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INTRODUCTION
The main and very basic need of security was fulfilled by using themechanical or electrical locks which are very heavy and designed for
only one key. Therefore a large number of locks of required for locking a
large industries there are many keys for different locks (i.e. a very
tedious task to arrange these keys). These locks are not so much
protective and could be broken by using some mechanical tools. All
these problems could be solved if we use electronic locking system in
place of these electrical & mechanical locks. There are also some more
features are available in these electronic locking system The electronicsecurity system are very light, flexible, reprogrammable, lower cost,
more accurate, highly secure and required less power. In this way due to
the introduction of the electronic security system the security need and
fulfilled to a great extent and we could protect a whole industry or
company very easily and rapidly. The main objective of this project is to
make an electronic device by which we could give access to the
authenticated persons in the sophisticated area of an organization or a
company with a very simple operability. We could also generate
codeword for different expensive equipment so that they could be made
protective and only the person who has the complete knowledge to
operate that machine or equipment is authenticated to operate. One
more advantage to use this security system is that we could easily
change the codeword according to the situation or security conditions
and easily get the information about the attempts of hacking or hackers.
This device is fully automated so that we dont need to monitor the
process. Basically the device would generate five passwords in which
there would be one master code and other four will be sub code wecould distribute these code to different persons who are permitted to get
access. These persons would be able to get access by using their code
and if a person leaks his code then he could easily be detected and his
code could be change with the help of master code. In this way this
device is a much protected electronic device in which the number of
codes can be increased according to the need which would be
reprogrammable. Here we can also lock different expensive machines or
equipment by giving the sub codes so that only those persons having
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the knowledge of the operability of the equipment had given these codes
so that any other person cant damage the machine.
BRIEF DESCRIPTION OF ASSOCIATED TECHNOLOGY:-
This project is basically a microcontroller based device which operates
according to the data saved into the EEPROM and run the program in
microcontroller. The hardware used in this project is as follows: MCU
89S8253, EEPROM, Relay driver, LEDs, LCD Module, Power supply,
Buzzer and Speaker etc. The main or central processing unit of this
project is 89C51 it consists of the following features i.e. This is basically
a 40 pin to 44 pin MCU depending upon its packaging it is available in
three types of packages PDIP(Plastic dual in line Package-40pin),
TQFP/PQFP(Thin Plastic Gull Wing Quad Flatpack-44pin) and
PLCC(Plastic J-Leaded Chip Carrier-44pin). It has a 4K Bytes of In-
System Reprogrammable Flash Memory which has a capacity of 1,000
Write/Erase Cycles. Fully Static operation from 0Hz to 24MHz and it has
also three-level Program Memory Lock. The internal RAM of this MCU is
128*8 bit and externally it could operate 64MB memory devices. It
consists of a two quartz crystal timer or oscillator of 16 Bit and 6 interrupt
sources therefore the programming of microcontroller is done withserially inserting the data. This microcontroller is cheap and also cost-
effective because it could be operated into two low power consuming
modes i.e. Low Power Idle & Power Down Modes. In case of Idle Mode
the CPU puts itself to sleep while all the on-chip peripherals remain
active. While in Power down Mode the oscillator is stopped, and the
instruction that invokes power down is the last executed instruction. This
MCU is given the industry standard MCS-51TM instruction set and
pinout. The device is manufactured using Atmels high densitynonvolatile memory technology and uses high performance CMOS
transistors. Some other requirements of this microcontroller are:
Operating temperature range -55 C to + 125C and storage
temperature range -65 C to + 150C, Voltage at any pin with respect to
ground -1.0V to +7.0V and the maximum operating voltage 6.6V. The
DC output current of 15.0mA. The external clock driver used to drive this
MCU should have oscillation frequency of 0-24MHz, clock period of
41.5ns, High Time and Low time 15ns each and Rise & Fall Time 20ns
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each. The operating voltage of this microcontroller is given through a DC
power supply of 12V.
PATH OF IMPLIMENTATION:-
Block Diagram:
Brief Description: The system comprises a small electronic unit with a
numeric keypad, which is fixed outside the entry door to control a
solenoid-operated lock. When an authorized person enterspredetermined number (password) via the keypad, the relay operated for
a limited time to unlatch the solenoid-operated lock so the door can be
pushed/pulled open. At the end of preset delay, the relay reenergizes
and the door gets locked again. If the entered password is correct the
unit opens the door. When the code has been incorrectly entered four
times in a row, the code lock will switch to alarm mode and operate an
alarm relay. Alarm relay are turned off after entering a valid User Access
Code. This function thwarts any attempt by hackers to quickly try a
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large number of codes in a sequence. The secret code can be changed
any time after entering the current code (Master code).
There will be three unique passwords for three users. This enables thatany person of the family can open the door with his own password even
if other is not available. There is a facility that each user can change
his/her password when required. After all this there is master password
available with designer which in case can be used to open when user
forget their password. The person knowing the master password can tell
the user password at present by opening the system.
WORKING
Access control is a system which enables an authority to control
access to areas and resources in a given physical facility or computer-
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based information system. An access control system, within the field
of physical security, is generally seen as the second layer in the security
of a physical structure.
Access control is, in reality, an everyday phenomenon. A lock on
a car door is essentially a form of access control. A PIN system at a
bank is another means of access control. Bouncers standing in front of
a night club are perhaps a more primitive mode of access control (given
the evident lack of information technology involved). The possession of
access control is of prime importance when persons seek to secure
important, confidential, or sensitive information and equipment.
Item control or electronic key management is an area within(and possibly integrated with) an access control system which concerns
the managing of possession and location of small assets or physical.
DESCRIPTION:-
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BlockDiagram:
Working in brief:- There is a switch matrix interfaced with the
controller .When a particular sequence is pressed then micro controller
decodes it allows the door to be opened through the relay driver and
relay. If the sequence is pressed wrong then buzzer will blow.
Key Components:- The major components of this project are:
Switch matrix
Microcontroller
Relay driver
Relay
Buzzer
The microcontroller used here is a common 8 bit Atmel microcontroller
AT89s8253.It is a low-power, high-performance CMOS 8-bitmicrocontroller with12K bytes of In-System Programmable (ISP) Flash
program memory
and 2K bytes of
EEPROM data
memory. It has 32
programmable input
output lines
Northern India Engineering college
SWITCH
MATRIX AS
KEYPAD
MICRO-
CONTROLLERRELAY DRIVER
RELAYBUZZER
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Programmable (ISP) Flash program memory and 2K bytes of EEPROM
data memory have been provided. It has 32 programmable input output
lines.
