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### Topic: LED matrix, common cathode or anode? with picture (Read 3134 times)previous topic - next topic

#### ex99

##### Feb 15, 2009, 10:48 pm
is this thing common cathode or anode? and how can i tell?

#### halley

#1
##### Feb 15, 2009, 11:51 pmLast Edit: Feb 15, 2009, 11:51 pm by halley Reason: 1
http://en.wikipedia.org/wiki/LED

Note how, at the bottom of your picture, each row pin feeds ALL of the LEDs in that row, regardless of color?  Note how the side of the LED symbol that is fed is the "anode" side?  That is, all the anodes for all the colors share a connection "in common"?  Note how all the columns have a pin of their own, with only one color in the column?  All the cathodes are sorted by color?

#### ex99

#2
##### Feb 16, 2009, 01:04 amLast Edit: Feb 16, 2009, 01:32 am by ex99125b Reason: 1
Thanks for going over the basics, but my question is more subtle than that, so, lets just take the green LEDS...CA or CC and why ?

What I dont understand is this...since this matrix is 8x8, I can turn it 90 degrees and its electrically the same. So as long as columns and rows are interchangeable(8x8, 5x5 etc) how can it be CC or CA?

Am I missing something here?

#### halley

#3
##### Feb 16, 2009, 01:47 am
For a single color matrix, there is no "common" anything.  A row of anodes and a column of cathodes, one-for-one.  You just have to put the cathode pins LOW and the anode pins HIGH and be able to source and sink enough current through the LED without frying it.

The only meaning the "common" has is when you're talking about multiple colors.  You show an RG matrix with common anodes (each cell has two LEDs wired to the same anode).

#### ex99

#4
##### Feb 16, 2009, 02:03 am
AHA!!!

Thank you, I thought perhaps I was crazy. I appreciate your patience and help. My plan is to drive these matrices with 7219's and wanted to be sure that I could (I can)

#### bHogan

#5
##### Feb 16, 2009, 03:15 am
Just to make sure . . .
The display you picture is a 2 color common anode display. The MAX7219 is designed for common cathode displays.

I don't think you can use it unless you want to use only one color.

"Data is not information, information is not knowledge, knowledge is not understanding, understanding is not wisdom."
~ Clifford Stoll

#### ex99

#6
##### Feb 16, 2009, 05:15 am
yes, that is correct. One color at a time, or both colors at once (tying the  column pins together)

#7
##### Sep 13, 2010, 09:11 pm
Hi,

If I want to use just one color then I have use the MAX72xx chip and it does not matter if the LED matrix is common anode or cathode. right

@ex99:
Did u manage to light up those LEDs can u post some pics ??

Thanks,

#### deSilva

#8
##### Sep 13, 2010, 09:20 pmLast Edit: Sep 13, 2010, 09:20 pm by mpeuser Reason: 1
A one color matrix is common anode and common cathode at the same time   (re-read reply #3)

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