I have built a couple of Nixie Tube clocks previously, using an Arduino Nixie Shield I bought on ebay here:
These boards come with a RTC (Real Time Clock) built in and make it very straightforward to get a simple nixie clock up and running. It’s just a matter of attaching the shield to your arduino (either uno or mega) and uploading the code supplied with the board (here on github for the latest version: https://github.com/afch/NixeTubesShieldNCS314/ ) and you’re good to go. But, I had an idea! Could I set up a system where I could use a pendulum to mark the time and somehow measure this and display it on the nixie tubes? Well, it turns out I could, and so can you. If you’re interested then read on!”