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INTRODUCTION
Electronic Toll Collection is a generally mature technology that allows for electronic
payment of highway tolls. It takes advantage of vehicle-to-roadside communication
technologies to perform an electronic monetary transaction between a vehicle passing
through a toll station and the toll agency. This project is implemented using the
innovative technology of Radio Frequency Identification (RFID). Radio-frequency
identification (RFID) is a technology that uses communication via electromagnetic
waves to exchange data between a terminal and an electronic tag attached to an
object, for the purpose of identification and tracking.
An RFID system consists of a reader and transponders. Transponders (derived from
the words "transmitter" and "responder") are attached to the items to be identified.
They are often called "tags". Radio Frequency Identification (RFID) involves contact
less reading and writing of data into an RFID tag's non-volatile memory through an
RF signal. The reader emits an RF signal and data is exchanged when the tag comes
in proximity to the reader signal. The RFID tag derives its power from the RF reader
signal and does not require a battery or external power source.
Each vehicle will be provided with an RFID tag. This transponder (tag) stores the
unique ID of the vehicle and related information. When interrogated by a reader, it
responds with that data over a radio frequency link. The readers are fixed in the toll
gates. So when the vehicle comes near the reader, the data from the tags can be easily
read by the readers.
This data is passed to the computer and thus the cash can be
deducted from the user’s account.
Here, in toll system RFID tags are attached to the vehicles .This application requires
both the server and client system.The client system reads the tag value from the reader
and pass it to the server for further processing .when the vehicles are passed through
the toll booth ,the RFID reader situated in booth reads the data(vehicle ID) transmitted
by the tag. Using this vehicle ID client retrives the credit card ID from the server .then
the amount will reduce from the owner’s bank account using the credit card ID.
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RFID SYSTEM
RFID is a wireless link to uniquely identify tags. These systems communicate via
radio signals that carry data either unidirectional or bidirectional. The tag is energized
by a time-varying electromagnetic radio frequency (RF) wave that is transmitted by
the reader. This RF signal is called carrier signal. When tag is energized the
information stored in the tag is transmitted back to the reader. This is often called
backscattering. By detecting the backscattering signal, the information stored in the
tag can be fully identified. RFID systems are comprised of two main components RF
reader and RF Tag.
RFID TAG
The RFID tag, or transponder, is located on the object to be identified and is the data
carrier in the RFID system. Typical transponders (transmitters/responders) consist of
a microchip that stores data and a coupling element, such as a coiled antenna, used to
communicate via radio frequency communication. Transponders may be either active
or passive.
Active transponders have an on-tag power supply (such as a battery) and actively send
an RF signal for communication while passive transponders obtain all of their power
from the interrogation signal of the transceiver and either reflect or load modulate the
transceiver’s signal for communication. Most transponders, both passive and active,
communicate only when they are interrogated by a transceiver.
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Active RFID and Passive RFID are fundamentally different technologies. While both
use radio frequency energy to communicate between a tag and a reader, the method of
powering the tags is different. Active RFID uses an internal power source (battery)
within the tag to continuously power the tag and its RF communication circuitry,
whereas Passive RFID relies on RF energy transferred from the reader to the tag to
power the tag. While this distinction may seem minor on the surface, its impact on the
functionality of the system is significant.
Passive RFID either 1) reflects energy from reader or 2) absorbs and temporarily
stores a very small amount of energy from the reader’s signal to generate its own
quick response. In either case passive RFID operation requires very strong signals
from the reader and the signal strength required from the tag is constrained to very
low levels by the limited energy.
Antenna sealed with RFID tag
On the other hand active RFID allows very low level signals to be received by the tag,
and the tag can generate high level signals back to the reader, driven from its internal
power source. Active RFID tag is continuously powered, whether in the reader field
or not.
In the following table the main difference between active and passive are highlighted.
Differences of active and passive tag
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The selection of active or passive tag affect factors like range of communication, data
storage capacity ,sensor ability etc. If the tag is active the reader can spot more tags
within seconds than the passive tag, but as the cost is compared the passive tags are
cheaper than the active tags. The life of the passive tags are more than the active tag
because , active tag requires tag power supply within the chip.
