How to Detect Line Audio Voltage

Discussion in 'The Projects Forum' started by vipergt023, Sep 29, 2008.

  1. vipergt023

    Thread Starter New Member

    Sep 29, 2008
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    Hello,

    I'm trying to make a circuit that will take in line level audio and is able to switch something on/off when sound is coming through (e.g. the sound from a headphone jack). I'm a newbie to circuits and any direction would be appreciated. Thanks.

    Vinoj
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    It's possible, but it will need it's own power, unless you have a handy source of, say, 12 volts DC.
     
  3. vipergt023

    Thread Starter New Member

    Sep 29, 2008
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    I've been reading - I think I may need a voltage comparator. I do have power - 5V from the USB port on a computer. I'd just hook up the two power lines and ignore the data pins.
     
  4. vipergt023

    Thread Starter New Member

    Sep 29, 2008
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    What about a comparator hooked to a relay? Then if the voltage exceeds a certain point, the output voltage could trigger the relay (switch) - could that work?
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    First you need a high impedance op amp to monitor and amplify the audio out. Then rectify it and apply it to the comparator, which can pull in a relay.
     
  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Last edited: Sep 30, 2008
  7. vipergt023

    Thread Starter New Member

    Sep 29, 2008
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    Thanks! That Scary Terry circuit looks like it'll do what I need it to. As I was looking around I came across a Schmitt-trigger. Would that work for this also? To provide more detail, the equipment I'm switching is a microphone - basically when the speaker is on, I want to mute the microphone. I heard something about a Schmitt trigger with an open collector. Is there an IC that anyone knows of that does the same as the Scary Terry or the Schmitt-trigger?
     
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