Tesseractive

Introduction

Tesseractive is my current electronics hobby project, a work in progress. At its core, Tesseractive is a rearrangeable, LED puzzle cube (Its name is a play on the word tesseract, the 4D analog of a cube, a type of hypercube). Each of the cube's six faces contains a 5x5 grid of individually addressable RGB LEDs, which form patterns of color and shape. The object of the puzzle is to solve these patterns by rearranging the faces (or "panels") of the cube, which are attached to a center frame via magnets. They can be removed and reconnected to any side of the cube in any orientation. The main circuit board is housed within the frame, along with batteries. Feedback is given to the user through sounds and vibration, as well as through an optional bluetooth-enabled smartphone application. Below you can view a scale rendering of the cube design and a single LED panel, and navigate in 3d space using your mouse and scroll wheel. Ensure hardware acceleration/WebGl is supported by your browser and enabled.

Created in Sketchup

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Technical Challenges

The most difficult aspects of this project are the intricate geometrical and spatial challenges that it poses, and the complex microcontroller logic required.

• Each panel can be oriented in any one of four ways and are only connected by magnets. How does each panel physically receive power and communicate with the microcontroller irrespective of which side it's on and its orientation?
• Each panel circuit board should need nothing more than LEDs and a few passive components. How does the microcontroller identify the panels, knowing which are connected, their locations, and orientations?
• Neodymium magnets lose their strength when exposed to extreme heat. Can magnets be electrically connected to copper wire and/or circuit board traces without interfering with its magnetic properties? Will they be strong enough? Will they be too strong to easily pull apart?

Identifying the Panels

Each LED panel needs power, ground, and an input signal for LED control (from the microcontroller). However, for the microcontroller to extrapolate the placement and orientation of any panel, it will need to identify at least one of its edges. For this purpose, each panel will have four additional "ID" outputs, one on each edge. Each ID output will generate an analog voltage unique to itself, easily accomplished through a pair of resistors acting as a voltage divider. A different ID output will connect to the microcontroller with each turn of the panel. An ID analog input from each side of the cube is the only information the microcontroller needs to construct a virtual map of the cube. In conclusion, each side of the frame will need four connections, a connection to power and ground, a control line for the LEDs, and connection to an ID.

Magnets Since the neodymium magnets that hold each panel of the cube onto the frame are normally coated in nickel, they are also perfect for supplying the four signals. No extra connectors are needed. However, research into transmitting current through magnets revealed that soldering onto them would weaken them and possibly destroy their magnetism all together. Other alternatives may need to be used if this occurs, such as a conductive epoxy or glue. After all, the magnets need to not only conduct current, but be strong enough to firmly hold each panel onto the frame without making it too difficult to pull off. The amount of force needed to pull the magnets apart can be estimated based on diameter, thickness, and grade. Once a panel has been fully assembled and weighed, a proper set of magnets can be selected.

Panel Geometry

Because each panel will be connected in one of four orientations, either the frame of the cube or the panel will need to have the four connections repeated in sequence on each side, so that no matter which way you rotate the face, the same connections still occur (with exception of the ID output since its entire point is to be different on each edge). Adding more complexity to the panel circuit will be much easier than having quadruple the number of wires running up and down the inner frame, so the latter approach will be used. Note that in the first image of the diagram below, if you rotate the panel any multiple of 90 degrees, at least one of the red lines within the cube aligns with the outer line. However we have three more connections. In the second image, those connections have been added. The only issue is that all of the outer connections are on one side. In real life, these connections will be magnetic, so they are best spread as evenly as possibly, preferable one on each side. The third image is an example of a proper configuration. Note that the cube can be rotated just like before and still make the appropriate connections. This explains why in renderings, the holes in the frame are placed so oddly.

LEDs

Rather than reinventing the wheel and wasting precious physical space, instead of wiring the LEDs from scratch, a set of 150 SK6812 controller/light emitting SMDs, also known as neopixels will be used. Besides being small (10mm x 10mm x 1mm), these LEDs are chainable, each LED input connected to the output of the previous. This means that for the Tesseractive project, only six digital pins will be needed to control the lights, one for each face. The disadvantage is that these circuits are power hungry. Each addressable LED will draw between 20 and 60 mA of current, for a rough estimate of 6A from the LEDs alone. This changes design requirements, thicker or wider circuit traces and possibly thicker wires to dissipate heat properly.

Enough of the technical challenges have been addressed to design a circuit for the LED panels. The following circuit diagram is shows all electrical connections of the design and is not meant to give an accurate representation of where components will be placed. However, it does give some indication of how the inputs and outputs will line up on the edge of the circuit.