I agree.  One might also be able to leverage the little microcontroller to monitor the supply voltage, and if it detects a severe voltage drop when the Neuros has decided to pull 1A, it can stop to protect the poor sap who has accidentally tried to charge his Neuros with a Razr charger.

Or you could put the Neuros logo on the USB connector to make sure they know what connector is for the Neuros.  That might be cheaper.

Joe Born wrote:
Well, agreed we certainly don't want shiny flames :)

But I guess the question that remains for me is that even if we use the
USB jack for both charging and connection to a PC, can't there be
separate modes for the two scenarios?

In other words, if the N3 connects to a PC, it knows to demand no more
than 500mA (and thus hopefully avoid the shiny flames).  If on the other
hand, the N3 connects to a wall adapter, it can know it's a wall adapter
and thus draw 1A (or whatever is appropriate for the wall adapter).
Since we're supplying both the N3 and the wall adapter can't we do that?
Now I recognize that this partially reduces the desirability of the
solution since the RZR wall adapter won't allow rapid charging, but it's
still ok in a pinch and allows the two other advantages.

Am I off base here?

Joe

-----Original Message-----
From: neuros442linux-main-admin@lists.sourceforge.net
[mailto:neuros442linux-main-admin@lists.sourceforge.net] On Behalf Of
Steven Robertson
Sent: Sunday, October 02, 2005 6:35 PM
To: neuros442linux-main@lists.sourceforge.net
Subject: Re: [Neuros 442 Linux Main] USB jack as power plug for N3 and
442-320?


  
 There are also some tricks that may be necessary to play in order to 
convince the hub to give you the full 500 mA. I need to study the spec
    

  
a little bit. The question is if full power is readily available from 
the USB connector or if we need to establish protocol and enumerate 
before the hub give us power. Does anybody know this part of the spec?
    

IIRC, you do need to establish a connection to grab the full 500 mA, 
*technically*.  The USB spec requires a device to register and be 
accepted as high-power before the bus will allow draw, so that it can 
keep software control over maximum power draw, etc.  On the other 
hand, low current power (20mA? 50mA?) is available as soon as the 
cable mates, but the thing being plugged in is still required to 
report its usage per specs.

However, I remember somewhere some USB coder grumbling about how 
nobody ever actually does this, and that the whole software control 
thing is pointless.  So if spec compliance isn't an issue, then you 
should be able to draw as much as you want without blowing the USB 
host.  Though that'd be kind of bad to do for the customers; I 
imagine "i plugged in my neuros and my computer caught fire" would 
rank pretty much above a color screen in terms of influence over 
buying patterns. Although some end-users do seem rather neanderthal 
in their approach to technology, the "ooh shiny" approach would 
likely backfire if they burned themselves on the shiny flames.

Steve


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