Download RFID PROJECT REPORT

Project Report
On
RFID- BASED SECURITY SYSTEM
In partial fulfillment of requirements for the degree of
Diploma of Engineering
In
EC Engineering
Submitted By:
1.Mayur Sakariya
Under the Guidance of
Mr. Niraj Bhadresha
Mr.Khodabhai Dobriya
2. Savan Kadivar
DEPARTMENT OF ELECTRONICS & COMMUNICATION
ENGINEERING
ATMIYA INSTITUTE OF TECHNOLOGY AND SCIENCE FOR
DIPLOMA STUDIES, RAJKOT- 360005.
[2012 – 2013]
CERTIFICATE
This is to certify that the project entitled “RFID based security system” has been
carried out by the team under my guidance in partial fulfillment of the Diploma
of Engineering in Electronics & Communication in GTU during the academic
year 2012-2013 (Semester-6).
Team:
• Mayur Sakariya
• Savan Kadivar
Date:
Place:
Guide
(Mr. Niraj Bhadresha)
Principal
(G.C. joshi)
Head, EC Department
(Dipak.M.Jethloja)
External guide
(Khodabhai Dobriya)
ACKNOWLEDGEMENT
This is an opportunity to humbly express our thankfulness to all
those people concerned with our project entitled “Voice controlled
automation & Security System”.
At the time of complication of this project, we would like to thank
everyone who made a great effort to make this possible. Our project
wouldn’t exist without help of our project leaders. Trying to cover next
to impossible then also we have bought all facts in the application with
the help of our guides.
I express very sincere thanks to our college faculties for their guidance
throughout preparation of project. Their valuable guidance has proved to
be a key to our success In overcoming challenges we faced during this
project. At last, we would like to thank all the members related to this
project for their kind co-operation and help during the project. Again as
the law of nature “No One Is PERFECT”, I will be very glad to know
my mistakes and also if any suggestions are there.
Mayur Sakariya
Savan Kadivar
RFID BASED SECURITY SYSTEM
Submitted By:
Mayur A.Sakariya (106030311047)
Savan V.Kadivar (106030311049)
INDEX
Topic
Page No.
Abstract…8……………………………………………………………..8888888
8888.............................................…..
Chapter 1: Introduction
1.1 Industry visited
10
Chapter 2:Feasibility
2.1 financial feasibility
11
2.2 resource feasibility
…
…………………………….
Chapter:3 Block Diagram of the project
12
3.1 construction……………………
1…
…………………
…………………
13
Chapter 4:Circuit Description
4.1circuit diagram
24
4.2list of components
25
4.3operation
25
Chapter 5: PCB Layout
28
Chapter 6: Components detail
6.1resistors
29
6.2capacitor
32
6.3diode
35
6.4LED
39
6.5microcontroller
43
6.6 LCD display
53
6.7 Transistor
54
6.8 IC
56
Chapter 7: Advantages and Limitations
60
Chapter 8: Conclusion and bibliography
62
ABSTRACT
The security system is basically an embedded one. Embedded stands for
hardware controlled by software. Here, the software using a microcontroller
controls all the hardware components. The microcontroller plays an important
role in the system.
The main objective of the system is to uniquely identify and to make
security for a person. This requires a unique product, which has the capability of
distinguishing different person. This is possible by the new emerging
technology RFID (Radio Frequency Identification). The main parts of an RFID
system are RFID tag (with unique ID number) and RFID reader (for reading the
RFID tag). In this system, RFID tag and RFID reader used are operating at
125KHz. The microcontroller internal memory is used for storing the details.
The PC can be used for restoring all the details of security made.
This report provides a clear picture of hardware and software used in the
system. It also provides an overall view with detailed discussion of the
operation of the system.
Chapter-1
Introduction
Introduction:
Most educational institutions administrators are concerned about
student security. The conventional method allowing acess to students inside a
college /educational campus is by showing photo i-card to security guard is
very time consuming and insecure, hence inefficient.
Radio Frequency Identification (RFID) based security system is one of
the solutions to address this problem. This system can be used to allow access
for student in school, college, and university. It also can be used to take
attendance for workers in working places. Its ability to uniquely identify each
person based on their RFID tag type of ID card make the process of allowing
security access easier, faster and secure as compared to conventional method.
Student or workers only need to place their ID card on the reader and they
will be allowed to enter the campus. And if any invalid card is shown then the
buzzer is turned on.
1.1
Industry visited:
For the industrial defined project I visited Simond fiber Tech Pvt. Lmt.
Works (Metoda). The industry is located in Metoda. The best part of this
industry is the beautiful environment and friendly atmosphere. The people
working in this industry are very genuine and down to earth. They co-operated
on my visit to this industry. And helped in every possible manner.
Simond was founded in 1955 by Mr. Khodabhai Dobariya. The company
adopted advanced gear technology. Step by step gear shaping, hobbling and
shaving and finally added gear is grinding technology also. The company
making Fiber Products and related to it. In last 4 years Mr. Ravi Dobariya,
grandson of Mr. Khodabhai Dobariya has become an added part of the
company.
Chapter 2
Feasibility
2.1 Financial feasibility:
The resources used in this project are quite feasible financially.
Components list:
 Resisters
 diode
 capacitor
 Transistor(BC 547 NPN,BC 556 PNP)
 LED
 Microcontroller(AT 89C2052)
 7805 IC
 7812 IC
 LCD Display
 RFID module
 Transformer(12V)
 Piezzo buzzer
 Crystal(11.0592Mhz)
 Relay (12v)
The list of components given above shows that all the components are cheap
and feasible. The company will not have any problem in using this simple
project circuit.
2.2 Resource feasibility:
All the resources used in this project are easily available.
The RFID module used in this project might be difficult to find in the
market. Then, finally we found RFID module at Sandip Electronics
Chapter 3
Block Diagram of The Project
3.1 construction
Block Diagram:-
History of RFID:
In a very interesting article, the San Jose Mercury News tells us about
Charles Walton, the man behind the radio frequency identification technology
(RFID). Since his first patent about it in 1973, Walton, now 83 years old,
collected about $3 million from royalties coming from his patents.
Unfortunately for him, his latest patent about RFID expired in the mid-1990s.
So he will not make any money from the billions of RFID tags that will appear
in the years to come. But he continues to invent and his latest patent about a
proximity card with incorporated PIN code protection was granted in June 2004.
What is RFID.
