Ah, the humble neon lamp. The familiar warm orange glow has graced the decks of many a DIY timepiece, sometimes in a purely indicating duty, and sometimes forming a memory element in place of a more conventional semiconductor device. Capable of many other tricks such as the ability to protect RF circuits from HV transients, its negative resistance operating region after it illuminates gives us usable hysteresis which can used to form a switching element and the way the pair of electrodes are arranged give it the ability to indicate whether a voltage source is AC or DC. Now, due to some recent research by [Johan Carlsson] and the team at Princeton University, the humble NE-2 tube has a new trick up its sleeve: acoustic transduction.
The idea is not new at all, with some previous attempts at using electric discharge in a gas to detect audio, going back to the early part of last century, but those attempts either used atmospheric pressure air or other non-sealed devices that exhibited quite a lot of electrical noise as well as producing noxious gases. Not ideal.
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When it comes to vintage displays, everyone gravitates to Nixies. These tubes look great, but you’re dealing with a certain aesthetic with these vintage numeric tubes. There is another option. For his Hackaday Prize entry, [castvee8] is making seven-segment displays out of vintage neon lamps. It looks great, and it’s the basis of an all-vacuum tube calculator.
The core of this build are a few tiny NE-2 neon bulbs. These are the same type of bulbs you’ll find in old indicators, and require somewhere around 100 volts to fire. These bulbs are then installed in a 3D-printed frame, giving [castvee] a real seven-segment display, a plus or minus sign, and an equals sign. It’s the beginnings of a calculator, right there.
One of the recent updates to this project is controlling these displays with modern logic. That might be a bit of a misnomer, because [castvee] is using diode steering and a TTL chip to cycle through the numbers 1 to 4. The actual code to do this is running on a microcontroller, though, so that might get a pass. This is just a test, though, and the real project looks to be an all-vacuum calculator. The project is still in its early stages, but there are still months to go in the Hackaday Prize, and we can’t wait to see what comes out of this project.
This looks like one of those projects that started out as a glimmer of an idea and led down a rabbit hole. But it’s a pretty cool rabbit hole that leads to homebrew neon seven-segment displays on a calculator with relay logic.
It’s a little thin on documentation so far, but that’s because [Mark Miller]’s build is one of those just-for-the-fun-of-it things. He started with a bag full of NE-2 tubes and the realization that a 3D-printed frame would let him create his own seven-segment displays. The frames have a slot for each segment, with a lamp and current limiting resistor tucked behind it; with leads brought out to pins and some epoxy potting, these displays would be hard to tell from a large LED seven-segment. Rolling your own displays has the benefit of being able to extend the character set, which [Mark] did with plus-minus and equal sign modules. All of these went together into a two-banger calculator — addition and subtraction only so far — executed in relays and vacuum tubes. Version 2.0 of the calculator regressed to all-relay logic, which must sound great.
We heartily regret the lack of a satisfyingly clicky video, but we’ll give it a pass since this is so cool. We’ll be watching for more on this project, but in the meantime, if you still need to get your click on, this electromechanical BCD counter should help.