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Zigbee and I-button based attendence

CHAPTER 1

1DEPARTMENT OF E.C.E., M.R.R.I.T.S, UDAYAGIRI


INTRODUCTION

1.1 INTRODUCTION:

Now days we taking the attendance by manually its take much time for taking the

attendance. It is difficult to man and time waste process .Different types of drawbacks are placed

by using i-button technology we can overcome those problems. The information about the

person is inbuilt in I-button chip. The chip contain 16mm stainless steel can. Because of this

unique and durable container , up-to-date information can travel with a person or object

anywhere they go. These I-button will provide the security for each and every person of our

organization or industry.

ZigBee is a wireless technology developed as an open global standard to address the

unique needs of low-cost, low-power, wireless sensor networks. Zigbee is the set of specs built

around the IEEE 802.15.4 wireless protocol. As Zigbee is the upcoming technology in wireless

field, we had tried to demonstrate its way of functionality and various aspects like kinds,

advantages and disadvantages using a small application of controlling the any kind of electronic

devices and machines. The Zigbee technology is broadly adopted for bulk and fast data

transmission over a dedicated channel.

This project consists of Zigbee based system that transmits the wireless signals according

to the voice input given by the user. At the receiver (airhostess) end the information will be

displayed on LCD in English language. Here when the user announces the voice command

stored predefined by the user while boarding the plane, then micro controller transmits that

information through Zigbee based transmitter. The information received by the Zigbee receiver

and fed to the controller at that system which process the information and displays the

appropriate information relating to data received will be displayed on LCD.


http://www.wisegeek.com/what-is-the-ieee.htm


1.2 PROJECT OVERVIEW:

An embedded system is a combination of software and hardware to perform a

dedicated task. Some of the main devices used in embedded products are Microprocessors and

Microcontrollers.

Microprocessors are commonly referred to as general purpose processors as they

simply accept the inputs, process it and give the output. In contrast, a microcontroller not only

accepts the data as inputs but also manipulates it, interfaces the data with various devices,

controls the data and thus finally gives the result.

The project is Zigbee based attendance alert system with person details by using i-button

technology..



CHAPTER 2

EMBEDDED SYSTEMS



2.1 EMBEDDED SYSTEMS:

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


http://en.wikipedia.org/wiki/Charles_Stark_Draper

http://en.wikipedia.org/wiki/Apollo_Guidance_Computer

http://en.wikipedia.org/wiki/Electromechanical

http://en.wikipedia.org/wiki/Programmable_controllers


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


http://en.wikipedia.org/wiki/Hard_disk

http://en.wikipedia.org/wiki/Hard_disk

http://en.wikipedia.org/wiki/Digital_circuit

http://en.wikipedia.org/wiki/Transistor

http://en.wikipedia.org/wiki/Minuteman_(missile)


(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 systems.

2.3.4 NETWORK COMMUNICATION EMBEDDED SYSTEMS:

A wide range network interfacing communication is provided by using embedded systems.

Eg:



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



CHAPTER 3



HARDWARE DESCRIPTION

3.1 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.

2.1 AT89S52

2.2.1 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.

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 Communic

ation 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.

2.1.2 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.

2.1.3 FEATURES

Compatible with MCS-51 Products

8K Bytes of In-System Reprogrammable Flash Memory

Fully Static Operation: 0 Hz to 33 MHz

Three-level Program Memory Lock

256 x 8-bit Internal RAM

32 Programmable I/O Lines

Three 16-bit Timer/Counters

Eight Interrupt Sources

Programmable Serial Channel

Low-power Idle and Power-down Modes

4.0V to 5.5V Operating Range



Full Duplex UART Serial Channel

Interrupt Recovery from Power-down Mode

Watchdog Timer

Dual Data Pointer

Power-off Flag

Fast Programming Time

Flexible ISP Programming (Byte and Page Mode)

2.1.4 PIN DIAGRAM

FIG-2 PIN DIAGRAM OF 89S52 IC

2.1.5 PIN DESCRIPTION

Pin DescriptionVCC: 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.


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.


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.

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 Functional block diagram of micro controller



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-4 Oscillator and timing circuit



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


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


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




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






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.

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.

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.

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:

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.

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) 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.

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 while the 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.

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 dissipate

the excessive voltage resistively as heat

2) Switching Regulators

They 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 produce the correct regulated voltage.

3 Circuit diagram:

Fig2.3. Circuit Diagram of power supply

IC 7805:

7805 is an integrated three-terminal positive fixed linear voltage regulator. It supports an

input voltage of 10 volts to 35 volts and output voltage of 5 volts. It has a current rating of 1 amp

although lower current models are available. Its output voltage fixed at 5.0V. The 7805 also has

a built-in current limiter as a safety feature. 7805 manufactured by many companies, including

National Semiconductors and Fairchild Semiconductors.

The 7805 will automatically reduce output current if it gets too hot. The last two digits

represent the voltage; for instance, the 7812 is a 12-volt regulator. The 78xx series of regulators

designed to work in complement with the 79xx series of negative voltage regulators in systems

that provide both positive and negative regulated voltages, since the 78xx series cannot regulate

negative voltages in such a system.



The 7805 & 78 is one of the most common and well-known of the 78xx series regulators,

as it's small component count and medium-power regulated 5V make it useful for powering TTL

devices.

Table2.1. Specifications of IC7805


SPECIFICATIONS IC 7805

Vout 5V

Vein - Vout Difference5V -

20V

Operation Ambient

Temp

0 -

125°C

Output Imax 1A


I-Button

IntroductionThe iButton® device is a computer chip enclosed in a 16mm thick stainless steel can. Because of this unique and durable container, up-to-date information can travel with a person or object anywhere they go. The steel iButton device can be mounted virtually anywhere because it is rugged enough to withstand harsh environments, indoors or outdoors. It is small and portable enough to attach to a key fob, ring, watch, or other personal items, and be used daily for applications such as access control to buildings and computers, asset management, and various data logging tasks.

i-Button ComponentsThe Can and Grommet

An iButton device uses its stainless steel 'can' as an electronic communications interface. Each can has a data contact, called the 'lid', and a ground contact, called the 'base'. Each of these contacts is connected to the silicon chip inside. The lid is the top of the can; the base forms the sides and the bottom of the can and includes a flange to simplify attaching the button to just about anything. The two contacts are separated by a polypropylene grommet.

The 1-Wire Interface

By simply touching the iButton device to the two contacts described above, you can communicate with it through our 1-Wire® protocol. The 1-Wire interface has two communication speeds: standard mode at 16kbps, and overdrive mode at 142kbps.."

i-Button Versions

The iButton product line now comprises over 20 different products with different functionality added to the basic button. iButton devices come in the following varieties:

Address Only

Memory

Real-Time Clock

Secure

Data Loggers



How Do I Get Information Into and Out of the iButton Device?

Information is transferred between your iButton device and a PC with a momentary contact at up to 142kbps. You simply touch your iButton device to a Blue Dot receptor or other iButton probe, which is connected to a PC. The Blue Dot™ receptor is cabled to a 1-Wire adapter that is attached to a spare PC port. 1-Wire adapters exist for USB, serial, and parallel ports. The Blue Dot receptor and 1-Wire adapter are inexpensive..

The iButton device is also the ultimate information carrier for AutoID and many portable applications. All the latest handheld computers and PDAs can communicate with iButton devices.

How Durable Is an i-Button Device?

The silicon chip within the iButton device is protected by the ultimate durable material: stainless steel. You can drop an iButton device, step on it, or scratch it. The iButton device is wear-tested for 10-year durability.

What Can I Do with the i-Button Device?

The i-Button device is ideal for any application where information needs to travel with a person or object. Affixed to a key fob, watch, or ring, an i-Button device can grant its owner access to a building, a PC, a piece of equipment, or a vehicle. Attached to a work tote, it can measure processes to improve efficiency, such as manufacturing, delivery, and maintenance. Some i-Button devices can be used to store electronic cash for small transactions,

such as transit systems, parking meters, and vending machines. The i-Button device can also be used as an electronic asset tag to store information needed to keep track of valuable capital equipment.

.

What Are the Advantages of iButton Devices over Other Technologies?

When developing an i-Button solution for an application, you can consider many complementary technologies. Bar codes, RFID tags, magnetic stripe, prox, and smart cards are some of the possibilities. Unlike bar codes and magnetic stripe cards, most of the i-Button devices can be read AND be written to. In addition, the communication rate and product breadth of i-Button devices go well beyond the simple memory products typically available with RFID. As for durability, the thin plastic of smart cards is no match for the strength of the stainless-steel-clad i-Button device.

I Do Not Want to Build My Application Myself. Do You Provide Turnkey Solutions?

We have partnered with a number of companies called Authorized Solutions Developers, ASDs for short, who develop turnkey i-Button systems for access control, time and attendance tracking, payroll, truck fleet maintenance, manufacturing control, fare collection, and more. The ASDs can also develop custom i-Button applications for you—just talk to them. You can use our i-Button Solutions Search to find our partners' solutions available worldwide.


http://www.maximintegrated.com/products/ibutton/solutions/search.cfm


3.6 ZIGBEE TECHNOLOGY

ZIGBEE Technology

Zig-bee

Zig-bee is a specification for a suite of high level communication protocols using small,

low-power digital radios based on the IEEE (Institute of Electrical and Electronics

Engineers)802.15.4,2006 standard for wireless personal area networks (WPANs), such as

wireless headphones connecting with cell phones via short-range radio. The technology defined

by the Zig-bee specification intended to be simpler and less expensive than other WPANs, such

as Bluetooth. Zig-bee is a targeted at radio frequency (RF) applications that require a low data

rate, long battery life, and secure networking.

Zig-bee is a low data rate, two-way standard for home automation and data networks. The

standard specification for up to 254 nodes including one master, managed from a single remote

control. Real usage examples of Zig-bee includes home automation tasks such as turning lights

on, setting the home security system, or starting the VCR. With Zig-bee all these tasks can be

done from anywhere in the home at the touch of a button. Zig-bee also allows for dial-in access

via the Internet for automation control.

Zig-bee protocol is optimized for very long battery life measured in months to years from

inexpensive, off-the-shelf non-rechargeable batteries, and can control lighting, air conditioning

and heating, smoke and fire alarms, and other security devices. The standard supports 2.4 GHz

(worldwide), 868 MHz (Europe) and 915 MHz (Americas) unlicensed radio bands with range up

to 100 meters.

