This is a re-try of a display assembly which I made long ago to combine five 8x8 LED modules to make a scrolling banner. Each module is driven by a MAX7219 SPI-parallel converter. However, the way it was wired a single command, which naturally corresponds to a column of a 5x7 character, results in a row, so the characters are at 90 degrees to the horizontal. I was not able at that time to rotate the characters, so the assembly languished on a shelf for many years and became obsolete.
So this is a Retro project like my Nixie clock.
It took three installations of 7219-specific libraries to find one with the necessary “setRotation()” function. It was a bit difficult to use this library since the comments are in Cyrillic font.
With that, the display can be used with print code like for a graphic LCD.
It is 6” wide with 8 rows x 40 columns.
It is actually a very good clock. It is easily read from across the room. It is very bright, but dimmable, fast, with not a hint of flicker or lag and a wide angle.
The 7219 has a screen buffer so the Arduino does not need one,
There are no manual controls. The only items on the front besides the display are a photocell for auto-dimming and a LIDAR distance-measuring module to switch pages.
There are two push-button switches on the back which are only used for setting the Real-Time Clock module. which is the low-drift DS4231.
The clock is also a home-automation timer with RF output which takes its commands from human-readable files on a micro-SD flash chip.