DIY Video Projector

[dragonhalf]

I think this page has someething that may be a solution to the issue of LCD sucking so much light.

http://www.nasatech.com/Briefs/June01/NPO20824.html

However I havent researched it enough to see how doable it is.

I am only up to febuary in following the thread.

[fender4]

Hi everybody. I don't have any real progress to report, but I wanted to drop in for a bit.

Xdreamer,
Sounds like an ambitious project! For a cheap, large screen, do a search on www.avsforum.com for DIY screens or something similar. I think there are several types of harware store paint that some have had success with. Just a thought.

Also, a reflector, of course, will not increase the actual output of the bulb. It will, however, make more of the light usable for our purposes. Without a reflector, more than half of the light will not be striking the LCD surface (radiating elsewhere), resulting in a very inefficient use of the light output. The purpose of using a well-designed elliptical reflector is that the light rays can be directed towards a focal point (near the projection lens), and hopefully this will allow us to leave out the frensel. Myren's pic a few posts ago is a good way to get the idea. On paper, it definitely can be done, but I haven't had any real success with it yet. I have only tried a rectangle of silver metal folded into the shape of an ellipse (roughly....within 5%). It was MUCH better than no reflector, but it didn't make that much of a difference. BTW, this was with the MV bulb.

Undream,
Is the metal you are using aluminum or tin? Mine looks similar, but I think it is tin or just some sort of sheet metal. I don't think it really matter...just curious . Good job on the polishing!

It was mentioned earlier that the CRI (color rendering index) of mercury vapor bulbs was not very good. I think this might be related to some of my problems. Just looking through the front of the LCD, it seems like the colors are not very "dynamic"...too much blue, no reds, etc. So in my opinion, I think that MH should be a BIG improvement over the MV. More efficient, better color, etc.

Myren,
Right now, I am just waiting for my OHP to come in so I can butcher it . Since the LCD area is smaller than the OHP fresnel, I would like to raise the bulb/reflector assembly to concentrate its light only on the LCD (possible? I'm not sure yet). Then I would like to "crop" the fresnel to the size of the LCD (once again...I don't know if that is possible. Maybe too fragile?). At least this would make for a smaller package and higher efficiency if they both work out. Pretty boring, but until my board exam is over, that will be the extent of my lens experimenation.

One other thing. In my lecture hall at school (about 250~300 seats, auditorium style), we have a screen that is larger than most movie theatre screens I've seen. About 95% of our lectures are on Powerpoint with some video, and there is always a fair amount of ambient light (more than enough to take notes with). Even with the full set of lights on, it is still viewable. So I got into the projection room the other day and saw that they used an Eiki LC-X1000 LCD Projector. I couldn't believe how small and quiet that thing is! The specs show 3500 ANSI lumens from a 200 watt bulb. Now THAT is impressive.

Good luck, everyone! Especially with the reflector project.

-f4

p.s. hey assailant--are the white stripes big down under?

[Marklar]

XDream yes there is a way you can make the paint your self basicly you start with a flat surface put a coat of white or light gray paint on it then you get some thing called reflective glass beads this is what they put on the painted stripes in the road to make them reflect your head lights I have seen it being sold on ebay search for "glass beads" you sprinkle them on the paint and shake off the excess.

http://cgi.ebay.com/ws/eBayISAPI.dll...tem=1730686078

[Undream]

It is in fact aluminum. And, I think that you may be right about the MV bulb. When I re-wired mine, I used all new wire, so, I saved the old stuff just in case I had to re-assemble the thing to take it back, and, I think I am going to do that. Too bad too. i am just not getting good results with it at all.

[jamie]

thanks for the info, but i allready had a luma screen before i got a projector. thats what got me into wanting to mAKe a projector in the first place i had a lonely screen with nothing to shine on it
anyway everyone here rocks! great info, great ideas, cool people!

[ZeCo]

dragonhalf: You found the solution !!!!

Im brand new on this forum as poster but have been reading for a long time.

