Mini project Report On

DTMF Tele switch

CONTENTS

Sl No. Contents Page No

1. Cover Page 2

2. Certificate 3

3. Acknowledgement 4

4. Contents 5

5. Abstract 6

6. Introduction 7

7. Block Diagram 8

8. Circuit Diagram

9. Components Description

10. Circuit Description

12. Results & Conclusion

13. Future Scope

14 Reference

APPENDIX

Data sheets

ABSTRACT

Traditionally electrical appliances in a home are controlled via switches that regulate the electricity to these devices. As the world gets more and more technologically advanced, we find new technology coming in deeper 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 technology 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 wireless 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. The encoder encodes the user choice and sends via a FM transmitter. The FM receiver receives the modulated signal and demodulates it and the user choice is determined by the DTMF decoder. Based upon this the required appliance is triggered.

INTRODUCTION

The aim of the proposed system is to develop a cost effective solution that will provide controlling of home appliances remotely and enable home security against intrusion in the absence of homeowner. 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. These devices should be controlled as well as turn on/off if required. Most of the times it was done manually. Now it is a necessity to control devices more effectively and efficiently at any time from anywhere. In this system, we are going to develop a cellular phone based home/office appliance. This system is designed for controlling arbitrary devices, it includes a cell phone (not included with the system kit, end user has to connect his/her cell phone to the system) which is connect to the system via head set. To active the cellular phone unit on the system a call is to be made and as the call is answered, in response the user would enter a two/three digit password to access the system to control devices. As the caller press the specific password, it results in turning ON or OFF specific device. The device switching is achieved by Relays. Security preserved because these dedicated passwords owned and known by selected persons only. For instance, our system contains an alarm unit giving the user a remote on/off mechanism, which is capable of informing up to five different numbers over telephony network about the nature of the event.The underlying principle mainly relies up on the ability of DTMF (Double Tune Multi Frequency) ICs to generate DTMF corresponding to a number or code in the number pad and to detect the same number or code from its corresponding DTMF. 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 frequencies. The DTMF frequencies representing the number/ codes are shown below.

BLOCK DIAGRAM

CIRCUIT DIAGRAM

Power Supply Circuit:

Control Circuit:

D2

LED

R1

330E

C2

100u

F/16

V

C1

470uF/25V

9V I/P

121

2U3

LM7805

1 3

2

IN OUT

GND

- +

D1

DB106

1

2

3

4

C30.1uF

WORKING:

The working of the circuit is quite simple and easily understandable by jus observing the circuit. The working can be mainly discussed as three parts which are the supply part, micro-controller part and the isolation part respectively. All these parts together describe the working of the design of Home automation system.

The supply part/section mainly deals with the supply given to the circuit. Actually it can be done in two ways i.e., either by giving 230V AC or by using a battery (9V) as source of supply. Now in this design we are using a 9V battery as source of supply. This 9v is regulated to 5V using a voltage regulator as only 5V is required to drive the microcontroller. This 5V is also given to the receiver. Actual working of this system involves an RC5 remote which is used as Transmitter and TSOP1738 as IR receiver. And here we are designed the system for only 6 applications. So only 6 buttons are used in the RC5 remote. Each button is given certain address depending on the number of duty cycles it has for 1ns. When a button is pressed, say 1, the receiver receives the signal from the RC5 remote and the next operation is done by the micro-controller part.

In micro-controller section, there are mainly 2 parts. They are AT89C2051 micro-controller and ULN 2003 driver (Darlington transistor). The microcontroller intakes the received signal from the IR receiver (TSOP 1738). The main use of this controller is that it recognizes and counts the number of duty cycles the received signal has and then makes the respective output pin high according to the calculations done by it internally. For example, let us consider that the button 1 has 1500 duty cycles in 1nS. When this button is pressed, the transmitter in the remote sends this signal and the receiver receives the signal. The received signal also contains same number of duty cycles but the micro controller confirms it with the help of the external timers it has. After confirmation, the controller makes the first output high. Here both the transmitter and receiver are of Infrared type. This output is connected to Darlington transistor (ULN 2003) which is used to drive the application. This gives a much higher current gain and also improves the life of the microcontroller. All the six out puts of micro controller are given as input to the Darlington transistor/pair IC which improves the gain of those outputs and gives the respective six outputs. These outputs are connected to the Opto-Isolator which is discussed in the isolation part.

The Isolation part involves the isolation of the AC and DC i.e., the output from the controller is DC and the Input to the application required is AC and to make difference of this nature of supply, an Opto isolator (MOC 3021) is used in between them. The MOC 3021 IC consists of a The input to the isolator is taken from the Darlington transistor IC. The pin1 of this Isolator IC is given to the supply or is in High state and the second pin is grounded. The output from the ULN2003 IC is connected to the second pin of the MOC 3021 IC which is low. The IC internally consists of a LED and a DIAC. Whenever the led glows, the DIAC gets triggered and hence fires the gate of the TRIAC connected to the IC. A feedback resistance is used for this operation.

Let us assume that a bulb is used as application here. One terminal of this bulb is connected to the AC supply and the other is connected to the TRIAC. When the TRIAC gets fired the bulb glows. This is the working of the Home Automation System using IR signal.

