What are touch screens. Types of touch screens
Designed primarily for displaying and entering information by gesturing or pressing the display. Now there are many varieties that allow you to directly interact with the device. Built-in sensors can be seen in many devices: smartphones, tablets, players, camcorders and cameras. Existing types touch screens have their own advantages and disadvantages. In order to decide which one is better, it is necessary to study in more detail the characteristics of each. In our case, we will focus on touch screens built into tablets.
Note that touch types are divided into four main types:
- Capacitive.
- Projected capacitive.
- Displays with surface acoustic waves (SAW).
- Resistive.
The most common are capacitive and resistive. Their main difference lies in the fact that the former recognize the touch, and the second press (with a stylus or finger). In truth, resistive sensors are found in cheaper tablet models and are considered relics. Capacitive devices are widely used in new models of mobile devices.
Why, strictly speaking, are they called that? A large object conducts an alternating current through the device. The surface is nothing more than a glass panel coated with a resistive transparent alloy. The conductive layer has a high level of voltage and current leakage occurs when it comes into contact with an object or finger. As a result, the sensors record a leakage of current, as a result of which the coordinates of the pressing point are instantaneously calculated.
Display Benefits
There are projection-capacitive types of screens. They are considered more advanced and are distinguished by increased sensitivity, quick response, and most importantly, they allow you to interact with the device through gloves. Highly important factor is multitouch technology support. Thanks to it, you can press on the surface with two or even three fingers. This is due to the fact that the coordinates of several points at which the action is directed are simultaneously found.
The main advantages of advanced touch screens are resistance to any pollution, strength and reliability. In addition, you can work safely on projected capacitive screens in cold weather. They are resistant to low temperatures. Fast response is a clear advantage over a capacitive display. One light touch is enough to display information.
Application in life
It should be said that capacitive displays are installed not only in tablets, but also in information kiosks, ATMs and guarded buildings. The range of use of projected capacitive displays is much wider. They can be found in payment terminals, laptops, electronic kiosks and any devices that support multitouch technology. A special conductive stylus can be used to interact with projected capacitive screens, but very few people use it. It is much more convenient to perform all actions in manual mode.
There is no need to talk about the disadvantages of capacitive and projection-capacitive screens. The only drawback, perhaps, is their high cost, but it fully justifies itself. If you want to buy a device with high quality sensory type screen, you will have to pay the corresponding amount.
Characteristics of resistive screens
Device and application
A simpler and cheaper technology is a resistive sensor consisting of a plastic membrane and a conductive substrate. When you press on the membrane part, a slight closure with the substrate occurs. In this case, the control electronics calculates the resistance that occurs between the edges of the two parts. As a result, the coordinates of the pressing point are calculated.
Often resistive touch screens are used in inexpensive models tablets and other mobile devices, communicators, PDAs, medical equipment and industrial control devices. Gadgets with a built-in resistive display come with a special stylus. Despite this, you can work with any other blunt object. Resistive displays also respond to fingers, even when wearing gloves. True, there is one small caveat - the impact on the surface should not be very strong otherwise, the screen may be damaged.
Features of use
If we talk about the disadvantages of resistive type displays, then they are very sensitive to any mechanical damage ... A device with such a screen should never be carried in a pocket with keys or used instead of a stylus. Otherwise, the display will leave unsightly scratches, and this may lead to a decrease in sensitivity. In order to protect yourself from such risks, it is necessary to stick a protective film on the resistive surface. Moreover, for low temperatures it will still work poorly. When it comes to transparency, only 84% of the light coming from the screen gets through - this is a very low figure.
Many users are wondering which type of touchscreen is better? There is no definite answer. If for the price, then the most inexpensive displays are the resistive type. In terms of quality, naturally, they are ahead of projection-capacitive ones. However, there is another type of touchscreen that is worth talking about.
Such displays work as follows: piezoelectric elements located at the corners of the device convert the incoming electrical signal into ultrasonic waves. They immediately go to the surface of the display. Reflective elements are distributed along the edges of the display, and on the opposite side there are sensors that record and transmit ultrasound waves. The converter converts them into an electrical signal. When touched, it is weakened, and the coordinates of the touch are calculated. It should be noted that the intensity of the touch is also calculated, which is not available for other types of screens. However, unlike its competitors, this option does not fully determine the coordinates, therefore, you will not be able to draw on such screens.
