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The   basic aim of the work is to minimize the queue at the electric billing counters and to
restrict the use of electricity automatically in case bill is not paid. The work also aims at
proposing a system that will reduce the loss of power and revenue due to Power thefts and
other illegal activities. The work system adopts totally new concept called prepaid
electricity. The implementation of this will help in better energy management, conservation
of energy and also in doing away with the unnecessary hassles over incorrect billing. The
automated billing system will help track the real time consumption and will leave little
scope for disagreement on consumption and billing.

          Every month we can see a person standing in front of our house from Electricity
board or water Board whose duty is to read the energy meter/water meter and handover
the bills (electric or water) to the owner of that house . This is nothing but meter reading.
According to that reading we have to pay the bills. The main drawback of this system is that
person has to go area by area and he has to read the meter of every house and handover the
bills. The Electricity board and Water authority has to give privileges for these people to do
their duty monthly. The thing is, Government will not appoint any particular persons for this
duty. The people working in these boards will go on a particular day and do their duty
leaving all their pending works. Due to this, their work will be delayed and this is great loss
for government. To overcome this drawback we have come up with an idea and this idea
will help the government and it will save the time of the employees working in these

Latest developments in the power measurement technology aim to enable the consumer to
be online in billing matters. The present day technologies work to first accurately measure
and then charge the consumer, thus bringing accountability and transparency in electronic
power utility and its transmission and distribution. The main objectives of this project are to
study about the powerful microcontroller AT89C52. An innovative technique is introduced
for the usage of electricity. An energy meter is presented for which we can charge specific
unit of energy, after the usage this charged unit automatically decremented. A different code
word is used for charging the meter. If the balance charge unit is zero then the meter
automatically disconnect from the line. This system can be recharged through keypad and
GSM technology. For this recharge coupon with security code is used. 89C52 is the main
component used. LCD display is used for displaying each stage. Charging is done with the
help of keypad. GSM modem verifies the charging of the system.
       By using this type of technology it is possible to stop the misuse of electricity.
Normally in every postpaid connection bill is much higher than the prepaid. When there is
postpaid, nobody wants to take care of the wastage, but at the end of month when bill is
present then bill is paid by the house incharge, small workers in the office, employees in the
school, in the entire private and govt. Office nobody wants to take care of the wastage. So
we add some innovative idea to avoid and save this valuable energy for every one. In this
project we use one lcd screen. Lcd screen displays the bal. Amount every time, lcd screen
not only shows the balance amount but at the same time Lcd displays the unit consumption.
When the balance is '0' then output is off.
       Microcontroller 89C51 acts as the primary controller. The primary controller
collects information from digital energy meter as well as from the smart card. Smart gives
information about the limitation of units. The digital energy meter reading is compared with
the smart card information by the primary controller and hence suitably primary controller
controls the relay.

This project is useful for billing purpose in Electricity board and in water authority. Instead
of going to every house & taking the readings, in this project by just sending an SMS we
can receive the readings of the house and we can recharge the electric bill. This system uses
Java Basics software, which is designed as the application platform to send or receive SMS
using the Modem, then process and stores the data. Java software has two main functions 1)
to interact with Modem and read the COM port 2) maintain the database.

In this project the micro controller & the GSM unit is interfaced with the Energy
meter/water meter of each house. Every house has a separate number, which is given by the
corresponding authority. The GSM unit is fixed in the energy meter/water meter.

The amount of consumption is stored in memory authority as SMS. Using this software we
can send the SMS through Modem to that particular number which is assigned by these
authorities and wait for the response. On other end the modem will receive the data in the
form of a command and informs the controller to do the readings. After the readings the
controller will send data to the modem. Modem, in turn sends data to the other end. In the
office the GSM unit will receive the data and the Java software will calculate the total
consumption. The number assigned by the authorities is Unique. Using GSM we can get the
response very fast due to which time is saved. After completion of the pulse the power will
cut again consumer wants to send an SMS for recharge.

This is due to reduce illegal power using with out paying the money.


