disable webcam C920 LED in Ubuntu?

[Sam Seagate]

I've just started using a Logitech C920 webcam in Ubuntu. I am using it
with Guvcview software, but I don't see any way to disable the blue
LEDs. Does anyone know of a way to disable them? So far, no solutions
presented in Ubuntu group have worked.

Thank,
Sam

[Markus Grob]

Sam Seagate schrieb:

> I've just started using a Logitech C920 webcam in Ubuntu. I am using it
> with Guvcview software, but I don't see any way to disable the blue
> LEDs.

Black paper in front of the LEDs?

Markus

[mrr]

Just tell us, you knew, still writing down your question, what would be
the answer? ;)

No clue except maybe that the led might be driven by the module so I
would check module options / try unloading stuff just to see or check
module code source but that's quite an adventure if you're not sure
about what you should search for.
The light might be driven by the system, in this case ask systemd, I
don't know much about it but I heard it was doing all and everything.

Cheers

--
mrr

[Sam Seagate]

Sorry, I wasn't clear enough originally, but the first response about
black paper might be ok but not for my application. I need to be able
to turn the light off and then on again at certain times to help with
focus.

I have been using Guvcview to control the C920. It has quite a
comprehensive list of functions available, but nothing for LED.
Apparently there are issues with Guvcview versions: my research shows
that apparently an earlier version allowed LED functionality and then an
even later version (I am using Ubuntu 12.04, but Guvcview in 10.10 and
14.04 has the function). I don't want to have to upgrade Ubuntu yet
just to have the functions.

People in Ubuntu suggested modifying the uvcdynctrl program (which I
install at their request) with terminal command sudo uvcdynctrl
--set='LED1 Mode' 0. This did not work. I also tried to modify the
logitech.xml file but to no avail.

Thanks in advance for any further help. I'm not very good getting too
deep into file mods through commands, but with step by step procedures,
I seem able to manage.

Sam

[Sam Seagate]

Just wanted to follow up. I think I'm getting a lot closer to LED
control. A Ubuntu user suggested I go here:

http://sourceforge.net/p/linux-uvc/mailman/linux-uvc-devel/thread/51141E46...@gmail.com/

I reread this carefully. I did see the reference to changing the following:

You should edid this values in ...
<entity>UVC_GUID_LOGITECH_USER_HW_CONTROL</entity>
<selector>XU_HW_CONTROL_LED1</selector>

This are current values:
<constant type="guid">
<id>UVC_GUID_LOGITECH_USER_HW_CONTROL</id>
<value>63610682-5070-49ab-b8cc-b3855e8d221f</value>
</constant>

<constant type="integer">
<id>XU_HW_CONTROL_LED1</id>
<value>1</value>
</constant>

you will need to use:
ffe52d21-8030-4e2c-82d9-f587d00540bd
or
212de5ff-3080-2c4e-82d9-f587d00540bd
and
9 instead of 1


So, I edited the xml appropriately and the good news is that now control
of both zoom and pan/tilt has returned in Guvcview. LED functions are
now selectable in Guvcview too, except they don't work and the LED stays
on constantly. When I switch options, the LED appears to blink as I'm
switching say, from on to off, but it won't go off.

So, a heck of a lot closer to having this solved but I don't have a clue
as to what to do next. My guess would be that something else needs
modified in the xml file.

Any ideas would be welcome. Thanks in advance.

[mrr]

On 03/06/2015 01:03 PM, Sam Seagate wrote:

>
> Sorry, I wasn't clear enough originally, but the first response about
> black paper might be ok but not for my application. I need to be able
> to turn the light off and then on again at certain times to help with
> focus.

...

> comprehensive list of functions available, but nothing for LED.
> Apparently there are issues with Guvcview versions: my research shows
> that apparently an earlier version allowed LED functionality and then an
> even later version (I am using Ubuntu 12.04, but Guvcview in 10.10 and
> 14.04 has the function). I don't want to have to upgrade Ubuntu yet
> just to have the functions.

I don't really know about ubuntu as I am on debian which is close enough
to say something (about installing a newer package without upgrading the
whole system):

So in debian you can add a "backport" line in /etc/apt/sources.list or
somewhere inside /etc/apt/sources.list.d directory.
This allows you to install newer version of some applications (not all,
an obvious example is that you'll never see a libc backport).

You can easily add some particular server (ppa:) in ubuntu, maybe you
could achieve something that way.

And you can always try to make it by hand:
Search the difference in dependencies between the newer and the actual
version (search their website, download sources and dive into README
files...).
Install new dependencies using apt if at all possible.
Make a deb package or actually just as usual a configure && make && make
install (or whatever).

> Thanks in advance for any further help. I'm not very good getting too
> deep into file mods through commands, but with step by step procedures,
> I seem able to manage.
>
> Sam

Led control is beyond my skills, I won't be of any help here!

About modules, you could try to locate the one which drive your webcam,
have a look in the output of "lsmod", "lspci -vv" (as root), or "lsusb"
(if usb of course), "dmesg" also.
If you can do a hot unplug/plug, you could do (as root) a "udevadm monitor".
You could locate the device in the /sys filesystem and play with device
properties. If (really really) lucky there could be something related to
the led activity.

And I think I remember that upstream led control was driven by the
kernel, not sure.

I know this doesn't help much but in the next message one can see you
made real progress!

--
mrr