Nowadays, each of us uses mobile devices: modern smartphones, tablets, smart watches and other devices. If earlier we controlled them using physical buttons, then relatively recently devices with a touch surface have become widespread, allowing us to control them by touching the screen.
The concept of “touchscreen” was formed after the concatenation of two words: “touch” (from English touch - pressing) + “screen” (from English screen - screen). Thanks to this panel, it became possible to issue commands to the device and interact with various elements on the screen.
The first touch display appeared back in 1971 as part of a graphics tablet. It was a resistive four-wire screen, which for many years was used in many other devices, most often in the medical and industrial sectors. The touchscreen entered the life of every person much later with the advent of large LCD screens.
The role of the touch surface in the screen
A standard liquid crystal display (TN, IPS, TFT and the like) consists of three parts: a touch surface (touchscreen), a matrix (a panel consisting of pixels or diodes that forms a picture on the screen) and a backlight. Each of them has a rather complex structure and plays an important role in the operation of the entire screen.
The main task of the matrix is to create an image on the screen by controlling each pixel or diode by adjusting their transparency. The backlight, although it may seem that this is the simplest element in the entire three-layer system, also has a complex structure. In the display device, it acts as an LED light source.
The touch surface, in turn, is the topmost layer in the structure of the screen, which, as we have already found out, allows us to control modern smartphones, tablets and other devices using touches. Among the most common types of such panels, it is worth highlighting capacitive and resistive. Next, we will consider all types of touchscreens, the principle of their operation, as well as the strengths and weaknesses of different types of touch surfaces.
How not to glue smartphones
You cannot glue with superglue, PVA glue, sealants or simple double-sided tape.
Superglue ruins the frame and can damage the part. A quick chemical reaction occurs with such glue; it destroys the surface and eats into it. Moreover, with such glue there will be only one attempt at repair; the second time you will have to buy a new part and tear the old one off the frame with tweezers, sand the surface from superglue. It is 100% not suitable for gluing parts in phones.
Sealants are bad because over time they begin to let dust through and the gluing technology itself is not suitable for them. At first the part will stick, but over time it will begin to peel off. No automotive or construction sealants are suitable for repairing electronics.
Most often, special glue is used when assembling phones and tablets. It holds up to changes in temperature, moisture, and does not damage touch surfaces. An example of such an adhesive is B7000.
The most common types of touchscreens
Standard capacitive (surface capacitive)
A huge number of modern devices currently use capacitive screens. They are also divided into two more categories: surface capacitive and projection capacitive. The first ones work on a fairly simple principle.
The screen itself consists of a glass panel on which a special resistive material is applied, which has the property of transparency so that it cannot interfere with viewing the picture (most often mixed indium-tin oxide is used as it). And at its corners electrodes are placed, which supply alternating voltage to the entire surface, which conducts current due to the coating of a substance already familiar to us.
When the user touches the screen panel with his finger, current leaks at a certain point (since the person also acts as a conductor). The current values that were recorded before touching in all four corners (electrodes) do not coincide with those recorded by special sensors after we touched the screen. Based on how much the characteristics of each electrode have changed, the controller mathematically calculates the point at which the press was made.
Source: commons.wikimedia.org
Most often, this type of screen was used in the very heyday of touchscreen smartphones, when old Nokias still existed on the Symbian operating system.
Advantages:
- They do not allow liquids to pass through.
- Extremely reliable design, withstands approximately 200 million clicks.
- Invulnerable to non-conductive contamination.
Flaws:
- It only reacts to heat (for example, you won’t be able to use such a screen with gloves).
- The conductive coating is vulnerable to harsh weather conditions, which affects performance.
Projected capacitive
There is another type of capacitive screens - projection-capacitive. This is a more modern type of touchscreen, which is used, for example, in the iPhone or AMOLED displays known to many. In some ways, the principle of operation is similar to the previous one, but has slight differences.
The projection-capacitive screen itself is also a glass plate, but on its reverse side we have not a transparent layer of a conductive substance, but a grid of electrodes. While surface capacitive panels have only four electrodes in the corners, here they are located over the entire display area.
