Vacuum fluorescent display
7 segments |
8 segments (Sharp EL-8) |
16 segments |
A vacuum fluorescent display (VFD) is a
A VFD operates on the principle of
Unlike
VFDs can display seven-segment numerals, multi-segment alpha-numeric characters or can be made in a dot-matrix to display different alphanumeric characters and symbols. In practice, there is little limit to the shape of the image that can be displayed: it depends solely on the shape of phosphor on the anode(s).
The first VFD was the single indication DM160 by Philips in 1959.[5] The first multi-segment VFD was a 1967 Japanese single-digit, seven-segment device made by Ise Electronics Corporation.[6] The displays became common on calculators and other consumer electronics devices.[7] In the late 1980s hundreds of millions of units were made yearly.[8]
Design
The device consists of a
The cathode wire to which the oxides are applied is made of tungsten or ruthenium-tungsten alloy. The oxides in the cathodes are not stable in air, so they are applied to the cathode as carbonates, the cathodes are assembled into the VFD, and the cathodes are heated by passing a current through them while inside the vacuum of the VFD to convert the carbonates into oxides.[2][10]
The principle of operation is identical to that of a vacuum tube triode. Electrons can only reach (and "illuminate") a given plate element if both the grid and the plate are at a positive potential with respect to the cathode.[12] This allows the displays to be organized as multiplexed displays where the multiple grids and plates form a matrix, minimizing the number of signal pins required. In the example of the VCR display shown to the right, the grids are arranged so that only one digit is illuminated at a time. All of the similar plates in all of the digits (for example, all of the lower-left plates in all of the digits) are connected in parallel. One by one, the microprocessor driving the display enables a digit by placing a positive voltage on that digit's grid and then placing a positive voltage on the appropriate plates. Electrons flow through that digit's grid and strike those plates that are at a positive potential. The microprocessor cycles through illuminating the digits in this way at a rate high enough to create the illusion of all digits glowing at once via persistence of vision.[citation needed]
The extra indicators (in our example, "VCR", "Hi-Fi", "STEREO", "SAP", etc.) are arranged as if they were segments of an additional digit or two or extra segments of existing digits and are scanned using the same multiplexed strategy as the real digits. Some of these extra indicators may use a phosphor that emits a different color of light, for example, orange.
The light emitted by most VFDs contains many colors and can often be
Use
Besides brightness, VFDs have the advantages of being rugged, inexpensive, and easily configured to display a wide variety of customized messages, and unlike LCDs, VFDs are not limited by the response time of rearranging liquid crystals and are thus able to function normally in cold, even sub-zero, temperatures, making them ideal for outdoor devices in cold climates. Early on, the main disadvantage of such displays was their use of significantly more power (0.2 watts) than a simple LCD. This was considered a significant drawback for battery-operated equipment like calculators, so VFDs ended up being used mainly in equipment powered by an AC supply or heavy-duty rechargeable batteries.
During the 1980s, this display began to be used in automobiles, especially where car makers were experimenting with digital displays for vehicle instruments such as speedometers and odometers. A good example of these were the high-end Subaru cars made in the early 1980s (referred to by Subaru enthusiasts as a digi-dash, or digital dashboard). The brightness of VFDs makes them well suited for use in cars. The Renault Espace Mk4 and Scenic Mk2 used VFD panels to show all functions on the dashboard including the radio and multi message panel. They are bright enough to read in full sunlight as well as dimmable for use at night. This panel uses four colors; the usual blue/green as well as deep blue, red and yellow/orange.
This technology was also used from 1979 to the mid-1980s in portable
From the mid-1980s onwards, VFDs were used for applications requiring smaller displays with high brightness specifications, though now the adoption of high-brightness
Vacuum fluorescent displays were once commonly used as floor indicators for
In addition to the widely used fixed character VFD, a graphic type made of an array of individually addressable pixels is also available. These more sophisticated displays offer the flexibility of displaying arbitrary images, and may still be a useful choice for some types of consumer equipment.
Multiplexing may be used in VFDs to reduce the number of connections necessary to drive the display.[2]
Use as amplifier
Several
Fade
Fading is sometimes a problem with VFDs. Light output drops over time due to falling emission and reduction of phosphor efficiency. How quickly and how far this falls depends on the construction and operation of the VFD. In some equipment, loss of VFD output can render the equipment inoperable. Fading can be slowed by using a display driver chip to lower the voltages necessary to drive a VFD. Fading can also occur due to evaporation and contamination of the cathode. Phosphors that contain sulfur are more susceptible to fading.[2]
Emission may usually be restored by raising filament voltage. Thirty-three percent voltage boost can rectify moderate fade, and 66% boost severe fade.[citation needed] This can make the filaments visible in use, though the usual green-blue VFD filter helps reduce any such red or orange light from the filament.
History
Of the three prevalent display technologies – VFD, LCD, and LED – the VFD was the first to be developed. It was used in early handheld calculators. LED displays displaced VFDs in this use as the very small LEDs used required less power, thereby extending battery life, though early LED displays had problems achieving uniform brightness levels across all display segments. Later, LCDs displaced LEDs, offering even lower power requirements.
