controlling leds with tft display quotation

In this Arduino touch screen tutorial we will learn how to use TFT LCD Touch Screen with Arduino. You can watch the following video or read the written tutorial below.

The next example is controlling an RGB LED using these three RGB sliders. For example if we start to slide the blue slider, the LED will light up in blue and increase the light as we would go to the maximum value. So the sliders can move from 0 to 255 and with their combination we can set any color to the RGB LED,  but just keep in mind that the LED cannot represent the colors that much accurate.

As an example I am using a 3.2” TFT Touch Screen in a combination with a TFT LCD Arduino Mega Shield. We need a shield because the TFT Touch screen works at 3.3V and the Arduino Mega outputs are 5 V. For the first example I have the HC-SR04 ultrasonic sensor, then for the second example an RGB LED with three resistors and a push button for the game example. Also I had to make a custom made pin header like this, by soldering pin headers and bend on of them so I could insert them in between the Arduino Board and the TFT Shield.

Here’s the circuit schematic. We will use the GND pin, the digital pins from 8 to 13, as well as the pin number 14. As the 5V pins are already used by the TFT Screen I will use the pin number 13 as VCC, by setting it right away high in the setup section of code.

As the code is a bit longer and for better understanding I will post the source code of the program in sections with description for each section. And at the end of this article I will post the complete source code.

I will use the UTFT and URTouch libraries made by Henning Karlsen. Here I would like to say thanks to him for the incredible work he has done. The libraries enable really easy use of the TFT Screens, and they work with many different TFT screens sizes, shields and controllers. You can download these libraries from his website, RinkyDinkElectronics.com and also find a lot of demo examples and detailed documentation of how to use them.

After we include the libraries we need to create UTFT and URTouch objects. The parameters of these objects depends on the model of the TFT Screen and Shield and these details can be also found in the documentation of the libraries.

Next we need to define the fonts that are coming with the libraries and also define some variables needed for the program. In the setup section we need to initiate the screen and the touch, define the pin modes for the connected sensor, the led and the button, and initially call the drawHomeSreen() custom function, which will draw the home screen of the program.

So now I will explain how we can make the home screen of the program. With the setBackColor() function we need to set the background color of the text, black one in our case. Then we need to set the color to white, set the big font and using the print() function, we will print the string “Arduino TFT Tutorial” at the center of the screen and 10 pixels  down the Y – Axis of the screen. Next we will set the color to red and draw the red line below the text. After that we need to set the color back to white, and print the two other strings, “by HowToMechatronics.com” using the small font and “Select Example” using the big font.

Next is the distance sensor button. First we need to set the color and then using the fillRoundRect() function we will draw the rounded rectangle. Then we will set the color back to white and using the drawRoundRect() function we will draw another rounded rectangle on top of the previous one, but this one will be without a fill so the overall appearance of the button looks like it has a frame. On top of the button we will print the text using the big font and the same background color as the fill of the button. The same procedure goes for the two other buttons.

Here’s that function which uses the ultrasonic sensor to calculate the distance and print the values with SevenSegNum font in green color, either in centimeters or inches. If you need more details how the ultrasonic sensor works you can check my particular tutorialfor that. Back in the loop section we can see what happens when we press the select unit buttons as well as the back button.

Ok next is the RGB LED Control example. If we press the second button, the drawLedControl() custom function will be called only once for drawing the graphic of that example and the setLedColor() custom function will be repeatedly called. In this function we use the touch screen to set the values of the 3 sliders from 0 to 255. With the if statements we confine the area of each slider and get the X value of the slider. So the values of the X coordinate of each slider are from 38 to 310 pixels and we need to map these values into values from 0 to 255 which will be used as a PWM signal for lighting up the LED. If you need more details how the RGB LED works you can check my particular tutorialfor that. The rest of the code in this custom function is for drawing the sliders. Back in the loop section we only have the back button which also turns off the LED when pressed.

In order the code to work and compile you will have to include an addition “.c” file in the same directory with the Arduino sketch. This file is for the third game example and it’s a bitmap of the bird. For more details how this part of the code work  you can check my particular tutorial. Here you can download that file:

were missing for my display (hailege, 2,8 tft, spi, il9431, https://www.amazon.de/-/en/gp/product/B07YTWRZGR/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1). so it might just be that the led backlight isnt being turned on. but of course the tip might not help with the st7796s.

The liquid crystal display (LCD) technology has been used in several electronic products over the years. There are more reasons for LCDs to be more endearing than CRTs.

We present the design of a 320x256 RGB LED electronic display board intended to be used as a platform to present information of current and future events in schools or office buildings. The proposed design can display up to eight different images, which may include text and graphics. The rendering of these images is done periodically, with the duration of the period being controlled by the user. The images can be created from slides of a power point presentation or directly from stored photos. Loading of new images to the display board is done wirelessly via WiFi from an Android App running on a portable device such as a tablet or a smartphone. We present experimental results on a completed and fully operational prototype system, which includes the RGB LED display board together with the custom-built microcontroller board as well as the Android App. While the current use-application is as an informative message board in a school set-up, the proposed system can be used in any other indoor application. For outdoor usage, the system would require an additional weather-proof enclosure and fixtures.Metadata Overview

There are generally three main categories of electronic displays. In the first category, simpler and more traditional, one can find the systems that use character LCD displays with two or more rows and 10, 20 or other number of characters per row, such as the 16x2 character LCD [1]. This type of display can typically display static or moving text messages [2]. The second category includes all systems that use graphic LCD displays. Examples in this category include small embedded LCD and touch-screen TFT displays (e.g., 320x240 pixels), digital photo displays, and systems that use LCD monitors as the primary method to display text and images [3]. Finally, in the third category, we can find RGB LED displays. Examples in this category include mostly outdoor scoreboard displays as well as highway and business side billboards. Their complexity and costs are high and depend on the size, which is typically large; see for example the commercial products from Daktronics [4]. However, one can find smaller size examples created by hobbyists, including designs that use just one 64x64 RGB LED matrix panels [5] or just one 32x32 matrix panel [6]. The advantages of RGB LED displays compared to the color LCD displays include better visibility in sunlight conditions, better contrast for crisper details, purer colors, and reduced reflection. However, their power consumption is typically large and their cost relatively high. Finally, while most of these example designs are controlled by microcontrollers, there are solutions that use field programmable gate arrays (FPGAs) as well for improved speeds [7].

