skks.pdf

A Mini Project Report on

IMPLEMENTATION OF MOBILE CONTROLLED HOME APPLIANCES USING DTMF

TECHNIQUE

Submitted in partial fulfillment of the requirement for the award of degree of

BACHELOR OF TECHNOLOGY In

ELECTRONICS AND COMMUNICATION ENGINEERING

Submitted by

Mr.T.Ratnachaitanya - 12FE1A04A0

Ms.ShaikShahina - 12FE1A0494

Mr.P.Aashish - 12FE1A0480

Mr. K.V.Vamsi Krishna - 12FE1A0466

Under the Esteemed Guidance of

Mr. B.HarishM.Tech, (Ph.D.)

Assistant Professor

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

VIGNAN’S LARA INSTITUTE OF TECHNOLOGY & SCIENCE (An ISO 9001:2008 Certified, Approved by AICTE, Affiliated to JNTU, KAKINADA)

VADLAMUDI-522213, GUNTUR Dist., ANDHRA PRADESH.

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DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

VIGNAN’S LARA INSTITUTE OF TECHNOLOGY & SCIENCE (An ISO 9001:2008 Certified, Approved by AICTE, Affiliated to JNTU, KAKINADA)

VADLAMUDI-522213, GUNTUR Dist., ANDHRA PRADESH.

CERTIFICATE

This is to certify that the project work entitled “IMPLEMENTATION OF MOBILE CONTROL OF HOME APPLIANCES USING DTMF TECHNIQUE” is a bonafide work done by Mr.T.RatnaChaitanya (12FE1A04A0), Ms.Shaik Shahina (12FE1A0494),Mr.P.Aashish(12FE1A0480),Mr.K.V.VamsiKrishna(12FE1A0466), under my guidance and submitted in partial fulfillment of the requirements for the award of the degree of Bachelor of Technology in Electronics and Communication Engineering by Jawaharlal Nehru Technological University, Kakinada.

Project Guide Head of the Department (Mr. B.Harish) (Mr. U.SRINIVASA RAO)

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ACKNOWLEDGEMENT We are grateful to the Department of Electronics and Communication Engineering,

VIGNAN’S LARA INSTITUTE OF TECHNOLOGY & SCIENCE, which gives us an

opportunity to have profound technical knowledge there by enabling us to complete the project.

We would like to thank our beloved principal Dr. PHANEENDRA KUMARPh.D,for

providing a great support for us in completing our project and for giving us the opportunity of

doing the project.

We feel elated to thank Mr. U.SRINIVASA RAOM.Tech(Ph.D) Associate Professor and

our Head of the Department, for inspiring us all the way and arranging all the facilities and

resources needed for our project.

It is with immense pleasure that we would like to express our indebted gratitude to our

guide Mr.B.HarishM.Tech,(Ph.D).Who guided us a lot and encouraged us in every step of our

project work. His invaluable moral support and guidance through the project helped us to a greater

extent. We are thankful to him for his valuable suggestions and discussions during this project.

We express our hearty thanks to all the staff members and non-teaching staff for all their

help and co-operation extended in bringing out this project successfully in time.

Project Associates

Mr.T.Ratnachaitanya

Ms.ShaikShahina

Mr.P.Aashish

Mr. K.V.Vamsi Krishna

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Abstract:- Sometimes unfortunately user may forget switch off the appliances while going to the outside and

many face the problems to switch off these devices when users are out of home to solve these type

of problems a simple circuit which will on the devices remotely and devices will off a The main

principle used in this circuit is DTMF communication. DTMF is acronym for dual-tone multi-

frequency when you make a call to customer care service they will ask you to press the numbers

to provide the appropriate services if you think about how they are recognizing the pressed number

then DTMF comes on the picture .if you press the button in your mobile phone then a tone is

generated with two frequencies. These two frequencies of the tone are row and column frequencies

of that particular button 1 then a tone generated with the sum of 697Hz and 1209Hz.

These generated forces are decoded at switching Centre to determine which button is pressed .

Now using these DTMF forces to control the devices from remote area. To decode these DTMF

forces at receiver it required to use a DTMF decoder. Decoder IC converts these forces into digital

form. The D-Flip Flop which is connected at the output of the decoder controls the acts as a switch

.when a pulse arrives at the D-Flip Flop the flip flop changes it present state . The output of the

flip is generally connected to the appliance end.

