CHAPTER 1

INTRODUCTION

Electricity is the driving force behind the development of any country. With the rapid increase in

residential, commercial and industrial consumer of electricity throughout the world, it has now become

imperative for utilities companies to device better, non intrusive, environmentally- safe techniques of

gauging utilities consumption, so that correct bills can be generated and invoiced. Traditionally,

electricity meter are installed on consumers premises and the consumption information is collected by

meter readings on their fortnightly or monthly visit to the premises. But energy meter reading is a

monotonous and expensive task. Now the meter reader people goes to each meter and take the meter

reading manually to issue the bill which will later be entered in the billing software for billing and

payment automation. If the manual meter reading and bill data entry process can be automated then it

would reduced the laborious task and financial wastage.” Wireless Energy meter Monitoring with

Automated Tariff Calculation” is a metering system that is to be used for data collecting from the meter

and processing the collector data for billing and other decision purposes. In this project we have

proposed an automatic meter reading system which is low cost, high performance, highest data rate, and

highest coverage area.

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CHAPTER 2

BLOCK DIAGRAM

2.1 TRANSMITTER SECTION

Fig 2.1.1 Block Diagram of Transmitter Section

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MICRO

CONTROLLER

RELAY

CRYSTAL OSCILLATOR

RESET

METER PULSE

LCD DISPLAY

TRANSMITTER

2.2 RECIEVER SECTION

Fig 2.2.1 Block Diagram of Receiver Section

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MICROCONTROLLER

RECIEVER

RESET

LCD DISPLAY

CRYSTAL OSCILLATOR

CHAPTER 3

COMPONENTS DESCRIPTION

3.1 ATmega 328(MICROCONTROLLER)

The AVR core combines a rich instruction set with 32 general purpose working registers. All the

32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two

independent registers to be accessed in one single instruction executed in one clock cycle. The

resulting architecture is more code efficient while achieving throughputs up toten times faster

than conventional CISC microcontrollers. The ATmega32 provides the following features: 32K

bytes of In-System Programmable Flash Program memory with Read-While-Write capabilities,

1024 bytes EEPROM, 2Kbyte SRAM, 32 general purpose I/O lines, 32 general purpose working

registers, a JTAG interface for Boundary-scan, On-chip Debugging support and programming,

three flexible Timer/Counters with compare modes, Internal and External Interrupts, a serial

programmable USART, a byte oriented Two-wire Serial Interface, an 8-channel, 10-bit ADC

with optional differential input stage with programmable gain (TQFP package only), a

programmable Watchdog Timer with Internal Oscillator, an SPI serial port, and six software

selectable power saving modes. The Idle mode stops the CPU while allowing the USART, Two-

wire interface, A/D Converter, SRAM, Timer/Counters, SPI port, and interrupt system to

continue functioning. The Power-down mode saves the register contents but freezes the

Oscillator, disabling all other chip functions until the next External Interrupt or Hardware Reset.

In Power-save mode, the Asynchronous Timer continues to run, allowing the user to maintain a

timer base while the rest of the device is sleeping. The ADC Noise Reduction mode stops the

CPU and all I/O modules except A synchronous Timer and ADC, to minimize switching noise

during ADC conversions. In Standby mode, the crystal/resonator Oscillator is running while the

rest of the device is sleeping. This allows very fast start-up combined with low-power

consumption. In Extended Standby mode, both the main Oscillator and the Asynchronous Timer

continue to run. The device is manufactured using Atmel’s high density nonvolatile memory

technology. The On-chip ISP Flash allows the program memory to be reprogrammed in-system

through an SPI serial interface, by a conventional nonvolatile memory programmer, or by an On-

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chip Boot program running on the AVR core. The boot program can use any interface to

download the application program in the Application Flash memory. Soft-ware in the Boot Flash

section will continue to run while the Application Flash section is updated, providing true Read-

While-Write operation. By combining an 8-bit RISC CPU with In-System Self-Programmable

Flash on a monolithic chip, the Atmel ATmega32 is a powerful microcontroller that provides a

highly-flexible and cost-effective solution to many embedded control applications. The

ATmega32 AVR is supported with a full suite of program and system development tools

including: C compilers, macro assemblers, program debugger/simulators, in-circuit emulators,

and evaluation kits.

Fig 3.1.1 ATmega 328 Microcontroller Pin out

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3.1.1 Features

High-performance, Low-power AVR 8-bit Microcontroller

Advanced RISC Architecture

– 131 Powerful Instructions – Most Single-clock Cycle Execution

– 32 x 8 General Purpose Working Registers

– Fully Static Operation

– Up to 16 MIPS Throughput at 16 MHz

– On-chip 2-cycle Multiplier

Nonvolatile Program and Data Memories

– 32K Bytes of In-System Self-Programmable Flash

Endurance: 10,000 Write/Erase Cycles

– Optional Boot Code Section with Independent Lock Bits

In-System Programming by On-chip Boot Program True Read-While-Write Operation

– 1024 Bytes EEPROM Endurance: 100,000 Write/Erase Cycles

– 2K Byte Internal SRAM

– Programming Lock for Software Security

JTAG (IEEE std. 1149.1 Compliant) Interface

– Boundary-scan Capabilities According to the JTAG Standard

– Extensive On-chip Debug Support

– Programming of Flash, EEPROM, Fuses, and Lock Bits through the JTAG

Interface

Peripheral Features

– Two 8-bit Timer/Counters with Separate Prescalers and Compare Modes

– One 16-bit Timer/Counter with Separate Prescaler, Compare Mode, and Capture

Mode

– Real Time Counter with Separate Oscillator

– Four PWM Channels

– 8-channel, 10-bit ADC

8 Single-ended Channels

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7 Differential Channels in TQFP Package Only

2 Differential Channels with Programmable Gain at 1x, 10x, or 200x

– Byte-oriented Two-wire Serial Interface

– Programmable Serial USART

– Master/Slave SPI Serial Interface

– Programmable Watchdog Timer with Separate On-chip Oscillator

– On-chip Analog Comparator

Special Microcontroller Features

– Power-on Reset and Programmable Brown-out Detection

– Internal Calibrated RC Oscillator

– External and Internal Interrupt Sources

– Six Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, Standby

and Extended Standby

I/O and Packages

– 32 Programmable I/O Lines

– 40-pin PDIP, 44-lead TQFP, and 44-pad QFN/MLF

Operating Voltages

– 2.7 - 5.5V for ATmega32L

– 4.5 - 5.5V for ATmega32

Speed Grades

– 0 - 8 MHz for ATmega32L

– 0 - 16 MHz for ATmega32

Power Consumption at 1 MHz, 3V, 25C for ATmega32L

– Active: 1.1 mA

– Idle Mode: 0.35 mA

– Power-down Mode: < 1 μA

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3.2 RF TRANSCEIVER

An RF module (radio frequency module) is a (usually) small electronic device used to transmit

and/or receive radio signals between two devices. In an embedded system it is often desirable to

communicate with another device wirelessly. This wireless communication may be

accomplished through optical communication or through radio frequency (RF) communication.

For many applications the medium of choice is RF since it does not require line of sight. RF

communications incorporate a transmitter and/or receiver.

RF modules are widely used in electronic design owing to the difficulty of designing radio

circuitry. Good electronic radio design is notoriously complex because of the sensitivity of radio

circuits and the accuracy of components and layouts required to achieve operation on a specific

frequency. In addition, reliable RF communication circuit requires careful monitoring of the

manufacturing process to ensure that the RF performance is not adversely affected. Finally, radio

circuits are usually subject to limits on radiated emissions, and require Conformance testing and

certification by a standardization organization such as ETSI or the U.S. Federal Communications

Commission (FCC). For these reasons, design engineers will often design a circuit for an

application which requires radio communication and then "drop in" a pre-made radio module

rather than attempt a discrete design, saving time and money on development.

RF modules are most often used in medium and low volume products for consumer applications

such as garage door openers, wireless alarm systems, industrial remote controls, smart sensor

applications, and wireless home automation systems. They are sometimes used to replace

older infra red communication designs as they have the advantage of not requiring line-of-sight

operation.

