About this 3D model
So here is a CAD drawing I did in OpenSCAD of a concept for a ring with a screw-on top. the top has a hole in it for an LED. There is a side hole in the ring for a mini-usb connector. That needs to be shaped a little more but good enough for now. Note the top has a cavity to increase the payload space. To think about the size of this, the ring will screw onto a 2-litre pop bottle like a bottle top. so vertically large, but we can overcome that later when we physically prototype.