Power problem

[Peter Chestna]

I have powered up with an Arduino Mega and I'm having a power problem. The power requirements to light all the pixels with anything but a very low brightness exceeds the Mega's output. I see a place to solder a connector for power/din which I presume is for cube to cube connectivity. Can this be used to power the pixels or do you have another suggestion?

[Peter Chestna]

So I've made the problem a little better by removing the Arduino and powering it with a 2A wall wart as you did with the Spark Core and wiring the necessary pins together. There is still a limitation with the power regulator on the Mega so I cannot use the entire 2A without burning out the board. It looks from the schematic that the LED reeds are powered in parallel which is good news. Ideally with this many pixels I'd like to apply 10A to get maximum flexibility in brightness. Looking forward to your response. I have my soldering iron at the ready.

[alex hornstein]

Hi Peter,

I looked up the schematic of the mega <http://arduino.cc/en/uploads/Main/arduino-mega-schematic.pdf>, and it looks like it has a 500mA resettable fuse in between the USB input and its 5V output.  This is different than the spark, which connects its USB power input directly to the 5V bus.  

Two suggestions:

The first is to limit the brightness of the LEDs in software.  For most of the spark code, we scale down the R,G, B values to a max value of 50 (instead of 255).  We found this value by trial and error — it kept the LEDs visible in daylight, but was low power enough that the current-limiting circuit didn’t kick in and distort the color during normal operation.  For a pure software fix, you could try using a scaling function like this one, to scale down your (R, G, B) values to something that works with the available power.  

color scaleColor(color voxelColor, int maxBrightness)

{

voxelColor.red=map(voxelColor.red, 0, 255, 0, maxBrightness);

voxelColor.green=map(voxelColor.green, 0, 255, 0, maxBrightness);

voxelColor.blue=map(voxelColor.blue, 0, 255, 0, maxBrightness);

return voxelColor;

}

If you want to remove the hardware constraint altogether, you can solder a separate 5V power supply to the connector you mention that's on the underside of the board (see attached image for reference).  BE CAREFUL — that connector drives straight in to the 5V bus, and if you apply more than 5V to your cube, it’s possible to blow out the LEDs.  

That will provide 5V power to your arduino, as well.  If you go this route, it’s best if you unplug the USB cable from your arduino, so you’re not driving the same bus with two competing power sources.

Happy hacking,

Alex

[Peter Chestna]

Will the bus be able to handle 10A? This is what I have: https://www.adafruit.com/products/658. I used it to drive a 350 led Christmas Tree project. Also was my reading of the schematic correct? All LED reeds connect directly to the common power bus? 

[Alex Hornstein]

Yes, the bus can handle 10A.  It’s basically a giant copper pour on both sides of the baseboard — one side is +5V, one side is GND.  And yes, you’re correct —all the LED sticks are connected directly and in parallel to the power bus.

—alex

On Dec 20, 2014, at 7:41 PM, Peter Chestna <peter....@gmail.com> wrote:

Will the bus be able to handle 10A? This is what I have: https://www.adafruit.com/products/658. I used it to drive a 350 led Christmas Tree project. Also was my reading of the schematic correct? All LED reeds connect directly to the common power bus? 

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[Peter Chestna]

So I've modded the cube and wired in a 2.1mm barrel jack to accept my 10A power supply. Now I have the headroom I need to really light it up. For those that are interested, here are the parts: 

https://www.adafruit.com/products/610, https://www.adafruit.com/product/658

I highly recommend this modification, especially if you are using an Arduino. I was a little nervous about drilling the plexi but it turned out alright. Would be great if a 1/2" hole was added to the panel so that people could just mount their power jack.

[Peter Chestna]

Expand 'quoted text' in my last comment for pictures.

[Werner M.]

Aah. Now I see what that hole in the lower back panel is for. It's in line with the power connection on the baseboard. Umm.
Got a 12Vx10A brick here doin' nothin' useful lately. Now I gotta get me one of those screw-on barrel connectors (didn't know those existed). And a couple those as well:
http://goo.gl/HO76Lu
I don't really need the acrylic enclosure (they also come without the case: http://goo.gl/nWwHsJ), but it does match the cube nicely. Wiring a couple these in parallel should give the current output needed (with both outputs adjusted to supply a 5V constant voltage)

That's a cheap and quick hack. And very much needed.
Thanks, both Peter and Alex.