LED display is a flat-panel display that integrates computer technology and information processing technology. It is currently widely used in commercial media, stage performances, information dissemination and other scenes. Basically, when you go out and look up, you can see the LED display.
From the development of the LED display to the present, it is no longer just the splicing of LED modules, but also the transparent LED display with the lamp beads embedded on the light bar. However, no matter which type of product, it is ultimately necessary to pass through the box. It is used by splicing. The difference lies in the different cabinets used for splicing, some use iron boxes, some use die-cast aluminum, and some use unique cabinets such as transparent screens.
When it comes to splicing, many people may think of LCD displays that look very similar to LED displays, so some people will be curious about the differences between LED display splicing and LCD display splicing.
What are the differences between LED display splicing and LCD display splicing?
1. Infinite splicing. The LED display screen can be cut into a small pixel point through a unique control system and filled on each LED lamp bead, so as long as the funds and materials are sufficient, theoretically infinite splicing. Like last year’s In the Beijing Winter Olympics, the super-large LED display of more than 10,000 square meters has been talked about by people all the time.
However, the current technology is temporarily unable to display large-area LCD splicing, and can only perform small-scale splicing. Looking at the world, there are currently very few LCD manufacturers that can produce a splicing area of 100 square meters, let alone that A variety of large and super large splicing areas are available.
2. Seamless splicing. The LED display can not only theoretically be spliced infinitely, but also can achieve perfect seamless splicing. Therefore, the larger the spliced screen, the more obvious the advantages of the LED display.
The corresponding LCD cannot deal with the problem of black borders very well at present, and generally there will be black borders of 0.8-12 mm. Although there are some supplementary methods to achieve similar effects, there is still a gap with the real seamless LED display.
3. Irregular splicing. At present, the LED display screen has flexible LED modules, and various special-shaped screens can be spliced through such modules, such as pentagonal, star, heart, diamond, etc., while the LCD display Only squares or rectangles can be spliced, there is no way to personalize them, and they can be spliced into other shapes irregularly.
However, it does not mean that LCD is not excellent. The same LCD display also has many advantages that LED can’t match, especially in the small and beautiful range, LCD has always occupied the main position. Although LED also has products such as small pitch, but its The price is 5-30 times higher than that of similar LCD displays (the smaller the dot pitch of the LED display, the more expensive the price). In this respect, the LED display cannot be compared with the LCD.
These infinite and seamless characteristics of LED display screen do not appear out of thin air, but are realized based on the technical principle of dot matrix LED display.
The principle of display technology of LED display
LED is the abbreviation of light-emitting diode. It is a diode made of compounds of gallium, arsenic, phosphorus, nitrogen, and indium by controlling the display mode of semiconductor light-emitting diodes. When electrons and holes recombine, they can radiate out visible light, so it can be used to make light-emitting diodes.
It is used as an indicator light in circuits and instruments, or according to a certain lattice arrangement to form a text or digital display. The gallium arsenide phosphide diode emits red light, the gallium phosphide diode emits green light, the silicon carbide diode emits yellow light, and the indium gallium nitrogen diode emits light. It emits blue light. This is the light-emitting principle of a single-color or single-primary LED display. In order to save manufacturing costs, most of the monochrome displays use the in-line method.
Putting red and green LED chips or tubes together as a display screen made of one pixel can realize a two-color and three-color display, so it is called a dual-color or three-color display.
A display that puts red, green, and blue LED chips or tubes together as a pixel is called a three-color display or a full-color display. In order to improve the display effect, some display screens may be composed of 4 diodes: 2 1 red LED, 1 green LED and 1 blue LED.
The indoor LED display is seen from a relatively close distance, so the pixel size of the indoor LED display is generally between 1.5-5 mm. It is often used to package several LED dies that can produce different primary colors into one. The viewing distance of the LED display is farther, so the pixel pitch is also much larger, generally 4-20 mm.
Whether LEDs are used to make a single-color, two-color or three-color display screen, the luminous brightness of each LED can be adjusted, and the fineness of the adjustment is also the gray level of the display screen. The higher the gray level, the better the displayed image. The more delicate, the richer the color, the more complex the corresponding display control system.
Generally, a 256-level grayscale image has a very soft color transition, while a 16-level grayscale color image has a very obvious color transition boundary. Therefore, the color LED screen display requires a grayscale of 256 to 4096, so that the display The picture is more beautiful and beautiful.
