tft display capacitive multi-touchscreen free sample

The Capacitive touch panel is activated with anything containing an inductive load such as a finger or stylus. It allows for multi-touch options. When using the capacitive touch screen, the display needs a separate controller to interface with the touch panel. The display for capacitive touch is brighter since the touch panel is transparent.

The Transmissive polarizer is best used for displays that run with the backlight on all the time. This polarizer provides the brightest backlight possible. If you have a need for a bright backlight with lower power drain, transmissive is a good choice for this TFT LCD display.

Focus LCDs can provide many accessories to go with your display. If you would like to source a connector, cable, test jig or other accessory preassembled to your LCD (or just included in the package), our team will make sure you get the items you need.Get in touch with a team member today to accessorize your display!

Focus Display Solutions (aka: Focus LCDs) offers the original purchaser who has purchased a product from the FocusLCDs.com a limited warranty that the product (including accessories in the product"s package) will be free from defects in material or workmanship.

The Capacitive touch panel is activated with anything containing an inductive load such as a finger or stylus. It allows for multi-touch options. When using the capacitive touch screen, the display needs a separate controller to interface with the touch panel. The display for capacitive touch is brighter since the touch panel is transparent.

The Transmissive polarizer is best used for displays that run with the backlight on all the time. This polarizer provides the brightest backlight possible. If you have a need for a bright backlight with lower power drain, transmissive is a good choice for this TFT LCD display.

Focus LCDs can provide many accessories to go with your display. If you would like to source a connector, cable, test jig or other accessory preassembled to your LCD (or just included in the package), our team will make sure you get the items you need.Get in touch with a team member today to accessorize your display!

Focus Display Solutions (aka: Focus LCDs) offers the original purchaser who has purchased a product from the FocusLCDs.com a limited warranty that the product (including accessories in the product"s package) will be free from defects in material or workmanship.

The CFAF800480E0-050SC is a 5-inch color TFT LCD graphic display module with high-brightness, sunlight-readable backlight and a capacitive touch panel (CTP).

The touch panel can detect up to 5 separate touch points. This TFT display is suitable for industrial, media, embedded and other general-purpose display applications.

The embedded EVE graphics accelerator chip simultaneously handles the display, touch, and audio functionality, lowering the development burden. The capacitive touchscreen overhangs the LCM making this display look fresh and clean when integrated into a product. The small TFT screen packs a punch. It"s sunlight-readable, has a high pixel density, and displays vibrant colors.

This module comprises our 2.4" Full-Color Capacitive Touchscreen TFT attached to an EVE accelerated board. Connect with this module using a simple 30-pin FFC ZIF connection.

This IPS TFT display has a high resolution 1024x600 screen. The IPS technology delivers exceptional image quality with superior color reproduction and contrast ratio at any angle. This 24-bit true color Liquid Crystal Display includes better FPC design with EMI shielding on the cable, is RoHS compliant, and has a 10-point multi-touch capacitive touchscreen.

Enhance your user experience with capacitive or resistive touch screen technology. We’ll adjust the glass thickness or shape of the touch panel so it’s a perfect fit for your design.

Choose from a wide selection of interface options or talk to our experts to select the best one for your project. We can incorporate HDMI, USB, SPI, VGA and more into your display to achieve your design goals.

Equip your display with a custom cut cover glass to improve durability. Choose from a variety of cover glass thicknesses and get optical bonding to protect against moisture and debris.

This 5" LCD is a 800x480 high resolution IPS TFT display. The IPS technology delivers sunlight readable image quality with higher brightness, better color reproduction, image consistency and optical characteristics at any angle. This 24-bit true color Liquid Crystal Display with parallel RGB interface, includes better FPC design with EMI shielding on the cable. It also has a built-in ST7262 IC driver and offers the same mechanical footprint and pinout as the TN display. This TFT is RoHS compliant and has a 5-point mulit-touch capacitive touchscreen.

Enhance your user experience with capacitive or resistive touch screen technology. We’ll adjust the glass thickness or shape of the touch panel so it’s a perfect fit for your design.

Choose from a wide selection of interface options or talk to our experts to select the best one for your project. We can incorporate HDMI, USB, SPI, VGA and more into your display to achieve your design goals.

Equip your display with a custom cut cover glass to improve durability. Choose from a variety of cover glass thicknesses and get optical bonding to protect against moisture and debris.

Capacitive touch technology is increasingly used in user interfaces for a variety of devices. A capacitive touch display is created by attaching a capacitive layer on top of a glass panel substrate. These components are then covered with a protective outer layer, and the surface of the device will maintain a static charge. As a person’s finger or a stylus touches the surface, the charge will transfer from the panel surface to the device or finger. This allows the capacitive device to register the touch location.

Thin-film transistor (TFT) LCD capacitive touch screens have become a popular choice when compared to the other leading touch screen technology – resistive touch. While resistive touch screens have been around for a longer time and can be built at a lower cost, capacitive touch displays offer several significant advantages over other display technologies. In this post, we’ll explore what makes capacitive touch technology unique and how it performs across several parameters.

