Khoa NguyenSep 6th 2010

ECE 299 – Circuits

Summer 2010

Lab report – Final Project

Build a Speaker

Student name: Khoa A. NguyenPartner: Thong T. VoLab’s date: Sep 6th 2010TA: Rehman Ashraf

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LOWPASS FILTER(control the bass)

HIGH PASS FILTER(control the treble)

POWER OPAMP(control the volume)

SUMMING CIRCUITINPUT BUFFER SPEAKER

Khoa NguyenSep 6th 2010

1. Abstract: Nowadays, speaker is very familiar with everyone. We can see speaker in a radio, mp3 players, computers, etc. To build a simple speaker and have fun with the design is necessary for electrical engineering students who just attend to the field and grow desire in study.

2. Introduction:The goal of this project is to design, simulate, build and test a simple speaker system that can connect to a portable audio device such as an mp3 player or laptop. The system has the following requirements:

Input: a standard audio device such as an mp3 player or computer.

Output: a speaker, the one included in the lab kit, or another.

It must provide a means of controlling the volume continuously.

It must also have a means of controlling the treble (frequencies > 900 Hz) and the bass (frequencies < 300 Hz) [1].

3. Equipment and Part lists:- Bread board, Resistors, Capacitors, Potention meter.- Speaker.- Mp3 player or laptop which provides mp3 files.- Opamps: LM741, LM386.- Power Supply, Function Generator, Oscilloscope.

4. Theories behind the experience: - Build a Low Pass Filter to control the bass (f<300Hz).- Build a High Pass Filter to control the treble (f>900Hz).- Use Power Opamp to control the volume.General circuit diagram:

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Khoa NguyenSep 6th 2010

5. Simulation results:LOWPASS FILTER:

Schematic Circuit: using Filter-Pro to come up with the design. This is a Chebyshev type (4 pole filter), which produces very good slope in trade off ripples.

Diagram: Ripple of 2.7 dB, cutoff frequency at 260 Hz, amplitude at 300Hz is -5 dB, amplitude at 900 Hz is -51 dB. From 300 Hz to 900 Hz, the amplitude decreases 46 dB. This Low Pass Filter has an acceptable ripple, and a good slope.

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Khoa NguyenSep 6th 2010

HIGHPASS FILTER:Schematic Circuit: using Filter-Pro to come up with the design. Again this is a Chebyshev

type (4 pole filter), which produces very good slope in trade off ripples.

Diagram: Ripple of 3 dB, cutoff frequency at 870 Hz, amplitude at 900Hz is 0 dB, amplitude at 900 Hz is -48 dB. From 300 Hz to 900 Hz, the amplitude increases 46 dB. This High Pass Filter has an acceptable ripple, and a good slope.

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Khoa NguyenSep 6th 2010

SUMMING CIRCUIT:Schematic Circuit:

R1, R2, R3 are 100kΩ potention meter which can adjust resistance from 100Ω to 100kΩ. These potention meters are used to adjust the amplitude of each signal.

This circuit follows the formula:Vout = (-Rf/R1)xV1 + (-Rf/R2)xV2 + (-Rf/R3)xV3

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Khoa NguyenSep 6th 2010

Diagram: applying a .wav file to test the circuit (with gain =1).Low Pass Filter – Input: the signal starts going out when it hits 300 Hz.

High Pass Filter – Input: the signal starts appearing when it hits 900 Hz.

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Khoa NguyenSep 6th 2010

Output – Input: the output signal and input signal pretty much have the same shape. There are still noises, which we will test the sound quality in the real circuit. Because Band Pass Filter is not built, the output signal between 300Hz – 900Hz is plus 1. It is not a problem since we have a potention meter to control its amplitude.

POWER OPAMP:Schematic circuit: this circuit is to control the volume of the sound through a potention

meter. The maximum gain is 20.

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- L M 3 8 6

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25

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14

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10k

Input

10V

10 uF1.2k

10

.5 uF

250 uF

S P E A K E R

Khoa NguyenSep 6th 2010

BUFFER: To make sure that the circuit and mp3 player going well, a buffer is connected before

input signal comes into the circuit. A capacitor (1000 µF) is also connected between Vcc and Ground to eliminate unexpected noise.

6. Test Results: Use Function Generator to supply a sine wave 1Vpp, frequency is varied. Because of internal impedance of the Oscillosope, the real input comes into the circuit is sine wave 2Vpp. It should be taken into account.Measure Wc, V300 amplitude at 300Hz, V900 amplitude at 900Hz for Low Pass Filter and High Pass Filter. Compare results with simulation. Measure the highest gain of the power opamp.

LOWPASS FILTER:o Wc = 260 Hz when Vmax/√2 = 780mV.o V300 = 300mV.o V900 = 400µV.

Comment: o Wc is similar with the simulation.o The amplitude decreases fast from 300Hz to 900Hz, which is what we need.

HIGHPASS FILTER:o Wc = 900 Hz when Vmax/√2 = 780mV.o V300 = 400µV.o V900 = 900mV.

Comment: o Wc is acceptable. In the simulation, Wc = 870 Hzo The amplitude increases fast from 300Hz to 900Hz, which is what we need.

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Khoa NguyenSep 6th 2010

POWER OPAMP: Measure the amplitude of signal before coming into Power OpAmp. It is 750mV.Adjust potention meter so that Power OpAmp is having maximum gain.Measure the amplitude of signal after coming out of Power OpAmp. It is 4240mV.Hence the maximum gain is = 4240/750 = 5.7.

7. Conclusion:- The simulation results and test results are similar.- The real circuit works well, sound quality is acceptable.- The circuit is not able to mute only the part of 300Hz – 900Hz because we don’t build

Band Pass Filter.

8. Discussion:- Speaker built in the project is a simple speaker. It is a long distance when compared with

marketable one. However, this lab project is very helpful for student to understand how components learned in class work, and have a handy experience working with real circuits.

- If we have more time, we would build the band pass filter to complete the design. We would also try different ways and styles to improve sound quality.

References:[1] Project requirement, Course ECE 299, Instructor: Melinda Holtzman, TA: Rehman Ashraf.

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