By combining 49 of them he’s put together a soda bicarb diode steering circuit for a 7-segment display capable of showing the digits 0 to 9. He takes the idea for his diode from electrolytic ...

Of course, there’s nothing unusual about using 7-segment displays, especially in a clock ... a 3D-printed case and an Arduino Nano coupled with a DS1307 make the clock part work.