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Thread: Issue with line in from android headset accessory

  1. #1

    Issue with line in from android headset accessory

    I am working on a project using the microphone of an android headset accessory, connecting it to a sparkfu opamp, and the into the line in of a teensy audio board.

    I am able to receive audio output from the teensy to the headset earpiece, but am having trouble getting the microphone signal to the teensy. Everything seems to be wired correctly (grounds are correct, mic is plugged into op amp input, output is connected to line in on teensy, op amp is receiving power and is grounded). the Voc between ground and output on the op amp is 2.6v, but does not change when microphone is in use.

    Any thoughts on my next steps? I have tripple checked my wiring (and confirmed the headset wiring with the android spec), and believe this has something to do with things I don't know about.

    Thanks!

  2. #2
    Senior Member+ Theremingenieur's Avatar
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    Your schematics? From your writing, nobody can see for example if the source impedance for the mic bias (2.2kOhm) is correct and if the op-amp has the correct input impedance and amplification factor (100 seems a little high for that purpose).

    Did you check the mic signal before and after the op amp with an oscilloscope?

  3. #3
    Okay, sorry for the delayed response but I didn't know how to answer your response at first...

    At this point in time, here is my wiring diagram

    Click image for larger version. 

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    When I first added this thread, I was not aware I needed a mic bias voltage and resistor. After adding these components, I am now getting signal to my teensy, but when I try to play it back I find that it is extremely noisy and distorted... maybe this has something to do with "the correct input impedance" for the op amp as you mentioned?

    Unfortuanely, I don't have an osilloscope, but I could get one if needed! I've never worked with audio before and so there is a lot I don't know, thank you for bearing with me.

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