Several carrier frequencies are commonly used in commercially-available RF modules, including

those in the industrial, scientific and medical (ISM) radio bands such as 433.92 MHz, 915 MHz,

and 2400 MHz. These frequencies are used because of national and international regulations

governing the used of radio for communication. Short Range Devices may also use frequencies

available for unlicensed such as 315 MHz and 868 MHz.

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3.2.1Types of RF modules

The term RF module can be applied to many different types, shapes and sizes of small electronic

sub assembly circuit board. It can also be applied to modules across a huge variation of

functionality and capability. RF modules typically incorporate a printed circuit board, transmit or

receive circuit, antenna, and serial interface for communication to the host processor.

Most standard, well known types are covered here:

Transmitter module

Receiver module

Transceiver module

System on a chip module

3.2.1.1 Transmitter modules

An RF transmitter module is a small PCB sub-assembly capable of transmitting a radio wave

and modulating that wave to carry data. Transmitter modules are usually implemented alongside

a micro controller which will provide data to the module which can be transmitted. RF

transmitters are usually subject to regulatory requirements which dictate the maximum

allowable transmitter power output , harmonics , and band edge requirements.

3.2.1.2 Receiver modules

An RF receiver module receives the modulated RF signal, and demodulates it. There are two

types of RF receiver modules: super heterodyne receivers and super-regenerative receivers .

Super-regenerative modules are usually low cost and low power designs using a series of

amplifiers to extract modulated data from a carrier wave. Super-regenerative modules are

generally imprecise as their frequency of operation varies considerably with temperature and

power supply voltage. Super heterodyne receivers have a performance advantage over super-

regenerative; they offer increased accuracy and stability over a large voltage and temperature

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range. This stability comes from a fixed crystal design which in turn leads to a comparatively

more expensive product.

Fig 3.2.1.1 RF Transceiver Module

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Fig 3.2.1.2 RF Transceiver Module

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3.3 LCD DISPLAY

LCD stands for Liquid Crystal Display, which is used to shows status of an application,

display values, debugging a program, etc.,

3.3.1 Construction of Liquid crystal display

A Liquid crystal display is a passive device, which means it doesn’t produce any light to

display characters, images, video and animations. But it simply alters the light travelling through

it. The internal construction of LCD describes how the light altered when it passes through it in

order to produce any characters, images, etc.

Consider a single pixel area in LCD, in which there are two polarization filters oriented at

90 degree angle to each other as shown in figure 1.1. These filters are used to polarize the

unpolarized light. The first filter (Vertical polarized filter in figure 1.1) polarizes the light with

one polarization plane (Vertical). When the vertically polarized light passes through the second

filter (Horizontal polarized filter) no light output will produce.

Fig 3.3.1.1 Orientation of two polarization filters in LCD

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The vertically polarized light should rotate 90 degrees in order to pass through the

horizontal polarized light. This can be achieving by embedding liquid crystal layer between two

polarization filters. The liquid crystal layer consists of rod shaped tiny molecules and ordering of

these molecules creates directional orientation property. These molecules in the liquid crystal are

twisted 90 degrees as shown in the figure 1.2. The vertically polarized light passes through

rotation of the molecules and twisted to 90 degrees. When the orientation of light matches with

the outer polarization filter light will pass it and brightens the screen.

Fig 3.3.1.2 Liquid Crystal molecules orientation.

If the Liquid crystal molecules are twisted 90 degrees more precisely, then more light

will pass through it. Two glass transparent electrodes are aligned front and back of the liquid

crystal in order to change the orientation of the crystal molecules by applying voltage between

them as shown in figure 1.3 and figure 1.4. If there is no voltage applied between the electrodes,

the orientation of molecules will remain twist at 90 degrees and the light passes through the outer

polarization filter thus pixel appears as complete white. If the voltage is applied large enough the

molecules in the liquid crystal layer changes its orientation (untwist) so that light orientation also

changes and then blocked by the outer polarization filter thus the pixel appears black. In this

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way, black and white images or characters are produced. By arranging small pixels together as a

matrix will produce on which it is possible to show different sizes of images and characters. By

controlling the voltage applied between liquid crystal layers in each pixel, light can be allowed to

pass through outer polarization filter in various amounts, so that it can possible to produce

different gray levels on the LCD screen.

Generally the electrodes is made up of Indium Tin Oxide (ITO) which is

transparent material, hence it is simply called glass electrodes plates. LCD display is also

“twisted neumatic LCD” because of twist and untwist of molecules in liquid crystal layer.

Fig

3.3.1.3 LCD Display

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Fig 3.3.1.4 Orientation of Liquid crystal molecules altered by applying voltage between two ITO

glass plates.

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3.4 ENCODER(HT12E)

HT12E is a 212 series encoder IC widely used in remote control and very common among Radio

Frequency RF applications. This HT12E IC capable of converting 12 bit Parallel data inputs into

serial outputs. These bits are classified into 8 (A0-A7) address bits and 4(AD0-AD3) data bits.

Using the address pins we can provide 8 bit security code for secured data transmission between

the encoder and the decoder. The encoder and decoder should use the same address and data

format. HT12E is capable of operating in a wide Voltage range from 2.4V to 12V and also

consists of a built in oscillator. Let’s move into the working of HT12E encoder IC.

3.4.1 Pin Description of IC HT12E:

The pin Description of the IC HT12E was pretty simple to understand with total of 18 pins.

VDD and VSS: Positive and negative power supply pins.

OSC1 and OSC2: Input and output pins of the internal oscillator present inside the IC.

TE: This pin is used for enabling the transmission, a low signal in this pin will enable the

transmission of data bits.

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A0 – A7: These are the input address pins used for secured transmission of this data.

Fig 3.4.1 Pin Diagram of HT12E

These pins can be connected to VSS for low signal or left open for high state.

AD0 – AD3: This pins are feeding data into the the IC. These pins may be connected to VSS

for sending LOW since it is a active low pin

DOUT: The output of the encoder can be obtained through this pin and can be connected to

the RF transmitter.

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3.4.2 Working of HT12E IC:

Fig 3.4.2 HT12E Transmission Timing

HT12E starts working with a low signal on the TE pin. After receiving a low signal the HT12E

starts the transmission of 4 data bits as shown in the timing diagram above. And the output cycle

will repeats based on the status of the TE pin in the IC. If the TE pin retains the low signal the

cycle repeats as long as the low signal in the TE pin exists. The encoder IC will be in standby

mode if the TE pin is disabled and thus the status of this pin was necessary for encoding process.

The address of these bits can be set through A0 – A7 and the same scheme should be used in

decoders to retrieve the signal bits.

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3.4.3 Practical Circuit Using HT12E:

Fig 3.4.3 Circuit for HT12E

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3.5 DECODER (HT12D)

HT12D is a decoder integrated circuit that belongs to 212 series of decoders. This series of

decoders are mainly used for remote control system applications, like burglar alarm, car door

controller, security system etc. It is mainly provided to interface RF and infrared circuits. They

are paired with 212 series of encoders. The chosen pair of encoder/decoder should have same

number of addresses and data format.

In simple terms, HT12D converts the serial input into parallel outputs. It decodes the serial

addresses and data received by, say, an RF receiver, into parallel data and sends them to output

data pins. The serial input data is compared with the local addresses three times continuously.

The input data code is decoded when no error or unmatched codes are found. A valid

transmission in indicated by a high signal at VT pin.

HT12D is capable of decoding 12 bits, of which 8 are address bits and 4 are data bits. The data

on 4 bit latch type output pins remain unchanged until new is received.

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3.5.1 Pin description of HT12D

Pin

No Function Name

1

8 bit Address pins for input

A0

2 A1

3 A2

4 A3

5 A4

6 A5

7 A6

8 A7

9 Ground (0V) Ground

10

4 bit Data/Address pins for output

D0

11 D1

12 D2

13 D3

14 Serial data input Input

15 Oscillator output Osc2

16 Oscillator input Osc1

17 Valid transmission; active high VT

18 Supply voltage; 5V (2.4V-12V) Vcc

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Fig 3.5.1 Circuit for HT12D

VDD and VSS are used to provide power to the IC, Positive and Negative of the power

supply respectively. As I said earlier its operating voltage can be in the range 2.4V to

12V

OSC1 and OSC2 are used to connect external resistor for internal oscillator of HT12D.