COMPONENTS USED:

1. Rectifier(IN4007 Diodes)2. Voltage Regulator3. TSOP 17384. Crystal oscillator5. Triac bt1366. Moc 30217. ULN 2003.8. 2051 Uc9. RTC

COMPONENTS DESCRIPTION

1.RectifierRectifier circuits are found in all dc power supplies that operate from an ac

voltage source. They convert the ac input voltage to a pulsating dc voltage. The most

basic type of rectifier circuit is the half-wave rectifier. Although half-wave rectifiers have

some applications, the full-wave rectifiers are the most commonly used type in dc power

supplies. These are two types of full-wave rectifiers:

(1) full-wave center-tapped rectifier

(2) full-wave bridge rectifier

Here in this particular design we are using a bridge rectifier which is discussed as

follows.

Full-wave Bridge Rectifier

The full –wave bridge rectifier uses four diodes, as shown in below figure. When

the input cycle is positive, diodes D1 and D2 are forward-biased and conduct current

through RL. During this time, diodes D3 and D4 are reverse-biased.

During positive half-cycles of the input, D1 and D2 are forward-biased and conduct

current, D3 and D4 are reverse-biased.

When the input cycle is negative as shown in below figure, diodes D3 and D4 are

forward-biased and conduct current in the same direction through RL as during the

positive half-cycle. During the negative half-cycle, D1 and D2 are reverse-biased. A full-

wave rectifier output voltage appears across RL as a result of this action.

During negative half-cycles of the input, D3 and D4 are forward-biased and conduct

current, D1 and D2 are reverse-biased.

The above two figures explain the full-wave Bridge Rectifier.The output graph of a full-wave rectifier is as shown below:

The diodes used in this rectifier are IN4007 which is discussed below.

IN4007 Diode

These diodes are used to convert AC into DC these are used as half wave rectifier or full wave rectifier. Three points must he kept in mind while using any type of diode.

1. Maximum forward current capacity 2. Maximum reverse voltage capacity 3. Maximum forward voltage capacity

The number and voltage capacity of some of the important diodes available in the market are as follows:

Diodes of number IN4001, IN4002, IN4003, IN4004, IN4005, IN4006 and IN4007 have maximum reverse bias voltage capacity of 50V and maximum forward current capacity of 1 Amp.

Diode of same capacities can be used in place of one another. Besides this diode of more capacity can be used in place of diode of low capacity but diode of low capacity cannot be used in place of diode of high capacity. For example, in place of IN4002; IN4001 or IN4007 can be used but IN4001 or IN4002 cannot be used in place of IN4007.The diode BY125made by company BEL is equivalent of diode from IN4001 to IN4003. BY 126 is equivalent to diodes IN4004 to 4006 and BY 127 is equivalent to diode IN4007.

2.Voltage Regulator

A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level. It may use an electromechanical mechanism, or passive or active electronic components. Depending on the design, it may be used to regulate one or more AC or DC voltages.

With the exception of passive shunt regulators, all modern electronic voltage regulators operate by comparing the actual output voltage to some internal fixed reference voltage. Any difference is amplified and used to control the regulation element in such a way as to reduce the voltage error. This forms a negative feedback servo control loop; increasing the open-loop gain tends to increase regulation accuracy but reduce stability (avoidance of oscillation, or ringing during step changes). There will also be a trade-off between stability and the speed of the response to changes. If the output voltage is too low (perhaps due to input voltage reducing or load current increasing), the regulation element is commanded, up to a point, to produce a higher output voltage - by dropping less of the input voltage (for linear series regulators and buck switching regulators), or to draw input current for longer periods (boost-type switching regulators); if the output voltage is too high, the regulation element will normally be commanded to produce a lower voltage. However, many regulators have over-current protection, so entirely stop sourcing current (or limit the current in some way) if the output current is too high, and some regulators may also shut down if the input voltage is outside a given range (see also: crowbar circuits).The voltage Regulator used in this design is LM 7812.LM78xx Regulator The LM78XX series of three terminal regulators is available with several fixed output voltages making them useful in a wide range of applications. One of these is local on card regulation, eliminating the distribution problems associated with single point regulation. The voltages available allow these regulators to be used in logic systems, instrumentation, Hi-Fi, and other solid state electronic equipment. Although designed primarily as fixed voltage regulators these devices can be used with external components to obtain adjustable voltages and currents. The LM78XX series is available in an aluminum TO-3 package which will allow over 1.0A load current if adequate heat sinking is provided. Current limiting is included to limit the peak output

current to a safe value. Safe area protection for the output transistor is provided to limit internal power dissipation.If internal power dissipation becomes too high for the heat sinking provided, the thermal shutdown circuit takes over preventing the IC from overheating. Considerable effort was expanded to make the LM78XX series of regulators easy to use and minimize the number of external components. It is not necessary to bypass the output, although this does improve transient response. Input bypassing is needed only if the regulator is located far from the filter capacitor of the power supply.For output voltage other than 5V, 12V and 15V the LM117 series provides an output voltage range from 1.2V to 57V.Features- Output current in excess of 1A- Internal thermal overload protection- No external components required- Output transistor safe area protection- Internal short circuit current limit- Available in the aluminum TO-3 packageVoltage Range

LM7805C 5VLM7812C 12VLM7815C 15V

3. TSOP1738 - Infrared Receiver

Introduction

TSOP1738 is an Infrared (IR) receiver which is widely used in large number of electronic products for receiving and demodulating infrared signals. The received demodulated signals can be easily decoded by a microcontroller. It supports RC5, RC6 code, Sony format (SIRCS), NEC code, Sharp code, etc.

