There are some advantages of LED Display Screen, such as: high brightness, low operating voltage, low power consumption, mini-size, simple driving mode, long life span, shock-proof, steady performance and matching with integrated circuit, moreover, the application is involved in most industry of the social economy, eg. Display information for security exchange, finance, ports, stations, stadiums, roads, etc, and indoor & outdoor advertising. LED Display Screen is a kind of new electronic product in the 80s of the 20thCentury, so the selection and maintenance of the product is new to maintenance staff of household electrical appliances, so we hope to create people’s interests to LED products through the text, especially LED Display Screen.
　　
A.Classification of LED Display Screen
1.There are two kinds of LED Screens according to the work mode: Full-featured LED Display Screen and Intelligent LED Display Screen, and both of them are assembled by the modules with 8X8 dots in international standard(the same surface and basic display function), while the difference is as follows:
It’s unnecessary for intelligent LED Screen to connect with the upper computer, for it can work independently, and there is built-in CPU which could save various images when it’s power off. There is clock chip in some screen, so it could display calendar and time. If we want to modify display contents, just connect the interface of RS232 with the computer. While, full-featured LED Display Screen could not work until it’s connected with one computer.
There are fewer display modes for intelligent LED Screen, such as the popup type, curtain display, rolling type and so on. However, there are various display modes for full-featured LED Screen (if we use professional software for broadcasting).
It’s easy to operate intelligent LED Screen, but some special staff is required to operate and maintain full-featured LED Screen (professional knowledge is required for making animations)
2.There are single-color and full-color LED Display Screen classified according to colors. Single-color modules with 8X8dots are made of single-color LED chips, and red is the common color. Single-color LED screen could display characters, data, and two-dimensional pictures. Indoor single-color LED screen is economic, merely the color is monotonic.
Full-color LED Display Screen is made of standard modules with 8X8dots and two primary colors, and there are one red and one green LED chips in each pixel. When two chips are both lightened, the pixel is yellow, so LED Screen with two primary colors could display three kinds of colors: red, green and yellow, what’s more, it can also display colorized characters, data and animation. Besides, LED Full-color Screen could connect with all kinds of data sets to display realtime dynamic data and advertisement with a better display effect, that is the most popular one at present in the LED market.
Full-color LED Gray-scaled Display Screen consists of many modules with 8X8 dots in two primary colors, and there are three primary colors in every pixel: red, yellow, and green, with 16X16 grayscale which is equivalent to 256X256 or 64k kinds of colors. LED Display Screen could display pictures, images, three-dimensional animation and video images in rich and vivid colors.
3.There are Normal density LED Display Screen and High-density LED Display Screen classified according to the pixel density. The density of LED Display Screen is related to the pixel diameter, smaller pixel diameter but much higher density. More closer viewing distance, more higher density, vice versa. The standard module for indoor use is 8X8 dots, and the general specification is φ5mm and φ3.7mm.
B. Required functions
　 1.The selection to LED Chips is the most important step. Manufacturers of Medium-high-grade LED Chips include ++Nichia Co., Toyota, Hp, Siemens, Cree, some brands made in Taiwan and so on. ++, Cree and Siemens major in pure green and pure blue LED chips, while the manufacturers in Taiwan major in red and green LED chips.
According to the practical use and color assortment of LED Screen with one red and four green LED chips, the red LED chip is made up of red LED chips of four elements, while the green LED chip of three elements. 712SOL red LED chips manufactured in Taiwan are usually used, and 113YGU green LED chips made in Taiwan Dingyuan Co. is one of the most advanced in configuration used for indoor display with two primary colors. Besides, the configuration of two red LED chips and one pure green is used for outdoor dual-color LED Screen.
2.The driving circuit of integrated components accepts the digital signals from computers to drive the PCB, then the characters or pictures are formed, the reliability of which determines whether the luminous components can work well or not. When we see it from the working situation of outdoor LED Screen, the driving circuit gets the highest failure rate which is resulted from the low quality of integrated IC. At present, the universal LED chips 4953 and HC595 are matched for outdoor use, what’s more, special driving LED chips and 595 of 6B series made in America are used for top grade LED Display Screen.
