1

CHAPTER 1

INTRODUCTION

1.1 Introduction of Project

―GSM based Control System‖ implements the emerging applications of the GSM technology.

Using GSM networks, a control system has been proposed that will act as an embedded

system which can monitor and control appliances and other devices locally using built-in

input and output peripherals. Remotely the system allows the user to effectively monitor and

control the house/office appliances and equipment via the mobile phone set by sending

commands in the form of DTMF TONE. The main concept behind the project is receiving the

CALL and a fix DTMF TONE and processing it further as required to perform several

operations. The type of the operation to be performed depends on the key pressed. The

principle in which the project is based is fairly simple. Firstly, the DTMF TONE is sent via

the mobile keypad and then it is decoded through a decoder and sent to the intermediate

hardware that we have designed according to the command received in form of the DTMF

TONE.

The DTMF TONE is sent from the mobile set that contains commands in DTMF form which

are then processed accordingly to perform the required task. A microcontroller based system

has been proposed for our project. There are several terminologies that are used extensively

throughout this project report. GSM (Global System for Mobile Communications): It is a

cellular communication standard.

1.2 Background

The new age of technology has redefined communication. Most people nowadays have access

to mobile phones and thus the world indeed has become a global village. At any given

moment, any particular individual can be contacted with the mobile phone. But the

application of mobile phone cannot just be restricted to sending SMS or starting

conversations. New innovations and ideas can be generated from it that can further enhance

its capabilities. Technologies such as Infra-red, Bluetooth, etc which has developed in recent

years goes to show the very fact that improvements are in fact possible and these

improvements have eased our life and the way we live. Remote management of several home

and office appliances is a subject of growing interest and in recent years we have seen many

systems providing such controls. We have designed a control system which is based on the

GSM technology that effectively allows control from a remote area to the desired location.

2

The application of our suggested system is immense in the ever changing technological

world. It allows a greater degree of freedom to an individual whether it is controlling the

household appliances or office equipments. The need to be physically present in order to

control appliances of a certain location is eliminated with the use of our system.

1.3 Problem Statement

Technology has advanced so much in the last decade or two that it has made life more

efficient and comfortable. The comfort of being able to take control of devices from one

particular location has become imperative as it saves a lot of time and effort. Therefore there

arises a need to do so in a systematic manner which we have tried to implement with our

system. The system we have proposed is an extended approach to automating a control

system. With the advancement and breakthroughs in technology over the years, the lives of

people have become more complicated and thus they have become busier than before. With

the adoption of our system, we can gain control over certain things that required constant

attention. The application of our system comes in handy when people who forget to do simple

things such as turn ON or OFF devices at their home or in their office, they can now do so

without their presence by the transmission of a simple call from their mobile phone. This

development, we believe, will ultimately save a lot of time especially when people don‘t have

to come back for simple things such as to turn ON/OFF switches at their home or at their

office once they set out for their respective work.

The objective of this project is to develop a device that allows for a user to remotely control

and monitor multiple home/office appliances using a cellular phone. This system will be a

powerful and flexible tool that will offer this service at any time, and from anywhere with the

constraints of the technologies being applied. Possible target appliances include (but are not

limited to) climate control system, security systems, lights; anything with an electrical

interface. The proposed approach for designing this system is to implement a microcontroller-

based control module that receives its instructions and command from a cellular phone over

the GSM network. The microcontroller then will carry out the issued commands and then

communicate the status of a given appliance or device back to the cellular phone.

3

1.4 Block Diagram

Fig1.1: Block Diagram

The figure shown above is the simple block diagram of our project. It is a simple illustration

of how we have implemented our project and the various parts involved in it. From the above

representation, the first Mobile station is used as a transmitting section from which the

subscriber sends DTMF tone that contain commands and instructions to the second mobile

station which is based on a specific area where our control system is located. The mobile

phone as indicated in the block diagram is a mobile set. The received DTMF tone is send to

the decoder via the head phone and then extracted by the microcontroller and processed

accordingly to carry out specific operations. The relay driver (BUFFER ULN2003) is used to

4

drive the relay circuits which switches the different appliances connected to the interface. The

APR is used to indicate the status of the operation performed by the microcontroller and also

its inclusion makes the overall system user-friendly.

The input from different sensors are feed to micro-controller and processed to operate

respective task semi autonomously and autonomously.

1.5 System Operation Flow Diagram

Fig1.2: System Operation Flow Diagram

Assuming that the control unit is powered and operating properly, the process of controlling a

device connected to the interface will proceed through the following steps;

• The remote user calls at the number designated at the control system.

• The remote user sends the commands in DTMF format through the keypad of cell phone.

• The designated cell phone decodes the sent DTMF tone and sends the commands to the

microcontroller.

• Microcontroller issues commands to the appliances and the devices connected will switch

ON/OFF.

5

CHAPTER 2

SYSTEM SPECIFICATION

2.1 Scopes and Purpose of System Specification

The system specification shows the description of the function and the performance of system

and the user. The scope of our project ―GSM Based control system‖ is immense. The future

implications of the project are very great considering the amount of time and resources it

saves. The project we have undertaken can be used as a reference or as a base for realizing a

scheme to be implemented in other projects of greater level such as weather forecasting,

temperature updates, device synchronization, etc. The project itself can be modified to

achieve a complete Home Automation system which will then create a platform for the user

to interface between himself and the household.

2.2 Goals and Objectives

The project ―GSM based Control System‖ at the title suggests is aimed to construct a control

system that enables the complete control of the interface on which it is based.

General objectives of the project are defined as;

a. To co-ordinate appliances and other devices through DTMF(Dual tone multi frequency).

b. To eliminate the need of being physically present in any location for tasks involving the

operation of appliances within a household/office.

c. Minimize power and time wastage

2.3 Operating Environment

The control system will include two separate units: the cellular phone, and the control unit.

