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Introduction. Power line communication or power line carrier (PLC), also known as power line digital subscriber line (PDSL), mains communication, power line telecom (PLT), power line networking (PLN), or broadband over power lines (BPL) are systems for carrying data on a conductor also used for electric power transmission. A wide range of power line communication technologies are needed for different applications, ranging from home automation to Internet access. Electrical power is transmitted over long distances using high voltage transmission lines, distributed over medium voltages, and used inside buildings at lower voltages. Most PLC technologies limit themselves to one set of wires (such as premises wiring within a single building), but some can cross between two levels (for example, both the distribution network and premises wiring). Typically transformers prevent propagating the signal, which requires multiple technologies to form very large networks. Various data rates and frequencies are used in different situations.A number of difficult technical problems are common between wireless and power line communication, notably those of spread spectrum radio signals operating in a crowded environment. Power line communications systems operate by impressing a modulated carrier signal on the wiring system. Different types of powerline communications use different frequency bands, depending on the signal transmission characteristics of the power wiring used. Since the power distribution system was originally intended for transmission of AC power at typical frequencies of 50 or 60Hz, power wire circuits have only a limited ability to carry higher frequencies. The propagation problem is a limiting factor for each type of power line communications.Data rates and distance limits vary widely over many power line communication standards. Low-frequency (about 100-200 kHz) carriers impressed on high-voltage transmission lines may carry one or two analog voice circuits, or telemetry and control circuits with an equivalent data rate of a few hundred bits per second; however, these circuits may be many miles long. Higher data rates generally imply shorter ranges; a local area network operating at millions of bits per second may only cover one floor of an office building, but eliminates the need for installation of dedicated network cabling.Utility companies use special coupling capacitors to connect radio transmitters to the power-frequency AC conductors. Frequencies used are in the range of 24 to 500 kHz, with transmitter power levels up to hundreds of watts. These signals may be impressed on one conductor, on two conductors or on all three conductors of a high-voltage AC transmission line. Several PLC channels may be coupled onto one HV line. Filtering devices are applied at substations to prevent the carrier frequency current from being bypassed through the station apparatus and to ensure that distant faults do not affect the isolated segments of the PLC system. These circuits are used for control of switchgear, and for protection of transmission lines. For example, a protective relay can use a PLC channel to trip a line if a fault is detected between its two terminals, but to leave the line in operation if the fault is elsewhere on the system. On some powerlines in the former Soviet Union, PLC-signals are not fed into the high voltage line, but in the ground conductors, which are mounted on insulators at the pylons While utility companies use microwave and now, increasingly, fiber optic cables for their primary system communication needs, the power-line carrier apparatus may still be useful as a backup channel or for very simple low-cost installations that do not warrant installing fiber optic lines.Power line carrier communication (PLCC) is mainly used for telecommunication, tele-protection and tele-monitoring between electrical substations through power lines at high voltages, such as 110 kV, 220 kV, 400 kV.[2] The major benefit is the union of two applications in a single system, which is particularly useful for monitoring electric equipment and advanced energy management techniques (such as OpenADR and OpenHAN). The modulation generally used in these system is amplitude modulation. The carrier frequency range is used for audio signals, protection and a pilot frequency. The pilot frequency is a signal in the audio range that is transmitted continuously for failure detection. The voice signal is compressed and filtered into the 300 Hz to 4000 Hz range, and this audio frequency is mixed with the carrier frequency. The carrier frequency is again filtered, amplified and transmitted. The transmission power of these HF carrier frequencies will be in the range of 0 to +32 dbW. This range is set according to the distance between substations. PLCC can be used for interconnecting private branch exchanges (PBXs).To sectionalize the transmission network and protect against failures, a "wave trap" is connected in series with the power (transmission) line. They consist of one or more sections of resonant circuits, which block the high frequency carrier waves (24 KHz to 500 KHz) and let power frequency current (50 Hz - 60 Hz) pass through. Wave traps are used in switchyard of most power stations to prevent carrier from entering the station equipment. Each wave trap has a lightning arrester to protect it from surge voltages. A coupling capacitor is used to connect the transmitters and receivers to the high voltage line. This provides low impedance path for carrier energy to HV line but blocks the power frequency circuit by being a high impedance path. The coupling capacitor may be part of a capacitor voltage transformer used for voltage measurement. Power line carriers may change its transmission system from analog to digital to enable Internet Protocol devices. Digital power line carrier (DPLC) was developed for digital transmission via power lines. DPLC has the required quality of bit error rate characteristics and transmission ability such as transmitting information from monitored electric-supply stations and images.[citation needed]Power line carrier systems have long been a favorite at many utilities because it allows them to reliably move data over an infrastructure that they control. Many technologies are capable of performing multiple applications. For example, a communication system bought initially for automatic meter reading can sometimes also be used for load control or for demand response applications.A PLC carrier repeating station is a facility, at which a power line communication (PLC) signal on a powerline is refreshed. Therefore the signal is filtered out from the powerline, demodulated and modulated on a new carrier frequency, and then reinjected onto the powerline again. As PLC signals can carry long distances (several 100 kilometres), such facilities only exist on very long power lines using PLC equipment.PLC is one of the technologies used for automatic meter reading. Both one-way and two-way systems have been successfully used for decades. Interest in this application has grown substantially in recent historynot so much because there is an interest in automating a manual process, but because there is an interest in obtaining fresh data from all metered points in order to better control and operate the system. PLC is one of the technologies being used in Advanced Metering Infrastructure (AMI) systems. In this project we show how we transfer digital data on the power line. We use one transmitter circuit and one receiver circuit where transmitter circuit use one dtmf generator circuit and receiver circuit use dtmf decoder circuit for data encoding and decoding. With the help of dtmf generator circuit we generate different codes at a time and in the receiver module we receive a different frequency at a time and we use it as a main controller circuit. In this project we use main power line as a carrier . We use neutral and earth wire as a data transfer line. In this project main power line is same in the whole line , If the phase is on the left point of the main plug then this should be same for every point in the home. We transfer all the data from the dtmf generator to neutral point in the main line with the help of the high voltage capacitor. On the receiver hand we receive the same data from the neutral line through the .01 high voltage capacitor and then we use dtmf decoder circuit.Power line communications technology can use the electrical power wiring within a home for home automation: for example, remote control of lighting and appliances without installation of additional control wiring. Typically home-control power line communication devices operate by modulating in a carrier wave of between 20 and 200 kHz into the household wiring at the transmitter. The carrier is modulated by digital signals. Each receiver in the system has an address and can be individually commanded by the signals transmitted over the household wiring and decoded at the receiver. Power line communications can also be used in a home to interconnect home computers and peripherals, and home entertainment devices that have an Ethernet port. Powerline adapter sets plug into power outlets and establish an Ethernet connection using the existing electrical wiring in the home. (Power strips with filtering may absorb the power line signal.) This allows devices to share video and data without the inconvenience of running dedicated network cables.The most widely deployed powerline networking standard is from the HomePlug Powerline Alliance. HomePlug AV is the most current of the HomePlug specifications and was adopted by the IEEE 1901 group as a baseline technology for their standard, published 30 December 2010. HomePlug estimates that over 45 million HomePlug devices have been deployed worldwide. Power-line technology enables in-vehicle network communication of data, voice, music and video signals by digital means over direct current (DC) battery power-line. Advanced digital communication techniques tailored to overcome hostile and noisy environment are implemented in a small size silicon device. One power line can be used for multiple independent networks. The benefits would be lower cost and weight (compared to separate power and control wiring), flexible modification, and ease of installation. Potential problems in vehicle applications would include the higher cost of end devices, which must be equipped with active controls and communication, and the possibility of intereference with other radio frequency devices in the vehicle or other places.

