Motorola Droid4 mount cable SKN6394A

Discussion in 'Droid 4 Hacks' started by bkenobi69, May 9, 2013.

  1. bkenobi69
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    bkenobi69 New Member

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    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.
  2. bkenobi69
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    bkenobi69 New Member

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    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?
  3. myfishbear
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    myfishbear Developer Developer

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    dont waste you dough on a ground loop isolator... it will kill your highs... ferrite core wont help cause the power is looping from the cig lighter thru your stereo ground. try running a new wire from the car bat to the cig lighter and a clean ground, or connect via wireless bluetooth or fm tuner or maybe try a external battery pack. you can also make a qi charger for your car and charge wireless with a qi back plate
    Last edited: May 13, 2013
  4. bkenobi69
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    bkenobi69 New Member

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    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. ;)
  5. myfishbear
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    myfishbear Developer Developer

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    the charger/wiring paths are the culprit(it has a shared ground point). dirty power= noise. believe me you already wasted some dough, don't invest more into it, its a loosing battle. btw the phone likes a 1a charge rate. the best fixes are ones that allow you to bypass the ground loop. which means either disconnect the 3.5mm jack or usb jack. the zen was manufactured with cleaner power handling circuity, i had your exact problem so i just stopped charging it while i listened to music cuz i didn't want to pay for accessories. my new droid dna does not have this problem (but the 4g caused interference until i got a thicker shielded 3.5mm cable)
  6. bkenobi69
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    bkenobi69 New Member

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    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...
  7. myfishbear
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    myfishbear Developer Developer

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    at least you didnt waste even more cash. ive done that b4 :(
  8. bkenobi69
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    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.
  9. bkenobi69
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  10. myfishbear
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    it may not be different. i think the common ground point is in the phone... not in the cables...
  11. bkenobi69
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    bkenobi69 New Member

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    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?
  12. myfishbear
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    myfishbear Developer Developer

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    it shouldn't be standard cuz its a moto cable. if you mean like qi induction or like a power mat it should eliminate any ground loop.
  13. bkenobi69
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    bkenobi69 New Member

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    I'm sure the inductive charging mat would work fine, I'd just rather not go that route yet since it makes the phone bulkier (and it's a good chunk of change). I was referring to the fact that the charging and audio cables were run next to each other for 3ft which could induce voltage from one to the other. I f that was the problem, a ferrite core could help. But, if that were truly the issue, then every ipod should have the same issue since running charge and audio in a cable is standard practice for them. I am doing that with the ZVM, but it's only a 6" run.
  14. myfishbear
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    then try it... just trying to save u a headache cuz that's not the problem. the problem comes from a spotty board design with common grounds which bleed power into each other. cable mods will not help you. you can try getting another adapter like this one if you don't want inductive charging http://www.amazon.com/BlueGate-Blue...1368555305&sr=8-3&keywords=bluetooth receiver
    Last edited: May 14, 2013
  15. bkenobi69
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    bkenobi69 New Member

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    It's not the inductive charging that I'm trying to avoid, it's the line level output I want to save. I don't really want to send audio out the headphone jack which would use the low quality headphone amp i n the phone. Using line level output should reduce quality loss when going to the vehicle stereo. But it sounds like you are saying that the wiring in either the phone or the adapter the mount have a shared ground somewhere. if so, then there is nothing that can be done. The only solution at that point is installing some form of isolation in the charging circuit to keep charge ground isolated from vehicle ground thus breaking the loop, right? That's effectively what using qi does for you, correct?
  16. myfishbear
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    myfishbear Developer Developer

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    Lol i thought i was clear but here i drew you a picture. IF THEY GROUNDED THE 3.5MM JACK TO THE SOUND CHIP YOU WOULD PROB NOT GET THE GROUND LOOP. Im out lol
    View attachment 62886
    Last edited: May 15, 2013
  17. bkenobi69
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    bkenobi69 New Member

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    Understood. Thanks for the help.
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