How the touch screen works. How touch screens work

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, the Fly X7 appeared - a fully touch-sensitive monoblock, unfortunately, with a number of hardware flaws, which, coupled with the then obscurity of the brand, 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 the 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 pressure - 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 back or side LED backlighting, 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 look at alternative semiconductors and as a result developed TAOS (Transparent Amorphous Oxide Semiconductors) technology - 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.

1

The structure of the touch screen (touchscreen) and the problems associated with its replacement

Touch screen- a device for input and output of information, which is a screen that reacts to touching it.

Resistive touch screen


The resistive touch screen consists of a glass panel and a flexible plastic membrane. Both the panel and the membrane have a resistive coating. The space between the glass and the membrane is filled with micro-insulators, which are evenly distributed over the active area of ​​the screen and reliably isolate conductive surfaces. When the screen is pressed, the panel and membrane are closed, and the controller, using an analog-to-digital converter, registers the change in resistance and converts it into touch coordinates (X and Y).


In general terms, the reading algorithm is as follows:
1. A voltage of + 5V is applied to the upper electrode, the lower one is grounded. The left and right are short-circuited and the voltage on them is checked. This voltage corresponds to the Y-coordinate of the screen.
2. Similarly, + 5V and “ground” are supplied to the left and right electrodes, the X-coordinate is read from the top and bottom.

Capacitive touch screens

A capacitive (or surface capacitive) screen takes advantage of the fact that an object of high capacity conducts alternating current.

A capacitive touch screen is a glass panel coated with a transparent resistive material (usually an alloy of indium oxide and tin oxide). Electrodes located at the corners of the screen apply a small alternating voltage (the same for all corners) to the conductive layer. When touching the screen with a finger or other conductive object, current leakage occurs. At the same time, the closer the finger is to the electrode, the lower the resistance of the screen, which means that the current strength is greater. The current in all four corners is recorded by sensors and transmitted to the controller, which calculates the coordinates of the touch point.

Earlier models of capacitive screens used direct current - this simplified the design, but with poor user contact with the ground, it led to failures.
Capacitive touch screens are reliable, with 200 million clicks (about 6 and a half years of clicks every one second), liquid-tight, and non-conductive pollution tolerant. Transparency at 90%. However, the conductive coating is still vulnerable. Therefore, capacitive screens are widely used in vending machines installed in a protected area. Not responsive to gloved hand.

Multitouch(eng. multi-touch) - a function of touch input systems that simultaneously determines the coordinates of two or more touch points. Multi-touch can be used, for example, to change the image scale: as the distance between touch points increases, the image is enlarged. In addition, multi-touch screens allow several users to work with the device at the same time. They are often used for other, simpler touch display functions such as single touch or quasi-multi-touch.
Multi-touch allows not only to determine the relative position of several touch points at any given time, it determines a pair of coordinates for each touch point, regardless of their position relative to each other and the boundaries of the touchpad. Proper recognition of all touch points enhances the interface capabilities of the touch input system. The range of tasks solved when using the multi-touch function depends on the speed, efficiency and intuitiveness of its application.

The most common multi-touch gestures

Move your fingers - smaller
Spread your fingers - bigger
Multi-finger move - scroll
Rotate with two fingers - Rotate an object/image/video

Resistive Touch Screen Installation Issues

Sometimes there is no complete analogue of the desired wheelbarrow at hand, or the pinout of the cable is different, the following problems may occur:
1. Touch rotated 90.270 degrees
- Swap X-Y



2. Turned the touch horizontally
- Swap X+ , X-


3. Turn the touch upside down
- Swap Y+ , Y-


These solutions should be carried out if the problem persists after calibrating the touch screen.

Replacing the touch screen did not help.
- Reflash phone

Resistance on TOUCHSCREEN contacts
Y-,Y+=550 Om Without pressing
X-,X+=350 Om Without pressing

Y +, X + = from 0.5 to 1.35 kOm Measurements were made in different corners of the touchscreen when pressed. Without touching the touchscreen, the resistance is infinity.
Y-,X-=from 1.35-0.5 kOm Measurements were made in different corners of the touchscreen when pressed. Without touching the touchscreen, the resistance is equal to infinity.

Depending on the touch screen model, the resistance may fluctuate. These measurements were made on the touch screen of an I9+++ phone.

When is it time to change the touch screen?

