Mini Project Report on

DTMF BASED HOME APPLIANCE CONTROL

USING 555 TIMER

A dissertation submitted in partial fulfilment of the requirements for the award of

BACHELOR OF TECHNOLOGY

IN

ELECTRONICS AND COMMUNICATION ENGINEERING

FROM

JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSIT Y HYDERABAD

Submitted by

R.Sushma Chowdary 10E51A0485

S.Umamaheshwar 10E51A0494

V.Hareesh 10E51A04B1

Y.Naga Sushma 10E51A04B8

Under the Esteemed Guidance of

Mrs.K.Bindu Madhavi M-Tech

Assoc.Professor

HYDERABAD INSTITUTE OF TECHNOLOGY AND MANAGEMENT

(Approved by AICTE, New Delhi & Affiliated to JNTU Hyderabad) Gowdavelly (v) , Medchal (M) , Ranga Reddy ( Dist)-501401, A.P.INDIA

1

HYDERABAD INSTITUTE OF TECHNOLOGY AND MANAGEMENT

(Approved by AICTE & Affiliated to JNTU University) Gowdavelly (v) , Medchal (M) , Ranga Reddy ( Dist)-501401, A.P.INDIA

Department of Electronics and Communication Engineering

CERTIFICATE

This is to certify that this report on “DTMF BASED HOME APPLIANCE

CONTROL USING 555 TIMER” is a bonafide work of R.Sushma

Chowdary(10E51A0485), S.Umamaheshwar(10E51A0494),

V.Hareesh(10E51A04B1),Y.Naga Sushma(10E51A04B8), who carried

out the project work under my guidance .The results embodied in this project

part or full have not been submitted to any university or institute for the award

of any degree.

MRS.K.Bindu Madhavi M.Tech Sri Thanam.P M.Tech, MIEEE,(Ph.D)

INTERNAL GUIDE H.O.D of ECE

external examiner

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ACKNOWLEDEMENT

I would like to express my gratitude to all the people behind the screen who helped us to transform an idea in to real application.

I would like to express myheart –felt gratitude to my parents with whom i would not have been privileged to achieve and ful fill my dreams.

We express my sincere thanks to the management of HYDERABAD INSTITUTE OF

TECHNOLOGY AND MANAGEMENT.

We would like to thank our chairman Sri. Arutla Prasanth for providing all the fa-

cilities to carry out project work successfully. We also express our sincere thanks to our Hon-

ourable Principal Dr. A Rajasekhar.

We are very thankful to our Head of the Department, Sri Thanam.P, M.Tech,

MIEEE, (PHD) and project Co-ordinators Mrs.S.V.Devika M.Tech (PHD) , Associate Pro-

fessor & Ms.T.Lavanya M.Tech, MIEEE, (PHD) , Associate Professor.

I would like to thank my internal supervisor Mrs.K.Bindhu Madhavi M.Tech, As-

sociate Professor for his technical guidance, constant encouragement and support me carrying

out my project work.

We take great pleasure in expressing my thanks to all the Faculty Members of De-

partment of ECE and Lab technicians who have helped me to complete the project suc-

cessfully.

We are very much thankful to our family & friends who contributed directly, indir-

ectly for giving us their valuable suggestions and in helping for completion of our project

successfully.

R.Sushma Chowdary 10E51A0485

S.Umamaheshwar 10E51A0494

V.Hareesh 10E51A04B1

Y.Naga Sushma 10E51A04B8

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ABSTRACT

Traditionally electrical appliances in a home are controlled via switches that regu-late the electricity to these devices. As the world gets more and deeper into our personal lives even at home. Home automation is becoming more and more popular around the world and is becoming a common practice. The process of home automation works by making everything in the house automatically controlled using techno-logy to control and do the jobs that we would normally do manually. Home automation takes care of a lot of different activities in the house. this project we propose a unique System for Home automation utilizing Dual Tone Multi Frequency (DTMF) that is paired with a wire-less module to provide seamless wireless control over many devices in a house. The block diagram is a shown below. This user console has many keys , each corresponding to the device that needs to be activated. In many cases it is desirable to turn on or off some appli-ances, such as air conditioning and heating units before arriving home, this is known as home automation systems.

A test to detect the DTMF signal received from different mobile phones was also car-ried out.The DTMF decoder was tested for accurate detection of the presence of these tones under various conditions. The automation features of this work makes it possible for homeowners to remotely control a large number of appliances, indoor and outdoor lamps and lights, landscape sprinkler timers and more using their mobile phones.

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INDEX

Chapter- 1

Overview Of Project

1.1 Introduction 8

1.2 System Overview 9

1.3 The system features 11

Chapter-2

Operational Discription

2.1 Block Diagram 12

2.2 Circuit Diagram 14

Chapter-3

Dual-Tone Multi-Frequency Signalling

3.1 MT8870 Decoder 18

3.2 One To Ten Decoder(74LS42) 26

3.3 Hex Inverting Gates(DM74LS04) 31

Chapter-4

Description of Components 33

Chapter-5 Results & Discussion 58 Conclusions & Future work 59

References 60

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LIST OF FIGURES

Figure No. Title Page No.

1 block diagram 12

2 circuit diagram 14

3 signalling tones 16

4 dtmf keypad 17

6 MT(8870) decoder pin diagram 18

7 basic steering circuit 20

8 response filter 21

9 dtmf decoded output 22

10 74LS42 pin diagram 27

11 logic diagram 28

12 truth table 29

13 Op-amp pin diagram 35

14 pin diagram of 555 timer 37

14 functional diagram of timer 38

15 bistable 555timer 40

16 input output waveforms of bistable 41

17 BC547 transistor 42

18 relays 43

18 transformer 43 19 regulator 48

20 leds 54

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DTMF BASED HOME APPLIANCE

CONTROL USING 555 TIMER

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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 thateveryone would like to enjoy, if they were not expensive to install, maintain, and able to beused from long distance. The idea of the remotely controlled home automation systems isshown in Figure 1.1.

The home automation have many features makes the homeowner remotely toggleappliances such as air conditioning and heating units, lamps or porch lights, landscapesprinkler 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 signaling such as dialing andautomatic redial. Each key-press on the phone keypad generates DTMF signal consists oftwo tones that must be generated simultaneously.

