Use of Stereo ADC/DAC

Discussion in 'The Projects Forum' started by MrL, Feb 7, 2012.

  1. MrL

    Thread Starter Member

    Oct 21, 2009
    46
    0
    Hi,

    I am working on a system that allows music to be played to a speaker through the use of optical fibre. I am using the 3.5mm headphone jack analogue output on the MP3 player, converting this into digital form, and then converting this back into analogue form again at the receiver, so the signal can be applied to the speaker.

    At the moment, i’m investigating the required timing for the ADC at the transmitter and the DAC at the receiver, and i was looking into the use of a stereo ADC and DAC. As this is new to me, I was looking for some help in this area from someone who may have experience in using these devices.

    I was looking at using a stereo ADC at the transmitter in slave mode, with the audio data in the format of 16 bit 12S. Is it possible to use a DAC at the receiver in master by providing it with the same system clock input frequency as used at the transmitter? Given that the DAC will know the data format and bit length, will it automatically detect the signal correctly, and know which bits represent the left and right channels?

    Any help would be greatly appreciated as these ADCs/DACs are something which are totally new to me.

    Thanks.
     
  2. mcasale

    Member

    Jul 18, 2011
    210
    12
    This is totally doable, but there's an easier and faster way, depending on where you are sending your music. I've been using a "sound bridge" for a number of years. They use your wireless (or even wires) to transmit music from a PC/MAC to a receiver at your stereo. Look at Roku and Sonos on the web.

    If you still want to do this project, your ADC needs to sample the music at least TWICE as fast as the highest frequency (Nyquist criterion). So each channel needs to be sampled at 40KHz or faster. This is possible.
     
  3. MrL

    Thread Starter Member

    Oct 21, 2009
    46
    0
    Thanks for the response. This is a project i've undertaken and i'm required to use optical fibre.

    So would the use of a stereo DAC in master mode automatically understand which 16-bits are for the left channel, and which 16 are for the right? I'm guessing it assumes that the first 16 bits it receives after power up are from the left channel?
     
  4. Experimentonomen

    Member

    Feb 16, 2011
    331
    46
    A ADC made for audio spits out I2S, to send this over toslink, you need a I2S to spdif converter ic, then hook your toslink transmitter to the spdif output.

    I have a eval board with 4-6 such adc's on it already wired up with 3.5mm phono jacks with I2S output, someday i'll find a use for them.

    Then on the receiver end is your usual toslink receiver and the spdif to I2S converter ic and then onto any commonly used popular dac ic.
     
  5. mcasale

    Member

    Jul 18, 2011
    210
    12
    It sounds like you have already picked an ADC. I don't know what a stereo ADC is.
    What parts have you selected? Do you have a schematic to share.
    It's tough to help in the abstract.
    You will probably have to write code to tell it what to do with the bits. What MPU are you using?
     
  6. MrL

    Thread Starter Member

    Oct 21, 2009
    46
    0
    Thanks for the help so far.

    My project is mainly based around the optical transmitter circuit and receiver design. I'll be using a multimode fibre, with a common emitter transmitter circuit (LED source) and a receiver circuit using a PIN diode. The stereo ADC is something that will come before that transmitter circuit, and the DAC after the receiver. At the moment i don't have a detailed schematic as that is what i'm trying to work towards.

    I'm looking at doing hardware design and no software, as the DAC can operate in hardware mode. Here the stereo ADC and DAC i was thinking of using:
    http://www.datasheetcatalog.org/datasheet/texasinstruments/pcm1801.pdf
    http://www.wolfsonmicro.com/documents/uploads/data_sheets/en/WM8766.pdf

    The main issue i was trying to address though was the stereo DAC. If i operate it in master mode, will it automatically detect the signal correctly along with the correct left/right channels?

    Thanks.
     
  7. mcasale

    Member

    Jul 18, 2011
    210
    12
    Wow, there's a lot if info on those data sheets. It's going to take some time to go through it - time I do not have.

    I don't think you're going to be able to just hook inputs to outputs and expect it to work.

    Is there a reason you chose audio? Can you just transmit a set of digital pulses to see how your hardware works?

    I recommend starting simple, and gradually add complexity.

    Good luck.
     
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