The problem of designing and prototyping large RGB LED displays has been less researched in the past literature. That is because this is more a problem of development rather than of theoretical research and because there exists already many commercial offerings of such displays from established companies, some of which were mentioned in the previous paragraph. Nevertheless, one can find prior research studies on power supplies for RGB LED displays or especially on new circuit solutions for LED drivers. For example, the study in [10] proposed a microcontroller-based driver whose objective was to maximize the LED efficiency. They reported a prototype for a 3x3 LED matrix and achieved efficiency greater than 92%. A dimmable multi-channel RGB LED driver was reported and studied with a nine LED string in [11]. Energy savings was the objective of the LED driver studied in [12]. The driver uses a multilevel pulse width modulation (MPWM) driving method combined with simple video signal conversion techniques. It was demonstrated for a 32x32 LED pixels display. The study in [13] addresses the challenges of active image adjustments and processing, considering the non-linearity of the LED display element. They propose a method for the nonlinear adjustment of the images contrast. The advantage of the proposed method is that the images can be displayed on OLED or LED displays with the unified luminance signal, for grayscale images, or with separate RGB controls. Other studies focused on the design of individual LEDs; such an example is the study in [14] that proposed solutions based on dielectric compound parabolic concentrators (CPCs) in order to increase brightness. Such studies are outside the scope of our paper, which focuses on the system integration design aspects, both hardware and software, and prototyping of large RGB LED displays.

In this paper, we present the completely open-source design of a 320x256 RGB LED electronic display board intended to be used a platform to present information of current and future events in schools or office buildings. While the current use-application is as an informative message board in a school set-up, the proposed system can be used in any other indoor or outdoor application (for outdoor usage, the system will need weather-proof casing though). Designed to be cost-effective yet extendable, we hope this design will be adopted and improved in other practical and educational settings.

The integrated 2MB of flash memory of the MCU is used as the primary frame buffer that stores the currently displayed image on the display. It is shown as the “Frame Buffer 2” in Fig. 2. An additional external 2MB parallel SRAM chip is used to store the image to be displayed next. This memory, indicated as “Frame Buffer 1” in Fig. 2, effectively plays the role of a cache between the MCU and the memory system formed by eight different Flash memory chips indicated as “Flash 1..8” in Fig. 2. The eight 2MB flash chips store the current presentation slides or “project”, with one slide per flash chip. The flash chips—physically placed close to the microcontroller to reduce communication delays—were chosen due to their low cost, ease of use, and large number of write cycles (100,000 cycles typically). High performance is achieved by the MCU’s 50MHz External Bus Interface (EBI) feature that is exploited to fetch image data into the primary frame buffer, “Frame Buffer 2”. The WiFi module is the popular and low cost ESP8266 module, which provides its own connection to the device that runs the Android App and thus it does not require a separate Internet service. A new “project” represents eight different images, which are uploaded via the WiFi connection from the App to the eight flash chips.

For debugging and programming purposes, an FT234 USB-UART bridge is included in the design, with its ground isolated from the rest of the system’s electric circuits. To power the RGB LED panels, an off-the-shelf 5V 50A power supply is used while the controller board is powered by a separate 12V 50A off-the-shelf power supply.

In addition to driving the display, the microcontroller also has several other tasks to service. During normal operation, up to eight images are stored across eight 256KB serial flash memory chips. This external non-volatile memory acts as long-term image storage, and stores image data across MCU resets and power cycles. It is accessed through a Serial Peripheral Interface (SPI). The MCU can read and write entire images worth of data to a flash chip in about three seconds. When a project is programmed into the system, each image is stored in the SPI flash, while the number of images for the project and the cycle time between images is stored into the microcontroller’s internal flash.

The microcontroller also has an external parallel 256KB SRAM. It is able to read and write data to this SRAM through the External Bus Interface (EBI). EBI allows external memory to be attached to the MCU and it treats it just like any other virtual memory address space. This allows data in EBI SRAM to be treated like a normal byte array in C firmware. During normal operation, while an image is being shown on the screen, the next image to be displayed is moved from SPI Flash into EBI SRAM. When the image is ready to be displayed, it is moved all at once from EBI SRAM into the internal frame buffer and shown on the screen. In this memory structure, EBI SRAM acts as a data cache, since moving data from EBI SRAM into internal RAM is much faster than moving data from SPI Flash into internal RAM. Using this technique, image transitions appear seamless.

The MCU has a serial interface with a WiFi module included on the logic board. This is the main interface between the Android app (described in the next section) and the system. Through the WiFi interface, the user can turn the screen on and off, adjust the brightness of the screen, and load new projects into the system. The WiFi module and the MCU communicate through a UART interface. A ring buffer in MCU firmware allows massive amounts of data to be transferred at a time from the WiFi module into the MCU.

A custom Android App, named MU-MatriX (available already for download on Google Play) was developed to allow the user to create and upload to the display system new “projects”. A “project” consists of eight images that form a presentation displayed periodically at a configured interval. The app stores each project’s name, set of images, and duration between image switch into its internal application storage. After naming a new project, a user can populate the project with images, selecting them one-by-one from their device. The images can maintain the aspect ratio of the original image or stretch to fit the size of the display board. There is also the option to rotate images in 90 degree intervals before adding them into the project. In the background, any selected image is saved off into a 320x256 bitmap with black background filling in any gaps created by the aspect ratio lock. As images are being added to a project, they can be reordered by simple up and down arrows next to their thumbnail on the “Edit Project” screen. A spinner widget provides a drop-down selection for the project-level property of duration between slides.

