Wireless remote LED billboard
Time:2018-10-22
Views:243
0 the introduction
LED billboard is a public information display terminal, which has a wide range of civil and commercial value.At present, most of the information displayed by LED billboards is fixed in the system in advance, which loses the real-time information and is particularly inconvenient for users to change the display content.A few LED billboards are directly connected to microcomputers, which are used to transmit information. This system solves the problem of information refresh, but due to the wired connection, the randomness of system placement is restricted, especially for the multi-area and multi-client advertising companies, which brings a lot of inconvenience to the real-time update and maintenance of the system.
In this paper, a new scheme of controlling LED billboard by handheld transmitter is proposed, which can change the content and display mode of the billboard flexibly and is very convenient to use.The scheme takes PC as the upper computer, and the transmitter and receiver are all based on the single chip microcomputer.
1 system scheme
1.1 wireless remote control
To achieve the goal of remote control, the information needed to be displayed and control commands must be transmitted wirelessly to the display terminal LED screen.
Commonly used wireless transmission methods are: sound (ultrasonic), light (infrared) and radio waves.Considering the following advantages of radio transmission:
1) the transmission distance is much farther than the other two;
2) a wide range of available components, good performance and low price;
3) technology is more mature.
Therefore, this system USES the wave transmission.That is, information is transmitted by radio waves between a handheld transmitter and a receiver.
The performance of high frequency wireless transmission and receiving module directly affects the remote control distance and communication quality.Its main advantage is good frequency consistency and no debugging.
1.2 data encoding method
The source coding and decoding is very important in wireless communication, which can improve the reliability and validity of signal transmission.
The signal to be transmitted in this system is the lattice data of the image, which is characterized by a large amount of data.The quality of transmitting and receiving data is directly related to whether the information displayed on the display terminal is correct or not.Billboard is placed outdoors, its interference source is very much.Therefore, in the design of this system, coding and decoding reliability and anti-interference is the key to design success.
This system starts with the theory of wireless communication, makes an in-depth study on the encoding and decoding technology and its influence on the system, and selects the special chip of encoding and decoding suitable for this system after repeated comparison.The module also USES the code division multiple access technology for data encoding and decoding, and can provide up to 531 441 (312) address codes, which can completely eliminate any code address conflict and the interference of unauthorized coding data.
1.3 algorithm for image lattice extraction and movement
The extraction of image lattice is to use the algorithm to calculate the offset address in the image source database, so as to extract the corresponding lattice data and generate new display data.The correctness of the extraction algorithm is directly related to the correctness of the display image.
The algorithm is used to calculate the offset address that should be superimposed on the next frame data in the display lattice database.Whether the mobile algorithm is correct or not is directly related to the synchronization and field effect of dynamic images or text and background, especially for color display screen.
1.4 system block diagram
The whole system consists of three relatively independent subsystems, namely, upper computer, handheld transmitter, receiver and display system.
The task of the upper computer is to complete the input and editing of the display information, and then transform the display information into the LED display data through the lattice extraction and moving algorithm, and transfer the grid data to the handheld transmitter through the serial port of the PC.
The role of the handheld transmitter is to transmit the bitmap data from the upper computer and the commands received on the panel keyboard, after being coded and modulated, to the outdoor user group by means of code division multiple access communication, and to set and debug the display format on the site.
After amplification and shaping and demodulation and decoding, the receiver outputs the received high-frequency signals to the MCU in parallel. The MCU recognizes and transfers the received data, changes the display mode and content in real time, and drives the LED display screen.
2 hardware configuration
The system hardware mainly has three major parts, namely upper computer, handheld transmitter, receiver and display module.
2.1 PC
The upper computer is directly selected from the general PC machine, which mainly takes into account that the PC machine has a strong ability of processing instructions, rich standard application software, strong versatility of interfaces, and the pc-based program has a strong compatibility and portability, with high cost performance.
Since the upper computer system needs to complete the input, editing and animation design of display information (image and text), it must be equipped with corresponding input peripherals, such as scanner, camera, keyboard, etc., besides the central PC.The network (INTERNET) interface is also necessary to realize remote download of information and network management of advertising systems.