OSC1 is the oscillator input pin and OSC2 is the oscillator output pin as shown in the

figure below.

Fig 3.5.2 Oscillator of HT12D

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A0 – A7 are the address input pins. Status of these pins should match with status of

address pin in HT12E (used in transmitter) to receive the data. These pins can be

connected to VSS or left open.

DIN is the serial data input pin and can be connected to a RF receiver output.

D8 – D11 are the data output pins. Status of these pins can be VSS or VDD depending

upon the received serial data through pin DIN.

VT stand for Valid Transmission. This output pin will be HIGH when valid data is

available at D8 – D11 data output pins.

3.5.2 Working

Fig 3.5.3 HT12D Decoder Timing

HT12D decoder will be in standby mode initially ie, oscillator is disabled and a HIGH on DIN

pin activates the oscillator. Thus the oscillator will be active when the decoder receives data

transmitted by an encoder. The device starts decoding the input address and data. The decoder

matches the received address three times continuously with the local address given to pin A0 –

A7. If all matches, data bits are decoded and output pins D8 – D11 are activated. This valid data

is indicated by making the pin VT (Valid Transmission) HIGH. This will continue till the

address code becomes incorrect or no signal is received.

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3.6 ARDUINO UNO BOARD

The Arduino Uno is a microcontroller board based on the ATmega328 (datasheet). It has 14

digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz

crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button. It

contains everything needed to support the microcontroller; simply connect it to a computer with

a USB cable or power it with a AC-to-DC adapter or battery to get started. The Uno differs from

all preceding boards in that it does not use the FTDI USB-to-serial driver chip. Instead, it

features the Atmega8U2 programmed as a USB-to-serial converter. "Uno" means one in Italian

and is named to mark the upcoming release of Arduino 1.0. The Uno and version 1.0 will be the

reference versions of Arduno, moving forward. The Uno is the latest in a series of USB Arduino

boards, and the reference model for the Arduino platform.

3.6.1 Summary

Microcontroller ATmega328

Operating Voltage 5V

Input Voltage (recommended) 7-12V

Input Voltage (limits) 6-20V

Digital I/O Pins 14 (of which 6 provide PWM output)

Analog Input Pins 6

DC Current per I/O Pin 40 mA

DC Current for 3.3V Pin 50 mA

Flash Memory 32 KB of which 0.5 KB used by

Boot loader

SRAM 2 KB

EEPROM 1 KB

Clock Speed 16 MHz

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3.6.2 Power

The Arduino Uno can be powered via the USB connection or with an external power supply. The

power source is selected automatically. External (non-USB) power can come either from an AC-

to-DC adapter (wall-wart) or battery. The adapter can be connected by plugging a 2.1mm center-

positive plug into the board's power jack. Leads from a battery can be inserted in the Gnd and

Vin pin headers of the POWER connector. The board can operate on an external supply of 6 to

20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and

the board may be unstable. If using more than 12V, the voltage regulator may overheat and

damage the board. The recommended range is 7 to 12 volts. The power pins are as follows:

VIN: The input voltage to the Arduino board when it's using an external power source (as

opposed to 5 volts from the USB connection or other regulated power source) . You can

supply voltage through this pin, or, if supplying voltage via the power jack, access it

through this pin.

5V: The regulated power supply used to power the microcontroller and other components

on the board. This can come either from VIN via an on-board regulator, or be supplied by

USB or another regulated 5V supply.

3V3: A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50

mA.

GND: Ground pins.

3.6.3 Memory

The Atmega328 has 32 KB of flash memory for storing code (of which 0,5 KB is used for the

boot loader); It has also 2 KB of SRAM and 1 KB of EEPROM (which can be read and written

with the EEPROM library).

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3.6.4 Input and Output

Each of the 14 digital pins on the Uno can be used as an input or output, using pinMode(),

digitalWrite(), and digitalRead() functions. They operate at 5 volts. Each pin can provide or

receive a maximum of 40 mA and has an internal pull-up resistor (disconnected by default) of

20-50 kOhms. In addition, some pins have specialized functions:

Serial: 0 (RX) and 1 (TX).

Used to receive (RX) and transmit (TX) TTL serial data. These pins are connected to the

corresponding pins of the ATmega8U2 USB-to-TTL Serial chip.

External Interrupts: 2 and 3.

These pins can be configured to trigger an interrupt on a low value, a rising or falling edge, or a

change in value. See the attachInterrupt() function for details.

PWM: 3, 5, 6, 9, 10, and 11.

Provide 8-bit PWM output with the analogWrite() function.

SPI: 10 (SS), 11 (MOSI), 12 (MISO), 13 (SCK).

These pins support SPI communication, which, although provided by the underlying hardware, is

not currently included in the Arduino language.

LED: 13.

There is a built-in LED connected to digital pin 13. When the pin is HIGH value, the LED is on,

when the pin is LOW, it's off.

The Uno has 6 analog inputs, each of which provides 10 bits of resolution (i.e. 1024 different

values). By default they measure from ground to 5 volts, though is it possible to change the

upper end of their range using the AREF pin and the

analogReference() function. Additionally, some pins have specialized functionality:

I²C: 4 (SDA) and 5 (SCL).Support I²C (TWI) communication using the Wire library.

There are a couple of other pins on the board:

AREF: Reference voltage for the analog inputs. Used with analogReference().

Reset: Bring this line LOW to reset the microcontroller. Typically used to add a reset

button to shields which block the one on the board.

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3.6.5 Communication

The Arduino Uno has a number of facilities for communicating with a computer, another

Arduino, or other microcontrollers. The ATmega328 provides UART TTL (5V) serial

communication, which is available on digital pins 0 (RX) and 1 (TX). An ATmega8U2 on the

board channels this serial communication over USB and appears as a virtual com port to

software on the computer. The '8U2 firmware uses the standard USBCOM drivers, and no

external driver is needed. However, on Windows, an *.inf file is required. The Arduino software

includes a serial monitor which allows simple textual data to be sent to and from the Arduino

board. The RX and TX LEDs on the board will flash when data is being transmitted via the

USB-to-serial chip and USB connection to the computer (but not for serial communication on

pins 0 and 1).A SoftwareSerial library allows for serial communication on any of the Uno's

digital pins. The ATmega328 also support I2C (TWI) and SPI communication. The Arduino

software includes a Wirelibrary to simplify use of the I2Cbus.

3.6.6 Programming

The Arduino Uno can be programmed with the Arduino software (download). Select "Arduino

Uno w/ATmega328" from the Tools > Boardmenu (according to the microcontroller on your

board).The ATmega328 on the Arduino Uno comes preburned with a bootloader that allows us

to upload new code to it without the use of an external hardware programmer. It communicates

using the original STK500

Protocol (reference,C header files). We can also bypass the bootloader and program the

microcontroller through the ICSP (In-Circuit Serial Programming) header. The ATmega8U2

firmware source code is available. The ATmega8U2 is loaded with a DFU bootloader, which can

be activated by connecting the solder jumper on the back of the board (near the map of Italy) and

then resetting the 8U2. We can then use Atmel's FLIP software (Windows) or the DFU

programmer (Mac OS X and Linux) to load a new firmware. Or we can use the ISP header with

an external programmer (overwriting the DFU bootloader).

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3.6.7 Automatic (Software) Reset

Rather than requiring a physical press of the reset button before an upload, the Arduino Uno is

designed in a way that allows it to be reset by software running on a connected computer. One of

the hardware flow control lines (DTR) of the ATmega8U2 is connected to the reset line of the

ATmega328 via a 100 nanofarad capacitor. When this line is asserted (taken low), the reset line

drops long enough to reset the chip. The Arduino software uses this capability to allow you to

upload code by simply pressing the upload button in the Arduino environment. This means that

the bootloader can have a shorter timeout, as the lowering of DTR can be well-coordinated with

the start of the upload. This setup has other implications. When the Uno is connected to either a

computer running Mac OS X or Linux, it resets each time a connection is made to it from

software (via USB). For the following half-second or so, the bootloader is running on the Uno.

