Power
line transmission:
power line telecommunications (plt) is
a rapidly evolving technology, aiming at the utilization of a.c. mains lines for transmission of data.
A main obstacle in the
realization of the information society is the investment required to
Provide the necessary
infrastructure which will reach the maximum number of information
Users. The currently
available technologies, i.e. wire/cable/fiber and wireless/satellite, have
Not yet given solutions to
this critical problem. This will certainly delay the implementation of the
information society.
It is important, however, to observe
that already every building is connected to the power grid and moreover every
room has power line contact points. The extent of this existing wiring cannot
be matched by either the telecommunications or cable TV wiring. Thus, the
emerging pelt technology opens up new opportunities for the mass provision of
local access at a reasonable cost.
In addition, pelt can provide a
multitude of new services to the users which are difficult to implement by
other technologies, e.g., remote electricity meter reading, appliance control
and maintenance, energy management, home automation, etc.
The technology and business impact of
the implementation of the pelt technology will be felt very strongly by all
players in the telecommunications and energy sectors. It is an enabler for
utilities and others to become important players in building the information
society, as it provides a new platform for interactive information-based
services in local communities. It will therefore be a factor in the faster
introduction on a mass scale of many new information society dependent
services.
Local access is a key issue in the
information society infrastructure. This local access may be provided, in
different situations and under varying conditions, by various telecommunication
technologies, of which power line telecommunication is one.
Block diagram
Block diagram description:
As our system is simplex one, it
basically consists of two main parts i.e. transmitter and receiver.
The transmitter consists of:
Keyboard:
This is used to enter the
data which is to be transmitted over ac mains and displayed on both transmitter
and receiver displays.
16*2 lcd display:
this is used to display the
data that is entered by the keyboard on the transmitter side.
micro-controller 89c52:
The micro-controller is
programmed to transmit the data with the appropriate baud rate to the fsk
modulator.
fsk
modulator:
In this block the digital data
from micro-controller is frequency modulated by the oscillator designed.
Now,
the modulated data is sent over 230 v a.c. mains. This will be the
communication link between the transmitter and receiver.
The receiver consists of:
fsk demodulator :
the modulated signal received through mains is demodulated in this
block.
micro-controller 89c52:
Here the micro-controller
reads the demodulated data and is given to the display.
16*2 lcd display:
The data read by
micro-controller is displayed on the display.
micro-controller at89c52:
we require a
micro-controller for programming it as a transmitter and a receiver. The
question arises here that why we prefer micro-controller over micro-processor. The answer to this can be given by following
points:
1
micro-processors are intended to be general purpose
digital computers whereas micro-controllers are intended to be special purpose digital controllers.
2
micro-processors contain a cpu, memory addressing
circuit and interrupt handling circuits. micro-controllers have these feature
as well as timers, parallel and serial i/o and internal ram and rom .
four bit units are
produced in huge volumes for very simple applications and 8-bit units are the
most versatile.
here we are
using following 8 bit micro-controller.
at89c52
micro-controller :
2
4 kilobytes of in-system re-programmable flash memory.
3
fully static operation; 0 hz -20 khz.
4
3 level program memory.
5
128*8 timer/counters.
6
32 programmable i/o lines.
7
two 16 bits timer/counters.
8
six interrupt sources.
9
programmable serial channels.
10 low
power idle and power down modes.
criteria for choosing
micro-controller:
1. the first and foremost criterion in choosing
a microcontroller is that it must meet the task at hand efficiently and cost
effectively. in analysing the needs of a microcontroller based project, we must
first see whether an 8-bit, 16-bit or 32-bit micro-controller can best handle
the computing needs of the task most effectively. among other cinsiderations in
this category are:
a) speed.
what is the highest speed that the microcontroller supprts.
b)
packaging. does it come in 40-pin dip (dual in-line package) or a qfp (quad
flat package), or some other packaging format? this is important in terms of
space, assembling and prototyping the end product.
c) power
consumption. this is especially critical for battery-powered products.
d) the
amount of ram and rom on chip.
e) the
number of i/o pins and the timer on the chip.
f) how
easy it is to upgrade to higher performance or lower power consumption
versions.
g) cost
per unit. this is important in terms of the final cost of the product in which
a micro-controller is used. for exmple, there are micro-controllers that cost
50 cents per unit when purchased 100,000
units at a time.