The LED display screen is an electronic display screen composed of LED dot matrix. By changing the red and green light beads on and off, the screen display content forms such as text, animation, pictures, and videos are converted in time, and the component display control is carried out through the modular structure.
LED display product composition
It is mainly divided into display module, control system and power system. In simple terms, the display module is a dot matrix of LED lights to form a screen to emit light; the control system is to control the on-off conditions in the area to realize the conversion of the content displayed on the screen; the power system is It is to convert the input voltage and current to meet the needs of the display screen.
In fact, there are a lot of things to do in the above three parts. For example, the control system not only controls the on and off lights, but also involves a lot of information control. The most common is the adjustment of color and brightness value. It is reported that the LED display must at least meet the 255 gray level, and the better the quality, the higher the gray level.
The gray level mainly depends on the number of digital-to-analog conversion bits of the system. Of course, the video processing chip, memory and transmission system of the system must provide the support of the corresponding number of bits. At present, the LED display mainly adopts:
1. 8-bit processing system, that is, 256 (2 to the 8th power) grayscale. A simple understanding is that there are 256 brightness changes from black to white.
2. 10-bit processing system, that is, 1024 (2 to the 10th power) grayscale. A simple understanding is that there are 1024 brightness changes from black to white.
3. 12-bit processing system, that is, 4096 (2 to the 12th power) grayscale. A simple understanding is that there are 4096 brightness changes from black to white.
4. 14-bit processing system, that is, 16384 (2 to the 14th power) grayscale. A simple understanding is that there are 16384 brightness changes from black to white.
The LED display screen is a mapping mode, so it can realize the conversion between different forms of various information presentation modes, and can be used indoors and outdoors. It has the incomparable advantages of other display screens. It has the characteristics of small size, low voltage demand, small and convenient equipment, long service life, stable impact resistance, and strong resistance to external interference. It has developed rapidly and is widely used in various fields.
The luminous color and luminous efficiency of LEDs are related to the materials and processes used to make the LEDs. The light bulbs are all blue at first, and phosphors are added later to adjust different light colors according to the different needs of users. Red is widely used. , green, blue and yellow. Due to the low operating voltage of the LED (only 1.2~4.0V), it can actively emit light and has a certain brightness, and the brightness can be adjusted by voltage (or current), and it is resistant to shock, vibration, and longevity. Long (100,000 hours), so in large display devices, there is no other display device that can match LED.
There are various classifications of LED displays, which are generally classified in the following ways:
(1) Divided by display device
LED digital display: The display device is a 7-segment digital tube, which is suitable for making electronic displays that display numbers such as clock screens and interest rate screens.
LED dot matrix graphic display: The display device is a dot matrix display module composed of many evenly arranged light-emitting diodes, which is suitable for playing text and image information.
(2) According to the use environment
The indoor screen area is generally less than ten square meters, and the point density is high. When used in non-direct sunlight or lighting environments, the viewing distance is several meters away, and the screen body does not have the ability to seal and waterproof. The diameter of the light-emitting point is small, generally 1.25～ 6mm, the brightness is 800-2000cd per square meter.
The outdoor screen area is generally from a few square meters to tens or even hundreds of square meters, the point density is relatively thin (mostly 1000-4000 points per square meter), and the luminous brightness is 3000-5000cd per square meter (different orientations, different brightness requirements), can be When used in direct sunlight, the viewing distance is tens of meters away, and the screen has good wind and rain resistance and lightning protection capabilities.
The basic unit of outdoor screen lighting is pixels, and the center diameter of the pixel’s light-emitting point is larger, such as P5mm, P8mm , P10mm, P16mm, etc.
There is also a semi-outdoor display screen, which is between indoor and outdoor. It has high luminous brightness and can be used outdoors without direct sunlight. The screen body has a certain seal, usually under the eaves or in the window. Products are generally classified in the category of outdoor.
(3) According to the control method
It means that the working mode of the LED display is basically the same as that of the computer monitor. It maps the image on the computer monitor correspondingly in real time at an update rate of at least 30 fields/s. Multimedia advertising effect.
Asynchronous (or communication) way:
It means that the LED screen has the ability of storage and automatic playback. The edited text and non-grayscale pictures on the PC are transmitted to the LED screen through the serial port or other network interfaces, and then automatically played offline by the LED screen. Generally, there is no multi-grayscale display. Ability, mainly used to display text information, can be multi-screen networking.