Features:-
12K Bytes of In-System Programmable (ISP) Flash Program Memory
SPI Serial Interface for Program Downloading Endurance: 10,000 Write/Erase Cycles
2K Bytes EEPROM Data Memory
Endurance: 100,000 Write/Erase Cycles
2.7V to 5.5V Operating Range
Fully Static Operation: 0 Hz to 24 MHz (in x1 and x2 Modes)
Three-level Program Memory Lock
256 x 8-bit Internal RAM
32 Programmable I/O Lines
Three 16-bit Timer/Counters
Nine Interrupt Sources
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Enhanced UART Serial Port with Framing Error Detection and
Automatic Address Recognition
Enhanced SPI (Double Write/Read Buffered) Serial Interface
Programmable Watchdog Timer
Relay driver:-
ULN2803 is a current driver IC which drives the relay. The eight
NPN Darlington connected transistors in this family of arrays are ideally
suited for interfacing between low logic level digital circuitry (such as
TTL, CMOS or PMOS/NMOS) and the higher current/voltage
requirements of lamps, relays, printer hammers or other similar loads for
a broad range of computer, industrial, and consumer applications. All
devices feature opencollector outputs and freewheeling clamp diodes
for transient Suppression. The ULN2803 is designed to be compatible
with standard TTL families while the ULN2804 is optimized for 6 to 15
volt high level CMOS or PMOS.
Relay:-
A relay is an electrically operated switch. Many relays use an
electromagnet to operate a switching mechanism mechanically, butother operating principles are also used. Relays are used where it is
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necessary to control a circuit by a low-power signal (with complete
electrical isolation between control and controlled circuits), or where
several circuits must be controlled by one sign. Here, relay is used to
switch on the devices.
BUZZER SYSTEM:-
A system consisting signaling devices, a console, and a reset
button to notify in the form of sound happening of some incidence. THE
buzzer used here is piezo buzzer controlled by micro controller
signaling.
EMBEDDED SYSTEM
The embedded system is a combination of computer hardware,software, additional electrical & mechanical parts. A computer is used in
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such devices primarily as a means to simplify the system design and to
provide flexibility.
Often the user of the device is not even aware that a computer ispresent.
Electronic devices that incorporate a computer (usually a
microprocessor) is within their implementation.
These are Real-time system process events. These events occur on
external inputs and cause other events to occur as outputs. Minimizing
response time is usually a primary objective, or otherwise the entire
system may fail to operate properly. Therefore embedded systems
employ the use of a RTOS (Real-Time Operating System). Its an
operating system with the necessary features to support a Real-Time
System.
Real-Time System:-
It is a system where correctness depends not only on the correctness of
the logical result of the computation, but also on the result delivery time.
It responds in a timely, predictable way to unpredictable external stimuliarrivals. The real Time Systems can be further divided into two types:
Soft Real-Time System: Compute output response as fast as
possible, but no specific deadlines that must be met.
Hard Real-Time System: Output response must be computed by
specified deadline or system.
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APPLICATION OF EMBEDDED SYSTEMS:-
Consumer electronics
Telecommunication
Automobile
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Medical instrumentation
Industrial control equipment
Defense
Communication satellite
Data communication
Internet appliances
MICROCONTROLLER
A microcontroller is a computer-on-a-chip, or, if you prefer, a single-chip
computer. Micro suggests that the device is small, and controller tells
you that the device might be used to control objects, processes, or
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events. Another term to describe a microcontroller is embedded
controller, because the microcontroller and its support circuits are often
built into, or embedded in, the devices they control.
You can find microcontrollers in all kinds of things these days. Any
device that measures, stores, controls, calculates, or displays
information is a candidate for putting a microcontroller inside. The
largest single use for microcontrollers is in automobilesjust about
every car manufactured today includes at least one microcontroller for
engine control, and often more to control additional systems in the car.
In desktop computers, you can find microcontrollers inside keyboards,
modems, printers, and other peripherals. In test equipment,microcontrollers make it easy to add features such as the ability to store
measurements, to create and store user routines, and to display
messages and waveforms. Consumer products that use microcontrollers
include cameras, video recorders, compact-disk players, and ovens. And
these are just a few examples.
Microcontroller Basics:-
A microcontroller is similar to the microprocessor inside a personal
computer. Examples of microprocessors include Intels 8086, Motorolas
68000, and Zilogs Z80. Both microprocessors and microcontrollers
contain a central processing unit, or CPU. The CPU executes
instructions that perform the basic logic, math, and data-moving
functions of a computer. To make a complete microprocessor requires
memory for storing data and programs and input/output(I/O) interfaces
for connecting external devices like keyboards and displays. In contrast,
a microcontroller is a single-chip computer because it contains memoryand I/O interfaces in addition to the CPU. Because the amount of
memory and interfaces that can fit on a single chip is limited,
microcontrollers tend to be used in smaller systems that require little
more than the microcontroller and a few support components. Examples
of popular microcontrollers are Intels 8052 (including the 8052-BASIC,
which is the focus of this book), Motorolas 68HC11, and Zilogs Z8.
Microcontroller History:-
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To understand how microcontrollers fit into the always-expanding world
of computers, we need to look back to the roots of micro computing.
In its January 1975 issue, Popular Electronics magazine featured anarticle describing the Altair 8800 computer, which was the first
microcomputer that hobbyists could build and program themselves. The
basic Altair included no keyboard, video display, disk drives, or other
elements we now think of as essential elements of a personal computer.
Its 8080 microprocessor was programmed by flipping toggle switches on
the front panel. Standard RAM was 256 bytes and a kit version cost
$397 ($498 assembled). A breakthrough in the Altairs usability occurred
when a small company called Microsoft offered a version of the BASICprogramming language for it. Of course, the computer world has
changed a lot since the introduction of the Altair. Microsoft has become
an enormous software publisher, and a typical personal computer now
includes a keyboard, video display, disk drives, and Megabytes of RAM.
Whats more, theres no longer any need to build a personal computer
from scratch, since mass production has drastically lowered the price of
assembled systems. At most, building a personal computer now involves
only installing assembled boards and other major components in an
enclosure. A personal computer like Apples Macintosh or IBMs PC is a
general-purpose machine, since you can use it for many applications
word processing, spreadsheets, computer-aided design, and morejust
by loading the appropriate software from disk into memory. Interfaces to
personal computers are for the most part standard ones like those to
video displays, keyboards, and printers.
