You can project as big or small as you like. For a bigger projection, move the projector away from the wall. Bare in mind that the further away you are, the fainter the image will be. Projecting onto shiny surfaces doesn't work so well, if you're not projecting too big then you can just stick a large piece of paper onto the wall and project onto that.
What you need (this isn't an exact science, you can swap bits out with whatever you have laying around:
20" length of 2x2
A magnifying glass (or camera lens, fresnel lens, magnifying sheet, anything that magnifies really)
A torch or bulb with minimal fittings
Sticky back velcro
The design might seem stupidly simple, and it is. But it didn't start there. It was originally more complex and I kept cutting back at it until it could literally be made by anyone with anything laying around the house.
The images on this intro show the finished project. It's projecting a hand drawn image of Mario.
Step 1: Test and measure
I tested with a macro camera lens, a canon 33mm DSLR lens and a magnifying glass, All worked perfectly fine. I also tested with a few different bulb types. I settled with a Philips spot light style bulb since it focuses the light in one direction.
Step 2: Prepare your base
I cut a piece of 2x2 wood that I had laying around. I purposely cut it longer than needs be incase I wanted to make some changes later on.
Step 4: Attach light source
(Note: Since this picture, I placed a block of wood under my light source to raise it to the same height as the magnifying glass)
Step 5: Measure maximum image size
Step 6: Create image holder
Step 7: Start projecting!
I'd like to add a spinning wheel so that multiple images can be projected, one after the over, create a basic animation effect.
Edit: Done! See Optional Step 8
I'd like to try replacing the magnifying glass with a Fresnel lens/magnifying sheet.
I'd like to see the quality of a printed image rather than hand drawn.
I'd like to spend more time testing colors. I tested yellow which came out pretty much okay. Light blue came out black.
The bulb I have is already quite effective at focusing the light in one direction but there's still a lot of rogue light. I could block this out by building an enclosure around the bulb and magnifying glass. However, this would produce a lot of heat inside the enclosure which would mean I'd need to factor in some kind of cooling. The bulb has a frosted exterior. If i was to get one without this frosting, I'd imagine it would produce a stronger projection.
Most likely my next step will be to swap from the light bulb to LED torch and build an enclosure around the torch and magnifying glass. This will prevent the shadow seen in the image and allow for a clearer projected image.
Step 8: Upgrades
Upgrade from single image holder to spinning disc
Start by cutting a circle out of a transparency sheet. The width only needs to be just over double the maximum height of your images. Although I made mine much larger, I'll probably scale it down.
If you make a larger disc like I did, you may need to cut two smaller circles from card paper to strengthen it.
Get a metal hanger and snip it to the correct height. You can work out the correct height by lining up one end with the bottom of your base (at the side) and the other to the top of your current image holder. Allow some extra length to bend the top to support the disc. See the pics if you're not sure.
Attach this new disc holder to the side of your base. I cut a short piece of hanger and bent it into a u-shape and then nailed it into the wood, holding it in place. Then used a glue gun over the top for extra measure.
Make a hole in the centre of your disc and slide it onto the holder. Make a hole in a bottle cap and slide that on after, this will add stability to the disc.
I've attached a video of the projector in use. My marker pen ran out of ink so I had to use face paints to write on the disc. The video doesn't really do it justice. It's much clearer and brighter when viewed in person. My webcam just isn't suited for this kind of recording.
If I happen across a small motor, I'd like to try attaching it in order to spin the disc automatically. I'd also like to print a disc of an animated character.