There will therefore be two operating environments. The cellular phone will operate indoors

and outdoors whereas the control unit will operate indoors within the temperature and

humidity limits for proper operation of the hardware.

2.4 Intended Users and Uses

This system is aimed toward all the average users who wish to control their household/office

appliances remotely from their cell phones provided that the appliances are electrically

controllable. Example of feasible appliances and applications under consideration include;

enable/disable security systems, fans, lights, kitchen appliances, and adjusting the

temperatures settings of a heating/ventilation/air conditioning system.

6

2.5 Major Constraints

Along the course of project completion we encountered various problems and obstacles. Not

everything that we had planned went smoothly during the project development span. Also we

had a limited amount of time for its completion so we were under a certain amount of

pressure as well. We had to start from the research phase at the beginning and needed to gain

knowledge on all the devices and components that we had intended to use for our project.

Other phases of the project included coding, debugging, testing, documentation and

implementation and it needed certain time for completion so we really had to manage the

limited time available to us and work accordingly to finish the project within the schedule.

2.6 Functional Requirements

The following is a list of functional requirements of the control unit/module.

a. The control unit will have the ability to connect to the cellular network automatically.

b. The control unit will be able to receive DTMF tone and will be able to parse and interpret

the tone and instructions to be sent to the microcontroller.

c. The microcontroller within the control unit will issue its command to the electrical

appliances through a simple control circuit.

d. The control unit will control the electrical appliances.

2.7 Constraints Considerations

The following is a list of constraint Considerations

a. The controlled appliances will need an electrical control interface. This system is only

capable of controlling electrical devices.

b. The control module will need to be shielded against electrostatic discharges. This will

increase the reliability of the system.

c. Battery backup for controlling unit can be implemented in case of power disruption.

2.8 Technology Considerations

The considerations for this system will include a choice of networks, communication

protocols and interfaces.

a. Cellular Networks: The widely available networks are based on GSM. This network

provides wide area coverage and can be utilized more cost-effectively for this project.

b. Communication Protocols: The available communication protocol that we have used is

DTMF tone.

7

c. I/O interfaces between microcontroller and devices: Serial I/O is considered as options for

connection between the GSM receiver and the microcontroller. Using the microcontroller, a

control circuit will be implemented to control the electrical appliances.

2.9 Limitations

Our project has certain limitations and a list of such is mentioned below;

a. The receiver must reside in a location where a signal with sufficient strength can be

received from a cellular phone network.

b. Only devices with electrical controlling input ports will be possible targets for control.

c. Operation of the controlling unit is only possible through a cell phone.

d. The Controlling unit must be able to receive and decode DTMF signals.

8

CHAPTER 3

GSM TECHNOLOGY

3.1 GSM Technology

GSM is a global system for mobile communication GSM is an international digital cellular

telecommunication. The GSM standard was released by ETSI (European Standard

Telecommunication Standard) back in 1989. The first commercial services were launched in

1991 and after its early introduction in Europe; the standard went global in 1992. Since then,

GSM has become the most widely adopted and fastest-growing digital cellular standard, and

it is positioned to become the world‘s dominant cellular standard. Today‘s second-generation

GSM networks deliver high quality and secure mobile voice services with full roaming

capabilities across the world.

GSM platform is a hugely successful technology and as unprecedented story of global

achievement. In less than ten years since the first GSM network was commercially launched,

it become, the world‘s leading and fastest growing mobile standard, spanning over 173

countries. Today, GSM technology is in use by more than one in ten of the world‘s

population and growth continues to sour with the number of subscriber worldwide expected

to surpass one billion by through end of 2003. Today‘s GSM platform is living, growing and

evolving and already offers an expanded and feature-rich ‗family‘ of voice and enabling

services. The Global System for Mobile Communication (GSM) network is a cellular

telecommunication network with a versatile architecture complying with the ETSI GSM

900/GSM 1800 standard. Siemen‘s implementation is the digital cellular mobile

communication system D900/1800/1900 that uses the very latest technology to meet every

requirement of the standard.

3.3 GSM Services

GSM services follow ISDN guidelines and classified as either tele services or data services.

Tele services may be divided into three major categories:

• Telephone services, include emergency calling and facsimile. GSM also supports Videotex

and Teletex, through they are not integral parts of the GSM standard.

• Bearer services or Data services, which are limited to layers 1, 2 and 3 of the OSI reference

model. Data may be transmitted using either a transparent mode or non transparent mode.

9

• Supplementary ISDN services, are digital in nature, and include call diversion, closed user

group, and caller identification. Supplementary services also include the short message

service (SMS).

Fig3.1: GSM Architecture

3.2 Basic Specification in GSM

S.No. PARAMETER SPECIFICATIONS

1. Reverse channel frequency 890-915MHz

2. Forward Channel frequency 935-960 MHz

3. Tx/Rx Frequency Spacing 45 MHz

4. Tx/Rx Time Slot Spacing 3 Time slots

5. Modulation Data Rate 270.833333kbps

6. Frame Period 4.615ms

7. Users per Frame 8

8. Time Slot Period 576.9microsec

9. Bit Period 3.692 microsecond

10. Modulation 0.3 GMSK

11. ARFCN Number 0 to 124 & 975 to 1023

12. ARFCN Channel Spacing 200 kHz

13. Interleaving 40 ms

14. Voice Coder Bit Rate 13.4kbps

10

CHAPTER 4

MICRO-CONTROLLER

4.1 Introduction

An embedded microcontroller is a chip, which has a computer processor with all its support

function (clocking and reset), memory (both program storage and RAM), and I/O (including

bus interfaces) built into the device. These built in function minimize the need for external

circuits and devices to the designed in the final applications. The improvements in micro-

controller technology has meant that it is often more cost effective, faster and more efficient

to develop an application using a micro-controller rather than discrete logic. Creating

applications for micro-controllers is completely different than any other development job in

computing and electronics. In most other applications, number of subsystems and interfaces

are available but this is not the case for the micro-controller where the following

responsibilities have to be taken.

