Gehn’s Holographic Imager Replica


Issue 78, January 2024

An impressive replica of one of Gehn’s holographic Imagers from the game Riven: The Sequel to Myst…

There appears to be no limit to what a maker can do when they set their mind to it. In this fine example, Mike has turned science fiction into reality, turning a holographic imager within a game into a real-world replica.

We caught up with Mike to learn all about this curious device.

Thanks for speaking with us, Mike. Can you tell our readers about yourself and what got you into electronics?

Hi there! I'm Mike Ando from Brisbane QLD. There's a running joke that I'm a time-travelling mad scientist, thanks to driving a DeLorean (better known as the car from the Back to the Future movies) and all the stuff I'm constantly building.

I think the thing that first got me into electronics was watching my dad build the first family computer, right at the edge of when it was still possible to save some money by building some parts of a computer instead of buying them outright - and by "build" I mean using a soldering iron.

It frequently surprises people, but I have no real qualifications. I was kicked out of uni for failing too hard and I only passed high school with a medical exemption. But Google etc is all you need to learn almost anything these days, so I'm entirely self-taught.

I'm currently a disabled pensioner due to mental health issues, but when I could work, my old job was in IT while also working as a Building Energy Efficiency Assessor. Basically, through things like thermal simulations and careful window/insulation optimisation, I helped people design buildings that use less energy.

Where may our readers have seen you in the past?

I've had a few of my projects featured by various tech outlets, but my previous most famous project was a functioning replica of a linking book from the game Myst (https://riumplus.com/mystbook).

That one went so viral even the Smithsonian wrote a piece about it, and Cyan (the company that made Myst) ended up using it as a texture for the in-game book in their 2014 remake.

Locally speaking, if you live in South-East Queensland you might've seen me either cruising around in my DeLorean or at various conventions/events/gigs which tends to draw a bit of attention.

I was also in Season 5 of Beauty and the Geek Australia, the one filmed in Fiji. And no, I was not a beauty. ;)

You do have great hair though! Ha Ha. Please tell our readers all about your intriguing Andotrope display?

This is going to sound a bit weird, but I genuinely didn't set out to create a brand new kind of display. I set out to build a functioning replica of a video game prop - one of Gehn's imagers from the 90s adventure game Riven: The Sequel to Myst.

No one had made one before and I thought I could pull it off. The display part was almost a secondary thought that seemed obvious to me, almost like "well of course I'll build the display like that, the real challenge will be stuff like designing & 3D printing the adapters to secure all the brass tubes in place and getting the rock texture right for the base etc". The video game prop came first; the new display tech came after.

The display at the heart of the machine is definitely the most interesting part. It seems to be new technology that I can't find prior examples of, and it doesn't quite fit the definition of any other type of existing display. So, I've been calling anything you could make that's similar to it by the generic name "Andotrope". It's purposefully not a trademarked term, named because it's similar to a Zoetrope.

How does it work, and what electronics does it use?

The way it works is similar to a Zoetrope, except I've brought a children's toy from the 1800s into the 21st century. Inside the black cylinder are two tablets back-to-back that have their displays synchronised, with a vertical viewing slit cut through the black cylinder directly in front of each tablet.

As the whole mechanism rotates, you see a slice of the screen wipe past through the viewing slit. This happens for not just you but for everyone all around it simultaneously, as everyone sees different stages of wipes of the screens through the viewing slits. Do this fast enough (my one rotates at 1200RPM), and persistence-of-vision kicks in and you end up with video.

The main differences between a Zoetrope and an Andotrope and why it needs its own name are:

  1. An Andotrope uses relatively few screens and can show infinitely-long animations, while a Zoetrope uses a dozen or more still pictures and is limited to showing only a second or so of looping animation.
  2. An Andotrope’s screens & slits are arranged so that you don’t see multiple animations at once, while in a Zoetrope you can usually see through multiple slits to see multiple animations at a time due to having so many slits/pictures.
  3. Also because it uses fewer screens & slits, an Andotrope rotates much faster to maintain an animation, rotating tens of times per second, while a Zoetrope might rotate only once per second.
  4. All combined, the main purpose of an Andotrope is to provide an omnidirectional, bill-boarding video to multiple simultaneous viewers in all directions.

