As time goes on, new possibilities of creating cool devices seem to endlessly pour on my head. This time I was invited to take part in Eurobot 2018 national qualifications to compete for the chance of going to the international grand finale. Aside from the obvious tasks of creating and programming robot's stage, I was also responsible for making a device that dynamically displayed the number of points that the robot earned in the match.

While the robot's electronic entrails were arguably the most enjoyable part of my contribution to our team, I'll publish the details of making the displaying device anyway.

I'm going to show how YOU can make a display like mine out of Arduino and those widespread WS2811 RGB LEDs.

For more details, visit my blog post here:

https://shortn0tes.blogspot.com/2018/04/ws2811-pov-display-on-pc-fan.html

Step 1: Components

For the display itself you're going to need:

An ordinary PC fan and a plastic top from any jar. Any disc of plastic will do.
Five WS2811 individually addressable RGB LEDs. I got mine online (aliexpress).
Hall sensor (ali) and a magnet to synchronize LED blinks to platform rotation.
Two 3x7cm perforated boards (ali again. Yeah, you got me, I like to order junk from this store). Actually, maximal allowed size will depend on the size of your fan, but it all fit snugly on two boards of this size, so I still recommend those. Also, you'll need something to fix one perfboard on top of another - I had some spare Arduino-style pin headers, but it's OK if you don't have one - you can connect the boards with four long bolts or stadoffs.
One lithium battery of any capacity that'll fit on top of the fan (rip it out of some unfortunate old cellphone about to be thrown into the trash. Everyone got one of those, ask your friends and family),
One charger for the battery.
One boost converter (battery voltage -> 5V),
One buck-boost converter (battery voltage -> 3.3V),
And a power switch.
One 3.3V Arduino (that's important to avoid level-shifting circuitry!) and one NRF24L01 RF transceiver.

For score transmitter:

Another NRF24L01 RF transceiver and any Arduino with USB port to set the score from PC. I only had 5V Arduino boards with USB, so that's what I had to use - my pick is Arduino Nano clone. 5V microcontroller won't fry the RF module, provided you power it from separate 3.3V power source. NRF24L01 data lines are 5V-tolerant. My 3.3V power source was LM1117-3.3 regulator - the beefier the better! No heatsink required. You'll be better off getting yourself an USB-connected 3.3V Arduino Pro Micro, though you'll still have to feed NRF24L01 off the separate 3.3V regulator - the stock regulator on most Arduino boards is only designed to power microcontroller itself and periphery with insignificant current consumption.

Step 2: Assembly: LED Strip Composition.

We'll start by making the rotating platform itself, a device conforming to the schematic attached. Each step below corresponds to one image.

Take a length of solid core wire, strip the insulation.
Start soldering the wire to WS2811 modules, one...
..by one.
Then, solder opposite ends of wires to another WS2811, so that they are connected head to tail (IN to OUT).
Keep the wire between LEDs short, but not too short. It should be as long as to allow modules to align to a single plank, not a smidge longer.
Rinse and repeat until you get a stipe of required length (5 in my case, enough to show numbers).
Now we have to install the stripe of LEDs at a right angle to the spinning platform.
Not having access to laser cutter, I clumsily cut the panel for LEDs out of acrylic sheet.
Then mounted and soldered the connector on to it. That's the result here.
Time to mount the strip on to the base! For simplicity's sake, I attached it with 2-part epoxy putty (a.k.a. cold weld).
The other bulky part of the electronics that my device incorporates is lithium battery. Slap it down with some epoxy as well!

Step 3: Assembly: Soldering the Circuit Board(s).

First, let's arrange the components on perfboards. Having sockets for each module will diminish your pain if you manage to destroy one of the parts - in fact, I accidentally applied reverse voltage to Lithium charger's microUSB connector(well, what do you know...), and charger replacement took no more than a minute.
I had a couple of Arduino-style headers in my drawer, and they double as power connectors between top and bottom boards in this application - neat!
Once everything's seems to be in its right place, solder it down.
My bottom board holds the power-related circuit parts. Battery will be connected to the white JST-style connector at the far side of the board. Connect everything according to schematics....
... and set up your dc-dc converters so that they output the right voltage.
Now that the bottom power-routing board is ready, you can get to the top board. It should contain all controlling peripherals. You can use Arduino-style connectors to transfer power. Don't forget to route 3 wires for hall sensor to the side of the board.
Insert Arduino and NRF24L01 in place and the circuit is almost ready!

Step 4: Testing and Post-assembly.

At this point you should be able to push the battery connector into position and behold the marvelously working circuit. Doesn't make sense to go farther if you see puffs of smoke, or if some overheated part burns your skin. Watch the video to see what my fully assembled circuit board looks like.
Add four standoffs. Makes for easier board to platform attachment.
I had to carve pieces from my platform to make board fit on top of it.
Then I just glued it all together - the fan's propeller, the platform and my board on standoffs.
Where do you cram the power switch in such a space-constrained build? Drill a hole in the top PCB and plug it there.
Now, the icing on the metaphorical cake of this assembly would be the hall sensor. Install it and you're done with hardware part of this device.

Step 5: Assembly: Another Device to Set the Message Via RF Channel.

Bet you forgot about it already! This device will be a minimalist way to connect NRF24L01 to PC.

Board to chip connectors for radio transceiver or microcontroller seemed unnecessary for such a tiny device, hence the wires soldered directly to pins and terminals. Also, deadbug-style capacitors piled on regulator legs.
This thing is going to be dragged around. A lot. Think about the enclosure - you can print one tailored to the electronics, or just grab an empty one from old daylight lamp ballast like I did.
Soldering this takes maybe 15 minutes tops. Flexibility goes to hell, but think about time saved!?
Screw the board with USB to the enclosure for added ruggedness...
...and close the lid! You're done.

Step 6: Some Dead Pixel Testing...

First sketch that I uploaded was a simple stock example for NeoPixelBus library, just to check that the most important part of device, RGB LEDs that is, is working all right (vid 1).

Wow, that display of colors sure was beautiful, but did it really check the display for dead pixels? Judging by the video, all the pixels are in perfectly working order, now let's upload this another sketch and see again (vid 2).