Două tehnologii multi-touch
Multi-touch, as the name implies, is to recognize the touch of two or more fingers. There are currently two multi-touch technologies: Multi-Touch Gesture and Multi-Touch All-Point. In layman's terms, multi-touch recognition of the gesture direction and multi-touch recognition of the finger position.
Recognize gesture direction
What we see most now is the Multi-Touch Gesture, that is, when two fingers are touched, the direction of movement of the two fingers can be recognized, but the specific position can not be determined, and operations such as zooming, translation, and rotation can be performed. This kind of multi-touch implementation is relatively simple, and the axis coordinate method can be implemented. Dividing the ITO into X and Y axes, two touch operations can be sensed, but the specific position of the touch and the specific position of the touch are two concepts. The XY-axis touch screen can detect the second touch, but cannot know the exact location of the second touch. A single touch produces a single maximum value on each axis to determine the location of the touch. If a second finger touches the screen, there will be two maximum values on each axis. These two maximum values can be generated by two different sets of touches, so the system cannot accurately judge. Some systems introduce timing to make judgments. It is assumed that two fingers are not put on at the same time. However, there are always situations where they are touched at the same time. At this time, the system cannot guess. We can call points that are not really touched "ghost points".
Recognize finger position
Multi-Touch All-Point is a popular topic recently. It can identify the specific location of the touch point, that is, there is no "ghost point" phenomenon. Multi-touch recognition position can be applied to the detection of any touch gesture. It can detect the simultaneous touch of ten fingers of both hands. It also allows other non-finger touch forms, such as palm, face, fist, etc., even wearing gloves. It is the most The user-friendly man-machine interface is very suitable for applications with multiple simultaneous operations, such as game control. The scanning method of Multi-Touch All-Point is that the intersection of each row and each column needs to be scanned separately, and the number of scans is the product of the number of rows and the number of columns. For example, a touch screen composed of 10 row lines and 15 column lines, using the axis coordinate method of Multi-Touch Gesture, requires 25 scans, while the multi-touch recognition position method requires 150 times.
Multi-Touch All-Point se bazează pe metoda de detectare a capacității reciproce, nu pe capacitatea proprie-. Auto-capacitanța detectează modificarea capacității fiecărei unități de detectare (adică capacitatea parazită Cp). Capacitatea parazită va crește atunci când există un deget, astfel încât să se determine Există o atingere, iar capacitatea reciprocă este de a detecta schimbarea capacității reciproce (adică capacitatea de cuplare Cm) la intersecția rândurilor și coloanelor. . Când rândurile și coloanele se încrucișează, capacitatea reciprocă va fi generată între rânduri și coloane (inclusiv: capacitatea franjelor dintre unitățile de detectare a rândurilor și coloanelor, capacitatea de cuplare generată la intersecția rândurilor și coloanelor), capacitatea reciprocă va scădea atunci când există este un deget, se poate aprecia că atingerea există, iar poziția fiecărui punct de atingere poate fi apreciată cu precizie.
Touch screen technology
Let's introduce the touch screen. The touch screen, to put it simply, is the combination of input and output. No mechanical buttons or sliders are needed. The display is a man-machine interface.
The whole touch screen module is composed of LCD, touch screen, touch screen controller, main CPU and LCD controller. Touch screen and touch screen controller are the core of the whole module, so we will focus on these two parts.
Structura ecranului tactil este în general de sus în jos: 1 scut de suprafață; 2 straturi de acoperire; 3 strat de mască strat de marcare; 4 lipici optic; 5 primul strat de unitate de detectare și substrat; 6 lipici optic; 7 al doilea strat de unitate de detectare și substrat; 8 strat de aer sau adeziv optic; 9 Ecran LCD.
The surface shield is usually less than 100um in thickness. A hard cover is required on all plastic coverings. This is because finger touch will scratch the plastic surface. If the covering is glass, the surface cover is not required, but the glass must be chemically strengthened or quenched. The surface cover needs to be covered. The layers are optically matched to avoid excessive light loss.
The cover layer can be 03 mm thick. Not all touch screens need a cover layer. The thinner the cover layer, the higher the signal-to-noise ratio and the better sensitivity of the sensor. Commonly used materials are: polycarbonate, plexiglass and glass.
The third layer is the mask layer and the marking layer, and its thickness is approximately 100mm. The mask layer is located under the cover, which can hide the wiring and the edge of the LCD. It is allowed to add marked text or icons in the design, but the marker must be pressed on the ITO substrate fairly flatly, and the marker material should be non-conductive.
The fourth layer is optical glue, the thickness is about 25200mm. The thinner the optical glue, the better the signal-to-noise ratio, and the high-permittivity (er) optical glue can better sense the finger capacitance, and thus can also obtain a higher signal-to-noise ratio. PSA pressure sensitive adhesive is usually used.
