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Hoverlay II

open hardware interactive midair screen

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This project was created on 02/26/2014 and last updated a day ago.

Hoverlay II is a low-cost, interactive, modular, open source vapor screen. It allows projection of images, videos and games right into midair and comes with it's own selection of interactive applications.

Short explained, the device creates a thin, stable film of vaporized water, continuously travelling upwards in midair, which then acts as a floating rear projection canvas.

It works great with Microsoft Kinect and we've also successfully tested it as a telepresence display device using Skype.

See the video:

Even though one Hoverlay II unit is still quite handy (326 mm wide), up to 5 units can be plugged together to form a badass big 1630 mm wide, floating screen of >1 m height. Bigger screens are possible by choosing more high-end components.

Hoverlay II is open hardware licensed under GPL V3.


Vaporization is done by cheap off-the-shelf ultrasonic atomizers (see picture below), air is moved by an array of strong and silent pc case fans, laminar flow is formed by 3D printed flow formers. Rear projection works with any kind of video or still image (even dia-) projector.

The housing

The housing is CNC-milled out of black PVC hard foam plates ("Palight", not to be mixed up with PVC soft foam plates) but can be made from pretty much any waterproof material that can be glued or welded, i.e. acrylic.

If you choose Palight, you can theoretically build this just with a paper template, patience, a steel ruler, some drill bits and a box cutter. All the DXF files for milling, lasercutting or box cutter samurai are available in the GitHub repo. Never put PVC in a laser cutter though (super carcinogenic). The BOM list in the repo (and also the filename) tells you, how often you need to mill or cut a certain file.

Operating principle

The diagram below shows an axial cross section of a Hoverlay II module, it's probably self explaining:

As you can see, there are three channels. The fans suck in air into the left and right channel, which then travels upwards while beeing compressed and accelerated by the convergent channel walls. The air then is pushed through the 3D printed flow formers, which is just many, many small, parallel channels packed into a honeycomb grid. When the air flow exits the flow formers, its mostly laminar, meaning it contains almost no turbulence anymore (such as rotary turbulence from the fans) and can continue travelling upwards almost turbulence-free for quite some distance (> 1 m).

The two fast laminar air flows from the left and right air channel then carry off the fog from the center fog channel, an effect that is known as "Venturi Effect", both accelerating the fog upwards and shaping it into a thin film layer right between them, as you can see in the picture below.

This thin layer of fog has the ability to diffuse incoming directional light (such as light from a projector), which then can be perceived as if it was diffusely emitted by the fog layer itself.

A perforated pressure compensation tube was meant to help delivering fresh air into the fog channel and lifting out the fog homogeneously. A few words about this tube: It's just a perforated (manually, on a drill press) ø 25 mm PVC tube, cut to length of one Hoverlay II module (326mm) that slides in though the corresponding cutouts in the side panels. The pressure compensation tube can be dismissed (the cutouts still have to stay there!) when only using one or two Hoverlay II modules in series. It was meant to help homogenizing the fog density over the full width of larger (3+ modules) installations. However, we found a way better method for that, by using some sort of "brightness booster" in form of two additional fans, blowing air into the pressure compensation holes on both ends of the Hoverlay II array. This both helps homogenizing the fog density over larger screens as well as visibly increasing the fog density (thus brightness). Here you can see the brightness booster in action, it's a true enhancements over all previously posted videos:

I will soon release a nice and tidy, 3D printable "brightness booster" that can be snap-fitted onto the existing pressure compensation tube holes for easy installation. Until then, just ignore the pressure compensation in the BOM, because it just turned out to be a intimidatingly dull solution to the homogeneity problem on larger screens.


A Microsoft Kinect is sitting right on top of the projector, requiring minimal calibration and mapping. It turns out that the fog layer does not disturb the pattern recognition of the Kinect at all, so it works just fine.

Some more technical details

I spent a lot of time on optimizing the printing process of the flow formers and tested different geometries. For achieving the lowest possible density, they consist of fragile, single-wall,...

