Resistive touchscreen. How the sensor works

A universal type of touch screen has not yet been developed, and the technologies currently used have both their advantages and disadvantages. Read about the pros and cons of the main types of touch screens in this material.

The use of touch screens is most appropriate in small portable devices. Firstly, this is due to the inconvenience of using a mouse, keyboard and other input devices in phones and other small electronics. Secondly, eliminating hardware buttons allows you to significantly increase the screen area. Thirdly, the production of touch panels is expensive, and their use in large screens is still at least economically unprofitable.

However, starting with such small devices as PDAs, touch screens have already reached medium format (tablets and some laptops), and their appearance on big screen It's just a matter of time.

There are only a few types of touch screens. Below we will discuss the three most common technologies, as well as several of its varieties.

RESISTIVE PANELS

The touch part of such screens consists of two layers separated by a small space, each of which has an array of resistive or conductive elements (depending on the specific implementation).

When you press with a finger, stylus (or any other object) on the surface of the screen, these layers come into contact, the elements close, and the screen “understands” where it was touched.

Considering that contact between the two layers is only possible using a flexible material that will bend under pressure, resistive screens are usually covered with a special flexible film rather than glass. This leads to scratches and more frequent damage to the screen when applying excessive pressure with the stylus.

The technology is one of the simplest, which is why it first appeared in touch devices. It still has some advantages, but there are more disadvantages than other types of touch screens.

Advantages

In addition to the low price (the cost of such displays is approximately half that of capacitive ones), the accuracy of resistive screens also depends little on the condition of the top layer, so if it gets dirty or wet, the responsiveness of the sensor practically does not change.

Despite the age of the technology, it still allows us to make the most accurate touch panels. In a properly calibrated display, you can actually hit a specific pixel with the stylus thanks to a dense lattice of resistive elements.

Flaws

Despite the fact that there are exceptions to this rule, most resistive screens do not recognize multi-touch, that is, the screen understands only one touch (the very first or the strongest), which significantly limits the ability to control the interface. Even in devices where multi-touch is implemented, fewer simultaneous touches are still recognized than in the most common capacitive screens.

Using multiple layers reduces the contrast and brightness of the screen. The light transmission coefficient is ~75%, which is ~15% lower than in capacitive screens. Thus, in devices with a resistive sensor, the contents of the screen are more difficult to view in direct sunlight or under strong artificial lighting.

The use of two layers separated by a small gap is an indirect reason for reducing the accuracy of the sensor. If you hold the stylus perpendicular to the screen, then the accuracy may be the same, but at an angle, the discrepancy will be several pixels due to the fact that the point on which the stylus presses is not directly above the desired pixel (parallax effect).

Protection against accidental input in resistive screens is a certain pressure that must be overcome in order for the device to count the command. Consequently, it is more difficult to equip resistive screens with an additional protective coating, which will only increase the response threshold. Paired with a plastic coating, which is necessary for the flexibility of the touch layer, resistive screens are more susceptible to damage than others, especially scratches, and if handled incorrectly (pressing hard with a sharp object), they can simply crack.

Despite the fact that the number of clicks at each specific point is estimated at 30 million, resistive screens still fail earlier than other types and are the most unreliable by this indicator.

Conclusion

Low cost and resistance to contamination (or rather, maintaining input accuracy when contaminated), coupled with all of the above disadvantages, have become the reason that resistive screens are slowly being forced out of use, although they have been able to gain a foothold in some niches, for example, in the sector of terminals for fast payment.

Styluses

A characteristic feature of devices with a resistive sensor is the widespread use of a stylus, the contact area of ​​which with the surface is smaller than that of a finger, and the pressure force is greater, which results in more accurate input.

The presence of a stylus is desirable, although not necessary for screens with a small diagonal (mainly phones, and a few years ago, PDAs), however, in tablets, sufficient accuracy can be achieved using your fingers.

After PDAs were completely replaced by smartphones and other devices several years ago, it seemed that styluses had left the scene along with them forever, but now you can increasingly see their reincarnation, especially in devices of intermediate sizes between smartphones and tablets.

Since resistive screens are used less and less now, styluses have also changed a bit. Adjusting to modern realities, they began to be produced with special attachments at the end, which are recognized by capacitive screens.