We are sending bills through post, instead of this, we can add a printer in every house and if we give
print command from the server, it will print the bill and the user can get the bill over there only.
List. Of components

  1) Integrated circuits

                i. IC1             89C51 (micro controller)

               ii. IC2              MAX 232

               iii. IC3            MCP 3201 (A to D Converter)

               iv. IC4             7805 (Voltage Regulator)

  2) Crystal

                i. 11.0592 MHz

  3) Transistor

                i. T1 SL100

               ii. T2 BC547

  4) Resistance

                i. R1=7.9 K

               ii. R2=22K, R4=10K,

               iii. VR1=10k Multi turn

               iv. VR2=10k
5) Capacitor
               i. C1= 10uf/63v electrolytic
              ii. C2, C3,= 33pf Disc type ceramic
             iii. C4 = 0.1uf/63v electrolytic
              iv. C5 = 0.01 disc type ceramic
              v. C6 = 1000uf/25v electrolytic
              vi. C19, C20, C21, C22, C23 = 10 uf/63v electrolytic

6) Diode
              i. D1 to D9      1N 4007 p – n junction diode

7) Relay
              i. 12v 2C/O PCB mounted

8) Buzzer:-
              i. Quartz ceramic buzzer

9) Current transformer (CT)
10)        16*2 LCD Display
11)        Transformer 230 V Primary to 0-15v-1A secondary.
12)        GSM MODEM
Block Diagram Operation

Fig. Shows basic Block Digram of GSM base prepaid energy meter system in this project
we atomize billing system for consumers for this purpose .we make electronic semi-
conductor memory card. And a reader section .in semi conductor card we step up initially
some rupees assumed as our card charged.

In reader Section we take following blocks.

1. Current transformer

2. Voltage converter

3. A/D converter

4. Micro controller

5. Display

6. Buzzer
         7. Relay

         8. Buffer circuit and level shifter circuit.

         9. Crystal and oscillator circuit

         10. Regulated power supply

                                                                       LCD (Display)

 GSM                           RS232
MODEM                                                                LCD         LCD
                               Converter                             Driver      Glass





                     Power Supply

                Trans        Regulator                    Micro
                                (7805)                  Controller
              Rectifier      Filter

1. Current transformer--
        In our project we have to calculate total power taken by load because as per
M.S.C.B. rule unit of meter depend upon how much power is taken in particular limit so
that to calculate power we apply formula P=VXI as V=230volt is constant we can find out
first current .So current transformer is our first block of project. Current transformer is a
transducer which can since current flowing through line and convert it in to corresponding
ratio voltage. The meaning of ratio voltage is depend upon step up current transformer or
step down current transformer and its winding ratio i.e. 1:2 or 2:1 etc suppose we take 2:1
step down current transformer then if current flowing through line is 2 amp. Then o/p of
current transformer is 2volt.
In our project we use 2:1 step-down current transformer for sensing current flowing through

2. Voltage converter--
   As in our project we use micro controller as main block to calculate and display power
then we must convert all physical quantity in to binary format because micro controller can
read only binary data .So to convert current in to equivalent binary we use A/D converter
and for A/D converter input we must required 0 to 5 volt D.C. voltage. As we know output
of current transformer is A.C. voltage then we must convert this A.C. voltage in to
corresponding range (0 to 5 volt D.C.) For this purpose we use voltage converter block in
which we use full wave bridge rectifier circuit, filter capacitor and voltage divider network.
The full wave bridge rectifier circuit convert A.C. in to D.C. then ripple is remove through
filter capacitor and by using voltage divider network we achieve range of 0 to 5 v D.C. for
A/ D converter input.

