INTRODUCTION OBJECTIVE: During a day library managers have to supervise many activities within their libraries. These activities have to be performed smoothly and simultaneously for the benefit of all persons concerned. Some of the important functions in library are: check –in/check-out of items, check inventory. If each of these functions is done by conventional methods, they will take time and lead to inefficiencies and unsatisfactory services to the library patrons. This is tedious and slow. If by using RFID technology this process is made for time efficient, then it could be recommended. As far as shelving is concerned, in a conventional library, it is done manually. In most busy libraries many books can be issued during the day so by using this RFID technology we can simplify the work for a librarian. Existing System: The present existing system is consisting of libraries and managing team for regular watching. It is in form of giving written slips to the students and regular renewals and returns. The present existing system requires regular maintenance and regular check up of students. This is 1
Transcript
INTRODUCTION
OBJECTIVE:
During a day library managers have to supervise many activities within their
libraries. These activities have to be performed smoothly and simultaneously for the benefit
of all persons concerned. Some of the important functions in library are: check –in/check-out
of items, check inventory.
If each of these functions is done by conventional methods, they will take time
and lead to inefficiencies and unsatisfactory services to the library patrons. This is tedious
and slow.
If by using RFID technology this process is made for time efficient, then it
could be recommended. As far as shelving is concerned, in a conventional library, it is done
manually. In most busy libraries many books can be issued during the day so by using this
RFID technology we can simplify the work for a librarian.
Existing System:
The present existing system is consisting of libraries and managing team for
regular watching. It is in form of giving written slips to the students and regular renewals and
returns. The present existing system requires regular maintenance and regular check up of
students. This is burdensome to librarian and time consuming process. As the number of
students increases it is it is burden to librarian.
The following made to new invention :
Need regular maintenance
Time consuming
Burden to librarian
Proposed System:
It is purely controller based system, which have following features
Time saving devices free them to help customer better
Can be flexible working schedules
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Faster and accurate
Check-in/check-out o all books
1.1 EMBEDDED SYSTEMS
An embedded system is some combination of computer hardware and software, either fixed
in capability or programmable, that is specifically designed for a particular function.
A general-purpose definition of embedded systems is that they are devices used to control,
monitor or assist the operation of equipment, machinery or plant. "Embedded" reflects the
fact that they are an integral part of the system. In many cases their embeddedness may be
such that their presence is far from obvious to the casual observer and even the more
technically skilled might need to examine the operation of a piece of equipment for some
time before being able to conclude that an embedded control system was involved in its
functioning. At the other extreme a general-purpose computer may be used to control the
operation of a large complex processing plant, and its presence will be obvious.
The very simplest embedded systems are capable of performing only a single function or set
of functions to meet a single predetermined purpose. In more complex systems an application
program that enables the embedded system to be used for a particular purpose in a specific
application determines the functioning of the embedded system. The ability to have programs
means that the same embedded system can be used for a variety of different purposes. In
some cases a microprocessor may be designed in such a way that application software for a
particular purpose can be added to the basic software in a second process, after which it is not
possible to make further changes. The applications software on such processors is sometimes
referred to as firmware
The simplest devices consist of a single microprocessor (often called a "chip”), which may
itself be packaged with other chips in a hybrid system or Application Specific Integrated
Circuit (ASIC). Its input comes from a detector or sensor and its output goes to a switch or
activator which (for example) may start or stop the operation of a machine or, by operating a
valve, may control the flow of fuel to an engine. As the embedded system is the combination
of both software and hardware
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Fig 1.1 Block diagram of Embedded System
Software deals with the languages like ALP, C, and VB etc., and Hardware deals with
Processors, Peripherals, and Memory.
Memory: It is used to store data or address.
Peripherals: These are the external devices connected
Processor: It is an IC which is used to perform some task
Processors are classified into four types like:
1. Micro Processor (µp)
2. Micro controller (µc)
3. Digital Signal Processor (DSP)
4. Application Specific Integrated Circuits (ASIC)
Micro Processor (µp):
It is an electronic chip which performs arithmetic and logical operations with assistance of
internal memory.
Embedded
System
Software Hardware
ALPCVB
Etc.,
ProcessorPeripheralsmemory
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Micro Controller (µc):
It is a highly integrated micro processor designed for specific use in embedded systems.
Applications of embedded system
Introduction
Embedded controllers may be found in many different kinds of system and are used for many
different applications. The list, which follows, is indicative rather than exhaustive. An item in
the list may be relevant to a particular company because either (a) it is or involves a core
process or product, (b) it is or involves an ancillary function or service performed by the
company or (c) it refers to a product or service provided by a contractor under some form of
agreement and the vulnerability of the supplier may need to be considered.
List of applications of embedded systems
Manufacturing and process control
Construction industry
Transport
Buildings and premises
Domestic service
A manufacturing company has provided the following list of embedded systems
Multi-loop control and monitoring - DCS, SCADA, telemetry
Panel mounted devices - Control, display, recording and operations
Safety and security - Alarm and trip systems, fire and gas systems, buildings and facilities
security
Field devices - measurement, actuation
Analytical systems - Laboratory systems; on-line/ plant systems
Tools - for design, documentation, testing, maintenance
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1.2 BLOCK DIAGRAM
Fig1.2 Block Diagram of RFID based LMS
1.3 BLOCK DIAGRAM EXPLANATION
This Project mainly consists of Power Supply section, Microcontroller section, LCD
display section, Serial Communication section and RFID section.