IEEE 802.15.4


http://www.webopedia.com/TERM/Z/ZigBee.html#%23


IEEE 802.15.4 is standard which specifies the physical layer and medium access control

for low-rate wireless personal area networks (LR-WPAN's).This standard was chartered to

investigate a low data rate solution with multi-month to multi-year battery life and very low

complexity. It is operating in an unlicensed, international frequency band. Potential

applications are sensors, interactive toys, smart badges, remote controls, and home

automation.

802.15.4 Is part of the 802.15 wireless personal-area network efforts at the IEEE? It is a

simple packet-based radio protocol aimed at very low-cost, battery-operated widgets and

sensors (whose batteries last years, not hours) that can intercommunicate and send low-

bandwidth data to a centralized device. As of 2007, the current version of the standard is the

2006 revision. It is maintained by the IEEE 802.15 working group. It is the basis for the Zig-bee

specification, which further attempts to offer a complete networking solution by developing the

upper layers which are not covered by the standard.

802.15.4 Protocol

Data rates of 250 kbps with 10-100 meter range.

Two addressing modes; 16-bit short and 64-bit IEEE addressing

CSMA-CA channel access.

Power management to ensure low power consumption

16 channels in the 2.4GHz ISM band

Low duty cycle - Provides long battery life

Low latency

Support for multiple network topologies: Static, dynamic, star and mesh

Up to 65,000 nodes on a network

Comparison with other technologies

Zig-Bee enables broad-based deployment of wireless networks with low-cost, low-power

solutions. It provides the ability to run for years on inexpensive batteries for a host of monitoring

applications: Lighting controls, AMR (Automatic Meter Reading), smoke and CO detectors,

wireless telemetry, HVAC control, heating control, home security, Environmental controls and

shade controls, etc.



Zigbee Technology: Wireless Control that Simply Works

Why is Zigbee needed?

– There are a multitude of standards that address mid to high data rates for voice, PC LANs,

video, etc. However, up till now there hasn’t been a wireless network standard that meets the

unique needs of sensors and control devices. Sensors and controls do not need high

bandwidth but they do need low latency and very low energy consumption for long battery

lives and for large device arrays.

– There are multitudes of proprietary wireless systems manufactured today to solve a multitude

of problems that also do not require high data rates but do require low cost and very low

current drain.

– These proprietary systems were designed because there were no standards that met their

requirements. These legacy systems are creating significant interoperability problems with

each other and with newer technologies.

Zigbee/IEEE 802.15.4 - General Characteristics

Dual PHY (2.4GHz and 868/915 MHz)

• Data rates of 250 kbps (@2.4 GHz), 40 kbps (@ 915 MHz), and 20 kbps (@868 MHz)

• Optimized for low duty-cycle applications (<0.1%)

• CSMA-CA channel access

– Yields high throughput and low latency for low duty cycle devices like sensors and

controls

• Low power (battery life multi-month to years)

• Multiple topologies: star, peer-to-peer, mesh

• Addressing space of up to:

– 18,450,000,000,000,000,000 devices (64 bit IEEE address)

– 65,535 network nodes.

• Optional guaranteed time slot for applications requiring low latency

• Fully hand-shaked protocol for transfer reliability

• Range: 50m typical (5-500m based on environment)



ZIGBEE NETWORK TOPOLOGY:


Star Topology

PAN

Coordinator

Full function device Communications flow

Peer-to-Peer topology Cluster Tree Topology

Full Function Device

Reduced Function Device

Communications Flow


Three devices in network

1. zigbee PAN coordinator (MASTER)

2. zigbee router (full function device)

3. zigbee end device(reduced function device)

ZIGBEE PROTOCOL STACK

ZigBee Stack System



PHYSICAL LAYER

The physical layer designed to accommodate the need for a low cost yet allowing for high

levels of integration. The use of direct sequence allows the analog circuitry to be very

simple and

The PHY provides two services: the PHY data service and PHY management service

interfacing to the physical layer management entity (PLME). The PHY data service enables the

transmission and reception of PHY protocol data units (PPDU) across the physical radio channel.

The features of the PHY are activation and deactivation of the radio transceiver, energy

detection(ED), link quality indication (LQI), channel selection, clear channel assessment (CCA)

and transmitting as well as receiving packets across the physical medium.

The standard offers two PHY options based on the frequency band. Both based on direct

sequence spread spectrum (DSSS). The data rate is 250kbps at 2.4GHz, 40kbps at 915MHz and

20kbps at 868MHz. The higher data rate at 2.4GHz attributed to a higher-order modulation

scheme. Lower frequency is providing longer range due to lower propagation losses. Low rate

translated into better sensitivity and larger coverage area. Higher rate means higher

throughput, Lower latency or lower duty cycle.

There is a single channel between 868 and 868.6MHz, 10 channels between 902.0 and

928.0MHz, and 16 channels between 2.4 and 2.4835GHz.

MAC LAYER

The media access control (MAC) layer designed to allow multiple topologies without

complexity. The power management operation does not require multiple modes of operation.

The MAC allows a reduced functionality device (RFD) that need not have flash nor large

amounts of ROM or RAM. The MAC designed to handle large numbers of devices without

requiring them to be “parked”.



