4x4x4 tricolor light cube

7/31/2019 4x4x4 Tricolor Light Cube

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4x4x4 Tricolor Light Cube

Brett Armstrong

IME 458Spring 2011

California Polytechnic State University

(916) 502-6819

[email protected]


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Abstract:

The 4x4x4 tricolor light cube is a 3 dimensional matrix of LED lights. Each LED can

display red, green, blue, or a combination of those three colors. A PIC microcontroller drives the

LED matrix to create a series of animated patterns by turning on and off LEDs in sequence.

Hardware:

The light cube hardware consists of two main sections, the driver circuit and the LED

matrix. Figure 1 (below) shows the schematic of the driver circuit. The driver circuit uses three

constant current sink LED drivers controlled by a PIC microcontroller. Each LED driver controls

one color and has 16 ports that connect to the cathodes of LEDs in the matrix. Each of the 16

ports corresponds to a location in the 2 dimensional top-down view of the LED matrix. All 4

LEDs (one per layer) in each location are connected to the corresponding port of the LED

drivers. The microcontroller also drives 4 BJT NPN transistors that are used to turn on and off

each layer. Because the cathodes for each color in each location are connected across all layers,

only one layer may be turned on at any one time.

The LED matrix consists of 64 tricolor LEDs. Each LED has 4 wires: a common anode

and 3 cathodes, one for each color. All anodes per layer are connected in parallel. All cathodes

per (vertical) location and color are connected in parallel. All LEDs are 1 inch apart in all

directions.


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Figure 1 : Schematic


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Assembly:

This project took about 25 hours of soldering and assembly to complete. The first step

was to create the LED matrix. To build the matrix, I first made a pattern to hold LEDs in a 4x4

grid with proper spacing and orientation to build each layer. All anodes across the layer were

then connected to a single point that would connect to the circuit board. I was able to use LED

leads to make all connections, but sturdy wire could also have been used. Additional wire is

needed to add stability to each layer. After completing all 4 layers individually, the next step was

to put the layers together. The tips of the LED leads were bent into a hook shape and attached to

the base of the LED on the layer below. Extra care must be taken to ensure that all colors are

matched up properly and no shorts exist between any of the wires on the LEDs. Once all

connections are made, repeat with the additional layers until the whole cube is complete.

The next step was board assembly. Although this should have been a very quick board to

solder, the DIP version of the LED driver was not available so a very small SMT component was

used instead. Each of the 3 LED drivers took longer than the rest of the components combined

(not including LED matrix). Solder bridges between pins were very hard to avoid and even more

difficult to remove. After those 3 components were complete, the rest of the board was very

quick to complete.

The final step to complete was a rework of the original schematic. There are two reworks

that had to be completed. The first was due to an oversight where one of the pins on the PIC

microcontroller is used as an output port even though it is input only. This simply required a

jumper to an adjacent unused output port. The other rework reassigned the way the pins on the

microcontroller connected to the LED drivers. This project could have been successfully


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completed without doing the second rework since the original schematic was not flawed.

However, this rework provides several software advantages such as improved speed and code

readability. All schematics and board layouts submitted reflect the latest reworked versions.

Software:

The software for this project uses a simple timer interrupt model to control the

multiplexed LED matrix. Each time an interrupt occurs, the current layer is turned off, data for

the next layer is written to the LED drivers, and the next layer is then turned on. Interrupts must

occur quickly enough that all layers are refreshed at > 30Hz to avoid flicker. The algorithms to

generate patterns run in between interrupts. Any number of patterns can be added and the cube

will loop through all of them indefinitely.

Conclusion:

This project really highlights the benefits of interdisciplinary collaboration. I was able to

do a project of much higher scope and complexity by combining my CPE and IME class projects

into a single design. This project also demonstrated how closely all phases of design must be

connected. The schematic has to be made with software design in mind, and therefore sometimes

software changes can force schematic changes. Once the board layout has been sent out for

manufacturing, schematic changes can be very difficult to do and will affect the look of the final

product. Planning ahead is key, however this also presents design issues such as how to write

software for hardware that doesnt exist yet because the board has not been sent out for

manufacturing yet.

4x4x4 tricolor light cube

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