(4) According to the common name of the industry
This is also a relatively common classification method, which generally includes the following:
Small pitch display or fine pitch display
Rental display, often used on stage, so it is also called stage rental display
Floor tile display
(5) According to the location of use
There are many names for this, and they are not uniform. For example, those installed on the ceiling are called sky screen screens, and those installed on the floor are called floor tile screens. If the floor and ceiling are installed together, they are called tunnel screens, and those installed on the car are called car screens. The roof screen is called the roof screen.
Performance characteristics of LED display
(1) High-intensity luminescence, under the refraction of sunlight, the content of the screen surface can be presented in high-definition within the visible range.
(2) The grayscale control level is high. The 1024-4096-level grayscale control can be used to display the colors above 16.7M clearly and vividly, ensuring the super three-dimensional image of the picture.
(3) The driving power is large, and the scanning mode is mainly static latching to ensure high-intensity bright light.
(4) In order to ensure the best playback effect, the brightness can be reasonably controlled by the automatic adjustment function in different background environments.
(5) Circuit integration mainly relies on large-scale imported devices to improve the reliability of operation and is conducive to maintenance and debugging.
(6) Use modern digital processing technology to process video, mainly choose the way of technology distribution for scanning, design and present modularization, adopt static constant current drive, and automatically adjust brightness, so as to achieve high fidelity of the picture, no ghosting, and improve the image. The clarity of the picture.
(7) There are rich types of information display such as icons, videos, texts, animations, pictures, etc., and various forms of reality, such as networking, remote reality, etc., and the combination of common colors and craftsmanship.
(1) Equipped with a full-color display screen and the introduction of higher-quality imported LED chips, the screen has high-definition imaging, uniform color, low power consumption, light screen body, thin screen layer, and wide-area viewing angle, so it fails. Low probability and easy maintenance.
(2) It mainly adopts the multimedia display card PCTV card that integrates various functions, with more excellent performance, more advanced acquisition methods, accurate video capture, and Studio editing software that matches the display card.
(3) DVI interface technology is relatively advanced. It does not need to use A/D and D/A for conversion, which ensures the integrity of the picture image, reduces the possibility of details, and completely reproduces the computer image on the display screen. DVI can support all display modes , to ensure the stability and reliability of the data display, and at the same time have a variety of integrated functions.
(4) Use the indoor full-color system to alleviate the hidden dangers of the system displaying and transmitting a large amount of complex data, and fully perform full-color restoration. The chip is used to complete the task of data distribution and display, and the received data is converted by pulse output, and the data is displayed by 8 bits (8bit). Convert to 12-bit PWM, upgrade to 4096 (12bit) grayscale control, realize non-linear 256-level visual grayscale display on the screen, and fully create full-true color visual enjoyment.
(5) The drive mode adopts constant current system. Through its high cost performance, it improves the lack of discrete voltage drop in LED tubes, overcomes the mosaic problem, and ensures the quality of the picture.
(6) Combine the mode of optical fiber transmission to reduce the loss of signal in transmission.
Color, Brightness and Viewing Angle
With the combination of diodes and semiconductors, its production materials and production processes have been gradually upgraded, breaking through the limitations of the original brightness and color, and a large number of blue diodes and pure green light-emitting diodes are used to improve the display brightness. And then improve the LED display screen The advantages in outdoor environments can adapt to different display requirements and improve the effective value of LEDs in different environments. The evaluation of LED display performance must be the result of comprehensive consideration, because the relevant performance indicators are closely related, brightness, Viewing angle, resolution and other indicators affect each other. Currently, surface mount LED devices are used in high-density, full-color indoor displays to improve the viewing angle and brightness performance of the display.
The gray level of the LED display is mainly used to evaluate its color reality. By judging the brightness level between the darkest single primary color and the brightest, the display color is evaluated based on the gray level. When When the gray level is high, the display is rich and colorful; when the gray level is low, the color change is single. Therefore, the improvement of the gray level is conducive to increasing the color display level of the image and the color depth. of improvement.
The contrast of the display screen affects the visual imaging effect. High contrast can improve the clarity of the picture, bright colors, and effectively improve the detail texture, clarity, and gray level of the image quality. In addition, the contrast also affects the resolution of dynamic video. To a certain extent, high contrast can make it easier for the naked eye to distinguish the light-dark transition process in dynamic images.