RFID is short for Radio Frequency Identification. Generally a RFID
system consists of 2 parts. A Reader, and one or more Transponders, also
known as Tags. RFID systems evolved from barcode labels as a means to
automatically identify and track products and people. You will be generally
familiar with RFID systems as seen in:
Access Control
RFID Readers placed at entrances that require a person to pass their
proximity card (RF tag) to be read before the access can be made.
Contact less Payment Systems
RFID tags used to carry payment information. RFIDs are particular suited
to electronic Toll collection system. Tags attached to vehicles, or carried by
people transmit payment information to a fixe reader attached to a Toll station.
Payments are then routinely deducted from a users account, or information is
changed directly on the RFID tag.
Product Tracking and Inventory Control
RFID systems are commonly used to track and record the
movement of ordinary items such as library books, clothes, factory
pallets, electrical goods and numerous items.
How do RFIDs work
Shown below is a typical RFID system. In every RFID system the
transponder Tags contain information. This information can be as little as a
single binary bit , or be a large array of bits representing such things as an
identity code, personal medical information, or literally any type of
information
that
can
be
stored
in
digital
binary
format .
Shown is a RFID transceiver that communicates with a passive Tag.
Passive tags have no power source of their own and instead derive power from
the incident electromagnetic field.
Commonly the heart of each tag is a microchip. When the Tag enters the
generated RF field it is able to draw enough power from the field to access its
internal memory and transmit its stored information.
When the transponder Tag draws power in this way the resultant
interaction of the RF fields causes the voltage at the transceiver antenna to
drop in value. This effect is utilized by the Tag to communicate its
information to the reader. The Tag is able to control the amount of power
drawn from the field and by doing so it can modulate the voltage sensed at the
Transceiver according to the bit pattern it wishes to transmit.
COMPONENTS OF RFID
A basic RFID system consist of three components:

An antenna or coil

A transceiver (with decoder)

A transponder (RF tag) electronically programmed with unique
information
These are described below:
1. ANTENNA
The antenna emits radio signals to activate the tag and read and write
data to it. Antennas are the conduits between the tag and the transceiver, which
controls the system's data acquisition and communication.
Antennas are available in a variety of shapes and sizes; they can be built
into a door frame to receive tag data from persons or things passing through the
door, or mounted on an interstate tollbooth to monitor traffic passing by on a
freeway.
The electromagnetic field produced by an antenna can be constantly
present when multiple tags are expected continually. If constant interrogation is
not required, a sensor device can activate the field.
Often the antenna is packaged with the transceiver and decoder to
become a reader (a.k.a. interrogator), which can be configured either as a
handheld or a fixed-mount device. The reader emits radio waves in ranges of
anywhere from one inch to 100 feet or more, depending upon its power output
and the radio frequency used.
When an RFID tag passes through the electromagnetic zone, it detects the
reader's activation signal. The reader decodes the data encoded in the tag's
integrated circuit (silicon chip) and the data is passed to the host computer for
processing.
2.
TAGS (Transponders)
An RFID tag is comprised of a microchip containing identifying
information and an antenna that transmits this data wirelessly to a reader. At its
most basic, the chip will contain a serialized identifier, or license plate number,
that uniquely identifies that item, similar to the way many bar codes are used
today.
A key difference, however is that RFID tags have a higher data capacity
than their bar code counterparts. This increases the options for the type of
information that can be encoded on the tag, including the manufacturer, batch or
lot number, weight, ownership, destination and history (such as the temperature
range to which an item has been exposed).
In fact, an unlimited list of other types of information can be stored on
RFID tags, depending on application needs. An RFID tag can be placed on
individual items, cases or pallets for identification purposes, as well as on fixed
assets such as trailers, containers, totes, etc.
Tags come in a variety of types, with a variety of capabilities. Key variables
include:"Read-only" versus "read-write"
There are three options in terms of how data can be encoded on tags: (1)
Read-only tags contain data such as a serialized tracking number, which is prewritten onto them by the tag manufacturer or distributor. These are generally the
least expensive tags because they cannot have any additional information
included as they move throughout the supply chain.
Any updates to that information would have to be maintained in the
application software that tracks SKU movement and activity. (2) "Write once"
tags enable a user to write data to the tag one time in production or distribution
processes. Again, this may include a serial number, but perhaps other data such
as a lot or batch number. (3) Full "read-write" tags allow new data to be written
to the tag as needed—and even written over the original data.
Examples for the latter capability might include the time and dateof
ownership transfer or updating the repair history of a fixed asset. While these
are the most costly of the three tag types and are not practical for tracking
inexpensive items, future standards for electronic product codes (EPC) appear
to be headed in this direction.
RFID TAGS
Data capacity
The amount of data storage on a tag can vary, ranging from 16 bits on the
low end to as much as several thousand bits on the high end. Of course, the
greater the storage capacity, the higher the price per tag.
Form factor
The tag and antenna structure can come in a variety of physical form
factors and can either be self-contained or embedded as part of a traditional
label structure (i.e., the tag is inside what looks like a regular bar code label—
this is termed a 'Smart Label') companies must choose the appropriate form
factors for the tag very carefully and should expect to use multiple form factors
to suit the tagging needs of different physical products and units of measure.
For example, a pallet may have an RFID tag fitted only to an area of
protected placement on the pallet itself. On the other hand, cartons on the pallet
have RFID tags inside bar code labels that also provide operators humanreadable information and a back-up should the tag fail or pass through non
RFID-capable supply chain links.
Passive versus active
“Passive” tags have no battery and "broadcast" their data only when
energized by a reader. That means they must be actively polled to send
information. "Active" tags are capable of broadcasting their data using their
own battery power.
In general, this means that the read ranges are much greater for active
tags than they are for passive tags—perhaps a read range of 100 feet or more,
versus 15 feet or less for most passive tags. The extra capability and read ranges
of active tags, however, come with a cost; they are several times more
expensive than passive tags.
Today, active tags are much more likely to be used for high-value items
or fixed assets such as trailers, where the cost is minimal compared to item
value, and very long read ranges are required. Most traditional supply chain
applications, such as the RFID-based tracking and compliance programs
emerging in the consumer goods retail chain, will use the less expensive passive
tags.
Frequencies
Like all wireless communications, there are a variety of frequencies or
spectra through which RFID tags can communicate with readers. Again, there
are trade-offs among cost, performance and application requirements. For
instance, low-frequency tags are cheaper than ultra high-frequency (UHF) tags,
use less power and are better able to penetrate non-metallic substances.
