24-08-2013, 04:30 PM
Electronic Toll Collection
[attachment=57462]
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.
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.
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.
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.
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.
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.
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.
[attachment=57462]
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.
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.
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.
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.
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.
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.
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.