Capacitive touch technology offers excellent screen sensitivity when used with a finger or stylus. The surface of these devices will respond to varying degrees of pressure, as opposed to a resistive touch screen where firm and direct pressure must be used. A TFT LCD capacitive touch screen is also sensitive enough to be used only with fingers without the need for a stylus.

Capacitive stylus devices can be used for added precision and niche applications such as digital drawing. Another related benefit is support for multi-touch operation using multiple fingers simultaneously. This includes advanced gestures such as pinch-zoom that is a popular feature in many device applications today.

TFT LCD capacitive displays are known for their excellent optical quality. The glass substrate that sits below the electrode film transmits most of the available light to the surface resulting in crisp sharpness and display contrast. These screens are also known for outstanding color fidelity that supports the viewing of high-quality images, video, and software content. This also has a positive impact on the user experience when integrated into larger kiosks and interactive displays.

Capacitive touch devices are very stable, with little to no shift in the image being transferred to the screen. This is an important advantage over other display types, as image shift can get worse over time and require manual correction with other types of displays. A capacitive touch device, therefore, does not require the periodic calibrations that are commonly necessary with many older display technologies. Maintaining a stable image is an essential requirement in high-performance display applications, such as those found in the broadcasting and entertainment industries.

The glass substrate of a capacitive touch display is very strong, and the protective layer helps prevent scratches and other marks. Like most displays, a capacitive touch screen can crack if dropped or exposed to significant pressure. It should be noted that a cracked resistive touch screen most often ceases to operate, while a cracked capacitive device will usually maintain some functionality. This has made capacitive screens popular for commercial applications that are exposed to significant wear and tear.

The screen of a capacitive touch device can be completely sealed, preventing contaminants from entering the seams on the outer edges of the display. Preventing dust and condensation from getting inside the display is important for long-term use. This also makes a capacitive touch display easy to clean. Due to the ease of cleaning and other advantages, capacitive touch technology is often used for public digital displays in high-traffic areas.

The sensitivity of a capacitive touch display also contributes to excellent response times. As a user touches the screen at different locations, the surface can register these movements with a high degree of accuracy. A capacitive touch screen also performs very well when the user’s finger or stylus is dragged across the surface. This makes capacitive touch a preferred choice for graphic design and audio-visual applications.

One final advantage of capacitive touch technology is false touch rejection. A resistive display can be easily confused if multiple fingers touch the screen at the same time, making it unable to register accurate movement. The improved sensitivity of a capacitive display increases the ability of the surface to differentiate between multiple points of contact. In addition to enabling the custom gestures, sliding motions, and light touches mentioned above, this also eliminates the potential for a missed touchpoint.

Capacitive touch is a relatively new touchscreen technology that is having a significant impact on the display industry. With several advantages over competing design options, the use of TFT LCD capacitive touch technology is expected to grow significantly in the coming years. This will be an important trend for device manufactures, designers, and end-users to follow as an opportunity to improve product quality and performance.

There are types of touch screen，such as resistive touch panel(RTP), capacitive touch panel (CTP), surface acoustic wave touch display, infrared touch screen. RTP and CTP are used more than others. Can you tell the difference between RTP and CTP? If not, you may want to read along.

Capacitive touchscreens, on the other hand, respond directly to the touch of your finger or an input device such as a stylus. On top of LCD panel, lies a thin layer of transparent electrodes. When a human finger touches the screen, some of the electrical charge travels from screen to user. The change of capacitance is then detected by sensors located at screen"s four corners, allowing controller determine the touched location.

Supporting of Multiple touches is a clear winner for capacitive touch screens (CTP). Thanks to smartphone and tablet, users are comfortable with using gesture on screen. And capacitive touch screen is what user is familiar with. In more specialized settings, such as multi-player gaming application, capacitiv e touch screens can support more than 10 inputs at a single time. Additionally, CTP needs no calibration and is highly accurate.

Resistive touch display cannot determine the location of a touch if more than one input is present. In terms of visibility, the film substrate commonly used as the top surface in resistive touch screens is less transmissive than glass. This leads to reduced brightness and a certain level of haze compared to touch screens with a top layer of glass. The film layer can also expand or contract based on temperature, which alters the distance between the two layers and affects touch accuracy. Additionally, the film substrates are susceptible to scratches and can start to wear away with repeated use, necessitating occasional recalibration or replacement over time.

Capacitive touch screens depend on variations in an electrical field to operate. While a passive stylus can activate this screen, a non-conductive tool like a pencil can"t. If cost is a top concern for a project, CTP may not align with budget limits. It is a more expensive technology than resistive screens, although it continues to grow more accessible in terms of price as the technology advances and improves.

A surface capacitive touchscreen uses a transparent layer of conductive film overlaid onto a glass sublayer. A protective layer is then applied to the conductive film. Voltage is applied to the electrodes on the four corners of the glass sublayer to generate a uniform electric field. When a conductor touches the screen, current flows from the electrodes to the conductor. The location of the conductor is then calculated based on the activity of the currents. Surface capacitive touchscreens are often used for large screen panels.

Projected capacitive touchscreens are extremely precise and quick to respond and are typically found on smaller devices such as iPhones, iPod touches, or iPads. Unlike the surface capacitive touchscreens, which use four electrodes and a transparent conductive film, the projected capacitive touchscreens use a vast amount of transparent electrodes arranged in a specific pattern and on two separate layers. When a conductor moves near the screen, the electrical field between the electrodes changes, and sensors can instantly identify the location on the screen. Projected capacitive touchscreens can accurately register multi-touch events.