They are ideal for scanning objects with high water content, such as fruit,
at close range. UHF frequencies typically offer better range and can transfer
data faster. But they use more power and are less likely to pass through some
materials. UHF tags are typically best suited for use with or near wood, paper,
cardboard or clothing products. Compared to low-frequency tags, UHF tags
might be better for scanning boxes of goods as they pass through a bay door
into a warehouse.
While the tag requirements for compliance mandates may be narrowly
defined, it is likely that a variety of tag types will be required to solve specific
operational issues. You will want to work with a company that is very
knowledgeable in tag and reader technology to appropriately identify the right
mix of RFID technology for your environment and applications.
EPC Tags
EPC refers to "electronic product code," an emerging specification for
RFID tags, readers and business applications first developed at the Auto-ID
Center at the Massachusetts Institute of Technology. This organization has
provided significant intellectual leadership toward the use and application of
RFID technology.
EPC represents a specific approach to item identification, including an
emerging standard for the tags themselves, including both the data content of
the tag and open wireless communication protocols. In a sense, the EPC
movement is combining the data standards embodied in certain bar code
specifications, such as the UPC or UCC-128 bar code standards, with the
wireless data communication standards that have been developed by ANSI and
other groups.
3. RF Transceiver:
The RF transceiver is the source of the RF energy used to activate and
power the passive RFID tags. The RF transceiver may be enclosed in the same
cabinet as the reader or it may be a separate piece of equipment. When provided
as a separate piece of equipment, the transceiver is commonly referred to as an
RF module.
The RF transceiver controls and modulates the radio frequencies that the
antenna transmits and receives. The transceiver filters and amplifies the
backscatter signal from a passive RFID tag.
Typical Applications for RFID

Automatic Vehicle identification

Inventory Management

Work-in-Process

Container/ Yard Management

Document/ Jewellery tracking

Patient Monitoring
Chapter 4
Circuit Description
4.1 Circuit Diagram:
Fig. of RFID Based Security System
4.2 List of components:
SR NO.
Name of component
Quantity
1
Microcontroller(AT89C52)
1
2
IC(7812,7805,RFID module)
1
3
Capacitor
5
4
Resister
6
5
LED
3
6
Switch
1
7
Crystal
1
8
Diode
5
9
Transformer
1
10
Relay
1
11
Transistor(NPN,PNP)
1
12
LCD display
1
13
Piezzo Buzzer
1
list of components of above circuit
4.3
Operation:
Fig. shows the circuit of the RFID based security system. The circuit can
be divided into different sections:
Power supply (Section 1)
To derive the power supply, the 230V, 50Hz AC mains is stepped down
by transformer X1 to deliver a secondary output of 15V, 500 mA. The
transformer output is rectified by a full-wave rectifier comprising diodes D1
through D4, filtered by capacitor C1 and regulated by ICs 7812 (IC2) and 7805
(IC3). Capacitor C2 bypasses the ripples present in the regulated supply. LED1
acts as the power indicator and R2 limits the current through LED1.
AT89C52 microcontroller (Section 2)
The compact circuitry is built around Atmel AT89C52 microcontroller.
The AT89C52 is a low-power, high performance CMOS 8-bit microcomputer
with 8 kB of Flash programmable and erasable read only memory (PEROM). It
has 256 bytes of RAM, 32 input/output (I/O) lines, three 16-bit timers/ counters,
a six-vector two-level interrupt architecture, a full-duplex serial port, an on-chip
oscillator and clock circuitry. The system clock also plays a significant role in
operation of the microcontroller.
Connectors CON2 through CON4 (Section 3)
CON2 and CON3 are two-pin connectors that connect the 12V DC
motors to the circuit for controlling the unique tag. CON4 is a tenpin dual-inline female connector that connects the RFID reader module to the circuit.
LCD display
All the data is sent to the LCD in ASCII format for display. Only the
commands are sent in hex form. Register-select (RS) signal is used to
distinguish between data (RS=1) and command (RS=0). Preset VR1 is used to
control the contrast of the LCD. Resistor R6 limits the current through the
backlight of the LCD. Port pins P3.0 (RXD) and P3.1 (TXD) of the
microcontroller
are
used
to
interface
with
the
RFID
reader.
When an authorized person having the tag enters the RF field generated
by the RFID reader, RF signal is generated by the RFID reader to transmit
energy to the tag and retrieve data from the tag. Then the RFID reader
communicates through RXD and TXD pins of the microcontroller for further
processing.
Thus on identifying the authorized person, port pin P3.2 goes high,
transistor T2 drives into saturation, and relay RL1energises to open the door for
the person. Simultaneously, the LCD shows “access granted” message and port
pin P1.7 drives piezo-buzzer PZ1 via transistor T1 aural indication.
If the person is unauthorized, the LCD shows “access denied” and the
door doesn’t open. LED2 and LED3show presence of the tag in the RFID
reader’s electromagnetic field.
IR transmitter and receiver
Two IR transmitter-receiver pairs are used. The IR LEDs are connected
in forward-biased condition to the +5V power supply through 220-ohm
resistors. These emit IR light, which is interrupted when an object comes into its
way to the IR receiver. The IR receiving photodiodes are connected in reversebiased condition to +5V power supply through 1-mega-ohm resistors. When the
IR light falls on the photodiodes, their resistance changes and so does their
output. This output is compared with a fixed voltage to give a digital output to
the microcontroller in order to judge the entry and exit of the vehicles.
CRYSTAL
An 11.0592MHz quartz crystal connected to pins 18 and 19 provides
basic clock to the microcontroller. Power-on reset is provided by the
combination of electrolytic capacitor C4 and resistor R1. Switch S1 is used for
manual reset. Port pins P2.0 through P2.7 of the microcontroller are connected
to data port pins D0 through D7 of the LCD, respectively. Port pins P3.7 and
P3.6 of the microcontroller are connected to register-select (RS) and enable (E)
pins of the LCD, respectively. Read/write
enable for write operation.
pin of the LCD is grounded to
Chapter 5
PCB Layout
An actual-size, single-side PCB for the RFID-based security system
Component layout for the PCB
Chapter 6
Components detail
Component details:
6.1 Resistor:
Register is a passive element. These components are split into two
categories; those which dissipate energy and those which store it. The property
of a substance, which opposes the flow of an electrical current through it, is
called the “resistance” (measured in ohms). Fixed resisters are used in circuit
diagram.
A linear resistor is a linear, passive two-terminal electrical component
that implements electrical resistance as a circuit element. The current through a
resistor is in direct proportion to the voltage across the resistor's terminals.
