Research Of Speech Transmission Based On RS485 Measure And Control Network

Along with the development and the expanding area using of speech communications, there are many important and dangerous areas in the industrial locations, which requires higher and higher requests about speech communications real time(for instance; installation, debugging, detection of equipments), especially in big industrial fields, for instance: under the surface of coal mine, large petrifaction equipments, room of hydrodynamic plants bottom, and so on. Because the environments is so complex, interphone, PHS phone and other equipments even are used in the field, bnt they can't exert their characters and aren't used popularly, it is important to design an especial communication mode or use the network in existence which is needed to use it to improve the efficiency, safty in the field. With automation technology, communication technology and computer technology developed rapidly, the speech compression and transmitting real time won't be limited by technology. So this paper put forward a field speech communication system which using the RS485 Bus as the transmission channel for the complex terrain, using the G.729A standard as the speech compression arithmetic, which is used under the coal mine as a assistant tool, design and realize it as well.The paper introduces the key significance to the research and the status of speech compression and transfers, and gives the arrangement of main work.The paper mainly researches the speech transfers of coal mine, and analyzes the theory and characteristic of normal data transmission. In order to improving the safety and trustiness, the system uses the RS485 Bus under the surface of coal mine for its simple hardware, convenient control and cheap cost, uses the fiber and CAN bus on the earth.Speech encode arithmetic is the basic of speech compression, the paper chooses the G.729A standard which is sustained by Code Excited linear Prediction and has the 8kb/s data rate, the 3.7~4.0 voice quality. Because the G.729A standard is complex and has much calculation, the paper is familiar with the ARM7 LPC2210 firstly, and optimize the arithmetic and program using the chip resources fully, then the calculate capacity is reduced to 40.9MIPS after plant the program to the chip, which meets the microprocessor fully. From the results of hardware simulation and subjective analyses, the voice quality is well after compression and decompression, and has little difference from the original voice. The hardware of system is made up of communicate system and phones, every phone is connected by the four way RS485 Bus, the system achieves the full duplex speech communication based on the theory of calling first and configuring receive and transmit dynamically. Which provides a fast, convenient and useful speech communication system for information transferred real time of the equipment's debugging, detection and so on in industrial fields.