The principle of operation of the sensor. Is it possible to replace the touchscreen? Operating principle of projected capacitive touch screens

For driving modern gadgets There is no longer any need to press buttons, just touch the screen. This became possible thanks to the touchscreen (among experts it is simply called “touch” or “touch panel”), which has become an integral part of smartphones and tablets, including iPhones and iPads. It is not surprising that due to frequent use it often breaks down and becomes a headache for the owner of the device. If you understand what this component is and by what principles it works, you can quickly detect a malfunction and avoid awkward situations when contacting a service center.

What is a touchscreen

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

Currently, city residents deal with touch panels almost every day: not only smartphones and tablets are equipped with them, but also ATMs, information terminals and payment acceptance points. Touchscreen connects to display and is sensitive to any touch. It can be described as an information input device that serves to replace a keyboard.

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

How the touch panel works

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

The cheapest to produce, resistant to dirt and temperature changes. Comprises glass panel and plastic membrane, between which insulators are located. Any pressure causes the glass to push through the micro-insulator, and the membrane and panel close. After this, a special controller reads the changes and converts them into contact coordinates. Weak sides This model has low light transmission, short service life and a high risk of damage if dropped.

Capacitive screen

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

Surface acoustic wave sensor

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

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

• Projected capacitive. On the inside of such screens there is a grid of electrodes, which, when pressed, forms a capacitor, the capacitance of which is measured by electronic sensors.
• Infrared. Along their edges there are light emitters and receivers in the IR range; when you touch the screen, part of the light is blocked and thereby the location of the click is determined.
• Tansometric. They are based on simple fixation of screen deformation, are resistant to damage and are often installed outdoors.
• Induction. Inside them there is an inductance coil and wires; when such a screen is touched with a special tool, the voltage of the existing magnetic field changes.

How to check the touchscreen

The touchpad may not work correctly due to physical damage mobile device, for no apparent reason. The following factors indicate that the problem is in the sensor:

There may be several reasons for such a malfunction:

1. Display dirty. If you do not wipe the sensor promptly by special means, then during operation it becomes abundantly covered with fingerprints and greasy marks, which can reduce its sensitivity.
2. Violation temperature regime . Too high or low temperatures, as well as their strong drop - common reason touchscreen malfunction.
3. Damage to the cable. It can peel off from the glass due to mechanical damage, thereby disrupting the connection between the latter and the touch coating.
4. Moisture ingress. If there is liquid inside the gadget, oxidation of the contacts may occur. Sometimes the problem can be solved with a hair dryer.
5. Crash software. In this case, you need to reflash the device; for this you will need a USB cable and the software itself.

How to replace the touchscreen on your phone yourself

Before removing the touch screen, you should turn off your smartphone, remove the battery and SIM card. It is important to remember the disassembly sequence so that you can later put the device back together without damaging the internal elements. Some models may require complete disassembly of the housing, which requires special knowledge. To replace the touch screen on your phone with your own hands, you need to prepare special equipment in advance, namely:

The process of replacing the touchscreen is as follows:

1. Take off back cover telephone;
2. Screwdriver remove all bolts along the perimeter of the body;
3. Carefully insert the spatula between the housing fastening and pry;
4. Hairdryer warm up the glue connecting the sensor to the matrix up to a maximum temperature of 80 °C;
5. Pin to display suction cup, which will allow you to separate the touchscreen from the matrix;
6. Apply thin layer of glue and install a new touchpad;
7. Carefully press it and remove any remaining glue;
8. Reassemble the device in reverse order.

What is the difference between touchscreen and display

The display is the part of the smartphone on which the image is displayed. He is the conductor visual information and makes it accessible to the human eye. A touchscreen is a touch glass, the main purpose of which is to call a particular function. That is, he is only information input tool, but no conclusion.

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

There is constant debate about which phone has the better screen. Especially between owners Apple technology and those who prefer devices on the Android platform.

This simple infographic beautifully breaks down all the benefits of each type of touchscreen. I hope that when you buy your next smartphone, it will help you do right choice and don’t overpay a tidy sum.