Block Diagram and explanation

Block Diagram(Transmitter Circuit)Voltage AmplifierPower Amplifier+PLLModulatorMICDTMF encoderReceiverTransmiiter

Block Diagram ofData/Voice Transmission Circuit using Power line

Description of Block Diagram(Transmitter Circuit):- In data Transmitter Circuit, The first component is DTMF encoder. In this Project we use only 10 keys of DTMF circuit but usually it is matrix of 16 keys. This Dtmf encoder encodes every key press with different frequency. This frequency signal is then then amplified by Voltage amplifier Circuit. After which complementary push pull amplifier is used for Power Amplification of Signal. Voltage of Voice signal is directly amplified by Voltage amplifier (741 IC) which is an operational amplifier. After that Power amplification of Voice signal is done by complementary push pull amplifier. This Signal is then Coupled to earth wire for transmission. Block Diagram(Receiver Circuit)7 segment displaySpeakerDTMF decoderVoltageamplifierPower amplifier

PLL demodulatorVoltage Amplifier

Block Diagram of Data/VoiceReceiver Circuit using Powerline Communication

Description of Block Diagram In data Receiver Circuit, The first component is Voltage Amplifier Circuit. Voltage of Voice signal / data signal is directly amplified by Voltage amplifier (741 IC) which is an operational amplifier. After that Power amplification of Voice signal is done by complementary push pull amplifier. Now, if it is voice signal then it is directly given to Speaker. But if Data is there then DTMF decoder IC first decodes the data, then through an IC this data is given to Common anode 7 segment Display.