The touch screens have greatly simplified the graphical interface and controls. Access to functions has become easier. Touch screens allow you to make a minimum of movements and receive information in full. Despite the fact that there are several types, they all have their own advantages. It is up to the user to decide which device to choose, based on their own financial capabilities and preferences.
Touch screen- This is an information input device, which is a screen that reacts to touching it.
The main comparative characteristics touch screens.
| Resistive | Capacitive | Projected capacitive | Surfactant | IR |
| - | + | + | - | + |
| 75-85 | 90 | 90 | 95 | 100 |
| H. | H. | H. | H. | H. |
| - | - | + | + | - |
| + | - | + | + | + |
| + | + | + | - | + |
| + | - | - | - | + |
| + | + | + | - | - |
The first most obvious advantage of touch technology is the intuitiveness and naturalness of the action itself - touching the screen with your hand.
Second undoubted advantage devices based on touch screens, compactness. Installation of touch monitors to qualitatively improve the efficiency of service in cinemas, restaurants, hotels, airports, administrative institutions, where every centimeter of the workplace is valuable. The touch monitor (especially if it is a liquid crystal monitor) allows you to save maximum space on the work surface.
The speed of work can be not only a matter of prestige, but also a vital important issue, in the truest sense of the word. Imagine what a won second can mean when you need the fastest possible response, for example, from a security center dispatcher. Thus, quick access is the third advantage of touch screens.
The fourth benefit of sensors is cost savings. Installing a touchscreen monitor can significantly increase the speed and accuracy of an employee working at a computer, and reduce the time required for employee training.
Touch screen - views:
Resistive touch screen.
In this design, the screen is a glass or acrylic plate covered with two conductive layers. The layers are separated by invisible spacers that prevent the network of vertical and horizontal conductors from touching. At the moment of pressing, the layers are in contact and the controller registers an electrical signal. The coordinates of pressing are determined based on the intersection of which conductors the impact was registered.
Application
- Communicators
- Cell Phones
- POS terminals
- Tablet PC
- Industry (control devices)
- Medical equipment
Capacitive (electrostatic) touch screen.
A person participates in the operation of a capacitive screen not only mechanically, but also electrically. The screen has some electrical charge before it is touched. The touch of a finger changes the picture of the charge, "pulling" part of the charge to the point of pressing. Screen sensors located at all four corners monitor the flow of charge in the screen, thus determining the coordinates of the "leak" of electrons.
Capacitive screens are also different high reliability(they lack flexible membranes) and high degree transparency. True, they are not suitable for use with a stylus or a glove - you need to press the screen with your “bare finger”. But the reliability of the capacitive screen is impressive - up to a billion clicks in the same place.
Application
- In guarded premises
- Information kiosks
- Some ATMs
Acoustic touch screen.
Such screens are built using miniature piezoelectric emitters of sound that cannot be heard by humans. The glass of such a screen constantly vibrates imperceptibly under the influence of emitters installed in three corners of the screen. Special reflectors distribute the acoustic wave in a special way over the entire surface of the screen. Touching the screen changes the picture of the propagation of acoustic vibrations, which is recorded by the sensors. By changing the nature of the oscillations, you can calculate the coordinates of the disturbances introduced by clicking on the screen. In addition, by analyzing the degree of change in vibrations, you can calculate the force of pressing the screen. This is useful when designing control systems for industrial equipment, for example, for smoothly changing the speed of rotation of motors and other parameters. Among the advantages of acoustic screens is the absence of coatings, which increases the reliability and transparency of the screen.
These acoustic touch screens are mainly used in slot machines, guarded information systems and educational institutions. As a rule, screens are distinguished into ordinary - 3 mm thick, and vandal-resistant - 6 mm. The latter can withstand a blow by a fist of an average man or a fall of a metal ball weighing 0.5 kg from a height of 1.3.
The main disadvantage of the screen is malfunction in the presence of vibration or when exposed to acoustic noise, as well as when the screen is dirty. Any foreign object placed on the screen (for example, chewing gum) completely blocks its operation. In addition, this technology requires touching with an object that necessarily absorbs acoustic waves.
Infrared touch screen.