• Power distribution

• System clocking

• Interface design and wiring

• System Programming

• Application programming

• Device programming

There are two types of micro-controller commonly in use. Embedded micro-controller is the

micro-controller, which has the entire hardware requirement to run the application, provided

on the chip. External memory micro-controller is the micro-controller that allows the

connection of external memory when the program memory is insufficient for an application

or during the work a separate ROM (or even RAM) will make the work easier.

4.2 ATMEL Micro-controller

The AT89C52 is a low-power; high performance CMOS 8-bit microcomputer with 8K bytes

of Flash programmable and erasable read only memory (PEROM). The device is

manufactured using Atmel‘s high-density non volatile memory technology and is compatible

with the industry-standard 80C51 and 80C52 instruction set and pin out. The on-chip Flash

allows the program memory to be reprogrammed in-system or by a conventional non volatile

memory programmer. By combining a versatile 8-bit CPU with Flash on a monolithic chip,

11

the ATMEL AT89C52 is a powerful microcomputer which provides a highly-flexible and

cost-effective solution to many embedded control applications.

The main features of this micro-controller are as follows;

• Compatible with MCS-51TM \Products

• 8K Bytes of In-system reprogrammable Flash Memory

• Endurance: 1,000 write/erase cycles

• Fully static operation: 0 Hz to 24 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

12

CHAPTER 5

RELAY

5.1 Inroduction

NC: - Normally Connected

NO: - Normally Open

COM: - Common

Fig5.1: Relay Switch Connection

The relay driver is used to isolate both the controlling and the controlled device. The relay is

an electromagnetic device, which consists of solenoid, moving contacts (switch) and restoring

spring and consumes comparatively large amount of power. Hence it is possible for the

interface IC to drive the relay satisfactorily. To enable this, a driver circuitry, which will act

as a buffer circuit, is to be incorporated between them. The driver circuitry senses the

presence of a ―high‖ level at the input and drives the relay from another voltage source.

Hence the relay is used to switch the electrical supply to the appliances.

From the figure when we connect the rated voltage across the coil the back emf opposes the

current flow but after the short time the supplied voltage will overcome the back emf and the

current flow through the coil increase. When the current is equal to the activating current of

relay the core is magnetized and it attracts the moving contacts. Now the moving contact

leaves from its initial position denoted ―(N/C)‖ normally closed terminal which is a fixed

13

terminal. The common contact or moving contact establishes the connection with a new

terminal which is indicated as a normally open terminal ―(N/O)‖. Whenever, the supply coil

is withdrawn the magnetizing force is vanished. Now, the spring pulls the moving contact

back to initial position, where it makes a connection makes with N/C terminal. However, it is

also to be noted that at this time also a back emf is produced. The withdrawal time may be in

microsecond, the back emf may be in the range of few kilovolts and in opposite polarity with

the supplied terminals the voltage is

known as surge voltage. It must be neutralized or else it may damage the system.

14

CHAPTER 6

ULN2003 IC

6.1 Introduction

The ULN2003 is a monolithic high voltage and high current Darlington transistor arrays. It

consists of seven NPN Darlington pairs that feature high-voltage outputs with common-

cathode clamp diode for switching inductive loads. The collector-current rating of a single

Darlington pairs 500mA. The Darlington pairs may be paralleled for higher current

capability. Applications include relay drivers, hammer drivers, lamp drivers, display drivers

(LED gas Discharge), line drivers, and logic buffers. The ULN2003 has a 2.7kW series base

resistor for each Darlington pair for operation directly with TTL or 5V CMOS devices.

Features:

• 500mA rated collector current ( Single output )

• High-voltage outputs: 50V

• Inputs compatible with various types of logic.

• Relay driver application.

15

6.2 Logical Diagram

Fig6.1: ULN2003 Logical Diagram

Fig6.2: Schematic Diagram

16

CHAPTER 7

APR 9301

7.1 Introduction

APR 9301 is a single chip Voice recorder and Play back device for 20 to 30 seconds voice

recording and play back. It is an ideal IC for automatic answering machine, door phones etc.

This IC has data storage capacity and requires no software and microcontroller. It provides

high quality voice recording and play back up to 30 seconds.

The IC requires minimum components to create a voice recorder. The IC has non volatile

flash memory technology with 100K recording cycles and 100 year message retention

capacity. The IC utilizes the Invox proprietary analog / multi level flash non volatile memory

cells that can store more than 256 voltage levels. It requires a single 5 volt supply and

operates in 25 mA current.

7.2 APR 9301 Voice Recorder Circuit

Fig7.1: Circuit Arrangement of APR.

17

7.3 Mode of operation

1.RecordMode

The LED glows when the IC records the voice obtained through the Mic. A single voice

message up to 20 seconds can be recorded. The IC remains in the recorded mode as long as

the pin 27 is grounded. Recoding will be terminated with the last memory when 20 seconds is

over. The Speaker driver will automatically mutes in the recording mode. By changing the

value of the OscR resistor R1 it is possible to increase the recording period as follows

A.R1 52K 20Sec.

B.R1 67K 24Sec

C. R1 89 K 30 Sec.

2.PlaybackMode

By pressing the play back switch, the play mode starts from the beginning of the message.

The input section will be muted during play back.

3.StandbyMode

After completing the Record or Play back function, the IC will enters into the standby mode.

4. Sampling frequency

A. 20 Sec 6.4 KHz

B. 24 Sec 5.3 KHz

C. 30 Sec 4 KHz

5. Recording

Press ,switch S1 and speak through the Mic or record music. LED will glow in the recording

mode. Open S1 after recording. Use a small condenser Mic.

6.Playback

Close S2. Recorded message will be heard from the speaker. Use a 2 inch 8 Ohms speaker.