While it is programmed to ignore malformed data (i.e. anything besides an upload of new code),

it will intercept the first few bytes of data sent to the board after a connection is opened. If a

sketch running on the board receives one-time configuration or other data when it first starts,

make sure that the software with which it communicates waits a second after opening the

connection and before sending this data. The Uno contains a trace that can be cut to disable the

auto-reset. The pads on either side of the trace can be soldered together to re-enable it. It's

labeled "RESET-EN". We may also be able to disable the auto-reset by connecting a 110 ohm

resistor from 5V to the reset line.

3.6.8 USB Overcurrent Protection

The Arduino Uno has a resettable poly fuse that protects your computer's USB ports from shorts

and overcurrent. Although most computers provide their own internal protection, the fuse

provides an extra layer of protection. If more than 500 mA is applied to the USB port, the fuse

will automatically break the connection until the short or overload is removed.

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3.6.9 Physical Characteristics

The maximum length and width of the Uno PCB are 2.7 and 2.1 inches respectively, with the

USB connector and power jack extending beyond the former dimension. Three screw holes allow

the board to be attached to a surface or case. Note that the distance between digital pins 7 and 8

is 160 mil(0.16"), not an even multiple of the 100 mil spacing of the other pins.

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3.7 BRIDGE RECTIFIER

A Full Wave Rectifier Circuit produces an output voltage or current which is purely DC or has

some specified DC component. Full wave rectifiers have some fundamental advantages over

their half wave rectifier counterparts. The average (DC) output voltage is higher than for half

wave, the output of the full wave rectifier has much less ripple than that of the half wave rectifier

producing a smoother output waveform.

In a Full Wave Rectifier circuit two diodes are now used, one for each half of the cycle. A

multiple winding transformer is used whose secondary winding is split equally into two halves

with a common centre tapped connection, (C). This configuration results in each diode

conducting in turn when its anode terminal is positive with respect to the transformer centre

point C producing an output during both half-cycles, twice that for the half wave rectifier so it is

100% efficient as shown below.

3.7.1 Full Wave Rectifier Circuit

Fig 3.7.1.1 Full wave Rectifier circuit

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The full wave rectifier circuit consists of two power diodes connected to a single load resistance

(RL) with each diode taking it in turn to supply current to the load. When point A of the

transformer is positive with respect to point C, diode D1 conducts in the forward direction as

indicated by the arrows.

When point B is positive (in the negative half of the cycle) with respect to point C,

diode D2conducts in the forward direction and the current flowing through resistor R is in the

same direction for both half-cycles. As the output voltage across the resistor R is the phasor sum

of the two waveforms combined, this type of full wave rectifier circuit is also known as a “bi-

phase” circuit.

As the spaces between each half-wave developed by each diode is now being filled in by the

other diode the average DC output voltage across the load resistor is now double that of the

single half-wave rectifier circuit and is about 0.637Vmax of the peak voltage, assuming no losses.

Where: VMAX is the maximum peak value in one half of the secondary winding and VRMS is the

rms value.

The peak voltage of the output waveform is the same as before for the half-wave rectifier

provided each half of the transformer windings have the same rms voltage value. To obtain a

different DC voltage output different transformer ratios can be used. The main disadvantage of

this type of full wave rectifier circuit is that a larger transformer for a given power output is

required with two separate but identical secondary windings making this type of full wave

rectifying circuit costly compared to the “Full Wave Bridge Rectifier” circuit equivalent.

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3.7.2 The Full Wave Bridge Rectifier

Another type of circuit that produces the same output waveform as the full wave rectifier circuit

above, is that of the Full Wave Bridge Rectifier. This type of single phase rectifier uses four

individual rectifying diodes connected in a closed loop “bridge” configuration to produce the

desired output. The main advantage of this bridge circuit is that it does not require a special

centre tapped transformer, thereby reducing its size and cost. The single secondary winding is

connected to one side of the diode bridge network and the load to the other side as shown below.

3.7.3 The Diode Bridge Rectifier

Fig 3.7.3.1 Diode Bridge Rectifier

The four diodes labeled D1 to D4 are arranged in “series pairs” with only two diodes conducting

current during each half cycle. During the positive half cycle of the supply,

diodesD1 and D2 conduct in series while diodes D3 and D4 are reverse biased and the current

flows through the load.

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3.7.3.1 The Positive Half-cycle

Fig 3.7.3.1.1 Current flow through the load

During the negative half cycle of the supply, diodes D3 and D4 conduct in series, but

diodes D1and D2 switch “OFF” as they are now reverse biased. The current flowing through the

load is the same direction as before.

3.7.3.2 The Negative Half-cycle

Fig 3.7.3.2.1 Current flow in Negative half cycle

As the current flowing through the load is unidirectional, so the voltage developed across the

load is also unidirectional the same as for the previous two diode full-wave rectifier, therefore

the average DC voltage across the load is 0.637Vmax.

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Fig 3.7.3.2.2 Four pin Bridge Rectifier

3.7.4 Typical Bridge Rectifier

However in reality, during each half cycle the current flows through two diodes instead of just

one so the amplitude of the output voltage is two voltage drops ( 2 x 0.7 = 1.4V ) less than the

input VMAX amplitude. The ripple frequency is now twice the supply frequency (e.g. 100Hz for a

50Hz supply or 120Hz for a 60Hz supply.)

Although we can use four individual power diodes to make a full wave bridge rectifier, pre-made

bridge rectifier components are available “off-the-shelf” in a range of different voltage and

current sizes that can be soldered directly into a PCB circuit board or be connected by spade

connectors.

The image to the right shows a typical single phase bridge rectifier with one corner cut off. This

cut-off corner indicates that the terminal nearest to the corner is the positive or +ve output

terminal or lead with the opposite (diagonal) lead being the negative or -ve output lead. The

other two connecting leads are for the input alternating voltage from a transformer secondary

winding.

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Fig 3.7.4.1 Bridge Rectifier

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3.8 TRANSFORMER

Energy from one circuit to another without any direct electrical connection and with the help of

mutual induction between two windings. It transforms power from one circuit to another without

changing its frequency but may be in different voltage level.

This is a very short and simple definition of transformer.

3.8.1 Working Principle of Transformer

The working principle of transformer is very simple. It depends upon Faraday's law of

electromagnetic induction. Actually, mutual induction between two or more winding is

responsible for transformation action in an electrical transformer.

Faraday's Laws of Electromagnetic Induction

According to these Faraday's laws , "Rate of change of flux linkage with respect to time is

directly proportional to the induced EMF in a conductor or coil".

Basic Theory of Transformer

Say you have one winding which is supplied by an alternating electrical source. The alternating

current through the winding produces a continually changing flux or alternating flux that

surrounds the winding. If any other winding is brought nearer to the previous one, obviously

some portion of this flux will link with the second. As this flux is continually changing in its

amplitude and direction, there must be a change in flux linkage in the second winding or coil.

According to Faraday's law of electromagnetic induction , there must be an EMF induced in the

second. If the circuit of the later winding is closed, there must be an current flowing through it.

This is the simplest form of electrical power transformer and this is the most basic of working

principle of transformer. For better understanding, we are trying to repeat the above

explanation in a more brief way here. Whenever we apply alternating current to an electric coil,

there will be an alternating flux surrounding that coil. Now if we bring another coil near the first

one, there will be an alternating flux linkage with that second coil. As the flux is alternating,

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there will be obviously a rate of change in flux linkage with respect to time in the second coil.