Specifications

Continuous data transmission possible (up to 2400 bps) High immunity against ambient light Photo detector and preamplifier in one package Improved shielding against electrical field disturbance TTL and CMOS compatibility Active low output Low power consumption Internal filter for PCM freq

The datasheet for TSOP1738 is as shown below;

**DATASHEET**

4. Crystal Oscillators

One of the most important features of an oscillator is its Frequency Stability, or in other words its ability to provide a constant frequency output under varying conditions. Some of the factors that affect the frequency stability of an oscillator include: temperature, variations in the load and changes in the power supply. Frequency stability of the output signal can be improved by the proper selection of the components used for the resonant feedback circuit including the amplifier but there is a limit to the stability that can be obtained from normal LC and RC tank circuits. For very high stability a quartz crystal is generally used as the frequency determining device to produce other types of oscillator circuit known generally as Crystal Oscillators.

When a voltage source is applied to a small thin piece of crystal quartz, it begins to change shape producing a characteristic known as the Piezo-electric Effect. This piezo-electric effect is the property of a crystal by which an electrical charge produces a mechanical force by changing the shape of the crystal and vice versa, a mechanical force applied to the crystal produces an electrical charge. Then, piezo-electric devices can be classed as transducers as they convert energy of one kind into energy of another. This piezo-electric effect produces mechanical vibrations or oscillations which are used to replace the LC tank circuit and can be seen in many different types of crystal substances with the most important of these for electronic circuits being the quartz minerals because of their greater mechanical strength.

The quartz crystal used in Crystal Oscillators is a very small, thin piece or wafer of cut quartz with the two parallel surfaces metalized to make the electrical connections. The physical size and thickness of a piece of quartz crystal is tightly controlled since it affects the final frequency of oscillations and is called the crystals "characteristic frequency". Then once cut and shaped the crystal can not be used at any other frequency. The crystals characteristic or resonant frequency is inversely proportional to its physical thickness between the two metalized surfaces. A mechanically vibrating crystal can be represented

by an equivalent electrical circuit consisting of low Resistance, large Inductance and small Capacitance as shown below.

Quartz Crystal

A quartz crystal has a resonant frequency similar to that of a electrically tuned tank circuit but with a much higher Q factor due to its low resistance, with typical frequencies ranging from 4kHz to 10MHz. The cut of the crystal also determines how it will behave as some crystals will vibrate at more than one frequency. Also, if the crystal is not of a parallel or uniform thickness it have two or more resonant frequencies having both a fundamental frequency and harmonics such as second or third harmonics. However, usually the fundamental frequency is more stronger or pronounced than the others and this is the one used. The equivalent circuit above has three reactive components and there are two resonant frequencies, the lowest is a series type frequency and the highest a parallel type resonant frequency.

We have seen in the previous tutorials, that an amplifier circuit will oscillate if it has a loop gain greater or equal to 1 and it has positive feedback. In a Crystal Oscillator circuit the oscillator will oscillate at the crystals fundamental series resonant frequency as the crystal always wants to oscillate when a voltage source is applied to it. However, it is also possible to "tune" a crystal oscillator to any even harmonic of the fundamental frequency, (2nd, 4th, 8th etc.) and these are known generally as Harmonic Oscillators while Overtone Oscillators vibrate at odd multiples of the fundamental frequency, 3rd, 5th, 11th etc). Generally, crystal oscillators that operate at overtone frequencies do so using their series resonant frequency.

**DATASHEET**

5. TRIAC

INTRODUCTION Approvals in their outer aspect, SCR and TRIAC are resembled like many water drops. To distinguish them, therefore, is impossible, if it is not rerun to the exact

acknowledgment of the acronym and to the ritrovamento of this on a common prontuario. But the acronyms, today attributed to these semiconductors, are many, too many for being collections all in a handbook modernized to the capacity of the amateurs. Which, often, during their activity, are found in embarrassment, because, ignoring the characteristic electrical workers, they cannot lead those tests that serve to identify the components and to know their state of efficiency. Here because the idea is risen us to conceive a simple circuit, of immediate realization, absolutely economic, to entrust our hobbyist readers, with which they can distinguish, with a sure rapidity, a SCR from a TRIAC, estimating some, at the same time, the behavior electrical worker, is worth to say the validity works them. But since the principle of operation of the device is based on the use, from part of the SCR, of average cycle of the alternated voltage, while the TRIAC works with the entire cycle of the same voltage, alla presentation of the apparatus must make to precede those theoretical slight knowledge that regulates the way to behave itself of these particular diode , that by now all know and whose employment is often from we prescribed for the construction of the many plans that, month for month, come publishes to you on this periodical.

SCR: STRUCTURES and SYMBOLS

Known also under the name of controlled diode, the SCR inner is composed from three P-N splices, that they form a semiconductor of P-N-P-N type, similar to two normal diode  connects to you in series. They finishes relative to the anode makes head more external the P semiconductor, while the cathode remains connected with the N semiconductor situated in the opposite part. A1 according to field of P material is connected the representative electrode of the gate ones, said also "door". The symbol electrical worker, that it characterizes diode  SCR, is that one represented in figure 1, while the outer aspect more common than this semiconductor it can be identified with one of the graphical expressions brought back in figure 2.

DIODE 

Fig. 1 - Symbol electrical worker of diode SCR, famous also with the denomination of controlled diode. With the G letter it comes indicated the electrode of gate, or door, through which it comes applied to the component the voltage impulse that of it provokes the conduction (primes). With the letter To the electrode of anode is marked and with the K that one of cathode.               