7. Power supply 5 Volt regulated supply or 6 volt battery.

18

CHAPTER 8

DTMF DECODER

8.1 Introduction

DTMF decoder is a very easy to use program to decode DTMF dial tones found on telephone

lines with touch tone phones. DTMF decoder is also used for receiving data transmissions

over the air in amateur radio frequency bands.

The following are the frequencies used for the DTMF (dual-tone, multi-frequency) system,

which is also referred to as tone dialling. The signal is encoded as a pair of sinusoidal (sine

wave) tones from the table below which are mixed with each other. DTMF is used by most

PSTN (public switched telephone networks) systems for number dialling, and is also used for

voice-response systems such as telephone banking and sometimes over private radio networks

to provide signalling and transferring of small amounts of data.

Detect DTMF tones from tape recorders, receivers, two-way radios, etc using the built-in

microphone or direct from the phone line (via the onboard line isolation transformer). The

numbers are displayed on a 16 character, single line display as they are received. Up to 32

numbers can be displayed by scrolling the display left and right. There is also a Serial Output

for connection to a PC. All data written to the LCD is also sent to the serial output, including

the RESET and READY messages. Data is sent as standard ASCII characters. The unit will

not detect numbers dialled using pulse dialling. Circuit uses a CM8870 DTMF receiver chip

and pre-programmed microcontroller. This product is NOT a caller ID unit!

19

CHAPTER 9

CAPACITOR

9.1 Introduction

A capacitor (known as condenser) is a passive two-terminal electrical component used to

store energy in an electric field. The forms of practical capacitors vary widely, but all contain

at least two electrical conductors separated by a dielectric (insulator); for example, one

common construction consists of metal foils separated by a thin layer of insulating film.

Capacitors are widely used as parts of electrical circuits in many common electrical devices.

When there is a potential difference (voltage) across the conductors, a static electric

field develops across the dielectric, causing positive charge to collect on one plate and

negative charge on the other plate. Energy is stored in the electrostatic field. An ideal

capacitor is characterized by a single constant value, capacitance, measured in farads. This is

the ratio of the electric charge on each conductor to the potential difference between them.

The capacitance is greatest when there is a narrow separation between large areas of

conductor, hence capacitor conductors are often called plates, referring to an early means of

construction. In practice, the dielectric between the plates passes a small amount of leakage

current and also has an electric field strength limit, resulting in a breakdown voltage, while

the conductors and leads introduce an undesired inductance and resistance.

9.2 Working Principle

A capacitor consists of two conductors separated by a non-conductive region. The non-

conductive region is called the dielectric. In simpler terms, the dielectric is just an electrical

insulator. Examples of dielectric media are glass, air, paper, vacuum, and even

a semiconductor depletion region chemically identical to the conductors. A capacitor is

assumed to be self-contained and isolated, with no net electric charge and no influence from

any external electric field. The conductors thus hold equal and opposite charges on their

facing surfaces, and the dielectric develops an electric field. In SI units, a capacitance of

one farad means that one coulomb of charge on each conductor causes a voltage of

one volt across the device.

20

The capacitor is a reasonably general model for electric fields within electric circuits. An

ideal capacitor is wholly characterized by a constant capacitance C, defined as the ratio of

charge ±Q on each conductor to the voltage V between them

Fig9.1: Working of Capacitor

Sometimes charge build-up affects the capacitor mechanically, causing its capacitance to

vary. In this case, capacitance is defined in terms of incremental changes:

9.3 Capacitance instability

The capacitance of certain capacitors decreases as the component ages. In ceramic capacitors,

this is caused by degradation of the dielectric. The type of dielectric, ambient operating and

storage temperatures are the most significant aging factors, while the operating voltage has a

smaller effect. The aging process may be reversed by heating the component above the Curie

point. Aging is fastest near the beginning of life of the component, and the device stabilizes

over time. Electrolytic capacitors age as the electrolyte evaporates. In contrast with ceramic

capacitors, this occurs towards the end of life of the component.

Temperature dependence of capacitance is usually expressed in parts per million (ppm) per

°C. It can usually be taken as a broadly linear function but can be noticeably non-linear at the

21

temperature extremes. The temperature coefficient can be either positive or negative,

sometimes even amongst different samples of the same type. In other words, the spread in the

range of temperature coefficients can encompass zero. See the data sheet in the leakage

current section above for an example.

Capacitors, especially ceramic capacitors, and older designs such as paper capacitors, can

absorb sound waves resulting in a micro phonic effect. Vibration moves the plates, causing

the capacitance to vary, in turn inducing AC current. Some dielectrics also

generate piezoelectricity. The resulting interference is especially problematic in audio

applications, potentially causing feedback or unintended recording. In the reverse micro

phonic effect, the varying electric field between the capacitor plates exerts a physical force,

moving them as a speaker. This can generate audible sound, but drains energy and stresses the

dielectric and the electrolyte, if any.

9.4 Application

1. Energy Storage

A capacitor can store electric energy when disconnected from its charging circuit, so it can be

used like a temporary battery. Capacitors are commonly used in electronic devices to

maintain power supply while batteries are being changed. (This prevents loss of information

in volatile memory.)

Conventional capacitors provide less than 360 joules per kilogram of energy density, whereas

a conventional alkaline battery has a density of 590 kJ/kg.

In car audio systems, large capacitors store energy for the amplifier to use on demand. Also

for a flash tube a capacitor is used to hold the high voltage.

2. Pulsed Power and Weapons

Groups of large, specially constructed, low-inductance high-voltage capacitors (capacitor

banks) are used to supply huge pulses of current for many pulsed power applications. These

include electromagnetic forming, Marx generators, pulsed lasers (especially TEA

lasers), pulse forming networks, radar, fusion research, and particle accelerators.

Large capacitor banks (reservoir) are used as energy sources for the exploding-bridgewire

detonators or slapper detonators in nuclear weapons and other specialty weapons.

Experimental work is under way using banks of capacitors as power sources

for electromagnetic armour and electromagnetic railgunsand coil guns.

