For this weekend, I built myself a cable between MSX data recorder port and 3.5mm TRRS jack that works with my Note9.
Picture:
https://www.msx.pics/image/Vc1FN
The cable works great for loading and saving from the MSX using standard Android software (e.g. voice recorder).
While I was building the cable, I tested the build while connected to the phone and I noticed that closing the mic line with gnd does certain things if done at certain times. For example, it triggers a Pause/Play command in the music player.. This got me to think about the phone headsets that have remote control buttons for volume/pause/mute and I wonder... is that done entirely via certain mic signals? But further more, can the remote line from the MSX be hooked up to trigger Android to start recording or loading as a regular data recorder? Or does that go beyond just line connections?
Cheers!