3. Analog to digital converter--
   To convert current in to its equivalent binary form we use 12 bit I2c type Analogue to
digital converter. This converter convert 0 to 5 volts D.C at input can convert its
corresponding binary value. For this purpose we use Microchip Company IC
MCP3201.This IC is very easy to interface with micro controller and at Internet there are
various web site at which directly program is written for that. This is 8 pin 5 volt operated
4. Micro controller--
      Micro controller is heart of our project because it performs total function such as
calculate power, unit and display it. Also read value in prepaid card, reduce it as per unit,
cut of relay etc. This all function is done by micro controller programmed .In market there
are various micro controller is available.
      But we select 89C52 because of following advantages.:-

         Computable with industrial most popular family MCS51 product
         8K Bytes of In-System Reprogram able Downloadable Flash Memory
         SPI Serial Interface for Program Downloading
         Endurance: 1,000 Write/Erase Cycles
         2K Bytes EEPROM
         4V to 6V Operating Range
         Fully Static Operation: 0 Hz to 24 MHz
         Three-level Program Memory Lock
         256 x 8-bit Internal RAM
         32 Programmable I/O Lines
         Three 16-bit Timer/Counters
         Nine Interrupt Sources
         Programmable UART Serial Channel
         SPI Serial Interface
         Low-power Idle and Power-down Modes
         Interrupt Recovery from Power-down
         Programmable Watchdog Timer
         Dual Data Pointer
         Power-off Flag

5. LCD display--
          In our project to show various parameters such as current, power, and timing balance
in card etc we use 16x2 LCD alphanumeric display with backlight. The advantages of this
are that we write 32 characters on it and due to backlight we can see it from long distance
also. This display has 8 data line and three control line through which micro controller write
character on it .The interfacing for display is given in book “8051 micro controller
programming “ by kneth J. Ayala

6. Buzzer--

   In this project we give facility to customer when ever a balance of card is reduce as per
last level. Near about 15- to 20 rupees then buzzer is turn on so that customer must know
that card is recharge now. When balance in card is reach to this level then micro controller
can turn on this buzzer.

7. Relay--
          If after warning of buzzer customer does not recharge its card and When the energy
is consumed balance in card reduced and when the balance is zero micro controller trip the
relay and cut of the main supply of home supply. So that person consumer recharges the
card and utilizes the. For this cut off purpose we use two change over relay which brake this

8. Buffer circuit and level shifter circuit--
          In this project we made a mobile decoder just like in mobile handset which is
connected to electric meter for mobile recharge purpose via SMS.
We will describe here of how to use an AT command on mobile decoders to be as a GSM
communication information node. This will be the cheapest means to create your own DIY
remote messaging system. Connect the mobile decoder to your micro controller via the Data
Cable. You can connect it through the RS232 TTL converter ic MAX 232 This ic can
convert signal from micro controller to mobile decoder to its proper operating voltage +,- 12
volt D.C. Select the baud rate of serial communication to be 9600 bps (actually, the module
will accept all the baud rate setting, any selection will work). The other parameters are:
Data Bits (8), Parity (None), With that, you are all set to test out the AT command with the
mobile decoder.
The following are some simple AT commands –
Call Control--

AT             Attention

ATA            Answer Command

ATD            Dial Command

ATH            Hang Up Call

The following are some simple AT commands to do SMS.

SMS Commands--

AT+CMGR       Read Message
AT+CMGS       Send Message

This mobile decoders circuit connects to the serial port of micro controller through MAX
232 ic . Its function is to provide an input and an output port capable of being remotely
controlled using another mobile.

9. Crystal & Reset Circuit—

       12 M Hz quartz ceramic crystal is connected between pin XTAL,and XTAL2 of
micro controller to produce machine cycle for fetch and execution      of instruction. And at
pin 9 RST pins we connect R.C n/w to provide reset pulse when power is turn on so that
programmed execution start from memory location 0000H.

10. Power Supply—

       For our all IC we require 5 v d.c. Supply, which can be generated by step down
transformer, full wave bridge rectifier, and filter condenser and voltage regulator IC 7805.
                              Figure 1 Circuit Diagram operation

Fig shows complete circuit Diagram of our project prepaid energy meter system recharge using
GSM. In this project we atomize the process of billing system for energy meter for home and
industries .At recent level electric bill is provided for customer for each month .For this purpose
M.S.E.B. required number of person for taking reading each month, giving bill for each customer
and all other number of activity .For this purpose M.S.E.B. required number of staff and giving
payment to this staff. And so it required lot of money. Shortly all this process is bulky and costly
and time consuming. To find out solution on it we develop our project prepaid energy meter system
recharge using GSM .