22

3. Power Conditioning

Reservoir capacitors are used in power supplies where they smooth the output of a full or half

wave rectifier. They can also be used in charge pump circuits as the energy storage element in

the generation of higher voltages than the input voltage.

Capacitors are connected in parallel with the power circuits of most electronic devices and

larger systems (such as factories) to shunt away and conceal current fluctuations from the

primary power source to provide a "clean" power supply for signal or control circuits. Audio

equipment, for example, uses several capacitors in this way, to shunt away power line hum

before it gets into the signal circuitry. The capacitors act as a local reserve for the DC power

source, and bypass AC currents from the power supply. This is used in car audio applications,

when a stiffening capacitor compensates for the inductance and resistance of the leads to

the lead-acid car battery.

4. Noise Filters

When an inductive circuit is opened, the current through the inductance collapses quickly,

creating a large voltage across the open circuit of the switch or relay. If the inductance is

large enough, the energy will generate a spark, causing the contact points to oxidize,

deteriorate, or sometimes weld together, or destroying a solid-state switch.

A snubber capacitor across the newly opened circuit creates a path for this impulse to bypass

the contact points, thereby preserving their life; these were commonly found in contact

breaker ignition systems, for instance. Similarly, in smaller scale circuits, the spark may not

be enough to damage the switch but will still radiate undesirable radio frequency

interference (RFI), which a filter capacitor absorbs. Snubber capacitors are usually employed

with a low-value resistor in series, to dissipate energy and minimize RFI. Such resistor-

capacitor combinations are available in a single package.

Capacitors are also used in parallel to interrupt units of a high-voltage circuit breaker in order

to equally distribute the voltage between these units. In this case they are called grading

capacitors.

In schematic diagrams, a capacitor used primarily for DC charge storage is often drawn

vertically in circuit diagrams with the lower, more negative, plate drawn as an arc. The

straight plate indicates the positive terminal of the device, if it is polarized (see electrolytic

capacitor).

23

5. Signal Processing

The energy stored in a capacitor can be used to represent information, either in binary form,

as in DRAMs, or in analogue form, as in analog sampled filters and CCDs. Capacitors can be

used inanalog circuits as components of integrators or more complex filters and in negative

feedback loop stabilization. Signal processing circuits also use capacitors to integrate a

current signal.

5.1 Tuned circuits

Capacitors and inductors are applied together in tuned circuits to select information in

particular frequency bands. For example, radio receivers rely on variable capacitors to tune

the station frequency. Speakers use passive analog crossovers, and analog equalizers use

capacitors to select different audio bands.

The resonant frequency f of a tuned circuit is a function of the inductance (L) and capacitance

(C) in series, and is given by:

where L is in henries and C is in farads.

5.2 Sensing

Most capacitors are designed to maintain a fixed physical structure. However, various factors

can change the structure of the capacitor, and the resulting change in capacitance can be used

to sense those factors.

5.3 Changing the Dielectric:

The effects of varying the characteristics of the dielectric can be used for sensing purposes.

Capacitors with an exposed and porous dielectric can be used to measure humidity in air.

Capacitors are used to accurately measure the fuel level in airplanes; as the fuel covers more

of a pair of plates, the circuit capacitance increases.

5.4 Changing the Distance between the Plates:

Capacitors with a flexible plate can be used to measure strain or pressure. Industrial pressure

transmitters used for process control use pressure-sensing diaphragms, which form a

capacitor plate of an oscillator circuit. Capacitors are used as the sensor in condenser

microphones, where one plate is moved by air pressure, relative to the fixed position of the

24

other plate. Some accelerometers use MEMS capacitors etched on a chip to measure the

magnitude and direction of the acceleration vector. They are used to detect changes in

acceleration, in tilt sensors, or to detect free fall, as sensors triggering airbag deployment, and

in many other applications. Some fingerprint sensors use capacitors. Additionally, a user can

adjust the pitch of a musical instrument by moving his hand since this changes the effective

capacitance between the user's hand and the antenna.

25

CHAPTER 10

TRANSFORMER

10.1 Introduction

A transformer is a power converter that transfers electrical energy from one circuit to another

through inductively coupled conductors—the transformer's coils. A varying current in the

first or primary winding creates a varying magnetic flux in the transformer's core and thus a

varying magnetic field through the secondary winding. This varying magnetic field induces a

varying electromotive force (EMF), or "voltage", in the secondary winding. This effect is

called inductive coupling.

If a load is connected to the secondary winding, current will flow in this winding, and

electrical energy will be transferred from the primary circuit through the transformer to the

load. In an ideal transformer, the induced voltage in the secondary winding (Vs) is in

proportion to the primary voltage (VP) and is given by the ratio of the number of turns in the

secondary (Ns) to the number of turns in the primary (Np) as follows:

10.2 Working Principle

The transformer is based on two principles: first, that an electric current can produce

a magnetic field (electromagnetism) and second that a changing magnetic field within a coil

of wire induces a voltage across the ends of the coil (electromagnetic induction). Changing

the current in the primary coil changes the magnetic flux that is developed. The changing

magnetic flux induces a voltage in the secondary coil.

An ideal transformer is shown in the adjacent figure. Current passing through the primary coil

creates a magnetic field. The primary and secondary coils are wrapped around a core of very

high magnetic permeability, such as iron, so that most of the magnetic flux passes through

both the primary and secondary coils. If a load is connected to the secondary winding, the

load current and voltage will be in the directions indicated, given the primary current and

voltage.

26

CHAPTER 11

RESISTOR

11.1 Introduction

A resistor is a passive two terminal electrical component that implements electrical resistance

as a circuit element.

The current through a resistor is in direct proportion to the voltage across the resistor's

terminals. This relationship is represented by Ohm's law:

where I is the current through the conductor in units of amperes, V is the potential difference

measured across the conductor in units of volts, and R is the resistance of the conductor in

units of ohms.

