52086734 Home Automation Using Powerline Communication PDF

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HOME AUTOMATION USING POWER LINE

COMMUNICATION

Final Year Design Project Report

Submitted by

M. Karim Shah

Muhammad ul Haque

Muhammad Umair

Zeeshan Sikandar Niazi

Advisor

Mr. Muhammad Umar Khan

Faculty of Electronic Engineering Ghulam Ishaq Khan Institute of Engineering Sciences and Technology.

April 2010

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CERTIFICATE OF APPROVAL

This is to certify that the work in this thesis entitled

Home Automation Using Powerline Communication

Carried out by Muhammad Karim Shah, Muhmmad ul Haque,

Muhammad Umair and Zeeshan Sikandar Niazi under the

supervision of Mr. Muhammad Umar Khan in partial fulfullment of

the requirement for the degree of Bachelor of Science in Electronic

Engineering at Ghulam Ishaq Khan Institute of Engineering

Sciences and Technology, Topi.

Certified by,

Mr. Muhammad Umar Khan

Project Advisor

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ACKNOWLEDGEMENTS

We would like to thank our advisor, Mr. Muhammad Umar Khan

for being our personal navigator who aided us whenever we needed

assistance and whose knowledge, approach and professionalism has

always inspired us and helped us understand, analyze and solve

problems in a practical manner.

We would also like to express our gratitude to all the Faculty

members of Electronic Engineering who provided us with all the

support we needed.

We would also like to thank Mr. Muhammad Zubair and Dr.

Nouman Khan for their guidance.

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ABSTRACT

Powerline communication is a progressing technology that utilizes

electric power lines for efficient, instantaneous transmission of data.

The objective of our project was to design and implement a power

line communication network capable of controlling and monitoring

multiple devices from a single node. Exacting matters were the

design of a suitable coupling circuit to connect multiple slave units

onto the already existent and extensive power line network.

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CONTENTS CHAPTER 1 INTRODUCTION ...............................1 1.1Overview.1 1.2 Project Aim....2 1.3 Project Modules.3 CHAPTER 2 POWERLINE COMMUNICATION....5 2.1 Background....5 2.2 Power line carrier challenges.................6 2.2.1 Noise...............................................................6 2.2.2 Attenuation..8 2.2.3 Signal-to-Noise Ratio....10 2.3 Relevant Regulatory Standards...11 CHAPTER 3 MODULATION..14 3.1 Need for Modulation and Techniques..................................................................................14 3.2 Digital Modulation...16 3.2.1 Amplitude shift keying (ASK).... .16 3.2.2 Phase Shift Keying (PSK) ....17 3.2.3 Frequency Shift Keying (FSK) .....18 CHAPTER 4 COUPLING CIRCUITRY ...19 4.1 Coupling Transformer ...............20 4.2 Coupling Capacitors ...21 CHAPTER 5 HARDWARE IMPLEMENTATION ..22 5.1 The Implementation of FSK.................................................................................................. 22 5.1.1 The FSK Modulator ............................................................................................................23 5.1.2 The FSK Demodulator ................................................................................................... .....23 5.2 The coupling circuitry....................................................................................................... ......24 5.3 The relay ................................................................................................................................25 CHAPTER 6 PROGRAMMING MASTER/SLAVE ................................................................28 6.1 Master Unit ............................................................................................................. ...............29 6.1.1 Transmission Protocol ................................................................................................. .......29 6.1.2 User Interface ......................................................................................................................30 6.1.3 Sample Code (Transmission) ..............................................................................................30 6.2 Slave Unit ...............................................................................................................................31 6.2.1 Sample Code (Receiving End) .............................................................................................31 REFERENCES and Bibliography..33

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APPENDIX ...35 APPENDIX A Schematics.........................................................................................................35 APPENDIX B Datasheets ...37

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CHAPTER 1

INTRODUCTION

1.1 Overview

Power line communications is a novel idea of communication which may help in

bridging the gap existing between the electrical and communication network. It is

basically the utilization of an extensive power line network and the connection of

multiple devices to this network that could communicate over this intricate system

allowing a multitude of devices to be accessed at any point throughout an office or

residential unit. It also offers the prospect of being able to construct intelligent

buildings, which would maintain themselves by the use of multiple sensors that

would monitor parameters such as temperature and sunshine, and then

communicate to any device on the power grid, through the power grid itself.

Extensive research is being conducted in powerline communications so as to

explore the new businees opportunties in indoor communications. If it would be

possible to supply this kind of network communication over the power-line, the

utilities could also become communication providers, a rapidly growing market.

Nowadays research is mainly focused on increasing the efficiency of such systems

and allowing more coverage.

The various concerns facing this medium are that unlike power related

applications, network communications require very high bit rates and in some

cases real-time responses are needed. This complicates the design of a

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communication system but has been the focus of many researchers during the last

years. Systems under trial exist today that claim a bit rate of 1 Mb/s, but most

commercially available systems use low bit rates.

The power-line was initially designed to distribute power in an efficient way, a

high power low frequency signal. The communication signal tends to be a low

power high frequency one which is one hurdle to overcome. Additional challenges

are the fact that the power lines are contaminated by noise and signal attenuation

through runs of power line get higher as the frequency of operation increases.

Uncertainty and variance in levels of channel impedance also present problems.

