i was trying to make a roaming device which helps me route my calls through internet, to save my bills while on international roaming.
my setup goes like this:
gsm module sim800l, raspberry pi4, a usb audio adapter Quantum-QHM623 and an android app to get calls redirected.
basically this setup routes all my calls from my simcard to my phone app via the internet
the project is almost complete but the only issue i am facing is, the speaker of sim800l when connected to mic of usb audio adapter, i get a whole lot of background noise, these are the trouble shooting steps i followed which might help you assess the situation. 1) i can hear the voice with a lot of interference only when i connect speaker +ve from 800l to the +ve of mic in the usb adapters +ve side. if i connect -ve of speaker out to the mic ground of audio adapter, all i hear is noise alone, no voice.
the other audio line which is mic from 800l < ---- > to speaker of the usb adapter works absolutely fine,
I tested the modules this way and they seem to work fine audio usb adapter: to see if the audio adapter is working, i tested shorting out the mic and speaker and simulated a call from the android app, and it worked fine(i was able to hear own voice after i speak some thing, and the voice quality is too good)
sim800l: ATcommands work fine, was able to send and receive messages, able to call receive calls and hang them up using minicom
audio lines of sim800l: i shorted the mic and speaker lines and made a voice call to my mobile number, and i was able hear my voice fine but the quality is ok.
any help with this noise issue is very much appreciated.
EDIT: I can work around this issue using a different power supply. I had previously used the same raspberry pi to power the sim module, but now I have used a different power supply to power the sim800l module, and now it's working quite well.
Is there any solution to use the same power supply and not get the noise?