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DEVELOPMENT OF WIRELESS MONITORING SYSTEM FOR PHOTOVOLTAIC PANEL

Student’s name: Ali Almaliky

Course: SCCC701 MG7001 Engineering Development Project

Student’s ID: 11352272

DEVELOPMENT OF WIRELESS

MONITORING SYSTEM FOR

PHOTOVOLTAIC PANELS

Development of Wireless Monitoring System for photovoltaic panels

i

ABSTRACT

This project aims at using a low-cost monitoring system based on wireless sensor networks

(WSN) for monitoring the output of each individual photovoltaic (PV) panel connected in an

array. There is a need for a low-cost monitoring system to get information from each

individual PV panel connected in an array. This project will help to increase the output

efficiency of each individual PV connected in the array and advise timely maintenance for

problems on the system. PV panels are connected in an array where each PV panel has a

voltage and a current sensor. The technology of wireless sensor networks (WSNs) consists of

small devices. Each WSN has its processing, communication and sensing capabilities. These

devices work together to perform monitoring tasks. The advantages of using WSNs over

wired technologies are; self-organization, flexibility, self-healing and using unlicensed radio

frequency channels. The ZigBee based WSN is integrated with an Arduino micro-controller,

plus a voltage and current sensor to sense the PV panel’s output at specific moments and

forward this data to a central unit. A liquid crystal screen is integrated with each transmitter

sensor to display the output parameters at the monitoring site. In the central unit, a Coolterm

based program is developed to receive the data and to store it into a database. By monitoring

each individual PV panel successfully, the monitoring system can later be extended to cover a

wide range of PV panels.


ii

i. Project Details

Wintec Students Involved:

Student’s name: Ali Almaliky

Course: SCCC701 MG7001 Engineering

Development Project

Mobile number: 0273162535

Email address:

[email protected]

Academic Supervisor:

Supervisor’s name: Alireza Gheitasi

Job Description: Academic supervisor– Electrical

Engineer

Phone number: +64-(0)7- 8348800 Ext: 3143

Email address: [email protected]

Academic program Leader &tutor:

Academic program Leader & tutor’s name:

Debbie Hogan

Job Description:

Academic Leader

Phone number:

+64-(0)7-834 8800 Ext 7839

Email address:

[email protected]

mailto:[email protected]




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ii. Abbreviations

PV: Photovoltaic

WSN Wireless sensor network

WLAN: Wireless Local Area Network.

LR-WPAN Low Rate - Wireless Local Area Network

WPAN: Wireless Personal Area Network

MAC: Medium Access Control

PHY: Physical layer

Wi-Fi: Wireless Fidelity

IEEE: Institute of Electrical and Electronics Engineers

COO: Coordinator

LR-WPAN: Low Rate-Wireless Personal Area Network

GHz: Gigahertz

MHz: Megahertz

ISM: Industrial, Scientific and Medical.

WSN wireless sensor network

kW Kilowatts

mW milliwatts

Zigbee Zonal interconnection global bee

GND Ground

R Resistance

V Voltage

I Current

Amps Ampere

ADC Analog digital converter

DC Direct current

Ω Ohms ACS Alternative and Direct current sensor

CSMA-CA Carrier Multiple Access with Collision Avoidance

LCD Liquid crystal display

I/O Input/Output

TTL Transistor Transistor Logic

ICS Linear current sensor

VCC Voltage Common Connector

PWM Pulse-width modulation

USB Universal Serial Bus

TX Transmit

RX Receive


iv

iii. Glossary

Gigahertz(GHz) A frequency unit equal to one billion cycles per second.

Megahertz(MHz) A of frequency unit equal to one million cycles per second.

Wireless Fidelity(Wi-Fi) Label assigned by WECA (Wi-Fi Alliance) to 802.11b-certified

equipment. Name used to denote the IEEE 802.11b norm.

Ad hoc Network A network made of mobile units which communicate between them

without an access point acting as an intermediary.

Bluetooth Standard defined by the Special Interest Group (SIG) consortium for

short-range systems with rates of 1 Mbps in the 2.4 GHz band. It is a

wireless technology enabling voice and data communication between

different electronic equipment, such as PCs, mobile phones or any

peripheral in general, over short distances.

ISM Frequency bands reserved for industrial, scientific and medical

applications (902 MHz, 2.4 GHz and 5.8 GHz).

IEEE The Institute of Electrical and Electronic Engineers. A professional body

working for the development of communication and networking

standards for electrical engineers.

DEVELOPMENT OF WIRELESS MONITORING SYSTEM FOR PHOTOVOLTAIC PANEL

Table of Contents

i. Project Details ................................................................................................................................ ii

ii. Abbreviations ................................................................................................................................ iii

iii. Glossary ......................................................................................................................................... iv

1. Introduction .................................................................................................................................... 2

2. Literature review ............................................................................................................................ 3

2.1 Monitoring PV panels ............................................................................................................ 3

2.2 Overview of a monitoring system................................................................................................. 3

2.3 Connection of Photovoltaic panels in an array ............................................................................. 4

2.3.1 Series String-Connection ....................................................................................................... 4

2.3.1 Parallel String-connection ..................................................................................................... 4

2.4 Measurement unit ......................................................................................................................... 5

2.4.1 Voltage Measurement ........................................................................................................... 5

2.4.2 Current Measurement ............................................................................................................ 6

2.5 Transmission and receive unit ...................................................................................................... 8

2.5.1 Networks types ...................................................................................................................... 8

2.5.2 Network topologies: .............................................................................................................. 8

2.5.3 Wireless sensor network (WSN) ........................................................................................... 9

2.5.4 RELATED WORK ............................................................................................................. 10

2.5.5 Zigbee / IEEE 802.15.4 ....................................................................................................... 10

2.5.6 Microcontroller (Arduino UNO) ......................................................................................... 12

3. Demonstration unit ....................................................................................................................... 13

4. Methodology ................................................................................................................................ 14

4.1 The scope of the monitoring project ........................................................................................... 14

4.2 Main parts of the Wireless Monitoring System for photovoltaic panels .................................... 14

4.3 Hardware of the monitoring project ........................................................................................... 15

4.4 The software of monitoring PV panel ........................................................................................ 20

5. Result and discussion ................................................................................................................... 22