        In this project we made mobile decoder with SIM card for receiving recharge voucher,
suppose we have a card and we charge for 100 rupees for it. Then this card is crash and send SMS to
GSM decoder SIM in to our project. Then project can read this SIM code and check balance on it. If
balance is present then it give supply i.e. connect phase and neutral wire to home through this
project. And when we turn on load i.e. appliances on in home then this load or appliances take some
current which is depend on that appliances for e.g. if we turn on tube light then it take 40 watt load,
if we turn on fan then it take 60 watt load. After that how much time we turn on this load or
appliances is determine your unit utilize .For e.g. you on fan for 1 hour then we utilize 60 watt load
for 1 hour form this M.S.E.B calculate how much unit you utilize.

        In our project we calculate this power and time by using ADC, RTC and other devices and
find out unit. After that there is fix ration of unit and charge in rupees. Suppose For 1 unit we have
to pay Rs2/-then for if 60-watt fan on for 1 hour can utilize 5unit then you must pay RS10 (5x2) for
this load. This amount is then deducted in to memory of microcontroller system. Also project show
this current, power, unit, timing, balance of memory etc on display. And when rupees in card is
reduces to predetermine level our project turn on buzzer which is indication to customer that her
balance in card is decries up to recharge Laval. After that he must recharge this card through
M.S.E.B. or from private vender. After that new value amount is feed in that card and it utilize
again. If customer cannot charge after warning, and if balance in memory become zero then our
project cut off phase and neutral line supply through relay.

        In our project to calculate power we apply formula P=V x I.

As we know that voltage of M.S.C.B is fix 230v for India then we need to calculate current for
finding out power. As shown in fig Phase and Neutral is provided to our project through Relay
contact this relay is electromagnetic type relay operated at 12v D.C. and 2 c/o type i.e. when it
operated its two contact is change over and supply is provided through it. After that we use current
transformer to since current of load. This C.T. is step down type and ratio is 2:1 when we turn on the
project then load i.e. 100watt bulb is on and current is flowing thro current transformer at secondary
terminal of this current transformer use four diode D1, D2, D3, D4 for conversion of A.C. voltage in
to D.C. voltage because we apply this voltage to A/D converter. This is full wave bridge rectifier we
use because of its high efficiency and low ripple advantage. After conversion in to D.C. we remove
its ripple through capacitorC4,C5 filter capacitor .This two filter capacitor are use with separate
values because they remove higher and lower frequencies separately. The voltage divider network
making by R4 and VR1 is use to adjust voltage in A/D converter range 0 to 5 v D.C. For this
purpose we place one variable and other fix resistance .By using this variable resistance we adjust
voltage at required range. After that main part is conversion of this voltage corresponding to load
current in to binary form so we use 12 bit ADC MCP3201 fro microchip compact. This ADC has 8
pins IN+ and IN- pin is connected to input voltage E o/p of voltage divider network and pin CLK
and DOUT pin is connected to micro controller. This MCP 3201 is successive approximation type
12 bit ADC with on board sample and hold circuit. How This ic convert analogue signal in to its
equivalent digital signal is given in to is datasheet please refer it The digital value read by micro
controller can be store it in to its internal memory location and apply formula for power calculation
.By calculating power micro controller deter mine time. After reading current timing for given load
micro controller read current value of rupees present in to memory of microcontroller.

        In this project we made a mobile decoder just like in mobile handset which is connected to
electric meter. We will describe here of how to use an AT command on mobile decoders to be as a
GSM communication information node. This will be the cheapest means to create your own DIY
remote messaging system. Connect the mobile decoder to your micro controller via the Data
Cable. You can connect it through the RS232 TTL converter ic MAX 232 This ic can convert signal
from micro controller to mobile decoder to its proper operating voltage +,- 5 volt D.C. Select the
baud rate of serial communication to be 9600 bps (actually, the module will accept all the baud rate
setting, any selection will work). The other parameters are: Data Bits (8), Parity (None), With that,
you are all set to test out the AT command with the mobile decoder.

