Aux in for an ISD 1820 (voice recorder chip)

Discussion in 'Electronics Resources' started by portreathbeach, Feb 25, 2015.

  1. portreathbeach

    Thread Starter Active Member

    Mar 7, 2010
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    I want to be able to use the headphone out of my Mac to input into an ISD 1820 voice record chip.

    The attached schematic, it shows the normal setup of the chip, using an elect microphone.



    I understand that the mic has a very small peak to peak, so I will obviously have to use resistor dividers to attenuate the output from the computer, but the output from the computer will be +/- around the ground line, so how can I centre it to be able to feed it into the ISD1820.
     
  2. portreathbeach

    Thread Starter Active Member

    Mar 7, 2010
    143
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  3. MrChips

    Moderator

    Oct 2, 2009
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    Attentuate the signal with two resistors and feed the signal directly into C4.
     
  4. portreathbeach

    Thread Starter Active Member

    Mar 7, 2010
    143
    5
    OK. Would I remove the other components associated with the elec mic? Would I remove R3, R4, mic and C5?

    The output from an audio source goes + and - with respect to ground, so I was thinking that when the output from the Mac was connected to C4, that the negative part wouldn't be seen.
     
  5. MrChips

    Moderator

    Oct 2, 2009
    12,442
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    Just remove the mic and R3.

    Leaving C5 and R4 should have no consequences.
     
  6. portreathbeach

    Thread Starter Active Member

    Mar 7, 2010
    143
    5
    Cool. I'll give it a go when my module finally arrives from China.

    On another note, still working with the same chip, I will be connecting the output of SP+ to an LN380 chip, similar to the schematic below for a LM386 (powered by 12v):

    http://www.elecfreaks.com/wiki/images/thumb/6/6a/BK_ISD1820-13.jpg/500px-BK_ISD1820-13.jpg

    This should work fine I think as long as I get the attenuation correct with a resistor divider on the output of the ISD1820.

    Now, I also want to use a PIC microprocessor (which I have done in the past) to output square waves to create different tones. I would also like to feed this into the LM380. So my question is..... If I put a large resistor (maybe 20K) on the output of the ISD1820 and a 20K resistor from the centre of my resistor divider from my PIC PWM pin, connect them together and feed the LM380, would that work. I was thinking was that the 20K resistors would stop any cross talk too and fro the 2 outputting devices and wouldn't damage them.

    By the way, the ISD1820 and the PIC will never be both outputting at the same time.
     
  7. portreathbeach

    Thread Starter Active Member

    Mar 7, 2010
    143
    5
    Would something like this work:

    Obviously I would have to work out the correct values for the resistor divider networks.
     
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