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

In the era of 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 it is

Touch display (screen) is a device for visualizing digital information with the ability to exert management influence 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 look at the operating principle of all common types of displays, their areas of application, strengths and weaknesses.

Among all the existing principles of device control 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 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 energized, 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 easily damaged) is partially compensated by the 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 – 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 large-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 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 DC voltage. 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 ones 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. The electronics (microcontroller and sensors) work to calculate the coordinates at and send the calculations to the 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 easily removed using the software method.

Most often, they are installed in 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.

Weak sides:

• poor performance in conditions of vibration and shaking (in transport, when walking);
• lack of resistance to dirt - 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.

Other varieties

We figured out what a touch screen is and how it works. Finally, let’s get acquainted with less common technologies for their functioning.

Optic

The top panel is equipped with infrared illumination, which causes a total reflection effect to appear at the air-glass interface, and the light is scattered between the glass and a finger or other object.

To achieve the effects, either a 4th subpixel is installed or a camera is mounted in the projection screen.

Supports multi-touch and work with large surfaces, up to the size of a full-fledged blackboard.

Infrared

The screen is covered with photodiode-LED pairs.

LEDs generate infrared rays that are absorbed by nearby photodiodes.

At the moment of touch, the light ceases to be absorbed or its intensity drops, which is reflected in a decrease in the current in the LED.

The event is recorded by the microcontroller, which calculates the coordinates of the point.

Due to the absence of substrates and other layers, changes in color rendering, brightness, contrast and other picture parameters are excluded. Optocouplers are very sensitive to moisture and dirt, and also have a short service life. Direct sunlight may cause malfunctions.

Induction

The screen contains an inductance coil and a network of sensitive conductors that react only to the pen, which is powered by the effect of electromagnetic induction.

Installed in, which are used, for example, by bank employees.

In this article we will look at different types of touch screens, their features, pros and cons of the technology.

"Multi-touch"

This technology allows you to recognize multiple taps at different points on the screen at the same time. This opens up new possibilities in device management. An example of multi-touch technology is the Apple iPhone.

Capacitive touch screens

For example: HTC Wildfire

The sensing element of a capacitive touch screen is glass coated with a transparent conductive compound (usually an alloy of indium oxide and tin oxide). At the corners of the panel there are four electrodes that apply a small alternating voltage to the conductive layer.

When a finger (or other conductive object) touches such a screen, a capacitive coupling is formed between the finger and the screen (current leakage), which causes a current pulse to the point of contact. The screen controller measures the strength of the current generated in all four electrodes. The electrical current from each corner of the screen is proportional to the distance to the touch point, so the controller can simply compare these currents to determine where the touch is made.

Pros: Reliable, transparent screen with fast response time, high strength and durability.

The disadvantages of such a screen are that it can only be controlled with your fingers or a special stylus with an electrical capacity. Therefore, in winter you can forget about using such a screen with gloves. And besides, at low temperatures the electrical characteristics of the sensor change, and sometimes it may not work correctly (from incorrectly determining the coordinates of the press to complete inoperability).

Projected capacitive screens

For example: Apple iPhone

There is another type of capacitive sensor - a projected capacitive screen. A grid of electrodes is applied to its back side, to which a weak current is supplied, and the place of contact is determined by points with increased capacitance.

Such screens, in addition to high transparency and durability, have two more important advantages - the glass substrate can be made as strong as desired (and quite thick), and they also allow the use of multi-touch technology, which conventional capacitive screens could not afford.

The downside may be a slightly lower accuracy in determining the coordinates of the press.

Resistive touch screens

For example: HTC Touch Diamond

The resistive screen only responds to pressure. The screen is a glass liquid crystal display on which a flexible membrane is applied. A resistive composition is applied to the contacting sides, and the space between the planes is divided by a dielectric.

When you press the screen with your finger (or any other object), it comes into contact with the membrane, and current begins to flow at the point of contact. To determine the location of the touch, the screen controller measures the voltage in pairs between the electrodes located at the edges of the panel. Such a screen is called 4-wire (there are also 5-6-7-wire ones, which have some differences).