It is time to change the touch screen in the following cases:
- if it does not respond to touch
- you found an "oily spot" on it (multi-color stains)
- unable to calibrate touch screen
- entering the message and selecting the English text input mode, try to put dots over the entire area, if dashes appear instead of dots, then it's time to change
- entering the service-miscellaneous-Touch Screen, try to put dots over the entire area, if green stripes appear instead of crosses - it's time to change
- if you try to click on the icon, the desktops scroll or the icons fall off (vertical shedding of icons in iPhone-like phones)
- if 5 minutes after the calibration you again do not hit the icon you click on

Mobile phone (smartphone) and tablet display device. LCD screen device. Types of displays, their differences.

Foreword

In this article, we will analyze the device displays of modern mobile phones, smartphones and tablets. The screens of large devices (monitors, TVs, etc.), with the exception of small nuances, are arranged in a similar way.

We will disassemble not only theoretically, but also practically, with the opening of the display of the "sacrificial" phone.

Consider how a modern display works, we will use the example of the most complex of them - liquid crystal (LCD - liquid crystal display). Sometimes they are called TFT LCD, where the abbreviation TFT stands for "thin-film transistor" - thin film transistor; since the control of liquid crystals is carried out thanks to such transistors deposited on the substrate along with liquid crystals.

As a "sacrificial" phone, the display of which will be opened, will be a cheap Nokia 105.

The main components of the display

Liquid crystal displays (TFT LCD, and their modifications - TN, IPS, IGZO, etc.) consist of three components: a touch surface, an imaging device (matrix) and a light source (backlight). Between the touch surface and the matrix there is another layer, passive. It is a transparent optical adhesive or simply an air gap. The existence of this layer is due to the fact that in LCDs the screen and the touch surface are completely different devices, combined purely mechanically.

Each of the "active" components has a fairly complex structure.

Let's start with the touch surface (touchscreen, touchscreen). It is located at the topmost layer in the display (if it is; but in push-button phones, for example, it is not).
Its most common type now is capacitive. The principle of operation of such a touchscreen is based on the change in electrical capacitance between vertical and horizontal conductors when the user's finger is touched.
Accordingly, so that these conductors do not interfere with viewing the image, they are made transparent from special materials (usually indium-tin oxide is used for this).

There are also touch surfaces that react to the force of pressing (the so-called resistive), but they are already "leaving the arena".
Recently, combined touch surfaces have appeared that respond simultaneously to both the capacitance of the finger and the force of pressing (3D-touch displays). They are based on a capacitive sensor, complemented by a pressure sensor on the screen.

The touchscreen can be separated from the screen by an air gap, or it can be glued to it (the so-called "one glass solution", OGS - one glass solution).
This option (OGS) has a significant quality advantage, as it reduces the level of reflection in the display from external light sources. This is achieved by reducing the number of reflective surfaces.
In a "normal" display (with an air gap) there are three such surfaces. These are the boundaries of transitions between media with different light refractive index: "air-glass", then - "glass-air", and, finally, again "air-glass". The strongest reflections are from the first and last boundaries.

In the variant with OGS, there is only one reflective surface (external), "air-to-glass".

Although the display with OGS is very convenient for the user and has good characteristics; he also has a drawback that "pops up" if the display is broken. If in a "normal" display (without OGS), only the touchscreen itself (sensitive surface) is broken upon impact, then when the display with OGS is hit, the entire display may also be broken. But this does not always happen, so the statements of some portals that displays with OGS are absolutely not repairable are not true. The probability that only the outer surface has crashed is quite high, above 50%. But repair with separation of layers and gluing a new touchscreen is possible only in a service center; It's extremely difficult to repair by hand.

Screen

Now let's move on to the next part - the actual screen.

It consists of a matrix with accompanying layers and a backlight (also multi-layered!).

The task of the matrix and related layers is to change the amount of light passing through each pixel from the backlight, thereby forming an image; that is, in this case, the transparency of the pixels is adjusted.

A little more detail about this process.

Adjustment of "transparency" is carried out by changing the direction of polarization of light when passing through liquid crystals in a pixel under the influence of an electric field on them (or vice versa, in the absence of influence). In this case, the change in polarization itself does not change the brightness of the transmitted light.

The change in brightness occurs when polarized light passes through the next layer - a polarizing film with a "fixed" direction of polarization.

Schematically, the structure and operation of the matrix in two states ("there is light" and "there is no light") is shown in the following figure:

(image used from the Dutch section of Wikipedia with a translation into Russian)

The rotation of light polarization occurs in the liquid crystal layer depending on the applied voltage.
The more the directions of polarization coincide in a pixel (at the output of liquid crystals) and in a film with a fixed polarization, the more light eventually passes through the entire system.

