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Thread: Questions about how to properly build a microphone input

  1. #1
    Junior Member
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    Questions about how to properly build a microphone input

    Hi! I'm new to teensy, but have experience with arduino and esp32.

    I'm very interested in teensy for it's audio shield capabilities. One piece of information which I haven't been able to find is what microphone input level range does it require?

    I'm confused about how to select the right microphone... some require external power and others don't, and some can be powered by a battery (like with some camera microphones). Will either theoretically work with this audio shield?

    Any guidance is appreciated. Thanks

  2. #2
    Senior Member
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    The mic input on the audio adapter is designed for a typical small electret capsule, and provides
    power for this (these capsules contain a JFET). For instance: https://www.pjrc.com/store/microphone.html
    This is mono only, note. You can feed any low impedance single-ended signal to the mic input (using a
    DC-blocking capacitor around 10F) too.

    Microphones with differential outputs requiring phantom power are not supported, for that a separate mic
    preamp would be needed, and fed to the line inputs of the adapter.

  3. #3
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    Thanks! Got it to work.

  4. #4
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    I'm experiencing a whistle noise when using the microphone line in. Is this common?

  5. #5
    Junior Member
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    Quote Originally Posted by MarkT View Post
    The mic input on the audio adapter is designed for a typical small electret capsule, and provides
    power for this (these capsules contain a JFET). For instance: https://www.pjrc.com/store/microphone.html
    This is mono only, note. You can feed any low impedance single-ended signal to the mic input (using a
    DC-blocking capacitor around 10F) too.

    Microphones with differential outputs requiring phantom power are not supported, for that a separate mic
    preamp would be needed, and fed to the line inputs of the adapter.
    Good day Mark, Im quite as clarkc5 just entering with the teensy, some background with arduino..., I was wondering if the electret can have an extension, is it possible?, and if so what length would you recommend not passing... I guess good mic cable would me a must, and with shielding...
    And also, if I try to put a piezo mic, as I understand they produce some current with the actual touch or working, what specs would you recommend for it? I guess the capacitor you mention? but anything else? would have to sort a JFET circuit maybe?
    I check the schematic for the shield, and I see along with the capacitor a mention to a 2.2k resistance, that would be necessary? or is it already present on the circuit?
    sorry if too newbie, maybe a source to study these stuff, the max impedance to support...
    good day!!

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