The peculiarity of the resistive screen is that it requires physical effort to operate, and it recognizes pressure with a fingernail better than with a pad, and reacts to any objects touching the surface. Devices with resistive screens are often equipped with styluses. Such a display provides higher precision control (with a stylus you can literally hit a pixel, while with a finger on a capacitive screen you can only hit a fairly large area), but due to constant contact with hard objects, the flexible membrane quickly becomes covered with scratches. Most mobile devices are equipped with resistive screens.

The disadvantages of resistive screens also include low light transmission - no more than 70-85%, which requires increased backlight brightness.

But these screens are extremely cheap to produce, which explains their wide distribution.

Nowadays you won’t surprise anyone with a touch screen. Moreover, it is already strange to see devices without a sensor, especially when it comes to mobile gadgets. This is due to the desire to increase the working surface area. But how often do we think about what type of display is used in a particular device? Has it ever happened that, having bought a new tablet or smartphone, we try to control it using the usual digital pen, but bad luck, the device simply does not respond to its touch. Apparently, the screen is made using a different technology, capacitive, which is gradually beginning to displace its predecessor, the resistive type display.

You can find a large number of touch screens that differ not only in design features, but also in their operating principle. Today, there are the following types of touch screens: resistive, capacitive, projection-capacitive, matrix, surface acoustic wave touch screen, infrared, strain gauge, inductive.

Currently, there are two main types of touch screens used in electronic technology: resistive and capacitive. We will talk about them in more detail, and also try to highlight the strengths and weaknesses of each.

First, let's look at the operating principle of a resistive touch screen. It consists of a glass panel and a flexible plastic membrane, on which a resistive coating is applied. The space between the glass and the membrane is filled with micro-insulators, which in turn reliably insulate the conductive surfaces, evenly distributed over the active area of ​​the screen. When you press the display, the panel and membrane close, and the controller, using an analog-to-digital converter, registers the change in resistance, converting it into touch coordinates. It is for this reason that such a screen can be pressed with any hard object, it can be a fingernail, a special stylus, or even an ordinary pencil. As a consequence of this structure, resistive screens gradually wear out, which is why there is a need to periodically calibrate the screen so that when you press the display, the coordinates of the touch point are correctly processed.

There are four-, eight-, five-, six- or seven-electrode screens. The simplest to manufacture, and therefore the cheapest, are four-electrode ones. They can withstand only 3 million clicks at one point. Five-wire ones will already be much more reliable - up to 35 million clicks; in them, four electrodes are located on the panel, and the fifth is located on a membrane, which is coated with a conductive composition. It is worth noting that five-wire and subsequent versions of six- and seven-wire screens continue to work even if part of the membrane is damaged.

Advantages

The advantages of a resistive screen include the low cost of its production, and, consequently, the low cost of the device in which it is used. In addition, it is worth noting that the sensor response here does not depend on the condition of the screen surface; even if dirty, the touchscreen remains just as sensitive. You should also highlight the accuracy of hitting the desired point, because a dense lattice of resistive elements is used.

Flaws

As a disadvantage of resistive screens, we highlight low light transmission, no more than 70% or 85%, so increased backlight brightness is required. It is also low sensitivity, i.e. Simply touching with your finger is not enough, pressure is required, so you cannot do without a digital pen or long nails. This type in most cases does not support multi-touch, i.e. the screen only understands one touch. When interacting with the screen, you need to make some effort to transmit any command, and if you overdo it, you can not only scratch it, but also damage the display. As mentioned above, for proper functioning it is necessary to periodically calibrate the screen.

Capacitive touch screen

A capacitive screen is a glass panel that is coated with a transparent resistive material, typically an alloy of indium oxide and tin oxide. Electrodes are installed at the corners of the panel, supplying a low-voltage alternating voltage to the conductive layer; they monitor the flow of charges in the screen and transmit data to the controller, thus determining the coordinates of the touch point. Before touching, the screen has some electrical charge; when touched with a finger, a point appears on the conductive layer, the potential of which is less than the potentials of the electrode, since the human body has the ability to conduct electric current and has a certain capacity. There are no flexible membranes on the screen, which ensures high reliability and allows you to reduce the brightness of the backlight. This type of screen is capable of simultaneously determining the coordinates of two or more touch points, which means multi-touch support.

Projection-capacitive screens have become a subtype of capacitive screens. They work on a similar principle. The difference is that the basic elements in them are located not on the outside of the screen, but on the inside, making the sensor more protected. This type of display is mainly used in modern mobile devices.