Tuning capacitive touch panels (CTP) needs tiny capacitance differences for its operation. Dirty power supplies and stainless-steel table can affect CTP performance.

Touchscreen displays are everywhere! Phones, tablets, self-serve kiosks, bank machines and thousands of other devices we interact with make use of touchscreen displays to provide an intuitive user interface.

Today we will learn how touchscreens work, and how to use a common inexpensive resistive touchscreen shield for the Arduino.  Future videos and articles will cover capacitive touchscreens, as well as a touchscreen HAT for the Raspberry Pi.

Eric A Johnson, a researcher at the Royal Radar Establishment in Malvern UK is credited for describing and then prototyping the first practical touchscreen. HIs device was a capacitive touchscreen, and it’s first commercial use was on air traffic control screens. However, the touchscreens used then were not transparent, instead, they were mounted on the frame of the CRT display.

In 1972, a group at the University of Illinois filed for a patent on an optical touchscreen. This device used a 16×16 array of LEDs and phototransistors, mounted on a frame around a CRT display. Placing your finger, or another solid object, on the screen would break two of the light beams, this was used to determine the position and respond accordingly.

In 1982 theUniversity of Toronto’sInput Research Group developed the first multi-touch touchscreen, a screen that could interpret more than one touch at the same time.  The original device used a video camera behind a frosted piece of glass. Three years later the same group developed a multi-touch tablet that used a capacitive touchscreen instead.

The first commercial product to use a touchscreen was a point-of-sale terminal developed by Atari and displayed at the 1986 COMDEX expo in Las Vegas. The next year Casio launched theCasio PB-1000 pocket computerwith a touchscreen consisting of a simple 4×4 matrix.

LG created the world’s first capacitive touchscreen phone, theLG Pradaused a capacitive touchscreen and was released in early 2007. A few weeks later Apple released its first iPhone.

Most early touchscreen devices were resistive, as this technology is generally less expensive than capacitive screens. However, nowadays capacitive screens are more common, being used in the majority of smartphones and tablets.

Although they were invented after capacitive touchscreens, resistive touchscreens are probably the most common type used by hobbyists. The reason for that is the price and performance, resistive touchscreens are cheaper than capacitive ones and they are generally more accurate.

This is the most inexpensive method of designing a resistive touchscreen. The touchscreen display that we will be working with today uses this arrangement.

Capacitive touchscreens are actually older technology than resistive displays.  They are commonly used in phones and tablets, so you’re probably familiar with them.

The capacitive touchscreen makes use of the conductivity of the human body. The touchscreen itself consists of a glass plate that has been treated with a conductive material.

The surface capacitive touchscreen is the most inexpensive design, so it is widely used. It consists of four electrodes placed at each corner of the touchscreen, which maintain a level voltage over the entire conductive layer.

This is a more advanced touchscreen technique. In a projected capacitive touchscreen transparent electrodes are placed along the protective glass coating and are arranged in a matrix.

You can also just use the shield as an LCD display and ignore the two other components, however, if you intend on doing that it would be cheaper just to buy an LCD display without any touchscreen features.

This is a TFT orThin Film Transistordevice that uses liquid crystals to produce a display.  These displays can produce a large number of colors with a pretty decent resolution.

You do need to be looking directly at the display for best color accuracy, as most of these inexpensive LCD displays suffer from distortion and “parallax error” when viewed from the side. But as the most common application for a device like this is as a User Interface (UI) this shouldn’t be a problem.

The microSD card socket is a convenience, it’s normally used for holding images for the display but it can also be used for program storage.  This can be handy for holding things like calibration settings and favorite selections.

The last paragraph regarding the microSD card may make you think that an Arduino Uno is the best choice for the Touchscreen Display Shield.  And it you require the microSD card then it probably is a good choice.

As there are three devices on the shield you will need libraries for each of the ones you want to use.  TheSD Libraryis already installed in your Arduino IDE, so you will just need libraries for the display and touchscreen.

This useful resource contains code, libraries and datasheets for a wealth of LCD displays, both touchscreen and non-touchscreen. You’ll also find code for some common OLED displays as well.

I ran my touchscreen through all of the code samples I obtained from the LCD Wiki. It’s an interesting exercise, and by examining the sketch for each demo you can learn a lot about programming the display.

This test does not make use of any of the extra libraries, it drives the LCD directly. It is only a test of the LCD display, it does not make use of the touchscreen membrane.

This example does use the custom libraries, and is a very good way to learn how to use them.  You’ll note that theLCDWIKI_GUI.hlibrary is loaded, which is the graphics library for the LCD display.

This sketch uses a number of functions from theLCDWIKI_GUI.hlibrary, along with some custom functions to draw geometric shapes. It then displays a cycle of graphs, shapes, and patterns on the LCD display.

One way in which this sketch differs is that most of the graphics routines are executed in the Setup function, so they only run once. The loop then displays some text with a selection of colors and fonts. The orientation is changed as it cycles through the loop.

