GUO Tao(郭 涛), YAN Ming-ming(闫明明), BAO Ai-da(鲍爱达)

(1. Key Laboratory of Instrumentation Science ＆ Dynamic Measurement (North University of China),Ministry of Education, Taiyuan 030051, China;2. Department of Electronic Science and Technology, North University of China, Taiyuan 030051, China)

Wireless sensor network based on CC2530*

GUO Tao(郭 涛)1,2, YAN Ming-ming(闫明明)1,2, BAO Ai-da(鲍爱达)1,2

(1. Key Laboratory of Instrumentation Science ＆ Dynamic Measurement (North University of China),Ministry of Education, Taiyuan 030051, China;2. Department of Electronic Science and Technology, North University of China, Taiyuan 030051, China)

This paper designs a wireless sensor network based on CC2530. The sensor nodes consist of multi-ranged accelerometer and CC2530, covering all the ranges of the acceleration signals which can be measured. The designed system solves the problems such as cable installation trouble of testing system, vulnerability to interference and complexity of circuit. Test results show that the designed wireless sensor network can transmit the signals that multi-ranged micro-accelerometer emits without spoilage, thus the measurement of acceleration of the covering region is completed.

multi-ranged micro-accelerometer; acceleration; wireless sensor network

With the development of micro-electro-mechanical systems (MEMS) technology, MEMS devices are widely used in the fields of industry, aerospace, etc. and MEMS devices can be seen everywhere[1]. As a new type of MEMS devices, multi-ranged micro-accelerometer solves some problems such as inconvenient installation and error due to the application of the accelerometers with different ranges when measuring[2]. But conventional cable testing methods need a lot of power for the data acquisition equipment, and the signal transmission will be interfered by noise, especially the long cable transmission may lead to signal distortion or signal invalidation[3]. To solve the above problems, this paper presents a wireless sensor network based on CC2530.

1 Wireless sensor network

Wireless sensor network (WSN) is formed by a large number of stationary or moving sensors in the self-organization and multi-hop mode, which is designed to collaboratively collect, process and transfer the monitoring information of the perceived objects in network coverage area and then it forwards the results to its users[4]. The following Fig.1 shows a WSN schematic diagram.

As mentioned, WSN can realize three functions: data acquisition, processing and transmission, which correspond with three basic technologies of modern information: sensor technology, computer technology and communication technology. They constitute the three parts of the information system, “sense”, “brain” and “nerve”, respectively. Therefore, WSN is the combination of these three technologies, and they all constitute an independent and modern information system.

Fig.1 Schematic diagram of wireless sensor network

2 System structure

As shown in Fig.2, WSN system mainly consists of sensor nodes, base station module and data center.

Fig.2 Block diagram of system structure

The sensors are installated in a distribation mode. Every node can induce and regulate acceleration signals which are converted into digital signal through A/D convertor. Wireless transceiver module configrated on sensor node can send digital signal to the base station in real-time. Base station sends them to data center by RS232 and finally the data is displayed on PC and saved.

2.1 Sensor network topology

There are three kinds of wireless network topology with Zigbee. They are star network topology, grid network topology and tree network topology[5], as shown in Fig.3.

Fig.3 Wireless network topology

Considering the decrease in the number of tree network topology structure, coordinate power consumption is a dozen of times even hundreds of times that of commonly-used user terminals[6].

By using star network the power consumption of the whole WSN system can be reduced. Moreover, data transmission in point-point network segment terminal equipment must go through coordinator. Because routing list in coordinator is complicated and it is difficult to maintain and regulate it in real-time, the design must use grid network topology.

2.2 Design of sensor node

The hardware structure of sensor node consists of multi-ranged micro-accelerameter signal-conditioning circuit, digital processing module and wireless transceiver module.

The faint voltage output signals by multi-ranged micro-accelerameter are sent to filter circuit after amplifiered by A/D convertor. Second-order high-pass filter circuit and low-pass filter circuit confine the transmission bands in 2 kHz-5 kHz and cut off the useless noise. ATmegal128 produced by ATMEL is chosen as digital control chip. It can convert analysis signal to digital signal then save it. After that the signal is sent to CC2530 on wireless transceiver module. CC2530 works in terminal node mode. After receiving the signal, CC2530 can package destination address, data and address itself, process them and send them to the air[7].

2.3 Design of base station module

The base station module is composed of wireless transceiver module, digital processing module and RS232 conversion circuit. The hardware architecture is shown in Fig.4.

Fig.4 Hardware structure of based staion module

CC2530 wireless transceiver module of base station module is a coordinator in WSN system, which is the core of the whole system. The wireless transceiver module detects the data from the network node in the air, then the data is captured and stored in the memory after demodulation chip in a fixed area. Each byte of data to be stored sends a pulse to inform master control chip (ATmega128) to read it[8]. Finally, TTL signal is converted into RS232 level signal and output to PC serial interface.

3 System test

3.1 Test of transmission distance

In order to determine the coverage area of WSN, the experiments test the communication distance between the sensor node and the base station firstly. The experiments include an indoor test and an outdoor test. Indoor test uses the walls for insulation, every wall placing a sensor node； Outdoor test sets a starting point 50 m apart from the base station, placing a sensor node every 50 m. Each sensor node sends three sets of data and processes the data received from the data center. The test results of the error rate of data are shown in Table 1. If the error rate of data is less than 3%, the communication is successful and it can guarantee correct and effective transmission of data within 300 m. The reason of transmission signal faster decay is that the walls absorb the radio signals[9].

Table 1 Error rate of data

3.2 Network test

This experiment is used for network test of WSN. Main steps are as sollow: selecting 3 sensor nodes placed on the table in the room according to star network structed and fixed by double-coated adhesive tape; Setting the mode to multi-point monitoring mode; Knocking the nodes in the center of the test surface, observing the monitoring waveform in the data center, recording the data and comparing the acceleration values collected by the 3 nodes. Table 2 shows the results of acceleration test. It can be seen that the measured acceleration value of each node is not very different, and the biggest difference is 2.73% via calculaton.

Table 2 Results of node acceleration test

3.3 Precision test

We observe the low-test-rangs of multi-ranged micro-accelerometer using calibration system for the sensors in the laboratory. There is only one set of calibration system, so the single-point monitoring mode is adopted. The results of accuracy test are shown in Table 3.

Table 3 Results of accuracy test

The test precision of the sensor node can reach 1.5%. Results show that WSN based on multi-ranged micro-accelerometer can not only achieve distributed measurement of the signal, but also ensure high precision of the test.

4 Conclusion

This paper introduces software and hardware designs of WSN based on multi-ranged micro-accelerometer. The sensor nodes using star network structure have the characteristics of low power consumption, high reliability, far transmission distance and high test precision. The system has achieved the expected effect after the test. This system solves complex problems of the installation in the acceleration measurement system using a plurality of single range accelerometer and improves the reliability of data transmission, which provides a strong guarantee for the realization of the simple and intelligent test.

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date： 2013-05-12

National Natural Science Foundation of China(No. 51075374)

YAN Ming-ming (mto19871028@126.com)

CLD number： TN926 Document code： A

1674-8042(2013)03-0286-03

10.3969/j.issn.1674-8042.2013.03.018