Reverse engineering a mini-USB to Line-in pinout

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Reverse engineering a mini-USB to Line-in pinout

Postby etatoby » January 13th, 2018, 10:51 am

Hello

I have a portable mono speaker similar to this one that I bought years ago and barely used:

DY-808+.png
DY-808+.png (67.13 KiB) Viewed 54 times

It has a surprisingly good audio quality, for its size and cost.

Now I'd like to use it in a project, but I lost the proprietary line-in cable. It was a Y cable, from mini-USB to both USB-A (for charging) and 3.5mm jack (for line-in.) Basically the unit is using some of the mini-USB pins for charging and some others for audio line-in. The unit is mono, so there is probably only one audio hot pin.

I made a few tests.

Connecting the audio source to USB GND and D+ (audio GND -> USB GND black; audio L+R -> USB D+ green) gives the right sound, but it's so weak as to be useless, even with source volume at Max and speaker volume quite high, so I don't understand what's going on.

Trying to use USB D-, either with (GND -> USB GND; L+R -> USB D- white) or (GND -> USB D-; L+R -> USB D+ green) gives an even weaker sound and I can only hear trebles, so that's probably some unintended capacitive effect.

Using USB GND and D+ seems to be the best guess, but I'm missing something. Why would the audio level be so low? Do I need to add a capacitor or something?
etatoby
 
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Re: Reverse engineering a mini-USB to Line-in pinout

Postby k-ww » January 13th, 2018, 3:37 pm

Have you tried with the power on the USB + & -, and the audio on the D+ & D- pins?
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