Memory from neon indicators - Page 1
Forum section: electronics / projects

author: Prehistoricman
author_rank: Regular Contributor
timestamp: March 27, 2021, 01:13:12 am
content: I got fascinated by this weird idea of using neon indicators as a kind of RAM, so I made a proof of concept.Now I'm thinking of where to take this next. I would like to build a bigger array and get some kind of usable digital interface set up.To switch the neon on and off, I use a pull-up or pull-down resistor connected to a switch. To do this while controlled by a digital signal, I think that each neon would need 3 transistors: 1 NPN for pull-down and 1 NPN-PNP pair for pull-up. Is there any way to get around the need for 3 transistors per bit?As for reading off the value from the indicator, that should be easy. A 50k resistor should drop enough voltage to interface directly to 5V logic.One fundamental problem with neon-based memory is switching time (Wikipedia says that decatrons using neon were limited to 10kHz). Even if I drive quite a high voltage for my turn-on switch, the neon indicator takes 100µs to start conducting. To make that worse, it seems the amount of time it takes to start conducting is different each time.

author: LaserSteve
author_rank: Super Contributor
timestamp: March 27, 2021, 03:18:20 am
content: A blue or uv led on the electrodes will give you some photoelectrons for speed. So will a Kr86 trace additive to the gas.Steve

author: BrokenYugo
author_rank: Super Contributor
timestamp: March 27, 2021, 04:31:00 am
content: It's a neat idea but from what I've read it's kinda hard to pull off now. Look into neon logic clocks some people have made. The trouble is the neons meant for logic work back in the day (and now unobtanium in quantity) are quite different from regular indicator lamps. They were designed for a extra wide difference between the ignition and extinguish voltage, and available indicator types age unpredictably even after burn in and sorting. I think I read somewhere some even contained a radioisotope to make the strike faster and light insensitive. You can build this stuff and make it work but it likely will take a lot of upkeep.

author: Prehistoricman
author_rank: Regular Contributor
timestamp: March 27, 2021, 11:17:44 am
content: Quote from: BrokenYugo on March 27, 2021, 04:31:00 amThat's right. I watched a video a couple of days ago on some Russian neon lamps that worked at only 40V thanks to some radiation. I didn't know they were light insensitive, but that makes sense.The indicators I have have a difference of about 8V between striking and extinction. That is smaller than the tolerance of striking voltage in this set of indicators, so I aimed to solve that problem just by tweaking a pot for each indicator.Thanks for the tip on neon clocks. I found this project where despite using special neon bulbs for the purpose of counting, it still broke down after a couple of years:http://www.pa3fwm.nl/projects/neonclock/Quote from: LaserSteve on March 27, 2021, 03:18:20 amI haven't played with that idea at all, but wouldn't that decrease the striking voltage but not affect the extinction voltage?I'll remember the krypton idea for when I become a glassblower

author: jonpaul
author_rank: Super Contributor
timestamp: March 28, 2021, 12:49:45 pm
content: Hello great notes....In 1950s the tube computers used neon's as indicators and perhaps in logic.Signalite in NJ made precision neon's with specified firing voltages and aging.A tiny radioactive isotope can supply ions to reduce the ionization voltage variability.There are three electrode triggered neon's as well.All of the physics of glow/arc in gasses was determined in 1850s..1920s.Many fine texts on these topics, just do a bit of research and reading.Bon Chance,Jon

author: Stray Electron
author_rank: Super Contributor
timestamp: March 28, 2021, 02:29:57 pm
content: Back in about 1968 or so Popular Electronics (I think!), carried an article about how to build a simple computer based on logic circuits that used neon lights. I build part of it but never built the entire thing since each "bit" required about 20 to 30 discrete parts and the cost added uptooquickly. However I did learn a lot about all of the different types of logic circuits such as full and half adders, FIFOs, D type flip flops, JK type flip flops, etc. It was truly amazing when those type circuits became available on a single IC a few years later. Now, I doubt that there's anyone that still uses individual logic circuits for anything. But you might want to try and find the article(s), you can learn a lot from it.