From above, the resistive material is covered with a conductive film.

A small alternating voltage is applied to all four electrodes. At the moment a person touches the screen, an electric charge flows through the skin to the body, and an electric current occurs. Its value is proportional to the distance from the electrode (panel corner) to the touch point. The controller measures the current strength across all four electrodes and, based on these values, calculates the coordinates of the touch point.

The positioning accuracy of capacitive screens is almost the same as that of resistive ones. At the same time, they transmit more light (up to 90%) emitted by the display device. And the absence of elements subject to deformation makes them more reliable: the capacitive screen withstands more than 200 million clicks at one point and can operate at low temperatures (down to -15 ° C). However, the front conductive coating used for position determination is sensitive to moisture, mechanical damage, and conductive contaminants. capacitive screens are triggered only when they are touched with a conductive object (hand without a glove or a special stylus). Screens of this type made according to the classical technology are also not able to track several clicks at the same time.

The projected-capacitive touch screen, which is used in iPhones and similar devices, has this capability. It has a more complex structure compared to conventional capacitive screens. Two layers of electrodes are deposited on a glass substrate, separated by a dielectric and forming a lattice (electrodes in the lower layer are located vertically, and in the upper layer - horizontally). The grid of electrodes together with the human body forms a capacitor. At the point where the finger is touched, its capacitance changes, the controller detects this change, determines at which intersection of the electrodes it occurred, and calculates the coordinate of the touch point from this data.

These screens also have a high transparency and are able to operate at even lower temperatures (up to -40 °C). Electrically conductive contaminants affect them to a lesser extent, they react to the gloved hand. High sensitivity makes it possible to use a thick layer of glass (up to 18 mm) to protect such screens.

Working principle of four-wire resistive touch screen

1. The upper resistive layer bends and comes into contact with the lower one.
2. The controller detects the voltage at the touch point on the bottom layer and calculates the X coordinate of the touch point.
3. The controller detects the voltage at the touch point on the top layer and determines the Y coordinate of the touch point.

Working principle of five-wire resistive touch screen

1. Touch the screen with any hard object.
2. The upper conductive layer flexes and touches the lower one, indicating that the screen has been touched.
3. Two of the four electrodes of the lower layer are grounded, the controller determines the voltage at the touch point and calculates the X coordinate of the point.
4. The other two electrodes are grounded, the controller determines the voltage at the touch point and calculates the Y coordinate of the point.

Advantages

• Low cost
• High resistance to dirt
• Can be touched by any hard object

disadvantages

• Low durability (1M single-point clicks for 4-wire, 35M clicks for 5-wire) and vandal resistance
• Low light transmission (no more than 85%)
• Do not support multitouch

Device examples

• Phones (eg Nokia 5800, HTC Touch Diamond), PDAs, computers (eg MSI Wind Top AE1900), industrial and medical equipment.

Principle of operation

1. The screen is touched with a conductive object (finger, special stylus).
2. Current flows from the screen to the object.
3. The controller measures the current strength at the corners of the screen and determines the coordinates of the touch point.

Advantages

• High durability (up to 200 million clicks), the ability to work at low temperatures (up to -15 ° C)

disadvantages

• Susceptible to moisture, conductive dirt
• Do not support multitouch

Device examples

• Phones, touchpads (for example, in the iRiver VZO player), PDAs, ATMs, kiosks.

Principle of operation

1. The screen is touched or a conductive object is brought close to it, forming a capacitor with it.
2. At the point of contact, the electrical capacitance changes.
3. The controller registers the change and determines at which intersection of the electrodes it occurred. Based on these data, the coordinates of the touch point are calculated.

Advantages

• High durability (up to 200 million clicks), the ability to work at low temperatures (down to -40 ° C)
• High vandal resistance (the screen can be covered with a layer of glass up to 18 mm thick)
• High light transmission (over 90%)
• Support Multitouch

disadvantages

• React to the touch of only a conductive object (finger, special stylus)

Device examples

• Phones (for example, iPhone), touchpads, screens of laptops and computers (for example, HP TouchSmart tx2) electronic kiosks, ATMs, payment terminals.

