I recently read this interesting article
in Wired magazine about "Light-Graffiti Hackers". The Problem with light-graffities is that you need a power source to make them permanent, so you usually can't put them everywhere you like. So I thought about making a small solar powered Light-Graffiti Projector that can be mounted nearly everywhere. The problem is that it mustn't be very expensive in case it gets stolen, confiscated or whatever. First I thought about using a cheap laser pointer as a projector source, but you can't make these caps to display different symbol by yourself. They are called "Holographic Optical Elements" and they are very expensive in production if you only need one with your special image (tell me if you know how to make them by your own). So I decided to use a LED. I also noticed that solar panels are still very expensive, but then I found one of these solar powered garden lights for only 5 Euros and transformed it into a "Solar Powered Light-Graffiti Projector".
Step 1: This is what you need
One solar powered garden lamp for about 5 Euros. Found mine at the German electronics supply store "Conrad". One optic lens to focus the projected image. One ultra bright LED, the one in the garden light is usually to dim. I took a red one. Two small pipes of aluminium or plastics, each about 5 cm in length, that fit into another. The outer tube should have the same radius as the lens.
The image you want to project on the wall, printed on a transparency film. You should print it with a high resolution because the image is magnified.
Step 2: Disassemble garden lamp
First of all you have to remove everything except the top of the garden light which houses the solar panel and the LED. After this replace the LED with the brighter one.
Step 3: Add smaller tube
Now take some hot glue and mount the LED at one end of the smaller tube. On the other end you have to attach the transparency film.
Step 4: Mount bigger tube
Finally slide the bigger tube on the smaller one and attach the lens on the bigger tube with some glue. If you like you can attach a stand like a tripod, as I did. You also should put some hot glue on all holes to make your projector weatherproof.
Step 5: Final projector
Now you only need to find a place where you can put it. You should carefully choose a place with a lot of sunlight. The advantage of the used solar garden light is that it only lights up at night when the graffiti can be seen. I've tested mine on the balcony the last days but I have to say that the sun here in winter is too weak to give the energy for a whole night of projection. Perhaps I should wait till spring until I expose my projector to the street. So watch out, perhaps you will see one of these someday in Munich.