First, I should start by saying that I got this idea from Killa-X's comments and photos on Tanntraad's "Make an Ipod Video Projector" Instructable. What I really wanted to do was take out a functional LCD screen that was roughly "slide sized" and place it where the slide would have gone in a slide projector.
Imagine if you took that digital camera that you dropped and broke the lens but it still reads memory cards and does photo slide shows on its little screen. If you take the backlight off the LCD you can project light through it so if you could fit it inside a cheap slide projector, you'd have a wall-sized digital photo frame.
I already had a slide projector from my $6 lens Instructable but I didn't have a spare digital camera to sacrifice so I decided to do a "proof of concept" projector using the backlight of the ipod as the light source. Of course it was never going to be very bright but hopefully someone will take the idea and run with it.
Step 1: Basic Concepts
A slide projector has a light source (in this case a 12v 50w bulb) which is reflected and diffused to make as much of its light directed and evenly spread across the focal plane (slide or LCD to be projected). It's also necessary to separate the heat source (light bulb) from the focal plane because slides and LCDs can melt and burn.
I'd love to use all of this, but as I said in the introduction, I don't have a spare LCD to project so I'm using my "hand-me-up" Ipod Nano as my light source, reflector, diffuser & LCD. This simplifies the process significantly as I just need to place the Ipod in the focal plane and then do some tidying up. I think an Ipod with a larger screen and adjustable brightness (or hacked super-brightness) would be even better.
If you are old enough to remember using a slide projector, you put the slides in upside-down and back-to-front for them to be projected right side up and front-to-front.
Luckily the Ipod easily fits upside-down but the back-to-front proved impossible. You'll see later that it's pretty obvious the projected images are reversed.
Step 2: Tidying Up
I made a slot so the Ipod slides into the focal plane. Measure, Mark, Cut is a favourite sequence of mine. I then taped some black card stock to the underside of the lid to get rid of some funny reflections that were being projected and to steady the Ipod.
If you do use the projector's light source, don't cover any of the vents. You will need all of them to be open to keep the heat from building up.
Step 3: Testing
So I set it up to project the Ipod image (39mm diagonally) to roughly the size of a DVD case (230mm diagonally). It turned out that the distance from the focal plane to the screen was 670mm (around 2 feet 2 inches). Any bigger and it was too dim to focus. Hopefully this might help you in your image size & distance calculations.
Hopefully I'll find a suitable donor camera or MP4 player and actually use the projector's light source.
AshishP40 made it!