Power Line Communication using an Audio Input

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Power Line Communication using an Audio Input

• ECE 445 Group 8
• TA Tony Mangognia
• Team Sam Tsu, Marshall Katz, Rajat Singhal

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AGENDA
Introduction
Objective
Proposed Design
Project Build and Tests
Challenges Solutions
Recommendations
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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.

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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.
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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

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Design Overview
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Modulation Circuit
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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

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Demodulation Circuit
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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.

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Filters

• Noise above 10Khz was minimal
• Standard HPF implemented.

Chosen values were R 15k? and C 1nF
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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

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Design and Testing Methodology

• Down-up approach
• Protoboard to PCB
• Individual components to integrated system
• Progressive stages of building and testing

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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)

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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
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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
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Modulator Testing
Computer
Audio Signal
Modulator
100 kHz FM Modulated Signal
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Timing Capacitor (pin 9) 100 kHz
Modulator output
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Demodulator Testing
DC Power
Demodulator
(No signal)
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Timing Capacitor (pin 9)
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Filter Testing
Filter
Input Signal 60 Hz 100kHz
Output Signal
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60 Hz Response Gain .01 V/V
100 kHz Response Gain .98 V/V
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Integration Testing
Speaker
Computer
Demodulator
Power Strip
Modulator
(Filter)
(Filter)
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Qualitative Evaluation -Clarity of signal (after
tuning) Quantitative Evaluation - SNR (at 10
kHz) - 29.06 dB
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Communication with simulated 60Hz
Speaker
Simulator 60 Hz, 20 volts
Computer
Demodulator
Power Strip
Modulator
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Qualitative Evaluation -Clarity of signal (after
addition tuning) Quantitative Evaluation - SNR
(at 10 kHz) - 17.19 dB
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Communication over Power Line
Speaker
Power Line 60 Hz, 120 volts
Computer
Demodulator
Power Strip
Modulator
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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

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Filter Performance
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Challenges - Power Line Connections

• Coupling the circuits together through the power
  line presented several sources of difficulties
  and errors.

• Use a 11 transformer to isolate circuits from
  power line and each other
• A 101 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

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Challenges - Power Line Connections
11 Transformer Frequency Response at 60Hz, 100kHz
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Challenges - Power Line Connections

• 101 transformer needed to be a high wire
  resistance and a ferrite core
• Commercial production was limited
• Transformer has resistance of 0.1?
• and reactivity of 0.3µH

• Winding of a home made transformer However,
  number of turns required was excessive

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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.

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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

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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.
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QUESTIONS/FEEDBACK