The default display board device is automatically stored under the user’s device list on app installation. The IP address and port number used by default for the ESP8266 WiFi module (on the logic board) are simply placed under a device name “Default Display Board”. The app allows more than just this one display board configuration to be saved in memory, allowing for this system to scale to multiple screens all managed under one app. A device control screen gives the app simple commands to send the Wifi module on the Logic Board: Power On, Power Off, and a screen brightness slider that sends a numeric value between 5 and 100. Simple WiFi messages holding single-line commands are sent over the network using the TCP protocol. Uploading a project to the Logic Board from the application takes a little bit more work and is given its own screen within the app. After selecting one of the projects, one of the hardware devices, and pressing “Upload”, a progress bar and message will become visible on the screen tracking the conversion and transmission of each image within that project. After all the images have been sent, a message will notify the user of the upload completion.

The conversion step of the project upload performs a variety of operations to turn the 320x256 bitmap into a 245,760 byte long array. This contains the hexadecimal values which represent the intensity of color for each LED in the pixel’s RGB matrix. The transmission operation starts by telling the Logic board to stop multiplexing images across its screen (to allow it to focus on receiving the new data) and clear the parallel RAM chip (about to be filled with the image data). The app separates the long byte array of data into smaller chunks that it sends across a TCP connection to the ESP8266 WiFi module on a new thread. This thread sends a chunk of the image data to the ESP module, and after receiving confirmation from the microcontroller that the message arrived safely, it updates the progress bar on the main thread via a Handler. After one full image is sent, commands are sent to specify which non-volatile flash chip to store the image into. After the full project is sent, a message containing the number of images the project contains and the time duration between images is sent over WiFi again to be stored into non-volatile program flash and used during the state machine operations.

The electronic display system consumes significant power due to the large number of LEDs. The power supply can provide up to 50 A. Thus, users must be cautious of the high currents supplied to the RGB LED panels. In our current prototype, connections are accessible on the back of the panel, so, there is the risk of immediate contact with such connections. We plan to enclose the entire panel inside a wood enclosure with a back lid such that no electrical contacts can be directly accessed (such an enclosure is not part of the current design and is not described in this paper or in the documentation).

As already mentioned earlier, the MCU on the controller board has many features to help with debugging. These features include a rugged USB debugging interface, which was implemented with a UART to USB bridge. This allows a user to connect to the microcontroller through a 115.2Kb serial connection from a software terminal such as Putty. This was a crucial debugging feature when developing the MCU firmware. The MCU’s analog to digital converter was also used to be able to measure system level power supply voltages. The ADC can be initialized through the USB interface, and results can be printed through the serial interface. The ADC is only initialized when the user requests it; this allows for the CPU bandwidth to be maximized when the debug feature is not needed.

The following table lists the metrics or figures of merit that were tested and validated using the complete hardware prototype of the electronic display system as well as the fully operational Android App.

The objective of this experiment was to verify that eight images can be saved to the flash chips located on the logic board and that all images can be displayed correctly in order and repeatedly. The testing strategy was to cycle through all eight flash chips, write and then read the image data from, and drive the LED panels to display each of the images. First, all eight flash chips were written to with eight different images. Then, each image was read from the flash chips and displayed onto the panels. The images displayed on the panels were verified whether they were the desired image. This was repeated five times and all images were changed each repetition to verify the reliability of the entire process of writing and reading images into the flash chips. During this process, we monitored the error (as percentage of pixel data written or read incorrectly) during both writing to and reading from the flash chips. This test was successful with an outcome of 0% error.

The objective for this experiment was to identify the optimal number of bits for the color representation used to render images. The constraints of this experiments included the amount of memory available inside the microcontroller to implement the buffer (stores the data of the image currently being displayed) as well as the time it takes to upload all eight images from the App to the board’s flash chips. The desired color representation was 12-bit color code, which would be capable of generating 4096 different colors per pixel. However, due to how the 5x4 panels (64x64 pixels each) are driven by the only 8 PWM frames (giving 3 bits per color channel) with information about pixels forming an image, we arrived at the compromise of using only a 9-bit color code, which is still capable of generating 512 different colors per pixel. This color code ensures that images have reasonable color resolution to make them appear in natural colors onto the display. While 12-bit color code would obviously be preferable, the 9-bit color code is sufficient to be able to display rich colors, yet to restrict the amount of memory required, achieve better performance (as refresh rate), and to naturally match the PWM control of the 64x64 LED panels.

The objective of this experiment was to verify the Android App and the logic board can communicate successfully via WiFi. The ESP8266 module, mounted on the logic board, was used for this connection. The test plan for this experiment involved sending 20 images of data from the Android App to the logic board and verifying that no data was lost during the transfer. Testing to be sure that no data was lost in the transfer involved displaying the image onto the screen and verifying that the image appeared as intended. This test was successful with an outcome of 0% error.

The objective of this experiment was to verify that the microcontroller was fast enough to properly display the images without any flicker. This was performed by using an oscilloscope to measure the frequency of the clock and latch signals and seeing that the images displayed on the panels did not flicker. This procedure was repeated five times on five different images to verify that a range of different detailed images can be shown without flickering. This test was successful with an achieved refresh rate of 30Hz.

The electronic display is completely reproducible as all the hardware components are readily available from various vendors and the complete design files are made publicly available. Designed to be cost-effective yet extendable, we hope this design will be adopted and improved upon in other practical and educational settings. At the minimum, the display can be replicated as presented and used out of the box. We envision two main ways to extend it. First, the display size could be increased by adding more 64x64 RGB LED panels to the rows and columns. This will potentially require power supplies capable of providing higher currents. Also, the firmware residing on the MCU of the controller board will need to be changed to account for display sizes different than the current 320x256 LEDs. Second, the system could be extended to add the capability of playing video. Such an extension will be more challenging. It could be done by keeping the display continuously connected to the App (or the Internet), which would stream desired videos. Another idea is to modify the controller board in order to include larger capacity flash memory or a micro SD card, which could store large video files. While doable, such changes are major changes to the current design.

We believe that our design has more unique value in educational contexts, because in business contexts, companies can purchase such display boards from established digital display power-houses such as Daktronics. In educational contexts, one can use the proposed design as an open-source flexible “workbench” for various studies in courses on embedded systems, digital signal processing and design, or wireless communications. For instance, in a typical embedded systems course, examples of such studies may include: 1) Investigation of the power consumption and of firmware techniques to reduce it, 2) Laboratory experiments where students are required to implement essential modules of the firmware. Examples of such modules can cover: the WiFi communication between the design and the mobile app, the module responsible for debugging features via the UART peripheral of the microcontroller, etc. The existing design could serve as a platform to verify software development tasks covering microcontroller firmware and mobile app development as well.

