This is my first project that I post on hackaday.
Example of working
Attiny13 have onboard 1 kBytes of Flash memory.
Program you see on video use only 882 byte of memory. It means that you can write message 100+ char long. If you off tests of pixel moving and line size of code 522. Almost ~500 chars text.
Attiny13 drive 20 LEDs by 5 pin;s. Let's look at the scheme:
This is "charlieplexing" you can read more on wikipedia.
In every moment of time you can only "on" 2 or 3 LEDs. What you need to do for switching "on" all leds? You must switch on every LED for small part of time.
You can see working version in commit "01940c8". I plan optimize code: remove duty cycle delays and use timers and sleep sequential. Work in progress.
Also on Github you can download all source and schematics with PCBs design. Also BOM list.