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Topic: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 (Read 43921 times) previous topic - next topic

Ok, thank you :)
I'll first see how my 4x4x4 test cube turns out and if the hardware and software parts both prove to be correct, then I'll most likely need an LED support board :) I'm still thinking about the other one...
Andras
http://iqjar.com

CrossRoads, I think I've spotted a mistake on all he connection diagrams that we've shown so far:


If you look carefully at the TPIC6B595 shift register on the bottom of the diagram (the one which drives 8 cathode columns) and at the connections to its pins 13 and 12 (SRCK and RCK), you'll see that according to the connection diagram the SRCK connects to the next shift register's RCK and the RCK connects to the next shift register's SRCK. It think that's messed up and should be the other way around. I think that all shift registers should have their SRCK pins connected together and their RCK pins connected together, including the shift register which drives the anode planes. In other words, the Arduino's D13 (SCK) should be connected to all shift registers' SRCK and the Arduino's D10 (SS) should be connected to all shift registers' RCK. Am I right?

Another question that came to my mind: looking at the TPIC6B595's data sheet, I se that its pin 2 is marked VCC. In our diagram pin 2 is not connected to the 5V rail. Is that OK?

Thanks,
Andras
Andras
http://iqjar.com

CrossRoads

The "To Next Device SCK" & "To Next Device SS" notes are swapped, I'll agree with that.
Pin 2 is shown connected to +5V.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Ouch! I missed the connection of pin 2.
OK, thank you! I will correct the diagram tonight so that others who read this in the future see the correct design.
Andras
http://iqjar.com


Hippynerd

After you get this going and tested, I'd like a copy of the schematic and BOM, I may make one, but like crossroads said, there isnt enough time in the day to build all the stuff that i want to build.

My initial tests with transistors has lead me to wonder why anyone would ever use anything but a mosfet, but I still have more transistor torture to do before I make any decisions.
https://sites.google.com/site/rgbledcubes

Sure thing, Hippynerd! I'll send you everything when it proves to be working, although I'm afraid that's going to take at least 2 weeks from now.
Andras
http://iqjar.com

Hippynerd

Sweet. Thank you :D
Please dont rush on my account, I would prefer that you insure success.

Also, thank you crossroads, youve done a great job here too.
https://sites.google.com/site/rgbledcubes

Yes, I think it's important to emphasize that CrossRoads is the mastermind behind this design. Thank you, CrossRoads!
Andras
http://iqjar.com

CrossRoads

Well, we'll see if you guys can make it work!
I used similar for an 12x8 matrix here
with 8 common cathode 'rows' sunk by ULN2803 (from arduino pins) and just resistors sourcing the anodes - two 6B595s pulled the anodes low for the "off" LEDs.

6B595 & PNP/row is a little more hightech, but is really needed for the much higher number of LEDs that can be on.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

A friend showed me these days a really nice piece of software called Sprint Layout, which can be used to design custom printed circuits. I started playing with it and found that it's very easy and straightforward to use. Driven by the desire to have the whole LED cube driver circuit on a single board, I've taken CrossRoads' design and tried to create a drawing for a printed circuit. Here's how it turned out:

Back:


Imaginary Front:


Real Front:


The board is 180 mm x 120 mm and holds all the components (except the Arduino and the LEDs, of course). The connections to the Arduino are marked with large rectangles and the connections to the LED cube are marked with small squares. The round connections are all internal.

I've struggled with it for about 6 hours until I have reached the current result. This is the first time in my life that I've ever done something like this, so it might be far from perfect. It might even have errors in it, unfortunately it's 3 o'clock in the morning here already, so I have to go to sleep, I can't verify it... If you guys notice anything strange or you have suggestions related to how it could be improved, let me know :)
I've spent quite a lot of time trying to squeeze things into the smallest space possible. A multi-layer PCB would have probably been smaller, but I don't know how to do that and I didn't even want to work on more than one layer because it might complicate the creation of the board.

Now, I haven't got the slightest idea yet if and how I can turn this design into a real board. I don't know anybody or any company who will accept such a design and make a board out of it. For now, it's just a design. If I can turn it into something concrete that's going to be great. If not... well, it has been a nice learning experience :)
Andras
http://iqjar.com

CrossRoads

Nice plan!
couple of thoughts:

Quote
The board is 180 mm x 120 mm
That's gonna be pricey.
5  boards for $76.20 for example at iteadstudio (2 layer >10cm x 10cm >> 15x20cm price.
Figure out 2 sided & shrink it down. May not be much smaller, my 12xTPIC6B595 board is 100x100mm,  not sure of removing the 'arduino' portion and 3 shift registers would let 64 resistors fit instead. Even 10 x 15cm would get you down to $44.20 for 5.
(mine was designed with LED strips on mind, which have their own current limit resistors).

Quote
holds all the components (except the Arduino and the LEDs, of course)

So put the 'arduino' on it. Just the 328P, xtal, two 22pf caps, couple of 0.1uF caps, 10K pullup resistor, header to attach USB/Serial adapter to.

Would be a lot easier to review from a schematic.
Add ground plane top & bottom will eliminate a bunch of traces.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Thank you for the advice CrossRoads!

"Put the 'Arduino' on it" - just when I thought that I've figured it all out, you got me tempted again into figuring it out even deeper :) It's a nice idea. Until now I haven't considered it because my understanding of things was just not deep enough. But I've learned a lot these days, so now it's a different perspective... Based on my test results with the 4x4x4 cube, I might consider this, replacing the Arduion with a built-in controller!

Ground plane - what a simple and efficient way to ground things! I've never thought of this until now, but that certainly would eliminate a lot of strips! But where would that ground plane be? The current bottom (with the strips) would be the top and the bottom would be the ground plane? I'll have to read up on this...

The first thing I'll have to figure out is who or what company can turn the design into a real circuit. Based on that I will be able to decide how many planes I can have (how many they can do). I'd rather find somebody who can just make 1 or 2 boards, there's nothing I can do with 5... But I guess it's not worth it for them do make less than 5...

Andras
http://iqjar.com

"Would be a lot easier to review from a schematic." - I'm not entirely sure what kind of schematic you mean, but I've done it based on your design:

Andras
http://iqjar.com

I've shown my circuit design to a friend who really knows about electronics. HE had two remarks/questions:

1. Will it not be a problem that the SCK and SS signals coming from the Arduino are connected to 9 shift registers? He says that the SCK and SS signals are probably carried by weak currents (10-20 mA) and if this gets divided into 9 parts, it might be a problem. He also says that he looked at the datasheet of the TPIC6B595 shift registers and that they can work with very low currents, so maybe it's not a problem after all. I thought I'd ask your opinion anyway, just to be on the safe side. According to my friend, if this is a problem, I could employ some buffers like the 74HC125 in order to get around the problem, but I'm not sure what that means in our case.

2. What is the frequency of the MOSI/SCK/SS signals coming from the Arduino? It seems that if the signals have a high frequency, the circuit design becomes more complicated. Now, I'm sure that the signals cannot be faster than 16 MHz, which is the CPU frequency of the Arduino, but I wonder how high is the actual SPI frequency. If it is too high, do I need to take into consideration some additional things? He mentioned something about impedance, but that's a bit high-level for me at the moment...
Andras
http://iqjar.com

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