1 | P a g e
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
2 | P a g e
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
3 | P a g e
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.
4 | P a g e
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.
5 | P a g e
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
6 | P a g e
APPENDIX ...35 APPENDIX A Schematics.........................................................................................................35 APPENDIX B Datasheets ...37
7 | P a g e
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
8 | P a g e
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.
9 | P a g e
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
10 | P a g e
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.
11 | P a g e
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
12 | P a g e
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.
13 | P a g e
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
14 | P a g e
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.
15 | P a g e
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
16 | P a g e
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
17 | P a g e
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.
18 | P a g e
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".
95 125 KHz: The use of this frequency band is limited to the energy
providers costumers; no access protocol is defined for this frequency
band. This frequency band is often referred as the "B-Band".
125 140 KHz: The use of this frequency band is limited to the energy
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.
19 | P a g e
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
20 | P a g e
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)
21 | P a g e
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.
22 | P a g e
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,
23 | P a g e
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.
24 | P a g e
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.
25 | P a g e
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.
26 | P a g e
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.
27 | P a g e
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.
28 | P a g e
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
29 | P a g e
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
30 | P a g e
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
31 | P a g e
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.
32 | P a g e
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
33 | P a g e
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
34 | P a g e
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
35 | P a g e
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
36 | P a g e
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
37 | P a g e
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
38 | P a g e
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
39 | P a g e
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
40 | P a g e
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
41 | P a g e
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
42 | P a g e
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
43 | P a g e
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
CJNE A,#00000111B,ROW1
MOV P1,#11111011B
MOV A,P2
ANL A,#00001111B
CJNE A,#00001111B,ROW2
LJMP K2
ROW0: MOV DPTR,#KCODE0
SJMP FIND
ROW1: MOV DPTR,#KCODE1
SJMP FIND
ROW2: MOV DPTR,#KCODE2
SJMP FIND
ROW3: MOV DPTR,#KCODE3
44 | P a g e
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
45 | P a g e
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
46 | P a g e
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
47 | P a g e
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
HERE11: DJNZ R0,HERE11
DJNZ R2,HERE12
DJNZ R1,HERE13
48 | P a g e
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
49 | P a g e
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
50 | P a g e
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
51 | P a g e
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
HERE11: DJNZ R0,HERE11
DJNZ R2,HERE12
DJNZ R1,HERE13
RET
END
52 | P a g e
APPENDIX B
SCHEMATIC DIAGRAMS
TRANSMITTING END
53 | P a g e
RECEIVING END
54 | P a g e
APPENDIX C
DATASHEETS
74HC4046 (PLL)
LF351CN( J-FET Op-amp)
55 | P a g e
56 | P a g e
57 | P a g e
58 | P a g e
59 | P a g e
60 | P a g e
61 | P a g e
62 | P a g e
63 | P a g e
64 | P a g e
65 | P a g e
66 | P a g e
67 | P a g e
68 | P a g e
69 | P a g e
70 | P a g e
71 | P a g e
72 | P a g e
73 | P a g e
Top Related