But along with cheap, powerful, and versatile personal computers has
developed a new interest in small, customized computers for specificuses. Each of these small computers is dedicated to one task, or a set of
closely related tasks. Adding computer power to a device can enable it
to do more, small display, a keypad or switches, sensors, relays, motors,
and so on. or do it faster, better, or more cheaply. For example,
automobile engine controllers have helped to reduce harmful exhaust
emissions. And microcontrollers inside computer modems have made it
easy to add features and abilities beyond the basic computer-to-phone-
line interface. In addition to their use in mass-produced products likethese, its also become feasible to design computer power into one-of-a-
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kind projects, such as an environmental controller for a scientific study or
an intelligent test fixture that ensures that a product meets its
specifications before its shipped to a customer. At the core of many of
these specialized computers is a microcontroller. The computersprogram is typically stored permanently in semiconductor memory such
as ROM or EPROM. The interfaces between the microcontroller and the
outside world vary with the application, and may include a
These small, special-purpose computers are sometimes called single-
board computers, or SBCs. The term can be misleading, however, since
the computer doesnt have to be on a single circuit board, and many
types of computer systems, such as laptop and notebook computers, arenow manufactured on a single board.
AT89S8253 microcontroller :-
The microcontroller development effort resulted in the 8051 architecture,
which was first introduced in 1980 and has gone on to be arguably the
most popular micro controller architecture available. The 8051 is a very
complete microcontroller with a large amount of built in control store
(ROM &EPROM) and RAM, enhanced I/O ports, and the ability to
access external memory. The maximum clock frequency with an 8051
micro controller can execute instructions is 20MHZ.Microcontroller is a
true computer on chip. The design incorporates all of the features found
in a microprocessor: CPU, ALU, PC, SP and registers. It also has the
other features needed to, make complete computer: ROM, RAM, parallel
I/O, serial I/O, counters and a clock circuit. The
89C51/89C52/89C54/89C58 contains a non-volatile FLASH program
memory that is parallel programmable. For devices that are serialprogrammable(In-System Programmable (ISP) and In-Application
Programmable (IAP) with a boot loader)All three families are Single-Chip
8-bit Microcontrollers manufactured in advanced CMOS process and are
Derivatives of the 80C51 microcontroller family. All the devices have the
same instruction set as the 80C51.
FEATURES:-
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8K Bytes of In-System Reprogrammable Flash Memory
Endurance: 1,000 Write/Erase Cycles
Fully Static Operation: 0 Hz to 33 MHz
Three-level Program Memory Lock
256 x 8-bit Internal RAM
32 Programmable I/O Lines
Three 16-bit Timer/Counters
Eight Interrupt Sources
Programmable Serial Channel
DESCRIPTION:-
The AT89S8253 is a low power, high performance CMOS 8-bit micro
computer with 8K bytes of flash programmable and erasable read only
memory(PEROM).The device is manufactured using Atmels 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. Bycombining a versatile 8-bit CPU with flash on a monolithic chip, the
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Atmel AT89s8253 is a powerful microcomputer which provides a highly
flexible and cost effective solution to many embedded control
applications. The main advantages of 89s8253 over 8051 are:-
Software Compatibility
Program Compatibility
Rewritability
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89S8253 PROCESSOR ARCHITECTURE:-
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A rchitecture contains the following :-
8 bit CPU with registers A and B
16 bit program counter(PC) and data pointer(DPTR)
8 bit program status word(PSW)
8 bit stack pointer
Internal ROM of 0(8031) to 4K(8051)
Internal RAM of 128 Bytes
4 register banks 00-1f
16 bytes(bit addressable) 20-2f
80 bytes of general purpose data memory 30-7f
32 I/O pins arranged as four 8 bit ports (P0 P3)
2 16-bit timer/counters: T0 and T1
Full duplex serial data receiver/transmitter: SBUF
Control registers: TCON, TMOD, SCON, PCON, IPand IE
2 external and 3 internal interrupt sources
Oscillator and clock circuits
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Pin Diagram of the 40 Pin DIP package of the 89S8253:-
DESCRIPTION:-
VCC:-
Pin no.40 is used for the supply to the microcontroller..
GND:-
Ground.
RST:-
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This is pin no.9, used to reset the device by keeping it high for 2
machine cycles. The microcontroller should be reset at the time of
starting.
Oscillator:-
Pins XTAL1 and XTAL2 are used for connecting a quartz crystal for the
internal oscillator.
Crystal Frequency-10 MHz
External Access (EA):-
The 8051 family members, all come with on-chip ROM to store the
program. In such case, EA pin is connected to Vcc. To indicate that the
code is stored in external ROM, EA pin must be connected to ground.
PSEN:-
PSEN stands for Program Store Enable. This is an output pin and isconnected to OE pin of ROM
Port 0:-
Port 0 is an 8-bit open drain bi-directional I/O 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 lower order address/data bus during accesses to external
program and data memory. In this mode, P0 has internal pull-ups. Port 0also receives the code bytes during Flash programming and outputs the
code bytes during program verification. External pull ups are required
during program verification.
Port 1 and Port 2:-
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Port 1 is an 8-bit bi-directional I/O port with internal pull-ups. The Port1
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 willsource 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.
Port 3:-
It has internal pull-ups and can sink/source 4 TTL inputs. Port 3
occupies a total of 8 pins, pins 10 through 17. It can be used as input or
output. Port 3 has additional function of providing some extremely signal
as interrupts.
ALE/PROG:-
Address Latch Enable is an output pulse for latching the low byte of the
address (on its falling edge) during accesses to external memory. This
pin is also the program pulse input (PROG) during Flash programming.
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
locking purposes. Note, however, that one ALE pulse is skipped during
each access to external data memory.
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PSEN:-
Program Store Enable. PSEN is the read strobe to external program
memory (active low). When the AT89S8253 is executing code fromexternal 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 program memory locations
starting at 0000H up to FFFFH. Note, however, that if lock bit 1 isprogrammed, 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.
PCB (PRINTED CIRCUIT BOARD)
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A printed circuit board, or PCB, is used to mechanically support and
electrically connect electronic components using conductive pathways,
tracks or traces etched from copper sheets laminated onto a non-
conductive substrate. It is also referred to as printed wiring board (PWB)or etched wiring board. A PCB populated with electronic components is
a printed circuit assembly (PCA), also known as a printed circuit board
assembly (PCBA).
PCBs are inexpensive, and can be highly reliable. They require much
more layout effort and higher initial cost than either wire-wrapped or
point-to-point constructed circuits, but are much cheaper and faster for
high-volume production. Much of the electronics industry's PCB design,assembly, and quality control needs are set by standards that are
published by the IPC organization.
