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Zero/Span Circuit for Audio Signal

  1. Mar 2, 2012 #1
    Hey all:

    I have an audio signal from an old portable CD player that on max volume outputs about 1-1.2V as shown when attached an oscilloscope. I want to feed this signal into a PIC microcontroller, but I hear you need to amplify and shift the signal into the 0V to +5V region for it to work correctly. I want to use the PIC to pulse modulate the audio signal.

    Does anyone know of any good zero-span circuits or if I even need one? Thanks!
  2. jcsd
  3. Mar 2, 2012 #2


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    Science Advisor

    You could but it would hardly be worth it.

    The output of the CD would be possibly producing outputs up to 2.5 volts peak to peak, so you could possibly make up an amplifier that gives you a gain of 2.

    You could use something like this:

    Which I just stole from another thread on this page.
    Remove the microphone from the left and feed your signal in there.
    Make R1 22K.

    At the micro input, put two resistors across the input (just like the two 47Ks in this diagram, but to +5 V and ground).
    This would set the input to 2.5 volts and the input would move this voltage centered on 2.5 volts.

    But to be reasonable about it, try it the way it is. It will probably sound just fine.
    Just put a capacitor in series with the signal path and two resistors across the A-D input of the micro just like the left of the above diagram as described above..
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