Download Load cells are the sensors used in industry to measure

ZigBee IEEE 802.15.4 LAN Standard Protocol Based Wireless
Sensor Network in Load Cell Monitoring
Abstract. ZigBee is a new technology now being deployed for wireless sensor networks. ZigBee is a low data rate
wireless network standard defined by the ZigBee Alliance and based on the IEEE 802.15.4.The ZigBee wireless
network has some advantages compared with other wireless networks, it has the characteristics of low power, low
price, highly secured and reliable. Data acquisition or data monitoring in an industry with hazardous environmental
conditions is a challenging job. In this paper, a novel technique is developed using the technology of wireless sensor
network (WSN) to monitor the weight of the product during the process with the help of load cell sensor for the user
to avoid accidents. This system includes ZigBee communication which uses IC-CC2500, RF transceiver of
2.4GHz(ISM). Low power consumption, low cost, accurate measurement and the flexible structure are the
characteristics of this module. The weight can be monitored from long distance in real time. The variations in the
weight of the product are transmitted from the load cell sensor node to the central computing unit placed within the
range of the network. The data is received at the central computing unit and is displayed using a LCD in the control
room to the user. A ‘LoadcellWSN’ algorithm was developed for this model to develop a communication between
load cell sensor node and the central computing unit.
Keywords: Load cell sensor, central computing unit, ZigBee transceiver, Load Cell WSN Alorithm
1.
INTRODUCTION
The vast potential in wireless personal area networks is an emerging area of research in recent years. By networking
large numbers of tiny motes or nodes, it is possible to obtain data about physical phenomena that was difficult or
even sometimes impossible to obtain in conventional ways. The wireless nodes have certain tradeoffs in terms of
size, power, cost, code size, and data rate. The hardware design is simple and cheap, but is larger in terms of size
when compared with Mica Mote. The three components that dominate power dissipation for slave
or mote are the
microcontroller, the radio and the buffers. The current needed to power up the Sensor Mote is measured 77mA,
which has been ensured with the optimum use of mote’s devices. This current is comparable to Mica Mote. The
battery with capacity 580Ah is deployed; hence implemented mote can be used continuously in an application for
around 254 days. Zigbee wireless standard was chosen as a communication protocol. The transmission achieved is a
real time data transmission with data rate of 250 kbps. This has been ensured with minimum use of radio module’s
buffers and keeping the back off exponent of CSMA zero. The signal strength of last packet received is found to be
– 77.0553dBmWireless Sensor networks are at a high demand in the industries with hazardous working
environments.They are the combination of an embedded system and a wireless communication system to allow data
data transmission among different sensor nodes. This setup does not require any communication medium such like
WLAN, cellular network for communication. The computing unit of the each node is a microcontroller which
processes and transmits the data from each sensor node to the other creating a personal network. The network thus
developed helps in data monitoring and controlling the physical quantities of remote locations in accurate and safe
way .WSN can be used in various fields such as temperature, pressure, load, level, flow, etc. various techniques have
been developed using WSN for monitoring different parameters. Most of the industries such as chemical,
pharmaceutical, steel plants, automobile and many more use weight as a basic requirement, as weight is the key
variable for any end product.
Load cells are the sensors used in industry to measure the weight of the object. Sometimes it becomes difficult to
monitor the weight in hazardous industries for the observer. The work flow on the low cost, low power sensors has
become easy with the advancement in the technologies such that wireless communications, digital electronics, micro
electro chemical systems (MEMS) . Load cells are used in almost all the industries irrespective of the environmental
conditions. Sometimes it becomes difficult for the user or the technician to get the weight of the product in a
hazardous environment during or after the process. This system consists of a Zigbee transceiver, microcontroller,
LCD and a Load cell sensor.
2. HARDWARE DEVELOPMENT
Hardware of this wireless system basically constitute of two parts: Transmitting or Slave End node design and
Receiving or Coordinator node design.
2.1 Transmitting Section- The block diagram shows the transmitter end. It consists of a Load Cell trainer
module, On board power supply, Atmega 16, LCD, Zigbee transmitter. Atmega16 receives the data from
the sensor node with the help of DB9 connected to the module. The weight is acquired into the controller
using USART protocol via MAX232. Once the weight is received it is converted into digital signal using
the inbuilt ADC in Atmega 16. The converted digital signal is transmitted to the receiving end via Zigbee
transceiver. On board power supply converts the applied voltage to 5V which is required for the
microcontroller, MAX 232, LCD and Zigbee to operate. The Load cell trainer module has inbuilt power
supply.
(a) Power supply modules-This module is basically designed to achieved 5V, 500mA.This consists
of a transformer which is used to step down the AC voltage, IN4007 diodes used to form a bridge
rectifier to convert AC to DC, capacitor 1000uF which used as a filter circuit, 7805 regulator to
obtain a 5V at the output of the regulator, 330 ohm resistance, LED as indicator.
