Motorola Droid4 mount cable SKN6394A

I have the Motorola dock and custom audio/charge cable (SKN6394A). I am currently planning on using the mount with a different base (Arkon GN097-2-MICRO) that has been modified to use a female USB A connector. I tested this configuration and it works fine. But, the cable is way too long and looks horrible. What I was hoping to do was build a shorter cable. I know I could simply buy a second cable (found one cheap on ebay actually) and just hard wire it to the mount, but I prefer to be a little more flexible.

I guess the simple question is, does anyone have any information on how the connectors are wired? I tried plugging the custom cable into the phone and pc directly just to see if it would blow things up...it did not. However, it does not work as a normal USB charge/data cable. I certainly can use my DMM to check continuity, but I don't know for sure if there isn't something else going on that I would miss. Anyone have a schematic?

If there's a better sub-forum to post this, please let me know. This is the same cable that Motorola is using for other devices, so it might fit better in a general Motorola hacking sub-forum.

 

I went on a road trip over the weekend and found another issue that I will have to resolve. When I listen to music through the cable, I get great quality sound. When I plug the USB in the charger works fine. But, when both the charger and the audio are plugged in (playing anything or not), I get a hiss through the speakers. I assume this is a ground loop issue, so I'm going to look for a ferrite core in my box of parts (found a thread out there that shows how that fixed one person's issues). Otherwise, I guess a ground loop isolator is my next guess. Any other thoughts?

 

The thing that confuses me is that I've been using a very similar audio setup for years without issue. I have a modified iPod dock that I used with my Creative Zen Vision:M and things sounded beautiful. The ZVM uses the same connector as the iPod (rewired) and connects to the same AUX cable and lighter outlet. Obviously, the charger and wiring path are different now (internal to the dock, that is), but I don't understand why the ZVM was ok with the setup and the Droid4 isn't. I was originally thinking of keeping the same dock, but the phone doesn't like charging with that USB port for whatever reason (probably not high enough juice).

I've already purchased a bunch of components to get this dock working and it feels like I'm going backwards. I only switched to the phone because the screen went out on the ZVM, but it still played fine. I did get some funny looks from people when i used the brick at my office though.

 

Ok, so that's part of the original question then I guess. The USB/audio cable has 5 pins on the micro side and 4 pins on the USB A side plus the 1/8" audio jack. I assumed that meant that there was a usb audio card in the mount and the cable was 5 conductors for +5v, ground, L audio, R audio, GND audio. Perhaps that's not the case and the ground is shared between charging and audio. If so, that's obviously an unresolvable issue (with that cable). I could easily build my own though. If I did that, I could just have an audio cable and a USB cable run in parallel (effectively). Probably not worth the effort though. Well, thanks for posting your experience. Just wish I knew that info prior to buying this stuff that's basically junk...

 

Since I already have the droid mount (which I do like) and the charging mount/adapter (joined by the 17mm ball/pivot), I'm wondering if it's worth trying to do something with the cable to isolate the grounds? I didn't like the length of the cable anyway, so as long as the issue is in the cable, perhaps I could make it work? Then again, if the 5 pins on the micro side are sharing a ground from audio and power, there's absolutely no solution. I'll try using the DMM on the cable to see if there is connectivity between the USB A and the Audio connector. If so, I'm done with it.

 

[DIY] "Car Dock" Cable - USB audio out + charging - UPDATED! (11-9-11) - xda-developers

This is cheap and a possibility. This seems like a good option assuming I can figure out the pinout from the Moto cable to verify it's connected correctly. HOWEVER, this cable still connects audio and charge ground so I'm skeptical it would be any different from what I have now.

 

I checked the cable and it definitely doesn't comply with the usb standard. Unless i missed a connection, it does makes sense why the cable won't charge a phone when plugged into a computer or charger.

Micro usb to
1 usb a pin 4
2 Red audio
3 Black audio
4 N/C
5 usb a pin 1
Shield Audio ground

In order to use a cable as a charger, pin 4 must be grounded optionally with a resistor. Also, the micro usb shield is used for audio ground, which isn't strictly allowed. But on the up side, it means that the cable is not sharing a ground. But, it is running a audio and charging ground in parallel for around 3 ft. Can a ground loop occur on an induced voltage?