This example makes use of a second file that contains fonts. The Display Scroll sketch illustrates a number of different methods of scrolling characters, in different fonts, colors and even languages.

One interesting thing about this test is that it illustrates how to display text in different “aspects”, Portrait and Landscape, Right side up and Reversed.

Unlike the previous examples that put the text in with a number of graphics, this example is a pretty simple one with just a block of text in different sizes and colors.  This makes it very simple to understand how the text is positioned on the display.

The result of running the sketch is the display screen fills with rows of hexadecimal values while the background alternates between blue and black and the orientation (or “aspect”) changes.  If you stand back to see the “big picture” you’ll note that the color values form “number patterns”.

The Display Phone Call sketch draws a mockup telephone keypad. Pressing one of the keys will display the result on a line of text at the top.  There is also a key to delete your entries, as well as ones to send and disconnect the call – the latter two are “dummy” functions of course as it’s only a demo.

As its name would imply, this sketch displays a bitmap image on the display. The images need to be placed onto the root of a microSD card, which in turn is plugged into the socket on the display shield.

The images will show off the display resolution, which is reasonably impressive. You’ll also note that to see them at their best, you need to be directly in front of the display, viewing the display at an angle causes the display to distort colors.

This example draws some small “switches” on the display. The switches are active and respond to touch.  There are slide switches, a push button, some radio buttons and some text-based expandable menus to test with.

After calibration, the sketch will display a number of calibration values for the resistive touchscreen. These values can be used in your future sketches to make the touchscreen more accurate.

The digital I/O connector at the back of the Mega is still accessible even when the touchscreen display shield is installed, so I used three of those connections for the LEDs. I hooked up each LED anode through a 220-ohm dropping resistor and connected them as follows:

The sketch is based upon the telephone keypad sketch. I modified it to eliminate the other functions and just display three buttons.  Then I added code to toggle the LEDs.

TheAdafruit GFX Libraryis a comprehensive graphics library that can be used in a variety of display applications.  It is a “core library”, meaning that it is called by other Adafruit libraries.

TheAdafruit TFTLCD Libraryis used. It uses the previous library to provide an easy method of drawing on the LCD display.  It works with LCD displays that use driver chips like the ILI9325 and ILI9328.

TheMCUFRIEND_kbvlibrary is also included in the software you obtained for your display shield. It takes care of supplying the correct hardware information for your display shield to the other libraries.

Next, we define some touchscreen parameters. You can ‘fine-tune” your code here by using parameters from your own display, which you can obtain from the Calibration Sketch we ran from the sample code.  Otherwise, just use the values here and you should be fine.

Next, we reset the display and try to identify it. This will run through a list of display chip drivers in the MCUFRIEND_kbv library and will attempt to select the correct one.

Now, still in the Setup, we set up the LCD display rotation and fill the background in black. Next step is to draw our buttons. Once we are done that the Setup is finished, and our screen should be displaying the three buttons on a black background.

We then need to reset the pin modes for two of the touchscreen pins back to outputs. This is done as these pins get shared with other LCD display functions and get set as inputs temporarily.

Touchscreen interfaces are used in a number of products, and now you can design your own devices using them. They can really make for an intuitive and advanced display and will give your project a very professional “look and feel” if done correctly.

This is not the only time we will look at touchscreen displays. Next time we’ll examine a capacitive touchscreen and we’ll explore the Adafruit Graphics libraries further to create some very fancy displays with controls and indicators.

ER-TFT028A3-4 is 240x320 dots 2.8" color tft lcd module display with ST7789V controller and optional capacitive touch panel and 4-wire resistive touch panel,superior display quality,super wide viewing angle and easily controlled by MCU such as 8051, PIC, AVR, ARDUINO ARM and Raspberry PI.It can be used in any embedded systems,industrial device,security and hand-held equipment which requires display in high quality and colorful image.It supports 8080 8-bit,9-bit,16-bit,18-bit parallel,3-wire,4-wire serial spi interface. FPC with zif connector is easily to assemble or remove.Lanscape mode is also available.

Of course, we wouldn"t just leave you with a datasheet and a "good luck!".Here is the link for 2.8"TFT Touch Shield with Libraries, Examples.Schematic Diagram for Arduino Due,Mega 2560 and Uno . For 8051 microcontroller user,we prepared the detailed tutorial such as interfacing, demo code and development kit at the bottom of this page.

Department of Information Display, Kyung Hee University, Seoul 02447, Korea; rk.ca.uhk@8118loes (K.-H.S.); rk.ca.uhk@7001ppolkj (J.L.); rk.ca.uhk@3170shohc (H.C.); rk.ca.uhk@gnujwsrm (S.W.J.)

Touchscreens have been studied and developed for a long time to provide user-friendly and intuitive interfaces on displays. This paper describes the touchscreen technologies in four categories of resistive, capacitive, acoustic wave, and optical methods. Then, it addresses the main studies of SNR improvement and stylus support on the capacitive touchscreens that have been widely adopted in most consumer electronics such as smartphones, tablet PCs, and notebook PCs. In addition, the machine learning approaches for capacitive touchscreens are explained in four applications of user identification/authentication, gesture detection, accuracy improvement, and input discrimination.

