we use MAX7219 to control the 5x7 LED (LTP2157AE, total of 8 pieces). Since the module normally drives the 8x8 LED, we have 3 column outputs and 1 row output free (see appendix).
We used MaxMAtrix Library to display the texts on the prototype display (consisting of 2 LEDs) and it never worked properly. Only after we connected the unused pins 10, 5, 6 and 22 to ground it worked. It has been working long and stable!
Has anyone here gained the experience? Is it not that too big a burden for MAX7219? What voltage is there on the output pins and what resistance do the outputs have when they are not being used?
Which solution would be the most optimal solution here? Go through a resistance to the mass? If so, what resistance should we choose, to which we connect all the 4 outputs in parallel?