is a wireless sensor network that monitors the environmental conditions such as light, temperature, and humidity. This network is comprised of nodes called motes that form an ad-hoc network to transmit this data to a computer that function as a server. The server stores the data in a database where it can later be retrieved and analyzed via a webbased interface. The network works successfully with an implementation of one sensor mote.
The technological drive for smaller devices using less power with greater functionality has created new potential applications in the sensor and data acquisition sectors. Low-power microcontrollers with RF transceivers and various digital and analog sensors allow a wireless, battery-operated network of sensor modules (motes) to acquire a wide range of data. The TinyOS is a real-time operating system to address the priorities of such a sensor network using low power, hard real-time constraints, and robust communications. The first goal of WISENET is to create a new hardware platform to take advantage of newer microcontrollers with greater functionality and more features. This involves selecting the hardware, designing the motes, and porting TinyOS. Once the platform is completed and TinyOS was ported to it, the next stage is to use this platform to create a small-scale system of wireless networked sensors.
There are two primary subsystems (Data Analysis and Data
Acquisition) comprised of three major components (Client, Server, Sensor Mote
There are two top-level subsystems â€œ
This subsystem is software-only (relative to WISENET). It relied on existing
Internet and web (HTTP) infrastructure to provide communications between the Client and Server
components. The focus of this subsystem was to selectively present the collected environmental data
to the end user in a graphical manner.
The purpose of this subsystem is to collect and store environmental data for later
processing by the Data Analysis subsystem. This is a mix of both PC & embedded system software, as
well as embedded system hardware. It is composed of both the Server and Sensor Mote Network
System components are Client, Server, and Sensor Mote Network.
The Client component is necessary but external to the development of WISENET.
That is, any computer with a web browser and Internet access could be a Client. It served only as a
user interface to the Data Analysis subsystem.
Requests WEB page Requested WEB page
Requested WEB page Requests WEB page
Figure 2: Client Component Inputs/Outputs
The Server is a critical component as the link between the Data Acquisition and
Data Analysis subsystems. On the Data Analysis side, an web (HTTP) server hosting a web
application. When a page request came in, the web server executes the web application, which
retrieved data from the database, processes it, and returns a web page that the web server
transmitted to the Client. For the Data Acquisition system there is a daemon (WiseDB) running to
facilitate communication with the Sensor Mote Network.
CLIENT SENSOR NETWORK
WEB page Requests Data packets
(Via GATEWAY MOTE)
CLIENT SENSOR NETWORK
This daemon is responsible for collecting raw data packets from the Sensor
Mote Network. These packets are then processed to convert the raw data into meaningful
environmental data. This processed data is then inserted into the database. Thus the database is
the link between the Data Analysis and Data Acquisition subsystems. The Server also had the
potential to send commands to the Sensor Mote Network (via the gateway mote), although this
functionality was not explored in WISENET.
It should be noted that since the SQL database connections can be made via
TCP/IP, only the web server and web-program (see figure 4) needed to be located on the same
physical machine. The web server, the database, and WiseDB could all be on different physical
machines connected via a LAN or the Internet. This allows a flexible Server component
implementation that is useful during WISENET development.
Figure 4: Server Component Block Diagram
The primary focus of WISENET is the development of the Sensor Mote
Network component. It is the component responsible for collecting and transmitting raw
environmental data to the Server. There is also the potential for the motes to receive commands
from the Server, although that functionality may not be implemented in WISENET. Uses for this
feature would include server-based synchronization and wireless network reprogramming.
SERVER PC SENSOR NETWORK
COMMANDS DATA PACKETS
(GATEWAY MOTE) SENSOR NETWORK
SERVER PC ENVIRONMENT
DATA PACKETS HUMIDITY, LIGHT etc.,
Figure 5: Sensor Mote Component Inputs/Outputs
This component consists of two parts. The first is the sensor mote. The primary
purpose of the sensor mote is to collect and transmit raw environmental data. When not doing this, it
went into a low-power idle mode to conserve energy. Another aspect of the sensor motes involved adhoc
networking and may be for multi-hop routing;
The gateway mote is the second part of the Sensor Mote Network. Its purpose is to
serve as the liaison between the Server and the Sensor Mote Network and deliver all the data packets
to WiseDB. In theory both standard and gateway motes could be implemented on the same hardware
PCB and with the same software. For WISENET, however, resource and time constraints necessitated
the use of slightly different hardware and software configurations for gateway versus standard motes,
as described below.
The selection of components for the sensor motes is a critical process in
the development of WISENET. Great functionality and low power are two of the highest
priorities in evaluating the fitness of both the microcontroller and the sensor candidates.
WISENET is introduced to the new state-of-the-art Chipcon CC1010 microcontroller
with integrated RF transceiver. After a little research it was decided the CC1010 would
make the perfect microcontroller.