Fig. 2 - These are the two types of diode SCR (silicon-controlled-rectifier) more commonly findable in commerce and mainly it uses you from the amateurs.

Operation of the SCRApplying to the anode of the SCR a negative voltage regarding the cathode, some conduction is not obtained electrical worker, therefore as it happens in a common semiconductor diode . The SCR can therefore be assimilated to an open switch. Inverting the polarity of the voltage, the SCR contrarily remains still blocked to how much happens in a normal diode , in which conduction would be had electrical worker; but the block remains until does not arrive on gate a positive impulse regarding the cathode, of such amplitude to put the diode  controlled in complete conduction. And this commutation happens in a extremely short time, of the order of 0,5 us. As it can immediately be deduced, this time is the much short one than that one demanded from the analogous electromechanical systems. Once primed, the SCR remains conductor without need of some voltage of commando on the gate. conserving this condition also when on the gate ones they come applies new impulses to you of commando. For turning off the SCR, that is in order to bring back it to the state of interdiction, two exist arrange: the voltage between anode can be reduced to zero and cathode, or the anode regarding the cathode can be made to become negative. In this case the alternated voltage is revealed much useful, because it passes for the zero when it inverts the own polarity to every semi period. In figure 5 light bulb to filament in alternating current is introduced the example of a according to electronic interrupting SCR in a circuit of feeding of one. We see of it hour the behavior theoretical.

Fig. 5 - Theoretical circuit of application of a according to interrupting diode  SCR, closed or open, of ignition of lamp LP.In absence of it marks them on the gate ones, the SCR is behaved like a opened switch, that is it does not lead current and lamp LP remains extinguished. But when an impulse

of voltage to every half-cycle of the alternated voltage is applied, the switch closes itself and lamp LP is ignited. Not however in the full load of its brightness, because the SCR is behaved like a normal diode  in series to the circuit, that it straightens the alternated voltage. In practical, the ignition of the lamp is reduced to 50%. In figure 6 the new condition is illustrated electrical worker of the circuit of figure 5, in which I SCR transforms in a diode  rectifier of the alternated voltage.

Fig. 6 - The diode  SCR, connected in series with a conductor covered from alternating current, is behaved like a rectifying element, leaving via free the passage of the sun positive semi-waves.OPERATION OF THE TRIACIn figure 7 the theoretical application of a TRIAC, analogous is brought back to that one of the SCR of figure 5.

Fig. 7 - Example of employment of a TRIAC, as electronic switch, in a circuit of ignition of one lamp fed in alternating current (C.A).In absence of tension impulse that in this case, with the exception of how much it happens in the SCR can be is positive that negative, the TRIAC does not lead, that is is behaved as an open switch and lamp LP remains extinguished. Applying instead one small tension, positive or negative, on the gate ones, the TRIAC becomes conductor and is equivalent to a closed switch. But this time the semiconductor let’s to cross from both the semi waves of the alternated tension, as it indicates the design of figure 8. 

Fig. 8 - Since in the TRIAC two diode  are contained connect to you in ant parallel, all the semi waves, those positive ones and those negatives of the alternating current cross the semiconductor.And that because the inner structure of the TRIAC is correspondent to that one of two diode  SCR connects to you in parallel, with the polarity opposite. in ant parallel. but with

the electrode of I prime in common.We have said that the TRIAC can be primed applying a tension impulse on its gate ones. But this auto innesca component when the value of the tension alternated applied on the two anodes exceeds a sure limit, called tension of breakdown. Making then to diminish the current and to increase the cargo resistance of the TRIAC, a point is caught up in which the current it is not more in a position to maintaining in conduction the semiconductor.The minimal value of the current that can maintain primed the TRIAC comes commonly indicated like current of Hold, that is maintenance current.

**DATASHEET**

6. Opto-isolator

An opto-isolator integrated circuit. The "MB 111", manufactured by RFT ("Rundfunk- und Fernmelde-Technik"), contains an infrared LED and silicon photodiode with an integrated amplifier stage.This article is about the electronic component. For the optical component, see optical isolator.

In electronics, an opto-isolator (or optical isolator, optical coupling device, opt coupler, photo coupler, or photoMOS) is a device that uses a short optical transmission path to transfer an electronic signal between elements of a circuit, typically a transmitter and a receiver, while keeping them electrically isolated—since the electrical signal is converted to a light beam, transferred, then converted back to an electrical signal, there is no need for electrical connection between the source and destination circuits. Isolation between input and output is rated at 7500 Volt peak for 1 second for a typical component costing less than 1 US$ in small quantities.

The opto-isolator is simply a package that contains both an infrared light-emitting diode (LED) and a photo detector such as a photosensitive silicon diode, transistor Darlington pair, or silicon controlled rectifier (SCR). The wave-length responses of the two devices are tailored to be as identical as possible to permit the highest measure of coupling possible. Other circuitry—for example an output amplifier—may be integrated into the package. An opto-isolator is usually thought of as a single integrated package, but opto-isolation can also be achieved by using separate devices.

Digital opto-isolators change the state of their output when the input state changes; analog isolators produce an analog signal which reproduces the input.

Configurations

Schematic diagram of a very simple opto-isolator with an LED and phototransistor. The dashed line represents the isolation barrier, over which there is no electrical contact.

