Touch screen: history of invention and principles of operation. Which is better: resistive or capacitive screen? Touch Screen Types

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 terms, 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 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. alternating 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 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

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%, 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 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.

The article was written based on materials from the site

Touch screen - This is an information input device, which is a screen that responds to touches.

Basic comparative characteristics touch screens.

The first most obvious advantage of touch technologies is the intuitiveness and naturalness of the action itself - touching the screen with your hand.

The second undoubted advantage of devices based on touch screens is compactness. Installing touch monitors will qualitatively improve the efficiency of service in cinemas, restaurants, hotels, airports, and administrative institutions, where every centimeter of the workplace is valuable. A touch monitor (especially if it is an LCD monitor) allows you to save maximum space on your work surface.

Speed ​​of work can be not only a matter of prestige, but also vital important issue, in the truest sense of the word. Imagine what winning a second could mean when the fastest possible response is required, for example, from a security center dispatcher. Thus, quick access- This is the third advantage of touch screens.

The fourth benefit of sensors is cost reduction. Installation touch monitor can significantly increase the speed and accuracy of actions of an employee working at a computer, and reduce the time required to train an employee.

Touch screen - types:

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 protect the network of vertical and horizontal conductors from contact. At the moment of pressing, the layers are in contact and the controller registers the electrical signal. The coordinates of the press are determined based on the intersection of which conductors the impact was recorded.

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. Before touching, the screen has some electrical charge. Touching the finger changes the charge pattern, “pulling” part of the charge to the point of pressure. Screen sensors located in all four corners monitor the flow of charge in the screen, thus determining the coordinates of the “leakage” of electrons.

Capacitive screens are also highly reliable (they do not have flexible membranes) and have a high degree of transparency. True, they are not suitable for working with a stylus or 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 secured premises
• Information kiosks
• Some ATMs

Acoustic touch screen.

Such screens are built using miniature piezoelectric sound emitters that are inaudible to 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 over the entire surface of the screen in a special way. Touching the screen changes the pattern of propagation of acoustic vibrations, which is recorded by sensors. By changing the nature of the oscillations, you can calculate the coordinates of the disturbances introduced by pressing 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 acoustic screens- absence of coatings, which increases the reliability and transparency of the screen.

These acoustic touch screens are mainly used in slot machines, secure help systems and educational institutions. As a rule, screens are distinguished into regular ones - 3 mm thick, and vandal-resistant ones - 6 mm. The latter can withstand a punch from an average man or a drop from a metal ball weighing 0.5 kg from a height of 1.3.

The main disadvantage of the screen is malfunctions 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 contact with an object that necessarily absorbs acoustic waves.

Infrared touch screen.

Infrared touch screens consist of 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 extraneous illumination. But for large screen diagonals, this technology is still indispensable. In addition, all of the above types of touch displays are subject to the so-called “hot point drift”.

Infrared touch screens are sensitive to contamination 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.

Multi-touch,

is not a touch screen type. 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 a projected capacitive principle) that allows the screen to recognize multiple points of contact on it. As a result, the multi-touch screen becomes capable of recognizing gestures.

Touch screen - views.

Everyone has probably heard about the development of display companies with tactile feedback, and this is no longer a myth. The only obstacle on the way to reaching a wide audience is the emergence of a universal screen with the highest sensitivity, that is, today specialists are faced with the task of making a tactile display practical in all respects. This alternative to vibration motors will help recreate contact with the device, as with a push-button device, and even more...

Touch displays of the near future

Thanks to some companies, technology progress is obvious, and now there are not one, but several prototypes. One of these was Microsoft Corporation, its research group "" under the leadership of Hong Tan, was able to advance in the tactile direction.

A group of specialists spent several years creating a screen with feedback, and their work is already presented in several variations, including one based on Nokia Lumia. You can verify the state of affairs from the video clip below:

According to lead researcher Hong Tan, touch displays are set to evolve into something more. "What's really cool is taking a smooth piece of glass and making it something special," says Ms. Tan. “It’s almost magical.”

Microsoft researchers are working in two directions, developing the hardware and software components of the technology. The main task is complete feedback, not only on pressing the number buttons, but also on the image in general. So some screen options give a real feeling of textures under your fingers. One example is a chessboard made of Nokia apps Lumia. Cells of different colors have different tactile effects.