The ratio of the voltage applied across a resistor's terminals to the intensity of current in the

circuit is called its resistance, and this can be assumed to be a constant (independent of the

voltage) for ordinary resistors working within their ratings.

Resistors are common elements of electrical networks and electronic circuits and are

ubiquitous in electronic equipment. Practical resistors can be made of various compounds and

films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel-

chrome). Resistors are also implemented within integrated circuits, particularly analog

devices, and can also be integrated into hybrid and printed circuits.

Unit

The ohm (symbol: Ω) is the SI unit of electrical resistance, named after Georg Simon Ohm.

An ohm is equivalent to a volt per ampere

11.2 Measurement

The value of a resistor can be measured with an ohmmeter, which may be one function of

a millimetre. Usually, probes on the ends of test leads connect to the resistor. A simple

ohmmeter may apply a voltage from a battery across the unknown resistor (with an internal

resistor of a known value in series) producing a current which drives a meter movement. The

current, in accordance with Ohm's Law, is inversely proportional to the sum of the internal

resistance and the resistor being tested, resulting in an analog meter scale which is very non-

linear, calibrated from infinity to 0 ohms. A digital millimetre, using active electronics, may

instead pass a specified current through the test resistance. The voltage generated across the

27

test resistance in that case is linearly proportional to its resistance, which is measured and

displayed. In either case the low-resistance ranges of the meter pass much more current

through the test leads than do high-resistance ranges, in order for the voltages present to be at

reasonable levels (generally below 10 volts) but still measurable.

Measuring low-value resistors, such as fractional-ohm resistors, with acceptable accuracy

requires four-terminal connections. One pair of terminals applies a known, calibrated current

to the resistor, while the other pair senses the voltage drop across the resistor. Some

laboratory quality ohmmeters, especially milli ohmmeters, and even some of the better digital

millimetres sense using four input terminals for this purpose, which may be used with special

test leads. Each of the two so-called Kelvin clips has a pair of jaws insulated from each other.

One side of each clip applies the measuring current, while the other connections are only to

sense the voltage drop. The resistance is again calculated using Ohm's Law as the measured

voltage divided by the applied current.

11.3 Production Resistors

Resistor characteristics are quantified and reported using various national standards. In the

US, MIL-STD-202 contains the relevant test methods to which other standards refer.

There are various standards specifying properties of resistors for use in equipment:

BS 1852

EIA-RS-279

MIL-PRF-26

MIL-PRF-39007 (Fixed Power, established reliability)

MIL-PRF-55342 (Surface-mount thick and thin film)

MIL-PRF-914

MIL-R-11 STANDARD CANCELED

MIL-R-39017 (Fixed, General Purpose, Established Reliability)

MIL-PRF-32159 (zero ohm jumpers)

There are other United States military procurement MIL-R- standards.

28

CHAPTER 12

MICROPHONE

12.1 Introduction

A microphone (colloquially called a mic or mike; both pronounced /ˈmaɪk/)[1]

is an acoustic-

to-electric transducer or sensor that converts sound into an electrical. Microphones are used in

many applications such as telephones, tape recorders, karaoke systems, hearing aids, motion

picture production, live and recorded audio engineering, FRS radios, megaphones,

in radio and television broadcasting and in computers for recording voice, speech

recognition, VoIP, and for non-acoustic purposes such as ultrasonic checking or knock

sensors.

12.2 Components

The sensitive transducer element of a microphone is called its element or capsule. A complete

microphone also includes a housing, some means of bringing the signal from the element to

other equipment, and often an electronic circuit to adapt the output of the capsule to the

equipment being driven. A wireless microphone contains a radio transmitter.

12.3 Variety

Microphones are referred to by their transducer principle, such as condenser, dynamic, etc.,

and by their directional characteristics. Sometimes other characteristics such as diaphragm

size, intended use or orientation of the principal sound input to the principal axis (end- or

side-address) of the microphone are used to describe the microphone.

12.4 Condenser Microphone

The condenser microphone, invented at Bell Labs in 1916 by E. C. Wente is also called

a capacitor microphone or electrostatic microphone capacitors were historically called

condensers. Here, the diaphragm acts as one plate of a capacitor, and the vibrations produce

changes in the distance between the plates. There are two types, depending on the method of

extracting the audio signal from the transducer: DC-biased microphones, and radio frequency

(RF) or high frequency (HF) condenser microphones. With a DC-biased microphone, the

plates are biased with a fixed charge (Q). The voltage maintained across the capacitor plates

changes with the vibrations in the air, according to the capacitance equation (C = Q⁄V), where

Q = charge in coulombs, C = capacitance in farads and V = potential difference in volts. The

capacitance of the plates is inversely proportional to the distance between them for a parallel-

29

plate capacitor. (See capacitance for details.) The assembly of fixed and movable plates is

called an "element" or "capsule".

12.5 Electret Condenser Microphone

An electret microphone is a type of capacitor microphone invented by Gerhard

Sesser and Jim West at Bell laboratories in 1962. [3]

The externally applied charge described

above under condenser microphones is replaced by a permanent charge in an electret

material. An electret is a ferro electric material that has been permanently electrically

charged or polarized. The name comes from electrostatic and magnet; a static charge is

embedded in an electret by alignment of the static charges in the material, much the way a

magnet is made by aligning the magnetic domains in a piece of iron.

12.6 Dynamic Microphone

Dynamic microphones work via electromagnetic induction. They are robust, relatively

inexpensive and resistant to moisture. This, coupled with their potentially high gain before

feedback, makes them ideal for on-stage use.

Moving-coil microphones use the same dynamic principle as in a loudspeaker, only reversed.

A small movable induction coil, positioned in the magnetic field of a permanent magnet, is

attached to the diaphragm. When sound enters through the windscreen of the microphone, the

sound wave moves the diaphragm. When the diaphragm vibrates, the coil moves in the

magnetic field, producing a varying current in the coil through electromagnetic induction. A

single dynamic membrane does not respond linearly to all audio frequencies.