Power line networks are usually made of a variety of conductor types and cross

sections joined almost at random. Therefore a wide variety of characteristic

impedances are encountered in the network. This imposes interesting difficulties

in designing the filters for these communication networks. Hence advanced

communication techniques are to be used for efficient transmission and receiving.

1.2 Project Aim

The project aims to understand and explore the theoretical and practical aspects of

power line communication techniques. This would lead to subsequent design and

implementation of a power line communications system that connected two

microcontrollers and the transmission of command signals over the power line to

switch on/off an electrical device. The microcontrollers would be able to transfer

data using the power lines as their only link of communication.

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1.3 Project Modules

Modulator/Demodulator:

The modulating circuitry would produce a specified high frequency signal, that

would be transmitted over the channel and then subsequently be demodulated at

the reciever to be decoded by the slave unit to activate/decactivate the appropriate

devices.

User Interface:

The user interface for the control of units is implemented by an LCD for display

of options and a keypad to choose the option of choice. This was connected to the

master microcontroller which would generate a unique bit pattern for each device,

which would be decoded at the slave unit.

Coupling:

This is the most essential module that couples the device to the power line. It must

isolate the system from the high power network and also act as a high pass filter

so that noise at lower frequencies may be filtered out and allowing the

communication signal through, without much attenuation.

Device activation:

The devices are to be activated using relays as they require high power which

cannot be provided by the microcontroller port. Each port is input to a latch which

is essential as it provides isolation to the microcontroller from the relay activation

mechanism. Without this latch the voltage level at the output port is not sufficient

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to energize the coil in the relay. After latching a BJT is used as a switching device

so that the high power signal is throughput to the N.O. of the relay which is

connected to the electrical device.

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CHAPTER 2

POWERLINE COMMUNICATION

2.1 Background

The technology was initiated back in the 1940s and has been used ever since in

low bitrate applications such as telemetering and control of electrical applicances

and devices in close proximity. Latest advancements are the attainment of higher

bandwidth and integration of outdoor applications which is evident from the fact

that broadband over power lines has been achieved in many western countries. A

number of protocols exist, which differ in the modulation techniques employed,

the frequency band utilized and the channel access mechanisms that are used.

The X-10 for example is one of the oldest protocols. It uses amplitude shift keying

and was initially used for simplex communication. The presence or absence of a

120kHz signal is used to detect the transmission of 1 or 0 bits respectively.

Each module is assigned an address and the transmission signal would typically

contain start bits, house address, device address and function code. This protocol

had its speed limitations and also the fact that multiple devices could be

transmitting signals simultaneously so collision resolution was to be attained later

on by protocols such as the CEBus.

The CEBus Protocol uses p2p communication model and employs Carrier Sensed

Multiple Access to avoid collisions. Power line physical layer of the CEBus is

based on spread spectrum technology which employs a frequency sweep from

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100-400kHz. This allows for synchronisation as an instantaneous frequency is

used as referance and it also aids in collision resolution. The 1 and 0 are

resolved by the time duration of the chirp with 100microseconds for a 1 and

200microseconds for 0.

Further protocols are progressively more efficient and employ techniques for the

integration of greater number of devices with sufficient reliance on the system to

function appropriately, as well as improving data rates to increase the applicability

of this technology.

2.3 Power line carrier challenges

2.3.1 Noise

Switching mode power supplies, light dimmers, computer networking systems,

poor connections that arc, and other "accidental transmitters" that either switch or

spark can create considerable RF energy on wiring. It is helpful, when attempting

to reduce such noise, that we understand how the noise travels from the source

into the receiving system. This noise can be classified as:

Corona Noise

Corona noise is the most common noise associated with transmission lines and is

heard as a crackling or hissing sound. Corona is the breakdown of air into charged

particles caused by the electrical field at the surface of conductors. This type of

noise varies with both weather and voltage of the line, and most often occurs in

conditions of heavy rain and high humidity (typically >80%). An electric field

surrounds power lines and causes implosion of ionized water droplets in the air,

which produces the sound.

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During relatively dry conditions, corona noise typically results in continuous noise

levels of 40 to 50 dBA in close proximity to the transmission line, such as at the

edge of the right-of-way. In many locations, this noise level is similar to ambient

noise conditions in the environment. During wet or high humidity conditions,

corona noise levels typically increase. Depending on conditions, wet weather

corona noise levels could increase to 50 to 60 dBA and could even increase to

over 60 dBA under some conditions. Corona noise levels are not consistent from

location to location because conductor surface defects, damage, dust, and other

inconsistencies can influence the corona effect.

Insulator noise

Insulator noise is similar to corona noise but it is not dependent on weather. It is

caused by dirty, nicked, or cracked insulators, and is mainly a problem with older

ceramic or glass insulators. New polymer insulators minimize this type of noise.

50 Hz periodic noise

Noise synchronous to the sinusoidal power line carrier can be found on the line.

The sources of this noise tend to be silicon-controlled rectifiers (SCRs) that switch

at a certain angle in the 50Hz cycle, placing a voltage spike on the line. This

category of noise has line spectra at multiples of 50 Hz.

Single-event impulse noise

Lightning strikes, ignition sparks and lights being turned on or off produce single-

event impulses which result in noise throughout the spectrum. Capacitor banks

switched in and out create impulse noise as well.

