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Thread: Audio Adaptor - misleading schematic

  1. #1

    Audio Adaptor - misleading schematic

    Hello all / Paul,
    as with every "serial" connection that is labeled RX or TX, there is a tendency to confuse who is actually receiving or transmitting the data.
    In case of the teensy audio adaptor, this is also the case for the I2S RX/TX pins.

    This RX/TX situation is easy to get from the implicit (though technically not guranteed) I2S 'master' role of the teensy on the pin usage overview picture:


    BUT: the following schematic centering on the audio chip uses the same teensy-centric I2S RX/TX identification for the internal chip pins without a teensy in sight and is therefore misleading.
    The I2S data lines come from the left, pin 22 going to the internal pin26 as well as Pin 13 going to the internal pin25, and they are mislabeled on the SGTL5000 block.
    As can be seen in the datasheet (page 3, top right), the internal pin26 is actually I2S_DIN (instead of 'TX') and internal pin25 I2S_DOUT (instead of 'RX'), and using those names would remove the confusion.


    I'm only mentioning this error in such length because it's a treacherous trap for anyone building experimental I2S configurations, and it would take hours to find.
    Keep up the good work on teensy!

  2. #2
    I will like to notice that also the MICBIAS 1.0uF capacitor is misplaced.
    It should be on the left of the 2.2K resistor. Between the pin 16 and ground.

  3. #3
    @Stendall: good catch, the "Typical Application Schematic" on page 59 of the SGTL5000 datasheet agrees.
    On a (very) quick look, the actual board layout looks correct in this regard, by the way, so it may only be a documentation error.
    Last edited by CyborgEars; 07-01-2015 at 03:39 PM. Reason: Link

  4. #4
    Senior Member PaulStoffregen's Avatar
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    The schematic has been updated, to fix the error on the mic input, and with the changes from version 1 to version 2.

    http://www.pjrc.com/store/teensy3_audio.html

  5. #5
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    Quote Originally Posted by PaulStoffregen View Post
    The schematic has been updated, to fix the error on the mic input, and with the changes from version 1 to version 2.

    http://www.pjrc.com/store/teensy3_audio.html
    Question:
    Is it correct that, in order to use two audio cards, I have to cut the traces in RX/TX/ADDR lines, solder ADDR to 3.3V, attach two wires to RX/TX and connect to the I2S RX1/TX1 pins at bottom of Teensy?

  6. #6
    Thank you very much Paul.

  7. #7
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by WMXZ View Post
    Question:
    I replied here:

    https://forum.pjrc.com/threads/29373...ll=1#post80525

    Let's discuss this hardware hack over on that thread.

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