Windows 7

In addition, it became possible to control the computer using the Scroll, Forward/Back, Rotate, and Zoom gestures. The Windows 7 operating system is much better adapted to work with touch displays than all previous versions. 06 this is evidenced by the modified interface and the taskbar, in which square icons appeared instead of rectangular buttons symbolizing running programs - they are much more convenient to press with your finger. In addition, there is a new feature - jump lists, allowing you to quickly find recently opened files or frequently used items. To activate this feature, just drag the program icon to the desktop.

For the first time in the Windows operating system, the option of recognizing touch gestures, to which the execution of certain functions is tied, has been added. So, in Windows 7 touch scrolling appeared and the same as, for example, in the Apple iPhone, the ability to enlarge pictures or documents by moving two fingers in different directions. Not without movement, responsible for the rotation of the image. Operations such as copy, delete, and paste can also be assigned separate gestures. The on-screen keyboard buttons light up when touched, making it easy to use on a touch screen. And the ability to recognize handwriting allows you to quickly enter small messages.

Touch screen devices (mobile phones, tablets, netbooks, even personal computers) are becoming more and more popular. But if you decide to buy a device whose screen responds to touch, you should know that there are different touch screen types.

Different types of touch screens work on different physical principles.. There are two main types of touch screens - capacitive and resistive. There are other types, for example, screens on surface acoustic waves, infrared, optical, strain gauge, induction (used in), etc. But the chance to encounter these types of screens in everyday life is quite small, so let's talk about the two most common types of touchscreens .

Touch screen types: resistive

Resistive touch screen is a simpler and cheaper technology. Such a screen consists of two main parts: a conductive substrate and a plastic membrane. When you press the membrane, it closes with the substrate. In this case, the control electronics calculates the resistance that occurs between the edges of the membrane and the substrate, and thus determines the coordinates of the pressure point.

Resistive touch screens are used in PDAs, communicators, some models of mobile phones, POS-terminals, tablet computers, industrial control devices, medical equipment. Usually, small-sized devices equipped with a resistive screen are equipped with a stylus to make it more convenient to press the membrane (with a small screen area, it is difficult to do this with a finger).

A significant advantage of resistive screens is their simplicity and low cost., which ultimately reduces the price of the entire device. They are also stain resistant. But the main thing is that even in the absence of a special stylus, you can work with them with almost any hard, blunt object that is at hand. They also react to the touch of fingers, even if the hand is in a glove, however, the touch should be strong enough.

But resistive screens also have their drawbacks.. This type of touch screen is sensitive to mechanical damage: if you use an inappropriate object instead of a stylus or, say, store your phone in the same pocket as your keys, you can easily scratch it. Therefore, for devices with this type of screens, it is better to additionally purchase a special protective film. The sensitivity of resistive screens decreases at low temperatures. In addition, their transparency also leaves much to be desired: they transmit a maximum of 85% of the light coming from the display.

Touch screen types: capacitive

Capacitive touch screens take advantage of the fact that high-capacity objects (in this case, a person) conduct alternating electrical current. Such screens are a panel of glass, which is covered with a transparent resistive alloy. A small alternating voltage is transmitted to the conductive layer. If you touch your finger with a screen or other conductive object, current leakage occurs, it is detected by sensors, and the coordinates of the point of pressing are calculated.

There are conventional capacitive screens and projective-capacitive. The second technology is more "advanced". Such screens are more sensitive (say, they react to a gloved hand, depending on just capacitive ones), support multi-touch technology(simultaneous determination of the coordinates of several touch points). Capacitive screens are used in ATMs, information kiosks and protected areas. Projection-capacitive - in outdoor electronic kiosks, payment terminals, ATMs, laptop touchpads, smartphones and other devices that support multi-touch technology.