So, there are three types of touch screens: Resistive, Capacitive and Infrared.

Resistive

Phones with resistive screens: Samsung Messager Touch, Samsung Instinct, HTC Touch Diamond, LG Dare

How do they work? Small dots separate several layers of material that transmit current. When the upper flexible layer presses against the lower layer, electricity The location of the impact, that is, the touch, changes and is calculated.

How much does it cost to manufacture? The cost of manufacturing resistive touch screens is not very high - $ .

Screen material. A layer of flexible material (usually a polyester film) is placed on top of the glass.

Tools of influence. Fingers, gloved fingers or stylus.

Visibility on the street. Poor visibility in sunny weather.

Possibility of multi-gestures. No.

Durability. For its price, the screen lasts quite a long time. Easily scratched and susceptible to other minor damage. It wears out quite quickly and requires replacement.

Capacitive

Phones with capacitive touch screens: Huawei Ascend, Sanyo Zio, iPhone, HTC Hero, DROID Eris, Palm Pre, Blackberry Storm.

How do they work? The current is broadcast from the corners of the screen. When a finger touches the screen, it changes the direction of the current and thus the location of the touch is calculated.

How much does it cost to manufacture? Quite expensive - $$ .

Screen material. Glass.

Tools of influence. Only fingers without gloves.

Visibility on the street. Visibility on a sunny day is good.

Possibility of multi-gestures. Eat.

Durability.

Infrared

Phones with infrared touch screens: Samsung U600 (heat), Neonode N2 (optical).

How do they work? In order for the heat-sensitive screen to react, you need to touch it with a warm object. Optical screen uses a grid of invisible sensors directly above the screen. The touch point is calculated based on the point where x-y axis was violated.

How much does it cost to manufacture? Very expensive - $$$ .

Screen material. Glass.

Tools of influence. Optical - fingers, gloves and stylus. Heat-sensitive - warm fingers without gloves.

Visibility on the street. Visibility in sunny weather is good, but strong sunlight affects productivity and accuracy.

Possibility of multi-gestures. Yes.

Durability. Lasts quite a long time. Glass breaks only from serious damage.

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 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 random 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 scheme the 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 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 – 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 most low 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 supply a small voltage alternating current 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 direct current. 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. 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, 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 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.

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

The beginning of the sensory boom

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

The touch screen was invented in the USA in the second half of the 60s of the last century, but until the early 90s it was used mainly in medical and industrial equipment to replace traditional input devices, the use of which is fraught with difficulties under certain operating conditions. As the size of computers decreased and PDAs appeared, the question arose about improving their control systems. In 1998, the first handheld with a touch screen and an input and handwriting recognition system appeared Apple Newton MessagePad, and soon communicators with touchscreens.

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

Working principle of resistive touch screen

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

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

At the edges of each layer there are thin metal plates - electrodes. In the rear layer with resistive material they are located vertically, and in the front layer - horizontally. In the first case, they are served constant pressure, and an electric current flows from one electrode to another. In this case, a voltage drop occurs proportional to the length of the screen section.

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

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

The operating principle and design of five-wire resistive touch screens are somewhat different from those described above. The front resistive coating layer is replaced by a conductive layer and is used solely for reading the voltage value on the rear resistive layer. It has four electrodes built into it at the corners of the screen, the fifth electrode is the output of the front conductive layer. Initially, all four electrodes of the rear layer are energized, and on the front layer it is zero. As soon as such a touch screen is touched, the top and bottom layers are connected at a certain point, and the controller senses the change in voltage on the front layer. This is how it detects that the screen has been touched. Next, the two electrodes in the back layer are grounded, the X-axis coordinate of the touch point is calculated, and then the other two electrodes are grounded, and the Y-axis coordinate of the touch point is calculated.

Working principle of capacitive touch screen

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

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

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

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

Such screens also have high transparency and are capable of operating at even lower temperatures (down to -40 °C). Electrically conductive contaminants affect them to a lesser extent; they react to a gloved hand. High sensitivity allows the use of a thick layer of glass (up to 18 mm) to protect such screens.