Instead of an afterword

Basically, the technology of future screens is based on stimulating receptors on the skin, as well as muscle motility. On the screens you will be able to feel not only the pressing of the surface under your finger, but also a characteristic click indicating contact.
"When you type on virtual keyboard smartphone, the outer layer literally instantly bends under your fingers. It's just a small amount of deflection, but it's enough to give your fingers a signal that you've pressed the button,” says Ms. Hong.

Resistive screen.

The simplest type is a four-wire one, which consists of a special glass panel as well as a plastic membrane. The space between the glass and the plastic membrane must be filled with microinsulators that can reliably isolate conductive surfaces from each other. Electrodes, which are thin plates made of metal, are installed over the entire surface of the layers. In the rear layer, the electrodes are in a vertical position, and in the front layer - in a horizontal position so that coordinates can be calculated. If you press on the display, the panel and membrane will automatically close, and a special sensor will sense the press, converting it into a signal. The most advanced type are eight-wire displays, which differ high level accuracy. However, these screens are different low level reliability and durability. If it is important that the display is reliable, you need to choose a five-wire type.

1 - glass panel, 2 - resistive coating, 3 - microinsulators, 4 - film with conductive coating

Matrix screens.

The design is similar to a resistive display, although it has been simplified. Vertical conductors were specially applied to the membrane, and horizontal conductors were applied to the glass. If you click on the display, the conductors will definitely touch and close crosswise. The processor can track which conductors are shorted, and this helps detect the coordinates of the press. Matrix screens cannot be called high-precision, so they are already for a long time do not use.

Capacitive screens.

The design of capacitive screens is quite complex, and it is based on the fact that the human body and the display together form a capacitor that conducts alternating current. Similar screens are made in the form of a glass panel, which is coated with a resistive material so that electrical contact is not hampered. The electrodes are located at the four corners of the display and are supplied with alternating voltage. If you touch the display surface, leakage will occur. AC through the above-mentioned "capacitor". This is recorded by sensors, after which the information is processed by the device’s microprocessor. Capacitive displays can withstand up to 200 million clicks, they have an average level of accuracy, but, alas, they are afraid of any influence of liquids.

Projective capacitive screens.

Projected capacitive screens can, unlike the previous types discussed, be able to detect several clicks at once. There is always a special grid of electrodes on the inside, and during contact with them a capacitor will certainly be formed. IN this place the electrical capacitance will change. The controller will be able to determine the point where the electrodes crossed. Then the calculations take place. If you press the screen in several places at once, not one capacitor will be formed, but several.

Screen with a grid of infrared rays.

The principle of operation of such displays is simple, and to some extent it is similar to a matrix display. In this case, the conductors are replaced with special infrared rays. Around this screen there is a frame in which there are built-in emitters, as well as receivers. If you tap on the screen, some beams will overlap and they cannot reach their own destination, namely the receiver. As a result, the controller calculates the contact location. Such screens can transmit light, they are durable, since there is no sensitive coating and there is no mechanical touch at all. However, such displays present moment do not meet high accuracy and are afraid of any contamination. But the diagonal of the frame of such a display can reach 150 inches.

Touch screens based on surface acoustic waves.

This display is always made in the form of a glass panel, into which piezoelectric transducers are built, located at different angles. There are also reflective and receiving sensors around the perimeter. The controller is responsible for generating signals whose frequency is high. After this, the signals are always sent to piezoelectric transducers, which can convert the incoming signals into acoustic vibrations, which are subsequently reflected from the reflective sensors. The waves can then be captured by receivers, re-sent to piezoelectric transducers, and then converted into electrical signal. If you press the display, the energy of the acoustic waves will be partially absorbed. Receivers are sensitive to such changes, and the processor can calculate the touch points. The main advantage is that touch screens based on surface acoustic waves track the coordinates of the point of pressing and the force of pressing. Displays of this type are durable, because they can withstand 50 million touches. Most often they are used for slot machines, help systems. It should be taken into account that the operation of such a display may not be accurate in the presence of ambient noise, vibration, or acoustic pollution.

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 is this characteristic that paved the way for them to a large number of users around the world. Currently, there are three main designs of touchscreens:

1. Capacitive.
2. Wave.
3. 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 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.

A rather important advantage of capacitive touchscreens is the ability of this type screens to maintain 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

The transducer-receiver “knows” absolutely exactly whether there was a press, as well as at what specific point it occurred, since the user interrupts the acoustic wave with his touch. 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

An electric charge passes through these two layers as the user interacts 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, a special driver translates the touches into commands known 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.

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 what technology will have great prospects for future use.

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.