USB power question?

Discussion in 'General Electronics Chat' started by tee2, Dec 7, 2009.

  1. tee2

    Thread Starter Active Member

    Nov 19, 2004
    46
    3
    Hi there,

    I am making a USB outlet on my motorcycle to run my GPS.

    I found a watertight USB outlet it had 5 wire on it, red power, black, ground, gray shield ground I think, green and white.

    I took a 7805 and added a 1uf and 10uf cap to get the 5v. I conected red to red and black to black. I cut the gray, white, and green, short and put some heat shrink on them.

    I got a watertight USB A male cable and cut it. For kicks I connected it to the outlet and put 18v to it (from my cheap 12v wal-wart) I had put my MM on the red and black to check voltage expecting to see 5v. But it was -5! I figured crossed wire some where, but no.

    Is this normal?


    Edit...

    I just connected the cable to my computer and I had +5v. So something it wired wrong from the 7805 to the outlet, or the outlet is wired wrong.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Good thing you checked the voltage before you fried your GPS. :eek:

    Are you certain it's a 7805, and not a 7905?

    Where did you get this watertight USB outlet? Do you have a manufacturer and part number?

    Where did you get the watertight USB A male cable?
     
  3. tee2

    Thread Starter Active Member

    Nov 19, 2004
    46
    3
    I am sure it is a 7805 because when I was soldering the caps and wires I keep checking with the MM to make sure everything was right.

    I checked the outlet and power is at pin 4, and ground is at pin 1. I Googled "USB pin out" to make sure I had the correct pins.

    http://www.l-com.com/item.aspx?id=7297

    http://www.l-com.com/item.aspx?id=7302

    I sent customer service an email, I'll have to wait and see.

    I could just cross red and black, but it should be right.

    Todd
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    You've wired something wrong between the 7805 and the outlet, or the wire color codes are not correct.
     
  5. tee2

    Thread Starter Active Member

    Nov 19, 2004
    46
    3
    The outlet is wired wrong.

    Todd
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    OK, so you can fix the immediate problem and make a note of it (contact the dealer they have problems with their stock) and get ready to use the GPS on your bike.

    Or you can wait until the argument with the dealer is done with.

    It's just a good thing you didn't burn up your GPS.
     
  7. BMorse

    Senior Member

    Sep 26, 2009
    2,675
    234

    If the outlet is wired wrong, why the -5 reading? did you try swapping the leads of the meter (Put red probe of meter to black wire and black probe to red wire) to read the USB port power again to see if you get a +5 reading? If so just swap the red and black connections.....

    You can double check your pinouts here >> http://pinouts.ru/Devices/mini-USB_pinout.shtml
     
  8. tee2

    Thread Starter Active Member

    Nov 19, 2004
    46
    3
    Yes, that is what I did. That is how I determined the out let was bad.

    I could swap the red and black, but should I have too? If I have to send the one I have back (on my dime, or should I say $8) that is what 'll do. But if they'll send me a new one (which is the right thing to do) I would rather to that.

    We'll see.
     
  9. BMorse

    Senior Member

    Sep 26, 2009
    2,675
    234
    well like sarge said, you can wait for them to replace it, or fix it for now and use your device.... that's your call....
     
  10. tee2

    Thread Starter Active Member

    Nov 19, 2004
    46
    3
    I'm waiting on some other parts to be shipped, so I have time.

    And that we had 1" of snow today:(, and the low tomorrow night is 8° and the high in the teens I can wait.;)

    Thanks
    Todd
     
  11. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    It costs you no money and very little time to simply notify the vendor about the problem via customer feedback/support, and you may be doing them and prospective customers a big favor.

    You used good sense when you tested the voltage before plugging in your GPS.

    I would simply swap the wiring around so the output polarity was correct, and on the correct pins, and put it into use. Putting the correct color shrink tubing over the incorrect color wires would be a good idea. That would help you to remember if there was occasion to replace it in the future.
     
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