2.2 hand-held transmitter
The transmitter is composed of microcontroller, keyboard, encoder, transmitter, serial communication interface and UPS power supply system.
The function of a single chip is to temporarily store the image dot array from a PC or in its own EPROM in the transmitting buffer RAM and send it serially to the encoder according to the command of the keyboard.The MCU is selected from 89S52 of ATMEL company. This chip has fast computing speed, stable performance and low price.
The keyboard is used to set the image movement speed, display mode and transmission communication protocol.
Encoder is one of the key parts of the system, which determines the reliability of communication.Its function is to receive MCU data, according to the format set for coding, and then serial output to the emitter.After comparison, we chose the chip of code division multiple access serial coding.The main features of the chip include CMOS technology, low power consumption, very high noise immunity (multi-frame synchronization), a maximum of 12 bit 3 state address pins (up to 312 address codes), a maximum of 6 bit data pins, a wide range of operating voltage, a single resistor oscillator, and output can be set as latching or transient.
The function of the transmitter is to modulate the coded digital signal to the high-frequency carrier wave, and then transmit it after power amplification. It determines the wireless remote control distance of the handheld transmitter.The system adopts modulating, driving and transmitting integrated modules.This module adopts acoustic meter resonator to stabilize frequency, SMT resin package, with good frequency consistency and no debugging, especially suitable for wireless remote control and data transmission system.However, the frequency stability and consistency of LC oscillator in general are poor. Even with the use of high quality fine-tuning capacitance, it is difficult to guarantee that the adjusted frequency point will not be offset by temperature variation and vibration.
UPS is used to ensure that data in the launch buffer RAM is not lost while the handheld transmitter is working outdoors.Due to the large amount of image dot matrix data required to be stored temporarily in the transmitting buffer zone, if super-capacity non-volatile memory is used, such as E2PROM, FLASH and FRAM, etc., it is not only costly but also difficult to purchase, so the system chooses common RAM as the buffer register.
2.3 receiver and display module
The receiver and display module consists of receiver, decoder, microcontroller, display driver, LED screen and power supply system.
The receiver demodulates the digital coded signal after amplifying and shaping the received high frequency signal.We chose the receiving demodulation module corresponding to the transmission module.This series of module adopts superheterodyne, secondary frequency technology, and all of the rf receiving, mixing, filtering, data demodulation, enlarge shaping circuit all integrated within the module, function is a highly integrated, from the instability of rf frequency debugging and super-regenerative receiver circuit, has high reliability, frequency stability, receive frequency free debugging, etc.
decoding
The digital coding signal will be decoded, and then output to the microcontroller in parallel.We chose the chip of code division multiple access serial decoding corresponding to the coding.
MCU is responsible for the recognition, preservation and display of data conversion.The single chip computer selects 89S52 of ATMEL company. It has good versatility and high cost performance.
Display module is used to display advertising information.The module includes LED display and display driver board, with a display buffer, and drives LED display with dynamic scanning mode, featuring low power consumption and large brightness.
There is no special requirement for the power supply of the receiving and display system, but it should be relatively generous and pay attention to ventilation and heat dissipation, because many LED billboard fires are caused by the power supply system.
3 software structure
The software of this system is mainly composed of three modules, namely upper computer main control program, transmitter main control program and receiver main control program.
3.1 master control program of upper computer
The host control program of the upper computer actually includes display information generation program, display lattice conversion program and serial communication program, which is the most complex part of the three main control programs.
Display information generation program to complete the display image and text input, editing and animation effects design.The program firstly combines the master control program under the DOS platform with the underlying communication software, and completes the multi-parameter input of users to source files, INTERNET interfaces and other input devices through serial and parallel communication ports.On this basis, the main control software is designed with Visual C++ language, animation is generated, and Visual control of the entire upper computer system is realized through interface and dialog.