CAPACITIVE PANELS

The principle of operation of capacitive screens is that a small voltage is applied to a special layer of electrical conductor located on the outer surface of the screen, forming a uniform electrostatic field. When a finger, which is a conductor of electricity, is applied to the screen, the properties of the field change due to the appearance of a leak (the user acts as a ground electrode and “steals” current from the screen). By changing the capacitance, you can determine the presence of a contact and its coordinates.

To determine the coordinates, electrodes are installed in the corners of the screen that measure the strength of the leakage current, and the stronger it is on each specific sensor, the closer the pressing occurred. By defining specific values, you can very accurately calculate the coordinates of the click.

A subclass of capacitive screens are projection-capacitive screens, the operating principle of which is also to measure capacitance, but the basic elements in them are not located on outside screen, but on the inside, which increases the security of the sensor. These are the screens that are now used everywhere in smartphones.

Unlike resistive panels, which use a flexible material, capacitive sensors are covered with glass. This better protects them from scratches, although they are more likely to cause cracks if subjected to a strong impact or fall.

Advantages

The absence of multiple layers of additional materials not only increases the brightness of the screen (transparency to light is approximately 90%), but also reduces the distance between the screen surface and the image, allowing you to more accurately hit the desired pixels. Even if the gain is not big, it is still noticeable, especially when the device is at a certain angle relative to the axis of view, that is, at those moments when the difference between the actual position of the desired pixel on the screen and the point you need to hit shift as much as possible relative to each other friend.

Displays Super AMOLED Samsung allows you to further reduce the thickness of the screen by eliminating the additional layer of capacitive elements. In this type of screen they are built directly into the matrix.

Capacitive screens are much more durable than resistive screens (almost by an order of magnitude) when it comes to the number of clicks before the touch elements fail. The number of such repetitions is estimated at 200+ million times.

Flaws

Capacitive screens are more expensive to manufacture than resistive screens and require that the material touching their surface must have the properties of a conductor. Therefore, it will not be possible to use any convenient object or work with ordinary gloves with capacitive screens. In this regard, special capacitive styluses and gloves for working with touch panels in cold weather are becoming widespread.

The accuracy of capacitive screens is somewhat lower than that of resistive screens, although in practical tasks this difference is not very noticeable, since it is literally 1-3 pixels, and given that in most cases the program interface is already designed to eliminate these errors, it is difficult to call this a disadvantage .

Conclusion

Capacitive panels, in terms of their characteristics and price, are best suited for mobile device screens, which is why they now dominate this sector.

INFRARED PANELS

Despite the fact that infrared sensors began to appear in devices later than other types of panels, they should not be considered more advanced. They have several advantages, however, most likely, like resistive screens, they will remain niche and will not be able to displace capacitive panels.

Optical

The main difference between infrared sensors and all others is that special sensors are located not on the surface of the screen, but along the edges of it and form a series of horizontal and vertical infrared rays directly above the display. When an object touches the screen, the rays are broken and thus the location of contact is determined.

Thermal

A type of infrared screens are screens with thermal sensors. In order for them to respond to touch, the object must be warm.

Like capacitive panels, devices with infrared sensors use a protective glass coating, which causes the same advantages and disadvantages: better scratch resistance, but more likely to crack if hit hard.

Advantages

The location of the sensors on the sides of the matrix makes it possible to eliminate the intermediate layer on the LCD matrix, which improves the brightness of the picture (the transparency of the coating is almost 100%), reduces the gap between the real image and the screen surface, makes the display more resistant to damage, and also allows you to work with contaminated screen, but provided that contamination does not interfere with the free propagation of infrared rays.

Infrared (optical) screens can be operated with gloves or using any other convenient objects.

Flaws

Any contamination at the edges of the matrix, obscuring infrared signal sources, leads to malfunctions of the sensors. Problems also arise with slight curvature of the device, when the rays leave a plane parallel to the screen.

However, one of the most common problems with infrared sensors is false alarms. Since users do not have to physically touch the screen, sometimes the sensors are activated when the finger is sufficiently close to the screen or while it moves from one point to another.

Despite the fact that infrared sensors are often used in devices with a relatively low cost (for example, e-readers), screens with an infrared sensor themselves are more expensive than both resistive and capacitive screens.

Conclusion

If resistive and capacitive screens could be conditionally classified as respectively dying out and dominant types of screens, then infrared sensors are a marginal device technology, since they are used in little-known models of portable electronics. The exception is e-books, for example Nook Touch.