Human beings collect a lot of information through their eyes, and many displays around us play a key role to transfer this visual information. Displays have evolved dramatically from cathode-ray tube (CRT) [1,2,3,4] via plasma display panel (PDP) [5,6,7,8,9,10] and liquid crystal display (LCD) [11,12,13,14,15] to cutting-edge organic light-emitting diode (OLED) [16,17,18,19,20,21,22] and micro-LED technologies [23,24,25,26,27,28]. This evolution has led to larger screen-size, slimmer design, lower weight, higher resolution, faster frame rate, brighter luminance, wider color gamut, longer life time, and lower power consumption in the large-size display applications such as monitors, televisions (TVs), and digital signage [29,30,31,32,33,34,35,36,37,38,39]. The resolutions of off-the-shelf displays have increased up to 8K (7680 × 4320) along with the high frame rate of 120 Hz and the larger screen sizes than 55-inch have taken more than 30% of overall TV set sales [40,41]. Even rollable OLED TVs were demonstrated in the consumer electronics show 2018 (CES2018) [42]. On the other side of the small-size display applications, higher density of pixels, narrower bezel, flexibility, bendability, rollability, and low power consumption have been achieved along with enhanced picture quality [43,44,45,46,47,48]. The latest smartphones contain the bezel-less screens of larger pixel densities than 450 pixel per inch (ppi) and smartphones with foldable displays are being sold on the market [49]. Recently, as augmented reality and virtual reality (AR/VR) attract substantial interest, the demand for high-performance near-eye displays is increasing further [50,51,52,53,54,55,56,57]. Consequently, the very high resolution OLED on silicon (OLEDoS) displays up to 4410 ppi have been reported [58,59,60,61,62,63].

On top of the role of a visual information provider, displays have supported the interaction with users by means of various user interfaces. Users can adjust the visual information on the screen by themselves. The very old but still popular representative user interfaces are mouse and keyboard [64,65,66]. There have also existed pen tablets for more elaborate works such as drawing and writing [67,68,69,70]. Because these devices work on the different planes separated from displays, additional markers such as cursors and pointers are needed. On the other hand, more intuitive input interfaces called touchscreens have been studied to directly interact with displays by touching displays [71,72,73,74]. Touchscreen technologies can be categorized into finger-touch and stylus-touch methods. While finger-touch methods include resistive, capacitive, acoustic wave, and optical approaches [75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101], stylus-touch ones cover up to electromagnetic resonance (EMR) schemes including finger-touch methodologies [102,103,104,105,106,107,108]. Recently, as wearable devices such as smartwatches and smartbands are becoming more popular, small-size displays are becoming further widespread with touch sensing functionality. However, because this very small-area screen cannot support multiple finger-touches and the whole area is covered even by a single finger, a variety of separate input modalities in the outside of the screen have been studied by using infrared (IR) line sensors, microphones, gaze trackers, IR proximity sensors, electric field sensors, deformation sensors, magnetic field sensors, and mechanical interfaces [109,110,111,112,113,114,115,116,117,118,119,120,121,122,123]. In addition, some approaches have coped with the limitation of the single touch by differentiating palm and finger or identifying pad, nail, tip, and knuckle of a finger [124,125]. Especially, because AR/VR displays are placed near to eyes, it is impossible to touch the screen directly. Therefore, other input tools using various sensors such as leap motion sensors, electromyograph sensors, inertial measurement units, eye-trackers, IR facial gesture sensors, cameras, and axis-tilt sensors, have been employed [126,127,128,129,130,131,132,133,134].

There have been brief reviews of touchscreen technologies [76,96]. Walker [165] published many overview papers about a variety of touchscreen technologies from resistive to optical and electromagnetic resonance (EMR) stylus schemes. Those papers explained their histories, principles of operation, pros and cons, and applications. However, the technological details have not been handled such as algorithms, driving circuits, and ML approaches. Kwon et al. [166] reviewed capacitive touchscreen technologies including sensors, driving circuits, sensing methods, and stylus schemes in more detail. However, ML approaches were not introduced. Bello et al. [164] summarized ML approaches to improve security on touchscreen devices without addressing the touchscreen technologies. A variety of ML applications only for the security issues were addressed. This paper provides a unified and broader view of the touchscreen technologies with the detailed explanation and ML approaches in various scenarios.

This paper is organized as follows. Section 2 addresses the overview of the touchscreen technologies, and then Section 3 describes various studies on capacitive touchscreen applications that are integrated in most smartphone and notebook displays. Section 4 shows the ML approaches working with existing capacitive touchscreen technologies. Section 5 concludes this paper with some suggestions of the future directions.

In this section, touchscreen technologies for finger as well as stylus have been simply addressed in terms of principles of operation, advantages, and drawbacks. We categorize the touchscreen technologies into four categories of resistive, capacitive, acoustic wave, and optical, and address further various techniques in each category as shown in Figure 1. Table 1 compares their specifications.

On the other hand, there have been efforts to support multi-touch capability. Some researchers were trying to add the multi-touch functionality to a conventional structure by sensing the current consumption at voltage sources [167,168,169]. Whereas, other researchers divide the conductive films into multiple lines and columns that give rise to many separate overlapped areas [170,171,172], where each area can detect touches separately. This scheme is named as the digital resistive touchscreen [165]. Since the resistive touchscreen methods fall short of the capacitive schemes, the resistive touchscreen panels are being applied to the limited areas such as toys, office electronics, and card payment machines.

