I have an ARTOGRAPH Light Pad with which I can sketch a design with guide lines, then trace over it for the final drawing. But this doesn't work with colored paper, which I also like to draw on. With a bit of research I found that an episcopic projector would project a sketch onto the drawing paper instead of through it from underneath, but they seem big and expensive.
So I decided to see if I could use my iPhone or iPad. Not by attaching a projector, but directly with some sort of lens arrangement. Turns out that yes this can be done, a fresnel lens will focus the output light from an iPhone into a projector-like image.
The projector attaches to an Ikea desk lamp, with the light bit removed. Easy to move up and down while keeping the projector parallel to the table, and this particular desk lamp has a nice heavy base so won't overbalance.
The phone is held in place with a couple of rubber bands - when I sketched The Plan there was going to be an iPhone case glued under the wood, but I realised that rubber bands would work just as well and be easier to adjust. The metal things on the upper frame are cable glands, which have a nut with a plastic liner so the rods can slide up and down when loose, but are locked in place when tightened.
The bottom half is a sandwich of two layers of plywood with round cutouts and a middle layer of heavy card with a cutout for the square plastic Fresnel lens. I wanted to be able to take the lens out again if it didn't work, so the upper layer of plywood is held in place by two rubber grommets rather than being glued down.
Here is the phone actually projecting some text onto the black paper. I'm pleased that this thing does actually work, but as you can see the projected image is rather faint. As expected, since this is a phone after all, not a flashlight. This photo is a bit misleading since I had to use some flash to get an image at all. In a dark room it is clearer than it looks here and fairly easy to trace over.
It was an interesting and educational project, but I may end up just buying an actual mini projector for my phone.
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