After some failures I decided to build the whole clock around a Mega8. It feeds time coded in BCD into the 74HC595 with a simple serial connection. Then each one of the three 74HC595 will drive two russian 74141, that then are driving the IN12B. The clock will display seconds, minutes and hours.
The clock has a 12V input from what the 5V for the Mega8 and the 150V for the nixies are generated. For the 5V I use a 7805 in TO220 and the 150V are provided by a MC34063A stepup.
The µC board was made by PCBway. The quality is really good. I will definitely order there again. Especially because they are fast in producing the boards too! And I got eleven boards instead of ten :D
It is my first board I had made by someone else. Till then I used grid hole boards for my circuits.
The stepup board was made by DirtyPCBs. It took six weeks to get to my, because I dind't choose fast shipping. The quality is ok, but not as good as the "processor board" I had made by PCBway. The best thing is I got 22 PCBs !! I choose the Protopack option, which means according to their page that I can get 8-12 boards. But I got 22 !! Awesome!
The clock is now finally working. It runs one the internal 16Mhz crystal with the Timer 1 CTC Interrupt. With three buttons on the clocks back, I can set the time.
Here's a video of the clock working: https://www.youtube.com/watch?v=JgsjMgxjqoA
This are some of the steps It took me to get the the final version of the nixie clock:
IN-12B testing: https://youtu.be/H-mg_gg13lE
Testing of a ZM1325: https://youtu.be/tY_VBX0xAtQ
Using a BC546 as a switch for the Nixie segments: https://youtu.be/-GDlDiYVv6Y