MAC Primitives:

MAC Data Service

• MCPS-DATA – exchange data packets between MAC and PHY

• MCPS-PURGE – purge an MSDU from the transaction queue

MAC Management Service

• MLME-ASSOCIATE/DISASSOCIATE – network association

• MLME-SYNC / SYNC-LOSS - device synchronization

• MLME-SCAN - scan radio channels

• MLME- COMM-STATUS – communication status

• MLME-GET / -SET– retrieve/set MAC PIB parameters

• MLME-START / BEACON-NOTIFY – beacon management

• MLME-POLL - beaconless synchronization

• MLME-GTS - GTS management

• MLME-RESET – request for MLME to perform reset

• MLME-ORPHAN - orphan device management

• MLME-RX-ENABLE - enabling/disabling of radio system



BEACON ENABLED NETWORK

Network Layer

The responsibilities of the Zigbee NWK layer include:

• Starting a network: The ability to successful establish a new network

• Joining and leaving a network: The ability to gain membership (join) or relinquish

membership (leave) a network.

• Configuring a new device: The ability to sufficiently configure the stack for operation as

required

• Addressing: The ability of a Zigbee coordinator to assign addresses to devices joining the

network

• Synchronization within a network: The ability for a device to achieve synchronization with

another device either through tracking beacons or by polling

• Security: applying security to outgoing frames and removing security to terminating frames

• Routing: routing frames to their intended destinations.

Network Routing Overview

Perhaps the most straightforward way to think of the Zigbee routing algorithm is as a hier

archical routing strategy with table-driven optimizations applied where possible.

– NWK uses an algorithm that allows stack implementers and application developers to balance

unit cost, battery drain, and complexity in producing Zigbee solutions to meet the specific

cost-performance profile of their application.

– Started with the well-studied public-domain algorithm AODV and Motorola’s Cluster-Tree

algorithm and folding in ideas from Ember Corporation’s GRAd.



Network Summary

The network layer builds upon the IEEE 802.15.4 MAC’s features to allow extensibility of

coverage. Additional clusters can be added networks can be consolidate or split up.

Application layer

The Zigbee application layer consists of the APS sub-layer, the ZDO and the manufacturer-

defined application objects. The responsibilities of the APS sub-layer include maintaining tables

for binding, which is the ability to match two devices together based on their services and their

needs, and forwarding messages between bound devices. Another responsibility of the APS

sub-layer is discovery, which is the ability to determine which other devices are operating in the

personal operating space of a device. The responsibilities of the ZDO include defining the role of

the device within the network (e.g., Zigbee coordinator or end device), initiating and/or

responding to binding requests and establishing a secure relationship between network

devices. The manufacturer-defined application objects implement the actual applications

according to the Zigbee-defined application descriptions

Zigbee Device Object

• Defines the role of the device within the network (e.g., Zigbee coordinator or end

device)

• Initiates and/or responds to binding requests

• Establish a secure relationship between network devices selecting one of ZigBee’s

security methods such as public key, symmetric key, etc.



Application Support Layer:

This layer provides the following services:

Discovery: The ability to determine which other devices are operating in the personal operating

space of a device

Binding: The ability to match two or more devices together based on their services and their

needs and forwarding messages between bound devices

APPLICATIONS OF ZIGBEE TECHNOLOGY

Typical application areas include

Home Entertainment and Control: Smart lighting, advanced temperature control, safety

and security, movies and music

Home Awareness — Water sensors, power sensors, energy monitoring, smoke and fire

detectors, smart appliances and access sensors

Mobile Services — m-payment, m-monitoring and control, m-security and access

control, m-healthcare and tele-assist

Commercial Building — Energy monitoring, HVAC, lighting, access control

Industrial Plant — Process control, asset management, environmental management,

energy management, industrial device control, machine-to-machine (M2M)

communication



Zigbee vs Bluetooth

Zigbee looks rather like Bluetooth but is simpler, has a lower data rate and spends most

of its time snoozing. This characteristic means that a node on a Zigbee network should be able

to run for six months to two years on just two AA batteries. The operational range of Zigbee is

10-75m compared to 10m for Bluetooth (without a power amplifier).

ZigBee sits below Bluetooth in terms of data rate. The data rate of Zigbee is 250kbps at

2.4GHz, 40kbps at 915MHz and 20kbps at 868MHz whereas that of Bluetooth is 1Mbps.

ZigBee uses a basic master-slave configuration suited to static star networks of many

infrequently used devices that talk via small data packets. It allows up to 254 nodes.

Bluetooth’s protocol is more complex since it is gear towards handling voice, images and

file transfers in ad hoc networks. Bluetooth devices can support scatter nets of multiple smaller

non-synchronized networks (piconets). It only allows up to 8 slave nodes in a basic master-slave

piconet set-up. When ZigBee node is powered down, it can wake up and get a packet in around

15 msec whereas Bluetooth device would take around 3sec to wake up and respond.