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INDEX

Chapter- 1

Overview Of Project

1.1 Introduction 8

1.2 System Overview 9

1.3 The system features 10

Chapter-2

Operational Description

2.1 Block Diagram 11

2.2 Circuit Diagram 12

Chapter-3

Dual-Tone Multi-Frequency Signalling

3.1 Introduction 14

3.2 MT8870 Decoder 23

3.3 D Flip Flop 25

Chapter-4

4.1 introduction to embedded systems 26

4.2 Description of Components 31

Chapter-5

5.1 Output 33

5.2 Results & Discussion 34

5.3 Conclusions& Future work 35

5.4 References 36

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List of figures & Tables

Figure no. Figure Name Page No

1.1 Home automation system 7

2.1 Block Diagram 11

2.2 Circuit Diagram 12

3.1 Signalling Tone 13

3.2 DTMF Keypad 14

3.3 Pin Diagram (MT8870) 15

3.4 Basic Steering Circuit 18

3.5 Flow Chart of Goertzel Algorithm 22

3.6 D-Flip Flop 24

3.7 Pin diagram of IC7474 24

4.1 BC547 Transistor 27

4.2 Operation of Relay 28

4.3 Relays 28

4.4 LED & LED Symbol 30

5.1 Practical Project Circuit photo 33

5.2 Practical Project Circuit Photo (output) 34

Tables 3.1 DTMF Frequencies 19

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Chapter-1 1.1 Introduction: Embedded system is an interesting field where every engineer can showcase his creative and

technical skills. Mobile phones today became an essential entity for one and all and so, for any

mobile based application there is great reception. In this scenario making a mobile phone operated

home appliance control system is a good idea.

The remote control used in home automation systems, is a wonderful feature that

everyone would like to enjoy, if they were not expensive to install, maintain, and able to be

used from long distance. The idea of the remotely controlled home automation systems is

shown in Figure 1.1.

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The home automation have many features makes the homeowner remotely toggle

appliances such as air conditioning and heating units, lamps or porch lights, landscape

sprinkler timers, snow-melt systems, outdoor property lighting, and safety lighting.

The mobile phones and Touch-Tone telephones use the Dual-Tone Multi Frequency

(DTMF). That was developed initially for telephony signalling such as dialling and

automatic redial. Each key-press on the phone keypad generates DTMF signal consists of

two tones that must be generated simultaneously.

1.2 System Overview In this project the appliances are controlled by a mobile phone that makes a call to the mobile

phone attached to the a control box which is connected to appliances needed to be control from

outside home or when user’s need not to go near to appliance for turning on the switch, just press

key from your mobile and the switch is on.

In the course of a call, if any button is pressed a tone corresponding to the button pressed

is heard at the other end called ‘Dual Tone Multiple frequency’ (DTMF) .The control box receives

these tones with help of phone stacked in the box

The received tone is processed by the D-Flip Flop with the help of DTMF decoder IC

MT8870.Conventionally, wireless controlled appliances use RF circuits, which have the

drawbacks of limited working range, limited frequency range and limited control. Use of mobile

phone for robotic control can overcome these limitations. It provides the advantage of robust

control, working range as large as the coverage area of the service provide. This Project “DTMF

based home appliance control using D-Flip Flop” is used to control the devices in home as well as

in industries.

Dual-tone multi-frequency signalling (DTMF) is used for telecommunication signalling over

analog telephone lines in the voice-frequency band between telephone handsets and other

communications devices and the switching centre. The version of DTMF that is used in telephones

for tone dialling is known as Touch-Tone.

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The relay takes advantage of the fact that when electricity flows through a coil, it becomes an

electromagnet. The electromagnetic coil attracts a steel plate, which is attached to a switch. So the

switch's motion (ON and OFF) is controlled by the current flowing to the coil, or not, respectively.

A very useful feature of a relay is that it can be used to electrically isolate different parts of a

circuit. It will allow a low voltage circuit (e.g. 5VDC) to switch the power in a high voltage circuit

(e.g. 100 VAC or more). The relay operates mechanically, so it cannot operate at high speed

BC547 is an NPN bi-polar junction transistor. A transistor, stands for transfer of resistance, is

commonly used to amplify current. A small current at its base controls a larger current at collector

& emitter terminals. BC547 is mainly used for amplification and switching purposes. It has a

maximum current gain of 800. Its equivalent transistors are BC548 and BC549.

