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Temperature Sensors (LM35)
Introduction:
The LM35 series are precision integrated-circuit temperature sensors, whose
output voltage is linearly proportional to the Celsius (Centigrade) temperature. The LM35
thus has an advantage over linear temperature sensors calibrated in Kelvin, as the user is
not required to subtract a large constant voltage from its output to obtain convenient
centigrade scaling. The LM35 does not require any external calibration or trimming to
provide typical accuracies of ±1/4°C at room temperature and ±3/4°C over a full -55 to
+150°C temperature range. Low cost is assured by trimming and calibration at the wafer
level. The LM35’s low output impedance, linear output, and precise inherent calibration
make interfacing to readout or control circuitry especially easy. It can be used with single
power supplies, or with plus and minus supplies. As it draws only 60 µA from its supply,
it has very low self-heating, less than 0.1°C in still air. The LM35 is rated to operate over
a -55° to +150°C temperature range, while the LM35C is rated for a -40° to +110°C
range (-10° with improved accuracy). The LM35 series is available packaged plastic TO-
92 transistor package. The LM35D is also available in an 8-lead surface mount small
outline package and a plastic TO-220 package.
Features:
1. Calibrated directly in ° Celsius (Centigrade)
2. Linear + 10.0 mV/°C scale factor
3. 0.5°C accuracy guaranteeable (at +25°C)
4. Rated for full -55° to +150°C range
5. Suitable for remote applications
6. Low cost due to wafer-level trimming
7. Operates from 4 to 30 volts
8. Less than 60 µA current drain
9. Low self-heating, 0.08°C in still air
10. Nonlinearity only ±1/4°C typical
11. Low impedance output, 0.1 for 1 mA load
Pin diagram:
Applications:
The LM35 can be applied easily in the same way as other integrated-circuit
temperature sensors. It can be glued or cemented to a surface and its temperature will be
within about 0.01°C of the surface temperature. This presumes that the ambient air
temperature is almost the same as the surface temperature; if the air temperature were
much higher or lower than the surface temperature, the actual temperature of the LM35
die would be at an intermediate temperature between the surface temperature and the air
temperature. This is expecially true for the TO-92 plastic package, where the copper
leads are the principal thermal path to carry heat into the device, so its temperature might
be closer to the air temperature than to the surface temperature. To minimize this
problem, be sure that the wiring to the LM35, as it leaves the device, is held at the same
temperature as the surface of interest. The easiest way to do this is to cover up these wires
with a bead of epoxy which will insure that the leads and wires are all at the same
temperature as the surface, and that the LM35 die’s temperature will not be affected by
the air temperature. The TO-46 metal package can also be soldered to a metal surface or
pipe without damage. Of course, in that case the V- terminal of the circuit will be
grounded to that metal. Alternatively, the LM35 can be mounted inside a sealed-end
metal tube, and can then be dipped into a bath or screwed into a threaded hole in a tank.
As with any IC, the LM35 and accompanying wiring and circuits must be kept insulated
and dry, to avoid leakage and corrosion. This is especially true if the circuit may operate
at cold temperatures where condensation can occur. Printed-circuit coatings and
varnishes such as Humiseal and epoxy paints or dips are often used to insure that
moisture cannot corrode the LM35 or its connections. These devices are sometimes
soldered to a small light-weight heat fin, to decrease the thermal time constant and speed
up the response in slowly-moving air. On the other hand, a small thermal mass may be
added to the sensor, to give the steadiest reading despite small deviations in the air
temperature.
A MAIN PROJECT REPORT ON
AUTOMATIC MEASUREMENT AND REPORTING SYSTEM OF WATER
QUALITY BASED ON GSM
Submitted to
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY
ANANTAPUR
For the partial fulfillment of the requirement for the Award of Degree for
BACHELOR OF TECHNOLOGY
In
ELECTRONICS AND COMMUNICATION ENGINEERING
By
M.NAJMA (09L41A0492)
G.KAMAL CHOWDHARY (09L41A04A0)
B.BHUVAN CHANDH (09L41A04A5)
B.RAJA RAO (09L41A0499)
Under the Esteemed Guidance of
Mr.G.NARENDRANATH REDDY, M.TECH.
(Assistant Professor, Dept. of ECE)
Department of Electronics and Communication Engineering
MEKAPATI RAJAMOHAN REDDY INSTITUTE OF TECHNOLOGY SCIENCE
(Affiliated to Jawaharlal Nehru Technology University, Anantapur-515001)
UDAYAGIRI-524226, S.P.S.R.NELLORE (D.T),A.P.
MEKAPATI RAJAMOHAN REDDY INSTITUTE OF
TECHNOLOGY AND SCIENCE
(Affiliated to Jawaharlal Nehru Technology University, Anantapur-515001)
UDAYAGIRI-524226, S.P.S.R.NELLORE (D.T), A.P
BONAFIED CERTIFICATE
This is to certify that the project work entitled
AUTOMATIC MEASUREMENT AND REPORTING SYSTEM OF WATER
QUALITY BASED ON GSM
Is the bonafide work done by
M.NAJMA (09L41A0492)
G.KAMAL CHOWDARY (09L41A04A0)
B.BHUVAN CHANDH (09L41A04A5)
B.RAJA RAO (09L41A0499)
In the department of ELECTRONICS AND COMMUNICATION ENGINEERING
in MEKAPATI RAJA MOHAN REDDY INSTITUTE OF TECHNOLOGY &
SCIENCE, Udayagiri. is submitted to JAWAHARLAL NEHRU TECHNOLOGICAL
UNIVERSITY, Ananthapur in the partial fulfillment of the requirements of the
requirements for the award of B.Tech degree in ELECTRONICS AND
COMMUNICATION ENGINEERING
Internal Guide Head of the Department
Mr.G.NARENDRANATH REDDY, M.Tech. Mr.
K.VENKATESHWARLU,M.Tech,(Ph.D).
(Assistant professor,Dept.of ECE ) (Assistant professor, Dept. of ECE)
______________________________________________________________________
Submitted for Viva Voce Examination held on________________
INTERNAL EXAMINER EXTERNAL
EXAMINER
ACKNOWLEDGEMENT
Our first and foremost thanks to the almighty for his blessings in the successful
completion of project.
We are extremely thankful to our beloved Chairman SRI
M.RAJAMOHANREDDY Sir who took interest and encouraged us in every effort
though the course.
We are extremely thankful to our beloved Secretary, SRI M.CHANDRA
SEKHAR REDDY Sir who took interest and encouraged us in every effort throughout
the course.
We are extremely thankful to our correspondent commodre
SRI.A.MASTHANAIAH Sir who took interest and encouraged us in every effort
throughout the course.
We owe our gratitude to our Principal SRI.Dr.V.K.R.JEYA SINGH, B.E,
M.Sc(Engg.), Ph.D ., F.I.E, M.I.S.T.E for his kind attention in the valuable guidance
to us throughout the course.
We profound respect, we express our deep sense of gratitude to our head of the
department SRI K.VENKATESWARULU, M.Tech, (Ph.D),Assistant professor. for
being the source of inspiration throughout our study in this college
We sincerely thank our guide SRI.G.NARENDRANATH REDDY, M.Tech.,
for his guidance, valuable suggestions and support in the completion of the mini project.
Above all we gratefully acknowledge and express our thanks to all teaching and
non teaching staff of “ELECTRONICS AND COMMUNICATION
ENGINEERING” department.
Finally, we thank all our friends who helped in getting this project report ready.
PROJECT MEMBERS
M.NAJMA (09L41A0492)
G.KAMAL CHOWDARY (09L41A04A0)
B.BHUVAN CHANDH
(09L41A04A5)
B.RAJARAO (09L41A0499)
CONTENTS
CHAPTER TITLE PAGE
NO
1 INTRODUCTION
2
1.1 INTRODUCTION 2
2 EMBEDDED SYSTEMS
4
2.1 INTRODUCTION To EMBEDDED SYSTEMS
4
2.1.1 HISTORY
5
2.1.2 TOOLS
6
2.1.3 RESOURCES
7
2.1.4 REAL TIME ISSUES
2.2.1 DEBUGGING
7
2.2.2 RELLABILITY
8
2.3 EXPLANATION OF EMBEDDED SYSTEMS
9
2.3.1 SOFTWARE ARCHITECTUE
9
2.3.2 STAND ALONE EMBEDDED SYSTEMS
10
2.3.3 REAL TIME EMBEDDED SYSTEMS
10
2.3.4 NETWORK COMMUNICATION
EMBEDDED SYSTEMS 11 2.4 OVERVIEW OF EMBEDDEE SYSTEM ARCHITECTURE
2.5 CONCLUSION
3. EXPLANATION OF EACH BLOCK AND COMPONENTS
3.1 POWER SUPPLY 3.1.1 TRANSFORMER
3.1.2 RECTIFIER 3.1.3 FILTER 3.1.4 VOLTAGE REGULATOR 3.2 AT89S52 MICROCONTROLLER
3.2.1 FEATURES
3.2.2 DESCRIPTION 15
3.2.3 PIN CONFIGURATION
3.2.4 PIN DESCRIPTION
3.2.5 MEMORIES 18
3.3 TEMPARATURE SENSOR
3.3.1 INTRODUCTION
3.3.2 FEATURES
3.3.3 PIN DIAGRAM
3.3.4 APPLICATIONS
3.4 pH METER
3.4.1 PRINCIPLE AND OPERATION
3.4.2 pH SENSOR
3.5 ANALOG TO DIGITAL CONVERTER3.5.1 INTRODUCTION3.5.2 FEATURES3.5.3 KEY SPECIFICATIONS3.5.4PINDIAGRAM3.5.5 I/O PINS3.8 LCD
3.8.1introduction
3.8.2 features 3.8.3 shapes&sizes3.7 SERIAL COMMUNICATION3.7.1 RS232 STANDADS3.7.2 DB253.7.3DB93.7.4 MAX2323.8 GSM 3.8.1 GSM ARCHITECTURE
3.8.2 THE GSM NETWORKS PARTS
3.9 BUZZER
4.ADVANTAGES
5.APPLICATIONS
6.FUTURE SCOPE
7.CONCLUSION
8.BIBILOGRAPH
ABSTRACT
With the rapid development of the economy, more and more serious problems of
environment arise. Water pollution is one of these problems.This method waste
too much manpower and material resource, has the limitations of the samples
collecting.
Various parameters of water quality are automatically detected under the
control of single chip ‘MICROOCONTROLLER’.The system uses SENSORS which
converts non-power information into electrical signals.
Microcontroller analyses the water samples and water quality.If it is abnormal
then the data will be sent to monitoring center and managements mobile in the same way
at the same time using GSM In this project implements automation, intelligence and
network of water quality monitoring, and uses manpower, material and financial
resources sparingly.
To develop an embedded system, which is used to
measure and report the water quality parameters such as pH and temperature,
therefore it will be automatically detected under the control of single chip
microcontroller all day using GSM technology .
