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Author Topic: USB car chargers...  (Read 1416 times)
N1DVJ
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Posts: 530




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« on: December 14, 2010, 11:44:31 AM »

I'm trying to set up a system in my car, and one of the things I plan on doing is put the GPS on the console above the ham stuff.  It's illegal in 2 states to have anything on the windshield now anyway. 

So, I plan on a small 5v switching regulator from a cheap USB charger feeding a cable to the GPS.  Since my GPS model doesn't car, I can pretty much do what I want, but someone raised the issue of 'specific' chargers.

My Magellan doesn't care.  5V on the two USB pins and it charges.  If I provide clock and data and hook to a PC USB port, then the GPS changes mode and appears as a storage device. 

Again, no big deal, I'm just using this as a power supply/charger in the car.

But...  Some devices seem to care.  A friend has an Apple device and it takes only a SPECIFIC USB charger.  If the wrong one is hooked up, the Apple device actually says "You cannot use xxxx charger for this device"  Furthermore, I've seen 'generic' USB chargers that say they work with this Apple device.

So...  it appears that at least SOME USB chargers 'talk' over the USB and say what they are.  And also that SOME USB chargers have a way of GENERICALLY saying they are a charger, and a valid charger, to devices that are picky.

 
Anyone know what the real / whole story is?
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KJ4OBR
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Posts: 104




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« Reply #1 on: December 15, 2010, 11:31:54 AM »

The only devices that really care are Apple products. Apple has "extended" the USB connection to "protect" their stuff. (Read "force you to by replacement chargers from Apple") from what I understand they have a series of resistors on the data lines that feed voltage into the data line that the Ipod/Ipad measures to decide if it can charge and at what rate.

The protection has of course been reverse engineered. You can read more here http://www.ladyada.net/make/mintyboost/icharge.html

I use a 12v to USB 5V to feed my APRS GPS receiver, works like a charm.

73

Dave
« Last Edit: December 15, 2010, 11:37:20 AM by Dave Sorenson » Logged
N1DVJ
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Posts: 530




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« Reply #2 on: December 15, 2010, 12:09:22 PM »

Thank you Dave!!  That was incredibly usefull information, and helped me solve a part of the problem I didn't post about!

Mike
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KJ4OBR
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Posts: 104




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« Reply #3 on: December 16, 2010, 06:56:36 PM »


Glad to help.

73
Dave


Thank you Dave!!  That was incredibly usefull information, and helped me solve a part of the problem I didn't post about!

Mike

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KB1OCC
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Posts: 172




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« Reply #4 on: December 20, 2010, 10:58:18 AM »

Creative labs also does this with their products.  Again, a proper resistor or two corrects this issue.
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N0HR
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Posts: 37


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« Reply #5 on: December 22, 2010, 06:26:14 PM »

Our company has faced this USB compatibility issue as well. We make a line of solar USB chargers (with rechargeable AAs) and have had to tweak our circuit designs several times to allow the charger to charge most devices that can be charged via USB. Notably, Apple (requires some resistor magic between a few USB pins) and several smartphones ignore the USB standard. Sigh.

Anyway, it's a challenge for those of us trying to make a USB charger that will charge (most) anything when phone makers don't follow the standards published.

Let me know if I can help with the USB questions.

Pat NØHR
http://www.n0hr.com
http://www.powerfilmsolar.com
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