Types of touch screens. Which is better? Types of touch screens for tablet computers
Based on the difference in how information is entered, screen sensors are divided into two types: resistive screens and capacitive ones.
Resistive type
Resistive type - a screen that responds to pressure from almost any hard object. As a rule, phones with this sensor come with a stylus - a special stick.
What can be attributed to the advantages of such a display: price! they are so inexpensive to produce and fill an extremely large niche.
Another important advantage is that they are very resistant to contamination. To put it quite simply, if you see (at least somehow) the buttons, then they work!
Regarding the disadvantages, it is worth noting that the light conductivity is not very high.
There are two types of resistive screens: four-wire and five-wire
Capacitive type
Capacitive type - just like the resistive type, there are two types of capacitive screens - surface capacitive type, and projected capacitive type.
Surface capacitive type: The screen uses the principle of conducting alternating electric current by an object with high capacitance.
The capacitive type sensor is a glass panel covered with a layer of conductor. Electrodes located at the corners of the screen supply alternating voltage to it. When a person touches with a finger or any other leading object, a flow of current occurs. The current in all corners of the screen is recorded by special sensors and transmitted to the controller, which calculates the coordinates of the touch point.
The capacitive type of screen is more reliable (designed for 200 million touches on one point versus 35 million), does not allow liquids to pass through and is resistant to non-conductive contaminants. Another advantage of this type is that the screen transparency is 90%.
Now about the disadvantages - the screen will not work when you are wearing a glove, this is the first drawback. The second disadvantage is that multi-touch is not possible on it.
Projected capacitive type: A grid of electrodes is applied inside the screen. Together with the human body, these electrodes create a capacitor.
The features of this type include: advantages - screen transparency is about 90%, an unusually wide temperature range, many screens can be operated even when you are wearing gloves. Multitouch appeared here. And finally, these screens are very durable.
The disadvantages include the price of such a sensor and the complexity of production.
Therefore, if you are choosing which touch screen to get a phone with, I personally advise you to get a projected capacitive type.
If you are not one of the tech-savvy users and you will soon be faced with the question of choosing a mobile phone or smartphone with a touch screen, you will probably come across terms such as “capacitive screen” or “resistive screen” when reading the specifications of mobile devices. And then a completely logical question will come to your mind - which one is better: resistive or capacitive? Let's find out how touch displays differ, what types exist, and what their advantages and disadvantages are.
RESISTIVE SCREENS
To put it in simple language, avoiding clever technical terms and phrases, a resistive touch screen is a flexible transparent membrane on which a conductive (in other words, resistive) coating is applied. Under the membrane there is glass, also covered with a conductive layer. The principle of operation of a resistive screen is that when you press the screen with a finger or stylus, the glass closes with the membrane at a specific point. The microprocessor records the change in membrane voltage and calculates the contact coordinates. The more precise the press, the easier it is for the processor to calculate the exact coordinates. Therefore, with resistive screens it is much easier to work with a stylus.
The main advantages of resistive screens are that they are relatively cheap to produce, and also that this type of display responds to pressure from any object. This is very useful when making presentations, especially since the prices of projectors today are falling every day.
The disadvantages of resistive screens are: low strength; low durability (about 35 million clicks per point); impossibility of implementation; a large number of errors when processing gestures such as sliding and flipping.
So which screen is better: resistive or capacitive?
If you have carefully read this article, you will be able to draw your own conclusion without any problems. I will only say that this dispute is doomed to failure. Some users like to work with a stylus and are not comfortable with capacitive displays. But most people are more comfortable operating a device equipped with a capacitive screen - it’s more convenient, and the multi-touch feature makes a big difference. It’s not for nothing that all modern smartphones and tablets running Android have capacitive displays.
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Surely all of you use computers and mobile devices, and only a few are generally able to tell how their processors, operating systems and other components work.
In the era of mobile gadgets, everyone has a touch screen (also called a smart screen), and almost no one knows what this touch screen is, how it works and what types of it exist.
What it is
Touch display (screen) is a device for visualizing digital information with the ability to exert management influence by touching the display surface.
Based on different technologies, different displays only respond to certain factors.
Some read the change capacitance or resistance in the area of contact, others on temperature changes, some sensors react only to a special pen to avoid accidental clicks.
