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Thread: Dynamic Mic capsule to Teensy 3.5 ADC (A2)

  1. #1
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    Dynamic Mic capsule to Teensy 3.5 ADC (A2)

    Hi, I want to connect a dynamic mic capsule to the A2 adc input of a Teensy 3.5. Can any one advise me on the best way to do this please? I've looked at the circuit given in the audio design tool but I'm not convinced this is the circuit for me. The input looks biased, am I right? If I'm correct, why is that? Where would the capsule ground go, to AGnd or Gnd? Should I use a preamp and if so how would I connect that? I'm not and audio engineer (in fact, I'm not any sort of electronics engineer) so please forgive my ignorance.

    Thanks.

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    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by Sharpie View Post
    Can any one advise me on the best way to do this please?
    That mic will produce a very tiny signal. You will need a low-noise amplifier to increase it to the line-level signal Teensy requires.

    I've looked at the circuit given in the audio design tool but I'm not convinced this is the circuit for me. The input looks biased, am I right? If I'm correct, why is that?
    You're correct about the bias. Teensy's input range (when using the internal reference) is 0 to 1.2V. That circuit is meant to take a line-level signal, like you'd get from a consumer stereo system, which varies from approx -0.5V to +0.5V. It translates that to 0.1V to 1.1V, which maps nicely onto most of Teensy's 0 to 1.2V range.

    Whether that's the circuit for you is a good question. It's certainly not your entire solution, so you'll have a voltage from that mic which is only a few microvolts. So you'll certainly need a low-noise amplifier to increase the voltage. You *also* need to get the voltage mapped into the 0 to 1.2V range (0.6V DC bias). Maybe whatever amplifier circuit you use can do that? Or maybe it can be modified so do so, as was done with this Adafruit mic amp? But if whatever amp you use can't produce the correct 0.6V DC bias, then you'd also need to use that circuit to translate its output, since Teensy's ADC pin only measures between 0 to 1.2 volts.

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    Quote Originally Posted by PaulStoffregen View Post
    That mic will produce a very tiny signal. You will need a low-noise amplifier to increase it to the line-level signal Teensy requires.



    You're correct about the bias. Teensy's input range (when using the internal reference) is 0 to 1.2V. That circuit is meant to take a line-level signal, like you'd get from a consumer stereo system, which varies from approx -0.5V to +0.5V. It translates that to 0.1V to 1.1V, which maps nicely onto most of Teensy's 0 to 1.2V range.

    Whether that's the circuit for you is a good question. It's certainly not your entire solution, so you'll have a voltage from that mic which is only a few microvolts. So you'll certainly need a low-noise amplifier to increase the voltage. You *also* need to get the voltage mapped into the 0 to 1.2V range (0.6V DC bias). Maybe whatever amplifier circuit you use can do that? Or maybe it can be modified so do so, as was done with this Adafruit mic amp? But if whatever amp you use can't produce the correct 0.6V DC bias, then you'd also need to use that circuit to translate its output, since Teensy's ADC pin only measures between 0 to 1.2 volts.
    Thanks Paul, that was very helpful.

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