Before considering a capacitive or resistive screen, you need to decide what kind of touch technology is in general. Everything is clear here: this is the screen that determines the coordinates of the press. Scientifically speaking, this refers to the method of managing the interface, with which the user can click directly on the place of interest. At the moment, there are several methods for implementing touch screens. It is worth considering each separately.
Resistive technology
To determine which type of screen, capacitive or resistive, is best for you, you need to consider them. The second option involves the use of a specific production technology. Below is a glass panel, on top of which there is a transparent flexible membrane. There is a conductive coating on the panel and membrane, that is, resistive. When you touch the screen, it closes at a certain point. If you know the voltage across the electrodes on one side and measure it on the membrane, you can track one coordinate. Two coordinates will require you to turn off one group of electrodes to turn on the other. All this is done automatically by the microprocessor as soon as the voltage across the membrane changes. Resistive screens do not allow multi-touch.
Features of resistive technology
Like any other type of implemented device, there are certain traits that are positive or negative, depending on the situation. As advantages, cheap production is usually noted, as well as the ability to press with anything, since you only need to push through the membrane. Positioning accuracy is increased by using stylus.
Negative moments
The main disadvantages are a low degree of light transmission, a high rate of scratches on the surface, the ability to press one point no more than 35 million times, and the impossibility of implementing multitouch. If you cannot decide whether to choose a capacitive or a resistive screen, then it is also important to note the impossibility of using gestures such as sliding, since you need to press your finger on the screen and keep holding it. In devices with such controls, it is better to use software that requires minimal use of “flipping” gestures.
Understanding the features of this technology, it is worth noting that it can be implemented in several ways that have certain differences. The capacitive touchscreen can be simply capacitive and projected-capacitive. The first option involves the use of certain elements. A transparent resistive material, such as an alloy of tin oxide or indium oxide, is placed over the glass panel. Electrodes are placed in the corners, which apply a small alternating voltage to the conductive layer. If a conductive object is touched to the screen, then a leak occurs, and the closer this object is to the electrode, the lower the resistance of the screen, that is, the current increases noticeably. And all this is called a capacitive screen, since the alternating current is conducted by an object of greater capacity. Most often we are talking about a finger.
Features of capacitive screens
Like other types of technologies, in this case we are talking about a combination of advantages and disadvantages. The advantages over the others include high light transmittance, significant resource of clicks, simplicity and ease of use by the “paging” method. There are also disadvantages here: you only need to use your fingers or specialized styluses. Conventional capacitive screen does not support multitouch technology. Accidental clicks are common. For example, the system can recognize the gesture as “flipping” even when it is not supposed to be, since it is difficult to keep the finger strictly in one place after pressing.
Projected capacitive touchscreen
In this case, the device differs from the previous ones quite strongly. The inner side of the screen is a grid of electrodes. If an object of larger capacity touches the electrode, then a capacitor is formed with a constant capacity. Such screens are used outdoors, as they allow you to install glass, the thickness of which reaches 18 mm, while it is possible to obtain not only the most hard surface, but also to ensure vandal resistance.
Features of Projection Capacitive Sensors
In this case, as in all others, there are certain advantages and disadvantages that you should be aware of. The advantages include the ability to implement multitouch, response to pressing with a glove, a high degree of light transmission, as well as the durability of the screen itself. Such screens are capable of responding to the approach of fingers without the fact of pressing. The threshold at which touch completion occurs is usually programmatically configurable. The extreme point is usually the screen itself, since it is completely useless to push through it.
If we consider a projection-capacitive screen, then it also has certain drawbacks, which are usually called complex and rather expensive electronics, the inability to use a conventional stylus, and the likelihood of accidental clicks.
Multi-touch technology
It is impossible to determine the appropriate type of touch screen, capacitive or resistive, without deciding the question regarding the implementation of this technology. Multi-touch is a multi-touch capability. This implementation assumes tracking the coordinates of several clicks at the same time. If such a technology is implemented in a smartphone or tablet, then it can be used to imitate playing a musical instrument, for example, a guitar. You should deal with this in more detail.
You can take a conventional capacitive or resistive screen. If you first press, for example, in the upper left corner, and then, without lifting your finger, press the other in the lower right corner, then the electronics will determine the center of the screen as coordinates, that is, the middle of the segment between a pair of these touches. This will be visible if you run a special application that tracks the coordinates of the press. However, the question arises: how is the scaling of pictures implemented if only one click is recognized anyway?