We will look at the operating principle of all common types of displays, their areas of application, strengths and weaknesses.
Among all the existing principles of device control through a matrix sensitive to any factors, Let's pay attention to the following technologies:
- resistive (4-5 wire);
- matrix;
- capacitive and its variants;
- surface acoustic;
- optical and other less common and practical.
In general, the scheme of work is as follows: the user touches an area of the screen, the sensors transmit data to the controller about changes in any variable (resistance, capacitance), which calculates the exact coordinates of the point of contact and sends them.
The latter, based on the program, reacts to pressing accordingly.
Resistive
The simplest touch screen is resistive. It reacts to changes in resistance in the area of contact between a foreign object and the screen.
This is the most primitive and widespread technology. The device consists of two main elements:
- a conductive transparent substrate (panel) made of polyester or other polymer several tens of molecules thick;
- a light-conducting membrane made of polymer material (usually a thin layer of plastic is used).
Both layers are coated with resistive material. Between them there are micro-insulators in the form of balls.
During this stage, the elastic membrane deforms (bends), comes into contact with the substrate layer and closes it.
The controller responds to a short circuit using an analog-to-digital converter. It calculates the difference between the original and current resistance (or conductivity) and the coordinates of the point or area where this occurs.
Practice quickly revealed the shortcomings of such devices, and engineers began to search for solutions, which were soon found by adding a 5th wire.
Four-wire
The upper electrode is energized at 5V, and the lower one is grounded.
The left and right are connected directly, they are an indicator of voltage changes along the Y axis.
Then the top and bottom are short-circuited, and 5V is supplied to the left and right to read the X-coordinate.
Five-wire
Reliability is due to the replacement of the resistive coating of the membrane with a conductive one.
The panel is made of glass and remains covered with a resistive material, and electrodes are placed at its corners.
First, all electrodes are grounded, and the membrane is energized, which is constantly monitored by the same analog-to-digital converter.
During the touch, the controller (microprocessor) detects the change in the parameter and carries out calculations of the point/area where the voltage has changed according to a four-wire circuit.
An important advantage is the ability to apply to convex and concave surfaces.
There are also 8-wire screens on the market. Their accuracy is higher than those considered, but this does not in any way affect the reliability, and the price is noticeably different.
Conclusion
The considered sensors are used everywhere due to their low cost and resistance to the influence of environmental factors, such as pollution and low temperatures (but not below zero).
They respond well to touch with almost any object, but not a sharp one.
The area of a pencil or match is usually not enough to trigger a controller response.
Such displays are installed on and used in the service sector (offices, banks, shops), medicine and education.
Wherever devices are isolated from the external environment and the likelihood of being damaged is minimal.
Low reliability (the screen is easily damaged) is partially compensated by the protective film.
Poor functioning in cold weather, low light transmission (0.75 and 0.85, respectively), resource (no more than 35 million clicks for a terminal that is constantly used, very little) are the weaknesses of the technology.
Matrix
A more simplified resistive technology that arose even before it.
The membrane is covered in rows vertical conductors, and the substrate is horizontal.
When pressed, the area where the conductors are connected is calculated and the resulting data is transmitted to the processor.
It already generates a control signal and the device reacts in a certain way, for example, performs the action assigned to the button).
Peculiarities:
- very low accuracy (the number of conductors is very limited);
- the lowest price among all;
- implementation of the multi-touch function due to the screen polling line by line.
They are used only in outdated electronics and have almost gone out of use due to the presence of progressive solutions.
Capacitive
The principle is based on the ability of large-capacity objects to become conductors of alternating electric current.
The screen is made in the form of a glass panel with a thin layer of sprayed resistive substance.
Electrodes at the corners of the display apply a small alternating current voltage to the conductive layer.
At the moment of contact, current leaks, if the object has a greater electrical capacity than the screen.
Current is recorded at the corners of the screen, and information from the sensors is sent to the controller for processing. Based on them, the contact area is calculated.
The first prototypes used DC voltage. The solution made the design simpler, but often crashed when the user was not in contact with the ground.
These devices are very reliable, their service life exceeds resistive ones by ~60 times (about 200 million clicks), they are moisture resistant and can withstand pollution that do not conduct electric current.
Transparency is at the level of 0.9, which is slightly higher than resistive ones, and operate at temperatures up to - 15 0 C.
