1 system program
1.1 wireless remote control mode
To achieve the purpose of remote control, you must pass the wireless transmission will need to display the information and control commands to the display terminal LED screen.
Commonly used wireless transmission methods are: sound waves (ultrasound), light (infrared) and radio waves. Taking into account the radio transmission has the following advantages:
1) transmission distance is much more than the other two;
2) available components of a wide range of performance is also very good, cheap;
3) technology is more mature.
Therefore, the system uses radio transmission. That is, information is transmitted between the handheld transmitter and the receiver via radio waves.
The same time as
High-frequency wireless transmitter and receiver module performance directly affects the remote control distance and communication quality, after multi-investigation and demonstration, the system uses integrated transmission, receiving module. Its main advantage is the frequency consistency is good, free debugging.
1.2 data encoding
The encoding and decoding of the source is critical in wireless communication, which can improve the reliability and effectiveness of signal transmission.
The signal to be transmitted in this system is the lattice data of the image, which is characterized by large amount of data. Transmission and reception of data is good or bad, directly related to the display terminal to display the correct or not information. Billboards are placed in the outdoors, the interference source a lot. Therefore, in the design of the system, coding, decoding reliability and anti-jamming is the key to the success of the design.
The system from the wireless communication theory, the coding and decoding technology and its impact on the system to do a thorough study, after repeated comparison, the final selection for the system of coding and decoding dedicated chip. The module also uses code division multiple access technology for data encoding and decoding, providing up to 531 441 (312) address codes, can completely eliminate any address conflict and unauthorized coding data interference.
1.3 image lattice extraction and motion algorithm
The extraction of the image lattice is to use the algorithm to calculate the offset address in the image source database, so as to remove the corresponding lattice data and generate new display data. The correctness of the extraction algorithm is directly related to the correctness of the displayed image.
And the image movement is to use the algorithm to calculate the next frame of data in the display lattice database should be superimposed offset address. The correctness of the mobile algorithm is directly related to the dynamic image or text and background synchronization and field effects, especially for color display is particularly important.
1.4 system block diagram
The whole system consists of three relatively independent subsystems, namely, host computer, handheld transmitter, receiver and display system.
The task of the host computer is to complete the input and edit of the display information, and then through the dot matrix extraction and movement algorithm to convert the display information to the LED display corresponding to the lattice data, and through the PC's serial port to transfer lattice data to Hand-held transmitter.
Hand-held transmitter is the role of the host computer came the lattice data and panel keyboard to receive the command encoded by the modulation, the code division multiple access to forward the way to the outdoor user base, and on-site settings and debugging display Screen display format.
The receiver will receive the high-frequency signal after amplification shaping, demodulation decoding, and then parallel output to the microcontroller, by the microcontroller to receive data to identify, dump, real-time changes in display and display content, and drive LED display.
2 hardware configuration
System hardware has three major parts, namely the host computer, handheld transmitter, receiver and display module.
2.1 host computer
PC is a direct choice of general-purpose PC, which is mainly taken into account the PC processing instructions very strong, the standard application software is rich, the interface has a strong versatility, PC-based program has a strong compatibility and portability, Cost-effective.
As the host computer system to complete the display information (images and text) input, editing and animation design, therefore, in addition to the central PC machine must also be equipped with the corresponding input peripherals, such as scanners, cameras, keyboard and so on. Network (INTERNET) interface is also essential, so you can achieve the information remote download and advertising system network management.
2.2 Handheld Transmitter
The transmitter consists of a microcontroller, a keyboard, an encoder, a transmitter, a serial communication interface and a UPS power supply system.
The role of the microcontroller is the PC came the image lattice or its own EPROM in the image lattice temporarily stored in the transmit buffer RAM, and then according to the keyboard command serial send to the encoder. MCU is selected ATMEL's 89S52, the chip computing faster, stable performance, and cheap.
The keyboard is used to set the image movement speed, display mode and transmit communication protocol.
Encoder is one of the key components of the system, determines the reliability of communication. Its function is to receive the microcontroller data, according to the format set to code, and then serial output to the transmitter. After comparison, we use the code division multiple access serial encoding dedicated chip. The main features of the chip are CMOS technology, low power consumption, very high noise immunity (multi-frame synchronization), up to 12-bit 3-state address pins (up to 312 address codes), up to 6 data pins, A wide range of operating voltage, single-resistive oscillator, the output can be set to latch or transient.
The role of the transmitter is to encode the encoded digital signal to the high-frequency carrier, and then amplified by the power after the launch, it determines the handheld transmitter's wireless remote control distance. The system uses the modulation, drive and launch integration module. The module uses SAW resonator frequency stabilization, SMT resin package, the frequency consistency is better, free debugging, especially for multiple wireless remote control and data transmission system. And the general LC oscillator frequency stability and consistency is poor, even with high-quality fine-tuning capacitor, temperature changes and vibration is difficult to ensure that the frequency has been adjusted does not shift.
UPS power supply is used to ensure that the handheld transmitter in outdoor work, the launch buffer RAM data is not lost. Because of the large amount of non-volatile memory, such as E2PROM, FLASH and FRAM, it is not only costly but also difficult to purchase, so the system chooses the ordinary RAM As a buffer register.
2.3 Receiver and display module
Receiver and display module by the receiver, decoder, microcontroller, display driver, LED screen and power supply system.
