06 August 2017

A cute VFD display

At the Marzagla rally I spotted a small box with a 7-segment symbol and "Nixie", all hand drawn/written. Inside there were three small 9-digit VFD's looking NOS. Five € for the three.

The display looked like the Russian IV-18 and IV-21, with all pins on one side, but they have no external markings and one extra digit. So they are not an IV-21. To simplify things these tubes had an insulator slipped over filament wires: that left [9 + (7+1) =] 17 more wires to idenfity (9 digits, 7 segments, 1 decimal point).

Back side. No markings!
The visual area is about 3.5 cm, and the whole tube is about 6.5 cm long. I can make a desktop clock/display since you won't be able to read at a distance.0

Since the filament was already identified, I began from it. I started at about 1Vdc and raised it in partial darkness in order to observe if the filament would start to glow (not good, sign of too much current). I settled at 1.5V and started looking for segments and digits. A good news is that it glows even at 12 V, so I will have not to worry of having and dealing with a higher voltage as most VFDs require (30 V, some even more).

Octopus!

Spreading the wires.
Luckily grid pins are on one side and segments on the other. Not willing to design a PCB for this display I took advantage of the long leads and build a simple adapter on veroboard. I will chop off the extra board under the display and let it hang out of some sort of vertical structure .... when I will be done with all the electronics involved.


A not-so-quick and dirty adapter.