INSTEAD OF AN EPILOGUE

Touch and conventional displays will see many more innovations in the near future (flexible matrix, new protective coatings), but when it comes to technologies responsible for input recognition, there are no revolutionary alternatives on the horizon, so capacitive sensors will continue to dominate. as the most convenient and relatively inexpensive compared to other types of sensors.

Display device for a mobile phone (smartphone) and tablet. LCD screen device. Types of displays, their differences.

Preface

In this article we will analyze the display structure of modern mobile phones, smartphones and tablets. The screens of large devices (monitors, televisions, etc.), with the exception of small nuances, are arranged similarly.

We will carry out disassembly not only theoretically, but also practically, by opening the display of the “sacrificial” phone.

Consider how it works modern display, we will use the example of the most complex of them - liquid crystal display (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 the liquid crystals.

The cheap Nokia 105 will serve as a “sacrificial” phone whose display will be opened.

Main components of the display

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

Each of the “active” components has a rather complex structure.

Let's start with the touch surface (touchscreen). It is located on the topmost layer of the display (if it exists; 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 a change in the electrical capacitance between vertical and horizontal conductors when touched by the user’s finger.
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 respond to pressure (so-called resistive), but they are already “leaving the arena”.
IN lately Combined touch surfaces have also appeared, reacting simultaneously to both the capacity 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, since it reduces the level of reflection in the display from external sources Sveta. This is achieved by reducing the number of reflective surfaces.
In a “regular” display (with an air gap) there are three such surfaces. These are the boundaries of transitions between media with different refractive indexes of light: “air-glass”, then “glass-air”, and finally again “air-glass”. The strongest reflections are from the first and last boundaries.

In the version 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; It also has a drawback that “pops up” if the display is broken. If in a “regular” display (without OGS) only the touchscreen itself (sensitive surface) breaks upon impact, then when a display with OGS is hit, the entire display may break. 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 broke is quite high, above 50%. But repairs involving the separation of layers and gluing of a new touchscreen are only possible at a service center; Repairing it yourself is extremely problematic.

Screen

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

It consists of a matrix with accompanying layers and a backlight lamp (also multilayer!).

The task of the matrix and its related layers is to change the amount of light passing through each pixel from the backlight, thereby forming an image; that is, in in this case pixel transparency 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 the liquid crystals in the pixel under the influence of an electric field (or vice versa, in the absence of influence). At the same time, a change in polarization in itself does not change the brightness of the transmitted light.

A change in brightness occurs when polarized light passes through the next layer - a polarizing film with a “fixed” polarization direction.

The structure and operation of the matrix in two states (“there is light” and “there is no light”) is schematically shown in the following figure:

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

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

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

In practice, such an “ideal” arrangement of polarization vectors cannot be created; moreover, both due to the “imperfection” of liquid crystals and the imperfect geometry of the display assembly. Therefore, there cannot be an absolutely black image on a TFT screen. On the best LCD screens, the white/black contrast can be over 1000; on average 500...1000, on the rest - below 500.

Just described matrix work, manufactured using LCD TN+film technology. Liquid crystal matrices using other technologies have similar operating principles, but a different technical implementation. The best color rendering results are obtained by IPS technologies, IGZO and *VA (MVA, PVA, etc.).

Backlight

Now we move on to the very “bottom” of the display - the backlight. Although modern lighting does not actually contain lamps.

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

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

In this regard, the most common now are not purely “flat” light sources, but “spot” LED lighting with the use of additional scattering and reflective layers.

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

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

Explanations for the photo. In the center of the frame is a display divided into layers mobile phone. In the middle in the foreground below is a matrix covered with cracks (damaged during disassembly). In the foreground at the top is the middle part of the backlight system (the remaining layers are temporarily removed to provide visibility of the emitting white LED and translucent "light guide" plate).
Visible from behind the display motherboard phone (green) and keyboard (bottom with round holes for transmitting presses from the buttons).

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). Enlarged, they look like this:

At the bottom of the image, to the left of the middle, a bright emitting white LED backlight is visible.

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

Ordinary white matte plastic sheets are placed on the bottom and top of this plate, evenly distributing the light flux over the area:

It can be conditionally called “a sheet with a translucent mirror and birefringence.” Do you remember in physics lessons they told us about Iceland spar, when light passed through it it split into two? This is similar to it, only with a little more mirror properties.