Power Supply Section: This section is meant for supplying Power to all the sections
mentioned above. It basically consists of a Transformer to step down the 230V ac to 9V ac
followed by diodes. Here diodes are used to rectify the ac to dc. After rectification the
obtained rippled dc is filtered using a capacitor Filter. A positive voltage regulator is used to
regulate the obtained dc voltage.
But here in this project two power supplies are used one is meant to supply operating
voltage for Microcontroller and the other is to supply control voltage for Relays.
MICRO
CONTROLLER
R
Power supply
RFID card
RFID
READER
M
A
X
2
3
2
BUZZER
LCD Display
EEPROM
AT24C08
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Microcontroller Section: This section forms the control unit of the whole project. This
section basically consists of a Microcontroller with its associated circuitry like Crystal with
capacitors, Reset circuitry, Pull up resistors (if needed) and so on. The Microcontroller forms
the heart of the project because it controls the devices being interfaced and communicates
with the devices according to the program being written.
LCD Display Section: This section is basically meant to show up the status of the project.
This project makes use of Liquid Crystal Display to display / prompt for necessary
information.
RFID Reader, RFID Card: RF transmitted is used for transmitting the RF signals in our
project. Transmitter is called as “Data in, Antenna out” used to convert serial data received
from RF card into RF wave which in then radiates in to space. Receiver called “antenna data
out” used to convert RF waves in to serial data.
Serial communication: A standard serial interface for PC, RS232C, requires negative logic,
i.e., logic 1 is -3V to -12V and logic 0 is +3V to +12V. To convert TTL logic, say, TxD and
RxD pins of the microcontroller thus need a converter chip. A MAX232 chip has long been
using in many microcontrollers boards. It is a dual RS232 receiver / transmitter that meets all
RS232 specifications while using only +5V power supply.
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1.4 SCHEMATIC
This schematic explanation includes the detailed pin connections of every device
with the microcontroller.
Let us see the pin connections of each and every device with the microcontroller
in detail.
Fig 1.3 Schematic of RFID based LMS
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1.4.1 SCHEMATIC EXPLANATION:
POWER SUPPY
Firstly, the required operating voltage for Microcontroller 89S52 is 5V. Hence the 5V
D.C. power supply is needed by the same. This regulated 5V is generated by first stepping
down the 230V to 9V by the step down transformer.
In the both the Power supplies the step downed a.c. voltage is being rectified by the
Bridge Rectifier. The diodes used are 1N4007. The rectified a.c voltage is now filtered using
a ‘C’ filter. Now the rectified, filtered D.C. voltage is fed to the Voltage Regulator. This
voltage regulator allows us to have a Regulated Voltage. In Power supply given to
Microcontroller 5V is generated using 7805. The rectified; filtered and regulated voltage is
again filtered for ripples using an electrolytic capacitor 100μF. Now the output from the first
section is fed to 40th pin of 89S52 microcontroller to supply operating voltage and from other
power supply to circuitry.
MICRO CONTROLLER
The microcontroller 89S52 with Pull up resistors at Port0 and crystal oscillator of
11.0592 MHz crystal in conjunction with couple of capacitors of is placed at 18 th& 19th pins
of 89S52 to make it work (execute) properly
RFID Reader, RFID Card: RF transmitter is used for transmitting the RF signals in
our project. Transmitter is called as “Data in, Antenna out” used to convert serial data
received from RF card into RF wave which in tern radiates in to space. Receiver called
“antenna data out” used to convert RF waves in to serial data.
Serial communication : A standard serial interface for PC, RS232C, requires negative
logic, i.e., logic 1 is -3V to -12V and logic 0 is +3V to +12V. To convert TTL logic, say, TxD
and RxD pins of the microcontroller thus need a converter chip. A MAX232 chip has long
been using in many microcontrollers boards. It is a dual RS232 receiver / transmitter that
meets all RS232 specifications while using only +5V power supply.
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LCD: A liquid crystal display (LCD) is a thin, flat display device made up of any number
of color or monochrome pixels arrayed in front of a light source or reflector. Each pixel
consists of a column of liquid crystal molecules suspended between two transparent
electrodes, and two polarizing filters, the axes of polarity of which are perpendicular to each
other. Without the liquid crystals between them, light passing through one would be blocked
by the other. The liquid crystal twists the polarization of light entering one filter to allow it to
pass through the other.
Switches: used for the entering input values
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HARDWARE DESCRIPTION
The Hardware components used in this project are
1. Microcontroller
2. RFID
3. RS 232
4. LCD
5. Regulated Power Supply
2.1 MICRO CONTROLLER AT89S52
2.1.1 Introduction:
A Micro controller consists of a powerful CPU tightly coupled with memory, various
I/O interfaces such as serial port, parallel port timer or counter, interrupt controller, data
acquisition interfaces-Analog to Digital converter, Digital to Analog converter, integrated on
to a single silicon chip.
