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I want to connect line-out of a device to the microphone input of an Android phone, a Xiaomi Mi 4X. Then I can record and live stream from the phone.

If I simply connect line-out left/right (red/white) to the sleeve and ground (yellow) to ring 2, then the microphone does work. However, the phone will still use the internal microphone in addition. This does not happen when I use a headset (Bose QC25). So apparently additional wiring is necessary, but how?

I also tried connecting the (unused) headphone connectors to ground, using a 220 Ω resistor. These are ring 2 and the tip. The idea is to match the 32–300 Ω impedance in the Android 3.5 mm Headset Jack Device Specification, hoping that this will make my adapter be recognized as a regular headset. It did not help.

Photo of four sleeve jack with 220 Ω resistor

feklee
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  • Reading left to right as shown in your photo we would label the poles of the plug as Sleeve, Ring 2, Ring 1 and Tip. Usually ground is the sleeve and the wire is soldered to the long cable clamp. It may help if you use this terminology in your post. – Transistor Mar 16 '20 at 02:24
  • @Transistor Hope it's correct now. Note that my adapter does work as a mic, so basic wiring is correct. Only the phone does not disable the internal mic, which it should. This indicates that it doesn't detect my adapter as a headset. – feklee Mar 16 '20 at 02:41
  • Note that there are 2 conventions : on some devices, (Apple?) Ring 2 is GND and Sleeve is mic. Which is the braided cable sleeve connected to? I can't see in this photo. You also need (for Apple) 1.6K impedance between mic and GND to make the device switch to external mic. (It provides DC bias for an electret mic, and senses the current) –  Mar 16 '20 at 14:14
  • @BrianDrummond The order of the rings is correct (CTIA standard), otherwise the mic input wouldn't work at all. Your comment about the impedance is interesting. How would I realize this? Just add a 1.6kΩ resistor between mic and GND? (The signal is coming from line-out of another device, not from an actual mic.) – feklee Mar 17 '20 at 01:39

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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:

Photo of plug

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.

feklee
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  • @feklee- can you help me in that question. I am not much in circuit stuff so you are my best hope. https://electronics.stackexchange.com/questions/560694/how-to-connect-one-android-mobile-audio-output-to-mic-of-another-android-mobile – Dheeraj Chauhan Apr 19 '21 at 11:10