Introduction to touch screen technology - telling you a different touch

Recently, with the launch of Kindle Touch and Fire, and the day of getting the desired device is approaching, various concerns have been lingering in my mind, such as whether the screen will be as crisp as K3, whether the touch screen is easy to use, etc., especially the touch screen, many people are not very clear, whether it is easy to use, and what is the difference between the capacitive screen and the resistive screen on the current mobile phone? Here I will briefly discuss with you, so that we can understand a different touch.

When it comes to touch, we have to mention Apple. Although Apple is never the first company to use new technologies, it is often the company that makes some niche new technologies truly familiar to everyone and makes the world crazy about them. The use of touch screens is no exception. Once upon a time, the use of resistive touch screens on mobile phones was more of a gimmick to add icing on the cake. When Apple first made mobile phones, it took a gamble to introduce capacitive screens into their only iPhone product and achieved unprecedented success. Now touch screens have spread to every corner of people's lives, greatly improving people's lives, but how do touch screens work?

In fact, the principle of the touch screen is simply to cover your screen with a piece of coordinate paper of the same size (students of science and engineering must be very familiar with it). The smaller the units of the horizontal and vertical coordinates on this coordinate paper (that is, the denser the grid), the higher the accuracy of the touch (this is no longer a problem now). When you want to realize the function of a certain image displayed on the screen, you specify a corresponding position on the coordinate paper (touch screen) with your finger, and there will be a corresponding XY coordinate. If this coordinate has been assigned a certain function before, this function will be triggered at this time. In fact, the biggest difference between different touch methods is that the coordinate paper is different.

There are two types of coordinate paper commonly used on mobile phones: resistive and capacitive. The similarity between the two is that they both require multiple layers of transparent film to be laid on the screen to realize the function of coordinate paper, and the difference lies in how to specify the coordinates. The resistive screen uses two layers of film filled with conductive substances, and the surface film is very elastic. When lightly pressed with a finger or pen, it will deform, thereby reducing the distance between the two layers of film, increasing the resistance value here, and thus determining the coordinate position. But there is a problem here. Since the surface film needs to be constantly deformed, although theoretically it can be completely restored within the elastic range of the material, there is always a gap between the actual and theoretical, and problems are still prone to occur after a long period of use. Moreover, there are high requirements for the material of the film. If it is too hard, it will not be pressed, and if it is too soft, it will be crushed accidentally. Moreover, because it is the most superficial film, it must also be wear-resistant, but hardness is often proportional to wear resistance, so it is difficult to have both requirements. Now the surface of the resistive screen is generally made of plastic, and of course it will be surface treated to enhance its wear resistance. Film is the best protection for the resistive screen.

Capacitive screens use a very thin layer of glass as the top film, and a conductive material underneath. The principle is that a layer of insulating glass is sandwiched between the hand as a conductor and the conductive material below, forming a typical capacitor structure to determine the coordinates. The top layer of glass does not need to be deformed, so the more wear-resistant the better, like the most popular "gorilla", but the disadvantage of glass is that it is brittle, so the biggest fear of mobile phones with capacitive screens is falling, and it is difficult to be used as a brick like Nokia back then, O (∩_∩) O~.

Finally... finally it's time for the protagonist Kindle! As we all know, the screen used for e-books is completely different from that of mobile phones and tablets. It uses Electronic Ink. The principle is shown in the figure.

The biggest difference from LCD is that it does not emit light by itself but reflects light to let people browse. I won't repeat the advantages. The key is those small "capsules". You can imagine it as a balloon filled with water, sandwiched between two boards. They are the most vulnerable Achilles' heel. The broken screens reported by everyone before are mostly caused by the spontaneous or external force rupture of these capsules. The surface layer of the upper and lower plywood is plastic, which is not easy to break, while the substrate is glass, and there is no buffer on the K3, so large pressure or impact will cause the substrate to break and the screen to break. This is said to have been improved on the K4. After talking about the screen, let's talk about the touch technology used in the K4 touch. Because the biggest advantage of electronic ink is the diffuse reflection of the surface (glass is full reflection), it brings a reading experience similar to that of paper. Even adding a stronger layer of glass to prevent the capsule from breaking is unacceptable, so it is definitely not appropriate to add a multi-layer film-like resistor or capacitor touch on it. Fortunately, we still have a choice, which is the so-called optical touch. Among them, the infrared touch (IR touch) using infrared wavelengths is used in e-books.

The principle is to use the infrared matrix densely distributed in the X and Y directions to detect and locate the user's touch, as shown in the figure. It is important to note that the infrared rays are parallel to the screen, rather than emitted from the bottom of the screen to detect body temperature. Those who have watched "Entrapment" must still remember the classic scene of Catherine Zeta-Jones passing through the infrared detector (actually a laser detector, the infrared band is invisible) (drooling all over the floor, right?), the principle should be the same.

This is why the frame of K4 touch is much higher than that of K4, because it is full of infrared transmitters! In nook and kobo, they both say they use neonode's zForce technology, but I haven't found it in K4 touch, but I think it should be similar.

According to the principle of infrared touch, you don't even need to touch the screen with your finger to complete the touch (as long as you can block the infrared rays), so it doesn't matter whether you use force or not. The main problem in the past was that the resolution was not high, because the density of the infrared emitting tube certainly could not reach the precision of the resistive screen or the capacitive screen, but now it has been greatly improved, especially on the kindle, there is no need for high-precision operation (if you want to play a game like CS where you point and shoot, it is probably impossible, the screen can't keep up, haha), and there is no reflection problem, so it is naturally the best choice at present.

Having said so much, many parts may not be very accurate, but generally speaking there should be no problem. I just hope that it can help everyone better understand the Kindle Touch that is about to arrive, a touch that is different from other devices we have.