The principle of operation of this kind of screen is that when touching the touch surface, the finger and the electrode located at a certain point (which we touched) form condensation. At the point of contact, charge and energy accumulate, due to which the voltage between the human body and the electrode responsible for a certain area on the surface increases. This is what special sensors determine and thus find the point on the screen with which the user interacts.
Source: commons.wikimedia.org
A great progress and step forward was the fact that projected capacitive panels learned to register several human touches at once - “multi-touch” appeared, first patented by Fingerworks, which was later bought by Apple. Surface capacitive displays have a theoretical maximum number of clicks of two.
Advantages:
- Able to register multiple points of contact.
- Reliability and durability (due to design features, they may have thick glass).
- Invulnerable to any contamination, including conductive ones (in extreme cases, they are controlled by software).
- High light transmission (90% or more).
Flaws:
- High production cost.
Resistive
Another type of touch screen, which has also gained immense popularity in devices intended for both industrial industries and personal use, is resistive. The main difference from previous types of touchscreens, without delving into the operating principle, is that such displays record any touch: with a finger (even with a glove), a pencil, a credit card, etc.
The resistive screen consists of two parts: a plastic membrane and a glass panel, on which a conductive coating is applied. When pressed in a certain place, the plastic and glass components of this type of touchscreen close, which is recorded by the microprocessor, subsequently determining the exact coordinates of the point.
Operation of a 4-wire resistive screen.
Source: commons.wikimedia.org
To be more precise, the “microprocessor” is an analog-to-digital converter that monitors the voltage across the entire surface of the panel. When nothing is in contact with the screen, the voltage at all points is 5 volts, but as soon as any interaction occurs, a different value is recorded at a certain location.
Resistive screens are divided into four-wire and five-wire screens. Structurally, there are no global differences between them, but the latter will be more reliable, since it continues to work even with a damaged membrane. Previously, this technology was used in old smartphones and PDAs, and now it is used in ATMs and various payment terminals.
Operation of a 5-wire resistive screen. Source: commons.wikimedia.org
Advantages:
- Record the pressure with any hard object.
- Inexpensive to produce.
Flaws:
- Low light transmission (the contrast of the picture and the brightness of the screen as a whole deteriorate).
- Less accuracy compared to projected capacitive and other types of screens.
- Inability to detect multiple clicks at the same time.
- Far from the most reliable and durable.
Infrared
For many, the structure of infrared touch screens may seem more interesting than the structure of other types of touchscreens. This technology is most relevant in cases where it is important to achieve the best image quality (for example, it is often used when creating e-books).
Imagine 2 lines of LEDs vertically and horizontally, forming a large rectangular grid on one side and a grid of photodiodes of the same size on the other. Each LED, which produces infrared radiation invisible to the human eye with a small scattering angle, is actually opposed to its own photodiode, which detects this radiation.
When a person touches the screen with a finger, a person blocks the light flux that is emitted by a certain LED. Because of this, infrared radiation does not reach the photodiode, which is responsible for receiving the light beam. This generates some signal coming from the screen grid to the control element, which determines the touch point.
The more LEDs are located in one line (horizontal and vertical, that is, in the grid as a whole), the higher the accuracy of determining the coordinates of the pressing point. This technology has found its main application in e-books, as well as in devices for educational institutions (for example, screens for video projectors).
Advantages:
- Excellent image quality.
- Good maintainability and simple design.
Flaws:
- Short service life due to aging of infrared LEDs.
- Very sensitive to dust and dirt.
- Vulnerable to direct sunlight.
Induction
No less interesting type of touch screens are the rarer (even in comparison with infrared panels) induction touchscreens. They work based on a grid of sensitive wires, somewhat similar to what we saw with an infrared screen, as well as an inductor.
When we touch the screen with a special inductive pen (such a device simply does not perceive any other taps), powered by electromagnetic resonance, the strength of the current magnetic field changes and a corresponding signal is generated, on the basis of which the sensors recognize the coordinates of the point we have chosen.
Induction touch panels have found their application in graphic art tablets, as well as some models of tablet computers that are quite typical for us.
Advantages:
- Maximum accuracy of click registration (that's why they are used in expensive graphics tablets).
- Distinguishes between pressures of different strengths.
