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BY

GOURAB GHOSH

Academy of Technology

[Guided by Prof J.Rakshit]

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WHAT IS A STEREO VU METER?

The LED meter is simpler and smaller than it'sanalogue counterpart, and is very common in audio

equipment. This version is based on a National

Semiconductor IC, and uses the logarithmic version.

Each LED operates with a 3dB difference from the

previous one, and a jumper is provided to allow dotor bar mode.

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LM3915

741C

LED

DIODE & RESISTANCE

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ITS A DOT/BAR DISPLAY DRIVER.

ITS A INTEGRATED CIRCUIT THAT SENSES ANALOG

VOLTAGE LEVELS & DRIVEN LEDS PROVIDING A

3DB/STEP ANALOG DISPLAY.

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BLOCK

DIAGRAMOF LM3915

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CONSTRUCTION

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LEDS WILL NOT WORK IN THE NEGATIVE POTENTIAL OF

A SINE WAVE. SO WE CONNECT A FULL TO HALF WAVERECTIFIER INTO THE CIRCUIT.

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AS THE VOLTAGE GENERATED BY

THE FREQUENCY GENERATOR IS

NOT SUFFICIENT FOR LIT ALL 10LEDS, SO WE USE A 741 OP-AMP

IN A NON-INVERTING AMPLIFIER

TO MAKE THE VOLTAGE TO

GENERATE A SUFFICIENT

VOLTAGE.

http://en.wikipedia.org/wiki/File:Op-Amp_Non-Inverting_Amplifier.svg

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WE USE 7 GREEN LEDS & 3 RED LEDS TO DISPLAY THE

OUTPUT OF THE BAR CODE.

ALSO WHILE CONNECTING THE LEDS WE HAVE TO SEEWHICH IS CATHODE & ANODE.

AFTER CONNECTING THE LEDS CORRECTLY WE HAVETO SUPPLY 2V OF ON A SINE WAVE OF 2KHz.

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1st LED 10th LED

Frequenc

y(KHz) Voltage Frequency(

KHz)

Voltage

0.163 1.18 0.163 0.76

0.736 1.34 0.736

1.08

1.76 1.59 1.76 1.25

1.93 1.2 1.93 1.25

10.00 1.69 10.00 1.35

11.03 1.7 11.03 1.35

13.85 1.73 13.85 0.4

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IT DOES NOT YIELD RESULTS FOR VERY LOWFREQUENCY VOLTAGE SUPPLY.

PROLONGED USAGE OF LM3915 MAY RESULT INOVERHEATING,LEADING TO MALFUNCTION OF THESETUP.

ITS SIMPLE TO DESIGN.

COMPONENTS ARE INEXPENSIVE.

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FINALLY THIS TECHNIQUE HAS BEEN SUCCESFULLY

IMPLIMENTED TO DEVICE A POTENTIAL STEREO VU

METER.THE PROBLEMS LIKE VOLTAGE FLUCTUATION,AS

WELL AS NEGATIVE POTENTIAL OF SINE WAVE HAS BEENOVERCOME BY NON INVERTING AMPLIFIER & HALF WAVE

RECTIFER RESPECTIVELY.