The fifth layer is the sensing unit and the substrate. The thickness of the ITO coating is less than 100nm. The ITO coating substrate can be 100 um 1mm glass (IR 1.52) or 25mm 300mm PET film (IR 1.65). The thicker the ITO, the lower the resistance per unit area, and the better the signal-to-noise ratio; the thinner the ITO, the better the light transmittance. The substrate can be a thin film or glass. If ITO is made on the lower surface of the glass substrate, the glass substrate can be used as a surface covering.
The sixth layer is another layer of optical adhesive. Compared with the previous layer of optical adhesive, the thicker this layer of optical adhesive, the better the signal-to-noise ratio. This layer of optical adhesive is usually combined with ACA-anisotropic conductive adhesive.
The seventh layer is also the sensing unit and the substrate, which is the same material as the first layer substrate. Be careful not to mix film and glass. If ITO is on the upper surface of the substrate, a thicker substrate can achieve a higher signal-to-noise ratio; if ITO is on the lower surface of the substrate, a thinner substrate can make the signal-to-noise ratio higher. It is also required to use anisotropic conductive adhesive in the edge area. There is a single substrate process to simplify production and reduce costs.
The eighth layer is air or optical adhesive layer. We know that the dielectric constant of air is equal to 1, which can reduce the parasitic capacitance from the upper surface of the LCD. If you use optical glue, you can make the installation more robust. It is necessary to match the optical parameters to make the light loss smaller. It is necessary to choose the optical glue with the lowest possible dielectric constant, and to ensure that the distance between the ITO sensor unit and the upper surface of the LCD is at least 250mm.
Ultimul este ecranul LCD. Pentru designul ecranului tactil, este o sursă de zgomot. Zgomotul provine de la iluminarea de fundal și de la semnalele de control ale unității pixelilor LCD. În general, ecranele cu matrice de puncte pasive nu sunt utilizate. Acest lucru va genera semnale de înaltă tensiune pe partea frontală a LCD-ului. Încercați să utilizați ecranul cu matrice de puncte Vcom Active, care poate constitui o funcție virtuală de pământ sau de ecranare; dacă într-adevăr trebuie să utilizați un ecran pasiv cu matrice de puncte, trebuie să adăugați un strat de ecranare ITO în ecranul tactil, iar stratul de ecranare trebuie să fie împământat pentru a elimina influența capacității parazitare CP.
Multi-point touch screen controller
The multi-point touch screen controller is the core of the touch screen module. This article takes Cypress's touch screen controller as an example to introduce.
Cypress's touch screen controller is the Truetouch series, which is based on the PSoC (Programmable System Chip) technology that has been widely used. PSoC is a mixed-signal array that integrates programmable analog and digital peripherals and MCU cores, so the flexibility, programmability, and high integration of PSoC are also suitable for Truetouch solutions.
The TrueTouch solution is an inductive capacitive touch screen solution. The structure of this touch screen has been introduced above. It can be said that there are many LCD manufacturers and types, as well as many sensing devices, such as glass, film, ITO, and even ITO models. Truetouch is based on PSoC technology, so the flexibility of PSoC makes it work well with many LCDs and ITOs.
Why is Cypress's touch screen controller named the Truetouch solution, or how did this "True" come from? Looking back at the development of the touch screen, from the beginning Single-touch—only one finger can touch or slide; later, Multi-touch gesture was also produced—you can recognize the direction of two fingers, but you can't determine their specific location. , Can zoom, pan, rotate and other operations; developed to today-Cypress's True touch can achieve Multi-touch all-point, can recognize multiple fingers and determine the exact position, it is a real multi-point touch, this is also The origin of True.
Truetouch product series can be divided into three categories, single-touch, multi-touch recognition direction (multi-touch gesture) and multi-touch recognition position (multi-touch all-point). Each category has various models, with differences in screen size, scanning speed, communication mode, memory size, power consumption, etc., to meet different applications. The Truetouch series is based on PSoC technology, so these devices can be designed using the simple and convenient but powerful PSoC designer software environment.
The value of the TrueTouch solution is mainly reflected in the following aspects: it maintains the inherent beauty, lightness, and thinness of the touch screen, which can make customers' products stand out; it adopts inductive capacitive touch screen technology, which does not require mechanical devices, and is more durable; it has a complete series, From single-point touch to multi-point touch recognition direction, and then to multi-point touch recognition position; based on PSoC technology, it is flexible to use and can be used with many LCDs and ITOs; all the values of PSoC can be reflected in Truetouch, such as flexibility Performance, programmability, etc., can shorten the development cycle, make products go to market quickly, and have a high level of integration. Many peripheral devices can be integrated into PSoC (ie Truetouch products), which can not only reduce system costs, but also reduce overall Power consumption, improve power efficiency.
