Screen sensor type is capacitive. Operating principle of projected capacitive touch screens

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 the following types touch screens: resistive, capacitive, projection-capacitive, matrix, touch screen on surface acoustic waves, 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 the operating principle of a resistive touch screen. It consists of a glass panel and a flexible plastic membrane, on which a resistive coating is applied. The space between the glass and the membrane is filled with micro-insulators, which in turn reliably insulate the conductive surfaces, evenly distributed over the active area of ​​the screen. When you press the display, the panel and membrane close, and the controller, using an analog-to-digital converter, registers the change in resistance, converting it into touch coordinates. It is for this reason that such a screen can be pressed with any hard object, it can be a fingernail, a special stylus, or even an ordinary pencil. As a consequence of this structure, resistive screens gradually wear out, which is why there is a need 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 the low cost of its production, and, consequently, the low cost of the device in which it is used. In addition, it is worth noting that the sensor response here does not depend on the condition of the screen surface; even if dirty, the touchscreen remains just as sensitive. It should also highlight the accuracy of hitting desired point, because a dense lattice of resistive elements is used.

Flaws

As disadvantages resistive screens Let's highlight low light transmission, no more than 70% or 85%, so increased backlight brightness is required. It is also low sensitivity, i.e. Simply touching with your finger is not enough, pressure is required, so you cannot do without a digital pen or long nails. This type in most cases it 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 low-voltage power to the conductive layer. AC voltage, 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 the basic elements in them are located not on the outside of the screen, but on the inside, making the sensor more protected. This type of display is mainly used in modern mobile devices.

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

Advantages

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

Flaws

TO negative aspects The use of a capacitive touch screen can be attributed to 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 the capacitive type is more reliable due to the absence of a flexible membrane, and fewer layers make them more transparent.

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

However, today 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.

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-books, 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 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 ones, 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 alternating voltage is applied to all four electrodes. 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 pollution. 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 all 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.

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

Usage

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

Laptop with touch screen

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

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

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

Types of touch screens

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

• Resistive
• Capacitive
• Projected capacitive

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

Resistive

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

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

Using a touch pen

Application

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

Communicator

Capacitive

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

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

Information kiosk

Application

• In secured premises
• Information kiosks
• Some ATMs

Projected capacitive

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

Payment terminal

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

Application

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

With determination of surface acoustic waves

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

Other, rare types of touch screens

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

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

About the benefits and disadvantages of touch screens

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

• Possibility to do minimal amount governing bodies
• Simplicity of the graphical interface
• Ease of control
• Ease of access to device functions
• Expanding multimedia capabilities

However, there are more than enough disadvantages:

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

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

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

Discuss on the forum

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:

1. 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.
2. 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:

1. 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.
2. 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 a large capacitance object 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 alternating voltage (the same for all corners) to the conductive layer. 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 if the user had poor contact with the ground, it 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

A grid of electrodes is applied on the inside of the screen. 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%, the temperature range is 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 outdoor machines. Many models react to a gloved hand. In modern models, 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

Your phone's touchscreen: resistive, capacitive or projected capacitive

Touch screens today are an integral attribute of a modern mobile phone, although they became widespread relatively recently - in 2007. And if you are planning to buy a smartphone, you are unlikely to find among the new models those that are not equipped with a touch screen. Despite the fact that adherents of conventional hardware keyboards have difficulty switching to touch control, sensory devices are being produced more and more. And for those who value convenient typing, they release touch phones in a classic form factor or in a side slider form factor, which are additionally equipped with hardware QWERTY keyboards.

Touch phones and smartphones in different form factors

Often the phrase “touch screen” is replaced by another - “touchscreen”, which is a combination of two English words (touch - touch, touch and screen - screen). We're so used to touch screens that we often don't think about what they can actually do. different types. This article will talk about touch screens that are used in mobile phones and smartphones, so we will consider their classification in relation to this technology. In practice, touch screens are often used in other multimedia devices(tablets, monitors, etc.), as well as in medical and engineering equipment.

So, resistive, capacitive and projection-capacitive screens come into our field of vision. Let's look at their advantages and disadvantages to decide which type of screen is most suitable for you.

Resistive touch screens

Screens of this type consist of two main layers - a flexible upper layer (mostly made of plastic) and a rigid lower layer (made of glass). The top layer has another function - protective. It protects the working area of ​​the display from damage. You touch the top layer while working with a mobile device, and information about the coordinates of the touch is transmitted to the bottom layer. The inner sides of these layers are covered with a special membrane and material that conducts current. The layer between the two layers is a dielectric.

Examples of models with resistive touch screens

The main advantage of resistive touch screens is their low cost. Such screens are now installed by manufacturers on many mobile phones and mid-range smartphones. price segment. It is the low cost of the screen that often allows one to reduce the price of such devices, making them more affordable.

