CHAPTER 1

INTRODUCTION

1

INTRODUCTION

The rapidly advancing mobile communication technology and the decrease

in costs make it possible to incorporate GSM technology into home automation

systems. We propose a SMS-based home automation system. The objective of this

project is to enable users to remotely control their home appliances and systems

using SMS. To access the control unit, the user should send an authentication code

along with the required/desired function/action to his/her home control system. The

home appliances are controlled by the home server, which operates according to

the user commands received from the SMS via the GSM modem.

2

CHAPTER 2

BLOCK DIAGRAM

3

Block Diagram :

LCD DISPLAY

4

MICROCONTROLLER

MEMORY

GSM MODEM

POWER SUPPLY

RELAYDRIVER

RELAY1

RELAY2

RELAY2

RELAY2

BLOCK DIAGRAM DESCRIPTION:

Microcontroller

The AT89S52 provides the following standard features: 8K bytes of Downloadable

Flash, 2K bytes of EEPROM, 256 bytes of RAM, 32 I/O lines, programmable

watchdog timer, two Data Pointers, three 16-bit timer/counters, a six-vector two-

level interrupt, a full duplex serial port, on-chip oscillator, and clock circuitry.

Memory

It is a type of non-volatile memory used in computers and other electronic devices

to store small amounts of data that must be saved when power is removed, e.g.,

calibration tables or device configuration. When larger amounts of static data are to

be stored (such as in USB flash drives) a specific type of EEPROM such as flash

memory is more economical than traditional EEPROM devices. EEPROMs are

realized as arrays of floating-gate transistors. EEPROMs were used for

configuration information, rather than random access memory.

Relay Driver IC

As we, all know ULN2803 is used as the relay driver IC. It consists of octal high

voltage, high current Darlington transistor arrays. The eight NPN Darlington

connected transistors in this family of arrays are ideally suited for interfacing

between low logic level digital circuitry (such as TTL, CMOS or PMOS/NMOS)

and the higher current/voltage requirements of lamps, relays, printer hammers or

other similar loads for abroad range of computer, industrial, and consumer

applications.

Relays

5

A relay is an electrically operated switch. It allows one circuit to switch a second

circuit that completely separated from the first. The output from the driver IC is

send to the corresponding relays that thus results in its excitation and are activated.

As a result, it controls the corresponding home appliance

Display Block

In this project, we are using 16X2 LCD displays, for displaying message.

GSM Technology

GSM MODEM is a class of wireless MODEM devices that are designed for

communication of a computer with the GSM network. It requires a SIM

(Subscriber Identity Module) card just like mobile phones to activate

communication with the network. Here GSM modem is used for sending message

to the home server.

Power Supply

Initial stage of every electronic circuit is power supply system that provides

required power to drive the whole system. The specification of power supply

depends on the power requirement and this requirement is determined by its rating.

Component Description:-

6

GSM TECHNOLOGY

GSM is widely used mobile communication architecture used in most of the

countries. This project demonstrates the interfacing of microcontroller AT89C51

with HyperTerminal and GSM module. It aims to familiarize with the syntax of

AT Commands and their Information Response and Result Codes. The ASCII

values of characters in the Information Response, Result Codes and their syntax

can be monitored by an LED array. For the basic concepts, working and operation

of AT commands and GSM module refer GSM/GPRS Module.

AT commands are used to control MODEMs. AT is the abbreviation for Attention.

These commands come from Hayes commands that were used by the Hayes smart

modems. The Hayes commands started with AT to indicate the attention from the

MODEM. The dial up and wireless MODEMs (devices that involve machine to

machine communication) need AT commands to interact with a computer. These

include the Hayes command set as a subset, along with other extended AT

commands.

AT commands with a GSM/GPRS MODEM or mobile phone can be used to

access following information and services:

1. Information and configuration pertaining to mobile device or MODEM

and SIM card

2. SMS services

3. MMS services

4. Fax services

5. Data and Voice link over mobile network.

7

The Hayes subset commands are called the basic commands and the commands

specific to a GSM network are called extended AT commands.