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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 we are present at we 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 555 timer 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 555 timer” is used to control the devices in home as well as in industries.

The system provides availability due to development of a low cost system. The home appliances control system with an affordable cost was thought to be built that should be mobile providing remote access to the appliances and allowing home security. Though devices connected as home and office appliances consume electrical power.

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 center. The version of DTMF that is used in push-button telephones for tone dialling is known as Touch-Tone.

The MT8870D/MT8870D-1 monolithic DTMF receiver offers small size, low power consumption and high performance. Its architecture consists of abandsplit 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. In detail, a DTMF generator generates two frequencies corresponding to a number or code in the number pad which will be transmitted through the communication networks, constituting the transmitter section which is simply equivalent to a mobile set. In the receiver part, the DTMF detector IC, for example IC MT 8870 detects the number or code represented by DTMF back, through the inspection of the two transmitted The LSTTL/MSI SN54/74LS42 is a Multipurpose Decoder designed to acceptfour BCD inputs and provide ten mutually exclusive outputs. The LS42 is fabricated with the Schottky barrier diode process for high speed and is completely compatible with all Motorola TTL families. It is a Multipurpose Decoder designed to accept four BCD inputs and provide ten mutually exclusive outputs. • Multifunction Capability• Mutually Exclusive Outputs• Demultiplexing Capability

• Input Clamp Diodes Limit High Speed Termination Effects. 9 555 timers are precision timing circuits capable of producing accurate time delays or oscillation. In the time-delay or monostable mode of operation, the timed interval is con-trolled by a single external resistor and capacitor network. In the astable mode of operation, the frequency and duty cycle can be controlled independently with two external resistors and a single external capacitor. The threshold and trigger levels normally are two-thirds and one-third, respectively, of VCC. These levels can be altered by use of the control-voltage ter-minal. When the trigger input falls below the trigger level, the flip-flop is set, and the output goes high. If the trigger input is above the trigger level and the threshold input is above the threshold level, the flip-flop is reset and the output is low.

A flip-flop is an electronic circuit that alternates between two output states. In a flip-flop, a short pulse on the trigger causes the output to go high and stay high, even after the trigger pulse ends. The output stays high until a reset pulse is received, at which time the out-put goes low.This type of circuit is called bistable because the circuit has two stable states: high and low. The circuit stays low until it's triggered. Then, it stays high until it's reset. This type of circuit is used extensively in computers and other digital circuits. For computer ap-plications, the 555 is a poor choice for use as a flip-flop. That’s because its output doesn’t change fast enough in response to trigger or reset pulses in computer circuits that are driven by high-speed clock pulses. For computer applications, better flip-flop chips are readily avail-able.

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 can not operate at high speed.

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. Here in our application we need a 5v DC power supply for all electronics involved in the project. This requires step down transformer, rectifier, voltage regulator, and filter circuit for generation of 5v DC power.

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 switch-

ing 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 for 10

amplifiers. The voltage divider is the commonly used biasing mode. For switching applica-

tions, transistor is biased so that it remains fully on if there is a signal at its base. In the ab-

sence of base Signal, it gets completely off.

Resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit. Resistors can also be used to provide a specific voltage for an active device such as a transistor. All other factors being equal, in a direct-current (DC) circuit, the current through a resistor is inversely proportional to its resistance and directly proportional to the voltage across it. This is the well-known Ohm's Law.

A capacitor is a tool consisting of two conductive plates, each of which hosts an opposite charge. These plates are separated by a dielectric or other form of insulator, which helps them maintain an electric charge. There are several types of insulators used in capacitors. Examples include ceramic, polyester, tantalum air, and polystyrene. Other common capacitor insulators include air, paper, and plastic. 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.

1.3 The System Features

This system can control devices that may be any electric or electronicappliances, 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 we 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:

Fig 1: block diagram

First we are giving the input dtmf signal to the decoder via audio jockey. audio jockey is nothing but the connector between the phone which we are using 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. 12

When we press keys in our cell Phone when call is in progress, the other person will hear some tones with respect to keys pressed. These tones are based on the DTMF technology. 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 micro-phone wire are processed by the DTMF decoder IC which generates the equivalent binary se-quence as a parallel output as Q1, Q2, Q3, and Q4.

The 74LS42 is a Multipurpose Decoder designed to accept four BCD inputs and provide ten mutually exclusive outputs. The LS42 is fabricated with the Schottky barrier di-ode process for high speed and is completely compatible with all Motorola TTL families. It is a Multipurpose Decoder designed to accept four BCD inputs and provide ten mutually exclusive outputs.here we are getting the ten low outputs.

Not gate contains six independent gates each of which performs the logic INVERT function. To get the high outputs we are using not gate block.

555 timers are precision timing circuits capable of producing accurate time delays or oscillation. In the time-delay or monostable mode of operation, the timed interval is con-trolled by a single external resistor and capacitor network. In the astable mode of operation, the frequency and duty cycle can be controlled independently with two external resistors and a single external capacitor. A flip-flop is an electronic circuit that alternates between two out-put states. In a flip-flop, a short pulse on the trigger causes the output to go high and stay high, even after the trigger pulse ends. The output stays high until a reset pulse is received, at which time the output goes low.This type of circuit is called bistable because the circuit has two stable states: high and low. The circuit stays low until it's triggered. Then, it stays high until it's reset. This type of circuit is used extensively in computers and other digital circuits. For computer applications, the 555 is a poor choice for use as a flip-flop.

The relay takes advantage of the fact that when electricity flows through a coil, it be-comes 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 isol-ate different parts of a circuit. Simply it acts as a switch.

Finally we are giving to load that is any electric or electronic appliance to control it.

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2.2 Circuit Diagram

In this circuit diagram first we are giving the 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.

This four outputs is given to the one to ten decoder..here we get the ten low outputs.To get the high output we are giving this to the not gate. here we get the high output and we should take any four outputs and given to the transistor.