ZIGBEE MODULE:

Comparison with other technologies

StandardZigBee®

802.15.4

Wi-Fi™

802.11b

Bluetooth™

802.15.1

Transmission Range (meters) 1 – 100* 1 – 100 1 – 10

Battery Life (days) 100 – 1,000 0.5 – 5.0 1 - 7

Network Size (# of nodes) > 64,000 32 7



Application Monitoring & Control Web, Email, Video Cable Replacement

Stack Size (KB) 4 – 32 1,000 250

Throughput kb/s) 20 – 250 11,000 720

Zigbee-compliant products operate in unlicensed bands worldwide, including 2.4GHz

(global), 902 to 928MHz (Americas), and 868MHz (Europe). Raw data throughput rates of

250Kbps can be achieved at 2.4GHz (16 channels), 40Kbps at 915MHz (10 channels), and

20Kbps at 868MHz (1 channel). The transmission distance is expected to range from 10 to

100m, depending on power output and environmental characteristics. Like Wi-Fi, Zigbee uses

direct-sequence spread spectrum in the 2.4GHz band, with offset-quadrature phase-shift keying

modulation. Channel width is 2MHz with 5MHz channel spacing. The 868 and 900MHz bands

also use direct-sequence spread spectrum but with binary-phase-shift keying modulation.

ZIGBEE MODULE SPECIFICATION:

Performance: XBee

Power output:: 1mW (+0 dBm) North American & International version

Indoor/Urban range: Up to 100 ft (30 m)

Outdoor/RF line-of-sight range: Up to 300 ft (90 m)

RF data rate: 250 Kbps

Interface data rate: Up to 115.2 Kbps

Operating frequency: 2.4 GHz

Receiver sensitivity: -92 dBm

Performance: XBee-PRO

Power output:

63 mW (+18 dBm) North American version

10 mW (+10 dBm) International version



Indoor/Urban range: Up to 300 ft (90 m)

Outdoor/RF line-of-sight range: Up to 1 mile (1.6 km) RF LOS

RF data rate: 250 Kbps

Interface data rate: Up to 115.2 Kbps

Operating frequency: 2.4 GHz

Receiver sensitivity: -100 dBm (all variants)

Networking

Spread Spectrum type: DSSS (Direct Sequence Spread Spectrum)

Networking topology: Point-to-point, point-to-multipoint, & peer-to-peer

Error handling: Retries & acknowledgements

Filtration options: PAN ID, Channel, and 64-bit addresses

Channel capacity:

XBee: 16 Channels

XBee-PRO: 12 Channels

Addressing: 65,000 network addresses available for each channel

Power

Supply voltage:

XBee: 2.8 - 3.4 VDC

XBee-PRO: 2.8 - 3.4 VDC

XBee Footprint Recommendation: 3.0 - 3.4 VDC

Transmit current:

XBee: 45 mA (@ 3.3 V) boost mode 35 mA (@ 3.3 V) normal mode

XBee-PRO: 215 mA (@ 3.3 V)

Receive current:

XBee: 50 mA (@ 3.3 V)

XBee-PRO: 55 mA (@ 3.3 V)

Power-down sleep current:



XBee: <10 µA at 25° C

XBee-PRO: <10 µA at 25° C

General

Frequency band: 2.4000 - 2.4835 GHz

Interface options: 3V CMOS UART

Physical Properties

Size:

XBee: 0.960 in x 1.087 in (2.438 cm x 2.761 cm)

XBee-PRO: 0.960 in x 1.297 in (2.438 cm x 3.294 cm)

Weight: 0.10 oz (3g)

Antenna options: U.FL, Reverse Polarity SMA (RPSMA), chip antenna or wired whip antenna

Operating temperature: -40° C to 85° C (industrial)

2. The full function device FFD:

The FFD is an intermediary router transmitting data from other devices. It needs lesser

memory than the ZigBee coordinator node, and entails lesser manufacturing costs. It can operate

in all topologies and can act as a coordinator.

3. The reduced function device RFD:

This device is just capable of talking in the network; it cannot relay data from other

devices. Requiring even less memory, (no flash, very little ROM and RAM), an RFD will thus be

cheaper than an FFD. This device talks only to a network coordinator and can be implemented

very simply in star topology.

3.6.3 ZIGBEE CHARACTERISTICS:



The focus of network applications under the IEEE 802.15.4 / ZigBee standard include the

features of low power consumption, needed for only two major modes (Tx/Rx or Sleep), high

density of nodes per network, low costs and simple implementation.

These features are enabled by the following characteristics:

1. 2.4GHz and 868/915 MHz dual PHY modes

This represents three license-free bands: 2.4-2.4835 GHz, 868-870 MHz

and 902-928 MHz. The number of channels allotted to each frequency band is fixed at

sixteen (numbered 11-26), one (numbered 0) and ten (numbered 1-10) respectively. The

higher frequency band is applicable worldwide, and the lower band in the areas of North

America, Europe, Australia and New Zealand.

2. Low power consumption, with battery life ranging from months to years.

Considering the number of devices with remotes in use at present, it is easy to see that

more numbers of batteries need to be provisioned every so often, entailing regular (as

well as timely), recurring expenditure. In the ZigBee standard, longer battery life is

achievable by either of two means: continuous network connection and slow but sure

battery drain, or intermittent connection and even slower battery drain.

3. Maximum data rates allowed for each of these frequency bands are fixed as 250 kbps

@2.4 GHz, 40 kbps @ 915 MHz, and 20 kbps @868 MHz.

4. High throughput and low latency for low duty-cycle applications (<0.1%)

5. Channel access using Carrier Sense Multiple Access with Collision Avoidance (CSMA

- CA)

6. Addressing space of up to 64 bit IEEE address devices, 65,535 networks

7. 50m typical range

8. Fully reliable “hand-shacked” data transfer protocol.



9. Different topologies as illustrated below: star, peer-to-peer, mesh

Figure 3.6.3: ZigBee Topologies

ZigBee employs either of two modes, beacon or non-beacon to enable the to-and-fro data

traffic. Beacon mode is used when the coordinator runs on batteries and thus offers maximum

power savings, whereas the non-beacon mode finds favor when the coordinator is mains-

powered.