If the directions of polarization turn out to be perpendicular, then theoretically the light should not pass at all - there should be a black screen.

In practice, such an "ideal" arrangement of polarization vectors is impossible to create; moreover, both because of the "non-ideal" liquid crystals, and not the ideal geometry of the display assembly. Therefore, there can be no absolutely black image on a TFT screen. On the best LCD screens, white/black contrast can be over 1000; on average 500 ... 1000, on the rest - below 500.

The operation of a matrix made using LCD TN + film technology has just been described. Liquid crystal matrices based on other technologies have similar operating principles, but a different technical implementation. The best color rendering results are obtained with IPS, IGZO and *VA (MVA, PVA, etc.) technologies.

Backlight

Now let's move on to the very "bottom" of the display - the backlight. Although modern lighting actually does not contain lamps.

Despite the simple name, the backlight has a complex multilayer structure.

This is due to the fact that the backlight lamp should be a flat light source with a uniform brightness of the entire surface, and there are very few such light sources in nature. And even those that exist are not very suitable for these purposes due to low efficiency, "bad" emission spectrum, or they require an "inappropriate" type and magnitude of glow voltage (for example, electroluminescent surfaces, see below). Wikipedia).

In this regard, now the most common are not purely "flat" light sources, but "point" LED backlighting with the use of additional scattering and reflective layers.

Let's consider this type of backlight by opening the display of the Nokia 105 phone.

Having disassembled the display backlight system to its middle layer, we will see in the lower left corner a single white LED that directs its radiation into an almost transparent plate through a flat edge on the inner “cut” of the corner:

Explanation for the picture. In the center of the frame is a mobile phone display divided into layers. In the middle in the foreground from below - a matrix covered with cracks (damaged during disassembly). In the foreground at the top - the middle part of the backlight system (the other layers are temporarily removed to ensure the visibility of the emitting white LED and the translucent "light guide" plate).
Behind the display, you can see the phone's motherboard (green) and the keyboard (bottom with round holes for transmitting button presses).

This translucent plate is both a light guide (due to internal reflections) and the first scattering element (due to "pimples" that create obstacles for the passage of light). When enlarged, they look like this:

In the lower part of the image, to the left of the middle, a bright emitting white backlight LED is visible.

The shape of the white backlight LED is better visible in the picture with a reduced brightness of its glow:

From below and above this plate, ordinary white matte plastic sheets are placed, evenly distributing the luminous flux over the area:

It can be conditionally called "a sheet with a translucent mirror and birefringence". Remember, in physics lessons, we were told about Icelandic spar, when passing through which the light split into two? This is similar to him, only with a little bit of mirror properties.

This is what an ordinary watch looks like if part of it is covered with this sheet:

The probable purpose of this sheet is a preliminary filtering of light by polarization (keep the necessary one, discard the unnecessary one). But it is possible that in terms of directing the light flux towards the matrix, this film also has some role.

This is how a "simple" backlight lamp is arranged in liquid crystal displays and monitors.

As for the "large" screens, their device is similar, but there are more LEDs in the backlight device.

Older LCD monitors used Cold Cathode Fluorescent Lamp (CCFL) instead of LED backlight.

Structure of AMOLED displays

Now - a few words about the device of a new and progressive type of displays - AMOLED (Active Matrix Organic Light-Emitting Diode).

The device of such displays is much simpler, since there is no backlight.

These displays are formed by an array of LEDs and each pixel individually glows there. The advantages of AMOLED displays are "infinite" contrast, excellent viewing angles and high energy efficiency; and the disadvantages are the reduced "life" of blue pixels and the technological difficulties in manufacturing large screens.

It should also be noted that, despite the simpler structure, the production cost of AMOLED displays is still higher than that of TFT LCD displays.

Surely all of you use computers and mobile devices, and only a few in general are able to tell how their processors, operating systems and other components work.

In the era of mobile gadgets, everyone has a touch (also called smart) screen, and almost no one knows what this touch screen is, how it works and what types of it exist.

What it is

Touch display (screen) is a device for visualizing digital information with the ability to exert a control effect by touching the display surface.

Based on different technologies, different displays only respond to certain factors.

Some read the change capacitance or resistance in the area of ​​contact, others on temperature changes, some sensors react only to a special pen to avoid accidental clicks.

We will consider the principle of operation of all common types of displays, their areas of application, strengths and weaknesses.

