energy meter reader (1).pdf

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PROGRAMMABLE
ENERGY METER READER
A PROJECT REPORT
Submitted by
V.MAYILRAJ (731220205014)
V.SRIRAM (731220205023)
R.RAVINDHIRAN (731220205302)
In partial fulfillment for the award of the degree
Of
BACHELOR OF TECHNOLOGY
In
INFORMATION TECHNOLOY
J.K.K.MUNIRAJAH COLLEGE OF TECHNOLOGY
T.N.PALAYAM,GOBI-638506
ANNA UNIVERSITY:: CHENNAI600 025
MAY 2023
as

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ANNA UNIVERSITY:: CHENNAI600 025
BONAFIDE CERTIFICATE
Certified that this project report on “PROGRAMMABLE ENERGY
METER READER” is the Bona fide work of “V.MAYILRAJ(731220205014),
V.SRIRAM(731220205023),R.RAVINDHIRAN(731220205302)”Who carried
out the project work under my supervision.
SIGNATURE SIGNATURE
Dr.N.SATHYABALAJIM.E.Ph.D.,M.I.S.T.E Dr.N.SATHYABALAJIM.E.Ph.D.,M.I.S.T.E
ASSOCIATE PROFESSOR ASSOCIATE PROFESSOR
HEAD OF THE DEPARTMENT SUPERVISOR
Dept. of Information Technoloy Dept. of Information Technoloy
J.K.K. Munirajah College of Technology J.K.K. Munirajah College of Technology
T.N.palayam T.N.palayam
Submitted for the Viva-Voce examination held on
INTERNALEXAMINER EXTERNALEXAMINER

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ACKNOWLEDGEMENT
We express our sincere thanks and grateful acknowledgement to our Chairman
Dr.J.K.K.Munirajah M.Tech (Bolton). D.Litt for providing all facilities during
the course of study in this college.
We would like to express thanks to our Secretary madam Mrs.KASTHURIPRIYA
KIRUPAKARMURALI, M.B.A., who has provided all the available facilities and
support that handle in the completion of our project.
We have immense pleasure in expressing my extreme gratitude thanks to
ourbelovedPrincipalDr.K.SRIDHARANM.E.,M.B.A.,Ph.D.,M.I.S.T.E.,forhisenc
ouragement and support.
We wish to express our heartfelt thanks to our respectful Head of the
DepartmentDr.N.SATHYABALAJIM.E.,M.I.S.T.E.,Ph.Dforhisinspiringhelp,gui
dance,effort and energy in the right direction for completing this project.
We also thank our guideDr.N.SATHYABALAJIM.E.,M.I.S.T.E.,Ph.DAssociate
Professor, Department of Information Technology, who has been driving force to
unveil the immense talent sinus.
We sincerely thank our lovable parents for their motivation and great support
to complete this project successfully.
We also thank all the teaching and non-teaching staffs of the Department of
Computer Science and Engineering and all my friends for their help and support to
complete this project successfully.

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ABSTRACT:
In conventional method of electricity billing, the responsibility of billing
for each consumer is a time consuming job for the distribution grid. Despite this,
the consumer can consciously consume extra amount of power than required and
still cease from paying the bill. So, nothing can be done to strict the electric power
supply. This spotlights the design of Smart Energy Meter (SEM) using GSM
Technology for domestic consumers. This SEM would insist consumers to
consume power during off-peak hours by providing incentives and thereby help to
achieve a uniform load curve. This is implemented by time-of-day billing also
known as variable billing scheme in which consumers would be charged a higher
tariff for power consumption during peak hours. For these reasons it uses Wireless
Peak-Hour Timing Update (WPTU) and Wireless Tariff Update (WTU) schemes.
In addition, this system also implements Prepaid Billing which would go a
extended way in making consumers conscious of the energy they use and be more
economical. This device uses ATMEGA 328P Micro Controller for computational
purposes, GSM Modem and RF Module for data transfer and updates. The
prototype model of this proposed energy meter was developed and was validated
with various loads in our laboratory during 19-1-2016 to 25-1-2016(Scale down
period as 2 months). It proves, this device is user friendly, make consumers
conscious about the amount of energy they spend and help to conserve the already
depleting resources. The automation of billing system eliminates labour resources
involvement, hence is more accurate.

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TABLE OF CONTENT
S.NO DESCRIPTION PAGE NO
ABSTRACT Iv
LIST OF FIGURES Vi
1 CHAPTER I 1
1.1 INTRODUCTION 1
2 CHAPTER II 2
2.1 LITERATURE SURVEY 2
3 CHAPTER III 4
3.1 DISCERPTION OF PARTS 4
3.2 LIQUID-CRYSTAL DISPLAY 4
3.3 MICROCONTROLLER 7
3.4 GSM MODULE 14
3.5 TRANSFORMER 19
3.6 RECTIFIER 25
4 CHAPTER IV 40
4.1 WORKING PRINCIPLE 40
4.2 SAMPLE CODING 40
4.3 BLOCK DIAGRAM 46
5 CHAPTER V 44
5.1 CONCLUSION 44
5.2 REFERENCES 47

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LIST OF FIGURES
FIGURE
NO
LIST OF FIGURES NAME PAGE
NO
3.2 LIQUID-CRYSTAL DISPLAY 04
3.3 MICROCONTROLLER 07
3.4 GSM MODULE 14
3.5 TRANSFARMER 19
3.6 RECTIFIER 25
4.3 BLOCK DIAGRAM 46

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CHAPTER -I
1.1. INTRODUCTION
Electricity has become vital in everyday life. It is tough to imagine a world
and human life without electricity. But the vitality of electricity has meant that
people consume vast amounts of energy unmindfully and carelessly. The world’s
energy consumption/capita stands at a staggering 2782 KWh. At this rate the
world’s energy resources would get depleted very soon. Already a big chunk of
fossil fuel resources got exhausted because of lavish and mindless usage. The
present system of energy metering uses electromechanical and somewhere digital
energy meter have poor accuracy and lack of configurability and also consumes
more time and labour. The conventional electromechanical meters are being
replaced by new electronic meters to improve accuracy in meter reading. Still, the
Indian power sector faces a serious problem of revenue collection for the actual
electric energy supplied owing to energy thefts and network losses. One of the
prime reasons is the traditional billing system which is inaccurate many times,
slow, costly, and lack in flexibility as well as reliability. Still accuracy cannot be
guaranteed as there can be errors in human reading. Also is a post paid scheme
makes the consumer to consume more amount of power than required and still
refrain from paying the bill and nothing can be done to severe the electric power
supply. Even though digital technologies like Power line communication and
Zigbee technology are use for meter reading still the problem of deliberately
making a false reading can exist (political reasons). Number of research works has
suggested prepaid Automatic meter reading (AMR) system provides better
customer services, by sending alert of power cuts and consummation updates.
Recent developments in this direction seem to provide opportunities in
implementing energy efficient metering technologies that are more precise,
accurate, error free, etc.

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CHAPTER -II
2.1. LITERATURE SURVEY
Bibek Kanti Barman, et al., proposed “smart meter using IoT”on efficient
energy utilization plays a very vital role for the development of smart grid in
power system. Hence proper monitoring and controlling of power consumption is
a main priority of the smart grid. The energy meter has many problems associated
to it and one of the key problems is there is no full duplex communication to solve
this problem, a smart energy meter is proposed based on Internet of Things. The
smart energy meter controls and calculate the consumption of energy using ESP
8266 12E, a Wi-Fi module and send it to the cloud from where the consumer or
customer can observe the reading. Therefore, energy examine has been by the
consumer becomes much easier and controllable. This system also helps in
detecting energy loss. Thus, this smart meter helps in home automation using IoT.
Himanshu K Patel et al., demonstrated “Arduino based smart energy meter”
that removes human intervention in meter readings and bill generation thereby
reducing the error that usually causes in India. The system consists the provision
of sending an SMS to user for update on energy consumption along with final bill
generation along with the freedom of reload via SMS. The disconnection of power
supply on demand or due to pending dues was implemented using a relay. The
system employs GSM for bidirectional communication.
Gonbinath.S, et al.,proposed “Internet of Things Based Energy Meter
system", In this system we reduce the human participation in electrical energy
maintenance. The theft of the electricity increases the costs paid by customer.
Hence this system is used for the detection of theft. The Arduino checks the main
meter and sub meter reading. If the difference between the main meter and sub
meter is occurred then that theft has occurred message will be display on the LCD
display and also display on the thing speak. Customer can be access the thing