5.2 Monitoring PV panel results, measurements and experiments ............................................. 22

5.1 Testing wireless connectivity and networking............................................................................ 25

6. Conclusion & recommendation .................................................................................................... 26

7. References .................................................................................................................................... 27

8. Appendix ...................................................................................................................................... 29


1

List of Figure

Figure 2-1 Overview of the monitoring system ...................................................................................... 4 Figure 2-2 layout of PV panel in an array is series and parallel connection ........................................... 5 Figure 2-3 measurement of a PV panel ................................................................................................... 5 Figure 2-4 voltage divider circuit ............................................................................................................ 6 Figure 2-5 current sensor datasheet [5] ................................................................................................... 6 Figure 2-6 Closed and Open loop Hall Effect sensors [6] ...................................................................... 7 Figure 2-7 Current Sensor ACS712 circuit ............................................................................................. 7 Figure 2-8 ZigBee pair, star, mesh, and cluster tree topologies [8] ........................................................ 9 Figure 2-9 overview of the wireless sensor communication ................................................................... 9 Figure 2-10 the free radio frequencies channels offered by Zigbee for communication [11] ............... 11 Figure 2-11 ZigBee devices in a network [9] ....................................................................................... 11 Figure 2-12 shows the Arduino PRO circuit board [14] ....................................................................... 13 Figure 4-1 shows the block diagram of communication scenario of the monitoring project ................ 14 Figure 4-2 shows the Schematic diagram of monitoring project .......................................................... 15 Figure 4-3 overview of the initial hardware components ..................................................................... 15 Figure 4-4 shows monitoring measurement circuit ............................................................................... 16 Figure 4-5 the voltage sensor hardware ................................................................................................ 16 Figure 4-6 the current sensor hardware ................................................................................................. 17 Figure 4-7 the hardware of a Zigbee router [15] ................................................................................... 17 Figure 4-8 the hardware of a Zigbee coordinator [15] .......................................................................... 18 Figure 4-9 the Zigbee router sensor in the monitoring site ................................................................... 19 Figure 4-10 the main parts of the COO board....................................................................................... 19 Figure 4-11 the overview of the monitoring system for each individual pane ..................................... 20 Figure 4-12 overview of a flowchart between receive and transmission units ..................................... 21 Figure 4-13 Analog and digital readings conversion ............................................................................ 22 Figure 5-1 overview of the different tests ............................................................................................ 22 Figure 5-2 PV panel output current ....................................................................................................... 23 Figure 5-3 PV panel output voltage ...................................................................................................... 23 Figure 5-4 overall PV outputs parameters ............................................................................................ 24


2

1. Introduction

Today, solar energy is an important source of renewable energy which is being developed to

replace using fossil fuels for power generation [1]. The environmental and electrical factors

that can reduce the efficiency of photovoltaic (PV) panels are weather, dust, dirt, accidental

damage, solar irradiation, power dissipation and temperature of the PV module. Solar energy

generation needs to be maintained to reduce the power loss from the PV panels. The lack of

maintenance of the PV panels can reduce the amount of energy generated by each panel [2].

Therefore, monitoring the energy output for PV panels will increase the overall efficiency of

the system. Monitoring the output of individual panels helps reduce the power loss from an

individual panel in an array.

The Thames energy group plans to supply renewable energy for power generation in the

town. They suggest that all domestic homes install PV panels as part of the plan. This

monitoring system can detect problems on the output efficiency and reduce maintenance

costs.

Often multiple PV panels feed into an array. Therefore it is hard to determine the individual

efficiency of a single PV panel attached to an array and note the amount of power that is

generated. This project researched and designed a monitoring system that can display the

operational condition of each individual PV panel. A liquid-crystal display (LCD) and a

computer have been used to display the individual performance of each PV panel.

Implementing this kind of monitoring system will help with detecting problems in short

period of time.

Currently, monitoring the PV system can be implemented through using many different

wireless sensors and wired protocols that are available on the market. This project aims to

implement a wireless sensor network (WSN) for monitoring PV panels based on the ZigBee

protocol. WSNs allow for communication and access to the facility of the sensors. A

measurement unit will read the output parameters of a single PV panel in an array. A

transmission unit will send readings to the receiver unit. A demonstration unit will display the

performance of each PV panel in order to solve problems on the system, if there any.


3

2. Literature review

The theatrical theory and calculations about the motoring project are as follows:

2.1 Monitoring PV panels

Photovoltaic panels convert solar energy into direct-current (DC) electricity. The PV panels

in an array can be electrically connected together in a series. They can also be placed parallel

but a series connection is generally preferred to give an increased output of voltage. For

instance, when two PV panels are connected together in a series, their voltage is doubled

while the current remains same [2]. The layout of a PV array can consist of a few individual

PV panels connected together or may consist of many hundreds of PV panels interconnected

together to supply power.

Monitoring PV panels will help to observe the status of the PV panel connected to multiple

other PV panels. Factors that lead to power loss on the photovoltaic system are grime, dust,

cloud and damage. These factors will reduce the amount of energy produced from a PV

system. This monitoring system will help to monitor the performance of the PV panel [3].

The total maximum output of power from the PV panels connected in an array, is the sum of

power generated from each individual PV panel. Therefore, the output of each individual PV

panel is different from other panels connected in same array. For example, environmental

factors like weather or accumulated dirt on the surface. The difference in the overall power

generated from a PV panel system is the total of the individual output of power from each

individual PV panel. Therefore, monitoring each individual PV panel will contribute to

maintaining the power produced from that PV panel and minimize problems on the PV panel

array by monitoring the operation of each individual PV panel [2].

PV panels can be supplied by DC appliances. The output must be inverted from a direct

current to an alternative current via an inverter device. Then it may be connected to a grid

where the energy can be shared by other consumers. The range of power generated from a PV

system can be from a few mW to several kW.

2.2 Overview of a monitoring system

The development of an individual PV panel monitoring system consists of the following

stages see figure (2-1).

1. PV panels’ are arranged in an array, for example in series or a parallel connection.

2. The output of the Individual PV panels is measured by a measurement unit.

3. Sensors will read the output of power from the PV panel by requesting that voltage

and current go through them.

4. The establishment of a transmission unit which will gather data from a sensor and

transmit a reading.

5. The establishment of a receiving unit which collects data from the transmission unit.

6. LCD screen to display the output reading of each individual PV panel at the

monitoring site.

