I used an IN-15A symbol nixie in this ornament. An IN-12 works great too.
A video of the ornament alone:
A video of the ornament in my tree. (Yes, the walls are changing color. I have the si-light system in my apartment: http://si-light.sourceforge.net )
Details you will find in this instructable:
1. A small high voltage power supply that runs the tube.
2. A tube carrier to mount the nixie tube in a socket so it can be changed.
3. Firmware that runs the power supply and changes the digit displayed on the tube.
Everything you need to make your own nixie tube ornament is included in the project archive:
1. Circuit board in Eagle (Cadsoft).
2. Compiled firmware HEX file, and Mikrobasic source for the free (demo) Mikro compiler.
3. This instructable in .odt (Open Office) format.
Step 1: Design overview
1. A power supply – boosts 5 volts to 180 volts for the nixie tube.
2. A tube driver – changes the lighted tube digit by grounding one of the 10 tube cathodes. I used the Russian KD155-whatever.
3. A microcontroller – a PIC microcontroller ties everything together – it runs the power supply and changes the digits shown in the nixie tube through a four wire interface to the tube driver IC (see previous).