Power Line Communication using an Audio Input

1. Power Line Communication using an Audio Input ECE 445 Group 8 TA: Tony Mangognia Team: Sam Tsu, Marshall Katz, Rajat Singhal

2. AGENDA

3. Introduction • ‘Wireless’ sound transmission using AC power lines. • Audio in through a standard device such as an Ipod. • Transmit the signal at the sending end through the AC power line. • Receive the signal at the receiving end and filter out the noise • Audio out through a standard speaker system.

4. A Detailed Look… • Interference from AC lines which operate at 60 Hz - 120 V. • FM modulation necessary to transmit at higher frequencies. MODULATION DEMODULATION • Demodulation circuit required to demodulate the modulated signal and convert to standard audio output. Filter circuits required to block 60Hz noise and any frequencies not part of the transmitted audio.

5. Features • Commercialization idea behind the project based on the fact that the signal is not being broadcasted through the air. • Security Issues • Intercom Systems • PA systems • Other advantages • Relatively inexpensive setup • Neat System • Increased efficiency

6. Design Overview

7. Modulation Circuit

8. Modulation Circuit Continued… • The VCO used for modulation purposes was the LM565 • The frequency production of the VCO was controlled using: where Rt = Timing Resistance on pin 8 Ct = Timing Capacitance on 9 Vcc = Power Supply Voltage Vc = The control voltage on Pin 7

9. Demodulation Circuit

10. Demodulation Circuit Continued.. • LM565 used to implement the VCO • The input signal coupled in to the circuit through pin 2 • A more complicated network of components at output for noise reduction purposes. • Potentiometer used to match current frequency to the carrier frequency.

11. Filters • Noise above 10Khz was minimal • Standard HPF implemented. Chosen values were R = 15kΩ and C = 1nF

12. Component Selection • LM 565 • Readily available • Carrier frequency adjustment through timing capacitor and resistor • High Voltage Capacitors • 250 Volts DC / 180 Volts AC • Potentiometers • Easy tuning manipulation • Fuses • .125 mA / 120 Volts AC

13. Design and Testing Methodology • Down-up approach • Protoboard to PCB • Individual components to integrated system • Progressive stages of building and testing

14. Design and Testing Methodology 1) Build Modulator/Demodulator 2) Test Modulator/Demodulator Functionality 3) Build Filters 4) Test Filter Functionality 5) Combine Modulator/Demodulator with Filter 6) Test Transmitter/Receiver Functionality 7) Combine Transmitter/Receiver with 60 Hz Simulated Noise 8) Test with Simulated Noise 9) Combine Transmitter/Receiver with 60 Hz Power Line 10) Test with Power Line (Variac)

15. Board Layout - Transmitter 1) Audio Input 4) Filter Stage (DC Power Input) 15 Volts .023 Amps .345 Watts 5) To Power Line 3) FM Modulation 2) Carrier Tuning

16. Board Layout - Receiver 3) Receiver Tuning (DC Power Input) 4) Demodulation 15 Volts .012 Amps .18 Watts 5) Audio Out 1) From Power Line 2) Filter Stage

17. Modulator Testing Computer Audio Signal Modulator 100 kHz FM Modulated Signal

18. Timing Capacitor (pin 9): ~100 kHz Modulator output :

19. Demodulator Testing DC Power Demodulator (No signal)

20. Timing Capacitor (pin 9):

21. Filter Testing Filter Input Signal 60 Hz 100kHz Output Signal

22. 60 Hz Response: Gain = .01 V/V 100 kHz Response: Gain = .98 V/V

23. Integration Testing Speaker Computer Demodulator Power Strip Modulator (Filter) (Filter)

24. Qualitative Evaluation -Clarity of signal (after tuning) Quantitative Evaluation - SNR (at 10 kHz) - 29.06 dB

25. Communication with simulated 60Hz Speaker Simulator 60 Hz, 20 volts Computer Demodulator Power Strip Modulator

26. Qualitative Evaluation -Clarity of signal (after addition tuning) Quantitative Evaluation - SNR (at 10 kHz) - 17.19 dB

27. Communication over Power Line Speaker Power Line 60 Hz, 120 volts Computer Demodulator Power Strip Modulator

28. Challenges - Filter Performance • Relative background noise persistent through the initial filter design. • DC offset distortion of the output signal • DC offset connected to ground through inductors causing over current conditions. • Proposed three stage RC filter design

29. Filter Performance

30. Challenges - Power Line Connections PROBLEMS SOLUTIONS • Use a 1:1 transformer to isolate circuits from power line and each other • A 10:1 transformer rated at 120V with ferrite core used to step down the voltage requirement in the circuit • Filter performance distorted at ratings of 120V • Ground issues Coupling the circuits together through the power line presented several sources of difficulties and errors.

31. Challenges - Power Line Connections 1:1 Transformer Frequency Response at 60Hz, 100kHz

32. Challenges - Power Line Connections PROBLEMS SOLUTIONS • 10:1 transformer needed to be a high wire resistance and a ferrite core • Commercial production was limited • Transformer has resistance of 0.1Ω and reactivity of 0.3μH • Winding of a ‘home made’ transformer – However, number of turns required was excessive

33. Challenges - Power Line Connections • Unavailability of high rated transformer promoted the use of a variable transformer – Variac • Physically transmit audio signal at the rated voltage of the home made transformer • Relative grounding issues resulted in short circuit and damage to the PCB.

34. Final ‘Working’ Design • New design connection - filter preceding transformer • Filter before transformer to reduce voltage across transformer • Dual capacitors to allow either input to be active wire

35. Future Stereo Implementation Two separate transmitters and receivers operating at 100KHz and 200KHz to enable stereo sound Audio Output Amplifier Amplification of output signal to have volume control, especially for commercial systems.

36. QUESTIONS/FEEDBACK