GSM/GPRS module is used to establish communication between a computer and

a GSM-GPRS system. Global System for Mobile communication (GSM) is an

architecture used for mobile communication in most of the countries. Global

Packet Radio Service (GPRS) is an extension of GSM that enables higher data

transmission rate. GSM/GPRS module consists of a GSM/GPRS modem

assembled together with power supply circuit and communication interfaces (like

RS-232, USB, etc) for computer. The MODEM is the soul of such modules.

GSM/GPRS MODEM

GSM/GPRS MODEM is a class of wireless MODEM devices that are designed for

communication of a computer with the GSM and GPRS network. It requires a SIM

(Subscriber Identity Module) card just like mobile phones to activate

communication with the network. Also they have IMEI (International Mobile

Equipment Identity) number similar to mobile phones for their identification. A

GSM/GPRS MODEM can perform the following operations:

 

1.      Receive, send or delete SMS messages in a SIM.

2.      Read, add, search phonebook entries of the SIM.

3.      Make, Receive, or reject a voice call.

 The MODEM needs AT commands, for interacting with processor or controller,

which are communicated through serial communication. These commands are sent

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by the controller/processor. The MODEM sends back a result after it receives a

command. Different AT commands supported by the MODEM can be sent by the

processor/controller/computer to interact with the GSM and GPRS cellular

network.

 

 GSM/GPRS Module

A GSM/GPRS module assembles a GSM/GPRS modem with standard

communication interfaces like RS-232 (Serial Port), USB etc., so that it can be

easily interfaced with a computer or a microprocessor / microcontroller based

system. The power supply circuit is also built in the module that can be activated

by using a suitable adaptor

 

 

9

Wireless MODEMs

Wireless MODEMs are the MODEM devices that generate, transmit or decode

data from a cellular network, for establishing communication between the cellular

network and the computer. These are manufactured for specific cellular network

(GSM/UMTS/CDMA) or specific cellular data standard (GSM/ UMTS/ GPRS/

EDGE/ HSDPA) or technology (GPS/SIM). Wireless MODEMs like other

MODEM devices use serial communication to interface with and need Hayes

compatible AT commands for communication with the computer (any

microprocessor or microcontroller system).

 

 

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Mobile Station (Cell phones and SIM)

A mobile phone and Subscriber Identity Module (SIM) together form a mobile

station. It is the user equipment that communicates with the mobile network. A

mobile phone comprises of Mobile Termination, Terminal Equipment and

Terminal Adapter.

 

Mobile Termination is interfaced with the GSM mobile network and is controlled

by a baseband processor. It handles access to SIM, speech encoding and decoding,

signaling and other network related tasks. The Terminal Equipment is an

application processor that deals with handling operations related to keypad, screen,

phone memory and other hardware and software services embedded into the

handset. The Terminal Adapter establishes communication between the Terminal

Equipment and the Mobile Termination using AT commands. The communication

with the network in a GSM/GPRS mobile is carried out by the baseband processor.

Difference between GSM mobile and GSM/GPRS module

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A GSM mobile is a complete system in itself with embedded processors that are

dedicated to provide an interface between the user and the mobile network. The

AT commands are served between the processors of the mobile termination and the

terminal equipment. The mobile handset can also be equipped with a USB

interface to connect with a computer, but it may or may not support AT commands

from the computer or an external processor/controller.

 

The GSM/GPRS module, on the other hand, always needs a computer or external

processor/controller to receive AT commands from. GSM/GPRS module itself

does not provide any interface between the user and the network, but the computer

to which module is connected is the interface between user and network.

 

An advantage that GSM/GPRS modules offer is that they support concatenated

SMS which may not be supported in some GSM mobile handsets. Also some

mobile handsets can’t receive MMS when connected to a computer.

Applications of GSM/GPRS module

The GSM/GPRS module demonstrates the use of AT commands. They can feature

all the functionalities of a mobile phone through computer like making and

receiving calls, SMS, MMS etc. These are mainly employed for computer based

SMS and MMS services.

AT Commands

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AT commands are used to control MODEMs. AT is the abbreviation for Attention.

These commands come from Hayes commands that were used by the Hayes smart

modems. The Hayes commands started with AT to indicate the attention from the

MODEM. The dial up and wireless MODEMs (devices that involve machine to

machine communication) need AT commands to interact with a computer. These

include the Hayes command set as a subset, along with other extended AT

commands.