If a system is developed with a microprocessor, the designer has to go for external
memory such as RAM, ROM, EPROM and peripherals. But controller is provided all these
facilities on a single chip. Development of a Micro controller reduces PCB size and cost of
design. Intel has introduced a family of Micro controllers called the MCS-51.
Fig 2.1 Picture of Micro Controller
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2.1.2 Difference between 8051 and 8052
The 8052 microcontroller is the 8051's "big brother." It is a slightly more powerful microcontroller, sporting a number of additional features which the developer may make use of:
256 bytes of Internal RAM (compared to 128 in the standard 8051).
A third 16-bit timer, capable of a number of new operation modes and 16-bit reloads.
Additional SFRs to support the functionality offered by the third timer.
AT89S52 is a low-power, high-performance CMOS 8-bit micro controller with
8Kbytes of in-system programmable Flash memory. The device is manufactured Using
Atmel’s AT89S52
2.1.3 Features of AT89S52
• Compatible with MCS-51 Products
• 8K Bytes of In-System Programmable (ISP) Flash Memory
– Endurance: 1000 Write/Erase Cycles
• 4.0V to 5.5V Operating Range
• Fully Static Operation: 0 Hz to 33 MHz
• Three-level Program Memory Lock
• 256K Internal RAM
• 32 Programmable I/O Lines
• 3 16-bit Timer/Counters
• Eight Interrupt Sources
• Full Duplex UART Serial Channel
• Low-power Idle and Power-down Modes
• Interrupt Recovery from Power-down Mode
• Watchdog Timer
• Dual Data Pointer
• Power-off Flag
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2.1.4 Description of Microcontroller 89S52
The high-density nonvolatile memory technology and is compatible with the industry-
standard 80C51 micro controller. The on-chip Flash allows the program memory to be
reprogrammed in-system or by a conventional nonvolatile memory programmer. By
combining a versatile 8-bit CPU with in-system programmable flash one monolithic chip; the
Atmel AT89S52 is a powerful micro controller, which provides a highly flexible and cost-
effective solution to many embedded control applications.
Fig 2.2 Architecture of micro controller 89S52
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2.1.5 TYPES OF MEMORY:
The 89S52 have three general types of memory. They are on-chip memory, external
Code memory and external Ram. On-Chip memory refers to physically existing memory on
the micro controller itself. External code memory is the code memory that resides off chip.
This is often in the form of an external EPROM. External RAM is the Ram that resides off
chip. This often is in the form of standard static RAM or flash RAM.
a) Code memory: Code memory is the memory that holds the actual 89S52 programs that is
to be run. This memory is limited to 64K. Code memory may be found on-chip or off-
chip. It is possible to have 4K of code memory on-chip and 60K off chip memory
simultaneously. If only off-chip memory is available then there can be 64K of off chip
ROM. This is controlled by pin provided as EA
b) Internal RAM: The 89S52 have a bank of 128 of internal RAM. The internal RAM is
found on-chip. So it is the fastest Ram available. And also it is most flexible in terms of
reading and writing. Internal Ram is volatile, so when 89S52 is reset, this memory is
cleared. 128 bytes of internal memory are subdivided. Internal RAM also contains 128
bits, which are addressed from 20h to 2Fh. These bits are bit addressed i.e. each
individual bit of a byte can be addressed by the user. They are numbered 00h to 7Fh. The
user may make use of these variables with commands such as SETB and CLR.
c) Flash Memory: Flash memory (sometimes called "flash RAM") is a type of constantly-
powered nonvolatile that can be erased and reprogrammed in units of memory called
blocks. Flash memory is often used to hold control code such as the basic input/output
system (BIOS) in a personal computer. When BIOS needs to be changed (rewritten), the
flash memory can be written to in block (rather than byte) sizes, making it easy to update.
On the other hand, flash memory is not useful as random access memory (RAM) because
RAM needs to be addressable at the byte (not the block) level.
Flash memory gets its name because the microchip is organized so that a section of
memory cells are erased in a single action or "flash." The erasure is caused by Fowler-
Nordheim tunneling in which electrons pierce through a thin dielectric material to remove
an electronic charge from a floating gate associated with each memory cell.
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Flash memory is used in digital cellular phones, digital cameras, LAN switches, PC
Cards for notebook computers, digital set-up boxes, embedded controllers, and other
devices.
TECHNICAL OVERVIEW OF FLASH MEMORY
Flash memory is a nonvolatile memory using NOR technology, which allows the user
to electrically program and erase information. Intel® Flash memory uses memory cells
similar to an EPROM, but with a much thinner, precisely grown oxide between the floating
gate and the source. Flash programming occurs when electrons are placed on the floating
gate. The charge is stored on the floating gate, with the oxide layer allowing the cell to be
electrically erased through the source.