Circuit Diagrams and Operation of Circuits

CIRCUIT DIAGRAM and Operation of Transmitter Circuit:-

Transmitter Circuit

Operation of Transmitter Circuit:- In case of transmission circuit we divide it into two different Sections, one is Data generation and second is Voice generation . In the data generator circuit we use ic um 91214 as a dtmf data encoder. Voltage required for operation of this ic is 3.3 volt dc. So that we use one 3.3 volt zener diode as a regulator and provide a regulated power supply to this circuit. Output signal is available on the pin no 7 . this output signal is coupled to the input of the amplifier through selector switch. One 3.58 mhz crystal is connected to the pin no 3 and 4 to give a carrier frequency to the circuit. IN this mode we use 3.58 mhz crystal as a main carrier source of the dtmf generator. All the switches are connected to the input of the dtmf generator to provide a multiple signals. All the switches are connected in four rows and three coloum. When we press any key then one row and one coloum is activate automatically. Data from the dtmf generator is further connected to the pin no 2 of the ic 741 through capacitor .04 micro farad. Here capacitor blocks the dc voltage and pass only signal to the amplifier circuit. Pin no 6 is the output pin no of the ic 741. Pin no 3 is connected to zero voltage through voltage divider circuit. Here we use two 10 k ohm resistor as a voltage divider components. Two 10 k ohm resistor provide a zero reference voltage to the pin no 3 of the ic 741. Output of the ic 741 is further amplify by the two transistor circuit. Here we use one is npn and second is pnp transistor . Collector of the npn transistor is connected to the positive voltage and collector of the pnp transistor is connected to the negative voltage. Analog signal from condenser mic is also feeded to the input of the op-amplifier using selector switch. Condenser mic converts the sound signal into electrical signal and this signal is coupled to the pin no 2 of the ic 741 through .04 microfarad capacitor. Resistor 10 k ohm provide a dc voltage to the condenser mic. Gain of the amplifier or op-amp is depend on the feedback connected to the circuit. In this project we use one 10 k ohm resistor in series with the 100 k ohm variable resistor. With the help of this variable resistor we control the gain of the op-amplifier. Now whatever we speak or press the switch this data is superimposed on the earth line of Powerline and we can receive this data at receiver circuit.

CIRCUIT Diagram of Receiver Circuit:-Receiver CircuitOperation of Receiver Circuit:- Data from the dtmf transmitter circuit is received via earth line at DTMF receiver circuit. Which is further connected to the pin no 2 of the ic 741 through capacitor .04 micro farad. Here capacitor blocks the dc voltage and pass only signal to the amplifier circuit. Pin no 6 is the output pin no of the ic 741. Pin no 3 is connected to zero voltage through voltage divider circuit. Here we use two 10 k ohm resistor as a voltage divider components. Two 10 k ohm resistor provide a zero reference voltage to the pin no 3 of the ic 741. Output of the ic 741 is further amplify by the two transistor circuit. Here we use one is npn and second is pnp transistor . Collector of the npn transistor is connected to the positive voltage and collector of the pnp transistor is connected to the negative voltage. Output of the fm receiver is now connected to the 8870 ic. This ic is dtmf decoder ic and dtmf decoder decode the signal and converted into bcd signal.. . Ic 8870 is a single chip dtmf receiver incorporating switches capacitor filter technology and an advanced digital counting averaging alogorithm for period measurement.

BCD from the 8870 is available on pin no 11,12,13,14 and this output is further connected to the pin no 20,21,22,23 of the ic 74154. Pin no 18 and 19 of the ic 74154 is enable control of the circuit. In our project we connect a one npn transistor to this point. Collector of the npn transistor is connected to the pin no 18 and 19 of the ic 74154 to provide a positive voltage on this point. Pin no 15 of the ic 8870 is a acknowledgement of the dtmf signal, when dtmf signal is available on the pin no 15 then with the help of this dtmf signal we switch on the npn transistor and further npn transistor provide a negative pulse to the pin no 18 and 19 of the ic 74154 and decimal signal is available on the output pins. Here we use only 10 output of the ic.. Output of the ic 74154 is active low. So to convert this active low output in to active high we use inverter ic. Here we use ic 4049 as a hex inverter and with the help of this hex inverter we convert the active low output in to active high output with the help of inverter logic.

