Charging Via Usb?

[mzeo77]

Hi! I ordered the pandora and I just realized I do not know if it is chargable via usb. Can any body direct me to an answer to this? I have tried to search the forum and looking at the faq, but didn't find any answer. So my fear is that it wont be.

I really don't like needing do carry loads of extra power bricks. Most of my current devices (ipod touch, phone, psp) are chargeable via usb, so it would be a shame to take a step back.

Still exited about the pandora, just trying to keep my a bit to hi expectations down so i wont be disappointed (It's a tendency I have, to have to hi expectations).

 

[gruso]

Yes.

Searching for source, hang on...

[edit] This'll do. Read from post #10:

http://www.gp32x.de/board/index.php?showtopic=41548

(When MWeston says "USB OTG" he's referring to the mini USB port. )

 

[mzeo77]

Yes.

I'm so happy. Happy.. happy.. joy.. joy..

 

[kin]

Me is happy tu!!!

Forgot about it... great question!

 

[Squidge]

It should be noted however that you will only be able to charge the Pandora via USB when the device is Off. USB doesn't supply enough power (~500mA) to both charge the battery and power the system at the same time.

 

[Polossatik]

It should be noted however that you will only be able to charge the Pandora via USB when the device is Off. USB doesn't supply enough power (~500mA) to both charge the battery and power the system at the same time.

Hum, if the pandora survives 10hours on 4000mA = roughly 400mA/hour when using "max current" (screen wifi etc on)...
Then when feeding 500mA into the USB there should be enough left over to charge it a bit ?
And from the moment it's "idle" it will not use much, hence every minute the pandora goes to "sleep" it will charge more...

Or do I miss something?

 

[kin]

I think that's not a big problem..

I don't know if they are on the market, but there are mobile miniusb chargers for cellphones pda's etc.. Would be nice if you're camping a few days in the wilderniss.

 

[AireTamStorm]

It should be noted however that you will only be able to charge the Pandora via USB when the device is Off. USB doesn't supply enough power (~500mA) to both charge the battery and power the system at the same time.

Hum, if the pandora survives 10hours on 4000mA = roughly 400mA/hour when using "max current" (screen wifi etc on)...
Then when feeding 500mA into the USB there should be enough left over to charge it a bit ?
And from the moment it's "idle" it will not use much, hence every minute the pandora goes to "sleep" it will charge more...

Or do I miss something?


This is probably a very rough representation, however, using your -extremely- conservative estimates, that would mean that there would be 100mA leftover to charge the battery. 4000mAh / 100mA = 40 hours charge time. Even so, you can probably guarantee you will not have that 100mA left over to work with during normal operation. At best you would have less than satisfactory results.

 

[MarkoeZ]

Should be just enough, with 500mA/Hr. charge, 8 hours of sleep (way optimistic, but hey ; ) and a 4000mA battery . Don't think i'll be using a full charge on a normal day anyway

 

[gruso]

The mAh rating (in this case 4000) does not really tell you how much current the battery can deliver at any one point in time. On paper you might say that 4000mAh means it can deliver 4000mA, or 4 amps, for one hour before it needs charging. Of course, the battery won't be delivering 4 amps, that's a lot of current for a handheld.

By scaling the same calculation then, if Pandora is drawing only 500mA, the battery would last for 8 hours. Now we're getting into more realistic territory, as we know that the battery life is up to 10 hours.

So using my grossly simplified maths, if Pandora is drawing 500mA while a USB cable is charging at 500mA, at best you're staying put, not gaining anything at all. Add in real world variations and losses, and even with Pandora running at lower power than my figure, it's still looking like an uphill battle to charge from USB while say, gaming or watching a video.

Interesting actually, I'd never really sat down and thought about that. Still great to have the USB charge option during downtime though.

 

[Drack]

If there's a USB slot around, either there's also a power outlet around, or that USB slot isn't going to charge you for very long.

 

[Squidge]

I don't know if Michael has put a restriction on the amount of current draw capable when powered via USB, but if the current goes over 500mA, there are PCs that will switch off the USB port completely, and others that just crash or reset (None of which are very practical). However, if he does limit current draw, then the Pandora itself may crash or reset if it tries to use more than 500mA.

The fact is that a battery will always suck as much as possible, unless throttled back. You can't really measure the current draw from the rest of the system in real time, say "Approx 400mA" and throttle the battery to 100mA (and you would have to have a seperate system when powered via the DC jack)

 

[joseluisjazz]

So I understand that the current drained from the USB port while Pandora is on, is gonna be actually used to feed the circuitry, and not simply ignored, right?
And, being that the case, does Pandora would only suck from battery when the current it receives from the USB port isn't enough?

That's a useful thing to know. I did thought the same thing as Gruso, but still don't know if that's the way is going to work.


EDIT: another question: Would it be possible to charge from both the USB and the main power at the same time, or would it be dangerous?
EDIT2: rephrased and clarified the questions

 

[mzeo77]

Would it be possible to reduce cpu frequency so that basic wifi/im/browser could still work, only a bit slow, for reducing power consumption so much that it would still be possible to charge the battery. Using the darkest screen backlighting.

How about when closing the lid but still being connected to wifi, having im sound notifications.

Will this limitation be enforced by hardware/software, or will it try, but fail silently by not charging the battery?

 

[sindbad]

Would it be possible to reduce cpu frequency so that basic wifi/im/browser could still work, only a bit slow, for reducing power consumption so much that it would still be possible to charge the battery. Using the darkest screen backlighting.

How about when closing the lid but still being connected to wifi, having im sound notifications.

Will this limitation be enforced by hardware/software, or will it try, but fail silently by not charging the battery?
The cpu speed doesn't need to be scaled down, it doesn't really eat power when it isn't doing anything.

The closing of the lid was said to be fully configurable.

 

[Squidge]

So I understand that the current drained from the USB port while Pandora is on, is gonna be actually used to feed the circuitry, and not simply ignored, right?
And, being that the case, does Pandora would only suck from battery when the current it receives from the USB port isn't enough?

I don't know how Michael has implemented it, but I wouldn't have thought charging between two seperate power supplies that each have there own ground reference would be a good thing. Unless theres some fancy stuff in the PMC, the device is not going to know if its not receiving enough juice until it crashes, and at that point it's a little late. I'd say the best thing it can do is share the load between battery and USB, but again, I'm not sure how it's implemented, so I don't know.

Considering the fact that the Pandora can draw over 700mA (@ 900Mhz), the safest mode might be to ignore USB power when the system is running, and charge the battery when it is off.

 

[mzeo77]

The cpu speed doesn't need to be scaled down, it doesn't really eat power when it isn't doing anything.

The closing of the lid was said to be fully configurable.

I was more thinking of using it to cap power consumption to something like 250mA leaving 250mA to charge the battery.

I know this is wishfull thinking, just thought I'd ask.

Does any body know how many mA:s the screen requires.

 

[Epoch]

It would be nice to know the maximum draw of a Pandora when connected via USB. I have some AC to USB power adapters that will put out 700ma and 1000mA, so if the Pandora will only draw 500mA the additional juice that those can put out wouldn't be useful.

 

[Squidge]

On a lot of devices, the amount of current draw is selectable by using the 5th pin on the USB connector. You can typically select between 100mA, 500mA and 1A. I don't know if Michael has implemented this or will be doing so for the retail boards. I'm guessing however that if it isn't done on the MK2 dev board he doesn't want to do any more changes for the final version, as it would just be another thing to test and have problems with.