Hello,
Greeting!!
We are using ICS- 40638 microphone in our patient monitor project. We are using microphone as an audio feedback to check whether the 2 loudspeakers working properly or not. The output signal from the microphone is pre-amplified and then fed to the peak detector circuit. When the monitor is open (without casing) then we have observe the output as shown in the attachment (Monitor_without_Casing) and when we closed our monitor in a case then the amplitude of the microphone signal decreases as shown in the attachment (Monitor_with_Casing)
We have built a circuit as shown in the attachment below (Microphone_Circuit). We have tried to do the required changes in our circuitry but couldn't succeed so far. Also we have placed the microphone on the PCB board as described in the datasheet. Please find the attachment of 3D placement of the microphone and 2 loudspeakers on the PCB board (Monitor_with_Loudspeakers).
Any idea why the output of the microphone behaves different in a closed envirnoment?
Waiting for your reply.
Regards,
Janhavi Rane
Hello Janhavi,
Firstly, I would like to apologize for the delayed response. We have been working on getting the forums up-to-date and are reviewing some older questions in an effort to do so.
Given the age of this question, it is possible that an answer is no longer needed but, in case this is not true, I did want to follow-up to see if I can help you resolve this question.
My initial thoughts go to two possibilities here.
1. By enclosing the system, the ambient temperature of the devices could be increased and if there are any components in the circuit that have a large temperature coefficient then I would start there. The impact of this might be minimal and the likelihood of this being the root case might be low, but it is possible that increased temperature could cause a shift in one of the parameters of a passive component. The distorted waveforms appear to show a transient response that is exponential in nature so it could be related to the charging or discharging of some reactance in the circuit.
2. I wonder if it might be the case that by enclosing the system, the acoustics are being altered in such a way that is absorption or reflection of the output of the speakers could be impacting what the microphone is actually picking up.
I would start by using a fan or some other means of controlling the ambient temperature inside the case to rule out temperature as the cause. After doing this, I would then start to experiment with the materials inside of the case to see if altering the acoustic characteristics inside of the case has any impact.
As I mentioned, I know this is an older question so I hope this information can still be of some help to you. If you have already determined the cause of this issue, I would be very interested to hear what you were able to find and how you resolved it. If not, feel free to update with any new information so we can try to root-cause it.
Regards,
Mike