I've done some research (not big research, but enough to know you found the solution)

here is a quote from a website:

In most LCDs linearly polarized light is needed. A polarizer in the rear of the LCD will transmit light from the backlight system only if it is used in the same orientation. In a LCD, the rear polarizer will absorb roughly 50% of the backlight's output before it reaches the display. A reflective polarizer (RP) is employed to reorient the backlight's lost (absorbed) output, thereby matching the polarization of the display. In a backlight, light in the orientation of the display's polarizer will transmit 100% of the light. Light oriented 90 degrees opposed will be 100% blocked. All light in between these two orientations will pass at some level. A reflective polarizer reflects backwards any of the backlight light that is not in orientation. Reflected, the light is compensated or rotated slightly. With its new orientation, the light is brought forward again to go through the polarizer. If it is in the proper orientation, it will pass and if not, it will be compensated again (and again) until it is finally in the orientation of the rear polarizer. The use of a reflective polarizer, the display's brightness can increase by 45%.


All we got to do is to forget about the reflector and go after the reflective polarizer using mirror and quarter-wave retarder. We'd gain 45% of brightness. That IS a great increase.

[mountain_nz]

Its been very interesting reading over the past days looking into to the way everyone has been focused in the LCD way. Yes it does work to a degree but alas the old resolution and dollars equation makes it a bit costly and the fact to get good res you need large panel area which makes the unit a bit obtrusive.

My thought and findings was to go with an old TV chassis (10" DC/AC powered) remove the LOPT and the CRT etc. I have made three mirrored tubes (RGB) (hi grade stainless) and in one end fitted a bank of 60 10,000mcd leds with a focusing lens at the other end. In the middle of the Leds I have placed a Fibre optic cable this feeds the focused light to a prisum that combines the RGB into one light source that is feed by a mirror to two small servo mounted mirrors to give vertical and horizontal deflection.

The DC supply to the three light sources is modulated from the RGB output of the TV chassis via a 10 ohm resistor and a 1uF electro. This give the luminance information to the individual light sources.

The combined output go to a beam focusing lens from on old Slide projector. The out put is strong enough to be clearly visable during daylight.

I am an the moment building one using diode laser modules, this should be able to project the image upto 200m ( why I dunno, but a picture thats 60'x40' will be great a partys)

PS total cost for the LED version was a little over NZD$300 or USD$140.

[Atomos]

I am new to the forum and I would like to say thanks to all you guys for doing this. I don't really want to read the 1000+ posts on this forum so could everyone
here who has a working projector post the parts and configuration. I am eager to build mine but I want to make sure it works well. I don't have enough money to
experiment otherwise I would.
Thanks
-Atomos

[fender4]

mountain_nz,

Wow! Do you have a website or someway we could see some pics of your setup? I'm very interested, impressed, and confused . Is this similar to the DIY "Laser projector" project?


Thanks!
-f4

[mountain_nz]

fender4,

I am unsure of the DIY Laser projector project as I am still sifting through all the interesting chat in this site.

Can you give me directions were to find this laser project, no doubt I am not the only one to think along these lines.

I am not that greater fan of LCD projectors especaily the tri-LCD (RGB) type as it gets real hard to get the convergance right across the picture. Which equals picture clarity.

Were as the scanning LED/Laser is much simpilar as we are not re-inventing the wheel as such only the output medium.

No I am afraid I do not have pictures of my current working version-yet anyway.

Most of the LCD projects listed that I have read thus far suffer from the same main problem- how to pack enough LED's in a fixed area. My solution to this was to put 80 odd 8.5cd White LEDs perpandicular to the LCD axis then have a mirror on a 45 angle to reshape the beam into the LCD, this worked well and space was saved.

HINT-: stagger the packing of the LED's then you dont need to diffuse the light into the LCD, else you get bright and dim lines in the output image which is anoying to say the least.

PS you can fit a White LED assembly to an existing LCD projector you just need to rethink your number of LEDs per string and resistor values as well as add a suitable full wave rectifier ahead of the LED string. Becareful as the volts across the string can be upto 300v DC in some countries. The benifit though is have a light output comparable to the old buld but lasts 10,000hrs for only 12watts!!! consumption.

Cheers

People will keep every whos interested informed best I can