The transistor terminals require a fixed DC voltage to operate in the desired region of its

characteristic curves. This is known as the biasing. For amplification applications, the transistor is

biased such that it is partly on for all input conditions. The input signal at base is amplified and

taken at the emitter. BC547 is used in common emitter configuration amplifiers. The voltage

divider is the commonly used biasing mode. For switching applications, transistor is biased so that

it remains fully on if there is a signal at its base. In the absence of base Signal, it gets completely

off.

LED falls within the family of P-N junction devices. The light emitting diode (LED) is a

diode that will give off visible light when it is energized. In any forward biased P-N junction there

is, with in the structure and primarily close to the junction, a recombination of hole and electrons.

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1.3 The System Features

This system can control devices that may be any electric or electronic appliances, and each

device is given a unique code.

There is no risk for false switching, it makes accurate switching any false switch in the

device are not done.

This system doesn’t cost a lot of money, and it’s easy to implement. Before changing the

state of the device user can confirm the present status of the device.

The system gives an acknowledgement tone after switching on the devices to confirm the

status of the devices.

This system can be controlled by multi users, this feature refer to user choice.

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Chapter-2

OPERATIONAL DESCRIPTION 2.1 Block Diagram:

Fig2.1 block diagram

First input are giving the input DTMF signal to the decoder via audio jockey. Audio jockey

is nothing but the connector between the phone through which DTMF keypad and the phone

connecting to the kit

The MT8870D/MT8870D-1 monolithic DTMF receiver offers small size, low power consumption

and high performance.When user press keys in our cell Phone when call is in progress, the other

person will hear some tones with respect to keys pressed. Data is transmitted in terms of pair of

tones. The receiver detects the valid frequency pair and gives the appropriate BCD code as the

output of the DTMF decoder IC.DTMF signal can be tapped directly from the microphone pin of

cell phone device. The signals from the microphone wire are processed by the DTMF decoder IC

which generates the equivalent binary sequence as a parallel output as Q1, Q2, Q3, and Q4.Finally

it is given to load that is any electric or electronic appliance to control it.

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2.2 Circuit Diagram

Fig2.2 circuit diagram

In this circuit diagram first an input DTMF signal from phone to the decoder is given. Here RC

filter reduces the noise and allows the desired frequency. The signals from the microphone wire

are processed by the DTMF decoder IC which generates the equivalent binary sequence as a

parallel output as Q1, Q2, Q3, and Q4.

Here transistor acts as a switch.BC547 is an NPN bi-polar junction transistor. A transistor,

stands for transfer of resistance, is commonly used to amplify current. A small current at its base

controls a larger current at collector & emitter terminals. BC547 is mainly used for amplification

and switching purposes. It has a maximum current gain of 800

Finally it is given to the relay. It acts as a switch. It takes low input and get the high output. And

it is given to the load that is electronic or electric appliance that to control.

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Chapter-3

Dual-tone multi-frequency signaling: Dual-tone multi-frequency signaling (DTMF) is used for telecommunication

signaling over analog telephone lines in the voice-frequency band between telephone handsets and

other communications devices and the switching center. The version of DTMF that is used in push-

button telephones for tone dialing is known as Touch-Tone. It was developed by Western

Electric and first used by the Bell System in commerce, using that name as a registered trademark.

DTMF is standardized by ITU-T Recommendation Q.23. It is also known in the UK as MF4.

Other multi-frequency systems are used for internal signaling within the telephone

network.

Introduced by AT&T in 1963, the Touch-Tone system using the telephone

keypad gradually replaced the use of rotary dial and has become the industry standard for

landline service.

Fig3.1: signaling tones

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Keypad:

1209 Hz 1336 Hz 1477 Hz

697 Hz 1 2 3

770 Hz 4 5 6

852 Hz 7 8 9

941 Hz * 0 #

Fig.3.2: DTMF keypad

1209 Hz on 697 Hz to make the 1 tone

The DTMF keypad is laid out in a 4×4 matrix in which each row represents

a low frequency and each column represents a high frequency.

Any key sends a sinusoidal tone for each of the two frequencies. For example, the key 1

produces a superposition of tones of 697 and 1209 hertz (Hz).

Initial pushbutton designs employed levers, so that each button activated two contacts.