Their second advantage is resistance to pollution. This means that even the screen surface covered with dust and water stains will still work well, and pressure sensitivity will not change.

The third is that you can touch such a screen with any hard object. This could be a stylus, a fingernail, the tip of a pencil, a key, or any moderately sharp object that you personally find convenient to use.

If we talk about the disadvantages of resistive touch screens, the first one can be called its low durability. If you translate the lifespan of such a screen into the number of clicks, it would be 1 million clicks for four-wire screens and 35 million clicks for five-wire screens (the two most common types of resistive touch screens). Resistive screens transmit light very poorly (only about 80%). Despite the used protective layer, the operation of such a screen can be quite easily disrupted by damaging it. Plastic is easily cut by sharp objects, and its surface does not withstand too much high temperatures and may melt.

The popularity of resistive touch screens is still very high. It was they who made touchscreen phones accessible and allowed many inexpensive devices costing up to $200 to be brought to market. Among the most popular devices in this segment are Star, 5530 XpressMusic.

Capacitive touch screens

This type of screen is based on the human body's ability to conduct electrical current. Most often, a capacitive screen is based on a glass substrate, on the surface of which a resistive material is applied, covered with a conductive film. When you touch the screen with your finger, an electric current is generated, and a special controller calculates the coordinates of the touch.

In terms of accuracy in determining coordinates, capacitive screens are in no way inferior to resistive screens, but they transmit light better (90% or more instead of 80%). The durability of such screens is much higher - they can withstand up to 200 million clicks. The impact of the environment on capacitive screens is less - ideally, they are able to work flawlessly in sultry heat and extreme cold.

Examples of models with capacitive touch screens

The main disadvantage of this type of screen is that it can only operate under the influence of a conductive object. That is, if you want to use a regular stylus or any other hard object, the screen will not react to your touch.

This problem manifests itself especially strongly in winter, when on a frosty day, when answering an important call, there is no opportunity (or desire) to take off the glove and press the corresponding button on the screen. True, some owners of such phones have already found a rather original way out of this situation - instead of using their fingers to press this button, they use... their nose! It must be said that in some cases it is possible to control it with a gloved hand - this will depend on the quality of the screen and its sensitivity, as well as the material from which the glove is made.

Another disadvantage of capacitive touchscreens is their high susceptibility to surface contamination. In this case, the sensitivity and accuracy of clicks can be significantly reduced.

To be fair, it is worth noting that styluses with electrical capacitance have already been created (for example, the manufacturer has such a model), but they have not gained much popularity due to their high cost (about $30).

Projected capacitive touch screens

This type of screen differs from classic capacitive screens in only one way - it supports Multitouch technology. Their design is also a little more complicated, but the principle of operation remains the same. Such screens are capable of tracking and processing multiple clicks simultaneously, which is widely used in mobile browsers and gaming applications. For example, a two-finger twist can rotate an image 90 degrees, and multi-finger swipes make it easier to scroll through the screen. True, the cost of screens made using this technology is still traditionally high, so they are installed on smartphones whose price is above the $300 mark.

Multitouch in action

Projected capacitive touch screens have many advantages - in addition to Multitouch support, they are durable (about 200 million touches), resistant to damage (can be used for protective purposes). strained glass or special plastic up to 18 mm thick), can withstand work at very low temperatures (down to -40 °C), and are capable of transmitting light well (over 90%). Projected capacitive screens have only one drawback - they can only be controlled using conductive objects (as is the case with conventional capacitive screens).

The most famous smartphones with projected capacitive screens are produced by Apple company, she also became a pioneer in this field. Also working Multitouch is available on models such as Galaxy S II, HTC Desire S.

What to choose

If you are faced with a choice mobile device Depending on the type of touch screen, you can first decide how much you are willing to spend on purchasing a phone or smartphone, what the operating conditions of the device will be, and whether you agree to use only your fingers for control. If you're willing to pay a hefty price for Multitouch support and need a modern, high-performance smartphone, choose a model with a projected capacitive display. If you are purchasing a phone with a touch screen for the first time and want to save money, a resistive screen will suit you. He will be the best solution, if you are embarrassed by the need to operate it exclusively with your fingers, or if you often work in less than sterile conditions, and particles of dirt and dust regularly fall on the surface of the screen.

Most experts in this field predict a gradual withdrawal from the market of resistive screens, but the range of models with such screens is still the largest, and the prices are pleasant to the eye and wallet. New versions appear at the same time operating systems, which are perfectly adapted for finger control: they do not have too small buttons that are difficult to hit, and the number of actions to perform one operation is reduced to a minimum.