RGB LED Cube Project....Common Anode or Common Cathode?
CassLan
Posts: 586
i was recently inspired by an 8x8x8 Led cube project on instructables, including great detail about making some really cool animations, I would highly recommend reading it:
http://www.instructables.com/id/Led-Cube-8x8x8/
So anyhow..I'd like to make one using RGB LEDs instead, and of course have the propeller drive it.
With the excellent development going on in the spinnerret forum, I think I would lke this device to change animations based on information received from the internet..ie weather, tweets, too many unread emails...lol And have a web based configuration page. So many possibilities!!!
So 8x8x8 is 512 LEDs, the only cheap source of RGB LEDs that are through-hole is ebay, currently 1000pcs going for about $320 (common cathode), and $270 (common anode).
So to the point now...common anode or common cathode? external circuitry will be built either way.
I'm thinking common cathode since the voltage required for the red color is different. But then the more I think about it, maybe it doesn't matter at all.
Can anyone share any related experience with a project like this and whether or not this descision will make things allot harder or easier?
http://www.instructables.com/id/Led-Cube-8x8x8/
So anyhow..I'd like to make one using RGB LEDs instead, and of course have the propeller drive it.
With the excellent development going on in the spinnerret forum, I think I would lke this device to change animations based on information received from the internet..ie weather, tweets, too many unread emails...lol And have a web based configuration page. So many possibilities!!!
So 8x8x8 is 512 LEDs, the only cheap source of RGB LEDs that are through-hole is ebay, currently 1000pcs going for about $320 (common cathode), and $270 (common anode).
So to the point now...common anode or common cathode? external circuitry will be built either way.
I'm thinking common cathode since the voltage required for the red color is different. But then the more I think about it, maybe it doesn't matter at all.
Can anyone share any related experience with a project like this and whether or not this descision will make things allot harder or easier?
Comments
What's the status of the Preditor? ;o) No, serious ... long time not seen ... how are you?
How do you want to drive the LEDs? I plan a multi LED project for my son currently. I plan to use a constant current driver IC like the TLC59xx which drives 16 LEDs . These things are connected to the cathode of the LED, so common anode would be the way to go with these.
8x8x8 x RGB = 1536 ... THAT's the real number of LEDs you have to drive then.
So first thing you need is an idea of how you want to do that and with wich drivers and they propably tell you what LEDs they can drive.
You ask "Can anyone share any related experience with a project like this..."
My 2 cents would be start with something much less ambitious. Seriously, you will learn so much even making 3x3x3 one color cube. I might look something like this. or not, who knows.
@Mag - Ok, so if Using POV, I would need to prepare for the possibility that one entire layer could have each LED on at once:
(8 x 8) (20mA + 20mA + 20mA) = 3.84A WOW Serious Power.... But another good reason for me to learn how to build this.
@Roger - I agree, a 3 x 3 x 3 is a a worthwhile stepping stone. I did this a while back: http://forums.parallax.com/showthread.php?117953-LED-Grid-Issue-Solved-thanks Which is not 3D, but still related.
Rick
We talk about multiplexing.
And again I have to correct your calculation. If you multiplex the LEDs you would not drive the LEDs with 20mA. You'd drive em with up to the max. peak current the LED allows. In your case you multiplex 8 complete planes, so brightness will be 1/8th compared to a non-multiplex LED. To compensate that you'd multiply the 20mA with a factor. I'm not sure what the right factor would be - I think recently I read that the amount of light emitted is not linear correlated to the current, so maybe 4 is enough, maybe you'd need more than 8 ... don't know.
But you definitely need a higher currency.
Depends. POV = Persistence Of Vision.
So, a row of LEDS physically moving back and forth or rotating and illuminating different patterns as they go can cause the perception of an overall image due to POV.if it all happens fast enough.
On the other hand, a matrix of LED's in which one row or column is illuminated at a time can also give rise to an overall image also due to POV if it's done fast enough.
POV is what happens in your visual system not what happens "out there" with the LEDs. Both systems rely on POV to work. As does good old fashioned TV and movie projectors.
I could also argue that "multiplexing" is done in both cases.
But yes, in general "POV" is used, somewhat incorrectly, to refer to the case of moving, flashing light sources and "multiplexing" to the case of actual arrays of light sources.
Sorry, just quibbling again:)
http://www.youtube.com/watch?v=ECl0XgiVDrI&feature=player_embedded
The idea that I would only "light" up one plane at a time, but speed it up to look like they were all one at once.
These are the Specs associated with the LEDs I'm looking at. It says 20mA....but your saying with the viewing technique I want to use I should be using more current per LED?
But you should be sure that your program works before you drive the LEDs with the peak forward current. If your program has a bug and does not multiplex correctly you can destroy the LEDs with this current because of the heat.
Do you want true RGB?
Thats like saying do you want "true HD"?
I actually have no idea what you mean by "true RGB"
WOW, 1536 LED elements.
Yes, I know you can make it happen. Do it.
I don't think "Persistence Of Vision" can be programmed, it just kind of happens inside our heads.
Multiplexing is the technique used to trick the brain.
I started with large resistors, then worked down to my final 100 ohm.
If you want full color you not only need multiplexing for switching the planes, additionally you might need PWM as well for the color (or maybe a driver chip can do the color?).
Where did you get the yellow and blue Test clips?
The first set I ordered from Digi-Key JameCo.
I picked up more just like them at Fry's Electronics in Downers Grove, ILL.
JameCo part number 135299 $10.95 for the set of 5.
They come in a pack of 5, red, black, yellow, green, and blue.
The ones I have are not high quality, but very handy if you use some care.
I agree. Common cathode means low side switching and generally high current drivers are cheaper when they are low side (eg mosfets, multiple relay drivers on one chip).
The project will need some support chips and it can grow in complexity and I'd second the comment about starting with a 3x3x3 first.