Communications and Network, 2013, 5, 549-553
http://dx.doi.org/10.4236/cn.2013.53B2099 Published Online September 2013 (http://www.scirp.org/journal/cn)
Wireless Distributed Monitoring Terminal Used for
On-Line Application
Fenggui Wang, Lin Zhang, Zhongmin Wang, Yanbo Zhang
Institute of Automation, Shandong Academy of Sciences, Jinan, China
Received June 2013
ABSTRACT
A wireless distributed monitoring terminal was designed with embedded Linux used on the basis of ARM board, and an
application program was developed for data collection, processing and transmission. Data were collected from the sur-
rounding environment and transmitted to a server via WLAN in the form of Extensible Markup Language (XML)
stream, so the terminal had good flexibility to be compatible with different sensors, network devices and information
systems from multiple manufacturers.
Keywords: On-Line Monitoring; Distributed Monitoring; Extensible Markup Language (XML) Stream; Wireless
Terminal
1. Introduction
On-line applications are becoming more and more wide-
spread along with the popularity of the Internet of Things
in various fields [1], such as environmental monitoring,
public safety, telemedicine, etc [2,3]. In these applica-
tions, some terminals are necessary to execute data ac-
quisition, processing and transmission. There may be dif-
ferent sensors, network devices and information systems
from multiple manufacturers even if in one application,
so it is important that every terminal has good flexibility
to be compatible with them.
ARM platform has been very popular in the area of
mobile devices such as smart phones, personal players of
audio and video, GPS systems and so forth, and can also
compete with desktop computers based on i386 architec-
ture microprocessors in some case [4]. ARM microcon-
trollers are convenient and efficient for designing and
developing especially with embedded operating system
used, so more and more terminals begin to adopt designs
based on them nowadays.
This paper deals with design of a wireless distributed
monitoring terminal with embedded Linux used on the
basis of ARM board, and development of an application
program for data collection, processing and transmission.
It collects data from the surrounding environment via
RS485 or A/D convertor, carries out data analysis and
processing, and transmits them to a server via Wireless
Local Area Network (WLAN). The server stores these
data to an oracle database and presents them through web
pages. It is needed to be specially noted that these data
are encapsulated into Extensible Markup Language (XML)
stream by terminal before transmitting and then parsed to
obtain the semantics by server after receiving [5], so as to
enhance the flexibility of whole system.
2. Hardware Design
The hardware of the wireless distributed monitoring ter-
minal includes ARM9 board based on S3C2440A and
Wi-Fi module to send and receive data wirelessly be-
tween it and the server. Also, it connects temperature/
humidity sensor and illumination sensor as example for
monitoring changes of the surrounding environment. The
structure diagram of the terminal is shown in Figure 1.
2.1. ARM9 Board
The board is based on S3C2440A microcontroller with
512 MB RAM and 512 MB flash memory. SAMSUNG’s
S3C2440A is designed to provide hand-held devices and
general applications with low-power, and high-perfor-
mance microcontroller solution in small die size. To re-
duce total system cost, the S3C2440A includes the fol-
lowing components: separate 16 KB Instruction and 16
KB Data Cache, MMU to handle virtual memory man-
agement, LCD Controller (STN & TFT), NAND Flash
Boot Loader, System Manager (chip select logic and
SDRA M Con tro ll er), 3-ch UART, 4-ch DMA, 4-ch Timers
with PWM, I/O Ports, RTC, 8-ch 10-bit ADC and Touch
Screen Interface, Camera interface, IIC-BUS Interface,

F. G. WANG ET AL.
Copyright © 2013 SciRe s. CN
550
Figure 1. Structure diagram of wireless distributed monitoring terminal.
IIS-BUS Interface, USB Host, USB Device, SD Host &
Multi-Media Card Interface, 2-ch SPI and PLL for clock
generation [6]. The platform also offers a large number
interface to support peripheral equipments, including USB
host, USB device, LCD touch screen interface, RS232,
RS485, 4 - 20 mA/0 - 5 V convertor and so on.
2.2. Wi-Fi Module
The Wi-Fi module adopted based on VIA Networking
VT6656 is fully compliant with IEEE’s security and
802.11 g standards [7]. Enabling data rates between wire-
less devices of up to 54 Mbps, it can deliver the band-
width necessary for real-time streaming of high-defini-
tion digital multimedia content in home networks, and
provide high-speed email, web and LAN access to mul-
tiple mobile users in corporate environments or public
hotspots. Integrated WLAN into USB 2.0 with it, device
also makes it more convenient to get on the net anywhere
you are.
2.3. Sensors
The temperature/humidity sensor and illumination sensor
are used to collect data from the surrounding environ-
ment in our system.
1) Temperature/humidity sensor
This sensor adopts the most advanced digital sensor
technology, overcoming disadvantages of the traditional
analog temperature sensor, such as instability, much devi-
ation from accurate data, v ulnerability to interferen ce, and
requiring regular calibration. It processes the function of
collecting information of temperature and humidity, w ith
calculating data stably and accurately. Its operating vol-
tage can be as low as 12 V, accuracy of temperature
±0.7˚C, accuracy of humidity ±3% RH.
Connected to the monitoring terminal via RS485, an
industrial level communication network with long-dis-
tance transmission, high speed and high stability com-
pared with RS232, the sensor transmits acquired temper-
ature/humidity data using Modbus standard. It is an ap-
plication layer messaging protocol that is positioned at
level 7 of the OSI model and widely used in industrial
environment.
2) Illumination sensor
This sensor has a wide light measurement range of 0 ~
200,000 Lux, with high precision linear amplifier circuit
and high sensitive photographic detectors. Its accuracy is
less than ±7%, and operating voltage is 12 - 24 V.
After data acquisition, the sensor transmits 4 - 20 mA
current signal to the monitoring terminal, and then the 4 -
20 mA current signal is converted to 0 - 3.3 V voltage
signal. Through an analog-digital converter, digital data
are acquired and they can easily be processed and ana-
lyzed by S3C2440 to make them understood by human.