We know that 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 cur-rent at its base controls a larger current at collector & emitter terminals. BC547 is mainly

14

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

555 timers are precision timing circuits capable of producing accurate time delays or os-cillation. In the time-delay or monostable mode of operation, the timed interval is controlled by a single external resistor and capacitor network. In the astable mode of operation, the fre-quency and duty cycle can be controlled independently with two external resistors and a single external capacitor. A flip-flop is an electronic circuit that alternates between two out-put states. In a flip-flop, a short pulse on the trigger causes the output to go high and stay high, even after the trigger pulse ends. The output stays high until a reset pulse is received, at which time the output goes low.This type of circuit is called bistable because the circuit has two stable states: high and low. The circuit stays low until it's triggered. Then, it stays high until it's reset. here in this we are using bistable mode because of two stable states.so we get the circuit always in stable state..

Finally we are giving to the relay. It acts as a switch. It takes low input and get the high out-put. 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 signalling:

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

signalling over analog telephone lines in the voice-frequency band between telephone hand-

sets and other communications devices and the switching center. The version of DTMF that

is used in push-button telephones for tone dialling is known as Touch-Tone. It was de-

veloped 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 signalling within the tele-

phone network.

Introduced by AT&T in 1963,[1] the Touch-Tone system using the telephone

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

for landline service.

Keypad:

Fig3: signalling tones

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1209 Hz on 697 Hz to make the 1 tone

1209 Hz 1336 Hz 1477 Hz

697 Hz 1 2 3

770 Hz 4 5 6

852 Hz 7 8 9

941 Hz * 0 #

Fig4: DTMF keypad

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

quency and each column represents a high frequency.

Pressing a si

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

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

Initial pushbutton designs employed levers, so that each button activated two con-

tacts.

The tones are decoded by the switching center to determine the keys pressed by the

user

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3.1  DTMF DECODER (MT8870) :

Pin diagram:

               Fig6: MT8870 pin diagram

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 connec-tion 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 os-cillator. This pin input is internally pulled down.

7.  OSC1   Clock (Input).

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

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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 corres-ponding 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 de-tected 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 abandsplit 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.

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 bandpassfilters, 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 a single order switched capacitor filter section which smooths the signals prior to limiting. Limiting is per-formed by high-gain comparators which are provided with hysteresis to prevent detection of unwanted low-level signals. Theoutputs of the comparators provide full rail logic swings at the frequencies of the incoming DTMF signals.

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Decoder Section

Following the filter section is a decoder employing digital counting techniques to de-termine 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 ex-traneous signals such as voice while Figure 7- Basic Steering Circuit providing tolerance to small frequency deviations and variations.

This averaging algorithm has been developed to ensure an optimum combination of immunity to talk-off and tolerance to the presence of interfering frequencies (third tones) and noise. When the detector recognizes the presence of two valid tones (this is referred to as the “signal condition” in some industry specifications) the “Early Steering” (ESt) output will go to an active state.

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

Fig7: basic steering circuit

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Fig8: response filter

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

The steering circuit works in reverse to validate the interdigit pause between signals. Thus, as well as rejecting signals too short to be considered valid, the receiver will tolerate signal interruptions (dropout) too short to be considered a valid pause. This facility, together with the capability of selecting the steering time constants externally, allows the designer to tailor performance to meet a wide variety of system requirements.

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Fig9: dtmf decoded output

 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 de-code 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 in-terface.

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 ahigh pass filter. The passband cutoff frequency of the low pass filter is slightly above 100Hz, whereas that of the high pass filter is slightly below 1200 Hz. The output of each filteris next converted into a square wave by a limiter and then processed by a bank of bandpassfilters with narrow passbands. The four bandpass filters in the low-frequency channel havecenter frequencies at 697 Hz, 770 Hz, 852 Hz, and 941 Hz. The four band pass filters inthe high-frequency channel have center frequencies at 1209 Hz, 1336 Hz, 1477 Hz, and 22

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

signal if its input voltage is above a certain threshold.

The entire signal processing functions described above are usually implemented inpractice in the analog domain. However, increasingly, these functions are being implemented using digital techniques. Digital techniques surpass analog equivalents in performance, since it provides better precision, stability, versatility, and reprogrammability to meet other tone standards. The DTMF digital decoder computes the Discrete Fourier Transform (DFT) samples closest in frequency to the eight DTMF fundamental tones. The DFT computation scheme employed is a slightly modified version of Goretzel’s Algorithm. The flow chart of DTMF detection using the modified Goertzel’s Algorithm is illustrated in Figure. Six tests are followed to determine if a valid DTMF digit has been detected [2].

Magnitude test: According to ITU Q.24, the maximum signal level transmit to the publicnetwork shall not exceed −9 dBm. This limits an average voice range of −35 dBm for avery weak long-distance call to −10 dBm for a local call. A DTMF receiver is expectedto operate at an average range of −29 to +1 dBm. Thus, the largest magnitude in eachband must be greater than a threshold of −29 dBm; otherwise, the DTMF signal shouldnot be detected.

Twist test: The tones may be attenuated according to the telephone system’s gains at thetonal frequencies. Therefore, we do not expect the received tones to have same 23

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 frequen-cies 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 toreject some broadband signals to further improve the robustness of a DTMF decoder. To per-form 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 fil-ter outputs.

Second harmonic test: The objective of this test is to reject speech that has harmonics closeto 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 har-monic, 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 toone of the 16 keys on a telephone touch-tone keypad [3]. Goertzel’s algorithm is very effi-cient for DTMF signal detection. However, some realworld 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 analyze 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 4-bit binary coded decimal (BCD) number.Flow chart for dtmf detector using goertzel algorithm

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Features

• Complete DTMF Receiver

• Low power consumption

• Internal gain setting amplifier

• Adjustable guard time

• Central office quality

• Power-down mode

• Inhibit mode

• Backward compatible with MT8870C/MT8870C-1

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 Applications

• 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.

3.2 ONE-OF-TEN DECODER:

The LSTTL/MSI SN54/74LS42 is a Multipurpose Decoder designed to acceptfour BCD inputs and provide ten mutually exclusive outputs. The LS42 is fabricated with the Schottky barrier diode process for high speed and is completely compatible with all Motorola TTL families.

• Multifunction Capability• Mutually Exclusive Outputs• Demultiplexing Capability• Input Clamp Diodes Limit High Speed Termination Effects

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Fig10: 74LS42 pin diagram

• It is a Multipurpose Decoder designed to accept four BCD inputs and provide ten mutually exclusive outputs.

