Building 3D LED cubes out of discrete, thru-hole LEDs is a popular right of passage project for many makers. Many of these cubes are small at 4x4x4 with some increasing to 8x8x8. Most feature single color LEDs. Less popular are cubes larger than 8x8x8 or with RGB full color LEDs. One aspect of these discrete LED cubes that poses a challenge is how to control the LEDs especially if the number of LEDs is large. An 8x8x8 cube has 512 discrete LEDs. If the cube is RGB then you have 512 red + 512 green + 512 blue = 1536 LEDs to control.

Regardless of how you choose to control them (individual wires, charlieplexing or some other method) you may have a lot of individual control signals to contend with. Assuming you have a controller board with the requisite GPIO pin count, you also have to contend with high current flow. While individual LEDs sip power, for large groups of LEDs the power requirements add up quickly. 

As we showed above, an 8x8x8 cube has 1536 discrete color LEDs to control. If each of these LEDs pulls 20 mA of current, then at full power with all LEDs turned on the cube will pull 1536 x .02 = 30.72 Amps! Discrete LEDs also require current limiting resistors to ensure that they don't pull more than the desired amount of current. You can use current driver chips or transistors but either way the number of discrete components grows quickly.

One way to overcome the LED control issue is to use so-called "smart" or "addressable" LEDs. These are usually surface mount devices that include individual R/G/B LEDs and all the circuitry required to drive them, including current limiting, all inside a single, small package. Current is pulled directly from the power supply the LED connects to and not from a GPIO pin of a micro. Additionally, no extra transistors or driver chips are required to handle large current flow.

More importantly, the color value of the LED is controlled via one or two digital control signals. A discrete RGB LED requires four control signals -- R, G, B, and common anode (or cathode). Addressable LEDs, in contrast, require only one or two signals. Furthermore, the addressable LEDs can be daisy-chained together such that controlling a large number of LEDs still only requires one or two signals to control the entire chain. Some common LEDs of this type are the WS2812 which uses one digital control signal, and the APA102 which uses two digital control signals.

The downside of using smart LEDs is that they tend to be surface mount devices, not thru-hole mount, so building a cube with them presents different construction challenges. The discrete wires used to construct cubes built with thru-hole LEDs have to be replaced with printed circuit boards for the surface mount LEDs.

Another thing to consider is that the thru-hole LED cubes required coarser soldering skills whereas surface mount LEDs require finer, more detailed soldering skills if assembled by hand. However, most of the hand soldering can be alleviated by using reflow techniques for the surface mount LEDs. Regardless of how the soldering is accomplished, surface mount LED cube assembly is quite different from thru-hole LED cube assembly.