Everything is simple here. This is the most common software trick. You pressed the capacitive screen - the electronics detected it. This will be point "A". Now, without releasing your finger, you press to another place, which will be point "B", it turns out that at this moment the point of pressing moved instantly to the side, forming "C". It was at this moment, when there was no actual release of the finger, and the point of pressure was instantly moved, it is programmatically processed as a multitouch. Further, if point "C" becomes closer to "A", then the shift of fingers is determined, that is, in the case of an image, the picture must be reduced, and vice versa. Another point: if point "C" describes an arc around one of the points, then the program defines this as rotation of one finger around the other, which necessitates the rotation of the picture in the appropriate direction.
Using resistive and capacitive screens
The first type is traditionally used by professional developers, since it allows you to control any object under various weather conditions. When implementing resistive technology, more sensors per square centimeter are used than capacitive ones, so the display can display the smallest icons that can be pressed with a needle. For example, the Windows Mobile operating system was designed with this feature in mind, so it works well with resistive screens. Such displays are almost insensitive to accidental presses. However, many developers are now aiming to create applications targeting capacitive touchscreens. This is already becoming a problem for devices using resistive technology.
Security degree
It is important to understand that for tablet computers and communicators, the display is the most vulnerable part. A capacitive screen is the preferred option in terms of reliability. Its performance in any conditions is noticeably higher, and resistive models can fail, for example, if they are carried down with glass. A capacitive screen is a fail-safe option. Even if it is broken, it will continue to perform its functions. If you decide whether to choose a capacitive or resistive screen, then it is worth noting that in the field, the first will be the best option.
conclusions
Summing up, it can be noted that both display options have their own advantages and disadvantages. While the capacitive screen is a whole set of possibilities, the resistive screen is focused on use in certain situations. Usually it all depends on the interface used in the gadget. it is convenient to use, its pressing area is noticeably smaller than that of a finger, however, with good surface responsiveness, it is convenient to do without this device. The constant improvement of resistive displays has led to the emergence of models that are quite solid, that is, resistant to the formation of scratches, but at the same time responsive. Such options have become very easy to use.
The need to use a special stylus for capacitive screens sometimes causes considerable inconvenience, since it usually does not come with the device. And the resistive technology presupposes both the accompaniment of a special device and the ability to press with any solid object. One of the reasons many people choose a capacitive touchscreen is multitouch, but it is worth noting that most often this is a software implementation, as already described, and with the proper approach, it can be applied to a resistive one. Projected Capacitive Technology has not yet become as affordable as we would like it to be.
At first, touchscreens (touch screens) were quite rare. They could be found only in some PDAs, PDAs (pocket computers). As you know, devices of this kind have not found widespread use, since they lacked the most important thing, that is, functionality. The history of smartphones is directly related to touchscreens. That is why nowadays you cannot surprise a person with a “smart phone” with a touch screen. The touchscreen is widely used not only in fashionable expensive devices, but even in relatively inexpensive models of modern phones. What are the principles of operation of 3 types of touch screens that can be found in modern devices.
Types of touchscreens
Touchscreens are no longer too expensive. In addition, touchscreens (touchscreen) today are much more "responsive" - \u200b\u200bthe user's touches are recognized just fine. It was this characteristic that paved the way for them to a large number of users around the world. Currently, there are three main touchscreen designs:
- Capacitive.
- Wave.
- Resistive or simply "elastic".
Capacitive touchscreen: how it works
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 of the electric charge at a certain point. This reduction is determined by microcircuits, which are located in each corner of the screen. The computer calculates the difference in electrical potentials that exist between different parts of the screen, while 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 of screens to maintain almost 90% of the original display brightness. Because of this, images on a capacitive screen look sharper than on touchscreens with a resistive design.
Capacitive touchscreen video:
The future: wave touch displays
At the ends of the axes of the coordinate grid of the glass screen there are two transducers. One of them is transmitting, the other is receiving. On the glass base, there are also reflectors that "reflect" the electrical signal that is transmitted from one to another transducer.