The bill of materials for the electronic display system is listed in Table 2. Detailed specifics on each of the electronic components (i.e., resistors, capacitors, etc.) are not included here for brevity (the list is too long); however, they are available in the online repository.

Complete design files, both hardware and software, and documentation are made publicly available in the online repository. In the simplest scenario, one can simply duplicate the proposed electronic display system. The most challenging aspect in this process would be the soldering of all the SMD components on the logic board, because it requires prior experience and SMD soldering skills as well as the availability of a reflow oven. Otherwise, everything is rather simple and straightforward to assemble and to program. Extensive efforts were put into implementing a comprehensive help and debugging capability for the logic board. To use this capability, one would only need to connect a serial terminal (such as Putty) to the USB port of the logic board, then, follow the prompts. More detailed information on this debug ability is provided in the documentation for the firmware.

Perhaps the most notable aspect regarding the technical implementation of this design is that it provided an excellent educational value for the duration of two semesters. More specifically, 1) it required us to develop our own method of “packetizing” the pixel data of all eight images transmitted from the mobile app to the display board via WiFi and 2) it provided a context where hardware and firmware designers needed to team-up with mobile app software developers and create a product that works reliably and  repeatedly. This required good communication skills and collaboration to develop common testing strategies.

The entire design is made open source and publicly available. The following repository contains both hardware and software design files. Additional information, including a project poster and a short video presentation is available at (project “RGB LED Electronic Display”): http://dejazzer.com/hardware.html (archived version)

We presented a completely open source design of a 320x256 RGB LED electronic display board created from a 5x4 array of 64x64 pixels RGB off-the-shelf panels. The electronic display is intended to be used as a display board of information of current and future events in schools or office buildings. The information is presented under the form of eight images or slides that are displayed periodically by the board. The images can be uploaded to the board system via WiFi from an Android App that was custom developed for this purpose. A complete prototype was built and tested successfully. Despite its relatively high overall cost, the proposed electronic display system is extremely easy to use. The complete design files, both hardware and software, are made publicly available. As such, we hope that this design can serve as a starting point for other researchers and educators who are interested in developing more complex RGB LED electronic displays.

As discussed in the Section “Reuse potential and adaptability” above, the proposed electronic display could be extended in several ways. Currently, we are planning to extend the design in order to be able to play video as well.

Use the ezPixel FPGA Board to Control Giant Arrays of Smart LEDs, IEEE Spectrum, 19 Dec. 2017, [Online]. Available: https://spectrum.ieee.org/geek-life/hands-on/use-the-ezpixel-fpga-board-to-control-giant-arrays-of-smart-leds

X. Lv, K.H. Loo, Y.M. Lai, and C.K. Tse, "Energy-saving driver design for full-color large-area LED display panel systems," IEEE Trans. on Industrial Electronics, vol. 61, no. 9, 2014.

M. Andrei, S. Moldovanu, and N. Nistor, "Nonlinear transformations applied to image processing on the RGB LED display," Int. Symposium for Design and Technology in Electronic Packaging​ (SIITME), 2018.

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Configurable: always the right power for your LED Rail; the SmartLEDRover software enables configuring SmartLED converters individually for different TFT display types

A thin-film-transistor liquid-crystal display (TFT LCD) is a variant of a liquid-crystal display that uses thin-film-transistor technologyactive matrix LCD, in contrast to passive matrix LCDs or simple, direct-driven (i.e. with segments directly connected to electronics outside the LCD) LCDs with a few segments.

In February 1957, John Wallmark of RCA filed a patent for a thin film MOSFET. Paul K. Weimer, also of RCA implemented Wallmark"s ideas and developed the thin-film transistor (TFT) in 1962, a type of MOSFET distinct from the standard bulk MOSFET. It was made with thin films of cadmium selenide and cadmium sulfide. The idea of a TFT-based liquid-crystal display (LCD) was conceived by Bernard Lechner of RCA Laboratories in 1968. In 1971, Lechner, F. J. Marlowe, E. O. Nester and J. Tults demonstrated a 2-by-18 matrix display driven by a hybrid circuit using the dynamic scattering mode of LCDs.T. Peter Brody, J. A. Asars and G. D. Dixon at Westinghouse Research Laboratories developed a CdSe (cadmium selenide) TFT, which they used to demonstrate the first CdSe thin-film-transistor liquid-crystal display (TFT LCD).active-matrix liquid-crystal display (AM LCD) using CdSe TFTs in 1974, and then Brody coined the term "active matrix" in 1975.high-resolution and high-quality electronic visual display devices use TFT-based active matrix displays.

The liquid crystal displays used in calculators and other devices with similarly simple displays have direct-driven image elements, and therefore a voltage can be easily applied across just one segment of these types of displays without interfering with the other segments. This would be impractical for a large display, because it would have a large number of (color) picture elements (pixels), and thus it would require millions of connections, both top and bottom for each one of the three colors (red, green and blue) of every pixel. To avoid this issue, the pixels are addressed in rows and columns, reducing the connection count from millions down to thousands. The column and row wires attach to transistor switches, one for each pixel. The one-way current passing characteristic of the transistor prevents the charge that is being applied to each pixel from being drained between refreshes to a display"s image. Each pixel is a small capacitor with a layer of insulating liquid crystal sandwiched between transparent conductive ITO layers.

The circuit layout process of a TFT-LCD is very similar to that of semiconductor products. However, rather than fabricating the transistors from silicon, that is formed into a crystalline silicon wafer, they are made from a thin film of amorphous silicon that is deposited on a glass panel. The silicon layer for TFT-LCDs is typically deposited using the PECVD process.

Polycrystalline silicon is sometimes used in displays requiring higher TFT performance. Examples include small high-resolution displays such as those found in projectors or viewfinders. Amorphous silicon-based TFTs are by far the most common, due to their lower production cost, whereas polycrystalline silicon TFTs are more costly and much more difficult to produce.