7. A demonstration unit to display the reading and to store the data in database.


4

Figure 2-1 Overview of the monitoring system

2.3 Connection of Photovoltaic panels in an array

The PV panels in an array can be connected in either a series or a parallel string format as

follows:

2.3.1 Series String-Connection

Multiple PV panels can be in a string-connection in a series as shown in Figure (2-2).

In series string-connection the layout of the total voltage will be the sum of the individual

voltage of the PVs, and the current remains the same. In other words, if each PV panel in the

Figure (2-2) has an output of 18 volt and 1 Amp , then the total voltage of the PV panel array

would be 18 × 4 = 72 V, and the current would remain at 1 Amp [4].

2.3.1 Parallel String-connection

Multiple PV panels can be also string-connected in a parallel, see Figure (2-2). Parallel

string- connection is connecting the positive connection of the first PV panel to the positive

connection of the next PV panel, and negative connection of the first PV panel to the negative

connection of the next, to increase the current.

In parallel string-connected layout, the individual amps of each PV panel are the same as the

series additive and the voltage remains the same. If each PV panel in Figure 2 has an output

of 18 volts and is 1 amp, then the total current of the solar array would be 1+1+1+1= 4 amps,

and the voltage would remain at 18 volts [4].


5

Figure 2-2 layout of PV panel in an array is series and parallel connection

2.4 Measurement unit

The measurement unit of each PV panel can be implemented in a parallel or in a series. The

current sensor reads the current running through the load while the voltage sensor reads the

voltage across it. The current is measured by passing a current through a current sensor, see

Figure (2-3). The current sensor has a different input range in amps or milliamps. The voltage

across the load is measured by connecting a different instrument, the voltage sensor, across

the terminals of the load; see Figure (2-3). As shown the current sensor always connects in a

series with the load, while the voltage sensor always connects across it (in parallel). The load

allows the sensors to read the current flow through the sensor and it can read the volatge that

goes across the load, see Figure (2-3).

Figure 2-3 measurement of a PV panel

2.4.1 Voltage Measurement

A voltage divider is used as part of a voltage measurement device. It is used to step voltage

down from 18 to 5 V because the micro-controller analog input reads the voltage from 0-5 V.

It consists of two resistors in a series as shown in Figure (2-4).

The output voltage depends on the value of the resistors. Therefore, the output voltage can be

calculated by the following formula.

𝑉𝑜𝑢𝑡 =𝑅2

(𝑅1+𝑅2)× 𝑉𝑖𝑛 𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛1

𝑅1 =𝑅2×𝑉𝑖𝑛

𝑉𝑜𝑢𝑡− 𝑅2 𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛2

𝑅2 =𝑅1

(𝑉𝑖𝑛

𝑉𝑜𝑢𝑡)

− 1 𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛3


6

Vin is the input voltage of the PV panel, 18 V and R1 ohms and R2 are 13 k ohms, 5 k ohms

respectively. Vout is the output voltage across the voltage divider resistors and it must be

between 0 to 5 volts because the micro-controller analog pins are scaled to read up to 5 V.

See Figure (2-4).

Therefore:

𝑉𝑜𝑢𝑡 =5𝑘Ω

(13𝑘Ω+5𝑘Ω)× 18 𝑣 = 5 𝑣𝑜𝑙𝑡𝑠 𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛4

Figure 2-4 voltage divider circuit

2.4.2 Current Measurement

The Hall-Effect linear current sensor, LCs are the most appropriate for this project. These sensors

deliver an output signal which has a linear function which is formed by the magnetic flux density

passing perpendicularly through its Hall plate. An example of the transfer curve for the ratio metric

linear is shown in Figure (2-5).

ACS 712 current sensor, has a range of ±5A and a typical sensitivity of 185mV/A. As shown in

Figure (2-6) the ACS712 output is an analog voltage output signal that varies linearly with the

measured current. The output voltage shows an offset of 2.5V. Therefore, when no current is

measured, the sensor output is 2.5V. This happens when the supply is 5VDC. The Arduino board can

supply the required voltage.

The Arduino analog inputs have certain requirements which are that the input voltage needs to be a

positive voltage between 0V and the ADC reference voltage (5V in this case). This sensor meets these

requirements as it is always positive charge and it is below 5V. However considering the sensitivity

(185mV/A), the output variation is not very strong because of this it requires amplification. Scaling up

of the output voltage is required so that the ADC range can be exploited.

Figure 2-5 current sensor datasheet [5]


7

Between the Hall Effect IC, two different types can be distinguished: closed loop and open loop

Figure 2-6 Closed and Open loop Hall Effect sensors [6]

Letter S is for the analog output port, V and G are for the voltage at the common collector

and ground respectively. Sign “+” is for the current inflow port and “-” is for the current

outflow port.

According to the datasheet:

1. ACS 712 measures the positive and negative 5Amps, corresponding to the analog output

185 mV/A

2. Even though there is no test for the current, the output voltage is VCC / 2 =5v/2=2.5V

Calibration:

The analog read produces a value of 0-1023, equating to 0v to 5v

So analog read 1 = (5/1024) V =4.89mv

Value = (4.89*analog read value)/1000 V

But as per the data sheets, the offset is 2.5V (When the current is zero you will get 2.5V

from the sensor's output)

Actual value = (value-2.5) V

Current in (amp) =actual value*5 A

Figure 2-7 Current Sensor ACS712 circuit


8

2.5 Transmission and receive unit

Wireless network

A Network is a collection of nodes connected to each other. The need for data exchange from

the nodes within a network has led to the advance of several network types, topologies and

communication protocols.

2.5.1 Networks types

Network types are categorized depending on their power expenditure, data rate, coverage

range and complexity of the technologies. Some examples of area network types are:

Wireless Local Area Network (WLAN) is the connection of two or more devices using a

wireless distribution method. The most typical is the spread-spectrum radio frequency. The

WLAN provides an access point through its connection to the wider Internet. The WLAN

operates on the standard 2.4 GHz, Industrial Science Medical (ISM) frequency bands. This

gives users the flexibility to move around within a local area and still be connected and

covered by the network. Wi-Fi is the most modern WLAN which is based on IEEE 802.11

standards [7].