COMPONENTS with Description:-

1. DTMF:- DTMF (Dual-tone Multi Frequency) is a tone composed of two sine waves of given frequencies. Individual frequencies are chosen so that it is quite easy to design frequency filters, and so that they can easily pass through telephone lines (where the maximum guaranteed bandwidth extends from about 300 Hz to 3.5 kHz). DTMF is the basic Keypad for voice communications control. Modern telephony uses DTMF to dial numbers, configure telephone exchanges (switchboards), and so on. Occasionally, simple floating codes are transmitted using DTMF - usually via a CB transceiver (27 MHz). It is used to transfer information between radio transceivers, in voice mail applications, etc. Almost any mobile (cellular) phone is able to generate DTMF after establishing connection. If your phone can't generate DTMF, you can use a stand-alone "dialer". DTMF was designed so that it is possible to use acoustic transfer, and receive the codes using standard microphone. The table shows how to compose any DTMF code. Each code, or "beep", consists of two simultaneous frequencies mixed together (added amplitudes). Standards specify 0.7% typical and 1.5% maximum tolerance. The higher of the two frequencies may have higher amplitude (be "louder") of 4 dB max. This shift is called a "twist". If the twist is equal to 3 dB, the higher frequency is 3 dB louder. If the lower frequency is louder, the twist is negative. Frequency table

1209 Hz1336 Hz1477 Hz1633 Hz

697 Hz123A

770 Hz456B

852 Hz789C

941 Hz*0#D

This table resembles a matrix keyboard. The X and Y coordinates of each code give the two frequencies that the code is composed of. Notice that there are 16 codes; however, common DTMF dialers use only 12 of them. The "A" through "D" are "system" codes. Most end users won't need any of those; they are used to configure phone exchanges or to perform other special functions. Most often, dedicated telephony circuits are used to generate DTMF (for example, MT8870). On the other hand, a microprocessor can do it, too. Just connect a RC filter to two output pins, and generate correct tones via software. However, getting the correct frequencies often requires usage of a suitable Xtal for the processor itself - at the cost of non-standard cycle length, etc. So, this method is used in simple applications only. It is not easy to detect and recognize DTMF with satisfactory precision. Often, dedicated integrated circuits are used, although a functional solution for DTMF transmission and receiving by a microprocessor (a PIC in most cases) exists. It is rather complicated, so it is used only marginally. Most often, a MT 8870 or compatible circuit would be used. Most decoders detect only the rising edges of the sine waves. So, DTMF generated by rectangular pulses and RC filters works reliably. The mentioned MT 8870 uses two 6th order band pass filters with switched capacitors. These produce nice clean sine waves even from distorted inputs, with any harmonics suppressed. The aim of this project is to develop a DTMF (Dual-Tone Multi-Frequency) decoder that can be used as a relay for various appliances and electronics used in homes, offices and other places and logging data in computer .The software for this purpose is developed in turbo C. We mainly intend to construct a device, which can recognize an individual tone over a telephone connection, and respond to a specific sequence of tones by activating some other device. DTMF tones are the very familiar tones we hear everyday when we dial a telephone number. These tones are all unique but simple to decode, which is why this technology has become increasingly popular. Answering machines use DTMF decoders so that you can remotely check the messages. Automated systems use them in several ways, such as to navigate through menus or grant authorization to banks records. My hope is to effectively design a remote, which uses DTMF tones to activate different devices in the vicinity, such as a light, or a fan, or an electric heater. I especially wish to make this project versatile and efficient so that it will be easy to use in any situation, which may call for it, which is a quality, which indubitably attracts everyone. DTMF tones are actually generated through the combination of two other tones belonging to a distinct set. There are eight tones in this set, and they are split into two groups: the highs and the lows. There are four tones in each group, yielding 16 tone pairs. Here is the matrix of the 16 DTMF tone pairs and the digits they represent on a telephone:LOWS HIGHS 1209 Hz1336 Hz1477 Hz1633 Hz

697 Hz123

770 Hz456

852 Hz789

941 Hz*0#

The frequency of a DTMF tone is simply the sum of the frequencies which comprise that tone, that is to say, the digit 4 corresponds to a tone with a frequency close to 1979 Hz (1209 Hz + 770 Hz = 1979 Hz) and so on. The last column of tones (pairs including the 1633 Hz signal) is not used in telephones or telecommunication systems, and this project will be geared towards using a telephone as the audio source. A secondary objective is to incorporate several types of input devices into the design of this DTMF decoder, such as a microphone and a headphone jack, in addition to a direct connection across the phone line.

