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Thread: Connecting a Teensy 3.6 to mic in on an Android phone?

  1. #1

    Connecting a Teensy 3.6 to mic in on an Android phone?

    I already asked this on Electrical Engineering Stack Exchange, but so far without an answer: How to connect a line-out to mic on Android plug? (CTIA)

    We have set up a sound installation in the Hong Kong jungle: Twitch live stream

    The output of a Teensy 3.6 is connected to the input of a Xiaomi Mi 4X Android phone using a 3.5mm plug with four rings, wired according to CTIA standard. This does work. However, there are two issues:
    • The phone still picks up ambient sound, meaning it doesn't turn off the internal mic. This issue does not happen with a regular headset. When a regular headset is connected, the internal mic is disabled.
    • The signal picked up by the phone from the Teensy is very weak, although if I connect my headphones to the Teensy it's actually very loud.

    Any idea how to wire a 3.5mm plug so that it is recognized as a headset by Android?

  2. #2
    I measured the resistance between the sleeve and ring 2 on my Bose QC25 headphones: 5.6 kΩ

    This led me to adding a 5.5 kΩ resistor to my plug:

    Click image for larger version. 

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    There were some other random audio issues, but they magically went away. Possibly there was also a short somewhere in my circuit, part of which I resoldered. Anyhow, now it works!


    • Rings 3 and 4 are intentionally left unconnected. I don’t need headphone output.
    • With another headset that I tried, the phone, a Xiaomi 4X, did not detect it properly. That headset did work on another phone. There seems something odd about the Xiaomi 4X.

    In case you’re curious:

    Click image for larger version. 

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    Live stream on Twitch (few more hours, until battery is dead)

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