POWER SUPPLY:-
There is 5V supply voltage required for this project. An ac 9-0-9 V mains
transformer is connected via a mains lead. The transistor is voltage
regulator IC. It regulates 4.8V dc (approx).
Working: - The working is quite clear. It is describe in following steps.
Step down transformer convert 220V AC into 4.8V AC
It convert AC voltage into pulsating DC voltage
The filter stage uses a shunt capacitor to filter out ripples from
pulsating DC
The regulator stage gives a regulated output of a fixed voltage.
The circuit runs on a power supply of 5V DC. A transformer 9-0-9V is
used to step down the ac mains voltage from 230V, to 9V AC. The
combination of transformer & diode converts this AC voltage into a
pulsating DC voltage, which is filtered by using an electrolytic capacitor
of rating 1000F, 25V. The IC BC547b provides a regulated power
supply of 5V DC. The 5V DC supply drives and the ICs in the circuit.
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http://en.wikipedia.org/wiki/Electronic_componenthttp://en.wikipedia.org/wiki/Conductor_(material)http://en.wikipedia.org/wiki/Signal_tracehttp://en.wikipedia.org/wiki/Industrial_etchinghttp://en.wikipedia.org/wiki/Laminatedhttp://en.wikipedia.org/wiki/Wire_wraphttp://en.wikipedia.org/wiki/Point-to-point_constructionhttp://en.wikipedia.org/wiki/IPC_(electronics)http://en.wikipedia.org/wiki/Electronic_componenthttp://en.wikipedia.org/wiki/Conductor_(material)http://en.wikipedia.org/wiki/Signal_tracehttp://en.wikipedia.org/wiki/Industrial_etchinghttp://en.wikipedia.org/wiki/Laminatedhttp://en.wikipedia.org/wiki/Wire_wraphttp://en.wikipedia.org/wiki/Point-to-point_constructionhttp://en.wikipedia.org/wiki/IPC_(electronics)7/31/2019 Door Locking System With 1 Master Password & 3 User Passwords
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PCB-DESIGNING:-
PCB Designing includes the following steps:-
Fig : PCB Designing process
PROCESSING :-
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PROCESSING
CLEANSING
PRINTING
ETCHING
DRILLING
SOLDERING
MASKING
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The layout of a PCB has to incorporate all the information on the board
before one can go on to the artwork preparation. This means that a
concept that clearly defines all the details of the circuit and partly also of
the final equipment, is a prerequisite before the actual layout can start.The detail circuit diagram is very important for the layout designer and
he must also be familiar with the design concept and with the philosophy
behind the equipment. The General Considerations are-
a-) Layout scale:- Depending on the accuracy required, artwork should
be produced at a 1:1 or 2:1 or even 4:1 scale. The layout is best
prepared on the same scale as the artwork. This prevents all the
problems which might be caused by redrawing of layout to the artwork
scale.
b-) Grid system or Graph Paper: - It is commonly accepted practice to
use these for designing.
c-) Board types:-There are two side of a PCB board Component side
& Solder side. Depending on these board are classified as-
Single-sided Boards:- These are used where costs
have to be kept at a minimum & a particular Circuit can beaccommodated on such board. To jump over conductor tracks,
components have to be utilized. If this is not feasible,
jumper wires are used. (Jumper wires should be less otherwise
double-sided PCB should be considered.
Double-sided Boards:- These are made with or
without plated through holes. Plated through holes are fairly
expensive.
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CLEANING:-
The cleaning of the copper surface prior to resist application is an
essential step for any type of PCB process using etches or plating resist.
After scrubbing with the abrasive, a water rinse will remove most of the
remaining slurry.
Fig :Cleaning process
ETCHING:-
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Scrubbing
Water Rinse
Wet Brushing
Acid dip
Final Rinse
Drying
Pumice/ Acid Slurry
Tap Water
Tap Water
Hydrochloric Acid-HCl
De-ionized Water
Oven or Blowing of air.
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It is of utmost importance to choose a suitable Etchant Systems.Number
of factors play a major role in it. There are many factors to be considered
Etching speed
Copper solving capacity
Etchant price
Pollution character
Operation characteristics of different etchants:-
Factor
Etchant
Corrosive
-ness
Neutralization
disposition
problem
Toxicity Required
ventilation
Operation
cost
FeCl3 High Medium Low Low Medium
CuCl2 High Low Medium Medium Low
Chromic
acid
High High High High High
Alkaline
ammonia
High Medium Medium High High
Table : Characteristics of different etchants
We have used FeCl3 (Conc. 120 g/litre 0.1 M) for etching.
Reactions Involved:-
FeCl3 + 3H 2O Fe(OH) 3 + 3HCl (Free acid attack to
copper)
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FeCl3 + Cu FeCl2 + CuCl
FeCl3 + CuCl FeCl2 + CuCl2
CuCl2 + Cu 2CuCl
DRILLING:-
The importance of hole drilling into PCBs has further gone with electronic
component miniaturization and its need for smaller holes diameters
(diameters less than half the board thickness) and higher package density.
The following hole diameter tolerances have been generally accepted
wherever no other specifications are mentioned.
Hole Diameter (D) 3 mm + / 0.1 mm
Drill bits are made up of high-speed steel (HSS), Glass epoxy material,
Tungsten Carbide.
SOLDERING:-
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Flux should be removed after Soldering. It is done through washing by 0.51
% HCl followed by Neutralization in dilute alkali to remove corrosive flux.Non-
corrosive is removed by Iso-Propanal.
MASKING:-
It is done for the protection of conductor track from Oxidation.
Designing of PCB Layout:-
A PCB layout is required to place components on the PCB so that the
component area can be minimized and the components can be placed in an
efficient manner. The components can be placed in two ways, either
manually or by software. The manual procedure is quiet cumbersome and is
very inefficient. The other method is by the use of computer software. This
method is advantageous as it saves time and valuable copper area. There
are various softwares available for this purpose like-
Express PCB
Pad2pad
Protel PCB
PCB design e.t.c.
Many of them are loaded with auto routing and auto placement facility. Thesoftware that we have used here is EXPRESS PCB. This software has a
good interface, easy editing options and a wide range of components.
Express P.C.B. :-
Express PCB is a very easy to use Windows application for laying
out printed circuit boards. There are two parts to Express PCB, Express
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SCH for drawing schematics and Express PCB for designing circuit
boards. We downloaded the software from the website
www.expresspcb.com.
There are lots of functions available in the software. This software
is free of cast and also it is very easy to use. The different layers of the
PCB can be viewed by just a click of a button on the interface. And we
easily get its print on paper which is utilized for further processing. We
can design single sided PCB as well as Double Sided PCB with this
Software.