BLOCK DIAGRAM:
Power supply:
CHAPTER-1
INTRODUCTION
With the rapid development of the economy, more and more serious problems of
environment arise. Water pollution is one of these problems.This method waste
too much manpower and material resource, has the limitations of the samples
collecting.The system uses SENSORS which converts non-power information into
electrical signals.
Microcontroller analyses the water samples and water
quality.If it is abnormal then the data will be sent to monitoring center and
managements mobile in the same way at the same time using GSM In this project
implements automation, intelligence and network of water quality monitoring, and
uses manpower, material and financial resources sparingly
CHAPTER-2
EMBEDDED SYSTEMS 2.1 Introduction To Embedded system:
An embedded system is a computer system designed to perform one or a few
dedicated functions often with real-time computing constraints. It is embedded as part of
a complete device often including hardware and mechanical parts. By contrast, a general-
purpose computer, such as a personal computer (PC), is designed to be flexible and to
meet a wide range of end-user needs. Embedded systems control many devices in
common use today.
Embedded systems are controlled by one or more main processing cores that are
typically either microcontrollers or digital signal processors (DSP). The key
characteristic, however, is being dedicated to handle a particular task, which may require
very powerful processors. For example, air traffic control systems may usefully be
viewed as embedded, even though they involve mainframe computers and dedicated
regional and national networks between airports and radar sites. (Each radar probably
includes one or more embedded systems of its own.)
Since the embedded system is dedicated to specific tasks, design engineers can
optimize it to reduce the size and cost of the product and increase the reliability and
performance. Some embedded systems are mass-produced, benefiting from economies of
scale.
Physically embedded systems range from portable devices such as digital watches
and MP3 players, to large stationary installations like traffic lights, factory controllers, or
the systems controlling nuclear power plants. Complexity varies from low, with a single
microcontroller chip, to very high with multiple units, peripherals and networks mounted
inside a large chassis or enclosure.
In general, "embedded system" is not a strictly definable term, as most systems
have some element of extensibility or programmability. For example, handheld
computers share some elements with embedded systems such as the operating systems
and microprocessors which power them, but they allow different applications to be
loaded and peripherals to be connected. Moreover, even systems which don't expose
programmability as a primary feature generally need to support software updates. On a
continuum from "general purpose" to "embedded", large application systems will have
subcomponents at most points even if the system as a whole is "designed to perform one
or a few dedicated functions", and is thus appropriate to call "embedded". A modern
example of embedded system is shown in fig: 2.1.
Fig 2.1:A modern example of embedded system
Labeled parts include microprocessor (4), RAM (6), flash memory (7).Embedded
systems programming is not like normal PC programming. In many ways, programming
for an embedded system is like programming PC 15 years ago. The hardware for the
system is usually chosen to make the device as cheap as possible. Spending an extra
dollar a unit in order to make things easier to program can cost millions. Hiring a
programmer for an extra month is cheap in comparison. This means the programmer must
make do with slow processors and low memory, while at the same time battling a need
for efficiency not seen in most PC applications. Below is a list of issues specific to the
embedded field.
2.1.1 HISTORY:
In the earliest years of computers in the 1930–40s, computers were sometimes
dedicated to a single task, but were far too large and expensive for most kinds of tasks
performed by embedded computers of today. Over time however, the concept
of programmable controllers evolved from traditional electromechanical sequencers, via
solid state devices, to the use of computer technology.
One of the first recognizably modern embedded systems was the Apollo Guidance
Computer, developed by Charles Stark Draper at the MIT Instrumentation Laboratory. At
the project's inception, the Apollo guidance computer was considered the riskiest item in
the Apollo project as it employed the then newly developed monolithic integrated circuits
to reduce the size and weight. An early mass-produced embedded system was the
autonetics D-17 guidance computer for the Minuteman missile, released in 1961. It was
built from transistor logic and had a hard disk for main memory. When the Minuteman II
went into production in 1966, the D-17 was replaced with a new computer that was the
first high-volume use of integrated circuits.
2.1.2 TOOLS
Embedded development makes up a small fraction of total programming. There's
also a large number of embedded architectures, unlike the PC world where 1 instruction
set rules, and the Unix world where there's only 3 or 4 major ones. This means that the
tools are more expensive. It also means that they're lowering featured, and less
developed. On a major embedded project, at some point you will almost always find a
compiler bug of some sort.
Debugging tools are another issue. Since you can't always run general programs
on your embedded processor, you can't always run a debugger on it. This makes fixing
your program difficult. Special hardware such as JTAG ports can overcome this issue in
part. However, if you stop on a breakpoint when your system is controlling real world
hardware (such as a motor), permanent equipment damage can occur. As a result, people
doing embedded programming quickly become masters at using serial IO channels and
error message style debugging.
2.1.3 RESOURCES:
To save costs, embedded systems frequently have the cheapest processors that can
do the job. This means your programs need to be written as efficiently as possible. When
dealing with large data sets, issues like memory cache misses that never matter in PC
programming can hurt you. Luckily, this won't happen too often- use reasonably efficient
algorithms to start, and optimize only when necessary. Of course, normal profilers won't
work well, due to the same reason debuggers don't work well.
Memory is also an issue. For the same cost savings reasons, embedded systems
usually have the least memory they can get away with. That means their algorithms must
be memory efficient
(unlike in PC programs, you will frequently sacrifice processor time for memory, rather
than the reverse). It also means you can't afford to leak memory. Embedded applications
generally use deterministic memory techniques and avoid the default "new" and "malloc"
functions.
2.1.4 REAL TIME ISSUES:
Embedded systems frequently control hardware, and must be able to respond to
them in real time. Failure to do so could cause inaccuracy in measurements, or even
damage hardware such as motors. This is made even more difficult by the lack of
resources available. Almost all embedded systems need to be able to prioritize some tasks
over others, and to be able to put off/skip low priority tasks such as UI in favor of high
priority tasks like hardware control.
2.2 NEED FOR EMBEDDED SYSTEMS:
The uses of embedded systems are virtually limitless, because every day new
products are introduced to the market that utilizes embedded computers in novel ways. In
recent years, hardware such as microprocessors, microcontrollers, and FPGA chips have
become much cheaper. So when implementing a new form of control, it's wiser to just
buy the generic chip and write your own custom software for it. Producing a custom-
made chip to handle a particular task or set of tasks costs far more time and money.
2.2.1 DEBUGGING:
Embedded debugging may be performed at different levels, depending on the
facilities available. From simplest to most sophisticate they can be roughly grouped into
the following areas:
1. Interactive resident debugging, using the simple shell provided by the
embedded operating system (e.g. Forth and Basic)
2. External debugging using logging or serial port output to trace operation
using either a monitor in flash or using a debug server like the Remedy
Debugger which even works for heterogeneous multi core systems.
3. An in-circuit debugger (ICD), a hardware device that connects to the
microprocessor via a JTAG or Nexus interface. This allows the operation of
the microprocessor to be controlled externally, but is typically restricted to
specific debugging capabilities in the processor.
4. An in-circuit emulator replaces the microprocessor with a simulated
equivalent, providing full control over all aspects of the microprocessor.
5. A complete emulator provides a simulation of all aspects of the hardware,
allowing all of it to be controlled and modified and allowing debugging on a
normal PC.
6. Unless restricted to external debugging, the programmer can typically load
and run software through the tools, view the code running in the processor,
and start or stop its operation. The view of the code may be as assembly
code or source-code.
2.2.2 RELIABILITY:
Embedded systems often reside in machines that are expected to run continuously
for years without errors and in some cases recover by them if an error occurs. Therefore
the software is usually developed and tested more carefully than that for personal
computers, and unreliable mechanical moving parts such as disk drives, switches or
buttons are avoided.
Specific reliability issues may include:
1. The system cannot safely be shut down for repair, or it is too inaccessible to
repair. Examples include space systems, undersea cables, navigational
beacons, bore-hole systems, and automobiles.
2. The system must be kept running for safety reasons. "Limp modes" are less
tolerable. Often backups are selected by an operator. Examples include
aircraft navigation, reactor control systems, safety-critical chemical factory
controls, train signals, engines on single-engine aircraft.
3. The system will lose large amounts of money when shut down: Telephone
switches, factory controls, bridge and elevator controls, funds transfer and
market making, automated sales and service.
2.3 EXPLANATION OF EMBEDDED SYSTEMS:
2.3.1 SOFTWARE ARCHITECTURE:
There are several different types of software architecture in common use.
1. Simple Control Loop:
In this design, the software simply has a loop. The loop calls subroutines, each of
which manages a part of the hardware or software.
2. Interrupt Controlled System:
Some embedded systems are predominantly interrupt controlled. This means that
tasks performed by the system are triggered by different kinds of events. An interrupt
could be generated for example by a timer in a predefined frequency, or by a serial port
controller receiving a byte. These kinds of systems are used if event handlers need low
latency and the event handlers are short and simple.
Usually these kinds of systems run a simple task in a main loop also, but this task
is not very sensitive to unexpected delays. Sometimes the interrupt handler will add
longer tasks to a queue structure. Later, after the interrupt handler has finished, these
tasks are executed by the main loop. This method brings the system close to a
multitasking kernel with discrete processes.
3. Cooperative Multitasking:
A non-preemptive multitasking system is very similar to the simple control loop
scheme, except that the loop is hidden in an API. The programmer defines a series of
tasks, and each task gets its own environment to “run” in. When a task is idle, it calls
an idle routine, usually called “pause”, “wait”, “yield”, “nop” (stands for no operation),
etc.
4. Primitive Multitasking:
In this type of system, a low-level piece of code switches between tasks or threads
based on a timer (connected to an interrupt). This is the level at which the system is
generally considered to have an "operating system" kernel. Depending on how much
functionality is required, it introduces more or less of the complexities of managing
multiple tasks running conceptually in parallel.
2.3.2 STAND ALONE EMBEDDED SYSTEM:
These systems takes the input in the form of electrical signals from transducers or
commands from human beings such as pressing of a button etc.., process them and
produces desired output. This entire process of taking input, processing it and giving
output is done in standalone mode. Such embedded systems comes under stand alone
embedded system.
2.3.3 REAL-TIME EMBEDDED SYSTEMS:
Embedded systems which are used to perform a specific task or operation in a
specific time period those systems are called as real-time embedded systems. There are
two types of real-time embedded systems.
1. Hard Real-time embedded systems:
These embedded systems follow an absolute dead line time period i.e.., if the
tasking is not done in a particular time period then there is a cause of damage to the entire
equipment.
Eg: consider a system in which we have to open a valve within 30 milliseconds. If
this valve is not opened in 30 ms this may cause damage to the entire equipment. So in
such cases we use embedded systems for doing automatic operations.
2. Soft Real Time embedded systems:
These embedded systems follow a relative dead line time period i.e.., if the task is
not done in a particular time that will not cause damage to the equipment.
Eg: Consider a TV remote control system, if the remote control takes a few
milliseconds delay it will not cause damage either to the TV or to the remote control.