12.7 Ribbon Microphone

Ribbon microphones use a thin, usually corrugated metal ribbon suspended in a magnetic

field. The ribbon is electrically connected to the microphone's output, and its vibration within

the magnetic field generates the electrical signal. Ribbon microphones are similar to moving

coil microphones in the sense that both produce sound by means of magnetic induction. Basic

ribbon microphones detect sound in a bi-directional pattern because the ribbon, which is

open to sound both front and back, responds to the pressure gradient rather than the sound

pressure. Though the symmetrical front and rear pickup can be a nuisance in normal stereo

recording, the high side rejection can be used to advantage by positioning a ribbon

microphone horizontally, for example above cymbals, so that the rear lobe picks up only

sound from the cymbals.

30

12.8 Speakers as Microphones:

A loudspeaker, a transducer that turns an electrical signal into sound waves, is the functional

opposite of a microphone. Since a conventional speaker is constructed much like a dynamic

microphone (with a diaphragm, coil and magnet), speakers can actually work "in reverse" as

microphones. The result, though, is a microphone with poor quality, limited frequency

response (particularly at the high end), and poor sensitivity.

31

CHAPTER 13

CRYSTAL OSCILLATOR

13.1 Introduction

A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a

vibrating crystal of piezoelectric material to create an electrical signal with a very

precise frequency. This frequency is commonly used to keep track of time (as in quartz

wristwatches), to provide a stable clock for digital integrated circuits, and to stabilize

frequencies for radio transmitters and receivers. The most common type of piezoelectric

resonator used is the quartz crystal, but other piezoelectric materials including polycrystalline

ceramics are used in similar circuits.

Quartz crystals are manufactured for frequencies from a few tens of kilohertz to tens of

megahertz. More than two billion crystals are manufactured annually. Most are used for

consumer devices such as wristwatches, clocks, radios, computers, and cell phones. Quartz

crystals are also found inside test and measurement equipment, such as counters, signal

generators, and oscilloscopes.

13.2 Operation

When a crystal of quartz is properly cut and mounted, it can be made to distort in an electric

field by applying a voltage to an electrode near or on the crystal. This property is known

as piezoelectricity. When the field is removed, the quartz will generate an electric field as it

returns to its previous shape, and this can generate a voltage. The result is that a quartz crystal

behaves like a circuit composed of an inductor, capacitor and resistor, with a precise resonant

frequency.

Quartz has the further advantage that its elastic constants and its size change in such a way

that the frequency dependence on temperature can be very low. The specific characteristics

will depend on the mode of vibration and the angle at which the quartz is cut (relative to its

crystallographic axes). Therefore, the resonant frequency of the plate, which depends on its

size, will not change much, either. This means that a quartz clock, filter or oscillator will

remain accurate. For critical applications the quartz oscillator is mounted in a temperature-

controlled container, called a crystal oven, and can also be mounted on shock absorbers to

prevent perturbation by external mechanical vibrations.

32

13.3 Crystal oscillator types and their abbreviations

ATCXO — Analog temperature controlled crystal oscillator

CDXO — Calibrated dual crystal oscillator

DTCXO — Digital temperature compensated crystal oscillator

EMXO — Evacuated miniature crystal oscillator

GPSDO — Global positioning system disciplined oscillator

MCXO — Microcomputer-compensated crystal oscillator

OCVCXO — oven-controlled voltage-controlled crystal oscillator

OCXO — Oven-controlled crystal oscillator

RbXO — Rubidium crystal oscillators (RbXO), a crystal oscillator (can be an MCXO)

synchronized with a built-in rubidium standard which is run only occasionally to save

power

TCVCXO — Temperature-compensated voltage-controlled crystal oscillator

TCXO — Temperature-compensated crystal oscillator

TMXO – Tactical miniature crystal oscillator[60]

TSXO — Temperature-sensing crystal oscillator, an adaptation of the TCXO

VCTCXO — Voltage-controlled temperature-compensated crystal oscillator

VCXO — Voltage-controlled crystal oscillator

33

CHAPTER 14

CIRCUIT ARRANGEMENT

14.1 Working

Fig14.1: Circuit Diagram

34

There is a circuit contains AT89C2051 micro- controller with its all basic components. For

power supply to provide 5V, the circuit consists of step down transformer of 230/12V. This

transformer steps down 230V AC from main supply to 12V AC. Then that 12V AC is

converted into 12V DC with the help of bridge rectifier. After that a 1000/25V capacitor is

used to filter the ripples and then it passes through voltage regulator 7805 which regulates it

to 5V.

Micro- controller AT89C51 is at heart of circuit. It is high performance, low power, 8 bit

micro- controller with 4 KB of flash programmable and erasable read only memory used as

on- chip program memory. An 11.0592MHz crystal oscillator is used to provide basic clock

frequency for micro- controller. A push to on switch connected between pin no. 9 of

controller and Vcc is used for manual reset of circuit.

The DTMF (Dual-tone multi-frequency) decode MT8870 is connected to port 1 of micro-

controller. It is used for decoding the mobile signal. It gets DTMF tone from the mobile

headphone and decodes it into 4 bit digital signal. There are four relays connected to the

ULN2003 IC to control four appliances or any load. These loads are connected to the relay.

DTMF decoder IC gets signal to ON or OFF any appliances it process it to micro- controller

and after then micro controller controls that appliance according to instruction.

An APR IC is connected to the port 0 of micro– controller. It is a playback and recording IC

which receives voice from a MIC connecting to it and records it. It also plays that recorded

sound when get signal from micro- controller to play it. There is a speaker connected to this

APR to play the sound. This is used for voice acknowledgement.

35

CHAPTER 15

SOFTWARE DEVELOPMENT

15.1 Software Introduction

The software for our project was developed using a simple high level language tool in C. The

software extracts the sent DTMF signal from the SIM location at a regular interval and

processes it to control the different appliances connected within the interface. We have made

use of the two cell phones along with a head phone. The DTMF signal through the keypad of

remote cell phone are send to the designated cell phone at the system. Which are then send to

the DTMF decoder through the head phone. The decoder decodes the signal and then send

them to the micro controller.