Note: some say this display is holographic. It's one of those things where people aren't using that word for its original definition any more, like how you can call someone "cool" or "hot" and they're both compliments but they have nothing to do with your temperature despite meaning the opposite thing.

People call VR headsets, spinning LEDs, even nail polish holographic these days. I don't really mind one way or the other how people describe it. I called it "holographic" in my blog post & presentation because I had to appeal to the lowest common demographic with google search terms so people could find it.

At the same time, the word doesn't appear once in my patent application where I had to be more technical. I'm not a prescriptivist that dictates what words mean or what words people should use; use whatever you want so long as it communicates the effect well to the intended audience!

For its technical components, the main display is made up of two 10" tablets by Blackvue, a company better known for their dash cams. They were very specifically picked for their specs, but otherwise they're just off-the-shelf unmodified tablets. Using normal tablets (or even phones) makes it much, much simpler to build an Andotrope.

The heart of the machine that controls & synchronises everything is a Raspberry Pi 4 wearing a DAC+ shield for audio out.

There's also an Arduino Pro Mini to act as a motor controller, a DFRobot DRI0042 motor driver, a Pololu Shunt Regulator in case of overvoltage during regenerative braking (yes it regens every time it slows down!), and a Meanwell LRS-150F-12 12V power supply.

The motor etc are by goBILDA, who usually cater to the robotics competition crowd but they're great for making quick prototypes too.

The remaining components are standard T-slot (used due to its slightly higher strength than the often-preferred V-slot) and a mix of sheet Aluminium & Stainless Steel depending on where strength was necessary.

The main axle was 8mm hexagonal Steel as its strength was very important & a hexagonal profile meant the tablets could be a couple millimetres closer to one another.

We read that you accidentally made a new technology, and now looking at a patent?

It was only when I was almost finished with the entire project that I started searching for other examples of this kind of display and I realised I couldn't find any examples of prior art. I spent a couple weeks brainstorming every search term I could think of to try & combine - "zoetrope LCD", "spinning LCD", "tube POV display", "cylindrical POV LCD" etc, and they all turned up empty-handed. I showed the Imager to a few close friends/family and none of them could recall ever seeing anything like it either.

On the suggestion of my other half, I spoke to a patent attorney to see if he thought the idea was of any value, and his response basically boiled down to "this's one of the best ideas I've seen in years"... And so now I've filed US Provisional Patent Application No. 63/511,582! It seems I've accidentally invented new display technology while trying to make a video game prop replica more screen-accurate... Um, oops?

What content can it display? Is it just for fun or could there be commercial applications?

Specifically regarding the replica of Gehn's imager that I built, it'll display anything that you can display on an Android tablet. While it was designed to play pre-recorded videos for the prop replica, it'll do other things like video chatting, YouTube, games, remote screen casting, other apps, etc. I've used it for video conferencing where it's amazing - stick it in the middle of the table and everyone sitting around not only sees the other person facing them but making eye contact with them.

In general, there's nothing stopping you scaling an Andotrope display up or down in size beyond the usual ruiner-of-all-things-fun, the laws of physics (specifically the g-forces when spinning something large fast).

For a smaller phone-screen-sized one, imagine a restaurant table with this in the middle, a digital assistant taking your orders, playing games with you until your food arrives. Or on your kitchen island table showing the weather, currently playing music, current recipe & other information from your Virtual Assistant, viewable no matter where you’re standing.

Or board games with friends, with this in the middle of the table, the dungeon master talking & pointing to you. Or putting one on your coffee table, everyone sitting around the Andotrope in a circle instead of all looking at a wall to one side. Or those cylindrical advertising posters/screens, like you see in airports with flight times, but everyone all around always sees the intended view. Or even theme parks with these futuristic displays around the place.

Anywhere people are in a group where you currently look at a display to one side or against a wall and some people get a worser view, an Andotrope puts the display in the middle of the group and gives everyone an equally great view.

