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Estel's Avatar
Posts: 4,839 | Thanked: 7,959 times | Joined on Mar 2011
#71
Generally it's good idea. dr_frost_dk's charging port connected to battery isn't bad thing, yet, it have some limitations. First of all, it can be charged only by Li-Ion charger of any kind (not power supply). Second, and more important thing, that it should *never* be left charging to 100% during device runtime - power used by device fools Li-Ion charger, which keeps charging battery more than needed = unhealthy for battery life. Last and least important thing, is that bypassing N900's charging circuit confuses bq27x00 chip, so no way for reading 100% accurate (after proper calibration) battery SoC readings (voltage-based reads can be great, but will be never even close-to being such accurate as chip measures).

On the other hand, using port other than semi-fragile USB got obvious benefits. Considering this, I'm more and more tempted to create some crazy solution for full body replacement, that would mean having external charging port connected to testpads. This way, we would have best of both worlds - charging by any 5V power source, without touching USB port, yet still processed by N900 charging circuit.

I can't promise anything, but I'll check what is possible - in meantime, could someone - fluent in reading N900's PCB schematics - check, if for 100%, testpads +5V and mass comes through same safety elements as USB charging? I'm sure about USB data lacking only common-mode choke, but about power lines, it's unverified info for now.

/Estel
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dr_frost_dk's Avatar
Posts: 1,454 | Thanked: 2,442 times | Joined on Oct 2010 @ Denmark, not far from redkarma
#72
If the test pads (5V) does not have protection then adding a small fuse to the 2.5mm plug base should not be a problem.

As for my system, it is sufficient for me since i have 20+ 4.2V sources/power supply's, else a 5V - 4.2V (with charge controller) chip does not take up much space, i have many laying around from the EGO-T E-Cigs i order home for people, they come with an actual LiPo/ION charger that takes 5V 400mA (USB 1/2 Limit) and have an indicator light to show when battery is at 4.2V, but this is just an example.

But having another method of charging is still very good, i on average use my USB one time a week MAX.

I have been thinking of upgrading my setup with some copper lanes (flat copper...) in the top of the cover to the 2.5mm and then some lanes on top of the battery, so when the cover is on the battery is connected to the 2.5mm, this is just to eliminate the wires that attaches my Dual Scud to my cover
 

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#73
I have two words for you: Inductive charging.

Contact plates always wear, or get grimy, or what not.
 

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dr_frost_dk's Avatar
Posts: 1,454 | Thanked: 2,442 times | Joined on Oct 2010 @ Denmark, not far from redkarma
#74
Originally Posted by woody14619 View Post
I have two words for you: Inductive charging.

Contact plates always wear, or get grimy, or what not.
Yes i know, but i just can't find the time for anything lately, still have an 4x TDA7293 amp that is only begun, gotta get going on making an E-Bike with my homemade electric motor, gotta fix our car etc...

Would be nice with an inductive charging pad, but the cheapo DX charger system is still working just nicely.
 

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Posts: 166 | Thanked: 253 times | Joined on Mar 2010
#75
Originally Posted by woody14619 View Post
I have two words for you: Inductive charging.

Contact plates always wear, or get grimy, or what not.
Oooh, +1!!!

Still got an old Palm Pre including touchstone here and it's still on my TODO to attempt this: http://talk.maemo.org/showthread.php?t=56950
Would be great if that could be an option for the custom cover, too.

Last edited by foobar; 2012-05-01 at 08:49.
 
ffha's Avatar
Posts: 131 | Thanked: 168 times | Joined on May 2010 @ Netherlands
#76
I'll buy a full body replacement (+ thin battery cover) once it becomes available, for sure.

Also: I have no need for any of the extras mentioned by some.
I, and I'm certain I'm not alone, only want a simple (slightly improved) aluminium replacement of the standard N900 housing (basically, your original plan without any interference from anyone else). Just something to keep in mind.

Thank you for your support of the Maemo community, Estel.
Surely you only offer us this option because it is the hobby you enjoy and you want to take your self-built baby for a spin, but it's efforts like these which remind of why I'm still using a magnificent, though dated device from late 2009 in 2012 - a significant reason for that, is the beautiful community that is powering the beast.
 

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Posts: 40 | Thanked: 25 times | Joined on Sep 2011
#77
Originally Posted by Estel View Post
Generally it's good idea. dr_frost_dk's charging port connected to battery isn't bad thing, yet, it have some limitations. First of all, it can be charged only by Li-Ion charger of any kind (not power supply). Second, and more important thing, that it should *never* be left charging to 100% during device runtime - power used by device fools Li-Ion charger, which keeps charging battery more than needed = unhealthy for battery life.
A LiIon charger circuit from 5v/1a (USB) to 4.2v costs around $4, delivered : http://cgi.ebay.com/universal-1A-lit...item35ba49263b

If you go the direct battery route, it is cheap enough and small enough that it might be included in the replacement cover to use direct USB power from a desktop computer to charge the battery by the jack bypass.

Regarding leakage causing overcharge and SoC confusion, these are real problems. A good solution would probably require a circuit sitting between the battery and the n900, to be able to take that leakage into account.

I'm not good in electronics- I don't even know how it could be done. Maybe someone with a good knowledge of charging circuits could help.

Originally Posted by Estel View Post
Considering this, I'm more and more tempted to create some crazy solution for full body replacement, that would mean having external charging port connected to testpads. This way, we would have best of both worlds - charging by any 5V power source, without touching USB port, yet still processed by N900 charging circuit.
Right on. No need for external circuits.

Regarding the USB test pads having all ESD protection (etc.) but missing coils, according to http://electronics.stackexchange.com...-needed-on-usb such coils are only needed for EMI, so yes they should not really be needed - or they could be easily added by modders who would absolutely require them for FCC compliance :-)
 

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Posts: 1,318 | Thanked: 903 times | Joined on Feb 2010
#78
Anychance you could CNC a more solid metal USB door for us N9 users?

The current one bends and breaks too friggin easily!
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Posts: 40 | Thanked: 25 times | Joined on Sep 2011
#79
Originally Posted by Estel View Post
I can't promise anything, but I'll check what is possible - in meantime, could someone - fluent in reading N900's PCB schematics - check, if for 100%, testpads +5V and mass comes through same safety elements as USB charging? I'm sure about USB data lacking only common-mode choke, but about power lines, it's unverified info for now.
I am not fluent with the PCB schematics but I have them open and trying to figure out.

About USB testpads, do you have informations not present in the schematics ? On page 4 testpad J5300 and J5301 (USB D+/D- seems to be *before* ESD protection.

Regarding +5v, J2061 which is usually identified as 5v in the pictures is nowhere to be found on the schematics.

I guess I will have to follow the traces on a scan of the PCB - this may be where you have checked D+ and D-? (but I don't know how to "connect" the 2 sides to follow J2061)

BTW It was reported the 2A fuse is missing from 5V but I have not checked that yet - http://talk.maemo.org/showpost.php?p...6&postcount=74

EDIT: Also, if using J2061, a switch or an optocoupler for D+/D- might be needed so that the N900 enters charging mode, as indicated in http://talk.maemo.org/showthread.php?t=72753

I'm thinking of a simpler solution : a Reed switch, and leaving a magnet when the N900 is charging.

Last edited by guylhem; 2012-05-01 at 19:12.
 

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Posts: 283 | Thanked: 219 times | Joined on Aug 2011 @ Egypt | Forum editor
#80
man i have a cnc roland modela i may help you here in egypt and send you part of the money ,btw it will be needed here we have a lots of broken n900s
my exams will be over at 4/7
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