Forum Rule: Always post complete source code & details to reproduce any issue!
Results 1 to 4 of 4

Thread: Differential output in mems mic

  1. #1
    Junior Member
    Join Date
    Oct 2018
    Posts
    8

    Differential output in mems mic

    Hi,
    I have some hardware questions and was hoping to find some help here.
    Some background:
    I work on a project about failures detection in an engine room with audio sensors. The concept is a small device with two microphones which will be able to detect chances in the tools normal behavior and send indication about the direction of the failed-tool relative to the device (thatís why two mics needed).
    I assembled a prototype with teensy4.0 and two Digilent mic module (https://reference.digilentinc.com/re...pmodmic3/start). It was very easy to assemble with itís SPI communication. We had a very nice and successful feasibility test that showed very promising result.
    Unfortunately, I noticed that when the noise level in the room increased to very high levels, the signal got corrupted. After some investigations, we came to conclusion that we need different mic with higher acoustic overload point and decided to try the following one: https://www.digikey.com/product-deta...-C-ND/10259330 . I briefly went over the ADC info from- https://www.pjrc.com/teensy/gui/?info=AudioInputAnalog but still have concerns about two issues (It might be trivialÖ):
    This mic has differential output. I read somewhere that I can just connect the V_out- to ground and measure V_out+. What is the penalty of such setup? Ideally, should I just measure both signals simultaneously in both ADC and reduce the results?
    Thanks in advance!

  2. #2
    Senior Member
    Join Date
    Jul 2014
    Posts
    2,566
    Quote Originally Posted by YL77 View Post
    This mic has differential output. I read somewhere that I can just connect the V_out- to ground and measure V_out+. What is the penalty of such setup?
    -6dB or half the voltage.

  3. #3
    Junior Member
    Join Date
    Oct 2018
    Posts
    8
    Got it! Thanks!
    Since I have no experience in using the analog input, I looked and found that I might need to use the following circuit to each input- https://dorkbotpdx.org/blog/paul/con...log_input_pin/ . Is that relevant for my mic as well? Should I change some of the component of the circuit in order to adjust the 0.8V bais to 0.6V?
    Thanks a lot for your help!

  4. #4
    Member
    Join Date
    Aug 2019
    Location
    Melbourne Australia
    Posts
    65
    Unfortunately, I noticed that when the noise level in the room increased to very high levels, the signal got corrupted.
    Possibly contains the answer. Assuming that the sound levels exceed the dynamic range of the Microphone itself, my suggestion would be to set up the mics in situ and look at their output on an oscilloscope to see if there is any clipping.

    I'd be thinking of dynamic mikes or playing with earbuds or laptop speakers. I'd use a buffer between it and the ADC input to prevent any excess signal from doing damage.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •