“Wireless” sound transmission using ac power lines

Design Review

Authors: Marshall Katz, Sam Tsu, Rajat Singhal

TA: Tony Mangognia

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Introduction

1.1 Title

“Wireless” sound transmission using AC power lines:

Since a long time, we have had the capability to transmit sound waves between any two locations. The way it has been traditionally done is to use a wired system to transmit the waves, or more recently, we have had the technology of wireless capability by transmitting using radio waves. However, there is a fundamental problem with both of these methods which currently has not been addressed. Wired system is just not a practical option for longer distances and the reliability of a completely wireless system is not the best. In lieu of this situation, we have come up with the idea of using an existing established network of AC power lines and use these lines for transmission purposes. And they have many advantages over the existing system. First of all, we get the reliability of a wired system without incurring any further costs, since it uses an already established network. In addition, it will be a relatively ‘wireless’ system since, even though we will be using coaxial cables to transmit the sound waves, there will be no ugly wires running throughout the location, which can also be a time consuming and an expensive.

1.2 Objectives

Our goal in this project, as mentioned above, is to use the existing AC power lines which operate at 60Hz to transmit sound waves at variable frequencies (in our case, we will be implementing the transmission of up to 10Khz sound waves). This will be done by having a set of devices at both the sending location and the receiving location. At the sending location, we will have a frequency generator and a FM transmitter, which will be our input. This input will then be passed on to a band pass filter so that we can obtain only the required frequency, and filter out the rest. The filtering out is a very important part because the AC lines have a tendency to pick up a lot of signals of variable frequency, which we want to filter out, especially the ones operating at 60Hz. At the receiving end, we will again be using a filter to filter out only our required signal (which will be close to the one generated from the frequency generator), and which will then be passed on to the FM receiver. In this way, we can create a reliable method of transmitting our audio waves between any two locations.

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Product Features:

Relatively small piece of circuitry at each of the sending and receiving ends.

Ability to connect headphones or speakers directly to the receiving end by using a 3.5mm audio jack.

Ability to work for a wide range of frequencies since the power lines operate on a small range of frequencies with small frequency values.

Radical improvements in reliability over the current standards.

Product Benefits:

Relatively small circuitry and no additional equipment means the overall cost of this project will negligible.

Ability to add further channels at the receiving end to convert the output into surround sound etc.

Quality of output will be really good since looses will be minimal.

A “neat” system without wires running throughout the place.

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Design

2.1 Block Diagram

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2.2 Block Descriptions

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1. Low Pass Filter: The function of the low pass filter is to allow the 120 volt 60Hz power from the power line through to the power supply while blocking the signal from the transmitter.

2. Power Supply: The power supply will provide power to either the receiver or the transmitter.

3. Band Pass Filter: The band pass filter will be connected between the power line and both the fm transmitter and fm receiver. The filter will block out noise and the 60Hz signal while allowing the signal from the transmitter though.

4. RF Amplifier: The RF amplifier is used to boast the signal from the transmitter before it goes out onto the power line and is used again to boast the power of the signal coming off the power line into the demodulator.

5. Frequency Modulated Oscillator: The purpose of the FM oscillator is to take frequency modulate a carrier signal of 1 MHz with an audio signal. The audio signal will come from a 2.5mm audio jack; the modulated signal will be connected to the band pass filter and go out to the power line.

6. Frequency Modulated Demodulated: The demodulator will take in a signal from the power line via the band pass filter and output the audio from the signal to a 3.5mm plug.

2.3 Schematics and Simulations

The schematics of our circuits were based on the block diagram which was shown above, with a schematic design proposed for the Modulator, Demodulator, power lines, the filters and the amplifiers. The detailed designs with pin numbers and part numbers are shown below:

A note on Simulations:

The simulation of the above schematics was obtained using Pspice to ensure that our circuit was operating to specification. One of the problems we had was in the simulation of the AC power lines. Since there is no direct way to simulate the AC

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lines and predict the losses from the lines, we went about this problem by introducing a resistor which, up to an extent, predicts the losses from the lines.

The other major problem that we encountered was the non availability of the LM 565 in Pspice to simulate our results. Since changing the VCO would have meant changing the whole circuit, we decided to implement the actual circuit on the breadboard and try to ‘physically’ simulate our circuit and obtain our results on the oscilloscope. The screenshot of the result of this actual circuit for the modulator is given below as well.

Other than that, the simulation results were as expected and are summarized below:

Low Pass Filter:

LL1

R=.05 OhmL=75 mH

CC2C=150 uF

CC1C=150 uF

TermTerm2

Z=50 OhmNum=2

TermTerm1

Z=50 OhmNum=1

7

20 40 60 800 100

-15

-10

-5

-20

0

freq, Hz

dB(S

(2,1)

)

Readout

m1

m1freq=dB(S(2,1))=-0.374

60.00 Hz

The low pass filter is a Chebyshev type 1 filter with the cutoff frequency located at 65 Hz to allow the maximum ripple to occur at 60Hz. The filter will be used to protect the power supplies from the RF noise of the transmitter and receivers.