The following are some simple AT commands :

Call Control
AT             Attention
ATA           Answer Command
ATD           Dial Command
ATH           Hang Up Call
Send "AT" on serial port. The GSM mobile decoders will respond with an "OK". This is the
simplest command to tell the mobile decoder to go on attention. It doesn't do
anything. However, this is also a means to test if the decoder responds on the baud rate and
all the serial settings.
The following are some simple AT commands to do SMS.
SMS Commands-

AT+CMGR          Read Message
AT+CMGS         Send       Message

This mobile decoders circuit connects to the serial port of micro controller through MAX
232 ic . Its function is to provide an input and an output port capable of being remotely
controlled using another mobile.

Control takes place by means of receiving SMS (Short text Messages Service). When the
micro controller receives a predefined recharge text message, like "100 rupees" or "your
unit charge is----", is send In this way we can control recharge the energy meter through
SMS After reading this value micro controller shows this all value i.e. current, power, time,
balance in rupees on 16x2 LCD display. And after fix time interval micro controller
calculate unit for load and deduct rupees from memory of micro controller and show on
display .When balance reaches to recharge value then micro controller turn on buzzer and
when balance is completely zero then turn off relay through transistor so that supply is cut

The first and most important step in production in PCB is to obtained copper clad sensor
consist of thin coating of copper on based insulated material. The insulating material may
be fiberglass or sensor raising bended proper fibber glass is transparent and it is possible to
see copper tracked from other side, which is helpful checking of the output fibber glass.
Fibber glass is stronger than S.R.B.P. due to these two reasons fibber glass is more popular
for hobby project. In industry through their cost is high.

       In the specification of the PCB thickness of the base material with lies between 1 to
2 mm for general 1 mm type base material is use; For the larger PCB were heavy
component or to be mounted on the base 1.6 to 2 mm thickness base material is used in the
specification of PCB thickness of copper material is also maintains. It is specified by 1 to 2
quality (It means the weight of the board) most of the electronic CKT handily flow current,
so one quality board are used. Fri this purpose the higher current specification is once
quality board are use. In the above description we have studied that by coding copper on the
electronic base material.

For Production of PCB: -
1.     Design of PCB or to prepare an artwork. While design the CKT. We                have to
       consider to technique by which PCB will manufacture. For ex. If we are using
       simple resists point, we should not design component are work while if we are using
       photographic method we may design compact artwork.
       While designing the artwork we must consider the size the size of component and
       the only place for it should be lift.

2.     Design the conducting part and draw this conduction path on the artwork. While
       drawing the conduction path the following rules must be in mind for most
       performance. To decide the conduction path it is essential to decide the position of
       the component while designing the conduction path. A care should be taken that
       cross over of conduction path should be avoided. Under this drawing of artwork
       accurately position in the board. Using the pointed hills the position of the
       component making holes carefully and securely a mark on the board. In this process
       of the artwork may get damage. So always keep another machine. Apply even resist
       material around the components mounting holes two drop copper plate in the hole.

3.     Each resist material don’t dissolve in the etching i.e. it opposes the process of
       etching. Apply the each resist material tracks according to the artwork for the
       application of even resist material pin in use.
       Once each resist is drive check the board for its conduction path and current it is
4.     After the correction of the board insert the board in the track condoning the enchant
       solution until all excess copper has been removed. Enchant is the solution which can
       remove or even the copper deposition of the board. The most popular exchange is
       ferric chloride which is used with concentrated hydrochloric acid (HCL) After the
       completion of etching process wash and clean the board through in water to remove
       the stress of enchant.

5.     The last step of in the production of PCB is 10 even the photo resist material for the
       purpose we can see in light a spread even resist material can remove.
       Using above procedure PCB for the temp. Measurement and control CKT is
       prepared a sin fig.


Conductor Orientation--
       For a high conductor density, the conductor should run as one side in the direction of
x. coordinate and corner side in the direction of Y coordinate where conductors have to be
placed in others directions. Preference is given to the 45 c to 30-60 directions. Since
observation of this rules helps in an optimum, utilization of the space, alive and gives well
organized appeared.