 

AT commands with a GSM/GPRS MODEM or mobile phone can be used to

access following information and services:

1. Information and configuration pertaining to mobile device or MODEM and

SIM card

2. SMS services

3. MMS services

4. Fax services.

5. Data and Voice link over mobile network.

The Hayes subset commands are called the basic commands and the commands

specific to a GSM network are called extended AT commands.

 

Command, Information response and Result Codes:

The AT commands are sent by the computer to the MODEM/ mobile phone. The

MODEM sends back an Information Response i.e. the information requested by or

pertaining to the action initiated by the AT command. This is followed by a Result

Code. The result code tells about the successful execution of that command.

13

 

There are also unsolicited Result Codes that are returned automatically by the

MODEM to notify the occurrence of an event. For example the reception of a SMS

will force MODEM to return an unsolicited result code

AT commands' syntax

Case Sensitivity -

The AT commands are generally used in uppercase letters. However some

MODEMs and mobile phones allow both uppercase and small case letters.

 

14

Single Command –

The AT commands include a prefix AT which indicates the beginning of the

command to MODEM; and a carriage returnwhich indicates the end of the

command.

 

However string ‘AT’ itself is not the part of the command. For example in ATD, D

is the command name not ATD.

The extended AT commands have a ‘+’ in the command name.

For example:   AT+CGMI<Carriage return>

 

Command Line –

Multiple AT commands can be sent to MODEM in a single command line. The

commands in a line are separated by a semi-colon (;).

15

For example:   AT+CGMI; +CBS<Carriage return>

 

String in Command Line –

Strings in a command line are enclosed in double quotes.

For example:   AT+CGML=”ALL”<Carriage return>

 

Information Response and Result Code –

The Information Response and Result Codes, returned by the MODEM, have a

carriage return and line feed in the beginning as well as at the end.

 

For example:

<Carriage return><Line feed>OK<Carriage return><Line feed>

<Carriage return><Line feed>ERROR<Carriage return><Line feed>

<Carriage return><Line feed>+CBC: 0, 60<Carriage return><Line feed> etc.

 

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Sequence of Execution –

In the command line, the command appearing first is executed first. The execution

then follows for second appeared command and so on. The execution of commands

in a command line takes place in sequential manner.

If an error occurs in the execution of a command, an error result code is returned

by the MODEM and the execution of the command line is terminated irrespective

of presence of other commands next in the command line.

z

Types of commands:

There are four types of AT commands:

1)        Test commands

2)        Read commands

3)        Set commands

4)        Execution commands

 

Different Result Codes:

RESULT CODE DESCRIPTIONOK Successful Execution of a commandERROR Execution of a command failed+CMS ERROR Message service failure, is returned with an error code Unsolicited Result Codes+CDS Notify receipt of SMS status report of a new message to

computer+CDSI Notify receipt of SMS status report of a new message and its

location in memory to computer+CMT Notify forwarding of a new SMS to computer+CMTI Notify receipt of SMS status report of a new message and its

location in memory to computer

17

 Interfacing MODEM/Mobile phone with Windows platform

The Windows (XP and lower versions) comes with an application

called HyperTerminal for data communication through serial port of the computer.

The interfacing of the GSM/GPRS module with the serial port of the computer

involves following steps:

 

1. Connect RS-232 port of GSM module with the serial port of the computer.

Insert a SIM card in the module.

2. Open HyperTerminal from Start -> All Programs -> Accessories -

> Communications -> HyperTerminal.

3. Enter a name for the connection and press OK.

4. Now select the communication port (COM) at which GSM module is

connected.

5. Create a new connection set on HyperTerminal. Set parameters, like baud

rate as 9600, handshaking mode as none, parity bit as none, stop bit as 1 and

data bit as 8. 

The project explains interfacing of the AT89C51 microcontroller with the GSM

module and the HyperTerminal. HyperTerminal is a Windows application. The AT

commands are sent by the HyperTerminal to the GSM module. The Information

Response and/or Result Codes are received at the microcontroller and

retransmitted to the HyperTerminal by the controller.

 

A GSM module has an RS232 interface for serial communication with an external

peripheral. In this case, the transmit pin (Tx) of the computer’s Serial port is

connected with the receive pin (Rx) of the GSM module’s RS-232 interface. The

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transmit pin (Tx) of the RS-232 of GSM module is connected to receive pin (Rx)

of microcontroller’s serial transmission pin. And the serial transmit pin of the

microcontroller is connected to the receive pin of the computer’s Serial port.

