Project, preliminary

Keegan and I are working on a new project. It should look something like this. We have the electrical stuff worked out, but may need some assistance with the mechanical aspects. The basic idea is to make a conveyor belt of phosphorescent fabric, then write things on it using a bar of ultraviolet LEDs.



  1. Something like this?

  2. I see.

    we seem to be having trouble forming truly novel projects. any suggestions ?

    .. I have a UV laser in my hand right now and everything. maybe we'll still build it.

  3. * we were just scheming about building the laser-phosphor display for drop day only a moment ago.

  4. ok, well this scrolling drum idea can be re-purposed to do a paint-roller style UV source for painting on phosphorescent walls.

  5. I've done a little work with conveyor belts. I think rollers made out of metal pipe should work, but you'll need bushings or bearings in the frame, and some kind of tensioning device. Shouldn't be hard, since there's not any real load. Check <> for parts.

    Here's another idea. Robots that lay and follow glowing trails on a UV sensitive surface according to various rules, exhibiting emergent swarm behavior.

  6. yeah I'm not sure we're mechanically inclined enough to manage even that; we'll see.

    also robots : way cooler, but also... robots. I can't build robots.

  7. Don't give up just cause someone else did it. Also, consider electric typewriters. The roller and motor are already in place in the frame. Wait...just got an idea, UV LED typewriter. Not sure of fun implications at the moment, but some are bound to arise in the next hour. Also, the write head would be a bitch to build. Has anyone ever built a turing machine for party purposes?

  8. Here's the easiest way to build such a device.

    Rip the rotating mirror/motor assembly out of a laser printer, and replace the printer's laser with the UV laser. Rip the laser apart to find out how to modulate the laser beam output.

    Put the assembly on a platform that can tilt (and has an optical encoder for measuring tilt) if you want to project on a non-moving surface like a wall.

    The only issue is that you don't know the horizontal angle of your reflected beam. You could:

    a. Use an rotary encoder to find out the angle of the rotating mirror. If the rotating mirror is spinning fast, that's gonna be a huge pain.

    b. Figure out when the mirror is at a certain position, which can be done by:

    b1. Using an optointerrupter that's blocked by a metal tab attached to the mirror. That'll probably make the mirror spin off-balance.

    b2. Use a photodiode with collimator to find out when the reflected beam is at a certain position. Send a synchronization pulse when you expect to start a new horizontal line, and use a phaselock loop to control your drive motor frequency/voltage to keep the synchronization pulse on the photodiode.

    If a good enough collimator can't be built, just have two adjacent photodiodes, and compare the phase difference of the received synchro pulse across the diodes, and lock the middle of the synchro pulse to be in the middle of the diodes. This is more elegant as it does not depend on collimation of the beam, only on the assumption that the photodiodes don't saturate (so the photodiode output is just the convolution of a Gaussian-like thingy (representing the optical response of the package to off-angle beams) with the beam profile).

    It's all very easy. You can PWM the laser diode to control amplitude of the phosphor, and to prevent saturation, so you can get good spatial resolution in the image.

    Also, all of this imagines that you scan each line very quickly. If your phosphor can last longer, you don't need to scan so fast, and then you can use electromechanical means to detect the mirror position, viz. a switch.

  9. ack. all very easy ? We've got the control hardware for discrete UV LEDs worked out already. No moving parts, no sensing mirror orientation, just a bit too much soldering.

    Now we have both a huge pile of UV LEDs and one UV laser, I think we can try both designs.

    Thinks with moving parts are definitely not my forte, so I would shy away from trying to build a laser projector.

  10. That "Fade Out" work is quite neat and technically similar to what we're doing, but quite different in the visual result. So I'm not worried about being unoriginal.