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Measure a DC signal with the aic3204 audio-codec on the VC5505 eZdsp evaluation bord

Peter Urban1
Prodigy 20 points
Other Parts Discussed in Thread: TMS320VC5505, REG103

Hello,

I am using the TMS320VC5505 eZdp USB Stick evaluation board to program the VC5505 DSP. For my project I need a high resolution (>16 bit) DAC and ADC. Instead of buying an external one I first wanted to try if the DAC and the ADC from the onboard aic3204 audio codec may already suit my purpose.

 I was able to initialize and use the DAC with the help of a Spectrum Digital example code (from the board support library).  But now I am facing a problem trying to use the aic3204’s ADC. Sampling a Sine wave or sound input was no problem, but I wasn’t able to Sample any DC data so far.

I used the Spectrum Digital aic3204 example (audio loopback test) as a code base. The ADC would give back a value of round about -80 not reacting on any dc input to the microphone in channels. Then I activated the DC Measurement in Mode A for both channels by writing to the Register page0/reg103.  As a result the AIC3204 would give back wildly changing values between 600 and -600, but still not react on any DC input.

 

My question is:

Is it possible to do good DC Measurements with the aic3204’s ADC or is this ADC really only in sampling audio data?

If it is possible, could you give me a hint on how to initialize the ADC in a DC-Measurement mode? Or is there any existing code example that could help me further?

 

I hope anyone can help me, thanks in advance

Peter

  • 0
    Prodigy 20 points

    In case anybody ever has the same Problem:

    Don't be as dumb as I. Check the boardschematics of the eZdsp. There are Capacitors(C18 and 19) put in row with the audio-in chanels of the aic3204. If you want to measure DC-Signals you simply have to bypass them by soldering a short cable. This will of cause make the SNR of the AIC3204 input chanel even worse. (Just as a note: It is the Boarddesign, that causes most of the Noise, as it is not optimized for low noise applications at all).

     greetings.