In the beacon mode, a device watches out for the coordinator's beacon that gets

transmitted at periodically, locks on and looks for messages addressed to it. If message

transmission is complete, the coordinator dictates a schedule for the next beacon so that the

device ‘goes to sleep'; in fact, the coordinator itself switches to sleep mode.

While using the beacon mode, all the devices in a mesh network know when to

communicate with each other. In this mode, necessarily, the timing circuits have to be quite

accurate, or wake up sooner to be sure not to miss the beacon. This in turn means an increase in

power consumption by the coordinator's receiver, entailing an optimal increase in costs.



Fig 3.6.4: Beacon Network Communication & Non-Beacon Network Communication

The non-beacon mode will be included in a system where devices are ‘asleep' nearly

always, as in smoke detectors and burglar alarms. The devices wake up and confirm their

continued presence in the network at random intervals.

On detection of activity, the sensors ‘spring to attention', as it were, and transmit to the

ever-waiting coordinator's receiver (since it is mains-powered). However, there is the remotest of

chances that a sensor finds the channel busy, in which case the receiver unfortunately would

‘miss a call'.

3.6.4. ZIGBEE APPLICATIONS:

1. The ZigBee Alliance targets applications "across consumer, commercial, industrial and

government markets worldwide". ZigBee technology is designed to best suit these

applications, for the reason that it enables reduced costs of development, very fast market

adoption, and rapid ROI.

2. Airbee Wireless Inc has tied up with Radio crafts AS to deliver "out-of-the-box" ZigBee-

ready solutions, the former supplying the software and the latter making the module

platforms. With even light controls and thermostat producers joining the ZigBee Alliance,

the list is growing healthily and includes big OEM names like HP, Philips, Motorola and

Intel.



3. With ZigBee designed to enable two-way communications, not only will the consumer be

able to monitor and keep track of domestic utilities usage, but also feed it to a computer

system for data analysis.

4. A recent analyst report issued by West Technology Research Solutions estimates that by

the year 2008, "annual shipments for ZigBee chipsets into the home automation segment

alone will exceed 339 million units," and will show up in "light switches, fire and smoke

detectors, thermostats, appliances in the kitchen, video and audio remote controls,

landscaping, and security systems."



MAX 232

2.3.1 RS-232 WAVEFORM

TTL/CMOS Serial Logic Waveform

The diagram above shows the expected waveform from the UART when using the

common 8N1 format. 8N1 signifies 8 Data bits, No Parity and 1 Stop Bit. The RS-232 line, when

idle is in the Mark State (Logic 1). A transmission starts with a start bit which is (Logic 0). Then

each bit is sent down the line, one at a time. The LSB (Least Significant Bit) is sent first. A Stop

Bit (Logic 1) is then appended to the signal to make up the transmission.

The data sent using this method, is said to be framed. That is the data is framed

between a Start and Stop Bit.

RS-232 Voltage levels

+3 to +25 volts to signify a "Space" (Logic 0)

-3 to -25 volts for a "Mark" (logic 1).

Any voltage in between these regions (i.e. between +3 and -3 Volts) is undefined.

The data byte is always transmitted least-significant-bit first.



The bits are transmitted at specific time intervals determined by the baud rate of the

serial signal. This is the signal present on the RS-232 Port of your computer, shown below.

RS-232 Logic Waveform

2.3.2 RS-232 LEVEL CONVERTER

Standard serial interfacing of microcontroller (TTL) with PC or any RS232C Standard

device, requires TTL to RS232 Level converter. A MAX232 is used for this purpose. It provides

2-channel RS232C port and requires external 10uF capacitors.

The driver requires a single supply of +5V.

MAX 232 includes a Charge Pump, which generates +10V and -10V from a single 5v supply.


http://www.bsc.nodak.edu/electron/rs232.htm

http://www.arcelect.com/rs232.htm


z

2.3.3 Serial communication

When a processor communicates with the outside world, it provides data in byte sized

chunks. Computers transfer data in two ways: parallel and serial. In parallel data transfers, often

more lines are used to transfer data to a device and 8 bit data path is expensive. The serial

communication transfer uses only a single data line instead of the 8 bit data line of parallel

communication which makes the data transfer not only cheaper but also makes it possible for

two computers located in two different cities to communicate over telephone.

Serial data communication uses two methods, asynchronous and synchronous. The

synchronous method transfers data at a time while the asynchronous transfers a single byte at a

time. There are some special IC chips made by many manufacturers for data communications.

These chips are commonly referred to as UART (universal asynchronous receiver-transmitter)

and USART (universal synchronous asynchronous receiver transmitter). The AT89C51 chip has

a built in UART.

In asynchronous method, each character is placed between start and stop bits. This

is called framing. In data framing of asynchronous communications, the data, such as ASCII

characters, are packed in between a start and stop bit. We have a total of 10 bits for a character: 8

bits for the ASCII code and 1 bit each for the start and stop bits. The rate of serial data transfer

communication is stated in bps or it can be called as baud rate.