The display raster conversion program converts the generated display information into the corresponding grid data of LED display screen through the raster extraction and moving algorithm.For the color display screen, it is necessary to sample RGB three-color data of image information, and store them in blocks and forward them in sequence.For continuous animation images, the offset shall be calculated respectively according to the frame. The key is to synchronize the background image with the animation text.The software for this part was written in the context of TURBO C3.0.
Serial communication program is relatively simple, attached to the lattice conversion program.
Due to limited space and technical reasons, the principle and structure of PC Chinese character extraction and transmission program are described here.
Set the terminal screen display is 16 x 16 Chinese character lattice.Therefore, in order to display the advertisement information on the terminal, the lattice data of Chinese characters contained in the information must be transmitted to the terminal.In TURBO C3.0, when the Chinese character is assigned to a variable, the location code of the Chinese character is actually assigned to the variable.By using ultraedit-32 in binary form and observing the Chinese character database file of DOS, chs16.fon, we find that Chinese characters are stored in the form of dot matrix.Each character is a grid of dots that are 16 by 16. The stroke is "1" and the rest is "0".Thus, in order from top to bottom, from left to right, a character consists of 256 dots, or 32 bytes.The Chinese characters are arranged in the Chinese character library in the order of location codes, with area codes as rows and bit codes as columns, and area 1 has 94 digits.Thus, the offset address of a Chinese character in the Chinese character library is (area code x 94+ bit code) x 32.The 32 - byte Chinese character dot matrix is taken out and sent to the transmitter through the serial port of PC.
3.2 main control program of transmitter
The function of the master control software of the transmitter is to receive the image dot array sent by the upper PC through the serial port, read the keyboard commands, and send the operation commands or display data to the encoder serial.
The software of this part is written under the environment of Keil C51, which can directly translate C language into assembly language and generate binary code into microcontroller, so that it can be written more efficiently.
The program works by interrupts, waiting for the serial port and INT0 to trigger after boot.When the serial port is triggered, it indicates that the PC machine has the image lattice data transmitted, and the SCM immediately receives the lattice data and stores it in RAM.When INT0 triggers, indicating that the keyboard has an action, it immediately receives the key value to determine the type of command, and sends the image grid data or operation command to the receiver.
3.3 main control program of the receiver
The function of this part of software is to realize the recognition, storage, transformation and display drive of the received data, and to realize local self-check and display solidified images.When the decoding chip of the receiving device has output, the single chip interrupts the current display and receives the marker word, and then determines the content of the marker word, and determines whether the image dot matrix or the operation control command will be received.If the raster data is present, it is received and stored in a display buffer database in the current manner.If ordered, change the display immediately.
Among them, the key is the real-time realization of moving image up, down, left and right.The specific implementation method is as follows:
1) the moving up and down of an image assigns the data of the top line in an image lattice to the corresponding next line in BUF[16][4] until the moving of an image is completed;Move on to the next dot matrix.The process of moving up is similar.
2) the left and right movement of the image shifts each line of data of an image to the left (using the shift instruction in C language), and the shifted lattice is stored in BUF to display.It‘s a similar process to shift right.
4 performance testing
Test results of system functions and parameters are as follows:
1) image input function scanner, camera, digital camera and image source files;
2) TEXT input function keyboard, WORD/TEXT source file;
3) animation design function text or graphics move and zoom relative to the background;
4) set the receiver serial number, image movement command, self-check command and launch command by the transmitter;
5) the receiver‘s self-check function shows the blue lawn background and "welcome" moving characters;
6) standby time of transmitter is greater than or equal to 120 h;
7) remote control distance of transmitter is more than 250 m;
8) transmitter cache space 8 MByte;
9) LED display, 320 x 640 DIP;
10) power consumption of the receiving display system is less than or equal to 4 kW.
5 conclusion
The conclusion of performance test and evaluation of the whole machine is as follows:
1) remote LED billboard with handheld transmitter is novel and practical with high market promotion value;
2) scientific hardware configuration, stable performance and high cost performance;
3) reasonable software structure, powerful function and easy to use.
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