What does capacitive touch mean? Other, rare types of touch screens. Sensors in phones

Or as they are also called - tablets, based on the operating room Android systems are some of the fairly new gadgets that will allow you to chat with your friends, view World Wide Web (Internet), as well as watch movies and listen to your favorite music. They are usually small flat shape, have lost a significant part of their mass and a rather voluminous keyboard, which is now associated with their older brother, the laptop. If there is no keyboard, you ask, then how to work with them?

Every tablet has a touch screen. It's a screen that responds to your touch, just like a laptop's touchpad. This way, instead of clicking on icons with your mouse, you can simply touch them with your finger or stylus (looks like a pen, but without the ink).

Exist different kinds touch displays, so let's figure out what they are and what the differences are between them:

Resistive touch screen

Resistive touch screen looks like a sandwich consisting of layers, if we speak by analogies. When you press the screen, it closes with the membrane, the device registers the change in resistance and converts it into coordinates, so your tablet knows that you pressed here and reacts accordingly. For example, opens an application or pauses the game. Their strengths are that they are quite durable, as they are made from various types of fiberglass. Considering that this is enough simple development, resistive screen It also has a relatively low cost, so it will reduce your costs. The disadvantage of the resistive type of screen is that some people feel that they are not sensitive enough, since the tablet has to wait a short time for your finger or stylus to close the layers. In addition, it is highly recommended to have a stylus or a long fingernail, as simple touches fingertip are not always recognized by the device.

Capacitive touch screen

Capacitive touch screen consists of flat and thick glass covered with a layer electrical conductor. The human body is also good guide electrical current, so when you touch the glass there is an electrical connection that is recognized as if you were clicking a mouse. Strengths of this type touch screens the fact that they produce a brighter and clearer picture than resistive ones, they are also made of glass, there is no plastic there, so they recognize touches quite accurately and quickly, thus eliminating the need for a stylus. Flaws capacitive screen take place here too. Since the production of such displays is quite complex, the price touch screen significantly more than resistive ones, and since they are made of glass they are susceptible to damage, for example when the tablet falls to the ground.

So which one should you choose? To be honest, there's no clear winner here, but it might be worth considering whether you'll be using a stylus or your finger. Capacitive displays tend to be brighter, so if you're going to watch movies on a tablet, a capacitive screen is preferable. They are also great for gamers, due to the ability to respond more quickly to touch. If you are not attracted by the above, and you just want to find yourself a tablet based on Android OS for browsing the Internet, Email, listening to music, then you can certainly save money without sacrificing performance and buy a tablet with a resistive display.

An information input device, which is a screen that responds to touches. There are many different types touch screens that operate on different physical principles. But we will consider only those that are found in mobile phones and other portable equipment.

How resistive touch screens work

Resistive touch screens come in two types, four-wire and five-wire. Let's consider the operating principle of each type separately.

Four-wire resistive screen

Operating principle of 4-wire resistive touch screen

A resistive touch screen consists of a glass panel and a flexible plastic membrane. A resistive coating is applied to both the panel and the membrane. The space between the glass and the membrane is filled with micro-insulators, which are evenly distributed over the active area of the screen and reliably isolate conductive surfaces. When the screen is pressed, the panel and membrane are closed, and the controller with analog-to-digital converter registers the change in resistance and converts it into touch coordinates (X and Y). IN general outline The reading algorithm is as follows:

A voltage of +5V is applied to the upper electrode, and the lower one is grounded. The left and right are short-circuited and the voltage on them is checked. This voltage corresponds to the Y-coordinate of the screen.
Similarly, +5V and ground are supplied to the left and right electrodes, and the X-coordinate is read from the top and bottom.

Five-wire resistive screen

The five-wire screen is more reliable due to the fact that the resistive coating on the membrane is replaced by a conductive one (the 5-wire screen continues to work even with a cut through membrane). The rear glass has a resistive coating with four electrodes at the corners.

Operating principle of 5-wire resistive touch screen

Initially, all four electrodes are grounded, and the membrane is “pulled up” by a resistor to +5V. The voltage level on the membrane is constantly monitored analog-to-digital converter. When nothing is touching the touch screen, the voltage is 5V.

As soon as the screen is pressed, the microprocessor detects the change in membrane voltage and begins to calculate the coordinates of the touch as follows:

A voltage of +5V is applied to the two right electrodes, the left ones are grounded. The voltage on the screen corresponds to the X-coordinate.
The Y-coordinate is read by connecting both upper electrodes to +5V and to ground both lower ones.

How capacitive touch screens work

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

Operating principle of a capacitive touch screen

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

In earlier models of capacitive screens, D.C.- this simplified the design, but bad contact the user with the ground led to failures.

Capacitive touchscreens are reliable, about 200 million clicks (about 6 and a half years of clicks every second), do not leak liquids, and tolerate non-conductive contaminants very well. Transparency at 90%. However, the conductive coating is still vulnerable. Therefore, capacitive screens are widely used in machines installed in protected areas. They do not respond to a gloved hand.

Operating principle of projected capacitive touch screens

On inside The screen is covered with a grid of electrodes. The electrode together with the human body forms a capacitor; the electronics measures the capacitance of this capacitor (supplies a current pulse and measures the voltage).

