Therefore, the nixie clock will have only four nixies. The seconds will be visualised by blinking a small neon lamp in between the hours and minutes nixies.
Also, I realised that, in the finished project, the nixies would be placed in the middle of whatever housing we'll make for it -- so having all the parts behind the nixie (like in my first layout) would not enhance the clock in any way. The width of the 12-pin header, however, did make the layout for a single nixie pretty wide (3.5 cm), which means there would be quite a bit of room in between the nixies.
Dividing the 12-pin header up into two headers of 6 pins and placing the parts both in front and behind the nixie made the layout quite a bit smaller: only 2 cm wide. The nixies will be placed much closer together, which is good.
I've also added the circuitry for the small neon lamp. It has only two leads, so it's not too interesting.
Doing this enables me to place the four nixies and single neon lamp on half a PCB, like this:
There is no part for a neon lamp, so I used an elco of the same size in the schematic and in the board layout.
There are some things that worry me, though:
- Some of the traces make angles of 90 degrees. That's supposed to be a no-no -- but I can't find an option in Eagle that tells it to make rounded corners.
- Trace widths and distances between traces. According to this (very yellow) calculator, a current of 2.5 mA should flow unhindered through traces with a width of 0.005739338316528049 mils. But some of those traces are very close together, and the voltage difference is 170V...
If anyone has any insights to offer, I'd like to hear them!