Wireless Data Acquisition and Transmission Terminal Based on GPRS

Terminal system composition

Wireless data acquisition and transmission terminal design can have two programs: The first set of "single chip + GPRS modem", although the hardware cost of this program is relatively low, but the function is relatively limited, in the development and support of the agreement have a certain degree of difficulty; The two solutions are "embedded CPU + GPRS module". Although this solution has a slightly higher hardware cost and requires an embedded CPU chip to support the embedded operating system, it can implement a rich protocol interface, facilitate porting and upgrade to high-end system applications, and is more convenient for data. Acquisition and transmission implementation.

Figure 1 shows a schematic diagram of a wireless data acquisition and transmission terminal. It uses the second implementation of the Motorola Semiconductor (Editor's Note, now renamed: Freescale) embedded CPU MPC8xx plus the GPRS module CMS91.

Figure 1 principle of the terminal composition reference

The working principle of the terminal is to receive user data through the RS232/485 port, then tag the data into IP packets, access the GPRS network through the GPRS module, and then send the data to the data processing center through various gateways and routes.

The following describes the composition principle in Figure 1 in detail:

The embedded CPU chip is the core of the entire data acquisition terminal and can well support the embedded operating system. Considering the portability and performance requirements of the embedded operating system, the current mature Motorola MPC8xx embedded CPU is used. Many operating system manufacturers develop microcode and suites (BSPs) for this type of CPU to facilitate user migration.

The GPRS module mainly completes the function of wireless Internet access. There are some mature products in the market, such as Sony/Ericsson's GM47; Simens' MC35. Cellon’s CMS91 is used here. It is a dual-band GSM/GPRS 10-level module. Its main advantages include low power consumption, simple interface, complete AT command function, support for GPRS CLASS 10, development of multimedia applications, and low price. At the same time, it also provides SMS (Short Message Service) and voice capabilities. GPRS module provides RS232 interface, through which you can complete the control of the module, such as dialing and switching modes. Once connected to the Internet through the module, the collected data can be sent to any host with a public IP address using TCP/IP transmission to achieve wireless transmission of collected data.

Data acquisition generally uses a standard RS232 or RS485 interface to collect pressure, temperature, and other sensor data. The CPU is responsible for calculating and processing the collected data, and then sends it to the GPRS module to send it to the remote data center.

Watchdog is mainly used to prevent the terminal system from crashing. The software periodically writes data to the WD hardware. Once the system crashes and the software is not working properly, the WD hardware generates a hardware interrupt due to no data reception, and the system automatically restarts.

The ROM is mainly used to save the embedded operating system, application programs and related configuration parameters, and communicate with the CPU directly through the internal bus. Intel Corp.’s 28F320-J3, 32M bytes were selected here. The file system can be completed on the ROM, but the file system processing module needs to be added to the operating system.

The LCD is an optional module for displaying status information and the like. 10Base-T is also an optional module for easy commissioning. You can also use NAT technology and 10Base-T port to use the terminal as a gateway to the Internet.

Technical difficulties in implementation

CPU communication port configuration

The MPC850 microprocessor is used in this design. It is a versatile general-purpose chip that integrates a microprocessor and commonly used peripheral components and can be used in various control areas. It is a low-cost implementation of MPC860 applied to communication systems, provides a higher cost performance, and has been enhanced in communications, such as universal serial bus (USB) support. The MPC850 integrates an embedded PowerPC core and a dedicated RISC communications processor module (CPM) for communication. The MPC850's CPM supports six serial channels: a serial communication controller (SCC), a USB, two serial management controllers (SMS), an I2C interface, and a serial peripheral interface circuit SPI. Usually one SCC and two SMS can be configured as a universal serial port UART to control different modules and the rate is adjustable.