Advantages of such touch screens- this is durability, resistance to most contaminants (to those that do not conduct current), high transparency of the screen, the ability to work at low temperatures. If necessary, high strength can be ensured - a glass layer on a capacitive screen can be up to 2 cm thick. Capacitive screens respond to the slightest touch. Projected capacitive screens also support multi-touch.

The disadvantage of capacitive screens is a higher cost compared to resistive ones.. In addition, such screens only respond to conductive objects: a finger or a special stylus (not the same as used with resistive screens). Some craftsmen manage to use sausages, but where is the guarantee that the sausage will be at hand at the right time?

As you can see Different types of touch screens have their own advantages and disadvantages., so it's up to you to decide which one is more suitable for you personally.

Humanity has always liked to be divided into groups: Catholics and Protestants, vegetarians and meat eaters, fans of touch screens and those who do not feel much attraction to them. Fortunately, tech geeks are unlikely to start a war or crusade against those who do not share their point of view, despite the fact that the army of adherents of "finger-oriented" interfaces is growing at the rate of development of the technology itself. How is it all arranged?

Smartphones and tablets: how does the screen work?

The first touch screen appeared 40 years ago in the USA. The IR beam grid, consisting of 16x16 blocks, was installed in the Plato IV computer system. The first touch-screen TV was shown at the 1982 World's Fair, a year later the first personal computer HP-150 was presented. In phones, touch screens appeared much later: in 2004, at 3GSM Congress (as the Mobile World Congress was called at that time), Philips presented three models (Philips 550, 755 and 759) to journalists. At that time, mobile operators had high hopes for the MMS service, so the main functions of the touch screen were entertaining: in order to make MMS more emotional, the developers offered users to process photos with a stylus - sign, add details - and only then send it to the addressee.

At the same time, it became possible to use a virtual keyboard, but since all models had a digital one, and the touch screen significantly increased the cost of devices, they were forgotten for a while. A year later, Fly X7 appeared - a fully touch-sensitive monoblock, unfortunately, with a number of hardware flaws, which, coupled with the brand's then obscurity, buried it among unremarkable models. And these were not the only attempts to create something new, however, despite a number of predecessors, only the Apple iPhone, LG KE850 PRADA and the HTC Touch line, which appeared on the market in 2007, can be called the first full-fledged "finger-oriented" models. It was they who initiated the era of touch phones.

Strictly speaking, the touch element is not a screen - it is a conductive surface that works in tandem with the screen and allows data to be entered using a finger or other object.

How does the screen recognize touch?

There are many types of touch screens, but we will focus only on those that are widely used in mobile devices: smartphones and tablets.

The resistive display consists of a flexible plastic membrane and a glass panel, the space between which is filled with micro-insulators that isolate the conductive surface. When you press the screen with your finger or stylus, the panel and membrane close, and the controller registers a change in resistance, based on which smart electronics determines the coordinates of pressing. The main advantages are low cost and ease of manufacture, which reduces the market value of the final device.

Also, the undoubted advantages include the fact that the screen responds to any pressing - when working with it, it is not necessary to use a special conductive stylus or finger, a fountain pen or any other object with which you can press on a certain point of the screen is quite suitable for this. The resistive screen is resistant to dirt. A number of operations can be carried out even with a gloved hand - for example, answer a call in the cold season. However, it was not without drawbacks. The resistive screen is easily scratched, so it is advisable to cover it with a special protective film, which in turn does not affect the image quality in the best way. Moreover, these scratches tend to increase in size.

The screen has a low transparency - only 85% of the light coming from the display passes through. At low temperatures, the screen "freezes" and reacts worse to pressing, it is not very durable (35 million clicks at one point). The forerunners of resistive screens were matrix touch screens, which were based on a sensor grid: horizontal conductors were applied to the glass, and vertical conductors to the membrane. When touching the screen, the guides closed and indicated the coordinates of the point. This technology is still used today, but it is almost never found in smartphones.