Naturally emf will be induced in it as per Faraday's law of electromagnetic induction. This is the

most basic concept of the theory of transformer. The winding which takes electrical power

from the source, is generally known as primary winding of transformer. Here in our above

example it is first winding. The winding which gives the desired output voltage due to mutual

induction in the transformer, is commonly known as secondary winding of transformer. Here in

our example it is second winding. The above mentioned form of transformer is theoretically

possible but not practically, because in open air very tiny portion of the flux of the first winding

will link with second; so the current that flows through the closed circuit of later, will be so small

in amount that it will be difficult to measure. The rate of change of flux linkage depends upon

the amount of linked flux with the second winding. So, it is desired to be linked to almost all flux

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of primary winding to the secondary winding. This is effectively and efficiently done by placing

one low reluctance path common to both of the winding. This low reluctance path is core of

transformer , through which maximum number of flux produced by the primary is passed through

and linked with the secondary winding. This is the most basic theory of transformer.

Main Constructional Parts of Transformer

The three main parts of a transformer are,

1. Primary Winding of transformer - it produces magnetic flux when it is connected to

electrical source.

2. Magnetic Core of transformer - the magnetic flux produced by the primary winding, that

will pass through this low reluctance path linked with secondary winding and create a closed

magnetic circuit .

3. Secondary Winding of transformer - the flux, produced by primary winding, passes

through the core, will link with the secondary winding. This winding also wounds on the

same core and gives the desired output of the transformer.

Fig 3.8.1 Transformer

3.9 RESISTORS

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A resistor is a passive two-terminal electrical component that implements electrical resistance as

a circuit element. Resistors act to reduce current flow, and, at the same time, act to lower voltage

levels within circuits. In electronic circuits, resistors are used to limit current flow, to adjust

signal levels, bias active elements, and terminate transmission lines among other uses. High-

power resistors, that can dissipate many watts of electrical power as heat, may be used as part of

motor controls, in power distribution systems, or as test loads for generators. Fixed resistors have

resistances that only change slightly with temperature, time or operating voltage. Variable

resistors can be used to adjust circuit elements (such as a volume control or a lamp dimmer), or

as sensing devices for heat, light, humidity, force, or chemical activity.

Resistors are common elements of electrical networks and electronic circuits and are ubiquitous

in electronic equipment. Practical resistors as discrete components can be composed of various

compounds and forms. Resistors are also implemented within integrated circuits.

The electrical function of a resistor is specified by its resistance: common commercial resistors

are manufactured over a range of more than nine orders of magnitude. The nominal value of the

resistance will fall within a manufacturing tolerance.

3.9.1 Theory of operation

The hydraulic analogy com pares electric current flowing through circuits to water flowing

through pipes. When a pipe (left) is filled with hair (right), it takes a larger pressure to achieve

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the same flow of water. Pushing electric current through a large resistance is like pushing water

through a pipe clogged with hair: It requires a larger push ( voltage drop ) to drive the same flow

( electric current ).

3.9.2 Ohm's law

The behavior of an ideal resistor is dictated by the relationship specified by Ohm's law :

Ohm's law states that the voltage (V) across a resistor is proportional to the current (I), where the

constant of proportionality is the resistance (R). For example, if a 300 ohm resistor is attached

across the terminals of a 12 volt battery, then a current of 12 / 300 = 0.04 amperes flows through

that resistor.

Practical resistors also have some inductance and capacitance which will also affect the relation

between voltage and current in alternating current circuits.

The ohm (symbol: Ω ) is the SI unit of electrical resistance , named after Georg Simon Ohm . An

ohm is equivalent to a volt per ampere . Since resistors are specified and manufactured over a

very large range of values, the derived units of milliohm (1 mΩ = 10 −3 Ω), kilohm (1 kΩ =

10 3 Ω), and megohm (1 MΩ = 10 6 Ω) are also in common usage.

3.9.3 Series and parallel resistors

The total resistance of resistors connected in series is the sum of their individual resistance

values.

The total resistance of resistors connected in parallel is the reciprocal of the sum of

the reciprocals of the individual resistors.

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So, for example, a 10 ohm resistor connected in parallel with a 5 ohm resistor and a 15 ohm

resistor will produce the inverse of 1/10+1/5+1/15 ohms of resistance, or 1/(.1+.2+.067)=2.725

ohms.

A resistor network that is a combination of parallel and series connections can be broken up into

smaller parts that are either one or the other. Some complex networks of resistors cannot be

resolved in this manner, requiring more sophisticated circuit analysis. Generally, the Y-Δ

transform, or matrix methods can be used to solve such problems.

3.9.4 Power dissipation

At any instant, the power P (watts) consumed by a resistor of resistance R (ohms) is calculated

as: where V (volts) is the voltage across the resistor and I (amps) is

the current flowing through it. Using Ohm's law, the two other forms can be derived. This power

is converted into heat which must be dissipated by the resistor's package before its temperature

rises excessively.

Resistors are rated according to their maximum power dissipation. Discrete resistors in solid-

state electronic systems are typically rated as 1/10, 1/8, or 1/4 watt. They usually absorb much

less than a watt of electrical power and require little attention to their power rating.

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Fig3.9.4.1 An aluminium-housed power resistor rated for 50 W when heat-sinked

Resistors required to dissipate substantial amounts of power, particularly used in power supplies,

power conversion circuits, and power amplifiers, are generally referred to as power resistors; this

designation is loosely applied to resistors with power ratings of 1 watt or greater. Power resistors

are physically larger and may not use the preferred values, color codes, and external packages

described below.

If the average power dissipated by a resistor is more than its power rating, damage to the resistor

may occur, permanently altering its resistance; this is distinct from the reversible change in

resistance due to its temperature coefficient when it warms. Excessive power dissipation may

raise the temperature of the resistor to a point where it can burn the circuit board or adjacent

components, or even cause a fire. There are flameproof resistors that fail (open circuit) before

they overheat dangerously.

Since poor air circulation, high altitude, or high operating temperatures may occur, resistors may

be specified with higher rated dissipation than will be experienced in service.

All resistors have a maximum voltage rating; this may limit the power dissipation for higher

resistance values.

3.10 CAPACITORS

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A capacitor (originally known as a condenser ) is a passive two-terminal electrical

component used to store electrical energy temporarily in an electric field. The forms of practical

capacitors vary widely, but all contain at least two electrical conductors (plates) separated by

a dielectric (i.e. an insulator that can store energy by becoming polarized). The conductors can be

thin films, foils or sintered beads of metal or conductive electrolyte, etc. The non conducting

dielectric acts to increase the capacitor's charge capacity. Materials commonly used as dielectrics

include glass, ceramic, plastic film, air, vacuum, paper, mica, and oxide layers. Capacitors are

widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor,

an ideal capacitor does not dissipate energy. Instead, a capacitor stores energy in the form of

an electrostatic field between its plates.

When there is a potential difference across the conductors (e.g., when a capacitor is attached

across a battery), an electric field develops across the dielectric, causing positive charge + Q to

collect on one plate and negative charge − Q to collect on the other plate. If a battery has been

attached to a capacitor for a sufficient amount of time, no current can flow through the capacitor.

However, if a time-varying voltage is applied across the leads of the capacitor, a displacement

current can flow.

An ideal capacitor is characterized by a single constant value, its capacitance. Capacitance is

defined as the ratio of the electric charge Q on each conductor to the potential

difference V between them. The SI unit of capacitance is the farad (F), which is equal to

one coulomb per volt (1 C/V). Typical capacitance values range from about 1 pF (10 −12 F) to

about 1 mF (10 −3 F).

The larger the surface area of the "plates" (conductors) and the narrower the gap between them,

the greater the capacitance is. In practice, the dielectric between the plates passes a small amount

of leakage current and also has an electric field strength limit, known as the breakdown voltage.

The conductors and leads introduce an undesired inductance and resistance.

Capacitors are widely used in electronic circuits for blocking direct current while

allowing alternating current to pass. In analog filter networks, they smooth the output of power

supplies. In resonant circuits they tune radios to particular frequencies. In electric power

transmission systems, they stabilize voltage and power flow.

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Fig 3.10.1 Capacitors

3.11 TRANSISTORS

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A transistor is a device that regulates current or voltage flow and acts as a switch or gate for

electronic signals. Transistors consist of three layers of a semiconductor material, each capable

of carrying a current.

