Finally finished my 15-month-long Nixie clock build.
The build begins with the ArduiNix, a nixie power supply and driver kit for the Arduino. That literally sits on top of an Arduino Uno R3. The tubes are salvaged Soviet IN-14 displays and five IN-3 neon bulbs. The display is switchable between time, date, and countdown timer. There’s a DS1307 RTC keeping time/date when the unit is otherwise powered off.
I used example code from ArduiNix to start with, but modified it heavily. They didn't have the exact setup I wanted for the display, and the code assumed you weren't doing anything else with your Arduino except running the display off its internal timer (which isn't super accurate). I made lots of nice additions like blinking the current digits while setting, and a cathode poisoning prevention mode that can be activated on startup. Perhaps most importantly, I've added a very easy method to change modes and set time. I used a rotary encoder and a standard button; just push in and dial up/down each of seconds/minutes/hours.
I’m pretty inexperienced with this kind of build, so it took me about 15 months to complete. One of my big stumbling blocks was in getting the IN-3 bulbs to light. The tube driver chips leak too much current to reliably switch them on and off. After exploring a number of avenues, I finally settled on using an output expander over I2C: an MCP23008. I set one Arduinix anode to always on, then set up transistors on the outputs of the MCP23008 to switch the voltage. That problem alone cost me a couple months.
The case is custom designed/built from oak, constructed in roughly one hour chunks once a week in my parents' basement workshop. A piece of perforated sheet metal is bent to an arc forming the window. I found a piece with a hex-pattern that matches the shielding internal to these tubes.
I’m really happy with how it all came out.