Hello,
We use in one of our project, a medical vital monitor device, the microphone ICS-40638 to detect alarm sounds generated by a loudspeaker. The whole system is integrated in a plastic housing case. The microphone is mounted on a PCB board under the loudspeaker. When the PCB board is not completely closed by the housing, the the output of the microphone is around of 200mV and the audio detection works fine but when the PCB board is closed completely by the housing case the output will be in range of 50mV so it's a 4 time smaller and the audio detection fails.
Could somebody tell me what can be the reason for this behaviour? How to overcome with this problem?
Thank you in advance.
Regards,
Alex
Hi Alex,
Thank you for reaching out.
I believe that a colleague of your may have asked about this issue a few months back. My response was a bit delayed but I did give them a few thoughts that came to mind regarding potential causes of this issue.
Please review my earlier response here: https://invensense.tdk.com/developers/forums/topic/ics%e2%80%9040638-high-aop-analog-mems-microphone-with-differential-output/
If you see any change to the issue or have any follow-up questions, please feel free to let me know here.
Regards,
Mike
Hi Mike,
Yes my colleague asked already about this issue some months ago. It is not a problem of temperature or charging or discharging of some reactance. This can be excluded because it's happen right after when the device case is closing.
I think we are facing your 2. thought which you have mentioned previously. The acoustic wave will be altered what the microphone is picking up.
The question is what can I do to overcome this problem? May be to use a filter material on the microphone hole or something similar?
Regards,
Alex
Hi Mike, it's possible that the high loudness of the acoustic wave(when the device case is closed) overdrive the microphone circuitry? Do you have in portfolio a microphone where the amplifier gain can be set/adjusted?
Regards,
Alex
Hi Mike, i just want to inform you that i solved the problem. I made a hole with a diameter of 1mm in the case of the loudspeker so the path of the acoustic wave is short and directly to the microphones hole.
Thank you for your help.
Regards,
Alex