The different frequencies that the tag can work are;
Low frequency (LF) - These tags work at a frequency of around 125 kHz and have a
reading range of less than 50 cm. The reading speed is relatively low and the tags are
relatively insensitive to interference. This band enjoys relative freedom from
regulatory limitations because it has not been reserved as an ISM frequency range,
although in this frequency interval other systems operate typically for aeronautical
and marine navigational services. Tags in this frequency range have been using now
in applications such as access control and animal tracking.
High frequency (HF) - Operate worldwide at 13.56 MHz and can be read at distances
of around one meter, but tags use more energy than low frequency tags. Existing uses
include tracking books in libraries and baggage at airports. At around 13.56MHz,
electromagnetic fields can propagate through water and tissue but cannot penetrate
metals. Antennas are made simply of turns of coils of small radius.
Ultra-High frequency (UHF)- These tags work at a range between 433 and 2000 MHz
and can be read from further away and at higher speed than HF tags. This makes this
frequency the most appropriate for supply chain applications, such as tracking pallets
and cases.
Characteristics of Different Frequencies
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RF READER
The interrogator consists of a reader and data processing subsystem. The RFID
reader, or transceiver, which may be able to both read data from and write data to a
transponder. The data processing subsystem which utilizes the data obtained from the
transceiver in some useful manner.
Typical transceivers (transmitter/receivers), or RFID readers, consist of a radio
frequency module, a control unit, and a coupling element to interrogate electronic tags
via radio frequency communication. In addition, many transceivers are fitted with an
interface that enables them to communicate their received data to a data processing
subsystem, e.g., a database running on a personal computer. The use of radio
frequencies for communication with transponders allows RFID readers to read passive
RFID tags at small to medium distances and active RFID tags at small to large
distances even when the tags are located in a hostile environment and are obscured
from view. The figure shows handheld and stationary reader modules.
A typical RFID reader
The basic components of an RFID system combine in essentially the same manner for
all applications and variations of RFID systems. All objects to be identified are
physically tagged with transponders. The type of tag used and the data stored on the
tag varies from application to application.
The RF field generated by a tag reader (the energy transmitter) has three purposes:
1. Induce enough power into the tag coil to energize the tag:
2. Provide a synchronized clock source to the tag:
3. Act as a carrier for return data from the tag:
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SYSTEM HANDSHAKE
Typical handshake of a tag and reader is as follows:
READ ONLY TAG
1. The reader continuously generates an RF carrier sine wave, watching always for
modulation to occur. Detected modulation of the field would indicate the presence of
a tag.
2. A tag enters the RF field generated by the reader. Once the tag has received
sufficient energy to operate correctly, it divides down the carrier and begins clocking
its data to an output transistor, which is normally connected across the coil inputs.
3. The tag’s output transistor shunts the coil, sequentially corresponding to the data
which is being clocked out of the memory array.
4. Shunting the coil causes a momentary fluctuation (dampening) of the carrier wave,
which is seen as a slight change in amplitude of the carrier.
5. The reader peak-detects the amplitude-modulated data and processes the resulting
bit stream according to the encoding and data modulation methods used.
READ AND WRITE TAG
1. The interrogator sends a command to initiate communication with tags in the fields.
This command signal is also used for energizing the passive device.
2. Once the tag has received sufficient energy and command, it responses back with
its ID for acknowledgment.
3. The interrogator now knows which tag is in the field. The interrogator sends a
command to the identified tag for what to do next: processing (read or write) or sleep.
4. If the tag receives processing and reading commands, it transmits a specified block
data and waits for the next command.
5. If the tag receives processing and writing commands along with block data, it
writes the block data into the specified memory block, and transmits the written block
data for verification.
6. After the processing, the interrogator sends an “end” command to send the tag into
the sleep (“silent”) mode.
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7. If the device receives “end” command after processing, it sends an
acknowledgement (8-bit preamble) and stays in sleep mode. During the sleep mode,
the device remains in non-modulating (detuned) condition as long as it remains in the
power-up. This time the handshake is over.
8. The interrogator is now looking for the next tag for processing, establishes a
handshake and repeats the processing.
READER –TAG COUPLING AND COMMUNICATION
Passive RFID tags obtain their operating power from the electromagnetic field of the
reader’s communication signal. The limited resources of a passive tag require it to
both harvest its energy and communicate with a reader within a narrow frequency
band as permitted by regulatory agencies. Passive tags typically obtain their power
from the communication signal either through inductive coupling or far field energy
harvesting.
Inductive coupling uses the magnetic field generated by the communication signal to
induce a current in its coupling element (usually a coiled antenna and a capacitor).
