For the last couple of years I've been keen to build a nixie tube clock.
Nixie tubes are those early (1950's-70s) display tubes often used in industrial and commercial applications, before the advent of LEDs and LCDs. They novelty and attractiveness led me to finally wanting to build one, but it wasn't until after I'd moved back to Sydney from Holland that I was able to get around to it.
My clock is built entirely from scratch, and is based on 4000 series logic ICs for the actual clock counting, and 74141 chips for the tube drivers. It's self contained, requiring only a 12v AC/DC plug pack to run. It features 6 digits (HH.MM.SS), buttons for setting hours, minutes, and zero seconds, 1 minute per year accuracy, supercap power backup and an LDR to shut the display off after a predetermined period of darkness (switch overridable).
click on images for fullsize
The schematic for the clock is show below. The first circuit shows the power supply circuitry, and the second shows the guts of the clock.
The main sections of the clock are:
The clock is built on two strips of standard stipboard. One has the power and logic circuitry, and the other has the nixie tubes, drivers and PSU.
It's all assembled in a home made case made from wood, perspex and brass strips. Cutting the holes for the nixies proved to be the most challenging aspect, but my dremel dod the job nicely, leaving me with perfectly circular holes for the tubes. Alignment for the plastic was a little tricky, but it's mostly lined up, except for a mm or so for the lid, but it can flex slightly to compensate.
The logic board is mounted on the wooden baseboard, and the driver board is mounted under the lid. The tubes are mounted high enough off the PCB to stick through the holes, whilst allowing the rest of the parts to sit under the lid. I mounted the lid with a hinge, allowing easy access to the innards (the set switches are on the logic board).
The development of the clock electronics was done on solderless breadboard. This allowed me to verify operation and fine tune any aspects of the clock. This ended up being very important as I had to work out some clever things for the time setting and daily rollover circuitry. As a result, I only had to make two minor changes to the clock after assembly. Below is a picture of the clock on a breadboard (after I'd started the display board). To the right is a homemade LC meter I used to get the inductor right.
Now that it's built, I am very happy with it. A major project is finally complete and it's so satisfying to know that I've done it all myself. It's even better than from a kit! The Maxim free samples program has been very useful to me for some key components, as was ebay for the tubes!