[gull] Mon adaptateur roline hdmi to VGA ne fonctionne pas sur ubuntu
Daniel Cordey
dc at mjt.ch
Sun Feb 28 20:11:47 CET 2016
>>>>>> Malheureusement, mon moniteur vga brancher à l'aide de cet
>>>>>> adaptateur m'affiche le message "no vidéo output" ou devient tout
>>>>>> simplement noir.
En effet, les commentaires au sujet de l'alimentation du dongle me
semblent pertinents. Le signal VGA étant analogique, le "convertisseur"
produisant un signal digital, il doit bien y avoir quelque chose qui
alimente le chip qui fait la conversion à l'intérieur du dongle...
Donc, soit celui-ci est alimenté par le HDMI, soit par le VGA, soit de
manière externe avec un mini-usb. S'il n'y a pas de mini-usb,
l'alimentation doit-être fournie par l'un des deux connecteurs...
Normalement, le "device" actif du HDMI devrait fournir 55 mA sous 5V,
mais...
An HDMI device that has active electronics should have a provision for
external power in order to be compliant (e.g. a receptacle to allow the
use of a standard power adapter, sometimes called a power “brick”). Here
we are drawing a distinction between “active” devices that actually have
some powered electronics, and “passive” devices, such as some switches
(more on those later).
Some active devices, such as actively powered HDMI cables or in-line
signal extender boxes, will by default attempt to power their
electronics by taking power from the 5V line (+5V power) available on
the HDMI connector. The HDMI specification requires all source devices
to provide at least 55mA (milliamps) on the 5V line for the purpose of
reading the EDID of a display. While 55mA is not enough current to
operate most HDMI accessory devices (which typically require about 100
to 150mA), most source devices on the market today provide significantly
more current on the 5V line than the HDMI specification requires. As a
result, the vast majority of accessory devices can operate when
interfaced with a source device that provides more than the required
current (i.e. over 100-150mA) on the 5V line. However, manufacturers
should provide a provision for their powered HDMI accessory devices to
obtain external power, and consumers are encouraged to look for this
external power provision when purchasing such products.
Looking to the future, not all HDMI devices may provide this much power
over the 5V line. For example, as HDMI expands into more and more
portable applications (cameras, camcorders, laptops, etc.), power
consumption is often much more of an issue, and such devices may not
power the 5V line with the > 100mA required by such “active” devices.
Again, consumers should consider ensuring that their active HDMI
accessory device purchases have a provision for external power for this
reason.
Any device which performs processing, amplification, or switching of the
HDMI signal should use actively powered electronics to be compliant and
perform reliably. As mentioned in the above question, the vast majority
of devices can utilize power that is supplied on the 5V line (+5V power)
of the HDMI connector to function properly, although we recommend that
such devices give the users an optional provision to use an external
power adapter. Completely passive, non-powered devices may work in some
short-cable length applications, but use them at your own risk, as they
may not operate reliably. Even if a passive device works in one
configuration, a change in equipment or cabling may introduce failures
in subsequent configurations.
J'aurais donc tendance à dire que le dongle n'est pas alimenté, ou qu'il
a besoin de trop de courant que ce que peut fournir le HDMI... Ce qu'il
fait qu'il ne sort aucun signal VGA du dongle...
dc
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