I used to skim through Instructables every now and then, and I happened to encountered pictures of Nixie Tubes and people building their own Nixie Clock. I quickly went on eBay and decided to buy at least 7. The reasoning was “oh well, I want 6 digits for the clock and one extra just in case”. The seller was Russian and I was not able to understand the full description on the site but I could read there were 7 IN-12A Nixie tubes, so I bought them all. Funny story, it took them a couple of months to arrive (to Lima, Peru) and when I went to pick them up from Customs, it turned out they were 7 dozens! That definitely explains the price. I genuinely thought they were just pricy (and they are) since they were hard to find.
I was able to find some preliminary designs for the tubes driver at RobotPirate’s website since they require 170 VDC, and a small current, in order to excite the low-pressure neon inside the tube and light up. I used an Arduino UNO to write a simple test code for the clock and designed a socket for my IN-12A tubes. Finally, I designed an Arduino UNO mod PCB that hosts the microcontroller, the RTC, and the HC-06 bluetooth module. The bluetooth addition was mainly implemented in order to set up the time wirelessly (even though I know with the RTC that time can be kept as long as there’s a coin cell battery, but the mobile app kinda gives it a nice wow factor). Everything fit nicely in a small black project case I had laying around.