How to connect a line-out to mic on Android plug? (CTIA)
I measured the resistance between the sleeve and ring 2 on my Bose QC25 headphones: 5.6 kΩ

This led me to adding a 5.5 kΩ resistor to my plug, and it works:



Notes:


Rings 3 and 4 are intentionally left unconnected. I don’t need headphone output.
With another headset that I tried, the phone, a Xiaomi 4X, did not detect it properly. That headset did work on another phone. There seems something odd about the Xiaomi 4X.