23-11-2012, 11:13 AM
A Zigbee-Based Wearable Physiological Parameters Monitoring System
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Abstract
The design and development of a Zigbee smart noninvasive
wearable physiological parameters monitoring device has
been developed and reported in this paper. The system can be used
to monitor physiological parameters, such as temperature and
heart rate, of a human subject. The system consists of an electronic
device which is worn on the wrist and finger, by an at-risk person.
Using several sensors to measure different vital signs, the person
is wirelessly monitored within his own home. An impact sensor
has been used to detect falls. The device detects if a person is
medically distressed and sends an alarm to a receiver unit that
is connected to a computer. This sets off an alarm, allowing help
to be provided to the user. The device is battery powered for use
outdoors. The device can be easily adapted to monitor athletes
and infants. The low cost of the device will help to lower the cost of
home monitoring of patients recovering from illness. A prototype
of the device has been fabricated and extensively tested with very
good results.
INTRODUCTION
I N RECENT TIMES, wireless sensors and sensor networks
have become a great interest to research, scientific and technological
community. Though sensor networks have been in
place for more than a few decades now, the wireless domain has
opened up a whole new application space of sensors. Wireless
sensors and sensor networks are different from traditional wireless
networks as well computer networks and, therefore, pose
more challenges to solve such as limited energy, restricted life
time, etc. [1].
Wireless sensing units integrate wireless communications
and mobile computing with transducers to deliver a sensor platform
which is inexpensive to install in numerous applications.
Indeed, co-locating computational power and radio frequency
(RF) communication within the sensor unit itself is a distinct
feature of wireless sensing. Today, the progress in science
and technology offers miniaturization, speed, intelligence,
sophistication.
SYSTEM OVERVIEW
Fig. 1 shows the functional block diagram of the system
hardware. The system has been designed to take several inputs
to measure physiological parameters of human such as temperature,
heart rate, and detection of any fall. The inputs from
the sensors are integrated and processed. The results are sent
through the XBee Module to a host computer, which stores the
data into an Access Database. The values can then be displayed
on the Graphical User Interface (GUI) running on a computer.
If it is inferred that the person is medically distressed, an alarm
may be generated. The program is a user interface, allowing a
report on the current status of the individual.
Temperature Sensor
The skin temperature measurement is done using an integrated
circuit, the DS600 temperature sensor produced by
MAXIM – Dallas Semiconductor [11]. The Sensor gives an
analog output depending on the measured temperature. This
voltage has to be measured by the microcontroller using a 12 bit
Analog-to-Digital converter (ADC). Fig. 2 shows the circuit application
of DS600 IC, used as temperature sensor This sensor
is mounted within the wrist strap, positioned in such a way that
it is in contact with the skin, allowing it to measure the external
temperature of the skin. From the skin temperature, the body
temperature is estimated. There can be different methods to estimate
the exact body temperature from skin temperature [23],
but with a rough estimation usually the body temperature is
5.1 C higher than skin temperature when the body temperature
is measured at the ear by the National DM-T2-A thermometer
used by a general practitioner compared to the skin temperature
measured at the wrist. Because an exact measurement of body
temperature is not required, this method is suitable. Rather,
relative changes are monitored within set threshold, which sets
off the alarm. This allows the device to detect changes in body
temperature that could indicate the patient is undergoing any
of the following conditions: trauma, injury, heart attack, stroke,
heat exhaustion, and burns [14].
Communication
Communication between the wrist units and the receiver unit
is wireless. The data measured by the sensors is saved by building
a network between the sensors and to set up a computer receiving
and storing the values. For the communication ZigBee modules
were used, powered by the Silabs C8051F020 microcontroller
and transmitted in the unlicensed 2.4GHzfrequency band. These
provide a wide range and a couple of low-power modes, which
could be used to reduce the current consumption of the circuit. In
addition, the network-setup is easy and fast, so that an extension
of new units is possible without problems. Fig. 14 shows the
connection overview of various sensor units, wirelessly.
DISCUSSIONS AND FUTURE DEVELOPMENTS
In this paper, we have presented the research, of applied nature,
done to monitor physiological parameters such as skin temperature,
heart rate, and body impact. A prototype was successfully
developed and tested to establish the proof of concept. The
algorithms were tested and found to be accurate and reliable
at this developed/development stage. The novel aspect of the
design is its low cost and detection of medical distress which
does not necessitate pressing any panic button. This is an enormous
improvement over existing commercial products. A panic
button has also been provided in the developed system which
can be used under an emergency situation.
An important aspect of the design was miniaturization, so
that the system was as nonintrusive as possible to the wearer.
This was achieved by the use of surface-mounted devices on the
PCBs designed. Low-power operational amplifiers were used to
minimize battery consumption. The major cost comes from the
use of ZigBee modules in the current design.