The tones are decoded by the switching centre to determine the keys pressed by the user

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3.1 DTMF DECODER (MT8870) :

Pin diagram:

Fig 3.3 pin diagram of DTMF decoder (MT 8870)

Pin Description:

1. IN+ Non-Inverting Op-Amp (Input).

2. IN- Inverting Op-Amp (Input).

3. GS Gain Select. Gives access to output of front end differential amplifier for connection of feedback resistor.

4. V-Ref Reference Voltage (Output). Nominally VDD/2 is used to bias inputs at mid-rail .

5. INH Inhibit (Input). Logic high inhibits the detection of tones representing characters A, B, C and D. This pin input is internally pulled down.

6. PWDN Power Down (Input). Active high. Powers down the device and inhibits the oscillator. This pin input is internally pulled down.

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7. OSC1 Clock (Input). 8. OSC2 Clock (Output). A 3.579545 MHz crystal connected between pins OSC1 and OSC2

9. VSS Ground (Input). 0 V typical.

10. TOE Three State Output Enable (Input). Logic high enables the outputs Q1-Q4. This pin

is pulled up internally.

11-14. Q1-Q4 Three State Data (Output). When enabled by TOE, provide the code

corresponding to the last valid tone-pair received (see Table 1). When TOE is logic low, the data

outputs are high impedance.

15. StD Delayed Steering (Output).Presents a logic high when a received tone-pair has been

registered and the output latch updated; returns to logic low when the voltage on St/GT falls below

VTSt.

16. ESt Early Steering (Output). Presents a logic high once the digital algorithm has detected

a valid tone pair (signal condition). Any momentary loss of signal condition will cause ESt to

return to a logic low.

17. St/GT Steering Input/Guard time (Output) Bidirectional. A voltage greater than VTSt

detected at St causes the device to register the detected tone pair and update the output latch. A

voltage less than VTSt frees the device to accept a new tone pair. The GT output acts to reset the

external steering time-constant; its state is a function of ESt and the voltage on St.

18. VDD Positive power supply (Input). +5 V typical.

Functional Description:

The MT8870D/MT8870D-1 monolithic DTMF receiver offers small size, low power

consumption and high performance. Its architecture consists of a

Band split filter section, which separates the high and low group tones, followed by a digital

counting section which verifies the frequency and duration of the received tones before passing

the corresponding code to the output bus.

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Filter Section

Separation of the low-group and high group tones is achieved by applying the DTMF signal

to the inputs of two sixth-order switched capacitor band pass

filters, the bandwidths of which correspond to the low and high group frequencies. The filter

section also incorporates notches at 350 and 440 HZ for exceptional dial tone rejection (see figure

3). Each filter output is followed by single order switched capacitor filter which smooth’s the

signal prior to the limiting .limiting is performed by gain comparators which are provided by

hysteresis to prevent the direction of the unwanted low level signals. The outputs of comparators

provide full rail logic swings at the frequencies of the incoming DTMF signals.

Decoder Section

Following the filter section is a decoder employing digital counting techniques to

determine the frequencies of the incoming tones and to verify that they correspond to standard

DTMF frequencies. A complex averaging algorithm protects against tone simulation by extraneous

signals such as voice while Figure 7- Basic Steering Circuit providing tolerance to small

frequency deviation sand variations.

Any subsequent loss of signal condition will cause ESt to assume an inactive state (see

“Steering Circuit”). Steering Circuit Before registration of a decoded tone pair, the receiver

checks for a valid signal duration (referred to as character recognition condition).

This check is performed by an external RC time constant driven by ESt. A logic high on

ESt causes vc (see Figure 4) to rise as the capacitor discharges. Provided signal

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Fig3.4: basic steering circuit condition is maintained (ESt remains high) for the validation period (tGTP), vc reaches the

threshold (VTSt) of the steering logic to register the tone pair,

latching its corresponding 4-bit code (see Table 1) into the output latch. At this point the GT output

is activated and drives vc to VDD.

GT continues to drive high as long as ESt remains high. Finally, after a short delay to

allow the output latch to settle, the delayed steering output flag (StD) goes high, signalling that a

received tone pair has been registered. The contents of the output latch are made available on the

4-bit output bus by raising the three state control input (TOE) to a logic high.

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Description

The MT8870D/MT8870D-1 is a complete DTMF receiver integrating both the band -split

filter and digital decoder functions. The filter section uses switched capacitor techniques for high

and low group filters; the decoder uses digital counting techniques to detect and decode all 16

DTMF tone-pairs into a 4-bit code. External component count is minimized by on chip provision

of a differential input amplifier, clock oscillator and latched three-state bus interface.