The transducer-receiver “knows” with absolute certainty whether it was pressed, as well as at what point it happened, 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, a wave screen is the best option for those users who work in graphics with fine details, because resistive and capacitive touchscreens are not ideal in terms of image clarity. Their coating traps light, which as a result significantly distorts the picture.
Video about the principle of operation of touch screens on SAW:
The past: on the resistive touchscreen
A resistive system is an ordinary glass, which is covered with a layer of a conductor of electricity, as well as an elastic metal "film", which also has conductive qualities. There is an empty space between these 2 layers using special spacers. The surface of the screen is covered with a special material that protects it from mechanical damage, such as scratches.
An electric charge in the process of a user working with a touchscreen passes through these two layers. How does this happen? The user touches the screen at a certain point and the elastic top layer is in 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 to the operating system. In this case, you can make analogs with the driver of the most ordinary 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. Just such a touchscreen display is equipped with IBM Simon - the most ancient smartphone of those that were recognized by our civilization.
Video about the principle of operation of a resistive touch screen:
Features of different types of touchscreens
The cheapest touchscreens, but, at the same time, the least clearly transmitting the image are resistive touchscreens. In addition, they are also the most vulnerable, because absolutely any sharp object can seriously damage the rather 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, refers, after all, to the past, the capacitive design to the present, and the wave design to the future. It is clear that the future is absolutely unknown to no one and, accordingly, at the present time, one can only assume which technology has great prospects for its use in the future.
For a resistive system of touchscreens, it does not really matter whether the user touches the device screen with the rubber tip of the stylus or just with his finger. It is enough that there is contact between the two layers. At the same time, the capacitive screen recognizes only touches with some conductive objects. Often, users of modern devices work with them with their own fingers. The screens of the wave structure in this respect are closer to resistive ones. It is possible to give a command with almost any object - while you only need to avoid using heavy or too small objects, for example, the shaft of a ballpoint pen will not work for this.
In our time, touch screens have long ceased to be exotic. Outwardly they are all similar, but are these displays really the same? Let's look at the design of the main types of sensitive screens, their advantages, disadvantages and scope.
Today, the most widespread sensors are based on capacitive and resistive technologies, as well as on their varieties.
"Multitouch"
This is the name of the technology that allows you to recognize clicks on the touch screen at several points at the same time. This opens up new possibilities in device management. An example of using multitouch technology is the Apple iPhone interface.
Capacitive touch screens
 | For example: Tne Prada Phoneby LG |
The capacitive touchscreen display actually responds to touch. It is a glass panel coated with a transparent conductive compound. In the corners of the panel there are four electrodes to which an alternating current is supplied. The moment the user touches such a screen with a finger, an electric charge from the conductive layer flows over the skin to the human body. The screen controller measures the current generated across all four electrodes - it is proportional to the distance from the corner of the panel to the touch point. Comparing the obtained values, you can find out the exact coordinates of the point of contact. Sensors operating on this principle can be distinguished "by touch" - they are triggered by a light touch, moreover, they react faster and more clearly to pressing with a fingertip than with a nail. Moreover, they do not react to pressing any other objects, especially if they are non-conductive. Therefore, a phone with such a screen cannot be operated with a gloved hand. In addition, as the temperature decreases, the electrical characteristics of the sensor change, and the screen begins to work worse. We add that this principle is usually used in notebook touchpads.
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 | For example: Apple iPhone |
Projected capacitive screens
There is another type of capacitive sensor - a projected capacitive screen. On the back there is a grid of electrodes. At the point where the hand touches, the electrical capacitance changes (according to the laws of electrodynamics, the human body is a capacitor), the controller determines at which intersection of the electrodes this happened, and calculates the coordinates. Such screens, in addition to high transparency and durability, have two more important advantages - the glass-substrate can be made arbitrarily strong (and rather thick), moreover, they support "multitouch". The downside is lower accuracy compared to conventional capacitive technology.
Resistive touch screens
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 | For example: HTC Touch Diamond |
The resistive sensor is de facto pressure sensitive. The screen consists of two plates, between which there is a non-conductive compound. If you touch the outer flexible (and transparent) plate with your finger (or any other object - in this case it does not matter), the plates are closed and current begins to flow at the point of contact. To determine the location of the touch, the screen controller measures the voltage between the electrodes located at the edges of the panel in pairs. Such a screen is called 4-wire (there are also 5-wires with some differences).