• A0 – A3 Address Inputs Outputs • 0 TO 9 Active LOW

NOTES:

a) 1 TTL Unit Load (U.L.) = 40 mA HIGH/1.6 mA LOW. b) The Output LOW drive factor is 2.5 U.L. for Military (54) and 5 U.L. for Commercial (74)Temperature Ranges.

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Fig11: logic diagram

FUNCTIONAL DESCRIPTION

The LS42 decoder accepts four active HIGH BCD inputs and provides ten mutually exclusive active LOW outputs, as shown by logic symbol or diagram. The active LOW out-puts facilitate addressing other MSI units with LOW input enables.

The logic design of the LS42 ensures that all outputs are HIGH when binary codes greater than nine are applied to the inputs. The most significant input A3 produces a useful inhibit function when the LS42 is used as a one-of-eight decoder. The A3 input can also be used as the Data input in an 8-output demultiplexer application.

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Fig12: truth table

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30

5.3 DM74LS04 Hex Inverting Gates:

General DescriptionThis device contains six independent gates each of which performs the logic INVERT func-tion.

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Note 1: The “Absolute Maximum Ratings” are those values beyond whichthe safety of the device cannot be guaranteed. The device should not beoperated at these limits. The parametric values defined in the ElectricalCharacteristics tables are not guaranteed at the absolute maximum ratings.The “Recommended Operating Conditions” table will define the conditionsfor actual device operation.

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Chapter-4

DESCRIPTION OF COMPONENTS

Embedded system

An embedded system is a computer system with a dedicated function within a lar-ger mechanical or electrical system, often with real-time computing constraints. It is embed-ded 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 di-gital signal processors (DSP).A processor is an important unit in the embedded system hard-ware. It is the heart of the embedded system.

The key characteristic, however, is being dedicated to handle a particular task. Since the embedded system is dedicated to specific tasks, design engineers can optimize it to reduce the size and cost of the product and increase the reliability and performance. Some embedded systems are mass-produced, benefiting from economies of scale.

Physically, embedded systems range from portable devices such as digital watches and MP3 players, to large stationary installations liketraffic lights, factory control-lers, and largely complex systems like hybrid vehicles, MRI, and avionics. Complexity varies from low, with a single microcontroller chip, to very high with multiple units, peripherals and networks mounted inside a large chassis or enclosure.

Embedded systems are commonly found in consumer, cooking, industrial, automot-ive, 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 dedic-ated routers andnetwork 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 

33

microwave ovens, washing machines and dishwashers, include embedded systems to provide flexibility, efficiency and features. Advanced HVAC systems use networkedthermostats to more accurately and efficiently control temperature that can change by time of day and sea-son. 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 sens-ing and controlling.

Transportation systems from flight to automobiles increasingly use embedded systems. New airplanes contain advanced avionics such as inertial guidance sys-tems and GPS receivers that also have considerable safety requirements. Various electric mo-tors — brushless DC motors, induction motors and DC motors — use electric/electronic mo-tor controllers. Automobiles, electric vehicles, and hybrid vehicles increasingly use embed-ded systems to maximize efficiency and reduce pollution. Other automotive safety systems include anti-lock braking system (ABS),Electronic Stability Control (ESC/ESP), traction control (TCS) and automatic four-wheel drive.

Medical equipment uses embedded systems for vital signs monitoring, electronic stethoscopes for amplifying sounds, and various medical imaging (PET, SPECT, CT, MRI) for non-invasive internal inspections. Embedded systems within medical equipment are often powered by industrial computers.[6]

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 more reliable.[citation needed] For fire safety, the systems can be designed to have greater ability to handle higher temperatures and continue to operate. In dealing with secur-ity, the embedded systems can be self-sufficient and be able to deal with cut electrical and communication systems.

A new class of miniature wireless devices called motes are quickly gaining pop-ularity as the field of wireless sensor networking is increasing. Wireless sensor network-ing, WSN, makes use of miniaturization made possible by advanced IC design to couple full wireless subsystems to sophisticated sensors, enabling people and companies to measure a myriad of things in the physical world and act on this information through IT monitoring and control systems. These motes are completely self-contained, and will typically run of a bat-tery source for many years before the batteries need to be changed or charged.Embedded Wi-Fi modules provide a simple means of wirelessly enabling any device which communicates via a serial port.

Characteristics

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

pose computer for multiple tasks. Some also have real-timeperformance constraints that must be met,

for reasons such as safety and usability; others may have low or no performance requirements, allow-

ing the system hardware to be simplified to reduce costs.

Embedded systems are not always standalone devices. Many embedded systems consist

of small, computerized parts within a larger device that serves a more general purpose. For example,

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the Gibson Robot Guitar features an embedded system for tuning the strings, but the overall purpose

of the Robot Guitar is, of course, to play music.[7] Similarly, an embedded system in an auto-

mobile provides a specific function as a subsystem of the car itself.

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 re-

sources: little memory, small or non-existent keyboard or screen.

THE 741 OPERATIONAL AMPLIFIER

The Operational Amplifier is probably the most versatile Integrated Circuit avail-able. It is very cheap especially keeping in mind the fact that it contains several hundred components. The most common Op-Amp is the 741 and it is used in many circuits. The OP AMP is a ‘Linear Amplifier’ with an amazing variety of uses. Its main purpose is to amplify (increase) a weak signal - a little like a Darlington Pair. The OP-AMP has two inputs, IN-VERTING (-) and NON-INVERTING (+), and one output at pin 6.

Fig5 : OP-AMP pin diagram

The 741 integrated circuit looks like any other ‘chip’. However, it is a general purpose OP-AMP. You need only to know basic information about its operation and use. The diagram opposite shows the pins of the 741 OP-AMP. The important pins are 2, 3 and 6 because these represent inverting, non-inverting and voltage out. Notice the triangular diagram that represents an Op-Amp integrated circuit.

THE 741 IS USED IN TWO WAYS

1) An inverting amplifier. Leg two is the input and the output is always reversed. In an inverting amplifier the voltage enters the 741 chip through leg two and comes out of the 741 chip at leg six. If the polarity is positive going into the chip, it negative by the time it comes out through leg six. The polarity has been ‘inverted’.