Wireless Personal Area Networks (WPAN) use wireless technology for physical connections

within an area with the range being, typically within a few meters. WPAN is based on the

standard IEEE 802.15 an enabling kind of wireless technology, which works in wireless areas

such as Bluetooth, Zigbee and HomeRF. IEEE 802.15.4 is the standard which states the

media access control and the physical layer for a lower-rate wireless personal area network

(LR-WPANs) [7]. It is maintained by the IEEE 802.15.4 working group. IEEE 802.15.4

focuses on a very low data-rate solution, operating at a few hundred kilobytes per second,

which is the first step towards developing body area networks. Several companies have

agreed that the ultra-wideband (UWB) is a low-data-rate solution for IEEE 802.15 [7].

2.5.2 Network topologies:

Network topologies are the configuration of nodes through a network. The physical layout of

the nodes in the network characterises as topology for example Star, and Mesh topology.

Pair network is two nodes. One node must be a coordinator so that the network can be

formed see Figure (2-7). These nodes can be configured to be used as a router or as an end

device [8].

The Star network arrangement is where a radio that acts as a coordinator sits at the center of

the star topology and then connects to a circle of end devices; see Figure (2-7). Each message

in the system must pass through the coordinator radio, which routes them as needed between

the other devices. The end devices are not able to communicate with each other directly [8].

The mesh network configuration employs router nodes in addition to a coordinator radio and

sub-radios connected to the mesh. These radios can pass messages between each other, to

other routers and end devices as needed. The coordinator radio manages the network as well

as route messages; see Figure (2-7). Various end device nodes may be attached to any router

or to the coordinator. These can generate and receive information, but will need their parent

device’s help to communicate with the other nodes [8].

Cluster tree network layout where routers form a backbone of sorts, with end devices

clustered around each router see Figure (2-7). It’s not very different from a mesh

configuration [8].


9

Figure 2-8 ZigBee pair, star, mesh, and cluster tree topologies [8]

2.5.3 Wireless sensor network (WSN)

WSN is used for transmitting, processing and for signal collection. A wireless sensor network

(WSN) is a collection of nodes lay in a network based in a network station. A node is

composed of sensors, radio frequency, processor, local memory and battery. A receive station

is responsible for receiving, processing data collected by the nodes and demonstration see

Figure (7-8).

A sensor network is an infrastructure that includes sensing, computing and communication

elements. The purpose of using the WSN is to sense any data from the desired location and

transmit it through the wireless network. The block diagram of the WSN consists of two main

parts, the transmitting side and the receiving side respectively. On the transmitting side, the

sensors are connected with the micro-controller and XBee. On the receiving side the

coordinator and the micro-controller receive the data from the transmission unit. The sensed

parameters are transmitted to the receiving unit through wireless communication and the

details are monitored by the demonstration unit.

Figure 2-9 overview of the wireless sensor communication


10

2.5.4 Related work

The implementation of a wireless sensor network to monitor each individual PV panels’

performance is to detect any failure. This has been explored and studied by many other

projects. A similar project about a wireless sensor network for monitoring a PV panel based

on Bluetooth was done effectively in Germany but the problem with this project was the short

transmission range of the Bluetooth sensor [4]. Bluetooth is wireless short-range

communication between several devices [5]. Therefore the implementation of Bluetooth

requires many nodes to transmit information. The range of transmission in Bluetooth

requires more than 100 sensors for 300 m distance because Bluetooth is able to transmit data

from 6 to 10 meters [5]. Because of this Bluetooth protocol is not discussed further in this

project.

2.5.5 Zigbee / IEEE 802.15.4

The IEEE 802.15.4 defines the physical layer and the data link specifications (MAC) for a

low data-rate of wireless communications between the devices with a low power

consumption. The Zigbee relies on IEEE 802.15.4 physical layer and data link (MAC) which

uses Carrier Multiple Access with Collision Avoidance (CSMA-CA). The ZigBee

specification is available as an unlicensed radio frequency channel 2.4 GHz which is

available to the general public. XBee is a brand of radio that supports a variety of

communication protocols, including ZigBee, 802.15.4, and WiFi, among others [8]. Each

ZigBee network will have a single coordinator sensor and every ZigBee network will also

have router sensor or an end device sensor.

The standard that controls this was established to address the applications requirements which

entail; a short transmitting range, low power, low data and for a low cost. Two PHY options

are supported by the IEEE 802.15.4. These are based on a direct sequence spread spectrum.

The 2.4GHz physical layer uses modulation, whereas 780/868/915MHz uses a binary phase

shift keying modulation. Both the 2.4GHz and 868/915 MHz offers a good bit error rate for

performance at a low signal to Noise Ratio. 31 channels are offered by the IEEE 802.15.4

physical layer. Four are in the 780MHz band wave for China (IEEE 802.15.4), 1 in 868MHz

band is used in Europe ,10 in 915MHz for North American countries, 16 in the 2.4GHz are

used throughout of the rest of the world, see Figure (2-9). The nominal radio data rates for

these four frequency bands are 20kbps, 40kbps, and 250kbps. The ZigBee defines

specifications for a low-rate WPAN [9] [10].

The Zigbee provides a multi-hop, self-organized, and reliable star/mesh/tree/peer to peer

networking with a long battery life. Currently, the ZigBee is widely used within WSN

applications. This is because the 2.4 GHz band is an unlicensed RF band throughout the

world. The advantages of using the Zigbee as a suitable protocol for monitor this PV project

is observable above, which is that it is intended to cover longer distances, the ease of

installation, the reliability of the data transfer for a short range operation, using an unlicensed

frequency band 2.4 GHz and supporting reasonable battery life [9] [10].

The standard offers two options for transmission and receiving based on different

frequencies. All methods use a modulation technique. The transmission rate is 20 kb/s (868

MHz), 40 kb/s (915 MHz) and 250 kb/s (2.4 GHz) see Figure (2-9). There are more than 16

channels between 2.4GHz and 2.4835GHz. There is only one channel between 868 and 868.3

MHz, while there are 10 channels between 902.0MHz and 928.0MHz. The IEEE 802.15.4

dynamically supports the selection of the channel by using a scanning function which allows

it to search the beacon frame (synchronization) in a useful channels list.