Among all the existing principles of device control by means of a matrix sensitive to any factors, Let's take a look at the following technologies:

• resistive (4-5 wire);
• matrix;
• capacitive and its variants;
• surface acoustic;
• optical and other less common and practical.

In general, the scheme of work is as follows: the user touches the screen area, the sensors transmit data to the controller about the change in any variable (resistance, capacitance), it calculates the exact coordinates of the contact point and sends them.

The latter, based on the program, responds appropriately to pressing.

Resistive

The simplest touch screen is resistive. It reacts to changes in resistance in the area of ​​​​touching a foreign object and the screen.

This is the most primitive and widespread technology. The device consists of two main elements:

• conductive transparent substrate (panel) made of polyester or other polymer with a thickness of several tens of molecules;
• a light-conducting membrane made of a polymeric material (usually a thin layer of plastic is used).

Both layers are coated with a resistive material. Between them are microinsulators in the form of balls.

During the stage, the elastic membrane deforms (bends), comes into contact with the substrate layer and closes it.

The controller reacts to a short circuit by means of an analog-to-digital converter. It calculates the difference between the original and current resistance (or conductivity) and the coordinates of the point or area where this is done.

Practice quickly revealed the shortcomings of such devices, and engineers began to look for solutions, which were soon found by adding a 5th wire.

Four-wire

The top electrode is energized with 5V, and the bottom one is grounded.

The left and right are connected directly, they are the indicator of voltage change along the Y axis.

Then the top and bottom are shorted, and 5V is applied to the left and right to read the X-coordinate.

Five-wire

Reliability is due to the replacement of the resistive coating of the membrane with a conductive one.

The panel is made of glass and remains coated with a resistive material., and electrodes are placed at its corners.

First, all electrodes are grounded, and the membrane is energized, which is constantly monitored by the same analog-to-digital converter.

At the time of touch, the controller (microprocessor) detects the change in parameter and calculates the point/area where the voltage has changed in a four-wire circuit.

An important advantage is the ability to apply on convex and concave surfaces.

There are also 8-wire screens on the market. Their accuracy is higher than those considered, but this does not affect reliability in any way, and the price differs markedly.

Conclusion

The considered sensors are used everywhere due to their low cost and resistance to the influence of environmental factors, such as pollution and low temperatures (but not below zero).

They respond well to touch with almost any object, but not sharp.

The area of ​​a pencil or match is usually not enough to trigger a controller response.

Such displays are put on, used in the service sector (offices, banks, shops), medicine and education.

Wherever the devices are isolated from the external environment, and the probability of being damaged is minimal.

Low reliability (the screen is easy to damage) is partially offset by a protective film.

Poor operation in cold weather, low light transmission (0.75 and 0.85, respectively), resource (no more than 35 million clicks for a terminal that is constantly used, quite a bit) are the weaknesses of the technology.

Matrix

A more simplified resistive technology that arose even before it.

The membrane is covered with rows vertical conductors, and the substrate horizontal.

When pressed, the area where the conductors are connected is calculated and the received data is transmitted to the processor.

It already generates a control signal and the device reacts in a certain way, for example, performs an action assigned to a button).

Peculiarities:

• very low accuracy (the number of conductors is very limited);
• the lowest price among all;
• implementation of the multitouch function due to polling the screen line by line.

They are used only in obsolete electronics and have almost gone out of use due to the availability of progressive solutions.

capacitive

The principle is based on the ability of high-capacity objects to become conductors of alternating electric current.

The screen is made in the form of a glass panel with a thin layer of sprayed resistive material.

Electrodes at the corners of the display apply a small AC voltage to the conductive layer.

At the moment of contact, current leakage occurs, if the object has a greater electrical capacitance than the screen.

Current is recorded at the corners of the screen, and information from the sensors is sent to the controller for processing. Based on them, the contact area is calculated.

The first prototypes used DC voltage. The solution made the design easier, but crashes often occurred when the user was not in contact with the ground.

These devices are very reliable, their resource exceeds resistive ones by ~ 60 times (about 200 million clicks), moisture resistant and perfectly tolerate pollution that does not conduct electric current.

Transparency is at the level of 0.9, which is slightly higher than resistive ones, and operate at temperatures up to - 15 0 C.

Flaws:

• does not react to the glove and most foreign objects;
• the conductive coating is in the top layer and is very vulnerable to mechanical damage.

Are used in the same ATMs and terminals under the closed sky.

Projected-capacitive

An electrode grid is applied to the inner surface, which forms a capacitance (capacitor) with the human body. Electronics (microcontroller and sensors) work on the calculation of coordinates at and sends the calculations to the central processor.