Working principle of four-wire resistive touch screen

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

Working principle of five-wire resistive touch screen

1. The screen can be touched with any hard object.
2. The top conductive layer flexes and comes into contact with the bottom, which indicates touching the screen.
3. Two of the four electrodes of the lower layer are grounded, the controller determines the voltage at the point of contact and calculates the coordinate of the point along the X axis.
4. The other two electrodes are grounded, the controller determines the voltage at the point of contact and calculates the coordinate of the point along the Y axis.

Advantages

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

Flaws

• Low durability (1 million clicks at one point for a four-wire, 35 million clicks for a five-wire) and vandal resistance
• Low light transmission (no more than 85%)
• Does not support Multitouch

Device examples

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

Principle of operation

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

Advantages

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

Flaws

• Susceptible to moisture, conductive contaminants
• Does not support Multitouch

Device examples

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

Principle of operation

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

Advantages

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

Flaws

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

Device examples

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

Windows 7

It became possible to control the computer using the “Scroll”, “Forward/backward”, “Rotate” and “Zoom” gestures. The Windows 7 operating system is much better adapted to work with touch displays than everything previous versions. 06 this is evidenced by the modified interface and the taskbar, in which in place of rectangular buttons symbolizing running programs, square icons have appeared - they are much more convenient to press with your finger. In addition, there was new feature- Jump lists that allow you to quickly find recently opened files or frequently launched items. To activate this feature, simply drag the program icon onto the Desktop.

First time in the operating room Windows system An option has been added to recognize touch gestures, which are associated with the execution of individual functions. Thus, in Windows 7, touch scrolling appeared and, the same as, for example, in the Apple iPhone, the ability to enlarge pictures or documents by moving two fingers different sides. There was also movement responsible for rotating the image. Operations such as copy, delete, and paste can also be assigned separate gestures. Buttons on-screen keyboard Lights up when touched, making it easy to use on a touch screen. And the ability to recognize handwritten text allows you to quickly enter small messages.

Screens modern devices can not only display an image, but also allow you to interact with the device via sensors.

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

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

Resistive touch screens

This technology is most widespread among mobile devices, which is explained by the simplicity of the technology and low production costs. The resistive screen is LCD display, on which two transparent plates are superimposed, separated by a dielectric layer. The top plate is flexible, as the user presses on it, while the bottom plate is rigidly fixed to the screen. Conductors are applied to surfaces facing each other.

Resistive touch screen

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

The advantages of resistive screens include simplicity and low cost, good sensitivity, and the ability to press the screen with either a finger or any object. Among the disadvantages, it is necessary to note poor light transmission (as a result, you have to use a brighter backlight), poor support for multiple clicks (multi-touch), they cannot determine the force of pressing, as well as fairly rapid mechanical wear, although in comparison with the life of the phone, this disadvantage is not so important, since the phone usually fails faster than the touch screen.

Application: Cell Phones, PDAs, smartphones, communicators, POS terminals, TabletPC, medical equipment.

Capacitive touch screens

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

Surface capacitive touch screen

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

Application: Information kiosks in secure areas, at some ATMs.

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

Projected capacitive touch screen

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

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

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

SAW touch screens (surface acoustic waves)

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

SAW touch screen

The advantages include high transparency, since the screen does not contain conductive surfaces, durability (up to 50 million touches), and surfactant touch screens allow you to determine not only the coordinates of pressing, but also the pressing force.

Among the disadvantages, we can note the lower accuracy of determining coordinates than capacitive ones, that is, you won’t be able to draw on such screens. A big disadvantage is malfunctions when exposed to acoustic noise, vibrations or when the screen is dirty, i.e. Any dirt on the screen will block its operation. Also, these screens only work correctly with objects that absorb acoustic waves.

Application: surfactant touch screens mainly in secured information kiosks, in educational institutions, V slot machines and so on.

Infrared touch screens

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

Infrared touch screen

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

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

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

The text was prepared based on materials from open sources Methodists in Technology Karabin A.S., L.V. Gavrik, S.V. Usachev