B-7971 Project

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7 months 3 days ago #9756 by jonboy
Replied by jonboy on topic B-7971 Project
Love the clockor whatever you call something like this!

Please don’t post a link so we can watch it live, I won’t get anything done! But how do you post a message.

I would live to read a write up on this. Where did you get the idea from? How did you decide how many bulbs to use? Etc.

Must go away and google B-7971 and see how much they are. Is anyone building a pcb for these tubes?

Love the whole idea.

Jon

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7 months 3 days ago #9757 by Ty_Eeberfest
Replied by Ty_Eeberfest on topic B-7971 Project
Jon, I guess I call it a Nixie Display Device. Originally (2007) I called it a "shout box" because at the time every Wordpress blog in the world was using a "Shout Box" widget that let visitors post short text "shout-outs" in a little box on the page - thus "shoutbox" was a well known term. Not so much now.

For the users posting a message is just a matter of typing into a 1-line textbox on a web page and clicking the Post button. Behind the scenes the web page is submitting the message as a field in a form. On the server the form is processed by a Perl script that "sanitizes" the message (checks for various malicious tricks) and then pushes it across my LAN to the Nixie device. The Nixie device handles displaying, scrolling, timing and queuing of messages.

In the late '90s a site called indigo.org did something vaguely similar: they had a streaming webcam pointed at a monitor and on the monitor was the old "flying text" screen saver. Users could enter short messages and see them displayed on the screen saver. 10 years later I was doing some work with video streaming, looking at my 1 (at the time) Nixie clock, thinking about the B7971s I'd played with in the '80s, and that indigo.org site came to mind. Decided to try it with Nixies instead of a monitor. 16 tubes just sounded like a good size, and also - since at the time I intended to control it with a PLC - 16 nicely matched the number of outputs per PLC output module. One 16-point module for 1-of-16 tube select and one 16-point module for the 15 segments + 1 point for a "latches GO" line. The fact I was making real good money at the time played into the decision too because the tubes were not cheap even back then. 8 probably would have been adequate but I felt like why not go big "since I can".

The tubes cost 50 cents (US) each as surplus in 1977. In the 2000s I accumulated my tubes from various sources at prices ranging from $35 to $65 per tube. Prices have only gone up since then. EBay is your best bet for finding people selling them. Most sellers are in the USA and maybe a few in Western Europe. The Russians never cloned this tube so you won't find the "usual suspects" selling them.

Look into it later when the dust is clearing off the crater.

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7 months 3 days ago #9758 by Ty_Eeberfest
Replied by Ty_Eeberfest on topic B-7971 Project
To clarify what I said about 1-of-16 tube select lines etc. The display is NOT actually multiplexed. If I was doing it over today I'd probably use 74HC595 SIPO latches (or Supertex HV latch / driver chips) but in 2007 I did not know they existed. So what I did was create something real close to 595 functionality without using 595s.

There are 15 data lines - 1 for each segment - and they connect in parallel to all tube boards. IOW all tube boards see all data. There are 16 tube select lines - 1 for each tube. Sounds like multiplexing so far, but the tube boards "double buffer". The data lines feed the data pins of all boards' "back" 16-bit (one bit not used) latches. The tube select lines control which tube board's latches actually read the data lines. Data representing the segment pattern for Tube 1 is put up on the data lines and Tube 1's select line is pulsed. The data is stored in Tube 1's "back" latches. Repeat rapidly for tubes 2 - 16. The entire refresh cycle takes just a few milliseconds. Now all tubes' "back" latches are filled with new data BUT the tubes are still displaying whatever is in the "FRONT" latches. Then the "latches GO" line is pulsed which causes the data in the "back" latches to be synchronously copied into the "front" latches. The "front" latches are what actually drive the tubes (thru MPSA42s) so the display updates synchronously when "latches GO" is fired.

Thus I get the signal count benefit of multiplex (32 lines instead of an impossible 256 lines) without the flickering of multiplex. By using 595s or Supertex I could reduce the count even more but right now I have no interest in redesigning the thing.

Look into it later when the dust is clearing off the crater.

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7 months 3 days ago #9759 by jonboy
Replied by jonboy on topic B-7971 Project
Maybe I won’t be making one anytime soon, at over a $100 a tube, even just displaying hours is out of my price range!!
Maybe you should make it a 8 tube nixie display device and sell the other 8?
I hope you have a spare in case one decides to quit on you!

Thanks for sharing

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7 months 3 days ago #9760 by Ty_Eeberfest
Replied by Ty_Eeberfest on topic B-7971 Project
Yep, I've got spares. B) But the thing has been running continuously for 11-1/2 years and so far I haven't had to replace any tubes. Maybe some day when the prices get high enough I'll sell off my spares but for now I'm holding on to all my tubes.

Look into it later when the dust is clearing off the crater.

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7 months 2 days ago - 7 months 2 days ago #9761 by Ty_Eeberfest
Replied by Ty_Eeberfest on topic B-7971 Project
Okay. I've decided to put it back online for a little while. Might take a couple days to get set up though. I ran into a problem already... it takes a good camera to run a decent looking video stream of operating Nixies. I've always used my ancient Sony TRV8 camcorder - it does a great job. The camera still works but today I discovered that for some stupid reason it won't output video if it doesn't have a blank tape cassette in it. Trouble is, a few years ago the cat pissed in my camera bag, destroying my stash of blank Mini-DV cassettes. Now I'm finding out you can't just run to the store and buy them anymore. I've ordered some from Amazon - now we wait...

Look into it later when the dust is clearing off the crater.
Last edit: 7 months 2 days ago by Ty_Eeberfest.
The following user(s) said Thank You: Peanut13

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