Memory Type Features
FLASH Low-cost, high-density, high-speed architecture; low power; high reliability
ROMRead-Only Memory
Mature, high-density, reliable, low cost; time-consuming mask required, suitable for high production with stable code
SRAMStatic Random-Access Memory
Highest speed, high-power, low-density memory; limited density drives up cost
EPROMElectrically Programmable Read-Only Memory
High-density memory; must be exposed to ultraviolet light for erasure
Under steady state (non-transient) conditions, IOL must be externally limited as follows:
Maximum IOL per port pin: 10 mA
Maximum IOL per 8-bit port: Port 0: 26 mA
Ports 1, 2, 3: 15 mA
Maximum total IOL for all output pins: 71 mA
If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current greater than the listed test conditions.
Minimum VCC for Power-down is 2V.
SPECIAL FUNCTION REGISTER (SFR) MEMORY:
Special Function Registers (SFR s) are areas of memory that control specific
functionality of the 8051 processor. For example, four SFRs permit access to the 8051’s 32
input/output lines. Another SFR allows the user to set the serial baud rate, control and access
timers, and configure the 8051’s interrupt system.
THE ACCUMULATOR:
The Accumulator, as its name suggests is used as a general register to accumulate the
results of a large number of instructions. It can hold 8-bit (1-byte) value and is the most
versatile register.
THE “R” REGISTERS:
The “R” registers are a set of eight registers that are named R0, R1. Etc up to R7.
These registers are used as auxiliary registers in many operations
THE “B” REGISTERS:
The “B” register is very similar to the accumulator in the sense that it may hold an 8-
bit (1-byte) value. Two only uses the “B” register 8051 instructions: MUL AB and DIV AB.
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THE DATA POINTER:
The Data pointer (DPTR) is the 8051’s only user accessible 16-bit (2Bytes) register.
The accumulator, “R” registers are all 1-Byte values. DPTR, as the name suggests, is used to
point to data. It is used by a number of commands, which allow the 8051 to access external
memory.
THE PROGRAM COUNTER AND STACK POINTER:
The program counter (PC) is a 2-byte address, which tells the 8051 where the next
instruction to execute is found in memory. The stack pointer like all registers except DPTR
and PC may hold an 8-bit (1-Byte) value
AD:
An “addressing mode” refers that you are addressing a given memory location. In
summary, the addressing modes are as follows, with an example of each:
This instruction causes the 8051 to analyze Special Function Register (SFR)
Memory: Special Function Registers (SFRs) are areas of memory that control specific
functionality of the 8051 processor. For example, four SFRs permit access to the 8051’s 32
input/output lines. Another SFR allows the user to set the serial baud rate, control and access
timers, and configure the 8051’s interrupt system.
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.
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Table 2.4 Interrupts
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 the oscillator frequency. In
the Counter function, the register is incremented in response to a 1-to-0 transition at its
corresponding external input pin , T2 .
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 current value in
TH2 and TL2 to be captured into RCAP2H and RCAP2L , respectively.
AUTO-RELOAD (UP OR DOWN COUNTER):
Timer2 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
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T2MOD.Upon reset , the DCEN bit is set to 0 so that timer2 will default to count up.
When DCEN is set, Timer2 can count up or down, depending on the value of the T2EX pin.
In this mode, two options are selected by bit EXEN2 in T2CON. If EXEN2 = 0 , Timer2
counts up to 0FFFFH and then sets the TF2 bit upon overflow . If EXEN2 = 1 , a 16-
bit reload can be triggered either by an overflow or by a 1-to-0 transition at external
input T2EX.
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 2 is used for the receiver or transmitter and Timer 1is used for the other
function .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
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Timer 0 functions as either a timer or event counter in four modes of operation. Timer
0 is controlled by the four lower bits of the TMOD register and bits 0, 1, 4 and 5 of the
TCON register Mode 0 ( 13-bit Timer). Mode 0 configures timer 0 as a 13-bit timer which is
set up as an 8-bit timer (TH0 register) with a modulo 32 prescaler implemented with the
lower five bits of the TL0 register.
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2.2 RFID (RADIO FREQUENCY IDENTIFIER)
Radio-frequency identification (RFID) is an automatic identification method, relying
on storing and remotely retrieving data using devices called RFID tags or transponders. An
RFID tag is an object that can be applied to or incorporated into a product, animal, or person
for the purpose of identification using radio waves. Some tags can be read from several
meters away and beyond the line of sight of the reader. Most RFID tags contain at least two
parts. One is an integrated circuit for storing and processing information, modulating and
demodulating a (RF) signal, and other specialized functions. The second is an antenna for
receiving and transmitting the signal. Chip less RFID allows for discrete identification of tags
without an integrated circuit, thereby allowing tags to be printed directly onto assets at a
lower cost than traditional tags.
Fig 2.5 RFID System
Primarily, the two main components involved in a Radio Frequency Identification
system are the Transponder (tags that are attached to the object) and the Interrogator (RFID
reader). Communication between the RFID reader and tags occurs wirelessly and generally
does not require a line of sight between the devices
2.2.1 RFID TRANSPONDER / TAG
An RFID transponder, considered as a next generation barcode, is a miniscule
microchip that is attached to an antenna. They come in a wide variety of sizes, shapes, and
forms and can be read through most materials with the exception of conductive materials like
water and metal, but with modifications and positioning even these can be overcome.