The peculiarity of the resistive screen is that it requires physical effort to trigger it, and it recognizes pressing with a fingernail better than a pad, reacts to any objects touching the surface. Devices with resistive screens are often equipped with styluses. Such a display provides a higher control accuracy (with a stylus it is possible to literally hit a pixel, while a finger on a capacitive screen can only hit a large enough area), but due to constant contact with hard objects, the flexible plate is quickly covered with scratches. Most mobile devices are equipped with resistive screens.
Other types of touch screens
There are also a number of sensor technologies, often quite exotic. For example, using a grid of infrared rays or even generating ultrasonic vibrations. The latter is known as surface acoustic wave technology. There are systems based on cameras that track motion ("multitouch" is also supported here), and on the basis of strain-gauge coatings, the deformation of which changes the electrical resistance.
Application
Touch screens are used in payment terminals, information kiosks, trade automation equipment, PDAs, mobile phones, game consoles, operator panels in industry.
Pros and cons of handheld devices
Advantages
- Simplicity of the interface.
- The device can combine small size and large screen.
- Fast dialing in a relaxed environment.
- The multimedia capabilities of the device are significantly expanded.
disadvantages
Advantages and disadvantages of stationary devices
Advantages
In information and vending machines, operator panels and other devices in which there is no active input, touch screens have established themselves as a very convenient way of human-machine interaction. Advantages:
- Increased reliability.
- Resistance to harsh external influences (including vandalism), dust and moisture resistance.
disadvantages
These disadvantages prevent the use of only touch screen in devices with which a person works for hours. However, in a well-designed device, the touch screen may not be the only input device - for example, at the cashier's workplace, the touch screen can be used to quickly select an item, and the keyboard can be used to enter numbers.
How touchscreens work
There are many different types of touch screens that work on different physical principles.
Resistive touch screens
Four-wire shield
How the 4-wire resistive touchscreen works
The resistive touchscreen consists of a glass panel and a flexible plastic membrane. Both the panel and the membrane are coated with a resistive coating. The space between the glass and the membrane is filled with micro-insulators, which are evenly distributed over the active area of \u200b\u200bthe screen and reliably insulate conductive surfaces. When the screen is pressed, the panel and membrane are closed, and the controller, using an 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:
- A voltage of + 5V is applied to the upper electrode, the lower one is grounded. The left and right are short-circuited, and the voltage across 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, the X-coordinate is read from the top and bottom.
There are also eight wire touchscreens. They improve tracking accuracy, but do not increase reliability.
Five-wire shield
The 5-wire shield is more reliable due to the fact that the resistive coating on the membrane is replaced by a conductive one (the 5-wire shield continues to work even with a cut membrane). The rear window has a resistive coating with four electrodes at the corners.
Initially, all four electrodes are grounded, and the membrane is "pulled up" by a resistor to + 5V. The diaphragm voltage level is constantly monitored by an analog-to-digital converter. When nothing touches the touch screen, the voltage is 5 V.
As soon as the screen is pressed, the microprocessor senses the change in membrane voltage and begins to calculate the coordinates of the touch as follows:
- The two right electrodes are supplied with a voltage of + 5V, the left ones are grounded. The voltage on the screen corresponds to the X-coordinate.
- The Y-coordinate is read by connecting both top electrodes to + 5V and both bottom electrodes to ground.
Features:
Resistive touchscreens are cheap and resistant to dirt. Resistive screens react to touch with any smooth solid object: hand (bare or gloved), pen, credit card, pick. They are used wherever vandalism and low temperatures are not excluded: for the automation of industrial processes, in medicine, in the service sector (POS terminals), in personal electronics (PDA). The best samples are accurate at 4096 x 4096 pixels.
The disadvantages of resistive screens are low light transmission (no more than 85% for 5-wire models and even lower for 4-wire models), low durability (no more than 35 million clicks per point) and insufficient vandal resistance (the film is easy to cut).
Matrix touch screens
Design and working principle
The design is similar to the resistive one, but simplified to the limit. Horizontal conductors are applied to the glass, and vertical conductors are applied to the membrane.
When you touch the screen, the conductors touch. The controller determines which conductors are closed and transmits the corresponding coordinates to the microprocessor.