Thus, the ratio of the voltage applied across a resistor's terminals to the intensity
of current through the circuit is called resistance. This relation is represented by
Ohm's law:
Resistors are common elements of electrical networks and electronic
circuits and are ubiquitous in most electronic equipment. Practical resistors can
be made of various compounds and films, as well as resistance wire (wire made
of a high-resistivity alloy, such as nickel-chrome). Resistors are also
implemented within integrated circuits, particularly analog devices, and can also
be integrated into hybrid and printed circuits.
The electrical functionality of a resistor is specified by its resistance:
common commercial resistors are manufactured over a range of more than nine
orders of magnitude. When specifying that resistance in an electronic design,
the required precision of the resistance may require attention to the
manufacturing tolerance of the chosen resistor, according to its specific
application.
The temperature coefficient of the resistance may also be of concern in
some precision applications. Practical resistors are also specified as having a
maximum power rating which must exceed the anticipated power dissipation of
that resistor in a particular circuit: this is mainly of concern in power electronics
applications. Resistors with higher power ratings are physically larger and may
require heat sinks. In a high-voltage circuit, attention must sometimes be paid to
the rated maximum working voltage of the resistor.
Practical resistors have a series inductance and a small parallel
capacitance; these specifications can be important in high-frequency
applications. In a low-noise amplifier or pre-amp, the noise characteristics of a
resistor may be an issue. The unwanted inductance, excess noise, and
temperature coefficient are mainly dependent on the technology used in
manufacturing the resistor. They are not normally specified individually for a
particular family of resistors manufactured using a particular technology.
A family of discrete resistors is also
characterized according to its form factor,
that is, the size of the device and the position
of its leads (or terminals) which is relevant in
the practical manufacturing of circuits using
Them
The symbol for a resistor is shown in the below.
Fig. of Register
Resistor symbols
The unit for measuring resistance is the OHM. (The Greek letter Ω called Omega). Higher resistance values are represented by "k" (kilo-ohms) and
M (Meg ohms).
Resistor Markings:Resistance value is marked on the resistor body. Most resistors have 4
bands. The first two bands provide the numbers for the resistance and the third
band provides the number of zeros. The fourth band indicates the tolerance.
Fig.of Resistor Marking Table
Fig. of Four-band resistor, c. Five-band resistor, d. Cylindrical SMD resistor, e.
Flat SMD resistor
6.2 Capacitor:
Fig. of Capacitor
A capacitor (formerly known as condenser) is a passive two-terminal
electrical component used to store energy in an electric field. The forms of
practical capacitors vary widely, but all contain at least two electrical
conductors separated by a dielectric (insulator); for example, one common
construction consists of metal foils separated by a thin layer of insulating film.
Capacitors are widely used as parts of electrical circuits in many common
electrical devices.
When there is a potential difference (voltage) across the conductors, a
static electric field develops across the dielectric, causing positive charge to
collect on one plate and negative charge on the other plate. Energy is stored in
the electrostatic field. An ideal capacitor is characterized by a single constant
value, capacitance, measured in farads. This is the ratio of the electric charge on
each conductor to the potential difference between them.
The capacitance is greatest when there is a narrow separation between
large areas of conductor; hence capacitor conductors are often called "plates,"
referring to an early means of construction. In practice, the dielectric between
the plates passes a small amount of leakage current and also has an electric field
strength limit, resulting in a breakdown voltage, while 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 filter networks, for smoothing the output of power supplies, in the
resonant circuits that tune radios to particular frequencies and for many other
purposes.
The simplest capacitor consists of two parallel conductive plates
separated by a dielectric with permittivity ε (such as air). The model may also
be used to make qualitative predictions for other device geometries. The plates
are considered to extend uniformly over an area A and a charge density ±ρ =
±Q/A exists on their surface. Assuming that the width of the plates is much
greater than their separation d, the electric field near the centre of the device
will be uniform with the magnitude E = ρ/ε. The voltage is defined as the line
integral of the electric field between the plates. Solving this for C = Q/V reveals
that capacitance increases with area and decreases with separation
…………………………..(1)
The capacitance is therefore greatest in devices made from materials with
a high permittivity, large plate area, and small distance between plates.
We see that the maximum energy is a function of dielectric volume,
permittivity, and dielectric strength per distance. So increasing the plate area
while decreasing the separation between the plates while maintaining the same
volume has no change on the amount of energy the capacitor can store. Care
must be taken when increasing the plate separation so that the above assumption
of the distance between plates being much smaller than the area of the plates is
still valid for these equations to be accurate.
Fig. of parallel plates of capacitor
6.3 Diode:
Diode Construction:
Fig. of construction of semiconductor diode
A diode is formed by joining two equivalently doped P-Type and N-Type
semiconductor. When they are joined an interesting phenomenon takes place.
The P-Type semiconductor has excess holes and is of positive charge. The NType semiconductor has excess electrons. At the point of contact of the P-Type
and N-Type regions, the holes in the P-Type attract electrons in the N-Type
material. Hence the electron diffuses and occupies the holes in the P-Type
material.
Causing a small region of the N-type near the junction to loose electrons
and behaves like intrinsic semiconductor material, in the P-type a small region
gets filled up by holes and behaves like a intrinsic semiconductor.
Fig. of Depletion region of semiconductor diode
Thin intrinsic region is called depletion layer, since its depleted of charge (see
diagram above) and hence offers high resistance. It’s this depletion region that
prevents the further diffusion of majority carriers. In physical terms the size of
the depletion layer is very thin.
Diode Biased Voltage
Zero Bias:
Fig. of Diode Biased Voltage
When a diode is zero biased, that is has no bias, it just stays. Almost no
current passes through the diode. However if you connect the anode and
cathode of the diode you might be able to observe small voltage or current that
is insignificant. This is because the electromagnetic spectrum that's present in
our environment by default (microwave background, heat, light, radio waves)
knocks off electrons in the semiconductor lattice that constitutes current. For
practical reasons this current can be considered zero.
Reverse Bias:-
Fig. of Reverse bias of diode
In reverse bias the P-type region is connected to negative voltage and Ntype is connected to positive terminal as shown above. In this condition the
holes in P-type gets filled by electrons from the battery / cell (in other words the
holes get sucked out of the diode).
The electron in N-type material is sucked out of the diode by the positive
terminal of the battery. So the diode gets depleted of charge.