2. IC 91214:-

This diagram shows PIN diagram of DTMF encoder IC 91214. This IC is the main DTMF encoder IC of the Circuit. In the data generator circuit we use ic um 91214 as a dtmf data encoder. Voltage required for operation of this ic is 3.3 volt dc. So that we use one 3.3 volt zener diode as a regulator and provide a regulated power supply to this circuit. Output signal is available on the pin no 7. This output signal is coupled to the input of the amplifier through selector switch. One 3.58 mhz crystal is connected to the pin no 3 and 4 to give a carrier frequency to the circuit. IN this mode we use 3.58 mhz crystal as a main carrier source of the dtmf generator. All the switches are connected to the input of the dtmf generator to provide a multiple signals. All the switches are connected in four rows and three coloum. When we press any key then one row and one coloum is activate automatically.

Pin 1:- Hook Switch input. This inverter input pin detects the state of hook switch contact. OFF HOOK is represented by a Vss Condition, On Hook is represented by a Vdd condition.

Pin 2:- Tri State mode Select pin. The mode selection pin is checked for tone/pulse dialing at each digit key entry. In pulse mode, the dialing rate is checked, along with the make/break ratio, at the first key entry.

Pin 3& 4:- Osc1 & Osc0 are oscillator input and output pins. The time base for this IC is a Crystal Controlled on chip Oscillator, which is completed by connecting a 3.58 Mhz Crystal resonator between OSC1 & OSC0 pins.

Pin 5 & 6:- Power Supply pins. This device is designed to operate from 2.0v to 5.5v.Pin 7:- Tone dialing output. When a valid key press is detected in the DTMF mode, appropriate low group and high frequencies are generated which hybridize the dual tone output.

Pin 8:- Dialing transmission mute output. This is an N-channel open drain output. Normally, the transmission mute output is OFF during pulse or DTMF dialing.

Pin9:- Dialing pulse Output. This is an N Channel open drain output. The normal output will be ON during break and OFF during make in the pulse dialing mode.

Pin 10-16:- Keyboard pins. This input serves as the interface to an XY matrix Keyboard. Here pin C4 is connected to Vss.

3. IC 741 (Operational Amplifier):-

The mA741 is a general-purpose operational amplifier featuring offset-voltage null capability. The high common-mode input voltage range and the absence of latch-up make the amplifier ideal for voltage-follower applications. The device is short-circuit protected and the internal frequency compensation ensures stability without external components. A low value potentiometer may be connected between the offset null inputs to null out the offset voltage as shown in Figure 2. The mA741C is characterized for operation from 0C to 70C. The mA741I is characterized for operation from 40C to 85C.The mA741M is characterized for operation over the full military temperature range of 55C to 125C.

The pin Diagram of 741 Op amp is Shown in above diagram. As Shown in Diagram, Input signal is given from PIN 3 and 4. While Pin 3 is for Inverting Input and Pin 4 is for Non Inverting Input. GND or Vcc is Connected to pin 5 and +Vcc is Connected to pin 8. Pin 1,9,10 are Not Connected to any circuit.

4. BC 548/ BC 538:- These transistor pairs are used in complementary push pull amplifier. it is transformer less amplifier using instead complementary or matching pairs of power transistors. As transformers are not needed this makes the amplifier circuit much smaller for the same amount of output, also there are no stray magnetic effects or transformer distortion to effect the quality of the output signal.

5. IC 7805:- In this circuit we use full wave rectifier with 7805 regulator circuit to regulate the voltage. Two high value capacitor is connected with two outer pins of 7805 to reduce the ripple factor of power supply.

6. IC 8870:- IC 8870 is a DTMF (dual tone multiple frequency) decoder IC. The CAMD CM8870/70C provides full DTMF receiver capability by integrating both the band-split filter and digital decoder functions into a single 18-pin DIP, SOIC, or 20-pin PLCC package. The CM8870/70C is manufactured using state-of-the-art CMOS process technology for low power consumption (35mW, MAX) and precise data handling. The filter section uses a switched capacitor technique tone rejection. The CM8870/70C decoder uses digital counting techniques for the detection and decoding of all 16 DTMF tone pairs into a 4-bit code. This DTMF receiver minimizes external component count by providing an on-chip differential input amplifier, clock generator, and a latched three-state interface bus. The on-chip clock generator requires only a low cost TV crystal or ceramic resonator as an external component. It converts dtmf pulse into the equivalent BCD signal. Pin no. 18 and 10 of this IC are connected to the positive supply. This positive supply is from the 5 volt regulator circuit. Pin no. 9,5,6 are connected to the negative supply. Signal from the telephone line is in the form of dtmf pulse is applied to pin no. 2 of this IC through 2.2k ohm resistor and .1mfd capacitor. This signal is also connected to pin no. 3 through 100k ohm resistor. Pin no. 7 and 8 are connected to a crystal of frequency 3.7945 mh. Pin no. 16 and 17 of this IC is reset pin. Pin no. 11,12,13,14 are the BCD output of this IC.

