Introducing ChibiCube

About

ChibiCube is a 3D LED matrix 8x8x8 composed by monochromatic LEDs individually addressable: that means not only every single LED could be in a ON or OFF state but everyone could be set at different light intensity.

Inception

In December 2012, students Ciro Domenico Pagano from University of Salerno, Antonio Galano from Federico II University of Naples and Vincenzo Brillante from University of Sannio start their training at Naples site of ST Microelectronics.

In order to understand uses of ChibiOS and STM32 MCUs, their Tutor Giovanni Di Sirio suggested the design of a small 4x4x4 LED cube. This first version was made on a prototyping board and driven by a STM32F407 Discovery using parallel wiring.

Months later, the cube was engineered in a new version 8x8x8 upgradable to 16x16x16 connecting 4 PCBs together.

ChibiCube prototype
A prototype of a 4x4x4 LED cube.

Meanwhile, a new trainee Rocco Marco Guglielmi, always under G. Di Sirio tutorship, began writing code for assembly tests. In few weeks they build more cubes and the newcomer writes demo code. Project name is: ChibiCube.

ChibiCube v1.0 bottom
The bottom of ChibiCube v1.0.

Thanks to the advice of Luca D’Onofrio, an ST associate Engineer, R. M. Guglielmi is able to develop a solid number of game light.

In November 2013, ST Microelectronics assigns a Scholarship to this one and A. Galano to re-design ChibiCube that reaches version 2.0: this new one provides hooks for a showcase an adapter for connect indiscriminately the STM32F3 Discovery and the SPC560D Discovery. MOSFETs are replaced to manage light intensity thought a software PWM.

Software is re-written and released under GPL3 as S3DL.

ChibiCube v2.0 bottom
The bottom of ChibiCube v2.0.

Notes on principle of operation

ChibiCube is based on multiplexing, that means cube horizontal planes are not driven at one time. Planes are actually refreshed at higher speed than persistence of vision.
Considering a LED cube 8x8x8 there are 8 horizontal floors: everyone is connected as common anode; that means every LED anode on a floor is interconnected each other. Every vertical column is connected as common cathode. There are so 8 anodes and 64 cathodes and their combination (64×8) provides 512 signals to drive every single LED.

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