Band Pass Filter:

LL2

R=0.025 OhmL=39 uH

LL1

R=0.025 OhmL=3.8 mH

TermTerm2

Z=50 OhmNum=2

TermTerm1

Z=50 OhmNum=1

CC1C=0.1 uF

8

m1freq=dB(S(2,1))=-0.005Peak

78.38kHzm4freq=dB(S(2,1))=-0.140

50.08kHz

40 60 80 100 120 140 160 18020 200

-15

-10

-5

-20

0

freq, KHz

dB(S

(2,1

))

Readout

m1

Readout

m4

Readout

m5

m1freq=dB(S(2,1))=-0.005Peak

78.38kHzm4freq=dB(S(2,1))=-0.140

50.08kHzm5freq=dB(S(2,1))=-0.303

149.9kHz

20 30 40 50 60 70 80 9010 100

-100

-80

-60

-40

-20

-120

0

freq, Hz

dB(S

(2,1)

)

Readout

m2

m2freq=dB(S(2,1))=-79.345

60.00 Hz

The high pass filter is designed to create an open at low frequencies instead of a short to ground. If the filter was designed to present a short to ground at low frequencies the components could overheat and become damaged due to the large voltage provided by the power supply mains. The filter is designed to allow frequencies from 50kHz to 500 KHz through as the signals are square waves at 100KHz and 200KHz. Since the signals are square waves the filter has to allow the harmonics caused by the use of a square wave to pass.

Amplifier:

R 1

1M

R 2

1M

R 4

1M

R 310 . 2K

0

-V c c-1 5V d c

0

V 10 . 1V a c0V d c

0

+3

-2

V +7

V -4

O U T6

O S 11

O S 25

U 1

LM741

0

V 215V dc

0

The amplifier design is based on a LM741 general purpose op-amp used in an inverting amplifier role. The gain of the amplifier stage is 20dB with an input impedance if 1M ohms. The amplifier is set up with 15V for VCC and -15V for –VEE, 15V was chosen because this is the same voltage as is used in the modulator and demodulator. By

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using the same voltage there will be the need for one less power supply saving money and board space.

Input impedance = R1 = 1MΩ

Gain =

R1 is 1MΩ to allow the input impedanceR2 and R4 are chosen to be 1MΩ; solving the above equation for a gain of 20dB or 100 R3 is 10.2KΩ.

Modulator:

Figure 1: Pspice Schematic of FM Modulator component using phase lock-loop chip LM565 at 100kHz carrier frequency.

Schematic Overview:

The circuit in figure 1 represents the FM modulator component of our transmission device. National Semiconductor’s LM565CN Phase Locked Loop (PLL) chip is utilized to implement the FM signal with a carrier frequency of 100 kHz.

An audio signal would enter into the AF input port and pass through low-pass and high-pass filtering implemented by capacitors C3 and C4 and resistor R6 mainly to suppress any DC offset from AF input. The alternating AF input voltage is then connected to the voltage control input (pin 7) of the VCO component of the PLL chip

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with an added DC offset provided by the voltage divider (R3 and R5). The frequency of the output signal would increase or decrease from the base carrier frequency depending on the voltage level of the audio signal. The capacitor, C2, and the resistor, R1, are respectively connected to the timing capacitor input (pin 9) and timing resistor input (pin 8) of the VCO. The values of the timing capacitor input and the timing resistor input determine the carrier frequency of the out put signal. Pins 2 and 3 are the inputs to the phase detector component of the PPL chip and are given a common signal. VCC is set to +15 volts and –VCC is connected to ground. Lastly, the output of the FM modulator comes from PLL chip (pin 4) which would connect with the signal/line coupling component and then enter into the power line.

The phase comparator input (pin 5) to the VCO and the reference output (pin 6) are not need for FM modulation of our audio signal and left unconnected.

Parameter Calculations:The frequency of the circuit is determined by the following equation:

if:

With no AF input (Vc = 0 volts), the output frequency should be the carrier frequency of 100 kHz as the equation below demonstrates.