In some ways this is actually better than a "true" hologram of eg a perfect floating head in space, because in that scenario 3/4 people standing around it see the back or sides of a person's holographic head while with an Andotrope display everyone sees not only their face but them making eye contact.

I'm working on a newer, cheaper, more compact prototype Andotrope that drops all the expensive brass video-game-prop-related parts; one that you just slip your phone into and go. So yeah, there's definitely a lot of commercial applications for something like this!

How the data is transmitted: Is it slip rings, or is it just power transfer, with a screen driver attached inside the rotating bit and wireless data fed to it for the screen?

That's one of the big secrets to this that the few examples I found on the internet of people trying to make one didn't seem able to overcome... There's no physical hardwired connection between the tablets and the Raspberry Pi controller in the base. Slip rings are expensive and video data needs a lot of bandwidth, so all communications happen through Wi-Fi, mostly through standard MQTT.

For now, the Android tablets inside are just powered by their own internal batteries and you charge them via their USB ports. There's no other programs running on the tablets or anything listening for updates in the background, and between videos it lowers the screen brightness to a minimum level.

This gives it an all-day battery life (which was confirmed to really last that long at Mysterium 2023). Charging the tablets overnight after a whole day of use isn't that much hassle given most people charge their phones overnight anyway. I did buy the parts for wirelessly charging the tablets, but I ran out of time to integrate them before my presentation.

The use of Android tablets instead of trying to DIY my own displays was intentional; it's much cheaper and easier to buy a tablet than DIY my own screen + driver + power delivery + battery + controller + transmitter etc, particularly given it needs a certain amount of ruggedness due to how fast they're spinning.

Avoid the temptation to over-complicate things with DIY; building stuff from scratch is great but sometimes buying ready-made items is worth the time/effort saved.

What prototyping or challenges did you have and how did you overcome them?

The brass tube cage was the trickiest part (and also surprisingly expensive - just the brass tubes, professionally bent, filled with resin, ended up costing $1000AUD).

The tubes are thin and long so they flex a lot, and brass isn't a very rigid material in the first place. They need to be strong to hold the top of the imager securely in place.

Making them started with 20 lengths of tube slowly bent into a semicircle by a professional so they wouldn't twist while bending. Afterwards, each tube was filled with resin to give it more rigidity, then they were cut to length.

Holes were drilled through both ends of each tube, and I 3D-printed sandwich clamps to secure them in place.

Getting everything working was a huge pain, and I ended up having to disassemble & reassemble that cage a bunch of times during the build process when I kept needing access to the Andotrope in the middle (once the tablets are in there, they're in there with no quick removal!).

All up there's 20 curved brass tubes, 20 3D-printed curved sandwich clamp pieces, and 90 nuts/bolts affixing those tubes to the holding plates.

Obviously, the crank is functional to get it started. Are the front mounted toggle switches functional, or just for aesthetics?

There's actually a generator attached to the crank, because I like some things to feel realistic and not just look realistic (which is why the crank's made of stainless steel and cast iron and not 3D-printed, because you can make them look close but they just don't feel the same in your hand).

The easiest way to make the crank's resistance feel right and have it make the proper speed-variable whirring sound as you turn it is to make it actually generate electricity. Any excess power generated is dumped into a 9000RPM cooling fan.

Human output is too intermittent to reliably power the entire machine though, so it's mainly powered from the wall, but the voltage sending the signal to start the motor & play the video is generated entirely from the crank.

The front switches are all functional three-way toggle switches too. The left is the power switch which directly controls the incoming 110-240V so you can manually cut the power to everything in case something goes wrong. Second is rotational speed; 20fps is quieter & more stable, 30fps looks best when filming, 40fps looks best in-person but is a bit noisier. Third switch is volume control, switching from silent to normal to "large demonstration crowd" levels. 3rd/4th/5th switches are video selection, so there's 27 videos it can play back from the switches, with more on there that you can play manually using your phone. The speed & volume can be changed at any time while it's playing, so you set the third switch to play the video then flip it to the volume you need after it's started.