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Fig 2.6 RFID Tag
PASSIVE TAGS
Passive tags are generally smaller, lighter and less expensive than those that are
active and can be applied to objects in harsh environments, are maintenance free and will last
for years. These transponders are only activated when within the response range of a reader.
The RFID reader emits a low-power radio wave field which is used to power up the tag so as
to pass on any information that is contained on the chip.
ACTIVE TAGS
Active tags differ in that they incorporate their own power source, where as the tag is
a transmitter rather than a reflector of radio frequency signals which enables a broader range
of functionality like programmable and read/write capabilities.
SEMI-PASSIVE TAGS
Semi-passive tags are similar to active tags in that they have their own power
source, but the battery only powers the microchip and does not power the broadcasting of a
signal. The response is usually powered by means of backscattering the RF energy from the
reader, where energy is reflected back to the reader as with passive tags. An additional
application for the battery is to power data storage. Semi-passive tags leads to greater
sensitivity than passive tags, typically 100 times more. The enhanced sensitivity can be
leveraged as Semi-passive tags have three main advantages: greater sensitivity than passive
tags; longer battery powered life cycle than active tags; they can perform active functions
(such as temperature logging) under their own power, even when no reader is present for
powering the circuitry.
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2.2.2 RFID READER/ INTERROGATOR
An RFID reader typically contains a module (transmitter and receiver), a control
unit and a coupling element (antenna). The reader has three main functions: energizing,
demodulating and decoding. In addition, readers can be fitted with an additional interface that
converts the radio waves returned from the RFID tag into a form that can then be passed on to
another system, like a computer or any programmable logic controller. Anti-Collision
algorithms permit the simultaneous reading of large numbers of tagged objects, while
ensuring that each tag is read only once.
Fig 2.7 RFID Reader
RFID operates in several frequency bands. The exact frequency is controlled by the Radio
Regulatory body in each country.
2.2.3 RFID Frequencies
The generic frequencies for RFID are:
125 - 134 kHz
13.56 MHz
UHF (400 – 930 MHz)
2.45 GHz
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5.8 GHz
Although there are other frequencies used, these are the main ones. In the UHF band,
there are two areas of interest. Several frequencies in the 400 MHz band and then the band
860 – 930 MHz Each of the frequency bands have advantages and disadvantages for
operation. The lower frequencies 125-134 kHz and 13.56 MHz work much better near water
or humans than do the higher frequency tags. Comparing passive tags, the lower frequencies
usually have less range, and they have a slower data transfer rate. The higher frequency
ranges have more regulatory controls and differences from country to country.
2.2.4 Applications
RFID tags are useful for a huge variety of applications. Some of these applications
prevention, and smart homes and offices. RFID tags are also implanted in all kinds of
personal and consumer goods, for example, passports, partially assembled cars, frozen
dinners, ski-lift passes, clothing, and public transportation tickets. Implantable RFID tags for
animals allow concerned owners to label their pets and livestock. Verichip Corp. has also
created a slightly adapted implantable RFID chip, the size of a grain of rice, for use in
humans. Since its introduction, the Verichip was approved by the U.S. Food and Drug
Administration, and this tiny chip is currently deployed in both commercial and medical
systems.
2.3 SERIAL COMMUNICATION
Computers can transfer data in two ways: parallel and serial. In parallel data
transfers, often 8 or more lines (wire conductors) are used to transfer data to a device that is
only a few feet away. Examples of parallel data transfer are printers and hard disks; each
uses cables with many wire strips. Although in such cases a lot of data can be transferred in a
short amount of time by using many wires in parallel, the distance cannot be great. To
transfer to a device located many meters away, the serial method is used. In serial
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communication, the data is sent one bit at a time, in contrast to parallel communication, in
which the data is sent a byte or more at a time
Serial data communication uses two methods, asynchronous and synchronous. The
synchronous method transfers a block of data at a time, while the asynchronous method
transfers a single byte at a time.
In data transmission if the data can be transmitted and received, it is a duplex
transmission. This is in contrast to simplex transmissions such as with printers, in which the
computer only sends data. Duplex transmissions can be half or full duplex, depending on
whether or not the data transfer can be simultaneous. If data is transmitted one way at a time,
it is referred to as half duplex. If the data can go both ways at the same time, it is full duplex.
Of course, full duplex requires two wire conductors for the data lines, one for transmission
and one for reception, in order to transfer and receive data simultaneously.
Asynchronous serial communication and data framing
The data coming in at the receiving end of the data line in a serial data transfer is all
0s and 1s; it is difficult to make sense of the data unless the sender and receiver agree on a set
of rules, a protocol, on how the data is packed, how many bits constitute a character, and
when the data begins and ends.
Start and stop bits
Asynchronous serial data communication is widely used for character-oriented
transmissions, while block-oriented data transfers use the synchronous method. In the
asynchronous method, each character is placed between start and stop bits. This is called
framing. In the data framing for asynchronous communications, the data, such as ASCII
characters, are packed between a start bit and a stop bit. The start bit is always one bit, but the
stop bit can be one or two bits. The start bit is always a 0 (low) and the stop bit (s) is 1
(high).
