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61  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 15, 2013, 04:15:44 pm
Extrenal  5V/GND connector it is then smiley This makes me wonder, though... the fact that I need to connect the Arduino's GND pin to the ground of the LED circuit still holds true, right?
62  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 15, 2013, 01:53:22 pm
Too bad... Well, then I'll just connect the LED driver board directly to the power supply unit.
63  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 15, 2013, 10:47:00 am
I have a really basic, but important question. The Arduino has some pins marked 5V and GND. See the group of pins which is leftmost on the bottom of the following image:



My question is: Are those 5V/GND pins directly connected to the power jack of the Arduino or the current passes through some circuitry in the Arduino before it reaches the 5V and GND pins? I'm asking because I want to determine whether I can feed my LED Cube Driver circuit from these 5V/GND pins of the arduino or I need to connect my LED Cube Driver to the real power supply's 5V and GND. As you know, my LED Driver Circuit can work with currents up to 1.3A and I'm wondering if it's safe to take that much current from the Arduino's 5V/GND pins...
It would be nice if I could feed my custom circuit from the 5V/GND pins of the Arduino because that way I would have only one power connector (on the Arduino), I would only need to solder some pin headers on my own custom circuit.

Thanks!
64  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 15, 2013, 04:30:15 am
Yepp, the top/front is the ground plane smiley
I'm not quite sure yet about how the pads (round and rectangular connection areas) are connected to the whole ground plane (which is mostly all a big copper rectangle), as they seem to have some isolation circle or rectangle around them, but I'll figure that out...
65  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 14, 2013, 08:31:18 pm
I've made a dual-layer version of the circuit smiley Unfortunately it's very late again and I haven't had time to properly verify it. Maybe tomorrow...

Front:


Back - Mirrored:


Back:


The ground plane really has helped a lot. The board size has decreased from 180 x 120 mm to 140 x 100 mm smiley Thanks for the tip, CrossRoads!
66  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 14, 2013, 08:30:58 am
I've found an article about the Arduino SPI, here: http://arduino.cc/en/Reference/SPISetClockDivider
It seems that the SPI frequency can be set from software. The default is 4 MHz. I wonder what the optimal value is. You don't want it to be too slow, because it will become visible in the cube. You don't want it to be too fast because high frequency signals complicate things...
67  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 14, 2013, 06:36:29 am
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...
68  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 14, 2013, 04:51:36 am
"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:

69  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 14, 2013, 04:47:23 am
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 smiley 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...

70  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 13, 2013, 08:00:30 pm
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 smiley
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 smiley
71  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 13, 2013, 03:26:00 pm
Yes, I think it's important to emphasize that CrossRoads is the mastermind behind this design. Thank you, CrossRoads!
72  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 13, 2013, 02:34:23 pm
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.
73  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 12, 2013, 05:24:38 pm
Updated schematic:
74  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 12, 2013, 11:30:18 am
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.
75  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 12, 2013, 08:53:37 am
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
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