The receiver demodulates the digitally encoded signal by amplifying the received high frequency signal. We use the transmitter and receiver module corresponding to the receiving and demodulation integration module. The series of modules using superheterodyne, the second frequency conversion technology, and all the RF reception, mixing, filtering, data demodulation, amplification and shaping circuit all integrated in the module, the function of highly integrated, free RF frequency debugging and super Regeneration of the receiving circuit instability, with high reliability, frequency stability, the receiving frequency and other debugging features.
Decoding
The digital coded signal is decoded and output to the microcontroller in parallel. We use the code is corresponding to the code division multiple access serial decoding dedicated chip.
SCM is responsible for receiving data recognition, preservation, display mode conversion. MCU selected ATMEL's 89S52, versatile, cost-effective.
The display module is used to display advertising information. The module includes LED display and display driver board, comes with display buffer, and dynamic scanning way to drive LED display, with low power consumption, brightness and other characteristics.
There is no special requirement to receive the power supply of the display system, but there is considerable margin and attention to ventilation and cooling, because many of the fire caused by LED billboards are caused by the power supply system.
3 software structure
The system software consists of three modules, namely the host computer master program, the transmitter master program and the receiver master program.
3.1 host computer master program
Host computer host program actually includes the display information generation program, display dot matrix conversion program and serial communication program, is the three main control program in the structure of the most complex part.
Display information generation program to complete the display image and text input, editing and animation design. The program first uses the DOS platform under the master program and the underlying communication software, through the serial and parallel communication port to complete the user source files, INTERNET interface and other input devices, multi-parameter entry. On this basis, Visual C ++ language is used to design the master software, generate animation, and realize the visual control of the whole PC system through the interface and dialog box.
Display lattice conversion program is to generate the display information through the dot matrix extraction and mobile algorithm will display the information converted to LED display corresponding to the lattice data. For the color display, it is necessary to sample the RGB three primary colors of the image information separately, and block the storage, the order of forward; for continuous animation images, according to the frame to calculate the offset, the key is the background image and animation text to be synchronized. The part of the software is written in the environment of TURBO C3.0.
Serial communication program is relatively simple, attached to the dot matrix conversion program.
Limited to space and technical reasons, here only PC machine to send the program as an example, describe its principles and structure.
Set the terminal display shows the 16 × 16 Chinese characters dot matrix. Therefore, in order to display the advertisement information on the terminal, the dot matrix data of the Chinese character contained in the information must be transmitted to the terminal. In TURBO C3.0, the Chinese characters assigned to a variable, in fact, the Chinese character code assigned to this variable. By using UltraEdit-32 in binary form, observe the DOS Chinese character library file chs16.fon, found that Chinese characters are stored in the form of lattice. Each character is 16 × 16 dot matrix, stroke through the place as "1", the rest is "0". In this way, from top to bottom, from left to right order, a Chinese character consists of 256 points, that is, 32 bytes. Chinese characters according to the order of the location code in the Chinese character font, the area code for the line, bit code for the column, a district has 94. In this way, the offset address of a Chinese character in the Chinese character library is (area code × 94 + bit code) × 32. Remove the 32-byte Chinese dot matrix, through the PC's serial port into the transmitter.
3.2 Transmitter master program
The function of the transmitter master software is to receive the image lattice sent by the upper PC through the serial port, read the keyboard command, and send the operation command or display data to the encoder serial.
The part of the software is written in the Keil C51 environment, it can be directly translated into assembly language C language, generate binary code into the microcontroller, so that the preparation of some higher efficiency.
The program is to rely on interrupt mode to work, after the boot waiting for the serial port and INT0 trigger. When the serial port is triggered, it indicates that the PC has the image lattice data, the microcontroller immediately receives the lattice data stored in the RAM; when the INT0 trigger, indicates that the keyboard has the action, immediately receives the key value judgment order category, The machine sends the image lattice data or the operation command.
3.3 receiver master program
The function of this part of the software is to complete the identification of the received data, storage, transformation and display driver, and can achieve the local self-test, display solidified images. When the decoder of the receiving device has output, the microcontroller interrupts the current display, receives the flag word, and then judges the contents of the flag word, determines whether it will receive the image lattice, or the operation control command. If the lattice data, it will continue to receive and stored in a display buffer database, according to the current way. If the command, then change the display mode immediately.
Among them, the key is the image up, down, left, right move real-time implementation. The specific implementation is as follows:
1) Move up and down the image Move the previous line of data in an image lattice to the corresponding next row in BUF [16] [4] until the end of an image is moved; then the dot matrix of the next image is removed. The process of moving up is similar.
2) The left and right movement of the image will be an image of each row of data to the left shift (using the C language shift instructions), the lattice will be stored in the BUF, you can display. The right shift process is similar.
4 performance test
System function and parameter test results are as follows:
1) image entry function scanner, camera, digital camera, image source file;
2) text entry function keyboard, WORD / TEXT source file;
3) animation design function text or graphics relative to the background to move, zoom;
4) Transmitter setting function Receiver serial number, image movement command, self-test command, launch command;
5) receiver self-test function display blue lawn background and "welcome to visit" mobile characters;
6) Transmitter standby time ≥ 120 h;
7) Transmitter remote control distance ≥ 250 m;
8) Transmitter cache space 8 MByte;
9) LED display 320 × 640 DIP;
10) receive display system power consumption ≤ 4 kW.
5 Conclusion
Machine performance test and identification conclusions are as follows:
1) through the handheld transmitter remote control LED billboards, the program is novel, practical and strong, with high marketing value;
2) hardware configuration science, stable performance, cost-effective;
3) software structure is reasonable, powerful, easy to use.