Hi,

i've read this tutorial about arduino and max7219 but i've a little problem(doubt)
http://www.arduino.cc/playground/LEDMatrix/Max7219

in this tutorial columns are from A-G(0..6) to DP(7) but A column don't match to the first matrix column, is the same for the third and fourth column.

i tried to modify the circuit and it work perfectly.

COLUMN ...... MAX7219 PIN
1...................pin G
2...................pin F
3...................pin E
4...................pin D
5...................pin C
6...................pin B
7...................pin A
8...................pin DP

I don't understood the tutorial or there is an error ?

first prototype 3x3
http://it.youtube.com/watch?v=K9d0COeVj9o

yeah  

i hope that someone will edit pdf.

thanks to confirm it

...and if these are your first steps with the MAX72XX here is an article you might be interested in :
http://www.arduino.cc/playground/Main/MAX72XXHardware
I have uploaded it just two hours ago,so if you find any mistakes,   please let me know.

Eberhard

Hi q,
Well its not really an error, it simply depends how you define the correct order of rows and columns.

Lets start with the columns:
The leds in a single row are turned on by sending a byte to the MAX72XX. The each of the 8 bits in the data resemble a single Led in this row.
The highest bit (bit7) in the data-byte will drive pin SegDP, bit6 will drive SegA, this goes on in the order seen in the schematic above.
Please have a look at the Max7221 datasheet, Table 6 on the bottom of Page 8 which is the same thing in tabular form.
The nice thing about this layout is that you can write down the data in binary encoding and it is obvious which Led is switched on.
Example:
The databyte
B10001000
will switch the Led SegDP and SegD on, all others off. You know it from siomply looking at the value.
The pins in the schematic are layed out so that they are the best match for binary encoded and even hex-encoded values.

I find this layout much more natural than the one used in the example-code you are refering to.

The same is true for the rows. In my schematic I choose a layout where row Dig0 is at the top. If you rather have this row at the bottom thats fine. The only thing that counts is, when I send the command Dig0 to the MAX7221 it will change the Leds in row Dig0. That's all. A schematic says nothing about the physical layout of the Leds.

I drew the schematic so that it matches the code from my own (LedControl) library. The code-example you seem to be using might drive different leds instead, This is a code- not a hardware-issue.

Eberhard

Hi,
q wrote on 30.11.2007 at 17:57:28:

I decided to put the origin of the matrix into the top left corner because:

• If you speak of rows and colmuns everybody imagines some like a spreadsheet
• In the mathematical matrix the origin is top,left
• All basic computer graphics programming uses the top/left origin,

From there I think the top/left origin is a bit more natural
You had this example
Quote:


With only one Led on, there is no real gain from my wiring, but what if you want something more complicated like a filled triangle pointing right?
This is my wiring:
maxSingle(1, B10000000);
maxSingle(2, B11000000);
maxSingle(3, B11100000);
maxSingle(4, B11110000);
maxSingle(5, B11100000);
maxSingle(6, B11000000);
maxSingle(7, B10000000);
maxSingle(8, B00000000);

You can't do that with your wiring since only decimal values make sense
maxSingle(1,128);
maxSingle(2,192);
maxSingle(3,224);
maxSingle(4,240);
maxSingle(5,224);
maxSingle(6,192);
maxSingle(7,128);
maxSingle(8,0);

With my wiring you need to type more and think less
This whole thing is really is up to personal preferences.

Quote:

I had a look at the Matrix-library this morning and was surprised that it doesn't even work on a MAX7221 without some minor modifications.
I have not yet found out how they organize their rows/columns thing.
There is no wiring information at at all and it seems they programming is for a specific Ledmatrix product since I found this comment in the sources Code:

  // wrap shift relative x for nexus module layout
  if (x == 0){
    x = 8;
  }
  --x;
 

This quirk isn't even documented.

The docs from the other playground article has a mistake in the wiring, (otherwise we wouldn't discuss this topic here).

So what is the  correct wiring?I don't know!
I think I will update my playground article with some notice on alternative wiring options and explain that this really is a software thing.

And one more on the row-issue:
The Matrix-Lib uses the index value 0..7 for addressing the rows
The playground article uses 1..8
You see 3 pieces of code 3 different solutions and all of them correct.

Eberhard

Hi,
q wrote on 01.12.2007 at 15:22:34:

sorry about that, but the confusion will quickly go away once you see the first led's light up

This is really only a theoretical problem. As long as you use a common cathode led-matrix, every type of wiring can
be made to work with just a little bit of software.  
Quote:

Yes.

Quote:

This really depends on the software again.
The Matrix-lib that is shipped with the arduino-ide and the LedControl-lib
both have a function that allows you to control each Led individually.
The playground-code doesn't have that feature, you can only set the status of complete rows.
This is about the major difference, apart from the 7-segment display support that is only available in the LedControl-lib.
I think it might be a bit easier to use one of the libraries. If you go for the playground code you will start from scratch.

When you decided on the Led-matrix product and have a link to the datasheet I can probably have a look what would be the perfect wiring for that product.

Eberhard

hej kompis,

i'm little bit late for this discussion, but anyway, the tutorial is related to the code and they work togehter, at least for me, and some other people which tryed it from time to time.

but thanks for your notes, i guess i have to work on this for a little while, but unfortunally i will not be able to try the stuff on a real ship or matrix, because i'm not "home" for the next 5 month, but i tryed the old one several times, maybe i didn't used the best way to explain it or maybe a stupid way of name the things etc.

on the otherhand i'm a little bit sad, because i don't think it was necessary to delete the link to the tutorial from the main wiki page, it would be great if it could return.
At some point i was spending a lot time on this and it is always sad if stuff you made just disapera in to the dark....


all the best
tomek

jup, i notcied that i don't explained the order of the collums and you are right that the reader can get confused, i will add some sentenc about this, thx

all the best
tomek