Flaws:
- does not react to the glove and most foreign objects;
- the conductive coating is in the top layer and is very vulnerable to mechanical damage.
They are used in the same ATMs and terminals under closed air.
Projected capacitive
An electrode grid is applied to the inner surface, forming a capacitance (capacitor) with the human body. The electronics (microcontroller and sensors) work to calculate the coordinates at and send the calculations to the central processor.
They have all the features of capacitive ones.
In addition, they can be equipped with a thick film up to 1.8 cm, which increases protection against mechanical influences.
Conductive contaminants, where they are difficult or impossible to remove, are easily removed using the software method.
Most often, they are installed in personal electronic devices, ATMs and various equipment installed virtually in the open air (under cover). Apple also prefers projected capacitive displays.
Surface acoustic wave
It is manufactured in the form of a glass panel equipped with piezoelectric transducers PET located at opposite corners and receivers.
There are also a pair of them and are located on opposite corners.
The generator sends an RF electrical signal to the probe, which converts a series of pulses into surfactants, and the reflectors distribute it.
The reflected waves are captured by sensors and sent to the probe, which converts them back into electricity.
The signal is sent to the controller, which analyzes it.
When touched, the parameters of the wave change, in particular, part of its energy is absorbed in a certain place. Based on this information, the area of contact and its strength are calculated.
The very high transparency (above 95%) is due to the absence of conductive/resistive surfaces.
Sometimes, to eliminate glare, light reflectors together with receivers mounted directly on the screen.
The complexity of the design in no way affects the operation of a device with such a screen, and the number of touches at one point is 50 million times, which slightly exceeds the service life of resistive technology (65 million times in total).
They are produced with a thin film of about 3 mm and a thick film of 6 mm. Thanks to this protection, the display can withstand a light blow from a fist.
Weak sides:
- poor performance in conditions of vibration and shaking (in transport, when walking);
- lack of resistance to dirt - any foreign object affects the functioning of the display;
- interference in the presence of acoustic noise of a certain configuration;
- the accuracy is slightly lower than in capacitive ones, which is why they are unsuitable for drawing.
To control modern gadgets, there is no longer any need to press buttons; you just need to touch the screen. This became possible thanks to the touchscreen (among experts it is simply called “touch” or “touch panel”), which has become an integral part of smartphones and tablets, including iPhones and iPads. It is not surprising that due to frequent use it often breaks down and becomes a headache for the owner of the device. If you understand what this component is and by what principles it works, you can quickly detect a malfunction and avoid awkward situations when contacting a service center.
What is a touchscreen
This term was formed from two English words - touch and screen, which literally translates as “touch screen”. The history of its appearance is long and occurred in several stages. The world's first finger-controlled display was invented and described in his scientific works by the American E. A. Johnson in 1965. Five years later, Dr. Samuel Hurst, through experiments, developed resistive touch screen, and the actual physical production of the product began only in 1973.
Currently, city residents deal with touch panels almost every day: not only smartphones and tablets are equipped with them, but also ATMs, information terminals and payment acceptance points. Touchscreen connects to display and is sensitive to any touch. It can be described as an information input device that serves to replace a keyboard.
It is important to know that the touchscreen is only part of the overall design, responsible only for the sensor. To transfer an image a display is used, which is a liquid crystal matrix. The unity of these two elements is called a display module, which is practically the main component of any high-tech device.
How the touch panel works
The principle of operation of the touchscreen is simple - any touch on it triggers some function or entails certain actions. The physical features of its operation directly depend on the type of touch panel. There are seven of them in total, but the most common today are three of them.
The cheapest to produce, resistant to dirt and temperature changes. Comprises glass panel and plastic membrane, between which insulators are located. Any pressure causes the glass to push through the micro-insulator, and the membrane and panel close. After this, a special controller reads the changes and converts them into contact coordinates. The weaknesses of this model are low light transmission, short service life and a high risk of damage if dropped. 
Capacitive screen
More reliable and durable, but vulnerable to bad weather, water and pollution. It uses a special touch glass coated with resistive material. An alternating current passes through it, which is supplied by electrodes located at the corners of the screen. That is, when you touch the touchscreen, a current leak occurs, which is detected by special sensors. They register these changes and transmit them to the controller.