11

Figure 2-10

the free radio

frequencies channels offered by Zigbee for communication [11]

The network layer that supports the advanced features of the ZigBee is IEEE 802.15.4. This

creates a set of standards that define the management of its power, error correction,

addressing, message formats, and other point-to-point specifics that are necessary for proper

communication to take place from one radio to another. The ZigBee has a set of layers built

on top of 802.15.4. These layers are routing, ad hoc network and self-healing mesh [9].

The routing tables define the process of one radio passing messages through a series of other

radios on the path to their final destination. An ad hoc network creates an entire network of

radios on the fly, without any human intervention automatically. The self-healing mesh

operates a similar process where it automatically works out if one or more of the radios is

missing and reconfigures the network to repair any broken paths or routes [9].

A ZigBee network is composed of various devices, and each device specializes in certain

types of actions see Figure (2-10). There are only three kinds of device types. The ZigBee

network will have a single coordinating device and at least one other device, either a router

node or an end node [9]. The Zigbee network will use both and often will be larger than just

two or three nodes:

A. The ZigBee coordinator

B. The ZigBee router

C. The ZigBee end-device

Figure 2-11 ZigBee devices in a network [9]


12

A. Coordinator

A ZigBee network will always have a single coordinator radio device which is responsible for

supporting the network. This includes; delivering addresses, managing the other functions

that define the network, keeping it secure and maintaining its health. Each network must be

created by a coordinator and there can only be one coordinator in a network.

B. Router

The router is a full-featured ZigBee node which can connect the existing networks. Its

purpose is to send information, receive and route information. Routing means that the device

is acting as a messenger for communication between other devices that are too far apart to

transmit information on their own. Routers need to be permanently connected to a battery or

an electrical outlet to maintain their constant power source. A network can have multiple

router radios.

C. End Device

The full time power connection and the hardware can seem excessive in comparison to the

job that a particular radio node is designed to do which is sending and receiving information

and connecting networks as well as acting as a messenger between other devices. An option

is to use less expensive hardware and utilising the sleep-mode where they can power

themselves down intermittently which will save energy. End devices always need a router or

the coordinator to be their parent device. The parent assists end devices to join the network,

store messages when they are asleep and the ZigBee network can have a number of end

devices connected to it.

2.5.6 Microcontroller (Arduino UNO)

The Arduino Uno is a micro-controller board which is based on the ATmega328. This section

will give an overview of the main functions however more details about it can be seen in

datasheet [12]. The Arduino Uno board has 14 digital input/output pins, 6 analog inputs, a 16

MHz ceramic resonator, a power jack, an ICSP header, a USB connection and a reset button

see Figure (2-11).The Arduino Uno board is a circuit for making a computer that can monitor

and control sensors which is based on a micro-controller. It has analog input pins and digital

output pins (I/O). Arduino has a development environment for writing C/C++ program for

processing information [13].


13

Figure 2-12

shows the Arduino UNO circuit board [14]

The Arduino Uno has 14 digital pins which can be used as an input or output. The function of

the Uno’s digital pins are; pin mode (), digital write (), and digital read (). The digital pins

operate at 5 volts and each pin can deliver or receive a maximum current of 40 mA. Some

digital pins also have specialized functions which follow.

The serial digital pin 0 (RX) is used to receive data and () pin 1 (TX) is used to send TTL

(Transistor Transistor Logic) serial data. These are then connected to the corresponding pins

of the ATmega328 USB-to-TTL Serial chip. The numbered 2 and 3 external interrupt pins

can be configured to trigger an interrupt when it senses a low. It can also sense a change in

value or a rise or fall in the edge. The numbered; 3, 5, 6, 9, 10, and 11pins PWM (Pulse-

width modulation) provide an 8-bit PWM output along with the analog Write () function [13].

The Uno has 6 analog inputs from A0 to A5, each pin provides 10 bits of resolution (i.e. 1024

different values). The voltage pin is from A0 to A5 which measures from ground (Zero) to 5

volts. It is also possible to change the upper end of the pins range by using the AREF pin and

the analog Reference () function [13].

The AREF pin (Reference voltage) is for the analog inputs and it uses with analog Reference

(). The reset button is to make the line LOW and reset the microcontroller. [13]

3. Demonstration unit

The demonstration unit has a Router connected with a PV panel. The ZigBee is used as a

coordinator which is then connected via a serial communication port with a computer for data

retrieval using an Arduino C/C++ simulator and coolterm programs. The demonstration unit

needs to open a serial connection as the ZigBee coordinator is connected with the PC through

the USB port. Secondly, the data will be converted to digital numbers before it is plotted into

a graphical form and sent through to EXCEL. In the database portion, the connectivity

between the cooltem program and EXCEL is established prior to the time of monitoring.

When the connection has happened, the incoming data can then be fed into the database table.

A liquid crystal display (LCD) screen displays the output parameters at the monitoring site

which makes inspection easy.


14

4. Methodology

4.1 The scope of the monitoring project

The aim of this project is to implement a wireless sensor monitoring based on a ZigBee

standard as a protocol for monitoring the PV panels’ output power. The system for

monitoring PV panels is set up with a ZigBee as a Router and a ZigBee as a Coordinator. The

current and voltage sensors are attached to individual PV panel’s output wires for

measurement. The Zigbee coordinator is responsible for receiving information from the

router and delivering data to the Arduino simulator software. The Arduino software used

C/C++ simulator software to identify variables on the Arduino board. The Arduino C/C++

simulator software displays the status of the monitoring system and the log data is sent to

Excel for graphing purposes.

4.2 Main parts of the Wireless Monitoring System for photovoltaic panels

In this project, the system of monitoring a PV panel array is simulated with a PV panel of

15Watts, 18 volts and 0.83 amps output. The PV panel was located for the test in the garden

of Wintec Rotokauri Campus (Waikato Institute of Technology) see Figure (2-12). The

receiver station was located at the Wintec power lab which received the data from the ZigBee

router; see Figure (2-12). The ZigBee coordinator was connected to the Laptop serial port in

order to display the information from the demonstration software.

Figure 4-1 shows the block diagram of communication scenario of the monitoring project

According to Figure (4-1), the wireless sensor (ZigBee) is implemented on three different

sides. At the PV panels’ side, the Arduino UNO micro-controller board and ZigBee work in

two stages. The current sensor and voltage divider circuit measures the output of each

individual PV and sends it to the coordinator by using an XBee for communication by RF

(2.4 GHz). On the other hand, the Zigbee coordinator’s sensor is connected with computer to

receive the data (The measured voltage and current) from Zigbee router sensor. At this side,

an Arduino serial monitor function and Coolterm software are designed to display data being

received. The Coolterm software uses log data in the EXCEL software directly for graphic

purposes. This schematic diagram described the monitoring in details see Figure (4.2).


