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Thread: Teensy 4 and Rev D Audio Board - LESSON LEARNED

  1. #1
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    Teensy 4 and Rev D Audio Board - LESSON LEARNED

    TLDR; If you want your SD card to work, hook up the ground next to the 3.3v pin, but ALSO hook up the other ground pin labeled "G" on the board. If you don't do both, it will not recognize the SD card.

    Details: I wired together a Teensy 4 and Rev D Audio board wired on a perf board with short wires between pins. I tested output with both a simple set of headphones, and also a small portable speaker.

    The Guitar demo worked fine, but was oddly noisy with the speaker, but OK with the headphones. Which was odd.

    Then I tried running the WavFilePlayer script, and found that it would NOT find the SD card if I used the headphones, but it would find it if I plugged into my speakers. However there was no sound, just odd static.

    Guessing it might be a ground issue, I discovered this: I had only hooked up GND that is next to 3.3V, and NOT the GND labeled "G" next to pin 0. I just figured ground is ground, and redundancy wasn't needed. But when I wired up GND G to GND, instant success. It found my SD card, and it played my WAV files fine.

    So - at least with Teensy 4 and Rev D board, hook up BOTH grounds, not just one.

  2. #2
    Senior Member+ MichaelMeissner's Avatar
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    Quote Originally Posted by holtt View Post
    So - at least with Teensy 4 and Rev D board, hook up BOTH grounds, not just one.
    I suspect the reason is on the Teensy 3.2/3.5/3.6, the two grounds are different. The ground next to pin 0 is the digital ground. The ground between VIN and 3.3v is the analog ground. The Teensy 4.0 does not have the notion of a separate analog ground. So I can imagine the revision D board only had changes for the I2S and SPI pin assignments that are different. Paul probably did not change the logic where digital ground was fed to the flash memory and SD card SPI devices, or the analog ground to the audio components.

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    Senior Member+ defragster's Avatar
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    Quote Originally Posted by MichaelMeissner View Post
    I suspect the reason is on the Teensy 3.2/3.5/3.6, the two grounds are different. The ground next to pin 0 is the digital ground. The ground between VIN and 3.3v is the analog ground. The Teensy 4.0 does not have the notion of a separate analog ground. So I can imagine the revision D board only had changes for the I2S and SPI pin assignments that are different. Paul probably did not change the logic where digital ground was fed to the flash memory and SD card SPI devices, or the analog ground to the audio components.
    @MichaelMeissner - think you hit that for the REV D board according to DMM::

    "Power Side":GND to "G":GND is 7-8 Meg Ohms.
    "G":GND to MIC body or SD shell is few tenths of an ohm.
    "Power Side":GND to MIC body or SD shell is 7-8 Meg Ohms.

    Both Rev C and D drawings for Audio Shield just label both pins as 'GND'

    No Rev C board here - but with Rev B it acts similar - except there must be some active component between the two 'GND' pins as the Meg Ohms reading varies between 18 and 4 in some fashion between probe hits and holding the probes.

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