peteg's blog - hacking - nixie clock - 2010 01 06 Nixie PS

The millionth nixie clock

/hacking/nixie_clock | Link

Late last year in a fit of procrastination I decided to try to build a nixie clock, following in the footsteps of multitudes. To that end I ordered some tubes and driver ICs from a bloke in Moscow who was amenable to a bit of bargaining. I have to wonder how the Russians get their hands on these new-old-stock devices from the cold war era.

I received the tubes — IN-8-2's, with long solderable wires — yesterday after about a fortnight, well packed. They are a bit larger than I expected.

For a power supply I synthesised something using an MC36043 switch-mode controller from a few designs around the net. If I was going to start from scratch now I would simply follow this guy's design and advice. I think he's quite active on the nixie mailing list.

Anyway, what I've got does fire up the tube, as you can see. It generates an open-circuit 180v or so that sags to 160-170v with the tube connected. I think this is due to my overly conservative current limiting resistor in the power supply - with a 11kΩ anode resistor the tube itself seems happy, though I won't be using such a small one long-term. From what I've measured the efficiency is at best 70%.

Many of the elements of this sacrificial nixie tube don't fire up evenly, which might be due to cathode poisoning. I have found that burning each digit in for a few hours greatly improves the coverage, reducing this partial illumination, but it remains to be seen if all digits come completely good.

The supply also generates copious amounts of RF interference, which I'm hoping some more capacitors will fix. Haven't shocked myself yet, but I am sure I will. The next step is to try to hook the driver ICs up to Andrew T's ts7260 ARM board, and see if I can bring the nixie under software control. Yes, this board is massively overkill just for a clock, but as all engineers know, you can never have too much overkill.