Fig 1: Diagram of supply section
(b) Microcontroller (ATmega16)-There is a whole wide range of microcontroller available in the
market. But this particular project is developed using AVR series of microcontroller
(ATMEGA16) because of its inbuilt ADC port and its variable frequency.ATmega16 is a lowpower CMOS 8-bit microcontroller based on the AVR RISC architecture. By executing powerful
instructions in a single clock cycle, the ATmega16 achieves throughputs approaching 1 MIPS per
MHz, allowing the system designed to optimize power consumption versus processing speed.
Further it also minimizes the cost of this personal area network.
(c) Zigbee module ( Transmitting module (RF Modem, 9600 bps , TTL logic) - It is a low power
and low cost 2.4 GHz transceiver designed for wireless applications. which can facilitate the OEM
designers to design their remote control applications in remote control in the quickest way. These
modules are based on IC CC2500 by Texas Instrument. The main operating parameters and the
64-byte transmit/receive FIFOs of CC2500 can be controlled with the help of an SPI interface. In
a typical system, the CC2500 can be used together with a microcontroller and some passive
components.
(d) DB9- It is 9 pin male /female connector. In DB9 9 represent total number of pins and D represents
the two parallel rows of pins that are in the shape of D alphabet
(e) MAX-232 (level converter)-MAX232 is a dual driver/receiver IC that includes a capacitive
voltage generator to supply EIA-232 voltage levels from a single 5-V supply. Each receiver
converts EIA-232 inputs to 5-V TTL/CMOS levels. These receivers have a typical threshold of
1.3 V and a typical hysteresis of 0.5 V, and can accept ±30-V inputs. Each driver converts
TTL/CMOS input levels into EIA-232 levels. This can be made to work with the help of a few
capacitors attached to it.
(f) Load Cell Sensor-Measurement of weight/load can be done with many sensors with a proper
signal conditioning. The load on the cantilever beam is measured using a strain gauge bridge
circuit having four arms. The principle of operation of strain gauge is, when stress is applied the
resistance of the gauge changes. The strain gauge is attached to one end of the beam and the other
end of the beam is fixed. When stress is applied a displacement is occurred on the beam which
sensed by the strain gauge and corresponding change in the resistance in the bridge circuit which
gives out voltage according to the change. In this project the load cell module ((Model No: ITB 04CE)) developed by VI Microsystems Pvt. Ltd,was used. The module consists of cantilever
beam, LED display, power supply. This module can measure weight up to 5kg which can be
viewed on a LED display on the system.
Fig 2: Block Diagram of Transmitter section
(g) Display module-The LCD(liquid crystal display) unit receives character codes (8 bits per
character) from a microprocessor or microcomputer, latches the codes to its display data RAM
(80-byte) DD RAM for storing 80 characters, transforms each character code into a 5 ´ 7 dotmatrix character pattern, and displays the characters on its LCD screen. We are 16*2 LCD‘s
which have 16 columns and 2 rows with 16 hardware pins connected as pin 1,3and 16 are
connected to ground, pin 2 and 15 are connected to +5v pin 3, 4, 5 are RS, RW and enable
respectively enable pin is always low. Data pins of LCD are 11,12,13,14 which are used for 4 bit
parallel communication.
2.2 Receiving Section -The figure shows the block diagram of the receiver module which consists of on board
power supply, Atmega 16 and LCD.Zigbee receiver will receive the data which is transmitted from the
transmitter end. Atmega 16 displays the received data on LCD. An on board power supply is developed which
supplies 5V to microcontroller and LCD. Thus the observer would be able to get the data from the plant area to
the control room.
(a) Power supply unit- This module is basically designed to achieved 5V, 500mA.This consists of a
transformer which is used to step down the AC voltage, IN4007 diodes used to form a bridge rectifier
to convert AC to DC, capacitor 1000uF which used as a filter circuit, 7805 regulator to obtain a 5V at
the output of the regulator, 330 ohm resistance, LED as indicator.
(b) Zigbee module-( Receiving module (RF Modem, 9600 bps , TTL logic) - It is a low power and low
cost 2.4 GHz transceiver designed for wireless applications. which can facilitate the OEM designers to
design their remote control applications in remote control in the quickest way. These modules are
based on IC CC2500 by Texas Instrument. The main operating parameters and the 64-byte
transmit/receive FIFOs of CC2500 can be controlled with the help of an SPI interface. In a typical
system, the CC2500 can be used together with a microcontroller and some passive components.
Fig 3: Block Diagram of receiving section
(c) Display module - The LCD(liquid crystal display) unit receives character codes (8 bits per character)
from a microprocessor or microcomputer, latches the codes to its display data RAM (80-byte) DD
RAM for storing 80 characters, transforms each character code into a 5 ´ 7 dot-matrix character
pattern, and displays the characters on its LCD screen. We are 16*2 LCD‘s which have 16 columns
and 2 rows with 16 hardware pins connected as pin 1,3and 16 are connected to ground, pin 2 and 15
are connected to +5v pin 3, 4, 5 are RS, RW and enable respectively enable pin is always low. Data
pins of LCD are 11,12,13,14 which are used for 4 bit parallel communication.