The modular sensitivity, K0, of the FM modulator is related by the change in output frequency (ΔF) with the change in input voltage (ΔV) and related by the following equation:

To determine our voltage input rating with consideration to our carrier frequency of 100 kHz and maintaining a minimum frequency deviation, δ, of 10 kHz, we solved for Vm (maximum voltage input) from frequency deviation equation:

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The screenshot of the results from the circuit of the modulator is shown below:

Information from power lines:

Power Line Simulation Schematic Overview:In order to get a general idea of the behavior of our design, we simulated a

standard home power line of 120 volts amplitude at 60 Hz with a source impedance of 50Ω. We modeled our transmitter through the placement of 10 volt amplitude, 100 kHz sinusoidal wave generator connected in parallel to the line. A 25 Ω resistor (R5) was placed to simulate the impedance of the transmitter and a 1.6 µF capacitor was place in series to as a one-way coupler with the power line. The high frequency 100 kHz signal will have low impedance into the line with the low frequency 20 Hz power line signal will have high impedance going into the transmitter device. The will help protect the device from experiencing large amounts of power being drawn into the system.

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The receiver is modeled by a 25 Ω resister (R6) and has a 100 kHz band-pass filter between the resister and the power line. Discussion on the filter is discussed in more detail in the latter part of this proposal.

Lastly, there is an arbitrary load connect in parallel with the home power lines. This is modeled by a 25 Ω resistor (R7). This resistor could represent any hypothetical appliance connected to the wire in another socket such as a lamp or television.

The resistance values for our resistances and for the transmitter voltage source are, for the most part, arbitrary values. The simulation primarily demonstrates the behaviors of the audio transmission design through the power lines and is intended to demonstrate the basic concepts pertaining to the design. Many assumptions and arbitrary values are made for line and load resistance values.

Simulation Overview:

A simulation was run for 30 ms so that two 60Hz periods could be recorded. The voltage across the arbitrary load voltage (R7) was recorded along with the voltage across the receiver resistor (R6). The above figure displays the result of the simulation. The bottom graph displays an enlarged view of the above simulation. For the arbitrary load, the 100 kHz signal is imposed over the 60 Hz power line signal to form a high voltage sinusoidal wave. The input signal after band pass filtering loses the high voltage, low frequency 60 Hz power line signal while retaining the 100 kHz FM modulated audio signal. Noise and lossy transmission lines was not taken into consideration for our model.

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Another simulation was run with the same timing parameters as the previous simulation. However, the power line voltage (across R4) and the transmitter voltage (across R5) were recorded. The above figure displays the power line signal which has a high voltage, low frequency base signal of 60 Hz which is superimposed by a low voltage, high frequency of 100 kHz. Due to the coupling capacitor (C1), the transmitter resistor only experiences low voltage values, protecting the transmitter components. Another AC ground can also be placed in the transmitter to redirect the high voltage power into the ground rather than into the capacitor. This, however, is not presently incorporated into the design.

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Demodulator:

0

R 1 03

4 . 7 k

R 102

4 . 7 k

R 101

10

R 10410k

R 1 0510k

C 1020 .1 u

0

C 1 010 . 1u

0

R 10610k

R 1071k

IN2

IN3

V IN5

-VCC

1

+VCC

10

V O U T4 R E F6

TRES

8

TCAP

9

V C O N7

U 1

LM565

C 1 03

0 . 1u

0

0

C 1 04470 p

C 1 0547p

C 1 0647p

0

C 107150 p

0

C 1080 . 0 0 22

0

C 1090 . 0 0 1u

0

R 10847k

R 1 09

10k

R 1 10

10k

C 1 10

10u

V 1

15V d c0

FM InputOutput

FM Demodulator Schematic(Reference: Lab 7: Frequency Modulation by tom Wheeler. c2002.)

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The FM Detector shown is based on the LM 565 Phase Locked Loop VCO. The R106 resistor can act as a potentiometer; hence the carrier frequency of the demodulator can be adjusted based on the carrier frequency of the input modulator.

Looking at the left half of the circuit, The Input FM signal from the power lines will be coupled to pin 2, the reference input, through the C103 capacitor. The single source power supply connected to the LM565 will split the input voltage across the 2 resistor 102 and 103 through voltage divider. The C102 capacitor will tend to act as an RF bias for the bias point, while the 104 and 105 resistors will be used to isolate the 2 inputs for the 565, in order to ensure that only one input is activated at any given time.

Similarly, looking at the right half of the circuit, the VCO control voltage of the 565 (on pin 7) contains 2 components. One is a DC level corresponding to the input frequency into the 565, which initially comes in from the FM modulator. The other one is the AC level which is actual detected information signal. The C106, C107 and R108 are the loop filters that which set up for the demodulation to take place, while the R109, R110, and the other capacitors form the components of the low pass filter to ensure that no component of the input carrier frequency is presented in the output. The final output is coupled with C110, leaving only the demodulated information at the output.

2.3 Mechanical Drawings

Since our project did not have a mechanical component, and was solely based on an electrical circuit input and output, we do not have any mechanical drawing. The only mechanical component that will be used is the speaker system to finally output our result of the demodulation from the power lines.

2.4 Performance Requirement

The range of the FM transmitter should be around 100 ft, but in practicality, should not exceed 500 ft. This is especially true in real life situation when you do not want the range to be interfering with the neighbors signal etc.