3.The failure rate of the power supply of LED Screen must be controlled less than 1% within 5years, and the quality of power supply is determined by the selection to components and the quality control. There are various brands of power supply in markets, such as Chuanglian, Sida, and Mingwei made in Taiwan, etc. Actually speaking, the brand Sida made in Changzhou is more reliable and the life span is longer.
4.Both the authoring software and the display software are required to supply simple and alternating programming and broadcasting environments, with distributed and modularized design, that is more reliable and extensible.
C. The structure and control mode of LED Graph Display Screen
　　 1.Basic structure LED Graph Display Screen consists of screen, computers, controller, dot matrix display unit and power supply, etc.
　　 a.The screen consists of dot-matrix, driving circuit or any other circuit(it’s determined by the PCB). Dot-matrix display is made up of single or dual-color modules with 8X8 dots, eg. The strip LED Screen with 32X128 dots, consist of 4X16 pcs modules, of which the dot is 8X8.
　　 b.Intelligent display unit: the unit is an independent system or only one part of the LED Graph Display Screen, and it can display characters, lines and simple pictures. The master device adopts single-chip, and communication interface RS-485, Chinese Character Library and display buffer, etc. Every intelligent display unit has its own number or address. In order to satisfy the demand of the size of LED graph display screen, the quantity of intelligent display unit is optional.
　　 c.Master device: It uses single-chip, Chinese Character Library, power-protect data memory, time of day clock and two communication interfaces HS-485, which are all embedded into the system of LED graph screen. One interface of the two communicates with the computer, and the communication distance is hundreds of meters, the other is used to communicate with each intelligent display unit.The main function of the master device: receive the order from computers and display data; transfer the order or data to related intelligent display unit, and to ensure the synchronism of the display.
In practical applications, LED Graph Display Screen is an independent display system which consists of master device and intelligent display unit.　　
d.Computers: the main function of the computer and related software: if change display contents, then transfer the new data to the master device; if change the display mode, transfer related order to the master device; if inline dynamic display is required, transfer realtime data to the master device.
LED Graph Display Screen only displays communication, no grayscale displayed, besides, the data volume is small, and the exchange speed of information is slow, so the asynchronous and serial communication mode is suitable for the data transfer between the upper and the lower computer.
　　 2.Control mode: With the wide application of LED Graph Display Screen, and different circumstances and requirements, various control modes are optional. (1)Group display is suitable for large scale LED Graph Display Screens, and each displays the same content, such as the same market or meeting place, etc. Moreover, in this control mode, one upper computer could connect with multi lower computers (in Figure 2). It’s controlled by the upper computer, and communicates through broadcasting: the upper computer sends signals which is received by the lower computers at the same time.
When LED Graph Display Screen displays different contents, they could be distinguished through numbering the lower computers. The upper computer sends the No. of the lower computers to them before sending data, and the lower computers will judge whether the data is acceptable or not at first as soon as they receive the No., then only the pointed lower computers could receive data, and other ones ignore it, so as to display different contents in different graph screens. (2) In some occasions, the display contents on LED Graph Screen are relatively simple with less frequency through the infrared remote control mode, so the upper computer is unnecessary. Lower computers storage necessary data by themselves, and display content could be chosen according to the situation. Infrared remote control of TV could be changed into remote controller for Graph LED Screen.
(3) Wireless remote control: LED Graph Display Screen is arranged dispersedly, so the distance among screens may be long. Under that circumstance, it’s uneconomic for the communication medium between the upper and the lower computer to be wired, while, the wireless communication is appropriate.
四. Selection of LED Display Screen
The selection of LED Display Screen must satisfy one’s need, moreover the space constraints and the investment are also the key factors. For instance, it’s not only up to the indoor use and outdoor use, but also depends on what it displays: only characters, or both simple pictures and characters, or various video signals, animations, images and characters, besides, both the control mode (synchronization control or asynchronous control or wireless control and so on) and the viewing distance are rather significant to the selection of LED Display Screen.
