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Topic: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 (Read 45527 times) previous topic - next topic

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...
Andras
http://iqjar.com

CrossRoads

1 & 2: I have daisy chained 20 TPIC6B595 shift registers spread over 2 boards.
The up-to-40mA capable IO pins had no problems driving them at default SPI speed of 4 MHz.

I don't know how your new program does a ground plane, ground pour, or what it might call it.  In eagle, you draw a polygon covering the area you want and then Name it GND.  I do on the top & bottom layer because iteadstudio does 2 sided boards as standard.  1-sided is usually just home board creaters - I won't be bothered doing that when compex designs can be had  & silkscreened & solder masked & have plated thru vias, all for $25 for 10 boards. (10cm x 10cm)
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.

I've made a dual-layer version of the circuit :) 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 :) Thanks for the tip, CrossRoads!
Andras
http://iqjar.com

CrossRoads

The front/top is the ground plane? Looks like it, just confirming.
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.

Yepp, the top/front is the ground plane :)
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...
Andras
http://iqjar.com

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!
Andras
http://iqjar.com

Hippynerd

Im not sure about the mega, but the 328 based units seem to be limited to 500ma at the 5v pin. My guess is that 1.3a is going to too much, even for the mega.  I think that the 5v pin limit is from the specific voltage regulator that is used (the part right next to the external power socket.)


https://sites.google.com/site/rgbledcubes

retrolefty


Im not sure about the mega, but the 328 based units seem to be limited to 500ma at the 5v pin. My guess is that 1.3a is going to too much, even for the mega.  I think that the 5v pin limit is from the specific voltage regulator that is used (the part right next to the external power socket.)





That and when using USB power there is a 500ma thermofuse that limits the maximum 5V current one can draw.

Lefty

Too bad... Well, then I'll just connect the LED driver board directly to the power supply unit.
Andras
http://iqjar.com

retrolefty


Too bad... Well, then I'll just connect the LED driver board directly to the power supply unit.


Always a better way to go. The arduino boards are great at controlling stuff but are pretty wimpy at powering things.

Lefty

CrossRoads

5V & Gnd are connected to the output of the 5V regulator, which is rated at 800mA,and is fed by a 1A rated diode from the barrel jack connector, or 500mA from the USB port.
For 1.3A, you need an external source for sure.
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.

Extrenal  5V/GND connector it is then :) 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?
Andras
http://iqjar.com

CrossRoads

Yes, Gnds must be connected. Arduino, LED "shield", power supply.
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.

I have perfected the dual layer design. Here is the result:

Front (ground layer):


Back (Mirrored):


The power supply is supposed to connect through a barrel jack identical to the one on the Arduino (this should be soldered onto the LED cube driver board's front). The MOSI, SCK, SS and GND of the Arduino are supposed to be connected via standard pins (breakable pins soldered onto the front of the circuit, either male or female). The anode planes and cathode columns are supposed to be connected to the board via standard pins (male/female pin headers soldered onto the front of the board).

If any of you guys want to try producing a real board from the design, I'm happy to send you the Sprint Layout file or some exported results (PDF, Gerber file, drill data, isolation milling, PCB outline milling, etc.). Please keep in mind that this has never been tested (except virtually inside Sprint Layout), so there's a chance that it has some bugs :)
Andras
http://iqjar.com

CrossRoads

Nice. See you figured out how to run some traces on the top too.
What's the size of the board now?
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.

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