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speak from anyplace. By using the consumer number it can be access on the globe
at the anytime.
Mohammed Hosseiu et al., presented a paper titled “Design and
implementation of smart meter using IoT” describing the growth of IoT and
digital technology. The future energy grid needs to be implemented in a
distributed topology that can dynamically absorb different energy sources. IoT can
be utilized for various applications of the smart grid consisting power
consumption, smart meter, electric power demand side management and various
area of energy production. In this paper, the Smart Energy Metering(SEM) is
explained as the main purpose of SEM is necessary for collecting information on
energy consumption of household appliances and monitor the environmental
parameters and provide the required services to home users Anitha et al.,
proposed “Smart energy meter surveillance using IoT” about IoT, internet of
things as an emerging field and IoT based devices have created a revolution in
electronics and IT. The foremost objective of this project is to create awareness
about energy consumption and. efficient use of home appliances for energy
savings. Due to manual work, existing electricity billing system has major
drawbacks. This system will give the information on meter reading, power cut
when power consumption exceeds beyond the specified limit using IoT. The
Arduino esp8266 micro controller is programmed toper form the objectives with
the help of GSM module. It is proposed to overcome all the disadvantages in the
already existing energy meter. All the details are sent to the consumer’s mobile
through the IoT and the GSM module and it is also displayed in the LCD.

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CHAPTER -III
3.1. DISCERPTION OF PARTS
3.2. LIQUID-CRYSTAL DISPLAY
Fig 3.2 Liquid-Crystal Display
A liquid-crystal display (LCD) is a flat panel display, electronic visual
display, or video display that uses the light modulating properties of liquid
crystals. Liquid crystals do not emit light directly.
LCDs are available to display arbitrary images (as in a general-purpose
computer display) or fixed images with low information content which can be
displayed or hidden, such as preset words, digits, and 7-segment displays as in a
digital clock. They use the same basic technology, except that arbitrary images are
made up of a large number of small pixels, while other displays have larger
elements.
LCDs are used in a wide range of applications including computer
monitors, televisions, instrument panels, aircraft cockpit displays, and signage.

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They are common in consumer devices such as DVD players, gaming devices,
clocks, watches, calculators, and telephones, and have replaced cathode ray tube
(CRT) displays in nearly all applications. They are available in a wider range of
screen sizes than CRT and plasma displays, and since they do not use phosphors,
they do not suffer image burn-in. LCDs are, however, susceptible to image
persistence.
The LCD screen is more energy efficient and can be disposed of more
safely than a CRT. Its low electrical power consumption enables it to be used in
battery-powered electronic equipment. It is an electronically modulated optical
device made up of any number of segments controlling a layer of liquid crystals
and arrayed in front of a light source (backlight) or reflector to produce images in
color or monochrome. Liquid crystals were first discovered in 1888. By 2008,
annual sales of televisions with LCD screens exceeded sales of CRT units
worldwide, and the CRT became obsolete for most purposes.
Each pixel of an LCD typically consists of a layer of molecules aligned
between two transparent electrodes, and two polarizing filters (parallel and
perpendicular), the axes of transmission of which are (in most of the cases)
perpendicular to each other. Without the liquid crystal between the polarizing
filters, light passing through the first filter would be blocked by the second
(crossed) polarizer.
Before an electric field is applied, the orientation of the liquid-crystal
molecules is determined by the alignment at the surfaces of electrodes. In a
twisted nematic (TN) device, the surface alignment directions at the two
electrodes are perpendicular to each other, and so the molecules arrange
themselves in a helical structure, or twist. This induces the rotation of the
polarization of the incident light, and the device appears gray. If the applied

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voltage is large enough, the liquid crystal molecules in the center of the layer are
almost completely untwisted and the polarization of the incident light is not
rotated as it passes through the liquid crystal layer. This light will then be mainly
polarized perpendicular to the second filter, and thus be blocked and the pixel will
appear black. By controlling the voltage applied across the liquid crystal layer in
each pixel, light can be allowed to pass through in varying amounts thus
constituting different levels of gray.
LCD with top polarizer removed from device and placed on top, such that
the top and bottom polarizers are perpendicular.
The optical effect of a TN device in the voltage-on state is far less
dependent on variations in the device thickness than that in the voltage-off state.
Because of this, TN displays with low information content and no backlighting are
usually operated between crossed polarizers such that they appear bright with no
voltage (the eye is much more sensitive to variations in the dark state than the
bright state).
As most of present-day LCDs used in television sets, monitors and smart
phones have high-resolution matrix arrays of pixels to display arbitrary images
using backlighting with a dark background when no image is displayed, different
arrangements are used. For this purpose, TN LCDs are operated between parallel
polarizers, whereas IPS LCDs feature crossed polarizers. In many applications IPS
LCDs have replaced TN LCDs, in particular in smart phones such as iPhones.
Both the liquid crystal material and the alignment layer material contain
ionic compounds. If an electric field of one particular polarity is applied for a long
period of time, this ionic material is attracted to the surfaces and degrades the
device performance. This is avoided either by applying an alternating current or
by reversing the polarity of the electric field as the device is addressed (the

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response of the liquid crystal layer is identical, regardless of the polarity of the
applied field).
Displays for a small number of individual digits and/or fixed symbols (as in
digital watches and pocket calculators) can be implemented with independent
electrodes for each segment. In contrast full alphanumeric and/or variable
graphics displays are usually implemented with pixels arranged as a matrix
consisting of electrically connected rows on one side of the LC layer and columns
on the other side, which makes it possible to address each pixel at the
intersections. The general method of matrix addressing consists of sequentially
addressing one side of the matrix, for example by selecting the rows one-by-one
and applying the picture information on the other side at the columns row-by-row.
For details on the various matrix addressing schemes see Passive-matrix and
active-matrix addressed LCDs.
3.3. MICROCONTROLLER
3.3.Microcontroller
A microcontroller is a small computer on a single integrated circuit
containing a processor core, memory, and programmable input/output peripherals.
Program memory in the form of Ferroelectric RAM, NOR flash or OTP ROM is
also often included on chip, as well as a typically small amount of RAM.

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Microcontrollers are designed for embedded applications, in contrast to the
microprocessors used in personal computers or other general purpose applications.
Microcontrollers are used in automatically controlled products and devices,
such as automobile engine control systems, implantable medical devices, remote
controls, office machines, appliances, power tools, toys and other embedded
systems. By reducing the size and cost compared to a design that uses a separate
microprocessor, memory, and input/output devices, microcontrollers make it
economical to digitally control even more devices and processes. Mixed signal
microcontrollers are common, integrating analog components needed to control
non-digital electronic systems.
Some microcontrollers may use four-bit words and operate at clock rate
frequencies as low as 4 kHz, for low power consumption (single-digit milliwatts
or microwatts). They will generally have the ability to retain functionality while
waiting for an event such as a button press or other interrupt; power consumption
while sleeping (CPU clock and most peripherals off) may be just nanowatts,
making many of them well suited for long lasting battery applications. Other
microcontrollers may serve performance-critical roles, where they may need to act
more like a digital signal processor (DSP), with higher clock speeds and power
consumption.
The first microprocessor was the 4-bit Intel 4004 released in 1971, with the
Intel 8008 and other more capable microprocessors becoming available over the
next several years. However, both processors required external chips to implement
a working system, raising total system cost, and making it impossible to
economically computerize appliances.
The Smithsonian Institution says TI engineers Gary Boone and Michael
Cochran succeeded in creating the first microcontroller in 1971. The result of their
work was the TMS 1000, which became commercially available in 1974. It