The current induced in the coupling element charges the on-tag capacitor that
provides the operating voltage, and power, for the tag. In this way, inductively
coupled systems behave much like loosely coupled transformers. Consequently,
inductive coupling works only in the near-field of the communication signal. For a
given tag, the operating voltage obtained at a distance d from the reader is directly
proportional to the flux density at that distance.
There is a fundamental limitation on the power detected a distance d away from a
reader antenna. In a loss less medium, the power transmitted by the reader decreases
as a function of the inverse square of the distance from the reader antenna in the far
field. A reader communicates with and powers a passive tag using the same signal.
The fact that the same signal is used to transmit power and communicate data creates
some challenging trade-offs.
First, any modulation of the signal causes a reduction in power to the tag. Second,
modulating information onto an otherwise spectrally pure sinusoid spreads the signal
in the frequency domain. This spread, referred to as a “side band,” along with the
maximum power transmitted at any frequency, is regulated by local government
bodies in most parts of the world. These regulations limit the rate of information that
can be sent from the reader to the tag. RFID systems usually operate in free bands
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known as Industrial- Scientific-Medical (ISM) bands, where the emitted power levels
and the side band limits tend to be especially stringent.
The signalling from the tag to the reader in passive RFID systems is not achieved by
active transmission. Since passive tags do not actively transmit a signal, they do not
have a regulated limit on the rate of information that can be sent from the passive tag
to the reader. In the near field, tag to reader communication is achieved via load
modulation. Load modulation is achieved by modulating the impedance of the tag as
seen by the reader. In the far field, tag to reader communication is achieved via
backscatter. Backscatter is achieved by modulating the radar cross-section of the tag
antenna.
There are many devices that rely upon reflection of signals - a technique known as
"backscatter" coupling. Backscatter coupling is a term used to describe a technique
that is slightly different from the inductive method (load modulation) mentioned
above. To understand how this works it is helpful to consider, say a red object. A red
object appears red because it absorbs all visible light frequencies except that of red
light, which it reflects. A similar effect can be observed in the non-visible EM
spectrum. By modulating the frequencies reflected back from an object, a similar
effect to that obtained with inductive coupling can be achieved. Inductive coupling is
perhaps the simplest since it is essentially the means by which transformers work.
ANTENNA AND READ RANGE
In a Radio Frequency Identification (RFID) application, an antenna coil is needed for
two main reasons:
• To transmit the RF carrier signal to power up the tag
• To receive data signals from the tag
An RF signal can be radiated effectively, if the linear dimension of the antenna
is comparable with the wavelength of the operating frequency. In an RFID application
utilizing the VLF (100 kHz – 500 kHz) band, the wavelength of the operating
frequency is a few kilometers (l = 2.4 Km for 125 kHz signal). Because of its long
wavelength, a true antenna can never be formed in a limited space of the device.
Alternatively, a small loop antenna coil that is resonating at the frequency of the
interest (i.e., 125 kHz) is used. This type of antenna utilizes near field magnetic
induction coupling between transmitting and receiving antenna coils. The field
produced by the small dipole loop antenna is not a propagating wave, but rather an
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attenuating wave. The field strength falls off with r-3 (where r = distance from the
antenna). This near field behaviour (r-3) is a main limiting factor of the read range in
RFID applications. When the time-varying magnetic field is passing through a coil
(antenna), it induces a voltage across the coil terminal. This voltage is utilized to
activate the passive tag device. The antenna coil must be designed to maximize this
induced voltage.
Read/write range is a communication distance between the reader (Interrogator)
and tag. Specifically, the read range is a maximum distance to read data out from the
tag and write range is a maximum distance to write data from interrogator to tag.
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BLOCK DIAGRAM
:
BLOCK DIAGRAM OF SYSTEM
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BLOCK DIAGRAM EXPLANATION
The block diagram consists of the following parts.





MICROCONTROLER
RFID READER
RFID TAG
ANTENNA
LCD
 BUZZER
 POWER SUPPLY
PIC MICROCONTROLLER
The pic16f877A is a low power, high performance CMOS 8-bit microcomputer with
8k*14 words of flash program memory. It has RISC CPU with eight level deep
hardware stack. PIC is a powerful microcomputer which provides a highly flexible
and cost effective solution to many embedded control application.