Read more »

  • 1 × AC power supply 24V AC 350W (for up to 5 Hoverlay units)
  • 8 × pc case fans 12V DC, approx. 40 CFM each
  • 1 × PVC hardfoam plates good material for building enclosures, easy to cut, easy to glue
  • 4 × ultrasonic atomizer 24V AC, approx. 14W each
  • 1 × DC power supply 12V DC 500W (for up to 5 Hoverlay units)
  • 12 × female power connectors 3,5 mm gold plated rc power connectors female
  • 6 × male power connectors 3,5 mm gold plated rc power connectors male
  • 1 × tons of screws size depends on your build
  • 1 × plastics glue
  • 1 × double sided adhesive tape

See all components

Project logs
  • "Feuertanz" & "Streiflicht"

    3 days ago • 0 comments

    I've had the luck to get the two truly amazing animation artists and fellow students of mine, David-Kim Hermsdorf and Philipp Kessling, to create this wonderful animation double "Feuertanz" and "Streiflicht" for the Hoverlay II.

    Thank you guys, you did a fantastic job there. I (and probably everybody else close by the live installation) immediately got goose pimples experiencing a deep visual stimulation accompanied by deep frequency quakes.

    To you, who are watching this on your regular, flat, non-hovering screen with laptop speakers, the experience might not be the same, but I hope it gives you an impression of what's happening there ;)

    Short fragments of the footage have also been showed in the Brightness Booster Demo video, I just wanted to get the official permittance to show off the whole thing on Youtube directly from the artists befor upping it completely. I hope you enjoy watching it!

  • Photos & Brightness Booster Enabled

    4 days ago • 0 comments

    Lots of cool stuff happened recently at the makerspace. For the first, one of our members volunteered to take professional photographs of the Hoverlay II and its internals. After one afternoon of incredibly focussed work on illumination and setup he gave me an USB stick packed with high resolution, high aesthetic quality shots, so I can take that material now and put it into the construction manual, make a nice web page from it and tease you with pictures like the ones below. Thanks, C.!

    Here's an impression of that incredible quality of pictures. Mind that these are photographs, not CGI renders.

    Also, one of the members of our local makerspace, Dirk, added some modifications to the Hoverlay which resulted in a much higher brighness of the Hoverlay screen. Check it out in the video:

    Basically, the modification makes use of the inlets formerly used for the pressure compensation tubes, feeding more air through them into the fog channel with two additional fans. This video shows the first result of this brighntess booster with the same 3000 ANSI lumen projector from the last videos.

  • System Design Document, Credits and Licensing

    6 days ago • 0 comments

    In order to get a proper System Design Document out I also had to sum up all the used libraries including their license information, open source software and what-so-open-ever else to pay appropriate appreciation to all those great projects out there. Reading this makes me feel like I actually did totally nothing in this project.


    Credits and Licensing

    The Hoverlay II hardware, CAD, and all application code is licensed under GPL V3

    This project would not have been possible without open source hard- and software. Special thanks the following open source projects, that have been used in making and/or are part of Hoverlay II:

    Hardware Design:

    - OpenScad (GPL V2)

    - Processing (GPL V2, LGPL, GPL)


    - RepRap Project (GPL)

    - Repetier (Apache License V2)

    - Slic3r (Perl Artistic License & AGPLv3)

    - LinuxCNC (GNU GPL)

    Application Development:

    - Processing (GPL V2, LGPL, GPL)

    - KinectA (GPL V3)

    - OpenNI (Apache License V2)

    - MSAFluid Processing library (MIT License)

    - oscP5 Processing library (GNU LGPL V2.1)

    - Minim Processing library (GNU LGPL)

    - saitoobjloader Processing library (MIT License)

    - Arduino (Creative Commons ShareAlike)

    Also thanks to Christian Knüll for his efforts in making an affordable CAM tool

    available. Check it out at (not open source!)

    All layouts have been made with Adobe Illustrator (also not open source!).

    Of course the used Microsoft Kinect is not open hardware. If you want to learn more about how the Microsoft Kinect is licensed, read the manual from page 14 here:

    And last but not least, without the support of my local makerspace "Attraktor", not a single prototype would have been realized. If you live in or nearby Hamburg, Germany, you should definitely give us a visit sometime!

View all 6 project logs

Build instructions
  • 1

    Get the BOM list from the project page:

  • 2

    Download the CAD files for the parts from the GitHub repository:

  • 3

    add the atomizers to the vat, prepare wiring

See all instructions


Jasmine wrote 15 days ago null point

Hello iamnotachoice, this looks really impressive. We'd love it if you could add a few more details to your project to give it the best chance of going through to the next round of The Hackaday Prize.

