|Indoor and outdoor LED display selection and maintenance|
LED display has the advantages of high brightness, low operating voltage, low power consumption, miniaturization, easy integration with integrated circuits, simple driving, long life, impact resistance, stable performance, etc. Its application involves many fields of social and economic life, such as securities. Trading, financial information; port and station passenger guidance information; stadiums, road traffic information; dispatching command center information; indoor and outdoor advertising display.
LED display is an electronic product that gradually emerged in the 1980s. Therefore, some appliance maintenance personnel are still relatively new to the knowledge of the selection and maintenance of LED display DIP. This article gives a narrative. Expectations will inspire everyone's interest in LED displays and other LED products.
First, the classification of sports LED display
1. There are two main categories according to the way of working: full-featured display and intelligent display. Both are assembled using international standard 8×8 LED matrix modules (the screen surfaces are identical and the basic display functions are the same). The main difference between the two is:
The intelligent display usually does not need to be connected to the host computer. The display has a built-in CPU, which can save multiple images after power-off, and can be run independently from the host computer. Some screens also have a clock chip that automatically displays the calendar and clock. When you need to modify the display content, you can modify it by connecting the microcomputer through the RS232 interface. The full-featured display must be connected to a microcomputer to work.
Intelligent display screens are usually displayed in a small number of ways, such as pop-up, pull-screen, roll-up, and roll-down. The full-featured display is displayed in a variety of ways (if you use professional software to create a program, there are unlimited ways to display it).
The intelligent display is easy to operate: the full-featured display requires dedicated operation and maintenance (requires expertise if you want to create an animated program).
2. There are monochrome and color displays by color type. The monochrome display uses the standard 8 x 8 monochrome LED matrix module standard components. Generally red, it can display various texts, data, and two-dimensional graphics. The indoor monochrome display is economical and practical, but the color is somewhat monotonous.
The color display adopts a standard 8×8 dual-base LED matrix module, and there are two red and green LEDs in each pixel. When both tubes are lit at the same time, yellow is displayed. Therefore, the dual primary color tube display can emit three colors of red, green and yellow, and can display various characters, data, animations and the like in color. In addition, it can be connected with various data devices to display real-time dynamic data and advertisements, and has better information display effect, which is the most widely used LED display.
The color grayscale display adopts the standard 8×8 double-base LED matrix module. Each pixel has three colors of red, yellow and green. Each primary color has 16×16 gray scale=256 or 256×256 gray scale= 64k colors, even more colors. The color grayscale screen is rich in layers and expressive. It can display photos, images, 3D graphics, animations, and video images. The performance is delicate and rich, and the visual effects are realistic and touching.
3. There are mainly ordinary density and high density displays according to dot matrix density. The density of the display is related to the pixel diameter. The smaller the pixel diameter, the higher the density of the display. In the specific selection, the closer the viewing distance is, the higher the density of the display screen; the farther the viewing distance is, the lower the density of the display screen can be appropriately reduced. The indoor standard is 8×8 LED matrix module, and φ5mm and φ3.7mm are the most common.
Second, the performance requirements of LED display
1. The light-emitting tube is mainly used for the selection of the light-emitting dies in the light-emitting tube. At present, the manufacturers of medium and high-grade LED tube cores mainly include Japan's Nichia Corporation, Toyota Corporation, American Corey Company, Hewlett-Packard Company, Dewei's Siemens Company, Taiwan's Guolian Company, Dingyuan Company and Guanglei Company, among others. Companies in Japan, the United States, and Europe mainly produce pure blue-green light-emitting dies, while Taiwanese companies mainly produce red-green tube dies.
From the current practical application and red-green color matching, a red and green display, the red tube uses four elements of red, and the green tube uses three elements of green. In the use of the die, the 712SOL red tube die of Taiwan Guolian Company is generally adopted, and the 113YGU green tube die of Taiwan Dingyuan Company is adopted. This type of die is a kind of high-level indoor display configuration. . In addition, there are 2 red plus 1 pure green configuration (outdoor two-color).
2. The integrated component optoelectronic drive circuit receives the digital signal transmitted from the computer to the distribution card, drives the light and dark of the illuminator, and forms the text or graphics we need. The quality is reliable and stable, which directly determines whether the illuminator can work normally. From the current operation of the outdoor screen, the highest failure rate occurs in the opto-electronic drive part, because the quality of the selected integrated IC device directly determines the quality of the opto-electronic drive part. Currently, the universal chip used in the outdoor display is a pair of 4953 and HC595. The higher the grade, the special drive chip and the 595 chip of the 6B series produced by Texas.