2. the second criterion in choosing a
microcontroller is how easy it is to develop products around it. key
considerations include the availability of an assembler, debugger, a
code-efficient c language compiler, emulator, technical support and both
in-house and outside expertise. in many cases, third party vendor supprt for
the chip is as good as, if not better than support from the chip manufacturer.
3. the third criterion in choosing a
microcontroller is its ready availability in needed quantities both now and in
the future.
chapter
3
design of circuit
design description:
a micro-controller is the brain behind the
whole system.at89c52 is programmed to work as a transmitter and receiver
resp.it basically reads the data as per the program or entered by the
key-board, displays it on lcd connected and transmits it via a.c mains.before
transmitting it, the digital data is modulated by using 'frequency shift
keying' technique. at the receiver the data is first demoulated and then read
by the micro-controller used in receiver.
transmitter:
1. lcd display :
displays
used to display are used to display the data which is transmitted by the
transmitter and received at the receiver side.
micro-controller 89c52 has 4 ports each having 8 i/o pins. port pins 4-7
of port 0 are connected to lcd display connector.16x2 lcd display is used so it
is connected by frc cable to 16 pin box connector. for brightness
adjustment trim pot of 5k is connected
to pin 3 of connector.
pins 4
and 6 are rs and enable resp. these are connected to 6th and 7 th
pins of port 1 resp. ‘write’ of lcd is not enabled so pin no. 5 is grounded.
pins 7 to 14 are used to read the 8 bit data. in our system we are converting 8
bit data4 bit one by swapping routine. so pins 7 to 10 are not connected. and
11 to 14 are connected to pins 4 to 7 of port 0. pins 15 and 16 are given to 5
v supply and gnd resp.
2. keyboard:
we
prepared a 4x4 matrix keyboard using push buttons as keys. this was connected
to micro-controller by 16 pin frc box type connector. ics hc138, 74hc14 and
hc245 are required to connecting and enabling the keyboard. here pins 1 to 5 of
hc138 decoder are connected to pins 0 to 4 of port 2. when pins 1,2 and 3 of hc
138 are 000, pin 15 goes ‘low’ it is given to inverting ic hc14 to make it
“high’. this is connected to connector
pin 10 which enables keys 1 to 9. similarly when pin 1,2 and3 are 001 resp. 14
pin goes ‘low’. it is made ‘high’ and is given to connector pin 11. this pin
enables keys from 10 to 16.
as shown in the diagram, key 1 is used as a ‘reset’ of the system. so
one of its leg is connected to reset
circuit and the other leg is connected to 5 v supply. here 2 leg push buttons
are used as all the 16 keys. out of these keys 2 to 9 are enabled by making 15
pin of hc138 ‘high’ .which is connected to pin 10 of connector. so one of the
leg of each key from 2 to 9 is connected to pin 10 and the other legs are
connected to connector pins 2 to 9 respectively. the remaining keys from 10 to
16 are enabled by making pin no. 14 of hc138 ‘high’ which is connected to pin
11 of the connector. so now out of the two legs of each key from 10 to 16, one
leg is connected to pin 11 of the connector. and the other legs are connected
to pins 2 to 7 of the connector respectively.
the
keyboard made here is used to enter the data which is read by the
micro-controller. all the keys are programmed to specific data. key 1 is used
as ‘reset’ key.keys2,3 and 4 are programmed to display particular messages on
the display.
now with the remaining keys a calculator is prepared
where keys from 5 to 14 are programmed as numbers from 1 to 0 respectively. and
keys 15 and 16 are assigned as + and =. now the program was written calculate
the sum of numbers entered by keys. so
whatever the message or calculation entered by pressing the key is given to the
micro-controller. micro-controller reads the data, displays it on transmits it.