Therefore the commands and their results are transmitted and received in a

triangular fashion as depicted below.

 

In subsequent projects (see MC075 & MC076), the HyperTerminal will be

replaced by the microcontroller itself; thus avoiding the need of using a Computer

to establish an interface. This would lead to an independent GSM based system.]

The microcontroller is programmed to receive and transmit data at a baud rate of

9600.

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CHAPTER 3

CIRCUIT OF SMS BASED HOME

AUTOMATION

20

CIRCUIT DIAGRAM & COMPONENT

21

POWER SUPPLY:

Power supply block consists of following units:

Step down transformer

Bridge rectifier circuit

Input filter

Voltage regulators

Output filter

Indicator unit

Step down transformer:

The step-down transformer is used to step down the supply voltage of 230v ac

from mains to lower values, as the various IC’s used in this project require reduced

voltages. The transformer consists of primary and secondary coils. To reduce or

step down the voltage, the transformer is designed to contain less number of turns

in its secondary core. The outputs from the secondary coil which is center tapped

are the ac values of 0v, 15v and 15v. The conversion of these ac values to dc

values to dc values is done using the full wave rectifier unit.

Rectifier Unit:

A diode bridge is an arrangement of four diodes connected in a bridge circuit. That

provides the polarity of output voltage of any polarity of the input voltage. When

used in its most common application, for conversion of alternating current (A.C)

input into direct current (D.C) output, it is known as a bridge rectifier. The diagram

describes a diode-bridge design known as a full wave rectifier. This design can be

22

used to rectify single phase A.C. when no transformer center tap is available. A

bridge rectifier makes use of four diodes in a bridge arrangement to achieve full

wave rectification. This is a widely used configuration, both with individual diodes

wired as shown and with single component bridges where the diode bridge is wired

internally.

For both positive and negative swings of the transformer, there is a forward path

through the diode bridge. Both conduction paths cause current to flow in the same

direction through the load resister, accomplishing full-wave rectification. While

one set of diodes is forward biased, the other set is reversing biased and effectively

eliminated from the circuit.

Input Filter: -

Capacitors are used as filters. The ripples from the dc voltages are removed and

pure dc voltage is obtained. The primary action performed by capacitor is

charging and discharging. It charges in positive half cycle of the ac voltage and it

will discharge in negative half cycle. Therefore, it allows only ac voltage and does

not allow the dc voltage. This filter is fixed before the regulator. Capacitors used

here are of the value 470uF

Regulator unit: -

Regulator regulates the output voltage to a specific value. The output voltage is

maintained irrespective of the fluctuations in the input dc voltage. Whenever there

are any ac voltage fluctuations, the dc voltage also changes, and to avoid this

regulators are used.

23

Regulators can be classified as: -

1. Positive regulator, which regulates the positive voltage(7805,7812)

1. > input pin

2. > ground pin

3. > output pin

Regulators used in this application are: -

7805 that provides 5v dc

Output Filter: -

This filter is fixed after the Regulator circuit to filter any of the possibly found

ripples in the output received finally. Capacitors used here are of value 10F.

24

MICROCONTROLLER

The AT89S52 provides the following standard features: 8K bytes of Downloadable

Flash, 2K bytes of EEPROM, 256 bytes of RAM, 32 I/O lines, programmable

watchdog timer, two Data Pointers, three 16-bit timer/counters, a six-vector two-

level interrupt, 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

interrupt or hardware reset. The Downloadable Flash can be changed a single byte

at a time and is accessible through the SPI serial interface. Holding RESET active

forces the SPI bus into a serial programming interface and allows the program

memory to be written to or read from unless Lock Bit 2 has been activated.