Periodic impulsive noise

Devices such as the triac-controlled dimmers on lights are the most common

source of indoor noise as they introduce impluses whenever they connect the lamp

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to the AC line part way through each AC cycle. These impulses occur at twice the

AC line frequency as this process is repeated every AC cycle.

Continuous Impulsive noise

Continuous impulsive noise is the most severe of all the noise sources as this kind

of noise is produced by a variety of series wound AC motors which are present in

multiple devices such as found in vacuum cleaners, drillers, electric shavers and

many common kitchen appliances. Commutator arcing from these motors

produces impulses at repetition rates in the several kilohertz range.

Non-synchronous periodic noise

This type of noise has line spectra uncorrelated with 50 Hz sinusoidal carriers.

Television sets generate noise synchronous to their 15734 Hz horizontal scanning

frequency. Multiples of this frequency must be avoided when designing a

communications transceiver.

It is found that noise levels in a closed residential environment fluctuate greatly as

measured from different locations in the building. Noise levels tend to decrease in

power level as the frequency increases; in other words, spectrum density of power

line noise tends to concentrate at lower frequencies. This implies that a

communications carrier frequency would compete with less noise if its frequency

were higher.

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2.3.2 Attenuation

Attenuation is the loss of signal strength as the signal travels over distance.

For a transmission line the input impedance depends on the type of line, its length

and the termination at the far end. The characteristic impedance of a transmission

line (Zo) is the impedance measured at the input of this line when its length is

infinite. Under these conditions the type of termination at the far end has no effect.

A standard distributed parameter model can obtain the characteristic impedance of

an unloaded power cable, and it is given

by

At the frequencies of interest for PLC communications (the high frequency range),

this approximates to

where L and C are the line impedance and capacitance per length.

High frequency signals can be injected on to the power line by using an

appropriately designed high pass filter. Maximum signal power will be received

when the impedance of the transmitter, power line and the receiver are matched.

Power line networks are usually made of a variety of conductor types and cross

sections joined almost at random. Therefore a wide variety of characteristic

impedances are encountered in the network. Unfortunately, a uniform distributed

line is not a suitable model for PLC communications, since the power line has a

number of loads (appliances) of differing impedances connected to it for variable

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amounts of time. Channel impedance is a strongly fluctuating variable that is

difficult to predict. The overall impedance of the low voltage network results from

a parallel connection of all the networks loads. so the small impedances will play

a dominant role in determining overall impedance. Overall network impedances

are not easy to predict either. The most typical coaxial cable impedances used are

50 and 75-ohm coaxial cables and measured 7dB attenuation for a 50 meter run

with a 10 ohm termination. A twisted pair of gauge-22wire with reasonable

insulation on the wires measures at about 120 ohms. Clearly, channel impedance

is low. This presents significant challenges when designing a coupling network for

PLC communications. Maximum power transfer theory states that the transmitter

and channel impedance must be matched for maximum power transfer. With

strongly varying channel impedance, this is tough. We need to design the

transmitter and receiver with sufficiently low output/input impedance

(respectively) to approximately match channel impedance in the majority of

expected situations.

2.3.3 Signal-to-Noise Ratio

As the name suggests, this parameter is an essential performance estimator and

must be considered for this medium of communication as well. The higher SNR

the better the communication as the signal is more dominant.

For indoor environments there are multiple noise sources as discussed earlier and

as seen from the attenuation in a power line channel it is apparent that the SNR is

majorly hampered. Improvements can be made by, for example, installing filters

at each household to block the noise generated from entering the grid and

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decreasing noise from the outdoor grid as well. This will mean higher costs.

Another test for locating noise sources is to go to the main breaker panel or fuse

box. Check the presence of the noise with a battery-powered radio. If the noise is

present, shut off all power to the premises by turning off the MAIN circuit breaker

or by pulling the MAIN fuses or meter. If the noise on the AM radio stops while

the power is off, the source of the interference is within the residence. If the noise

continues, you can assume it is coming from a point external to the customer's

home. Restore the main circuit breaker or fuses or meter. If the noise stopped

while the power was off, locate the circuit supplying the power to the noise source

using an AM radio as before, and de-energize the individual circuit breakers one

at a time until the noise stops. Next, determine what is on the circuit by going

from room to room to isolate outlets, appliances and lights until the offending

device is found.

2.4 Relevant Regulatory Standards

Frequencies used by the devices communicating over the power line are restricted

by the limitations imposed by the regulatory agencies. These regulations are

developed to ensure harmonious coexistence of various electromagnetic devices in

the same environment. The frequency restrictions imposed by FCC and

CENELEC are shown in figures 2.1 and 2.2.

Federal Communications Commission (FCC) and European Committee for

Electro technical Standardization (CENELEC) govern regulatory rules in North

America and Europe respectively.

In North America frequency band from 0 to 500 KHz can be used for power line

communications. However the regulatory rules in Europe are more stringent.

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Here, the CENELEC standard only allows frequencies between 3 kHz and 148.5

kHz. This puts a hard restriction on power line communications and might not be

enough to support high bit rate applications, such as real-time video, depending on

the performance needed. According to this standard the spectrum is divided into

five bands based on the regulations. They are

3 9 KHz: The use of this frequency band is limited to energy provides;

9 95 KHz: The use of this frequency band is limited to the energy

providers and their concession-holders. This frequency band is often

referred as the "A-Band".


providers costumers; no access protocol is defined for this frequency

band. This frequency band is often referred as the "B-Band".


providers customers; in order to make simultaneous operation of several

systems within this frequency band possible, a carrier sense multiple

access protocol using center frequency of 132.5 KHz was defined. This

frequency band is often referred to as the "C-Band".

