DIY Video Projector

[Scot_lad]

I don't think that the polarizing filters are the whole problem here. They are just there to make sure that the light that goes through is parallel, because it gives better performance from the LCD. I think this is right, isn't it true that if light goes through the LCD at different angles the contrast is reduced, because of several different rays of light going through the screen?

Anyway, even without the polarizing filter, the basic design of an LCD means that any light not hitting it as a parallel beam will be attenuated. The way an LCD works is to rotate a tiny structure (in each pixel) so that light can go straight through, when a voltage is applied. If you go to the amazing www.howstuffworks.com, you can get a better idea, probably with some nice flash animations.

On another note, if anybody's still interested in CRT (and if they are give me a heads-up), here are some links.

Once again, www.howstuffworks.com has a good video of someone shooting a CRT, and it doesn't blow up. Magic eh?

Good links for the inner detailed workings of TVs here:
http://www.bithose.com/serfaq/sam/tvfaq.htm
as does this:
http://www.lesbell.com.au/Home.nsf/e...0?OpenDocument
and this:
http://sure.org.ru/docs/hardware/pcrepair/chap33.html

You can read into a lot of these for some very good information, like sticking a raw RGB/composite signal into a TV without a composite input.

And the next door neighbour's got their washing machine on so that's my queue to go - the whole floor is vibrating, she must have knickers like tents.

[fender4]

tech head,
OHP's will work fine as they are, and building a projector like an OHP will also work great! I was just trying stir the DIY Kool-Aid, and I didn't even know what flavor it was .

SuperDave,
I made a baby step with the MV bulb issues. I took my Delta 20 lens apart and removed the middle lens (looks to be a very short focal length DCX lens with one side much flatter than the other...almost a PCX lens). I then placed it between the bulb and the fresnel/LCD, and this greatly improved the intensity and spread of light across the LCD. Without a suitable reflector, I am still losing at least 75% of the light to scatter . Hopefully this will help you out if you decide to upgrade the bulb in your OHP.

Scot_lad,
You weren't kidding about that www.howstuffworks.com website. What a great resource! I just spent an hour reading about LCD's, CRT's, and Stirling engines.

OK, I need to get back to studying. I have 8 finals/boards over the next 10 days . Good luck, everybody.

-f4

[ravide]

fender4,
you mentioned using a 0.8" hi-res lcd panel,
would the small size of the panel be an issue?
isn't it true that the larger the lcd panel the more the light can pass through? Is it possible to converge all the light to pass through this small area?

Thanks in advance...

[CHARTO]

IV'E BEEN FOLLOWING THIS PROJECT FOR SOME TIME NOW,
WHILE YOUR ON THE SUBJECT OF PARRALEL LIGHT TAKE A LOOK
AT THIS PAGE I FOUND IT MAY BE OF SOME HELP,IF ANYONE CAN
UNDERSTAND IT

ITS IN PDF FORMAT SO YOU WILL NEED ACROBAT READER

http://www.fresnel-optics.com/pdf/condenser_lenses.PDF

[Hellfire]

Thanks för the links Scot_lad

I´m catching up on how a CRT works but the progress is slow

And no word from the university . . . .

What do You think about using the electronics from a PC monitor and feed 3 proper projection tubes with it?

Is there any simularity bethween a prpjection tube and a monitor tube when it komes to voltidge and current and stuff?

I guess it is a long shoot but I´m throing it out on the thread anyways

Bye for now

[Myren]

hey all. been gone a while. been busy watching movies and making crazy plans for the future. diy projectors have become an addiction. not altogether DIY anymore, but man.....

anyways, where to begin. lets see.

yeah, with the fresnels, the lcd has to come after the fresnels. its not that bad a problem though: as long as the light is within a certain viewing angle %, there should be no (or near enough so) attenuation. its really not a problem.

ballasted light systems rock. MV sounds great. personally, i'm a big fan of metal halide. 400 watt metal halide is freaking beautiful. really. theres nothing like seeing a wall light up.

someone was talking about heat in light bulbs. well, conservation of energy states that any energy being put in and not coming out is having to go somewhere. theres just about two forms: light and heat. bulbs which produce more light for the same wattage are also more heat efficient. whoot to that.

so back to metal halides. they have BAR NONE the best efficiency around. is heat still a problem? oh yes. 400 watts will never be non-trivial. but with 3 times the efficiency of fluorescents.... well... damn. check out metal halide. yes, they need a $60 - $70 ballast. but bulbs are only $30 and last 20,000 hours. compare at $215 for the various 575 watt short arc bulbs a lot of your projectors are probably using (that last at most 1000 hours). the advantage is crystal clear.

