Instructables

Step 1: The Principle

 
The principle is very simple. There is a powerful light that is projected through an LCD into a lens so the image is projected.

Some things you want to take into consideration:

 -The better the quality on the LCD, the better the projected image. (I'm using a LCD with 640X480 pixels)

  -The LCD can't take more than 40C, so if you decide to use some other type of light source, pay good attention to the cooling system.

 -Without a good fresnel lens will be really difficult to light the LCD evenly. (I'm using the always faithful fresnel lens from an old OHP)

 -The fresnel from the OHP is really a twin fresnel, the one that faces the light is expanding the light to the full area of the lens, the other one is focusing all the light to one point. If you keep the two of them together (like this projector) it will be a lot easier and less danger of damaging or scratching them. Any big scratch will be reflected in the projected image. The down bit is that you won't be able to do keystoning adjustment. So the projector will have to be placed in a perpendicular position with the screen.

  -The use of mirrors allows you to make the box smaller as if there are no mirrors, you will have to place the LED farther from the fresnel lens, and also the LCD from the main lens.

  -You need to have everything inside some sort of enclosure, or the light will be coming out and it will light the room making the projector a lot less efficient. 

 
 
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Azurial4 years ago
great work you got here Im using an old OHP monitor and LED assembly in my projector project. with that said, what would i need to do to get the image to display properly? any hints would be great! Thanks in advance!
Hi Newtonn, been following your work closely. I'm currently in the middle of my first projector build. You mention here about "Keystoning". How would this be possible? I don't quite understand from what you've written how you would impliment this into the projector. I have 2 fresnel lens from ohp projectors, and can seperate them easily enough, how would i use them to produce keystoning effects?
newtonn2 (author)  bennygorilla4 years ago

In my other projector the one I made with OHP part, you could see what I mean.   have a look at this pictures....

FODCNUBFRXWGXGB.jpg (1600×1200)

F2P3ZDKFRXWGXGD.jpg (1600×1200)

F9YJYWJFRXWGXGC.jpg (1600×1200)

You need the front lens to do what mine is doing in that picture.

I hope that helps.







































































































































Hi Newtonn thanks for that. It's really helped.

I have another problem, and i haven't been able to find the solution. I hope you will be able to help. I'll try to describe as best I can:

I have my light ( nice and Bright) fitted with condenser Lens. which is this shape: •|)   ...the dot is the light and the line and bracket is the shape of the lens...is that correct arrangement/type?
 
I also have a fresnel lens from an OHP and i've cut it to the size for the screen I have. I think this is where the problem is, my screen is 4.5" diagonal( or 100mm x 55.4mm) and the lens I got from the projector has a diameter at the beginning of 70mm with a focal length on 50mm I know the screen that used to be in the projector was only 1".

So basically my question is, how do i work the placement of all the components?

Does it matter how far the Fresnel lens and are from the LED/Lens array?

When I try to use the fresnel to focus it can focus on the LED perfectly, it appears perfectly sharp at about 1.5 meters away, enlarged about 16X or maybe more.
Where am I going wrong, It's driving me crazy!!

Thanks in advance for any advice anyone can give.

newtonn2 (author)  bennygorilla4 years ago

 I have my light ( nice and Bright) fitted with condenser Lens. which is this shape: •|)   ...the dot is the light and the line and bracket is the shape of the lens...is that correct arrangement/type?

-YES THAT IS THE CORRECT SETTING.
 
I also have a fresnel lens from an OHP and i've cut it to the size for the screen I have. I think this is where the problem is, my screen is 4.5" diagonal( or 100mm x 55.4mm) and the lens I got from the projector has a diameter at the beginning of 70mm with a focal length on 50mm I know the screen that used to be in the projector was only 1".

i DON'T UNDERSTAND EVERYTHING, BUT THE FRESNEL NEED TO BE A BIT BIGGER THAN THE SCREEN. IT NEED TO COVER THE FULL SCREEN. YOU NEED TO PLACE IT NEAR THE LCD ABOUT 2CN MORE OR LESS. IF YOU ARE TRYING TO USE A PROJECTOR LENS THAT WAS IN A PROJECTOR WITH ONLY 1" SCREEN, I'M AFRAID THAT WILL NOT BE POSSIBLE.  DO YOU HAVE THE OHP LENS? YOU COULD USE THAT ONE NOT PROBLEM.

Does it matter how far the Fresnel lens and are from the LED/Lens array?

THE FRESNEL NEED TO BE IN AT THE RIGHT DISTANCE SO IT WILL GET GOOD EVENLY LIGHT. 

If you send me some pictures I may be able to help a bit more. I hope you get the problems solve soon. 
h9831 newtonn24 years ago
What is the total cost of your LED projector ? thanks,
newtonn2 (author) 4 years ago
 
If your screen is bigger than 2" you can't use that lens couse it'll only focus on the side of a slide.  But maybe you can use the condenser lens that is on the second picture.
samr37l4 years ago
If I have a old projector, could I use the lenses from it?
Sam R.
P.S. I think it is 3.5mm, but I'm not sure 
newtonn2 (author)  samr37l4 years ago
 Is it an LCD projector? Could you send me a picture?
ok, here is my projector. the first picture is the projector, and the secound is of the inside where all the lenses are.Tell me if you need any more pics.
Thanks,
Sam R.
P.S. The lens in the front say triplet lens. 
samr37l samr37l4 years ago
here are the pics.
Sam R. 
IMG_1389.JPGIMG_1390.JPG