Build a Nixie Clock – 1 – Introduction
In this tutorial I’m going to show you step by step how to build a clock with a nixie tube display, based on the ATmega48. All the functions, including timekeeping and high voltage generation, are controlled by the mega48 and it only needs a few additional components. It has power-cut backup, an alarm and a snooze function. I’ll explain the hardware and software in detail and give some guidance about component selection and physical construction. Some of the tips and tricks are applicable to other projects besides clocks.
First, why a nixie clock? Well, because nixie tubes are pretty. For people who haven’t seen equipment that uses them, which is practically everyone under the age of 40, they consist of a glass tube similar to a vacuum tube containing electrodes in the shape of numbers that light up with a soft orange glow. They were introduced in the 1960s as readout devices for the emerging digital technology and were pretty common into the early 1970s, when more complex ICs and LEDs offered a cheaper and more convenient alternative. Then they practically disappeared for a quarter century. Presently they are experiencing something of a revival thanks to the availability of large quantities from Russia, where (so I’m told) a factory was forgotten by the central planning authorities and continued producing them long after demand had ceased. But once these stocks are gone there will never be any more made, so if you want to build a nixie clock the time is now. Go on, do it – leave your grandchildren something to fight over. (If you don’t care to use nixies you can use LEDs or other alternative displays – I’ll cover that later.)
The first problem is getting hold of some nixie tubes. You can’t buy these at Digikey. Ebay is the best source, though all the sellers are in Russia or Ukraine and this makes some people nervous. I’ve done business with four of these vendors and can say they’ve all been honest, helpful and quick. Here are their Ebay IDs – EXLAND, FUTURGLAS, UBITDRAPOM, NIXIESTORE. They all have different stuff, so you have to know what you want and find the appropriate seller. If you don’t care to use Ebay, and in connection with deciding what kind you want, there is a good selection (with pictures) for sale at Jan Wusten’s store in Germany. Jan’s prices are higher because he’s a retailer, but they’re not unreasonable.
I have some recommendations. All these are Russian. “IN” presumably stands for “indicator neon”.
First, smallest and cheapest, is the IN-17. This is an end view tube with about 0.4 inch (9mm) digits. The current market price on Ebay is about $10 for twenty. It isn’t the prettiest nixie but surely they don’t come any cheaper. With these you can afford to take chances and make mistakes.
Next, going up a size, is the IN-16. This is a slender upright tube, half an inch in diameter, with nicely formed digits about 0.5 inches (13mm) high. You’ll pay around $1 to $1.50 each for IN-16s on Ebay, depending how many you buy at once.
Going up in size again, the IN-8 is fatter than the IN-16 with larger digits, 0.75 inch, 18mm. This is a pleasing size and quite sought-after - you’ll pay at least $2 on Ebay. Look for the IN-8-2 version, which has wire leads. This is about the same size as the cheaper IN-14, but the IN-14 doesn’t have a proper “5” digit.
For plutocrats, consider the IN-18. This guy is huge and extremely beautiful with 1.6 inch, 40mm digits. They cost $20 to $30 each at present so you have to be rich, or really really confident, to pick them for a first project. These tubes have a base with pins, which presents some problems for prototyping. All the others I mentioned have solderable wire leads.
There are many other kinds available from time to time, at prices ranging from a dollar or two up to hundreds of dollars each for the rarest types. You can use anything you can get your hands on, but for a construction project like this I need to base it on what’s available in quantity – I’d hate to see a bunch of motivated AVR Freaks all bidding against each other for the same set of rare tubes. Here are some pictures. In the next section I’ll post the schematic and software, and then I’ll get down to the business of how it works and how to make it.