A common implementation is a LED and a phototransistor in a light-tight housing to exclude ambient light and without common electrical connection, positioned so that light from the LED will impinge on the photo detector. When an electrical signal is applied to the input of the opto-isolator, its LED lights and illuminates the photo detector, producing a corresponding electrical signal in the output circuit. Unlike a transformer the opto-isolator allows DC coupling and can provide any desired degree of electrical isolation and protection from serious overvoltage conditions in one circuit affecting the other. A higher transmission ratio can be obtained by using a Darlington instead of a simple phototransistor, at the cost of reduced noise immunity and higher delay.

With a photodiode as the detector, the output current is proportional to the intensity of incident light supplied by the emitter. The diode can be used in a photovoltaic mode or a photoconductive mode. In photovoltaic mode, the diode acts as a current source in parallel with a forward-biased diode. The output current and voltage are dependent on the load impedance and light intensity. In photoconductive mode, the diode is connected to a supply voltage, and the magnitude of the current conducted is directly proportional to the intensity of light. This optocoupler type is significantly faster than photo transistor type, but the transmission ratio is very low; it is common to integrate an output amplifier circuit into the same package.

The optical path may be air or a dielectric waveguide. When high noise immunity is required an optical conductive shield can be integrated into the optical path. The transmitting and receiving elements of an optical isolator may be contained within a single compact module, for mounting, for example, on a circuit board; in this case, the module is often called an optoisolator or opto-isolator. The photo sensor may be a photocell, phototransistor, or an optically triggered SCR or TRIAC. This device may in turn operate a power relay or contactor.

Analog opt isolators often have two independent, closely matched output phototransistors, one of which is used to linearize the response using negative feedback.

Application

A simple circuit with an opto-isolator. When switch S1 is closed, LED D1 lights, which trigger phototransistor Q1, which pulls the output pin low. This circuit, thus, acts as a NOT gate.

Among other applications, opto-isolators can help cut down on ground loops, block voltage spikes, and provide electrical isolation.

Switched-mode power supplies use optocouplers for mains isolation. As they work in an environment with much electrical noise and with signals which are not small, optocouplers with low transmission ratio are preferred.

Where electrical safety is paramount, optocouplers can totally isolate circuitry which may be touched by humans from mains electricity.

o Medical equipment often uses optocouplers.o One of the requirements of the MIDI (Musical Instrument Digital

Interface) standard is that input connections be opto-isolated.o Oscilloscope and digital millimeters with computer interface.

Optocouplers are used to isolate low-current control or signal circuitry from transients generated or transmitted by power supply and high-current control circuits. The latter are used within motor and machine control function blocks.

7. ULN 2003In electronics, the Darlington transistor (often called a Darlington pair) is a

compound structure consisting of two bipolar transistors (either integrated or separated devices) connected in such a way that the current amplified by the first transistor is amplified further by the second one. This configuration gives a much higher current gain (written β, hfe, or hFE) than each transistor taken separately and, in the case of integrated devices, can take less space than two individual transistors because they can use a shared collector. Integrated Darlington pairs come packaged in transistor-like packages.

A Darlington pair can be sensitive enough to respond to the current passed by skin contact even at safe voltages. Thus it can form the input stage of a touch-sensitive switch.The datasheet of this transistor is as shown below.**DATASHEET**

8. 2051 Microcontroller:

The 2051 is a 20 pin version of the 8051. It is a low-voltage, high-performance CMOS 8-bit microcomputer with 2K bytes of Flash programmable and erasable read only memory. Atmel manufactures the chip using high-density nonvolatile memory technology. The 2051 and is compatible with the industry-standard MCS-51 instruction set. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel 2051 is a powerful microcontroller. It provides a very flexible, cost-effective solution to many embedded control applications.  Operational features of the 2051The 2051 features Compatibility with MCS-51 ™ Products, 2K Bytes of Reprogrammable Flash Memory with 1,000 Write/Erase Cycles. The operating range of the 2051 is 2.7V to 6V. Among these features, the 2051 also contains the following features:Fully Static Operation: 0 Hz to 24 MHz Two-level Program Memory Lock 128 x 8-bit Internal RAM 15 Programmable I/O Lines Two 16-bit Timer/Counters Six Interrupt Sources Programmable Serial UART Channel Direct LED Drive Outputs On-chip Analog Comparator Low-power Idle and Power-down Modes 2051 Pin-out and Description

 Pin Description Pin Name:                                       Purpose:VCC                                                               Supplies voltage and power. GND                                                               Ground. Port 1                                                              Port 1 is an 8-bit bi-directional I/O port. Port pins P1.2 toP1.7 provide internal pull-ups. P1.0 and P1.1 require external pull-ups. P1.0 and P1.1 also serve as the positive input (AIN0) and the negative input (AIN1), respectively, of the on-chip precision analog comparator. The Port 1 output buffers can sink 20mA and can drive LED displays directly. When 1s are written to Port 1 pins, they can be used as inputs. When pins P1.2 to P1.7 are used as inputs and are externally pulled low, they will source current (IIL) because of the internal pull-ups. Port 1 also receives code data during Flash programming and verification. Port 3                                                              Port 3 pins P3.0 to P3.5, P3.7 are seven bi-directional I/O pins with internal pull-ups. P3.6 is hard-wired as an input to the output of the on-chip comparator and is not accessible as a general purpose I/O pin. The Port 3 output buffers can sink 20mA. When 1s are written to Port 3 pins they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 3 pins that are externally being pulled low will source current (IIL) because of the pull-ups.

