So, what is a Nixie tube?
If you’re on this site, there’s a good chance you already know what a Nixie is. But in case you don’t, here is my brief guide.
In a nutshell
A Nixie tube is a type of display for electronics. It’s one of the oldest display technologies, invented nearly a century ago and now uncommon and vintage. As it existed before modern silicon, it operates at relatively high voltages – hundreds of volts, instead of the 3.3V most electronics and displays use today – like most electronics and relay-based machines of the era. It’s a kind of vacuum tube and works like a neon lamp, by ionizing a noble gas to make it generate light (more on this later).
The basic structure of a Nixie
A Nixie consists mainly of a set of stacked symbol-shaped electrodes, separated by ceramic disks. Each electrode is wired to a pin at the bottom of the tube; these are the cathodes. The electrode stack is placed behind a grid, which is also connected to a pin and forms the anode. A sealed glass tube houses the electrodes, the grid and a noble gas (neon in most tubes, but sometimes argon) surrounding them.
How they work
As I already said a Nixie tube is a neon lamp on steroids. Applying voltage on a cathode generates an electric field between it and the anode. The noble gas between them ionizes: some of the electrons split from their atoms to accelerate towards the anode, where they enter its electronic cloud.
Meanwhile, the now positively charged atoms (they have more protons then electrons) move in the opposite direction, towards the cathode. Because of their large size, however, they are likely to hit other non-ionized atoms and discharge by stripping their electrons. This causes some of the energy to be dissipated as visible light. The final effect of all this is the powered cathode lighting up.
Durability and issues
Compared to other display technologies, Nixies are very fragile. As with light bulbs and vacuum tubes in general, they need to remain sealed and cannot withstand glass breakage: a tube without its gas is just a set of metal pieces. Cathodes also deteriorate during operation – the last generations of tubes could reach 200,000 hours, but the first commercially available models failed past 5000 hours.
Other common problems with these tubes include burn-in of the cathodes, which stops some parts of the metal from attracting atoms and causes uneven lighting, flickering due to fluctuations of the input voltage (old electronics worked at high voltages, so they did not have regulated power supplies), opacification of the glass and electrical issues with the electrodes (such as broken connections or short circuits).
History of Nixie tubes
These tubes have a long history. The very first Nixie display was invented by a small vacuum tube company, Haydu Brothers Laboratories, which was then bought by the larger Burroughs Corporation. Their internal name was “Numeric Indicator Experimental No. 1”, abbreciated to “NIX 1”, so Burroughs invented and trademarked the “Nixie” brand. Similar devices were patented in 1930, while the first large batches of them were produced and sold by the National Union Co., which sold them as “Inditrons”.
Haydu had also designed a vacuum tube that acted as a digital counter and could interface to a Nixie digit. Burroughs marketed it under the “Trochotron” name, later renamed to “Beam-X Switch”; however, driving the digits by means of discrete logic was more common. Meanwhile, many manufacturers also produced Nixie-compatible tubes, each with their own trademark such as the already mentioned Inditron, Digitron, or Numicator. Not unlike Sharpie or Coke, “Nixie” became a common term to define all of them.
What happened to them
Nixies have been unused for several decades now. Their demise has followed the evolution of electronics, mostly due to their large size and high voltage. Controlling Nixies from a 5V chip required an additional power supply and circuitry that could withstand the voltage. There were a few solutions, such as the 74141 BCD-to-Nixie adapter.
Instead, Nixies paved the way for a similar technology: vacuum fluorescent displays, or VFDs. You may have seen one of them in a vending machine or DVD player. They also work by ionizing a gas, but they’re much smaller and produce blue light. Unlike Nixies, VFDs only required 12V to work; it’s a really common voltage in electronics, so extra power supplies were not needed.
Later, VFDs also fell in favor of other technologies that existed before, but became cheaper over time: LEDs and LCDs. These work at very low voltages and almost anything can drive them – in fact adding LEDs is a common practice to debug electronics. And they are thin, light and cheap to manufacture (so cheap that almost every electric appliance now has a full-color touchscreen, or at least an LCD with custom symbols). They are still evolving today in the form of OLEDs and higher resolution screens.
And… that’s it. I hope you enjoyed this article as much as I did when I wrote it. Stay tuned for more Nixie tubes (here’s the list); I will also post some projects using them in the near future.