Conductor Routing Practice--
       The conductors should begin and end in a solder pad. In cases where this would
increases the Length of conductor. Giving another conductor see in fig can terminate it.
Are Conductor making a sharp increases angles of less than 60 must be avoided this is
important especially in board which have to be wave solder see in fig.
When several conductors have to pass between pass the spacing have go be equality-
distributed max. Spacing is obtained, if conductor is put perpendicular to a narrow passage.

Hole Diameter solder pad diameter and solder ability--
          The no. Of different hole diameter on PCB must be kept min. hole diameters of
about 0.5 mm is suitable for component leads. The solder used pad size should be
approximately three ties. The driller holes size to give mechanical 7 to the solder pads. The
conductor pads should always be less than the solder pad diameter preferable one third see
in fig.


Component Mounting:-
          After the completion of the PCB fabrication and manufacturing it is require the
placing of the components in the liquid it is necessary to analyze the CKT and identify the
priorities for a particular CKT following will help to solve the problem.
         In highly sensitive CKT critical component are placed first in such as to require min.
          length for critical conductors
         In less critical CKT the components are arrange in order of signal flow. This will
          result in min. overall conductor length for critical conductors,
         In a CKT where a few components have more connecting point have to be placed
          forest and remaining group around them.

The priorities of different component to be mounted and solder on the PCB is as per
following sequence.
         First the flat radial component such as resistor, diode indicators, and mounted and
         Then IC bases were solder.
         Then the vertical component such as transistor, gang condenser and FET are
          mounted ands solder.
        The next process after the component mounting is soldering; solder point is achieve
by heating the solder of and base metal about the melting point of the solders used.
The method in which necessary heat is depend upon --
       The nature and type of joint.
       Melting temp. Of the solder.
       Flux.
Soldering techniques are of so many types but we are having only iron soldering for
soldering component in out PCB.
Iron Soldering:-
    Soldering iron consists of an insulated handle connected through a metal shaft, to a bit.
The face of the bit accuracy makes contact with the components parts of the joint and solder
ands heat them up. The electrical heaving element is located in the hallow shank or handle
to heat the bit. Function of the Bit--
       It stores heat and conveys it form the heat source to the work.
       It may be require to store surplus solder and flux to the work
       It may have required store molten solder and flux to the work.

    The bit surface must be lined or waited. This encourages flow of solder into the joint.
When the surface of the work becomes waited by solder continuous film of liquid metal
between the bit and the work provided a path of high thermal conductivity align with heat
can flow into the work into the piece.
                Solder bits are made or copper this metal has a good wetting proper; heat
capability and thermal conductivity. Tin led solder affects copper during soldering
operation. Production of copper bit can be made with thick iron coating followed by Ni.
/Tin platting. The life of the bit is increased by a factor of 10 to 15. Solder irons are
specified in term of watt. Depending on heat input input in intended for the working and
type of work (continuous or individual) the choice of the solder iron can be made.

Procedure of soldering:-
        The pairs to be joint must be cleaned and first and fluxed. The heard solder iron
must be removed after the joint is sufficient field and joint as followed to be cooled.

                           Figure 2 PCB layout

Design of Relay driver circuit.

                  Figure 3 Design of Relay driver circuit.
Specification of Relay—

Operating voltage=+12v

dcContact = 2 change over

Coil resistance=150ohm

Contact rating for 48v dc=5A


According to ohms low maximum current flowing through collector of transistor Q1 when
relay is ON is-

       Ic = Vcc/Rc

       Ic = 12/150

       Ic = 80mA

For safety margin of 100% so we choose a transistor which can switch at least 160ma again
voltage rating of transistor i.e.Vce is Grater than 12V so we choose a transistor(Q1) SL 100
which has following specification--

Ic max.=500mA


 =150

Selection of resistance RB. As transistor operated in common emitter configuration from
transistor equation

        = Ic/IB

       so IB=Ic/ 

       IB = 80ma/150

       i/p to base of transistor is Vcc1=5v

so applying Kirchhoff’s voltage low to loop of base of transistor is,

       Vcc1 = IB RB + VBE

       VBE of silicon transistor is 0.7v





                                     Figure 4 Buzzer ckt

Specification of buzzer is--
       Sound o/p > 95d at 12v d.c.

