A Basic understanding of Touch Screen

04-03-2020

Touch panels have become a part of daily life


Touch Panel is a sensor type device fabricated by forming a transparent electrode on a substrate of glass or film. ... This provides an intuitive user interface by directly touching the screen without any input devices required such as a keyboard or mouse.

It's perhaps not something we think of often, but touch panels have integrated themselves into every aspect of our lives. People who enjoy using digital devices like smartphones interact with touch panels all the time in everyday life—but so do others, at devices like bank ATMs, ticket vending machines in railway stations, electronic kiosks inside convenience stores, digital photo printers at mass merchandisers, library information terminals, photocopiers, and car navigation systems.






capacitive touch screen

A major factor driving the spread of touch panels is the benefits they offer in the way of intuitive operation. Since they can be used for input through direct contact with icons and buttons, they're easy to understand and easily used, even by people unaccustomed to using computers. Touch panels also contribute to miniaturization and simplification of devices by combining display and input into a single piece of equipment. Since touch panel buttons are software, not hardware, their interfaces are easily changed through software.

resistive touch screen

Primary applications of LCD monitors with touch panels. These devices are used in many widespread spheres.


While a touch panel requires a wide range of characteristics, including display visibility above all, along with precision in position sensing, rapid response to input, durability, and installation costs, their characteristics differ greatly depending on the methods used to sense touch input. Some typical touch-panel sensing methods are discussed below.


Resistive film touch panels


As of 2010, resistive film represented the most widely used sensing method in the touch panel market. Touch panels based on this method are called pressure-sensitive or analog-resistive film touch panels. In addition to standalone LCD monitors, this technology is used in a wide range of small to mid-sized devices, including smartphones, mobile phones, PDAs, car navigation systems, and the Nintendo DS.

With this method, the position on screen contacted by a finger, stylus, or other object is detected using changes in pressure. The monitor features a simple internal structure: a glass screen and a film screen separated by a narrow gap, each with a transparent electrode film (electrode layer) attached. Pressing the surface of the screen presses the electrodes in the film and the glass to come into contact, resulting in the flow of electrical current. The point of contact is identified by detecting this change in voltage.


The advantages of this system include the low-cost manufacture, thanks to its simple structure. The system also uses less electricity than other methods, and the resulting configurations are strongly resistant to dust and water since the surface is covered in film. Since input involves pressure applied to the film, it can be used for input not just with bare fingers, but even when wearing gloves or using a stylus. These screens can also be used to input handwritten text.

Drawbacks include lower light transmittance (reduced display quality) due to the film and two electrode layers; relatively lower durability and shock resistance; and reduced precision of detection with larger screen sizes. (Precision can be maintained in other ways—for example, splitting the screen into multiple areas for detection.)

 custom touch screen

Capacitive touch panels


Capacitive touch panels represent the second most widely used sensing method after resistive film touch panels. Corresponding to the terms used for the above analog resistive touch panels, these also are called analog capacitive touch panels. Aside from standalone LCD monitors, these are often used in the same devices with resistive film touch panels, such as smartphones and mobile phones.

With this method, the point at which the touch occurs is identified using sensors to sense minor changes in electrical current generated by contact with a finger or changes in electrostatic capacity (load). Since the sensors react to the static electrical capacity of the human body when a finger approaches the screen, they also can be operated in a manner similar to moving a pointer within an area touched on screen.

Two types of touch panels use this method: surface capacitive touch panels and projective capacitive touch panels. The internal structures differ between the two types.


 

Surface capacitive touch panels
Surface capacitive touch panels are often used in relatively large panels. Inside these panels, a transparent electrode film (electrode layer) is placed atop a glass substrate, covered by a protective cover. Electric voltage is applied to electrodes positioned in the four corners of the glass substrate, generating a uniform low-voltage electrical field across the entire panel. The coordinates of the position at which the finger touches the screen are identified by measuring the resulting changes in electrostatic capacity at the four corners of the panel.

capacitive touch screen

While this type of capacitive touch panel has a simpler structure than a projected capacitive touch panel and for this reason offers lower cost, it is structurally difficult to detect contact at two or more points at the same time (multi-touch).


Projected capacitive touch panels


Projected capacitive touch panels are often used for smaller screen sizes than surface capacitive touch panels. They've attracted significant attention in mobile devices.
The internal structure of these touch panels consists of a substrate incorporating an IC chip for processing computations, over which is a layer of numerous transparent electrodes is positioned in specific patterns. The surface is covered with an insulating glass or plastic cover. When a finger approaches the surface, electrostatic capacity among multiple electrodes changes simultaneously, and the position where contact occurs can be identified precisely by measuring the ratios between these electrical currents.

resistive touch screen

A unique characteristic of a projected capacitive touch panel is the fact that the large number of electrodes enables accurate detection of contact at multiple points (multi-touch). However, the projected capacitive touch panels featuring indium-tin-oxide (ITO) found in smartphones and similar devices are poorly suited for use in large screens, since increased screen size results in increased resistance (i.e., slower transmission of electrical current), increasing the amount of error and noise in detecting the points touched.

Larger touch panels use center-wire projected capacitive touch panels in which very thin electrical wires are laid out in a grid as a transparent electrode layer. While lower resistance makes center-wire projected capacitive touch panels highly sensitive, they are less suited to mass production than ITO etching.

Above, we've summarized the differences between the two types of capacitive touch panels. The overall characteristics of such panels include the fact that unlike resistive film touch panels, they do not respond to touch by clothing or standard styli. They feature strong resistance to dust and water drops and high durability and scratch resistance. In addition, their light transmittance is higher, as compared to resistive film touch panels.

On the other hand, these touch panels require either a finger or a special stylus. They cannot be operated while wearing gloves, and they are susceptible to the effects of nearby metal structures.

 

Optical touch panels (infrared optical imaging touch panels)

The category of optical touch panels includes multiple sensing methods. The number of products employing infrared optical imaging touch panels based on infrared image sensors to sense position through triangulation has grown in recent years, chiefly among larger panels.

A touch panel in this category features one infrared LED each at the left and right ends of the top of the panel, along with an image sensor (camera). Retroreflective tape that reflects incident light along the axis of incidence is affixed along the remaining left, right, and bottom sides. When a finger or other object touches the screen, the image sensor captures the shadows formed when the infrared light is blocked. The coordinates of the location of contact are derived by triangulation.


Reshine TFT-LCD display modules are available in various sizes,such as 1.77", 2.4”,2.8" ,3.2”,3.5”,4.0”,4.5”,5.0”,5.5”,6.0”,7.0”,8.0”,10.1”,10.4”,11.6”,12.1”,13.3”,15.6”,19” and 21.5” TFT LCD for smart home displays.These TFT LCD modules are including options of TFT panel, TFT LCM with controller board, industry standard TFT LCM, TFT color display, and wide operating temperatures of -20°C to +70°C or -30°C to +80°C,and also Higher brightness or wider viewing angle displays.

Many of Reshine TFT display modules have more than one interface available including MCU, RGB, TTL and LVDS as well as two touch panels optional in resistive and capacitive technology.

 

Reshine’s lcd displays are wildly used in smart home,car navigator,home security system,POS,medical devices,table advertising machine,industrial measuring inintrument,industrial control system,HMI devices,game player machine,detectors and so on.Please contact us freely if you are looking for a perfet LCD display with a custom Capacitive touch screen for your new Smart display design.

custom touch screen

capacitive touch screen


Reshine Display (HK) Technology Co., Limited

w:www.reshine-display.com

e:caroline@reshine-display.com


 

 


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