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[Lcdproc] MtxOrb adjustable backlight and display detection

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  • From: ehrnam45 at (Samuel Rogers)
  • Subject: [Lcdproc] MtxOrb adjustable backlight and display detection
  • Date: Mon, 4 May 2009 13:38:13 -0400

Ok, after some digging around in the driver source code, I found that there
is a provision for using the correct brightness levels, but the mauals
differ on what the settings do, as well as have some rather glaring errors.
Here's what I found:

Unit Version Notes
VK162-12 2.20/2.30 OK
VK162-12 3.0 1
VK202-25 1.40/1.50 OK
VK202-25 2.0/2.20 OK
VK202-25 3.0 2
VK204-25 1.23 1
VK202-24-USB 1.6 OK
VK204-24-USB 1.0 OK
VK202-25-USB 1.0 2
VK204-25-USB 1.0 2

1) The brightness table is backwards, i.e. 0x00=100%, 0x03=25%
2) The manual has 0x00=0% and 0x01 is listed as BOTH 25% and 50%.

Not all of the manuals list "Y" as the command for brightness, but they do
agree on the decimal value 89 (0x59) which shouldn't present a problem. I
tried changing the 'Y' to "\x59" on line 756 to match what was listed below
for the standard LCDs but didn't see any change to the brightness once I
restarted LCDd. Changing the brightness level in my LCDd.conf file doesn't
do anything for the startup brightness either. Could it be that the
declaration on line 759 as 'long' is generating a decimal point value and
therefore not sending data the display is expecting? Unless the remainder
is chopped off, there isn't any setting that will give you exactly 1 or 2.
Since there is already a branch checking for IS_VKD_DISPLAY, couldn't we
just skip the promille conversion and add a comment about VKD devices having
valid settings of 0-3 in the .conf file?

On Mon, May 4, 2009 at 9:03 AM, Samuel Rogers <ehrnam45 at> wrote:

> On a related note, I also have a MO VFD (VK202-24-USB) and I would like a
> bit more intuitive brightness control for these modules. The VK series only
> have 4 brightness settings--5 if you include off--sent as 0x00 (25%) to 0x03
> (100%). I looked over the source for the driver and didn't see anything
> that checked for this type of display in the brightness settings nor
> anything that would convert the promille value to these brighness values.
> As a result, changing the default brigtness in LCDd.conf has no effect on
> the brightness of the display. I also don't see anything in the client
> language reference about changing the brightness of a display (unless it's
> supposed to be controlled by the backlight setting) and I'd really like to
> be able to control that from a client since LCDd doesn't let you pass the
> commands directly to the module. Speaking of which, would it be possible to
> make an 'expert' command that allows a client to speak directly to the
> module, or is it better to build that functionality into the driver and
> access that with screens/widgets? Would it be helpful for me to tinker with
> it on my end and see what I can get working?
> Sam
> On Mon, Apr 6, 2009 at 2:17 AM, Markus Dolze <bsdfan at
>> Ethan Dicks wrote:
>>> On Tue, Mar 24, 2009 at 4:04 AM, Markus Dolze <bsdfan at>
>>> wrote:
>>>> Hi,
>>>> I have questions on how the Display On / Off and Set Brightness commands
>>>> of
>>>> Matrix Orbital displays work:
>>>> 1. If I use the 'Display Off' command, does it just turns the
>>>> backlight off like for older versions or does it completely turns
>>>> the display off?
>>>> 2. If the display's backlight is off, what happens if I issue a 'Set
>>>> Brightness' command? Does the backlight stays off until a 'Display
>>>> On' command is issued or does the backlight automatically turns on?
>>> ..
>>> I send "display off", the display goes off *and* the backlight goes
>>> off. I had to send both a "backlight brightness" _and_ a "display on"
>>> command to see chars again. It does not matter which is sent first,
>>> but both have to be sent.
>>> When the backlight is off sending a "set brightness" does not turn the
>>> backlight on right away. It stays off until the "display on" is sent.
>>> This is the only Matrix Orbital textual LCD I have (an "LKD"). My
>>> other textual MO display is that VFD display that "doesn't like" the
>>> newer LCD commands (but worked fine the last time I tested it as a
>>> "VKD" type display).
>> Hi,
>> my idea was to implement 'offbrightness=0' as 'display off' command. On
>> older displays this turns off the backlight. But as newer displays turn off
>> completely this is not an option anymore.
>> My second idea was to overload the 'onbrightness' value. As the displays
>> support only 255 brightness values and the driver maps 0-1000 => 0-255 you
>> will increase the brightness values by four to see an effect. I wanted to
>> use 'onbrightness=1' to make the driver send a 'display on' command for
>> those older displays. This is still possible, but does only make sense with
>> 'offbrightness=0' as above.
>> Do you have any other ideas beside adding a new option to the config file?
>> Regards,
>> Markus
>> _______________________________________________
>> LCDproc mailing list
>> LCDproc at
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