15

Figure 4-2 shows the Schematic diagram of monitoring project

4.3 Hardware of the monitoring project

The initial hardware Zigbee wireless sensors did not work because the USB serial port

connection between the Zigbee coordinator and the computer was impossible to set up, see

Figure (4-3). Therefore, XBee and Arduino were implemented to achieve the physical work

of the project. The new components installed and worked successfully.

Figure 4-3 overview of the initial hardware components

This section gives a description of setting up the hardware components for monitoring the PV

panels. The hardware consisted of three parts:

a. Voltage and Current Sensors Integrated With ZigBee and Arduino

b. The first part is dedicated to the coordinator board

c. The second to the Router board.

d. The third is the load circuit


16

Voltage Measurement

The ACS712 data sheet and calculations are mentioned in the measurement unit page 5 .The

hardware was arranged as follows:

The Voltage measured was helped by using a voltage divider circuit; as shown in Figure (4-

4). The ARDUINO analog pin’s input voltage was limited to 5V and the voltage divider was

designed in such a way that the output voltage would be less than 5V. The PV panel is rated

at 18 volts, 0.83 amps. The voltage stepped down from 18 to a voltage of no more than 5V.

Figure 4-4 shows monitoring measurement circuit

The theory of a voltage divider and the calculation is mentioned in the measurement unit on

page 5.The hardware was arranged as follows:

1- The output pin lay across a resistor which was connected to the Arduino input pin

(A5) as shown in Figure (4-5).

2- The output ground pin connected two the Arduino input pin (GND).

Figure 4-5 the voltage sensor hardware


17

The current sensor (ACS712) datasheet and calculations are mentioned in the measurement

unit on page 6. The current sensor’s hardware was arranged as follows:

1- The ACS 712 analog pin was connected to the Arduino analog input pin (0) see

Figure (4-6).

2- The ACS 712 VCC pin was connected to the Arduino through the Arduino analog

input pin (5V).

3- The current sensor’s ground was connected to the Arduino ground input pin (GND)

Figure 4-6 the current sensor hardware

The Zigbee router parts are the XBee and the Arduino board. The hardware of the Zigbee

router was connected as follows:

1- The XBee voltage input pin was connected to the Arduino VCC pin (3.3V) as shown

in Figure (4-7).

2- The XBee receiver’s input pin was connected to the Arduino (RX) pin.

3- The XBee transmitter input pin was connected to the Arduino (TX) pin.

4- The XBee

ground input

pin was

connected to

the Arduino

(GND) pin

Figure 4-7 the hardware of a Zigbee router [15]


18

The Zigbee coordinator parts are the XBee and the Arduino board. The hardware of the

Zigbee router was connected as follow:

5- The XBee voltage input pin was connected to the Arduino VCC pin (3.3V) see Figure

(4-8).

6- The XBee receiver input pin was connected to the Arduino pin (2).

7- The XBee transmitter input pin was connected to the Arduino pin (3).

8- The XBee ground input pin was connected to the Arduino (GND) pin

Figure 4-8 the hardware of a Zigbee coordinator [15]

The monitoring system was designed with a liquid crystal display (LCD) to display the

parameters of the monitoring site. Three variables were measured and displayed as shown in

Figure (….). The chosen LCD was 4 lines by 20 characters. The parameters that were

measured and displayed on the LCD were 3 parameters which are the voltage, the current and

the power.

1. The LCD wiring diagram was connected to the Arduino digital pins (D), VCC and

GND as shown in Figure (4-9).

2. The LCD screen displayed the output parameters of the individual PV panels as

shown in Figure (4-9)

3. The Zigbee router sensor and the PV were connected together see Figure


19

Figure 4-9 the Zigbee router sensor in the monitoring site

The Parts of Zigbee coordinator and router

The main parts of the COO board see Figure A (4-10).

1- The Arduino UNO microcontroller board.

2- The XBee wire.

3- The USB connection.

4- The laptop

The main parts of the router board see Figure B (4-10):

1- The Arduino UNO microcontroller board.

2- The XBee wire.

3- The voltage and current sensor.

4- The load ( DC motor)

Figure 4-10 the main parts of the COO board

B A


20

The completed process of connecting the monitoring system hardware with all the

components connected. Figure (4-11).

Figure 4-11

the

overview of the monitoring system for each individual pane

4.4 The software of monitoring PV panel

The monitoring software implementation was written in C and uploaded to a microcontroller

using an IDE provided by Arduino. The operation of the software is illustrated in the

flowchart shown in Figure (4-12).

1. Read voltage and current sensors and covert value to decimals.

2. Transmission unit operates in cycle loop and sends readings every 5 seconds.

3. The receiving unit (Zigbee coordinator sensor) received data from the transmission

unit (Zigbee router sensor).

4. It needed to open a serial connection with the ZigBee coordinator and then was

connected with the computer by using a USB port.

5. The incoming data was read as a string and sent to a database.

6. The database portion was connected to Coolterm and sent on to EXCEL.

7. When the connection was ensured, the incoming data then could be fed in to the

database table.


21

Figure 4-12 overview of a flowchart between receive and transmission units

The XBee module is the main part of the project. The process diagram of the XBee Pro

module is shown in Figure (4-12). The first step is the sensing part and the rest is digitalizing

the readings. The Arduino UNO was turned on for monitoring the running parameters. The

XBee Pro module was turned on and initialized for wireless communication. The initialized

parameter of XBee Pro module included setting PANID, channel, encryption mode, link key

and etc. After initialization of all modules, the program goes into the loop part. In the loop

part, the environmental data including the voltage and the current were collected by

corresponding sensors such as the current and voltage sensors. Then the collected data was

displayed and stored. The C program codes, X-CTU set-up, stored the data in the Excel

program and they are displayed in the appendix section.

In order for the transmission to accept the input from the voltage and the current sensors, the

analog signal input must be filtered and digitized. Ideally the signal must be within

acceptable ranges for the rated values of the Analog to Digital converters within the micro-

controller. These components should allow for DC voltage and the current measurements

from an individual PV panel to be read by the display and store the readings. As shown in

Figure (4-13).