3. The power supply requirements of the power LED display are guaranteed to be less than 1% in 5 years. The quality of the power supply depends on the screening of components and the quality control of the power supply manufacturer. At present, there are many brands of power supply on the market, such as Changzhou Chuanglian, Sida, Shanghai Hengfu and Taiwan's Mingwei. From the actual use point of view, the domestic power supply Changzhou Star has a good power supply stability and long service life.
4. The overall requirement of the editing system and the playback system software system software is to provide a simple and interactive program production/playback environment, which can adopt a hierarchical and modular design method with good reliability and expandability.
Third, the basic structure and control of the graphic display
1. Basic structure The LED graphic display consists of the screen body, computer, controller, dot matrix display unit and power supply. Figure 1 is a block diagram of the LED display circuit.
(1) The main part of the screen body is to display the dot matrix, the row and column drive circuit, or other circuits (not strictly defined, depending on the needs and layout of the printed circuit board). The display dot matrix is mostly formed by splicing 8×8 monochrome or two-color display units. For example, a 32×128 strip screen requires all 64 8×8 display units to be composed of 4×16 blocks.
(2) Intelligent display unit This unit is a small system that performs display tasks independently or a part of the entire LED graphic display system. It can display Chinese characters, lines and simple graphics. The main control device is generally a single-chip microcomputer, and has an RS-485 communication interface, a Chinese character library and a display buffer. Each smart display unit has its own number or address. According to the size of the LED graphic display system, a corresponding number of intelligent display units can be selected.
(3) The main controller of its main controller adopts single-chip microcomputer, and expands the Chinese character library, data memory with power-down protection, real-time calendar clock and two HS-485 communication interfaces, etc., which are all embedded in the LED graphic display. In the system. One of the two communication interfaces communicates with the computer, and the communication distance can be several hundred meters; the other completes communication with each intelligent display unit.
The main functions of the main controller are: receiving commands and display data sent by the computer; transmitting commands or data to the corresponding intelligent display unit, and being responsible for synchronizing the display of each intelligent display unit.
In practical applications, the LED graphic display system composed of the main controller and each intelligent display unit is a display system that can work independently.
(4) The main function of the computer computer and the corresponding application software is: when the display content needs to be replaced, the updated display data is sent to the main controller; when the display mode needs to be changed, the corresponding control is transmitted to the main controller. Command; when the online dynamic display is required, the real-time display data is transmitted to the master.
Since the display data of the graphic display screen only has the on-off information, and does not include the gray scale information, the amount of data is not large, and the update speed of the display content is relatively slow, so the data transfer between the upper and lower computers can be serial. Asynchronous communication method. The serial communication interface level can be selected according to the needs of RS232, RS422 or RS485 standards.
2. Control mode LED graphic screen is widely used, and different control methods can be adopted for different application environments and application requirements. (1) Group explicit It is suitable for a large number of graphic screens, and the content displayed on each screen is the same, such as shopping malls, venues, etc. Group display can use a host computer to connect multiple lower computers (picture screen), as shown in Figure 2. It is controlled by the upper computer in a unified manner, and the communication adopts the broadcast mode: the signal is sent by the upper computer, and each lower computer receives the same at the same time.
When each graphic screen needs to display different contents, it can be distinguished by the lower machine number. When the host computer sends the information, it sends the lower computer number that needs to receive the information before sending the display data. After receiving the number, each lower computer determines whether it should receive the following display data. In this way, only the lower computer that should receive the display data continues to receive, and the other lower computers ignore the subsequent data, so that each graphic screen can display different contents. (2) Infrared remote control In some occasions, the display content of the graphic screen is relatively simple, and the content changes are not frequent. You can consider not to use the upper computer. The lower computer itself stores a number of necessary display data, and the on-duty personnel select the content on site by means of infrared remote control. We can use the infrared remote control of the TV to transform into a remote control for the graphic screen.
(3) In some applications of wireless remote control, the layout of the graphic screen is very scattered, and the distance between the screen and the screen may be long. under these circumstances. The communication medium between the upper computer and the lower computer is wired. It may be uneconomical or unrealistic. At this time, communication between the upper and lower computers can be performed wirelessly. Fourth, the choice of display
Choosing an LED display is determined by a combination of factors such as its own needs, site constraints, and investment. For example: to see whether the display is used indoors or outdoors; the main purpose is to mainly display text, or mainly display simple pictures and texts, or mainly play various video signals, animations, images and texts; The viewing distance and the type of control to be taken (synchronous control or asynchronous control or wireless control, etc.) are also very important factors.