Features

Compatible with MCS-51™Products

8K bytes of In-System Reprogrammable Downloadable Flash Memory

SPI Serial Interface for Program Downloading

Endurance: 1,000 Write/Erase Cycles

4.0V to 5.5V Operating Range

Fully Static Operation: 0 Hz to 33 MHz

256 x 8 bit Internal RAM

32 Programmable I/O Lines

Three 16 bit Timer/Counters

Eight Interrupt Sources

25

Full Duplex UART Serial Channel

Low Power Idle and Power Down Modes

Interrupt Recovery from Power Down Mode

Advantages

Less power consumption

Low cost

Less space required

High speed

EEPROM MEMORY:

EEPROM (also written E2PROM and pronounced "e-e-prom," "double-e prom,"

"e-squared," or simply "e-prom") stands for Electrically Erasable Programmable

Read-Only Memory and is a type of non-volatile memory used in computers and

other electronic devices to store small amounts of data that must be saved when

power is removed, e.g., calibration tables or device configuration.

When larger amounts of static data are to be stored (such as in USB flash drives) a

specific type of EEPROM such as flash memory is more economical than

traditional EEPROM devices. EEPROMs are realized as arrays of floating-gate

transistors.

EEPROM is user-modifiable read-only memory (ROM) that can be erased and

reprogrammed (written to) repeatedly through the application of higher than

normal electrical voltage generated externally or internally in the case of modern

EEPROMs. EPROM usually must be removed from the device for erasing and

26

programming, whereas EEPROMs can be programmed and erased in circuit.

Originally, EEPROMs were limited to single byte operations that made them

slower, but modern EEPROMs allow multi-byte page operations. It also has a

limited life - that is, the number of times it could be reprogrammed was limited to

tens or hundreds of thousands of times. That limitation has been extended to a

million write operations in modern EEPROMs. In an EEPROM that is frequently

reprogrammed while the computer is in use, the life of the EEPROM can be an

important design consideration. It is for this reason that EEPROMs were used for

configuration information, rather than random access memory.

LCD DISPLAY

LCD (Liquid Crystal Display) screen is an electronic display module and find a

wide range of applications. A 16x2 LCD display is very basic module and is very

commonly used in various devices and circuits. These modules are preferred over

seven segments and other multi segment LEDs. The reasons being: LCDs are

economical; easily programmable; have no limitation of displaying special & even

custom characters (unlike in seven segments), animations and so on.

A 16x2 LCD means it can display 16 characters per line and there are 2 such lines.

In this LCD, each character is displayed in 5x7-pixel matrix. This LCD has two

registers, namely, Command and Data.

The command register stores the command instructions given to the LCD. A

command is an instruction given to LCD to do a predefined task like initializing it,

clearing its screen, setting the cursor position, controlling display etc. The data

27

register stores the data to be displayed on the LCD. The data is the ASCII value of

the character to be displayed on the LCD

Relay Driver (ULN 2003) :

Feature;

Seven darling tons per package

output current 500ma per driver(600ma peak)

output voltage 50v integrated suppression diodes for inductive loads outputs

can be paralleled for higher current

ttl/cmos/pmos/dtlcompatible inputs

inputs pinned opposite outputs to Simplify layout

DESCRIPTION

The ULN2001A, ULN2002A, ULN2003 and ULN2004Aare high voltage, high

current darlington arrays each containing seven open collector darling ton pairs

28

with common emitters. Each channel rated at 500mAand can withstand peak

currents of 600mA. Suppression diodes are included for inductive load driving and

the inputs are pinned opposite the outputs to simplify board layout.

RELAYS:

The relay is a device by means of which an electrical circuit can be controlled

(opened or closed) by sensing a change in the circuit in which it is connected. The

relays can be either electromagnetic or electronic. In this circuit, the

electromagnetic relay is used to connect or disconnect the supply to the appliance

to be controlled. It works on the principle of electromagnetic attraction and

electromagnetic induction. These relays can be actuated by AC or DC quantities.

In these relays, there are one or more coils, movable elements, contact systems etc.

CIRCUIT DIAGRAM DESCRIPTION:

29

In this project, we have used AT89S52 microcontroller. This controller is very

famous because it has 8 kb of flash memory and 256 k RAM and it is easily

available in the market. Port configuration is similar like 8051 microcontroller.