The twisted nematic display is one of the oldest and frequently cheapest kind of LCD display technologies available. TN displays benefit from fast pixel response times and less smearing than other LCD display technology, but suffer from poor color reproduction and limited viewing angles, especially in the vertical direction. Colors will shift, potentially to the point of completely inverting, when viewed at an angle that is not perpendicular to the display. Modern, high end consumer products have developed methods to overcome the technology"s shortcomings, such as RTC (Response Time Compensation / Overdrive) technologies. Modern TN displays can look significantly better than older TN displays from decades earlier, but overall TN has inferior viewing angles and poor color in comparison to other technology.

Most TN panels can represent colors using only six bits per RGB channel, or 18 bit in total, and are unable to display the 16.7 million color shades (24-bit truecolor) that are available using 24-bit color. Instead, these panels display interpolated 24-bit color using a dithering method that combines adjacent pixels to simulate the desired shade. They can also use a form of temporal dithering called Frame Rate Control (FRC), which cycles between different shades with each new frame to simulate an intermediate shade. Such 18 bit panels with dithering are sometimes advertised as having "16.2 million colors". These color simulation methods are noticeable to many people and highly bothersome to some.gamut (often referred to as a percentage of the NTSC 1953 color gamut) are also due to backlighting technology. It is not uncommon for older displays to range from 10% to 26% of the NTSC color gamut, whereas other kind of displays, utilizing more complicated CCFL or LED phosphor formulations or RGB LED backlights, may extend past 100% of the NTSC color gamut, a difference quite perceivable by the human eye.

The transmittance of a pixel of an LCD panel typically does not change linearly with the applied voltage,sRGB standard for computer monitors requires a specific nonlinear dependence of the amount of emitted light as a function of the RGB value.

Initial iterations of IPS technology were characterised by slow response time and a low contrast ratio but later revisions have made marked improvements to these shortcomings. Because of its wide viewing angle and accurate color reproduction (with almost no off-angle color shift), IPS is widely employed in high-end monitors aimed at professional graphic artists, although with the recent fall in price it has been seen in the mainstream market as well. IPS technology was sold to Panasonic by Hitachi.

IPS has since been superseded by S-IPS (Super-IPS, Hitachi Ltd. in 1998), which has all the benefits of IPS technology with the addition of improved pixel refresh timing.

In 2004, Hydis Technologies Co., Ltd licensed its AFFS patent to Japan"s Hitachi Displays. Hitachi is using AFFS to manufacture high end panels in their product line. In 2006, Hydis also licensed its AFFS to Sanyo Epson Imaging Devices Corporation.

A technology developed by Samsung is Super PLS, which bears similarities to IPS panels, has wider viewing angles, better image quality, increased brightness, and lower production costs. PLS technology debuted in the PC display market with the release of the Samsung S27A850 and S24A850 monitors in September 2011.

TFT dual-transistor pixel or cell technology is a reflective-display technology for use in very-low-power-consumption applications such as electronic shelf labels (ESL), digital watches, or metering. DTP involves adding a secondary transistor gate in the single TFT cell to maintain the display of a pixel during a period of 1s without loss of image or without degrading the TFT transistors over time. By slowing the refresh rate of the standard frequency from 60 Hz to 1 Hz, DTP claims to increase the power efficiency by multiple orders of magnitude.

Due to the very high cost of building TFT factories, there are few major OEM panel vendors for large display panels. The glass panel suppliers are as follows:

External consumer display devices like a TFT LCD feature one or more analog VGA, DVI, HDMI, or DisplayPort interface, with many featuring a selection of these interfaces. Inside external display devices there is a controller board that will convert the video signal using color mapping and image scaling usually employing the discrete cosine transform (DCT) in order to convert any video source like CVBS, VGA, DVI, HDMI, etc. into digital RGB at the native resolution of the display panel. In a laptop the graphics chip will directly produce a signal suitable for connection to the built-in TFT display. A control mechanism for the backlight is usually included on the same controller board.

The low level interface of STN, DSTN, or TFT display panels use either single ended TTL 5 V signal for older displays or TTL 3.3 V for slightly newer displays that transmits the pixel clock, horizontal sync, vertical sync, digital red, digital green, digital blue in parallel. Some models (for example the AT070TN92) also feature input/display enable, horizontal scan direction and vertical scan direction signals.

New and large (>15") TFT displays often use LVDS signaling that transmits the same contents as the parallel interface (Hsync, Vsync, RGB) but will put control and RGB bits into a number of serial transmission lines synchronized to a clock whose rate is equal to the pixel rate. LVDS transmits seven bits per clock per data line, with six bits being data and one bit used to signal if the other six bits need to be inverted in order to maintain DC balance. Low-cost TFT displays often have three data lines and therefore only directly support 18 bits per pixel. Upscale displays have four or five data lines to support 24 bits per pixel (truecolor) or 30 bits per pixel respectively. Panel manufacturers are slowly replacing LVDS with Internal DisplayPort and Embedded DisplayPort, which allow sixfold reduction of the number of differential pairs.

Backlight intensity is usually controlled by varying a few volts DC, or generating a PWM signal, or adjusting a potentiometer or simply fixed. This in turn controls a high-voltage (1.3 kV) DC-AC inverter or a matrix of LEDs. The method to control the intensity of LED is to pulse them with PWM which can be source of harmonic flicker.

The bare display panel will only accept a digital video signal at the resolution determined by the panel pixel matrix designed at manufacture. Some screen panels will ignore the LSB bits of the color information to present a consistent interface (8 bit -> 6 bit/color x3).

With analogue signals like VGA, the display controller also needs to perform a high speed analog to digital conversion. With digital input signals like DVI or HDMI some simple reordering of the bits is needed before feeding it to the rescaler if the input resolution doesn"t match the display panel resolution.

Kawamoto, H. (2012). "The Inventors of TFT Active-Matrix LCD Receive the 2011 IEEE Nishizawa Medal". Journal of Display Technology. 8 (1): 3–4. Bibcode:2012JDisT...8....3K. doi:10.1109/JDT.2011.2177740. ISSN 1551-319X.

