A design for a network end node, based on Arduino and XBee.
Bujdei, Catalin ; Moraru, Sorin-Aurel
Abstract: We needed a design for a network end node which to be
used for implementing a wireless sensors network, with the role of
making intelligent an office building. The automation process supposes
to monitor different ambient parameters values and also to control the
existent systems (e.g. air-conditioning, heating, ventilation). This
paper presents the research work done for determining the best suitable
node design necessary for our purpose, the node device developed as a
result of this research, the tests accomplished with it and
possibilities of optimization. The main characteristics of the proposed
node design are: easily implementable at a low cost, modular, could be
easily adapted for different types of applications and it has a small
physical size.
Key words: wireless sensors network, network node design, Arduino,
XBee, building automation
1. INTRODUCTION
In the last years the wireless sensors networks (WSN) domain knew a
wide development. The technology has been perfected, in a try to avoid
the main existent problems or constraints. The wireless communication
has multiple advantages compared to the wired communication, but also
disadvantages. Even the technology evolved, the implementation of this
type of networks in real life is limited, limitation determined
especially because of the high cost of the network devices (nodes) or,
for some types of nodes, because they could not be adapted to specific
types of applications. It is important to consider, at the design stage
of a device, the general aspect of it (do not limit its features only
for one application).
Into a wireless sensors network, there could be 3 logical types of
network devices (nodes): coordinator (one and only one could exist into
a network; it initializes the network), router (there could be many
nodes of this type into a network; they are used for increasing the
range area of transmitting the wireless data) and end node (dedicated
especially for collecting information from the environment). All router
nodes have usually the same design, but the end nodes could be dedicated
for monitoring different parameters, even they are part of the same
network.
In the last year we have worked at the development of a wireless
sensors network dedicated for building automation, but which to be used
also for other purposes (it is important to have a general design). We
are not interested only to measure ambient parameters values, but also
to be able to control different external systems, characteristic for an
office building (e.g. ventilation, heating, air-conditioning). For being
able to control, the network node design should include actuators.
2. THE EXISTENT NETWORK NODE DESIGNS
A recent research study has been accomplished, for determining the
most important types of network nodes developed until now and to choose
from them the most suitable for the development of our wireless sensors
network. Each type found has been analyzed from the following points of
view: possibility to be used in different types of applications (without
or with few modifications to its design), modularity (easy hardware
reconfiguration of the node, necessary for different characteristics of
the device), cost and size (it is important that the node do not disturb visually or other ways the activities of the people nearby). The life
time of the network node, directly related to its power consumption, was
not much analyzed in the nodes comparison process, since it is much
related to the application type. It is very important that the node to
have a general structure, and in this way to ensure the possibility to
use it in a variety of situations, without fixed constraints related to
the type of sensors, communication with the sensors or other elements
attachable to the node (Bujdei et al., 2010).
Most of the network nodes, available on the market today, have been
developed mainly for educational purposes (e.g. TI CC2420DB) and
doesn't allow an extension of their existent tasks (none or too few
inputs or outputs for connecting other dedicated sensors and actuators).
They usually are with some test sensors already attached and they
don't allow other sensors to be easily connected. The cost of them
is high and they don't have a physical small size.
Other types ensure a compact and modular architecture but at a high
price (e.g. Tyndal, Mica2Dot, iSense, Libelium WaspMote, Particle zPart,
MeshBean, MicroStrain). Since we want the entire solution to be
implemented at low cost, to use a high cost network node is not a good
starting point.
3. OUR OWN NETWORK NODE DESIGN
Since we considered not suitable what we have found for our needs,
we have decided, believing in the success of our goal, to design and
develop one node by our own, taking in consideration the necessities
presented above. The first version of the design for the node supposed
to build the node device from the scratch. The complexity of this job is
high and in short time it was proved that we don't have sufficient
time for this task, as we planned.
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
Meantime a new low cost and open source solution has been found:
Seeeduino Stalker v2, a development platform created especially for
being used for wireless sensors networks. Advantages of it are multiple
and it was chosen for our WSN development. The single disadvantages of
the platform have been considered to be the non-modular format (many
features are not used at each application type) and its physical size.
Since we got meanwhile some experience working with the modules
Arduino and XBee, we decided to try in the same time another approach
for our node development, based on them (Boonsawat et al., 2010).
A network end node should include some main functional modules:
processing unit (micro-processor, analog inputs, digital inputs and
outputs), wireless communication unit and power supply (ensure energy to
all modules). Auxiliary, other modules could be attached as it is
necessary (Bellis et al., 2005).