As shown in the circuit diagram we have connected 10 k 9-pin SIP

resistor in the port line of microcontroller. 10k ohm resistor and 2.2uF capacitor

form the reset circuit for microcontroller. 11.0592 MHz crystal in connected in 18

and 19 pin of microcontroller with 33 pf capacitor. Data line of LCD display

connected with Port 0 of microcontroller and control lines of LCD connected with

Port 2 of microcontroller. Four Relays are used which is connected with ULN

2003. These ULN 2003 is connected with port P1. EEPROM memory is connected

with port P3 for storing device status. Externally we are connected GSM modem

for MSG receiving. Power Supply is made up of simple bridge diode filter and

regulator ic. Here we required5v and 12v.

Working:

In this project, we have to control different home devices using SMS. The message

will be send by SMS and according to it the action will be performed. For SMS we

are using GSM modem. When we send SMS message receive by modem. This

modem connected to the RXD and TXD pin of microcontroller. According to the

message, controller operated the device. It ON/OFF the device as per instruction

receives. Simultaneously, controller displays the message on LCD and stored that

message to the memory. Memory stores the device status. If due to power failure

device get off then after regaining power device ON/OFF as per their previous

status.

SOFTWARE USED:

30

Express SCH

Express SCH software used for Circuit designing.

Steps for Designing:

1.Begin a new schematic by running Express SCH. You can launch Express SCH

from your desktop by clicking on the icon.

2 Select New from the File menu. Then start designing a schematic diagram.

3.Take component from Components and Symbols manager as per required and it

by using wire.

4.In this way, we can make schematic diagram.

PCB ARTIST

Introduction to PCB Artist

Printed Circuit Boards Basics

PCB’s are the backbone of any electronic devices, and therefore knowledge of

PCB layout tools can be a vital skill. Both analog and digital circuits used in PCBs

depending on the application, and with different types of circuits, the designer

must take into account certain design considerations. More Advance circuits like

RF circuits or Power circuits take more thought in the layout and design because

the circuit is more sensitive to component placement and the lengths of the

connections between them.

The process for PCB design is to first create a list of parts you will use in the

circuit, and then take the footprint of the component from libraries available. After

31

taking footprint, you have to connect that component by track. Then finally place

all the components’ in this manner and connect them physically how you want

them to be fabricated on the board.

Keil uvision

32

The µVision IDE from Keil combines project management, make facilities, source

code editing, program debugging, and complete simulation in one powerful

environment. The µVision development platform is easy-to-use and helping you

quickly create embedded programs that work. The µVision editor and debugger are

integrated in a single application that provides a seamless embedded project

development environment.

33

CHAPTER 4

APPLICATIONS

APPLICATIONS

34

The main application of this project is that we can control any appliances by just

SMS from anywhere. This is very much helpful if we are outside home and we

forget to switch off device. This is also helpful for elderly people as well as for

those who are physically challenging.

35

CHAPTER 5

CONCLUSION & FUTURE WORK

36

CONCLUSION & FUTURE WORK

In the paper low cost, secure, ubiquitously accessible, auto-configurable,

remotely controlled solution for automation of homes has been introduced. The

approach discussed in the paper is novel and has achieved the target to control

home appliances remotely using the SMS-based system satisfying user needs and

requirements. GSM technology capable solution has proved to be controlled

remotely, provide home security and is cost-effective as compared to the previously

existing systems. Hence we can conclude that the required goals and objectives of

HACS have been achieved.

The basic level of home appliance control and remote monitoring has been

implemented. The system is extensible and more levels can be further developed

using automatic motion/glass breaking detectors so the solution can be integrated

with these and other detection systems. In case of remote monitoring other

appliances can also be monitored such that if the level of temperature rises above

certain level then it should generate SMS or sensors can also be applied that can

detect gas, smoke or fire in case of emergency the system will automatically

generate SMS. In future the system will be small box combining the PC and GSM

modem. The hardware will be self contained and cannot be prone to electric failure.

This appliance will have its own encapsulated UPS and charging system.

37

CHAPTER 6

REFERENCES

38

REFERENCES

The 8051 microcontroller – Kenneth J. Ayala

Wireless Communication – Theobores S. Rappaport

GSM Architecture, Protocols and Services – Althos Publication

R.S GAONKAR Microprocessor architecture programming and application”

WILEY EASTERN LTD, NEWDELHI

WILLIAM STALLING “Wireless communication and networks”,2nd

edition,2005 prentice hall of India

DANIEL .W.LEWIS “Fundamental of embedded software “prentice hall of

India, 2004

39

PHOTOGRAPH

40