As far as I'm aware, the make-or-break is that your aux cord of choice must be a TRRS-type cable. You can tell the difference because the male ends have three black stripes instead of two.
Cables of this type are capable of sending signals from a mono mic as well as left and right stereo audio out. The 3DS has a TRRS jack, and according to this thread standard headsets with mono mics work with the 3DS (as do headsets with inline controls that use the mic line.)
Admittedly I'm not too knowledgeable in this area beyond this; you'll probably need to use an adapter to patch your PC's line/headphone out into a mic line. Just know you need a TRRS cable going into the 3DS.
Once you've figured this bit out, the input will just behave like the 3DS mic (remember, it's mono!) You just have to use the microphone reading API SmileBASIC exposes to you to get the input (as raw PCM, I believe.)
Cables of this type are capable of sending signals from a mono mic as well as left and right stereo audio out. The 3DS has a TRRS jack, and according to this thread standard headsets with mono mics work with the 3DS (as do headsets with inline controls that use the mic line.)
Admittedly I'm not too knowledgeable in this area beyond this; you'll probably need to use an adapter to patch your PC's line/headphone out into a mic line. Just know you need a TRRS cable going into the 3DS.
Once you've figured this bit out, the input will just behave like the 3DS mic (remember, it's mono!) You just have to use the microphone reading API SmileBASIC exposes to you to get the input (as raw PCM, I believe.)