0 Preface
The automatic weather station is composed of meteorological sensors such as barometric pressure, temperature, humidity, wind speed, rainfall, radiation, etc., as well as data collection, processing, and management systems. Automatic weather stations have long-term stability problems, and regular calibration of weather sensors is required to ensure accurate observation data.
The meteorological observation data cannot be interrupted, so it cannot be dismantled and sent to the testing room like ordinary measuring instruments. A better method is to use a standard instrument to perform calibration and calibration directly at the observation site. Therefore, a hand-held calibrator is designed, which uses wireless sensor network to read the observation data of the automatic weather station and the indication value of the standard device, and calibrates.
1 System design and realization principle
This design uses a wireless sensor network, Windows CE operating system, ARM processor developed a handheld calibrator for meteorological elements sensor calibration. During calibration, the data of the tested sensor is sent to the coordinator through the wireless sensor network using ZigBee technology, and the coordinator transmits the data to the handheld calibrator. The calibrator calculates the error. If the error exists is greater than the preset error of the corresponding element, it will automatically generate a calibration command and send the calibration value to the sensor until the error is eliminated. The working principle of the entire system is shown in Figure 1 [1].
Figure 1 Working principle of the system
2 System hardware design
The hardware functional block diagram of the calibrator is shown in Figure 2. The hardware is mainly composed of a data acquisition module based on CC2530 and a hardware platform module with an ARM9 core.
Figure 2 Hardware block diagram of the handheld calibrator
The data acquisition module is mainly composed of CC2530 chip, sensor and peripheral components. The function of transplanting operating system and data calibration on the hardware platform [2].
2.1 Data acquisition module design
The data acquisition module uses the ZigBee wireless sensor network, which is mainly composed of the ZigBee network coordinator node and the ZigBee sensor terminal node. This system uses the TI company ’s CC2530 as the wireless sensor network node [3]. CC2530 is used for 2.4GHz IEEE 802.15 .4, a true system-on-chip solution for ZigBee and RF4CE applications, it can build a powerful network node with a very low total material cost.
CC2530 has extremely high receiving sensitivity and anti-interference, only need to cooperate with a few peripheral components to realize the signal sending and receiving function [4].
2.2 Hardware platform design
This system uses the 32-bit ARM920T RISC processor SamsungS3C2440A, the main frequency is 400MHz. It adopts 320 & TImes; 240 resolution 3.5-inch touch true color LCD screen. SDRAM uses H57V2562GTR with 32 MB of storage space, NANDFLASH uses Samsung ’s K9F2G08ROA. The network coordinator node uses CC2530, which has a lower cost and only needs to work with a few peripheral components. S3C2440 and CC2530, NAND FLASH, SDRAM connection diagram is shown in Figure 3. The hardware system is simple in structure, small in size, and fast in operation speed, and can be installed with operating systems such as WindowsCE and Linux [5].
Figure 3 Schematic diagram of system connection
3 Software design
The calibrator enters the corresponding calibration interface according to the meteorological elements to be calibrated, and automatically receives the processed data. If the detection error is greater than the preset error, after confirming the calibration password, a calibration command is automatically generated and sent wirelessly to the corresponding meteorological sensor.
The system has installed Windows CE 5.0 operating system. WindowsCE is the foundation of Microsoft's embedded and mobile computing platform. It is an open and scalable 32-bit embedded operating system with good reliability, high real-time performance, small kernel size and scalability, and powerful communication capabilities. And other characteristics, are widely used in the development of embedded intelligent devices [6]. The calibrator system software part is mainly composed of two parts: one is serial communication, which is mainly used for real-time data transmission between the coordinator and the handheld calibrator, and the other part is user interface software design and function implementation, both of which use embedded Written in C # language, using VS 2005 form interface for visual software development. Figure 4 is the system software flow chart.
3.1 The transplantation of embedded operating system Windows CE.NET
After the hardware system is completed, you need to port the operating system to the hardware platform and develop application programs. Platform Builder is an integrated development environment (IDE) provided by building a customized embedded platform based on the WindowsCE.NET operating system. It provides design, creation, compilation, testing, and debugging functions, as well as platform development wizard and BSP development wizard, basic configuration, Emulator, Windows CE Test Kit, etc. The specific transplant steps are as follows:
Figure 4 System flow chart
(1) Tailoring the operating system, configuring various components and modifying related configuration files; (2) developing drivers on the target device and creating customized CE operating system image files; 44 Hyundai Electronic Technology 2012 Vol. 35 (3) Download the target file to the target device for debugging; (4) After customizing the operating system kernel, export the platform SDK for developing upper-layer application software in Visual Studio 2005 [7].
3.2 Construction of development environment
For Windows CE 5.0 operating system, the selection is based on. Developed using the Visual Studio 2005 environment of the .NET 2.0 framework. This article is accessed through. NET Compact FrameWork class library, graphical window programming, select smart device WindowsCE 5.0 device application program template for development in the development environment.
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