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combined read-only memory, read/write memory, processor and clock on one chip
and was targeted at embedded systems.
Partly in response to the existence of the single-chip TMS 1000, Intel
developed a computer system on a chip optimized for control applications, the
Intel 8048, with commercial parts first shipping in 1977.[2] It combined RAM and
ROM on the same chip. This chip would find its way into over one billion PC
keyboards, and other numerous applications. At that time Intel's President, Luke J.
Valenter, stated that the microcontroller was one of the most successful in the
company's history, and expanded the division's budget over 25%.
Most microcontrollers at this time had two variants. One had an erasable
EPROM program memory, with a transparent quartz window in the lid of the
package to allow it to be erased by exposure to ultraviolet light. The other was a
PROM variant which was only programmable once; sometimes this was signified
with the designation OTP, standing for "one-time programmable". The PROM
was actually exactly the same type of memory as the EPROM, but because there
was no way to expose it to ultraviolet light, it could not be erased. The erasable
versions required ceramic packages with quartz windows, making them
significantly more expensive than the OTP versions, which could be made in
lower-cost opaque plastic packages. For the erasable variants, quartz was required,
instead of less expensive glass, for its transparency to ultraviolet—glass is largely
opaque to UV—but the main cost differentiator was the ceramic package itself.
In 1993, the introduction of EEPROM memory allowed microcontrollers
(beginning with the Microchip PIC16x84)[citation needed] to be electrically
erased quickly without an expensive package as required for EPROM, allowing
both rapid prototyping, and In System Programming. (EEPROM technology had
been available prior to this time, but the earlier EEPROM was more expensive and
less durable, making it unsuitable for low-cost mass-produced microcontrollers.)

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The same year, Atmel introduced the first microcontroller using Flash memory, a
special type of EEPROM. Other companies rapidly followed suit, with both
memory types.
Cost has plummeted over time, with the cheapest 8-bit microcontrollers
being available for under 0.25 USD in quantity (thousands) in 2009,[citation
needed] and some 32-bit microcontrollers around US$1 for similar quantities.
Nowadays microcontrollers are cheap and readily available for hobbyists, with
large online communities around certain processors.
In the future, MRAM could potentially be used in microcontrollers as it has
infinite endurance and its incremental semiconductor wafer process cost is
relatively low. In 2002, about 55% of all CPUs sold in the world were 8-bit
microcontrollers and microprocessors. Over two billion 8-bit microcontrollers
were sold in 1997,[5] and according to Semico, over four billion 8-bit
microcontrollers were sold in 2006.[6] More recently, Semico has claimed the
MCU market grew 36.5% in 2010 and 12% in 2011.
A typical home in a developed country is likely to have only four general-
purpose microprocessors but around three dozen microcontrollers. A typical mid-
range automobile has as many as 30 or more microcontrollers. They can also be
found in many electrical devices such as washing machines, microwave ovens,
and telephones.
Embedded design:
A microcontroller can be considered a self-contained system with a
processor, memory and peripherals and can be used as an embedded system. The
majority of microcontrollers in use today are embedded in other machinery, such
as automobiles, telephones, appliances, and peripherals for computer systems.

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While some embedded systems are very sophisticated, many have minimal
requirements for memory and program length, with no operating system, and low
software complexity. Typical input and output devices include switches, relays,
solenoids, LEDs, small or custom LCD displays, radio frequency devices, and
sensors for data such as temperature, humidity, light level etc. Embedded systems
usually have no keyboard, screen, disks, printers, or other recognizable I/O
devices of a personal computer, and may lack human interaction devices of any
kind.
Interrupts:
Micro controllers must provide real time (predictable, though not
necessarily fast) response to events in the embedded system they are controlling.
When certain events occur, an interrupt system can signal the processor to
suspend processing the current instruction sequence and to begin an interrupt
service routine (ISR, or "interrupt handler"). The ISR will perform any processing
required based on the source of the interrupt, before returning to the original
instruction sequence. Possible interrupt sources are device dependent, and often
include events such as an internal timer overflow, completing an analog to digital
conversion, a logic level change on an input such as from a button being pressed,
and data received on a communication link. Where power consumption is
important as in battery operated devices, interrupts may also wake a
microcontroller from a low power sleep state where the processor is halted until
required to do something by a peripheral event.
Programs:
Typically microcontroller programs must fit in the available on-chip
program memory, since it would be costly to provide a system with external,
expandable, memory. Compilers and assemblers are used to convert high-level
language and assembler language codes into a compact machine code for storage

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in the microcontroller's memory. Depending on the device, the program memory
may be permanent, read-only memory that can only be programmed at the factory,
or program memory that may be field-alterable flash or erasable read-only
memory.
Manufacturers have often produced special versions of their
microcontrollers in order to help the hardware and software development of the
target system. Originally these included EPROM versions that have a "window"
on the top of the device through which program memory can be erased by
ultraviolet light, ready for reprogramming after a programming ("burn") and test
cycle. Since 1998, EPROM versions are rare and have been replaced by EEPROM
and flash, which are easier to use (can be erased electronically) and cheaper to
manufacture.
Other versions may be available where the ROM is accessed as an external
device rather than as internal memory, however these are becoming increasingly
rare due to the widespread availability of cheap microcontroller programmers.
The use of field-programmable devices on a microcontroller may allow
field update of the firmware or permit late factory revisions to products that have
been assembled but not yet shipped. Programmable memory also reduces the lead
time required for deployment of a new product.
Where hundreds of thousands of identical devices are required, using parts
programmed at the time of manufacture can be an economical option. These
"mask programmed" parts have the program laid down in the same way as the
logic of the chip, at the same time.
A customizable microcontroller incorporates a block of digital logic that
can be personalized in order to provide additional processing capability,
peripherals and interfaces that are adapted to the requirements of the application.

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For example, the AT91CAP from Atmel has a block of logic that can be
customized during manufacture according to user requirements.
Other microcontroller features:
Microcontrollers usually contain from several to dozens of general purpose
input/output pins (GPIO). GPIO pins are software configurable to either an input
or an output state. When GPIO pins are configured to an input state, they are often
used to read sensors or external signals. Configured to the output state, GPIO pins
can drive external devices such as LEDs or motors, often indirectly, through
external power electronics.
Many embedded systems need to read sensors that produce analog signals.
This is the purpose of the analog-to-digital converter (ADC). Since processors are
built to interpret and process digital data, i.e. 1s and 0s, they are not able to do
anything with the analog signals that may be sent to it by a device. So the analog
to digital converter is used to convert the incoming data into a form that the
processor can recognize. A less common feature on some microcontrollers is a
digital-to-analog converter (DAC) that allows the processor to output analog
signals or voltage levels.
In addition to the converters, many embedded microprocessors include a
variety of timers as well. One of the most common types of timers is the
Programmable Interval Timer (PIT). A PIT may either count down from some
value to zero, or up to the capacity of the count register, overflowing to zero. Once
it reaches zero, it sends an interrupt to the processor indicating that it has finished
counting. This is useful for devices such as thermostats, which periodically test
the temperature around them to see if they need to turn the air conditioner on, the
heater on, etc.

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A dedicated Pulse Width Modulation (PWM) block makes it possible for
the CPU to control power converters, resistive loads, motors, etc., without using
lots of CPU resources in tight timer loops.
Universal Asynchronous Receiver/Transmitter (UART) block makes it
possible to receive and transmit data over a serial line with very little load on the
CPU. Dedicated on-chip hardware also often includes capabilities to communicate
with other devices (chips) in digital formats such as Inter-Integrated Circuit (I²C),
Serial Peripheral Interface (SPI), Universal Serial Bus (USB), and Ethernet.
3.4. GSM MODULE
A GSM module or a GPRS module is a chip or circuit that will be used to
establish communication between a mobile device or a computing machine and a
.
Fig 3.4.GSM Module
The modem (modulator-demodulator) is a critical partere. SIM900 GSM Module
These modules consist of a GSM module or GPRS modem powered by
a power supply circuit and communication interfaces (like RS-232, USB 2.0, and
others) for computers.

