• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 96 subscribers
  • Views 862 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

ezdsp microphone input

Michal Szymanski
Expert 1215 points

Hello, I wonder - is there any way to use as input microphone, instead line input? Right now I'm testing aic3204 sample project for ezdsp with headset plugged in to audio connectors. First phase of program works fine, I hear 1kHz tone signal. But during loopback section headphones remain silent. I know, that signal from microphone is lower than line signal, so I have also tried to increase CODECs MICPGA gain. The only difference is, that now I hear noise. I would be grateful if someone would give me some tips or project with proper codec configuration.

 Thanks in advance

 

  • 0
    TI__Mastermind 30110 points

    Hi Michael,

    Electret-condenser microphones (typical) need a bias current to produce signal. Here's a good paper on how the electret microphones work.

    Unfortunately, the current version of the eZdsp does not route the MICBIAS pin of the AIC3204 codec to the audio input jack. This will be provided in the next version C5505 eZdsp

    See Section 5.9.1 "Microphone Bias" of the AIC3204 Datasheet, Figure 4-7 "MICBIAS LOAD CURRENT", and  Section 5.1 TYPICAL CIRCUIT CONFIGURATION to learn how the MIC BIAS should interface to the microphone.

    There are a few approaches you could take:

    1) Use a battery-powered microphone that supplies its own power to the electret-condenser. Or another type of microphone that produces signal without the MICBIAS. Electric guitars also work.

    2) Solder pull-up/pull-down resistors to the two channels of the audio input jack. I have had success soldering one channel to GPIO and the other channel to ground, but there was noise. I haven't tried powering it with a pull-up to 3.3V or 1.8V, which are also available on the eZdsp. If you try that make sure there is no voltage drop on the 1.8V signal, it powers the core! See the AIC3204 Typical Circuit Configuration for the schematic.

    3) Provide your own external current bias that resembles the MICBIAS signal from the AIC3204.

    4) Wait until the new C5505 eZdsp ships (few weeks) with the MICBIAS connected to the audio input jack.

    Hope this helps,
    Mark

  • 0 in reply to Mark M
    Expert 1215 points

    Thank you, Mark. Your reply explained all my doubts.