TESTING
After assembling the circuit components on the PCB and soldering
them according to the layout, testing is the next step to be taken. Testing
includes measurement of the parameters such as current, voltage, clock
frequency and comparing them with the standard values provided with
the circuit. Any sort of deviation from the actual values should be
measured and corrected accordingly. This part is known as
troubleshooting.
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Testing forms a very necessary part of any project. Without testing
a project work never culminates. It is only after testing that one can
guarantee the successful ending of the project. It is only through this
step by which one can determine the faults and also come to knowabout the changes to be introduced.
DIODES
A diode is a device having two terminals and a low resistance to
electrical current in one direction and a high resistance in the other
direction. Diode is a two-element device which passes a signal in one
direction only. They are used most commonly to convert AC to DC,
because they pass the positive part of the wave, and block the negative
part of the AC signal, or, if they are reversed, they pass only the
negative part and not the positive part. Here we used only two types of
diode:
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1) Zener Diode
2) 1N4007
1) ZENER DIODE:-
A Zener diode is a type of diode that permits current in the forward
direction like a normal diode, but also in the reverse direction if the
voltage is larger than the breakdown voltage known as "Zener knee
voltage" or "Zener voltage". The device was named after Clarence
Zener, who discovered this electrical property. The Zener effect asembodied in the zener diode has many applications for control and
regulation.
Northern India Engineering college
http://en.wikipedia.org/wiki/Diodehttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Breakdown_voltagehttp://en.wikipedia.org/wiki/Clarence_Zenerhttp://en.wikipedia.org/wiki/Clarence_Zenerhttp://hyperphysics.phy-astr.gsu.edu/Hbase/solids/zener.html#c1http://hyperphysics.phy-astr.gsu.edu/Hbase/solids/zener.html#c3http://en.wikipedia.org/wiki/Diodehttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Breakdown_voltagehttp://en.wikipedia.org/wiki/Clarence_Zenerhttp://en.wikipedia.org/wiki/Clarence_Zenerhttp://hyperphysics.phy-astr.gsu.edu/Hbase/solids/zener.html#c1http://hyperphysics.phy-astr.gsu.edu/Hbase/solids/zener.html#c37/31/2019 Door Locking System With 1 Master Password & 3 User Passwords
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Fig 4.10: Characteristic graph of Zener Diode
The Zener diode is operated in reverse bias mode (positive on its
cathode). It relies on the reverse breakdown voltage occurring at a
specified value. This value is printed on it.
APPLICATIONS:-
1. As a reference source, where the voltage across it is compared with
another voltage.
2. As a voltage regulator, smoothing out any voltages variations
occurring in the supply voltage across the load.
2) RECTIFICATION DIODE [1N4007]:-
The stripe stamped on one end of the diode shows indicates the polarity
of the diode. The stripe shows the cathode side. The top two devices
shown in the picture are diodes used for rectification. They are made to
handle relatively high currents. The device on top can handle as high as
6A, and the one below it can safely handle up to 1A.However, it is best
used at about 70% of its rating because this current value is a maximum
rating. The third device from the top (red color) has a part number of
1S1588. This diode is used for switching, because it can switch on and
off at very high speed. However, the maximum current it can handle is
120 mA. This makes it well suited to use within digital circuits. The
maximum reverse voltage (reverse bias) this diode can handle is 30V.
The device at the bottom of the picture is a voltage regulation diode with
a rating of 6V. When this type of diode is reverse biased, it will resist
changes in voltage. If the input voltage is increased, the output voltagewill not change. (Or any change will be an insignificant amount.) While
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the output voltage does not increase with an increase in input voltage,
the output current will.
This requires some thought for a protection circuit so that too muchcurrent does not flow. The rated current limit for the device is 30 mA.
Generally, a 3-terminal voltage regulator is used for the stabilization of a
power supply. Therefore, this diode is typically used to protect the circuit
from momentary voltage spikes. 3 terminal regulators use voltage
regulation diodes inside.
FEATURES:-
Low forward voltage drop.
Diffused Junction.
AT89S8253 (8-bit Microcontroller with 12 KbyteFlash)
Features:-
Compatible with MCS51 Products
12K Bytes of In-System Programmable (ISP) Flash Program Memory
SPI Serial Interface for Program Downloading
Endurance: 10,000 Write/Erase Cycles
2K Bytes EEPROM Data Memory
Endurance: 100,000 Write/Erase Cycles
64-byte User Signature Array
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2.7V to 5.5V Operating Range
Fully Static Operation: 0 Hz to 24 MHz (in x1 and x2 Modes)
Three-level Program Memory Lock
256 x 8-bit Internal RAM
32 Programmable I/O Lines
Three 16-bit Timer/Counters
Nine Interrupt Sources
Enhanced UART Serial Port with Framing Error Detection and
Automatic Address Recognition
Enhanced SPI (Double Write/Read Buffered) Serial Interface
Low-power Idle and Power-down Modes
Interrupt Recovery from Power-down Mode
Programmable Watchdog Timer
Dual Data Pointer
Power-off Flag
Flexible ISP Programming (Byte and Page Modes)
Page Mode: 64 Bytes/Page for Code Memory, 32 Bytes/Page for
Data Memory
Four-level Enhanced Interrupt Controller
Programmable and Fuseable x2 Clock Option
Internal Power-on Reset
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42-pin PDIP Package Option for Reduced EMC Emission
Green (Pb/Halide-free) Packaging Option
1. Description :-
The AT89S8253 is a low-power, high-performance CMOS 8-bit
microcontroller with 12K bytes of In-System Programmable (ISP) Flash
program memory and 2K bytes of EEPROM data memory. The device is
manufactured using Atmels high-density non- volatile memory
technology and is compatible with the industry-standard MCS-
51instruction set and pinout. The on-chip downloadable Flash allows the
program memory to be reprogrammed in-system through an SPI serial
interface or by a conventional nonvolatile memory programmer. By
combining a versatile 8-bit CPU with downloadable Flash on amonolithic chip, the Atmel AT89S8253 is a powerful microcontroller
which provides a highly-flexible and cost-effective solution to many
embedded control applications.
The AT89S8253 provides the following standard features: 12K bytes of
In-System Programmable Flash, 2K bytes of EEPROM, 256 bytes of
RAM, 32 I/O lines, programmable watchdog timer, two data pointers,
three 16-bit timer/counters, a six-vector, four-level interrupt architecture,a full duplex serial port, on-chip oscillator, and clock circuitry. In addition,
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the AT89S8253 is designed with static logic for operation down to zero
frequency and supports two software selectable power saving modes.
