One might recognize them from the bomb-defusing scene in the Bond movie ‘Goldfinger’ or the Divergence Meter from ‘Steins;Gate’. In short, they consist of ten (0-9) wires glowing neon yellow in a vacuum tube. First replaced by seven-segment displays, they are becoming increasingly popular nowadays due to their aesthetic appeal.
While there are many kits available online, where’s the fun in buying one?
Designing the Circuit:
The main difficulty in a Nixie clock lies in its operating voltage, which is around 170V.
To overcome this challenge, I decided to use two circuits - one high-powered circuit to drive the tubes and one low-powered circuit for switching the power to the digits on and off. For switching, I used a common shift register - the SN74HC595DR, along with some 20k Ohm resistors and high-power transistors.
As you can see, using a shift register allows us to daisy-chain as many tubes together as we like in theory. Therefore, I tried to make the PCB as modular as possible, with the input on the left and output on the right.
Note that I added RGB just for the sake of it; having LEDs under a Nixie clock is pure blasphemy.
Making it Real:
Since most of the parts are SMD components that are too difficult to solder by hand, I switched to EasyEda mid-development because they had a list of parts that JLCPCB could assemble.
While redoing the layout, a little mishap happened - the description was in the solder mask and not the silkscreen mask… F.
Apart from that, it turned out great:
Now, for the moment of truth - does it actually work? To drive the shift registers, I used an Arduino Nano, and for the 170V circuit, I used a high-power supply from eBay.
See for yourself:
Since it looks rather barebones for now, my plan was to go to my local FABLAB @FAU and build a wooden case for it. However, due to the pandemic, the FABLAB has been closed, so this project is not yet finished.
To be continued…