Mod's Choice!
A little Teensy4.1 project I've been working on
I am super proud of how this project is turning out. I still have some tweaks to make, but I finally got full videos playing and wanted to share.
This is a "Persistence of Vision" (PoV) display driven by a Teensy 4.1 and SK9822 LED strips.
There are 4 strips of 32 LEDs, each slightly offset in order give me 128 addressable pixel "rows". So each strip is responsible for every 4th row.
360 pixel "columns" around the perimeter makes for roughly square pixels, so thats what i went with. Each LED is updated 360 times every revolution...at around 1500rpm.
A hall effect sensor at the top of the rotor passes by a stationary magnet in the upper frame once per revolution. The Teensy measures the time between the resulting signals, and uses that to calculate how fast it is spinning, and therefore how fast to update the LEDs. This lets the animation look correct regardless of rotor speed.
I have a (currently very slow) python script that resizes/crops and formats .mp4 files into a binary format that the Teensy can use very efficiently. The resulting binary gets saved to a microSD, that the Teensy can read from.
Im happy to answer any questions. I may do a better build/explanation video if there is enough interest.
That's really nice! Some questions:
Is the motor speed controllable?
How are you powering the spinning electronics?
Any balance issues you had to take care of?
The silver box with the knob is a 12v PWM motor controller. Im using that to set the speed to whatever feels right. Im thinking of upgrading to a closed-loop bldc system in the future for better control.
That 12v also passes through a high speed mercury slip ring onto the rotor. This part was easily half the cost of the whole build. Each rotor blade has a tiny 5v buck converter embedded underneath to power the LEDs. One of those also powers the Teensy.
I was worried about balance, but it all just kinda worked out. Its not perfect, it could probably be better. But the large diameter bearings im using help a lot
Depending on the power requirement. I would probably check if one can get away with using Power transfer coils.
Those can and have been used for Persistence of Vision displays in order to avoid slip rings. Though if they have enough power transferring capability for something with this many leds? idk.
I would have needed some pretty big coils, and additional components to smooth out the noise. I looked into it, and it really wouldn't have saved me much for how much complexity it added.
radio, optical link, or transformer again. radio might be easiest. transformer or optical I would try at the end of the main axle, working axially. all are complicated by the need to construct frames of data, serialize, apply a modulation code, modulate, then the reverse on receiver.
Batteries and motor on the rotating part. Wireless to control. Lower friction and higher rotational inertia. You could use a direct drive brushless motor.
I am more interested in knowing about slip ring for my another project , which one did you buy(and if I could get a name, website, link anything) and how many tracks it had?
If my math is right, 720 should be pushing the limit, but maybe just barely possible. Theres a hard limit to how fast i can shove bits out and clock the LED strips. I did all my math at 1500rpm, which seems to be the sweet spot where the blades disappear, but slowing things down would give me more overhead.
When you push the data to the strips, are you doing that "manually" through code you have written (or an API like shiftOut)? Or, are you using the DMA controller?
Also, is it configured as just one long strip or four individually connected strips? That is, is it just one long channel or 4 shorter ones?
Nice project, I assume that you have a plan for it beyond the sample video?
DMA and FlexIO. Full disclosure, I did have chatGPT help me some with the low level stuff. Its basically shifting 4 bits at a time into a specific shift register which drives 4 very specific gpio pins. Each pin is wired to the data line on a different strip, and then a single clock pulse syncronizes all 4. Hence the slow python formatting/bitpacking script. Every 4 contiguous bits is meant for a different LED strip. The benefit is that the main processor is effectively left idle.
Future plans? No idea really. It might be fun to throw a couple piezo buzzers on there for audio
This was destined to get a "Mod Choice" flair from one of us so let me have the honor!
Your post will also be included in it's own section of the next edition of our Monthly Digest (thank you u/gm310509!) and live in the collection of projects we love
Thanks so much for sharing your project! Great engineering and math ftw 😄
Love the Teensy. 600MHz just makes everything work like it was supposed to instead of playing the "let's overburden the interrupts on a less resourceful processor to the point that there's more time spent in the background than the foreground" 😉
1500rpm. It does look better in person, but you'll just have to trust me on that. I had to play with my cameras shutter speed to get a good video, and you can still see artifacts from that.
Oh, I trust you! I explored these systems and building my own 16 years ago. At the time it was so expensive to me I ended up creating 3D printed zoetropes for a film and museums instead of holographics.
Really nice job. What prompted you to explore this?
I honestly dont know what prompted this. It sorta just popped into my head while i was bored at work. I started researching if it was possible to make something like this, and suddenly a design was coming together.