Surface acoustic wave sensor
One of the most complex screens. The peculiarity of its work is that in the thickness of the glass there are ultrasonic vibrations. When you press the touchscreen, the waves are absorbed and converted into an electrical signal, which is then transmitted to the controller. The advantage of this technology is its long service life, equal to at least 45 million touches. The main drawback is that the screen is extremely sensitive to dirt and electromagnetic interference.
In addition to this, there are several more types of touch panels. These include:
- Projected capacitive. On the inside of such screens there is a grid of electrodes, which, when pressed, forms a capacitor, the capacitance of which is measured by electronic sensors.
- Infrared. Along their edges there are light emitters and receivers in the IR range; when you touch the screen, part of the light is blocked and thereby the location of the click is determined.
- Tansometric. They are based on simple fixation of screen deformation, are resistant to damage and are often installed outdoors.
- Induction. Inside them there is an inductance coil and wires; when such a screen is touched with a special tool, the voltage of the existing magnetic field changes.
How to check the touchscreen
The touchpad may not work correctly either if the mobile device is physically damaged or for no apparent reason. The following factors indicate that the problem is in the sensor:
There may be several reasons for such a malfunction:
- Display dirty. If you do not promptly wipe the sensor with special means, then during operation it will become abundantly covered with fingerprints and greasy marks, which can reduce its sensitivity.
- Violation temperature regime. Too high or low temperatures, as well as their strong drop, are a common cause of touchscreen malfunctions.
- Damage to the cable. It can peel off from the glass due to mechanical damage, thereby disrupting the connection between the latter and the touch coating.
- Moisture ingress. If there is liquid inside the gadget, oxidation of the contacts may occur. Sometimes the problem can be solved with a hair dryer.
- Crash software. In this case, you need to reflash the device; for this you will need a USB cable and the software itself.
How to replace the touchscreen on your phone yourself
Before removing the touch screen, you should turn off your smartphone, remove the battery and SIM card. It is important to remember the disassembly sequence so that you can later put the device back together without damaging the internal elements. Some models may require complete disassembly of the housing, which requires special knowledge. To replace the touch screen on your phone with your own hands, you need to prepare special equipment in advance, namely:
The process of replacing the touchscreen is as follows:
- Take off back cover of the phone;
- Screwdriver remove all bolts along the perimeter of the body;
- Carefully insert the spatula between the housing fastening and pry;
- Hairdryer warm up the glue connecting the sensor to the matrix up to a maximum temperature of 80 °C;
- Pin to display suction cup, which will allow you to separate the touchscreen from the matrix;
- Apply thin layer of glue and install a new touchpad;
- Carefully press it and remove any remaining glue;
- Reassemble the device in reverse order.
What is the difference between touchscreen and display
The display is the part of the smartphone on which the image is displayed. It is he who is the conductor of visual information and makes it accessible to the human eye. A touchscreen is a touch glass, the main purpose of which is to call a particular function. That is, he is only information input tool, but no conclusion. 
If the phone is broken and cobwebs appear on it, but the screen continues to work and you can clearly see the picture, then only the sensor needs to be replaced. When the device distorts the image and shows blots, you will have to change the display, which is a more time-consuming and expensive procedure.
The iPhone 2G was the first mobile phone to operate entirely on a touch screen. More than ten years have passed since its presentation, but many of us still do not know how the Touchscreen works. But we encounter this intuitive input tool not only in smartphones, but also in ATMs, payment terminals, computers, cars and airplanes - literally everywhere.
Before touchscreens, the most common interface for entering commands into electronic devices was various keyboards. Although they seem to have nothing in common with touchscreens, in fact, how similar a touchscreen is to a keyboard can be surprising. Let's look at their device in detail.
The keyboard is a printed circuit board on which several rows of switches-buttons are installed. Regardless of their design, membrane or mechanical, when you press each of the keys, the same thing happens. An electrical circuit is closed on the computer board under the button, the computer registers the passage of current in this place of the circuit, “understands” which key is pressed and executes the corresponding command. In the case of a touch screen, almost the same thing happens.
There are about a dozen different types of touch screens, but most of these models are either outdated and not used, or are experimental and are unlikely to ever appear in production devices. First of all, I will talk about the structure of current technologies, those that you constantly interact with or at least may encounter in everyday life.