Capacitive touchscreens sense the change of the capacitance caused by the finger to estimate the touch position. While resistive schemes need the pressing force to make the actual contact between two conductive layers, capacitive methods can obtain the capacitance change just by the light touch on the screen. Consequently, it enables the smooth and fast scrolling, high durability, and excellent optical performance. In addition, any materials can be adopted for layers, for example, glasses and plastics, while resistive technologies require one flexible layer at least. Because the parasitic capacitance added by fingers is very small, large-size capacitive touchscreen panels are very difficult to implement and contaminants such as water and dusts can be also recognized as touches. Recently, the large size capacitive touchscreens have been reported based on the metal mesh structure [108,173]. It can support only capacitive input tools including fingers to make parasitic capacitors with electrodes of the touchscreen panel.

The capacitive scheme is divided into surface-capacitive [81,83] and projected-capacitive methods [82,84]. Surface-capacitive touchscreens consist of one conductive layer of which four corners are connected to four perfectly synchronized alternative current (AC) voltage signals as described in Figure 3. While any difference does not occur without touches at these voltage sources, the finger touching the screen brings out the current difference in four voltage sources. As the voltage source is located nearer to the touch point, the current variation becomes larger due to the smaller resistive load. As a result, the touch locations are extracted from the ratio of the currents over four voltage sources. Even though it cannot deal with multiple touches at the same time, its high durability enables the integration in automated teller machines (ATMs).

Surface-capacitive touchscreen. The touch location can be estimated from the current variation at four corner AC voltage sources caused by the finger touch.

The projected-capacitive methods can be further divided into self-capacitance and mutual capacitance architectures. Especially, the mutual capacitance has been the mainstream technology used in most consumer electronics such as smartphones, tablet PCs, and notebook PCs since the appearance of iPhones in 2007, because it can support multi-touch functions along with high durability and good optical clarity.

In general, the projected-capacitive touchscreen panels use two patterned conductive layers that are separated and crossed to each other in the shape of a matrix. Horizontal and vertical patterns correspond to the position information of the touch event. While the self-capacitance senses the capacitance between layers and ground as shown in Figure 4a, the mutual capacitance measures the capacitance at the overlapped areas of horizontal and vertical patterns as presented in Figure 4b. Consequently, the finger touch increases the self-capacitance due to the additional parasitic capacitor in parallel and decreases the mutual capacitance due to the electric field loss by the finger placed between two electrodes.

While additional touchscreen panels on the displays require further electronics, the embedded touchscreen solutions that are called an in-cell touch can merge panel and touchscreen electronics into a single driver integrated circuit. Therefore, various in-cell approaches have been developed including self-capacitance cells and capacitive sensors embedded in pixel areas [174,175,176,177,178,179].

The optical touchscreens are developed based on the invisible infrared (IR). The traditional IR-based touchscreen places transmitters at two sides and receivers at their opposite sides without any additional layers. Because the touches block the light path over the screen between a pair of transmitter and receiver, x-axis and y-axis coordinates can be obtained by finding the receivers’ positions that do not receive IR. While large-size displays and excellent optical clarity can be supported, the bezel needs some height over the screen for IR transmitters and receivers and the multiple touches cause the ghost touch issue.

As explained in the previous section, there have exist various touchscreen technologies by means of resistance, capacitance, sound wave, and IR. Among them, the capacitive touchscreen has become a mainstream scheme, especially, the mutual capacitance touchscreen is the most widely used technology on many consumer electronics such as smartphones, notebook PCs, tablet PCs, and smartwatches, because of its multi-touch support, slim form factor, high optical quality, excellent durability, smooth scrolling, and so on. Particularly, this section addresses the mutual capacitance capacitive touchscreens in more details. Unlike the self-capacitance method where the parasitic capacitor of a finger touch is connected to the self-capacitor in parallel, the mutual capacitance scheme experiences the capacitance reduced by electric field leakages into a finger. As a result, the touch location can be found out by searching the position which mutual capacitance is reduced.

As shown in Figure 7, a conventional mutual capacitance capacitive touchscreen panel is composed of excitation (EX) electrodes and sensing (SE) electrodes, which give rise to the mutual capacitor array at their intersection areas [181,182]. Excitation drivers generate EX pulses sequentially in the way of line-by-line that arrive at charge amplifiers attached to SE lines through mutual capacitors. The non-inverting input terminals of these charge amplifiers are connected to the reference voltage (VREF) and the charge transferred through a mutual capacitor (Cm) is converted through a feedback capacitor (Cf) into analog voltages (VOUT) that are proportional to the mutual capacitance as presented in Equation (1). VEX is the amplitude of the EX pulse. When a user touches on the screen with a finger, the reduction on the mutual capacitance is sensed as the different output voltage of the charge amplifier from the voltage level obtained without any touches as illustrated in Figure 8. To improve the precision of the touch detection, the transferred charge is accumulated at the charge amplifiers over multiple EX pulses. In addition, a multiplexer (MUX) allows one analog-to-digital converter (ADC) to sample the output voltages of charge amplifiers in all SE lines sequentially. Finally, a host processor handles the digital data to determine the touch locations and it also controls excitation drivers.