Generally, if the image is required to be high and the visible distance is close, a double-primary or full-color display with a high dot density specification is selected; if the amount of text is large, a specification with a low dot density is selected. In addition, you should choose a full-color, double-primary or monochrome display according to the funding situation, select different frame materials according to the decoration, and choose different control methods according to the use characteristics.
Specifically, the following points should be noted when selecting an LED display:
1. Try to use a new wide viewing angle tube. It has a wide viewing angle, pure color, consistent coordination, and a life span of more than 100,000 hours.
2. The outer package of the display screen is currently the most popular outer package with a rectangular cylinder with a cover, a silicone seal, and no metallization. Its appearance is exquisite and beautiful, sturdy and durable, and it has the characteristics of anti-sunlight direct, dustproof, waterproof, anti-high temperature and anti-circuit short circuit.
3. According to the characteristics of different LED displays, combined with the actual needs of users, choose the appropriate display.
(1) For the entrance and exit of the station, the dock, the big market, and the flow of people at the elevator, use a d5.0mm monochrome display. It has the advantages of clear font, low price and cluster control.
(2) For banks, shopping malls and other occasions to display corporate image, advertising and other applications, the price is low, using φ3.75mm dual primary color display. If the display is required to be good, use a φ5mm full color display.
(3) For large areas such as halls, use a φ5mm dual primary color display. If a display is required, use a φ10mm full color display.
(4) For the business halls such as banks, postal services, and electric power, the function definition for the service window is displayed using a φ3mm or φ5mm display screen, so that the service function of the window can be changed at any time.
4. Due to the harsh environment and the higher quality requirements, the outdoor display has many factors to consider.
(1) From the perspective of use, full-color screen is the mainstream in the future. Because of its high brightness, full color, and can work all day, but the price is high. (2) From the perspective of application, there are reasons for the existence of products that meet the needs of users. The dual-primary color display screens occupy a large market with low price, mature and stable when the display text and color requirements are not high and there is no blue color.
(3) The orientation and distance of the outdoor screen play a decisive role in the price. The farther the distance is, the larger the pixel and the higher the brightness. It is much cheaper to face the northeast than to the southwest.
(4) The screen body and the joint between the screen body and the building must be strictly waterproof and leakproof. The screen body should have good drainage measures, and once the water accumulation occurs, it can be discharged smoothly.
(5) Install lightning protection devices on the display screen and buildings. The main body and the outer casing of the display are well grounded, and the grounding resistance is less than 3Ω, so that the large current caused by lightning is discharged in time.
(6) Install the ventilation equipment to cool down, so that the internal temperature of the screen is between -10 °C and 40 °C. An axial fan can also be installed above the back of the screen to dissipate heat.
(7) Select an industrial-grade integrated circuit chip with a working temperature between -40 ° C and 80 ° C to prevent the display from failing to start when the temperature is too low in winter.
Fourth, common faults and treatment
1. Display not shown
(1) Check the power supply of the screen body, and use the test pencil or multimeter to check whether the power supply end of the switch connection has electricity. Is there a problem with the switch or checking if the line is broken?
(2) The display synchronized with the computer first checks whether the computer enters the hibernation state; if it enters hibernation, first enter the control panel, click on the power management, and select the option to wait for and disable the monitor from the system, so that the computer will not Sleep, the display can work normally; if it does not go to sleep, you can open the chassis, check whether the control card and communication cable are firmly connected, and check if the communication cable is disconnected. 2. Incomplete display file or incorrect location
(3) Check whether the parameters of the display position and screen size in the software are consistent with those given by the installation engineer. If you don't know the parameters, you can first count the length and width of the pixels on the screen. When the screen size is determined, look at the difference between the display area on the screen, and then go back to the computer to adjust until the position is consistent. until.
(4) If the display is not comprehensive, you should check whether the file size is the same as the screen size of the screen.
(5) Open the chassis and check if there is a short circuit on the control card. 3. Communication display is not available
(6) Check that the parameters in the software are consistent with those given by the installation engineer.
(7) Check if the serial port is securely connected and the communication line has a broken line.
2. The display is dithered and has a horizontal bar
Check if the common ground wire connected to the computer is loose, or communicate