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Using PC's sound out to drive bar display?

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wilykat

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I would like to use a few LM3914 to tap into the sound out of my PC (5.1 channel, 3 lines) and typically they are low voltage, I think 1v max.

Is there a project somewhere I could use to tap into the sound out and make it into bar display?

TIA
 

audioguru

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An LM3914 is a linear voltmeter. An LM3915 has logarithmically spaced steps for showing sound and light levels.

There are lots of projects on the internet with some driven from a microphone and others driven from line-level.
 

audioguru

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The circuit at Electronics-Lab is an Instructable with some errors:
1) It doesn't have a peak detector circuit at its input so the LEDs will be a dim blur.
2) It uses two 1.2k resistors but doesn't show where the second one goes. Does it replace the 7.5k resistor on the datasheet? Then the LEDs will be dim and the signal must be 2.5V peak which is too high.
 

wilykat

Member
I think this just what you're looking for:

Electronics-Lab.com Blog LM3915
I hadn't seen that one. The few project I found with Google has a transistor to handle input. However I don't have a convenient transistor cross reference, and BC series transistor isn't exactly readily found locally. Could I get away using 2n3904 or 2n3906 instead of BC series?
 

audioguru

Well-Known Member
Most Helpful Member
You should make the transistor peak detector circuit for the input of the LM3915 as shown in its datasheet.

A 2N3904 is the same as a BC547.
a 2N3906 is the same as a BC557.
But the pins are reversed between the American and European transistors.
 
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