Our proposed end node design, presented in figure 1, is based on
using an Arduino Pro Mini platform (3.3V/8MHz) as a processing unit and
an XBee Series 2 module as communication unit. The power supply would be
ensured from a simple 9V battery. The Arduino board has integrated a
3.3V voltage regulator which could provide necessary voltage for the
XBee module. In figure 2 it is presented the implementation of the end
node. For connecting the Arduino to XBee module a dedicated adapter has
been used. At the Arduino board it has been attached female pin headers
which allow the developer to connect other auxiliary boards. For this
stage it was planned to be developed and use a sensors board, an
actuators board or a mixed board of sensors and actuators. One of the
biggest advantage of using Arduino and XBee modules is that they could
be easily configured and applications for them could also be easily
developed (Faludi, 2010; Varchola et al., 2005).
The XBee module, configured to function as an end node, would enter
normally a sleep mode for reducing the energy consumption. It just wakes
from time to time to verify if there are network messages dedicated to
him and to execute eventually scheduled tasks.
The solution proposed is modular (each module could be easily
detached and replaced if it is necessary) and could be implemented at a
low cost (about 455, for the main components). Also it could be used to
any type of applications, even it is necessary to read information from
sensors or control any external equipment. The only limitation is
imposed by the number of inputs and outputs of the processing board. The
size is quite small, comparing to other similar devices, and it could be
further minimized.
The first tests made with this design of the end node supposed to
attach a sensors board, where it was installed only one light sensor.
The measured value of the light intensity was send from the end node to
the coordinator node and displayed on a LCD screen. Other tests supposed
to attach an actuators board which command a lamp attached to the
network node. The command of the lamp, at 230V voltage, was simply done
using relay components.
4. FUTURE WORK AT THE PROPOSED DESIGN
The accomplished tests proved to have an acceptable design
solution, with multiple possibilities for future implementing. Even so,
some optimizations could be done for improving the whole node's
functionality:
* another type of power supply is searched to be found, which to
have a smaller size and to ensure in the same time a high energy
capacity;
* change the existent adapter or the connection, between the
Arduino and XBee, for being able to control also the Sleep pin
(available on XBee board and which could allow us to wake up the board
only when it is necessary), the CTS (Clear to Send) pin and RTS (Ready
to Send) pin. The CTS and RTS signals are used to ensure the serial data
flow control between the modules.
* change the Arduino Pro Mini, from the 3.3V version to 5V version.
The 5V voltage will allow us to control better the actuators (relays)
and to connect specific sensors which are not functioning at lower
voltage. For the other components which require 3.3V a voltage regulator
would have to be integrated.
5. CONCLUSION
The modular architecture, the general concept, the low cost
implementation and the possibility of easy reconfiguration make the
presented design of the end node to be a future solution with many usage
possibilities. The new versions of the design will come even with more
benefits. Any new application type, necessary to be developed using this
type of end node, will represent a challenge and a step further in our
research.
6. ACKNOWLEDGEMENTS
This paper is supported by the Sectoral Operational Programme Human
Resources Development (SOP HRD), financed from the European Social Fund
and by the Romanian Government under the project number
POSDRU/89/1.5/S/59323.
7. REFERENCES
Bellis, S. J.; Delaney, K.; O'Flynn, B.; Barton, J.; Razeeb,
K.M. & O'Mathuna C.(2005). Development of field programmable
modular wireless sensor network nodes for ambient systems, Computer
Communications, Vol. 28, No. 13, August 2005, pp. 1531-1544, ISSN:
0140-3664
Boonsawat, V.; Ekchamanonta, J.; Bumrungkhet, K. &
Kittipiyakul, S. (2010). XBee Wireless Sensor Networks for Temperature
Monitoring, Proceedings of the 2nd ECTI-Conference on Application
Research and Development, May 10-12, 2010, Pattaya, Chonburi, Thailand
Bujdei, C.; Moraru, S. A. & Ungnreanu, D. (2010). Designing a
layered node architecture to be used in Wireless Sensor Networks,
Proceedings of the 16 International Conference The Knowledge-Based
Organization, November 25-27, 2010, Sibiu, Romania, ISSN: 1843-6722, pp.
370-375, Nicolae Balcescu Land Forces Academy, Sibiu
Faludi, R. (2010). Building Wireless Sensor Networks with ZigBee,
XBee, Arduino and Processing, O'Reilly Media, ISBN:
978-0-596-80773-3, Sebastopol
Varchola M. & Drutarovsky M. (2007), Zigbee based home
automation wireless sensor network, Acta Electronica et Informatica, no.
4, vol. 7, ISSN: 1335-8243