The cheapest i could find thats rated for these speeds is the A2H from AsianTools. Got it on ebaiy for about $85...probably half the cost of the whole build
you mentioned mercury slip bearings, some normal stainless steel bearings on top and bottom, maybe more in parallel would not be an option to transfer power ?
but couldnt you just use the bearings itself to transfer power ? Did you tried it, or just gone with straight to the slip ring ? Im really curious about how well would the power transfer through standard bearing would work, as those slip rings are not the easiest to come by.
I wouldn't send power through a bearing. The grease is an insulator. And with all the moving parts, you're going to end up with a lot of internal arcing. It would likely corrode the bearings pretty fast.
That's really fucking awesome!! I've been thinking of getting into Arduino with my grandson who's going to be 8 next year and he's already advanced a year in school. He's into computers and video gaming, and something like this, I think it would be right up his alley. I'll be showing this to him on Friday when he comes over to spend a few days with? Wife savvy! This has just put me over the fence. I will be doing more research to get him started, come the new year!
Thanks! I've been trying to get him into anything computer, but he's got ADHD, so he only lasts a few minutes with most things. He can sit on Roblox or Minecraft for hours on end designing things, and Google has their old doodles, and one of them had a dungeon designer type game that he absolutely loves. He's designed some ratchet elaborate dungeons with traps and everything.
I've been trying to find that "thing" that he engages with. Arduino is the best of both, hands on and mild programming, so I'm hoping by next year he will be a bit more interested in the hands on stuff. He loves Lego, and I have an old electronics kit that he will sit and make lights light up with simple writing layouts, or make the little elevator go up and down, etc...
So with a little luck, this will be something I can get him to do with me.
I wonder what would happen if you made the LED panels into LED pillars such that each pillar had like 8 columns of LEDs all pointing in a different direction. 🤔 Do you think you'd be able to display 4-8 different videos at once depending on what angle you viewed it from? Or would it just be a blurry mess?
Its certainly possible. I'd probably start with faster LED strips first. A lot of the jitter comes from the PWM the strips themselves use internally to control brightness.
this is so cool. i’d love a longer video / post and if you’d be willing to share more details, i would definitely try something like this in my spare time. amazing work!
my first question would be part sourcing and figuring out compatibility? was it painstaking trial and error process? or just a few changes here and there, compared to your initial planned parts? where did you source?
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You'll have to wait outside. We don't want any trouble.
I think you just need a couple more layers to even it out and the image will look great it's not bad as it is I probably buy it would've loved this back in the '90s definitely early 2000s
I’ve never thought about it, but after seeing all the wires and seeing it spin, how do you prevent electrical wiring from twisting up to power something like this?
Ill have to play around more. this clip is running at 25fps, but my math says much more should be possible. The framerate and rotation speed are completely independent, but coincidentally are about the same withis this one. It would be interesting to see how it looks if they were drastically different.
Denser/more LED strips would increase the resolution, but this feels like the sweet spot for effort/complexity/results.
You'll have to trust me on this, but it actually looks a lot better in person. I had to play with my cameras shutter speed to get the video as clear as it is.
1500rpm and you got it that stable? My desk fan sounds like a helicopter at half that speed. The mercury slip ring was a smart call though, Ive seen too many diy builds where the wires just slowly strangle themselves over time.
Nice! My senior project was making one of these, but with a whole matrix of LEDs so it could display a 3D image. But we had issues with getting it up to speed without flinging itself apart, and storing all the frames for our 3D model. (EDIT: and also issues with converting Blender models into usable frames)
Reminds me of this hologram I once made.
How are you powering the rotating assembly? A slip ring? when I built mine all the slip rings I could find rated for a suitable RPM where industrial ones so I settled for a battery.
Thats exactly the biggest problem i ran into. I found a 2 circuit mercury slipring rated for 1800rpm on ebay for $85. Decided to just spend the money.
Battery would have been my second choice, but thts a lot of mass to add to a fast spinning rotor. And needing to keep it charged when I'm already powering a motor just felt wrong.
Looks like a cool project! Do you have a video of it running?
I like to think about, "If i were to build XYZ how would i do it. I wouldnt do it like That De Vinci guy. No, he was a genius, and im a normal dude. So I'd build XYZ with built in fire extinguishers." I use to scare my younger family by sticking my finger in there and acting hurt. I think if some drunk idiot (couldn't be me) where stick a finger in, it might hurt a bit much. Also things can fly off.
Id put some glass over it. Preventative maintenance.
I looked it up, and i think theres some more going on with that one.
With the way this project works, rotating the frame the opposite way would just make the image rotate with it. All the timing is referenced to the frame.
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u/ExtensionGlum1206 Aug 20 '26
That's the highest effort rickroll I've ever seen.