Block diagram of a conventional mutual capacitance capacitive touchscreen system. NEX and NSE are the numbers of excitation and sensing electrodes, respectively. The touch locations are estimated from the mutual capacitor array formed at the intersection areas of EX and SE lines.

For the SNR improvement, various noises such as display noises, charger noises, and hum noises need to be addressed. Usually, the most sensing circuits employ the voltage accumulation at the output of the charge amplifier as shown in Figure 9, to suppress the noise power over the main signal, based on the assumption that the noise is independent and identically distributed [188]. Because the noise power and the signal power are proportional to the number of pulses and its squared value, respectively, the SNR improvement is achieved.

Kim et al. [190] proposed the common-mode noise cancellation by subtracting the signals of the adjacent EX lines. Since the parasitic capacitance between neighboring EX lines of a touchscreen panel and display panel are almost equal, the injected noises from the display to the touchscreen would be similar, therefore, the differential sensing method over EX pulses of two neighboring lines could eliminate the common-mode display noise. Yang et al. [191] added a charge-interpolation filtered-delta-integration (CI-FDI) scheme to cancel the charger noise. The large noise is detected, and then the noise is prevented by the charge-interpolation.

As the other method to reduce the display noise components, it was proposed that the sensing operation was conducted only during the vertical blank interval as presented in Figure 11a. However, the sensing operation over the whole touchscreen area should be finished within very short period of time at the end of a frame time. Since it could not support smooth scrolling motions, the time division multiple sensing (TDMS) was introduced to spread the touch sensing functions evenly over a frame time [174,192], where the divided vertical blank parts were added in the middle of the active interval by stopping the scanning operations as illustrated in Figure 11b.

While previous passive and active ways are grounded in the capacitive touchscreen panel, there is a stylus with a different approach that works with an electro-magnetic resonance (EMR) technology [107]. Since EMR responds only to the stylus and the capacitive touchscreen panel senses only the fingers, two separate touch sensing schemes enable the finger to be distinguished from the stylus. However, this technique needs additional layers that increase hardware complexity as well as manufacturing cost.

The stylus technologies that can be implemented on the capacitive touchscreen are summarized in Table 3 in terms of tip size, stylus discrimination support, SNR degradation, computational cost, and hardware complexity.

Several ML algorithms have been employed to the capacitive touchscreen in a variety of applications such as user identification/authentication, gesture detection, accuracy improvement, and input discrimination. While many approaches used traditional ML techniques of decision tree (DT), random forest (RF), naive Bayes (NB), radial basis function network (RBFN), back propagation neural network (BPNN), support vector machine (SVM), and Gaussian process regression (GPR), the latest ML networks, such as convolutional neural network (CNN), anomaly detection (AD), and recurrent neural network (RNN), have been also utilized in the touchscreen field. The following machine learning applications are implemented on the off-the-shelf smartphones and tablet PCs with mutual capacitance capacitive touchscreens.

Guo et al. [143] proposed CapAuth that is a user identification and authentication technique based on capacitive touchscreen data combined with machine learning classifiers. It used the capacitive image of the hands-flat pose revealing the more distinguishing features. CapAuth was built based on quadratic-kernel SVM classifiers, a binary classifier for authentication and a multi-class one-to-one classifier for identification. The measure FRR and FAR for authentication were 5.5% and 0.1%, respectively. The accuracy of the identification was 94.0% for 20 users.

The user identification and authentication require various touch data such as location, speed, force, and gestures as features that are of the most importance for the better performance. Therefore, there have been researches to extract the gesture data from the touch data by means of machine learning algorithms. Xiao et al. [146] came up with an approach for estimating 3D finger angles such as pitch and yaw relative to a touchscreen’s surface. It used the capacitive image that was the capacitance measured at each point of a touch sensor’s capacitive grid. The pitch was estimated by a Gaussian process regression with 42 features and the yaw was computed by the major axis of the ellipsoid of the sensed touch pixels. While mean pitch errors were 9.7 and 14.5, mean yaw errors were 26.8 and 31.7 for phone and watch, respectively. It also proposed the possible applications such as zoom and rotate functions even with a single-touch event which would be very useful in small-size watch displays.

Boceck et al. [161] extracted the pressure from capacitive images by using CNN. It used a ReLU function as an activation function, and dropout layers. Final fully connected layers contained LeakyReLU and L1/L2 regularization. They achieved the lower root mean square error of 471.99 g, compared to 583.36 g and 593.51 g of RF and SVM.

Schweigert et al. [162] added knuckle related features by differentiating knuckles from fingers and classified 17 finger and knuckle gestures by CNN and long short-term memory (LSTM). CNN layers extracted the representation from the 15 × 27 capacitive image and then LSTM layers generated 17 outputs over 50 consecutive images through a softmax activation function. Seventeen gestures contained tap, two tap, swipe left, swipe right, swipe up, swipe down, two swipe up, two swipe down, circle, arrowhead left, arrowhead right, rotate, and five additional gestures. It achieved the accuracies of 97.9% and 86.8% on train and test sets, respectively.