The whole front control panel isn't present on the original in-game asset but I had to have some way to control it, so I kept it in-theme for the game with 5 switches in a row, against a polished brass backing affixed with pentagonal bolts.

The game has pentagonal bolts in other places so I've gotta be as accurate as I can, so I tracked down some that are usually used as security bolts and sanded off the existing manufacturer markings on the heads.

And every pentagonal bolt present isn't just frivolous decoration; they're all functional; both as the only thing holding the front control panel on, and as what clamps together the sandwich holders for the brass tubes.

The front control panel also acts as a hidden speaker, with a 24W exciter attached to the metal plate's rear, so there's no speaker holes anywhere to ruin the device's aesthetic.

The front control panel is also removable to provide access to the interior electronics.

What were the most challenging parts of your build?

Metalworking was definitely the most challenging part for me. I have shaky hands thanks to medication, so I'm much better with software or digital fabrication techniques. My dodgy $300 CNC wasn't up to the task of machining brass, but it helped to mark the drill holes for me.

The software part was a bit tricky, not because it was actually difficult, but because there were lots of different programming languages and operating systems involved. I hadn't worked with them before, so I had to learn a lot of new things. As an example, the Python script on the Raspberry Pi is only around 400 lines, but my prior experience with Python was basic commands & running other people's scripts, not controlling GPIO and communicating over MQTT. ChatGPT helped a lot to generate the base structure that I manually fixed up. In fact, as an experiment all code on this project started with ChatGPT, but all of it was manually edited afterwards. So I consider it a great tool but it won't make programmers obsolete yet.

If you were to start over, what would you do differently?

My partner says use less brass because they're still finding brass chips with their foot in the garage despite me sweeping & vacuuming twice! In hindsight now that I know for certain the Andotrope technique works so well, I think I'd use a different quieter motor with a better mounting technique than one designed for robotics competitions - not that I regret my choice or think it was bad at the time, but now that I know the whole thing works I don't need the full flexibility & customizability it gave me.

I also put some rather expensive 3M anti-reflective film on the slits to reduce reflections. Honestly, they made things a tiny bit better but I was very disappointed in how little change there was. I wouldn't pay that much for some again, nor would I recommend your readers bother with it for other projects

Is there anything that our readers should know that we haven't already covered?

The majority of this project's exterior is stuff to make it look like the original video game asset. The brass cage could be replaced by a simple clear cylinder to keep fingers away, the crank handle is only there because that's what's in the game, the base has a lot of empty space, etc. The Andotrope display in the middle could be made a lot smaller, and at a fraction of the cost.

3D printing is great (and there's 25 3D-printed parts in this build), but some parts are just better in other materials if they're handled or need a very specific surface finish. A 3D-printed crank would've worked just as well, but a turned stainless steel handle on a cast iron crank with a brass axle feels so much more "real" to touch.

I'm a big fan of the thinking that small little touches are what really tie together a project. I've mentioned some of the things already like the stainless steel/cast iron handle, and the pentagonal bolts.

But other examples are things like the 3D-printed holder for the spirit level on the very top of the Imager. That was designed so the top looks like a bunch of 90's basic 3D-modelling primitive shapes.

The exterior screws on the crank handle are all slotted brass with matching brass washers to look vintage. The power cord is braided, twisted jute so there's no modern white PVC cable ruining the look. The power plug is an old-fashioned industrial design, too. And the toggle switches were imported from America because I wanted ones with a very long handle like in the game, that I could also affix in place with slimline brass nuts.

Oh yeah, the case - the case was 3D printed in 4 parts, bolted together, painted in noise/vibration absorbing paint, covered in flexible automotive body filler, and painted up to look like rock.

Did I mention I can control the whole Imager from an app on my phone, including making it play videos that aren't accessible via the switches? I mean, it's all communicating via Wi-Fi anyway, so of course I'd use Wi-Fi to debug it!

For some generic stats, the final part count was over 300 bolts, it's 71cm tall and weighs 14kg.