Infrared touch screens are a frame around the monitor in which infrared emitters and receivers are installed. The disadvantages of this design are the low resolution of the sensors and the possibility of false alarms as a result of ambient light. But with large screen diagonals, this technology is still irreplaceable. In addition, all of the above types of touchscreen displays are subject to the so-called "hotspot drift".
Infrared touch screens are sensitive to dirt and are therefore used where image quality is important. Due to its simplicity and maintainability, the scheme is popular with the military. This type of screen is also used in mobile phones.
Multitouch,
is not a type of touch screen. At its core, multi-touch technology - which is a loose translation of the phrase multi-touch - is an addition to a touch screen (most often built on the projected-capacitive principle), allowing the screen to recognize multiple points of contact with it. As a result, the multi-touch screen becomes capable of gesture recognition.
Touch screen - views.
Many people think that the era of touch screens began in the 2000s, with the release of the first PDAs (I hope there are no people who think that the first touch screen appeared in the iPhone?) However, this is not so - the first consumer device with a touch screen was ... a TV in 1982 year. A year later, the first touchscreen PC from HP appeared. 10 years later, in 1993, Apple Newton appeared - the founder of the PDA, which introduced the fashion for styluses (although it was rather a necessity - the screen was resistive), and already in 2007, with the release of the iPhone, a modern capacitive screen appeared in the form of which we are all used to seeing it. So the history of touch screens goes back 35 years, and a lot has happened during that time.
Already from the name it is clear what lies at the heart of such a display - it is electrical resistance... The device of such a screen is simple: there is a substrate above the display (so that it does not deform with a strong pressure), after which there is one resistive layer, an insulator and a second resistive layer already on the membrane: 
Voltage is applied to the left and right edges of the membrane and to the lower and upper edges of the resistive layer on the substrate. What happens when we click on such a display? The resistive layers are closed, the resistance changes, which means that the voltage also changes - and this is easy to register, after which, knowing the resistance of a unit of the resistive layer, you can easily find out the resistance on both axes to the point of depression, and therefore calculate the point of depression itself:
This is the principle of operation of a four-wire resistive screen, and such are no longer used for one simple reason: the slightest damage to the membrane with a resistive layer leads to the fact that the screen stops working correctly. And given the fact that such a screen is usually poked with a sharp stylus, it is not at all difficult to achieve damage.
Then they decided to do it differently: the membrane became conductive, and all 4 electrodes are now located on the resistive layer of the substrate, but at the corners, and the voltage is supplied only to the membrane - that is, the screen has become five-wire. What happens when you click? The membrane touches the resistive layer, a current begins to flow, which is removed from 4 electrodes, which again allows, knowing the resistance of the resistive layer, to determine the point of contact:
This type is already more "vandal-resistant" - even if the membrane is cut, the screen will continue to function normally (except, of course, the place of the cut). But, alas, this does not negate other problems common to all resistive screens, and there are many of them.
Firstly, such a screen perceives only one touch: it is easy to guess that when you press with two fingers at once, the screen will think that you have pressed in the middle of the line connecting the points of pressing. The second problem is that you really need to press on the screen, and preferably with a sharp object (fingernail, stylus). Of course, you can get used to it, but this often led to characteristic scratches, which did not add beauty to the screen. The third problem is that such a screen transmits no more than 85% of the light flux, and because of its thickness, there is no feeling that you are directly touching the image with your finger.
But, nevertheless, it also has pluses: firstly, it is very, very difficult to break the display in such a screen - it has "triple protection" in the form of a membrane, insulators and a substrate. The second plus is that the screen doesn't care what you poke at it - you can work with it even with ordinary gloves (which is very important in winter). But, alas, these advantages did not outweigh the disadvantages, and with the release of the iPhone, a boom in capacitive screens began.
Surface Capacitive Screens
This can be said to be a transitional type between the capacitive screens we are used to (which are projection screens) and the old resistive ones. The principle of operation here is similar to a five-wire screen: there is a glass plate covered with a resistive layer, and 4 electrodes at the corners, which apply a small alternating voltage to the plate (why not a constant one - I will explain below). When you press such a screen with a conductive grounded object, we get a current leakage at the point of pressing, which can be easily registered: 
Here is the answer why the voltage is variable - with a constant voltage with poor grounding, there may be interruptions in work, but with a variable this is not.