22

Figure 4-13

Analog and digital readings conversion

5. Results and discussion

In this section, there are three parameters showing the output efficiency of the monitoring system.

5.2 Monitoring PV panel results, measurements and experiments

A single PV panel’s results were recorded at different times by the monitoring system. This

result presented the output efficiency for one individual PV from an array which included

multiple PV panels. It was then tested by putting accumulated dirt on the PV panel’s surface.

The following results represent the conditions of the test. Therefore, if the PV is clean, the

results will be demonstrated as follows. These can then be compared to the result and to find

out which panel has reduced efficiency and then attend to the problem. The monitoring result

showed the issues that reduced the efficiency of the PV panel.

Figure 5-1 overview of the different tests


23

The first graph shows the reading from the current sensor and the second graph shows the

reading of the voltage sensor. These two tests show the efficiency drop on the PV panel

caused by dirt, cloud and shade on the surface. The surface of the PV panel was fully covered

with powder used as dirt for the experiment test as shown in Figure (5-1). The rated current

sensor output was 0.83 A. The sensor output graph indicated a gradually drop in the current

caused by the accumulation of dirt on the PV panel’s surface. The sharp drop was an

indication that the surface was shaded. It was shade that became the most critical factor that

rapidly decreased the PV output’s current as shown in Figure (5-2).

Figure 5-2 PV panel output current

The following graph is from the voltage sensor’s reading and the change of the output was

remarkable as it occurred on the output of the current sensor. The same situation is shown in

Figure (5-1) which was observed on the voltage sensor. The sensor’s output graph indicated

fluctuations of the voltage sensor, caused by the accumulation of dirt on the PV panel’s

surface. The rated output voltage was 18 volts. The declined drop was caused from shade on

the surface. Shade was the most critical factor that sharply reduced the PV panel’s output

voltage, as shown in Figure (5-3).

Figure 5-3 PV panel output voltage

0

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Current sesnor


24

The graph diagram in Figure (5-4) shows the power output measured from the current and the

voltage sensors. The rated power output was 15 watts. The small variations on the PV output

power indicates that there was less accumulated dirt on the PV surface. The sharp drop

caused by shade.

Figure (5-4) shows the voltage, the current and the power output from the monitoring PV panel. It is

observable that the monitoring system can show the changes in the PV’s efficiency. The change in the

current and voltage sensor reduced the power output as is demonstrated in Figure (5-4).

Figure 5-4

overall PV

outputs

parameters

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ou

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ater

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Voltage sensor Current sesnor Power


25

5.1 Testing wireless connectivity and networking

There were many challenges with implementing the monitoring system of each PV panel in

an array. There are the technical challenges that were explored with the existing monitoring

project. Communication was also challenging.

The technical challenges with the Zigbee wireless sensor were internal, such as the power

consumption as well as the networks such as a connection to the Internet. The two aspects

affect each other and make matters more complex for the Zigbee power consumption. The

Zigbee transmitter (coordinator) should support the 802.15.4 standard. It collecteds data from

the environment and shared the gathered information with the other sensor nodes in the

network. The transmission and receiving had the greatest impact over the node’s energy

consumption.

The calculation also occurred in the processing part where a micro-controller read the data,

defined the communication protocol and made the data ready to be transferred. The power

consumption of processing information in a microcontroller depended on how long the node

expansion time was in different radio modes.

The power consumption of the Zigbee is a critical factor because it consumed more power in

a short time during the monitoring test. The high consumption was due to processing

information inside the micro-controller and the transmission period.

The communication was tested in different transition times where the first test was every 5

seconds. It was observed that the battery drained in a short time and it required replacing in

order to maintain continuous transmission. The transmission time changed in the second test

to 30 seconds and the battery life lasted longer. Overall, the power consumption depended on

the transmission time.


26

6. Conclusion & recommendation

Overall, the main aim of this monitoring project was reached. A complete system for

monitoring each individual PV panel in a PV array by a Zigbee wireless sensor was achieved.

Throughout the research and designing processes several difficulties with monitoring the

system’s software and hardware were encountered and then overcome.

A good solution for monitoring the output of power for a single PV panel was designed. The

output of each individual PV panel was captured correctly by connecting a voltage and a

current sensor to the Arduino micro-controller. Afterwards, the data from the sensors was

processed by the micro-controller to calculate the desired variables. Next, the data was stored

in a database using Cooltrem software. Later it was given the correct format so it could be

properly graphed using EXCEL. The final result was the Coolterm software and LCD screen

which displayed real time graphs, as well as the last day’s consumption graphs.

From this project a series of recommend points have become noticeable:

Implementing and monitoring multiple PV panels is possible and achievable

Using google drive or iCloud to display the status of the monitoring system would

allow access to the data from any internet linked computer

A human machine interface can be integrated with the Labview to be able better

monitor any changes.

The Zigbee is expensive and it is recommended to try cheaper technology options

Implementing a wireless sensor network that consumes less power

Future work could include researching the alternatives to extend the battery life for the

wireless sensors. Advance plans could look for more accuracy and cheaper wireless

technology to monitor multiple PV panels in a system. Also, the monitoring system could be

integrated with a cleaning system by making a connection between them.


27

7. References

[1] S. A. Kalogirou, "Solar Energy Engineering," 25 10 2013. [Online]. Available:

http://books.google.co.nz/books?id=wYRqAAAAQBAJ&dq=Today,+solar+energy+is+an+impo

rtant+source+of+renewable+energy&source=gbs_navlinks_s. [Accessed 3 03 2014].

[2] W. Achim, R. Mauricio, M. David, M. Stefan, R. Nils and J. Ulrike, "MONITORING OF

PHOTOVOLTAIC SYSTEMS: GOOD PRACTICES AND SYSTEMATIC ANALYSIS," 4 10

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2013/28th-eupvsec/woyte.pdf. [Accessed 4 03 2014].

[3] S. H. Antonio Luque, "Handbook of Photovoltaic Science and Engineering," 2 12 2002.

[Online]. Available:

http://www.kepu.dicp.ac.cn/photo/07sl02/Handbook%20of%20Photovoltaic%20Science%20and

%20Engineering/Front%20Matter.pdf. [Accessed 2 03 2014].

