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USB Hard Drive support

rbouzereau Dec 24, 2007

  1. rbouzereau

    rbouzereau New Member

    Hi guys,

    Please use the following recommendations at your own risk.You'll take full responsibility for the consequences of implementing the recommendations below.

    I bought an A3 sportback Ambiante TDI 140hp 2007 with the concert radio and USB connection option in the glove box (option UF2). The problem was that the USB connector doesn't provide enough current for USB hard drives.

    I found a very clean and way to solve this problem: I was able to add an extra cigarette lighter style outlet inside the UF2 plastic case. All the modifications I will describe below are embedded inside the plastic case of the UF2 USB box==> So no modification at all is done to the glove box or glove box wires. And it looks just as if the extra 12V outlet was original from Audi! I am using this extra 12V plug to supply my USB hard drive, but I can also use it to charge other devices when I don't want to use the outlet by the shift stick.

    I have a 2.5" laptop drive inside a USB enclosure, that comes with USB cable with 2 plugs on one end and 1 plug on the other end. The second plug on the first end is used to provide more current: even on a laptop a USB port is not supposed to deliver more than 500mA, so if your drive needs more than 500mA you need 2 ports to reach 1A. Back to my problem: I needed more current for my hard drive to work as the USB port from the UF2 only supports Flash bades USB devices which use much less current than a hard drive.

    I unmounted the UF2 box (just like an oldstyle car radio): to do so, I should have used the 2 unmounting keys from Audi, but I didn't have them. Thus I unmounted the glove box (6 screws to remove: 2 by the feet, 3 on the top, 1 on the side behind a removable plastic part). Once the UF2 box was removed from the glove box, I removed 2 screws from the plastic case of the UF2 to access the PCB inside. Using a tester in my car I found the 12V and Ground cables inside the connector that fits the UF2 connector. I then took the UF2 box PCB and found these 2 cables arriving on the PCB: the 12V (red color in the UF2) and ground were the biggest cables and located on top of each other. Please note that in the car I found another 12V signal but the corresponding cable in the UF2 box is smaller: keep this one for later.

    Now, don't do the same mistake I did: at first I bought the 12V outlet, made a hole just next to the USB connector of the UF2 box. Then I soldered the 2 + and - pins of the 12V outlet to the 2 big cables of the PCB. Then I bought a 12V to USB car adapter and connected the second USB plug of the cable, and here I was with my hardndrive (formatted in FAT32!, because NTFS doesn't work) working great! Ok, I had the known limitation of the iPod adapter (UF1): only track #s and 6 directories displayed. It's strange Audi couldn't display the titles since the song titles are displayed when I play a CD with MP3s in the Concert radion itself.

    :no: The problem with connecting the 12V outlet pin directly to the big 12V cable is that is that when you stop the radio and/or your car, the 12V will still be there and run your hard drive===> this may kill your battery if you leave your car for a long time. By the way, the original 12V outlet located next to the shift stick has the same limitation: when you turn off the car, whatever is connected to the outlet stays ON after you leave the car! This limitation is mentioned in the Audi A3 User's manual.

    To solve this problem, I had to use a VN610SP chip from ST Microelectronics. Check out the datasheet at the following link:

    You will need to have some soldering talent if you can't make a PCB==> a PCB requires some material to get the chip foot print, draw the strips and remove the copper with acid. In my case, as I didn't have the equipment I decided to use use a prototype board with 1.27 pitch (see page 15 of the datasheet). Check out online: search for "Prototype board for surface mounted devices, pitch 1.27". You just need a board with a field of holes located at 1.27mils from each other. If you pay attention the soldering process can be done easily still.

    Solder pins 1, 2, 3, 4 and 5 together, and solder a cable from these pins to the + pin of the 12V outlet you have installed in the glove box.
    Solder pin 6 to ground.
    Solder pin 7 to a resistor divider: 1kohm connected on 1 end to pin7 and on the other end to ground. Add another 1 kohm resistor connected to pin 7 also on one end and connect the other end to the small 12V cable I asked you to keep for later: this 12V signal will be the control of the system as it is turned off when you turn off the radio or when you remove your key.
    Solder pin 8 to a 1kohm resistor, and solder the other end of the resistor to ground.
    Finally, solder pin 11 (the metal case) to the big 12V cable (red cable). You are done :rockwoot:

    Check your board for bad connections and shortcuts. Re-assemble the UF2 box and slide it back inside the glove box. Be careful, if you disconnected the connector for the passenger airbag key and the glove box light, you will have the passenger airbarg red signal on the dash board that needs to be removed by your dealer (or yourself if you have the OBD2 CAN interface tool). I read somewhere that if you don't want to get the signal on the dash board you just need to turn off the passenger airbag (use the switch in located in the glove box) BEFORE you disconnect the cable.

    Ok, I could have just connected the small 12V cable to the + pin of the 12V outlet, but as the cable was smaller than the other one I thought there would be less current available on it. If you plan to use this new outlet to charge handhled devices such as a laptop, you may need some current.

    Just ask me if you have questions. It's great to have many gigabytes of songs without having to waste money on an expensive iPod that would stay in your car anyway...

    Take care,

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