Implements an analog clock using an arduino shield at https://threeneurons.wordpress.com/arduino/dekatron-shield-kit/. It assumes you are using an A101 dekatron.
Video at https://youtu.be/NQM1M31fNoU. It is not as flickery in real life!
To control the time and the animations, you will need a rotary encoder with a built-in switch. I use the pec11r-4015f-s0024. Others may or may not work with the code. The suggested filter circuit on the datasheet doesn't work for me. Use this one instead. Use a pull-down resistor on the switch. The code assumes it is high when closed.
The clock will also use a DS3231 real-time clock if one is present. This is available from Adafruit as a module.
The code relies on the Adafruit RTCLib library. If you don't want to install that library, and you aren't going to use the DS3231 RTC module, you can just comment out the first line of the .ino file.