Implementation of file system on ROM

The ordinary ROM operation can only be operated by the module, which is inconvenient to maintain, and because there is no buffering operation during reading and writing, the data is easily lost and mistaken. The file system implemented on ROM can reasonably allocate and use each block, reducing block migration and over-use of blocks. In this design, Intel J3 series (28F320J3) flash memory was used as a storage device to implement TrueFFS. First, configure the three-tier structure of TFFS in the system startup configuration file and modify the MTD. Initializes the file system and default path at system startup. If successful, an operable file device character is generated. Since then, users can use the normal file operations (generate, read, write, and delete). It should be noted that after reading and writing the file, close the file to prevent data loss.

Network address translation (NAT) implementation when the device acts as a gateway

Using NAT to access the Internet has changed the original way of using proxy software to access the Internet. Two kinds of NAT settings (dynamic NAT and static NAT) can be used to implement Internet access. Dynamic NAT enables all hosts to access the Internet. Because NAT has the ability to hide the internal topology of the network, external hosts cannot directly access internal websites or hosts. However, through the joint use of dynamic and static NAT, both internal and external exchanges can be achieved, and the internal network topology can be hidden to ensure network security. In a specific implementation, the PPP dial-up GPRS network is first used to obtain the assigned address. If you get the internal IP address of the network communication assigned on the CPU communication port, and then configure the NAT parameters, configure the two port parameters as GPRS network address and internal communication address. Finally, the NAT is initialized with the configured NAT parameters.

The use of GPRS module operating mode

There are three main methods for data transmission using the CMS91:

1. SMS Messages - can be used to transmit characters or binary data, under normal circumstances the length of each SMS byte is 140 bytes, SMS for small amount of data on real-time requirements of the occasion is not high.

2. Data Calls - Transparent or non-transparent data transmission can be performed after the data link is established. It is mainly suitable for occasions where the amount of data is large and the number of transmissions is small.

3. GPRS data transmission - suitable for all situations of data transmission, is the future development trend.

The use of CMS91 GPRS module for Internet-based data communication SMS and Data Call applications are very different, whether it is SMS or Data Call are supported by the corresponding AT instructions, use is relatively simple, without understanding the actual operation process However, for the data application of GPRS, the knowledge of the involved network protocols must be relatively high.

In this application, the CMS91 GPRS module is equivalent to a wireless modem user application system. It needs to be connected to the operator's Internet access server through PPP (LCP/PAP/IPCP) before it can use TCP/IP, UDP, or more. The application layer program http, FTP, etc. is used for communication. In the current GPRS application, if the application system is based on the operating system, the complete PPP protocol can be used due to the relatively strong system function, but if the application system adopts the MCU, the simplified PPP protocol is generally used to make some incompatibility. The information is rejected.

There are two structures for data transmission using GPRS. The main difference lies in the location of the server: The server uses the host mode on the Internet, or the server directly connects to the CMNET through the DDN (or other high-speed connection such as ASDL). the way. According to the design and implementation techniques introduced above, it is not difficult to write a complete data communication process based on the Internet using the GPRS module.

Conclusion

This article introduced a method of realization of wireless data collection and transmission terminal based on GPRS from the system structure and implementation method, especially described how to use GPRS for data communication. General wireless data acquisition terminals are used in dedicated systems, such as power, water conservancy, etc., which are particularly suitable for low-data-rate data transmission requirements for small data, and generally have higher requirements for job stability. Here are some ideas for cost and compatibility: 1. The embedded CPU chip is converted from MPC8xx to ARM chip. 2. Network Support Upgrading from GPRS to CDMA can be achieved by replacing the wireless communication module.

references:
1. Chen Kaixuan and Xie Haijun, Principles and Applications of GPRS, Railway Communication Signals, July 2003, Vol.39, No.7

Walsin Ceramic Chip Capacitors

Walsin Capacitor,Walsin Chip Capacitor,103K Chip Capacitors,Walsin Ceramic Chip Capacitors

JINGGANGSHAN MEICHENG ELECTRONIC TRADING CO.,LTD , https://www.meicheng-tra.com