140 148.5 KHz: The use of this frequency band is limited to the energy

providers customers; no access protocol is defined for this frequency

band. This frequency band is often referred to as the "D-Band".

Thus in Europe power line communications is restricted to operate in the

frequency range from 95 148.5 KHz. Apart from band allocation, regulatory

bodies also impose limits on the radiations that may be emitted by these devices.

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These reflect as restrictions on the transmitted power in each of these frequency

bands.

Bandwidth is proportional to bit rate, in order to increase the bit rate, larger

bandwidth may be needed. Recent research has suggested the use of frequencies

in the interval between 1 and 20 MHz. If this range could be used, it would make

an enormous increase in bandwidth and would perhaps allow high bit rate

applications on the power-line. An important problem is that parts of this

frequency band is assigned to other communication system and must not be

disturbed. Other communication systems using these frequencies might also

disturb the communication on the power-line.

Figure 2.1: CENELEC frequency band allocation

Figure 2.2: FCC frequency band allocation

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CHAPTER 3

MODULATION

3.1 Need for Modulation and Techniques

When data is transmitted over long distance there should be some mechanism of

coding so that the data can easily be distinguished from noise and other signals

being transmitted in the same channel and decoded. Modulation is the used to

transmit signal over long distances. modulation is the process of varying one or

more properties of high frequency periodic waveform, called the carrier signal,

with respect to a modulating signal.

In modulation the signal to be transmitted, called the carrier signal, is modulated

by some high frequency signal and transmitted and at the receiving end the signal

is received and demodulated to recover the original signal. An analogue signal is

mathematically expressed as

There are only three characteristics of a signal that can be changed over time:

amplitude, phase, or frequency. However, phase and frequency are just different

ways to view or measure the same signal change. So, we have three parameter

which can be altered

The amplitude of the signal (A)

The frequency of the signal (w)

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And the phase of the signal ( )

And based on these three parameters there are three different types of modulations

1. Amplitude modulation (AM)

2. Frequency modulation (FM)

3. Phase modulation (PM)

In AM, the amplitude of a high-frequency carrier signal is varied in proportion to

the instantaneous amplitude of the modulating message signal. Frequency

Modulation (FM) is the most popular analog modulation technique used in mobile

communications systems. In FM, the amplitude of the modulating carrier is kept

constant while its frequency is varied by the modulating message signal and in

phase modulation the phase of the carrier signal is varied with the amplitude of the

modulating signal while amplitude and frequency is kept constant.

There are three basic purposes of modulation in general:

1. To reduce the wavelength for efficient transmission and reception. A

typical audio frequency of 3000 Hz will have a wavelength of 100 km and

would need an effective antenna length of 25 km! By comparison, a

typical carrier for FM is 100 MHz, with a wavelength of 3 m, and could

use an antenna only 80 cm long.

2. To allow simultaneous use of the same channel, called multiplexing. Each

unique signal can be assigned a different carrier frequency (like radio

stations) and still share the same channel.

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3. Modulation also serves as a source of coding mechanism.

3.2 Digital Modulation

Types of digital modulation

Amplitude shift keying (ASK)

Frequency shift keying (FSK)

Phase shift keying (PSK)

In FSK, the frequency of the carrier is changed as a function of the modulating

signal (data) being transmitted. Amplitude remains unchanged. In binary FSK a

1 is represented by one frequency and a 0 is represented by another

frequency.

Now all these three are discussed in detail.

3.2.1 Amplitude shift keying (ASK)

In ASK, the amplitude of the carrier is changed in response to information and

frequency and phase are kept constant. Bit 1 is transmitted by a carrier of one

particular frequency and to transmit bit 0, the amplitude is changed keeping the

other two parameters constant. ON=OFF keying is a special form of ASK, where

one of the amplitude is zero.

A binary amplitude-shift keying (BASK) signal can be defined by

Where,

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A is the amplitude

m(t) is the digital data

is the carrier frequency

m(t) is either 0 or 1. For 1

and for m(t) = 0

Which implies that the carrier signal is present when the digital signal is at logic

high absent when it is at low level.

Since the amplitude of the signal is varied corresponding to the instantaneous

change in the amplitude of the carrier signal and noise is always present. During

the transmission of the signal it is amplified at different locations (before sending

on the power line and after receiving the signal before demodulation). As a result

the noise will also be amplified. This is one of the drawback due to which we

avoided using Ask as our modulation scheme.

3.2.2 Phase Shift Keying (PSK)

In PSK, we change the phase of the carrier signal to indicate the information.

Phase in this context is the starting angle at which the carrier signal (sinusoid)

starts. To transmit 0, we shift the phase of the sinusoid by 1800

. Phase shift

represent the change in the state of the information.

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for logic level 1

for logic level 0

Where,

A is a constant

m(t) is the digital signal either +1 or -1

is the carrier frequency

3.2.3 Frequency Shift Keying (FSK)

In FSK, we change the frequency of the carrier signal in response to the

information signal, one particular frequency for logic 1 and another frequency for

logic level 0. Mathemathically.

for logic level 1

for logic level 0

FSK is the most favorable scheme of modulation for power line communication

since the carrier frequency is always present and we can recover the original filter

easily because the amplitude is not important anymore so the effect of noise is

reduced as compared to the other modulation schemes.