2) A non-inverting amplifier. Leg three is the input and the output is not reversed. In a non-inverting amplifier the voltage enters the 741 chip through leg three and leaves the 741 chip

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through leg six. This time if it is positive going into the 741 then it is still positive coming out. Polarity remains the same. Integrated circuit:

An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or

a microchip) is a set of electronic circuits on one small plate ("chip") of semiconductor material, nor-

mally silicon. This can be made much smaller than a discrete circuit made from independent compon-

ents.

Integrated circuits are used in virtually all electronic equipment today and have revolutionized

the world of electronics. Computers, mobile phones, and other digital home appliances are now inex-

tricable parts of the structure of modern societies, made possible by the low cost of producing integ-

rated circuits.

ICs can be made very compact, having up to several billion transistors and other electronic

components in an area the size of a fingernail. The width of each conducting line in a circuit (the line

width) can be made smaller and smaller as the technology advances; in 2008 it dropped below

100nanometers and in 2013 it is expected to be in the tens of nanometers.

ICs were made possible by experimental discoveries showing that semiconductor devices could

perform the functions of vacuum tubes and by mid-20th-century technology advancements in semi-

conductor device fabrication. The integration of large numbers of tiny transistors into a small chip was

an enormous improvement over the manual assembly of circuits using discrete electronic compon-

ents. The integrated circuit's mass production capability, reliability, and building-block approach to cir-

cuit design ensured the rapid adoption of standardized integrated circuits in place of designs using

discrete transistors.

There are two main advantages of ICs over discrete circuits: cost and performance. Cost is low

because the chips, with all their components, are printed as a unit by photolithography rather than be-

ing constructed one transistor at a time. Furthermore, much less material is used to construct a pack-

aged IC die than to construct a discrete circuit. Performance is high because the components switch

quickly and consume little power (compared to their discrete counterparts) as a result of the small size

and close proximity of the components. As of 2012, typical chip areas range from a few square milli-

meters to around 450 mm2, with up to 9 million transistors per mm2.

An integrated circuit is defined as:

A circuit in which all or some of the circuit elements are inseparably associated and electrically in-

terconnected so that it is considered to be indivisible for the purposes of construction and commerce.

Circuits meeting this definition can be constructed using many different technologies 36

TIMERS:

1FEATURES

• Timing From Microseconds to Hours • Adjustable Duty Cycle• Astable or Monostable or Bistable Operation • TTL-Compatible Output Can Sink or Source up to 200 mA

Pin diagram:

Fig 13: 555 timer pin diagram

DESCRIPTION/ORDERING INFORMATION

These devices are precision timing circuits capable of producing accurate time delays or oscillation. In the time-delay or monostable mode of operation, the timed interval is con-trolled by a single external resistor and capacitor network. In the astable mode of operation, the frequency and duty cycle can be controlled independently with two external resistors and a single external capacitor. The threshold and trigger levels normally are two-thirds and one-third, respectively, of VCC. These levels can be altered by use of the control-voltage terminal. When the trigger in-put falls below the trigger level, the flip-flop is set, and the output goes high. If the trigger in-put is above the trigger level and the threshold input is above the threshold level, the flip-flop is reset and the output is low. The reset (RESET) input can override all other inputs and can be used to initiate a new timing cycle. When RESET goes low, the flip-flop is reset, and the output goes low. When the output is low, a low-impedance path is provided between

37

discharge (DISCH) and ground. The output circuit is capable of sinking or sourcing current up to 200 mA. Operation is specified for supplies of 5 V to 15 V. With a 5-V supply, output levels are compatible with TTL inputs.

Fig14: functional diagram of timer

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APPLICATION:

The 555 in Bistable (Flip-Flop) Mode

A flip-flop is an electronic circuit that alternates between two output states. In a flip-flop, a short pulse on the trigger causes the output to go high and stay high, even after the trigger pulse ends. The output stays high until a reset pulse is received, at which time the out-put goes low.

This type of circuit is called bistable because the circuit has two stable states: high and low. The circuit stays low until it's triggered. Then, it stays high until it's reset. This type of circuit is used extensively in computers and other digital circuits.

For computer applications, the 555 is a poor choice for use as a flip-flop. That’s be-cause its output doesn’t change fast enough in response to trigger or reset pulses in computer circuits that are driven by high-speed clock pulses. For computer applications, better flip-flop chips are readily available.

That being said, the 555 is often used in bistable mode for noncomputer applications where high-speed response isn’t necessary. For example, imagine a simple robot that drives itself forward until it bumps into something in front of it, and then drives backward until it bumps into something behind it.

The robot would be equipped with contact switches on the front and rear connected to the trigger and reset inputs of a 555 in bistable mode. The robot’s drive motor would be connected to the output such that when the output is low, the motor runs forward, and when the output is high, the motor runs backward. Then, the bistable 555 would cause the robot to drive back and forth between two obstacles.

This is a schematic for a 555 used in bistable mode. As you can see, this circuit doesn't require a capacitor. That’s because in bistable mode, the 555 isn't used as a timer. The highs and lows of the output signal are controlled by the trigger and reset inputs, not by the charging and discharging of a capacitor.

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Fig15: bistable 555timer

Both the trigger (pin 2) and the reset (pin 4) inputs are connected to Vcc through a 10 kΩ resistor. When the set switch is depressed, pin 2 is shorted to ground. This causes the voltage to bypass pin 2, resulting in a momentary low pulse, which triggers the 555. Once triggered, the output pin goes high.

In astable or monostable mode, the output pin would remain high until the voltage at the threshold pin (pin 6) reaches two-thirds of the supply voltage. However, because pin 6 isn't connected to anything in this circuit, no voltage is ever present on pin 6. Thus, the threshold is never reached, so the output remains high indefinitely until the 555 is reset by a low pulse on the reset pin (pin 4).

The reset input (pin 4) is connected to Vcc in the same manner as the trigger input. As a result, when the reset switch is pressed, pin 4 is short circuited to ground, creating a low pulse, which resets the 555 and brings the output back to high.

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Fig16: bistable input output waveforms

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.

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 tran-

sistor 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 for amp-

lifiers. 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.

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Fig17: BC547transistor

RELAY

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 can not operate at high speed.

42Internal circuit of Relay

Fig17: relays

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. Here in our application we need a 5v DC power supply for all electronics involved in the project. This requires 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:

TRANSFORMER:

transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors — the transformer's coils or "windings". Except for air-core transformers, the conductors are commonly wound around a single iron-rich core, or around separate but magnetically-coupled cores. A varying current in the first or "primary" winding creates a varying magnetic field in the core (or cores) of the transformer. This varying magnetic field induces a varying electromotive force (EMF) or "voltage" in the "secondary" winding. This effect is called mutual induction.

