Mjolnir! Revisiting the base board.

A project log for CUBEx8

An 8x8x8 RGB LED cube kit using addressable LEDs!

burkethosburkethos 05/11/2019 at 17:350 Comments

With the fingers removed from the base board it looked like Thor’s hammer, Mjolnir. It is a simple, much-less-busy-looking design. It will keep an observer’s focus where it belongs -- on the LEDs.

Regarding controller circuits, I looked at many of the most popular controller boards -- Arduino, Teensy, Raspberry Pi etc. -- and noticed that most of them would require voltage translators to make the cube work properly. Most of the boards these days have 3.3V GPIO compatibility. A smaller number have 5V GPIO. The LEDs require 5V signal levels.

I decided to include a 3.3V to 5V level translator chip on the base board so that many controller boards can be used directly. It also became clear that there wasn't going to be an easy way to figure out which GPIO pins would be used to drive the LEDs. I figured that this should again be left to the builder using the board of their choice.

The best way to allow the most flexibility was to simply provide a sea of 0.1" spaced holes to mount the chosen board onto. The builder will then have to discretely wire their chosen GPIO to the level translator. I'll be adding in additional holes scattered around the board for+5V and GND connections to make it easier to power the chosen controller board.

Each level of the cube has its own level translator and therefore 64 LEDs per translator. Something like a FadeCandy can drive this configuration. Teensy boards are also well suited. Other board types can be made to work as well -- it is up to you to pick your board and connect it into the translators. 

Holes are provided on both sides of the translator in the event that your board can already drive 5V logic directly. In other words, the translator can be bypassed.

The last major thing to be concerned with is the power supply. As we calculated earlier, a full cube at full brightness can pull almost 31 amps at 5V. But, I've noticed that I don't need to run the cube at anywhere near full brightness to get a great effect. In fact, at 10% brightness I get a great result. My first prototype was built using a 7A supply and it looks great.

Worrying about how to power the cube was another issue with many, many options to choose from. Ultimately, I decided that the easiest, most universal way to power the cube was simple terminal blocks. These blocks can accept a wide range of wire gauges and all the builder needs to do is strip wires and screw down the wire clamps. Not the least expensive option, but we're only talking about pennies of difference in connector costs and for the build volumes I envision, these are an ideal solution. 

The terminal block I chose can handle up to 16A per pin so I've included two pins each for +5VDC and GND. Depending on how brightly you want to light your cube, only one power and ground pin may be required. The connector can handle the full 31A that the LEDs can draw if you choose to melt your eyeballs. I’d wear a welder’s mask at that level of brightness!

Lastly is the enclosure. You want a nice cube to have a nice case covering the controller area of the base board. I’ll be adding some plans for a simple laser cut enclosure to the repository.