RFID READER
The RFID reader consists of transmitting and receiving sections. It transmits a carrier
signal, receives the backscattering signal, and performs data processing. The reader
also communicates with an external host computer.
RFID TAG
The RFID tag, or transponder, is located on the object to be identified and is the data
carrier in the RFID system. Typical transponders (transmitters/responders) consist of
a microchip that stores data and a coupling element, such as a coiled antenna, used to
communicate via radio frequency communication.Here a read only tag(TK5530) is
used as data carrier.
ANTENNA
The reader circuit uses a single coil for both transmitting and receiving signals. An
antenna coil and a resonant capacitor forms a series resonant circuit for a 125khz
resonanance frequency. The circuit provides a minimum impedance at the resonance
frequency.This resulting maximizing the antenna current ,and therefore, the magnetic
field strength is maximized.
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LCD
The LCD module, which is connected to the microcontroller. The interface is through
the two ports. The port D is used to give data to display. Three pins of the port C are
used to give commands to the LCD.
BUZZER
Another interface to the circuit is the buzzer. When the data received is valid the
microcontroller gives logic high to the pin 8(RE0).It is connected to the base of
transistor BC 547 through a resistor of 4.7 K. so when the pin becomes high the
buzzer turns on and makes sound. The collector of bc547 is connected to 5v supply
and working in the switching mode.
POWER SUPPLY
The power supply section for the reader can be explained as two distinct
sections. One is external, considering as an adaptor module designed to work the
reader in the ac supply. Another is built in the reader board itself. The external power
supply section contains a step-down transformer for stepping down 230volt ac to
9volt.then it is passed through the full wave rectifier. The rectified signal is applied
between the capacitor to reduce ripples. The dc voltage generated will be 11-12volt.
Reader board is designed to connect to dc voltage 10-18 volts. The incoming voltage
is given as input to a 9 V voltage regulator, LM7809 (U4). To reduce the ripples one
capacitor is connected in the input line of voltage regulator and one at the output line
as specified in the datasheet of LM78XX. The regulated 9v is given to anther
regulator which is LM7805 (U3). The 5V dc is used for microcontroller and other IC
modules. 9V is for amplifier sections.
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READER BLOCK DIAGRAM
Block Diagram of Reader
The RFID reader consists of transmitting and receiving sections. It transmits a
carrier signal, receives the backscattering signal, and performs data processing. The
reader also communicates with an external host computer.
The transmitting section contains circuitry for a carrier signal (125 kHz), power
amplifiers, and a tuned antenna coil. The time base signal generator consists of a 4
MHz crystal. The 125 kHz carrier signal is typically generated by dividing a 4 MHz
(4 MHz/32 = 125 kHz) crystal oscillator signal. The signal is amplified before it is fed
into the antenna tuning circuit. A complementary power amplifier circuit is typically
used to boost the transmitting signal level. The amplified signal is passed through the
antenna section. An antenna impedance tuning circuit consisting of capacitors is used
to maximize the signal level at the carrier frequency.
The receiving section consists of an antenna coil, demodulator, filters,
amplifiers, and microcontroller. In applications for close proximity read range, a
single coil is often used for both transmitting and receiving. For long read-range
applications, however, separated Antennas may be used. In the ASK communication
protocol, a ‘0’ and a ‘1’ are represented by an amplitude status of receiving signal.
The demodulation of the ASK signal is accomplished by detecting the
envelope of the carrier signal. A half wave capacitor-filtered rectifier circuit is used
for the demodulation process. The peak voltage of the back-scattering signal is
detected by a diode, and this voltage is then fed into an RC charging/discharging
circuit. The RC time constant must be small enough to allow the voltage across C to
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fall fast enough to keep in step with the envelope. However, the time constant must
not be so small as to introduce excessive ripple.
The demodulated signal must then pass through a filter and signal shaping circuit
before it is fed to the microcontroller. The microcontroller performs data decoding
and communicates with the host computer through an RS-232 or other serial interface.
THE MICROCONTROLLER (PIC16F877)
The core of the reader is PIC16f877a. It has the name “Peripheral Interface
Controller”. The PIC uses the Harvard architecture. The 16F87X series micro
controller contains flash memory. It is an 8 bit 40 pin microcontroler. It has five
biderectional IO ports (A,B,C,D & E). PortA has 6 pins , Port B,C & D has 8 pins and
PortE has 3 pins. PIC16F877 has a high performance RISC CPU. Only 35 single
word instructions are there for the programing.