Operating principle of projected capacitive touch screen

The transparency of such screens is up to 90%, temperature Range extremely wide. Very durable (the bottleneck is the complex electronics that process clicks). POE can use glass up to 18 mm thick, which results in extreme vandal resistance. They do not react to non-conductive contaminants; conductive contaminants are easily suppressed using software methods. Therefore, projected capacitive touch screens are used in vending machines installed on the street. Many models react to a gloved hand. IN modern models The designers have achieved very high accuracy - however, vandal-resistant versions are less accurate.

PEEs even react to the approach of a hand - the response threshold is set by software. Distinguish between pressing by hand and pressing with a conductive pen. Some models support multi-touch. Therefore, this technology is used in touchpads and multi-touch screens.

It is worth noting that due to differences in terminology, surface- and projected-capacitive screens are often confused. According to the classification used in this article, the iPhone screen is projected capacitive.

Conclusion

Each type of touch screen has its own advantages and disadvantages; for clarity, let’s look at the table.

	Resistive 4-wire	Resistive 5-wire	Capacitive	Projected capacitive
Functionality
Hand in glove	Yes	Yes	No	Yes
Solid conductive object	Yes	Yes	Yes	Yes
Solid non-conductive object	Yes	Yes	No	No
Multi-touch	No	Yes	Yes	Yes
Pressure measurement	No	No	No	Yes
Ultimate transparency, %	75	85	90	90
Accuracy	High	High	High	High
Reliability
Lifetime, million clicks	10	35	200	∞
Protection from dirt and liquids	Yes	Yes	Yes	Yes
Resistance to vandalism	No	No	No	Yes

The article was written based on materials from the site

Nowadays you won’t surprise anyone with a touch screen. Moreover, it is already strange to see devices without a sensor, especially when we're talking about O 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 new tablet or a 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.

Can be found a large number of touch displays, differing not only design features, but also the principle of operation. Today there are following types touch screens: resistive, capacitive, projected capacitive, matrix, surface acoustic wave touch screen, infrared, strain gauge, inductive.

IN currently There are two main types of touch screens used in electronics: resistive and capacitive. We will talk about them in more detail, and also try to highlight the strong and weak sides everyone.

Resistive touch screen

First, let's look at how a resistive touch screen works. 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 for periodic calibration of 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 low cost its production, and, consequently, 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. It should also highlight the accuracy of hitting 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 it is required increased brightness backlight. 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 electricity and has some 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 basic elements they are located not on the outside of the screen, but on the inside, making the sensor more protected. Displays of this type are 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 a touch without using additional accessories. The undoubted advantage of screens of this type is the longer service life of the sensor compared to 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.

Conclusion

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 capacitive type more different high reliability due to the absence of a flexible membrane, and a smaller number of layers makes 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 on the market electronic technology There are still a large number of devices with resistive screens, 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.

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

Types of touchscreens

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

Capacitive.
Wave.
Resistive or simply “elastic”.

Capacitive touchscreen: operating principle

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

Enough important advantage Capacitive touchscreens are the ability of this type of screen to retain almost 90% of the original display brightness. Because of this, images on a capacitive screen appear sharper than on touchscreens that have a resistive design.

Video about capacitive touch screen:

The future: waveform touch displays

At the ends of the coordinate grid axes of the glass screen there are two transducers. One of them is the transmitter, the second is the receiver. There are also reflectors on a glass base that “reflect” the electrical signal that is transmitted from one converter to another.

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

Video about the operating principle of surfactant touch screens:

Past: about resistive touchscreen

A resistive system is ordinary glass, which is covered with a layer of electrical conductor, as well as an elastic metal “film” that also has conductive properties. Between these 2 layers, using special spacers, there is empty space. The surface of the screen is covered with a special material that provides it with protection from mechanical damage eg scratches.

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

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

Resistive screens can be found in relatively old devices. The IBM Simon, the oldest smartphone known to our civilization, is equipped with just such a touch screen.

Video about the operating principle of a resistive touch screen:

Features of different types of touchscreens

The cheapest touch screens, but at the same time the least clearly broadcasting the image are resistive touchscreens. In addition, they are also the most vulnerable, because absolutely any sharp object can seriously damage a fairly delicate resistive “film”.

The next type, i.e. wave touchscreens are the most expensive among their kind. At the same time, the resistive design most likely belongs to the past, the capacitive design to the present, and the wave design to the future. It is clear that absolutely no one knows the future one hundred percent and, accordingly, at the present time one can only guess which technology has great prospects for its use in the future.

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

The screens of modern devices can not only display images, but also allow you to interact with the device through sensors.

Initially, touch screens were used in some pocket computers, and today touch screens are widely used in mobile devices, players, photo and video cameras, information kiosks, and so on. Moreover, in each of listed devices one or another type of touch screen may be used. Currently, several types have been developed touch panels, 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 more bright backlight), poor support for multiple clicks (multi-touch), cannot determine the force of pressing, as well as fairly rapid mechanical wear, although in comparison with the life of the phone, this drawback is not so important, since it usually faster phone fails 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 great resource touches. 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)

The composition and operating principle of this type of screen is 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, the 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 one stored in memory digital matrix screen, 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, V 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), they cannot determine the force of pressing, the accuracy of determining coordinates is average.

P.S. So, we looked at the main types of the most common touch 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 widespread in mobile devices, as they have high accuracy determining the point of contact. Of them best characteristics have projected capacitive touch screens.

The text was prepared based on materials from open sources by Technological methodologists Karabin A.S., L.V. Gavrik, S.V. Usachev