These systems which will not cause damage when they are not operated at considerable
time period those systems comes under soft real-time embedded system.
2.3.4 NETWORK COMMUNICATION EMBEDDED SYSTEMS:
A wide range network interfacing communication is provided by using embedded.
1. Consider a web camera that is connected to the computer with internet can be used
to spread communication like sending pictures, images, videos etc.., to another
computer with internet connection throughout anywhere in the world.
2. Consider a web camera that is connected at the door lock.Whenever a person comes
near the door, it captures the image of a person and sends to the desktop of your
computer which is connected to internet. This gives an alerting message with image
on to the desktop of your computer, and then you can open the door lock just by
clicking the mouse. Fig: 2.2 show the network communications in embedded
systems.
Fig 2.3.4: Network communication embedded systems
2.2 OVERVIEW OF EMBEDDED SYSTEM ARCHITECTURE
Every embedded system consists of custom-built hardware built around a Central
Processing Unit (CPU). This hardware also contains memory chips onto which the
software is dded system for security applications is one of the most lucrative businesses
nowadays. loaded. The software residing on the memory chip is also called the
‘firmware’. The embedded system architecture can be represented as a layered
architecture as shown in Fig
The operating system runs above the hardware, and the application software runs
above the operating system. The same architecture is applicable to any computer
including a desktop computer. However, there are significant differences. It is not
compulsory to have an operating system in every embedded system. For small appliances
such as remote control units, air conditioners, toys etc., there is no need for an operating
system and you can write only the software specific to that application. For applications
involving complex processing, it is advisable to have an operating system. In such a case,
you need to integrate the application software with the operating system and then transfer
the entire software on to the memory chip. Once the software is transferred to the
memory chip, the software will continue to run for a long time you don’t need to reload
new software.
Now, let us see the details of the various building blocks of the hardware of an
embedded system. As shown in Fig. the building blocks are;
a. Central Processing Unit (CPU)
b. Memory (Read-only Memory and Random Access Memory)
c. Input Devises
d. Output devises
e. Communication interfaces
f. Application-specific circuitry
Fig.1.3: blocks of the hardware of an embedded system
2.2.1 CENTRAL PROCESSING UNIT (CPU)
The Central Processing Unit (processor in short) can be any of the following:
microcontroller, microprocessor or Digital Signal Processor (DSP). A micro-controller is
a low-cost processor. Its main attraction is that on the chip itself, there will be many other
components such as memory, serial communication interface, analog-to digital converter
etc. So, for small applications, a micro-controller is the best choice as the number of
external components required will be very less. On the other hand, microprocessors are
more powerful, but you need to use many external components with them. D5P is used
mainly for applications in which signal processing is involved such as audio and video
processing.
2.2.2 MEMORY
The memory is categorized as Random Access 11emory (RAM) and Read Only
Memory (ROM). The contents of the RAM will be erased if power is switched off to the
chip, whereas ROM retains the contents even if the power is switched off. So, the
firmware is stored in the ROM. When power is switched on, the processor reads the
ROM; the program is program is execute.
INPUT DEVICES:
Unlike the desktops, the input devices to an embedded system have very limited
capability. There will be no keyboard or a mouse, and hence interacting with the
embedded system is no easy task. Many embedded systems will have a small keypad-you
press one key to give a specific command. A keypad may be used to input only the digits.
Many embedded systems used in process control do not have any input device for user
interaction; they take inputs from sensors or transducers 1’fnd produce electrical signals
that are in turn fed to other systems.
2.2.4 OUTPUT DEVICES
The output devices of the embedded systems also have very limited capability.
Some embedded systems will have a few Light Emitting Diodes (LEDs) to indicate the
health status of the system modules, or for visual indication of alarms. A small Liquid
Crystal Display (LCD) may also be used to display some important parameters.
COMMUNICATION INTERFACES:
The embedded systems may need to, interact with other embedded systems at they may
have to transmit data to a desktop. To facilitate this, the embedded systems are provided
with one or a few communication interfaces such as RS232, RS422, RS485, Universal
Serial Bus (USB), IEEE 1394, Ethernet etc.
2.2.6 APPLICATION-SPECIFIC CIRCUITRY
Sensors, transducers, special processing and control circuitry may be required fat
an embedded system, depending on its application. This circuitry interacts with the
processor to carry out the necessary work. The entire hardware has to be given power
supply either through the 230 volts main supply or through a battery. The hardware has to
design in such a way that the power consumption is minimized.
2.3 CONCLUSION:
Embedded systems plays a vital role in our day to day life. They are used for household
appliances like microwave oven to the satellite applications. They provide good man to
machine interface.
Automation is the further step in the world of embedded systems, which includes the
elimination of the human being in the mundane applications. They are cost effective,
accurate and can work in any conditions and round the clock
CHAPTER-3
EXPLANATION OF EACH BLOCK AND COMPONENTS
3.1 Power supply:
All digital circuits require regulated power supply. In this article, we are going to learn
how to get a regulated positive supply from the mains supply.
Figure 1 shows the basic block diagram of a fixed regulated power supply. Let us go
through each block.
3.1.1 TRANSFORMER:
A transformer consists of two coils also called as “WINDINGS” namely PRIMARY &
SECONDARY.
They linked together through inductively coupled electrical conductors also called as
CORE. A changing current in the primary causes a change in the Magnetic Field in the
core & this in turn induces an alternating voltage in the secondary coil. If load applied to
the secondary then an alternating current will flow through the load. If we consider an
ideal condition then all the energy from the primary circuit will transferred to the
secondary circuit through the magnetic field.
So
The secondary voltage of the transformer depends on the number of turns in the Primary as well as in
the secondary.
3.1.2 RECTIFIER:
A rectifier is a device that converts an AC signal into DC signal. For rectification purpose
we use a diode, a diode is a device that allows current to pass only in one direction i.e.
when the anode of the diode is positive with respect to the cathode also called as forward
biased condition & blocks current in the reversed biased condition.
Rectifier classified as follows:
3.1.2.1 Half Wave rectifier
This is the simplest type of rectifier as you can see in the diagram a half wave rectifier
consists of only one diode. When an AC signal applied to it during the positive half cycle,
the diode is forward biased & current flows through it. However, during the negative half
cycle diode is reverse biased & no current flows through it. Since only one-half of the
input reaches the output, it is very inefficient to use in power supplies.
3.1.2.2 Full wave rectifier
Half wave rectifier is quite simple but it is very inefficient, for greater efficiency
we would like to use both the half cycles of the AC signal. This can achieve by using a
center-tapped transformer i.e. we would have to double the size of secondary winding &
provide connection to the center. Therefore, during the positive half cycle diode, D1
conducts & D2 is in reverse biased condition. During the negative half cycle diode, D2
conducts & D1 is reverse biased. Thus, we get both the half cycles across the load.
One of the disadvantages of Full Wave Rectifier design is the necessity of using a center
tapped transformer, thus increasing the size & cost of the circuit. This can avoid by using
the Full Wave Bridge Rectifier.
3.1.2.3 Bridge Rectifier
As the name suggests it converts the full wave i.e. both the positive & the negative half
cycle into DC thus it is much more efficient than Half Wave Rectifier & that too without
using a center tapped transformer thus much more cost effective than Full Wave
Rectifier.
Full Bridge Wave Rectifier consists of four diodes namely D1, D2, D3 and D4. During
the positive half cycle diodes D1 & D4 conduct whereas in the negative half cycle diodes
D2 & D3 conduct thus the diodes keep switching the transformer connections so we get
positive half cycles in the output.
If we use a center-tapped transformer for a bridge rectifier, we can get both positive &
negative half cycles, which can thus used for generating fixed positive & fixed negative
voltages.
3.1.3 FILTER CAPACITOR
Even though half wave & full wave rectifier give DC output, none of them provides a
constant output voltage. For this we require to smoothen the waveform received from the
rectifier. This can be done by using a capacitor at the output of the rectifier this capacitor
is also called as “FILTER CAPACITOR” or “SMOOTHING CAPACITOR” or
“RESERVOIR CAPACITOR”. Even after using this capacitor a small amount of ripple
will remain.
We place the Filter Capacitor at the output of the rectifier the capacitor will charge to the peak voltage
during each half cycle then will discharge its stored energy slowly through the load whilethe rectified
voltage drops to zero, thus trying to keep the voltage as constant as possible.
If we go on increasing the value of the filter capacitor then the Ripple will decrease. Then the costing
will increase. The value of the Filter capacitor depends on the current consumed by the circuit, the
frequency of the waveform & the accepted ripple.
Where,
Vr= accepted ripple voltage.( should not be more than 10% of the voltage)
I= current consumed by the circuit in Amperes.
F= frequency of the waveform. A half wave rectifier has only one peak in one cycle so F=25 Hz
Whereas a full wave rectifier has Two peaks in one cycle so F=100 Hz.
3.1.4 VOLTAGE REGULATOR
A Voltage regulator is a device which converts varying input voltage into a constant
regulated output voltage. Voltage regulator can be of two types
1). Linear Voltage Regulator: Also called as Resistive Voltage regulator because they dis
sipate the excessive voltage resistively as heat.
2) Switching RegulatorsThey regulate the output voltage by switching the Current
ON/OFF very rapidly. Since either their output is ON or OFF it dissipates very low
power thus achieving higher efficiency as compared to linear voltage regulators.
However, they are more complex & generate high noise due to their switching action. For
low level of output power, switching regulators tend to be costly but for higher output
wattage, they are much cheaper than linear regulators.
The most commonly available Linear Positive Voltage Regulators are the 78XX series
where the XX indicates the output voltage. In addition, 79XX series is for Negative
Voltage Regulators.
After filtering the rectifier output, the signal is given to a voltage regulator. The
maximum input voltage that can be applied at the input is 35V.Normally there is a 2-3
Volts drop across the regulator so the input voltage should be at least 2-3 Volts higher
than the output voltage. If the input voltage gets below the Vmin of the regulator due to
the ripple voltage or due to any other reason the voltage regulator will not be able
To pro produce the correct regulated voltage.
3.Circuitdiagram:
Fig2.3circuitdiagramofpowersupply
HARDWARE DESCRIPTION
3.2 INTRODUCTION:
In this chapter the block diagram of the project and design aspect of independent
modules are considered. In this diagram the main modules are micro controller, zigbee
transmitter LCD,crystal oscillator,reset and LED indicators.