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A GSM modem can be a dedicated modem device with a serial, USB, or
Bluetooth connection, or it can be a mobile phone that provides GSM modem
capabilities.
Difference between GSM/GPRS Modems, Modules, and Mobiles
A GSM module or GPRS modules are similar to modems, but there’s one
difference: A GSM/GPRS Modem is external equipment, whereas the
GSM/GPRS module is a module that can be integrated within the equipment. It is
an embedded piece of hardware.
A GSM mobile, on the other hand, is a complete system in itself with
embedded processors that are dedicated to providing an interface between the user
and the mobile network.
Understanding Modems
Wireless modems generate, transmit or decode data from a cellular network, in
order to establish communication.
A GSM/GPRS modem is a class of wireless modems, designed for
communication over the GSM and GPRS network. It requires a SIM (Subscriber
Identity Module) card just like mobile phones to activate communication with the
network. Also, they have IMEI (International Mobile Equipment Identity)
numbers similar to mobile phones for their identification.
1. The MODEM needs AT commands, for interacting with the processor or
controller, which are communicated through serial communication.
2. These commands are sent by the controller/processor.
3. The MODEM sends back a result after it receives a command.

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4. Different AT commands supported by the MODEM can be sent by the
processor/controller/computer to interact with the GSM and GPRS cellular
network.
Its functions include:
 Read, write and delete SMS messages.
 Send SMS messages.
 Monitor the signal strength.
 Monitor the charging status and charge level of the battery.
 Read, write and search phone book entries.
What is a Mobile Station?
A mobile phone and Subscriber Identity Module (SIM) together form a
mobile station. It is the user equipment that communicates with the mobile
network. A mobile phone comprises Mobile Termination, Terminal Equipment,
and Terminal Adapter. Mobile Termination is interfaced with the GSM mobile
network and is controlled by a baseband processor. It handles access to SIM,
speech encoding and decoding, signaling, and other network-related tasks.
Terminal Equipment is an application processor that deals with handling
operations related to keypads, screens, phone memory, and other hardware and
software services embedded into the handset.
The Terminal Adapter establishes communication between the Terminal
Equipment and the Mobile Termination using AT commands. The communication
with the network in a GSM/GPRS mobile is carried out by the baseband
processor.

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Applications of GSM Module or GPRS Module
The GSM/GPRS module demonstrates the use of AT commands. They can
feature all the functionalities of a mobile phone through a computer like making
and receiving calls, SMS, MMS, etc. These are mainly employed for computer-
based SMS and MMS services.
GSM Example: Arduino Projects: Sending SMS using GSM
What is AT Command?
They are known as AT commands because every command line starts with
“AT” or “at”. AT commands are instructions used to control a modem. AT is the
abbreviation of ATtention.
GSM/GPRS modems and mobile phones support an AT command set that is
specific to the GSM technology, which includes SMS-related commands like
AT+CMGS (Send SMS message), AT+CMSS (Send SMS message from storage),
AT+CMGL (List SMS messages) and AT+CMGR (Read SMS messages).
Note that the starting “AT” is the prefix that informs the modem about the start of
a command line. It is not part of the AT command name.
For example, D is the actual AT command name in ATD and +CMGS is the
actual AT command name in AT+CMGS. However, some books and websites use
them interchangeably as the name of an AT command.
Tasks that can be done by AT Commands
Here are some of the tasks that can be done using AT commands with a
GSM/GPRS modem or mobile phone:

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 Get basic information about the mobile phone or GSM/GPRS modem. For
example, the name of the manufacturer (AT+CGMI), model number
(AT+CGMM), IMEI number (International Mobile Equipment Identity)
(AT+CGSN), and software version (AT+CGMR).
 Get basic information about the subscriber. For example, MSISDN
(AT+CNUM) and IMSI number (International Mobile Subscriber Identity)
(AT+CIMI).
 Get the current status of the mobile phone or GSM/GPRS modem. For
example, mobile phone activity status (AT+CPAS), mobile network
registration status (AT+CREG), radio signal strength (AT+CSQ), battery
charge level, and battery charging status (AT+CBC).
 Establish a data connection or voice connection to a remote modem (ATD,
ATA, etc).
 Send and receive a fax (ATD, ATA, AT+F*).
 Send (AT+CMGS, AT+CMSS), read (AT+CMGR, AT+CMGL), write
(AT+CMGW) or delete (AT+CMGD) SMS messages and obtain notifications
of newly received SMS messages (AT+CNMI).
 Read (AT+CPBR), write (AT+CPBW) or search (AT+CPBF) phonebook
entries.
 Perform security-related tasks, such as opening or closing facility locks
(AT+CLCK), checking whether a facility is locked (AT+CLCK), and changing
passwords (AT+CPWD).
(Facility lock examples: SIM lock [a password must be given to the SIM card
every time the mobile phone is switched on] and PH-SIM lock [a certain SIM
card is associated with the mobile phone. To use other SIM cards with the
mobile phone, a password must be entered.])

19
 Control the presentation of result codes/error messages of AT commands. For
example, you can control whether to enable certain error messages
(AT+CMEE) and whether error messages should be displayed in numeric
format or verbose format (AT+CMEE=1 or AT+CMEE=2).
 Get or change the configurations of the mobile phone or GSM/GPRS modem.
For example, change the GSM network (AT+COPS), bearer service type
(AT+CBST), radio link protocol parameters (AT+CRLP), SMS center address
(AT+CSCA), and storage of SMS messages (AT+CPMS).
 Save and restore configurations of the mobile phone or GSM/GPRS modem.
For example, save (AT+CSAS) and restore (AT+CRES) settings related to
SMS messaging such as the SMS center address.
3.5. TRANSFORMER:
Fig 3.5.Transformer
A transformer is an electrical device that transfers electrical energy between
two or more circuits through electromagnetic induction. Electromagnetic
induction produces an electromotive force across a conductor which is exposed to
time varying magnetic fields. Commonly, transformers are used to increase or
decrease the voltages of alternating current in electric power applications.

20
A varying current in the transformer's primary winding creates a varying
magnetic flux in the transformer core and a varying magnetic field impinging on
the transformer's secondary winding. This varying magnetic field at the secondary
winding induces a varying electromotive force (EMF) or voltage in the secondary
winding due to electromagnetic induction. Making use of Faraday's Law
(discovered in 1831) in conjunction with high magnetic permeability core
properties, transformers can thus be designed to efficiently change AC voltages
from one voltage level to another within power networks.
Since the invention of the first constant potential transformer in 1885,
transformers have become essential for the transmission, distribution, and
utilization of alternating current electrical energy.[3] A wide range of transformer
designs are encountered in electronic and electric power applications.
Transformers range in size from RF transformers less than a cubic centimeter in
volume to units interconnecting the power grid weighing hundreds of tons.
For simplification or approximation purposes, it is very common to analyze
the transformer as an ideal transformer model as presented in the two images. An
ideal transformer is a theoretical, linear transformer that is lossless and perfectly
coupled; that is, there are no energy losses and flux is completely confined within
the magnetic core. Perfect coupling implies infinitely high core magnetic
permeability and winding inductances and zero net magnetomotive force.
Ideal transformer connected with source VP on primary and load
impedance ZL on secondary, where 0 < ZL < ∞.
A varying current in the transformer's primary winding creates a varying
magnetic flux in the core and a varying magnetic field impinging on the secondary
winding. This varying magnetic field at the secondary induces a varying
electromotive force (EMF) or voltage in the secondary winding. The primary and
secondary windings are wrapped around a core of infinitely high magnetic

21
permeability[d] so that all of the magnetic flux passes through both the primary
and secondary windings. With a voltage source connected to the primary winding
and load impedance connected to the secondary winding, the transformer currents
flow in the indicated directions. (See also Polarity.)
Ideal transformer and induction law
According to Faraday's law of induction, since the same magnetic flux
passes through both the primary and secondary windings in an ideal transformer,
voltage is induced in each winding, according to eq. (1) in the secondary winding
case, according to eq. in the primary winding caseThe primary EMF is sometimes
termed counter EMF.[9][10][f] This is in accordance with Lenz's law, which states
that induction of EMF always opposes development of any such change in
magnetic field.
The transformer winding voltage ratio is thus shown to be directly
proportional to the winding turns ratio according to eq.
According to the law of Conservation of Energy, any load impedance
connected to the ideal transformer's secondary winding results in conservation of
apparent, real and reactive power consistent with eq
Instrument transformer, with polarity dot and X1 markings on LV side
terminal The ideal transformer identity shown in eq. (5) is a reasonable
approximation for the typical commercial transformer, with voltage ratio and
winding turns ratio both being inversely proportional to the corresponding current
ratio.

