The LED matrix. First 2 Planes done.

October 26th, 2011

So I’ve started on the LED matrix.

I have finally decided on how I am going to structure the matrix, but after creating 2 planes, I already regret one of my decisions 😉
Although it’s probably a minor thing.

I thought about how each LED in the matrix should be mounted, and came up with three points:

  • Too many brass rods will block the light.
  • If you place the support rods close to the LEDs, they will cast a fairly large shadow.
  • Too little brass rods will cause the cube to become unstable and wobble when moved.

With this in mind, I came up with this design:

LED close up.

RGB LED close up.

I decided to use 1 brass rod for every row and column in a vertical plane. It might be a bit overkill. I believe eightcubed only  uses 3 vertical rods per plane, but you can’t really make a uniform distribution of rods if you go higher than 2, which is too weak.  I decided to go for a uniform look, and think the extra rods will provide a bit more stability, hoping they won’t block too much light 🙂

I could have used a different orientation on the LED to have the leads all point in the same direction. However, since these are 5mm RGB Leds, the 4 leads are really close together. Bending them like this makes for a better “distribution” of the space between the leads, and puts them a bit further apart which leaves me a bit more room for error 🙂

As you can see, there is quite some space between the vertical support rods and copper wire, and the LEDs. As noted above, I did this to reduce the shadows cast by the rods. The result is actually quite nice. After finishing 2 planes and putting them together however, I noticed that the 3 horizontal leads block quite a bit of light if you view the cube from the top. I’m not starting over 😉 But were I ever to make a second cube, I would place the copper wires closer to the LED. The copper is 0.2mm and doesn’t cast a big shadow, and this way the length of 2 of the 3 leads could be reduces, which makes the cube slightly more transparent 🙂

With 2 planes finished  I’m rather happy with the result so far. I will finish 8 planes first before I go and try to build the cube. I’m building vertical planes. I guess this way it will be easiest to de-solder an entire plane, and take it out if any repairs need to be done to a single LED. Making vertical planes means de-soldering the brass connections on the outside and bottom and lifting plane out. Making horizontal planes would mean de-soldering all the LED cathodes, which  is 3 per led 🙂 I test every LED, row and plane before putting it in, so I don’t expect any problems, but hey, better be safe then sorry right? 😀

Well, that’s it for now! Don’t know when I’ll be making my next blog post, since the next part is just a WHOLE LOT of soldering work to do. After that I’ll start on programming a single led driver, to decide on my circuitry based on what I’ve learned from that 🙂

Talk to you later!

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Comment by iduktech — December 15, 2011 @ 11:33 am

hi, how do you controll these? doyou have a sketch?

Comment by Wracky — December 15, 2011 @ 3:58 pm

Hi iduktech, and thanks for commenting!

I don’t have a final design yet, but I’ve learned a lot from vespine.
I’m planning on using 12 TLC5940 LED drivers which should give me enough channels for 192 leds (64 dots per layer, RGB per dot) and 8 mosfets to multiplex the layers. I’m going to try a 100Hz refresh rate on the cube, like vespine did. The TLCs will be daisy-chained. I’m not sure if I can pull off a chain of 12, but I could also split them into smaller chains. The MOSFETs and TLCs will be driven by a microcontroller. (I use the Pic32 starter kit).

The TLCs control the current per LED. The MOSFETs switch the horizontal layers. Since the TLC drivers supply a constant current sink, these have to be common ANODE leds. All the anodes will be connected per layer, and the TLCs give you column adressing. FUN! 🙂

I will do a full article on my design once I’ve figured out how I want it exactly.
Hope this helps!


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