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2003 chevy trailblazer_ls
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Discussion Starter #1
Hey Everyone,

I have a 2003 Trailblazer. I recently moved to a Droid X and have found that it is an excellent GPS unit for the car. Currently it is powered by a cig lighter adapter to a micro-USB port.

I would like to hardwire 2 USB ports into my truck (preferably w/ an on/off switch) so that I can get rid of the unsightly cig adapter and cable running down the front of my dash.

I understand the best way to go is probably to pull power off of one of the fuses in the back seat... but I don't know which one to use.

Any help?
 

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2005 gmc envoy_sle
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234 Posts
separate power source

If your running a the 5v and want the most our of it, I would use power from the battery, and not relying on any other types of power elsewhere, this would ensure you have clean power. You should look into a fuse and of course a switch to turn the USB's on and off. Drawing power from areas like the BCM are kind of sketchy.
 

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2003 chevy trailblazer_ls
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Discussion Starter #4
Thanks for the link roadie... although I'm not exactly sure what information I need to glean out of that post...

I'm guessing I should pick one of the fuses that are powered in the RUN/ACCY mode. W/ 2 USB ports I would think I would (assuming extra power) need roughly 2 amps, like maybe running it off of the Rain sensor?
 

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2006 chevy trailblazer_ls
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115 Posts
I was thinking about doing something similar. Did you find a good source for USB female plugs that when installed actually look like they belong there?
 

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2002 chevy trailblazer_lt
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846 Posts
could you just hard wire it into the cig lighter harnesses?
 

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2004 gmc envoy_slt_xuv
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i would probly look for a internal USB computer HUB. Those are designed, I beleive, to run off 12V. Then you can look at the wiring schematic, and find out which wires to splice into.

The reason I suggest to do it this way is because a computers internal USB HUB is usually smaller, the one I use is 1.5 inch by 1.5 inch, borrowed from a old HP desktop computer. This will make the hole you might make in the dash smaller. My HUB is also a 4 port. I power my GPS, my Droid Vibrant, and charge my wifes phone off it. I also have the ability to charge my Creative ZEN or ITouch on the 4th port. Leaving my lower dash clear of wiring clutter. It does not matter if its a 1.0, 2.0, or 3.0 hub. You are only after the charging aspect, and they are the same on all 3.
 

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chevy
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USB Wiring diagram. ^^^^

1. Pick up a standard micro USB cable from somewhere cheap (monoprice.com).

2. Pick up a 7805 DC regulator and capacitors listed here: http://electronic-circuit.net/7805-regulator/ . Radio Shack has these. Assemble the circuit as shown.

3. Find an ignition hot source. If you have an aftermarket radio the GMOS adapter supplies ignition on voltage on the red wire. This gives you RAP functionality as well. Otherwise tap the cigarette lighter. USB draws 250mA maximum, so the chances of drawing down your battery are nearly nonexistent.

4. Cut off the big end of the USB cable and strip back the wires. Wire your ignition source to the 12V line of the 7805 circuit and the red lead of the USB to the 5V line of the 7805 circuit. The negative line of the 7805 circuit should be wired to the black lead of the USB plug and to ground.

5. I recommend you solder/heat shrink all connections. I also recommend you ask for a small heat sink to attach to the regulator.

6. Secure the regulator circuit behind the dash somewhere and route the cable to where you want it. I have mine poking out next to the driver side vent so I can plug my phone in when it's in it's windshield holder.

Android > iPhone.
 

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2004 gmc
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The USB 2.0 spec is actually 500mA of 5V per port (maybe 250mA of 12V to run the switcher in the charger?), and I was considering a 7805 solution until I read that some lazy device designers DEPEND on current limiting in the port to reduce their battery recharge current to safe levels. Some car chargers are intentionally designed to deliver less than 500mA to do the same function, and swapping chargers can be dangerous for those sorts of devices. I hate lazy designs, but frugal and elegant ones can be very difficult to distinguish sometimes. ;)
 

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2002 chevy trailblazer_ls
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This would be a great addition! I hate having the GPS powercord running up and across the dash. If you find a good location and install a port or two, you should post a set of build instructions.

And Droid X is the bomb! :D
 

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2003 chevy trailblazer_ls
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Discussion Starter #15
Thanks for the tips everyone.

My brother has already done this on his truck, but since he is in Virginia and I am in Florida, I couldn't get any pictures. He wired his mount into his car and added another micro-USB plug sticking out down next to the cup holders for charging his Bluetooth or another phone, then stuck an on/off switch inside the armrest.

Being a grad student, I have significant time constraints until the semester is over, and then I will be able to take the time needed to do it. I'm simply starting my research now so that I can do it as soon as time permits.

If anyone happens to try this in the interim... please post pics. I'll make sure to take pics while I do it to mine.
 

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Northwest Chapter
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You're right. I don't know what I was thinking when I said 250mA... :duh:

I had a hack on my old Touch Pro that would allow it to pull 900mA off the USB port. Battery charged fast, but sure did get warm.
Yep, and if the manufacture sets the drivers up properly, you can get 1000mA from the USB ports on a laptop/desktop. Doesnt help much in a car, but it does make a difference!
 
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