So initially the depletion layer widens (see image above) and it occupies
the entire diode. The resistance offered by the diode is very huge. The current
that flows in reverse bias is only due to minority charge which is in nano
amperes in silicon and micro amperes in high power silicon and germanium
diodes.
Forward Bias:-
Fig. of Forward Bias of diode
In forward bias the P-Region of the diode is connected with the positive
terminal of the battery and N-region is connected with the negative region.
During the forward bias the following process occurs.
The positive of the battery pumps more holes into the P-region of the
diode. The negative terminal pumps electrons into the N-region
The excess of charge in P and N region will apply pressure on the
depletion region and will make it shrink. As the voltage increases the depletion
layer will become thinner and thinner and hence diode will offer lesser and
lesser resistance. Since the resistance decreases the current will increase (though
not proportional) to the voltage.
At one particular voltage level Vf called the threshold / firing / cut-off
voltage the depletion layer disappears (overwhelmed by the charge) and hence
from this point on the diode starts to conduct very easily. From this point on the
diode current increases exponentially to the voltage applied.
6.4 LED:
A light-emitting diode (LED) is a semiconductor light source. LEDs are
used as indicator lamps in many devices and are increasingly used for other
lighting. Introduced as a practical electronic component in 1962, early LEDs
emitted low-intensity red light, but modern versions are available across the
visible, ultraviolet, and infrared wavelengths, with very high brightness.
When a light-emitting diode is forward-biased (switched on), electrons
are able to recombine with electron holes within the device, releasing energy in
the form of photons. This effect is called electroluminescence and the color of
the light (corresponding to the energy of the photon) is determined by the
energy gap of the semiconductor. LEDs are often small in area (less than
1 mm2), and integrated optical components may be used to shape its radiation
pattern.
Fig. of Diagram of LED
LEDs present many advantages over incandescent light sources including
lower energy consumption, longer lifetime, improved robustness, smaller size,
and faster switching. LEDs powerful enough for room lighting are relatively
expensive and require more precise current and heat management than compact
fluorescent lamp sources of comparable output.
Light-emitting diodes are used in applications as diverse as replacements
for aviation lighting, automotive lighting (in particular brake lamps, turn
signals, and indicators) as well as in traffic signals. LEDs have allowed new
text, video displays, and sensors to be developed, while their high switching
rates are also useful in advanced communications technology.
Infrared LEDs are also used in the remote control units of many
commercial products including televisions, DVD players, and other domestic
appliances.
Practical use:
The first commercial LEDs were commonly used as replacements for
incandescent and neon indicator lamps, and in seven-segment displays, first in
expensive equipment such as laboratory and electronics test equipment, then
later in such appliances as TVs, radios, telephones, calculators, and even
watches (see list of signal uses).
These red LEDs were bright enough only for use as indicators, as the
light output was not enough to illuminate an area. Readouts in calculators were
so small that plastic lenses were built over each digit to make them legible.
Later, other colors grew widely available and also appeared in appliances and
equipment. As LED materials technology grew more advanced, light output
rose, while maintaining efficiency and reliability at acceptable levels.
The invention and development of the high-power white-light LED to use
for illumination, which is fast replacing incandescent and fluorescent lighting.
(See list of illumination applications).
Most LEDs were made in the very common 5 mm T1¾ and 3 mm T1
packages, but with rising power output, it has grown increasingly necessary to
shed excess heat to maintain reliability, so more complex packages have been
adapted for efficient heat dissipation. Packages for state-of-the-art high-power
LEDs bear little resemblance to early LEDs.
Fig. of LED
Working of LED
The LED consists of a chip of semiconducting material doped with
impurities to create a p-n junction. As in other diodes, current flows easily from
the p-side, or anode, to the n-side, or cathode, but not in the reverse direction.
Charge-carriers electrons and holes — flow into the junction from electrodes
with different voltages. When an electron meets a hole, it falls into a lower
energy level, and releases energy in the form of a photon.
Fig. of Inner workings of LED
The wavelength of the light emitted, and thus its color depends on the
band gap energy of the materials forming the p-n junction. In silicon or
germanium diodes, the electrons and holes recombine by a non-radiative
transition, which produces no optical emission, because these are indirect band
gap materials. The materials used for the LED have a direct band gap with
energies corresponding to near-infrared, visible, or near-ultraviolet light.
Fig. of diagram for a diode. An LED will begin to emit light when the onvoltage is exceeded. Typical on voltages are 2–3 volts.
LED development began with infrared and red devices made with gallium
arsenide. Advances in materials science have enabled making devices with
ever-shorter wavelengths, emitting light in a variety of colors.
LEDs are usually built on an n-type substrate, with an electrode attached
to the p-type layer deposited on its surface. P-type substrates, while less
common, occur as well. Many commercial LEDs, especially GaN/InGaN, also
use sapphire substrate.
Most materials used for LED production have very high refractive
indices. This means that much light will be reflected back into the material at
the material/air surface interface. Thus, light extraction in LEDs is an important
aspect of LED production, subject to much research and development.
6.5 Microcontroller AT89C52:
The AT89C52 is a low-power , high-performance CMOS 8-bit
microcomputer with 8K bytes of flash programmable and erasable read only
memory (PEROM). The device is manufactured using Atmel’s high-density
nonvolatile memory technology and is compatible with the industry-standard
80C51 and 80C52 instruction set and pin out.
The on-chip Flash allows the program memory to be reprogrammed insystem or by a conventional nonvolatile memory programmer. By combining a
versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89C52 is a
powerful microcomputer which provides a highly-flexible and cost-effective
solution to many embedded control ‘applications
The AT89C52 provides the following standard features : 8K bytes of
Flash , 256 bytes of RAM, 32 I/O lines , three 16-bit timer/counters , a sixvector two-level interrupt architecture a full-duplex serial port , on-chip
oscillator ,and clock circuitry.
In addition , the AT89C52 is designed with static logic for operation
down to zero frequency and supports two software selectable power saving
modes.
Pin Configuration:
Fig.of Pin Diagram
Pin Description :
VCC
Supply voltage.
GND
Ground.
Port 0
Port 0 is an 8-bit open drain bi-directional I/O port. As an output port,
each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the
pins can be used as high- impedance inputs
Port 0 can also be configured to be the multiplexed low- order
address/data bus during accesses to external pro- gram and data memory. In
this mode, P0 has internal pull ups.
Port 0 also receives the code bytes during Flash programming and
output is the c o de b y test during p r o g r a m verification. External pull ups
are required during program verification.