3. Software Development
Microcontroller, when it is used to operate as a wireless network involves following steps:
Fig 4: Steps for software development
The coding is done in AVR Studio4 using embedded ‘C’ programming language. An embedded code is
developed in Atmega 32 at the transmitting end for the peripherals like MAX 232 to receive the data, ADC to
convert received analog data to digital data, LCD to display the data, ‘LoadCellWSN’ algorithm to convert the
received voltage value into the approximate weight of the object and for the Zigbee transceiver to send the data.
At the receiving end an embedded code is developed for the Atmega 32 to receive the data from Zigbee receiver
and display the data in the LCD. For the whole process to run a software development procedure has been
followed. The following steps are involved in the software development:
 Coding / debugging-The process of designing a problem using a high level programming language such as
C, Java or assembly language is known as coding. Coding is done to create a set of instructions or an
algorithm for the microcontroller to perform the specific task. In our case the task is to read the data from
the sensor and transmit them wirelessly to a display device for the observer to acquire or monitor the. For
this project ‘LoadCellWSN’ algorithm is coded in AVR studio4 using embedded C programming language.
 Compiling-The microcontroller understands only the machine level language. Therefore a C code must
always be converted into machine level language for the controller to understand. A compiler converts the
C program into machine level language. Apart from the main code there are source codes developed for the
supporting protocol to run and are merged with the main code (algorithm). In this project a source code for
USART, LCD, ADC and Zigbee was developed and are used along with the main ‘loadCellWSN’
algorithm. To program the microcontroller WinAvr was used. Although inline assembly was possible, the
programming was done in strictly in C.
 Burning- Burning the machine language (hex) file into the microcontroller’s program memory is achieved
with a dedicated programmer, which attaches to a PC’s peripheral. PC’s serial port has been used for the
purpose. for this purpose Ponyprog programmer was used to burn the machine language file into the
microcontroller’s program memory. Ponyprog is serial device programmer software with a user-friendly
GUI framework available for Windows95/98/ME/NT/2000/XP and Intel Linux. Its purpose is reading and
writing every serial device. It supports I²C Bus, Micro wire, SPI EEPROM, and the Atmel AVR and
Microchip PIC microcontroller. The microcontrollers were programmed in approximately two seconds with
a high speed-programming mode. The program memory, which is of Flash type, has, just like the
EEPROM, a limited lifespan. On AVR microcontroller family it may be reprogrammed up to a thousand
times without any risk of data corruption Atmega16 Programmer (ISP) which is used to burn the program
into AVR microcontrollers.
Fig 5: ISP Programmer
 Evaluation-If the system performs as desired by the user and performs all the tasks efficiently and
effectively the software development phase is over and the project is ready to be installed in any of the
industrial sites as a personal area network. If not, the entire process is repeated again to rectify the errors.
One of the difficulties of programming microcontrollers is the limited amount of resources the programmer
has to deal with. In PCs resources such as RAM and processing speed are basically limitless when
compared to microcontrollers. In contrast to a PC, the code on microcontrollers should be as low on
resources as possible, but being cost effective and power efficient makes it a better option.
3.1 LoadCellWSN algorithm
A proper step by step algorithm is developed and written in AVRStudio4 in embedded C and compiled successfully
using WINAVR. The compiled code was burnt into Atmega 32 micro controller using ISP programmer. The
LoadCellWSN algorithm is written in the following way in Embedded C.The module is switched on and the Zigbee
transmitter and receiver are initialized. Initially the load cell sensor sends the weight in terms of voltage to the
microcontroller via DB9 and MAX232 as shown in the figure.
The received value is stored in a variable named Va.
• Initialize the transmitter and reciever
1
2
• Recieve the weight in terms of voltage
and store in variable Va
3
• Convert the analog value (weight, Va)
into digital value (Vd)
The received data Va is converted into digital value by
𝑉𝑑 = 1024 × 𝑉𝑎
The digital data Vd is then converted into actual weight by
𝑀𝑤
𝑤=(
) × 𝑉𝑑
𝑀𝑣
4
• Convert the digitalised voltage (Vd) into
weight (w)
5
• Transmit the weight (w) to the user via
Zigbee
6
7
• Receiver end receives the weight (w)
• Display the data
The digitalized data is transmitted via Zigbee transmitter to the Zigbee receiver at the receiver end. At the receiver
end the microcontroller receives data bit by bit and displays the data on the LCD.
4. Conclusion
The same technology can be used to monitor pressure, temperature, flow, level and different parameters which used
in industries. The range can be increased from 200mts to 20km.
Acknowledgments
We hereby acknowledge our Co-ordinator Sunil Semwal and Dr. Rajesh Kumar for guiding us in the right direction
and for giving tremendous support and encouragement to make this project a success.
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