Port 3 also serves the functions of various special features of the AT89C2051 as listed below:                                                                 

Port 3 also receives some control signals for Flash programming and verification. RST                                                                Reset input. All I/O pins are reset to 1s as soon as RST goes high. Holding the RST pin high for two machine cycles while the oscillator is running resets the device.Restrictions on InstructionsThe AT89C2051 and is the economical and cost-effective member of Atmel’s family of microcontrollers. Therefore, it contains only 2K bytes of flash program memory. It is fully compatible with the MCS-51 architecture, and can be programmed using the MCS-51 instruction set. However, there are a few considerations one must keep in mind when utilizing certain instructions to program this device. All the instructions related to jumping or branching should be restricted such that the destination address falls within the physical program memory space of the device, which is 2K for the AT89C2051. This should be the responsibility of the software programmer. For example, LJMP 7E0H would be a valid instruction for the AT89C2051 (with 2K of memory), whereas LJMP 900H would not.  1. Branching instructions: LCALL, LJMP, ACALL, AJMP, SJMP, JMP @A+DPTR These unconditional branching instructions will execute correctly as long as the programmer keeps in mind that the destination branching address must fall within the physical boundaries of the program memory size (locations 00H to 7FFH for the 89C2051). Violating the physical space limits may cause unknown program behavior.CJNE [...], DJNZ [...], JB, JNB, JC, JNC, JBC, JZ, JNZ  With these conditional branching instructions the same rule above applies. Again, violating the memory boundaries may cause erratic execution. For applications involving interrupts the normal interrupt service routine address locations of the 80C51 family architecture have been preserved. 

2. MOVX-related instructions, Data Memory: The 2051 contains 128 bytes of internal data memory. Thus, in the 2051 the stack depth is limited to 128 bytes, the amount of available RAM. External DATAmemory access is not supported in this device, nor is external PROGRAM memory execution. Therefore, no MOVX [...] instructions should be included in the program. A typical 80C51 assembler will still assemble instructions,even if they are written in violation of the restrictions mentioned above. It is the responsibility of the controller user to know the physical features and limitations of the device being used and adjust the instructions used correspondingly.BLOCK DIAGRAM OF 2051

Power-down ModeIn the power down mode the oscillator is stopped, and the instruction that invokes power down is the last instruction executed. The on-chip RAM and Special Function Registers retain their values until the power down mode is terminated. The only exit from power down is a hardware reset. Reset redefines the SFRs but does not change the on-chip RAM. The reset should not be activated before VCC is restored to its normal operating level and must be held active long enough to allow the oscillator to restart and stabilize.P1.0 and P1.1 should be set to “0” if no external pull-ups are used, or set to “1” if external pull-ups are used.The 2051 is a low voltage (2.7V - 6V), high performance CMOS 8-bit microcontroller with 2 Kbytes of Flash programmable and erasable read only memory (PEROM). This device is compatible with the industry standard 8051 instruction set and pin-out. The 2051 is a powerful microcomputer which provides a highly flexible and cost effective solution to many embedded control applications.   In addition, the 2051 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port and interrupt system to continue functioning. The Power Down Mode saves the RAM contents but freezes the oscillator disabling all other chip functions until the next hardware reset. Uses of the 2051 Microcontroller: The 2051 is used in many applications.          Controlling 7-segment displays -         Clocks        Sensor projects -         TemperatureUsed to Control LCD ( 8051 )**DATASHEET**

CIRCUIT DESCRIPTION

Now let's have a detailed look into the whole circuit section wisely. Before getting in to the description, for the sake of easiness, let's confirm our aim or let's predict our expectation regarding its working. We are supposed to send a code word from the mobile phone, which is the transmitter and is sending the corresponding DTMF frequencies along. At the receiver end, i.e. at the land line end we need to detect the code back using our circuitry and it is to be used for driving the devices, represented by the LEDs.

RING DETECTION_SECTION

Refer the circuit diagram of this sectionregarding the need of this section, we want to use this circuitry in the device mode i.e. to control the device's turn off and turn on while maintaining the normal functionality and usage of the land line to make and accept calls. So we must allow sometime for the land line to get into the off hook mode, also it is necessary to get the landline from on hook mode to off hook mode to enable the DTMF reception. If the land line is already in the off hook mode, then it won't be able to receive any signal as in the normal speech communication through networks. So using this section we are aiming to automatically activate our circuitry after a number of rings are heard from the landline, while the coupling for automation is done using a relay. Here we have designed such that the DTMF signals will automatically be coupled to the Decoding section just after the 6th ring.

Now getting into the detailed analysis, the initial high ring voltage is coupled to a zener diode circuitry to reduce the voltage level for protection, at the same time maintaining the enough magnitude for detection using the opto-coupler. See the details in the circuit diagram. Whenever a ring occurs a sufficient amount of ring voltage is established across the inputs of the opto-coupler which causes the internal transistor to conduct and effectively the output 5th and 4th pin to get short. This results in an effective coupling of input ring voltage to pass through. Now we will exploit this signal to use it as a clock signal for the decade counter IC 4017, which will produce a high logic level at its Q5 pin upon reception of the 6th ring, which was changed into a quality clock signal. The diode-resistor- capacitor network along with the NAND gates of the IC 4093 is used to shape up the irregular voltage signal obtained at the output of the opto- coupler into a quality clock pulse for the IC 4017. Because of this, as mentioned earlier, just after the 6th ring the counter 4017 will produce a high level at the Q5 pin till the next clock occurs. This logic 1 level of Q5 pin is then used to drive the monostable multivibrator using 555 timer IC through BC 547 transistor coupling. The monostable multivibrator is designed for a period of about 60 seconds which is the allotted time for the operator to control the device using the palm device he has. Thus the monostable multivibrator will produce logic 1 level for a period of about 60 seconds at its output which is used to drive a relay as shown through transistor coupling, which will couple a low resistance in between the RING and the TIP terminals of the landline, resulting in the manifestation of a DC loop driving the landline from ON HOOK to OFF HOOK preparing the decoding section for the reliable reception of the signal transmitted from the mobile phone.

