A touchscreen is a type of display that is in demand in a variety of sectors of the electronic equipment market. What are the features of this device?
What is a touchscreen?
Under touchscreen it is generally accepted to understand any touch screen- one that can be controlled by touching a finger or using an additional device (electronic pen, stylus, etc.). The first touchscreens were invented in the 70s. Devices equipped with them appeared on the market in the 80s.
Sometimes only a part is called a touchscreen touch display- directly the one that is responsible for processing signals generated as a result of contact with the user’s finger or control device. But this element, strictly speaking, has its own name - “active panel”, or “membrane”. This element is located between the screen matrix on which the image is built and the external protective glass.
Initially, touch displays were used mainly in industry, in medicine - as a control element various types equipment. Later, touchscreens began to be used in the production of devices aimed at the consumer sector - computers, smartphones, tablets, game consoles. Touch displays were designed to replace traditional hardware controls for corresponding devices - keyboards, mice, joysticks, etc. In fact, this is what happened - these types of devices equipped with a touchscreen, in many cases do not require connecting additional controls.
Touch displays are also used as hardware components of ATMs, payment terminals and other devices for similar purposes.
The main advantages of touchscreens:
- Ease of Management;
- compactness (the traditional display and touchscreen are no different in size);
- compactness in terms of the dimensions of the device on which the touchscreen is installed (as we noted above, in many cases there is no need to connect external control components to them - a keyboard, mouse);
- functionality (the touchscreen allows you to enter text, move objects on the screen, control characters in games and perform many other useful actions).
Touch displays also have disadvantages:
- sensitivity to mechanical stress, as well as rather poor maintainability;
- additional energy consumption;
- lack of tactile response to touch - which often complicates the use of touchscreens for people accustomed to working with a keyboard.
It can be noted that touchscreens are almost always assembled on the basis of an LCD, LED or OLED matrix. Cathode ray touchscreens are extremely rare devices.
Classic displays
What can be said about “non-touch”, classic displays? In essence, all that distinguishes them from touchscreens is the absence in the design of those elements that can become tools for managing screen content. Classic displays can only display data. To enter information, you must use third-party devices - keyboard, mouse, joystick.
Classic displays are presented on the market in the same technological modifications as touch screens - LCD, LED, OLED. They can also be electron beam - in which case they are almost guaranteed not to be touchscreens.
Comparison
The main difference between a touchscreen and a classic type display is the presence in the design of the former of elements capable of converting external touches (with a finger or a special device) into digital signals. With their help, you can control the device to which the touch screen is connected.
The difference between the terms “touchscreen” and “display” is also found at the conceptual level: as we noted above, “touchscreen” is sometimes called the part of the display that is directly responsible for converting external touches into digital signals.
Touchscreens in the meaning of “touch display” are extremely rarely presented in the electron beam modification. In turn, a significant part of classical displays are electron beam displays.
Having determined what the difference is between a touchscreen and a traditional type display, we will record the conclusions in a small table.
Table
| Touchscreen | Display (traditional type) |
| What do they have in common? | |
| Displaying information on the screen in both devices is carried out according to the same technological principles - a screen matrix such as LCD, LCD, OLED is used | |
| What is the difference between them? | |
| Is a display touch type, capable of converting external touches into digital signals to control screen content | Unable to convert external touches into digital signals |
| Extremely rarely presented in electron beam modifications | A significant part of traditional type displays are electron beam |
| Touchscreen (as a hardware component) | Display (touch) |
| A touchscreen is sometimes referred to as an active panel or membrane, which is the hardware component of a touch display responsible for converting external touches into digital signals. | It is a complete device, the design of which uses a touchscreen |
The term " touchscreen“appeared as a result of the merger of the words “touch” and “screen”, which can be translated literally from English as “touch-responsive screen”.
Touch screen ( touchscreen) is an information input device, which is a screen that responds to touches.
More often it is called a “touch” screen - touching a certain area of the screen with a finger or a special device (stylus) launches the program provided by the algorithm.
A device with a touch screen is encountered by city residents almost every day: these are ATMs, a bank box for accepting payments, a reference terminal, a screen mobile phone and much more.
Types of touch screens
Touch screens are divided into resistive, matrix, projected capacitive, surface acoustic wave touch screens, infrared, optical, strain gauge, DST and induction touch screens .
Resistive touch screens
They are divided into four-wire and five-wire.
Four-wire 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, 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, and the lower one is grounded. The left and right are short-circuited, and the voltage on them is checked. This voltage corresponds to the Y-coordinate of the screen.
Similarly, +5V and ground are supplied to the left and right electrodes, and the X-coordinate is read from the top and bottom.
There are also eight-wire touch screens. They improve tracking accuracy, but do not improve reliability.
Five-wire 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.
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 by an analog-to-digital converter. When nothing is touching the touch screen, the voltage is 5V.