The Idle Mode stops the CPU while allowing the RAM, timer/counters,
serial port, and interrupt system to continue functioning. The Power-down mode saves the RAM contents but freezes the oscillator, disabling
all other chip functions until the next external interrupt or hardware
reset.
The on-board Flash/EEPROM is accessible through the SPI serial
interface. Holding RESET active forces the SPI bus into a serial
programming interface and allows the program memory to be written to
or read from, unless one or more lock bits have been activated.
2. Pin Configurations :-
2.1 40P6 40-lead PDIP
2.2 44A 44-lead TQFP
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2.3 44J 44-lead PLCC
2.4 42PS6 PDIP
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3. Pin Description:-
3.1 VCC: Supply voltage (all packages except 42-PDIP).
3.2 GND: Ground (all packages except 42-PDIP; for 42-PDIP GND
connects only the logic core and the embedded program/data
memories).
3.3 VDD: Supply voltage for the 42-PDIP which connects only the
logic core and the embedded pro-
gram/data memories.
3.4 PWRVDD: Supply voltage for the 42-PDIP which connects only
the I/O Pad Drivers. The application board must connect both VDD andPWRVDD to the board supply voltage.
3.5 PWRGND: Ground for the 42-PDIP which connects only the I/O
Pad Drivers. PWRGND and GND are weakly connected through the
common silicon substrate, but not through any metal links. The
application board must connect both GND and PWRGND to the board
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ground.
3.6 Port 0: Port 0 is an 8-bit open drain bi-directional I/O port. As an
output port, each pin can sink six 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 program and data
memory. In this mode, P0 has internal pull-ups. Port 0 also receives the
code bytes during Flash programming and outputs the code bytes during
program verification. External pull-ups are required during programverification.
3.7 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 six TTL inputs. When 1s are written to Port 1 pins, they are
pulled high by the weak
internal pull-ups and can be used as inputs. As inputs, Port 1 pins that
are externally being pulled low will source current (IIL,150 A typical)
because of the weak internal pull-ups. Some Port 1 pins provide
additional functions. 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. Furthermore, P1.4, P1.5, P1.6,
and P1.7 can be configured as the SPI slave port select, datainput/output and shift clock input/output pins as shown in the following
table.
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3.8 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 six TTL inputs. When 1s
are written to Port 2 pins, they are pulled high by the weak internal pull-
ups and can be used as inputs. As inputs, Port 2 pins that are externally
being pulled low will source current (IIL,150 A typical) because of the
weak 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 16-bit 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.
3.9 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 six TTL inputs. When 1s
are written to Port 3 pins, they are pulled high by the weak internal pull-
ups and can be used as inputs. As inputs, Port 3 pins that are externally
being pulled low will source current (IIL,150 A typical) because of the
weak internal pull-ups. Port 3 receives some control signals for Flash
programming and verification. Port 3 also serves the functions of various
special features of the AT89S8253, as shown in the following table.
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3.10 RST: Reset input. A high on this pin for at least two machine
cycles while the oscillator is running resets the device.
3.11 ALE/PROG:Address Latch Enable. ALE/PROG is an output pulsefor latching the low byte of the address (on its falling edge) 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 bedisabled by setting bit 0 of the AUXR SFR at 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 ALE-disable bit has no effect if
the microcontroller is in external execution mode.
3.12 PSEN: Program Store Enable. PSEN is the read strobe to external
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program memory (active low). When the AT89S8253 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.
3.13 EA/VPP: External Access Enable. EA must be strapped to GND in
order to enable the device to fetch code from external program 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 pinalso receives the 12-volt programming enable voltage (VPP) during Flash
programming when 12-volt programming is selected.
3.14 XTAL1: Input to the inverting oscillator amplifier and input to the
internal clock operating circuit.
3.15 XTAL2: Output from the inverting oscillator amplifier. XTAL2
should not drive a board-level clock without a buffer.
4. Block Diagram:-
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5. Data Memory EEPROM and RAM:-
The AT89S8253 implements 2K bytes of on-chip EEPROM for data
storage and 256 bytes of RAM. The upper 128 bytes of RAM occupy a
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parallel 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 theinstruction specifies whether the CPU accesses the upper 128 bytes of
RAM or the SFR space. Instructions that use direct addressing access
the 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 available as stack space. The on-chip
EEPROM data memory is selected by setting the EEMEN bit in theEECON register at SFR address location 96H. The EEPROM address
range is from 000H to 7FFH. MOVX instructions are used to access the
EEPROM. To access off-chip data memory with the MOVX instructions,
the EEMEN bit needs to be set to 0. During program execution mode
(using the MOVX instruction) there is an auto-erase capability at the byte
level. This means that the user can update or modify a single EEPROM
byte location in real-time without affecting any other bytes. The EEMWE
bit in the EECON register needs to be set to 1 before any byte location
in the EEPROM can be written. User software should reset EEMWE bit
to 0 if no further EEPROM write is required. EEPROM write cycles in
the serial programming mode are self-timed and typically take 4 ms. The
progress of EEPROM write can be monitored by reading the RDY/BSY
bit (read-only) in SFR EECON. RDY/BSY = 0 means programming is still
in progress and RDY/BSY= 1 means an EEPROM write cycle is
completed and another write cycle can be initiated. Bit EELD in EECON
controls whether the next MOVX instruction will only load the write buffer
of the EEPROM or will actually start the programming cycle. By setting
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EELD, only load will occur. Before the last MOVX in a given page of 32
bytes, EELD should be cleared so that after the last MOVX the entire
page will be programmed at the same time. This way, 32 bytes will only
require 4 ms of programming time instead of 128 ms required in singlebyte programming.
16 CHARACTER LCD x 2
Features:-
5 x 8 dots with cursor
Built-in controller (KS 0066 or Equivalent)
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+ 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
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LM78XX
3-Terminal 1A Positive Voltage Regulator
Features:-
Output Current up to 1A
Output Voltages of 5, 6, 8, 9, 10, 12, 15, 18, 24
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Thermal Overload Protection
Short Circuit Protection
Output Transistor Safe Operating Area Protection
General description:-
The LM78XX series of three terminal positive regulators are available in
the TO-220 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 with external
components to obtain adjustable voltages and currents.
Block Diagram:-
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Pin Assignment:-
Absolute Maximum Rating:-
Absolute maximum ratings are those values beyond which damage tothe device may occur. The datasheet specifications should be met,
without exception, to ensure that the system design is reliable over its
power supply, temperature, and output/input loading variables. Fairchild
does not recommend operation outside datasheet specifications.