3.2.1 AT89S52
3.2.1.1 A BRIEF HISTORY OF 8051
In 1981, Intel Corporation introduced an 8 bit microcontroller called 8051. This
microcontroller had 128 bytes of RAM, 4K bytes of chip ROM, two timers, one serial
port, and four ports all on a single chip. At the time it was also referred as “A SYSTEM
ON A CHIP”
AT89S52:
The AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with 8K
bytes of in-system programmable Flash memory. The device is manufactured using
Atmel’s high-density nonvolatile memory technology and is compatible with the
industry-standard 80C51 instruction set and pin out. 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 on a monolithic chip, the Atmel AT89S52 is a powerful micro-controller, which
provides a highly flexible and cost-effective solution to many, embedded control
applications. The AT89S52 provides the following standard features: 8K bytes of Flash,
256 bytes of RAM, 32 I/O lines, Watchdog timer, two data pointers, three 16-bit
timer/counters, a six-vector two-level interrupt architecture, a full duplex serial port, on-
chip oscillator, and clock circuitry. In addition, the AT89S52 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 con-tents but freezes the oscillator, disabling all other chip functions until the next
interrupt
8031 has 128 bytes of RAM, two timers and 6 interrupts.
8051 has 4K ROM, 128 bytes of RAM, two timers and 6
interrupts.
8052 has 8K ROM, 256 bytes of RAM, three timers and 8
interrupts.
Of the three microcontrollers, 8051 is the most preferable. Microcontroller
supports both serial and parallel communication.
In the concerned project 8052 microcontroller is used. Here microcontroller used
is AT89S52, which is manufactured by ATMEL laboratories.
The 8051 is the name of a big family of microcontrollers. The device which we
are going to use along this tutorial is the 'AT89S52' which is a typical 8051
microcontroller manufactured by Atmel™. Note that this part doesn't aim to explain the
functioning of the different components of a 89S52 microcontroller, but rather to give
you a general idea of the organization of the chip and the available features, which shall
be explained in detail along this tutorial.
The block diagram provided by Atmel™ in their datasheet showing the architecture the
89S52 device can seem very complicated, and since we are going to use the C high level
language to program it, a simpler architecture can be represented as the figure 1.2.A.
This figure shows the main features and components that the designer can interact with.
You can notice that the 89S52 has 4 different ports, each one having 8 Input/output lines
providing a total of 32 I/O lines. Those ports can be used to output DATA and orders do
other devices, or to read the state of a sensor, or a switch. Most of the ports of the 89S52
have 'dual function' meaning that they can be used for two different functions: the fist one
is to perform input/output operations and the second one is used to implement special
features of the microcontroller like counting external pulses, interrupting the execution of
the program according to external events, performing serial data transfer or connecting
the chip to a computer to update the software.
3.2.2 NECESSITY OF MICROCONTROLLERS:
Microprocessors brought the concept of programmable devices and made many
applications of intelligent equipment. Most applications, which do not need large amount
of data and program memory, tended to be costly.
The microprocessor system had to satisfy the data and program requirements so,
sufficient RAM and ROM are used to satisfy most applications .The peripheral control
equipment also had to be satisfied. Therefore, almost all-peripheral chips were used in the
design. Because of these additional peripherals cost will be comparatively high.
An example:
8085 chip needs:
An Address latch for separating address from multiplex address and data.32-KB RAM
and 32-KB ROM to be able to satisfy most applications. As also Timer / Counter, Parallel
programmable port, Serial port, and Interrupt controller are needed for its efficient
applications.
In comparison a typical Micro controller 8051 chip has all that the 8051 board has
except a reduced memory as follows. 4K bytes of ROM as compared to 32-KB, 128
Bytes of RAM as compared to 32-KB.
Bulky: On comparing a board full of chips (Microprocessors) with one chip with all
components in it (Microcontroller).
Debugging: Lots of Microprocessor circuitry and program to debug. In Micro controller
there is no Microprocessor circuitry to debug.
Slower Development time: As we have observed Microprocessors need a lot of
debugging at board level and at program level, where as, Micro controller do not have the
excessive circuitry and the built-in peripheral chips are easier to program for operation.
So peripheral devices like Timer/Counter, Parallel programmable port, Serial Co
mmunication Port, Interrupt controller and so on, which were most often used were
integrated with the Microprocessor to present the Micro controller .RAM and ROM also
were integrated in the same chip. The ROM size was anything from 256 bytes to 32Kb or
more. RAM was optimized to minimum of 64 bytes to 256 bytes or more.
Microprocessor has following instructions to perform:
1. Reading instructions or data from program memory ROM.
2. Interpreting the instruction and executing it.
3. Microprocessor Program is a collection of instructions stored in a Nonvolatile memory.
4. Read Data from I/O device
5. Process the input read, as per the instructions read in program memory.
6. Read or write data to Data memory.
7. Write data to I/O device and output the result of processing to O/P device.
3.2.3 INTRODUCTION TO AT89S52
The system requirements and control specifications clearly rule out the use of 16,
32 or 64 bit micro controllers or microprocessors. Systems using these may be earlier to
implement due to large number of internal features. They are also faster and more reliable
but, the above application is satisfactorily served by 8-bit micro controller. Using an
inexpensive 8-bit Microcontroller will doom the 32-bit product failure in any competitive
market place. Coming to the question of why to use 89S52 of all the 8-bit Microcontroller
available in the market the main answer would be because it has 8kB Flash and 256 bytes
of data RAM32 I/O lines, three 16-bit timer/counters, a Eight-vector two-level interrupt
architecture, a full duplex serial port, on-chip oscillator, and clock circuitry.
In addition, the AT89S52 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 hardware reset. The Flash
program memory supports both parallel programming and in Serial In-System
Programming (ISP). The 89S52 is also In-Application Programmable (IAP), allowing the
Flash program memory to be reconfigured even while the application is running.
By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel
AT89S52 is a powerful microcomputer which provides a highly flexible and cost
effective solution to many embedded control applications.
3.2.4 FEATURES
1.Compatible with MCS-51 Products
2.8K Bytes of In-System Reprogrammable Flash Memory
3.Fully Static Operation: 0 Hz to 33 MHz
4.Three-level Program Memory Lock
5.256 x 8-bit Internal RAM
6.32 Programmable I/O Lines
7.Three 16-bit Timer/Counters
8.Eight Interrupt Sources
9.Programmable Serial Channel
10.Low-power Idle and Power-down Modes
11.Operating Range.4.0V to 5.5V
12.Full Duplex UART Serial Channel
13.Interrupt Recovery from Power-down Mode
14.Watchdog Timer
15.Dual Data Pointer
16.Power-off Flag
17.Fast Programming Time
18.Flexible ISP Programming (Byte and Page Mode)
3.2.5 DESCRIPTIONThe AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with 8K
bytes of in-system programmable Flash memory. The device is manufactured using
Atmel’s high-density nonvolatile memory technology and is compatible with the
industry-standard 80C51 instruction set and pin out. 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 on a monolithic chip, the Atmel AT89S52 is a powerful micro-controller, which
provides a highly flexible and cost-effective solution to many embedded control
applications.
The AT89S52 provides the following standard features:
8K bytes of Flash, 256 bytes of RAM, 32 I/O lines, Watchdog timer, two data pointers,
three 16-bit timer/counters, a six-vector two-level interrupt architecture, a full duplex
serial port, on-chip oscillator, and clock circuitry. In addition, the AT89S52 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
con-tents but freezes the oscillator, disabling all other chip functions until the next
interrupt
3.2.6 PIN CONFIGURATIONS Block diagram:
3.2.6.1 Pin diagram of AT9S52 Microcontroller
3.2.7 PIN DIAGRAM:
FIG-3.2.7.1 Pin diagram of 89S52 IC
3.2.8 PIN DESCRIPTION
VCC:
Supply voltage.
GND: Ground
Port 0
Port 0 is an 8-bit open drain bidirectional I/O port. As an output port, each pin can sink
eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high
impedance inputs. Port 0 can also be configured to be the multiplexed low order
address/data bus during accesses to external 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
program verification.
Port 1Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 1 output buffers
can sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled high
by the internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are
externally being pulled low will source current (IIL) because of the internal pull-ups. In
addition, P1.0 and P1.1 can be configured to be the timer/counter 2 external count input
(P1.0/T2) and the timer/counter 2 trigger input (P1.1/T2EX), respectively, as shown in
the following table. Port 1 also receives the low-order address bytes during Flash
programming and verification.
Table:3.2.8.1: Alternative Functions Of Port1 Pins
Port 2Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 2 output buffers
can sink/source four TTL inputs. When 1s are written to Port 2 pins, they are pulled high
by
the internal pull-ups and can be used as inputs. As inputs, Port 2 pins that are externally
being pulled low will source current (IIL) because of the internal pull-ups. Port 2 emits
the high-order address byte during fetches from external program memory and during
accesses to external data memory that uses 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 uses 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.
Port3
Port3 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 3 output buffers
can sink/source four TTL inputs. When 1s are written to Port 3 pins, they are pulled high
by the internal pull-ups and can be used as inputs. As inputs, Port 3 pins that are
externally being pulled low will source current (IIL) because of the pull-ups. Port 3 also
serves the functions of various special features of the AT89S52, as shown in the
following table. Port 3 also receives some control signals for Flash programming and
verification.
Table:3.2.8.2:Alternative functions of port3 pin
RSTReset input. A high on this pin for two machine cycles while the oscillator is
running resets the device. This pin drives High for 96 oscillator periods after the
Watchdog times out. The DISRTO bit in SFR AUXR (address 8EH) can be used to
disable this feature. In the default state of bit DISRTO, the RESET HIGH out feature is
enabled.
ALE/PROG
Address Latch Enable (ALE) is an output pulse for latching the low byte of the address
during accesses to external memory. This pin is also the program pulse input (PROG)
during Flash programming. In normal operation, ALE is emitted at a constant rate of 1/6
the oscillator frequency and may be used for external timing or clocking purposes. Note,
however, that one ALE pulse is skipped during each access to external data memory. If
desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit
set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is
weakly pulled high. Setting the ALE-disable bit has no effect if the microcontroller is in
external execution mode.
PSEN
Program Store Enable (PSEN) is the read strobe to external program memory. When the
AT89S52 is executing code from external program memory, PSEN is activated twice
each machine cycle, except that two PSEN activations are skipped during each access to
external data memory.
EA/VPPExternal 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 pin also
receives the 12-volt programming enable voltage (VPP) during Flash programming.
XTAL1Input to the inverting oscillator amplifier and input to the internal clock operating
circuit.XTAL2: Output from the inverting oscillator amplifier.
FIG-3.2.8.3Functional block diagram of microcontroller
3.2.9 THE 8052 OSCILLATOR AND CLOCK:
The heart of the 8051 circuitry that generates the clock pulses by
which all the internal all internal operations are synchronized. Pins XTAL1
And XTAL2 is provided for connecting a resonant network to form an
oscillator. Typically a quartz crystal and capacitors are employed. The
crystal frequency is the basic internal clock frequency of the microcontroller.
The manufacturers make 8051 designs that run at specific minimum and
maximum frequencies typically 1 to 16 MHz
Fig-3.2.9.1Oscillator and timing circuit
3.2.10 MEMORIES
Types of memory:
The 8052 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 8052 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 8K 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 8052 have a bank of 256 bytes 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 8051 is reset, this memory is cleared. 256
bytes of internal memory are subdivided. The first 32 bytes are divided into 4 register
banks. Each bank contains 8 registers. Internal RAM also contains 256 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 FFh. The user may make use of
these variables with commands such as SETB and CLR.
