The NeonMatrix 8x8 matrix uses common neon indicator bulbs to display simple graphics.
They can be chained and controlled directly via SPI.
Operating voltage is about ~70V AC.
The circuit is pretty dangerous, all neon bulbs have high voltages on their legs, the 74HC595 shift registers are floating at mains/AC potential.
Safe data in/output is realized through 3 ADUM1200 digital isolator ICs and one B0505S DC-DC isolating converter.