LED billboard is a public-oriented information display terminal, with a very wide range of civil and commercial value. Now most of the LED billboard displayed information is pre-cured real-time information is lost, particularly inconvenient for users to change the display; several LED billboards, used in conjunction with a computer connected directly to the computer system, the system solved the problem of information to be refreshed , but due to a wired connection, limiting the arbitrariness of the system, especially for multi-regional multi-customer-oriented advertising agency, real-time updates to the system and to pass information to keep a lot of inconvenience.
In this paper, by hand-held remote control transmitter LED billboard new programs to achieve three advertising content and flexibility to change the display mode, use very convenient. PC as the host, the transmitter and the receiver is the procedure microcontroller core, high performance and low cost.
1.1 wireless remote control mode
In order to achieve remote control purposes, it must be through wireless transmission will need to display information and control commands are sent to the display terminal LED screen.
Using a wireless transmission method: Acoustic (ultrasonic), light (IR) and radio. Considering the wireless transmission to have the following advantages:
1) Transmission distance is more than the other two;
2) a wide variety of components, performance is also very good, the price is cheap;
3) technology is relatively mature.
Thus, the system uses radio transmission. That is, the transmitter and the receiver in the hand information between rely on radio wave transmission.
HF radio transmitter and receiver module performance directly affects the quality of the communication distance, after careful investigation and deliberation, the system uses the integrated transmitter and receiver modules. Its main advantage is the frequency of consistency, free debugging.
1.2 Data Coding
In wireless communication source coding and decoding is essential, it can improve the signal transmission reliability and validity.
In this system, a signal to be transmitted image, characterized in that the large-capacity data matrix data. Data transmission and reception is directly related to the correctness of the information display terminal. Billboard placed outdoors, and its many sources of interference. Thus, in this system design, coding, decoding reliability and durability of the design success.
The theory from the wireless communication system of coding and decoding technology and its impact on the system to do a thorough research, after repeated comparisons, and finally select the appropriate codec system ASIC. The module also uses CDMA technology, data encoding and decoding, can provide up to 531 441 (312) of the address of the code, you can completely eliminate any code, conflict resolution and unlawful interference with the encoded data.
1.3 Image lattice algorithm to extract and move
Grid computing image extraction algorithm, the source address of the database image offset, thus eliminating the corresponding lattice data to generate new display data. Extraction algorithm is correct, or not directly related to the accuracy of the displayed image.
This is to use an image algorithm to compute the dot matrix display database should be the next frame overlay offset address. The algorithm is correct movement, or not directly related to the moving picture or text and background synchronous FET, is particularly important for the color display.
1.4 System Block Diagram
The system consists of three relatively independent subsystems, namely personal computers, handheld transmitter, receiver and display systems.
Completion of the task information portal personal computer display and edit, and then move through the lattice algorithm to extract and display information to a dot matrix LED display corresponding data through the PC's serial port to transmit data to a hand-held transmitter dot matrix .
Handheld Transmitter's role is to come from the host computer and the panel keyboard commands received coding, modulation, code division multiple access communication forwarded to the outside user group lattice data, and on-site set up and debug screen display format.
The receiver receives the high frequency signal amplification shaping, demodulation and decoding, and the parallel output to the microcontroller, the microcontroller to determine the received data, dump, changes the display mode and display the real-time content, and drives LED display.
2 Hardware Configuration
There are three major system hardware, namely PC, handheld transmitter, receiver and display module.
PC directly using a common PC, which is mainly on account of the PC's processing instructions are strong, rich set of standard application software, the interface has a very versatile PC-based program has a strong compatibility and portability resistance, and cost-effective.
As the host computer system to complete the display information input, editing and animation design (pictures and text), therefore, must be the center beyond the PC can also be equipped with the appropriate input peripherals, such as scanners, digital cameras, keyboards and other . Network (Internet) interface is also essential, so you can remotely download information and advertising system and network management.
2.2 Handheld Transmitter
The transmitter consists of microcontroller, keyboard, encoder, transmitter, a serial communication interface and UPS power systems.
EPROM microcontroller itself from raster or bitmap image image in the send buffer of RAM is temporary role of the PC, according to keyboard commands sent serially to the encoder. MCU of choice is ATMEL Corporation 89S52, computing faster chip, stable performance, low price.
Keyboard is used to set the speed of the image, display mode and launch communication protocols.
Encoder is a key component of the system, one to determine the reliability of communication. Its function is to receive the data microcontroller encoded in a format according to the set, and serial output to the transmitter. By comparison, we choose a sequence of code division multiple access to a dedicated chip. This chip CMOS technology, low-power, anti-interference ability is very high (multi-frame synchronization), up to 12 tri-state address pins (up to 312 address codes), up to six data pin, wide range of operating the main features voltage, single-resistance oscillator, the output format can be set to latch or transient.
The transmitter is coded digital signal modulated onto a carrier frequency, effect, then amplified by the power emitted, which determines the distance of a hand-held wireless remote control transmitter. System selects modulation, drive and launch integration modules. The module uses SAW resonator frequency stabilization, SMT resin package, frequency better consistency, free testing, especially for multi overcharging wireless remote control and data transmission systems. And the general stability of the LC oscillator frequency and consistency is poor, even with high-quality tuning capacitor, temperature changes and vibration is difficult to ensure that the tuned frequency shift does not occur.
UPS power supply using a handheld transmitter to ensure outdoor work, the transmit buffer RAM data is not lost. Because the buffer need to start a temporary raster image data is large, the use of a large-capacity nonvolatile memory, such as E2PROM, FLASH and FRAM, not only the cost is higher, procurement difficulties, this system uses a common RAM buffer register .
2.3 receiver and display module
By the receiver of the receiver and display modules, decoders, microcontroller, display drivers, LED screen and power systems.
The receiver receives the high frequency signal is amplified, after shaping the demodulated digital code signal. We will use the corresponding receiver transmitter module demodulation integrated circuit modules. This series of modules superheterodyne, dual conversion technology, all of the RF receiver, mixing, filtering, data demodulation, amplification shaping circuit all integrated in the module, features a highly integrated, eliminating the RF frequency and ultra-super-regenerative receiver circuit debugging instability, high reliability, frequency stability, the receiving frequency free debugging functions.
Digital coded signal decoding apparatus, and parallel output to the microcontroller. We use CDMA encoding corresponding serial decode ASIC.
MCU is responsible for receiving identification data stored, the display mode switching. Select 89S52 microcontroller ATMEL Corporation, versatility and cost-effectiveness.
Display module for displaying advertising information. The module includes an LED display and display driver board with display buffer, the dynamic scan mode to drive the LED display with low power consumption, brightness, and other features.
Display system power received no special requirements, but leaving a considerable margin, and pay attention to ventilation, LED billboards, because many are due to fires caused by the power supply system.