Last weekend of October a curious teenager guest noticed the Nixie clock in our living room. The most eye-catching element was the short depoisoning routine that runs once a minute. B-5750 Nixies have their numbers 0-to-9 back-to-front, which is an even more eye-catching feature.
So I quickly explained him and his family some basics of these lovely tubes, showed them my lab/workshop/messy room and of course I told them I had designed and built that clock.
The next day I came up with a self-challenge: design and build a fully functional Nixie clock that I could give the teen at our next (and probably last for a very long time) meeting four weeks ahead.
With a small personal "library" of hardware design and AVR firmware I was quite sure I could get over all the small challenges inside this project:
- design a working circuit and receive the PCB from the fabhouse
- sub-task: fix the KiCAD footprint for the chosen ZM1020 Nixie
- design a suitable case and get it 3D printed (this then turned to laser cut)
- build it without easy access to my lab for the same period of time
- write a user's manual
The PCB was designed with KiCAD and etched by JLCPCB. To save on board space and stay into the chosen round design I used a bare AVR ATmega uC with its internal 8 MHz clock; it also drives the voltage booster. On the board I included an ICSP header which is very useful if you're debugging or adjusting the firmware code. I used a ZM1020 round top view tube
While waiting for PCBs to arrive I learned how to use OpenSCAD to design the case, which is plain geometry applied to programming. I also risked to have no AVR microcontroller for the clock as the ATmega48 doesn't have enough program memory (or I would have needed to do heavy optimizations). I managed to unbrick a couple of ATmega168 that are enough for my firmware (wrong fuse settings).
The circuit diagram was correct. The PCB was suitable, meaning I kept HV and LV separated enough. The laser cut case (two plates) was perfect and I picked it at 3.5 weeks into the challenge. In the last week I did some firmware corrections and upgrades and today the clock has been delivered to a happy teenager.
Here it is!
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| Single Digit Nixie Clock with ZM1020 |