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CHAPTER 4

COUPLING CIRCUITRY

One of the most critical components of any Power Line Communication system is

its interface circuit (or coupling circuit) with the power distribution network. This

is by no means a simple unit considering the challenging characteristics of the

PLC channel. Due to high voltages, varying impedances, high amplitudes and

time dependent disturbances, coupling circuits need to be carefully designed to

provide both the specific signal transmission with the appropriate bandwidth, and

the safety level required by the applicable domestic or international standard. A

coupling circuit in a power line communications system is actually used for

coupling an information signal from a transmitter unit to a power line and

decoupling that signal from the power line to a receiver unit. The coupling circuit

includes: (a) a ferrite core inductive coupler for isolating the transmitter unit and

the receiver unit from a power line and for coupling information signals from the

transmitter unit to the power line and from the power line to the receiver unit, (b)

a high pass filter (capacitive coupler) which not only blocks random noise from

entering into the modem but also suppresses 50Hz power signal. Hence it is the

core part of Power Line Communication which isolates the modem from high

voltages and allows only the information signal to pass through unattenuated.

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4.1 Coupling Transformer

Coupling transformer is used for two reasons (a)To attain galvanic isolation (b)

For impedance matching. Coupling transformer used here should be designed as a

high frequency transformer, as our information signal is a high frequency signal.

The power signal tends to have a saturating influence on the magnetic core and in

the order of atleast 105 time more as compared to the communication signal. This

means that the transformer must be placed after the capacitive coupler so as to

prevent the power signal from saturating the core, and hence deforming the

communication signal. Another consideration regarding the transformer is its

frequency response. Operating at lower frequencies and high power ratings, most

power transformers have transfer functions which do not allow for the

communication signal to get through. In the inductive coupling, PLC signal

current is injected into the power distribution lines. This is achieved through an

inductive transformer coupler using appropriate high-frequency ferrites. The

inductive injection method is most effective when the mains impedance is low at

the signal injection point. This is typically the case when injecting the signal into a

bus network where several power cables are connected together. Connecting

several power cables to a single point or bus effectively results in a parallel

connection of the individual cable impedances. This results in low input

impedance. The inductive coupling is often the preferred method for coupling due

to its better performance in low impedance situations, lower radiation from power

mains and its simplicity to use.

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4.2 Coupling Capacitors

A high pass passive filter is needed to remove noise coming from the power line

and to act as a capacitive coupling circuit, blocking 50Hz power signal. The

requirements and essential characteristics of coupling capacitors have been

standardized in ANSI C93.1-1972. All filter components need to be able to with

stand voltage surges and must have high power ratings.

Capacitive coupling can be used as a standalone isolation circuit provided we

employ perfect grounds at the transmitting and receiving side. This provides a

proper referance for the communication signal allowing a 0.6V signal to be

detected at a distance of 20m with an input signal of 3.6V.

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CHAPTER 5

HARDWARE IMPLEMENTATION

5.1 The Implementation of FSK

In this project we are using HEF4046B IC for modulation and demodulation. The

internal circuitry is shown

Figure 5.1 Functional Diagram

This IC contains VCO as well as the PLL which are used for modulation and

demodulation respectively. There are two phase comparators. Phase comparator 1

is the exclusive OR gate. This comparator has the feature that it does not only lock

on to the fundamental frequency but also at its harmonics which is undesired for

us as we do not want to lock the PLL at the harmonics which might be any noise

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on the power line (there is always noise at different frequencies on the power

line). Phase comparator 2 locks only at the fundamental frequency so we will be

using this comparator in our project.

The VCO gives both square or triangular signal of particular frequency set by the

external Resistors (R1 and R2) and capacitor (C1).

5.1.1 The FSK Modulator

We are using 190KHz for logic level 1 and 150KHz for logic level 0. For these

frequencies we will find the external components as follow.

Step 1

Since we have fmax = 190KHZ

and fmin = 150KHZ

Given fmin use fig.8 (all these

graphs are in the data sheet of

4046 at the appendix) to

determine R2 and C1

Step 2

Use with fig.9

to determine the ratio to obtain R1

From the first step we get R2 =10K (for Vcc = 10V) and C1 = 5nf

And from step 2 we get R2 = 10K

Figure 5.2 Modulator Biasing

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5.1.2 The FSK Demodulator

The values of R1, R2 and C1 for the demodulator are the same as for the

modulator since we want to recover the original signal.

The low pass filter at the

comparator output is required to

eliminate the small flotation in the

output wave form. The values for

this filter are calculated as:

The cutoff frequency of the low

pass filter should be:

and fserial in our system is very low.

fmin = 150kHz so we will choose the cutoff frequency as

fc = 100zHz

now using for fc =100KHZ and C2 = 1nf

R3 =1.5KHz

5.2 The coupling circuitry

Figure 5.3 Demodulator Biasing

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According to the standard used for isolation of the low voltage circuitry from the

high voltage power line, an isolation transformer and coupling capacitors are used.

The transformer serves two purposes, first it serves as an isolating device and

secondly it also helps in impedance matching.