Fig18:transformer 43

If a load is connected to the secondary circuit, electric charge will flow in the secondary winding of the transformer and transfer energy from the primary circuit to the load connected in the secondary circuit.

BASIC PARTS OF A TRANSFORMER In its most basic form a transformer consists of: A primary coil or winding.

A secondary coil or winding.

A core that supports the coils or windings.

Refer to the transformer circuit in figure as you read the following explanation: The primary winding is connected to a 60-hertz ac voltage source. The magnetic field (flux) builds up (expands) and collapses (contracts) about the primary winding. The expanding and contracting magnetic field around the primary winding cuts the secondary winding and induces an alternating voltage into the winding. This voltage causes alternating current to flow through the load. The voltage may be stepped up or down depending on the design of the primary and secondary windings.

THE COMPONENTS OF A TRANSFORMER Two coils of wire (called windings) are wound on some type of core material. In some cases the coils of wire are wound on a cylindrical or rectangular cardboard form. In effect, the core material is air and the transformer is called an AIR-CORE TRANSFORMER. Transformers used at low frequencies, such as 60 hertz and 400 hertz, require a core of low-reluctance magnetic material, usually iron. This type of transformer is called an IRON-CORE TRANSFORMER. Most power transformers are of the iron-core type. The principle parts of a transformer and their functions are:

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The CORE, which provides a path for the magnetic lines of flux.

The PRIMARY WINDING, which receives energy from the ac source.

The SECONDARY WINDING, which receives energy from the primary winding and delivers it to the load.

The ENCLOSURE, which protects the above components from dirt, moisture, and mechanical damage.

BRIDGE RECTIFIER

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. Basic operation :

According to the conventional model of current flow originally established by Benjamin Franklin and still followed by most engineers today, current is assumed to flow through electrical conductors from the positive to the negative pole. In actuality, free electrons in a conductor nearly always flow from the negative to the positive pole. In the vast majority of applications, however, the actual direction of current flow is irrelevant. Therefore, in the discussion below the conventional model is retained. In the diagrams below, when the input connected to the left corner of the diamond is positive, and the input connected to the right corner is negative, current flows from the upper supply terminal to the right along the red (positive) path to the output, and returns to the lower supply terminal via the blue (negative) path.

When the input connected to the left corner is negative, and the input connected to the right corner is positive, current flows from the lower supply terminal to the right along the red path to the output, and returns to the upper supply terminal via the blue path.

In each case, the upper right output remains positive and lower right output negative. Since this is true whether the input is AC or DC, this circuit not only produces a DC output from an AC input, it can also provide what is sometimes called "reverse polarity protection". That is, 45it permits normal functioning of DC-powered equipment when batteries have been installed backwards, or when the leads (wires) from a DC power source have been reversed, and protects the equipment from potential damage caused by reverse polarity. Prior to availability of integrated electronics, such a bridge rectifier was always constructed from discrete components. Since about 1950, a single four-terminal component containing the four diodes connected in the bridge configuration became a standard commercial component and is now available with various voltage and current ratings.

OUTPUT SMOOTHING For many applications, especially with single phase AC where the full-wave bridge serves to convert an AC input into a DC output, the addition of a capacitor may be desired because the bridge alone supplies an output of fixed polarity but continuously varying or "pulsating" magnitude (see diagram above).

The function of this capacitor, known as a reservoir capacitor (or smoothing capacitor) is to lessen the variation in (or 'smooth') the rectified AC output voltage waveform from the bridge. One explanation of 'smoothing' is that the capacitor provides a low impedance path to the AC component of the output, reducing the AC voltage across, and AC current through, the resistive load. In less technical terms, any drop in the output voltage and current of the bridge tends to be canceled by loss of charge in the capacitor. This charge flows out as additional current through the load. Thus the change of load current and voltage is reduced relative to what would occur without the capacitor. Increases of voltage correspondingly store excess charge in the capacitor, thus moderating the change in output voltage / current.

The simplified circuit shown has a well-deserved reputation for being dangerous, because, in some applications, the capacitor can retain a lethal charge after the AC power source is removed. If supplying a dangerous voltage, a practical circuit should include a reliable way to safely discharge the capacitor. If the normal load cannot be guaranteed to perform this function, perhaps because it can be disconnected, the circuit should include a bleeder resistor connected as close as practical across the capacitor. This resistor should consume a current large enough to discharge the capacitor in a reasonable time, but small enough to minimize unnecessary power waste.

Because a bleeder sets a minimum current drain, the regulation of the circuit, defined as percentage voltage change from minimum to maximum load, is improved. However in many cases the improvement is of insignificant magnitude.

46one ripple cycle, the above configuration will produce a smoothed DC voltage across the load. In some designs, a series resistor at the load side of the capacitor is added. The smoothing can then be improved by adding additional stages of capacitor–resistor pairs, often done only for sub-supplies to critical high-gain circuits that tend to be sensitive to supply voltage noise. The idealized waveforms shown above are seen for both voltage and current when the load on the bridge is resistive. When the load includes a smoothing capacitor, both the voltage and the current waveforms will be greatly changed. While the voltage is smoothed, as described above, current will flow through the bridge only during the time when the input voltage is greater than the capacitor voltage. For example, if the load draws an average current of n Amps, and the diodes conduct for 10% of the time, the average diode current during conduction must be 10n Amps. This non-sinusoidal current leads to harmonic distortion and a poor power factor in the AC supply.

The capacitor and the load resistance have a typical time constant τ = RC where C and R are the capacitance and load resistance respectively. As long as the load resistor is large enough so that this time constant is much longer than the time of In a practical circuit, when a capacitor is directly connected to the output of a bridge, the bridge diodes must be sized to withstand the current surge that occurs when the power is turned on at the peak of the AC voltage and the capacitor is fully discharged. Sometimes a small series resistor is included before the capacitor to limit this current, though in most applications the power supply transformer's resistance is already sufficient. Output can also be smoothed using a choke and second capacitor. The choke tends to keep the current (rather than the voltage) more constant. Due to the relatively high cost of an effective choke compared to a resistor and capacitor this is not employed in modern equipment. Some early console radios created the speaker's constant field with the current from the high voltage ("B +") power supply, which was then routed to the consuming circuits, (permanent magnets were then too weak for good performance) to create the speaker's constant magnetic field. The speaker field coil thus performed 2 jobs in one: it acted as a choke, filtering the power supply, and it produced the magnetic field to operate the speaker.

