Android phone not detecting audio line in (how to fix?)

Thread Starter

wrybread

Joined Jul 3, 2005
32
I added a line-in to my car's stereo by soldering to the output of the tape deck, so now I have an 1/8" audio jack that I can connect to my phone or whatever. It works well with most things (tested with a laptop and a discman), but my Android phone doesn't detect it when I plug it in. It just keeps playing music from it's internal speakers even with the cable connected. If I connect regular headphones it switches over to the headphones though.

From a bit of googling I think I need to add a resistor between the right and the common pins of my audio cable. Someone in the comments of this thread is suggesting a 16 to 32 ohm resistor.

Here's what the connection to the tape deck look like:

pict8076.jpg

And after soldering my cable to it:

PICT8122.jpg

Could I simply solder a 40 ohm resistor between Right and Ground?

Thanks for any help.
 

wayneh

Joined Sep 9, 2010
17,152
Could I simply solder a 40 ohm resistor between Right and Ground?
Personally I'd experiment a little to use as high a resistance (low load) that still works reliably. I mean, try a 1K. Didn't work? Try 100Ω. And so on.

There's no guarantee that the two channels behave identically. So with each test, try both channels.
 

Thread Starter

wrybread

Joined Jul 3, 2005
32
Well I tested the impedance between R and common of a few different pairs of headphones, all were 30 ohms, except one, the "high impedance headphones" and they were 50 ohms. And I had a pack of 47 ohm resistors so I soldered that onto the board between R and common.

20210211_124318.jpg

On the bench my Samsung phone was now detecting the audio jack! Whoo hoo! But once I got it all powered up my phone wasn't detecting it again. Measuring the impedance I see it just says 0 ohms. If I turn the tape deck off it goes back to 47 ohms. Any idea why that would be? Guessing the tape deck signal is interfering?

Interestingly an iPhone 8 (oops I mean iPhone 7) I tested with had no problems detecting the jack. And there's a workaround for my Samsung: connect it with the tape deck off and it detects it. Can then stop and start music, change apps, whatever, and it stays connected, as long as I don't unplug the jack. I can see that getting old though.
 
Last edited:

djsfantasi

Joined Apr 11, 2010
7,689
Interestingly an iPhone 8 I tested with had no problems detecting the jack.
What model of an iPhone 8 do you have? I’m amazed that it had no problems detecting the jack, SINCE AS OF THE IPHONE 8, APPLE REMOVED THE AUDIO JACK ON IPHONES!

I have an iPhone 8s and there’s no jack anywhere.
 
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