This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Connecting an electret microphone to stereo in jack?

Other Parts Discussed in Thread: TLV320AIC3204

Hello!


I am trying to connect an electret microphone to the stereo in jack. I soldered 1,3V  (pin 8 from U8) through an 1k ohm resistor to stereo in pin 2. This should be enough to feed an electret microphone capsule connected to the stereo in jack. The mic is a standard headset mic with a stereo plug. On my oscilloscope only extreme loud sound shows up. Did I miss something? I use the aic3204 project, because it provides a simple pass-through demo. The headphones remain silent, except when I blow very hard directly on the mic. Are there any other ways to connect a mic?
Kind regards,
Holo


PS: I did not use the MICBIAS pin as power supply because our soldering equipment is not fine enough.

  • Hi Holo,

    The audio input on the board is connected to the CODEC line in inputs.  This means it is expecting a line level signal on the inputs.

    If you want to use a mic, construct a simple OPAMP amplifier to bring the electret mic's level up to a line level (around 1V should do if memory serves me right).  Google should have plenty of examples.  

    If your PC allows routing of audio signals, you can plug the mic into the PC and use the earphone or line out socket on your soundcard to connect to the board, that's what I'm using for testing at the moment.

    Hope this helps,

    Cheers,

    André

  • In addition to that, I have noticed that the AIC3204 sample program requires less audio input than the

    USB_Stick_AudioFilter1  sample program.  So, it seems that there must be a software way to influence the input

    sensitivity.  I have looked thru the code some and can't fine it.  If we can find that, it might be worth a

    try to make the input as sensitive as possible.

    Tom

     

  • I changed the MicPGA amplifier from 0dB to 30dB. Now I can hear the sound comming in through the mic and then played over headphones. The problem now is strong noise. I will dig into that, I am new to both the DSP and the codec, maybe there are some other nice options I missed. If a software solution fails I will have to build the mic ampilfier sugested above.

    Holo

  • I had a quick look at the TLV320aic3204 datasheet and it is actually much more flexible than I assumed.  The noise you are experiencing is most probably due to the lower output impedance of the electret microphone feeding a high input impedance.  I see there is a register to change the input impedance of the TLV320aic3204, try and lower that to 10k and see if it makes any difference to the perceived noise.

    Man, I wish I had more time to play with this thing, it's silly season at work so it'll have to wait for a bit.

    Keep us updated on your progress.

    Cheers,

    André

  • Lowering the impedance to 10k did help. I think the rest of the noise comes from the way I power the mic. The "long" wire to U8 certainly catches some noise of the digital traces below.

    Holo

  • Hello again,

    I switched the microphone power supply from board powered to battery powered. Most of the noise is gone now so my assumption above was correct. Because the battery has a slightly higher voltage (1,5V) I also was able to reduce MICPGA from 30db down to 10db, which also reduced some of the noise.

    Holo