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How To Hack A USB Charge Cable
Article by: Darren Griffin
Date: 20 Apr 2011
This issue has been discussed in our forums a number of times and affects devices from quite a number of manufacturers. When connected to the PC they mount as a disk drive and when connected to the supplied USB car charger they will charge and function as normal.
But, when connected to a third party 12v USB charger they act as if connected to a PC and refuse to charge or to offer the normal GPS related display and functionality.
This occurs because the manufacturer has chosen, for reasons best known only to them as USB is supposed to be a standard, to short USB pins 4 and 5. The device looks to see if pin 4 is grounded and if not, it switches to USB disk mode.
It's naughty because there is no good reason for doing this. A correctly wired device should be able to mount as a disk and charge when connected to a PC without this subterfuge and all it achieves is to prevent you from using third party chargers.
A Hackaday reader investigate as this problem affected his Magellan and, having found the cause, set out to hack a standard USB cable and ground the unused pin 4 to pin 5 on the microUSB plug. Now he can use the cable with any USB charger.
He has posted the Hack with an explanation on Flickr and whilst it may not be for everybody, anyone who has a spare USB-MiniUSB cable, a steady hand and a soldering iron may want to give it a go.
This issue affects Magellan, Mio and Navman devices and I'm sure Garmin has this issue with some models.
| Comments
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 Posted by smartroad on Fri Apr 22, 2011 7:45 am |
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Just as a thought, before having a go at manufacturers, is this done in case the device draws more then the 500mA a standard usb port is specced the provide? Like I said, said just a thought.
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| Posted by smiley1081 on Fri Apr 22, 2011 8:10 am |
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I have exactly the opposite problem.
If I connect my Nuvifone A10 to a computer using its cable, it is recognised by the computer as a USB device, if I use a third party cable it can be charged but not used as a USB device.
Could it be that this is caused by the same connection between pin 4 and pin 5?
FNORD |
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| Posted by Darren on Fri Apr 22, 2011 10:16 am |
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| smiley1081 Wrote: | I have exactly the opposite problem.
If I connect my Nuvifone A10 to a computer using its cable, it is recognised by the computer as a USB device, if I use a third party cable it can be charged but not used as a USB device.
Could it be that this is caused by the same connection between pin 4 and pin 5? |
Almost certainly yes.
Darren Griffin |
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| Posted by Andy_P on Fri Apr 22, 2011 10:42 am |
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| smartroad Wrote: | | Just as a thought, before having a go at manufacturers, is this done in case the device draws more then the 500mA a standard usb port is specced the provide? Like I said, said just a thought. |
I would have thought it shouldn't affect a "standard USB port", because that implies a port with intelligence. In that case there will be communication between the device and the computer and the device can only "request" current (in 100mA steps) upto the max 500mA.
But you're right that it could be said to be a protection against under-powered USB chargers from other places..... although there's nothing to stop you accidentally using a 'too-small' charger from a different device that just happens to have the same link between the pins! 
"Settling in nicely" ;-) |
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| Posted by wrinklyninja on Fri Apr 22, 2011 11:46 am |
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I had exactly the same problem with my Palm Treo Pro. The fix of shorting out the data pins worked a treat. The only comment I would make is make sure that your 3rd party charger delivers the same output as the OEM eg 800ma etc
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| Posted by treeboa on Fri Apr 22, 2011 1:11 pm |
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same problem with this device using the supplied usb cable and a third party charger, in this case a 2000ma one, bloody annoying really as the charge cable is not a standard easy/cheap replace cable, you can by pass it with a few button presses but still it smacks of `dealer part only`
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| Posted by dvd8n on Sat Apr 23, 2011 11:34 am |
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This isn't dirty tricks, this is the new USB compatible charger standard.
The idea is that if a device is connected to a computer then the USB's data lines are not shorted. The device knows that it is connected to a computer and, while it charges, it knows to draw a max of .5 amps. And it can talk to the computer.
However, if a device is connected to a charger then the data lines are shorted. The device knows that it is connected to a charger and, while it charges, it knows that it is a standards compliant charger, it can draw a lot of current as it is connected to a charger, and it charges to a max of 2 amps, charging much faster.
Now this is all fine until someone tries to charge a new device with an old charger. The device, as the lines are not shorted, thinks that it is connected to a computer, tries to talk to it and gets confused, and often discharges itself faster in its communication attempts rather than charging.
Now you can short the data lines on a USB cable. Or you can even crack open the charger and short the lines there. And this is fine - it will work. But there are two warnings. The charger must be capable of supplying 2 amps. And you must never use the modified cable on a computer as it will draw more than the .5 amps that a USB port is rated at and potentially blow the power supply.
Or you could stop being so tight and buy a charger to the new standard. You will find that you need it more and more over the coming years as more devices become compliant. 
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| Posted by BigPerk on Sat Apr 23, 2011 4:49 pm |
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So do you know what the new USB standard is (ie ISO, ..., Number) dvd8n? It would be a good idea to be able to check for compliance when purchasing off, eg, Amazon.
David
(Navigon 70 Live, Nuvi 360) |
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| Posted by dvd8n on Sat Apr 23, 2011 6:37 pm |
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| BigPerk Wrote: | | So do you know what the new USB standard is (ie ISO, ..., Number) dvd8n? It would be a good idea to be able to check for compliance when purchasing off, eg, Amazon. |
I'm afraid I don't. I've had the same problem myself. The only way I've found to do it is to check compatibility with a device that needs these chargers.
David
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| Posted by wrinklyninja on Sat Apr 23, 2011 6:51 pm |
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I agree with the sentiment that it would be nice to know what you are buying. I bought 3 different car chargers for my Palm Treo Pro (all of which claimed full compatibility) and none of them worked. It's OK to say don't be tight and buy an OEM part but the Palm charger is over £20 and is crap. I know because I had one.
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. Thank goodness that at least they don't have a Dirty-Tricks department 
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