3. fsk modulator:
the circuit consisting of two oscillators is simplified using a diode
ie.4148.the diode performs the work of making the oscillator on &off as txd of microcontroller ic89c52 goes
low & high
respectively.now the output of 89c52 is a ttl output.when txd of
89c52 goes high, the diode conducts as it is forward biased also charging the
capacitor of 1nf . as ic 74hc14 is a inverter it's output goes low. as feedback
is not obtained the oscillator stops giving
the output frequency. when the txd is low i.e. digital 0 the diode is
reversed biased.
the
output of inverter is high & it is fed back ,thus the oscillator generates
frequency of 15khz. the feedback path
consists of a resistor of value 4k7& a100k pot. output current of 74hc14 is
about 5 -10ma.this ic is nothing but a schmitt trigger whose output
sharply turns on & off the output is inverted in the next stage.
this stage is used to avoid loading on the oscillator. it also allows fast
switching i.e. on & off of the oscillator. output of this is given to transistor bc547 which is used as a buffer amplifier . it is
used to boost the current. output of bc547 is connected to transistor 2n2218
which acts as a switch.
toroid
is wounded with insulating wire which acts as a supply transformer. one arm of toroid is connected to 100ohm
resistor which is the input impedance. one end of the two parallel capacitors
of value 0.1uf & 10uf are also connected to this arm while the other end is
grounded. these capacitors provide a low impedance path. second arm of toroid
is connected to collector of 2n2218. secondary forms a tuned circuit with two
capacitors of value 0.1uf/250v/x2 each . this passes frequency modulated data
on to the mains.
receiver
:
at the receiver side teh data
is first demodulated usin pll ic cd 4046. it has feature of being used as a
frequency demodulator.
cd 4046:
cd 4046 is a micropower ic. we have used it as
frequency demodulator. it consists of low power, linear, voltage controlled
oscillator (vco), a source follower, a zener diode and two phase comparators.
here we will be using phase comparator 2.
phase
comparator is an edge-controlled digital memory network. it provides a digital
error signal and lock in signal to indicate locked condition and maintains 0
degrees phase shift i/p and comparator out.
the
linear voltage controlled oscillator produces an o/p signal vco out whose
frequency is determined by the voltage at vco in i/p and capacitor value
connected at pins 6,7 which is kept 1 nf and resistance at pin11. we have
connected 1 m trimpot in series with 10 k to pin11.
typical waveforms employing phase comparator 2 in locked position
now
mains pin is connected to two 0.1 uf ac capacitors in series with primary
winding supply transformer. this forms tuned circuit. this is two avoid 50 hz
frequency to interface with amlifier circuit. the capacitor value is selected
such that it is low enough not to avoid 50 hz frequency and large enough to
allow frequency of 5 khz. here capacitor value is selected as 0.1 uf/250v/ac.
toroid use is of 12 mm dimensions as the size of toroid increases the
effect due to increase in the cross section area. this increases the
permeability increasing the inductance. here supply transformer is provided
with sufficient no. of turns. to form a tuned circuit at desired frequency the
necessary condition is to have
xc=xl
to get the condition xc=xl at desired frequency, no.
of turns of the windings are adjusted accordingly.
now here we have kept no. of turns as 20.
xc=1/2*pi*fc
since there are two capacitors in series having a
value .1 uf they form total capacitance of .05 uf.
therefore c=0.05 uf
fc=15khz
hence,
xc=160 ohms
now the required condition is xc=xl, so considering
xl=160 ohms we get the value of inductance around 1.2 mhenry.
to get this much inductance around 20 turns of wire
on the toroid are required. if the condition xc=xl is fulfilled, it forms a
series pass circuit passing 15 khz frequency to the amplifier.
two diodes are connected after toroid to the supply transformer. these
are current limiting diodes. one conducts for positive half cycle and another
for negative half cycle. so only the voltage of forward drop across the diode
is obtained avoiding any danger to the further circuitry.
the signal coming from the mains requires large amplification as it may
get attenuated to an appreciable value due to noise and interferences in the
mains. for amplification ic 74c04 is used. ic 74c04 is used for a specific
reason of linear amplification. it is a digital amplifier i.e its output is
digital. ic 74c04 is p channel cmos inverter ic. in this, p channel and n
channel cmos transistors are connected in complementary symmetry fashion.
because of the symmetry and negative feedback around the pair will bias itself
appropriately to a value vcc/2. under the ac condition positive going input
will cause output to go negative as vice versa. here supply current is constant
since the inverter is biased for class a operation. so we get will get the
stable output.