In our system the microcontroller receives the demodulated tag data. It then processes
the data and makes it in the user understandable manner. The following block diagram
gives the details about the user interfaces to the microcontrollers.
LCD
DISPLAY
BUZZER
PIC
16F877
MAX 232
DB9
Incoming
bit
stream
PC
INTERFACE
Microcontroller and Interfaces
1.BUZZER
It is a piezoelectric device which produces an audible beep. When a valid tag
is acknowledged it gets activated. The goal of buzzer is to capture the attention of the
user when tag is being received.
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2. LIQUID CRYSTAL DISPLAY
LCD is a module used for displaying the tag data that the reader recognizes.
The LCD has its own controller IC, RAM and ROM. To display objects in the LCD
the controller IC is to be programmed. The data to display is stored in the RAM of
LCD module. The contrast of display can be adjusted by a potentiometer. Once an
object is displayed, it remains there until display is cleared or it is overwritten.
3. MAX 232
It is serial interface controller IC. The USART in the PIC send the serial data via this
device. This device receives the data, buffers it and sends the data to COM port of PC
through DB9 connector.
BLOCK DIAGRAM OF TAG
Block Diagram of Tag
The tag is powered by rectifying an incoming RF signal from the reader. The tag
requires an external LC resonant circuit to receive the incoming RF signal and to send
data. In the case of passive tag, it develops a sufficient DC voltage for operation when
its external coil voltage reaches a predefined threshold level (approximately 10 VPP).
The tag has a user programmable memory. The user can manually program the user
memory.
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The tag has a modulation transistor between the two antenna connections (VA and
VB). The modulation transistor damps or undamps the coil voltage when it sends
data. The variation of coil voltage controlled by the modulation transistor results in a
perturbation of voltage in reader antenna coil. By monitoring the changes in reader
coil voltage, the data transmitted from the device can be reconstructed. The RF frontend of the tag includes circuits for rectification of the carrier, VDD (operating
voltage) and high-voltage clamping. This section also includes a clock generator and
modulation circuit.
The rectifier circuit rectifies RF voltage on the external LC antenna circuit. Any
excessive voltage on the tuned circuit is clamped down by the internal circuitry to a
safe level to prevent damage to the IC.The clock generator circuit generates a clock
based on the carrier frequency from the reader. This clock is used to derive all timing
in the device, including the baud rate and modulation rate (if any modulation present).
The device sends the encoded data to the reader by AM-modulating the coil voltage
across the tuned LC circuit. The transistor placed between the two antenna coil pads;
turns on and off based on the modulation signal. As a result, the amplitude of the
antenna coil voltage varies with the modulation signal.
Modulation in the tag
The user program memory contains the program for specific application. The program
contains the method of modulation and encoding details. The modulation transistor is
external to the chip. The microcontroller outs the data bits in serial mode through one
of its output pins. The output pin directly connected to the base of the modulating
transistor. As the data bit is one the transistor turns on and the parallel resonant circuit
damps and when data bit zero the transistor is off and circuit undamps. The
microcontroller outs the data bits with correct delay timings.
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Diagram of TK5530
The TK 5530 is a complete transponder, which implements all important functions for
immobilizer and identification systems. It consists of a plastic cube which
accommodates the read only identification integral circuit (IDIC) e5530 and the
antenna is realised by LC circuit. The identifying data are stored in a 128 bit PROM
on the e5530, realized as an array of laser -programmable fuses. The data are sent as
bit – serially as a code.
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CIRCUIT DIAGRAM
CIRCUIT DIAGRAM OF READER
CIRCUIT DESCRIPTION
POWER SUPPLY SECTION
The power supply section for the reader can be explained as two distinct sections.
One is external, considering as an adaptor module designed to work the reader in the
ac supply. Another is built in the reader board itself.
The external power supply section contains a step-down transformer for stepping
down 230volt ac to 12 volt. Then it is passed through the full wave rectifier. The
rectified signal is applied between the capacitor to reduce ripples. The dc voltage
generated will be 11-12volt.
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Reader board is designed to connect to dc voltage 10-18volts. The incoming
voltage is given as input to a 9 V voltage regulator, LM7809 (U4). To reduce the
ripples one capacitor is connected in the input line of voltage regulator and one at the
output line as specified in the datasheet of LM78XX. The 12V supply is given to
another regulator which is LM7805 (U3). The 5V dc is used for microcontroller and
other IC modules. 9V is for amplifier sections.