They have all the features of capacitive.

In addition, they can be equipped with a thick film up to 1.8 cm, which increases protection against mechanical stress.

Conductive pollution, where it is difficult or impossible to eliminate them, is removed without problems by the software method.

Most of all others are installed in personal electronic devices, ATMs and various equipment actually installed in the open (under cover). Apple also favors projected capacitive displays.

Surface acoustic wave

It is made in the form of a glass panel equipped with piezoelectric probe transducers located at opposite corners and receivers.

They are also a pair and are on opposite corners.

The generator sends an RF electrical signal to the PET, which turns a series of pulses into a SAW, and the reflectors distribute it.

The reflected waves are picked up by sensors and sent to the probe, which converts them back into electricity.

The signal is sent to the controller, which analyzes it.

When touched, the parameters of the wave change, in particular, part of its energy is absorbed in a certain place. Based on this information, the area of ​​contact and its strength are calculated.

The very high transparency (above 95%) is due to the absence of conductive/resistive surfaces.

Sometimes, to eliminate glare, light reflectors along with receivers mounted directly on the screen.

The complexity of the design in no way affects the operation of a device with such a screen, and the number of touches at one point is 50 million times, which slightly exceeds the resource of resistive technology (65 million times in total).

They are produced with a thin film of about 3 mm and a thickened one - 6 mm. Thanks to this protection, the display can withstand a slight blow with a fist.

Weak sides:

• poor performance in conditions of vibration and shaking (in transport, when walking);
• lack of resistance to pollution - any foreign object affects the functioning of the display;
• interference in the presence of acoustic noise of a certain configuration;
• the accuracy is slightly lower than in capacitive ones, which is why they are unsuitable for drawing.

Smartphone users who do not speak English well are puzzled when they hear the name "touchscreen" - what is this part of the phone? Usually, this is the name of any touch screen, regardless of which device it is installed on. Currently, such displays are used not only for mobile gadgets, but are also built into various self-service terminals.

What is a touchscreen?

This term comes from the merger of 2 English words: touch and screen, which means “touch screen” in translation. Such a display responds to touch and makes it easier to control equipment. However, it is worth distinguishing between several types of equipment, since the principle of their operation is not quite similar.

In modern gadgets, for example, on an iPhone, capacitive and projected-capacitive displays are installed. The latter type can be called more advanced, since it is able to read a certain number of touches at the same time. By themselves, such touchscreens are glass panels with a layer of resistive material and electrodes.

There are also displays on which a flexible membrane is applied. Between it and the glass are microinsulators, pressing on which provokes a change in resistance. It is fixed by the controller and converted into coordinates, as a result of which the device is controlled.

The main difference between these types of technologies is that the capacitive display does not respond to touch with any object and even a simple stylus, which cannot be said about the resistive touchscreen. Thus, blocking a smartphone on it works much better than on its outdated “brother”.

How different screens work

There are only 3 types of Touch Screen, 2 of which have already been briefly described:

• capacitive;
• wave;
• resistive.

It is worth starting with the most used, i.e. capacitive display. How does such a screen work on a phone? Everything is pretty simple. The resistive layer serves as a charge storage that the electrodes let through, while the user pushes out some of the energy at a certain point with their touch. This works because there is also current in the human body. When the degree of charge decreases, this change is fixed by microcircuits and transferred to the touchscreen driver.

The main advantage of such displays is that they are quite durable. For a long time, they do not lose their original brightness and are able to transmit clearer images.

The principle of operation of the resistive screen was described above. If we understand this in more detail, then it should be said that a flexible membrane is an elastic metal plate that passes current. There is an empty space between it and the conductor layer. Interacting with the display, the user makes a light pressure on its surface, closing the membrane with the conductor at this point. Then everything happens according to the same scheme: the system reads the coordinates, and the driver issues commands to the OS.

Resistive displays are no longer popular, as their functionality is somewhat limited compared to capacitive touchscreens. Such screens can only be found in very outdated equipment or various terminals, but less often.

What is a wave touchscreen? It is also a glass surface with coordinate grid and transducers. One of them transmits impulses, while the other receives signals reflected by the reflector. Thus, the charge "walks" through the transducers, creating an acoustic wave, which the user interrupts by pressing. This is how the touch point is determined.

This type of display is the best option for artists and graphic designers, because it does not distort the image due to the lack of a metal coating. It is also the most expensive, while many refer it to the technologies of the future, believing that even a capacitive display will go into oblivion, giving way to wave technology.

Video review: types of touchscreen