Resistive touch screen
Resistive touch screens were invented back in 1970 and have changed little since then.
In displays with such sensors, a couple of additional layers are located above the matrix. However, I’ll make a reservation that the matrix is not at all necessary here. The first resistive touch devices were not screens at all.
The bottom sensor layer consists of a glass base and is called the resistive layer. A transparent metal coating is applied to it that transmits current well, for example, from a semiconductor such as indium tin oxide. The top layer of the touchscreen, with which the user interacts by pressing the screen, is made of a flexible and elastic membrane. It is called the conductive layer. An air gap is left in the space between the layers, or it is evenly dotted with microscopic insulating particles. Along the edges, four, five or eight electrodes are connected to the sensor layer, connecting it with sensors and a microcontroller. The more electrodes, the higher the sensitivity of the resistive touchscreen, since changes in voltage across them are constantly monitored.
Here is the screen with the resistive touchscreen turned on. Nothing is happening yet. Electric current flows freely through the conductive layer, but when the user touches the screen, the membrane on top bends, the insulating particles part, and it touches the bottom layer of the touchscreen and comes into contact. This is followed by a change in voltage at once on all electrodes of the screen.
The touchscreen controller detects voltage changes and reads readings from the electrodes. Four, five, eight meanings and all different. Based on the difference in readings between the right and left electrodes, the microcontroller will calculate the X-coordinate of the press, and based on the differences in voltage on the upper and lower electrodes, it will determine the Y-coordinate and thus tell the computer the point at which the layers of the touch screen layer touched.
Resistive touch screens have a long list of disadvantages. So, in principle, they are not able to recognize two simultaneous clicks, let alone a larger number. They don't behave well in the cold. Due to the need for a layer between the sensor layers, the matrices of such screens noticeably lose brightness and contrast, tend to glare in the sun, and generally look noticeably worse. However, where image quality is of secondary importance, they continue to be used due to their resistance to stains, their ability to be used with gloves and, most importantly, their low cost.
Such input devices are ubiquitous in inexpensive mass-produced devices, such as information terminals in public places, and are still found in aging gadgets, such as cheap MP3 players.
Infrared touch screen
The next, much less common, but nevertheless relevant option for a touch screen is an infrared touchscreen. It has nothing in common with a resistive sensor, although it performs similar functions.
The infrared touchscreen is constructed from arrays of LEDs and light-sensitive photocells located on opposite sides of the screen. LEDs illuminate the surface of the screen with invisible infrared light, forming something like a spider's web or coordinate grid on it. This is reminiscent of a security alarm, as shown in spy action films or computer games.
When something touches the screen, whether it's a finger, a gloved hand, a stylus, or a pencil, two or more beams are interrupted. Photocells record this event, the touchscreen controller finds out which of them are not receiving enough infrared light and, based on their position, calculates the area of the screen in which an obstacle has arisen. The rest is to match the touch with what interface element is on the screen at that location - the software's job.
Today, infrared touch screens can be found in those gadgets whose screens have a non-standard design, where adding additional touch layers is technically difficult or impractical - in e-books based on E-link displays, for example, Amazon Kindle Touch and Sony Ebook. In addition, devices with similar sensors, due to their simplicity and maintainability, attracted the attention of the military.
Capacitive touch screen
If in resistive touch screens the computer registers the change in conductivity that follows a press on the screen directly between the layers of the sensor, then capacitive sensors record the touch directly.
The human body and skin are good conductors of electricity and have an electrical charge. You usually notice this by walking on a wool carpet or taking off your favorite sweater and then touching something metal. We are all familiar with static electricity, have experienced its effects ourselves and have seen tiny sparks flying off our fingers in the dark. A weaker, imperceptible exchange of electrons between the human body and various conductive surfaces occurs constantly and this is what capacitive screens record.
The first such touchscreens were called surface capacitive and were a logical development of resistive sensors. In them, only one conductive layer, similar to the one used previously, was installed directly on top of the screen. Sensitive electrodes were also attached to it, this time at the corners of the touchpad. The sensors that monitor the voltage on the electrodes and their software were made noticeably more sensitive and could now detect the slightest changes in the flow of electric current across the screen. When a finger (another conductive object, such as a stylus) touches the surface with a surface capacitive touchscreen, the conductive layer immediately begins to exchange electrons with it, and the microcontroller notices this.