To allow the compatibility among data communication equipment made by various

manufacturers, and interfacing standard called RS232 was set by the Electronics industries

Association in 1960. Today RS232 is the most widely used I/O interfacing standard. This

standard is used in PCs and numerous types of equipment. However, since the standard was set

long before the advent of the TTL logic family, its input and output voltage levels are not TTL

compatible. In RS232, a 1 bit is represented by -3 to -25V, while a 0 bit is represented +3 to +25

V, 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 connect the TTL logic levels to RS232

voltage levels and vice versa. MAX232 ICs are commonly referred to as line drivers.

The RS232 cables are generally referred to as DB-9 connector. In labeling, DB-9P

refers to the plug connector (male) and DB-9S is for the socket connector (female). The simplest

connection between a PC and microcontroller requires a minimum of three pin, TXD, RXD, and

ground. Many of the pins of the RS232 connector are used for handshaking signals. They are

bypassed since they are not supported by the UART chip.

IBM PC/ compatible computers based on x86(8086, 80286, 386, 486 and Pentium)

microprocessors normally have two COM ports. Both COM ports have RS232 type connectors.

Many PCs use one each of the DB-25 and DB-9 RS232 connectors. The COM ports are



designated as COM1 and COM2. We can connect the serial port to the COM 2 port of a PC for

serial communication experiments. We use a DB9 connector in our arrangement.



3.7 LCD DISPLAY

3.7.1 LCD BACKGROUND:

One of the most common devices attached to a micro controller is an LCD display. Some

of the most common LCD’s connected to the many microcontrollers are 16x2 and 20x2 displays.

This means 16 characters per line by 2 lines and 20 characters per line by 2 lines, respectively.

3.7.2 BASIC 16X 2 CHARACTERS LCD

Fig3.7.2: LCD pin diagram



The EN line is called "Enable." This control line is used to tell the LCD that we are

sending it data. To send data to the LCD, our 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.

The LCD requires 3 control lines as well as either 4 or 8 I/O lines for the data bus. The

user may select whether the LCD is to operate with a 4-bit data bus or an 8-bit data bus. If a 4-bit

data bus is used the LCD will require a total of 7 data lines (3 control lines plus the 4 lines for the

data bus). If an 8-bit data bus is used the LCD will require a total of 11 data lines (3 control lines

plus the 8 lines for the data bus).

The three control lines are referred to as EN, RS, and RW.

The EN line is called "Enable." This control line is used to tell the LCD that we are

sending it data. To send data to the LCD, our 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.

The 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 should be displayed on the screen. For example, to display

the letter "T" on the screen we would set RS high.

The 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.



3.7.3 CIRCUIT DESCRIPTION:

Above is the quite simple schematic. The LCD panel's Enable and Register Select is

connected to the Control Port. The Control Port is an open collector / open drain output. While

most Parallel Ports have internal pull-up resistors, there is a few which don't. Therefore by

incorporating the two 10K external pull up resistors, the circuit is more portable for a wider

range of computers, some of which may have no internal pull up resistors.

We make no effort to place the Data bus into reverse direction. Therefore we hard wire

the R/W line of the LCD panel, into write mode. This will cause no bus conflicts on the data

lines. As a result we cannot read back the LCD's internal Busy Flag which tells us if the LCD has

accepted and finished processing the last instruction. This problem is overcome by inserting

known delays into our program.

The 10k Potentiometer controls the contrast of the LCD panel. Nothing fancy here. As

with all the examples, I've left the power supply out. We can use a bench power supply set to 5v

or use an onboard +5 regulator. Remember a few de-coupling capacitors, especially if we have

trouble with the circuit working properly.

a) SETB RW

Handling the EN control line:

As we mentioned above, the EN line is used to tell the LCD that we are ready for it to

execute an instruction that we've prepared on the data bus and on the other control lines. Note

that the EN line must be raised/ lowered before/after each instruction sent to the LCD regardless

of whether that instruction is read or write text or instruction. In short, we must always

manipulate EN when communicating with the LCD. EN is the LCD's way of knowing that we

are talking to it. If we don't raise/lower EN, the LCD doesn't know we're talking to it on the other

lines.

Thus, before we interact in any way with the LCD we will always bring the EN line low

with the following instruction:



b) CLR EN

And once we've finished setting up our instruction with the other control lines and data

bus lines, we'll always bring this line high:

c) SETB EN

The line must be left high for the amount of time required by the LCD as specified in its

datasheet. This is normally on the order of about 250 nanoseconds, but checks the datasheet. In

the case of a typical microcontroller running at 12 MHz, an instruction requires 1.08

microseconds to execute so the EN line can be brought low the very next instruction. However,

faster microcontrollers (such as the DS89C420 which executes an instruction in 90 nanoseconds

given an 11.0592 MHz crystal) will require a number of NOPs to create a delay while EN is held

high. The number of NOPs that must be inserted depends on the microcontroller we are using

and the crystal we have selected.

The instruction is executed by the LCD at the moment the EN line is brought low with a

final CLR EN instruction.

3.7.4 CHECKING THE BUSY STATUS OF THE LCD:

As previously mentioned, it takes a certain amount of time for each instruction to be

executed by the LCD. The delay varies depending on the frequency of the crystal attached to the

oscillator input of the LCD as well as the instruction which is being executed.