Filter SectionSeparation of the low-group and high-group tones is achieved by applying the dual-tone signal to the inputs of two 9th-order switched capacitor bandpass filters. The bandwidths of these filters correspond to the bands enclosing the low-group and high-group tones. The filter section also incorporates notches at 350Hz and 440Hz which provides excellent dial tone rejection. Each filter output is followed by a single order switched capacitor section which smooths the signals prior to limiting. Signal limiting is performed by high-gain comparators. These comparators are provided with a hysteresis to prevent detection of unwanted low-level signals and noise. The outputs of the comparators provide full-rail logic swings at the frequencies of the incoming tones.

Decoder SectionThe CM8870/70C decoder uses a digital counting technique to determine the frequencies of the limited tones and to verify that these tones correspond to standard DTMF frequencies. A complex averaging algorithm is used to protect against tone simulation by extraneous signals (such as voice) while providing tolerance to small frequency variations. The averaging algorithm has been developed to ensure an optimum combination of immunity to talk-off and tolerance to the presence of interfering signals (third tones) and noise. When the detector recognizes the simultaneous presence of two valid tones (known as signal condition), it raises the Early Steering flag (ESt). Any subsequent loss of signal condition will cause ESt to fall.

Substitute ICs: 9170, 3170.

PIN description of 8870 IC

7. IC DM74LS154:- IC 74154 is a BCD to Decimal converter. This IC is a 24 pin IC. Pin no.20,21, 22,23 are the BCD input pins of this IC,pin no. 2,3,4,5,6,7,8,9,10,11, are the output pins, pin no.24 is connected to the positive 5 volt supply and pin no.12 is the negative supply pin. Pin no. 18 and pin no. 19 of this IC is enable pin. If the data available on the pin no. 19 is negative then output is negative for a time. The negative pulse is given by the NPN transistor collector point. IC 74154 is a special package may be used to provide a 1 low output out of 16 outputs or may be used to send input data to one selected output of 16, the remaining 15 staying high. Each of these 4-line-to-16-line decoders utilizes TTL circuitry to decode four binary-coded inputs into one of sixteen mutually exclusive outputs when both the strobe inputs, G1 and G2, are low. The demultiplexing function is performed by using the 4 input lines to address the output line, passing data from one of the strobe inputs with the other strobe input low. When either strobe input is high, all outputs are high. These demultiplexers are ideally suited for implementing high-performance memory decoders. All inputs are buffered and input clamping diodes are provided to minimize transmission-line effects and thereby simplify system design.

8. Seven Segment Display:- A seven segment display, as its name indicates, is composed of seven elements. Individually on or off, they can be combined to produce simplified representations of the arabic numerals. Often the seven segments are arranged in an oblique (slanted) arrangement, which aids readability. In most applications, the seven segments are of nearly uniform shape and size (usually elongated hexagons, though trapezoids and rectangles can also be used), though in the case of adding machines, the vertical segments are longer and more oddly shaped at the ends in an effort to further enhance readability. Each of the numbers 0, 6, 7 and 9 may be represented by two or more different glyphs on seven-segment displays. The seven segments are arranged as a rectangle of two vertical segments on each side with one horizontal segment on the top, middle, and bottom. Additionally, the seventh segment bisects the rectangle horizontally. There are also fourteen-segment displays and sixteen-segment displays (for full alphanumerics); however, these have mostly been replaced by dot-matrix displays. The segments of a 7-segment display are referred to by the letters A to G, as shown to the right, where the optional DP decimal point (an "eighth segment") is used for the display of non-integer numbers.

Noise in Power Line Communication:- The major sources of noise on power line are from electrical appliances, which utilize the 50 Hz electric supplies and generate noise components, which extend well into the high frequency spectrum. Apart from these induced radio frequency signals from broadcast, commercial, military, citizen band and amateur stations severely impair certain frequency bands on power line. The primary sources of noise in residential environments are universal motors, light dimmers and televisions. This noise can be classified as:50 Hz periodic noise: Noise synchronous to the sinusoidal power line carrier can be found on the line. The sources of this noise tend to be silicon-controlled rectifiers (SCRs) that switch when the power crosses a certain value, placing a voltage spike on the line. This category of noise has line spectra at multiples of 50 Hz.

Single-event impulse noise:This category includes spikes placed on the line by single events, such as a lightning strike or a light switch turn on or off. Capacitor banks switched in and out create impulse noise.