Interaction with a capacitive screen should only be carried out with a conductive object, a bare finger or a special stylus that has electrical capacitance. The number of clicks before the sensor elements fail reaches more than 200 million times.

Advantages

One of the advantages of capacitive screens is that even in bright sunshine, visibility remains quite good, which cannot be said about a resistive screen, since it reflects a lot of ambient light. Another advantage was the ability to quickly and accurately recognize touch without the use of additional accessories. The undoubted advantage of screens of this type is the longer service life of the sensor compared to the previous type. A “multi-finger” interface or multi-touch has also appeared, although not all devices with a screen of this type are fully implemented.

Flaws

The negative aspects of using a capacitive touch screen include a higher cost due to the complexity of production. Interaction with the display is only possible by touching a material that is a conductor. For this reason, special capacitive styluses or gloves are purchased to work with it; this becomes especially important in cold weather, and this is another expense item.

To summarize, let us recall that resistive screens are pressure sensitive, while capacitive screens are touch sensitive. The accuracy of capacitive displays is comparable to that of resistive displays, but the capacitive type is more reliable due to the absence of a flexible membrane, and fewer layers make them more transparent.

There is an opinion that resistive displays have already outlived their usefulness, and the future belongs to capacitive displays. Indeed, the transition from mechanical-electrical input to electrical already means a lot, since the accuracy of determining coordinates has increased, and multi-touch has appeared.

However, today there are still a large number of devices with resistive screens on the electronics market, but they are slowly beginning to be replaced by gadgets with capacitive sensors. Observing this trend, one can assume that the former will soon disappear altogether.

A touch screen is a device for input and output of information through a touch- and gesture-sensitive display. As you know, the screens of modern devices not only display images, but also allow you to interact with the device. Initially, familiar buttons were used for such interaction, then the equally famous “mouse” manipulator appeared, which significantly simplified the manipulation of information on the computer display. However, the “mouse” requires a horizontal surface to work and is not very suitable for mobile devices. This is where an addition to a regular screen comes to the rescue - Touch Screen, which is also known as Touch Panel, touch panel, touch film. That is, in fact, the touch element is not a screen - it is an additional device installed on top of the display from the outside, protecting it and serving to enter the coordinates of touching the screen with a finger or other object.

Usage

Today, touch screens are widely used in mobile electronic devices. Initially, the touchscreen was used in the design of pocket personal computers (PDAs, PDAs), now communicators, mobile phones, players and even photo and video cameras hold the lead. However, the technology of finger control through virtual buttons on the screen has proven to be so convenient that almost all payment terminals, many modern ATMs, electronic information kiosks and other devices used in public places are equipped with it.

Laptop with touch screen

It should also be noted that laptops, some models of which are equipped with a rotating touch screen, which gives the mobile computer not only wider functionality, but also greater flexibility in controlling it on the street and in weight.

Unfortunately, there are not many similar laptop models, popularly called “transformers,” but they do exist.

In general, touch screen technology can be described as the most convenient when you need instant access to control the device without prior preparation and with amazing interactivity: controls can change each other depending on the activated function. Anyone who has ever worked with a touch device understands the above perfectly well.

Types of touch screens

There are several types of touch panels known today. Naturally, each of them has its own advantages and disadvantages. Let us highlight four main structures:

• Resistive
• Capacitive
• Projected capacitive

In addition to the indicated screens, matrix and infrared screens are used, but due to their low accuracy, their scope of application is extremely limited.

Resistive

Resistive touch panels are among the simplest devices. At its core, such a panel consists of a conductive substrate and a plastic membrane that have a certain resistance. When you press the membrane, it closes with the substrate, and the control electronics determines the resulting resistance between the edges of the substrate and the membrane, calculating the coordinates of the point of pressure.

The advantage of a resistive screen is its low cost and simplicity of design. They have excellent resistance to stains. The main advantage of resistive technology is sensitivity to any touch: you can work with your hand (including gloves), a stylus (pen) and any other hard, blunt object (for example, the upper end of a ballpoint pen or the corner of a plastic card). However, there are also quite serious disadvantages: resistive screens are sensitive to mechanical damage, such a screen is easy to scratch, so a special protective film is often additionally purchased to protect the screen. In addition, resistive panels do not work very well at low temperatures, and also have low transparency - they transmit no more than 85% of the display's luminous flux.