Special Function registered memory:
Special function registers are the areas of memory that control specific
functionality of the 8052 micro controller.
a) Accumulator (0E0h)
As its name suggests, it is used to accumulate the results of large no of
instructions. It can hold 8 bit values.
b) B registers (0F0h)
The B register is very similar to accumulator. It may hold 8-bit value. The b
register is only used by MUL AB and DIV AB instructions. In MUL AB the higher byte
of the product gets stored in B register. In div AB the quotient gets stored in B with the
remainder in A.
c) Stack pointer (81h)
The stack pointer holds 8-bit value. This is used to indicate where the next value
to be removed from the stack should be taken from. When a value is to be pushed on to
the stack, the 8052 first store the value of SP and then stores the value at the resulting
memory location. When a value is to be popped from the stack, the 8052 returns the
value from the memory location indicated by SP and then decrements the value of SP.
d) Data pointer
The SFRs DPL and DPH work together work together to represent a 16-bit value
called the data pointer. The data pointer is used in operations regarding external RAM
and some instructions code memory. It is a 16-bit SFR and also an addressable SFR.
e) Program counter
The program counter is a 16 bit register, which contains the 2 byte address, which
tells the 8052 where the next instruction to execute to be found in memory. When the
8052 is initialized PC starts at 0000h. And is incremented each time an instruction is
executes. It is not addressable SFR.
f) PCON (power control, 87h)
The power control SFR is used to control the 8051’s power control modes.
Certain operation modes of the 8051 allow the 8051 to go into a type of “sleep mode”
which consumes much lee power.
g) TCON (timer control, 88h)
The timer control SFR is used to configure and modify the way in which the
8051’s two timers operate. This SFR controls whether each of the two timers is running
or stopped and contains a flag to indicate that each timer has overflowed. Additionally,
some non-timer related bits are located in TCON SFR. These bits are used to configure
the way in which the external interrupt flags are activated, which are set when an
external interrupt occurs.
h) TMOD (Timer Mode, 89h)
The timer mode SFR is used to configure the mode of operation of each of the
two timers. Using this SFR your program may configure each timer to be a 16-bit timer,
or 13 bit timer, 8-bit auto reload timer, or two separate timers. Additionally you may
configure the timers to only count when an external pin is activated or to count “events”
that are indicated on an external pin.
i) TO (Timer 0 low/high, address 8A/8C h)
These two SFRs taken together represent timer 0. Their exact behavior depends
on how the timer is configured in the TMOD SFR; however, these timers always count
up. What is configurable is how and when they increment in value.
j) T1 (Timer 1 Low/High, address 8B/ 8D h)
These two SFRs, taken together, represent timer 1. Their exact behavior depends on
how the timer is configured in the TMOD SFR; however, these timers always count up.
k)P0 (Port 0, address 90h, bit addressable)
This is port 0 latch. Each bit of this SFR corresponds to one of the pins on a micro
controller. Any data to be outputted to port 0 is first written on P0 register. For e.g., bit 0
of port 0 is pin P0.0, bit 7 is pin p0.7. Writing a value of 1 to a bit of this SFR will send a
high level on the corresponding I/O pin whereas a value of 0 will bring it to low level.
l) P1 (port 1, address 90h, bit addressable)
This is port latch1. Each bit of this SFR corresponds to one of the pins on a micro
controller. Any data to be outputted to port 0 is first written on P0 register. For e.g., bit 0
of port 0 is pin P1.0, bit 7 is pin P1.7. Writing a value of 1 to a bit of this SFR will send
a high level on the corresponding I/O pin whereas a value of 0 will bring it to low level.
m) P2 (port 2, address 0A0h, bit addressable):
This is a port latch2. Each bit of this SFR corresponds to one of the pins on a
micro controller. Any data to be outputted to port 0 is first written on P0 register. For e.g.,
bit 0 of port 0 is pin P2.0, bit 7 is pin P2.7. Writing a value of 1 to a bit of this SFR will
send a high level on the corresponding I/O pin whereas a value of 0 will bring it to low
level.
n) P3 (port 3, address B0h, bit addressable) :
This is a port latch3. Each bit of this SFR corresponds to one of the pins on a
micro controller. Any data to be outputted to port 0 is first written on P0 register. For e.g.,
bit 0 of port 0 is pin P3.0, bit 7 is pin P3.7. Writing a value of 1 to a bit of this SFR will
send a high level on the corresponding I/O pin whereas a value of 0 will bring it to low
level.
o) IE (interrupt enable, 0A8h)
The Interrupt Enable SFR is used to enable and disable specific interrupts. The low 7 bits
of the SFR are used to enable/disable the specific interrupts, where the MSB bit is used to
enable or disable all the interrupts. Thus, if the high bit of IE is 0 all interrupts are
disabled regardless of whether an individual interrupt is enabled by setting a lower bit
p) IP (Interrupt Priority, 0B8h)
The interrupt priority SFR is used to specify the relative priority of each interrupt.
On 8051, an interrupt may be either low or high priority. An interrupt may interrupt
interrupts. For e.g., if we configure all interrupts as low priority other than serial
interrupt. The serial interrupt always interrupts the system, even if another interrupt is
currently executing. However, if a serial interrupt is executing no other interrupt will be
able to interrupt the serial interrupt routine since the serial interrupt routine has the
highest priority.
q) PSW (Program Status Word, 0D0h)
The program Status Word is used to store a number of important bits that are set
and cleared by 8052 instructions. The PSW SFR contains the carry flag, the auxiliary
carry flag, the parity flag and the overflow flag. Additionally, it also contains the register
bank select flags, which are used to select, which of the “R” register banks currently in
use.
r) SBUF (Serial Buffer, 99h)
SBUF is used to hold data in serial communication. It is physically two registers. One is writing only and is used to hold data to be transmitted out of 8052 via TXD. The
other is read only and holds received data from external sources via RXD. Both mutually exclusive registers use address 99h.
3.3 Temperature Sensor (LM35)3.3.1 INTRODUCTION:
The LM35 series are precision integrated-circuit temperature sensors, whose
output voltage is linearly proportional to the Celsius (Centigrade) temperature. The LM35
thus has an advantage over linear temperature sensors calibrated in Kelvin, as the user is
not required to subtract a large constant voltage from its output to obtain convenient
centigrade scaling. The LM35 does not require any external calibration or trimming to
provide typical accuracies of ±1/4°C at room temperature and ±3/4°C over a full -55 to
+150°C temperature range. Low cost is assured by trimming and calibration at the wafer
level. The LM35’s low output impedance, linear output, and precise inherent calibration
make interfacing to readout or control circuitry especially easy. It can be used with single
power supplies, or with plus and minus supplies. As it draws only 60 µA from its supply,
it has very low self-heating, less than 0.1°C in still air. The LM35 is rated to operate over
a -55° to +150°C temperature range, while the LM35C is rated for a -40° to +110°C
range (-10° with improved accuracy). The LM35 series is available packaged plastic TO-
92 transistor package. The LM35D is also available in an 8-lead surface mount small
outline package and a plastic TO-220 package.
3.3.2 FEATURES:
12. Calibrated directly in ° Celsius (Centigrade)
13. Linear + 10.0 mV/°C scale factor
14. 0.5°C accuracy guaranteeable (at +25°C)
15. Rated for full -55° to +150°C range
16. Suitable for remote applications
17. Low cost due to wafer-level trimming
18. Operates from 4 to 30 volts
19. Less than 60 µA current drain
20. Low self-heating, 0.08°C in still air
21. Nonlinearity only ±1/4°C typical
22. Low impedance
3.3.3 PIN DIAGRAM:
Fig 3.3.3.1 Lm35 Temparature sensor
3.3.4 APPLICATIONS: The LM35 can be applied easily in the same way as other integrated-circuit temperature sensors. It can be glued or cemented to a surface and its temperature will be within about 0.01°C of the surface temperature. This presumes that the ambient air temperature is almost the same as the surface temperature; if the air temperature were much higher or lower than the surface temperature, the actual temperature of the LM35
die would be at an intermediate temperature between the surface temperature and the air temperature. This is expecially true for the TO-92 plastic package, where the copper leads are the principal thermal path to carry heat into the device, so its temperature might be closer to the air temperature than to the surface temperature. To minimize this problem, be sure that the wiring to the LM35, as it leaves the device, is held at the same temperature as the surface of interest. The easiest way to do this is to cover up these wires with a bead of epoxy which will insure that the leads and wires are all at the same temperature as the surface, and that the LM35 die’s temperature will not be affected by the air temperature. The TO-46 metal package can also be soldered to a metal surface or pipe without damage. Of course, in that case the V- terminal of the circuit will be grounded to that metal. Alternatively, the LM35 can be mounted inside a sealed-end metal tube, and can then be dipped into a bath or screwed into a threaded hole in a tank. As with any IC, the LM35 and accompanying wiring and circuits must be kept insulated and dry, to avoid leakage and corrosion. This is especially true if the circuit may operate at cold temperatures where condensation can occur. Printed-circuit coatings and varnishes such as Humiseal and epoxy paints or dips are often used to insure that moisture cannot corrode the LM35 or its connections. These devices are sometimes soldered to a small light-weight heat fin, to decrease the thermal time constant and speed up the response in slowly-moving air. On the other hand, a small thermal mass may be added to the sensor, to give the steadiest reading despite small deviations in the air temperature.
3.4 pH METER
3.4.1Principles of operation of a pH meter
A pH meter is essentially a voltmeter with a high input impedance which
measures the voltage of an electrode sensitive to the hydrogen ion concentration, relative
to another electrode which exhibits a constant voltage. The key feature of the pH-
sensitive electrode is a thin glass membrane whose outside surface contacts the solution
to be tested. The inside surface of the glass membrane is exposed to a constant
concentration of hydrogen ions (0.1 M HCl).
Inside the glass electrode assembly, a silver wire, coated with silver chloride and
immersed in the HCl solution, is called an Ag/AgCl electrode. This electrode carries
current through the half-cell reaction. The potential between the electrode and the
solution depends on the chloride ion concentration, but, since this is constant (0.1 M), the
electrode potential is also constant.
A reference electrode is needed to complete the electrical circuit. A common choice is to
use another Ag/AgCl electrode as the reference. The Ag/AgCl electrode is immersed in
an 0.1 M KCl solution which makes contact with the test solution through a porous fiber
which allows a small flow of ions back and forth to conduct the current. The potential
created at this junction between the KCl solution and the test solution is nearly zero and
nearly unaffected by anything in the solution, including hydrogen ions.
Using the pH Meter: Allow the meter a few minutes to stabilize after you plug it in.
When you are not using the meter, keep the electrode immersed in pH 7.0 buffer to a
depth of about one inch. The meter must be calibrated by using standards of known pH
before an unknown is measured. Since the unknowns are acidic, the pH 4.00 and pH 7.00
standards should be used.