Periodic impulsive noise:The most common impulse noise sources are triac controlled light dimmers. These devices introduce noise as they connect the lamp to the AC line part way through each AC cycle. These impulses occur at twice the AC line frequency as this process is repeatedevery AC cycle.

Continuous Impulsive noise:This kind of noise is produced by a variety of series wound AC motors. This type of motor is found in devices such as found in vacuum cleaners, drillers, electric shavers and many common kitchen appliances. Commutator arcing from these motors produces impulses at repetition rates in the several kilohertz range.Continuous impulsive noise is the most severe of all the noise sources.

Non-synchronous periodic noise:This type of noise has line spectra uncorrelated with 50 Hz sinusoidal carriers. Television sets generate noise synchronous to their 15734 Hz horizontal scanning frequency. Multiples of this frequency must be avoided when designing a communications transceiver. It was found that noise levels in a closed residential environment fluctuate greatly as measured from different locations in the building. Noise levels tend to decrease in power level as the frequency increases; in other words, spectrum density of power line noise tends to concentrate at lower frequencies. This implies that a communications carrier frequency would compete with less noise if its frequency were higher.Background Noise:This is what every subscriber sees as already present on the line, and not caused by subscribers'14 appliances. Typically, this originates from the Distribution Transformer, public lighting systems etc.

AttenuationAttenuation is the loss of signal strength as the signal travels over distance. For a transmission line the input impedance depends on the type of line, its length and the termination at the far end. The characteristic impedance of a transmission line (Zo) is the impedance measured atthe input of this line when its length is infinite. Under these conditions the type of termination at the far end has no effect. High frequency signals can be injected on to the power line by using an appropriately designed high pass filter. Maximum signal power will be received when the impedance of the transmitter, power line and the receiver are matched. Power line networks are usually made of a variety of conductor types and cross sections joined almost at random. Therefore a wide variety of characteristic impedances are encountered in the network. Unfortunately, a uniform distributed line is not a suitable model for PLC communications, since the power line has a number of loads (appliances) of differing impedances connected to it for variable amounts of time. Channel impedance is a strongly fluctuating variable that is difficult to predict. The overall impedance of the low voltage network results from a parallel connection of all the networks loads, so the small impedances will play a dominant role in determining overall impedance. Overall network impedances are not easy to predict either. The most typical coaxial cable impedances used are 50 and 75-ohm coaxial cables. A twisted pair of guage-22wire with reasonable insulation on the wires measures at about 120 ohms. Clearly, channel impedance is low. This presents significant challenges when designing a coupling network for PLC communications. Maximum power transfer theory states that the transmitter and channel impedance must be matched for maximum power transfer. With strongly varying channel impedance, this is tough. We need to design the transmitter and receiver with sufficiently low output/input impedance (respectively) to approximately match channel impedance in the majority of expected situations.

DIFFERENT TOOLS USED

Hardware:- Soldering Iron and Soldering wire:- A soldering iron is a hand tool most commonly used in soldering. It supplies heat to melt the solder so that it can flow into the joint between two work pieces. A soldering iron is composed of a heated metal tip and an insulated handle. Heating is often achieved electrically, by passing an electric current (supplied through an electrical cord or battery cables) through the resistive material of a heating element. Another heating method includes combustion of a suitable gas, which can either be delivered through a tank mounted on the iron (flameless), or through an external flame. A soldering iron stand keeps the iron away from flammable materials, and often also comes with a cellulose sponge and flux pot for cleaning the tip. Some soldering irons for continuous and professional use come as part of a soldering station, which allows the exact temperature of the tip to be adjusted, kept constant, and sometimes displayed.

Tin/lead solders, also called soft solders, are commercially available with tin concentrations between 5% and 70% by weight. The greater the tin concentration, the greater the solders tensile and shear strengths. At the retail level, the two most common alloys are 60/40Tin/lead (Sn/Pb) which melts at 370F or 188C and 63/37Sn/Pb used principally in electrical/electronic work. The 63/37 ratio is notable in that it is a eutectic mixture, which means:1. It has the lowest melting point (183C or 361.4F) of all the tin/lead alloys; and2. The melting point is truly a point not a range.In plumbing, a higher proportion of lead was used, commonly 50/50. This had the advantage of making the alloy solidify more slowly, so that it could be wiped over the joint to ensure watertightness, the pipes being physically fitted together before soldering. Although lead water pipes were displaced by copper when the significance of lead poisoning began to be fully appreciated, lead solder was still used until the 1980s because it was thought that the amount of lead that could leach into water from the solder was negligible from a properly soldered joint. The electrochemical couple of copper and lead promotes corrosion of the lead and tin, however tin is protected by insoluble oxide. Since even small amounts of lead have been found detrimental to health,[5] lead in plumbing solder was replaced by silver (food grade applications) or antimony, with copper often added, and the proportion of tin was increased.