22
By Ohm's Law and the ideal transformer identity:
the secondary circuit load impedance can be expressed as eq.the apparent
load impedance referred to the primary circuit is derived in eq. (7) to be equal to
the turns ratio squared times the secondary circuit load impedance.
Polarity:
A dot convention is often used in transformer circuit diagrams, nameplates
or terminal markings to define the relative polarity of transformer windings.
Positively increasing instantaneous current entering the primary winding's dot end
induces positive polarity voltage at the secondary winding's dot end.
Real transformer:
The ideal transformer model neglects the following basic linear aspects in
real transformers. Core losses, collectively called magnetizing current losses,
consist of Hysteresis losses due to nonlinear application of the voltage applied in
the transformer core, and Eddy current losses due to joule heating in the core that
are proportional to the square of the transformer's applied voltage. Whereas
windings in the ideal model have no resistances and infinite inductances, the
windings in a real transformer have finite non-zero resistances and inductances
associated with: Leakage flux that escapes from the core and passes through one
winding only resulting in primary and secondary reactive impedance.
Leakage flux of a transformer
The ideal transformer model assumes that all flux generated by the primary
winding links all the turns of every winding, including itself. In practice, some
flux traverses paths that take it outside the windings. Such flux is termed leakage
flux, and results in leakage inductance in series with the mutually coupled
transformer windings. Leakage flux results in energy being alternately stored in
and discharged from the magnetic fields with each cycle of the power supply. It is

23
not directly a power loss, but results in inferior voltage regulation, causing the
secondary voltage not to be directly proportional to the primary voltage,
particularly under heavy load. Transformers are therefore normally designed to
have very low leakage inductance.
In some applications increased leakage is desired, and long magnetic paths,
air gaps, or magnetic bypass shunts may deliberately be introduced in a
transformer design to limit the short-circuit current it will supply. Leaky
transformers may be used to supply loads that exhibit negative resistance, such as
electric arcs, mercury vapor lamps, and neon signs or for safely handling loads
that become periodically short-circuited such as electric arc welders.
Air gaps are also used to keep a transformer from saturating, especially
audio-frequency transformers in circuits that have a DC component flowing in the
windings.
Knowledge of leakage inductance is also useful when transformers are
operated in parallel. It can be shown that if the percent impedance and associated
winding leakage reactance-to-resistance (X/R) ratio of two transformers were
hypothetically exactly the same, the transformers would share power in proportion
to their respective volt-ampere ratings (e.g. 500 kVA unit in parallel with 1,000
kVA unit, the larger unit would carry twice the current). However, the impedance
tolerances of commercial transformers are significant. Also, the Z impedance and
X/R ratio of different capacity transformers tends to vary, corresponding 1,000
kVA and 500 kVA units' values being, to illustrate, respectively, Z ≈ 5.75%, X/R
≈ 3.75 and Z ≈ 5%, X/R ≈ 4.75.
Equivalent circuit:
Referring to the diagram, a practical transformer's physical behavior may be
represented by an equivalent circuit model, which can incorporate an ideal
transformer.[30]

24
Winding joule losses and leakage reactances are represented by the
following series loop impedances of the model: In normal course of circuit
equivalence transformation, RS and XS are in practice usually referred to the
primary side by multiplying these impedances by the turns ratio squared, (NP/NS)
2 = a2.
Real transformer equivalent circuit
Core loss and reactance is represented by the following shunt leg
impedances of the model:
Core losses are caused mostly by hysteresis and eddy current effects in the
core and are proportional to the square of the core flux for operation at a given
frequency.[31] The finite permeability core requires a magnetizing current IM to
maintain mutual flux in the core. Magnetizing current is in phase with the flux, the
relationship between the two being non-linear due to saturation effects. However,
all impedances of the equivalent circuit shown are by definition linear and such
non-linearity effects are not typically reflected in transformer equivalent circuits.
With sinusoidal supply, core flux lags the induced EMF by 90°. With open-
circuited secondary winding, magnetizing branch current I0 equals transformer
no-load current.
The resulting model, though sometimes termed 'exact' equivalent circuit
based on linearity assumptions, retains a number of approximations.[30] Analysis
may be simplified by assuming that magnetizing branch impedance is relatively
high and relocating the branch to the left of the primary impedances. This
introduces error but allows combination of primary and referred secondary
resistances and reactances by simple summation as two series impedances.
Transformer equivalent circuit impedance and transformer ratio parameters
can be derived from the following tests: open-circuit test,[m] short-circuit test,
winding resistance test, and transformer ratio test.

25
3.6. RECTIFIER:
Fig 3.6.Rectifier
A rectifier is an electrical device that converts alternating current (AC),
which periodically reverses direction, to direct current (DC), which flows in only
one direction. The process is known as rectification. Physically, rectifiers take a
number of forms, including vacuum tube diodes, mercury-arc valves, copper and
selenium oxide rectifiers, semiconductor diodes, silicon-controlled rectifiers and
other silicon-based semiconductor switches. Historically, even synchronous
electromechanical switches and motors have been used. Early radio receivers,
called crystal radios, used a "cat's whisker" of fine wire pressing on a crystal of
galena (lead sulfide) to serve as a point-contact rectifier or "crystal detector".
Rectifiers have many uses, but are often found serving as components of
DC power supplies and high-voltage direct current power transmission systems.
Rectification may serve in roles other than to generate direct current for use as a
source of power. As noted, detectors of radio signals serve as rectifiers. In gas
heating systems flame rectification is used to detect presence of a flame.

26
Because of the alternating nature of the input AC sine wave, the process of
rectification alone produces a DC current that, though unidirectional, consists of
pulses of current. Many applications of rectifiers, such as power supplies for
radio, television and computer equipment, require a steady constant DC current
(as would be produced by a battery). In these applications the output of the
rectifier is smoothed by an electronic filter (usually a capacitor) to produce a
steady current.
Rectifier devices:
Before the development of silicon semiconductor rectifiers, vacuum tube
thermionic diodes and copper oxide- or selenium-based metal rectifier stacks were
used.[1] With the introduction of semiconductor electronics, vacuum tube
rectifiers became obsolete, except for some enthusiasts of vacuum tube audio
equipment. For power rectification from very low to very high current,
semiconductor diodes of various types (junction diodes, Schottky diodes, etc.) are
widely used.
Other devices that have control electrodes as well as acting as unidirectional
current valves are used where more than simple rectification is required—e.g.,
where variable output voltage is needed. High-power rectifiers, such as those used
in high-voltage direct current power transmission, employ silicon semiconductor
devices of various types. These are thyristors or other controlled switching solid-
state switches, which effectively function as diodes to pass current in only one
direction.
Rectifier circuits:
Rectifier circuits may be single-phase or multi-phase (three being the most
common number of phases). Most low power rectifiers for domestic equipment
are single-phase, but three-phase rectification is very important for industrial
applications and for the transmission of energy as DC (HVDC).

27
Half-wave rectification:
In half wave rectification of a single-phase supply, either the positive or
negative half of the AC wave is passed, while the other half is blocked. Because
only one half of the input waveform reaches the output, mean voltage is lower.
Half-wave rectification requires a single diode in a single-phase supply, or three in
a three-phase supply. Rectifiers yield a unidirectional but pulsating direct current;
half-wave rectifiers produce far more ripple than full-wave rectifiers, and much
more filtering is needed to eliminate harmonics of the AC frequency from the
output.
Full-wave rectification:
A full-wave rectifier converts the whole of the input waveform to one of
constant polarity (positive or negative) at its output. Full-wave rectification
converts both polarities of the input waveform to pulsating DC (direct current),
and yields a higher average output voltage. Two diodes and a center tapped
transformer, or four diodes in a bridge configuration and any AC source
(including a transformer without center tap), are needed.[3] Single semiconductor
diodes, double diodes with common cathode or common anode, and four-diode
bridges, are manufactured as single components.
Graetz bridge rectifier: a full-wave rectifier using 4 diodes. For single-phase
AC, if the transformer is center-tapped, then two diodes back-to-back (cathode-to-
cathode or anode-to-anode, depending upon output polarity required) can form a
full-wave rectifier. Twice as many turns are required on the transformer secondary
to obtain the same output voltage than for a bridge rectifier, but the power rating is
unchanged. Full-wave rectifier using a center tap transformer and 2 diodes. Full-
wave rectifier, with vacuum tube having two anodes.
The average and root-mean-square no-load output voltages of an ideal
single-phase full-wave rectifier are:

