Instructables

Nixie Watch, Part 1: Development Board

This is a multipart instructable. The development board presented here is not a final project, but draft work presented in hopes of helping others (and possibly some collaboration towards a better final project).

Two ultra fabulous nixie watches currently grace the web. The first was created by Jeff Thomas ( http://www.amug.org/~jthomas/watch.html ). This watch has four small end-view tubes for time display. The nixies are powered using a camera flash circuit and an AA battery. Two button cells power the clock logic. This watch is logic based, and does not contain a microcontroller. David Forbes at the Cathode Corner has the only nixie watch currently available for sale ( http://www.cathodecorner.com/nixiewatch/ ). This watch uses two small side view nixies to display the time. Time keeping is done on a PIC microcontroller. High voltage for the nixie tubes is provided by a boost converter IC and transformer. This watch is powered by a single 'CR2' lithium camera battery.

Both of these designs employ much surface mount mojo. Consider the picture of Jeff's nixie watch: seven surface mount ICs and a dozen or more surface mount transistors. The goal of this instructable is to create a prototype 'poor man's' nixie watch using as few surface mount components as possible. In Part 1:Development Board, we will consider various design problems while creating an all through-hole version of the nixie watch. Part 2: Surface Mount Mojo, will present the final design incorporating a few surface mount components to save space.
 
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Step 1: The Nixie Tube

The watch display is a single IN-2 Russian nixie tube. These are not the smallest nixie tubes available, but I have a big bag of them on-hand:
These tubes are cheap, I think I paid ~0.50 cents each.
These tubes are readily available from tube vendors and Ebay.
These tubes are socketed, rather than soldered, for easy replacement.
These tubes will work at lower voltages (~140 volts @ 0.9mA).

This is a tall tube (its longest dimension being height), so the design will use height wherever possible to save space. The Eagle socket footprint was created using Nick de Smith's value socket calculator:

( http://www.desmith.net/NMdS/Electronics/soculator.html )
(removed by author or community request)
Basically a 7 segment LED, except older, and analog (pretty sure it's neon).
A nixie tube has no addressable segments which make up the digits in the way that a seven segment display does.

A nixie usually has a set of 10 discrete metal cathodes, displaying the numbers 0 to 9 and which are stacked one behind the other in a glass envelope containing neon gas or, more probably, a cocktail of gasses known as the Penning mix.

Nixies tend to require a power supply of around 180v. They provided a way of displaying numbers before the LED was invented.

Nixies are also available showing symbols rather than numerals.
12V5 years ago
where does the 140v come from?
jforb5 years ago
The schematic for David's watch is on his web page. Find the Nixie Watch page, look for the Docs link on the left, find the User Manual, look at the last page...
miloh8 years ago
Maxim's AN1109 directly addresses the issue of driving a power FET from low voltages... Although it is Maxim centric (Max1605), I believe it can be used as a guide to build a generic SMPS using an autotransformer... power from a single 3v cell or a couple AAA's....
westfw8 years ago
Have you tried doing the voltage converter with a high-voltage bipolar transistor like a mpsa42 instead of a mostet? The currents involved aren't huge; I've been trying to figure out why MOSFets are so prevalent. The bipolar transistor should run OK with 3V power.
ian (author)  westfw8 years ago
I have tried the mpsa42 in an smps, but not THIS smps. I should give it a try. That is a great idea.
Where does one find nixies these days? "Antique chips" makes me feel really old. Which is why this project just feels right.
ian (author)  geezer-trainee8 years ago
Ebay is a good source. There are some very expensive webshops as well.
Johntron8 years ago
o.O O.o I <3 Nixies
Heh, I guess Instructables didn't like my less-than sign :P I wrote: I (heart) Nixies Great project, and a great start. Thanks!
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