simple LCD projector for still images?

I've read the "Beginners Must Know" thread and searched thru the threads.... now i'd like to ask a lil n hope to hear from u guys gurus!

I have an old ohp with singlet lens and fresnel (ya, fray-nel en francais!), it's not usable for me since i'm in 240V world while it's a 110V (bought from ebay sometime ago...). Then, i oso have a Proxima Ovation 840 (7" lcd?) with 640x480 colour. I need u guys' help/guide to transform these "rubbish" into something i think it's possible to achieve.....

What i want is actually an "OHP" projector (projects still images like transparency slides in schoollll....). It needs to be "as bright as possible" (abap..) BUTTT color n slight image distortions ARE NOT the problem for me. As long as the image projected can be seen in a decent lighted indoor, it's consider a SUCCESS already. Of course, there's shudnt have problem with excessive heat that will melt my "plastic" fresnel lens or it's top cover....... My purpose is to have something similar to both OHP and SLIDEPROJECTOR which can project color images BUT with additional function which the "image" is changeable. Forgot to say, the image source is from a CCTV camera that input analog video signal into my LCD projection panel...... Then, wherever the camera is pointing, the image gets shown in the proj panel and thus projected by the "bright ohp setup"!

Big metal halide, HQI, HMI??? Ballast??? Reflector? Condensor? Focal distance??
What i've gathered here are only: fresnel lens of 210mm focal length (from the ohp), projection panel of 640x480 resolution 8.5" (proxima ovation 842) and singlet lens (from ohp)....

wat is the possibility result i could get from these + additional/replacements from perhaps what kind of lamp/ballast suits best for my case? ywh has a great lamp from what i've read here, something like 250W HQI. Is it the one to go with?

i wish i could swallow all the info here, but i think i'm abit slow n the info here is too overwhelming. So i hope can be guided by u guys here.......
junk => working projector

It sounds like all you really need to do is to convert your OHP to 240 VAC. You could do that VERY cheap: One way to do it is to get a 240 to 120 VAC transformer that can supply enough current to run the OHP.

Another way is to to replace the OHP parts with 240 VAC parts: Remove the lamp and fan, and mount a similar size 240 VAC halogen lamp exactly where the original lamp was. If you can find a 240 VAC OHP lamp, then that would be ideal, but almost any 240 VAC halogen lamp with a short filament will do. (Look for a lamp of at least 250 Watts.) You need to find a socket that fits the new lamp and wire it directly to the lamp power circuit. (If there was a transformer or voltage dropping diode, then those can be removed.)

Then you need to install a 240 VAC fan in place of the original fan. If you can't find one small enough, that's okay: Mount your new fan outside the box and build a duct, so the airflow goes where the old fan sent it. Wire the new fan directly to the fan power circuit.

Voila: A 240 VAC OHP ready for your projection panel.

You could spend more money (and have a cooler projector) by using a MH lamp and ballast kit, but those would cost you at least $100 US. The halogen lamp should cost you less than $10 US.

Please don't electrocute yourself! If you are not familiar with wiring power circuits, find an electrician to do it for you.

so, if not mistaken, Halogen is the "optimum" choice for my case since MH is intended for high resolution, precised color and sharp images. Thus, for such "still images" like i want, will barely need a high wattage small halogen such as a 250W or more will do...... erm, i'll try to get the highest wattage like 360 or even 600 locally here if possible (maybe osram, philips etc...)!

from the original circuit, it has a full-bridge of diode like u said, i think it's convert a 110VAC to something like 110/1.4142=78VDC to power the original halogen lamp that is rated 82V 360W..... so, it will all become useless for me since i'm going to operate it and transplant new organs like u said. btw, the reflector is attached to the lamp, which the 2 comes in together as 1 part. so, probably i will need to do some sugery again with my B&D RTX (sth like Dremel) to fit in the new lamp.......

however, do u think it's possible to use a soup ladle as reflector if i'm getting a new lamp??? what should i look for when choosing such a soup ladle?

