24 X 24 X 24 RGB LED Cube

The project to be accomplished this term in Robotics Project is the first layer of a 24 X 24 X 24 RGB LED cube. The design of the cube will use panels of 24 X 24 LEDs, and feature a PCB in the corner. The cube itself will feature a door that will provide access to each of the panels. Each row provides power for the LEDs, while we are going to use PWM chips to provide ground and PWM capabilities. The plan is to use 16 brightness levels, which translates into 4096 different colors per LED.

Each panel will be connected between the layers by 11 data wires, power, and ground. This connection is shown below, in Figure 1.

Figure 1. Layers and connections.

Let’s look into a single layer. One layer is located on one panel from above. Each layer features 3 major parts, the LEDs, the power circuit, and the ground circuit. We plan on using a row/column select format by putting the LEDs in a grid. The LEDs will appear in the small grid pattern shown in Figure 2, except it will be extended 8 times in each direction.

Figure 2. 3 X 3 grid of LEDs.

This grid pattern covers the LEDs, which are common anode in the current situation. Each row of LEDs requires about 1.4 A of power. This will be taken care of on the power side, which will use demuxes to drive a given transistor. This transistor is hooked up to a 5V, 30A line to drive every layer. This schematic is show in Figure 3 below.

Figure 3. Power side schematic.

On the ground side of the panel, each TLC5940 (PWM driver) is a current sink driver. The TLC chip offers resistance on each output channel, set by a resistor on the IREF pin. The ground circuit is laid out in Figure 4.

Figure 4. Ground side schematic.

Software has not yet been worked out. The idea is to use a 3D array of Pixels. Each Pixel holds a 4 bit number for red, green, and blue values representing the brightness levels. These brightness levels will then be translated into a 12 bit value, which will then be bit banged out of the microprocessor into the TLCs.

More details to come!