Now, we have to contend with a problem arising from the past counting of the IC 4017. Suppose a fellow called to our landline and cut the phone at the 4th or 5th ring. After this if somebody calls again then right at the first ring the landline will get into the OFF HOOK mode contrary to our expectation at the 6th ring. How can we avoid this error? To solve this, what we have with us is only the RESET pin of IC 4017. So the solution is that we must reset the IC 4017 every time just after once the 6th ring has occurred or the decoding section is coupled for decoding.

So for this we use the retrigerrable monostable multivibrator using IC 74LS123 commonly called as the ISS-PULSE-DETECTOR. For this we supply the same clock pulse of 4017 to the IC74123, which has been designed for a period of more than twice as long as the duration of a single ring signal, which is about 5 seconds.

The out put from the 4th pin of IC 74123, which is the TOGGLED Q output, is then supplied to the active high RESET pin of IC 4017. Thus this arrangement will avoid the past counting nature of IC 4017 by resetting it just after the completion of the 6th ring and the consequent coupling of the decoding section. Now that we have effectively coupled the signals from the palm device to the decoding section, let's see how the decoding section performs the decoding function.

DECODING_ SECTION

Refer the circuit diagram of this section.when the 1k resistor is brought across the RING and TIP terminals the landline also brought to OFF HOOK mode so that the decoding section is now connected to the transmitted signal and can receive it.

The input capacitor-zener-resistor network is meant for both the protection of the DTMF decoder IC 8870 from comparatively higher ring voltage and the coupling of the signal to the same IC. Based on the reference DTMF frequencies the DTMF decoder IC 8870 decodes the binary equivalent of the keys or numbers in the number pad of the transmitting mobile phones. The decoding scenario of the IC 8870 can be consolidated as given below.

KEYS Q4 Q3 Q2 Q1 1 Off Off Off On

2 Off Off On Off

3 Off Off On On

4 Off On Off Off

5 O ff On Off On

6 Off On On Off

7 Off On On On

8 On Off Off O ff

9 On Off Off On

0 On Off On Off

* On Off On On

# On On Off On A On On Off On B On On On Off C On On On On D Off Off Off Off

The output of the DTMF decoder IC 8870 is binary code, which is then fed to the binary to decimal decoder IC 74HC154 retrieving the original transmitted key or number. But the IC 74HC154 has active low output pins. So these active low outputs are converted to active high ones by passing them through NOT gates. Note that here we are using only five outputs of IC 74HC154 to control four devices represented by LEDs as an instance. Specifically the pins we are using are the 13th pin which produces an active low corresponding to the code *, the 2nd pin which produces an active low corresponding to the code 1, the 3rd one for the code 2, the 4th one for the code 3 and finally the 5th one for the code 4. Thus in the decoding section we retrieve back the same number or code transmitted from the mobile phone.

OUT PUT_ SECTION Refer the circuit diagram of this section.using the converted active high

outputs of the decoding section we are now supposed to control the TURN OFF and TURN ON of four LEDs. The output corresponding to the code * from the decoding section is used to trigger a monostable circuitry in the output section, which is designed to produce a high pulse at it's output for a period of about 5 seconds. This high pulse with the duration of 5 seconds is used to activate the four tri-state buffers i.e. the ICs 74LS126 enabling the coupling of the respective inputs of the buffers to their respective outputs. Now with in this 5 second duration we can have our control signals to pass through the buffers and can be used to control the D flip flops i.e. the ICs 74LS74, which has been set in the latching mode to get its output toggled upon receiving consequent clock pulses, thus triggering the turn ON and turn OFF of the devices once the same code is transmitted for a second time. In a nutshell, the latching mode peration of D flip flops causes a device to get turn on from off state or vice versa on reception of the code word. The IC 74LS74 is a positive edge triggered IC. One of the practical limitation we face here is to create a positive edge at the clock input of the D flip flop IC, using the isolated pulse coming through the buffer to its output. If we directly apply the pulse to the D flip flop to work in the latching mode it won't work due to the lack of establishment of the positive edge to its clock input, resulting from the occurrence of logic 1 level at the clock input of D flip flop right at the time of biasing or when connected to the power supply. For this purpose to create a positive edge going from logic 0 level to logic 1 level we pass the pulse coming out of the buffer through another NOT gate as shown.

Finally, we need to find out a code which we have to transmit from the mobile phone so that we can establish a well shaped pulse as clock pulse at the clock input pin of the D flip flop for it to work in latching mode i.e. to get the LEDs turned on if they were in the off state and vice versa.

First of all we must activate the buffer in the output section for the predetermined time by triggering the monostable circuitry there in. So the first symbol in the code word should be *. Now, we need to transmit a high level through the activated buffer using another symbol specific to each of the device represented. From the circuit diagram we can see it can be 1 for the 1st device, 2 for the second one and so on.

