Thread: Solution: N900 Charging from dumb power sources *UPDATED*
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joerg_rw is offline joerg_rw
2012-10-14 , 14:07
Posts: 2,222 | Thanked: 12,651 times | Joined on Mar 2010 @ SOL 3
#126
Originally Posted by Master of Gizmo View Post
As i've already written in another thread: The spec does not say to shorten them. Instead the spec says that you are supposed to connect them via 200 ohms. The n900 may work fine when shortening them, but shortening something always means that some significant power may flow over this short circuit. Using 200ohms instead is safe for any hardware as the current over the resistor is limited to 3.3V/200Ohms = 17mA.

These resistors cost nothing and may protect that hardware, so they are really a good investment.
Originally Posted by peppino View Post
Hi, I trying this project for load battery on the road.
5V is generated without problem, the signal D- and D+ has 1.9V, when I try to attach N900 to my step up the charge not start. In dmesg I see:
Code:
twl4030_usb twl4030_usb: HW_CONDITIONS 0x50/80; link 1
twl4030_usb twl4030_usb: HW_CONDITIONS 0xd0/208; link 2
I tried also with 0.7V on D- D+ as written in batt_charging_1_1_FINAL.pdf but nothing.
I have the kernel 2.6.28.10power46.
I would like start the charge with only 500mA and not 1000mA. With 200 Ohms between D- and D+ which is the maximum source current?

Thank you for the help

Originally Posted by zimon View Post
I browsed through all these 10 pages rather quickly, so sorry if this is already answered;
Could this however correct way (USB standard) of demand to shortcircuit D+ and D- be overridden somehow in software, through dbus or kernel parameter perhaps?

It would just be so convenient to click something from a menu, than always carry both either self made or bought adapter and normal USB-data cable.
So both synchronizations, fast data transfers and charge anywhere could be achieved.

Since somebody referred to this thread today, I like to add some late clarifications:

The spec says "SHORT D+ and D-", the 200Ohm are MAXIMUM. For any EE that's a pretty unambiguous spec that defines a valid range of 0 .. 200 Ohm for the shorting - pin to pin, including all cable resistance, contact resistance and all, which is what the 200 Ohm are meant to specify: you must not exceed this value.
Bottom line: using resistor is BAD, short the pins by simple solder jumper.

The max current with shorted (by significantly less than MAX 200Ohm, best value:0) D-pins is basically undefined, N900 will try to draw up to ~900mA from any charger that signals "fastcharger" by the shorting method.

For charging in software, there's shadowJK's http://enivax.net/jk/n900/charge21.sh.txt script now, based on my original draft quoted some posts back.
Alternative source edited by me for 500mA charge: http://maemo.cloud-7.de/maemo5/patch...t__UNTESTED.sh
Keep in mind you probably have to `stop bme`, otherwise the charging script and BME will conflict and not work correctly.

/j
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