[4] E. Engineering, "A GUIDE TO PHOTOVOLTAIC (PV) SYSTEM DESIGN AND

INSTALLATION," 14 06 2001. [Online]. Available: http://www.energy.ca.gov/reports/2001-09-

04_500-01-020.PDF. [Accessed 15 05 2014].

[5] Iteadstudio, "iteadstudio," 18 04 2013. [Online]. Available:

http://imall.iteadstudio.com/Electronic_Brick/IM120710011/DS_IM120710011.pdf. [Accessed

25 05 2014].

[6] P. Trigo, "ONLINE ENERGY MONITORING SYSTEM," 02 05 2013. [Online]. Available:

http://repositorio.unican.es/xmlui/bitstream/handle/10902/3840/359541.pdf?sequence=1.

[Accessed 02 06 2014].

[7] P. Ramjee, "OFDM for Wireless Communications Systems," 1 01 2004. [Online]. Available:

http://books.google.co.nz/books?id=gVE9vkreKWMC&dq=ofdm+for+wireless+communication

s+systems&source=gbs_navlinks_s. [Accessed 26 02 2014].

[8] R. Faludi, "Building Wireless Sensor Networks," 12 2010. [Online]. Available: http://ab-

log.ru/files/File/books/WirelessSensorNetwork.pdf. [Accessed 24 05 2014].

[9] L. Houda, A. Hossam and D. S. Costantino, "Wi-Fi™, Bluetooth™, Zigbee™ and WiMax™,"

30 08 2007. [Online]. Available:

http://books.google.co.nz/books?id=1DThCUwfRAIC&dq=WI-

FI+T+M+,+BLUETOOTH+T+M+,+ZIGBEE+T+M+A+ND+WIMAX+TM&source=gbs_navli

nks_s. [Accessed 26 02 2014].

[10] Atmel, "Atmel AT02845: Coexistence between ZigBee and Other 2.4GHz Products," 09 2013.

[Online]. Available: http://www.atmel.com/Images/Atmel-42190-Coexistence-between-ZigBee-

and-Other-24GHz-Products_AP-Note_AT02845.pdf. [Accessed 26 02 2014].

[11] C. Ed, "Low Power Consumption Features of the IEEE 802.15.4/ZigBee LR-WPAN Standard,"

6 11 2003. [Online]. Available: http://cens.ucla.edu/sensys03/sensys03-callaway.pdf. [Accessed

2 03 2014].

[12] A. Corporation, "ATmega48PA/88PA/168PA/328P," 2009. [Online]. Available:

http://www.atmel.com/Images/8161s.pdf.

[13] A. Uno, "Arduino Uno," 2014. [Online]. Available: http://arduino.cc/en/Main/arduinoBoardUno.


28

[Accessed 21 05 2014].

[14] MrLndr, "The Arduino UNO Anatomy," 9 08 2011. [Online]. Available:

http://arduinoarts.com/2011/08/the-arduino-uno-anatomy/. [Accessed 24 05 2014].

[15] XbeeCommunication, "XbeeCommunication," [Online]. Available:

http://itp.nyu.edu/physcomp/uploads/XbeeCommunication.png. [Accessed 25 05 2014].

[16] G. 3. Tim Cutler Vice President Sales and Marketing Cirronet Incorporated Norcross, "Wireless

Ethernet in Factory and Industrial Applications," [Online]. Available:

http://www.isa.org/fmo/newsweb/pdf/wireless.pdf. [Accessed 4 03 2014].

[17] C. Zarader, "How ZigBee/802.15.4 Protocol Simplifies," 4 06 2008. [Online]. Available:

http://docbox.etsi.org/workshop/2008/2008_06_M2MWORKSHOP/FREESCALE_ZARADER_

M2MWORKSHOP.pdf. [Accessed 6 03 2014].

[18] R. Winters, "Jameco Product Manager," 2014. [Online]. Available:

http://www.jameco.com/jameco/workshop/jamecobuilds/arduinocircuit.html. [Accessed 14 05

2014].

[19] M. Michael, L. Stefan, K. Rolf, Z. Mario, K. Peter and P. Steffen, "Real-Life Deployment of

Bluetooth Scatternets for Wireless Sensor Networks," [Online]. Available:

http://www.ics.uci.edu/~steffenp/files/methfessel2013bluetooth.pdf. [Accessed 18 05 2014].

[20] Alselectro, "XBEE RADIO– 4. XBEE MODULE From DIGI," 3 12 2012. [Online]. Available:

http://alselectro.wordpress.com/tag/xbee-series-1/. [Accessed 5 05 2014].

[21] Buzzle, "Advantages and Disadvantages of Different Network Topologies," 28 08 2013.

[Online]. Available: http://www.buzzle.com/articles/advantages-and-disadvantages-of-different-

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[22] S. Professor, "How to Connect an Arduino to an XBee Radio," 7 02 2011. [Online]. Available:

http://answers.oreilly.com/topic/2458-how-to-connect-an-arduino-to-an-xbee-radio/. [Accessed 5

05 2014].


29

8. Appendix

Software of the monitoring project

The software consisted of three stages:

1- The X-CTU software used for configuring Zigbee coordinator and router.

The XBee configured via X_CTU software utility. This application is designed to interact

with the firmware files found on Digi’s RF products.

The serial port selected and Zigbee communication tested see Figure (…) (…). The XBee set

up to be a Coordinator and Router in the modem Configuration tab, Function Set is selected

for both. The Zigbee coordinator at firmware was found and selected see Figure (….). After

that the Zigbee Router set up with small change in modification see Figure (…). The

configuration set up as follow:

The serial port and communication test for Zigbee

The serial port for Xbee connection selected and tested from X_CTU


30

Configuration for Zigbee coordinator and router

Node identifier for Zigbee Coordinator and Router


31

The following program was written for Zigbee coordinator or receive unit on the Arduino

software . The rest of the program is in the appendix.

The Zigbee coordinator C program on the Arduino simulator software


32

2- The data received from receive unit and saved in EXCEL file by using Coolterm

software.

Setting up the coolterm to save data in EXCEL

The data saved in EXCEL file by using Coolterm software


33

Results were recorded in Coolterm

Results were recorded on Arduino serial monitor


34

Receive unit coding


35


36


37

Transmission unit coding


38

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