XFree86 On Computer Projectors?

Bruce Ingalls asks: "Ask Slashdot ran some computer projector recommendations back on June 4, concerning quality, cost of replacing bulbs, but I have have had problems connecting XFree86 on a laptop to computer projectors. These projectors always work in console mode, or with Microsoft Windows. I find that a projector will work with some Linux laptops, but not others. One workaround that sometimes works is to start X where it displays to the external screen only, and then hit the hotkeys to enable the laptop's internal screen, afterwards. Any other recommendations?"

Modelines?

[aliastnb]

Surely the refresh rate will be different for the projector than the built in display?

I've had similar problems getting X to appear on my TV using the TV out feature on my video card. The TV needs to be set to have a refresh rate of 50Hz or less (PAL) for the TV to display a picture. Therefore, I needed different modelines for the TV than just with the monitor.

Text mode will work for both as the refresh rate is less than 50 Hz and MS Windows will automagically move the refresh rate down to one that the projector supports- which is why each of these work. Again, if the internal display is disabled, then X is forced into using a lower refresh rate and so the projector works.

In short, specify *exactly* what refresh rate and res to use, comment out all the rest and it should work fine.

Re:Modelines?

[bueller]

The previous comments about modelines/refresh rates/resolution are correct

Each projector has different capabilities, and later model projectors attempt to work out the correct resolution and refresh rate based on their input. Sometimes they get confused and display nothing. I've seen this happen on a regular basis with a projector attached to a windows laptop, and the projector can need power cycling to regain the plot. Moving between the laptop and external screen achieves a similar re-evaluation of the input when the projector hasn't totally confused itself.

The projector displaying nothing is in someways similar to when you try to overdrive your monitor and it goes into powersave mode. Likewise, changing settings (mode/resolution/refresh) too quickly powersaves some monitors and it can also confuse some projectors. This makes it hard to cycle through your 'available' modes.

Chances are the projector is a less capable screen than the laptop one - so while you might be able to run a 1024x768x16M laptop screen, the projector might max out at 800x600x256. This is all dependent on how much you've spent on the projector.

Set aside some time one afternoon with the projector and your laptop to work out what set of modes displays both on your laptop and projector. If you've got the specs handy for both your laptop and projector you can probably speed things up, but I'd suggest starting at 800x600x256 and work up from there.

Remember to always have a working backup copy of your XF86config file, and if you are using Xservers to specify a bpp (colour depth), keep a working copy of start line commented!

My one experience

[Daffy Duck]

I have a Kapok laptop that's about a year and a half old, and had to get it to work with a Sony projector. Random fiddling with the modelines did not really help. What did the trick was going to Sony's web site and looking up the horizontal and vertical frequency ranges of the projector, then plugging them into the HorizSync and VertRefresh ranges in XF86Config. This doesn't seem to affect how the laptop's display looks at all, and it got the projector working. I still have to do a little magic dance by starting X in 1280x1024 mode and then kicking down to 1024*768, but it works every time.

Video timings

[Scott Wunsch]

I've found that a lot of projectors are rather fussy about video timings... and LCD displays on laptops aren't. I haven't spent too much time figuring out what's different in it, but I have an XF86Config file from an old installation that I hang onto, because projectors like it :-).

So, I'm not sure how much help this'll be, but try fiddling with different video timings until the projector likes you...