A Laser Effect Projector Built with Safety in Mind

There’s just something about wielding a laser pointer on a dark, foggy night. Watching the beam cut through the mist is fun – makes you feel a little Jedi-esque. If you can’t get enough of lasers and mist, you might want to check out this DIY “laser sky” effect projector.

The laser sky effect will probably remind you of other sci-fi movies – think of the “egg scene” from Alien. The effect is achieved by sweeping a laser beam in a plane through swirling smoke or mist. The laser highlights a cross section of the otherwise hidden air currents and makes for some trippy displays. The working principle of [Chris Guichet]’s projector is simplicity itself – an octagonal mirror spun by an old brushless fan motor and a laser pointer. But after a quick proof of concept build, he added the extras that took this from prototype to product. The little laser pointer was replaced with a 200mW laser module, the hexagonal mirror mount and case were 3D printed, and the mirrors were painstakingly aligned so the laser sweeps out a plane. An Arduino was added to control the motor and provide safety interlocks to make sure the laser fires only when the mirror is up to speed. The effect of the deep ruby red laser cutting through smoke is mesmerizing.

If laser sky is a little too one-dimensional for you, expand into two dimensions with this vector laser projector, and if monochrome isn’t your thing try an RGB vector projector.

28 thoughts on “A Laser Effect Projector Built with Safety in Mind

  1. Or just use a freq to voltage chip, a comparator, and a transistor.

    And a note, only DPSS lasers like found in green pointers can emit unwanted IR. Red and most blues/violets will not.

    1. precision, lenses have diffraction and reflection where mirrors for most practical purposes are only reflective, this means it is easier and cheaper to do with mirrors, on the grand scale mirrors are also more effective at how much light is transmitted, this is also why you see huge mirrors on telescopes (besides the obvious mechanical issues with suspending tens if not hundreds of tons of glass and swinging it around the sky)

    2. You can, most line generator now use diffractive optics. Though it is harder to get as wide of a spread and keeping the intensity of the light consistent though the length of the line requires more specialized optics.

      Coherent makes laser line generators that have a non-gaussian beam power spread.

    3. here, I don’t really see any problem with this, those lenses cost like $2 or $5 max and the effects are beautiful. While I can imagine that the light distribution is not too even, but for this liquid sky effect it doesn’t matter. I still think the rotating mirrors are an overkill.

    4. I honestly goofed up. I didn’t do any googling before making it and after I posted the vid I saw that it’s super easy to do with a lens. One benefit of the spinning mirror is that you can strobe the light in conjunction with the sweeping to do various animations.

    5. None, it is a beautiful but pointless build when you can just spread the laser beam with a cylindrical piece of polished metal, however if he took it one step further and modulated the laser, or even added a second mirror wheel then he has something way more advanced.

    1. Actually, those assemblies have::
      – A rotating assembly with precision, first surface mirrors
      – A brushless dc motor to drive the mirror
      – A phase locked looo to rotate the mirror in precise synchronization wirh a digital pulse.

      So, to rotate the mirror at a super-precise speed, you just provide a square wave at the right pin. Power( (usually 12 volts) and some digital signals for enable and braking and you are good to go.

      The brushless motors are astonishingly good..

      Basically, this project is a lesser version of what you can scavenge from any laser printer or fax machine. There are literally millions of these out there waiting to be put to use.

  2. A good source of first surface mirrors are found in flat bed scanners and fax machines. A compass and you can divide a circle into six segments. Try grinding a cylindrical lense. The ones in B&D levels aren’t to good.

  3. I see a potential problem with his safety arduino code. If the motor stops at exactly the wrong position where the interrupting tab is on the position sensor then it will detect the mirror assembly as constantly rotating and never shut off the laser since the logic execution is binary and doesn’t keep track of any sensor state change to rule out this case. Sure it’s a relatively small chance of happening but if you are going to do something it’s best to go all the way. An easy fix would be to use an enable flag that is only set by a state change and cleared in a reasonable timeout on the input so that way if the sensor value doesn’t change then the flag disables the laser. That or better yet use a watchdog timer for better reliability.

    1. Videomaker here. The way I wrote the code, the arduino is constantly estimating the period of the previous rotation (I used period instead of velocity to avoid having to divide anything). If the mirror stops anywhere, the previous period estimate starts to climb until it crosses a threshold and everything turns off. So it should be tolerant to stopping in any positon. I tested it lots of times, although I didn’t check to make sure that I stopped it in the occluded and unoccluded positions (good point).

    2. Good consideration, however the code I wrote is constantly estimating the period of the previous rotation. If the mirror stops anywhere then the period estimate starts climbing and quickly crosses the safe mode threshold. I tested it lots of times, but now that I think about it I didn’t check to make sure that I successfully tested it in both the occluded and unoccluded positions.

  4. Why did you choose to not use the laser light to measure rotation of the mirror disk ?
    the optical switch is educational, but the build can be simpler.

    and another Q : didn’t you need to mechanically balance the mirror wheel ? it seems quite a weight to spin so fast.

    1. Hey I considered that! I decided not to go with it because I wanted to make sure the mirror was spinning correctly before turning on the laser. If you use the laser light then you can only measure speed while the mirror is on.

      I didn’t do any mechanical balancing. I just trusted in the consistency of the mass of the mirrors. I guess I should have weighed them. The one consideration I made for balancing was to get the diameter of the pocket for the fan as small as possible, so that the fan axis would be as concentric as possible with the wheel axis.

    1. I think that could probably work. One thing I’d be worried about is after the light passes through the slit it wouldn’t make a flat plane, but a wedge that would get thicker and thicker. But ya I could see it working.

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