So it all started one fine afternoon on August 26. I acquired an old box containing old models of LED matrices.
Quite happy, I started by trying the "classic" matrices (8X8 red and green) because the latter already had a suitable driver.
So I got to work. I inquire about this controller model and discover that it is very old (dating from 2008).
It works with two 74HC595 chips and an ATMEGA328 microcontroller, unlike most modern chips that work with MAX7219 controllers.
So I connect it to the SPI bus of my Arduino, as described on the datasheet (itself dating from 2006, a time when Arduinos were not of this world).
I test by trying to send signals that would normally light up the first pixels, but... Nothing happens.
Not understanding the cause of the failure, I wander around the forums and product comments for an hour.
When finally, I realize that the designers of the driver had simply reversed the SPI input (MOSI) and the output (MISO).
Error beginner, coming all the same from a company whose only business is to sell electronic cards of this type!
I will not advertise them in this article, but they are quite well-known in their field.