The transistor was invented by three scientists at the Bell Laboratories in 1947, and it rapidly

replaced the vacuum tube as an electronic signal regulator. A transistor regulates current or

voltage flow and acts as a switch or gate for electronic signals. A transistor consists of three

layers of a semiconductor material, each capable of carrying a current. A semiconductor is a

material such as germanium and silicon that conducts electricity in a "semi-enthusiastic" way. It's

somewhere between a real conductor such as copper and an insulator (like the plastic wrapped

around wires).

The semiconductor material is given special properties by a chemical process called doping. The

doping results in a material that either adds extra electrons to the material (which is then

called N-type for the extra negative charge carriers) or creates "holes" in the material's crystal

structure (which is then called P-type because it results in more positive charge carriers) . The

transistor's three-layer structure contains an N-type semiconductor layer sandwiched between P-

type layers (a PNP configuration) or a P-type layer between N-type layers (an NPN

configuration).

A small change in the current or voltage at the inner semiconductor layer (which acts as the

control electrode) produces a large, rapid change in the current passing through the entire

component. The component can thus act as a switch, opening and closing an electronic gate

many times per second. Today's computers use circuitry made with complementary metal oxide

semiconductor (CMOS) technology. CMOS uses two complementary transistors per gate (one

with N-type material; the other with P-type material). When one transistor is maintaining a logic

state, it requires almost no power.

Transistors are the basic elements in integrated circuits (IC), which consist of very large numbers

of transistors interconnected with circuitry and baked into a single silicon microchip.

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Fig 3.11.1 Transistors

3.12 RELAY

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A relay is an electrically operated switch. Many relays use an electromagnet to mechanically

operate a switch, but other operating principles are also used, such as solid-state relays. Relays

are used where it is necessary to control a circuit by a low-power signal (with complete electrical

isolation between control and controlled circuits), or where several circuits must be controlled by

one signal. The first relays were used in long distance telegraph circuits as amplifiers: they

repeated the signal coming in from one circuit and re-transmitted it on another circuit. Relays

were used extensively in telephone exchanges and early computers to perform logical operations.

Fig 3.12.1 Relay

A type of relay that can handle the high power required to directly control an electric motor or

other loads is called a contactor. Solid-state relays control power circuits with no moving parts,

instead using a semiconductor device to perform switching. Relays with calibrated operating

characteristics and sometimes multiple operating coils are used to protect electrical circuits from

overload or faults; in modern electric power systems these functions are performed by digital

instruments still called "protective relays".

Magnetic latching relays require one pulse of coil power to move their contacts in one direction,

and another, redirected pulse to move them back. Repeated pulses from the same input have no

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effect. Magnetic latching relays are useful in applications where interrupted power should not be

able to transition the contacts.

Magnetic latching relays can have either single or dual coils. On a single coil device, the relay

will operate in one direction when power is applied with one polarity, and will reset when the

polarity is reversed. On a dual coil device, when polarized voltage is applied to the reset coil the

contacts will transition. AC controlled magnetic latch relays have single coils that employ

steering diodes to differentiate between operate and reset commands.

A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core, an iron

yoke which provides a low reluctance path for magnetic flux, a movable iron armature, and one

or more sets of contacts (there are two in the relay pictured). The armature is hinged to the yoke

and mechanically linked to one or more sets of moving contacts. It is held in place by a spring so

that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition,

one of the two sets of contacts in the relay pictured is closed, and the other set is open. Other

relays may have more or fewer sets of contacts depending on their function. The relay in the

picture also has a wire connecting the armature to the yoke. This ensures continuity of the circuit

between the moving contacts on the armature, and the circuit track on the printed circuit

board (PCB) via the yoke, which is soldered to the PCB.

When an electric current is passed through the coil it generates a magnetic field that activates the

armature, and the consequent movement of the movable contact (s) either makes or breaks

(depending upon construction) a connection with a fixed contact. If the set of contacts was closed

when the relay was de-energized, then the movement opens the contacts and breaks the

connection, and vice versa if the contacts were open. When the current to the coil is switched off,

the armature is returned by a force, approximately half as strong as the magnetic force, to its

relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in

industrial motor starters. Most relays are manufactured to operate quickly. In a low-voltage

application this reduces noise; in a high voltage or current application it reduces arcing.

When the coil is energized with direct current, a diode is often placed across the coil to dissipate

the energy from the collapsing magnetic field at deactivation, which would otherwise generate

a voltage spike dangerous to semiconductor circuit components. Such diodes were not widely

used before the application of transistors as relay drivers, but soon became ubiquitous as

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early germanium transistors were easily destroyed by this surge. Some automotive relays include

a diode inside the relay case.

If the relay is driving a large, or especially a reactive load, there may be a similar problem of

surge currents around the relay output contacts. In this case a snubber circuit (a capacitor and

resistor in series) across the contacts may absorb the surge. Suitably rated capacitors and the

associated resistor are sold as a single packaged component for this commonplace use.

If the coil is designed to be energized with alternating current (AC), some method is used to split

the flux into two out-of-phase components which add together, increasing the minimum pull on

the armature during the AC cycle. Typically this is done with a small copper "shading ring"

crimped around a portion of the core that creates the delayed, out-of-phase component,[9] which

holds the contacts during the zero crossings of the control voltage.

3.13 ELECTRONIC ENERGY METER

Energy meter or watt-hour meter or is an electrical instrument that measures the amount of

electrical energy used by the consumers. Utilities is one of the electrical departments, which

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install these instruments at every place like homes, industries, organizations, commercial

buildings to charge for the electricity consumption by loads such as lights, fans, refrigerator

and other home appliances

Fig 3.13.1 Electronic energy meter

The basic unit of power is watts and it is measured by using a watt meter. One thousand watts

make one kilowatt. If one uses one kilowatt in one hour duration, one unit of energy gets

consumed. So energy meters measure the rapid voltage and currents, calculate their product and

give instantaneous power. This power is integrated over a time interval, which gives the energy

utilized over that time period.

3.13.1 Two Basic Types of Watt-Hour Meter

The energy meters are classified into two basic categories, such as:

o Electromechanical Type Induction Meter

o Electronic Energy Meter

Watt hour meters are classified into two types by taking the following factors into

considerations:

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o Types of displays analog or digital electric meter.

o Types of metering points: secondary transmission, grid, local and primary distribution.

o End applications like commercial, industrial and domestic purpose

o Technical aspects like single phases, three phases, High Tension (HT), Low Tension (LT) and

accuracy class materials.

The electricity supply connection may be either single phase or three phase depending on the

supply utilized by the domestic or commercial installations. Particularly in this article we are

going to study about the working principles of single-phase electromechanical induction type

watt- hour meter and also about three-phase electronic watt hour meter from the explanation of

two basic energy meters as described below .

3.13.2 Single Phase Electromechanical Induction Watt Hour Meter

It is a well-known and most common type of age-old watt-hour meter. It comprises a rotating

aluminum disc placed on a spindle between two electromagnets. The rotation speed of the disc is

proportional to the power, and this power is integrated by the use of gear trains and counter

mechanism. It is made of two silicon steel laminated electromagnets: shunt and series magnets.

Series magnet carries a coil which is of a few turns of thickness wire connected in series with the

line; whereas the shunt magnet carries a coil with numerous turns of thin wire connected across

the supply.

Braking magnet is a kind of permanent magnet that applies the force opposite to the normal disc

rotation to move that disc a balanced position and to stop the disc while power gets off.

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Fig 3.13.2.1 Single Phase Electromechanical Induction Energy Meter

Series magnet produces a flux which is proportional to the flowing current, and shunt magnet

produces a flux proportional to the voltage. These two fluxes lag at 90 degrees due to inductive

nature. The interface of these two fields produces eddy current in the disk, utilizing a force,

which is proportional to the product of instantaneous voltage, current and the phase-angle

between them. A braking magnet is placed over one side of the disc, which produces a break

torque on the disc by a constant field provided by using a permanent magnet. Whenever

the braking and driving torques become equal, the speed of the disc becomes steady.

A Shaft or vertical spindle of the aluminum disc is associated with the gear arrangement that

records a number proportional to the revolutions of the disc. This gear arrangement sets the

number in a series of dials and indicates energy consumed over a time.

