Our wonderful industrial designers came up with a neat concept of having a cube, with a tunnel through the centre. This provided us with 8 surfaces for LEDs, and diffuse light washing out in all directions. But it also gave a challenge of building a support structure for all the LEDs.
The current prototypes use RGB LED light strips, attached to a plastic frame, but we are currently designing our own PCBs to provide the frame structure as well as replace the necessary hacking of the LED strip.
If you wish to build your own unit, you need to cut out 5 pieces of support material, and about 2m of 32 LED per metre, 32 pixel per metre, LPD8806 RGB LED strip.
We used 1.5mm thick polycarbonate cut by CNC, but it could be made from any (non conductive) material, possibly even thick cardboard cut by hand, with holes punched for the wiring to pass through.
The two side pieces are 100x113mm. The top, bottom, and middle pieces are 100×87.4mm. Actually they are effectively 100×86.4mm as we CNC machined 0.5mm grooves in the side panels these slot into. We also have small triangular braces to add strength.
The inner LEDs are a very easy to wire up, and not too hard to install. They just need to be cut into standard sections of two LEDs each, with 4 interconnecting wires between each section. I think the interconnections were about 32mm.
Make sure you wire the outputs (DO/CO) of one section, to inputs (DI/CI) on the next section. This photo shows 4 inner strips prepared and ready for installation.
Install one side at a time – check the annotated photos at the end to make sure you install them in a sensible order for later interconnection.
The total outside width of the finished cube is 89.4mm, which was intentional as it allowed us to bend our three LED strips at a point so that we got a three by three matrix of evenly spaced LEDs on three sides. So you need to cut three 12 LED strips at just the right spot as shown in the photos below, then wrap the long 9 LED strips around the top. Note the bend is right at the edge of one of the ICs – be careful not to damage the strip or solder joints when bending here.
The fourth side (at the bottom) is actually closer to the outer face as we have a compartment for the electronics above it. It holds the remaining cut off strip with three LEDs. We had to trim a little off the final end of the strip to make these fit, as seen on the right of the photo below, but leave some of the solder pads so you can add interconnection wires later.
As we have to cut the strips at a non-standard point, some extra wiring (7 connections per strip) is needed to re-connect the signals. This is time consuming, and requires a bit a soldering experience due to the small soldering points. This also provides a hinge for the bottom plate to open up, allowing access to the compartment for the CPU.
Finally, you need to wire up all the LEDs sections, essentially in a long “spiral” chain – just as if it was back to being a straight 1.625m strip. I connected the data and clock signals from one loop to the next in the chain, but brought all the power connections back from the start of each of the five loops to a central point. This helps avoid voltage drop along the full length of the strip.
The following annotated photos show the LED order of our prototypes, but our software has an abstraction layer so that the LED ordering can be different. Our earlier prototypes were different from this, and we expect our production models to be different again!
36 LEDs in the outer 3 strips, numbered clockwise, starting at left rear bottom corner.
16 LEDs in the inner 2 strips, numbered clockwise, starting at right rear bottom corner.
If anyone has an interest, I can make the CamBam or G-code files available for our prototype plastic pieces. They use a 1.6mm cutter for the grooves, and a 2mm cutter for the routing.