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Driving a VFD Display

Discussion in 'General Electronics Discussion' started by Rayregula, Mar 16, 2017.

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  1. Rayregula

    Rayregula

    84
    18
    Dec 20, 2016
    I have two of these VFD(?) displays salvaged from old DVD players and I was wondering how to drive them if it's posible without a dedicated IC. Even if I can only get a segment to glow at least I would have a start. Do you power the filament and segment or does it use a matrix? Thank you :)

    Photo Mar 13, 10 59 23 AM.jpg Photo Mar 13, 10 59 41 AM.jpg Photo Mar 13, 11 01 38 AM.jpg Photo Mar 13, 11 02 28 AM.jpg
     
  2. 73's de Edd

    73's de Edd

    3,080
    1,301
    Aug 21, 2015
    Sir Rayregula . . . . .

    Note the tandem H connectors on each opposite end which are each of your 3.3 volts ALTERNATING CURRENT filamant supply points.
    And then, as low as 12 VDC to a segment might light it up, although usually on up in the 40 VDC ranges are being used . . . . their segment current pull is microscopic in level.
    Top one looks to have been '84ish vintage.

    REFERENCING:

    http://lizard43.blogspot.com/2009/01/seven-segment-vacuum-fluorescent.html


    73's de Edd
     
  3. Rayregula

    Rayregula

    84
    18
    Dec 20, 2016
    Thank you I will try this soon. :)
     
  4. Rayregula

    Rayregula

    84
    18
    Dec 20, 2016
    Success! 3.3V on the filament and 20V on the other pins. Thank you :)

    File Mar 17, 9 48 55 PM.jpg
     
  5. 73's de Edd

    73's de Edd

    3,080
    1,301
    Aug 21, 2015
    Sir Rayregula . . . . . . . .

    Indeed ! . . . it does look as if you have mastered the activation of your " message" display sections, with only 10 others left to try . . . . however, it seems like you are hitting it with a bit too high voltage for maximim lifespan, if then being used other than intemitently.

    Lower down . . . . you have 2 digits with their 7 segments , then a smaller set of four digits with their 7 segments and additionally with their minus and decimal point.
    They can be organized as either a counter or clock display.
    BUT this involves a MUCH - MUCH-MUCH MORE complex multiplexing of those digits and segments such that the info is updated and repeated at such a fast rate of speed . . . such that the display seem to be on continually . . . . . by virtue of persistance of vison.
    That is where that supply voltage uppage might then just come into play, to make the FAST intermittent displays come up in their brightness , to mate up in luminosity with any activated "message" display areas.


    73s de Edd
     
    Last edited by a moderator: Mar 19, 2017
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,489
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    Jan 21, 2010
    One other detail is that there is typically a specified range of current (as well as voltage) for the segments.

    The voltage range ensures that the segment will light but is low enough not to flash over to other segments.

    The current determines the brightness. Too low and the entire segment may not light. Too high and the life will be short.

    The required current depends on the area that lights up. A large enunciator may require much higher current than a decimal point.

    Typically the current is set by using a series resistor. A rough idea of the value can be obtained by subtracting from your supply voltage the voltage across the device one illuminated (this will be significantly less than the minimum voltage recommended) and dividing it by the current you require.

    Let's say your HT voltage is 40V and the voltage across the device when conducting is 15V. If you want 0.1mA, the resistor will be (40 - 15)/0.0001 = 250k.

    Edit: oh I forgot to mention that if you look at datasheets for a range of similar displays you should get a feel for the voltage and current ranges that are likely to be suitable.
     
  7. Rayregula

    Rayregula

    84
    18
    Dec 20, 2016
    Ok thanks.
     
  8. Rayregula

    Rayregula

    84
    18
    Dec 20, 2016
    I might make a clock out of it someday but for now it goes back into the drawer with the other projects. :)

    Thank you for your help.
     
  9. daberbaber

    daberbaber

    18
    1
    Feb 2, 2012
    What is missing from this Q & A is that you are dealing with vacuum tube technology and mostly the control grid is absent. The phosphor is on the plate and the electrons "burn off" the filament that is not glowing. It is an important part of electronics history. The tuning eye tube of the older radios is one of the first uses of this concept. The fluorescent light tube is another mostly driven by AC. I believe RADAR and oscilloscope tubes are others. The VFD was a deployment of the concept interfacing originally to PMOS in some of the first calculators and when the LED was introduced as a low voltage direct drive interface.
     
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