28
Very common double-diode rectifier vacuum tubes contained a single
common cathode and two anodes inside a single envelope, achieving full-wave
rectification with positive output. The 5U4 and 5Y3 were popular examples of this
configuration.
Three-phase rectifiers:
3-phase AC input, half and full-wave rectified DC output waveforms Single-phase
rectifiers are commonly used for power supplies for domestic equipment.
However, for most industrial and high-power applications, three-phase rectifier
circuits are the norm. As with single-phase rectifiers, three-phase rectifiers can
take the form of a half-wave circuit, a full-wave circuit using a center-tapped
transformer, or a full-wave bridge circuit.
Thyristors are commonly used in place of diodes to create a circuit that can
regulate the output voltage. Many devices that provide direct current actually
generate three-phase AC. For example, an automobile alternator contains six
diodes, which function as a full-wave rectifier for battery charging.
Three-phase, half-wave circuit:
An uncontrolled three-phase, half-wave circuit requires three diodes, one
connected to each phase. This is the simplest type of three-phase rectifier but
suffers from relatively high harmonic distortion on both the AC and DC
connections. This type of rectifier is said to have a pulse-number of three, since
the output voltage on the DC side contains three distinct pulses per cycle of the
grid frequency.
Three-phase, full-wave circuit using center-tapped transformer:
If the AC supply is fed via a transformer with a center tap, a rectifier circuit
with improved harmonic performance can be obtained. This rectifier now requires
six diodes, one connected to each end of each transformer secondary winding.

29
This circuit has a pulse-number of six, and in effect, can be thought of as a six-
phase, half-wave circuit.
Before solid state devices became available, the half-wave circuit, and the
full-wave circuit using a center-tapped transformer, were very commonly used in
industrial rectifiers using mercury-arc valves. This was because the three or six
AC supply inputs could be fed to a corresponding number of anode electrodes on
a single tank, sharing a common cathode.
With the advent of diodes and thyristors, these circuits have become less
popular and the three-phase bridge circuit has become the most common circuit.
Voltage-multiplying rectifiers:
The simple half wave rectifier can be built in two electrical configurations
with the diode pointing in opposite directions, one version connects the negative
terminal of the output direct to the AC supply and the other connects the positive
terminal of the output direct to the AC supply. By combining both of these with
separate output smoothing it is possible to get an output voltage of nearly double
the peak AC input voltage. This also provides a tap in the middle, which allows
use of such a circuit as a split rail power supply.
A variant of this is to use two capacitors in series for the output smoothing
on a bridge rectifier then place a switch between the midpoint of those capacitors
and one of the AC input terminals. With the switch open, this circuit acts like a
normal bridge rectifier. With the switch closed, it act like a voltage doubling
rectifier. In other words, this makes it easy to derive a voltage of roughly 320 V
(±15%, approx.) DC from any 120 V or 230 V mains supply in the world, this can
then be fed into a relatively simple switched-mode power supply. However, for a
given desired ripple, the value of both capacitors must be twice the value of the
single one required for a normal bridge rectifier; when the switch is closed each
one must filter the output of a half-wave rectifier, and when the switch is open the

30
two capacitors are connected in series with an equivalent value of half one of
them.
Cockcroft Walton Voltage multiplier
Cascaded diode and capacitor stages can be added to make a voltage
multiplier (Cockroft-Walton circuit). These circuits are capable of producing a DC
output voltage potential tens of times that of the peak AC input voltage, but are
limited in current capacity and regulation. Diode voltage multipliers, frequently
used as a trailing boost stage or primary high voltage (HV) source, are used in HV
laser power supplies, powering devices such as cathode ray tubes (CRT) (like
those used in CRT based television, radar and sonar displays), photon amplifying
devices found in image intensifying and photo multiplier tubes (PMT), and
magnetron based radio frequency (RF) devices used in radar transmitters and
microwave ovens. Before the introduction of semiconductor electronics,
transformerless powered vacuum tube receivers powered directly from AC power
sometimes used voltage doublers to generate about 170 VDC from a 100–120 V
power line.
Rectifier efficiency:
Rectifier efficiency (η) is defined as the ratio of DC output power to the
input power from the AC supply. Even with ideal rectifiers with no losses, the
efficiency is less than 100% because some of the output power is AC power rather
than DC which manifests as ripple superimposed on the DC waveform. For a half-
wave rectifier efficiency is very poor,
Efficiency is reduced by losses in transformer windings and power
dissipation in the rectifier element itself. Efficiency can be improved with the use
of smoothing circuits which reduce the ripple and hence reduce the AC content of

31
the output. Three-phase rectifiers, especially three-phase full-wave rectifiers, have
much greater efficiencies because the ripple is intrinsically smaller. In some three-
phase and multi-phase applications the efficiency is high enough that smoothing
circuitry is unnecessary.
Rectifier losses:
A real rectifier characteristically drops part of the input voltage (a voltage
drop, for silicon devices, of typically 0.7 volts plus an equivalent resistance, in
general non-linear)—and at high frequencies, distorts waveforms in other ways.
Unlike an ideal rectifier, it dissipates some power.
An aspect of most rectification is a loss from the peak input voltage to the
peak output voltage, caused by the built-in voltage drop across the diodes (around
0.7 V for ordinary silicon p–n junction diodes and 0.3 V for Schottky diodes).
Half-wave rectification and full-wave rectification using a center-tapped
secondary produces a peak voltage loss of one diode drop. Bridge rectification has
a loss of two diode drops. This reduces output voltage, and limits the available
output voltage if a very low alternating voltage must be rectified. As the diodes do
not conduct below this voltage, the circuit only passes current through for a
portion of each half-cycle, causing short segments of zero voltage (where
instantaneous input voltage is below one or two diode drops) to appear between
each "hump". Peak loss is very important for low voltage rectifiers (for example,
12 V or less) but is insignificant in high-voltage applications such as HVDC.
Rectifier output smoothing:
The AC input (yellow) and DC output (green) of a half-wave rectifier with
a smoothing capacitor. Note the ripple in the DC signal.
While half-wave and full-wave rectification can deliver unidirectional
current, neither produces a constant voltage. Producing steady DC from a rectified

32
AC supply requires a smoothing circuit or filter.[8] In its simplest form this can be
just a reservoir capacitor or smoothing capacitor, placed at the DC output of the
rectifier. There is still an AC ripple voltage component at the power supply
frequency for a half-wave rectifier, twice that for full-wave, where the voltage is
not completely smoothed.
RC-Filter Rectifier: This circuit was designed and simulated using Multisim
8 software.
Sizing of the capacitor represents a tradeoff. For a given load, a larger
capacitor reduces ripple but costs more and creates higher peak currents in the
transformer secondary and in the supply that feeds it. The peak current is set in
principle by the rate of rise of the supply voltage on the rising edge of the
incoming sine-wave, but in practice it is reduced by the resistance of the
transformer windings. In extreme cases where many rectifiers are loaded onto a
power distribution circuit, peak currents may cause difficulty in maintaining a
correctly shaped sinusoidal voltage on the ac supply.
To limit ripple to a specified value the required capacitor size is
proportional to the load current and inversely proportional to the supply frequency
and the number of output peaks of the rectifier per input cycle. The load current
and the supply frequency are generally outside the control of the designer of the
rectifier system but the number of peaks per input cycle can be affected by the
choice of rectifier design.
A half-wave rectifier only gives one peak per cycle, and for this and other
reasons is only used in very small power supplies. A full wave rectifier achieves
two peaks per cycle, the best possible with a single-phase input. For three-phase
inputs a three-phase bridge gives six peaks per cycle. Higher numbers of peaks
can be achieved by using transformer networks placed before the rectifier to
convert to a higher phase order.

