Nixie clocks have become popular enough that these days there’s no shortage of turn-key options that let you experience that warm glow with a minimum of fuss. Many still come as little more than a bare PCB, giving the purchaser some freedom to come up with their own enclosure, but at least the electronics are handled.

But for [Justin Scott], putting his new two-digit Nixie clock board into a handsome box was only half the battle. He also wanted to do something a bit more interesting than just tell the time. To convert the board from a simple clock to a device that could show how many minutes until the next bus showed up at his local stop, he had to hack the firmware and establish a communication link to a Raspberry Pi to do the heavy lifting.

The first step was to get a modified firmware on the clock PCB, and that required a ST-LINK V2 programmer and some time tracing out the pins on the STM8 microcontroller to determine how they controlled the various elements of the Nixie tubes. Fortunately, there were just I/O pins left over to stand up a serial link to a Raspberry Pi Zero through a level converter.

On the Pi side, a Python script hits the bus API to figure out what’s coming and when. There’s some creative blinking of the decimal points to indicate what’s happening behind the scenes, but primarily the display simply shows how many minutes are left before [Justin] should be out waiting for his ride.

It would be nice if all those commercial Nixie boards would talk I2C, but at least projects like this show it’s possible to get more out of them than just the time.