Software Tools:- Circuit Designing of this Circuit is done by using software NI Multisim and its Printed circuit board is designed by using NI Ultiboard Software.

Conclusion and Applications

This project is based on power-line communication i.e. communication over the existing power-lines. The main advantage of this kind of communication system is the existing infrastructure, which simplifies the implementation. We have been successful in implementing a working PLCC link. During the design and construction phases of this project we were faced with a number of difficulties due to the unpredictable nature of the power line. Due to thisreason we had to redesign and test a number of circuits. However at the end of rigorous testing we were able to come up with a working PLCC link. This link is only a prototype and may not be able to transfer data satisfactorily over long distances, however it definitely brings to surface the tremendous potential in using the power line as a data communication link. In this section we would also like to discuss some major applications driving the Power Line Communication (PLC) technology. They are:

Automatic Meter Reading (AMR) For the readings of Electricity, Water, Gas or any other meters in the customer premises to be transmitted to a central base station for further processing, billing etc. With tens of millions of meters to be read periodically and regularly, this alone represents an enormous market.

Home Bus- For making the buildings "Intelligent", where all appliances are to be monitored or controlled continuously and automatically for convenience comfort, safety and energy - saving. This makes use of the intra-building wiring. EIectricitC de'France (EDF) has used PLC for a long time for managemcnt and their own transmission network, in energy control, street lighting, and remote service ( a large project with 3600 terminals). Around 1998 the Tokyo Electronic Power Company (TEPCO) was involved in several projects linking consumers and utilities for meter reading and lowering.peak loads. PLC networking in the home is another application area serving two goals: providing a local home network with the advantages of the power line, and combining access and in-home network capabilities for service and system integration. There are several applications for a PLC network in the home: shared Internet, printers; files, homc control, games, distributed video, remote monitoringisecurity. The key asset is ':no new wires." Available products are in net-connected security, safety, and convenience service systems using narrowband communications. In the United States, home networking is becoming a mass market (10 percent over PLC). In the beginning of 2000 the HomePlug Powerline Alliance, Cogency, Conexant, Enikia, Intel- Ion, Netgear, RadioShack Co., Sharp, and Texas Instruments, together with several other major companies as participants and adopters (http://homeplug.com), began work toward a common standard in the United States. The HomcPlug Powerline Alliance is a non-profit corporation formed to provide a forum for the creation.of open specifications for high-speed home power line networking products and services. Adopters of the HomePlug 1.0 standard have developed products for in-home networking reaching 14 Mhis. The European Home Systcm (EHS) consortium [www.ehsa.com] defines a bus and communication protocol for communications between appliances and a central processing unit in the home. The EHS specification, EHS 1.3, covers several medium types to transport control data, power,and information, all sharing the logical link control (LLC) sublayer. At the moment, the best supported medium types are power line carrier (230 Vac + data, 2.4 khk, CSMNack, topology- free) and low-speed twisted pair (15 Vdc, 48 kbis, CSMNCG topology-frec).

Distribution Automation, and Supervisory Control andDistribution Automation (DA and SCADA) This is for the utility companies themselves to monitor and control the Power Distribution Process.

Rural Communication Applications - Where user densities are low and distances are large which makes installation of fresh infrastructure expensive and also non-profitable.Also during the last years the use of Internet has increased. If it would be possible to supply such a kind of network communication over the power-line, it would bring this technology out of the embedded systems area right to the personal computer industry. Systems under trial exist today that claim a bit rate of 1 Mb/s, but most commercially available systems use low bitrates, about 10-100 kb/s, and provides low-demanding services such as meter reading. With the availability of power line communications speeds similar to those of Ethernet, the technology will soon become available in products for personal computer networking within the residence. As electric utilities begin to explore this avenue for enhanced services, a far greater value will befound in the power line than simply delivering electrical power.

Datasheets

References

1. DIGITAL SYSTEMS PRINCIPLES AND APPLICATION RONALD L TOCCI. (Sixth addition)

2. ELECTRONICS FOR YOU (MARCH 1998).

3. CMOS DATA BOOK (74SERIES) ECA. (Bpb-publishers)

4. PRACTICAL TRANSFORMER DESIGN HAND BOOK LABON. E. (Bpb-publishers)

5. The Art of ElectronicsPaul Horowitz ,Winfield Hill(Massachusetts Institute of Technology, CA)6. www.wikipedia.org7. www.google.com