The transformer should be of high frequency. Since we are using 190KHZ and

150KHZ for logic high and low respectively, the frequency ratings of the

transformer should also be in this frequency ranges. But due to the unavailability

of such a high frequency transformer we modified the coupling circuitry at the

cost of impedance mismatch. The coupling circuitry which we are using is an RC

second order high pass filter. Keeping in view the high voltage, the resistors used

are of 10watts and the capacitors are of high voltage rating (800V). and the cutoff

frequency of the filter is calculated from

With R = 1K and C = 2.2nF the cutoff frequency was calculated as

fc = 72.3KHZ

This helps to suppress the 50HZ high voltage signal and the noise below this

frequency ranges is also suppressed. (To further minimize noise the signal is

passed through band pass filter before demodulation).

5.3 The relay

Relays are electro-magnetically activated switches. Literally, there is an

electromagnet inside the relay, and energizing that electromagnet causes the

switch to change position by pulling the movable parts of the switch mechanism

to a different position. To the greatest extent possible, the electromagnet is made

to be electrically isolated from the signal path.

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There are two main classes of relays - latching and non-latching. Non-latching

relays are the simplest kind.

In a non-latching relay, the electromagnet pulls on a switch that is spring-loaded

to one side, which is called the "normal" or "reset" side. Whenever the

electromagnet's coil carries enough current (called the pull-in current), it makes

enough ampere-turns of magnetic force to pull the switch to the "energized" or

"set" position. The switch stays in the energized position as long as the current in

the coil is enough to make the electromagnet overcome the force of the spring. As

soon as the current drops below the holding current, the spring pulls the switch

back to the non-energized condition. Because of the way magnetic attraction

works, it takes less magnetic force - and therefore less current in the coil - to hold

the relay set than it did to move it there in the first place, so the holding current is

less than the pull-in current.

The nonlatching relay is shown schematically on left hand corner of fig below.

The switch portion of the basic relay is shown as a switch that consists of a pole

which can be switched to one of two throws. The throw that the pole connects to

when no current flows in the coil is called the normally closed (NC) throw. The

normally open (NO) contact is - well, normally open. A spring holds the switch in

this position. The pole and throws are the only signal connections on the relay.

The coil is only used to control the relay, not to conduct signal

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currents.

Figure 5.4 Two types of relays one employing a spring (L) and one using a magnet (R)

On the right hand side of the figure above, we see the other major kind of relay,

the latching relay. If we have no spring, but make the swinging arm a magnet

(indicated by the n and s poles), then the swinging arm will be made to be

attracted to the closest of the two iron coil cores. It will stay in that position

forever unless something makes it move. We can make it move by briefly

connecting the switch and battery to make the two electromagnets energize in a

way that repels the magnet in the swing arm away from its current position. If the

polarity of the battery is such that the iron core attracts the swinging arm, the arm

stays right where it is and nothing happens. Only if the polarity of the battery is

such that the iron core repels the swinging arm, and the other iron core attracts the

swinging arm, will the swinging arm will flip to the other side and stay there. By

proper winding and connections, this forms a magnetically latching relay. This

particular kind is called a "single coil" latching relay. You make it change states

by putting a reverse pulse into the single coil. To flip it back, you have to invert

the coil polarities again.

The switch in the above figure is practically replaced in the Power Line

Communication system by a BJT transistor. The base of the transistor is

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connected to the output of the latch IC. As the output current of the

microcontroller is too small and cannot provide the sufficient base current for the

transistor, it is first latched and then connected to the base. The relay is connected

to the emitter and VCC is applied at the collector. The transistor turns ON and

OFF in response to the microcontroller.

Figure 5.5 System Block Diagram

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CHAPTER 6

PROGRAMMING MASTER/SLAVE

Language Assembly Language

Microcontroller Atmel AT89C51

Software MIDE-51

6.1 Master Unit

Microcontroller sends the digital data at data rate of 5kb/s which is fed into the

FSK modulator thus we have 190Khz frequency burst for 1 and 140Khz

frequency burst for 0. Serial port of the microconroller is not used for the data

communication because of synchornization problem between transmitter and

receiver due to high baud rate, instead P1.7 of the master microcontroller is

manually used for transmitting the data serially.

6.1.1 Transmission Protocol

First two bits are the starting bits which tells the slave unit to take the next byte as

a data byte. Microcontroller concatenates a pair of ones before the address of the

corresponding device.

6.1.2 Address Mapping

1 1 DATA (8 Bits )

Figure 6.1 Transmission Protocol

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Each device which is to be controlled is mapped with a unique address. So when a

device is to be activated/deactivated microcontroller transmits the binary of that

address. Address mapping is as follows:

Device Address (decimal) Binary

A 1 00000001

B 2 00000010

C 3 00000011

. . .

Z . .

6.1.3 User Interface

At the control side user is provided with an interface which includes LCD display

and a numeric keypad. LCD is used for visual purpose and user guidance where

keypad is used to intake the data or corresponding address of the device to be

switched on/off. The detail Pin configuration of LCD and working of keypad is

described in Appendix A.