Weir et al. [137] adopted GPR to find a mapping between two-dimensional reported touch locations and a corresponding intended two-dimensional touch location on the display. It collected the touch data by randomly displaying the crosshairs that the users had to touch. The resultant average reductions in error rates were 23.79% for 2 mm buttons, 14.79% for 3 mm buttons, and 5.11% for 4 mm buttons.

Fischer et al. [155] presented a system using capacitive sensing to accurately classify hand touches and proximity. Touch data were collected through 50 finger touches with different fingers, angles, locations and speeds, 25 glove touches, and 20 non-valid touches. Then, the collected data were further processed by dimensionality reduction, data augmentation, and normalization. Hidden Markov model (HMM) and RNN of gated recurrent units (GRUs) were evaluated as the classifier over three classes of non-touch, near, and touch. The RNN model showed the better overall accuracy of 97.1% even with gloves while HMM achieved the accuracy performance of 84.21%.

Kumar et al. [158] improved the accuracy of touch locations by CNN. The dataset consisted of capacitive images at the dimension of 15 × 27 as well as the estimated touch positions represented by the centroid of the touch blob. The proposed CNN achieved an average error offset of 41.23 pixels based on a screen resolution of 1920 × 1080 on a 4.94 inch display. It was the improvement of 23.0%, compared to the error offset of 50.7 pixels of the standard touch controller.

Kim et al. [160] introduced a sensor substitution system that generates time-series sensor data based on RNN. It estimated capacitive touch sensor signals by motion and audio signals caused by touch. By other types of multivariate time-series signals, the touch sensor sequences were supplemented even at dynamic and hostile environments that degraded the touch sensor’s performance.

Le et al. [154] differentiated between touches of fingers and palm to devise an additional input modality. Their PalmTouch showed possible one-handed and two-handed palm interactions by placing flat hand or fist on the screen. It used the capacitive images for the features and CNN for the classification, leading to the accuracy of 99.53%.

Le et al. [153] proposed the finger-aware interaction that identified fingers touching the whole device surface to add the input modalities. In a prototype, front and back side touchscreens were developed by two stacked smartphones and their three edges were attached with 37 capacitive sensors. It used CNN with L2 regularization to obtain 15 outputs that were a three-dimensional coordinate, (x, y, z), for five fingers. The identification accuracy was 95.78% with the position error of 0.74 cm.

Seol et al. [157,163,203] employed the machine learning based classifiers such as SVM and autoencoder-based AD for finger and stylus discrimination. The higher frequency pulses were transmitted from a stylus to a capacitive touchscreen and the outputs of the charge amplifiers were sampled by ADC and classified by the classifier into no-touch, finger-touch, and stylus-touch. While no-touch and finger-touch were the constant level sample sequences, the stylus-touch was the random sequence between two constant levels. Therefore, SVM and AD classifiers achieved lower bit error rates (BERs) than 10−6 with the palm rejection. In addition, it was shown that its data communication algorithm could be applied in data transmission and user identification.

In this paper, we have provided an extensive review on touchscreen technologies. We mainly dealt with the overview of various touchscreen schemes from resistive to optical methods, and two main research directions of SNR improvement and stylus support as well as machine learning approaches in mutual capacitance capacitive touchscreens that are the most widely adopted scheme at present in smartphones, tablet PCs, notebook PCs, and smartwatches. For the aspect of the SNR improvement, accumulation, differential sensing, TMDS, dual mode of self and mutual capacitance, CDMS, delta-sigma modulation, and multiple-frequency driving have been introduced. High SNRs have been achieved by reduced noises and increased dynamic ranges. For the stylus support, passive, active, multiple frequency driving, ECR, and ML-based schemes have been addressed along with their pressure sensing capabilities. The machine learning applications in capacitive touchscreens have been classified in four categories of user identification/authentication, gesture detection, accuracy improvement, and input discrimination by means of a variety of algorithms such as DT, RF, NB, RBFN, BPNN, SVM, GPR, CNN, AD, and RNN.

Although many advancements have been accomplished in touchscreen technologies, challenges still exist in various fields. We will point out some of these challenges. We hope that this review not only helps the understanding of the touchscreen technologies but also paves the way to future researches on integrating machine learning algorithms into touchscreens for more various applications. As the resolutions of touchscreens are getting larger, fingerprints can be detected on any locations of the screen without additional sensors [204,205]. However, high power consumption and low scan rate should be addressed. One of possible solutions would be the super-resolution (SR) that gives rise to the high resolution capacitive image from the low resolution capacitive image. Many deep-learning-based SR algorithms have been reported [206,207]. As discussed in the previous sections, the SNR is one of the most important performance metrics and the high SNR is required to integrate touch sensing and display driving electronics into one integrated circuit. There exists the research field of de-noising that generates the clean one from the noisy image. Therefore, this de-noising scheme can be applied to enhance the SNR over the acquired capacitive images. Lastly, because latest smartphones, tablet PCs, and notebook PCs contain many sensors such as cameras, IR sensors, microphones, accelerometers, and gyroscopes besides touchscreens, there will keep being many approaches based on multi-sensor fusion technologies in the user interface field.

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