DIY Video Projector

[Mundi]

I found a great web presentation (multimedia audio + slides) about driving white LEDs. It gives lots of information about getting equal light levels out of each LED.

It also talks about who makes the brightest devices for miniature devices like cell phones and for large devices, like signs.

National Semiconductor: Differentiate Mobile Devices with White
LED Driver Solutions from National
http://seminar2.techonline.com/~nsc22/jan1702/

[pask]

skilzygw :
DVI output is not a parallel output, but a serial one (maybe, but I don't know the protocol for the moment), so you cannot drive directly an LCD panel from a laptop you'll need fast electonic (serial to parallel converter)
flat screen such as viesonic or LG is a good idea, it's a nice size for an OHP to get the maximum light, an you can drive it directly
I don't wanna use that for the moment because it's a little bit expensive for me !
My 10.4 inches panel works fine on my OHP, but the contrast is not very good : 150:1 from the panel, and some reflections on the projection lense.
I didn't let it for a long time, but i think it will be a little bit too warm
50°C is the max recommended operation temperature for a LCD, and with dark pictures, it will become hotter.
I have to build a case (pastic, or wood) to protect my panel (I've already broke a ribbon connector, hapilly I've been able to solder it
Moreover, the LCD won't be direrctlin over the fresnel lens, but I'll let about 1 inch to blow some cold air.

fender4 :
I don't understand why you are looking for UV filter. the heat problem is due to InfraRed, no ?

[skilzygw]

Ive checked out some controllers for laptop lcd's and they seem to be an average of 200 bucks. For that its just not worth it. I'd rather go panel or an lcd monitor and open it up...something like a 15inch viewsonic.



Hey I was wondering I see really cheap 4inch lcd's. Like the kind used for vans and cars to quite the kids. SO can that be used? They are relatively cheap average of 90 bucks.

I know its a smaller size but is it active matrix? How easy would it be to open that thing up? Basically these are backlit screens but we're supplying the light right?

[Axeman]

I have a 4" TFT screen that I bought from Ebay, and I'm working on making a projector out of it. it's active matrix, and definately speedy enough for everything I've thrown at it(video games and movies). It's downfall is the resolution- only 383x234. but it does work well and has fairly good contrast.

[skilzygw]

Hmmm interesting.

Why are are we looking for contrast of 350:1 in lcd monitors. WHat exactly does the contrast due for us? Thanks.

Im asking because I've found a cheap 15inch lcd monitor but its contrast is 150:1 will this be unusable?

Thanks!

[pask]

with higher contrast, you can see more details, for exemple on dark clothes on a night movie, with low contrast, the scene looks like a big black part, but with higher contrast, you'll see the details

[fender4]

pask,

The UV filter might be the wrong approach. I was just basing this on a link Vince posted at the beginning of this thread: Sharp projector and Fiat1's post a few days ago (I hope it's ok if I quote you, Fiat1 )

"Well I was looking inside an old slide projector of mine, and removed the UV filter, I then placed it over the globe inside my OHP and put the cover back down and turned it on, there was no noticable light loss and it almost clear with the tinnest barly noticable tint to it. I placed my hand ontop of the fresnel lens expecting the ussual magnified heat you feel, and there was nothing, it had cut out all the heat! I had it running for 1 min and I heard the sound of breaking glass. I tunred it off and opened the cover and the filter had shatter, it is quite thick yet is had shatter, it was only a 250watt globe but it was too hot. This shows that instead of a cold mirror we could use one of these that can take more heat and this makes aligment of the optics easier. Rember that the filiment has to be aligented with the center of the fresnel lens, it may also work better to use a condenser lens then the fresnel. I am now going to look for a good UV filter!"

Everything I know about optics I learned from this thread, so I'm sure I misunderstood some things along. PLEASE correct me if I am on the wrong track...I don't want to be the source of incorrect info!

skilzygw,

The type of LCD you described (the small ones made for mobile video) can be used, just as zark has used a 5" one: Zark's website.
Several others are taking this approach, including myself. They probably wouldn't be as ideal as a projection panel for OHP, unless the large lighting surface was concentrated down to the size of the LCD. Otherwise, there would be a great deal of "wasted" light.

I personally like the idea of using small mobile LCD's because of their small size and low price. Of course, resolution is a drawback, but Zark has produced some impressive screenshots with his. The OHP approach seems to be better suited for high resolution setups, but the size of the actual projector will be fairly large.

Good luck, everybody!

-f4

[ds21]

I opened up my 5.6" LCD and found out that instead of one set of ribbons that attach to the screen there are two, one on the bottom as in Zarks and one from the side, these are on two seprate boards with a very, very small ribbon cable connectiong then. I don't see any way to move them out of the way without some kind of extention cable. Just a warning for those who are looking into the smaller LCD's.

[jquinn]

Hello,
I was talking to one of the techs that builds the displays for our machines where I work, and he said that the higher the contrast of the screen, the less transmissive it is when its on, so you would need a brighter light behind it to reveal the detail.
Thanks,
Joel
Also, it seems that the thinner the module, the more likely that the driver is attatched at one side and can be moved aside more easily.

[Myren]

major cooling bitches we've got:

first off, film has the advantage of being film. when a movie projector is rolling, each frame only gets blasted for what, 1/24 of a second or something? with the panels were using, we have no such luxury. we need serious freaking cooling to keep a single frame cool under constant usage.

stage techies seem to relish in 150 degree catwalks, and as such a lot of the stage bulbs we've been finding in our projectors produce excess amounts of heat.

there arent that many things we can cool directly. conventional cooling (as i think of it at least) usually doesnt involve optical elements. we cant just go around sticking on heat sinks and adding water coolers to everything (the quiet alternative to fans), as much as we'd like to.

overhead projectors put the heat source at the bottom of the system, which is possibly the worst place for it to be.



there are a number of potential ways to address these problems:

use better bulbs. in the past couple days i've become a huge proponent of metal halide high intensity discharge (hid) lights. damn these things rock. available anywhere between fifty and a thousand kilowatts, these are bar none the single most efficient light sources around. they require starter circuitry, but the 20,000 hour bulb life, low bulb cost and unsurpassed energy efficiency will more than make up for it. i'd suggest S.C.W.A metal halide high intensity discharge systems, which are a certain type of pulse start hid.

Assailant's suggestion of waterblocking cold mirrors sounds really top notch. finding cold mirrors for a reasonable price is a major pain in the *** though.

try to use convection as best as you can, dont fight it. smart placement of vents can help direct heat to where you want it to go, or more percisely, away from where you dont want it to go.

i had a lot more to say about this, but i've had my head crammed in so many optics books i forgot most of it.

myren