Fi

gure 6.2 Block diagram of GUI

Table 6.1 Address mapping

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6.1.4 Sample Code (Transmission)

TRANS:MOV R4,#8

SETB P2.1

ACALL DELAY3 ;Starting bits

ACALL DELAY3

UNT: RRC A ;Address fed by user

MOV P1.7,C ;Transmitting serially

ACALL DELAY3 ;Setting specified baud rate

DJNZ R4,UNT

ACALL DELAY1 ;Ending bits

ACALL DELAY1

ACALL DELAY1

LJMP START ;Jump for next data byte

6.2 Slave Unit

At the receving end slave unit takes in the serial data through P2.1 and after

processing the address activates/deactivates the corresponding device through a

latching and relay circuitry.

6.2.1 Sample Code (Receving End)

START:MOV A,#0H

JNB P2.1,START

ACALL DELAY3 ;Check for first starting bit

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JNB P2.1,START ;Check for Second starting bit

MOV R4,#8

JMP DAT

DAT: DJNZ R4,NEXT

JMP ACTIV ;Activate the corresponding device

NEXT: JB P2.1,ADD1 ;Detecting 1

JNB P2.1,ADD2 ;Detecting 0

ADD1: RL A ;Retreiving address

ADD A,#0H

ACALL DELAY3

JMP DAT

ADD2: RL A ;Retreiving address

ADD A,#01H

ACALL DELAY3

JMP DAT

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REFERENCES

I. Muhammad Ali Mazidi, and Janice Cillisie Mazidi. The 8051 Microcontroller and

Embedded Systems, pg 236-237

II. M Zubair M Atif Siddiqui, Wajahat Ali Shah, M Rashid, Power Line

Communication Network, BS Final Year, July 2009

III. B. A. Mork, D. Ishchenko, X. Wang, A.D. Yerrabelli, R.P. Quest, C.P.

Kinne, Power Line Carrier Communications System Modeling

IV. http://www.merl.com/projects/SCP/ , Simple Control Protocol for Power Line

Communications.

V. Niovi Pavlidou, A. J. Han Vinck, Javad Yazdani and Bahram Honary, Power Line

Communications: State of the Art and Future Trends, IEEE Communications

Magazine, Vol.41 No. 4 pp. 34-39, April 2003.

VI. Echelon Corporation, A Power Line Communication Tutorial Challenges and

Technologies.