Data transfer rate
The rate of data transfer in serial data communication is stated in bps (bits per
second). Another widely used terminology for bps is baud rate. However, the baud and bps
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rates are not necessarily equal. This is due to the fact that baud rate is the modem
terminology and is defined as the number of signal changes per second. In modems a single
change of signal, sometimes transfers several bits of data. As far as the conductor wire is
concerned, the baud rate and bps are the same, and for this reason we use the bps and baud
interchangeably.
The data transfer rate of given computer system depends on communication ports
incorporated into that system. For example, the early IBMPC/XT could transfer data at the
rate of 100 to 9600 bps. In recent years, however, Pentium based PCS transfer data at rates
as high as 56K bps. It must be noted that in asynchronous serial data communication, the
baud rate is generally limited to 100,000bps.
2.3.1 MAX 232
A standard serial interface for PC, RS232C, requires negative logic, i.e., logic 1
is -3V to -12V and logic 0 is +3V to +12V. To convert TTL logic, say, TxD and RxD pins of
the microcontroller thus need a converter chip. A MAX232 chip has long been using in many
microcontrollers boards. It is a dual RS232 receiver / transmitter that meets all RS232
specifications while using only +5V power supply. It has two onboard charge pump voltage
converters which generate +10V to -10V power supplies from a single 5V supply. It has four
level translators, two of which are RS232 transmitters that convert TTL/CMOS input levels
into +9V RS232 outputs. The other two level translators are RS232 receivers that convert
RS232 input to 5V. Typical MAX232 circuit is shown below.
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Fig 2.8 Pin Configuration of MAX 232
2.3.2 Features
1. Operates With Single 5-V Power Supply
2. Lin Bi CMOS Process Technology
3. Two Drivers and Two Receivers
4. ±30-V Input Levels
5. Low Supply Current. 8 mA Typical
6. Meets or Exceeds TIA/EIA-232-F and ITU Recommendation V.28
7. Designed to be Interchangeable with Maximum MAX 232
8. Applications
TIA/EIA-232-F
Battery-Powered Systems
Terminals
Modems
Computers
9. ESD Protection Exceeds 2000 V Per MIL-STD-883, Method 3015
10. Package Options Include Plastic Small-Outline (D, DW) Packages
2.3.3 Circuit Connections
A standard serial interfacing for PC, RS232C, requires negative logic, i.e., logic '1'
is -3V to -12V and logic '0' is +3V to +12V. To convert a TTL logic, say, TxD and RxD pins
of the uC chips, thus need a converter chip. A MAX232 chip has long been using in many uC
boards. It provides 2-channel RS232C port and requires external 10uF capacitors. Carefully
check the polarity of capacitor when soldering the board. A DS275 however, no need external
capacitor and smaller. Either circuit can be used without any problems.
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It provides 2-channel RS232C port and requires external 10uF capacitors. Carefully
check the polarity of capacitor when soldering the board. A DS275 however, no need external
capacitor and smaller. Either circuit can be used without any problems.
Fig 2.9 Circuit connections of Max 232
2.3.4 MAX-232 to DB9 Interface
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Fig 2.10 Max 232 to DB9 interface
2.4 LIQUID CRYSTAL DISPLAY
2.4.1 INTRODUCTION TO LCD:
Liquid crystal displays (LCDs) have materials which combine the properties of both
liquids and crystals. Rather than having a melting point, they have a temperature range within
which the molecules are almost as mobile as they would be in a liquid, but are grouped
together in an ordered form similar to a crystal.
An LCD consists of two glass panels, with the liquid crystal material sand witched in
between them. The inner surface of the glass plates are coated with transparent electrodes
which define the character, symbols or patterns to be displayed polymeric layers are present
in between the electrodes and the liquid crystal, which makes the liquid crystal molecules to
maintain a defined orientation angle.
One each polarizers are pasted outside the two glass panels. These polarizers would
rotate the light rays passing through them to a definite angle, in a particular direction
When the LCD is in the off state, light rays are rotated by the two polarizers and the
liquid crystal, such that the light rays come out of the LCD without any orientation, and
hence the LCD appears transparent.
When sufficient voltage is applied to the electrodes, the liquid crystal molecules
would be aligned in a specific direction. The light rays passing through the LCD would be
rotated by the polarizers, which would result in activating / highlighting the desired
characters.
The LCD’s are lightweight with only a few millimeters thickness. Since the LCD’s
consume less power, they are compatible with low power electronic circuits, and can be
powered for long durations.
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The LCD s doesn’t generate light and so light is needed to read the display. By using
backlighting, reading is possible in the dark. The LCD’s have long life and a wide operating
temperature range.
Changing the display size or the layout size is relatively simple which makes the
LCD’s more customer friendly.
In recent years the LCD is finding widespread use replacing LED s (seven-segment
LED s or other multi-segment LED s).This is due to the following reasons:
1. The declining prices of LCDs.
2. The ability to display numbers, characters and graphics. This is in contrast to LED which is limited to numbers and a few characters.