15.2 Algorithm

Step 1: Start

Step 2: Phone initialization

Step 3: Get Hardware Software

Step 4: Make a call from mobile phone

Step 5: If new call received go to step3 else, go to step1

Step 6: Receive DTMF signal

Step 7: Check DTMF signal

Step 8: Control the device based on status

Step 9: Notify user via voice acknowledgement through APR IC.

Step 10: Go to step1

15.3 Coding

Line I Address Code Source

1: B 00B3 RELAY1 EQU P3.3

2: B 00B4 RELAY2 EQU P3.4

3: B 00B5 RELAY3 EQU P3.5

4: B 00B6 RELAY4 EQU P3.6

5: B 0080 M1 EQU P0.0

36

6: B 0081 M2 EQU P0.1

7: B 0082 M3 EQU P0.2

8: B 0083 M4 EQU P0.3

9: B 0084 M5 EQU P0.4

10: B 0085 M6 EQU P0.5

11: B 0086 M7 EQU P0.6

12: B 0087 M8 EQU P0.7

13: N 0000 ORG 00H

14: 0000 75 B0 00 MOV P3,#00H

15: 0003 80 00 SJMP CH0

16: 0005 E5 90 CH0:MOV A,P1

17: 0007 B4 F8 08 CJNE A,#0F8H,CH1

18: 000A 11 7B ACALL DELAYMS

19: 000C 11 6C ACALL DELAY

20: 000E C2 80 CLR M1

21: 0010 11 6C ACALL DELAY

22: 0012 E5 90 CH1:MOV A,P1

23: 0014 B4 F4 0C CJNE A,#0F4H,CH2

24: 0017 11 7B ACALL DELAYMS

25: 0019 D2 B4 SETB RELAY2

26: 001B 11 6C ACALL DELAY

27: 001D 11 6C ACALL DELAY

28: 001F C2 81 CLR M2

29: 0021 11 6C ACALL DELAY

30: 0023 E5 90 CH2: MOV A,P1

31: 0025 B4 FC 0C CJNE A,#0FCH,CH3

32: 0028 11 7B ACALL DELAYMS

33: 002A D2 B5 SETB RELAY3

34: 002C 11 6C ACALL DELAY

35: 002E 11 6C ACALL DELAY

36: 0030 C2 82 CLR M3

37: 0032 11 6C ACALL DELAY

38: 0034 E5 90 CH3: MOV A,P1

39: 0036 B4 F2 0C CJNE A,#0F2H,CH4

37

40: 0039 11 7B ACALL DELAYMS

41: 003B D2 B6 SETB RELAY4

42: 003D 11 6C ACALL DELAY

43: 003F 11 6C ACALL DELAY

44: 0041 C2 83 CLR M4

45: 0043 11 6C ACALL DELAY

46: 0045 E5 90 CH4: MOV A,P1

47: 0047 B4 FA 0D CJNE A,#0FAH,CH5

48: 004A 11 7B ACALL DELAYMS

49: 004C 75 B0 00 MOV P3,#00H

50: 004F 11 6C ACALL DELAY

51: 0051 11 6C ACALL DELAY

52: 0053 C2 84 CLR M5

53: 0055 11 6C ACALL DELAY

54: 0057 E5 90 CH5: MOV A,P1

55: 0059 B4 F6 0D CJNE A,#0F6H,CH6

56: 005C 11 7B ACALL DELAYMS

57: 005E 75 B0 FF MOV P3,#0FFH

58: 0061 11 6C ACALL DELAY

59: 0063 11 6C ACALL DELAY

60: 0065 C2 85 CLR M6

61: 0067 11 6C ACALL DELAY

62: 0069 02 00 05 CH6: LJMP CH0

63: 006C 11 01 DELAY:

64: 006C 7E 00 MOV R6, #00H

65: 006E 7D 04 MOV R5, #04H

66: 0070 13 02 LOOPB:

67: 0070 0E 0A INC R6

68: 0071 11 7B ACALL DELAYMS

69: 0073 EE B0FF MOV A, R6

70: 0074 70 FA JNZ LOOPB

71: 0076 1D 11 DEC R5

72: 0077 ED 2A MOV A, R5

73: 0078 70 F6 JNZ LOOPB

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74: 007A 22 F6 RET

75: 007B 11 A2 DELAYMS:

76: 007B 7F 00 MOV R7,#00H

77: 007D LOOPA:

78: 007D 0F INC R7

79: 007E EF MOV A,R7

80: 007F B4 FF FB CJNE A,#0FFH,LOOPA

81: 0082 22 RET

82: END

39

CONCLUSION

The project we have undertaken has helped us gain a better perspective on various aspects

related to our course of study as well as practical knowledge of electronic equipments and

communication. We became familiar with software analysis, designing, implementation,

testing and maintenance concerned with our project.

The extensive capabilities of this system are what make it so interesting. From the

convenience of a simple cell phone, a user is able to control and monitor virtually any

electrical devices. This makes it possible for users to rest assured that their belongings are

secure and that the television and other electrical appliances was not left running when they

left the house to just list a few of the many uses of this system.

The end product will have a simplistic design making it easy for users to interact with. This

will be essential because of the wide range of technical knowledge that homeowners have.

40

REFRENCES

Mazidi, Muhammad Ali, The 8051 Microcontroller and Embedded Systems,Second

Edition, Prentice Hall, 2007.

Renato Jorge Caleria Nunes, ―Decentralized Supervision for Home Automation‖,

IEEE MELCON 2006, May 16-19, Page(s):785-788.

http://www.thaieei.com/embedded/pdf/Automation/20022.pdf

http://www.bmf.hu/conferences/saci2006/Ciubotaru.pdf