Using a touch pen

Application

• Communicators
• Cell Phones
• POS terminals
• Tablet PC
• Industry (control devices)
• Medical equipment

Communicator

Capacitive

Capacitive touchscreen technology is based on the principle that a large capacitive object (in this case a person) is capable of conducting electrical current. The essence of capacitive technology is to apply an electrically conductive layer to the glass, while a weak alternating current is supplied to each of the four corners of the screen. If you touch the screen with a grounded object of large capacity (finger), current will leak. The closer the point of contact (and therefore the leakage) is to the electrodes in the corners of the screen, the greater the strength of the leakage current, which is recorded by the control electronics, which calculates the coordinates of the point of contact.

Capacitive screens are very reliable and durable, their service life is hundreds of millions of clicks, they perfectly resist pollution, but only those that do not conduct electric current. Compared to resistive ones, they are more transparent. However, the disadvantages are still the possibility of damage to the electrically conductive coating and insensitivity to touch with non-conductive objects, even with gloved hands.

Information kiosk

Application

• In secured premises
• Information kiosks
• Some ATMs

Projected capacitive

Projective-capacitive screens are based on measuring the capacitance of a capacitor formed between the human body and a transparent electrode on the surface of the glass, which in this case is a dielectric. Due to the fact that the electrodes are applied to the inner surface of the screen, such a screen is extremely resistant to mechanical damage, and taking into account the possibility of using thick glass, projective capacitive screens can be used in public places and on the street without any special restrictions. In addition, this type of screen recognizes pressing with a gloved finger.

Payment terminal

These screens are quite sensitive and distinguish between finger and conductive pen presses, and some models can recognize multiple presses (multi-touch). Features of a projective capacitive screen are high transparency, durability, and immunity to most contaminants. The disadvantage of such a screen is its not very high accuracy, as well as the complexity of the electronics that process the coordinates of the press.

Application

• Electronic kiosks on the streets
• Payment terminals
• ATMs
• Laptop touchpads
• iPhone

With determination of surface acoustic waves

The essence of the operation of the touch panel with the determination of surface acoustic waves is the presence of ultrasonic vibrations in the thickness of the screen. When you touch the vibrating glass, the waves are absorbed, and the point of contact is recorded by the screen sensors. The advantages of the technology include high reliability and touch recognition (unlike capacitive screens). The disadvantages are poor protection from environmental factors, so screens with surface acoustic waves cannot be used outdoors, and in addition, such screens are afraid of any contamination that blocks their operation. Rarely used.

Other, rare types of touch screens

• Optical screens. The glass is illuminated with infrared light; as a result of touching such glass, light scatters, which is detected by a sensor.
• Induction screens. Inside the screen there is a coil and a grid of sensitive wires that respond to touch by an active pen powered by electromagnetic resonance. It is logical that such screens respond to touches only with a special pen. Used in expensive graphics tablets.
• Strain gauges – react to screen deformation. Such screens have low accuracy, but are very durable.
• The infrared ray grid is one of the very first technologies that allows you to recognize touches on the screen. The grid consists of many light emitters and receivers located on the sides of the screen. It reacts to the blocking of the corresponding rays by objects, on the basis of which it determines the coordinates of the press.

• Move two fingers together – zoom out the image (text)
• Spread two fingers to the sides – increase (Zoom)
• Movement of several fingers at the same time - scrolling text, pages in the browser
• Rotate with two fingers on the screen – rotate the image (screen)

About the benefits and disadvantages of touch screens

Touch screens have been around for a long time in handheld devices. There are several reasons for this:

• Ability to make a minimum number of controls
• Simplicity of the graphical interface
• Ease of control
• Ease of access to device functions
• Expanding multimedia capabilities

However, there are more than enough disadvantages:

• Lack of haptic feedback
• Frequent need to use a pen (stylus)
• Possibility of screen damage
• The appearance of fingerprints and other dirt on the screen
• Higher energy consumption

As a result, it is not always possible to completely get rid of the keyboard, because it is much more convenient to type text using familiar keys. But the touch screen is more interactive, thanks to faster access to menu items and settings of modern gadgets.

We hope this material will help you when choosing a touch screen device.

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