Sansa USB / charger support

[scharkalvin]

I understand that Rockbox does support charging the Sansa E200 via usb, but perhaps
not at full rate compared to the OF.  I also read someplace that the OF won't top off the battery to 100%, while rockbox will.

What happens if I plug the usb cable into a power supply / charger?  I have a home brew ipod charger that is just a 5v regulated power supply.  As per Apples specification, each usb data line is pulled up by a 75k 1% resistor and pulled down by a 49.9k 1% resistor to set the usb current draw at 500ma.  If I plug the Sansa E200 into this supply the OF shows charging, while the rockbox WPS just shows the battery at 100%
(I know that you have to enable display of charging in the wps screen using the correct %sequences and my WPS currently doesn't do this).  But does the software support charging with such a power supply or is it just done in hw and reported by the sw?

Also if running rockbox and I plug the USB cable into my computer a USB icon pops up, but that's it.  I guess this is a place holder for when full USB file transfer support is finally added.

[dedalus]

As per Apples specification, each usb data line is pulled up by a 75k 1% resistor and pulled down by a 49.9k 1% resistor to set the usb current draw at 500ma.

What do you mean by data line? You are kind of scaring me. You are aware I hope that you don't even need pins 2 and 3 for a charger? Also, this really needs to be implemented in an RC network to to properly regulate the voltage, and that's just assuming a DC source...

Considering that they sell these things for like 3 USD at Fry's... I can't imagine why you would want to build one.

[scharkalvin]

There are 4 wires in the usb cable.  Power, ground, data+ and data-.
When connected to a power source you can leave the data lines floating, or tie them to ground.  In the ipod, Apple uses them to set the charging current.
They expect the data lines to be set at some percentage of the power supply voltage
which the ipod uses to set the maximum current that it can draw from the usb power lines.  Note that a usb device can ask the usb host how much current it may draw.  Since the charger isn't a true usb host, Apple added an A/D converter to the ipod to measure the static voltage on the data lines.  My USB charger device follows the Apple specification to set the max current allowed to 500ma.  (The company I work for builds some iPod compatible hw and we got the specs from Apple).

Why build your own charger?  In my case I had all the parts, I was too lazy to go out and buy one, and I like hacking hardware.

[dedalus]

As I understand it, in absence of negotation most bus-powered devices just take as much as they can get, and most USB "chargers" just put out w/e up to even beyond 500mA. The process of providing and intital 100mA current and ramping it up on demand is a concession for a true host.

My wild guess about the sansa is that it would just pull whatever the battery can in absence of pins 2 and 3, and just be utterly confused about/ignore a voltage divider on the data pins if present. That sounds very Apple-specific to me.

[scharkalvin]

My wild guess about the sansa is that it would just pull whatever the battery can in absence of pins 2 and 3, and just be utterly confused about/ignore a voltage divider on the data pins if present. That sounds very Apple-specific to me.

Yes it probably is.  I put the voltage dividers in because I use this charger with my ipods.  It works fine with the sansa too.  I mentioned it here in case anybody wants to build a charger for use with ipods.  Unless you happen to have a female usb connector (from an old pc motherboard cable) and the required ps parts (6v filament xfmr, bridge rectifier, lm7805 regulator, 1000uf 16v capacitor and a small project box) you can probably buy one cheaper.  But us home brew hw freaks wouldn't do it any other way.