The input signal will be connected to a frequency generator producing an input at a particular frequency range. The

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frequency received at the output (measured using an oscilloscope) should be within 5% of our input frequency.

The power ranges throughout the whole system should be fairly constant, with the range no exceeding 3db between the input and the output.

Verification

3.1 Testing Procedures

- The low pass filters will be tested by applying a range of frequencies on the inputs and measuring how much the power from the signal drops on the outputs. The filter will also be tested by plugging it into a wall jack and ensuring the 60Hz wave is not blocked and that the filter does not over heat.

- The band pass filters will be tested by applying a range of frequencies on the inputs and measuring how much the power from the signal drops on the outputs. The filter will also be tested by plugging it into a wall jack and ensuring the 60Hz wave is blocked and that the filter does not over heat.

- The RF amplifier test will involve sending a range of frequencies that correspond to carrier frequency with a width equal to the bandwidth of the signal. The output power of the amplifier will be measured along with how much distortion the amplifier has.

- The demodulator will be tested by sending a signal from a frequency generator with a 100 KHz carrier frequency modulated with a range of signals from 100 Hz to 10 kHz. The output of the demodulator will be connected to an oscilloscope and the frequency and power levels will be measured.

- The FM oscillator testing will consist of connecting a frequency generator to the input with a range of frequencies between 100Hz and 10 kHz, the output will be connected to an oscilloscope, the power and signal will be measured.

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- The entire project will be tested by plugging the transmitter and receiver units into different outlets. At the input of the transmitter a frequency generator will be hooked up to generate tones while output of the receiver will be hooked up to an oscilloscope to measure the frequency and power levels.

3.2 Tolerance Analysis

The audio signal that needs to be transmitted may have especially high or low frequency components, the transmitter and receiver needs to be able to transmit those signals. To test that the system can transmit a very wide range of frequencies the system will be tested to determine what the highest frequency and lowest frequency the system can transmit. The test will entail slowly lowering the input frequency until the output power drops by 6dB relative to the power of a 1 KHz signal. Then the frequency will be slowly raised until the output power drops by 6dB relative to the power of a 1 KHz signal.

Cost and Schedule

4.1 Cost Analysis

Labor:

Dream Salary: $35Hours to complete: 12 hrs a week * 12weeks = 144 hrsLabor Costs = Dream Salary * 2.5 * Hours per week = 35 * 2.5 * 144 = $12600 (per person)

Parts:

We would be requiring very few parts since we will be building all the components from scratch using resistor, capacitors etc.

We will need:

Power Supply:

Cost: $25Amount: 2Total Cost: $50

Misc. Components: (High rating capacitors, resistors, op amp etc.)

Cost: ~$10

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GRAND TOTAL: LABOR + PARTS

= $12600 + $60 = $12660

4.2 Schedule

Sam Tsu Rajat Singhal Marshall KatzFebruary 4 – 10

Proposal (Research/Design)

Proposal (Intro/Objective)

Proposal (Testing/Cost)

February 11 – 17

Start Design of Frequency Modulated Oscillator

Start Design of Frequency Modulated Demodulator

Start Design of Filters and RF

Amplifier

February 18 – 24(Design Review)

Simulate oscillator in PSPICE and combine with other circuits

Simulate demodulator in PSPICE and combine with other circuits

Simulate filters and amplifier in PSPICE and combine with other circuits

February 25 –March 3

Order parts and start construction of oscillator

Obtain the necessary parts based on the design review and being construction.

Order parts and start construction of filters

March 4 – 10 Finish construction of oscillator on bread board and begin testing.

Finish construction of the demodulator circuit and begin testing operations.

Finish construction of filters in bread board and start amplifier,

March 11 – 17

Continue testing and modification of oscillator. Design interface with other components.

Finish testing to confirm the individual device is operating and connect it to Sam and Marshall’s component.

Finish construction of amplifier and test filters and amplifier

March 18 – 24

SPRING BREAK SPRING BREAK SPRING BREAK

March 25 – 31(Mock-up

Prepare for mock up demo and order the PCB’s

Prepare for mock up demo

Prepare for mock up demo.

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Demo) based on our overall design.

April 1 – 7 Start process for integration of all design components

Start process for integration of all design components

Start process for integration of all design components

April 8 – 14 Test whether the oscillator is successfully transmitting the signal.

Test the amplifier and filters to ensure proper gain and low distortion

Test whether the oscillator is successfully receiving the signal and is being outputted to the speaker.

April 15 – 21(Demo and Presentations)

Integrated system testing and fine-tuning

Integrated system testing and fine-tuning

Integrated system testing and fine-tuning

April 22 – 28 Prepare for presentation

Prepare for presentation

Prepare for presentation

April 29 – May 5(Final Paper)

Prepare final report

Prepare final report

Prepare final report

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