The number of times the content of the LED display can be repeatedly displayed per second is called the refresh rate. When the refresh rate is low, there will be image flickering, especially in the process of video shooting. The flickering is too obvious, so it must be maximized. Improve the refresh rate to ensure the stability of the display screen.
The display of the image by the LED uses the electronic light-emitting system to display the result of image conversion of the digital signal. The special video card JMC-LED emerges as the times require, which forms a unity with the VGA and video functions on the basis of the PCI bus using a 64-bit graphics accelerator Compatible, making video data superimposed on VGA data to improve the deficiencies in compatibility.
Using full-screen mode to capture resolution, the video image can achieve full-angle resolution and enhance the resolution effect, eliminate the problem of edge blurring, and can zoom and move images at any time. All requirements can be dealt with in time. Effective separation of red, green and blue colors can improve the true color imaging effect of electronic display screen playback.
True Image Color Reproduction
In general, the combination of red, green and blue should satisfy the light intensity ratio of 3:6:1; the red imaging sensitivity is stronger, so the red in the spatial display must be evenly distributed; due to the different light intensities of the three colors, People’s visual perception presents different nonlinear curves of resolution. Therefore, it is necessary to take advantage of white light with different light intensities to correct the internal light emitted by the TV.
The color resolution ability is different due to individual differences and environmental differences, and color reproduction needs to be carried out according to certain objective indicators, such as:
(1) Position the 660nm red light, 525nm green light, and 470nm blue light as the fundamental wavelengths.
(2) According to the actual situation of light intensity, use 4 or more white light units for matching.
(3) The gray level is 256 levels.
(4) The LED pixels must be processed by nonlinear calibration. The three-color piping can be controlled by the cooperation of the hardware system and the playback system software.
Brightness control D/T conversion
The controller is used to control the light-emitting of the pixels to promote the independence of the drive. When the color video needs to be presented, the brightness and color of each pixel must be effectively controlled, and the scanning operation can be completed synchronously within the specified time. However, large LEDs There are thousands of pixels on the electronic display screen, which increases the complexity of control and the difficulty of data transmission.
It is unrealistic to use D/A to control each pixel in actual work, and a brand new one is required at this time. The control scheme to meet the complex requirements of the pixel system. Based on the analysis of the visual principle, the on/off ratio of the pixel point is the main basis for people to analyze the average brightness.
Effective adjustment of this ratio can achieve effective control of the pixel brightness. The application of LED electronic displays Under this principle, the digital signal can be converted into a time signal to achieve effective conversion between D/A.
Data reconstruction and storage
At present, the combined pixel method and the bit-level pixel method are the common memory combination methods. The advantage of the bit-plane method is more obvious, which can effectively improve the best display effect of the LED screen.
After the bit-plane data is reconstructed to the circuit, the RGB data is converted, and the organic Combine different pixels in the same weight bit, and use adjacent storage structures for data storage.
ISP in Logic Circuit Design
With the emergence of system programmable technology (ISP), users can repeatedly repair the deficiencies in the design and design the target, system or circuit board by themselves, and realize the designer application function of software integration. At this time, the digital system and system programmable technology The combination brings new application effects.
The introduction and use of new technologies effectively shortens the design time, expands the limited use of components, simplifies on-site maintenance, and facilitates the realization of target device functions.
When the system software inputs logic, the selected device can be ignored. You can select input components at will, or select virtual components, and perform adaptation after completing the input.
Precautions for using LED display
1. Switch sequence:
When opening the screen: turn on first, then open the screen.
When the screen is turned off: turn off the screen first, then turn off the screen.
(Turn off the computer first without turning off the display screen, which will cause bright spots on the screen body, and the LED will burn the lamp, which will cause serious consequences.)
2. The time interval between switching on and off the screen should be greater than 5 minutes.
3. After the computer enters the engineering control software, the screen can be turned on and powered on.
4. Avoid opening the screen in a completely white screen state, because the inrush current of the system is the largest at this time.
5. Avoid opening the screen in an out-of-control state, because the inrush current of the system is the largest at this time.
6. When a part of the electronic display screen appears very bright, you should pay attention to closing the screen in time. In this state, it is not advisable to open the screen for a long time.
7. The power switch of the display screen often trips, and the screen body should be checked or the power switch should be replaced in time.
8. Regularly check the firmness of the connection. If there is any looseness, pay attention to timely adjustment, re-reinforce or update the hanger.
9. When the ambient temperature is too high or the heat dissipation conditions are not good, the LED lighting should be careful not to open the screen for a long time.