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AUDIO POWER METER WITH LM3915

This VU (volume-unit) meter is capable of monitoring anddisplaying power
levels present at the speaker terminals ofan stereo audio power
amplifier.

The levels are displayed in ten discrete steps. This meter is not
designed to give an accurate display of the power levels.It is designed
to give an approximate visual indication of the audio power output of
each channel. For many situations - disco, parties - this is all which
is required: the flashing LED's add atmosphere to the situation.

LM3915. This is a monolithic Dot/Bar Display Driver IC made by National
Semiconductor. It takes an analog voltage input on pin 5 then drives 10
LED's providing a logarithmic 3dB/step analog display. When measuring
power, a 3dB increase means that the power input has doubled. As the
power doubles, an additional LED will be lit until the maximum is
reached. The display can be bar or moving dot depending on the
connection of pin 9 to the positive supply. The LED drive current is
regulated which eliminates the need for current limiting resistors.

The supply voltage can be between 3V to 25V. You can download the data sheet from the National Semiconductor website at: http://www.national.com/

The IC is suited to signals with a wide dynamic range such as audio,
power, light intensity. In many applications a bargraph meter is faster,
more rugged and has higher visibility than an analog (moving coil) or
LCD meter.



PARTS LIST



R1-----10K

R2------1K

R3-----390

R4-----2,7K

P1-----100K TRIMMER POT.

C1-----10mf 25v

D1..D10---LED red

I.C. ----LM3915