8x8x8_RGB_LED_project

03/08/2009
I'm going to start blogging this project. I don't like the way this site is growing and I think on a blog it will be easier to add updates the way I've been doing here.
Click the below link.



30/07/2009
So I'm back, I actually had to move house and my internet access has taken about 3 weeks to reconnect. I have had a bit of a chance to work more on the cube, but packing and moving has taken a lot of time too. I'm up to 3 planes out of 8 finished and i'm working on the 4th. I have also started working on the base connectors and board so it's all coming together as planned. I have one photo showing how each plane will fit into the connectors. I'll have some more updates of my recent work soon. I'm also very much not liking how  this site is growing. I thought just adding newer posts to the top would be alright, but it's obvious that if I post a photo or two each time, very soon this page will be too big to be practical, so i'll have to think of a better way to format it. Maybe a page of links by date and thumbnail or something... Maybe I should be blogging this after all.
 
 
10/06/2009 Production starts in earnest.
This is only 200 of the 500 LEDs, I still have to get the rest.. I figure I'm going to make i "plane" of 8x8 LEDs first to make sure everything measures up and fits the way I expect. Once that is confirmed, i'll do the rest.. I'm hoping it takes me only 2 or 3 days to make one "plane". I'll post the results when I'm done with the 1st one. 

On the left you can see the boards I plan to use as the base with the sockets I've placed to test the spacing. I'm planning to paint them black so the sockets don't stick out as much, i think black will suit it better anyway. 

Later that day:
Well, later the next morning, just. It took about 5 hours of solid soldering but i have completed the 1st blade ! :) I don't think I'll be doing that again, my back is sore and my eyes are crossed, from now I think I'll split it over 2 nights..  The horizontal wires look a lot wonkier then they are, i think it's a combination of angle, lens distortion and the fact the flash reflected off them.. The actual LEDs are quite well lined up, i spent a lot of effort on this because I know if any aren't lined up very well along any axis, it will look very out of place when viewed in the 3d lattice...




06/06/2009 I've been thinking a lot about the lay out of everything. I'd like to make this as modular as possible. I'd like to be able to take things apart and improve or replace components if I come up with better ideas or if something doesn't work the way I imagine it. So, I've come up with a couple of good ideas I think, to help make it as modifiable and accessible as possible, even when it is all assembled. A lesson I learned the hard way in my 4x4x4 cube project was once it was assembled, it was very hard to get into the midst of the LEDs.

So I went to Bunnings yesterday and I was looking for inspiration and I found it in the MDF section. What I've decided to do is have 2 sheets of MDF, maybe 9mm. One sheet will have all the electronics on it, the other will be stood off maybe 5cm on top of it and will be the base for the actual cube assembly. I think this will work really well. 

The cube assembly it self will be copied from hypnocube it looks like several RGB cube projects use the same method, not sure who came up with it, but i'm not going to pretend I made it up myself.. Anyone really faced with the same challenge would no doubt come up with something similar. 

The 0.7mm wire fits quite snugly into a header connector so I've decided to try to use 4x1 header sockets to mount the 8x8 LED "blades" onto the PCB.. One of my main concerns before coming up with that idea was that  hard soldering the blades onto the PCB would be irreversible, then if anything went wrong in the middle of the cube it would be very hard to do anything about it. I very much like the idea that the blades are "plugged into" the PCB.

On the bottom of the PCB, i will use 16 core ribbon cable to bring all the LED columns to one side of the rectangle where I will solder it to right angle male header connectors. Then, i will use 16 core ribbon with female sockets on both ends to bring that to the 2 driver boards which will sit beneath with the rest of the electronics, including the uC board which will possibly have the power and layer MOSFETS on it. 


Here is an updated concept diagram of how the cube will be connected.. There are 16 LEDs in 2 "rows" of cube, so each TLC will control 2 rows of a particular color, only red is shown in the diagram for clarity, green and blue will be wire exactly the same way. 

This is different to how I first imagined it on my pipe dream page.  In the previous picture I didn't quite understand how the serial communication worked.. I could technically use GPIO pins to communicate to the driver chips, this is called bit banging, since the software is just driving pins high or low to send the data, BUT this is actually a very slow and ineffective way to communicate. The far superior way is to use the uC's "SPI" module. Serial Peripheral Interface is a serial communitcation standard capable of very fast communitcation, in the order of 10MB a second. The AVRs i was playing with only have 1 SPI module, that's still better then 6 parallel channels of bit bang. 

The pic24 does have 2 SPI modules but I'm not sure I'm going to use them both for the drivers, i MIGHT have one chip drive the TLCs and one chip purely dedicated to making patterns, which could also have a serial interface to PC. Even if it won't improve the performance, it would be lots of fun to implement.. 







04/06/2009 Not really sure how to start this page. i've been working for months leading up to this point so not sure where the beginning is. I'll make a short inventory of all the bits I've collected that i'm planning to use and give a brief outline of my design so far. 

As the base of the physical cube i'm using 6 "experimenters boards" from futurlec EXPBRDLGPHEN

I haven't worked out how i'm going to mount them yet, but I'm thinking a sheet of perspex and some standoffs.

The main controller is a PIC24HJ256GP206 I bought from farnell.

The LED drivers are of course the great Texas Instruments TLC5940, also from farnell on special now for $4.61 each!! Hot price, i paid nearly $8 each for the 1st 3 I bought!

Main power supply is courtesy of LM338T linear regulator. Once i have this all going i'm planning to make my next project a nice simple switcher based power supply to swap instead of the relatively inefficient linear regulator.

My main next step now is to get some bulk LEDs and make up a jig and start soldering up the actual cube, that will require quite a lot of work. The main difference between my cube and the other 8x8x8 I've seen online is I'm using 10mm LEDs, not 5mm LEDs. woof!  I'm waiting on delivery of 200 LEDs, once they arrive I'll order the remaining 300. I already have enough to make up the remaining 12 I'll need for 8x8x8.

The wire I'm going to try to use is plain old 0.7mm galvanized tie wire, i'm not sure this will be very strong, but it'll look very good with the 10mm LEDs. I'm considering different ideas of some sort of frame or exo skeleton for the cube since i'm worried it might be a bit fragile. I don't think a big perspex box is an option since i think it will create too many reflections and diffractions.. At the moment I'm imagining a simple frame of much sturdier rod just for the edges of the cube.. 

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