As soon as the screen is pressed, the microprocessor detects the change in membrane voltage and begins to calculate the coordinates of the touch as follows:
A voltage of +5V is applied to the two right electrodes, the left ones are grounded. The voltage on the screen corresponds to the X-coordinate.
The Y-coordinate is read by connecting both upper electrodes to +5V and to ground both lower ones.
Peculiarities:
Resistive touch screens are cheap and resistant to contamination. Resistive screens respond to touch with any smooth, hard object: a hand (bare or gloved), a stylus, credit card, mediator. They are used wherever vandalism and low temperatures are possible: for automation of industrial processes, in medicine, in the service sector (POS terminals), in personal electronics (PDA). The best samples provide an accuracy of 4096x4096 pixels.
Disadvantages 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
The design is similar to resistive, 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 shorted and transmits the corresponding coordinates to the microprocessor.
Peculiarities:
They have very low accuracy. Interface elements have to be specially positioned taking into account the cells of the matrix screen. The only advantage is simplicity, cheapness and unpretentiousness. Typically matrix screens are queried row by row (similar to a button matrix); this allows you to set up multi-touch. They are gradually being replaced by resistive ones.
Capacitive touch screens
Operating principle of a capacitive touch screen
A capacitive (or surface capacitive) screen takes advantage of the fact that a large capacitance object conducts alternating current.
A capacitive touch screen is a glass panel coated with a transparent resistive material (usually an alloy of indium oxide and tin oxide). Electrodes located at the corners of the screen apply a small amount of energy to the conductive layer. AC voltage(same for all corners). When you touch the screen with your finger or other conductive object, current leaks. Moreover, the closer the finger is to the electrode, the lower the screen resistance, which means the greater the current. The current in all four corners is recorded by sensors and transmitted to the controller, which calculates the coordinates of the touch point.
In earlier models of capacitive screens, D.C.- this simplified the design, but if the user had poor 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 leak liquids and tolerate non-conductive contaminants very well. Transparency at 90%. However, the conductive coating located directly on the outer surface is still vulnerable. That's why capacitive screens They are widely used in machines that are only installed in a weather-protected room. They do not respond to a gloved hand.
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 of, for example, the iPhone is projected capacitive, not capacitive.
Projected capacitive touch screens
Operating principle of projected capacitive touch screen
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).
Samsung has managed to install sensitive electrodes directly between the subpixels of the AMOLED screen, which simplifies the design and increases transparency.
Peculiarities:
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). PESE 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 widely used in personal electronics and in vending machines, including those installed on the street. Many varieties support multi-touch.
Touch screens based on surface acoustic waves
The screen is a glass panel with piezoelectric transducers (PETs) located in the corners. At the edges of the panel there are reflective and receiving sensors. The operating principle 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 surfactant, and the reflective sensors reflect it accordingly.
These reflected waves are received by the corresponding sensors and sent to the probe. The probes, 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 energy from the acoustic waves is absorbed. The receivers record this change, and the microcontroller calculates the position of the touch point. Reacts to touch with an object capable of absorbing the wave (finger, gloved hand, porous rubber).
Peculiarities:
The main advantage of a surface acoustic wave (SAW) screen is the ability to track not only the coordinates of a point, but also the pressing force (here, rather, the ability to accurately determine the radius or area of pressing), due to the fact that the degree of absorption of acoustic waves depends on the pressure at the point touch (the screen does not bend under finger pressure and is not deformed, so the pressing force does not entail qualitative changes in the controller’s processing of data on the coordinates of the impact, which records only the area that overlaps the path of acoustic impulses).
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 emitters, receivers and reflectors are attached directly to the screen of the display device. Despite the complexity of the design, these screens are quite durable. According to, for example, the American company Tyco Electronics and the Taiwanese company GeneralTouch, they can withstand up to 50 million touches at one point, which exceeds the life of a 5-wire resistive screen.
Surfactant-based screens are used mainly in slot machines, in secure information systems and educational institutions. As a rule, surfactant screens are divided into regular ones, 3 mm thick, and vandal-resistant ones, 6 mm thick. The latter can withstand a blow from the fist of an average man or a drop of a metal ball weighing 0.5 kg 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 USB interface. On this moment The most popular controllers for SAW touch screens are those that support both types of connection—combo (data from Elo Touch Systems).
The main disadvantage of a surfactant 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. Besides, this technology requires touching an object that necessarily absorbs acoustic waves - that is, for example, a plastic bank card in in this case not applicable.
The accuracy of these screens is higher than matrix ones, but lower than traditional capacitive ones. As a rule, they are not used for drawing and entering text.
Infrared touch screens
Working principle of infrared touchpad simple - the grid formed by horizontal and vertical infrared rays is interrupted when any object touches the monitor. The controller determines the location where the beam was interrupted.
Peculiarities:
Infrared touch screens are sensitive to contamination and are therefore used where image quality is important, for example in e-books. Due to its simplicity and maintainability, the scheme is popular with the military. Intercom keypads are often made using this principle. This type screen is used in numerous Neonode phones.
