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prop1 to control a VFD tube — Parallax Forums

prop1 to control a VFD tube

NNNNNNNN Posts: 3
edited 2007-04-03 22:37 in Propeller 1
I have some old school vfd tubes... I also have a prop-1 chip, and I'm trying to figure out how to use it to control a number of tubes, maybe to do scrolling text or something like that. All I can think though is to use the 8 outputs to control 8 segments of one tube, but each tube has 16 segments (each lead coming off corresponds to a segment to light individually. Is there a more economical way? There's some french guy on the internet that's done it, but he's using a maxim ic driver and a 32 pin flash memory chip....and some other stuff. Not that I wouldn't be opposed to doing it that way, but I'm totally new to all this and wouldn't know how to put it all together. Any ideas?

thanks!

1.jpg

Comments

  • rjo_rjo_ Posts: 1,825
    edited 2007-04-02 06:32
    NNNM

    Well, you are on the right track. As far as I know there are no Propellers in France.

    I am a theory guy... when it comes to practical issues, I frequently ruin things. I think you are going to want to know what happens when you put 3.3 volts across any of those leads.
    Then I think you are going to want to use a multiplexer... you will have to choose that before you can ask for any real help. Then you are going to need a circuit design of some sort so that the engineers don't blow a gasket. And then you should relate the whole thing to global warming to get the political support you deserve, but probably won't get without a little pandering.

    None of this is intended to be sarcastic... if it sounds that way... it isn't.

    I do try to entertain the guys at Parallax... but I wouldn't do it at your expense.

    As you go along... please remember that there are a lot of people here who are trying to learn just as you are... such is me. And we would really like to get the full story and see all of the essentials.

    Rich
  • HarleyHarley Posts: 997
    edited 2007-04-02 16:50
    NNNN,

    You have the parts. Is there a part number anywhere on them? Have you a data sheet for them? Who made them? How old are they? Etc.

    Some details would be helpful.

    Depending on how many you want to use, it may be the Propeller can do that easily. I have a PIC driving 6 7-segment LEDs at about a 80 Hz rate (so each is ON about 1/6th of that period) and they are bright and usable.

    Details, as much as you can supply...

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    Harley Shanko
    h.a.s. designn
  • BergamotBergamot Posts: 185
    edited 2007-04-02 17:40
    Does anybody speak Russian?

    It might be possible to use a shift register to control the pins, and perhaps some sort of transistor setup if it requires larger voltages than the propeller can provide.
  • Graham StablerGraham Stabler Posts: 2,510
    edited 2007-04-02 18:01
    напряжение means voltage

    Being vacuum devices you are bound to need quite a few volts to run them.

    Graham
  • HarleyHarley Posts: 997
    edited 2007-04-02 18:12
    Plus voltage swings on the segment pins, most likely, besides Graham's comment.

    Back to the 'vacuum tube' days, eh?

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    Harley Shanko
    h.a.s. designn
  • JonathanJonathan Posts: 1,023
    edited 2007-04-02 18:55
    I've played with a few similar tubes, although not an identical one. Filiment voltage is usually low, around 3V. Segment voltage is higher, in the 20-30V range. It's only neon type tubes (nixie) that take 170V or so. No matter what the spec sheet says, I would ramp up the filiments voltage slowly, and use the minimum that works properly. If you use a variable regualtor, you can increase it later if need be.

    There is a great forum for these types of tubes, with many folks who know them really well. Search for the Google group neonnixie.

    Jonathan

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    www.madlabs.info - Home of the Hydrogen Fuel Cell Robot
  • SkogsgurraSkogsgurra Posts: 231
    edited 2007-04-02 21:43
    First. What you show is not a VFD, it is a Nixie (Numerical indicator, Experimental, #1) as the Burroughs guy that invented it hand-printed on his drawing. NIXIE being an abbreviation of the full name.

    There used to be 74xx drivers that could handle the 100 - 200 V levels used to drive them. And, BTW, no filament in these. just raw field emission in a "rarefied" neon gas. Transistors like the BSW68 can be used - or little high-voltage mosfets. Always remember that a series resistor is needed - or you will short your HV supply. Not home now, will try and find a diagram later.
  • SkogsgurraSkogsgurra Posts: 231
    edited 2007-04-02 21:46
    Sorry. When I have a closer look at the picture - it IS actually a VFD. They usually come in long, and often multiple, rows. That's why I made the mistake.
  • NNNNNNNN Posts: 3
    edited 2007-04-03 22:05
    filament voltage is 2.6v, segment and grid voltages are 25v. I have a 24v supply on the way, which should cover the 25v okay, and I'll drop it down to 5v and use a resistor to cover 2.6v. I can get them to work, but the problem is in all the leads - sixteen leads for sixteen segments per tube - how can I use a prop 1 to manipulate all segments of the display tube when there are only 8 outputs? Is there a way other than connecting one output to one lead? I can get the 16 output expander, but that will only allow for complete control of one tube (or one and a half tubes), and I would like to use many. These things are so old...they managed to do it before prop·chips existed...

    I looked into multiplexers. they look like they could be helpful, but I'm not entirely sure how to use them, as a 1 to 16 multiplexor must cover all possible scenarios for on and off, and then I'd be using 4 outputs (the one that gets split into 16, and 3 selectors). Is that right? would I need to manipulate one somehow (in term of ANDs and ORs) to get it to cover all possibilities, or do they come like that?

    Any other ideas? thanks a ton!
  • HarleyHarley Posts: 997
    edited 2007-04-03 22:37
    If you can't find any documentation on the device, you'll need to make up a chart on which segments are turned on for all the letters, numbers, and other punctuation characters.

    The device appears to actually have 18 segments, if you intend to use the two 'decimal points' on each side at the bottom. So the code table will be quite wide to 'mark' the ON segments.

    So the table will have 26 entries for letters, 10 for numbers, plus all the 'special' characters. 19 columns wide by at least 36 rows.

    Appears you'll need a rather large look-up table or EPROM to drive the segments. And 'voltage translators' (3.3v from Prop to 25v to devices)

    The mode the devices will be used (a register for each device, or a multiplexed drive directly from the Prop) will determine the other hardware and number of lines from the Prop.

    Hopefully you can find documentation on your devices. Save lots of trial and error effort. Enjoy!

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    Harley Shanko
    h.a.s. designn
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