Linkable LED modules

 

Making LED rings for my unicycle led me to explore ways to build LED arrangements in arbitrary shapes. I designed a system of modular sections with concentric connectors that allow them to be stacked and arranged at any planar angle. These are boards designed for WS2812 LEDs so there are 3 conductors (power, ground and data) that have to be connected at every joint.

First prototype

The first version had concentric arcs at each end that when aligned and tightened with bolts and wing nuts would be pressed together. Since the joints rely on the surfaces to stay in contact, I went with gold plated contacts so they would be as consistently flat as possible. I later increased the thickness of the traces and experimented with other surface finishes, but the joints still have to stay pretty tight for it to be stable.

An interesting result of this is that the data path can be branched at any connection point, so you can make pretty complex shapes as long as you’re conscious of the data path. The LEDs are addressable, but they only know which number they are in line so once you split the path you can’t control one branch separately from its counterpart.

Next I imagined something like LED lego blocks that can be plugged together instantly, and ideally be able to rotate about the connectors while maintaining connection the whole time. To make them stackable I used conductive fabric snaps. Female snaps one side surrounded by thick gold plated tracks, and male snaps on the opposite side with springs positioned to ride on the mating board’s traces.

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 These springs actually worked really well, the springyness is necessary because as the joints are stressed, they compress to stay in contact even when the boards aren’t totally parallel. It probably isn’t a great idea to snap them together when its being powered, but nothing bad happened.

I attached a couple segments to a servo and let it rotate back and forth all night. Eventually a spring broke, so although they work well they may not be up to the long term repeated movement. I also assembled all of them by hand so the springs are not perfectly tangent to the tracks so as its rotating it is also pushing the spring laterally somewhat and eventually it fails.

I tried a couple iterations using rigid copper bullet-shaped pieces instead of springs, but if the joint is stressed there is a lot more leverage to pop the snaps apart, so that’s no good.

I then designed some coil springs to make the outer two connections. The first springs I designed were too thin and could short together too easily, then I arrived at the ones shown below. The factory that made them initially told me they would grind the ends down so that they would sit flat on both sides but later changed their mind and said they couldn’t, so I ground them down myself with a belt sander.

Ignoring some variance in the springs from my manual sanding, this seems to be a good reliable solution.

I decided to make a permanent version too, so this design has large vias on the output side of the board that line up with the circular traces on the input side. Once the pieces are lined up, you can flow solder into the holes to connect them.