If our readers want to build one for themselves, is everything on your website for this?

The basic concept of an Andotrope is surprisingly simple. On my website there's an exploded 3D render of the main assembly as well as a photo of the insides, which should be enough for someone knowledgeable to replicate the idea (as is required for a patent). There's a lot of fine-tuning and experimentation involved to make the effect look as good as possible though, so much that you could write a dedicated article on it, but a couple of big points - you want the brightest screen possible because you're only seeing it for a fraction of a second, and you want a screen with the least flicker possible. OLED screens would be great but they all flicker a certain amount, which is the main reason I used the specific model tablet that I did. Also, you want the blackest black you can get on the cylinder for the best contrast ratio - I used Musou black fabric because I found that to be much blacker & more durable than any of the "blackest black" paints available at the time that I tried, particularly regarding the paint staying stuck to the acrylic at high RPMs. There's lots of ways you can iterate on the Andotrope design too - for instance it doesn't need to be two screens, I just did that for ease of balancing it and to have twice the brightness. My first prototype was literally a rugged phone, wedged inside a tomato soup can painted black & cut open, hot-glued to a pedestal fan - hacky as heck but it proved the concept worked! I should mention though that since this is patent pending, if someone's looking to commercialise it or turn it into an actual product, they should get in touch with me for licensing details ;)

What other projects have you made that our readers may be interested in knowing about?

Whether or not you're a Myst fan, readers might appreciate this digital 25-hour D'ni clock/chronometer I made, notably the custom "25-segment" displays riumplus.com/25-hour-digital-myst-dni-clock-chronometer . They're styled to look like the common 7-segment displays but in a completely custom design that readers could copy for whatever design they want. I go through how I made the digits on my website as well as during my presentation of the clock, which you can see at

There's also the previously-mentioned Myst book replica, which still impresses some people today. At the time its hardware was considered incredibly fast for such a small portable machine (I bought the CPU/GPU/motherboard from Broadcom's Advanced Research division) and for a period of time that individual book was one of the fastest computers in the world in a certain size & power envelope. Apple's Mac Mini was the go-to "fast small computer" back then, but that was 17cm wide while I had 12cm to work with and I included a battery, power supply and touch screen. These days we have compute sticks and NUCs, but things were different back in so-long-ago 2013! riumplus.com/mystbook

What projects are you working on now?

I just finished what I like to call "digital archaeology" by restoring & upgrading a pre-Flash web game from 1996/1997 to work on more modern browsers, including phones/tablets, with optional AI upscaling of its 640x480 graphics.

It's called The Riven Journals, and it was a series of puzzle games made as a promotional thing for Riven: The Sequel to Myst, the same game my Imager comes from.

The pages are still technically HTML but it was literally designed for Netscape Navigator 3 so things have changed a lot. The Java applets have been replaced with JavaScript, and the server code has been completely rewritten from scratch from 3 different languages to just modern PHP. Readers can check it out at journals.riumplus.com.

Other than that, the Imager project took me only 9 months which is a record time for me to finish such a complex project, so I'm taking a bit of a well-deserved break.

I have an idea for another Andotrope prototype that's much cheaper & more compact that skips all the video-game-prop stuff, one you just drop your phone into, and another idea for one that's partially transparent... But we'll see how long it takes me to finish things!

Any final words?

I'm very lucky to have found myself a partner who is better with a soldering iron than I am. We complement each other's skill sets well; you could say that I'm the kind of person that uses a torque wrench while they're the kind that uses a breaker bar.

Otherwise, due to mental health reasons I've been living in a bit of a vacuum for the last couple years and don't really follow any makers or tech websites. Making a project entirely "on my own" for once has been different!

Thank you so much for sharing your poject with us. We wish you all the best for the future.

Wire Frame
Wire Frame
Wire Frame
Work in Progress Selfie
3D Printed Tube Holders
3D Printed Tube Holders
Assembly Yoga
My cat Lana supervised the assembly process, because the Internet insists that all decent build logs should include at least one picture of a cat.
Wire Frame
What the original looks like in-game