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Old 02-23-2008, 05:39 PM
Peabody Peabody is offline
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Default Using a dedicated AC or car charger

I wanted to report the results of measurements I made with a breadboarded charging circuit - in case this might be relevant to others who may be having problems.

But first, a quick reminder. When connected to an AC or car charger, the Clip behaves normally, meaning that the screen goes dark after 15 seconds, and you can play songs, etc., just as if it wasn't plugged it. However, the Clip does actually have to be turned ON to charge. So, you need to turn Auto Power and Sleep OFF when charging. Otherwise, the Clip will shut down at the end of the Auto Power or Sleep period, and charging will stop.

Anyway, in March, 2007, a new USB standard was issued for charging through a USB port. The standard says that a "dedicated charger", which is just a non-intelligent power source provided through a USB socket, should have its Data lines shorted together. The Data lines are the two middle pins of the socket. A connecting device, upon detecting that these two pins are shorted together, will know it need not try to negotiate a formal connection, and can just proceed to draw current. Older chargers, and possibly newer proprietary USB chargers for other devices, may not have the Data lines shorted.

My 1 GB Clip with .20A firmware, turned ON but with audio playback paused and the screen allowed to go dark, and with the Data pins of the charger shorted together, draws 154 ma. from a 5VDC supply. After charging has completed, current drops to 62 ma. It looks like the net charging current is therefore 92 ma.

With the Data lines in any other configuration - either unconnected, or tied high or low through a number of different resistor values - the total current is only 114 ma. Since the new standard requires the downstream device to negotiate permission to draw more than 100 ma., perhaps the Clip refuses to draw more than that from what *might* be a normal USB port.

In any case, it appears the net charging current drops from 92 ma. to 52 ma. if the Data lines are not shorted, which would roughly double the time required to charge the batteries. But even a non-compliant charger would still charge the Clip overnight. So if someone gets no significant charging at all through a USB charger, it may well be because Auto Power or Sleep is turning charging off after 10 minutes, or whatever the setting is.

Hope this is helpful.
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  #2  
Old 02-25-2008, 05:58 PM
ishturkish ishturkish is offline
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Great information, Peabody.
Thanks!

This sounds like an issue that can be resolved with a firmware update.
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  #3  
Old 03-06-2008, 06:49 PM
Matt K Matt K is offline
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Quote:
Originally Posted by Peabody View Post
Anyway, in March, 2007, a new USB standard was issued for charging through a USB port. The standard says that a "dedicated charger", which is just a non-intelligent power source provided through a USB socket, should have its Data lines shorted together. The Data lines are the two middle pins of the socket. A connecting device, upon detecting that these two pins are shorted together, will know it need not try to negotiate a formal connection, and can just proceed to draw current. Older chargers, and possibly newer proprietary USB chargers for other devices, may not have the Data lines shorted.

Hope this is helpful.

I actually have a question about this. I've been trying to find a charger with a shorted data line. The one I got gave me the same amount of charge time when I plug it into the computer.

So, the question is, how do I know if the charger has a shorted data line?
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Old 03-07-2008, 05:11 PM
Peabody Peabody is offline
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Quote:
Originally Posted by Matt K View Post
I actually have a question about this. I've been trying to find a charger with a shorted data line. The one I got gave me the same amount of charge time when I plug it into the computer.

So, the question is, how do I know if the charger has a shorted data line?
Well, I know mine has shorted data pins because that's the way I built it. :-)

But seriously, if you have, or have access to, a multimeter, you would set it to measure resistance/ohms, unplug the charger from the wall, and measure the resistance between the two middle pins of the USB socket. If shorted together the reading will be close to zero ohms. The spec actually just says it must be less than 200 ohms.

If you can't actually measure it that way, you would need to contact the charger's manufacturer and ask.

But you know, if you get the same charge time on the charger as you do plugged into your computer, which would be about four hours from a low-charge state, then that charger is probably compliant with the new spec, and I wouldn't worry about it.
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