Features:
They have very low accuracy. The interface elements have to be specially arranged taking into account the cells of the matrix screen. The only advantage is simplicity, low cost and unpretentiousness. Typically, matrix screens are polled row by row (similar to a matrix of buttons); this allows you to establish multitouch. They are gradually replaced by resistive ones.
Capacitive touch screens
Design and working principle
A capacitive (or surface-capacitive) screen takes advantage of the fact that a large object conducts alternating current.
The capacitive touchscreen is a glass panel covered with a transparent resistive material (usually an indium oxide / tin oxide alloy). The electrodes located at the corners of the screen apply a small alternating voltage to the conductive layer (the same for all corners). When you touch the screen with a finger or other conductive object, current leakage occurs. In this case, the closer the finger is to the electrode, the lower the resistance of the screen, which means that the current is greater. The current in all four corners is recorded by sensors and transmitted to the controller, which calculates the coordinates of the touch point.
Earlier models of capacitive screens used direct current - this simplified the design, but with poor user contact with the ground, it led to failures.
Capacitive touch screens are reliable, about 200 million clicks (about 6 and a half years of clicks with an interval of one second), do not let liquids through and perfectly tolerate non-conductive pollution. Transparency at 90%. However, the conductive coating directly on the outer surface is still vulnerable. Therefore, capacitive screens are widely used in machines only installed in a weather-protected room. Does not respond to gloved hands.
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 screen, for example, iPhone is projection-capacitive, but not capacitive.
Projected capacitive touch screens
Design and working principle
A grid of electrodes is applied to the inside of the screen. The electrode together with the human body forms a capacitor; electronics measure the capacity of this capacitor (gives a current pulse and measures voltage).
Features:
The transparency of such screens is up to 90%, the temperature range is extremely wide. Very durable (bottleneck - complex electronics that handle pressing). Glass with a thickness of up to 18 mm can be used on PёSE, which leads to extreme vandal resistance. They do not react to non-conductive pollution, conductive ones are easily suppressed by software methods. Therefore, projected capacitive touch screens are widely used both in personal electronics and in automatic machines, including those installed on the street.
It should be noted 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 (the founder of the "technology boom", circa 2007) is projected-capacitive.
Touchscreens on surface acoustic waves
Design and working principle
The screen is a glass panel with piezoelectric transducers (PEP) located in the corners. There are reflective and receiving sensors at the edges of the panel. The principle of operation of such a screen is as follows. A special controller generates a high-frequency electrical signal and sends it to the probe. The probe converts this signal into a SAW, and the reflective sensors reflect it accordingly. These reflected waves are received by appropriate sensors and sent to the probe. The transducers, in turn, receive the reflected waves and convert them into an electrical signal, which is then analyzed by the controller. When you touch the screen with your finger, some of the acoustic energy is absorbed. The receivers record this change, and the microcontroller calculates the position of the touch point. Reacts to contact with an object capable of absorbing a wave (finger, gloved hand, porous rubber).
Features:
The main dignity screen on surface acoustic waves (SAW) is the ability to track not only the coordinates of the point, but also the force of pressing (here, rather, the ability to accurately determine the radius or area of \u200b\u200bpressing), due to the fact that the degree of absorption of acoustic waves depends on the pressure at the point of contact ( the screen does not bend under the pressure of the finger and does not deform, therefore, the pressing force does not entail qualitative changes in the processing of the data on the coordinates of the impact by the controller, which records only the area that blocks the path of acoustic pulses). This device has very high transparency because the light from the imaging device passes through glass that does not contain resistive or conductive coatings. In some cases, glass is not used at all to combat glare, and the emitters, receivers and reflectors are attached directly to the display device screen. Despite the complexity of the design, these screens are quite durable. According to the statement, for example, of the American company Tyco Electronics and the Taiwanese company GeneralTouch, they can withstand up to 50 million touches at one point, which exceeds the resource of a 5-wire resistive screen. Surfactant screens are mainly used in slot machines, in guarded information systems and educational institutions. As a rule, surfactant screens are distinguished into ordinary - 3 mm thick, and vandal-resistant - 6 mm. The latter can withstand a fist hit by an average man or a 0.5 kg metal ball falling from a height of 1.3 meters (according to Elo Touch Systems). The market offers options for connecting to a computer both via the RS232 interface and via the USB interface. At the moment, the most popular are controllers for SAW touch screens that support both types of connection - combo (data from Elo Touch Systems).