This type of energy meter is simple in construction and the accuracy is somewhat less due to

creeping and other external fields. A foremost problem with these types of energy meters is their

proneness to tampering, which necessitate an electrical-energy-monitoring system. These series

and shunt type meters are widely used in domestic and industrial applications.

Electronic energy meters are accurate, precise and reliable type of measuring instruments when

compared to electromechanical induction type meters. When connected to loads, they consume

less power and start measuring instantaneous. So, electronic type of three phase energy meter is

explained below with its working principle.

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3.13.3 3-Phase Electronic Watt Hour Meter

This meter is able to perform current, voltage and power measurements in three phase supply

systems. By using these three phase meters, it is also possible to measure high voltages and

currents by using appropriate transducers. One of the types of three phase energy meters is

shown below (given as an example) that ensures reliable and accurate energy measurement

compared to the electromechanical meters.

Fig 3.13.3.1 Three Phase Watt Hour Meter

It uses AD7755, a single-phase energy measurement IC to acquire and process the input voltage

and current parameters. The voltage and currents of the power line are rated down to signal level

using transducers like voltage and current transformers and given to that IC as shown in figure.

These signals are sampled and converted into digital, multiplied by one another to get the

instantaneous power. Later these digital outputs are converted to frequency to drive an

electromechanical counter. The frequency rate of the output pulse is proportional to the

instantaneous power, and (in a given interval) it gives energy transfers to the load for a particular

number of pulses.

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The microcontroller accepts the inputs from all the three energy measurement ICs for three phase

energy measurement and serves as the brain of the system by performing all the necessary

operations like: storing and retrieving data from EEPROM, operating the meter using buttons to

view energy consumption, calibrating phases and clearing readings; and, it also drives the

display using decoder IC .

Till now we have read about the energy meters and their working principles. For a deeper

understanding of this concept, the following description about the watt hour meter gives

complete circuit details and its connections using a microcontroller.

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3.14 LIGHT DEPENDENT RESISTOR

A Light Dependent Resistor (LDR) or a photo resistor is a device whose resistivity is a function

of the incident electromagnetic radiation. Hence, they are light sensitive devices. They are also

called as photo conductors, photo conductive cells or simply photocells. They are made up of

semiconductor materials having high resistance. There are many different symbols used to

indicate a LDR, one of the most commonly used symbol is shown in the figure below. The arrow

indicates light falling on it.

Fig3.14.1 Representation of LDR

3.14.1 Working Principle of LDR

A light dependent resistor works on the principle of photo conductivity. Photo conductivity is

an optical phenomenon in which the materials conductivity is increased when light is absorbed

by the material. When light falls i.e. when the photons fall on the device, the electrons in the

valence band of the semiconductor material are excited to the conduction band. These photons in

the incident light should have energy greater than the band gap of the semiconductor material to

make the electrons jump from the valence band to the conduction band. Hence when light having

enough energy strikes on the device, more and more electrons are excited to the conduction band

which results in large number of charge carriers. The result of this process is more and more

current starts flowing through the device when the circuit is closed and hence it is said that the

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resistance of the device has been decreased. This is the most common working principle of

LDR

3.14.2 Characteristics of LDR

LDR’s are light dependent devices whose resistance is decreased when light falls on them and

that is increased in the dark. When a light dependent resistor is kept in dark, its resistance is

very high. This resistance is called as dark resistance. It can be as high as 1012 Ω and if the device

is allowed to absorb light its resistance will be decreased drastically. If a constant voltage is

applied to it and intensity of light is increased the current starts increasing. Figure below shows

resistance vs. illumination curve for a particular LDR.

Fig 3.14.2.1 Characteristics curve for LDR

Photocells or LDR’s are non linear devices. There sensitivity varies with the wavelength of light

incident on them. Some photocells might not at all response to a certain range of wavelengths.

Based on the material used different cells have different spectral response curves. When light is

incident on a photocell it usually takes about 8 to 12ms for the change in resistance to take place,

while it takes one or more seconds for the resistance to rise back again to its initial value after

removal of light. This phenomenon is called as resistance recovery rate. This property is used in

audio compressors. Also, LDR’s are less sensitive than photo diodes and photo transistor. (A

photo diode and a photocell (LDR) are not the same, a photo-diode is a p-n junction

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semiconductor device that converts light to electricity, whereas a photocell is a passive device,

there is no p-n junction in this nor it “converts” light to electricity). Types of Light Dependent

Resistors: Based on the materials used they are classified as: i) Intrinsic photo resistors (Un

doped semiconductor): These are made of pure semiconductor materials such as silicon or

germanium. Electrons get excited from valance band to conduction band when photons of

enough energy fall on it and number charge carriers is increased. ii) Extrinsic photo resistors:

These are semiconductor materials doped with impurities which are called as dopants. These

dopants create new energy bands above the valence band which are filled with electrons. Hence

this reduces the band gap and less energy is required in exciting them. Extrinsic photo resistors

are generally used for long wavelengths.

3.14.3 Construction of a Photocell

The structure of a light dependent resistor consists of a light sensitive material which is deposited

on an insulating substrate such as ceramic. The material is deposited in zigzag pattern in order to

obtain the desired resistance & power rating. This zigzag area separates the metal deposited areas

into two regions. Then the ohmic contacts are made on the either sides of the area. The

resistances of these contacts should be as less as possible to make sure that the resistance mainly

changes due to the effect of light only. Materials normally used are cadmium sulphide , cadmium

selenide, indium antimonide and cadmium sulphonide. The use of lead and cadmium is avoided

as they are harmful to the environment.

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3.14.4 Applications of LDR

LDR’s have low cost and simple structure. They are often used as light sensors. They are used

when there is a need to detect absences or presences of light like in a camera light meter. Used in

street lamps, alarm clock, burglar alarm circuits, light intensity meters, for counting the packages

moving on a conveyor belt, etc.

Fig 3.14.4.1 LDR

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3.15 VOLTAGE REGULATOR (7805)

The 78xx (sometimes L78xx, LM78xx, MC78xx….) is a family of self-contained fixed linear

voltage regulator integrated circuits. The 78xx family is commonly used in electronic circuits

requiring a regulated power supply due to their ease-of-use and low cost. For ICs within the

family, the xx is replaced with two digits, indicating the output voltage (for example, the 7805

has a 5 volt output, while the 7812 produces 12 volts). The 78xx line are positive voltage

regulators, they produce a voltage that a positive relative to a common ground. There is a related

line of 79xx devices which are complementary negative voltage regulators. 78xx and 79xx ICs

can be used in combination to provide positive and negative supply voltages in the same circuit.

Fig 3.15.1 Pin out of 7805 Regulator

3.15.1 Advantages

78xx series ICs do not require additional components to provide a constant, regulated source of

power, making them easy to use, as well as economical and efficient uses of space. Other voltage

regulators may require additional components to set the output voltage level, or to assist in the

regulation process. Some other designs (such as a switched-mode power supply) may need

substantial engineering expertise to implement.

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3.15.2 Disadvantage

The input voltage must always be higher than the output voltage by some minimum amount

(typically 2.5 volts). This can make these devices unsuitable for powering some devices from

certain types of power sources(for example, powering a circuit that requires 5 volts using 6 volts

batteries will not work using a 7805)

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CHAPTER 4

WORKING

4.1 TRANSMITTER SECTION

Fig 4.1.1 Block diagram for Transmitting section

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ENERGY

METER

RF TRANSMITTER

LCD DISPLAY

ARDUINO UNO-ATMEGA 328 INTERFACED BOARD

4.2 RECEIVER SECTION

Fig 4.2.1 Block Diagram for Receiver Section

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RF RECIEVER

ARDUINO UNO- ATMEGA328 INTERFACED BOARD

LCD DISPLAY

CHAPTER 5

CIRCUIT DIAGRAM

5.1 TRANSMITTER SECTION

Fig 5.1.1 Circuit diagram for Transmitter Section

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5.1.1 Description

The transmitter section consists of a RF Transmitting module, an energy meter, a LCD display

and an Arduino UNO board. The Arduino UNO board used here is a base for the

microcontroller, ATmega 328.

