introduction
With the development and improvement of LED technology, large-scale LED displays have been widely used in various public places for displaying multimedia information such as text, graphics, and video images. In the modernization of urban information, LED display has become one of the important media for modern information dissemination. With the rapid increase in the number of outdoor LED screens and the expansion of the range of use, new requirements have been placed on the management and control of LED displays.
1, the system works
The system is mainly composed of a host computer and a lower computer. The host computer is a device that has LED screen management software and can connect to an Internet or GPRS network, such as a PC or a mobile device. The lower computer is an LED screen wireless controller based on the AVR microcontroller control module. The system topology is shown in Figure 1.
The system mainly uses the GPRS module as the wireless Modem, realizes the LED display wireless controller (as the client) dial-up Internet, and performs TCP wireless communication with the host computer (as the server) on the Internet network to realize data transmission and complete the LED screen. Wireless data update.
2, lower computer hardware design
As shown in Figure 2, the LED screen wireless controller is mainly composed of four parts: power module, GPRS module, AVR microcontroller control module, LED display .
2.1 AVR MCU Control Module
In order to ensure the real-time and efficiency of communication data, and to drive the LED display, the MCU used in this module is ATME 162 of ATMEL with dual serial port. It is an AVRRISC-based low-power CMOS 8-bit MCU. It has high stability and reliability, can adapt to various environments, and is suitable for various wireless LED display environments.
This module mainly deals with the information received by the GPRS module, and transmits the received on-screen information to the LED screen. At the same time, it sends an AT command through the serial port to monitor whether the GPRS module has a new message. Once there is, immediately enter the serial port interrupt and process the data. Under the TCP/IP protocol, the data is transmitted in hexadecimal mode, which does not require Chinese character decoding, which greatly simplifies the design of the peripheral circuits of the system.
2.2 GPRS module circuit
The GPRS module uses SIMCOM's SIM300. The module is compact and has outstanding performance. It can be widely used in wireless voice transmission, in-vehicle systems, remote meter reading, security monitoring, remote telemetry, handheld devices and other fields.
The SIM300 module has a fully functional system interface, integrates the TCP/IP protocol stack internally, and extends the TCP/IP AT commands. It can interoperate with the AT commands provided by the serial port. This can reduce the development difficulty, easy to achieve data transmission, and low cost, system scalability.
The SIM300 needs an external SIM card holder. The serial port is connected to the serial port of the MCU, and the information received by the GPRS module is transmitted to the MCU, and then the data is processed. The AVR MCU controls the switch of the SIM300 module. The connection diagram between the AVR MCU and the SIM300 module is shown in Figure 3.
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