An accurate pH reading depends on standardization, the degree of static charge, and the
temperature of the solution.
Glass electrode Reference electrode Combined electrode
1. The pH meter should be standardized each time it is used with a buffer of known
pH, preferably one closest to the desired final pH. To calibrate the pH meter, expose
the hole in the electrode, rinse the electrode with deionized water, and place the
electrode in a standard solution, e.g., pH 7. Turn the selector to "pH". Adjust the pH
meter to the appropriate pH. Rinse electrode with deionized water and place in a
second standard buffer solution. The choice of the second standard depends on the
final he standard pH buffers used should be 7 and 10. If the final pH desired, for
example, if the final pH desired is 8.5, t pH desired is 5.5, the standard pH buffers
used should be 4 and 7. Turn the selector to "pH". Adjust the temperature knob to the
second standard pH. Rinse the electrode with deionized water, and return the
electrode to the soaking solution.
2. When rinsing the electrode, never wipe the end, but blot gently since wiping can
create a static electric charge, which can cause erroneous readings,
3. Make sure the solution you are measuring is at room temperature since the pH can
change with a change in temperature.
4. The pH-sensitive glass membrane is very thin and very easily broken. Do not
touch the membrane with anything harder than a Kim-Wipe and do that very gently.
Do not drop the electrode or bump it on the bottom of the beaker when immersing it
in a solution.
5. The glass membrane must be thoroughly hydrated to work properly. Do not allow
the electrode to remain out of water any longer than necessary. When the electrode is
not in use, keep it immersed in the pH 7.00 buffer. Do not put the electrode down on
the desk.
3.4.2 pH SENSOR:-It is converted non electrical information into electrical form .The lower-case letter pH stands for the negative common(base ten)log.while the uppercase letter’H’ stands for the eiement hydrogen.Thus pH is a logarithmic measurement of the number of moles of hydrogen(H+)per liter of solution.pH = 0 for neutrals >7 for bases <7for acidsMeasuring range=0to 14.00pH
Sensitivity=0.002Ph
Weight=1lb(0.45kgs)
3.4.3pH SENSOR ( pH100):- 3.4.3.1 Diagram:
t 3.5 ANALOG TO DIGITAL CONVERTER 08083.5.1 INTRODUCTION The ADC0808 data acquisition component is a monolithic CMOS device with
an 8-bit analog-to-digital converter, 8-channel multiplexer and microprocessor
compatible control logic. The 8-bit A/D converter uses successive approximation as the
conversion technique. The converter features a high impedance chopper stabilized
comparator, a 256R voltage divider with analog switch tree and a successive
approximation register. The 8-channel multiplexer can directly access any of 8-single-
ended analog signals. The device eliminates the need for external zero and full-scale
adjustments. Easy interfacing to microprocessors is provided by the latched and decoded
multiplexer address inputs and latched TTL tri-state outputs. The design of the ADC0808
has been optimized by incorporating the most desirable aspects of several A/D
conversion techniques. The ADC0808 offers high speed, high accuracy, minimal
temperature dependence, excellent long-term accuracy and repeatability, and consumes
minimal power. These features make this device ideally suited to applications from
process and machine control to consumer and automotive applications.
3.5.2 FEATURES:
1. Easy interface to all microprocessors
2. Operates ratio metrically or with 5 VDC or analog span
adjusted voltage reference
3. No zero or full-scale adjust required
4. 8-channel multiplexer with address logic
5. 0V to 5V input range with single 5V power supply
6. Outputs meet TTL voltage level specifications
7. Standard hermetic or molded 28-pin DIP package
8. 28-pin molded chip carrier package
9. ADC0808 equivalent to MM74C949
3.5.3 KEY SPECIFICATIONS:1. Resolution 8 Bits
2. Total Unadjusted Error ±1/2 LSB and ±1 LSB
3. Single Supply 5 VDC
4. Low Power 15 mW
5. Conversion Time 100 µs
3.5.4 PIN DIAGRAM OF ADC0808
Fig: 3.5.4.1 pin diagram of ADC0808
3.5.5 I/O PINS
3.5.5.1 ADDRESS LINES A, B, C
The device contains 8-channels. A particular channel is selected by using the
address decoder line. The table shown below the input states for address lines to select
any channel.
Fig 3.5.5.1 Address linesAB,C
3.5.5.2 ADDRESS LATCH ENABLE ALE
The address is latched on the Low – High transition of ALE.
3.5.5.2a START
The ADC’s Successive Approximation Register (SAR) is reset on the positive edge
i.e. Low- High of the Start Conversion pulse. Whereas the conversion is begun on the
falling edge i.e. High – Low of the pulse.
3.5.5.2b OUTPUT ENABLE
Whenever data has to be read from the ADC, Output Enable pin has to be pulled high
thus enabling the TRI-STATE outputs, allowing data to be read from the data pins D0-
D7.
The device contains 8-channels. A particular channel is selected by
using the addres s decoder line. The table shown below t he input states for address
lines to select any channel
3.5.5..2c END OF CONVERSION (EOC)
This Pin becomes High when the conversion has ended, so the controller comes to
know that the data can now be read from the data pins.
3.5.5.3 Clock
External clock pulses are to be given to the ADC; this can be given either from
LM 555 in Astable mode or the controller can also be used to give the pulses.
3.6 LCD (LIQUID CRYSTAL DISPLAY)3.6.1 INTRODUCTION: 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. A program must interact
with the outside world using input and output devices that communicate directly with a
human being. One of the most common devices attached to an controller is an LCD
display. Some of the most common LCDs connected to the contollers are 16X1, 16x2 and
20x2 displays. This means 16 characters per line by 1 line 16 characters per line by 2
lines and 20 characters per line by 2 lines, respectively.
Many microcontroller devices use 'smart LCD' displays to output visual
information. LCD displays designed around LCD NT-C1611 module, are inexpensive,
easy to use, and it is even possible to produce a readout using the 5X7 dots plus cursor of
the display.
available. Line lengths of 8, 16, 20, 24, 32 and 40 characters are all standard, in one, two
They have a standard ASCII set of characters and mathematical
symbols. For an 8-bit data bus, the display requires a +5V supply plus 10 I/O lines (RS
RW D7 D6 D5 D4 D3 D2 D1 D0). For a 4-bit data bus it only requires the supply lines
plus 6 extra lines(RS RW D7 D6 D5 D4). When the LCD display is not enabled, data
lines are tri-state and they do not interfere with the operation of the microcontroller.
3.6.2FEATURES:
(1) Interface with either 4-bit or 8-bit microprocessor.
(2) Display data RAM
(3) 80x8 bits (80 characters).
(4) Character generator ROM
(5). 160 different 5 7 dot-matrix character patterns.
(6). Character generator RAM
(7) 8 different user programmed 5 7 dot-matrix patterns.
(8).Display data RAM and character generator RAM may be
Accessed by the microprocessor.
(9) Numerous instructions
(10) .Clear Display, Cursor Home, Display ON/OFF,
CursorON/OFF, Blink Character, Cursor Shift, Display Shift.
(11). Built-in reset circuit is triggered at power ON.
(12). Built-in oscillator.
Data can be placed at any location on the LCD. For 16×1 LCD, the address locations are:
Fig : 3.6.2 .1Address locations for a 1x16 line LCD3.6.3SHAPES AND SIZES:
Fig 3.6.3.1 different shapes and size Even limited to character based modules,there is still a wide variety of shapes
and sizes available. Line lenghs of 8,16,20,24,32 and 40 charecters are all standard, in one, two and four line versions. Several different LC technoCDlogies exists. “supertwist” types, for example, offer
Improved contrast and viewing angle over the older “twisted nematic” types. Some
modules are available with back lighting, so so that they can be viewed in dimly-lit
conditions. The back lighting may be either “electro-luminescent”, requiring a high
voltage inverter circuit, or simple LED illumination.
3.6.4ELECTRICAL BLOCK DIAGRAM:
Fig 3.6.4.1 LCD electrical block diagram
3.6.5POWER SUPPLY FOR LCD DRIVING:
Fig 3.6.5.1 LCD power supply and driving circuit
3.6.6 PIN DESCRIPTION:Most LCDs with 1 controller has 14 Pins and LCDs with 2 controller has 16 Pins
(two pins are extra in both for back-light LED connections).
Fig:3.6.6.1 pin diagram of 1x16 lines lcd
3.6.7 CONTROL LINES:
EN:
Line is called "Enable." This control line is used to tell the LCD that you are
sending it data. To send data to the LCD, your program should make sure this line is low
(0) and then set the other two control lines and/or put data on the data bus. When the
other lines are completely ready, bring EN high (1) and wait for the minimum
amount of time required by the LCD datasheet (this varies from LCD to LCD), and end
by bringing it low (0) again.
RS:
Line is the "Register Select" line. When RS is low (0), the data is to be treated as
a command or special instruction (such as clear screen, position cursor, etc.). When RS is
high (1), the data being sent is text data which sould be displayed on the screen. For
example, to display the letter "T" on the screen you would set RS high.
RW:
Line is the "Read/Write" control line. When RW is low (0), the information on the
data bus is being written to the LCD. When RW is high (1), the program is effectively
querying (or reading) the LCD. Only one instruction ("Get LCD status") is a read
command. All others are write commands, so RW will almost always be low.
Finally, the data bus consists of 4 or 8 lines (depending on the mode of operation
selected by the user). In the case of an 8-bit data bus, the lines are referred to as DB0,
DB1, DB2, DB3, DB4, DB5, DB6, and DB7.
3.6.8 LOGIC STATUS ON CONTROL LINES:
• E - 0 Access to LCD disabled
- 1 Access to LCD enabled
• R/W - 0 Writing data to LCD
- 1 Reading data from LCD
• RS - 0 Instructions
- 1 Character
3.6.9 WRITING DATA TO LCD:
1) Set R/W bit to low
2) Set RS bit to logic 0 or 1 (instruction or character)
3) Set data to data lines (if it is writing)
4) Set E line to high
5) Set E line to low
3.6.10 READ DATA FROM DATA LINES (if it is reading)ON LCD:1) Set R/W bit to high
2) Set RS bit to logic 0 or 1 (instruction or character)
3) Set data to data lines (if it is writing)
4) Set E line to high
5) Set E line to low
3.6.11 ENTERING TEXT: First, a little tip: it is manually a lot easier to enter characters and commands in
hexadecimal rather than binary (although, of course, you will need to translate commands
from binary couple of sub-miniature hexadecimal rotary switches is a simple matter,
although a little bit into hex so that you know which bits you are setting). Replacing the
d.i.l. switch pack with a of re-wiring is necessary.
The switches must be the type where On = 0, so that when they are turned to the
zero position, all four outputs are shorted to the common pin, and in position “F”, all four
outputs are open circuit.
All the available characters that are built into the module are shown in Table 3.
