Re: Open hardware AV to digital conversion

On Mon, Jan 5, 2015 at 4:54 PM, Ingo Korb <ml@akana.de> wrote:

> Marko Mäkelä <msmakela@gmail.com> writes:
>
> (powering an HDMI source from the sink)
>
> > Oh, I see. However, let me quote a comment on
> >
> http://www.androidauthority.com/chromecast-dongle-official-specs-features-release-date-pricing-248120/
> > "A reviewer on Amazon who apparently already has the device (developer I
> > think) says that the device can be powered directly off an HDMI v1.4
> > connector without using the USB power brick.
>
> I suspect that is a fluke caused by an HDMI sink that applies power to
> the 5V pin even though it should not. When powered from USB the
> Chromecast draws about 300mA with peaks up to 400mA, so it's waaaay
> beyond the 55mA you officially get anyway.
>
> I'm not really surprised though - there are also quite a few USB hubs
> out there that try to power the computer from their own 5V power brick
> even though that is also the wrong direction.
>

I wound up with a USB hub that did exactly this.  It had a 9VDC unregulated
brick, no internal regulator, and feedback to the PC.  It fed everything 9
volts.  Good thing I look inside things before I trust them!

PS: don't trust cheap multiport hubs ;)

In the end it's just another case of "don't expect it to work but be
> happy if it does" as well as "be suspicious of the other guy and try to
> make sure that he can't kill you". ;)
>
> > See http://www.hdmi.org/learningcenter/kb.aspx?c=13 for more info
> > about HDMI accessory power requirements."
> >
> > The linked FAQ page says that HDMI-powered devices should offer a
> > fallback of an alternative power supply.
>
> Yes, but the wording of that FAQ entry seems to suggest to me that it is
> meant only for HDMI sinks that are powered by a source device.
>
> -ik
>
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>


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