DIY Video Projector

[thelaw]

A question to ppl with ohp setups, how many lumens are needed for a nice, impressive and sharp projection? would 4000 be ok?

cheers

[Scot_lad]

Good morning people, I'm back again with progress on the CRT issue if anyone is interested...

Firstly, I'm sure somebody wrote (although I can't find it now) a comment on the lack of true "DIY Projectors" going on here. I have to agree, since everyone seems to be going the OHP route with a ready-made projection panel. But this isn't a bad thing, I think as long as the end product is something decent to watch big-screen movies and games on, then it doesn't really matter how we get there. Perhaps a little more discussion on the good panel/bad panel board might be an idea though.

Anyway, for the people that were looking to increase the brightness of the CRT: I posted a while back that you could increase the signal to the CRT, but that would be a bit complicated. In any case, you have to be careful you don't get the opposite effect, because in cathode-driven CRTs, too high a bias voltage will result in a darker image.

There is another way to increase the brightness, which will definitely increase the brightness, but WILL reduce the lifespan of the CRT and could reduce it down to several seconds if you are unlucky or not too careful. I know all you clever people know how a CRT works but just in case... The electron gun has a heater in it, which heats up the cathode to release electrons which are then accelerated towards the screen by a positive charge (on the anode). Look at www.howstuffworks.com for details

One way to brighten the image is to increase the amount of electrons which hit the screen. Most hardware stores sell bags of electrons, so get a reasonably big bag and pour the electrons into the back of the CRT, in the hole marked 'top-up'.

Now that we've got the dumb-*** contingent busy, the rest of us can concentrate on increasing the number of electrons hitting the screen by increasing the voltage to the filament, thus making it run hotter and eject more electrons. Obviously, the inherent danger to this approach is that the electrons will run out (seriously) more quickly, although this may still soldier on for some time. Also, the tube may die pretty quickly if you're unlucky, so don't blame me for any disasters, fires or divorces resulting from this advice. And DON'T TRY IT ON ANYTHING EXPENSIVE!!! I am using cheap small CRTs which are replaceable at little cost. If you use it on your expensive 21" monitor you've only got yourself to blame. Don't say I didn't warn you.

Check out http://www.repairfaq.org/REPAIR/F_cr...tml#CRTFAQ_053 for more information on this topic if you're interested. I strongly advise you to read up on CRT safety (also in this article), which is very important!

Once more, be very careful with CRTs, they pack many thousands of volts in them for several days after use, which could easily prove fatal or at the very least make you shout some colourful language. Don't blame me for any bad stuff that happens, I'm just pointing you in the right direction.

Hope somebody finds this useful,

Cheers.

[Gunawan W]

hi guys,
this is another diagram & calculation I made, but now I used
2 lenses, I used 50mm focal-length for first lens and Delta 20 for second lens. It works! but need powerfull light and good quality lens to get crisps, bright image.
Hopely this will not add more headache.

Lcd projector diagram & calculation part2

have a nice weekend.

[xblocker]

FrankBatzen, to modify the focal lenght of normal OHP lenssystem, have a look at the american patent database patent# 4,350,415
There are attached 2 meniscus lenses at each side of the projection head to get a longer throwdistance.

Thelaw, my OHP has 5200 lumens, that's good, but could be little more. 6000 lumens upwards with MH lamp is better, especially colortemp.

xblocker

[xblocker]

add:
Thelaw, forgot to say ,of course the range of lumen output depends of the image size to be projected and also the screen material. My example refers to 110" diagonal, 4:3 ratio, matte white screen, 10" LCD panel.

xblocker

[jjasniew]

My analogy still stands; No one takes a piece of paper, folds it around into a cone, glues the tube from from the TP roll onto the apex, winds some turns of copper wire around this...etc, etc - to make a "DIY" speaker.

There's a practical granularity point where the components available preclude rolling your own from the ground up. Why re-invent the wheel? You can go through all your calculations and chances are you'll end up with the same thing the guy decades earlier found out, that the circumference is indeed 2pi(r).

I've personally shown, at significant expense, that it can be fairly impractical to try to make a projection panel out of a LCD monitor.
While it is adventurous to get something like this to work, in many ways it makes logical sense to start with components intended for this application.

