Main display

Christoph TackChristoph Tack wrote 10/06/2019 at 08:58 • 2 min read • Like

Main display

To be readable in the dark without glasses from about 0.5m distance, the characters should be around 50mm high.

There are a few options here:

After putting a lot of effort into making my own module for the 8x8 3mm LED matrix (see Tileable 8x8 LED matrix), I discovered that 32x8 LED matrices are on sale for close to no money (€2.93).  These modules use the MAX7219, which is controlled by SPI.

Writing first texts to display

Development is ongoing : two 32x8 display units are stuck together with tape.  I had some trouble writing data to the MAX7219 modules.  It seems that only bit banging SPI works.  Maybe that's because the modules are only powered with 3V3, while it should normally by 5V.

All the libraries I tried (LedControl, LEDMatrixDriver, ...), had issues.  I adapted the arduino-Max72xxPanel to suit my needs.

Choosing font

The font should be easily readable without glasses.  So we want it as big as possible.

Font comparison

The fonts have been recovered from the Xronos clock.  That clock contains five different fonts of which four are shown here.  The character '8' is chosen, because it's one of the most difficult ones to read.  The two fonts on the right are easiest to read.  The rightmost font has been chosen because it looks nicer.