Port 1
Port 1 is an 8-bit bi-directional I/O port with internal pull ups. The Port 1
output buffers can sink/source four TTL inputs. When 1s are written to Port 1
pins, they are pulled high by the internal pull ups and can be used as inputs.
As inputs, Port 1 pins that are externally being pulled low will source current
(IIL) because of the internal pull ups
In addition, P1.0 and P1.1 can be configured to be the timer/counter 2
external count input (P1.0/T2) and the timer/counter 2 trigger input
(P1.1/T2EX), respectively, as shown in the following table.
Port 1 also receives the low-order address bytes during
Flash
programming and verification.
Port 2
Port 2 is an 8-bit bi-directional I/O port with internal pull ups. The Port 2
output buffers can sink/source four TTL inputs. When 1s are written to Port 2
pins, they are pulled high by the internal pull ups and can be used as inputs.
As inputs, Port 2 pins that are externally being pulled low will source current
(IIL) because of the internal pull ups.
Port 2 emits the high-order address byte during fetches from external
program memory and during accesses to external data memory that use 16bit addresses (MOVX @ DPTR). In this application, Port 2 uses strong
internal pull ups when emitting 1s. During accesses to external data memory
that use 8-bit addresses (MOVX @ RI), Port 2 emits the contents of the P2
Special Function Register.
Port 2 also receives the high-order address bits and some control signals
during Flash programming and verification.
Port 3
Port 3 is an 8-bit bi-directional I/O port with internal pull ups. The Port 3
output buffers can sink/source four TTL inputs. When 1s are written to Port 3
pins, they are pulled high by the internal pull ups and can be used as inputs.
As inputs, Port 3 pins that are externally being pulled low will source current
(IIL) because of the pull ups.
Port 3 also serves the functions of various special features of the
AT89C51, as shown in the following table.
Port 3 also receives some control signals for Flash programming and
verification.
Port Pin
P3.0
P3.1
P3.2
P3.3
P3.4
external P3.5
P3.6
P3.7
Alternate Functions
RXD (serial input port)
TXD (serial output port)
INT0 (external interrupt 0)
INT1 (interrupt 1)
T0 (timer 0 external input)
T1 (timer 1 external input)
WR (external data memory write strobe)
RD (external data memory read strobe)
RST
Reset input. A high on this pin for two machine cycles while the
oscillator is running resets the device.
ALE/PROG
Address Latch Enable is an output pulse for latching the low byte of
the address during accesses to external memory. This pin is also the program
pulse input (PROG) during Flash programming.
In normal operation, ALE is emitted at a constant rate of 1/6 the
oscillator frequency and may be used for external timing or clocking
purposes. Note, however, that one ALE pulse is skipped during each access
to external data memory.
If desired, ALE operation can be disabled by setting bit 0 of SFR location
8EH. With the bit set, ALE is active only during a MOVX or MOVC
instruction. Otherwise, the pin is weakly pulled high. Setting the ALEdisable bit has no effect if the microcontroller is in external execution mode.
PSEN
Program store enable is the read strobe to external program memory.
when the AT89C52 is executing code from external program memory, PSEN is
activated twice each machine cycle, except that two PSEN activations are
skipped during each access to external data memory.
EA/VPP
External access enable. EA must be strapped to GND in order to enable
the device to fetch code from external pro gram memory locations starting at
0000H up to FFFFH. Note, however, that if lock bit 1 is programmed, EA will
be internally latched on reset.
EA should be strapped to Vcc for internal program executions.
This pin also receives the 12-volt programming enable voltage (Vpp)
during flash programming when 12-volt programming is selected.
XTAL 1
Input to the inverting oscillator amplifier and input to the internal
clock operating circuit.
XTAL 2
Output from the inverting oscillator amplifier.
Special Function Registers
A map of the on-chip memory area called the Special Function Register
(SFR). Note that not all of the addresses are occupied, and unoccupied
addresses may not be implemented on the chip. Read accesses to these
addresses will in general return random data, and write accesses will have an
indeterminate effect.
User software should not write 1s to these unlisted locations, since they
may be used in future products to invoke new features. In that case, the reset
or inactive values of the new bits will always be 0.
Timer 2 Registers
Control and status bits are contained in registers T2CON and T2MOD
for Timer 2. The register pair (RCAP2H, RCAP2L) are the Capture/Reload
registers for Timer 2 in 16-bit capture mode or 16-bit auto-reload mode.
Interrupt Registers
The individual interrupt enable bits are in the IE register. Two priorities
can be set for each of the six interrupt sources in the IP register.
Data Memory
The AT89C52 implements 256 bytes of on-chip RAM. The upper 128
bytes occupy a parallel address space to the Special Function Registers.
That means the upper 128 bytes have the same addresses as the SFR space but
are physically separate from SFR space.
When an instruction accesses an internal location above address 7FH,
the address mode used in the instruction specifies whether the CPU accesses
the upper 128 bytes of RAM or the SFR space. Instructions that use direct
addressing access SFR space.
For example, the following direct addressing instruction accesses the
SFR at location 0A0H (which is P2).
MOV 0A0H, #data
Instructions that use indirect addressing access the upper 128 bytes of
RAM. For example, the following indirect addressing instruction, where R0
contains 0A0H, accesses the data byte at address 0A0H, rather than P2
(whose address is 0A0H).
MOV @ R0 , #data
Note that stack operations are examples of indirect addressing, so
the upper 128 bytes of data RAM are avail- able as stack space.
Timer 0 and 1
Timer 0 and Timer 1 in the AT89C52 operate the same way as Timer 0
and Timer 1 in the AT89C51.
Timer 2
Timer 2 is a 16-bit Timer/Counter that can operate as either a timer or an
event counter. The type of operation is selected by bit C/T2 in the SFR
T2CON. Timer 2 has three operating modes: capture, auto-reload (up or
down counting), and baud rate generator. The modes are selected by bits in
T2CON.
Timer 2 consists of two 8-bit registers, TH2 and TL2. In the Timer
function, the TL2 register is incremented every machine cycle. Since a
machine cycle consists of 12 oscillator periods, the count rate is 1/12 of
t h e oscillator frequency.