33
To further reduce ripple, a capacitor-input filter can be used. This
complements the reservoir capacitor with a choke (inductor) and a second filter
capacitor, so that a steadier DC output can be obtained across the terminals of the
filter capacitor. The choke presents a high impedance to the ripple current.[8] For
use at power-line frequencies inductors require cores of iron or other magnetic
materials, and add weight and size. Their use in power supplies for electronic
equipment has therefore dwindled in favour of semiconductor circuits such as
voltage regulators.
A more usual alternative to a filter, and essential if the DC load requires
very low ripple voltage, is to follow the reservoir capacitor with an active voltage
regulator circuit. The reservoir capacitor must be large enough to prevent the
troughs of the ripple dropping below the minimum voltage required by the
regulator to produce the required output voltage. The regulator serves both to
significantly reduce the ripple and to deal with variations in supply and load
characteristics. It would be possible to use a smaller reservoir capacitor (these can
be large on high-current power supplies) and then apply some filtering as well as
the regulator, but this is not a common strategy. The extreme of this approach is to
dispense with the reservoir capacitor altogether and put the rectified waveform
straight into a choke-input filter. The advantage of this circuit is that the current
waveform is smoother and consequently the rectifier no longer has to deal with
the current as a large current pulse, but instead the current delivery is spread over
the entire cycle. The disadvantage, apart from extra size and weight, is that the
voltage output is much lower – approximately the average of an AC half-cycle
rather than the peak.

34
Applications:
The primary application of rectifiers is to derive DC power from an AC
supply (AC to DC converter). Virtually all electronic devices require DC, so
rectifiers are used inside the power supplies of virtually all electronic equipment
Converting DC power from one voltage to another is much more
complicated. One method of DC-to-DC conversion first converts power to AC
(using a device called an inverter), then uses a transformer to change the voltage,
and finally rectifies power back to DC. A frequency of typically several tens of
kilohertz is used, as this requires much smaller inductance than at lower
frequencies and obviates the use of heavy, bulky, and expensive iron-cored units.
Output voltage of a full-wave rectifier with controlled thyristors Rectifiers
are also used for detection of amplitude modulated radio signals. The signal may
be amplified before detection. If not, a very low voltage drop diode or a diode
biased with a fixed voltage must be used. When using a rectifier for demodulation
the capacitor and load resistance must be carefully matched: too low a capacitance
makes the high frequency carrier pass to the output, and too high makes the
capacitor just charge and stay charged.
Rectifiers supply polarised voltage for welding. In such circuits control of
the output current is required; this is sometimes achieved by replacing some of the
diodes in a bridge rectifier with thyristors, effectively diodes whose voltage output
can be regulated by switching on and off with phase fired controllers.
Thyristors are used in various classes of railway rolling stock systems so
that fine control of the traction motors can be achieved. Gate turn-off thyristors
are used to produce alternating current from a DC supply, for example on the
Eurostar Trains to power the three-phase traction motors.

35
Rectification technologies:
Before about 1905 when tube type rectifiers were developed, power
conversion devices were purely electro-mechanical in design. Mechanical
rectification systems used some form of rotation or resonant vibration (e.g.
vibrators) driven by electromagnets, which operated a switch or commutator to
reverse the current.
These mechanical rectifiers were noisy and had high maintenance
requirements. The moving parts had friction, which required lubrication and
replacement due to wear. Opening mechanical contacts under load resulted in
electrical arcs and sparks that heated and eroded the contacts. They also were not
able to handle AC frequencies above several thousand cycles per second.
Synchronous rectifier:
To convert alternating into direct current in electric locomotives, a
synchronous rectifier may be used[citation needed]. It consists of a synchronous
motor driving a set of heavy-duty electrical contacts. The motor spins in time with
the AC frequency and periodically reverses the connections to the load at an
instant when the sinusoidal current goes through a zero-crossing. The contacts do
not have to switch a large current, but they must be able to carry a large current to
supply the locomotive's DC traction motors.
Vibrating rectifier:
A vibrator battery charger from 1922. It produced 6A DC at 6V to charge
automobile batteries. These consisted of a resonant reed, vibrated by an
alternating magnetic field created by an AC electromagnet, with contacts that
reversed the direction of the current on the negative half cycles. They were used in
low power devices, such as battery chargers, to rectify the low voltage produced
by a step-down transformer. Another use was in battery power supplies for

36
portable vacuum tube radios, to provide the high DC voltage for the tubes. These
operated as a mechanical version of modern solid state switching inverters, with a
transformer to step the battery voltage up, and a set of vibrator contacts on the
transformer core, operated by its magnetic field, to repeatedly break the DC
battery current to create a pulsing AC to power the transformer. Then a second set
of rectifier contacts on the vibrator rectified the high AC voltage from the
transformer secondary to DC.
Motor-generator set:
A motor-generator set, or the similar rotary converter, is not strictly a
rectifier as it does not actually rectify current, but rather generates DC from an AC
source. In an "M-G set", the shaft of an AC motor is mechanically coupled to that
of a DC generator. The DC generator produces multiphase alternating currents in
its armature windings, which a commutator on the armature shaft converts into a
direct current output; or a homopolar generator produces a direct current without
the need for a commutator. M-G sets are useful for producing DC for railway
traction motors, industrial motors and other high-current applications, and were
common in many high-power D.C. uses (for example, carbon-arc lamp projectors
for outdoor theaters) before high-power semiconductors became widely available.
Electrolytic:
The electrolytic rectifier[10] was a device from the early twentieth century
that is no longer used. A home-made version is illustrated in the 1913 book The
Boy Mechanic [11] but it would only be suitable for use at very low voltages
because of the low breakdown voltage and the risk of electric shock. A more
complex device of this kind was patented by G. W. Carpenter in 1928 (US Patent
1671970).
When two different metals are suspended in an electrolyte solution, direct
current flowing one way through the solution sees less resistance than in the other

37
direction. Electrolytic rectifiers most commonly used an aluminum anode and a
lead or steel cathode, suspended in a solution of tri-ammonium ortho-phosphate.
HVDC in 1971: this 150 kV mercury-arc valve converted AC hydropower
voltage for transmission to distant cities from Manitoba Hydro generators.
The rectification action is due to a thin coating of aluminum hydroxide on
the aluminum electrode, formed by first applying a strong current to the cell to
build up the coating. The rectification process is temperature-sensitive, and for
best efficiency should not operate above 86 °F (30 °C). There is also a breakdown
voltage where the coating is penetrated and the cell is short-circuited.
Electrochemical methods are often more fragile than mechanical methods, and can
be sensitive to usage variations, which can drastically change or completely
disrupt the rectification processes.
Similar electrolytic devices were used as lightning arresters around the
same era by suspending many aluminium cones in a tank of tri-ammonium ortho-
phosphate solution. Unlike the rectifier above, only aluminium electrodes were
used, and used on A.C., there was no polarization and thus no rectifier action, but
the chemistry was similar.
The modern electrolytic capacitor, an essential component of most rectifier
circuit configurations was also developed from the electrolytic rectifier.
Plasma type:
A rectifier used in high-voltage direct current (HVDC) power transmission
systems and industrial processing between about 1909 to 1975 is a mercury-arc
rectifier or mercury-arc valve. The device is enclosed in a bulbous glass vessel or
large metal tub. One electrode, the cathode, is submerged in a pool of liquid
mercury at the bottom of the vessel and one or more high purity graphite
electrodes, called anodes, are suspended above the pool. There may be several

38
auxiliary electrodes to aid in starting and maintaining the arc. When an electric arc
is established between the cathode pool and suspended anodes, a stream of
electrons flows from the cathode to the anodes through the ionized mercury, but
not the other way (in principle, this is a higher-power counterpart to flame
rectification, which uses the same one-way current transmission properties of the
plasma naturally present in a flame)
These devices can be used at power levels of hundreds of kilowatts, and
may be built to handle one to six phases of AC current. Mercury-arc rectifiers
have been replaced by silicon semiconductor rectifiers and high-power thyristor
circuits in the mid 1970s. The most powerful mercury-arc rectifiers ever built
were installed in the Manitoba Hydro Nelson River Bipole HVDC project, with a
combined rating of more than 1 GW and 450 kV.
Argon gas electron tube:
The General Electric Tungar rectifier was an argon gas-filled electron tube
device with a tungsten filament cathode and a carbon button anode. It operated
similarly to the thermionic vacuum tube diode, but the gas in the tube ionized
during forward conduction, giving it a much lower forward voltage drop so it
could rectify lower voltages. It was used for battery chargers and similar
applications from the 1920s until lower-cost metal rectifiers, and later
semiconductor diodes, supplanted it. These were made up to a few hundred volts
and a few amperes rating, and in some sizes strongly resembled an incandescent
lamp with an additional electrode.
The 0Z4 was a gas-filled rectifier tube commonly used in vacuum tube car
radios in the 1940s and 1950s. It was a conventional full-wave rectifier tube with
two anodes and one cathode, but was unique in that it had no filament (thus the
"0" in its type number). The electrodes were shaped such that the reverse
breakdown voltage was much higher than the forward breakdown voltage. Once