Optical touch screens
The glass panel is equipped with infrared illumination. At the glass-air interface, total internal reflection is obtained; at the glass-foreign object interface, light is scattered. All that remains is to capture the scattering picture; for this there are two technologies:
IN projection screens A camera is placed next to the projector.
This is how Microsoft PixelSense works, for example.
Or the additional fourth subpixel of the LCD screen is made photosensitive.
Peculiarities:
They allow you to distinguish hand presses from presses with any objects, there is a multi-touch. Large touch surfaces are possible, up to a blackboard.
Strain gauge touch screens
React to screen deformation. Accuracy strain gauge screens They are small, but they withstand vandalism very well. The main application is ATMs, ticket machines and other devices located on the street.
DST touch screens
Main article: Dispersive Signal Technology
The DST (Dispersive Signal Technology) touch screen detects the piezoelectric effect in the glass. It is possible to press the screen with your hand or any object.
A distinctive feature is the high reaction speed and the ability to work in conditions of heavily soiled screens. However, the finger must move; the system does not notice a stationary finger.
Induction touch screens
The inductive touch screen is Graphics tablet with built-in screen. Such screens only respond to a special pen.
They are used when a response is required specifically to pressing with a pen (and not with a hand): high-end art tablets, some models of tablet PCs.
- Supported with limitations, maximum 2 touch points.
- If you only need a glass panel, without any transparent conductive films - roughly 95%. If you don’t even need it (you can use the standard screen covering) - conditionally 100%
- High - up to the pixel (accurately tracks with a sharp pen). Medium - up to several pixels (enough for finger clicks). Low - large screen blocks (drawing is impossible, very large interface elements are required).
- Limited by electronics reliability.
- Limited by contamination of the sensor.
- Ogran - restricted access equipment (personal electronics, industrial equipment). Placed - general access in a secured area. Street - general access on the street.
Information sources:
ru.wikipedia.org - touch screen;
The screen of any iPhone can be considered the most important component of the device. Of course, if you do not take into account the amount of memory, operating system, the overall quality of the device, but judged only by appearance. And since the screen is so important, you should treat it with care. But practice stubbornly shows the opposite. Although it must be admitted that this part of the smartphone is the least secure and the human factor has almost nothing to do with it. The materials that cover the front of the iPhone can fail, and this is where the fun begins. We run to the service center and ask in a trembling voice to replace only the glass and not touch the display itself.
- So do we change the glass or the display?
- Is there a difference?
That's all the short dialogue demonstrating our incompetence. Therefore, let's try to find out the difference between replacing the glass on an iPhone and replacing the display.
There is a difference
First of all, it should be firmly understood that glass and iPhone display it's like a chandelier and a light bulb. There is no point in replacing the entire chandelier if only the light bulb has burned out, but you can replace the entire chandelier along with the light bulbs or leave them from the old chandelier. Did you get the point? Touch glass and the iPhone display are two parts that we are used to calling either a screen, a monitor, or something else. But the essence remains the same: glass and display are not the same thing, although they are mechanically connected to each other and form a display module.
So that our fingers can work wonders on iPhone screen, the devices are equipped with sensitive touch glass, which is installed on top of the display. Consequently, each of these parts has its own functions and purpose: the glass is responsible for finger touches, and the display displays the image.
You don't need to be Einstein to guess: you can replace the glass and display separately if one of them has stopped performing its function. The display may fail, but the touch layer remains fully functional. The situation is similar if you swap parts: the touch glass may be damaged, but the display remains operational.
A spoon of tar
Everything that was said above is the holy truth. But there is one caveat that somewhat aggravates the situation. The fact is that earlier iPhone models actually had a display module that could be disassembled into its components. The later iPhone series are designed in such a way that the display module is not disassembled and is treated as a single whole. Is it good or bad, whether it is advisable or not is not for us to decide. So far, for the iPhone starting with the 4th model, it is impossible to replace the glass and leave the display the same, or vice versa.
But nothing is impossible. The touch glass and display are securely glued together, and you have to try hard to separate this cake. Not every master and not every service center will undertake such an operation. It is simpler and more reliable, although much more expensive, to replace the entire display module if it breaks.
But only use original spare parts! Because native, certified and original is the key to long-term use and correct operation. And everything else, of dubious production, means new headaches and a shattered nervous system.
Brief description of the process
Replacing glass on smartphones accounts for approximately 65% of all repair cases. Therefore, the masters service centers I had to get my hands dirty to make this operation successful. The third generation iPhones were easy to repair - the display and glass were separate. But in the next generations of smartphones, glass replacement required the intervention of special tools. The separator (that’s what the tool is called) heats up the display so that you can easily separate the glass using a special string.
Important note: spare parts (glass or display) can either be removed from another similar device, or be close in quality to the original ones. The second option does not mean that the glass or display will necessarily be from Apple. You shouldn’t be afraid of the first option either: among the iPhone cemetery there will always be “donors” with a fully working display or intact glass.