Flaws:
- Capable of recognizing touches only from a special pen.
- Production cost.
What is this
This technique is designed for entering information, it looks like a multi-level matter, with a layer of transparent resistive layer applied to it.
In the corners there are electrodes that supply low-voltage alternating voltage to the conductive layer. Be careful when handling your mobile phone display, because if it breaks, you will not be able to protect your personal information hidden from prying eyes!
Imagine what will happen if a crack appears on it and you have to remain without it for a very long time? And if a breakdown puts it out of action, then you imagine losing forever the phone numbers of a fan and the email address from that very dream company that you hide under a password, and the phone itself is set to lock the screen even at home.
Less current types of touch screens
Optical
Another type of touch screen that cannot be called widespread today is optical. As in the case of infrared touchscreens, a lot here is also tied to LED radiation invisible to our eyes, but the principle of detecting the coordinates of the press point is somewhat different.
This touch screen consists of an infrared backlight that generates radiation, as well as a glass panel. Registration of interaction with the screen is carried out according to the principle of observing the path of rays. If nothing touches the touchscreen (the glass-air interface), then the light from the backlight will not be refracted, which means we are faced with total internal reflection. But as soon as any object (the glass-object boundary) touches the panel, one of the infrared rays is scattered.
This refraction of the light beam is recorded by special sensors, restoring the original picture and finding the point of pressure. Optical touchscreens have found their application in projection screens, as well as some models of liquid crystal displays (for example, the Microsoft PixelSense touchscreen desktop).
Advantages:
- There is multi-touch support.
- They are able to distinguish between touching with a finger and touching with foreign objects.
- Can be used on large touch surfaces.
- The maximum transparency is 100%.
Flaws:
- The same as for infrared screens.
Matrix
This type of touch screen is most similar in principle to the resistive touchscreens we are already familiar with. The only difference between them is that the conductors in this design are divided into horizontal and vertical. The former are applied to glass, the latter to a flexible plastic membrane.
Otherwise, everything is identical: after contact with the screen, conductors located on different surfaces close, which gives a certain signal that fixes a special device and determines the coordinates of the point.
It is not entirely clear why history needed such a branch and, in principle, this type of touch screens, because this design, in comparison with resistive ones, does not bring any new advantages. Well, perhaps matrix touchscreens are a little simpler and cheaper to produce. The technology has not become particularly widespread.
Advantages:
- It is possible to configure multi-touch.
- Very simple and affordable.
Flaws:
- Extremely low accuracy.
Necessary tools and consumables
The bare minimum is a plastic pick. Why plastic? It leaves fewer marks on the body, reduces the risk of damage to cables, and is more resilient than a metal pick. A plastic pick can be made from an ordinary plastic bottle; just cut out a small piece and level it.
For a better replacement, you need to heat the smartphone screen. There are two heating options:
Isopropanol (isopropyl alcohol) or Galosh gasoline will also come in handy. Using these products you can remove old glue and speed up the process of peeling off parts.
For gluing you will need B7000 glue. This is a universal glue, it is great for gluing touchscreens or screen modules to the frame of a smartphone and tablet. There are different types of such glue. T7000, B7000, E8000, etc. They differ in color, adhesion, price and other characteristics. For most repairs the B7000 will be suitable.
Description
A touch display is an electronic element that visualizes digital information by touching the surface of the monitor. Different types of these structures respond to several moments or one specific factor (change in capacitance and resistance, thermal difference, special pointer).
According to the principle of operation, touch screens are divided as follows:
- Resistive versions.
- Matrix models.
- Capacitive options.
- Surface acoustic modifications.
- Optical sensors and their varieties.
Let's consider common display models of this category, scope, features and advantages.
Capacitive projection versions
The operating principle of the touch screen of smartphones of some configurations is based on this type. An electrode grid is applied to the inner surface of the device, which, when in contact with the human body, forms a capacitor. After touching the display with your finger, the sensors and microcontroller process the information, and the calculations are sent to the main processor.
Peculiarities:
- These designs have all the capabilities of capacitive sensors;
- they can be equipped with a film coating up to 18 millimeters thick, which provides additional protection against mechanical stress;
- Contaminants on hard-to-reach conductive parts are removed using a software method.