TIME BASE GENERATOR SECTION
The crystal oscillator generates 4MHz frequency. This frequency is applied to
external clock source input of the microcontroller. The RC2 of port C generates PWM
signal output of 125 KHz. The frequency is divide by 32 of input frequency. The 125
KHz square wave generated is passed through 74HC04 for impedance matching (act
as buffer). The square wave is given to the RLC series resonant circuit. it is resonating
at 125 KHz. the sinusoidal signal thus produced is given to the preamplifier formed
by 2N2907.
POWER AMPLIFIER
The preamplifier output signal is given to the complimentary symmetry class B
amplifier. The transistor 2N2222 which is NPN and 2N2907 which is PNP forms the
complimentary pairs. The amplifier has unity gain. The output of the amplifier is
connected to the series resonant circuit.
ANTENNA SECTION
The reader circuit uses a single coil for both transmitting and receiving signals. An
antenna coil (L1 1.62 mH) and a resonant capacitor (C19, 1000 pF) forms a series
resonant circuit for a 125 kHz resonance frequency. Since the C19 is grounded, the
carrier signal (125 kHz) is filtered out to ground after passing the antenna coil. The
circuit provides minimum impedance at the resonance frequency. This result in
maximizing the antenna current, and therefore, the magnetic field strength is
maximized.
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DEMODULATOR SECTION
The tag reflects energy from the reader and which is ASK modulated and then the
voltage across the capacitor C19 is changing accordance with the data bits. The
change is in the envelope. The diode D6 passes the positive half wave only and forms
part of the demodulator circuit. D6 and C18 forms the capacitive filter .The envelope
is charged in the C18. R10 provides a discharge path for the voltage charged in C18.
C17 and R9 grounds the carrier in the demodulated signal. The R8 and C19 pass the
alternating envelope signal to the active filter.
FILTER SECTION
U7D forms the active filter section. The output of the high pass filter is given to the
U7C which integrates the filtered signal which is almost square in shape.
PULSE SHAPING SECTION
The output of U7C is connected to the +ve terminal of op-amp. The –ve
terminal is at +5 volt reference. There is a feedback resistor R16 connected to the +ve
terminal .the op-amp compares the two voltages and produces a logic high or logic
low depending on the + ve terminal input which is from the integrator output. The
capacitor acts as the bypass capacitor. In order to change the voltage in to the readable
range of microcontroller a voltage divider is connected. The data is the fed to the RB0
pin of pic16f877 for processing.
The PIC16f877 microcontroller performs data decoding and communicates with the
host computer via an RS-232 serial interface.
There is a LCD module which is connected to the microcontroller. The interface is
through the two ports. The port D is used to give data to display. Three pins of the
port C are used to give commands to the LCD.Another interface to the circuit is the
buzzer. When the data received is valid the microcontroller gives logic high to the pin
8(RE0).It is connected to the base of transistor BC 547 through a resistor of 4.7 K. so
when the pin becomes high the buzzer turns on and makes sound. The collector of
bc547 is connected to 5v supply and working in the switching mode.
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ADVANTAGES
 Increase in toll collection capacity
 Reduction in motorist waiting time
 Convenience for toll payers
 Fuel savings and a decrease in mobile emissions by reducing or eliminating
waiting times
 Reduction in toll collection costs and enhancement of audit control by
centralizing user accounts
 Simple to implement.
 Cost effective.
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CONCLUSION
The electronic toll Collection systems are a combination of completely automated toll
collection systems and semi-automatic lanes. Various traffic and payment data are
collected and stored by the system as vehicles pass through. The different
technologies involved are logically integrated with each other but remain flexible for
upgrades. They also include sophisticated video and image capturing equipment for
full-time violation enforcement. So this basic arrangement developed by us will
applicable for the future developments in road transport by proper modifications.
RFID systems have a secure place in the automatic identification sector. The system
can made free from the challenges and will be cost effective in near future.
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REFERENCES
1. www.rfidjournal.com
2. www.microchip.com
3. www.rfida.com
4. www.alldatasheet.com
5. Design with PIC microcontrollers, Pearson Education Pte. Ltd, Second Edition
-John.B.Peatman
6. Op-Amps and Linear Integrated Circuits, Prentice Hall of India Private Ltd
-Ramakanth.A.Gayakwad
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