F. G. WANG ET AL.
551
3. Software Design
The linux-2.6.28 distribution compiled for ARM9 plat-
form is chosen as the operating system. The application
program residing on the ARM platform is written in C
language and compiled using the Linux GNU C compiler,
which can be downloaded from the network free of
charge.
3.1. Device Drivers
Device drivers take on a special role in Linux kernel.
They are distinct “black boxes” that make a particular
piece of hardware respond to a well -defined internal pro-
gramming interface, and the details of how the device
works are hidde n completely by them [8]. User activ ities
are performed by means of a set of standardized calls that
are independent of the specific driver, mapping those
calls to device-specific operations that act on real hard-
ware is then the role of the device driver. This program-
ming interface is such that drivers can be built separately
from the rest of the kernel and “plugged in” at runtime
when needed. This modularity makes Linux drivers easy
to write, to the point that there are now hundreds of them
available.
Linux device driver belongs to the kernel part, and
there are two ways of compiling and loading it into Li-
nux kernel. One way is to directly compile device driver
into the kernel, along with Linux starts when loading.
Another way is to compile device drivers as dynamic
loading and deleting modules, using the command of
“insmod” to load and “rmmod” to delete. This way con-
trols the size of the kernel, while the other way increases
redundancy of the kernel, so it is adopted to compile
USB wireless network card driver, exit key driver, A/D
driver, etc.
3.2. Work Flow
The monitoring terminal firstly initializes, including start-
ing Linux system, loading USB wireless network card
driver, exit key driver and A/D driver and setting serial
port, and sends archived data, which is stored in a local
file when the network is unconnected. Then real time
data is frequently acquired from sensors, analyzed by
classification, stored into local file, and sent in the form
of XML stream. When sent successfully, the data will be
deleted from the local file immediately. Due to being
stored into a local file first, data will not be lost even if
the terminal is powered down suddenly. Next, the ter-
minal will check whether the time point set beforehand
has arrived. If the time point is up, it will send archived
data stored in the local file, otherwise it still conducts as
before. Also, if the terminal detects the exit key has been
pressed, it will ex it normally including re leasing memory
closing devices, unloading drivers, etc. The work flow of
the terminal is shown in Figure 2.
4. Testing
There is a wireless distributed monitoring terminal tested
which collects data from the surrounding environment
and transmits them to a server via WLAN. These data are
stored to an oracle database and presented through web
pages, as shown in Figures 3 and 4.
5. Conclusion
In this paper, an embedded Linux operation system com-
bined with ARM9 platform is adopted to implement a
Figure 2. Flow chart of wireless distributed monitoring
terminal.
Power on &
Self-start
Y
Load drivers
Analyze and store
the data
Receive successful reply?
Send the data
Delete the data
Time point has arrived?
Acquire real time
data
Y
Three times？
Send archived data
Receive successful reply?
Delete historical
data
Y
Y
Send archived data
Receive successful reply?
Delete historical
data
Y
Exit key pressed?
Y
Exit
Start
N
N
N
N
N
N

F. G. WANG ET AL.
Copyright © 2013 SciRe s. CN
552
Figure 3. Data stored to oracle database.
Figure 4. Data presented through web pages.

F. G. WANG ET AL.
553
wireless distributed monitoring terminal, and an applica-
tion program is developed for data collection, processing
and transmission. Data are sent in the form of XML
stream, stored in oracle database and presented through
web pages, so it’s feasible to add any sensor to the ter-
minal. Future possible works based on this terminal are
adding more environment sensors and improving the
XML streami ng protocol .
6. Acknowledgements
The paper is supported by Youth Science and Technolo-
gy Star Program of Jinan City, China (Grant No. 20100105)
and Youth Science Funds of Shandong Academy of
Sciences, China (Grant No. 20100106). The authors would
like to thank all collaborators, especially who are in the
UWB & THz Innovation Team, Shandong Academy of
Sciences, China.
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