Neo Sound and USB Questions

Rusty Chris reverendbean at
Fri Aug 17 19:51:30 CEST 2007

danimanns at wrote:
> Tilman Baumann wrote:
>> danimanns at wrote:
>>> Are there plans to provide a car adapter for the Neo?
>> This is a general problem. Where are USB-Power Adator out there. Also
>> for cars.
>> But most of them just power the 5V line. This is bad with 99% of the
>> bad behaving usb gadgets out there.
>> But Neo is prolite and asks the host if it could draw it's 500mA and
>> if not only takes 100mA out of the bus.
>> This is how the usb specs tell you to do it.
>> But most devices (like usb microovens and the like) just draw power
>> as there would be no tomorrow and don't care how much the host can
>> privice. If your usb-powersupply burns out - bummer. :)
> Don't know if I understood right. Do you mean,
> the Neo asks the power supply how much power it's able to provide?
> Why should the Neo do this? Like I described below I guess
> the Neo uses the 5V channel only for charging, and so
> the 500mA are always okay. Why not use a normal 500mA
> power supply then?
The USB specification only guarantees 100ma available to each client-mode
device (in theory the Neo can be host or client, though currently only
mode is functional).  If a device wants to draw more power it is required to
"ask permission" from the host/hub.  Many simple [non-compliant] devices
skip this step and
just assume that they can draw as much power as they want, which leads to
problems of overloading the host/hub.  The Neo will not draw more than 100ma
until it has gotten "permission".  There is one exception - the neo can
detect its
own 'dumb' charger by the presence of 48kOhm resistance between USB pin 5
and ground.  In this case the power mgmt unit will allow the full 500ma

So if you have a decently noise-free 5V USB car charger, it would be fairly
simple to solder in a 48k resistor (note that it should be low-tolerance
- 1%)
and have the neo pull 500mA for fast charging. 

As for forcing the neo to ignore USB power negotiation, I don't know if this
is a kernel driver issue (hackable) or a USB chipset issue (less


>> A button that puts your Neo in the same "i don't care about specs or
>> your usb interface asshole" mode other deivces use and just draws
>> it's power. (No idea if that would even work. But i think it might)
> Does this mean, if we push this button, it's not possible
> anymore to use a second USB device at the same time?
> I guess that doesn't change anything because if I understood right,
> the 5V channel is used only for charging the Neo, (No power output
> for attached devices) what is the reason for why we need those
> external powered USB hub.

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