and for the FREAKS in the audience, you can even get 10,000 K color temperature bulbs.

i really wanna start poking people towards elliptical mirrors. they are the ****. they're hard to build and probably nigh impossible to find, but hot damn are they ever perfect. it'd be a DIY project in and of itself to make them, but so worth it. basically, you'd put a light at one foci, put a panel between the two foci and have a projection lense system around the other foci. perfection.

custom lenses suck. i've been *** deal in optical design. it sucks. avoid if possible. if your really serious, go buy a book.

as a final note, a good projection screen is ESSENTIAL. i'm running **** right now and barely hacking it. i moved my system temporarily over to a real projection screen and nearly wet myself all over again. my oh my.

oh, yeah, for anyone really really really interested in how to take apart a vg150, look here. warning: 24 megs.

whew
good to be back
myren

[contrapasta]

Hey Myren, welcome back. I've been waiting for for VG150 pics for like weeks now Too bad, I think I've already decided to with projection panels, even though I already have a vg150 in my hands. It looks just too sweet and innocent to to take it apart and do rude things to it I'm just going sell it, I'm not too happy with its color rendtion abilites, and can't justify $320 for it (I bought it before my little vg150 for $230 post). If I cant get perfect picture quality, I think LCD panels are a sweeter spot on the price vs performance curve.... Gotta go, I have two midterms to study for

[fender4]

ravide,
I was referring to the 0.8" LCDs that are used in many of the high-end commercial projectors. Unfortunately, these are unavailable to the DIYer, and if they were, they would probably be pricey. They would allow us to forego all of the fresnel optics by using a parallel light source all the way to the projection lens...nice, but not practical for us.

Myren,
Good to hear from you! Those MH bulbs are VERY nice...I've seen them on reef aquariums several times, and I don't think anything can beat their intensity, color, or efficiency. I'm trying the MV setup because it is so cheap (~$25 for bulb, ballast, and socket). If I can figure out a reflector, then I can upgrade to a metal halide if the MV doesn't work out. I think the bulbs have similar dimensions.

I have looked everywhere on the internet over the last few weeks for info on building an elliptical reflector, and I can't find anything useful. Can you point me to any resources? That is exactly what I need to make my MV bulb functional. Could a properly designed elliptical reflector eliminate the need for fresnels? I was assuming it would, but I'm not 100% sure.

Good luck everyone!
-f4

[Fiat1]

Hello

Well I have been working on my projector, rather then just make it for home use I have set myself the task of making a projector that can be used in a cinema type setup. I am looking into using carbon arcs for the light sorce, not the most practical by is very very very very very bright and fun to play with. Just a thought. I need a good reflector, not one with a hole it but one that the globe sits in front of, what can I do? The reflector is a huge part of making a sucessful DIY projector.

[Scot_lad]

Hello,

Interesting questions, not sure where to start. The tubes in PC monitors and projectors are similar only in that they are tubes, which have the cathode, anode, etc. that all CRTs have. The one big difference between the two is that projector tubes are essentially single colour tubes which have different coloured phosphors. This means that there is no aperture grid or associated circuitry to align the RGB guns to the RGB pixels. In any case, there are no pixels on the projector tubes, just a mass of phosphors.

The voltages involved would be in roughly the same range, although the scan rate on a monitor would usually be much higher than on a TV. Scan rate affects things like the deflection coils. The inductive load in these coils increases with increasing frequency, so if they were designed for a TV, would not be able to handle the MUCH higher (sometimes 3x) frequencies for a monitor.

The same basic bits and pieces make up TVs and monitors, ie flyback transformers, etc. and these are present in all CRT systems, whether projector or monitor. But, all of these components are designed to work with each other, and overall with the tube itself. So I do not think you could use the PC electronics to drive three projection tubes. For a start, a projection tube itself costs upwards of £600, and that's for rear-projection. Front may be more. Secondly, to connect up all the components would be very complicated and time consuming. Not to mention dangerous. And you're not guaranteed a result at the end either. The flyback transformer is only designed to run one tube after all, whereas it would run three in a projector system. (the same one drives the three to make sure they're in sync I think)

So to answer your question, I don't think the PC monitor pieces would be ideally suited or powered for the projector. But it has crossed my mind to take the three tubes I have and build a system round it. I decided it was too complicated.

Sorry I cannot be more useful! I will look into this with my projector tubes and see how easy it would be to build a system round those.