I tried to find a thread related to this but didn't
I have a solar panel that can provide a 5v regulated voltage, and I wonder if it could be possible to use the usb plug to prolongate the battery life, I don't want to charge the battery (although it could be possible, but I'm not aware of the electrical requirements of the n800) but just to use the panel to 'reverse' feed the device through usb plug...
is it possible?
thanks
JLM

No, this is not possible.
BUt if you want to charge your device via USB, there are cables available for charging Nokia phones via USB. They can be used with the N800 as well. So if you can get your solar panel to provide a female USB-A port, you can charge your device with it.

Hmm, something like this?

http://communitizer.blogspot.com/200...ging-n810.html

:P

thanks, do someone know why nokia designer did stupidly chosen to not wire the 0/5V of the usb?
the problem of charging the battery thought the solar panel is that it involve a loss of power at charging level.... charging a battery is much less efficient than directly power the device...
so if I'm correct it's impossible also to use the n800 as a master usb device?
JL

Small devices like the Nokia N8x0 are usually designed to charge the battery when connected to power, then run the device from the battery. The N8x0 won't even turn on without a battery in it. If I had to guess why they did it this way, I'd assume it was because it made the device either cheaper or simpler to produce...or maybe smaller.

It is of course possible to use the N8x0 as a USB master. 5v positive is hooked up to the USB port.

To answer some questions here:

"Why doesn't the Nokia charge through USB"
- because that would be impractical. When you plug in USB, the two flash drives (internal + SD) are made available to the host computer and are no longer available to the Nokia. If you want to avoid using an AC adapter, get the nifty USB-to-charger cable. That allows the Nokia to charge from USB without mounting drives

"Why doesn't the Nokia run without a battery"
- because this would easily lead to unexpected power-loss and un-controlled shutdown. This carries a significant risk of corrupting the flash (internal+SD) file systems (possibly even the internal system drive). With a battery in place, a controlled shutdown can be initiated when the battery gets too low (but before the battery is completely drained). Note: Some networked attached hard drives have a similar provision in that they turn off write-caching (=> reduced peformance) unless they are connected to a UPS (detected via USB connection to UPS)

Martin

That's true for the SD due to the VFAT (or ext2/3 fs)...
However, internal flash uses jffs2, which, by design, is resilient to ungraceful disconnection (e.g. power-loss).

So, no risk for your "internal system drive".

"Why doesn't the Nokia charge through USB"
I think promoting vendor lock in is a much more likely reason. Those same problems have not stopped other devices from charging over usb just dandily.

I also agree...... why did nokia change from their commonly used previous power plug? if they wanted to gain size and make more compact using the usb plug would have been a better choice, and the previous plug wouldn't have been so much place taking.....
however if we can put the usb into host configuration then it means that we can 'wire' the 5v usb to the internal 5v, hoping that the design allow to feed the internal vcc core (ie not a dedicated regulated 5v, but the vcc core derivated from it)
will give a try
JL

Not all cell phones, BT headsets, etc. use USB connections, so they'd still need a standard power connector (and the 2mm one is better than the old one for headsets and the like; why not make it universal?). And it makes very little sense to support charging only through the USB port, and make a USB connection (to charge) render the SD cards unavailable, and then also allow the USB port to be used in host mode. This would actually get very annoying in practice.
It doesn't mean that; the two are unrelated. As for trying it, if I were you, I wouldn't. You don't seem to have a particularly extensive understanding of the tablets.

There are some 770 schematics publicly available; it might be wise to look at them, even though the N800 is not the same, they'll give you a better idea if the mod you're considering is workable.