VII. Transmission Theory for X10 Technology, http://www.x10.com/technology1.htm.

VIII. P K DALELA , M V S N PRASAD , ANAND MOHAN, A new concept of digital

power line carrier communication for rural applications

IX. IEEEJ OURNAL ON SELECTED AREAS IN COMMUNICATIONS,VOL.24,NO.7,

Masaaki Katayama, A Mathematical Model of Noise in Narrowband Power

Line Communication Systems, JULY2006,

X. http://www.tpub.com/neets/book2/5i.htm

XI. http://www.oas.org/en/citel/infocitel/2006/noviembre/bpl_e.asp

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APPENDIX A

PROGRAMMING CODE TRANSMITTING END

ORG 0h

START: MOV DPTR,#COM1

HERE1: CLR A

MOVC A,@A+DPTR

JZ PRINT15

ACALL COMWRT

ACALL DELAY1

INC DPTR

SJMP HERE1

PRINT15:MOV DPTR,#DATA1

PRINT1: CLR A

MOVC A,@A+DPTR

JZ COMM2

ACALL DATAWRT

ACALL DELAY1

INC DPTR

SJMP PRINT1

COMM2: MOV DPTR,#COM2

HERE6: CLR A

MOVC A,@A+DPTR

JZ DAT2

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ACALL COMWRT

ACALL DELAY1

INC DPTR

SJMP HERE6

DAT2: MOV DPTR,#DATA2

PRINT2: CLR A

MOVC A,@A+DPTR

JZ START1

ACALL DATAWRT

ACALL DELAY1

INC DPTR

SJMP PRINT2

START1: ACALL DELAY3

MOV DPTR,#COM3

HERE7: CLR A

MOVC A,@A+DPTR

JZ START2

ACALL COMWRT

ACALL DELAY1

INC DPTR

SJMP HERE7

START2: MOV DPTR,#MENUE1

PRINT3: CLR A

MOVC A,@A+DPTR

JZ CNTRL

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ACALL DATAWRT

ACALL DELAY1

INC DPTR

SJMP PRINT3

START3: MOV A,#0C0H

ACALL COMWRT

ACALL DELAY1

; MOV DPTR,#MENUE2

PRINT4: CLR A

MOVC A,@A+DPTR

JZ CNTRL

ACALL DATAWRT

ACALL DELAY1

INC DPTR

SJMP PRINT4

KEYCHK: MOV P2,#0FFH

K1: MOV P1,#0

MOV A,P2

ANL A,#00000111B

CJNE A,#00000111B,K1

K2: ACALL DELAY1

MOV A,P2

ANL A,#00000111B

CJNE A,#00000111B,OVER

SJMP K2

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OVER: ACALL DELAY1

MOV A,P2

ANL A,#00000111B

CJNE A,#00000111B,OVER1

SJMP K2

OVER1: MOV P1,#11111110B

MOV A,P2

ANL A,#00000111B

CJNE A,#00000111B,ROW0

MOV P1,#11111101B

MOV A,P2

ANL A,#00000111B


MOV P1,#11111011B

MOV A,P2

ANL A,#00001111B


LJMP K2

ROW0: MOV DPTR,#KCODE0

SJMP FIND


SJMP FIND


SJMP FIND


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FIND: RRC A

JNC MATCH

INC DPTR

SJMP FIND

MATCH: CLR A

MOVC A,@A+DPTR

RET

CNTRL: ACALL KEYCHK

MOV R6,A

XRL A,#1

JZ STATUS

MOV A,R6

XRL A,#2

JZ OF

SJMP CNTRL

OF: MOV DPTR,#COM3

HERE9: CLR A

MOVC A,@A+DPTR

JZ OFPRINT

ACALL COMWRT

ACALL DELAY1

INC DPTR

SJMP HERE9

OFPRINT:MOV DPTR,#STAT1

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PRINT6: CLR A

MOVC A,@A+DPTR

JZ ADDRESS1

ACALL DATAWRT

ACALL DELAY1

INC DPTR

SJMP PRINT6

STATUS: MOV DPTR,#COM3

HERE8: CLR A

MOVC A,@A+DPTR

JZ STPRINT

ACALL COMWRT

ACALL DELAY1

INC DPTR

SJMP HERE8

STPRINT:MOV DPTR,#STAT1

PRINT5: CLR A

MOVC A,@A+DPTR

JZ ADDRESS1

ACALL DATAWRT

ACALL DELAY1

INC DPTR

SJMP PRINT5

ADDRESS1:ACALL KEYCHK

JMP TRANS

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TRANS: MOV R4,#8

SETB P2.1

ACALL DELAY3 ;STARTING BITS

ACALL DELAY3

UNT: MOV R5

MOV B,#2 ;CHECKING EVEN PARITY

RRC A

INC R5

MOV P2.1,C

ACALL DELAY3

DJNZ R4,UNT

MOV A,R5

DIV AB

MOV A,B

JZ PARITY

SETB P2.1

JMP FIN

PARITY: CLR P2.1

ACALL DELAY3

FIN: ACALL DELAY1

ACALL DELAY1

ACALL DELAY1

LJMP START

COMWRT: MOV P0,A

CLR P3.0 ;RS

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CLR P3.1 ;R/W

SETB P3.2 ;E=1

ACALL DELAY1

CLR P3.2 ;E=2

RET

DATAWRT:MOV P0,A

SETB P3.0 ;RS=1

CLR P3.1 ;R/W=0

SETB P3.2 ;E=1

ACALL DELAY1

CLR P3.2 ;E=0

RET

DELAY2: MOV R1,#80

HERE5: MOV R2,#255

HERE4: MOV R0,#255

HERE3: DJNZ R0,HERE3

DJNZ R2,HERE4

DJNZ R1,HERE5

RET

DELAY3: MOV R1,#08

HERE13: MOV R2,#255

HERE12: MOV R0,#255


DJNZ R2,HERE12

DJNZ R1,HERE13

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RET

DELAY1: MOV R1,#20

X: MOV R0,#145

ST: DJNZ R0,ST

DJNZ R1,X

RET

COM1: DB 38H,0EH,01,06,81H,0 ;Commands for initializing

LCD

COM3: DB 1,80H,0

COM2: DB 0C2H,0

DATA1: DB "WELCOME TO",0 ;Starting up

DATA2: DB "CONTROL PANEL",0

MENUE1: DB "1 O/F:",0 ;Press 1 for switching

STAT1: DB "ADDRESS:",0

KCODE0: DB 1,2,3

KCODE1: DB 4,5,6

KCODE2: DB 7,8,9

KCODE3: DB 10,11,12

END

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RECEIVING END

ORG 00H

SETB P2.1

START: MOV A,#0H

JNB P2.1,START

ACALL DELAY3 ;CHECK FOR 1ST STARTING BITS

JNB P2.1,START ;CHECK FOR 2ND STARTING BITS

MOV R4,#5

JMP DAT

DAT: DJNZ R4,NEXT

JMP ACTIV ;ACTIVATE THE CORESSPONDING DEVICE

NEXT: JB P2.1,ADD1

JNB P2.1,ADD2

ADD1: RL A

ADD A,#0H

ACALL DELAY3

JMP DAT

ADD2: RL A

ADD A,#01H

ACALL DELAY3

JMP DAT

ACTIV: XRL A,#1

JZ ONE

XRL A,#2

JZ TWO

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XRL A,#3

JZ THREE

XRL A,#4

JZ FOUR

XRL A,#5

JZ FIVE

XRL A,#6

JZ SIX

XRL A,#7

JZ SEVEN

XRL A,#8

JZ EIGHT

XRL A,#9

JZ NINE

ONE: CPL P1.0

LJMP START

TWO: CPL P1.1

LJMP START

THREE: CPL P1.2

LJMP START

FOUR: CPL P1.3

LJMP START

FIVE: CPL P1.4

LJMP START

SIX: CPL P1.5

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LJMP START

SEVEN: CPL P1.6

LJMP START

EIGHT: CPL P1.7

LJMP START

NINE: CPL P2.1

LJMP START

DELAY3: MOV R1,#08

HERE13: MOV R2,#255

HERE12: MOV R0,#255


DJNZ R2,HERE12

DJNZ R1,HERE13

RET

END

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APPENDIX B

SCHEMATIC DIAGRAMS

TRANSMITTING END

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RECEIVING END

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APPENDIX C

DATASHEETS

74HC4046 (PLL)

LF351CN( J-FET Op-amp)

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