DTMF Detection Methods

The scheme used to identify the two frequencies associated with the button that has been

pressed. Here, the two tones are first separated by a low pass and a

high pass filter. The pass band cut off frequency of the low pass filter is slightly above 100

Table 3.1 DTMF Frequencies

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Hz, whereas that of the high pass filter is slightly below 1200 Hz. The output of each filter

Is next converted into a square wave by a limiter and then processed by a bank of band pass

Filters with narrow pass bands. The four band pass filters in the low-frequency channel have

Centre frequencies at 697 Hz, 770 Hz, 852 Hz, and 941 Hz. The four band pass filters in

the high-frequency channel have centre frequencies at 1209 Hz, 1336 Hz, 1477 Hz, and

1633 Hz. The detector following each band pass filter develops the necessary dc switching

Signal if its input voltage is above a certain threshold.

Magnitude test: According to ITU Q.24, the maximum signal level transmit to the public network

shall not exceed −9 dBm. This limits an average voice range of −35 dBm for a very weak long-

distance call to −10 dBm for a local call. A DTMF receiver is expected to operate at an average

range of −29 to +1 dBm. Thus, the largest magnitude in each band must be greater than a threshold

of −29 dBm; otherwise, the DTMF signal should not be detected.

Twist test: The tones may be attenuated according to the telephone system’s gains at the

tonal frequencies. Therefore, It is not expect the received tones to have same

amplitude, even though they may be transmitted with the same strength. Twist is

defined as the difference, in decibels, between the low and high-frequency tone levels.

Frequency-offset test: This test prevents some broadband signals from being detected as DTMF

tones. If the effective DTMF tones are present, the power levels at those two frequencies should

be much higher than the power levels at the other frequencies. To perform this test, the largest

magnitude in each group is compared to the magnitudes of other frequencies in that group. The

difference must be greater than the predetermined threshold in each group.

Total-energy test: Similar to the frequency-offset test, the goal of total-energy test is to

reject some broadband signals to further improve the robustness of a DTMF decoder. To perform

this test, three different constants c1, c2, and c3 are used. The energy of the detected tone in the

low-frequency group is weighted by c1, the energy of the detected tone in the high-frequency

group is weighted by c2, and the sum of the two energies is weighted by c3. Each of these terms

must be greater than the summation of the energy from the rest of the filter outputs.

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Second harmonic test: The objective of this test is to reject speech that has harmonics close

to the DTMF frequencies so that they might be falsely detected as DTMF tones. Since DTMF

tones are pure sinusoids, they contain very little second harmonic energy. Speech, on the other

hand, contains a significant amount of second harmonic. To test the level of second harmonic, the

detector must evaluate the second harmonic frequencies of all eight DTMF tones. These second

harmonic frequencies (1394, 1540, 1704, 1882, 2418, 2672, 2954, and 3266 Hz) can also be

detected using the Goertzel algorithm.

Digit decoder: Finally, if all five tests are passed, the tone pair is decoded and mapped to

One of the 16 keys on a telephone touch-tone keypad. Goertzel’s algorithm is very efficient for

DTMF signal detection. However, some real world applications may already have other DSP

modules that can be used for DTMF detection. For example, some noise reduction applications

use Fast Fourier Transform (FFT) algorithm to analyse the spectrum of noise, and some speech-

coding algorithms use the linear prediction coding (LPC). In these cases, the FFT or the LPC

coefficients can be used for DTMF detection.

The integrated DTMF Decoder:

The integrated DTMF decoder is the device that receives the incoming DTMF data and

converts it into a respective e4-bit binary coded decimal (BCD) number.

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Fig3.5 flow chart of Goertzel algorithm

Features

• Complete DTMF Receiver

• Low power consumption

• Internal gain setting amplifier

• Adjustable guard time

• Central office quality

• Power-down mode

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• Inhibit mode

• Backward compatible with MT8870C/MT8870C-1

Application

• Receiver system for British Telecom (BT) or CEPT Spec (MT8870D-1)

• Paging systems

• Repeater systems/mobile radio

• Credit card systems

• Remote control

• Personal computers

• Telephone answering machine.

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3.3 D-Flip Flop

The D flip-flop is widely used. It is also known as a "data" or "delay" flip-flop. The D flip-flop

captures the value of the D-input at a definite portion of the clock cycle (such as the rising edge

of the clock). That captured value becomes the Q output. At other times, the output Q does not

change. The D flip-flop can be viewed as a memory cell, a Zero order hold or delay line.