While it is possible to write code that waits for a specific amount of time to allow the

LCD to execute instructions, this method of "waiting" is not very flexible. If the crystal

frequency is changed, the software will need to be modified. A more robust method of

programming is to use the "Get LCD Status" command to determine whether the LCD is still

busy executing the last instruction received.

The "Get LCD Status" command will return to us two tidbits of information; the

information that is useful to us right now is found in DB7. In summary, when we issue the "Get

LCD Status" command the LCD will immediately raise DB7 if it's still busy executing a



command or lower DB7 to indicate that the LCD is no longer occupied. Thus our program can

query the LCD until DB7 goes low, indicating the LCD is no longer busy. At that point we are

free to continue and send the next command.

CHAPTER 4



SOFTWARE DESCRIPTION



CHAPTER 5

PROJECT DESCRIPTION

In this chapter, schematic diagram and interfacing of PIC16f73 microcontroller

with each module is considered.

1. Transmitter Section

Fig 5.1(i): schematic diagram of transmitter section of Zigbee based attendance alert

system with person details by using I button technology



2. Receiver Section

Fig 5.1(ii): schematic diagram of transmitter section of Zigbee based attendance alert

system with person details by using I button technology

Fig 5.2: crystal oscillator and reset input interfacing with micro controller



CHAPTER 6

ADVANTAGES AND DISADVANTAGES

6.1 ADVANTAGES:

1. Low power consumption.

2. Easy to take attendance with i-button technology

3. Very effective and efficient design.

4. Usage of wireless technology (Zigbee).

5. Can be used with any language.

6. Fast response.

7. Reduce man power

6.2 DISADVANTAGES:

1.Buttons can fall of easily; and are a choking hazard on children's products.



2. Also, they aren't a very strong fastening. Finally, buttons can be damaged when being washed

6.3 APPLICATIONS:

1. useful for authority person

2. Faster and secure data transmission.

3. Easy to install.

4. Helpful in abroad to express user’s needs.

5. Deaf and dump people also can interact with others.

6. Can be used with any languages.



CHAPTER 7

RESULTS&CONCLUSION

7.1 RESULT:

The project “Zigbee based wireless Voice to Text translator in Airlines/Hospital assistant

system for blind/Illiterates” was designed a user friendly multi-language communication system

for illiterate/dumb people traveling by Airlines. The language of translated text can be set as user

requirement. But, mostly English is preferred as it has prominence of international language.



FIG 7.1: TRANSMITTER AND RECIVER PARTS OF ZIGBEE BASED WIRELESS

VOICE TO TEXT TRANSLATOR



7.2 CONCLUSION:

Integrating features of all the hardware components used have been developed in it.

Presence of every module has been reasoned out and placed carefully, thus contributing to the

best working of the unit. Secondly, using highly advanced IC’s with the help of growing

technology, the project has been successfully implemented. Thus the project has been

successfully designed and tested.



CHAPTER 8



FUTURE SCOPE

8.1 FUTURE SCOPE

Our project “Zigbee based wireless Voice to Text translator in Airlines/Hospital assistant

system for blind/Illiterates” is mainly intended design a user friendly multi-language

communication system for illiterate/dumb people traveling by Airlines.

This project consists of Zigbee based system that transmits the wireless signals according

to the input given by the user using voice commands. At the receiver (airhostess) end the

information will be displayed on LCD in English language. Here when user sends his need

through voice commands, then micro controller transmits that information through Zigbee

transmitter. The information received by the Zigbee receiver will be displayed on LCD.

This project provides an efficient device that helps dumb/illiterate to communicate with

airhostess in airlines. Zigbee used in this project provides a typical range of 50m. By using high

power Zigbee module we can extend this range up to 1.3 km. using Zigbee we can send text

only. By using IR/RF transmitter and receiver we can send audio and video signals also. But

Zigbee provides better data security and range is also more compared to IR. And another thing

to be noted is Zigbee works in license free bands. Zigbee is most preferable where data security

is important. Further enhancements yet to be made in field of Zigbee

Touch screen can also be used as 4wire resistive touch screen. This is chosen because

resistive touch screen’s stability and durability are more compared to other touch screens.

Response time is also very less. Resistant to intense light and not very sensitive as compared to

other technologies but it accepts only one touch at a time. By using other technology like surface

acoustic wave or infrared we can further improve project so that it can accept more than touch at

a time. But those touch screens are very sensitive and less resistant to instance light. And also

they can’t produce accurate results as they are sensitive to environment changes.



BIBLIOGRAPHY

REFERENCES

The sites which were used while doing this project:

1. www.wikipedia.com

2. www.allaboutcircuits.com

3. www.microchip.com

4. www.howstuffworks.com

5. www.google.com

BOOKS REFERRED:

1. Raj kamal –Microcontrollers Architecture, Programming, Interfacing and System Design.

2. Mazidi and Mazidi –Embedded Systems.

3. PCB Design Tutorial –David.L.Jones.

4. PIC Microcontroller Manual – Microchip.

5. Pyroelectric Sensor Module- Murata.

6. Embedded C –Michael.J.Pont.


http://www.howstuffworks.com/

http://www.microchip.com/

http://www.allaboutcircuits.com/

http://www.wikipedia.com/

b12_-_copy

Documents

embedded systems programming

embedded products

operating systems

computer system

zigbee technology

large application systems

zigbee receiver

attendance alert system