The project (finished about a year ago) was a lesson in humility in hardware design. I designed the PCB for flexibility, with IO headers, and initially wanted to receive WWVB or GPS for accurate time.

But radio reception is annoyingly analog so instead this is driven by the Saddest Raspberry Pi Ever: its entire job is to send the time over a serial port, in ASCII, 20 times per second, via "nixieclockd". At least I get NTP-accurate time!