They also have enough problems: the screen is now less protected, and if the glass plate is damaged, the whole one stops working. Again, multitouch is not supported, and moreover - now the screen does not respond to a gloved hand or stylus - they basically do not conduct current.
The only plus of such a screen is that it has become thinner and more transparent than a resistive one, but in general, few have appreciated it. But that all changed with the release of the iPhone, which used a slightly different type of touchscreen that already supported multitouch.
Projected capacitive screens
Now we have gotten to the modern type of touch screens. According to the principle of operation, it differs significantly from the previous ones - here the electrodes are located with a grid on inside screen (and not 4 electrodes in the corners), and when you press the screen, your finger forms capacitors with the electrodes, according to the capacitance of which you can determine the location of pressing: 
With such a screen device, you can press on it with several fingers at once - if they are located far enough (farther than two adjacent electrodes in the grid), then such presses will be determined as different - this is how multitouch appeared, first by 2 fingers in the iPhone, and now already for 10 fingers in tablets. Large quantity you no longer need to press (there are not enough people with more than 10 fingers), and the definition of more than 5-7 clicks at the same time imposes a serious load on the controller of the wheelbarrow.
One of the advantages of such a screen, in addition to multitouch support, is the ability to make OGS (One Glass Solution): the protective glass of the screen with an integrated grid of electrodes and the display are one piece: in this case, the thickness turns out to be the smallest, and it seems that you are touching the image with your fingers. This also leads to the problem of fragility: when a crack appears on the glass, the grid of electrodes is guaranteed to break, and the screen stops responding to pressing.
These are the main types of touch screens, but there are many others. Let's start with the oldest type that touchscreens started with.
Infrared screens
Again, the principle of operation is clear from the name: at the edges of the screen there are many light emitters and receivers in the infrared range. When pressed, the finger blocks part of the light, which allows you to determine the location of the pressure. The advantages of such screens at the dawn of their appearance was that they could be equipped with any display, which was done with the TV in 1982. The disadvantages are also obvious - the thickness of such a design turns out to be impressive, and the positioning accuracy is rather low.
Strain gauge screens
Screens that respond to pressure (strong pressure). Their huge plus is that they are as "vandal-proof" as possible, and therefore they are used in various ATMs on the street.
Induction screens
Again, everything is clear from the name: inside the screen there is an inductor and a mesh of wires. When you touch the screen with a special active pen, the tension of the created magnetic field- with the help of this, the press is registered. The main advantage of such a screen is the maximum possible accuracy, so they have proven themselves well in expensive graphic tablets.
Optical screens
The principle is based on total internal reflection: the glass is illuminated with infrared illumination, and while there is no pressing, the rays of light are completely reflected at the border of glass and air (that is, there is no refracted ray). When you click on such a screen, a refracted ray appears, and by the angle of refraction (well, or reflection), you can calculate the point of pressure.
Screens on surface acoustic waves
Perhaps one of the most complex screens. The principle of operation is that ultrasonic vibrations are created in the thickness of the glass. When you touch the vibrating glass, the waves are absorbed, and special sensors in the corners register this and calculate the point of contact: 
The advantage of this technology is that you can touch the screen with any object, not necessarily conductive and grounded. Minus - the screen is afraid of any dirt, so it will be impossible to use it, for example, in the rain.
DST screens
Their principle of operation is based on the piezoelectric effect - when the dielectric is deformed, it is polarized, which means that a potential difference arises - and it can already be calculated. Of the advantages - a very fast reaction speed and the ability to work with a seriously dirty screen. Minus - to determine the location of the finger, he must constantly move.
These are, in general, all types of touch screens. Of course, most of them are outlandish and you are unlikely to encounter them, but the very diversity and development of this technology pleases.
Surely all of you use computers and mobile devices, and only a few are generally able to tell how their processors work, OS and other components.
In the era of mobile gadgets, everyone has a touchscreen (also called smart) screen, and almost no one knows what this touchscreen is, how it works and what types of it exist.
What it is
Touch display (screen) Is a device for visualizing digital information with the ability to exert a managerial influence by touching the display surface.
Based on different technologies, different displays only react to certain factors.
Some read the change capacitance or resistance in the area of contact, others on temperature changes, some sensors only react to a special pen to avoid accidental clicks.
We will consider the principle of operation of all common types of displays, their areas of application, strengths and weaknesses.