       Oscillator frequency= 4kHz

       Current consumption<20mA

       Operating temp. range = -20 deg. To +50 deg. Centigrade

       Operating voltage range = 3v to 15 v dc
From specification of buzzer current consumption of buzzer coil is 20mA

       So Ic max =20 mA

Again we select transistor BC 547 for buzzer driver because its ic max is 80 mA and it is
low cost ,eaisely avaible in market.

For common emitter configuration of transistor its current equation is

       IB = Ic/

        = 110 for BC 547 transistor

       = 20 mA / 110

       = 0.18mA

applying Kirchhoff’s voltage low to loop of base of transistor

       Vcc1 = IB RB + VBE

       Vcc1=+5v dc         VBE=0.7v for silicon transistor

       RB = 5 - 0.7 / IB

       RB = 4.3 / 0.18mA

       RB = 23K

  Power supply design:-

          Power supply is the first and the most important part of our project. For our project
  we require +5V regulated power supply with maximum current rating 500mA

  Following basic building blocks are required to generate regulated power supply.

                                                                                   Regulated O/P
Mains 230 V
               Step-down          Rectifie            Filter         Terminal
   A.C.                                                                               Voltage
              transformer            r
                                                      Ckt.         Voltage req.

  Step Down Transformer:-

  Step down transformer is the first part of regulated power supply. To step down the mains
  230V A.C. we require step down transformer. Following are the main characteristic of
  electronic transformer.

         Power transformers are usually designed to operate from source of low impedance at
          a single freq. It is required to construct with sufficient insulation of necessary
          dielectric strength.
         Transformer ratings are expressed in volt–amp. The volt-amp of each secondary
          winding or windings are added for the total secondary VA. To this are added the
          load losses.
         Temperature rise of a transformer is decided on two well-known factors i.e. losses
          on transformer and heat dissipating or cooling facility provided unit.

  Rectifier Unit

  Rectifier unit is a ckt. which converts A.C. into pulsating D.C. Generally semi-conducting
  diode is used as rectifying element due to its property of conducting current in one direction
  only. Generally there are two types of rectifier.

      1. Half wave rectifier
      2. Full wave rectifier.
In half wave rectifier only half cycle of mains A.C. is rectified so its efficiency is very poor.
So we use full wave bridge type rectifier, in which four diodes are used. In each half cycle,
two diodes conduct at a time and we get maximum efficiency at o/p.
        Following are the main advantages and disadvantages of a full-wave bridge type
rectifier ckt.


    1. The need of center tapped transformer is eliminated.
    2. The o/p is twice that of center tap circuit for the same secondary voltage.
    3. The PIV rating of diode is half of the center tap circuit.

    1. It requires four diodes.
    2. As during each half cycle of A.C. input, two diodes are conducting therefore voltage
        drop in internal resistance of rectifying unit will be twice as compared to center tap

Filter Circuit:

        Generally a rectifier is required to produce pure D.C. supply for using at various
places in the electronic circuit. However, the o/p of rectifier has pulsating character i.e. if
such a D.C. is applied to electronic circuit it will produce a hum i.e. it will contain A.C. and
D.C. components. The A.C. components are undesirable and must be kept away from the
load. To do so a filter circuit is used which removes (or filters out) the A.C. components
reaching the load. Obviously a filter circuit is installed between rectifier and voltage
regulator. In our project we use capacitor filter because of its low cost, small size and little
weight and good characteristic. Capacitors are connected in parallel to the rectifier o/p
because it passes A.C. but does not pass D.C. at all.

