Notices by James Brown (ancientjames@mastodon.social), page 4

This is still using software bit banging. I'm going to switch it to using DPI, but the current interface board wasn't designed with that in mind, and the GPIO mapping doesn't put all 3 displays on valid DPI pins.

Slowly turning up the dial at arm’s length.

I massively overestimated how much lead would be needed to counterbalance the small amount of slightly off-axis electronics.

The new platform now has enough bits to display an image while spinning.

Trademark flickery mess

It would be convenient to address the voxel data as a stack of horizontal slices, because that's how it's exported from lots of existing tools. I have to rotate it 90 degrees though, because scanning out is faster if each column's data can be addressed as consecutive bytes.
It's a small change, but there's a 6.5x difference in speed between the two orientations, which directly translates into voxel density in the final output.

The advantages of this approach - occlusion and view-dependent lighting - are undermined by the fact that too much of the colour depth is sacrificed to hitting the necessary framerate. The sort of simple scenes it can display could be displayed better by a swept volume.

I’ve mentally moved on from this design, but I went ahead and built it to the point I can call it finished.

Most of the time we don't move our heads up and down very much, so the lack of vertical parallax seemed like it wouldn't be a big limitation. But one of the situations where we do move our heads quite a lot is when presented with a neat little 3D effect sitting on a desk.

Anyway, the new display is going to be amazing.

I even remembered to take some pictures before I put it all together.

Scouring Aliexpress for LED panels for the new display, and it seems the higher resolution ones tend to be flexible. I spent a while investigating developable surfaces* to see how I could take advantage of this, but couldn't come up with a layout that offers any advantages over a flat square centred on the axis. Seems disappointingly pedestrian.

(*Twisting a sheet of paper in my hands)

Display 1 currently serving as convenient rotating testbed.

If the lines were completely independent, you could evenly scan a sector with half the number of line updates compared to updating the whole frame. As it is, each line has to be updated in parallel with one that's half a panel further down, so it ends up taking 3/4 of the line updates instead (because some updates have to update the outer line while scanning out black to the inner line).

I'm arranging it as two rectangular panels arranged with their bottom edges touching on the axis, which lets me update columns at the same radius simultaneously. The outer columns need to be updated more frequently than the inner columns, and one of the nice things about these LED panels is that you choose your own update strategy - you're not stuck with scanning a whole frame each time.

The thing about voxels is that even when they’re not working, they look cool.

If my calculations are correct, when this baby hits 300rpm you're going to see some serious shit.

This is the current approach for reducing the horizontal field of view of the screens - a big heavy box o' slats. I'd like to make a lenticular array, but that's a whole side quest.

It's already slightly terrifying.

The black filament is surprisingly shiny. My first attempt turned out to be a light pipe, and didn't restrict the view. In this version, the slats have a zigzag profile.