REGULATOR IC(78XX):

It is a three pin IC used as a voltage regulator. It converts unregulated DC current into regulated DC current. Normally we get fixed output by connecting the voltage regulator at the output of the filtered DC (see in above diagram). It can also be used in circuits to get a low DC voltage from a high DC voltage (for example we use 7805 to get 5V from 12V). There are two types of voltage regulators 1. fixed voltage regulators (78xx, 79xx) 2. variable voltage regulators(LM317) In fixed voltage regulators there is another classification 1. +ve voltage regulators 2. -ve voltage regulators POSITIVE VOLTAGE

REGULATORS This include 78xx voltage regulators. The most commonly used ones are 7805 and 7812. 7805 gives fixed 5V DC voltage if input voltage is in (7.5V, 20V).

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Fig19: regulator ic

The Capacitor Filter The simple capacitor filter is the most basic type of power supply filter. The application of the simple capacitor filter is very limited. It is sometimes used on extremely high-voltage, low-current power supplies for cathode-ray and similar electron tubes, which require very little load current from the supply. The capacitor filter is also used where the power-supply ripple frequency is not critical; this frequency can be relatively high. The capacitor (C1) shown in figure 4-15 is a simple filter connected across the output of the rectifier in parallel with the load.

Full-wave rectifier with a capacitor filter:

When this filter is used, the RC charge time of the filter capacitor (C1) must be short and the RC discharge time must be long to eliminate ripple action. In other words, the capacitor must charge up fast, preferably with no discharge at all. Better filtering also results when the input frequency is high; therefore, the full-wave rectifier output is easier to filter than that of the half-wave rectifier because of its higher frequency. For you to have a better understanding of the effect that filtering has on Eavg, a comparison of a rectifier circuit with a filter and one without a filter is illustrated in views A and B of figure 4-16. The output waveforms in figure 4-16 represent the unfiltered and filtered outputs of the half-wave rectifier circuit. Current pulses flow through the load resistance (RL) each time a diode conducts. The dashed line indicates the average value of

output voltage. For the half-wave rectifier, Eavg is less than half (or approximately 0.318) of the peak output voltage. This value is still much less than that of the applied voltage. With no capacitor connected across the output of the rectifier circuit, the waveform in view A has a large pulsating component (ripple) compared with the average or dc component. When a capacitor is

48connected across the output (view B), the average value of output voltage (Eavg) is increased due to the filtering action of capacitor C1.

UNFILTERED

Half-wave rectifier with and without filtering

FILTERED

The value of the capacitor is fairly large (several microfarads), thus it presents a relatively low reactance to the pulsating current and it stores a substantial charge. The rate of charge for the capacitor is limited only by the resistance of the conducting diode, which is relatively low. Therefore, the RC charge time of the circuit is relatively short. As a

result, when the pulsating voltage is first applied to the circuit, the capacitor charges rapidly and almost reaches the peak value of the rectified voltage within the first few cycles. The capacitor attempts to charge to the peak value of the rectified voltage anytime a diode is conducting, and tends to retain its charge when the rectifier output falls to zero. (The capacitor cannot discharge immediately.) The capacitor slowly

49

CIRCUIT DIAGRAM OF POWER SUPPLY

discharges through the load resistance (RL) during the time the rectifier is non-conducting. The rate of discharge of the capacitor is determined by the value of capacitance and the value of the load resistance. If the capacitance and load-resistance values are large, the RC discharge time for the circuit is relatively long. A comparison of the waveforms shown in figure 4-16 (view A and view B) illustrates that the addition of C1 to the circuit results in an increase in the average of the output voltage (Eavg) and a reduction in the amplitude of the ripple component (Er) which is normally present across the load resistance. Now, let's consider a complete cycle of operation using a half-wave rectifier, a capacitive filter (C1), and a load resistor (RL). As shown in view A of figure 4-17, the capacitive filter (C1) is assumed to be large enough to ensure a small reactance to the pulsating rectified current. The resistance of RL is assumed to be much greater than the reactance of C1 at the input frequency. When the circuit is energized, the diode conducts on the positive half cycle

and current flows through the circuit, allowing C1 to charge. C1 will charge to approximately the peak value of the input voltage. (The charge is less than the peak value because of the voltage drop across the diode (D1)). In view A of the figure, the charge on C1 is indicated by the heavy solid line on the waveform. As illustrated in view B, the diode cannot conduct on the negative half cycle because the anode of D1 is negative with respect to the cathode.

During this interval, C1 discharges through the load resistor (RL). The discharge of C1 produces the downward slope as indicated by the solid line on the waveform in view B. In contrast to the abrupt fall of the applied ac voltage from peak value to zero, the voltage across C1 (and thus across RL) during the discharge period gradually decreases until the time of the next half cycle of rectifier operation. Keep in mind that for good filtering, the filter capacitor should charge up as fast as possible and discharge as little as possible.

50After the capacitor has charged to its peak value, the diode will cut off and the capacitor will start to discharge. Since the fall of the ac input voltage on the anode is considerably more rapid than the decrease on the capacitor voltage, the cathode quickly become more positive than the anode, and the diode ceases to conduct. Operation of the simple capacitor filter using a full-wave rectifier is basically the same as that discussed for the half-wave rectifier. Referring to figure 4-18, you should notice that because one of the diodes is always conducting on. either alternation, the filter capacitor charges and discharges during each half cycle. (Note that each diode conducts only for that portion of time when the peak secondary voltage is greater than the charge across the capacitor.)

Full-wave rectifier (with capacitor filter).

Another thing to keep in mind is that the ripple component (E r) of the output voltage is an ac voltage and the average output voltage (Eavg) is the dc component of the output. Since the filter capacitor offers a relatively low impedance to ac, the majority of the ac component flows through the filter capacitor. The ac component is therefore bypassed (shunted) around the load resistance, and the entire dc component (or Eavg) flows through the load resistance. This statement can be clarified by using the formula for XC in a half-wave and full-wave rectifier. First, you must establish some values for the circuit.

