nils.faerber at kernelconcepts.de
Mon Feb 12 13:05:13 CET 2007
Joshua Hoblitt schrieb:
> On Mon, Feb 12, 2007 at 01:34:51PM +0200, Mikko J Rauhala wrote:
>> I do also appreciate that adding Bluetooth back in wasn't trivial, but
>> it does make the first edition much more useful (esp. local wireless
>> internet, in lieu of wifi), so thanks for reacting to those requests.
> Quick thought: Shouldn't wifi be possible via the use of a USB "dongle"?
Pretty sure not.
>From my experience WiFi USB dongles really suck tremendous amounts of
power. The problem with USB is that it uses +5V power supply, which is
quite uncommon in embedded portable devices - here you mostly have 3.3V
or even 2.5V. So what you need to power USB devices is a step-up
converter from low voltage to higher voltage. Those chips are quite
inefficient and the higher power you want to supply the more space you
need for external analog parts, like capacitors and coils.
So buttomline is that +5V for powering external USB devices is too
"expensive" in terms of extra parts and precious space inside the device
- not even counting in the extreme high power consumption it would
cause. I assume unless some genious invents a much higher efficient step
up converter you will not see any small portable device to support bus
powered USB devices.
The low power stuff like SD/IO seems much more reasonable in this respect...
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