The DIY part, if I intended to refine it, would be to somehow "drop" the LCD into the OHP, in an effort to focus more of the light through its "smaller than the OHP's stage" aperature. Secondly, I'd work on the cooling of both the panel and OHP, possibly integrate the two, because taken together, the noise is ridiculously distracting. (The dont tell you about this when they get $300 for OHP / panel combos on ebay. OK, that set was probably quieter than mine!)

Actually, I'm dropping out of DIY, and I've gone over to the CRT side, in just buying a solution off ebay. I've weathered too many dissappointments in screwing around with various panels, including the latest clanger, the superlative sharp qa-2500 I just got. A $200+ dissappointment! It's NOT perfect and far enough from it I really wish I just kept those two bills in my pocket...

I figure I can sell all this stuff, break reasonably even, and put it toward a substantial part of the CRT unit credit bill. Even the dead VP140 goes if only for the case, VGA interface card and backlight. Every $25 contributes!

Besides, I got other audio projects I'd like to get to, like modifying my marantz cd63 and putting the Curcio driver boards into my MKIII amplifiers. The projector thing has really been consuming me.

[fender4]

Sorry to see you leave, Joe. You have contributed much to this board, even in your disappointments. Congrats on the CRT.

Good job with the Excel spreadsheet, Gunawan! Very useful.

With all of the successes with OHP+panel setups, I have recently looked further into what makes an OHP tick with hopes that this can lead to some DIY improvement .I have found several interesting things...some of which are speculation, so jump in if you know something different.

Bulbs--Most bulbs for OHP's that I have looked up are quartz-halogen type in various shapes and sizes. One thing that is consistent is the color temp, which is usually in the low 3000K range. That is a fairly "red" temp, which makes me wonder if OHP panels were designed with this in mind. In our searches for bulbs in the past, we have tried for the 5000-6000K range...is this neccesary? I'm not sure what the CRI is for these bulbs, but maybe that has something to do with it. Regardless, halogen type bulbs are much less efficient than any HID bulb which makes fans a necessity even on low-lumen projectors (many of the watts are going to heat production instead of light). Example: 400 watt MH=36,000 lumens
600 watt DYS OHP bulb=17,000 lumens
The MH bulb is more than 3X efficient.

Some bulbs have a built in reflector that disperses light equally to the fresnel, and some are "naked" bulbs with no reflector. In one example, a "naked" bulb is placed horizontally above a flat reflective surface and below a lens the disperses the light to the fresnel. I'm sure each has its pro's and con's, but it seems that the built-in reflector type would be more efficient. The "naked" type might be more convenient for a DIY bulb upgrade, like a metal halide or mercury vapor (I still haven't determined if the MV bulb will work for us...reflector issues).

Lenses--I think that the fresnel lens of an OHP is actually TWO fresnel lenses: one for collecting the diverging light from the point-source bulb and producing parallel light rays, and one for taking this parallel light and converging it to the head lens. This might be why I have never had much success with my Office Depot page magnifier fresnel...I need another one to direct the light to the projection lens (can't beat physics ).

Well, that's enough rambling for now. Sorry if I am pointing out the obvious...I have never even touched an OHP before. I've thought about ordering one and finishing this project, but I don't think I would be happy with it--too inefficient and not enough DIY. But that's just me...congrats to everyone that has been successful with OHP's!

-f4

p.s. Scot-Lad, I can't find those electron bags anywhere around here. Do you know of any internet shops that sell them?
Interesting link. Good luck with that, and be careful!

[jvisaria]

I recently procured some OHP fresnels (6 to be exact), and to confirm your inquiries, fender4, you are correct. Each one is indeed two lenses adhered together.

[Jaro]

Hi all

Does anyone know if this would be true or not?

I have an lcd srceen out of a car stereo unit and have pulled it a part so that I just have the lcd screen and the ribbon from it.

What I what to know is, can I just find the connections that powers the lcd screen and then find the signal connections that use to come from the main board should only be two I think, four connection pionts in total on the end of the ribbon, and not use any of the others.

The two for the signal, could I just hook them up to the monitor or tv output on the amp of my Home Theatre system so it would go through like an av input for the lcd?

This hopefully means that what ever I have whether it be tv or dvd, sky etc running through the amp it should go out of the output of the amp and into the input of the lcd screen or tv which is how I run my system at the moment, I dont use anything on the tv, it is basicly only a screen.

Any thoughs

Cheers Jason

[thelaw]

Joe:

Whats wrong with the Sharp QA-2500, i thought that would be the best one

cheers.