How to Build a Simple LED Cube 4x4x4 - Part 1

Project Features

• Easy to build
• Only two active components (apart from the LEDs, of course)
• Includes detailed build instructions, schematics and software

Introduction
When I posted my charlieplexed 4x4x4 LED cube I did so in order to show an alternative implementation for such a cube. Its unique feature is that it only uses 9 controller ports. For some reason it gets a lot of interest from lots of people. And I had quite a few requests for schematics because people wanted to build it.

The problem with it is that it is only simple in terms of hardware requirements. But it is relatively complicated to understand its structure. So I thought I should try my hands on a really simple, easy to build LED cube and write a post including build instructions for people with basic skills in electronics.

Required skills and knowledge
Unfortunately I cannot cover every last detail about how to build electronic circuits. So this is what you should be able to do:

• Soldering wires and components
• Programming the flash memory of an AVR ATMega8L
• Reading simple schematics

Components you need

LEDs:
Obviously you will need 64 LEDs. I am using ultra-bright red 5mm LEDs for this project. They have a special shape called "straw hat" which give you a wide viewing angle.

Some LEDs have a very narrow viewing angle, like 15° for example. This means that most of the light goes straight up. But we want to look on the cube sideways. This is the reason why I chose the wide angle.

Choose what shape, size or colour you want. But if you use any other colour, this might mean that you need a higher operating voltage. My LEDs have a forward voltage (Uf) of around 2 Volts and the whole circuit will run off two AA batteries (3 Volts). It is also possible to run the cube with three AA cells to get brighter light. In that case the pulse current per LED will be around 50 mA which is fine.

My set of 100 pieces cost me under 3€. Value for money...

The only problem that I had with my LEDs was that their leads where relatively short. I simply didn't notice that, when I ordered them. But what it means is, that the cube got a bit smaller than intended. This is because I only use the leads to connect the LEDs to each other.

In general it is probably a good idea to get the gaps between the LEDs as wide as possible. Otherwise you have problems seeing all LEDs at the same time. But I didn't want to wait for another batch to arrive, so I went ahead anyway.

Controller:
Not much to say there. It is an ATMega8L in a DIP28 package. The "L" is important, because it means that the microcontroller can run at voltages down to 2.7 Volts. The version without the "L" needs at least 4.5 Volts. The Mega8 has got more than plenty of memory for generating a variety of effects or patterns - if you know how to generate them efficiently.

Prices vary depending on where you buy (2 € or more)

Driver:
The microcontroller's ports cannot drive more than one LED, so they need the help of drivers. I am using an ULN2803, which contains 8 separate drivers. It is available for under 0.50€.

Optional / Misc Components:
You will need some wire and quite likely a piece of perfboard. It might be a good idea to use sockets for the ICs. Depending on your power source you might need a battery holder. And finally, if you want to be able to change the firmware of the controller, a ISP connector will be useful.

The whole set of components can be bought for under 10€. Not too bad, I think.

How it Works
Basically, the cube is wired like a standard multiplexed LED matrix in a 8x8 configuration.

Most people seem to base their design on a 16x4 matrix. This has the advantage that the LEDs are multiplexed with a 1:4 duty cycle, whereas my design has a 1:8 duty cycle. So my design is less bright. But I found that even my charlieplexed LED cube with a duty cycle of only 1:9 is very bright - because I use ultrabright LEDs.

Another advantage of the 16x4 matrix is, that you only need to drive 4 groups of LEDs, for which many people use discrete transistor stages. There are 8 groups in my design. So I need 8 drivers. But since the IC that I chose has got 8 drivers, that is no real disadvantage.

One advantage which my 8x8 structure has, is that I need only 8+8=16 controller ports, whereas the 16x4 design needs 16+4=20 ports. This means less connections (i.e. less soldering, less wiring) and it leaves you with some ports for further extensions (e.g. switches, a serial connection, etc.)

Also,  I think, that my version is a little easier to build. This is because it really isn't a 4x4x4 cube, but instead consists of two independent 2x4x4 "half-cubes". In my opinion, these are much easier to assemble. Find the details about that in the next paragraph.

Building the Cube Structure
This is the hardest part. Building the 3D structure will take about 3 - 4 hours, depending on your soldering skills and patience. There are several steps in this build. Keep testing it! Once the cube is assembled, it is next to impossible to repair anything. So keep testing! I know why I say this, believe me...

TIP: A simple way to test LEDs is with a multimeter set to "diode test". The multimeter will drive a small current through the LED, so it will light up dimly. Try all possible combinations of connecting columns and levels of your cube with your test leads. Do this after every step. 

But first:

Step 1: Prepare the LEDs
The LEDs need some preforming of theirs anodes. We start with a standard LED.

Use pliers to hold the longer wire (the anode).

Make a 90° bend.

 And finally bend it the other way.

This is the result.

And here is the reason why we have to do this. The LEDs will be stacked later. In each column of the cube, the anodes of the LEDs will be used for this. And without the preforming, it would be difficult to reach the anode below. Here is a photo just to demonstrate that point. Note that we don't stack yet.

So keep repeating this until all of your 64 LEDs are prepared for step 2.