Just remember that a properly setup metal hallide of the same wattage as the halogen you will be using will be much brighter, and have a much whiter light. You said you wanted to project in daylight right? maybe a silver screen or some sort of other high gain screen is in order, and depending on the size, your projection may become dull or even invisible with lots of lights on, thus its best to go with metal hallide if you can afford it.



2005-03-14 12:47 am
In my opinion, if you're trying to get a still image worth looking at, it's no less work or expense than just making a projector capable of video. In fact, I don't know HOW to make a projector that's only good for still images, unless you have an EXTREMELY slow response LCD.
still frame projector

Right: To make it a still frame projector, you would have to add a frame buffer between the camera and LCD. You could do that with a VCR, a DVD recorder, or a computer with a video capture card. So "still" is much harder and more expensive!

(But I think you just wanted to show the continuous camera image on the projector. That would just take a composite video connection between the video camera and the OHP panel.)

MH is almost always better for projection than halogen, but it requires a lot more money for the lamp & ballast kit. The one case MH is not better, is when you need a projector than can turn on instantly, shut off, and then turn on again less than 10 minutes later. MH lamps can't do that: They take a few minutes to warm up, and they don't restart without a complete cooldown.

MH is better for continuous projection because it makes more light and less heat than the same wattage halogen lamp. I suggested halogen because it would be very cheap & easy to retrofit into your OHP. But if you need a really bright image (without frying your LCD panel), then you need a 400 or 575 Watt MH setup.

Soup ladles are okay, as long as you have some cooling air flowing around the lamp. Look for a really shiny one with a perfect half-sphere shape. It has to be large enough to fit your lamp arc (or filament) to sit right at the center of the sphere. You will probably need to cut out some metal to fit your lamp in there. It you use a 575 Watt MH, then a soup ladle will probably be too small. Look for a mirror-finished half-sphere mixing bowl.
u guys have been really helpful for a lost kid like me...

anyway, i'm in the process of getting a 250W UHP (near to point source lamp).... and perhaps a triplet with 310mm FL....

then, as for the reflector, i'll try to get a friend who's working in a precision machining factory to CNC lathe out a ellipsoidal reflector that will fit my lamp, out of a aluminium billet cylinder. might ask for "heatsink" like fins for the outer surface of the reflector. HOWEVER, i'm not very sure of the distance of the 2 foci & the size (perimeter) of the ellipse i really need..... any1 could give a hand on this???? i will draft out the CAD drawing for the lathe profile for my friend to do 1 for me......

Thanks again!

ps: as Guy said, i'll use a camera to input signal for the LCD panel... so i'll have an image (still but infact MOVING IMAGES...) depends on what i point my camera to...... kinda like an Opaque projector, so that i could trace the line of the object being pointer onto the surface i project.... maybe a wall..... it's to copy the shape in exact proportion..... hope this doesnt confuse u guys...
elliptical reflector

Here is a drawing of what you need. You can figure it all out with a full scale drawing, two pushpins, and a piece of string!

Start by drawing the full size of the condensor fresnel diagonal (vertical line on right side of drawing). The goal is to fill that fresnel with light that comes from a point source that is located the focal distance away. So draw the F2 point of the ellipse exactly 220 mm away from the middle of the fresnel for a 220 mm fl fresnel, 330 mm away for a 330 mm fl fresnel, etc. If the light comes from that point, then the fresnel will give you parallel rays out the other side.

Project lines from the edges of the fresnel through the F2 point and out several more inches. Your reflector has to be wide enough to supply light along these lines. If you know the diameter of the billet cylinder, then you can add that to the drawing to show where the edges of that diameter reflector intersect the projected lines. (Otherwise, pick a reflector width and draw it in.)

Then put a push pin at F2 and the other pin at a trial F1 point. Tie the loop of string so it just fits between F1, F2, and one of the reflector edge intersection points. Use the loop of string to guide a pencil through the arc of the ellipse from one edge intersection point to the other.

Don't like it? Not deep enough to capture much light? Not enough room for the lamp? That's why I said to use a pencil! Adjust the loop size, move the F1 pin, and try again. It's easy, quick, and it gives you a feel for how different size and shape ellipses will work.


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