LED 8x8 Matrix

On Banggood I've purchased a bunch of 8x8 LED Matrix with control IC MAX7219 (link) and after a short soldering exercise the parts were ready to us. On Instructables I found an entry from Marcelo showing exactly what I was looking for: a simple ticker application runing on a Arduino.

Set up

Not sure how many Matrix can be used ('daisy chained') as I only tried five at one time so far, but for sure couple more should work as well. You need to define the number of connected displays in this line

int maxInUse = 5;    //change this variable to set how many MAX7219's you'll use

you can simply change the character map in order to build own ones (e.g. 'ä','ö','ü'). note: all characters consists out of only 5 columns and 8 rows.

The linked example is using a Uno and has for wiring the below

int data = 8;    // DIN pin of MAX7219 module

int load = 9;    // CS pin of MAX7219 module

int clock = 10;  // CLK pin of MAX7219 module

furthermore I've attached an potentiometer to manually control the speed of the ticker - this is optional and can simply be removed.

Bugfix

However I was struggeling on two subjects

With arduino 1.6.X (and perhaps before), there is an "'prog_uchar' does not name a type" error that can be corrected by commenting the line and change it for this:
mashed visualization from the first matrix
1. There's a bug in Example_Display_Scrolling_Text:
  1. m.writeSprite(32, 0, buffer);
  2. m.setColumn(32 + buffer[0], 0);
2. in method void printCharWithShift(char c, int shift_speed)
3. This works for up to 4 MAX7219's only because of writing to X coordinate of 32.
4. It should be:
  1. m.writeSprite(maxInUse * 8, 0, buffer);
  2. m.setColumn(maxInUse * 8 + buffer[0], 0);
5. to work for more than 4 MAX7219's.
6. (reported here)

LED 8x8 Matrix

Set up

Bugfix

Links