I used 3D printed black plastic for my spacers, but 1/4" dowelling would work just as well. We don't want to create a Leaning Tower of Pisa! To put rings together, you will need spacers 22mm high to create the 1" space between rings.
The initial assembly of the lower four rings is probably the most critical part of construction. But after that, I used this template approach with a much improved result.) Once you have at least four rings built, you can start the process of assembling the tower. (If you look closely at my tower, the first two rings don't line up with each other very well. If the LEDs are spaced out perfectly, this isn't an issue, but I had enough small variations in spacing that I found it necessary to use one ring as a template for the others, always carefully placing the open data-in lead (the one not connected to a data-out lead) in the same place. It is important that the LEDs in each ring line up with their counterparts on the other rings. It's a lot of work, but with a little practice, you can get the task of making one ring down to a couple of hours.
And if you want to use a separate power supply, 2 amps seems to work fine. So in practice, I never had any problem using the USB port to power it. And turning the whole tower white isn't really done anywhere either. APA106 LEDs can draw 60 ma at max brightness and white, so worst case, this tower could draw 17 amps! But these LEDs are so bright that I seldom have the brightness set at more than 10% in software. Acrylic rod is used to fasten the rings together to form the tower. The rings are themselves separated by 1 inch, so LEDs are 1" apart in both directions. The rings are 8" in diameter, and each ring contains 24 LEDs spaced 1 " apart (actually π * 8 / 24 but close to an inch). I decided to build my cylinder/tower as a set of 12 rings stacked on top of each other. And no ISR (interrupt service routine) and no multiplexing between layers of LEDs - these LEDs are on all the time.
No shift registers - everything is controlled by two data lines.
There're more expensive than regular RGB LEDs, but they are so much easier to work with both from a hardware and software standpoint. I've chosen to use 8mm APA106 programmable LEDs for this tower.
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