Capture Mode
In the capture mode, two options are selected by bit EXEN2 in
T2CON. If EXEN2 = 0, Timer 2 is a 16-bit timer or counter which upon
overflow sets bit TF2 in T2CON. This bit can then be used to generate an
interrupt. If EXEN2 = 1, Timer 2 performs the same operation, but a 1- to-0
transition at external input T2EX also causes the cur- rent value in TH2 and
TL2 to be captured into RCAP2H and RCAP2L, respectively. In addition, the
transition at T2EX causes bit EXF2 in T2CON to be set. The EXF2 bit, like
TF2, can generate an interrupt. The capture mode is illustrated.
AUTO- RELOAD (UP OR DOWN COUNTER)
Timer 2 can be programmed to count up or down when configured in its
16-bit auto-reload mode. This feature is invoked by the DCEN (down counter
enable) bit located in the SFR T2MOD. upon reset , the DCEN bit is set to 0
so that timer 2 will default to count up. When DCEN is set Timer 2 can count
up or down, depending on the value of the T2EX pin.
Baud Rate Generator
Timer 2 is selected as the baud rate generator by setting TCLK and/or
RCLK in T2CON. Note that the baud rates for transmit and receive can be
different if Timer for the other function. Setting RCLK and/or TCLK puts
timer 2 into its baud rate generator mode. The baud rate generator mode is
similar to the auto-reload mode, in that a rollover in TH2 causes the Timer 2
registers to be reloaded with the 16-bit value in registers RCAP2H and
RCAP2L, which are preset by software.
The baud rates in Modes 1 and 3 are determined by Timer 2’s overflow
rate according to the following equation.
Modes 1 and 3 baud rates = timer 2 overflow rate
16
The Timer can be configured for either timer or counter operation. In
most applications, it is configured for timer operation (CP/T2 = 0). The timer
operation is different for Timer 2 when it is used as a baud rate generator.
Normally, as a timer, it increments every machine cycle (at 1/12 the oscillator
frequency).
UART
The UART in the AT89C52 operates the same way as the UART in the
AT89C51.
Interrupts
The AT89C52 has a total of six interrupt vectors: two external interrupts
(INT0 and INT1), three timer interrupts (Timers 0, 1, and 2), and the serial
port interrupt.
Each of these interrupt sources can be individually enabled or disabled by
setting or clearing a bit in Special Function Register IE. IE also contains a
global disable bit, EA, which disables all interrupts at once.
Note that Table shows that bit position IE.6 is unimplemented. In the
A T 89 C 5 1, bit position IE.5 is a l s o unimplemented. User software
should not write 1s to these bit positions, since they ma y be used in future
AT8 9 products.
Timer 2 interrupt is generated by the logical OR of bits TF2 and EXF2 in
register T2CON. Neither of these flags is cleared by hardware when the
service routine is vectored to. In fact, the service routine may have to
determine whether it was TF2 or EXF2 that generated the interrupt, and that
bit will have to be cleared in software.
The Timer 0 and Timer 1 flags, TF0 and TF1, are set at S5P2 of the
cycle in which the timers overflow. The values are then polled by the circuitry
in the next cycle. However, the Timer 2 flag, TF2, is set at S2P2 and is
polled in the same cycle in which the timer overflows.
Ideal Mode
In idle mode, the CPU puts itself to sleep while all the on- chip
peripherals remain active. The mode is invoked by software. The content of
the on-chip RAM and all the special functions registers remain unchanged
during this mode. The idle mode can be terminated by any enabled interrupt
or by a hardware reset.
Note that when idle mode is terminated by a hardware reset, the device
normally resumes program execution from where it left off, up to two
machine cycles before the internal reset algorithm takes control. On-chip
hardware inhibits access to internal RAM in this event, but access to the port
pins is not inhibited. To eliminate the possibility of an unexpected write to a
port pin when idle mode is terminated by a reset, the instruction following
the one that invokes idle mode should not write to a port pin or to external
memory.
Power down Mode
In the power-down mode, the oscillator is stopped, and the instruction
that invokes power-down is the last instruction executed. The on-chip RAM
and Special Function Register in their values until the power-down mode
is terminated. The only exit from power-down is a hardware reset. Reset
redefines the SFRs but does not change the on-chip RAM. The reset should
not be activated before VCC.is restored to its normal operating level and must
be held active long enough to allow the oscillator to restart and stabilize.
6.6 16*2 LCD display
Fig. of LCD Display
FEATURES
• 5 x 8 dots with cursor
• Built-in controller (KS 0066 or Equivalent)
• + 5V power supply (Also available for + 3V)
• 1/16 duty cycle
• B/L to be driven by pin 1, pin 2 or pin 15, pin 16 or A.K (LED)
• N.V. optional for + 3V power supply
6.7 Transistor
A transistor is a semiconductor device used to amplify and switch
electronic signals and power. It is composed of a semiconductor material with at
least three terminals for connection to an external circuit. A voltage or current
applied to one pair of the transistor's terminals changes the current flowing
through another pair of terminals. Because the controlled (output) power can be
much more than the controlling (input) power, a transistor can amplify a signal.
Today, some transistors are packaged individually, but many more are found
embedded in integrated circuits.
The transistor is the fundamental building block of modern electronic
devices, and is ubiquitous in modern electronic systems. Following its release in
the early 1950s the transistor revolutionized the field of electronics, and paved
the way for smaller and cheaper radios, calculators, and computers, among other
things.
The essential usefulness of a transistor comes from its ability to use a
small signal applied between one pair of its terminals to control a much larger
signal at another pair of terminals. This property is called gain. A transistor can
control its output in proportion to the input signal; that is, it can act as an
amplifier. Alternatively, the transistor can be used to turn current on or off in a
circuit as an electrically controlled switch, where the amount of current is
determined by other circuit elements.
There are two types of transistors, which have slight differences in how
they are used in a circuit. A bipolar transistor has terminals labeled base,
collector, and emitter. A small current at the base terminal (that is, flowing from
the base to the emitter) can control or switch a much larger current between the
collector and emitter terminals. For a field-effect transistor, the terminals are
labeled gate, source, and drain, and a voltage at the gate can control a current
between source and drain.
The image to the right represents a typical bipolar transistor in a circuit.
Charge will flow between emitter and collector terminals depending on the
current in the base. Since internally the base and emitter connections behave
like a semiconductor diode, a voltage drop develops between base and emitter
while the base current exists. The amount of this voltage depends on the
material the transistor is made from, and is referred to as VBE.
Transistor
FEATURES
Low current (max. 100 mA) Low voltage (max. 65 V).
APPLICATIONS
General purpose switching and amplification.
DESCRIPTION
NPN transistor in a TO-92; SOT54 plastic package. PNP complements:
BC556 and BC557.