Brody, T. Peter; Asars, J. A.; Dixon, G. D. (November 1973). "A 6 × 6 inch 20 lines-per-inch liquid-crystal display panel". 20 (11): 995–1001. Bibcode:1973ITED...20..995B. doi:10.1109/T-ED.1973.17780. ISSN 0018-9383.

K. H. Lee; H. Y. Kim; K. H. Park; S. J. Jang; I. C. Park & J. Y. Lee (June 2006). "A Novel Outdoor Readability of Portable TFT-LCD with AFFS Technology". SID Symposium Digest of Technical Papers. AIP. 37 (1): 1079–82. doi:10.1889/1.2433159. S2CID 129569963.

Kim, Sae-Bom; Kim, Woong-Ki; Chounlamany, Vanseng; Seo, Jaehwan; Yoo, Jisu; Jo, Hun-Je; Jung, Jinho (15 August 2012). "Identification of multi-level toxicity of liquid crystal display wastewater toward Daphnia magna and Moina macrocopa". Journal of Hazardous Materials. Seoul, Korea; Laos, Lao. 227–228: 327–333. doi:10.1016/j.jhazmat.2012.05.059. PMID 22677053.

Display graphics, text, or video with HED’s range of color graphical display modules. Rugged, sunlight readable and sealed to IP67, HED displays can be mounted in the cab or outside your vehicle. Do-It-Yourself programming and diagnostic software tools allows users to easily and quickly develop screens to show all the critical system parameters using gauges, bar graphs, text and other graphical methods for easy user interpretation. These features allow for gauges and camera monitors to be consolidated all onto one display.

For full-colour display solutions, conventional RGB colour conversion chips have inadequate luminance and low yield issues when the LED chip size is <20 μm

Recently, halide perovskites with the general formula of APbX3 (A = CH3NH3+, Cs+, FA+, or mixture; X = I−, Br−, Cl−) have become an emerging class of colloidal QDs for next-generation displays11)

Perovskite QDs for wide colour gamut conversion. a Colloidal CsPbX3 (X = Cl, Br, I) QD solutions in toluene under a UV lamp and b their representative PL spectra. c CIE chromaticity coordinates (dark points) from the emissions of CsPbX3 QDs compared with those of commercialised LCD TVs (dashed white line), reaching 140% of the NTSC colour standard (solid white line). Reproduced from ref.

Now, we divert our attention to PL-based PQD-LEDs, which are closer to commercial applications than are EL-based devices. PQDs are very attractive materials for QDPL-based µ-LEDs because of their excellent optical and physical properties as mentioned above. With superior colour conversion capability to generate RGB lights, PQDs have been utilised in PL-based white LEDs, and ultrahigh luminous efficiency >100 lm/W (the standard for practical use in room lighting)

Strategies for improving the stability of perovskite QDs. a A-site or B-site doping. b Surface engineering. c Encapsulation with a polymer or oxide matrix. d More efficient device packaging (i.e., remote-type design can enhance the stability of QDs compared with the prototype structure). Reproduced from a ref. b ref. c ref. d ref.

Currently, the combination of ligand cross-linking and polymeric encapsulation has been widely used to protect CdSe-/InP-based QDs in commercial QD displays. Moreover, it is well known that QD shell layers are very critical to enhance the QD stability as well as the device performance, such as colour purity, quantum yield, and efficiency roll-off. Type I core/shell QDs are commonly used in QD-based LEDs, in which the core QDs are overcoated with wide bandgap shell materials that passivate surface defects and confine excitons to the core, thus increasing the PLQY of the QDs∼150 °C)

Typical QD-converted µ-LED displays require the deposition of red and green QDs on blue µ-LED chips. Conventional QD deposition methods, including spin-coating, phase-separation, self-assembly, dip-coating, and layer-by-layer deposition, have many limitations for fabrication, such as complicated and multiple steps, low resolution, and difficult patterning control. Additionally, these techniques usually need a large amount of QDs in solution form but actually transfer a very limited amount, thereby considerably increasing the production cost. Therefore, advanced techniques for patterning QDs on µ-LEDs have been proposed, such as photolithography

Generally, using electron-beam lithography, QD films with patterns scaled down to sub-µm can be achieved4. Thus, the pixel and pitch resolution is not an issue for QD film deposition on µ-LEDs by using any techniques mentioned as long as the LED size is in the range of µm. However, each technique has its own limitations. The microcontact and transfer printing approaches need a template, making the procedure more complicated. Inkjet printing has problems such as easy clog of the jagged nozzle, the coffee ring effect, and nonuniform film thickness and rough surface of the printed film, even though it is the most desirable manufacturing process in the display industry. In the QD deposition process with photolithography and electron-beam lithography techniques, QD films could be easily damaged, and the production costs are high.

So far, printing technology can satisfy most of the demands because the pixel sizes of displays are still above microns in the current market. From the viewpoint of simple and rapid fabrication, printing techniques should be mainstream in the future display industry. However, the problem of nonuniform printing should be further addressed. Developing a stable, high-resolution, and cost-effective process that can directly print uniform QD layers with diverse sub-micron patterns is important for ultrahigh-resolution QD-converted µ-LED displays, although this remains a challenge.

Currently, many critical issues in µ-LED displays including the quantum-confined Stark effect, display resolution, pixel pitch, device EQE, colour conversion efficiency, and optical crosstalk have been relieved along with the development of nanofabrication capability and new structural design, such as super-inkjet printing, high-resolution lithography, advanced QD encapsulation, mould architecture design, and FRET nanostructure patterning. However, there are still some remaining obstacles for the high-throughput manufacturing of µ-LED displays.

Mass transfer is regarded as the greatest technical challenge in µ-LED display manufacturing. Damage should be avoided when the µ-LED is transferred from the mother wafer to the target substrate. However, rapid transfer can significantly increase the dead pixel number, resulting in a low manufacturing yield. The elastomer stamping approach can be applied to products of ~10 μm, with a high transfer yield of 99.99%;

Because the µ-LED display uses self-emission technology, a TFT matrix drive array is required to switch each pixel ON and OFF separately. The adoption of the TFT control matrix can significantly reduce the power consumption by ceasing unnecessary pixels and maintaining the operation of the display at low power. However, the small feature of µ-LEDs leads to the high spatial density of the TFT array and makes the circuit design more complicated. The bonding between the TFT matrix and µ-LED array is also problematic. Large-scale bonding with very small chip elements may cause short circuits due to the use of a large amount of metal in the solder paste.