By August 20th you must have the following:
- A video. You've got several, so pick the one (or make a new one) which best describes your project. It should be less than 2 minutes long. Put it on YouTube (or Youku), and make it the only video in the 'External Links' section on your project page.
- At least 4 Project Logs
- A system design document
- Links to code repositories, and remember to mention any licenses or permissions needed for your project. For example, if you are using software libraries you need to document that information.

You should also try to highlight how your project is 'Connected' and 'Open' in the details and video.

There are a couple of tutorial video's with more info here:

Good luck!

Are you sure? [yes] / [no]

iamnotachoice wrote 15 days ago null point

Thanks for the instructions, a better video and the other stuffs are on the way :)

Are you sure? [yes] / [no]

Jared Sanson wrote 17 days ago null point

Wow pretty cool!
Do you have problems with things getting damp in your room after running it for a while? I would assume spraying water mist into the air can't be that great for computers in the room!

Are you sure? [yes] / [no]

iamnotachoice wrote 17 days ago null point

Thanks! This is dry fog, so your hand does not get wet when you touch it. However, it does increase overall humidity in a (fully closed) room with about 250 ml per hour. That seems to be less than if you'd fill the room with transpirating programmers. So far no computers near it have failed, even after 20 hours of continuous operation.

Are you sure? [yes] / [no]

Gabriel wrote a month ago null point

Does the air speed have influence on image quality?

Are you sure? [yes] / [no]

iamnotachoice wrote a month ago null point

I tested different flow rates by pwm'ing the fans down, finding out that a high flow rate of air results in a better image. Though, increasing the flow rate means decreasing the fog density (thus perceived brighness of the image) and needs to be compensated by adding more foggers (increasing fog density again).

Are you sure? [yes] / [no]

Rocket501 wrote a month ago null point

Awesome project! I am interested in making this. How much does it cost? Do you recommend any of the ultrasonic atomizers?

Are you sure? [yes] / [no]

iamnotachoice wrote a month ago null point

Thanks! My recommendation would be: use the strongest and most rugged foggers you can find or afford for this application. I honestly cannot recommend the ones I used, still looking for better ones. Will be glad to see another build, feel free to contact me if something's unclear.

Are you sure? [yes] / [no]

Adam Fabio wrote a month ago null point

Hoverlay is looking better and better every time I see it! Thanks for submitting it to The Hackaday Prize! Your superstring video is just incredible! Don't forget to keep the updates rolling in for the contest - you might just find out how well hoverlay works in space!

Are you sure? [yes] / [no]

iamnotachoice wrote a month ago null point

Thanks a lot! Be assured I keep you guys updated!

Are you sure? [yes] / [no]

anfractuosity wrote 3 months ago null point

Very cool! I'm curious if you could use multiple projectors somehow to get 3D?

Are you sure? [yes] / [no]

iamnotachoice wrote 3 months ago null point

There is a nice effect you can get with this by shooting onto the screen with two projectors from back and front. That setup could at least show you an object from --- wait for it :) -- back and front. I also tested shooting in there with two projectors from slightly different angles. That however does not yield good R/L channel separation for the spectator (actually you wouldn't call that "channel separation" anymore), the fog is just too diffusing. Using a regular 3D projector with active shutter glasses gives good results though.

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Mike Szczys wrote 5 months ago null point

Early prototype is fantastic! Can the ultrasonic atomizers be used continuously for long periods of time?

Are you sure? [yes] / [no]

iamnotachoice wrote 3 months ago null point

Depends on your definition of "long periods of time". It works for many hours (gets warm though). The membrane wears out due to mechanical stress and scale sooner or later, but can be replaced in most foggers.

Are you sure? [yes] / [no]

akohlsmith wrote 6 months ago null point

Trèz cool. Is the top of the laminar flow distorting due to the ambient air not being still? I don't know enough about laminar flow to know the limitations.

Are you sure? [yes] / [no]

iamnotachoice wrote 6 months ago null point

Thanks! The quality of the fog wall is best in still air. Though the laminar flow is quite robust against slight ambient air streams, it's steadiness will decrease a little, but it still works good enough for getting a picture.

Are you sure? [yes] / [no]