International Journal of Electrical and Electronics Engineering Research (IJEEER) ISSN:2250-155X Vol.2, Issue 2 June 2012 39-46 TJPRC Pvt. Ltd., COMMUNICATION THROUGH POWER LINES ENGR.BILAL SAID & KHURRAM SHEHZAD ABSTRACT The Power Line at homes usually consists of external wiring or wireless, both are complicated and expensive. Power line communication has been around for quite some time, but been used for Narrow band tele remote relay applications, public lighting and home automation. Power Line communications basically means any technology that enables data transfer at narrow or broadband speeds through power lines by using advanced modulation technology. A prototype has been designed for power line communication using audio as an input signal at the receiver. Transmitter/Receiver module has been designed which is capable of controlling the signal and transferring it to the receiver side without any external wiring. The control signals is send on the power line using transmitter and all the appliances on that phase are able to sense that signal using receiver. The internal circuitry works on frequency modulation technique for digital data transmission generated by microcontrollers. Each module has its on auxiliary power supply for it,s digital circuit control.finally described a communication strategy that eventually could be used for information transfer over the power line communication channel. KEYWORDS :- Power Line, Transmitter, Receiver,plc, DTMF. INTRODUCTION Power line communication refers to the concept of the transmitting information using the main power line as communication channel. The Greatest benefit of the power line communication systems is that they use existing power lines as communication medium instead of using costly wireless equipment or dedicated communication wiring and hardware. This provides a strong motivation to use an existing power lines for communication purposes in addition to their use for power distribution thereby, taking advantage of already existing electrical network that is present in almost any building, whether industrial, commercial or residential. In recent times there has been a large growth in the number of small communication networks n the home or offices, cash registers, burgler alarams, computers and their side cells all relay on small interconnected networks. A number of networking technologies are aimed purely at implementing these small home networks. Many remain costly over limited or difficult to install in pre-existing buildings. One communication medium is often overlooked for implementing such networks and that is the power line.
Bilal Said & Khurram Shehzad 40 IMPLEMENTATION OF POWER LINE COMMUNICATION A prototype has been designed for power line communication using audio as an input signal at the receiver. For this purpose we designed Transmitter/Receiver module, which is capable of controlling the signal and transferring it to the receiver side without any external wiring. The control signal is send on the power line using transmitter and all the appliances on that phase are able to sense that signal using receiver. The internal circuitry works on frequency modulation technique for digital data transmission generated by microcontrollers. Each module has its on auxiliary power supply for its digital circuit control.finally described a communication strategy that eventually could be used for information transfer over the PLC. a) Transmitter To Transmit the desired data on the power line to be sensed at receiver for the purpose of home automation.digital modulation code has been used using microcontroller which was then transmitted through Power Line using Frequency modulation technique. Transmitter module, we used manual input technique modes. In manual mode user can set the appliance identity using the DIP switch at p1.0-1.3. We select the desired appliance using switch. As the appliance is selected, the mc generates the code. Once the code is generated, it is ready to be transmitted from the MC. We used P2.0 for DATA out. Once the data is transmitted, the MC goes back to the start of the program.. Idle state is LOW. Code of the program is given in the Results. After the production of Digital signal by an AT89C51 microcontroller, the digital data is transmitted through Power Line using Frequency modulation technique. The basic circuit diagram of the transmitter circuit is as shown in figure 1.1. Basic Circuit Diagram -1.1 Frequency modulation is a widely proven method in noisy environments such as Power Line. We selected LM566 VCO IC for FM signal production. Various other ICs were also available in the market like XR2206 but we selected this IC because of its easy use and nominal cost. The basic circuit diagram of LM566 IC can be seen in figure 1.1. The frequency we used for carrier is 200 KHz. The input signal level is adjustable by R1 to prevent over modulation of the carrier. Adding C2 across input resistor R7
41 Communication through Power Lines improves the frequency response to 20 khz as shown in Figure 1.1.The VCO carrier frequency fc, determined by R4 and C4 is set at 200 khz which is high enough to be effectively coupled to the AC line. VCO selected bias is 12V. For minimum distortion, the deviation should be limited to 10%; thus maximum input at pin Ý5 of the VCO is 0.15V peak. Input potentiometer R1 is provided to set the required level. The output at pin Ý3 of the LM566,being a frequency modulated square wave of approximately 6V pk-pk amplitude, is amplified by a single transistor Q1 and coupled to the AC line via the tuned transformer T1. Because T1 is tuned to fc, it appears as a high impedance collector load, so Q1 need not have additional current limiting. The collector signal may be as much as 40±50V pk-pk. Coupling capacitor C8 isolates the transformer from the line at 60 Hz. A Voltage regulator provides necessary supply rejection for the VCO. The power transformer is sized for peak secondary voltage somewhat below the regulator breakdown voltage spec (35V) with a 125V line.