Thus by sending *(ordinal number of the device) we can create a low to high transition at the out of the buffer. But it's not yet been a well defined pulse with both trailing and falling edge. So to get a falling edge we should now send a symbol other than ordinal number of the device. Let it also be * to have a convenient code. Now, as we know we use * for triggering the monostable circuitry in the output section we

must not end our code word with *. Other wise, it will cause the triggering input of the monostable multivibrator to continue in the logic 1 level even after the specified 5 seconds which in turn forces it not to get triggered for a second time on pressing * as there lacks the transition from low to high level at it's triggering input. Hence we must end our code word with a symbol other than both * and ordinal number of the device. Let it be 0. Thus, we got the code word that is to be send for our expected control as * ordinal number of the device*0. For example, to change the state of first device we have to send a code-*1*0, for the 2nd one *2*0 etc.

By following the similar logic, it is possible to find some other formats of code words. For example, the code word * ordinal number of the device 0 is also seeming to be worthy of.

Thus the whole control procedure can be consolidated as first of all we need to make a call to the land line, just after the 6th ring it will automatically get on to the OFF HOOK mode for about 1minutes, during this time we can control the required devices with code words of specified format with in the installments of 5 seconds.

Source Code:;///////// DTMF HAS\\\\\\\\\\\;---------=========------------; Ashwin LABS......;---------==========-----------

ORG 0000H MOV P0,#00H MOV P2,#00H

SWITCH4 EQU P3.0 SWITCH3 EQU P3.1 SWITCH2 EQU P3.2 SWITCH1 EQU P3.3

LED1 EQU P1.0 ; FF MODE ,RIGHT MODE LED2 EQU P1.1 ; BACK MODE LED3 EQU P1.6 ; BACK MODE LED4 EQU P1.7 ; FF MODE ,LIFT MODE LED5 EQU P0.1 ; LAMP , CAM NO/OFF STOPLED EQU P2.5 ; STOP LAMP

MOV P0,#0ffH MOV P2,#00H

ACALL DELAY

SJMP MAIN

;;;;;;;;;;;;;;;; MAIN PROG....;;;;;;;;;;;;MAIN:

JB SWITCH1,NEXT1JNB SWITCH3,LAMP134

JNB SWITCH2,LAMPOFFSETB LED2 ; BACK MODESETB LED3 ; BACK MODECLR STOPLED ; STOPLED

OFFCLR LED1CLR LED4 ACALL DELAY SJMP MAIN

NEXT1:JB SWITCH3,NEXT2JNB SWITCH2,RIGHTSETB LED1 ; FF MODESETB LED4 ; FF MODECLR STOPLED ; STOP LED

OFFCLR LED2CLR LED3ACALL DELAYSJMP MAIN

NEXT2:JB SWITCH2,NEXT3JNB SWITCH4,STOPSETB LED4 ; LIFT MODECLR STOPLED ; STOP LED OFFCLR LED1CLR LED2CLR LED3

ACALL DELAYacJMP MAIN

NEXT3: ACALL DELAY SJMP MAIN

RIGHT:

SETB LED1 ; RIGHT MODE CLR STOPLED ; STOP LED OFF CLR LED4 CLR LED2 CLR LED3 ACALL DELAY SJMP MAIN

STOP: SETB STOPLED ; STOP LED ON

CLR LED1 CLR LED2 CLR LED3 CLR LED4 ACALL DELAY LJMP MAIN

LAMP134:JNB SWITCH4,LAMPONACALL DELAYLJMP MAIN

LAMPON: SETB LED5 ACALL DELAY ; LAMP , CAM NO

LJMP MAINLAMPOFF: CLR LED5 ; LAMP , CAM OFF

ACALL DELAY LJMP MAIN

JB SWITCH1,NEXT1JNB SWITCH3,LAMP134

JNB SWITCHDD,LAMPOFFSETB LED2 ; BACK MODESETB LED3 ; BACK MODECLR STOPLED ; STOPLED

OFFCLR LED1CLR LED4 ACALL DELAY SJMP MAIN

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;DELAYA:

MOV 71H,#0FFH MOV 72H03H

LOOP: DJNZ 70H,LOOP DJNZ 71H,LOOP

RET END

DJNZ 70H,LOOP DJNZ 71H,LOOP

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

CONCLUSION

This project presents a dtmf based home appliances controlling. The controller based on closed loop algorithm is designed and implemented with Atmel MCU in embedded system the domain.

Experimental work has been carried out carefully.

Hence we are controlling 6 home appliances controlling through DTMF technology effectively. Because now a days GSM technology became very popular,here its very easy to use for any applications with the help of 8051 controller.In all low end applications now a days we are using 8051 controllers like industrial automation and data acquisition.

The Remote Automation using Networks [RAN] on test performed exceptionally well to its capability and accuracy. All the inherent parts of the circuit performed consistently. It helped us to come out with good judgment. With the features what it inherits, it seems to be advantageous to the present era.

Future Scope

The controller we used having the following featurtes like 8 bit 8051 architecture in a tiny

20pin DIP package,128B RAM and 4kB on-chip Flash Program Memory. For low end

applications this controller is very easy to use and at the same time GSM also widely

accepted protocol for mobile communication.

In future for small scale systems 8051 controllers can be widely used along with the help

of GSM technology.

Refrences

Text Books:

8051 and Embedded systems BY Mazidi

Website:

www.howstuffworks.com

www.answers.com

www.radiotronix.com

Magazines:

Electronics for you

Electrikindia

Let us Go Wireless