It had the following feature list:
1. Optimized 8051-core
2. Active (14.8 mA), Idle (29 _A) and sleep (0.2 _A) power modes
3. 32 kB flash memory
4. 2 kB +128 bytes SRAM
5. Three channel 10-bit ADC
6. Four timers / Two PWM's
7. Hardware DES encryption/decryption
8. Hardware random bit-generator
9. Fully integrated UHF RF transceiver (433 MHz / 868 MHz nominal)
_ Programmable output power (-20 to 10 dBm)
_ Low current consumption (11.9 mA for RX, 17.0 mA for TX at 0dBm)
_ RSSI output that can be sampled by the on-chip ADC
WISENET includes a socketed evaluation board (CC1010EB) and two
evaluation modules (CC1010EM). The evaluation board provided access to all of the
analog and digital pins on the CC1010, as well as two serial ports, a parallel
programming port, RF network analysis ports, and other peripherals. Each evaluation
module featured the CC1010, RF network hardware, an antenna port, and an analog
temperature sensor. The modules connected to the evaluation board via two TFM-D
sockets. These sockets also allowed the possibility of designing a custom expansion
WISENET is designed to measure light, temperature, and humidity.
There are many digital temperature sensors available, but there is a much smaller
selection of digital humidity and light sensors. A larger selection of analog sensors are
available; however, analog sensors tended to require more power and be less precise than
their digital counterparts, in addition to requiring more complex circuitry. For these
reasons, digital sensors are given higher priority. Two new sensors provided the required
functionality. First, Sensirion released the SHT11, a digital temperature and humidity
sensor with ultra low power consumption (550 MicroA while measuring, 1 MicroA when
in sleep mode), a 14 bit analog to digital converter, and the desired accuracy (Ã‚Â±5%
relative humidity, Ã‚Â±3Ã‚ÂºC). It also featured a simple serial interface. The light sensor chosen
was the Texas Advanced Optoelectonic Solutions (TAOS) TSL2550 ambient light sensor
with SMBus interface. This sensor also featured ultra-low power (600 MicroA active, 10
MicroA power down), a 12-bit analog to digital converter, and dual photo diodes. The
TSL2550 uses both photo diodes to compensate for infrared light and to produce a
measurement that approximates the human eye response.
The final stage of hardware design involved creating the Add-on
module. The WISENET Add-On Module has the two digital sensors described above.
The Sensirion SHT-11 humidity and temperature sensor has a 2-wire proprietary serial
interface. The TAOS TSL2550 digital light sensor uses an SMBus serial interface.
SMBus is a standardized 2-wire serial interface. The layout must be carefully designed
such that the light, temperature and humidity sensors does not underneath the evaluation
module when it is plugged into the board, which would make them useless.
Software Design-shelf products:
The server using for WISENET should have four commercial off the shelf
applications installed on it that worked together to create the Data Analysis portion of the
Server component. Apache, MySQL, and PHP are open-source products freely available
on the Internet. In addition, Chart-Director the trial version of the commercial application
Chart-Director was used.
Apache is a standard web-server, which makes a web document available on the
PHP is a web programming language, which allows dynamic web-pages. It
should also be designed to use along with a database and included many built-in
functions for interfacing with MySQL.
MySQL is a database that can contain any type of data and is accessed by a
TCP/IP (Internet) call.
Chart-Director is a program that generates a graph from raw data. It is
available in many languages such as PHP, ASP, C++, and others.
Software Components â€œ Custom:
WISENET is also composed of three custom software components:
The Web program, WiseDB, and a port of TinyOS.
WISENETâ„¢s web program was written in PHP and utilized the Chart-
Director charting software. The web application queried MySQL database for the data in
the requested date range, then we use a Chart-Director to generate a graph of that data.
WiseDB is the custom software component that interfaced with the
Sensor Mote Network via a serial link to the gateway mote and with the MySQL database
via a TCP/IP link to the MySQL server application. Already we know about how
WiseDB interacted with the rest of the system. WiseDB was written in C++ and utilized
two open-source APIâ„¢s (application programming interface).
The final custom software component involves porting TinyOS to the
CC1010-based hardware platform described in the Hardware Design section. As
previously mentioned, TinyOS is a real-time operating system designed for use in sensor
network applications where low-power, limited resources and hard real-time constraints
are critical parameters. After implementing all the software and embedding in a single
system other important goal of WISENET is to completely replace the lower-layer
functionality to permit existing higher-level components and applications to be
immediately implemented on the new hardware platform without modification.
There are a number of future extensions for this WISENET. A few are:
We can expand the sensor mote network by adding more motes. This
would allow the development and testing of advanced network-layer functions, such as
By creating a new PCB design that integrates the CC1010EM design with
the sensors and power hardware on a single-board another interesting feature can be
developed or adopt a standard expandable plug-in sensor interface in both hardware and
In researching alternative energy sources to extend mote battery life.
Possibilities include solar cells and rechargeable batteries.
Wireless sensor networks are getting smaller and faster, increasing their
potential applications in commercial, industrial, and residential environments.
WISENET, as implemented, represents one commercial application. However, the limit
of applications depends only upon the sensors used and the interpretation of the data
obtained. As the technology improves and new low-power digital sensors become more
readily available, motes will increase functionality without increasing power
consumption and will expand the wireless sensing market.
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