This is what regular ones look like wrist watch, if some of them are covered with this sheet:

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

This is how a “simple” backlight lamp in liquid crystal displays and monitors works.

As for “large” screens, their structure is similar, but there are more LEDs in the backlighting device.

In older LCD monitors, instead of LED backlight used gas-light lamps with a cold cathode (CCFL, Cold Cathode Fluorescent Lamp).

Structure of AMOLED displays

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

The design 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. Advantages AMOLED displays are “infinite” contrast, excellent viewing angles and high energy efficiency; and the disadvantages are the reduced lifespan of blue pixels and the technological difficulties of manufacturing large screens.

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

At first, touchscreens (touch screens) were quite rare. They could only be found in some PDAs, PDAs ( pocket computers). As you know, devices of this kind never became widespread, since they lacked the most important thing, that is, functionality. The history of smartphones is directly related to touchscreens. That is why at the present time a person with “ smart phone“You won’t be surprised by a touch screen these days. The touchscreen is widely used not only in fashionable expensive devices, but even in relatively inexpensive models modern phones. What are the principles of operation of the 3 types of touch screens that can be found in modern devices Oh.

Types of touchscreens

Touch screens are no longer too expensive. In addition, touchscreens today are much more “responsive” - they recognize user touches simply perfectly. It is this characteristic that paved the way for them to a large number of users around the world. Currently, there are three main designs of touchscreens:

1. Capacitive.
2. Wave.
3. Resistive or simply “elastic”.

Capacitive touchscreen: operating principle

In touchscreen designs of this kind, the glass base is covered with a layer that acts as a charge storage container. The user, with his touch, releases a part at a certain point electric charge. This reduction is determined by microcircuits that are located in each corner of the screen. The computer calculates the difference in electrical potentials existing between in different parts screen, in this case, information about the touch in detail is transmitted immediately to the touchscreen driver program.

A rather important advantage of capacitive touchscreens is the ability of this type screens to maintain almost 90% of the original display brightness. Because of this, images on a capacitive screen appear sharper than on touchscreens that have a resistive design.

Video about capacitive touch screen:

The future: waveform touch displays

The transducer-receiver “knows” absolutely exactly whether there was a press, as well as at what specific point it occurred, since the user interrupts the acoustic wave with his touch. At the same time, the glass of the wave display does not have a metal coating - this makes it possible to preserve 100% of the original light in full. In this regard, the wave screen is best option for those users who work in graphics with small details, because resistive and capacitive touchscreens are not ideal in terms of image clarity. Their coating blocks light, which results in significantly distorted images.

Video about the operating principle of surfactant touch screens:

Past: about resistive touchscreen

An electric charge passes through these two layers as the user interacts with the touchscreen. How does this happen? The user touches the screen at a certain point and the elastic top layer comes into contact with the conductive layer - only at this point. Then the computer determines the coordinates of the point that the user touched.

When the coordinates become known to the device, a special driver translates touches into commands known to the operating system. In this case, you can draw analogies with the driver of the most common computer mouse, because it does exactly the same thing: it explains to the operating system what the user specifically wanted to tell it by moving the manipulator or pressing a button. As a rule, special styluses are used with screens of this type.

Video about the operating principle of a resistive touch screen:

Features of different types of touchscreens

The cheapest touch screens, but at the same time the least clearly transmitting the image, are resistive touchscreens. In addition, they are also the most vulnerable, because absolutely any sharp object can seriously damage a fairly 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 belongs to the past, the capacitive design to the present, and the wave design to the future. It is clear that absolutely no one knows the future one hundred percent and, accordingly, at the present time one can only guess what technology will have great prospects for future use.

For a resistive touchscreen system, it does not make any special difference whether the user touches the device screen with the rubber tip of the stylus or simply with a finger. It is enough that there is contact between the two layers. At the same time, the capacitive screen only recognizes touches by some conductive objects. Often, users of modern devices operate them using their own fingers. Wave design screens in this regard are closer to resistive. It is possible to give a command with almost any object - you just need to avoid using heavy or too small objects, for example, the refill of a ballpoint pen is not suitable for this.

Just recently, few could believe that phones with familiar buttons would give way to devices that were controlled by touching the screen. But times change and the demand for push-button phones is gradually falling, and on smartphones it is growing.

