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Old 01/12/2008, 03:29 AM
kgross kgross is offline
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Join Date: Nov 1999
Location: Nampa, ID
Posts: 2,343
It should not be to hard to do. I'm not sure what the line voltage is on your audio in, but you could use a op amp and relay to turn on the LED if the voltage was above 1/4 max, or even just little bit above the background noise level.

Get a multimeter and measure the voltage on the jack and see what your average voltage is, should be zero with no sound, make some noise and see what voltage you get with sound, and then you could use a comparator to turn on the relay when ever the voltage on the line is above the set voltage. If you know much about electronics it would not be to difficult to build.
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