How to remove noise between raspberry pi PWM0 and SIM800L mic pin?

Question

In my project SIM800L module(GSM Module) is interfaced with raspberry pi zero. Whenever user call Pi zero play an audio so that user can hear it. To send audio signal from pi zero to SIM800L, PWM0 pin is connected to MICP pin of SIM800L.

Please check below image for connection information:

Here When PI zero detect incoming call, It's start playing audio, So PWM0 audio is sent to MICP of SIM800L. But when audio start i can hear noise in that call but once audio start playing noise gradually stop. So every time i call, for few second i can hear noise and then after audio noise stop gradually.

I don't have any idea why this noise is generated and how to remove this noise.

I am following below tutorial for reference: https://othermod.com/raspberry-pi-zero-audio-circuit/

If anyone can help me with this, it will be good help for me.

Thanks

Answer 1

Try to use this diagram attached to the shield sim800, which explains that the signal must be filtered before entering it through the mic input of the shield because it operates in millivolts and has sensitivity to change. Save the signal voltage. Refer to this diagram (the answer may be needed by anyone) Microphone installation diagram for shield sim800l