39
the breakdown voltage was exceeded, the 0Z4 switched to a low-resistance state
with a forward voltage drop of about 24 V.
Vacuum tube diodes
The thermionic vacuum tube diode, originally called the Fleming valve,
was invented by John Ambrose Fleming in 1904 as a detector for radio waves in
radio receivers, and evolved into a general rectifier. It consisted of an evacuated
glass bulb with a filament heated by a separate current, and a metal plate anode.
The filament emitted electrons by thermionic emission (the Edison effect),
discovered by Thomas Edison in 1884, and a positive voltage on the plate caused
a current of electrons through the tube from filament to plate. Since only the
filament produced electrons, the tube would only conduct current in one direction,
allowing the tube to rectify an alternating current.
Vacuum diode rectifiers were widely used in power supplies in vacuum
tube consumer electronic products, such as phonographs, radios, and televisions,
for example the All American Five radio receiver, to provide the high DC plate
voltage needed by other vacuum tubes.
In musical instrument amplification (especially for electric guitars), the
slight delay or "sag" between a signal increase (for instance, when a guitar chord
is struck hard and fast) and the corresponding increase in output voltage is a
notable effect of tube rectification, and results in compression. The choice
between tube rectification and diode rectification is a matter of taste; some
amplifiers have both and allow the player to choose.

40
CHAPTER -IV
4.1. WORKING PRINCIPLE
With proper authentication, users can access the developed web page details
from anywhere in the world. The complete monthly usage and due bill is
messaged back to the customer after processing these data. Accordingly, the
prepaid card is recharged for a certain amount and can be given as input to the
Microcontroller. The power from the Electricity Board (EB) is given to the load
through the energy meter and a relay. Energy meter pulses are tapped and given as
input to Microcontroller which acts as a data processing and transmission system.
It computes energy consumed and decrements the credit balance consequently.
The RF Module receives commands from the distribution system regarding tariff
and peak hour. The units consumed and balance remaining is indicated by LCD.
Whenever the balance becomes zero, the alert signal is given to the consumer
through Buzzer. The user can be notified about the detailing usage statistics with
the help of the GSM module through SMS. The relay trips the load if bill is not
paid for a long duration after allowing some emergency credit as leeway. The
power will be supplied again only if the meter is recharged with adequate credit.
4.2 SAMPLE CODING
#include <EEPROM.h>
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 16, 2);
#include <SoftwareSerial.h>
SoftwareSerial GSM(10, 11);
#define buzzer 7
#define relay 8
#define bt_theft A0
#define pulse_in 2
char inchar;

41
int unt_a = 0, unt_b = 0, unt_c = 0, unt_d = 0;
long total_unt = 7;
int price = 0;
int v=12;
int c=0;
int a=0;
int aa=0;
int b=0;
int addr = 0;
char inchar; //Will hold the incoming character from
the Serial Port.
void setup()
{
lcd.init(); // initialize the
lc
// Print a message to the LCD.
lcd.backlight();
mySerial.begin(9600);
pinMode(v, OUTPUT);
digitalWrite(v, LOW);
lcd.setCursor(0,0);
aa = EEPROM.read(10);
b = EEPROM.read(11);
}
void loop()
{
{
mySerial.println("AT+CMGS="+916382460434"");//Change
the receiver phone number
delay(500);
mySerial.println("Power
Consumption in unit = "); //the message you want to
send
mySerial.println(aa);
mySerial.println("Bill Amount =
");
mySerial.println(b);
delay(500);
mySerial.write(26);
delay(500);
}
else if(inchar=='P')

42
{
lcd.setCursor(0,0);
lcd.print("BILL PAID ");
lcd.setCursor(0,1);
lcd.print("THANK YOU.... ");
mySerial.println("AT+CMGF=1");
delay(500);
mySerial.println("AT+CMGS="+916382460434"");//Change
the receiver phone number
delay(500);
mySerial.println("Bill Amount Paid
Rs. "); //the message you want to send
mySerial.println(b);
mySerial.println("THANK YOU");
delay(500);
mySerial.write(26);
delay(500);
a=0;
aa=0;
b=0;
EEPROM.write(10, aa);
EEPROM.write(11, b);
}
else if(inchar=='S')
{
delay(10);
}
else if(c==0)
{
lcd.setCursor(12,1);
lcd.print(b);
}
}
}
if (digitalRead (bt_theft) == 0)
{
if (flag3 == 0)
{
flag3 = 1;
sendSMS(phone_no2, "Theft Alarm");
}

43
}
else
{
flag3 = 0;
}
delay(5);
}
{
pulse = pulse + 1;
if (pulse > 9)
{
pulse = 0;
if (total_unt > 0)
{
total_unt = total_unt - 1;
}
Write();
Read();
}
EEPROM.write(10, pulse);
}
}
4.3. BLOCK DIAGRAM

44
CHAPTER -V
5.1. CONCLUSION
In the proposed SEM using GSM would go a long way in making people
conscious of the amount of energy they spend and help to conserve the
conventional depleting resources. The automation of billing system eliminates
human involvement hence more accurate and reliable. The implementation of time
of-day billing can control the usage of electricity on consumer side to avoid
wastage of power which helps in reduction of energy generation costs. The
introduced Prepaid Billing System minimizes the Electricity theft in a cost
effective manner. Automation of meter reading also gives the information of total
load used in a house on request at any time as well as to make consumers to keep
track of energy usage. It sends a SMS alert to energy provider company whether a
person using more than specify limit of load. The use of a web-service developed
at load centre has made it possible to overcome the computational complexity of
smart meters currently used on the market.

45
5.2. REFERENCES
A K Shawhney , “Electrical and Electronics Measurements and Instrumentation”
by Dhanpat Roy & Sons, 4th Edition 2007.
[2] Vivek Kumar Sehgal,Nitesh Panda, Nipun Rai Handa, “Electronic Energy
Meter with instant billing”,,UKSim Fourth European Modelling Symposium on
Computer Modelling and Simulation.
[3] Devidas, A.R., Ramesh, M.V. ,”Wireless Smart Grid Design for Monitoring
and Optimizing Electric Transmission in India, 2010 Fourth International
Conference on Sensor Technologies and Applications (SENSORCOMM)”,
pp.637-640, 2010.
[4] Kwang-il Hwang , “Fault-tolerant ZigBee-based Automatic Meter Reading
Infrastructure”, Journal of Information Processing Systems, 5(4), 2009, pp. 221-
228.
[5] Md. Mejbaul Haque, Md. Kamal Hossain, Md. Mortuza Ali, Md. Rafiqul
Islam Sheikh, “Microcontroller Based Single Phase Digital Prepaid Energy Meter
for Improved Metering and Billing System”, International Journal of Power
Electronics and Drive System (IJPEDS),1(2), 2011.
[6] O.Homa Kesav, B. Abdul Rahim, “Automated Wireless Meter Reading
System for Monitoring and Controlling Power Consumption”, International
Journal of Recent Technology and Engineering (IJRTE) ISSN: 2277-3878
,1(2),2012.
[7] B.O.Omijeh, G.I.Ighalo,”Design of A Robust Prepaid Energy Metering And
Billing System”,JORIND,10(3),2012. [8] Syed Khizar Ali Zaidi I, HuraMasroor I,
Syed Rehan Ashraf I and Ahmed Hassan, “Design and Implementation of Low
Cost Electronic Prepaid Energy Meter”, NED University of Engineering and
Technology, Karachi, Pakistan, 2010.

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