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Note: 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.
These parameters, although guaranteed, are not 100% tested in production.
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Note: 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.
These parameters, although guaranteed, are not 100% tested in production.
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Note: 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.
These parameters, although guaranteed, are not 100% tested in production.
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Note: 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.
These parameters, although guaranteed, are not 100% tested in production.
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Note: 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.
These parameters, although guaranteed, are not 100% tested in production.
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Note: 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.
These parameters, although guaranteed, are not 100% tested in production.
Note: 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.
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These parameters, although guaranteed, are not 100% tested in production.
Note:
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.
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These parameters, although guaranteed, are not 100% tested in production.
Note: 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.
These parameters, although guaranteed, are not 100% tested in production.
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UNDERSTANDING RELAYS
Relays:-
Relays are used throughout the automobile. Relays which come in
assorted sizes, ratings, and applications, are used as remote control
switches. A typical vehicle can have 20 relays or more
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Relay Locations:-
Relays are located throughout the entire vehicle. Relay blocks, both
large and small, are located in the engine compartment; behind the left
or right kick panels, or under the dash are common locations. Relays are
often grouped together or with other components like fuses or placed by
themselves.
Relay Position Identification:-
Relay / Fuse block covers usually label the location and position of each
fuse, relay, or fuse element contained within.
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Relay Applications:-
Relays are remote control electrical switches that are controlled by
another switch, such as a horn switch or a computer as in a power traincontrol module. Relays allow a small current flow circuit to control a
higher current circuit. Several designs of relays are in use today, 3-pin,
4-pin, 5-pin, and 6-pin, single switch or dual switches.
Relay Operation:-
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All relays operate using the same basic principle. Our example will use a
commonly used 4 -pin relay. Relays have two circuits: A control circuit
(shown in GREEN) and a load circuit (shown in RED). The control circuit
has a small control coil while the load circuit has a switch. The coilcontrols the operation of the switch.
Relay Energized (On):-
Current flowing through the control circuit coil
(pins 1 and 3) creates a small magnetic field which causes the switch toclose, pins 2 and 4. The switch, which is part of the load circuit, is used
to control an electrical circuit that may connect to it. Current now flows
through pins 2 and 4 shown in RED, when the relay in energized.
Relay De-Energized (Off):-
When current stops flowing through the controlcircuit, pins 1 and 3, the relay becomes de-
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energized. Without the magnetic field, the switch opens and current is
prevented from flowing through pins 2 and 4. The relay is now OFF.
Relay Operation:-
When no voltage is applied to pin 1, there is no current flow through the
coil. No current means no magnetic field is developed, and the switch is
open. When voltage is supplied to pin 1, current flow though the coil
creates the magnetic field needed to close the switch allowing continuity
between pins 2 and 4.
Relay Design Id:-
Relays are either Normally Open or Normally Closed. Notice the position
of the switches in the two relays shown below. Normally open relayshave a switch that remains open until energized (ON) while normally
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closed relays are closed until energized. Relays are always shown in the
de-energized position (no current flowing through the control circuit -
OFF). Normally open relays are the most common in vehicles; however
either can be use in Automotive applications.
Normal ly open (NO)
Normally
closed (NC)
Normally Closed Relays:-
The operation of a Normally Closed relay is the same to that of a
Normally Open relay, except backwards. In other words, when the relay
control coil is NOT energized, the relay switch contacts are closed,
completing the circuit through pins 2 and 4. When the control coil isenergized, the relay switch contacts opens, which breaks the circuit
open and no continuity exists between pins 2 and 4.
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DE-ENERGIZED (OFF) ENERGIZED (ON)
Actual Relay Design:-
Current flows through the control coil, which is wrapped around an iron
core. The iron core intensifies the magnetic field. The magnetic field
attracts the upper contact arm and pulls it down, closing the contacts
and allowing power from the power source to go to the load.
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Relay Variations:-
Other relay variations include three and five pin relays. A 3-PIN relay
instead of two B+ input sources, this relay has one B+ input at pin 1.
Current splits inside the relay, supplying power to both the control and
load circuits. A 5-PIN relay has a single control circuit, but two separate
current paths for the switch: One when the relay is de-energized (OFF
no current through the control coil) and the other the energized (ON -
current is flowing through the control coil). When the 5-PIN relay is de-
energized (OFF), pins 4 and 5 have continuity. When the relay is
energized (ON), pins 3 and 5 have continuity.
3-PIN 4-PIN 5-PIN
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ISO Standardized Relays:-
ISO relays were designed to try and standardize relay connections,
making it easier to test and design systems. ISO relays are currentlyused by almost all automotive manufacturers today. Both 4 and 5 pin
designs are used in both standard mini and micro sizes. FYI: ISO is
short for International Standard Organization.
STANDARD MINI SHOWN
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Standard Mini Iso Relays Types:-
Below are two popular standard MINI ISO relay configurations. The size
of a ISO Standard MINI relay is a 1" square cube. Both 4 and 5 pins
designs are used.
5 PIN
MINI RELAY
4 PIN
MINI RELAY
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ISO Micro Relay Types:-
Below are two popular MICRO ISO relay configurations. The size of a
ISO MICRO relay is a 1" x 1" x 1/2" square (1/2 as thick as a Mini relay).Both 4 and 5 pins designs are used.
5 PIN
MICRO RELAY
4 PIN
MICRO RELAY
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Voltage Spikes:-
When the switch is closed (shown left), current flows through the coil
from positive to negative as shown in red. This current flow creates amagnetic field around the coil. The top of the coil is positive, and the
bottom is negative.
When the switch is opened (shown on right), current stops flowing
through the control circuit coil, and the magnetic field surrounding the
coil cannot be maintained. As the magnetic field collapses across the
coil, it induces a voltage into itself, creating a reverse polarity voltage
spike of several hundred volts. Although the top of the coil is still 12 volts
positive, the bottom of the coil produces several hundred positive volts
(200+ volts or
more); 200 is "more positive" and stronger than 12 volts, so current flows
from the bottom of the coil up towards the top.
Voltage Suppression Relays:-
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Relays are often controlled by a computer. When relays are controlled
by semiconductors such as transistors, they require some type of
voltage suppression device. Solid state circuits are vulnerable to voltage
spikes. Voltage spikes slam against transistors, destroying them. Whilesome computer circuits have voltage suppression built inside the
computer,
others rely on voltage suppression from within the relay. High ohm
resistors, diodes, or capacitors can be used for voltage suppression.
