Looking for Microphone Suggestions

Thread Starter

electronicpenguin

Joined May 10, 2022
8
Hello!

This is my first forum post so hopefully I'm posting in the correct discussion forum. Long story short, I'm looking for some microphone suggestions. I'm currently working on a project that is trying to record respiration with a small microphone positioned 1-2cm away from the mouth. So far I've tested two microphones with an Arduino: The electret microphone amplifier Max 4466 from Adafruit and CUI Devices CMC-6015-47P electret condenser microphone.

Both of the above microphones work fairly well for detecting medium and strong mouth exhalations. However, I find that both struggle to record weaker exhalations that tend to be more quiet. Any advice when it comes to selecting small microphones good at recording breath/mouth-exhalations? Eventually the microphone breath sensor will be used with a VR game. I'm not an audio expert so any suggestions would be appreciated very much!

Thank you!
 

Yaakov

Joined Jan 27, 2019
5,495
Welcome to AAC.

WIthout more information it is my speculation that you will need to amplify the output and probably also employ a limiter.

The microphone is probably not your issue.
 

Thread Starter

electronicpenguin

Joined May 10, 2022
8
Welcome to AAC.

WIthout more information it is my speculation that you will need to amplify the output and probably also employ a limiter.

The microphone is probably not your issue.
Thank you for the quick reply! I'll definitely look more into amplifiers and limiters. I currently just have the electret condenser microphone connected to the Arduino Nano 33 IoT with jumper wires (VDD--> 3.3V, GND --> GND, OUT--> A1).
 

Ian0

Joined Aug 7, 2020
4,838
What is the problem with the microphone you have that doesn't work at low levels? Do you simply need more amplification? or do you need better amplification, with reduced background noise? or does the microphone itself have high background noise? Or does your A/D have insufficient resolution?
Have you tried an amplifier with automatic gain control such as
https://datasheets.maximintegrated.com/en/ds/MAX9814.pdf
Have you tried MEMS microphones? I find them to be better than the usual condensors. You can even get the with I2S interfaces.
 

Thread Starter

electronicpenguin

Joined May 10, 2022
8
I don't think I have tried an amplifier with automatic gain control but I will definitely look into testing one of those, along with some MEMS microphones. I think just having more amplification would be ideal for now. The microphone can detect weaker breaths most of the time, but the signal is not very big compared to the baseline. Thanks for the suggestions!
 

Audioguru again

Joined Oct 21, 2019
4,523
I hope your microphone is at the side of the mouth then it does not get blasting loud air puffs on it.
You do not want AGC that tries to keep all sounds the same level.

The MAX4466 Adafruit mic preamp has a volume control on its back and the maximum output level from it is adequate for most recorders. Maybe your recorder has poor sensitivity?
 

KeithWalker

Joined Jul 10, 2017
2,297
Have you considered using thermistors for sensing the airflow? With them it is relatively easy to detect very low flow rates without the problem of interference from ambient noise. The usual arrangement is with two similar thermistors connected in a balanced bridge, with only one in the air flow. The second one is used to balance out temperature variations.
 
Before suggesting a type of microphone it is important to know what aspect of the sound matters for the application. If respiration rate is all that matters then a very high gain along with some hard limiting will serve the purpose. But if the need is to check the quality of breathing to detect impairment then less gain and better fidelity are needed.
I am aware that there are, or were, baby monitors marketed that would detect an infants breathing sounds and deliver an alarm if it stopped detecting them for more than a few seconds. So that would be an additional application.
So the application will have quite an effect on the quality and frequency response of the microphone required.
 

Thread Starter

electronicpenguin

Joined May 10, 2022
8
Before suggesting a type of microphone it is important to know what aspect of the sound matters for the application. If respiration rate is all that matters then a very high gain along with some hard limiting will serve the purpose. But if the need is to check the quality of breathing to detect impairment then less gain and better fidelity are needed.
I am aware that there are, or were, baby monitors marketed that would detect an infants breathing sounds and deliver an alarm if it stopped detecting them for more than a few seconds. So that would be an additional application.
So the application will have quite an effect on the quality and frequency response of the microphone required.
Thank you for your input! In this case, the quality of the breathing is more important to detect so I will look into lessening the gain and increasing the fidelity.
 

Thread Starter

electronicpenguin

Joined May 10, 2022
8
Have you considered using thermistors for sensing the airflow? With them it is relatively easy to detect very low flow rates without the problem of interference from ambient noise. The usual arrangement is with two similar thermistors connected in a balanced bridge, with only one in the air flow. The second one is used to balance out temperature variations.
I have tested a few thermistors (10k) but I found that my breath added heat to the thermistor mass after each breath. As a result, the thermistor wasn't able to cool down completely before the next breath. However, I'll look into testing the thermistor bridge to see if that gives me a different result!
 

Thread Starter

electronicpenguin

Joined May 10, 2022
8
I have tested a few thermistors (10k) but I found that my breath added heat to the thermistor mass after each breath. As a result, the thermistor wasn't able to cool down completely before the next breath. However, I'll look into testing the thermistor bridge to see if that gives me a different result!
Does the thermistor need to cool down if your testing for is there a breath
your looking for th efairly rapid up / down movement of the thermistor in the air flow compared to that of a reference one outside the air flow

Another alternative is may be a Co2 sensor
e.g. https://www.adafruit.com/product/3709

again your looking for the up / down , relative to ambient, not the absolute level
 

MisterBill2

Joined Jan 23, 2018
11,580
As the intention and purpose appears to include listening for "roughness" and raspiness in the breathing, and none of the suggested flow detection schemes can capture that very well. So the sensor needs to be an actual microphone with adequate frequency response. Actually that should not be difficult, unless really cheap and totally waterproof are requirements.
 
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