Although obstacles exist, the current progress on µ-LED displays still provides an optimistic perspective for next-generation applications. According to UBI Research’s forecast, the market size of µ-LED displays will grow from around $100 million as of 2019 to over $6 billion by 2025, and the new emerging displays will widely be used in wearables, smartphones, TVs, and other applications

Recent demands of high-speed data transmission in VLC have motivated the adaptation of white lighting µ-LED arrays with pixel size approximately 100 µm, providing a peak data rate of >1 Gbit/s without complicated signal processing

µ-LEDs are suitable for advanced display applications such as smartphones, wearable watches, micro-projectors, AR/VR, automotive heads-up displays, and ultra HD (>4K resolution) televisions due to their advantages such as better colour accuracy, higher colour saturation, high contrast ratio, high peak brightness, low power consumption, and longer lifespan. Figure 13 shows the requirements for µ-LEDs in advanced display applications

In particular, QD-based µ-LED displays make a strong appeal to 8K ultra HD displays and AR/VR displays; 8K displays have a very high resolution of 7680 × 4320 and employ the Rec. 2020 system as a colour gamut standard. The most important feature of the Rec. 2020 standard is 99.9% reproducibility of colours in nature, and it leads to a drastically wider colour gamut than that of the HDTV standard (Rec. 709). Ultra HD displays require LEDs with better chromaticity in order to achieve a wider colour gamut as well as high efficiency and a long lifetime.

Moreover, displays for VR/AR applications require a light weight, small form factor, high pixel density, wide field-of-view (FoV), and high refresh rate to satisfy the human visual system. Generally, the FoV for each human eye is ~160° (horizontal) × 150° (vertical)

Finally, µ-LEDs with flexible substrates represent a vital application, attracting enormous attention in the fields of displays, wearable electronics, lighting and biomedicine, and light guide plates because of their high efficiency, small form factor, and low power consumption. In particular, flexible and wearable µ-LED displays have thin, lightweight, and nonbreakable features, thus enabling the application of displays on curvilinear surfaces. Impressive colour purity and high brightness with low power consumption, high-resolution QD array patterning and ultrathin/ultrasmall form factors make QD-based µ-LEDs promising for flexible/wearable electronics.

The PD-49 from AG Neovo is a 48.5" LED-Backlit TFT LCD Monitor. It is Built for digital signage, the PD-Series video wall display features a 6.5mm narrow bezel and a full slate of inputs including HDMI with HDCP, DisplayPort 1.2 for 4K 2x2 video wall solution setups, and RS-232 and RJ45 ports for remote and network-based control. The displays also include other signage-friendly features such as landscape and portrait modes, scheduling capabilities, and a switch-on delay mechanism for use in video walls. Furthermore, the PD-Series also fits for security control room usages with its premium-grade panel and 24/7 design. The PD-Series narrow bezel video wall display offers pristine images that maximize visibility, making videos shown on the video wall display stand out in any digital signage setting. The 700 nits high brightness, 10 bit color depth, and 4ms response time ensure life-like visuals, all complemented by a 178-degree viewing angle that allows the video wall display to be seen by all.

The PD-Series narrow bezel video wall display is an excellent choice for video walls with a variety of features, which make video wall installation and setup convenient including DisplayPort 1.2 chaisy-chain support for easy 4K 2x2 video wall setup, a switch-on delay mechanism, a logo free design, and a premium-grade panel for 24/7 operation. The embedded USB media player allows users to conveniently play content from a USB drive. Simply create scheduled playlists and configure playback settings with the included remote control to video wall display your personalized content. Its built-in scheduler and OPS slot are complemented by IR / RS-232 looping and Ethernet control capabilities to easily control, setup and maintain large-scale digital signage video walls installations. PID Command & Ctrl is a software that allows users to control AG Neovo narrow bezel video wall display via LAN or RS232 connections. It provides a simple and intuitive interface for remote management, OSD-related settings, and easy control on deployed video wall displays. It also can be used to create video walls within minutes and assist system integrators with setting up displays.

The new line of 3.5” TFT displays with IPS technology is now available! Three touchscreen options are available: capacitive, resistive, or without a touchscreen.

For over 20 years Newhaven Display has been one of the most trusted suppliers in the digital display industry. We’ve earned this reputation by providing top quality products, services, and custom design solutions to customers worldwide.

The wide range of conditions over which LCD monitors are used means that it is desirable to produce displays whose luminance (brightness) can be altered to match both bright and dim environments. This allows a user to set the screen to a comfortable level of brightness depending on their working conditions and ambient lighting. Manufacturers will normally quote a maximum brightness figure in their display specification, but it is also important to consider the lower range of adjustments possible from the screen as you would probably never want to use it at its highest setting. Indeed with specs often ranging up to 500 cd/m2, you will certainly need to use the screen at something a little less harsh on the eyes. As a reminder, we test the full range of backlight adjustments and the corresponding brightness values during each of our reviews. During our calibration process as well we try to adjust the screen to a setting of 120 cd/m2 which is considered the recommended luminance for an LCD monitor in normal lighting conditions. This process helps to give you an idea of what adjustments you need to make to the screen in order to return a luminance which you might actually want to use day to day.

Changing the display luminance is achieved by reducing the total light output for both CCFL- and LED-based backlights. By far the most prevalent technique for dimming the backlight is called Pulse Width Modulation (PWM), which has been in use for many years in desktop and laptop displays. However, this technique is not without some issues and the introduction of displays with high brightness levels and the popularisation of LED backlights has made the side-effects of PWM more visible than before, and in some cases may be a source of visible flicker, eyestrain, eye fatigue, headaches and other associated issues for people sensitive to it. This article is not intended to alarm, but is intended to show how PWM works and why it is used, as well as how to test a display to see its effects more clearly. We will also take a look at the methods some manufacturers are now adopting to address these concerns and provide flicker-free backlights instead. As awareness grows, more and more manufacturers are focusing on eye health with their monitor ranges.

Pulse Width Modulation (PWM) is one method of reducing the perceived luminance in displays, which it achieves by cycling the backlight on and off very rapidly, at a frequency you can’t necessary detect with the naked eye, but which could lead to eye issues, headaches etc. This method generally means that at 100% brightness a constant voltage is applied to the backlight and it is continuously lit. As you lower the brightness control the perceived luminance for the user reduces due to a number of possible controlling factors:

1) Frequency –The backlight is cycled on and off very rapidly, and this cycling typically occurs at a fixed frequency (in Hz). How fast this cycling occurs can impact whether flicker is visible or perceivable to the user, with higher frequencies being potentially less problematic. PWM has been known to operate at low frequencies of 180 – 240Hz for example which are likely to be more problematic than higher frequencies ranging up in to the Kilohertz range (e.g. 18,000Hz).

2) Modulation –The modulation of the cycling has an impact on the perceived brightness, and this describes the difference between the luminance in an “on” and in an “off” state. In some examples the backlight is completely turned off during the cycle so it is literally being turned on/off rapidly across the full brightness adjustment range. In those examples the luminance output is controlled really by the duty cycle only (see point 3). In other examples the backlight is not always being completely turned off but rather the voltage applied to the backlight is being rapidly alternated, resulting in less extreme differences between the on and off states. Often this modulation will be narrow in the high brightness range of the display, but as you reduce further, the modulation becomes wider until it reaches a point where the backlight is being switched completely off. From there, the change in the duty cycle (point 3) controls the further changes in the luminance output.

While PWM is attractive to hardware makers for the reasons outlined above, it can also introduce distracting visual effects if not used carefully. Flicker from LED backlights is typically much more visible than for older CCFL backlights at the same duty cycle because the LED’s are able to switch on and off much faster, and do not continue to “glow” after the power is cut off. This means that where the CCFL backlight showed rather smooth luminance variation, the LED version shows sharper transitions between on and off states. This is why more recently the subject of PWM has cropped up online and in reviews, since more and more displays are moving to W-LED backlighting units now.

Where the effect of flicker can really come into play is any time the user’s eyes are moving. Under constant illumination with no flickering (e.g. sunlight) the image is smoothly blurred and is how we normally perceive motion. However, when combined with a light source using PWM several discrete afterimages of the screen may be perceived simultaneously and reduce readability and the ability of the eyes to lock onto objects. From the earlier analysis of the CCFL backlighting we know that false colour may be introduced as well, even when the original image is monochromatic. Below are shown examples of how text might appear while the eyes are moving horizontally under different backlights.

It is important to remember that this is entirely due to the backlight, and the display itself is showing a static image. Often it is said that humans cannot see more than 24 frames per second (fps), which is not true and actually corresponds to the approximate frame rate needed to perceive continuous motion. In fact, while the eyes are moving (such as when reading) it is possible to see the effects of flicker at several hundred hertz. The ability to observe flicker varies greatly between individuals, and even depends on where a user is looking since peripheral vision is most sensitive.

So how fast is PWM cycling backlights on and off? This seems to depend on the backlight type used, with CCFL-based backlights nearly all cycling at 175Hz or 175 times per second. LED backlights have been reported typically running from 180 – 420Hz, with those at the lower end flickering much more visibly. Some have even faster frequencies of >2000Hz so it really can vary. While this might seem too fast to be visible, keep in mind that 175Hz is not much faster than the 100-120Hz flicker observed in lights connected directly to the mains power.

100-120Hz flickering of fluorescent lights has in fact been linked to symptoms such as severe eye strain and headaches in a portion of the population, which is why high-frequency ballast circuits were developed that provide almost continuous output. Using PWM at low frequencies negates the advantages of using these better ballasts in backlights because it turns an almost constant light source back into one that flickers. An additional consideration is that poor quality or defective ballasts in fluorescent backlights can produce audible noise. In many cases this is exacerbated when PWM is introduced since the electronics are now dealing with an additional frequency at which power usage is changing.

It is also important to distinguish the difference between flicker in CRT displays and CCFL and LED backlit TFT displays. While a CRT may flicker as low as 60Hz, only a small strip is illuminated at any time as the electron gun scans from top to bottom. With CCFL and LED backlit TFT displays the entire screen surface illuminates at once, meaning much more light is emitted over a short time. This can be more distracting than in CRTs in some cases, especially if short duty cycles are used.

The flicker itself in display backlights may be subtle and not easily perceptible for some people, but the natural variation in human vision seems to make it clearly visible to others. With the use of high-brightness LED’s on the rise it is becoming increasingly necessary to use short PWM duty cycles to control brightness, making flicker more of a problem. With users spending many hours every day looking at their monitors, shouldn’t we consider the long term effects of both perceptible and imperceptible flicker?

A much better method of course would be to purchase a display not relying on PWM for dimming, or at least one which uses a much higher cycling frequency. Few manufacturers seem to have implemented PWM at frequencies that would limit visible artefacts (well above 500Hz for CCFL and above 2000 Hz for LED). Additionally, some displays using PWM do not use a 100% duty cycle even at full brightness, meaning they will always produce flicker. Several LED-based displays may in fact be currently available which do not use PWM, but until backlight frequency and modulation become listed in specifications it will be necessary to see the display in person. Some manufacturers promote “flicker free” monitors in their range (BenQ, Acer for example) which are designed to not use PWM at all and instead use a Direct Current (DC) method of backlight dimming. Other manufacturers such as Eizo talk about flicker free backlights but also list a hybrid solution for their backlight dimming, where PWM is used for some of the brightness adjustment range at the lower end. In fact it seems an increasingly common practice for a screen to be PWM free down to a certain point, and then fro PWM to be used to really drive down the minimum luminance from there.

(Optional) Set the camera white balance by getting a reading off the screen while displaying only white. If not possible, then manually set the white balance to about 6000K.

Display a single vertical thin white line on a black background on the monitor (1-3 pixels wide should be fine). The image should be the only thing visible. Here is an example you may wish to save and use, show it full