Smartphone from the inside: Touchscreen – how does it work?

In previous reviews, we already told you about the matrix and camera lens of a smartphone, about its other technologies that allow you to take better photos, and also began to “dissect” the display so that every curious reader can find out how they are arranged.

But understanding the operation of the smartphone’s screen will be incomplete without analyzing the principles of the functioning of its main layer, with which, in fact, we contact several hundred times a day – a touchscreen.

Content:

  1. Types of touchscreen
  2. Capacitive touch screen type
  3. Projection Capacitive Touch Screen
  4. Projection Capacitive Touch Screen Features
  5. Projection Capacitive Touch Screen Strengths
  6. Invisible and irreplaceable technology

Types of touchscreen

At the dawn of the appearance of the touch screen in smartphones, about ten years ago, this technology was just beginning its active development (like smartphones themselves) and was significantly different from what we already know today. The force of pressing the screen should have been greater, the accuracy was lower, and there was no talk of multitouch; but there were pluses – you could click on the screen with anything, even with a branch torn from a tree, instead of a stylus. This type of screen was called resistive and could recognize only one click on its surface..

At that time, it was a significant breakthrough and even this type of screen was very impressive for the then owners of smartphones. The ability to poke a finger right on the screen and select some action was equivalent to the plot of a science fiction film, with cutting-edge technology from the future. Today, with this functionality, most users are likely to simply smash the phone against the wall, because modern applications are no longer even designed with one click. And as soon as it comes to enlarging any photo, especially where double-clicking plays a completely different role, you are faced with the problem of taking at least Instangam.

However, the touchscreen was developing rapidly and even the resistive screen learned to understand a few taps, there were varieties of touch panels that manufacturers experimented with. Thus, everyone brought something useful to the process of improving the touch surface and today we can see a completely new, sensitive, reliable and multi-touch screen.

Capacitive touch screen type

By inventing the capacitive screen, which is now supplied with the vast majority of smartphones, mankind has received an unsurpassed control tool. And, although today they will not surprise anyone, and most importantly, many do not even think about how it works, its principle of operation is quite interesting.

Two types of capacitive touch screens can be distinguished – the first is called surface-capacitive, and the second, the most high-quality and accurate – projection-capacitive type. This is the last screen that all modern smartphones are equipped with, including the iPhone, the flagships of Samsung, Huawei and many other brands. It was about this type of touch screen that we wanted to tell.

Projection Capacitive Touch Screen

As you already recall from our last review, the screen consists of a multilayer backlit LCD matrix or OLED matrix, which works on its own and does not need any additional touch screen. But, if we want to click on it, and not just look at it like on TV, we need one more layer on which many conductive electrodes will be placed. This will be the touch screen, or touchscreen.

The principle of the projection-capacitive touch screen device is much simpler than any display matrix – it contains only two layers of electrodes, separated by an insulating layer. A negative charge is applied to the lower electrode layer, which creates the so-called cathode, and the upper layer, you guessed it, is an electrode connected to the positive pole of the battery and is called the anode.

These layers constantly create an electric field between themselves and when a conductive material or, for example, a finger is brought to the screen, some particles begin to fall onto this object (or finger), forming a “capacitance” (capacitor) and special electronics fix this “deviation from the norm”.

In total, such electrodes on the screen can be up to 80 vertically and up to 40 horizontally. They create a network of 3200 pressure-sensitive intersections that record the slightest movement of a finger or other conductive object.

The status of each electrode is updated line by line and very quickly, hundreds of updates of each line are recorded per second. And if at some of their intersections there is a leak to the “extraneous capacity”, then these coordinates are immediately transmitted to the processing values ​​of the controller.

The signal processing electronics registers the signal at a multitude of intersections, because when we press a small button with our finger we touch dozens of such electrodes. But, even taking into account this fact, the information received from the touch screen is processed by special algorithms and correctly understands that the center of pressure falls on a particular parameter or “cross” for closing another annoying advertisement.

Thus, repeatedly and continuously line-by-line scanning the entire screen for an electric field leak, the touchscreen can detect up to ten clicks, with accurate recognition of the point where you want to go and the trajectory of movement. However, there are other features of such capacitive screens that are not always liked.

Projection Capacitive Touch Screen Features

As we have already said, the use of resistive screens, despite their large number of minuses, was simplified by the ability to press with any object, which cannot be said about modern capacitive touchscreens. In order for the screen to register a click, the object must pass (pick up on itself) an electric charge. Special styluses or fingers are suitable for this..

Such a screen will not pass current through cloth, leather or knitted gloves, or mittens, which is a big minus in the winter. Also, a capacitive screen will respond very poorly to pressing with high humidity and droplets falling onto the screen – drops also conduct current and finger presses will not be accurately registered. The more problematic is the use of such a screen under water, despite the support of many manufacturers to protect the case from moisture, which can withstand short dives to a shallow depth.

Another drawback that appears in all LCD screens is the absorption of up to 10% of the light by the touch screen, because its transparency is only 90%. Therefore, creating such screens for all manufacturers should take this factor into account when calculating the brightness of the backlight or constantly improve technology to reduce the light absorption of each layer.

Projection Capacitive Touch Screen Strengths

However, most of these shortcomings can be corrected using program code. You can “teach” the screen to correctly recognize pressing with wet hands, to register touches with gloves with a special conductive coating. All this eliminates a number of problems and the main disadvantages of this type of touchscreen, which leaves us alone with its undeniable advantages.

The electric field created by the electrodes in the screen goes far beyond it and can respond to the touch of a finger even if the screen is covered with glass up to 18 mm. This helps to protect the thin layer from damage, which is used in ATMs and various street terminals..

In addition, the working life of such a screen is theoretically endless – there are no parts that wear out and if it is not broken in half, then it can work for a very, very long time. In any case, you should not worry about its breakdown, because even the most reliable component of the smartphone will fail earlier than the touch layer of the screen. This is very pleasing, because there will be less potential damage.

As for light transmission, there is no such problem in OLED or AMOLED matrices, as manufacturers have come up with a way to integrate the electrode layer directly onto the matrix, between subpixels.

Invisible and irreplaceable technology

In the modern world, which literally overwhelmed us with the technologies of the “future”, we very often do not notice simple and important little things for everyone. Such spectacular discoveries as the Internet, linking everyone to each other, flying motorcycles, self-driving cars and the ongoing space exploration, undoubtedly overshadow the importance of almost everything that we know about electronics. But now, at least every time using a smartphone you will realize that you are interfering in the stable electric field of the touchscreen by touching the screen, and thereby forcing dozens of electrodes to work for your needs .

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