Truth table:

Clock D Qnext

Rising edge 0 0

Rising edge 1 1

Non-Rising X Q

'X' denotes a don’t care condition.

Inputs Outputs

S R D > Q Q'

0 1 X X 0 1

1 0 X X 1 0

1 1 X X 1 1

Fig 3.6 D Flip Flop

Fig 3.7 pin diagram of IC 7474

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The D flip-flop tracks the input, making transitions with match those of the input D. The D

stands for "data"; this flip-flop stores the value that is on the data line. It can be thought of as a

basic memory cell. A D flip-flop can be made from a set/reset flip flop by tying the set to the

reset through an inverter. The result may be clocked.

The output Q will track the input D so long as the flip-flop remains enabled.

A D-Flip Flop constructed from a NAND LATCH.

The D flip-flop tries to follow the input D but cannot make the required transitions unless it is enabled

by the clock. Note that if the clock is low when a transition in D occurs, the tracking transition in Q

occurs at the next upward transition of the clock.

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Chapter-4

DESCRIPTION OF COMPONENTS Embedded system

An embedded system is a computer system with a dedicated function within a larger

mechanical or electrical system, 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 contain processing cores that are either microcontrollers, or digital

signal processors (DSP).A processor is an important unit in the embedded system hardware. It is

the heart of the embedded system.

Embedded systems are commonly found in consumer, cooking, industrial,

automotive, medical, commercial and military applications.

Telecommunications systems employ numerous embedded systems from telephone

switches for the network to mobile phones at the end-user. Computer networking uses

dedicated routers and network bridges to route data. Consumer electronics include personal digital

assistants (PDAs), mp3 players, mobile phones, videogame consoles, digital cameras, DVD

players, GPS receivers, and printers. Many household appliances, such as

Microwave ovens, washing machines and dishwashers, include embedded systems to provide

flexibility, efficiency and features. Advanced HVAC systems use networked thermostats to more

accurately and efficiently control temperature that can change by time of day and season. Home

automation uses wired- and wireless-networking that can be used to control lights, climate,

security, audio/visual, surveillance, etc., all of which use embedded devices for sensing and

controlling.

Embedded systems are used in transportation, fire safety, safety and security, medical

applications and life critical systems, as these systems can be isolated from hacking and thus, be

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more reliable. For fire safety, the systems can be designed to have greater ability to handle higher

temperatures and continue to operate. In dealing with security, the embedded systems can be self-

sufficient and be able to deal with cut electrical and communication systems.

Characteristics

Embedded systems are designed to do some specific task, rather than be a general-

purpose computer for multiple tasks. Some also have real-time performance constraints that must

be met, for reasons such as safety and usability; others may have low or no performance

requirements, allowing the system hardware to be simplified to reduce costs. The program

instructions written for embedded systems are referred to as firmware, and are stored in read-

only memory or Flash memory chips. They run with limited computer hardware resources: little

memory, small or non-existent keyboard or screen

BC547 TRANSISTOR:

BC547 is an NPN bi-polar junction transistor. A transistor, stands for transfer of

resistance, is commonly used to amplify current. A small current at its base controls a larger current

at collector & emitter terminals.

BC547 is mainly used for amplification and switching purposes. It has a maximum

current gain of 800. Its equivalent transistors are BC548 and BC549.

Fig4.1: BC547transistor

RELAY

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The relay takes advantage of the fact that when electricity flows through a coil, it becomes

an electromagnet. The electromagnetic coil attracts a steel plate, which is attached to a switch. So

the switch's motion (ON and OFF) is controlled by the current flowing to the coil, or not,

respectively.

A very useful feature of a relay is that it can be used to electrically isolate different parts of a

circuit. It will allow a low voltage circuit (e.g. 5VDC) to switch the power in a high voltage circuit

(e.g. 100 VAC or more).

The relay operates mechanically, so it cannot operate at high speed.

Internal circuit of Relay

Fig4.3: relays

Fig 4.2 Operation of Relay

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There are many kind of relays. You can select one according to your needs. The various

things to consider when selecting a relay are its size, voltage and current capacity of the contact

points, drive voltage, impedance, number of contacts, resistance of the contacts, etc. The resistance

voltage of the contacts is the maximum voltage that can be conducted at the point of contact in the

switch. When the maximum is exceeded, the contacts will spark and melt, sometimes fusing

together. The relay will fail. The value is printed on the relay.