Resistive screen circuit

The technology of capacitive screens is based on the fact that a person has a large electrical capacity and is able to conduct current. In order for everything to work, a thin conductive layer is applied to the screen, and a weak alternating current of small magnitude is applied to each of the four corners. Touching the screen causes a leak point, which depends on how far from the corner of the display the touch occurred. According to this value, the coordinates of the point are determined. Such screens are more resistant to scratches, do not let liquid through, are more durable (about 200 million clicks) and transparent compared to resistive ones, moreover, they respond to the lightest touches. However, this has its drawbacks - during a conversation, you can awkwardly touch your phone with your ear and easily launch some application, you won’t answer a call with a gloved hand - the electrical conductivity is not the same. The higher cost of the screen, of course, affects the price of the device.

Capacitive Screen Diagram

How does my iPhone work?

More advanced types of capacitive screens include projected capacitive screens. An electrode is applied to the inner surface of the glass, and a person acts as the second electrode. When you touch the screen, a capacitor is formed, by measuring the capacitance of which you can determine the coordinates of pressing. Since the electrode is applied to the inner surface of the screen, it is very resistant to dirt; the glass layer can reach 18 mm, which can significantly increase the life of the display and resistance to mechanical damage.

One of the most interesting features of projected capacitive screens is the support for multi-touch technology. They also have great sensitivity and have a relatively wide temperature range of operation, but they still do not interact very well with a gloved hand. It would seem that this may confuse potential buyers, but a few years ago, one of the enterprising Korean iPhone fans guessed to use an ordinary sausage as a stylus, the electrical conductivity of which made it possible to answer a call. The controversial trend caused a storm of enthusiasm on the forums and attracted the attention of accessory manufacturers, who launched a special sausage stylus for sale. Before the usual sausage, he has at least one plus - he does not leave greasy marks on the device screen.

Diagram of a projection-capacitive screen

Regardless of the screen technology, it has a number of typical characteristics. In addition to resolution, the main characteristics of the screen include the viewing angle and color reproduction, which depends on the type of display. The concept of color reproduction is inextricably linked with "color depth" - a term that refers to the amount of memory in the number of bits used to store and transmit color. The more bits, the deeper the colors. Modern LCD displays in smartphones and tablets display 18-bit color (more than 262,000 shades). The maximum possible at the moment is 24-bit TrueColor, which is capable of reproducing more than 16 million colors in AMOLED and IPS matrices.

The viewing angle, like any angle, is measured in degrees and characterizes the value at which the brightness and readability of the screen drops no more than twice, if you look at it directly perpendicular. LCDs have this characteristic, but not OLEDs.

Comparison of media players: pros and cons

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Screen types of smartphones and tablets

At the moment, in the production of smartphones and tablets, as a rule, either LCD or OLED displays are used.

LCD-screens are based on liquid crystals, which do not have their own glow, therefore, in the ultimate order, they require a backlight lamp. Under external influence (temperature or electric), crystals can change their structure and become opaque. By controlling the current, you can create inscriptions or pictures on the display.

LCD pixel circuit

Liquid crystal displays used in smartphones and tablets are mostly active matrix (TFT). TFT-matrices use transparent thin-film transistors, which are located directly under the surface of the screen. A separate transistor is responsible for each point of the image, so the picture is updated quickly and naturally.

With the advent of LCD TFT matrices, the display response time has increased significantly, but problems with color reproduction, viewing angles and dead pixels remain.