Diodes and resistors are the most common. NOTE: Relays are usually
clearly marked if a suppression diode or resistor is present.
Relays With De-Spiking Diodes:-
A de-spiking (clamping) diode is connected in
parallel with the relay coil. It is in the reverse biased position when the
relay is turned on; therefore no current will flow through the diode. When
the relay control circuit is opened (turned OFF), current stops flowing
through the coil, causing the magnetic field to collapse. The magneticlines of force cut through the coil and induce a counter voltage (a voltage
in reverse polarity) into the winding. The counter voltage begins to raise.
When the bottom side of the diode sees .7 volts more positive voltage
than the top, the diode becomes forward biased, allowing the excess
voltage to pass, completing the circuit to the other end of the coil. The
current flows around in the diode and coil circuit until the voltage is
dissipated.
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Relays With
De- Spiking
Resistors:-
High ohm resistors are sometimes used instead of diodes. A resistor is
more durable than a diode and can suppress voltage spikes similar to a
diode, but the resistor will allow current to flow through it whenever the
relay is on. Therefore resistance of the resistor must be fairly high (about600 ohms) in order to prevent too much current flow in the circuit. High
ohm resistors are not quite as efficient at suppressing a voltage spike as
diodes.
Circuit Identification:-
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Relays are easy to test but often misunderstood. Using a 4 pin relay for
our example, we must first identify the pins. Some manufacturers place
a diagram and pin ID on the outside of the relay case to show which pins
are part of the control circuit and which pins are part of the load circuit.
Continuity Check For Id:-
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If the relay is not labeled, use an ohmmeter and check to see which pins
are connected to each other. You should typically find an ohm value of
approximately 50 to 120 ohms between two of the pins. This is the
control circuit. If the coil is less that 50 ohms it could be suspect. Referto manual to verify reading. The remaining two pins should read OL
(infinite) if it's a normally open relay, or 0 ohms (continuity) if it's a
normally closed relay. If the readings are correct, proceed to the next
test. Note: If none of the relay pins showed a coil value and all pins show
OL or 0 ohms, the control coil is damaged and should be replaced.
Practical Testing:-
Once the pins have been identified, energize the control circuit by
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supplying B+ to pin 1 and a ground to pin 3. A faint "click" will be heard;
although this "click" means the switch has moved (closed), it does not
mean the relay is good. The load circuit switch contacts could still be
faulty (high resistance), and further testing is required. A commonmistake technicians make is they hear a "click" and assume the relay is
good. Take the extra step and verify operation.
Operational Check With Testlight:-
Now start the second part of the test. Energize the relay (control side) bysupplying B+ to pin 1 and a ground to pin 3. A click should be heard.
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With the relay still energized, supply B+ pin 2 of the load circuit. The test
light will be on. De-energize (remove B+) the control circuit at pin 1; the
test light at pin 4 should go off. A test light is preferred because a test
light will draw current through the switch.
Operational Check With Voltmeter:-
A voltmeter can be substituted in place of a test light; however be aware
if the contacts are partially burned, the voltmeter will show voltage
indicating good contact even when bad. Remember high impedance
digital voltmeters draw almost no current. Energize the relay (control
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side) by supplying B+ to pin 1 and a ground to pin 3. A click should be
heard. With the relay still energized supply B+ to pin 2 of the load circuit.
Connect the RED lead to pin 4 and the BLACK lead to ground. The
voltmeter will indicate source voltage (12V).De-energize (remove B+) thecontrol circuit at pin 1; the voltmeter should now read "zero". Re-
energize the relay and the voltmeter should return to 12 volts.
Operational Check With An Ohmmeter:-
An ohmmeter can also be used to test the load circuit, but the same
problem as the voltmeter comes into play. Energize the relay (control
side). Supply B+ to pin 1 and a ground (neg.) to pin 3. A click should be
heard. Place the leads on an ohmmeter to across pin 2 and pin 4.
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Assuming it is a normally open relay the ohmmeter will indicate a
complete circuit (close to zero -0 ohms). De-energize the control circuit
at pin 1(remove B+). The ohmmeter should indicate OL (an open circuit -
infinite). Re-energize the relay and the ohmmeter should return to "zero"ohms. Note: some manufactures provide a maximum ohm value when
the switch contacts are closed, example 5 ohms max.
ULN2803A 500-mA Rated Collector Current
High-Voltage Outputs . . . 50 V
Output Clamp Diodes
Inputs Compatible With Various Types of Logic
Relay Driver Applications
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Compatible with ULN2800A Series
Description/ordering information:-
The ULN2803A is a high-voltage, high-current Darlington transistor
array. The device consists of eight npn Darlington pairs that feature high
voltage outputs with common-cathode clamp
diodes for switching inductive loads. The
collector-current rating of each Darlington pair
is 500mA.The Darlington pairs may be
connected in parallel for higher current
capability.
Applications include relay drivers, hammer
drivers, lamp drivers, display drivers (LED and
gas discharge), line drivers, and logic buffers.
The ULN2803A has a 2.7-k series base
resistor for each Darlington pair for operation
directly with TTL or 5-V CMOS devices.
Logic Diagram :-
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Schematic (each Darlington pair) :-
Absolute maximum ratings at 25 C free-air temperature (unless
otherwise noted):-
Collector-emitter voltage 50V
Input voltage ... 30V
Continuous collector current .. 500mA
Output clamp diode current ... 500mA
Total substrate-terminal current .. -2.5A
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Operating virtual junction
temperature, TJ . 1500C
Storage temperature range, Tstg. -650C to
1500C
Parameter measurement information:-
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Parameter measurement information:-
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Propagation delay times
Parameter measurement information:-
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Latch-up Test
REFERENCES
Websites:-
www.8051projects.info
www.wikipedia.org
www.atmel.com
www.fairchildsemi.com
www.alldatasheet.com
Books:-
Northern India Engineering college
http://www.8051projects.info/http://www.wikipedia.org/http://www.fairchildsemi.com/http://www.alldatasheet.com/http://www.8051projects.info/http://www.wikipedia.org/http://www.fairchildsemi.com/http://www.alldatasheet.com/7/31/2019 Door Locking System With 1 Master Password & 3 User Passwords
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The 8051 Microcontroller
By I. Scott MacKenzie, Raphael C.-W. Phan
Published By Dorling Kindersley (India) Pvt. Ltd. Published in 2008
Electronic Devices And Circuit Theory
By Robert L. Boylestad, Louis Nashelsky
Published By Dorling Kindersley (India) Pvt. Ltd.
Published in 2008