POWER SUPPLY:

Power supply is a reference to a source of electrical power. A device or system that

supplies electrical or other types of energy to an output load or group of loads is called a power

supply unit or PSU. The term is most commonly applied to electrical energy supplies, less often

to mechanical ones, and rarely to others.. This also can be done using a step down transformer,

rectifier, voltage regulator, and filter circuit for generation of 5v DC power. Here a brief

description of all the components are given as follows:

LED

LED falls within the family of P-N junction devices. The light emitting diode (LED) is a diode that will give off visible light when it is energized. In any forward biased P-N junction there is, with in the structure and primarily close to the junction, a recombination of hole and electrons. This recombination requires that the energy possessed by the unbound free electron be transferred to another state. The process of giving off light by applying an electrical source is called electroluminescence. [Grab your reader’s attention with a great quote from the document or use this space to emphasize a key point. To place this text box anywhere on the page, just drag it.]

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LED is a component used for indication. All the functions being carried out are displayed

by led .The LED is diode which glows when the current is being flown through it in forward bias

condition. The LEDs are available in the round shell and also in the flat shells. The positive leg is

longer than negative leg.

Benefits of LEDs

Low power requirement: Most types can be operated with battery power supplies.

High efficiency: Most of the power supplied to an LED or IRED is converted into radiation in

the desired form, with minimal heat production.

Long life: When properly installed, an LED or IRED can function for decades.

Typical Applications

Indicator lights: These can be two-state (i.e., on/off), bar-graph, or alphabetic-numeric

readouts.

LCD panel backlighting: Specialized white LEDs are used in flat-panel computer displays.

Fibre optic data transmission: Ease of modulation allows wide communications bandwidth

with minimal noise, resulting in high speed and accuracy.

Fig 4.4 LED& LED Symbol

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Remote control: Most home-entertainment "remotes" use IREDs to transmit data to the main

unit.

Opt isolator: Stages in an electronic system can be connected together without unwanted

interaction.

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Chapter-5 Project practical circuit photo:

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Project practical circuit photo (output)

:

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5.2 Results & Discussions

APPLICATIONS:

• This system can be used in industrial applications.

• This system can be employed in houses ,where people often forget to switch off electrical

appliances

• This system can be used to control AC’s to set the room temperature

when user are outside .

• user can extend this circuit to control many electrical devices with some modifications

using 4 x16 decoder IC.

ADVANTAGES:

• Quick response is achieved.

• Construction is easy.

• Easy to maintain and repair

• Design is efficient.

• Power consumption is low.

• Controlling electrical devices wirelessly.

• Saves electricity (when user forget to switch off and go out).

• user can control appliances from any place round the globe.

DISADVANTAGES:

• This system needs a cell phone to be placed in circuit.

.

• Number of electrical appliances that can be controlled by this circuit is limited

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5.3 Conclusions & Future work

During the realization of the presented project the following points can be depicted:

It is simple to control the operation of anywhere appliances by exploiting the existing

mobile network, i.e. it’s not necessary to install a specific network. Any type of

mobiles can do the job.

The control circuit is reliable and simple to build.

The system is secure, by black listing all the call number except that of the specific

users (installed in the white list).

The system can let the user know the status of the appliances, before and after the

switching.

The system is implemented practically and the expected results are obtained.

Future Work:

In this system there is no use of any applications on the control mobile, so for a future

work it will be useful to develop programs for the mobile devices to give more control options and

security control.

As a future work in the field of the presented project, it is recommended develop the

system using PLCs or Microcontrollers, to give more reliability and control options, as temperature

control, security and more computational work so the system can do more than just turn On/Off

the devices.

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By placing the GSM module and sensors user can able get more advance for this project

to get the message.

REFERENCES;-

1). Telecommunication Switching Systems and networks by Thiagarajan Viswanathan

2).http://www.circuitsgallery.com/2012/07/dtmf-cell-phone-controlled-home-appliances-

automation-project.html

3). http://www.microsemi.com/products/telephony/dtmf-receivers/mt8870d

4.) http://www.edgefxkits.com/blog/dtmf-decoder-application-circuits

5). http://www.elctronicshub.com.

6).http://electronics4you.com/led

7).http://answers.com/topic/led