The term “touchscreen” is formed from two words - Touch and Screen, which is translated from English language translated as "touch screen". Yes, that's right - a touchscreen is a touchscreen that you touch when you use your smartphone or tablet. In fact, touch screens are found not only in the world of mobile technology. So, you could see them when depositing funds into your mobile device account through a terminal, at an ATM, in ticket devices, etc.

It's important to note that there are several different ways touch screens work, depending on where and what they're used for. Of course, the cost of technology also varies. So, there is no point in using high-tech touch screens for replenishment terminals mobile communications, which cannot be said about the same smartphones.

What is a touchscreen?

IN modern smartphones Capacitive touch screens are used. They are a glass panel on which a layer of transparent resistive material is applied. In the corners there are electrodes that supply low voltage to the conductive layer. alternating voltage. The human body can conduct through itself electric current, and also has a certain capacity. Therefore, when you touch the screen, a leak occurs and the location of this leak is determined by the controller, which uses data from the electrodes at the corners of the panel.

PDAs, which are almost never found on sale today, use resistive screens, which in addition to glass panel there is a flexible membrane. The surface between them is filled with micro-insulators. When the screen is pressed, the membrane and panel close, after which the controller records the change in resistance and converts it into touch coordinates.

Remember, a capacitive screen does not respond to pressing an object or even the simplest one (you need a stylus with a special tip), while resistive screens respond to absolutely any touch.

Is it possible to replace the touchscreen?

If the user breaks the touchscreen or it fails for one reason or another (for example, it stops responding to touches), it is possible to replace the touchscreen. It is advisable to make the replacement in specialized service with a guarantee.

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

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

What is it

Touch display(screen) is a visualization device digital information with the ability to exert management influence by touching the display surface.

Based on various technologies, different displays respond only 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 random clicks.

We will look at the operating principle of all common types of displays, their areas of application, strengths and weaknesses.

Among all existing principles controlling the device through a matrix sensitive to any factors, Let's pay attention to 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 an area of ​​the screen, the sensors transmit data to the controller about changes in any variable (resistance, capacitance), which calculates the exact coordinates of the point of contact and sends them.

The latter, based on the program, reacts to pressing accordingly.

Resistive

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

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

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

Both layers are coated with resistive material. Between them there are micro-insulators in the form of balls.

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

The controller responds to a short circuit using 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 occurs.

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

Four-wire

The upper electrode is energized at 5V, and the lower one is grounded.

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

Then the top and bottom are short-circuited, and 5V is supplied 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 covered with a resistive material, and electrodes are placed at its corners.

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

During the touch, the controller (microprocessor) detects the change in the parameter and carries out calculations of the point/area where the voltage has changed according to a four-wire circuit.

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

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

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 a sharp one.

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

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

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

Low reliability (the screen is easy to damage) is partially compensated protective film.

Poor functioning 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, very little) are the weaknesses of the technology.

Matrix

A more simplified resistive technology that arose even before it.

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

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

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

Peculiarities:

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

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

Capacitive

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

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

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

At the moment of contact, current leaks, if the object has a greater electrical capacity 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 voltage DC. The solution made the design simpler, but often crashed when the user was not in contact with the ground.

These devices are very reliable, their service life exceeds resistive devices by ~60 times (about 200 million clicks), they are moisture resistant and can withstand pollution that do 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.

They are used in the same ATMs and terminals under closed air.

Projected capacitive

An electrode grid is applied to the inner surface, forming a capacitance (capacitor) with the human body. Electronics (microcontroller and sensors) work on calculating coordinates at and send calculations central processor.

They have all the features of capacitive ones.

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

Conductive contaminants, where they are difficult or impossible to remove, are removed without problems programmatic method.

Most often, others are set to personal electronic devices, ATMs and various equipment installed virtually in the open air (under cover). Apple also prefers projected capacitive displays.

Surface acoustic wave

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

There are also a pair of them and are located on opposite corners.

The generator sends an RF electrical signal to the probe, which converts a series of pulses into surfactants, and the reflectors distribute it.

The reflected waves are captured 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 together 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 service life of resistive technology (65 million times in total).

They are produced with a thin film of about 3 mm and a thick film of 6 mm. Thanks to this protection, the display can withstand a light blow from a fist.

Weaknesses:

• bad job in conditions of vibration and shaking (in transport, when walking);
• lack of resistance to stains – 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.