As you can see from the calculations, by doubling the frequency of the rectifier, you reduce the impedance of the capacitor by one-half. This allows the ac component to pass through the capacitor more easily. As a result, a full-wave rectifier output is much easier to filter than that of a half-wave rectifier. Remember, the smaller the XC of the filter capacitor with respect to the load resistance, the better the filtering action. Since the largest possible capacitor will provide the best filtering. Remember, also, that the load resistance is an important consideration. If load resistance is made small, the load current increases, and the average value of output voltage (Eavg) decreases. The RC discharge time constant is a direct function of the value of

the load resistance; therefore, the rate of capacitor voltage discharge is a direct function of the current through the load. The greater the load current, the more rapid the discharge of the capacitor, and the lower the average value of output voltage. For this reason, the simple

capacitive filter is seldom used with rectifier circuits that must supply a relatively large load current. Using the simple capacitive filter in conjunction with a full-wave or bridge rectifier provides improved filtering because the increased ripple frequency decreases the capacitive reactance of the filter capacitor.

51 RESISTORS Resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit. Resistors can also be used to provide a specific voltage for an active device such as a transistor. All other factors being equal, in a direct-current (DC) circuit, the current through a resistor is inversely proportional to its resistance and directly proportional to the voltage across it. This is the well-known Ohm's Law. In alternating-current (AC) circuits, this rule also applies as long as the resistor does not contain inductance or capacitance. Resistors can be fabricated in a variety of ways. The most common type in electronic devices and systems is the carbon-composition resistor. Fine granulated carbon (graphite) is mixed with clay and hardened. The resistance depends on the proportion of carbon to clay; the higher this ratio, the lower the resistance. Another type of resistor is made from winding Nichrome or similar wire on an insulat-ing form. This component, called a wire wound resistor, is able to handle higher currents than a carbon-composition resistor of the same physical size. However, because the wire is wound into a coil, the component acts as an inductors as well as exhibiting resistance. This does not affect performance in DC circuits, but can have an adverse effect in AC circuits because in-ductance renders the device sensitive to changes in output.

VARIABLE RESISTOR

Variable resistors consist of a resistance track with connections at both ends and a wiper which moves along the track as you turn the spindle. The track may be made from carbon, cermets (ceramic and metal mixture) or a coil of wire (for low resistances). The track is usually rotary but straight track versions, usually called sliders, are also available.Variable resistors may be used as a rheostat with two connections (the wiper and just one end of the track) or as a potentiometer with all three connections in use. Miniature versions called presets are made for setting up circuits which will not require further adjustment.

Variable resistors are often called potentiometers in books and catalogues. They are specified by their maximum resistance, linear or logarithmic track, and their physical size. The standard spindle diameter is 6mm.

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CAPACITOR:

A capacitor is a tool consisting of two conductive plates, each of which hosts an opposite charge. These plates are separated by a dielectric or other form of insulator, which helps them maintain an electric charge. There are several types of insulators used in capacitors. Examples include ceramic, polyester, tantalum air, and polystyrene. Other common capacitor insulators include air, paper, and plastic. Each effectively prevents the plates from touching each other. A capacitor is often used to store analogue signals and digital data. Another type of capacitor is used in the telecommunications equipment industry. This type of capacitor is able to adjust the frequency and tuning of telecommunications equipment and is often referred to a variable capacitor. A capacitor is also ideal for storing an electron. A capacitor cannot, however, make electrons.

SYMBOL

A capacitor measures in voltage, which differs on each of the two interior plates. Both plates of the capacitor are charged, but the current flows in opposite directions. A capacitor contains 1.5 volts, which is the same voltage found in a common AA battery. As voltage is used in a capacitor, one of the two plates becomes filled with a steady flow of current. At the same time, the current flows away from the other plate. To understand the flow of voltage in a capacitor, it is helpful to look at naturally occurring examples. Lightning, for example, is similar to a capacitor. The cloud represents one of the plates and the ground represents the other. The lightning is the charging factor moving between the ground and the cloud.

Image of Capacitor

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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.

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.

Fiber optic data transmission: Ease of modulation allows wide communications bandwidth with minimal noise, resulting in high speed and accuracy.

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

optoisolator: Stages in an electronic system can be connected together without unwanted interaction.

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Project practical circuit photo:

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Practical circuit output photo:

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Chapter-5

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 we are outside .• We 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 we forget to switch off and go out).• We 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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Conclusions & Future work

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

It is simple to control the operation of any where appliances by exploiting the ex-isting 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 spe-cific 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 we did not use 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 op-tions and security control. As a future work in the field of the presented project, we suggest to develop the sys-tem using PLCs or Microcontrollers, to give more reliability and control options, as temperat-ure control, security and more computational work so the system can do more than just turn On/Off the devices. By placing the gsm module and sensors we can able get more advance for this pro-ject to get the message.

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References:

[1] Fathia H. A. Salem, A Design of a Home Appliances Control System using Cell phone.

[2] Sen M Kuo, Bob H Lee, Wenshun Tian, Real-Time Digital Signal Processing

Implementations and Applications, Second Edition, John Wiley & Sons, Ltd, 2006.

[3] Electronics Devices And Circuits by A.P.Godse,U.A.Bakshi

[4] Electronics Devices And Circuits by shalivahanan

[5] Analysis and Design of Analog Integrated Circuits by Paul R.Gray

[6] Gunter Schmer, DTMF Tone Generation and Detection: An Implementation Using the

TMS320C54x, Application Report, Texas Instrument, May 2000

[7] Sanjit K. Mitra, Digital Signal Processing, Second Edition, McGraw-Hill, University

of California, International Edition, 2002.

[8] “8051 and embedded system” by Mazidi .

[9] Theodore S. Rappaport, Wireless Communications, second edition, PHI. NewDelhi

[10] R.S. Sedha, 2002. A Text Book of Applied Electronics, S. Chand andCompany Ltd., New Delhi

[9] Embedded system design by Frank Vahid

[10] Integrated circuits by bakshi.

[11]www.engineersgarage.com

[12]www.ehow.com

[13] www.gnokii.org,

[14] www.google.com

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