The main disadvantage the screen on the SAW are 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 touching with an object that necessarily absorbs acoustic waves - that is, for example, a plastic bank card is not applicable in this case.
The accuracy of these screens is higher than matrix screens, but lower than traditional capacitive screens. They are generally not used for drawing and typing.
Infrared touch screens
The principle of operation of the infrared touch panel is simple - the grid formed by horizontal and vertical infrared rays is interrupted when any object touches the monitor. The controller determines where the beam was interrupted.
Features:
Infrared touch screens are afraid of contamination and are therefore used where image quality is important, such as e-books. Due to its simplicity and maintainability, the scheme is popular with the military. Intercom keyboards are often made on this principle. This type of screen is used in mobile phones from Neonode.
Optical touch screens
The glass panel is equipped with infrared illumination. At the “glass-air” border, a complete internal reflection is obtained, at the “glass-foreign object” border, light is scattered. It remains to capture the scattering pattern, for this there are two technologies:
Features:
They allow you to distinguish between pressing with your hand and pressing any objects, there is a multitouch. Large touch surfaces are possible, right up to the chalkboard.
Strain gauge touch screens
React to screen deformation. The accuracy of the strain gauge screens is low, but they can withstand vandalism perfectly. The application is similar to projection-capacitive: ATMs, ticket machines and other devices located on the street.
DST touch screens
Main article: Dispersive Signal Technology
The DST (Dispersiv'e Signal Technology) touch screen reacts to glass deformation. It is possible to press the screen with your hand or any object. A distinctive feature is a high reaction speed and the ability to work in conditions of severe screen pollution.
Induction touch screens
An induction touchscreen is a graphics tablet with an integrated display. These screens only respond to a special pen.
They are used when it is required to respond specifically to pressing with a pen (and not with a hand): high-end art tablets, some models of tablet PCs.
Pivot table
| Matr | 4-wire | 5-wire | Yomk | Pr-cap | Surfactant | IR grid | Wholesale | Tenzo | DST | Indukts | |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Functionality | |||||||||||
| Gloved hand | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | ||
| Solid conductive object | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | ||
| Solid non-conductive object | Yes | Yes | Yes | Yes | Yes | Yes | Yes | ||||
| Multitouch | Yes 1 | Yes 7 | Yes | Yes | Yes 1 | Yes | |||||
| Measuring pressing force | Yes | Yes | Yes | Yes | Yes | ||||||
| Limiting transparency,% 2 | 85 | 75 | 85 | 90 | 90 | 100 | 100 | 100 | 95 | 90 | |
| Accuracy 3 | Bottom | Height | Height | Height | Height | Wednesday | Bottom | Wednesday | Bottom | Height | Height |
| Reliability | |||||||||||
| Lifetime, million clicks | 35 | 10 | 35 | 200 | ∞ 4 | 50 | ∞ 5 | ∞ 4 | ??? | ∞ 4 | ∞ 4 |
| Protection against dirt and liquids | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | ||
| Resistant to vandalism | Yes | Yes | Yes | ||||||||
| Application 6 | Ogran | Ogran | Ogran | Premises | Street | Premises | Premises | Premises | Street | Premises | Ogran |
1 Supported with limitations.
2 If only a glass panel is needed, without any transparent conductive films - conventionally 95%. If you don't even need it (you can apply the standard screen coverage) - conditionally 100%
3 High - to the pixel (accurately tracks a sharp pen). Medium - up to several pixels (sufficient for finger clicks). Low - in large blocks of the screen (drawing is impossible, very large interface elements are required).
4 Limited by electronics reliability
5 Limited by contamination of the sensor
6 Ogran - limited access equipment (personal electronics, industrial equipment). Premises - general access in a protected area. Street - Shared on the street.
7 Software emulation, handles a maximum of 2 clicks.
see also
- Touchphone
In the movie Die Hard, Bruce Willis's character takes a close look at a technical novelty of the time - the visitor touchpad at Nakatomi Plaza.
Links
- Replacing the touchscreen Instructions for replacing the touchscreen
Notes
- Touch Screen - History of the Touch Screen Computer Interface (eng.)
