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I wanted to build something out of my new-old-stock soviet IV-21 VFD displays that I bought last year, but they have 19 fucking pins!! I can’t find any mount that fits that many pins, and I don’t wanna pay a small fortune to print a custom PCB 😞

@brunoph PCB's are really cheap now! Dunno if shipping to europe would make them too expensive, but i can get 10 boards for like $23 shipped from china

@mdszy hm I’ll look into that, thanks! I’ve never built any circuit that complex before, but at the same time I only wanna built something to handle the high voltage, and with a memory bank plus parallel access so I could just write numbers into it from a raspberry pi, for example.

It should be a simple circuit since it only needs a single seven-segment controller (since you can only illuminate one of the digits at a time), but I really have no clue how to even get started lol

@brunoph ohh, okay, so you'd be multiplexing the digits?

yes, a BCD to 7 seg driver would work well, you'd just possibly need high-ish voltage transistors to do it

i'm sure you'd be able to find a schematic online that could do it

please feel free to hit me up if you want help with the schematic or pcb design, i've done a bunch of that for my own projects and i like to think i really know my way around it, and i'd love to help out if i can!

@mdszy oh thank you! I’ll try to find some time for that.

The segment control circuit is low voltage (1.2V) but VFD circuitry is very weird. The high and low voltage circuits share a rail and at least in my head it is not straightforward.

VFDs rely on persistence of vision, which ends up making the circuit simpler. I think I need a clock to cycle over each digit in memory and sync that with the pin that powers the cathode for each individual digit.

I’ll try finding a test schematic that explains this. 😂

@brunoph yep, i totally know what you mean, multiplexing is that process by which you make it look like multiple displays are on when they're not due to POV

i'm not sure what you mean by the high and low voltages sharing a rail, but like i said, hopefully you can find some driver circuit examples that'll help!

@mdszy Here is what I mean: notice the high voltage circuit is 27V and the low voltage circuit is 1.5V in this example. It’s also important to notice that the circuit works by having electrons fly from the filaments to the grid, and also to the segment in case it has a positive charge. Until I realized that the circuit always looked “open” in my head.

@brunoph ah, interesting!

seems like it uses a resistor to drop the voltage down, then?

@mdszy That’s the thing, it doesn’t! It uses two power “circuits”. The specs are very clear that the 1.5V “circuit” has very low tolerance to higher voltage. I don’t know how this works, but if you literally wire up the display like in that schematic it will light up correctly. I even tried it when I bought the displays. It shows two digits because I was simultaneously powering the cathodes for both of them.

@brunoph huh! very neat!

good luck, and like i said, i'm more than happy to help with the schematic/pcb design, if you haven't done any before, i recommend kicad, it's the software i use a TON and can help out as much as you need!

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