3. Incorporation of a refreshing controller into the LCD, there by relieving the CPU of the task of refreshing the LCD. In the case of LED s, they must be refreshed by the CPU to keep on displaying the data.
4. Ease of programming for characters and graphics.
Fig 2.11(a) Picture of a LCD Display
Uses
The LCDs used exclusively in watches, calculators and measuring instruments are the
simple seven-segment displays, having a limited amount of numeric data. The recent
advances in technology have resulted in better legibility, more information displaying
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capability and a wider temperature range. These have resulted in the LCDs being extensively
used in telecommunications and entertainment electronics. The LCDs have even started
replacing the cathode ray tubes (CRTs) used for the display of text and graphics, and also in
small TV applications.
F i g 2 . 1 1 ( b ) P i c t u r e s o f L C D C r o s s S e c t i o n a l V i e w
2 . 4 . 2 S P E C I F I C A T I O N S :
Number of Characters: 16 characters x 2 Lines
Character Table: English-European (RS in Datasheet)
This section describes the operation modes of LCD’s then describe how to program and
interface an LCD to 8051 using Assembly and C.
2.4.4 LCD PIN DESCRIPTION:
The LCD discussed in this section has 14 pins. The function of each pin is given in table.
Pin Symbol I/O Description
1 Vss -- Ground
2 Vcc -- +5V power supply
3 VEE -- Power supply to control contrast
4 RS I RS=0 to select command register RS=1 to select data register
5 R/W I R/W=0 for write
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R/W=1 for read
6 E I/O Enable
7 DB0 I/O The 8-bit data bus
8 DB1 I/O The 8-bit data bus
9 DB2 I/O The 8-bit data bus
10 DB3 I/O The 8-bit data bus
11 DB4 I/O The 8-bit data bus
12 DB5 I/O The 8-bit data bus
13 DB6 I/O The 8-bit data bus
14 DB7 I/O The 8-bit data bus
Table 2.5 Pin description for LCD
2.4.5 COMMAND CODES:
The LCD can display a character successfully by placing the
1. Data in Data Register
2. Command in Command Register of LCD
1. Data corresponds to the ASCII value of the character to be printed. This can be done by placing the ASCII value on the LCD Data lines and selecting the Data Register of the LCD by selecting the RS (Register Select) pin.
2. Each and every display location is accessed and controlled by placing respective command on the data lines and selecting the Command Register of LCD by selecting the (Register Select) RS pin.
The commonly used commands are shown below with their operations.
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Code (hex) Command to LCD Instruction Register
1 Clear display screen
2 Return home
4 Decrement cursor
6 Increment cursor
5 Shift display right
7 Shift display left
8 Display off, cursor off
A Display off, cursor on
C Display on, cursor off
E Display on, cursor on
F Display on, cursor blinking
10 Shift cursor position to left
14 Shift cursor position to right
18 Shift the entire display to the left
1C Shift the entire display to the right
80 Force cursor to beginning of 1st line
C0 Force cursor to beginning of 2nd line
38 2 lines and 5x7 matrix
Table 2.6 LCD Command Codes
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2.4.6 LCD INTERFACING:
Sending commands and data to LCDs with a time delay:
To send any command from table 2 to the LCD, make pin RS=0. For data, make RS=1.Then
place a high to low pulse on the E pin to enable the internal latch of the LCD.
Fig 2.12(b) LCD Interfacing
2.5 REGULATEDPOWER SUPPLY
The power supplies are designed to convert high voltage AC mains electricity to a
suitable low voltage supply for electronic circuits and other devices. A RPS (Regulated
Power Supply) is the Power Supply with Rectification, Filtering and Regulation being done
on the AC mains to get a Regulated power supply for Microcontroller and for the other
devices being interfaced to it.
A power supply can by broken down into a series of blocks, each of which performs a
particular function. A d.c power supply which maintains the output voltage constant
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irrespective of a.c mains fluctuations or load variations is known as “Regulated D.C Power
Supply”
For example a 5V regulated power supply system as shown below:
Fig 2.13 Regulated Power Supply
2.5.1 TRANSFORMER:
A transformer is an electrical device which is used to convert electrical power
from one Electrical circuit to another without change in frequency.
Transformers convert AC electricity from one voltage to another with little loss of power.
Transformers work only with AC and this is one of the reasons why mains electricity is AC.
Step-up transformers increase in output voltage, step-down transformers decrease in output
voltage. Most power supplies use a step-down transformer to reduce the dangerously high
mains voltage to a safer low voltage. The input coil is called the primary and the output coil
is called the secondary. There is no electrical connection between the two coils; instead they
are linked by an alternating magnetic field created in the soft-iron core of the transformer.
The two lines in the middle of the circuit symbol represent the core. Transformers waste
very little power so the power out is (almost) equal to the power in. Note that as voltage is
stepped down current is stepped up. The ratio of the number of turns on each coil, called the
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turn’s ratio, determines the ratio of the voltages. A step-down transformer has a large number
of turns on its primary (input) coil which is connected to the high voltage mains supply, and a
small number of turns on its secondary (output) coil to give a low output voltage.
