Welcome to CuVoodoo,
the sorcery of copper.
there is a typo on the VFD :$
VFD: Vacuum Fluorescent Display
*displays
*flash
or at least I paid more attention to it
there are also more powerfull AVR micro-controllers, with more I/Os
but they are less common and more expensive
and I wanted to try another architecture
*throwaways
*work
you can also find IC logos on https://iclogos.cuvoodoo.info
*clock
the data line is forwarded
aka. notch
*5x7
actually you can still see it
*color
the outer ring disappeared
it turned white
*the grids are driven individually
thanks the the persistence of vision all grids appear as glowing simultaneously
*mean
*increasing the voltage
*high frequency noise
5.0 VDD - 0.5 margin = 4.5V for high