LCD pixel circuit

The most common TFT matrices are TN+film and IPS. TN+film is the simplest technology. Film is an additional layer that is used to increase the viewing angle. Of the advantages of such matrices - a short response time and low cost, cons - poor color reproduction and, alas, viewing angles (120-140 degrees). In IPS-matrices (In-Plane-Switchin), it was possible to increase the viewing angle to 178 degrees, increase the contrast and color reproduction to 24 bits and achieve deep blacks: in this matrix, the second filter is always perpendicular to the first, so light does not pass through it. But the response time is still low. Super-IPS is a direct successor to IPS with a reduced response time.

PLS-matrix (Plain-to-Line Switchin) appeared in the bowels of Samsung as an alternative to IPS. Its advantages include a higher pixel density than IPS, high brightness and good color reproduction, low power consumption, large viewing angles. The response time is comparable to Super-IPS. Among the shortcomings - uneven illumination. The next generation, Super-PLS, outperformed IPS in viewing angles by 100% and by 10% in contrast ratios. Also, these matrices turned out to be cheaper in production by as much as 15%.

OLED displays use organic light-emitting diodes, which emit their own glow when exposed to electricity. Compared to LCDs, OLEDs have many advantages. Firstly, they do not use additional backlighting, which means that the smartphone battery does not run out as quickly as in the case of LCDs. Secondly, OLED displays are thinner. The thickness and design of the device directly depends on this characteristic. In addition, OLED displays can be flexible, which bodes well for development. OLED does not have such a parameter as "viewing angle" - the image is well viewed from any angle. In terms of brightness and contrast (1,000,000:1), OLED also leads.

He is praised for vibrant and rich colors and separately for deep blacks. But there are, of course, downsides. One of the main ones can be called fragility: organic compounds are unstable to the environment and tend to burn out, and some colors of the spectrum suffer more than others. Although if you change your phone every three years, this is unlikely to be an argument against the purchase. In addition, OLEDs are still more expensive to manufacture than LCDs.

OLED circuit

Second-generation OLED screens also mostly have an active TFT matrix. They are called AMOLED. The main advantage is even lower power consumption, the disadvantages are the unreadability of the picture in bright sunlight.

AMOLED circuit

The next step in the development of technology was SuperAMOLED screens, which Samsung first began to use. Their fundamental difference from AMOLED is that films with active transistors (TFT) are integrated into a film of semiconductors. This results in a 20% increase in brightness, a 20% reduction in power consumption and an increase in sunlight readability by as much as 80%!

SUPERAMOLED circuit

Do not confuse OLED screens with LED-backlit screens - they are completely different things. In the latter case, a regular LCD gets a back or side LED backlight, which certainly improves image quality, but still falls short of AMOLED or SuperAMOLED.

What awaits us in the future?

At the moment, the clearest and most predictable prospects await OLED screens. Already now on the Web you can find information about the technology of the near future QLED - LEDs based on quantum dots (a semiconductor nanocrystal that glows when exposed to current or light). The strengths of this technology are high brightness, low production cost, wide color range, low power consumption. Quantum dots, which underlie the new technology, have another important property - they are able to emit spectrally pure colors. Already, this technology is predicted to have a bright future. Samsung has already developed a full-color 4-inch QLED display, but they are not in a hurry to launch the new product into mass production.

Prototype QLED display

But Samsung confirmed that this year will begin mass production of flexible OLED displays. Probably the first devices will be smartphones and tablets. The small thickness of the screen and the physical properties of the panel will significantly increase the useful area of ​​the screen and free up the hands of techno designers.

Another promising technology is IGZO, which is being developed by Sharp. It is based on the research of Professor Hideo Hosono, who decided to take a closer look at alternative semiconductors and as a result developed TAOS technology (Transparent Amorphous Oxide Semiconductors) - transparent amorphous oxide semiconductors that contain oxides of indium, gallium and zinc (InGaZnO), abbreviated as IGZO. Differences of the mixture from amorphous silicon, which was used in the production of TFT, can significantly reduce the response time, significantly increase the screen resolution, make it brighter and more contrast. Apple was very interested in the prospects of this technology and invested a billion dollars in the production of IGZO displays.