3x3x3 LED Cube – Part #1

Posted on by hukl

Until now I haven’t posted any schematics. This is because the cubes I’ve shown so far were too trivial. This also the case with this 3x3x3 LED cube and its board. As you can see it uses a lot of wires. 9 Wires for addressing the LEDs on a layer, 3 more wires for multiplexing / switching the layers and one more wire for GND. The Arduino Board provides enough pins and so no fancy techniques are necessary yet. While the board looks clean and simple on the top, the actual wiring on the bottom is a little more complicated.

Even a 3x3x3 cube involves some work. The only new concept here is the use of transistors for switching the layers.

Power

This cube has common cathode layers and common anode columns. This is because each column is directly connected to one of the Arduino IO pins. These pins can provide a current up to 40mA. A typical LED needs around 20mA for full brightness and since there is only one layer connected to GND (-) at the same time each column only draws 20mA at any given time.

The layers are connected to transistors which allows switching the layers to GND with three IO pins. The transistors are all connected to a common GND which has the advantage of requiring only one GND wire instead of having individual wires to  for each transistor.

Also notice that all the LEDs are connected via the cathode which means that if an entire layer is lid up at once, a 180mA (9 * 20mA) are flowing through the transistor.

I don’t have the code for running the cube on that board anymore but I build a second board with shift registers which I will show in the next post.

Arduino Quicky

Posted on by hukl

There are many good websites about getting started with Arduino. Here are two of them:

First of all the Arduino website itself which contains a lot of tutorials, reference documentation, schematics of the Arduino boards and more. http://www.arduino.cc/

The second resources is a tutorial PDF which is available for free and covering all the basics. http://www.earthshineelectronics.com/files/ASKManualRev4.pdf

5×5 Matrix Demo

Posted on by hukl

Next Stop: 27 LED Cube Street

Posted on by hukl

Building the 2x2x2 cube was really easy. We literally bought the Arduino, a couple of LEDs and cables (as described here), put it together and it worked. Of course we wanted to go to the next level immediately, just like in a video game. With the same principles we built a 3x3x3 cube but this time it featured resistors in series with the LEDs, transistors for switching the levels and a socket which allowed us to switch the board or the cube easily. I will explain each step starting with the soldering.

Soldering the LEDs together

Basically there a different ways to do it but all variants share the same principle of having layers and columns. Also its best to have some kind of grid to make sure the connections are as straight as possible.

One way of building a cube is to solder horizontal layers and stack them on top of each other by connecting the cathodes, only using the LED pins. 

Instructions for horizontal layer soldering:

1. Get cheap wood like MDF and draw the desired grid onto it. For regular LEDs the grid width should be 2,5cm.

2. Drill holes where the lines of the grid cross and make the holes 5mm wide (if you’re using regular 5mm LEDs). Start with a 4mm wood drill which could be sufficient.

3. Bend the anode (longer LEG) 90° like you can see on the picture below and put the LEDs inside of the holes

4. Solder the anodes together

5. Cut of two anodes (longer leg) of other LEDs and use them to stabilize the layer

6. Cut of the overlapping wire and the first layer is complete

7. Bend the cathodes to the side like you can see it in the picture so that you can stack the layers on top of each other. You can skip bending the cathodes for the last layer. In the following picture I did only bend the front LEDs. 

8. Build two more layers and solder them together.

Instructions for vertical layer soldering:

The other way of soldering together a cube is to build vertical layers. This has the advantage of being able to switch single vertical layers. In the horizontal version it is close to impossible to fix a broken LED in the middle of the cube. Also allows to build larger cubes that a more solid and straight. This is how you do it:

1. Get some cheap wood like MDF and draw your desired grid onto it. Then use a saw, a screwdriver or a cutter knife to cut out the grid like in the following picture.

2. Get some copper wire and cut it to pieces. Then use two pliers to straighten the wire. Grab the ends of the piece of wire and pull it straight. You can feel when the wire is extending. Release it carefully and you should have a straight piece of wire. I used copper wire which is mixed with silver. I couldn’t find any good translation for “Versilberter Kupferdraht”.

3. Get 9 LEDs and bend them like you can see on the picture. Then shorten the cathode

4. Hold the soldering iron onto the junctions and apply solder. Then grab an LED, head up the solder on the wire, hold the LED like on the picture. Distribute the solder and remove the soldering iron while still holding the LED for a second or two.

5. Attach all the LEDs that way. You can shorten the anode as well by the way.

6. Lay out the columns onto the grid. Cut and straighten three more wires and connect the LEDs horizontally.

7. Cut of the overlapping wires and you have your first vertical layer

8. Now build two more layers. Put them next to each other, then connect these LED walls horizontally with some more wire but just on the outer sides. Does that make sense? This cube, even if its built from vertical layers will have horizontal common anode layers just like the other cube had. Its just built in a more modular way. Therefor the vertical LED modules need to be connected horizontally in each row. 

Now while this seems more work in the beginning, it saves a lot of hassle later on. Imagine building a cube in the horizontal layer way. When the LED layers are stacked on top of each other, 9 cathode connections need to be made every time. As you cube grows it is getting harder and harder to solder it straight. A mentioned before it is also getting harder to extract an LED from the middle. Imagine building a 10x10x10 cube where 100 cathodes need be be soldered together for each layer! 

With the vertical LED module approach the stacking is already done. They can be be easily plugged one after another into their sockets and only need a few connections horizontally so connect them and to stabilize the cube. Since the horizontal connections are mostly on the outside of the cube, they can be easily removed to take out / replace individual modules.

Finally the cube will be more stable if straightened wires are used instead of the LED pins. I build a 5x5x5 test module which I could stick into my breadboard. I even attached a bunch of cables and its still stable.

 

This 5×5 matrix is again completely powered by the Arduino which is connected to my MacBook Pro. There are only a few Arduino pins used. Two of them supply the power and five control the LED driver chip which is called TLC5940.

If something about the soldering part is still unclear, contact me please.

2x2x2 Multiplexing Demo

Posted on by hukl

Today I decided to use the small 2x2x2 cube to demonstrate multiplexing and so I got out my breadboard and connected it in most simple way possible. All six cube pins go directly into the Arduino IO pins. I uploaded the program which I mentioned in one of the previous posts and it worked right away. It is actually bad to connect the LEDs directly to the Arduino without any resistor in between but the Arduino is very forgiving and works with like that with smaller loads. This should not be a permanent design pattern however. The video shows that the LEDs can not be addressed individually when powering both layers because they share cathodes horizontally and their anodes vertically. Therefor its not possible to switch on the upper left and the lower right LED individually at the same time as all the other LEDs in the same column would light up as well. This is shown in the beginning of the video. To solve this problem the layers are switched on one after another in such a fast way that the human eye does not recognize it. This is the basic principle for most kinds of LED matrices. Again the corresponding program is trivial. Next up: Bigger cubes and more advanced techniques.