Razr / Razr Maxx "line-out" questions

[rgthorpe]

I know that the Razr car kits have included a micro-usb cable that branched out to a micro-usb plug and a 3.5 mm audio jack, so the Razr is capable of putting out (analog) audio through the micro-usb port. I would like to know (a) is this a true line-out (bypassing the Razr's own amp / volume control) or just a redirected headphone output, and (b) what triggers the switch of audio from the headphone jack to the usb -- is it a resistor between pins 4 and 5 as on some other phones (and if so, what value) or is there some other circuitry in the dock itself? (If it is just a resistor, then I would think it would be an easy matter to put together my own cable for this purpose.)

 

[mattman5000]

I'm almost positive that there was a thread on this site with a full discussion about that cable and how to build one, with pictures and everything. I just did a quick search and did not find it, but I didn't spend much time searching.

 

[rgthorpe]

I've spent a good amount of time googling, and while I've found instructions for diy usb-otg and factory cables I haven't found anything thus far on a diy line-out.