Bilal Said & Khurram Shehzad 42 (Real picture of Transmitter) Figure 1.3 covers the data input section of power line communication transmitter. We have used 89c51 microcontroller to take input from port 1 via push key button as shown figure 1.3 We program 89c51 as any of push key button is pressed it sends its output to port 1and port 2 and at the output of port 2 we connect a driver IC ULN2003A as shown in figure 1.2. The ULN2003A drives the opt coupler circuit, it drives LED of opt coupler with require sufficient voltage to emit light which operate the phototransistor in on condition. Which produces the the amount of voltage at collector and emitter terminal to give the input to the tone generator IC PSB8510-6 as shown in figure 1.3.there are different inputs of the tone generator IC. In our project we use four different frequency combinations for low and high frequency called dual tone multi frequency B) Receiver The receiver amplifies, limits, and demodulates the received FM signal in the presence of line transient interference sometimes as high as several hundred volts peak. The carrier signal is capacitive coupled from the line to the tuned transformer T1. Loaded Q of the secondary tank T1C2 is decreased by shunt resistor R1 to enable acceptance of the ±10% modulated carrier, and to prevent excessive tank circuit ringing on noise spikes. The secondary of T1 is tapped to match the base input impedance of Q1A. Recovered carrier at the secondary of T1 ranging from 0.2 to 45V p-p; the base of Q1A required pk-to-pk signal levels from 12 mv to 2.6V. Q1A±Q1D operates as a two-stage limiter amplifier whose output is a symmetrical square wave of about 7V pk-pk.the output of the limiting amplifier is applied directly to the mute peak detector, but is reduced to 1V pk±pk for driving the PLL detector. The PLL detector operates as a narrow band tracking filter which tracks the input signal and provides a low-
43 Communication through Power Lines distortion demodulated audio output with high S/N. The oscillator within the PLL is set to free-run at or near the carrier frequency of 200 khz. The free-run frequency is fo & 1/(3.7 R16C13). Since the PLL will lock to a carrier near its free-run frequency, an adjustment of R16 is not strictly necessary; R16 could be fixed at 4700 or 5100X. Actually, the PLL with the indicated value of C11 can lock on a carrier within about ±40 khz of its center frequency. However, rejection of impulse noise in difficult circumstances can be maximized by carefully adjusting C10 e 100 pf will reduce the carrier level fed to the power amplifier. Even though the listener cannot hear the carrier, the audio amplifier could overload due to carrier signal power. A mute circuit is included to quiet the receiver in the absence of a carrier. Otherwise, when the transmitter is turned OFF, an excessive noise level would result as the PLL attempts to lock on noise. The mute detector consists of a voltage doubling peak detector D1Q2C7. The peak detector shunts the 1±2 ma bias away from Q1E without loading the limiter amplifier. When no carrier is present, the a4v line biases Q1E ON via R10 and R11; and the audio signal is shorted to ground. When a carrier is present, the 7V square wave from the limiter amplifier is peak detected*, and the resultant negative output is integrated by R9C7, averaged by R10 across C7, and further integrated by R11C6. The resultant output of about ±4V subtracts from the ±4V bias supply, thus depriving Q1E of base current. Peak detector integration and averaging prevents noise spikes from deactivating the mute in the absence of a carrier when the limiter amplifier output is a series of narrow 7V spikes. The LM380 supplies 2.5W of audio power to an 8X load. Although this is adequate for casual listening in the kitchen or garage, for hifi listening, a larger amplifier may be direct. (Real Picture of Receiver)
Bilal Said & Khurram Shehzad 44 (Amplifying and demodulating section) For the digital control at AT89C51 microcontroller, receiver MC receives the DATA at P1.0. Now, whenever receiver senses the std bit, it starts receiving DATA. It stores DATA in the buffer. On complete reception it compares the DATA with the preprogrammed codes and manual code fed in the memory. After detection correct code, MC will operate the corresponding relay. Fig. 1.4 b ((Data decoder and output section)
45 Communication through Power Lines RESULTS & DISCUSSIONS Our approach in designing a communication system for the power line channel is a simple implementation of the receiver, which lowers the cost. This prototype can be used and upgraded for future adaptations, as it is very simple and flexible. This is all about PLC over the existing power Lines. The main advantage of this kind of communication system is the existing infra- structure, which simplifies the implementation. After a general introduction to power-line communication, by doing some measurements of basic properties, to understand the behavior of the power-line as a communication channel. Then we use these results combined with coding, modulation methods, different receiver structures, diversity and coding to present a communication strategy for the powerline channel. CONCLUSIONS Approach in designing a communication system for the power line channel is a simple implementation of the receiver, which lowers the cost. This prototype can be used and upgraded for future adaptations, as it is very simple and flexible. FUTURE ENHANCEMENTS To implement the communication link at longer distances. Our designed circuit at final stage is capable of transmitting signal in about 20m power line. This distance can be increased by increasing the amplification strength of the transmitted signal. To make it a Commercial Product. To introduce timing & memory feature at receiver side. Our designed circuit in final stage does not include memory content i.e. in case of power loss the on/off conditions of the appliances will not be maintained. A proper design should also include that feature.to introduce voltage spike circuitry to bypass unwanted spikes. To provide error correction code in the software part. REFERENCES 1) O'Neal Jr., J.B. (1986). "The residential power circuit as a communication medium," IEEE Trans. on Consumer Electronics, vol. CE-32, No. 3, pp. 567-577. 2) Karl, M. & Dostert, K. (1996). "Selection of an Optimal Modulation Scheme for Digital Communications Over Low Voltage Power Lines," IEEE internation symposium on spread spectrum, pp. 1087-1091. 3) Chan, M.H.L., Friedman, D. & Donaldson, R.W. (1994). "Performance Enhancement Using Forward Error Correction on Power Line Communication Channels," IEEE Transactions on Power Delivery, Vol. 9, No. 2, pp. 645-653. 4) Strassberg, D. (1996)"Powerline Communication: Wireless Technology," EDN, pp. 71-78.
Bilal Said & Khurram Shehzad 46 5) Malek, J.A. & Engstorm, J.R. (1976)"The residential power circuit as a communication medium," IEEE Trans. on Consumer Electronics, vol. CE-32, No. 3, pp. 567-577. 6) Winder S. Analog and Digital Filter Design, 2nd edition, Butterworth-Heinemann, 2002. 7) Karris S. T. Electronic Devices and amplifier Circuits. Orchard Publications, 2005 8) Dostert K.Telecommunication over the power Distribution Grid Possibilities and Limitations, Proc. 1997 Internet. Symp. On Power Line Comms. And it s Applications, pp. 1 9.