ic 7404 is connected in high gain amplifier configuration with biasing
of vcc/2. by cascading the basic amplifier stages a high gain amplifier can be
achieved. the gain will be increased by the no. of stages used. if more than 1
inverter is used inside the feedback loop a higher gain loop is achieved which
results in more accurate output the output remains stable as frequency of
operation increases the gain provided by amplifier decreases. by using 74c04 as
amplifier the signal is approximately 400 times amplified. one thing is noted
that 74c04 is only an ac amplifier and
not a dc one.
when the signal is sufficiently amplified it is given as input to pin 14
i. signal in of cd4046. 0.1 uf capacitor is connected to this pin to filter the
noise. cd4046 consists of an amplifier, vco and pll. one input of pll is the
input signal given and the other input is the output of vco. the output of pll
is fed to vco as i/p forming a loop which matches the frequency of output
exactly to the input frequency. 1 nf capacitor connected between pin 6 and 7
and the trim pot of 1 m at pin 11 control the voltage at pin 9 i.e vco in. the
changing current in capacitor decides the frequency of the oscillator. the
output of 4046 is obtained in demodulated form i.e the frequencies are
converted into voltages. t the output of 4046 we have a low pass filter formed
by 47k and 1nf. one more resistor of 4k7 is added in series with 1 nf to avoid
its charging and discharging. so the output passed through low pass filter is
connected to bc 547 which acts as a buffer. after that one more low pass filter
is formed by 100k and 1 nf with frequency 150 hz. the output of this is
inverted by a not gate and is given to the rxd i.e pin no. 10 of 89c52 in the
receiver. at this pin an led is connected for the indication of data reception.
power
supply:
in the whole system, all the ics including
microcontroller require 5v dc supply. here this is derived from 230 v ac mains
itself. the basic block diagram of dc supply is given as,
here the
transformer output is given to bridge formed by diodes in4007. the transformer
used is 9v, 500ma. the bridge rectifier then rectifies the ac input which
is filtered after rectification. and
this is given to the regulator. here we have used three terminal regulator
ic7805 which gives 5 v fixed dc output.
three terminal ic regulators:
the
voltage regulator is a circuit which provides a constant voltage regardless of
changes in the load currents. hence such circuits are widely used in the
various applications. after the op-amp, the integrated circuit (ic) voltage
regulators are probably most widely used integrated circuits.
as the
name suggests, three terminal voltage regulators have three terminals namely
input which is unregulated (vin), regulated output (vo)
and common or
a ground terminal. these regulators do not require any feedback connections.
the following figure shows the basic connection diagram of ic 7805.
the
capacitor cin is required if regulator is located at appreciable distance ,
more than 5 cm from power supply filter. the output capacitor co may not be
needed but if used it improves the transient response of the regulator i.e regulator
response to the transient changes in the load. this capacitor also reduces the
noise present at the output.
for ic 7805 regulator the maximum input voltage that can be applied
is 35 v. the maximum dropout voltage is 2.5 v. the output of 7805 regulator is
5 vfixed. hence the minimum input voltage required is 5+2.5=7.5v. so the input
range of ic 7805 regulator is 7.5 to 35 v to get fixed 5 v as regulated output.
this is basically a series voltage regulator circuit. a part of output voltage is taken with the help of potential divider formed by r1 and r2. this is compared with the reference voltage, vref internally generated with the help of zener diode. after comparison, a control signal generated which is applied through protective circuit to the series pass transistor working as control element. this element works as a variable resistance. the control signal adjusts the control element in such a way that output voltage remains constant.
thermal shutdown means that the chip will automatically turn itself off
if the internal temperature exceeds, typically, 175° c. the current limiting
circuit will protect the chip from excessive load current. because of the
thermal shut down and current limiting, the ic voltage regulator chip is almost
indestructible.
typical
performance parameters:
a
number of performance parameters are generally specified for the ic voltage
regulators by the manufacturers. these are as follows:
- line regulation.
- load regulation.
- ripple rejection
- dropout voltage
- output resistance
- maximum input voltage
- maximum power dissipation
- quiescent current
- rated output current
- output noise voltage
- maximum operating junction temperature.
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