The advent of surface capacitive touchscreens was a breakthrough, but due to the fact that the conductive layer applied directly on top of the glass was easily damaged, they were not suitable for the new generation of devices.
To create the first iPhone, projected capacitive sensors were required. This type of touchscreen has quickly become the most common in modern consumer electronics: smartphones, tablets, laptops, all-in-one PCs and other household devices.
The top layer of this type of touchscreen screen has a protective function and can be made of tempered glass, such as the famous Gorilla Glass. Below are the thinnest electrodes that form a grid. At first they were placed on top of each other in two layers, then to reduce the thickness of the screen they began to be placed on the same level.
Made from semiconductor materials, including the aforementioned indium tin oxide, these conductive hairs create an electrostatic field where they intersect.
When a finger touches the glass, due to the electrically conductive properties of the skin, it distorts the local electric field at the points of closest intersection of the electrodes. This distortion can be measured as the change in capacitance at a single grid point.
Because the electrode array is made quite small and dense, such a system is able to track touch very accurately and can easily pick up multiple touches at once. In addition, the absence of additional layers and interlayers in the sandwich of the matrix, sensor and protective glass has a positive effect on image quality. True, for the same reason, broken screens, as a rule, are completely replaced. Once put together, the projected capacitive touch screen is extremely difficult to repair.
Now the advantages of projective-capacitive touchscreens do not sound like anything surprising, but at the time of the iPhone’s presentation they provided the technology with tremendous success, despite the objective disadvantages - sensitivity to dirt and humidity.
Pressure-sensitive touch screens - 3D Touch
The ideological predecessor of pressure-sensitive touch screens was Apple's proprietary technology, called Force Touch, used in the company's smart watches, MacBook, MackBook Pro and Magic Trackpad 2.
Having tested interface solutions and various scenarios for using pressure recognition on these devices, Apple began implementing a similar solution in its smartphones. In the iPhone 6s and 6s Plus, pressure recognition and measurement became one of the touchscreen functions and received the commercial name 3D Touch.
Although Apple did not hide the fact that the new technology only modifies the capacitive sensors we are used to and even showed a diagram that generally explained the principle of its operation, details about the design of touch screens with 3D Touch appeared only after the first iPhones of the new generation were disassembled by enthusiasts .
In order to teach the capacitive touch screen to recognize clicks and distinguish between several degrees of pressure, engineers from Cupertino needed to rebuild the touch screen sandwich. They made changes to individual parts of it and added another, new layer to the capacitive one. And, interestingly, when doing this, they were clearly inspired by outdated resistive screens.
The grid of capacitive sensors remained unchanged, but it was moved back, closer to the matrix. An additional array of 96 individual sensors was integrated between a set of electrical contacts that monitor where the display is touched and the protective glass.
Its task was not to determine the location of a finger on the iPhone screen. The capacitive touchscreen still handled this perfectly. These plates are necessary to detect and measure the degree of bending of the safety glass. Apple specifically for the iPhone ordered Gorilla Glass to develop and produce a protective coating that would retain the same strength and, at the same time, be flexible enough for the screen to respond to pressure.
This development could have been the end of the material about touch screens, if not for another technology that was predicted to have a great future several years ago.
Wave touch screens
Surprisingly, they don't use electricity and don't even have anything to do with light. Surface Acoustic Wave system technology uses surface acoustic waves propagating along the surface of the screen to detect the point of touch. The ultrasound generated by the piezoelectric elements at the corners is too high to be detected by human hearing. It spreads back and forth, bouncing off the edges of the screen multiple times. The sound is analyzed for anomalies caused by objects touching the screen.
Wave touch screens have few disadvantages. They begin to make mistakes after the glass is heavily soiled and in conditions of strong noise, but at the same time, in screens with such a sensor there are no additional layers that increase the thickness and affect the image quality. All sensor components are hidden under the display frame. In addition, wave sensors allow you to accurately calculate the area of contact between the screen and a finger or other object and, based on this area, indirectly calculate the force of pressing the screen.
We are unlikely to encounter this technology in smartphones due to the current fashion for frameless displays, but several years ago Samsung experimented with the Surface Acoustic Wave system in monoblocks, and panels with acoustic touchscreens are also sold as components for gaming machines and advertising terminals. Now
