MAX7219 not behaving as expected

Question

I have 2 rows of 12 MAX7219 connected in series with DOUT to DIN (rows are isolated). Now the thing is I am using LedControl Library to work with it. The problem is the last 4 Matrices on both the rows don't work. The sequence in my code is like this where (row, column, matrix) is used to define the row and column of the matrix and I am talking about a single ROW from two ROWs of 12.

Sequence in Code      What Happens
----------------      -----------------
(0, 1, 0)             (0, 1, 0)
(0, 1, 1)             (0, 1, 9)
(0, 1, 2)             (0, 1, 1)
(0, 1, 3)             (0, 1, 10)
(0, 1, 4)             (0, 1, 2)
(0, 1, 5)             (0, 1, 11)
(0, 1, 6)             (0, 1, 3)
.                     .
.                     .
.                     .
(0, 1, 11)            (0, 1, 8)

Now I can understand why does this happens. This code works like this even if the Device Count is 8.

Code:

#include "LedControl.h"
LedControl row1=LedControl(2,4,3,12);
LedControl row2=LedControl(5,7,6,12);

unsigned long delaytime=500;

void setup() {
  int d_row1 =row1.getDeviceCount();
  for(int address=0;address<d_row1;address++) {
    row1.shutdown(address,false);
    row1.setIntensity(address,15);
    row1.clearDisplay(address);
  }

  int d_row2 =row2.getDeviceCount();
  for(int address=0;address<d_row2;address++) {
    row2.shutdown(address,false);
    row2.setIntensity(address,15);
    row2.clearDisplay(address);
  }
}

void loop() { 
  int devices=row1.getDeviceCount();
  for (int i = 0; i < devices; i++){
    delay(delaytime);
    row1.setLed(i,0,0,true);
    row2.setLed(i,0,0,true);
    delay(delaytime);
    row1.setLed(i,0,0,false);
    row2.setLed(i,0,0,false);
  }
}

EDIT I just noticed something, there is no data going to the last 4 matrices. The timings of the blinking of the LEDs on last 4 matrices does not ties correctly (500ms) but it is in fact 250ms (i.e. half time). It means the blinks on last 4 matrices are between pulses of the first 4 matrices.

Answer 1

Have you checked the wiring between matrices and/or swapped modules in case there is a faulty one in the sequence?

Answer 2

Looking at your library source, it seems the number of devices is clamped at 8. This isn't a hard limit imposed by the chip but rather practical design. SPI, especially at high speeds, can get unreliable when the bus capacitance, related to the cable lengths, gets so high that signals are skewed beyond recognition. Also the buffer in the library used to hold the row data is 64 bytes in size, intended to hold the data for 8 devices with 8 rows each.

You can edit the library to make it support 12 devices though it will require attention to detail like, increasing the buffer to 96 bytes, getting rid of short-circuits within the methods that make sure that no more than 8 devices can be addressed, for-loops, etc.

Answer 3

After fiddling around with various Libraries, I came across this one.

MD_MAX72XX

It has all the functionalities that I needed with a good Simple Wiki to get you started.

Also it is simple enough that even a noob like me could figure it out.

Regards