I have this peculiar fascination with obsolete display technologies like nixies and numitrons; they emanate a warm, inviting glow, they have a bit of heft, you can physically see how they work, and they’re nicely encased in glass. It’s little wonder, then, that my first “real” electronics project was a nixie clock. Nixies are fantastic eye candy, but they are also somewhat of a hassle to work with because they require a high-voltage power supply (180V) and something like the long-outdated TTL “power pig” 74141 to drive their respective cathodes. Recently, however, I got a hold of a bunch of Russian IV-9 “Numitrons” for additional, cheaper, clock projects — an easier-to-use display technology that doubles as a nice Nixie alternative. I use “Numitron” in quotes because the word Numitron is originally a trademarked name of RCA, the originator of Numitron technology (circa 1970), and what I have are cheap Russian knock-offs of the real thing. (Real RCA Numitrons currently cost about $10 a piece on eBay, whereas the IV-9 can be purchased in bulk for less than $1 per unit.)

If you’re at all familiar with common anode 7-segment LED displays, then working with like a Numitron shouldn’t prove too difficult. In fact, the procedure is pretty much the same — just substitute each individual LED in a 7-segment LED with a glowing filament (like an incandescent bulb) and you have a Numitron. And because they use a glowing filament, unlike LEDs, Numitrons do not require a current-limiting resistor on each cathode.

I read — somewhere — that the recommended max voltage for IV-9s is 4.2V. Standard Arduinos run at 5V, but a simple 1N4001 diode in series with the Numitron anode gives the exact 0.8V drop needed to achieve 4.2V.

In the video above I use an Allegro A6278 serial-parallel LED driver to drive each of the individual cathodes. Shift registers like these are a great way to conserve I/O pins on the Arduino (I always give out A6278s at my “Intro to Arduino” workshops) and they are not at all difficult to use, even for the beginner. This tutorial, which uses the popular 74HC595 will get you up and running with shift registers if you’ve never used them before. (Pay particular attention to the shiftOut() function provided in the code samples.) The A6278 works almost identically to the 74HC595, with the exception of an REXT pin on the A6278 that requires an external resistor for setting the desired current for the outputs. The beauty of this feature, however, is that for LED applications you need only 1 external resistor instead of the normal 7 (1 per cathode) you’d need with the 74HC595! A 900Ω resistor on the REXT pin, for instance, will give you a 20mA output on each output pin, exactly what you’d need for a red LED display.

IV-9s are readily available on eBay, so if this is a display technology that tickles your fancy, try picking up a few to hack around with on your next project.