Studying the table, you will see that codes associated with the characters are quoted in
binary and hexadecimal, most significant bits (“left-hand” four bits) across the top, and
least significant bits (“right-hand” four bits) down the left.
Most of the characters conform to the ASCII standard, although the Japanese and
Greek characters (and a few other things) are obvious exceptions. Since these intelligent
modules were designed in the “Land of the Rising Sun,” it seems only fair that their
Katakana phonetic symbols should also be incorporated.
The more extensive Kanji character set, which the Japanese share with the
Chinese, consisting of several thousand different characters, is not included! Using the
switches, of whatever type, and referring to Table 3, enter a few characters onto the
display, both letters and numbers. The RS switch (S10) must be “up” (logic 1) when
sending the characters, and switch E (S9) must be pressed for each of them. Thus the
operational order is: set RS high, enter character, trigger E, leave RS high, enter another
character, trigger E, and so on.
The first 16 codes in Table 3, 00000000 to 00001111, ($00 to $0F) refer to the
CGRAM. This is the Character Generator RAM (random access memory), which can be
used to hold user-defined graphics characters. This is where these modules really start to
show their potential, offering such capabilities as bar graphs, flashing symbols, even
animated characters. Before the user-defined characters are set up, these codes will just
bring up strange looking symbols.
Codes 00010000 to 00011111 ($10 to $1F) are not used and just display blank
characters. ASCII codes “proper” start at 00100000 ($20) and end with 01111111 ($7F).
Codes 10000000 to 10011111 ($80 to $9F) are not used, and 10100000 to 11011111 ($A0
to $DF) are the Japanese characters.
3.6.12 INTIALIZATION BY INSTRUCTIONS:
If the power conditions for the normal operation of the internal reset circuit
are not satisfied, then executing a series of instructions must initialize LCD unit. The
procedure for this initialization process is as above show.
3.7 SERIAL DATA COMMUNICATION:
For serial data communication to work the byte of data must be converted to
serial bits using a parallel-in-serial-out shift register; then it can be transmitted over a
single data line. This also means that at the receiving end there must be a serial-in-
parallel-out shift register to receive the serial data and pack them into a byte. Of course, if
data is to be transferred on the telephone line, it must be converted from 0s and 1s to
audio tones, which are sinusoidal-shaped signals. This conversion is performed by a
peripheral device called a modem, which stands for “modulator/demodulator”.
3.7.1: RS232 STANDARDS:
To allow compatibility among data communication equipment made by various
manufacturers, an interfacing standard called RS232 was set by the Electronics Industries
Association (EIA) in 1960. Today, RS232 is the most widely used serial I/O interfacing
standard. However, since the standard was set long before the advent of TTL logic
family, its input and output voltage levels are not TTL compatible. In RS232, a 1 is
represented by -3 to -25V, while a 0 bit is +3 to +25V, making -3 to +3 undefined. For
this reason, to connect any RS232 to a microcontroller system we must use voltage
converters such as MAX232 to convert the TTL logic levels to the RS232 voltage levels,
and vice versa. MAX232 IC chips are commonly referred to as line drivers.
3.7.2: DB-25 Connector:
The following table provides the pins and their labels for the RS232 cable,
commonly referred to as the DB-25 connector. In labeling, DB-25P refers to the plug
connector (male) and DB-25S is for the socket connector (female).
PIN DESCRIPTION
1 Protective ground
2 Transmitted data (TxD)
3 Received data (RxD)
4 Request to send (RTS)
5 Clear to send (CTS)
6 Data set ready (DSR)
7 Signal ground (GND)
8 Data carrier detect (DCD)
9/10 Reserved for data testing
11 Unassigned
12 Secondary data carrier detect
13 Secondary clear to send
14 Secondary transmitted data
15 Transmit signal element timing
16 Secondary received data
17 Receive signal element timing
18 Unassigned
19 Secondary request to send
20 Data terminal ready (DTR)
21 Signal quality detector
22 Ring indicator
23 Data signal rate select
24 Transmit signal element timing
Unassigned
Table 3.7.2.1: Pin Description of DB-25 Connector.
3.7.3: DB-9 Connector:
Since not all the pins are used in PC cables, IBM introduced the DB-9 version
of the serial I/O standard, which uses 9 pins only, as shown in the following table:
PIN DESCRIPTION
1 Data carrier detect (DCD)2 Received data (RxD)
3 Transmitted data (TxD)
4 Data terminal ready (DTR)
5 Signal ground (GND)
6 Data set ready (DSR)
7 Request to send (RTS)
8 Clear to send (CTS)
9 Ring indicator (RI)
Table 3.7.3.1: Pin Description of DB-9 Connector.
Fig 3.7.3.2: D-Subminiature.
The D-subminiature or D-sub is a common type of electrical connector used
particularly in computers. At the time of introduction they were some of the smaller
connectors used on computer systems. A D-sub contains two or more parallel rows of
pins or sockets usually surrounded by a D-shaped metal shield that provides mechanical
support, some screening against electromagnetic interference, and ensures
correctorientation.
3.7.4 MAX 232
3.7.4.1INTRODUCTION: 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.
3.7.5 Pin diagram of MAX232:
3.7.5.1 SCHEMATIC DIAGRAM OF MAX 232
3.7.6 FEATURES:1. Operates With Single 5-V Power Supply
2.LinBiCMOSE 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 ITURecommendation V.28
7.Designed to be Interch Maxim MAX232
3.7.7APPLICATIONS:
TIA/EIA-232-F
Battery-Powered Systems
Terminals
Modems
Computers
9.ESD Protection ExceedMIL-STD-883, Method 3015
10.Package Options Include small-Outline (D, DW) Packages and
Standard Plastic (N) DIPs
3.7.8CIRCUIT 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 pacitors.
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 3.7.8.2 circuit connection of MAX232
3. 8 GSM (Global System for Mobile communications)3.8.1 1INTRODUCTION
GSM (Global System for Mobile communications) is a cellular network, which means
that mobile phones connect to it by searching for cells in the immediate vicinity. GSM
networks operate in four different frequency ranges. Most GSM networks operate in the
900 MHz or 1800 MHz bands. Some countries in the Americas use the 850 MHz and
1900 MHz bands because the 900 and 1800 MHz frequency bands were already
allocated.
The rarer 400 and 450 MHz frequency bands are assigned in some countries, where these
frequencies were previously used for first-generation systems.
GSM-900 uses 890–915 MHz to send information from the mobile station to the base
station (uplink) and 935–960 MHz for the other direction (downlink), providing 124 RF
channels (channel numbers 1 to 124) spaced at 200 kHz. Duplex spacing of 45 MHz is
used. In some countries the GSM-900 band has been extended to cover a larger frequency
range. This 'extended GSM', E-GSM, uses 880–915 MHz (uplink) and 925–960 MHz
(downlink), adding 50 channels (channel numbers 975 to 1023 and 0) to the original
GSM-900 band. Time division multiplexing is used to allow eight full-rate or sixteen
half-rate speech channels per radio frequency channel. There are eight radio timeslots
(giving eight burst periods) grouped into what is called a TDMA frame. Half rate
channels use alternate frames in the same timeslot. The channel data rate is
270.833 kbit/s, and the frame duration is 4.615 ms.
3.8.2 GSM ADVANTAGES:
GSM also pioneered a low-cost, to the network carrier, alternative to voice calls, the
Short t message service (SMS, also called "text messaging"), which is now supported on
other mobile standards as well. Another advantage is that the standard includes one
worldwide Emergency telephone number, 112. This makes it easier for international
travelers to connect to emergency services without knowing the local emergency number.
3.8.3 THE GSM NETWORK:
GSM provides recommendations, not requirements. The GSM specifications
define the functions and interface requirements in detail but do not address the hardware.
The GSM network is divided into three major systems: the
switching system (SS), the base station system (BSS), and the operation and support
system (OSS).
Fig 3.8.3.1 The architecture of GSM
3.6.3.1The Switching System:
The switching system (SS) is responsible for performing call processing and subscriber-
related functions. The switching system includes the following functional units.
Home location register (HLR): The HLR is a database used for storage and
management of subscriptions. The HLR is considered the most important
database, as it stores permanent data about subscribers, including a subscriber's
service profile, location information, and activity status. When an individual buys
a subscription from one of the PCS operators, he or she is registered in the HLR
of that operator.
Mobile services switching center (MSC): The MSC performs the telephony
switching functions of the system. It controls calls to and from other telephone
and data systems. It also performs such functions as toll ticketing, network
interfacing, common channel signaling, and others.
Visitor location register (VLR): The VLR is a database that contains temporary
information about subscribers that is needed by the MSC in order to service
visiting subscribers. The VLR is always integrated with the MSC. When a mobile
station roams into a new MSC area, the VLR connected to that MSC will request
data about the mobile station from the HLR. Later, if the mobile station makes a
call, the VLR will have the information needed for call setup without having to
interrogate the HLR each time.
Authentication center (AUC): A unit called the AUC provides authentication
and encryption parameters that verify the user's identity and ensure the
confidentiality of each call. The AUC protects network operators from different
types of fraud found in today's cellular world.
Equipment identity register (EIR): The EIR is a database that contains
information about the identity of mobile equipment that prevents calls from
stolen, unauthorized, or defective mobile stations. The AUC and EIR are
implemented as stand-alone nodes or as a combined AUC/EIR node.
3.8.3.2The Base Station System (BSS):
All radio-related functions are performed in the BSS, which consists of base station
controllers (BSCs) and the base transceiver stations (BTSs).
BSC: The BSC provides all the control functions and physical links between the
MSC and BTS. It is a high-capacity switch that provides functions such as
handover, cell configuration data, and control of radio frequency (RF) power
levels in base transceiver stations. A number of BSCs are served by an MSC.
BTS: The BTS handles the radio interface to the mobile station. The BTS is the
radio equipment (transceivers and antennas) needed to service each cell in the
network. A group of BTSs are controlled by a BSC.
3.8.3.3The Operation and Support System
The operations and maintenance center (OMC) is connected to all equipment in the
switching system and to the BSC. The implementation of OMC is called the operation
and support system (OSS). The OSS is the functional entity from which the network
operator monitors and controls the system. The purpose of OSS is to offer the customer
cost-effective support for centralized, regional and local operational and maintenance
activities that are required for a GSM network. An important function of OSS is to
provide a network overview and support the maintenance activities of different operation
and maintenance organizations.
3.8.4 ADDITIONAL FUNCTIONAL ELEMENTS
Message center (MXE): The MXE is a node that provides integrated voice, fax,
and data messaging. Specifically, the MXE handles short message service, cell
broadcast, voice mail, fax mail, e-mail, and notification.
Mobile service node (MSN): The MSN is the node that handles the mobile
intelligent network (IN) services.
Gateway mobile services switching center (GMSC): A gateway is a node used
to interconnect two networks. The gateway is often implemented in an MSC. The
MSC is then referred to as the GMSC.
