27-11-2012, 05:31 PM
DESIGN AND IMPLEMENTATION OF SENSOR NODE FOR
WIRELESS SENSORS NETWORK TO MONITOR HUMIDITY OF
HIGH-TECH POLYHOUSE ENVIRONMENT
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ABSTRACT
Wireless Sensors Network is a novel field shows tremendous application potential. To monitor the
environmental parameters of high-tech polyhouse the Wireless Sensors Network (WSN) is developed. The heart
of this ubiquitous field is the Wireless Sensor Node. Moreover, the field of microcontroller based embedded
technology is innovative and more reliable. Therefore, based on an embedded technology and the RF module
Zigbee a wireless senor node is designed about highly promising AVR ATmega8L microcontroller and
implemented for WSN development. Recently, the modern agriculturists are demanding sophisticated
instrumentation for measurement and control of environmental parameters of the polyhouse. To enhance crop
yield one has to provide controlled environment to the crop. The humidity is important parameter, which plays
vital role on the crop yield. Therefore, a Wireless Sensors Network (WSN) is designed and implemented for
monitoring of humidity of polyhouse and the results of implementation are interpreted in this paper.
INTRODUCTION
Wireless Sensors Network (WSN) is the ubiquitous field showing wide spectrum of applications in
various sectors [1]. It combines sensing, computation and communication also [2]. It consists of the
sensor nodes, which are networked, by deploying network topologies, with each other and also with
the based station. Majority of the applications of the WSN lies in information sensing, real time
tracking, monitoring of the various physical parameters of industrial, environmental, health,
automobile etc sectors [3]. This technology also helps to record the meteorological parameters. The
architecture of the WSN is deployed by Chintalapudi [4] for monitoring the health parameters and
suggested new architecture, NETSHM, wherein the constraints of network programming are
minimized. Focusing on the investigation of the application potential Das et al [5] have reviewed this
new domain of research, extensively. Wireless Sensor Network (WSN) is an emerging field of
electronics ensuring the research of applied nature. Therefore, many researchers show interest in
development of Wireless Sensor Network for various applications. Zhu et al [6] have designed
Wireless Sensor Network system based on Zigbee compliant RF module CC2420. Moreover, they
deployed the 8051 microcontroller for each node. A distributed control system based on Wireless
Sensor Network is developed and presented by Pereira and Cugnasca [7] in 2005. In order to monitor
the concentration of hydrocarbons particularly, in chemical industries a Wireless Sensor Network
based system is designed by Kane et al[8] and interpreted the results, which could support the
optimization of production. Mahfuz and Ahmed reviewed the field of Wireless Sensor Network and
suggested its suitability for environmental protection [9, 11]. They reported features of both Zigbee as
well as Bluetooth technologies. Erdongan et al [10] have developed Wireless sensor to monitor a
pressure inside a tyre of automobiles. Zigbee technology supports IEEE 802.15.4 protocol and
operates in the frequency of 2.4 GHZ, ISM band [11]. Emphasizing the low power requirement of
Wireless Sensor Network, Francisco et al have employed WSN for medical applications [12].
Signal Conditioner:
As stated earlier, a smart humidity sensor SY-HS-220 provides the D.C. output voltage (mV) linearly
proportional to the humidity in RH%. To pick up this signal and to amplify the same, an
instrumentation amplifier AD 620 is employed. Fig. 2 (a) depicts the circuit designed about AD 620.
This is programmable instrumentation amplifier exhibiting very high input impedance, which could
really help to isolate the sensor from remaining analog part of the hardware.
Data Acquisition System:
Designing of DAS, is highly important and tedious job for instrumentation design. Generally, it
consists of the blocks such as multiplexer, ADC etc. However, present embedded system is
developed about the advanced microcontroller, AVR Atmega8L, which has promising on chip
resources. The 6 channel ADC with 10-bit resolution is available in this microcontroller. Moreover,
the microcontroller it self has the source of reference voltage of 2.56V [23]. Deploying this on-chip
facility of ADC the digitization of the signal is carried out.
The AVR ATmega8L has six channels, multiplexed analog to digital Converters, each of ten bit in
resolution. Deployment of such on chip facilities results in the reduction of not only in the hardware
and software complexity, but also in the cost. Moreover, it enhances the reliability embedded system.
The port C has this alternate function. The pin number PC0 to PC5 respectively provide analog inputs
ADC0 to ADC5. Internal multiplexer can be used for channel selection [23].
Here, in this hardware the channel ADC0 (PC0 Pin No. 23) is used as analog input. The SFR
ADCMUX (ADC multiplexer selection) is configured. It is known that AVR microcontroller has
internal reference voltage facility [23]. Therefore, by selecting REFS1:0 bits to 11, the internal source
of reference voltage of 2.56 volt is enabled. By default digital data is right justified which gives
preciseness in the result. The left justified data causes the reduction in the preciseness. The MUX bits
of ADCMUX register are configured as 000 for analog input ADC0.