- Company history from Elographics to Elo TouchSystems, 1971 - present - Elo TouchSystems - Tyco Electronics
- HP History: 1980s
- In resistive screens, there is a recoil when pressed - this makes working with your hands more comfortable. Besides, in some phones a successful press is confirmed by vibration. But such feedback, of course, is not enough to distinguish one interface element from another by touch.
- Mukhin I.A.
Today it is no longer surprising to surprise anyone with a touchscreen phone. Manual control has become fashionable, but few people think about what happens when you touch the display. I will explain how the most common types of touch screens work. The convenience and productivity of working with digital technology depends primarily on the information input devices used, with the help of which a person controls equipment and downloads data. The most widespread and universal instrument is the keyboard, which is now ubiquitous. However, it is not always convenient to use it. For example, the dimensions of mobile phones do not allow installing large keys, as a result of which the speed of information input decreases. This problem was solved through the use of touch screens. In just a few years, they have revolutionized the marketplace and have begun to take root in everything from mobile phones and e-books to monitors and printers.
The beginning of the sensory boom
Buying new smartphone, on the body of which there is not a single button or joystick, you hardly think about how you will operate it. From the user's point of view, this is not difficult: just touch the icon on the screen with your finger, which will lead to the performance of an action - opening a window for entering a phone number, SMS or address book. And yet 20 years ago such opportunities could only be dreamed of.
The touchscreen was invented in the United States in the second half of the 1960s, but until the early 1990s it was mainly used in medical and industrial equipment to replace traditional input devices, which are difficult to use under certain operating conditions. With the decrease in the size of computers and the emergence of PDAs, the question arose about improving their control systems. In 1998, the first handheld with a touch screen and a system of input and handwriting recognition appeared Apple Newton MessagePad, and soon communicators with touchscreens.
In 2006, almost all major manufacturers began to release 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 of computers, etc. What happens when you touch the touch screen, and how does the device "know" exactly where you pressed?
How a resistive touchscreen works
Over the 40-year history of the development 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 a touch. Currently, the most common are two types of displays - resistive and capacitive. In addition, there are screens that can register several clicks at the same time ( Multitouch) or just one.
Screens made using resistive technology consist of two main parts - a flexible top layer and a rigid bottom layer. As the first, various plastic or polyester films can be used, and the second is made of glass. On the inner sides of both surfaces, layers of a flexible membrane and a resistive (having electrical resistance) material that conduct an electric current are applied. The space between them is filled with a dielectric.
At the edges of each layer, thin metal plates are installed - electrodes. In the back layer with resistive material, they are located vertically, and in the front layer - horizontally. In the first case, a constant voltage is applied to them, and an electric current flows from one electrode to another. This results in a voltage drop proportional to the length of the screen section.
When you touch the touch screen, the front layer flexes and interacts with the back layer, which allows the controller to determine the voltage on it and calculate 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 done: the voltage is applied to the electrodes of the front layer, and those located in the back layer are grounded - this is how it is possible to calculate the coordinate of the point of contact along the vertical (Y axis). This is how a four-wire (named after the number of electrodes) resistive touchscreen works.
In addition to four-wire, there are also five- and eight-wire touch screens. The latter have a similar operating principle, but a higher positioning accuracy.
The principle of operation and design of five-wire resistive touch screens are slightly different from those described above. The front resistive layer is replaced with a conductive layer and is used exclusively for reading the voltage value on the back resistive layer. It contains four electrodes at the corners of the screen, the fifth electrode is the output of the front conductive layer. Initially, all four electrodes of the back layer are energized, and on the front layer it is zero. As soon as such a touch screen is touched, the upper and lower layers are connected at a certain point, and the controller detects the change in voltage on the front layer. So he determines that the screen has been touched. Next, the two electrodes in the back layer are grounded, the X coordinate of the touch point is calculated, and then the other two electrodes are grounded, and the Y coordinate of the touch point is calculated.
How Capacitive Touch Screen Works
The principle of operation of capacitive touch screens is based on the ability of the human body to conduct electric current, which indicates the presence of electrical capacity. In the simplest case, such a screen consists of a strong glass substrate on which a layer of resistive material is applied. Four electrodes are placed in its corners. From above, the resistive material is covered with a conductive film.