Among all the existing principles of device control by means of a matrix sensitive to any factors, let's pay attention to the following technologies:
- resistive (4-5 wires);
- matrix;
- capacitive and its variants;
- surface acoustic;
- optical and other less common and practical.
V general scheme works as follows: the user touches the area of the screen, the sensors transmit data to the controller about a change in any variable (resistance, capacitance), which calculates the exact coordinates of the point of contact and sends them.
The latter, based on the program, responds appropriately to pressing.
Resistive
The simplest touch screen is resistive. It reacts to changes in resistance in the area of touching a foreign object and the screen.
This is the most primitive and widespread technology. The device consists of two main elements:
- conductive transparent substrate (panel) made of polyester or other polymer with a thickness of several tens of molecules;
- light guide membrane made of polymer material(usually a thin layer of plastic is used).
Resistive material is deposited on both layers. Micro-insulators in the form of balls are located between them.
During the stage, the elastic membrane deforms (bends), comes into contact with the backing layer and closes it.
The controller, by means of an analog-to-digital converter, reacts to a short circuit. It calculates the difference between the original and current resistance (or conductivity) and the coordinates of the point or area where it is carried out.
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 top electrode is at 5V and the bottom is grounded.
The left and right are directly connected, they are an indicator of voltage changes along the Y axis.
Then the top and bottom are short-circuited, and 5V is applied to the left and right to read the X-coordinate.
Five-wire
Reliability is due to the replacement of the resistive membrane coating with a conductive one.
The panel is made of glass and remains covered with a resistive material., and electrodes are placed on its corners.
First, all electrodes are grounded, and the membrane is energized, which is constantly monitored by the same analog-to-digital converter.
When touched, the controller (microprocessor) detects the change in the parameter and calculates the point / area where the voltage has changed according to the four-wire scheme.
An important advantage is the ability to apply on convex and concave surfaces.
There are also 8-wire screens on the market. Their accuracy is higher than the ones considered, but this in no way affects the reliability, and the price is noticeably different.
Conclusion
The considered sensors are used everywhere due to their low cost and resistance to the influence of factors. external environment 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 large enough to trigger a controller response.
Such displays are installed on, 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 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 predates it.
Membrane covered in rows vertical conductors, and the substrate is horizontal.
When pressed, the area is calculated where the conductors are closed and the received data is transmitted to the processor.
It already generates a control signal and the device reacts in a certain way, for example, it performs an action assigned to a button).
Peculiarities:
- very low accuracy (the number of conductors is very limited);
- the most low price among all;
- implementation of the multitouch function due to screen polling line by line.
They are used only in outdated electronics and are almost out of use due to the availability 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 glass panel with a thin layer of sprayed resistive substance.
Electrodes at the corners of the display deliver a low voltage alternating current on the conductive layer.
At the moment of contact, current leakage occurs if the object has a higher electrical capacity than the screen.
The current is recorded at the corners of the screen, and the 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 there were frequent failures when the user did not touch the ground.
These devices are very reliable, their resource exceeds resistive ~ 60 times (about 200 million clicks), moisture resistant and perfectly tolerate pollution that is not conductive electricity.
Transparency is at the level of 0.9, which is slightly higher, resistive, and work at temperatures down to -15 0 C.
Disadvantages:
- does not react to the glove and most foreign objects;
- the conductive coating is in top layer and is very vulnerable to mechanical damage.
They are used in the same ATMs and terminals under the closed sky.
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 sends 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 stress.
Conductive contaminants, where it is difficult or impossible to remove them, are removed without problems using the software method.
More often than all others are installed in personal electronic devices, ATMs and various techniques, actually installed in the open air (under cover). Apple also favors projected capacitive displays.
Surface acoustic wave
It is made in the form of a glass panel equipped with piezoelectric transducers, probes, located at opposite corners, and receivers.
They are also a pair and are located at opposite corners.
The generator sends an HF electrical signal to the probe, which converts the train of pulses into a SAW, and the reflectors distribute it.
The reflected waves are picked up by sensors and fed to a 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 tangency 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 resource of resistive technology (65 million times in total).
Available from thin film about 3 mm and thickened - 6 mm. Thanks to this protection, the display can withstand a slight blow from a fist.
- poor performance under vibration and shaking conditions (in transport, while 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.