Generally speaking, dual-color or full-color LED Display Screen in high dot-density is suitable for displaying images which requires close viewing distance, while, the specification in low dot-density is suitable for plenty of characters display. In addition, the color of LED Display Screen is based on the investment, the materials used for outline border based on the decoration states, and the control mode based on the application.
To be specific, more attention should be paid to the selection:
1.Try to select LED Chips in new style with wide viewing angle, and there are some advantages: colors are pure, operation is consistent, and the life span is more than 100,000 hours.
2.The most popular outer-encapsulation to LED Display Screen is required, such as the quadrate barrel with hood, silicone glue sealing, metal-free assembling. It’s exquisite and firm, sun-resistant, dustproof, waterproof, high-temperature resistant and short-circuit-proof output, etc.
3.Try to select suitable LED Display Screens based on different features of products and customers’ actual demand.
(1) LED Display Screen with φ5.0mm is suitable for stations, port, entrance of large-scale supermarkets or elevators, Some advantages are as follows, vivid characters, cheap price and controlled by computer-group.
(2)φ3.75mm Dual-color LED Display Screen is cheap, and suitable for revealing cooperate images and advertising, widely used in banks and marketplace, etc. While, φ5mm Full-color LED Screen could supply much better display effect.
(3)φ5mm dual-color LED Display Screen is suitable for large-scale place, while φ10mm LED Screen is superior in better display effect.
(4)φ3mm &φ5mm LED Display Screen is widely used in service windows of banks, post rooms, and electric-power, to display information at any time when service windows changed.
4.The quality of outdoor LED Display Screen must be superior because of the hostile environment outside, so a lot of factors should be considered.
(1) From the perspective of use, Full-color LED Display Screen will be the main trend in the near future because of the high brightness, rich colors and all-weather operations, except the higher price.
(2) From the perspective of application, products satisfying customers’ demand exist. Dual-color LED Display Screen is not good at characters display or supply rich colors, however, it’s superior in low price and steady performance.
(3) The orientation and viewing distance of outdoor LED Screen are crucial to the price. The farther of the viewing distance, the bigger and brighter of the pixel. Compared with the screen oriented Southwest, the screen oriented Northeast is much more cheaper.
(4) Both LED Display Screens and the combination between screens and architectures must be completely waterproof, moreover some good drainage measure must be provided as soon as the seeping occurs
(5) Lightning protection must be installed in LED Display Screen and architectures, and the ground connection between the main part and the shell of LED Screens must be good, meanwhile, the ground resistance must be less than 3Ω, to release the excessive electricity resulted from thunder and lightning
(6) Set up ventilation installation to lower the temperature in screens to -10～40, or install a cooling fan on the top at the back of one screen to release heat.
(7) Select industrial-grade integrated circuit, of which the operating temperature is between -40～80, to protect LED Display Screen from freezing.
　　 D.Common problems and solutions
　　 1．No display
a.Check the power-supply of LED Screens, and test that whether the electrical appliances connected with the switch is electrically live by test pencil or multimeter, or whether there is something wrong with the switch or the circuit.
b. Check whether the computer synchronously with LED Screen is in the dormancy situation at first; If it is, then open “the control panel”, click “power-supply management”, choose “never” from the menu “system waiting and turn off the monitor”, so the dormancy will never occur again, and the LED Screen could work normally; if not, try to open the cabinet to check whether the control card and communication cable are connected well or not.
2.Incomplete document or display in the wrong location
c.Check whether the arrange of software and the parameter of the size of LED Screen is identified with what engineers design. If the parameter is unknown, try to count the pixel dots on the length and the width, after make sure the size of the screen, check what’s the difference among display areas, then back to adjust the location on the computer until it’s correct.
d.If there is incomplete display, please check whether the size of documents is identified with that of the screen.
e.Open the case of the LED Screen to check whether the control card is short circuited.
3.The communication is disrupted.
f.Check the parameter revealed in software is the same as the one provided by engineers.
g.Check whether the serial port is firm or the communication cable is broken or not.
2.Check whether the earth wire connected with the computer or the communication cable is loose. If staffs could not judge what is the matter or they are not familiar with computers, please do not disassemble cases, but contact us at fi