A small alternating voltage is applied to all four electrodes. At the moment a person touches the screen, an electric charge flows over the skin to the body, and an electric current is generated. Its value is proportional to the distance from the electrode (panel corner) to the point of contact. The controller measures the current at all four electrodes and, based on these values, calculates the coordinates of the point of contact.
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 work at low temperatures (down to -15 ° C). However, the conductive front coating used for positioning is sensitive to moisture, mechanical damage and conductive dirt. Capacitive screens are triggered only when touched with a conductive object (hand without a glove or a special stylus). Screens of this type made according to the classical technology are also not able to track several clicks at the same time.
This capability is provided by the projected capacitive touch screen, which is used in iPhones and similar devices. It has a more complex structure than conventional capacitive screens. On a glass substrate, two layers of electrodes are applied, separated by a dielectric and forming a grating (the electrodes are located vertically in the lower layer, and horizontally in the upper layer). The grid of electrodes together with the human body forms a capacitor. At the point of touching with a finger, a change in its capacitance occurs, the controller catches this change, determines at which intersection of the electrodes it occurred, and calculates the coordinate of the touch point from this data.
Such screens also have a high transparency and are capable of operating at even lower temperatures (down to -40 ° C). Electrically conductive pollution affects 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 the four-wire resistive touchscreen
- The upper resistive layer flexes and touches the lower one.
- The controller detects the voltage at the touch point on the bottom layer and calculates the X coordinate of the touch point.
- The controller detects the voltage at the touch point on the top layer and determines the Y coordinate of the touch point.
How the 5-wire resistive touchscreen works
- Touch the screen with any hard object.
- The top conductive layer flexes and touches the bottom, indicating touching the screen.
- Two of the four electrodes of the lower layer are grounded, the controller detects the voltage at the point of contact and calculates the coordinate of the point along the X axis.
- The other two electrodes are grounded, the controller detects the voltage at the touch point and calculates the y-coordinate of the point.
Benefits
- Low cost
- High resistance to dirt
- Can be touched with any hard object
disadvantages
- Low durability (1M clicks at one point for 4-wire, 35M clicks for 5-wire) and vandal resistance
- Low light transmission (no more than 85%)
- Do not support Multitouch
Device examples
- Phones (for example, Nokia 5800, НТС Touch Diamond), PDAs, computers (for example, MSI Wind Top AE1900), industrial and medical equipment.
Principle of operation
- The screen is touched with a conductive object (finger, special stylus).
- The current flows from the screen to the object.
- The controller measures the current at the corners of the screen and determines the coordinates of the touch point.
Benefits
- High durability (up to 200 million clicks), the ability to work at low temperatures (down to -15 ° C)
disadvantages
- Susceptible to moisture, conductive contamination
- Do not support Multitouch
Device examples
- Phones, touchpads (for example, in the VZO iRiver player), PDAs, ATMs, kiosks.
Principle of operation
- The screen is touched or brought close to it by a conductive object that forms a capacitor with it.
- At the point of contact, the electrical capacitance changes.
- The controller registers the change and determines at which intersection of the electrodes it occurred. Based on this data, the coordinates of the touch point are calculated.
Benefits
- High durability (up to 200 million clicks), the ability to work 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 transmission (more than 90%)
- Support Multitouch
disadvantages
- React to the touch of only a conductive object (finger, special stylus)
Device examples
- Phones (for example, iPhones), touchpads, laptop and computer screens (for example, HP TouchSmart tx2), electronic kiosks, ATMs, payment terminals.
Windows 7
Now you can control your 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 square icons appeared instead of rectangular buttons symbolizing running programs - it is much more convenient to press them with your finger. In addition, there is a new feature - Jump Lists, allowing you to quickly find recently opened files or frequently launched items. To activate this feature, just drag the program icon to the Desktop.
For the first time, an option has been added to the Windows operating system to recognize touch gestures, to which the execution of certain functions is tied. So, in Windows 7, touch scrolling appeared and, like, for example, in the Apple iPhone, the ability to enlarge pictures or documents by moving two fingers in different directions. Not without movement, which is responsible for image rotation. Operations such as copy, delete, and paste can also be assigned separate gestures. The onscreen keyboard buttons are backlit when touched, making it easy to use on the touchscreen. And with handwriting recognition, you can quickly type small messages.