Fig 2.14 Step down Transformer
AN ELECTRICAL TRANSFORMER
Turns ratio = Vp/ VS = Np/NS
Power Out= Power In
VS X IS=VP X IP
Vp = primary (input) voltage
Np = number of turns on primary coil
Ip = primary (input) current
2.5.2 RECTIFIER:
A circuit which is used to convert a.c to dc is known as RECTIFIER. The process of
conversion a.c to d.c is called “rectification”
2.5.2(a) TYPES OF RECTIFIERS:
Half wave Rectifier
Full wave rectifier
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1. Centre tap full wave rectifier.
2. Bridge type full bridge rectifier
Comparison of rectifier circuits:
Parameter
Type of Rectifier
Half wave Full wave Bridge
Number of diodes
1 2 4
PIV of diodes Vm 2Vm Vm
D.C output voltageVm/ 2Vm/ 2Vm/
Vdc,at no-load 0.318Vm 0.636Vm 0.636Vm
Ripple factor 1.21 0.482 0.482
Ripple frequency F 2f 2f
Rectification
efficiency
0.406 0.812 0.812
Transformer
Utilization
Factor(TUF)
0.287 0.693 0.812
RMS voltage Vrms Vm/2 Vm/√2 Vm/√2
Table 2.7 Comparison of rectifier circuits
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Full-wave Rectifier:
From the above comparison we came to know that full wave bridge rectifier as
more advantages than the other two rectifiers. So, in our project we are using full wave bridge
rectifier circuit.
Bridge Rectifier:
A bridge rectifier makes use of four diodes in a bridge arrangement to achieve full-
wave rectification. This is a widely used configuration, both with individual diodes wired as
shown and with single component bridges where the diode bridge is wired internally.
Fig 2.15(a): Linear Power Supply
2.5.2(b) OPERATION:
During positive half cycle of secondary, the diodes D2 and D3 are in forward biased
while D1 and D4 are in reverse biased as shown in the fig(b). The current flow direction is
shown in the fig (b) with dotted arrows.
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Fig 2.15(b): Electrical Transformer
During negative half cycle of secondary voltage, the diodes D1 and D4 are in
forward biased while D2 and D3 are in reverse biased as shown in the fig(c). The current
flow direction is shown in the fig (c) with dotted arrows.
Fig2.15(c): Bridge Rectifier & Operation
Filter:
A Filter is a device which removes the a.c component of rectifier output but allows the d.c
component to reach the load
Capacitor Filter:
We have seen that the ripple content in the rectified output of half wave rectifier is
121% or that of full-wave or bridge rectifier or bridge rectifier is 48% such high percentages
of ripples is not acceptable for most of the applications. Ripples can be removed by one of the
following methods of filtering.
(a) A capacitor, in parallel to the load, provides an easier by –pass for the ripples voltage
though it due to low impedance. At ripple frequency and leave the D.C. to appear at the load.
(b) An inductor, in series with the load, prevents the passage of the ripple current (due to high
impedance at ripple frequency) while allowing the d.c (due to low resistance to d.c)
(c) Various combinations of capacitor and inductor, such as L-section filter ∏ section filter,
multiple section filter etc. which make use of both the properties mentioned in (a) and (b)
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above. Two cases of capacitor filter, one applied on half wave rectifier and another with full
wave rectifier.
Filtering is performed by a large value electrolytic capacitor connected across the DC
supply to act as a reservoir, supplying current to the output when the varying DC voltage
from the rectifier is falling. The capacitor charges quickly near the peak of the varying DC,
and then discharges as it supplies current to the output. Filtering significantly increases the
average DC voltage to almost the peak value (1.4 × RMS value).
To calculate the value of capacitor(C),
C = ¼*√3*f*r*Rl
Where,
f = supply frequency,
r = ripple factor,
Rl = load resistance
Note: In our circuit we are using 1000µF hence large value of capacitor is placed to
reduce ripples and to improve the DC component.
2.5.3 VOLTAGE REGULATOR:
Voltage regulator ICs is available with fixed (typically 5, 12 and 15V) or variable
output voltages. The maximum current they can pass also rates them. Negative voltage
regulators are available, mainly for use in dual supplies. Most regulators include some
automatic protection from excessive current ('overload protection') and overheating ('thermal
protection'). Many of the fixed voltage regulators ICs have 3 leads and look like power
transistors, such as the 7805 +5V 1A regulator shown on the right. The LM7805 is simple to
use. You simply connect the positive lead of your unregulated DC power supply (anything
from 9VDC to 24VDC) to the Input pin, connect the negative lead to the Common pin and
then when you turn on the power, you get a 5 volt supply from the output pin.
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Fig 2.16 Three Terminal Voltage Regulator
78XX:
The Bay Linear LM78XX is integrated linear positive regulator with three terminals.
The LM78XX offer several fixed output voltages making them useful in wide range of
applications. When used as a zener diode/resistor combination replacement, the LM78XX
usually results in an effective output impedance improvement of two orders of magnitude,
lower quiescent current. The LM78XX is available in the TO-252, TO-220 & TO-