The specified configurations are mounted on many personal devices and terminals operating outdoors under cover. It's worth noting that Apple also prefers projected capacitive monitors.
Matrix modifications
These are simplified versions of resistive technology. The membrane is equipped with a number of vertical conductors, and the substrate is equipped with horizontal analogues. The principle of operation of the touch screen: when touched, the point at which the conductors made contact is calculated, and the information obtained is sent to the processor. This, in turn, determines the control signal, after which the device reacts in a given way, for example, performs the action assigned to a specific button.
Peculiarities:
- due to the limited number of conductors, a low accuracy rate is observed;
- price – the lowest among all sensors;
- The multi-touch function is implemented by polling the display point by point.
This model is used exclusively in outdated devices, and is practically not used in modern times due to the emergence of innovative solutions.
Module repair: replacement of glass or touchscreen assembly
The most difficult thing to restore is a modular screen. In such screens, the adhesive covers the entire area of the module, and it is very difficult to peel off the protective glass (this design is usually used by Apple and Samsung manufacturers) or the touchscreen (Xiaomi, Lenovo). The sensors and glass themselves are not expensive; their cost can be around 500 rubles, with the price of the original module being 5,000 rubles. For modules of top Samsung models, the price for original Amoled can reach 23,500 rubles.
During module repair, any error can lead to complete loss of display functionality.
The smartphone is disassembled in the same way as when replacing the module, but now this will have to be done extremely carefully so as not to damage the working display. It also peels off from the frame of the device.
There are three methods for posting a module:
Some displays are so thin that repair requires a specially designed machine. Even laser machines have been adapted to replace back covers with glue.
After removing the broken glass, you need to remove the old glue from the module. Special cleaning products are available on the market. Isopropyl alcohol will also work.
Now all that remains is to glue the glass or sensor onto the module. Of course, before this, the screen needs to be checked for functionality by connecting it to a smartphone.
If you do not fill the space between the glass and the module, colors may change, glare will appear, strength will decrease and there will be a high risk of glass peeling off.
The main methods of filling the space between glass and display are OCA film and LOCA glue.
LOCA glue dries when exposed to ultraviolet light. It is applied to the screen, then placed against the glass and pressed using small clamps. Next, this entire structure is placed in an ultraviolet lamp for ten minutes. The glue hardens and the module is ready for use. There are some problems with this method. For example, bubbles may appear during gluing, which will need to be removed with tweezers or the whole thing will need to be re-glued.
OCA film is applied to the module. And for this you need a vacuum separator. Without it, it will not be possible to remove air bubbles.
Next, after all the procedures, the repaired module is sealed in exactly the same way as a new part.
Repairing a display module yourself at home is a very difficult task. It requires a lot of experience, effort, patience and equipment. But that doesn't mean it can't be done.
History of invention
For the first time in the world, a prototype sensor device was used by Sam Hurst, a teacher from the United States. In 1970, he developed the idea of reading data from a large number of strip recorders. Automation of this process became a kind of springboard to the creation of touch monitors known as Elotouch. The development of a group of Hurst's colleagues was published in 1971, and included resistive four-wire technology for determining touch points.
The PLATO IV system is considered the first computer sensor. It was also published in the USA, as a result of special research concerning the computerization of education. It consisted of a block panel (256 pieces) and operated on the principle of using a grid of infrared streams.
Usage
Thanks to the simplest operating principle of a resistive touch screen, it can be used everywhere. Design Features:
- low cost;
- resistance to environmental influences, with the exception of negative temperatures;
- good reaction to contact with any non-sharp suitable object.
Such displays are mounted on replenishment and money transfer terminals, ATMs and other devices that are isolated from the environment. The monitor's poor protection from damage is compensated by the presence of a protective film coating.
Layer of additional sensors
This layer appeared in the iPhone starting with the iPhone 6s model and is needed to recognize the force of pressing the display.
A special grid of capacitor boards is connected to the power source. Its task is to ultra-precisely measure the distance from the finger to the matrix. Software algorithms analyze information from this grid and allow 3D-Touch technology to work.