GSM inter-working unit (GIWU): The GIWU consists of both hardware and
software that provides an interface to various networks for data communications.
Through the GIWU, users can alternate between speech and data during the same
call. The GIWU hardware equipment is physically located at the MSC/VLR.
3.8.5 GSM NETWORK AREAS:
The GSM network is made up of geographic areas. As shown in bellow figure, these
areas include cells, location areas (LAs), MSC/VLR service areas, and public land mobile
network (PLMN) areas.
Fig 3.8.5.1 GSM network area
Location Areas:
The cell is the area given radio coverage by one base transceiver station. The GSM
network identifies each cell via the cell global identity (CGI) number assigned to each
cell. The location area is a group of cells. It is the area in which the subscriber is paged.
Each LA is served by one or more base station controllers, yet only by a single MSC
Each LA is assigned a location area identity (LAI) number.
MSC/VLR service areas:
An MSC/VLR service area represents the part of the GSM network that is covered by one
MSC and which is reachable, as it is registered in the VLR of the MSC.
PLMN service areas:
The PLMN service area is an area served by one network operator.
3.8.6 GSM SPECIFICATIONS:
Specifications for different personal communication services (PCS) systems vary among the different PCS networks. Listed below is a description of the specifications and characteristics for GSM.
Frequency band: The frequency range specified for GSM is 1,850 to 1,990 MHz
(mobile station to base station).
Duplex distance: The duplex distance is 80 MHz. Duplex distance is the distance
between the uplink and downlink frequencies. A channel has two frequencies, 80
MHz apart.
Channel separation: The separation between adjacent carrier frequencies. In
GSM, this is 200 kHz.
Modulation: Modulation is the process of sending a signal by changing the
characteristics of a carrier frequency. This is done in GSM via Gaussian minimum
shift keying (GMSK).
Transmission rate: GSM is a digital system with an over-the-air bit rate of 270
kbps.
Access method: GSM utilizes the time division multiple access (TDMA) concept.
TDMA is a technique in which several different calls may share the same carrier.
Each call is assigned a particular time slot.
Speech coder: GSM uses linear predictive coding (LPC). The purpose of LPC is
to reduce the bit rate. The LPC provides parameters for a filter that mimics the
vocal tract. The signal passes through this filter, leaving behind a residual signal.
Speech is encoded at 13 kbps.
3.8.7 GSM SUBSCRIBER SERVICE:
Dual-tone multifrequency (DTMF): DTMF is a tone signaling scheme often used for
various control purposes via the telephone network, such as remote control of an
answering machine. GSM supports full-originating DTMF.
Facsimile group III—GSM supports CCITT Group 3 facsimile. As standard fax
machines are designed to be connected to a telephone using analog signals, a special fax
converter connected to the exchange is used in the GSM system. This enables a GSM–
connected fax to communicate with any analog fax in the network.
Short message services: A convenient facility of the GSM network is the short message
service. A message consisting of a maximum of 160 alphanumeric characters can be sent
to or from a mobile station. This service can be viewed as an advanced form of
alphanumeric paging with a number of advantages. If the subscriber's mobile unit is
powered off or has left the coverage area, the message is stored and offered back to the
subscriber when the mobile is powered on or has reentered the coverage area of the
network. This function ensures that the message will be received.
Cell broadcast: A variation of the short message service is the cell broadcast facility. A
message of a maximum of 93 characters can be broadcast to all mobile subscribers in a
certain geographic area. Typical applications include traffic congestion warnings and
reports on accidents.
Voice mail: This service is actually an answering machine within the network, which is
controlled by the subscriber. Calls can be forwarded to the subscriber's voice-mail box
and the subscriber checks for messages via a personal security code.
Fax mail: With this service, the subscriber can receive fax messages at any fax machine.
The messages are stored in a service center from which they can be retrieved by the
subscriber via a personal security code to the desired fax number
3.8.8 SUPPLEMENTARY SERVICES:
GSM supports a comprehensive set of supplementary services that can complement and
support both telephony and data services.
Call forwarding: This service gives the subscriber the ability to forward incoming calls
to another number if the called mobile unit is not reachable, if it is busy, if there is no
reply, or if call forwarding is allowed unconditionally.
Barring of outgoing calls: This service makes it possible for a mobile subscriber to
prevent all outgoing calls.
Barring of incoming calls: This function allows the subscriber to prevent incoming
calls. The following two conditions for incoming call barring exist: baring of all
incoming calls and barring of incoming calls when roaming outside the home PLMN.
Advice of charge (AoC): The AoC service provides the mobile subscriber with an
estimate of the call charges. There are two types of AoC information: one that provides
the subscriber with an estimate of the bill and one that can be used for immediate
charging purposes. AoC for data calls is provided on the basis of time measurements.
Call hold: This service enables the subscriber to interrupt an ongoing call and then
subsequently reestablish the call. The call hold service is only applicable to normal
telephony.
Call waiting: This service enables the mobile subscriber to be notified of an incoming
call during a conversation. The subscriber can answer, reject, or ignore the incoming call.
Call waiting is applicable to all GSM telecommunications services using a circuit-
switched connection.
Multiparty service: The multiparty service enables a mobile subscriber to establish a
multiparty conversation—that is, a simultaneous conversation between three and six
subscribers. This service is only applicable to normal telephony.
Calling line identification presentation/restriction: These services supply the called
party with the integrated services digital network (ISDN) number of the calling party.
The restriction service enables the calling party to restrict the presentation. The restriction
overrides the presentation.
Closed user groups (CUGs): CUGs are generally comparable to a PBX. They are a
group of subscribers who are capable of only calling themselves and certain numbers
3.8.9 MAIN AT COMMANDS:
"AT command set for GSM Mobile Equipment” describes the Main AT commands to
communicate via a serial interface with the GSM subsystem of the phone.
AT commands are instructions used to control a modem. AT is the abbreviation of
Attention. Every command line starts with "AT" or "at". That's why modem commands
are called AT commands. Many of the commands that are used to control wired dial-up
modems, such as ATD (Dial), ATA (Answer), ATH (Hook control) and ATO (Return to
online data state), are also supported by GSM/GPRS modems and mobile phones.
Besides this common AT command set, GSM/GPRS modems and mobile phones support
an AT command set that is specific to the GSM technology, which includes SMS-related
commands like AT+CMGS (Send SMS message), AT+CMSS (Send SMS message from
storage), AT+CMGL (List SMS messages) and AT+CMGR (Read SMS messages).
Note that the starting "AT" is the prefix that informs the modem about the start of a
command line. It is not part of the AT command name. For example, D is the actual AT
command name in ATD and +CMGS is the actual AT command name in AT+CMGS.
However, some books and web sites use them interchangeably as the name of an AT
command.
Here are some of the tasks that can be done using AT commands with a GSM/GPRS
modem or mobile phone:
Get basic information about the mobile phone or GSM/GPRS modem. For
example, name of manufacturer (AT+CGMI), model number (AT+CGMM),
IMEI number (International Mobile Equipment Identity) (AT+CGSN) and
software version (AT+CGMR).
Get basic information about the subscriber. For example, MSISDN (AT+CNUM)
and IMSI number (International Mobile Subscriber Identity) (AT+CIMI).
Get the current status of the mobile phone or GSM/GPRS modem. For example,
mobile phone activity status (AT+CPAS), mobile network registration status
(AT+CREG), radio signal strength (AT+CSQ), battery charge level and battery
charging status (AT+CBC).
Establish a data connection or voice connection to a remote modem (ATD, ATA,
etc).
Send and receive fax (ATD, ATA, AT+F*).
Send (AT+CMGS, AT+CMSS), read (AT+CMGR, AT+CMGL), write
(AT+CMGW) or delete (AT+CMGD) SMS messages and obtain notifications of
newly received SMS messages (AT+CNMI).
Read (AT+CPBR), write (AT+CPBW) or search (AT+CPBF) phonebook entries.
Perform security-related tasks, such as opening or closing facility locks
(AT+CLCK), checking whether a facility is locked (AT+CLCK) and changing
passwords (AT+CPWD).
(Facility lock examples: SIM lock [a password must be given to the SIM card
every time the mobile phone is switched on] and PH-SIM lock [a certain SIM
card is associated with the mobile phone. To use other SIM cards with the mobile
phone, a password must be entered.])
Control the presentation of result codes / error messages of AT commands. For
example, you can control whether to enable certain error messages (AT+CMEE)
and whether error messages should be displayed in numeric format or verbose
format (AT+CMEE=1 or AT+CMEE=2).
Get or change the configurations of the mobile phone or GSM/GPRS modem. For
example, change the GSM network (AT+COPS), bearer service type
(AT+CBST), radio link protocol parameters (AT+CRLP), SMS center address
(AT+CSCA) and storage of SMS messages (AT+CPMS).
Save and restore configurations of the mobile phone or GSM/GPRS modem. For
example, save (AT+CSAS) and restore (AT+CRES) settings related to SMS
messaging such as the SMS center address.
3. 9 BUZZER
A buzzer or beeper is a signaling device, usually electronic, typically used in
automobiles, household appliances such as a microwave oven, or game shows.
Fig 3.9.1 buzzer diagram
It most commonly consists of a number of switches or sensors connected to a control unit
that determines if and which button was pushed or a preset time has lapsed, and usually
illuminates a light on the appropriate button or control panel, and sounds a warning in the
form of a continuous or intermittent buzzing or beeping sound. Initially this device was
based on an electromechanical system which was identical to an electric bell without the
metal gong . Often these units were anchored to a wall or ceiling and used the ceiling or
wall as a sounding board. Another implementation with some AC-connected devices was
to implement a circuit to make the AC current into a noise loud enough to drive a
loudspeaker and hook this circuit up to a cheap 8-ohm speaker.
Nowadays, it is more popular to use a ceramic-based piezoelectric sounder like a
Son alert which makes a high-pitched tone. Usually these were hooked up to "driver"
circuits which varied the pitch of the sound or pulsed the sound on and off.In game shows
it is also known as a "lockout system," because when one person signals ("buzzes in"), all
others are locked out from signaling. Several game shows have large buzzer buttons
which are identified as "plungers".
The word "buzzer" comes from th e
rasping noise that buzzers made when they were electromechanica l devices,
operated from stepped- down AC lin e voltage at 50 or 60 cycles. Other sounds
commonly used to indicate that a button has been pressed are a ring or a beep. Features:
Rated Frequency: 2 KHz Continuous Tone
Operating Voltage: 5 - 7Vdc
Sound Pressure Level (10cm): 80dB @ 5Vdc
These high reliability electromagnetic buzzers are applicable to
general electronics equipment. Compact, pin terminal type electromagnetic buzzer with
2048 Hz output. Pin type terminal construction enables direct mounting onto printed
circuit boards
APPLICATIONS: Security Alerts,
Clocks,
Travel watches,
Keyboards,
Toys,
Various all.
CHAPTER-4
ADVANTAGES:
APPLICATIONS& FUTURE SCOPE
CONCLUSION:-