Three terminal voltage regulator:

        A voltage regulator is a ckt. that supplies constant voltage regardless of change in
load current. IC voltage regulators are versatile and relatively cheaper. The 7800 series
consists of three terminal positive voltage regulator. These ICs are designed as fixed voltage
regulator and with adequate heat sink, can deliver o/p current in excess of 1A. These
devices do not require external component. This IC also has internal thermal overload
protection and internal short circuit and current limiting protection. For our project we use
7805 voltage regulator IC.

Design of Step down Transformer:

       The following information must be available to the designer before he commences
for the design of transformer.

   1. Power Output.
   2. Operating Voltage.
   3. Frequency Range.
   4. Efficiency and Regulation.

Size of core
       Size of core is one of the first considerations in regard of weight and volume of
transformer. This depends on type of core and winding configuration used. Generally
following formula is used to find area or size of core.

                       Ai =         -----------
       Ai      = Area of cross - section in Sq. cm. and

       P1      = Primary voltage.

In transformer P1 = P2
For our project we required +5V regulated output. So transformer secondary rating is 12V,

So secondary power wattage is,

                       P2         = 12 x 500 x 10-3 w.

                                  = 6w.

               So      Ai     =
                              =      2.62

Generally 10% of area should be added to core to accommodate all turns for low Iron losses
and compact size.

                       So Ai = 2.88.

Turns per volt:

Turns per volt of transformer are given by relation

               Turns / Volt       = -----------------------
                                          4.44 f Bm Ai

               f is the frequency in Hz

               Bm is flux density in Wb/m2

               Ai is net area of cross section.

Following table gives the value of turns per volt for 50 Hz frequency.
      Flux density Wb/m2          1.14              1.01      0.91   0.83    0.76

      Turns per volt             40/Ai              45/Ai   50/Ai    55/Ai   60/Ai

Generally lower the flux density better be quality of transformer.

For project for 50 Hz the turns per Volt for 0.91 Wb/m2 from above table.

               Turns per Volt            = 50 / Ai
                                          17

       Thus for Primary winding          = 220 x 17 = 3800.

       & for Secondary winding           = 12 x 17 = 204.

Wire size:

       As stated above size depends upon the current to be carried out by the winding,
which depends upon current density of 3.1 A/mm2. For less copper losses 1.6 A/mm2 or 2.4
A/mm2 may be used. Generally even size guage of wire are used.

Rectifier Design:
       R.M.S. Secondary voltage at secondary of transformer is 12V.

So maximum voltage Vm across Secondary is

                        Vm      = Rms. Voltage x 2

                                = 12 x 2

                                = 16.97
D.C. O/p Voltage at rectifier O/p is

                                          2 Vm
               Vdc               =     ----------
                                          2 x 16.97

                                = -----------------------


                                = 10.80 V

PIV rating of each diode is

                      PIV       = 2 Vm.
                                = 2 x 16.97

                                = 34 V

& maximum forward current which flow from each diode is 500mA.

So from above parameter we select diode IN 4007 from diode selection manual.

Design of Filter Capacitor:

               Formula for calculating filter capacitor is


               C       =      ----------------------
                                 43 r f RL.

               r      = ripple present at o/p of rectifier.

                      (Which is maximum 0.1 for full wave rectifier.)

               F      = frequency of mains A.C.

               RL     = I/p impedance of voltage regulator IC.

               C      =     ------------------------------

                              43 x 0.1 x 50 x 28

                      = 1030 f  1000 f.

And voltage rating of filter capacitor is double of Vdc i.e. rectifier o/p which is 20V. So we
choose 1000 f / 25V filter capacitor.

IC 7805 (Voltage Regulator IC.)

    1 2 3

Specifications :

       Available o/p D.C. Voltage = + 5V.

       Line Regulation = 0.03

       Load Regulation = 0.5

       Vin maximum = 35 V

       Ripple Rejection       = 66-80 (db)
Advantages of project

  1. Due to this system electricity thief is wash out.
  2. So easy to recharge for using GSM technique.
  3. Saving of electricity because of displaying balance on display.
  4. Due to micro controller system is compact.
  5. Operating system is very easy.
  6. System give buzzer indication before pre define level of recharge.

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