6.8 IC (7805,7812)
Features
• Output Current up to 1A
• Output Voltages of 5, 6, 8, 9, 10, 12, 15, 18, 24V
• Thermal Overload Protection
• Short Circuit Protection
• Output Transistor Safe Operating Area Protection
DESCRIPTION
The MC78XX/LM78XX/MC78XXA series of three terminal
positive regulators are available in the TO-220/D-PAK package and with
several fixed output voltages, making them useful in a wide range of
applications. Each type employs internal current limiting, thermal shut
down and safe operating area protection, making it essentially
indestructible. If adequate heat sinking is provided, they can deliver
over 1A output current. Although designed primarily as fixed
voltage
regulators, these
devices
can
be
used
components to obtain adjustable voltages and currents.
Internal Block Digram
with
external
Electrical Characteristics (7805)
(Refer to test circuit ,0 C < TJ < 125 C, IO = 500mA, VI = 10V, CI=
0.33 F, CO= 0.1 F, unless otherwise specified)
Parameter
Symbol
Conditions
Min.
Typ.
Max.
4.9
5
5.1
4.8
5
5.2
VI = 7.5V to 25V
IO = 500mA
-
5
50
VI = 8V to 12V
-
3
50
TJ
Output Voltage
Line Regulation (Note1)
VO
Regline
=+25 oC
IO = 5mA to 1A, PO  15W
VI = 7.5V to 20V
VI= 7.3V to 20V
-
5
50
VI= 8V to 12V
-
1.5
25
TJ
IO = 5mA to 1.5A
-
9
100
IO = 5mA to 1A
-
9
100
IO = 250mA to 750mA
-
4
50
TJ =+25 Oc
-
5.0
6
IO = 5mA to 1A
-
-
0.5
VI = 8 V to 25V, IO = 500mA
-
-
0.8
=+25 oC
-
-
0.8
TJ =+25 oC
=+25 oC
Load Regulation (Note1)
Quiescent Current
Quiescent Current
Change
Regload
IQ
IQ
VI = 7.5V to 20V, TJ
Unit
V
mV
mV
mA
mA
Output Voltage Drift
V/ T
Io = 5mA
-
-0.8
-
mV/ oC
Output Noise Voltage
VN
f = 10Hz to 100KHz
TA =+25 oC
-
10
-
V/Vo
Ripple Rejection
RR
f = 120Hz, IO = 500mA
VI = 8V to 18V
-
68
-
dB
Dropout Voltage
VDrop
IO = 1A, TJ =+25 oC
-
2
-
V
Output Resistance
rO
f = 1KHz
-
17
-
m
Short Circuit Current
ISC
VI= 35V, TA =+25 oC
-
250
-
mA
-
2.2
-
A
Peak Current
IPK
T J=
+25 oC
Load and line regulation are specified at constant junction temperature.
Changes in Vo due to heating effects must be taken into account
separately. Pulse testing with low duty is used.
Electrical Characteristics (7812)
(Refer to test circuit ,0 C < TJ < 125 C, IO = 500mA, VI =19V, CI=
0.33 F, CO=0.1 F, unless otherwise specified)
Parameter
Output Voltage
Symbol
VO
12
12.5
11.4
12
12.6
VI = 14.5V to 30V
-
10
240
VI = 16V to 22V
-
3.0
120
IO = 5mA to 1.5A
-
11
240
IO = 250mA to 750mA
-
5.0
120
TJ =+25 oC
-
5.1
8.0
IO = 5mA to 1.0A
-
0.1
0.5
VI = 14.5V to 30V
-
0.5
1.0
-
-1
-
mV/ oC
-
76
-
V/Vo
55
71
-
dB
IO = 1A, TJ=+25 oC
-
2
-
V
TJ =+25 oC
Regload TJ =+25 oC
IQ
Output Voltage Drift
VO/ T
Unit
11.5
Load Regulation (Note1)
Quiescent Current Change
Typ. Max.
5.0mA  IO1.0A, PO15W
VI = 14.5V to 27V
Regline
IQ
Min.
TJ =+25 oC
Line Regulation (Note1)
Quiescent Current
MC7812
Conditions
IO = 5mA
o
Output Noise Voltage
VN
f = 10Hz to 100KHz, TA =+25 C
Ripple Rejection
RR
f = 120Hz
VI = 15V to 25V
Dropout Voltage
VDrop
V
mV
mV
mA
mA
Output Resistance
rO
f = 1KHz
-
18
-
m
Short Circuit Current
ISC
VI = 35V, TA=+25 oC
-
230
-
mA
-
2.2
-
A
Peak Current
IPK
TJ =
+25 oC
Load and line regulation are specified at constant junction temperature.
Changes in VO due to heating effects must be taken into account separately.
Pulse testing with low duty is used.
Chapter 7
Advantages and limitations
Advantages of RFID over bar coding:
1. No "line of sight" requirements: Bar code reads can sometimes be limited
or problematic due to the need to have a direct "line of sight" between a
scanner and a bar code. RFID tags can be read through materials without
line of sight.
2. More automated reading: RFID tags can be read automatically when a
tagged product comes past or near a reader, reducing the labor required to
scan product and allowing more proactive, real-time tracking.
3. Improved read rates: RFID tags ultimately offer the promise of higher read
rates than bar codes, especially in high-speed operations such as carton
sortation.
4. Greater data capacity: RFID tags can be easily encoded with item details
such as lot and batch, weight, etc.
5. "Write" capabilities: Because RFID tags can be rewritten with new data as
supply chain activities are completed, tagged products carry updated
information as they move throughout the supply chain.
Common Problems with RFID
Some common problems with RFID are reader collision and tag collision.
Reader collision occurs when the signals from two or more readers overlap. The
tag is unable to respond to simultaneous queries. Systems must be carefully set
up to avoid this problem Tag collision occurs when many tags are present in a
small area; but since the read time is very fast, it is easier for vendors to develop
systems that ensure that tags respond one at a time. See Problems with RFID for
more details.
Chapter 8
Conclusion and Bibliography
CONCLUSION:
Thus, There are various applications of this project at different-different
places. This project is also cheap and can be used on large scale. One more is by
adding different types of controllers like ATMEL(AT89C51/52) etc. and also
replacing latest RFID module and some compatible component we can use
some different applications at low cost.
BIBLIOGRAPHY
•
Circuit reference taken
www.electronicsforu.com
from
www.circuitstoday.com
•
Reference from www.technologystudent.com
•
Reference from the book
and