I am trying to play audio over the call by using SIM800l
I am using this "DFPlayer mp3 module" to play audio and connected its AUDIO OUT to the MIC IN of "SIM800L GSM module" and I hear a humming noise.
I tried to put those capacitors as in this schematic:
as recommended in the datasheet to amplify the audio and it reduced the noise a little bit but it still there.
After a lot of searching a found that this noise may be because of a ground loop, but I don't have the reasons of the ground loop I use the same power source and I grounded the two modules with the same ground.
I also tried to use shielded and insulated cables between the two modules but also nothing happened, and the noise remains.
I tried to make a low pass filter using resistors and capacitors like this schamatic, but this makes the sound distorted.
I also tried to decrease the sound level from the DFPlayer, and the sound actually decreases, but the noise remains.
I also tried to change the gain from the SIM800L's AT+ commands but nothing happened.
After another search I found that maybe the audio from the DFPlayer is very high level and the SIM800L needs the signal from an electret microphone. Can that be the problem, and what can be the solution?
NOTE: The sound from the Dfplayer module is very clear when I connect it to a speaker AND also the sound is very clear on the other call when I connect the SIM800L with an electret microphone.