The energy meter pulse is taken out by using a LDR and is given as an input to the 10 th pin of an

encoder IC HT12E. (10-13) pins are called DATA pins, in which the input data can be given to

any one of these four pins. The pin from 1 to 9 in HT12E IC is grounded, where 1 to 8 pins are

called ADDRESS pins.

The 15th and 16th pin is shorted by a 750kΩ resistance. So we connect one 680kΩ, three 22kΩ

and three 1kΩ resistors in series to obtain a resistance value of 750kΩ. The Vcc(5V) is given to

the encoder IC through the 18th pin. The output of the encoder IC will be a signal which is

modulated as well as encoded in the proper way for transmission.

The output from the IC HT12E is given to the DATA pin of the RF Transmitter module. The RF

Transmitter module consists of 4 pins in total, a GND pin, a DATA pin, a Vcc pin and an ANT

(antenna). The GND pin is grounded and a 5V is fed to the Vcc pin. The other fourth pin will

acts as an antenna.

The transmitter section here is the consumer’s house. So inorder to display the meter reading and

cost of consumption , a part of the output from the IC HT12E is taken out and given to an

Arduino UNO board.

An Arduino UNO board is a platform which comprises of the microcontroller ATmega 328,

programmer, reset pin and various other controllers which is used to operate the UNO board. The

program for what to display and how to display in the LCD is given to the microcontroller

(ATmega 328) which is inbuilt within the UNO board.

The program used here is the C programming which has been buildup using a programmer called

Arduino Software. The C program is installed into the microcontroller within the Arduino board

which consists of a programmer along with the board to convert the given C language to the

controller’s language. According to the command given, the Arduino board sends signal to the

LCD to display the rate and cost of consumption to the consumer.

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5.2 RECEIVER SECTION

Fig 5.2.1 Circuit diagram for Receiver Section

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5.2.1 Description

The Receiver section consists of a RF Receiver module, IC HT12D decoder, an Arduino UNO

board and a LCD. The transmitted data from the transmitter section is received in the receiver

section through an antenna. The RF Receiver module present here has 8 pins, in which 3 are

GND, 2 pins are DATA and one is ANT (antenna). The output is taken out from the DATA pin

and it is given to the decoder IC HT12D.

HT12D is the decoder IC. It has 18 pins in total, in which (1-8)pins are called the ADDRESS

pins, (10-13) are DATA pins, 14th pin is the DATAIN (DIN) pin, 15 and 16th pins are shorted

with a resistance off 33kΩ and 18th pin is the Vcc. The pins from 1 to 9 are grounded.

Now the 14th pin of IC HT12D will input the data from the RF Receiver module. The decoder

will decodes and unmodulate the signals received. These unmodulated signals are taken out

through the 17th pin to the Arduino UNO board.

The Arduino UNO board will receives the data (signal) from the decoder IC and displays the rate

and units consumed by the consumer in the LCD as explained in the transmitter section.

The hand held device as well as the LCD is placed in the Electricity Department (KSEB). So that

the authority could analyze the consumption and rate of consumption of each and every

consumer without any error in less time.

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CHAPTER 6

PROGRAMMING CODE

#include <LiquidCrystal.h>

LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

#include <SoftwareSerial.h>

#define LCDtxPin 2

SoftwareSerial LCD = SoftwareSerial(2,LCDtxPin);

const int buttonPin = 7;

int buttonPushCounter = 0;

int buttonState = 0;

int lastButtonState = 0;

float rate = 0;

float rate1 = 0;

float unit=0;

float unit1=0;

int buttonState1 = 0;

void setup()

LCD.begin(9600);

lcd.begin(16, 2);

pinMode(LCDtxPin, OUTPUT);

pinMode(buttonPin, INPUT);

Serial.begin(9600);

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void loop()

buttonState = digitalRead(buttonPin);

if (buttonState != lastButtonState)

if (buttonState == HIGH )

buttonPushCounter++;

Serial.println("on");

Serial.print("number of button pushes: ");

Serial.println(buttonPushCounter);

else

Serial.println("off");

delay(50);

unit=buttonPushCounter*1;

unit1=unit/1000;

rate=buttonPushCounter*7;

rate1=rate/1000;

Serial.println("rate");

Serial.println(rate1);

Serial.println("unit");

Serial.println(unit1);

lcd.setCursor(0, 0);

lcd.print("YOUR CONSUMPTION");

delay(50);

lcd.setCursor(0, 4);

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lcd.print("Rs:");

lcd.print(rate1);

lcd.print("UNIT:");

lcd.print(unit1);

delay(50);

lastButtonState = buttonState;

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CHAPTER 7

APPLICATIONS

The wireless energy meter design in this project could find application in every state distribution company for reading energy consumption. It can also be extended for metering and monitoring other utility commodities, such as internet access, wireless drinking water consumption reading etc.

5.1 ADVANTAGES

Accurate meter reading, no more estimates Improved billing Accurate profile classes and measurement classes, true cost applied Improved security and tamper detection for equipment Energy management through profile data graphs Less financial burden correcting mistakes Less accrued expenditure

5.2 DISADVANTAGES

Cause malfunction due to interference with other RF devices Higher electrical power drive.

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CHAPTER 8FUTURE SCOPE

The Wireless energy meter for India has the potential to change the future of the energy

billing system. It could help the energy distribution companies reduce cost and increase

profits, improve billing accuracy and efficiency, and contribute to the energy

sustainability! The wireless energy meter reading method used here can be replaced with

GSM modems and can be extended to make the energy billing system more widespread

and make it one system for the entire state.

The mode of payment by the consumers can be extended to credit cards, internet based

payments, ATM centers etc. This makes the wireless energy meter system simpler and

eliminating the need for customers to go to the recharge centers allowing the user

anytime recharge.

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CHAPTER 9

ESTIMATION AND COSTING

COMPONENTS RANGE QUANTITY PRICE (RS)

ARUINO UNO

BOARD

- 2 1800

ADAPTER FOR

UNO BOARD- 2 400

LCD DISPLAY 16 Chr X 2 Line 2 500

TRANSFORMER 12-0-12V\1A 1 200

TRANSISTOR BC549 2 50

RESISTOR 680KΩ 1 25

RESISTOR 22KΩ 3 30

RESISTOR 33KΩ 1 15

RESISTOR 1KΩ 3 15

CAPACITOR 1000µF 1 10

RELAY 12V 1 75

LDR - 1 20

ENERGY METER - 1 850

PCB BOARD - 2 40

ENERGY METER

BOARD

- 1 100

2PIN AC CHORD - 1 125

BRIDGE

RECTIFIER

- 1 40

RF TRANCEIVER

MODULE

434MHz 1 475

18 PIN IC HT12E - 1 25

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18 PIN IC HT12D - 1 25

7805 VOLTAGE

REGULATOR

- 1 15

COMPONENTS COST 5000

TRAVELLING EXPENCES 2500

PROGRAMMING STUDY 7000

TOTAL 14,500

Tab 9.1 Estimation and costing

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CHAPTER 10

CONCLUSION

The present system is used for meter reading for electricity using RF Communication.

The system can be further modified to detect power theft between pole and individual

subscribers by installing the units at each subscriber end. For the readings of electricity

meters in the consumer premises to be transmitted to a central base station for further

processing billing etc. With tens of millions of meters to be read periodically and

regularly, this alone represents an enormous market. The cost of one system is on higher

side but if more number of systems are produced, and then the cost of mass production

will get reduced. The present system is implemented to send non voice data only. The

system can be further developed to transfer voice data through RF. But the system should

be robust enough to handle interference in the RF.

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CHAPTER 11

BIBILIOGRAPHY

1. Loss. P.V.A, Lamego.M.M and Vieira.J.L.F,1998. A single phase microcontroller

based energy meter, IEEE Instrumentation and Measurements

2.Saptarshi De, Rahul Anand, A Naveen and Sirat Moinuddin, 2003. E-Metering Solution

for checking energy thefts and stearmlining revenue collection in INDIA,IEEE

3. Krzysztof Iniewski,2008. Wireless Technologies, CRC Press.

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