The first VFD was the single indication DM160 by Philips in 1959. It could easily be driven by transistors, so was aimed at computer applications as it was easier to drive than a neon and had longer life than a light bulb. The 1967 Japanese single digit seven segment display in terms of anode was more like the Philips DM70 / DM71 Magic Eye as the DM160 has a spiral wire anode. The Japanese seven segment VFD meant that no patent royalties needed to be paid on desk calculator displays as would have been the case using Nixies or Panaplex neon digits. In the UK the Philips designs were made and marketed by Mullard (almost wholly owned by Philips even before WWII).
The Russian IV-15 VFD tube is very similar to the DM160. The DM160, DM70/DM71 and Russian IV-15 can (like a VFD panel) be used as triodes. The DM160 is thus the smallest VFD and smallest triode valve. The IV-15 is slightly different shape (see photo of DM160 and IV-15 for comparison).
See also
- Nixie tube
- Sixteen-segment display
- LCD
- LED Display
References
- ISBN 978-0-8493-7560-6.
- ^ a b c d e f g h Chen, J., Cranton, W., & Fihn, M. (Eds.). (2016). Handbook of Visual Display Technology. doi:10.1007/978-3-319-14346-0 page 1610 onwards
- ^ ISBN 978-3-540-79566-7.
- ^ "Fluorescent phosphorescent coating free from sulphur and cadmium". Archived from the original on 2021-02-02. Retrieved 2020-10-03.
- ^ (HB9RXQ), Ernst Erb. "DM 160, Tube DM160; Röhre DM 160 ID19445, INDICATOR, in gene". www.radiomuseum.org. Archived from the original on 2012-01-13. Retrieved 2012-08-13.
{{cite web}}
: CS1 maint: numeric names: authors list (link) - ^ Kiyozumi, K., & Nakamura, T. (1983). Vacuum fluorescent displays: from single digits to colour TV. Displays, 4(4), 213–220. doi:10.1016/0141-9382(83)90116-6
- ISBN 0-12-163420-5page 9
- ISBN 0-12-163420-5page 176
- ^ "VFD|Futaba Corporation". www.futaba.co.jp. Archived from the original on 2019-12-20. Retrieved 2019-12-15.
- ^ a b "Directly-heated oxide cathode and fluorescent display tube using the same". Archived from the original on 2021-02-02. Retrieved 2020-10-29.
- ISBN 0-12-163420-5Chapter 7 Vacuum Fluorescent Displays pp. 163 and following
- ISBN 3142250379.
- ISBN 0-8493-3564-7Chapter 8
- ^ "Front Luminous VFD|Futaba Corporation". www.futaba.co.jp. 27 February 2021. Archived from the original on 21 December 2019. Retrieved 4 January 2020.
- ^ "Bi-Planar VFD|Futaba Corporation". www.futaba.co.jp. 27 February 2021. Archived from the original on 21 December 2019. Retrieved 4 January 2020.
- ^ "Gradation VFD|Futaba Corporation". www.futaba.co.jp. 27 February 2021. Archived from the original on 21 December 2019. Retrieved 4 January 2020.
- ^ "Hybrid VFD|Futaba Corporation". www.futaba.co.jp. 27 February 2021. Archived from the original on 21 December 2019. Retrieved 4 January 2020.
- ^ "VFD (Vacuum Fluorescent Display) | Products | NORITAKE ITRON CORPORATION". www.noritake-itron.jp. Archived from the original on 2018-06-19. Retrieved 2020-01-04.
- ^ "Chip In Glass VFD(CIG VFD)|Futaba Corporation". www.futaba.co.jp. 27 February 2021. Archived from the original on 18 January 2020. Retrieved 4 January 2020.
- ^ "Double Layer Phosphor Printing VFD|Futaba Corporation". www.futaba.co.jp. 27 February 2021. Archived from the original on 21 December 2019. Retrieved 4 January 2020.
- ^ "Ultra-high luminance, full dot matrix display|Futaba Corporation". www.futaba.co.jp. 27 February 2021. Archived from the original on 21 December 2019. Retrieved 4 January 2020.
- ^ "Clear Background VFD|Futaba Corporation". www.futaba.co.jp. 27 February 2021. Archived from the original on 21 December 2019. Retrieved 4 January 2020.
- ^ N9WOS (29 July 2005). "VFD as an audio/RF amplifier?". Electronics Point forums. Archived from the original on 11 March 2018. Retrieved 11 March 2018.
{{cite web}}
: CS1 maint: numeric names: authors list (link) - ^ "H. P. Friedrichs, Vacuum Fluorescent Display Amplifiers For Primitive Radio, eHam.net December 2008, retrieved 2010 Feb 8". Eham.net. Archived from the original on 2009-08-26. Retrieved 2012-12-11.
- ^ "Des. Kostryca, A VFD Receiver (Triodes in Disguise), eHam.net January 2009, retrieved 2010 Feb 8". Eham.net. Retrieved 2012-12-11.
- ^ "Vox MV50 AC guitar amplifier". Archived from the original on 16 March 2018. Retrieved 11 March 2018.
- ^ "The Sangaku headphone amplifier". Archived from the original on 22 April 2018. Retrieved 11 March 2018.
- ^ "News | KORG INC and Noritake Co., Limited Release Innovative Vacuum Tube: The Nutube | KORG (USA)". Archived from the original on 2020-11-01. Retrieved 2020-10-29.
- ^ "Calculator.org website". Archived from the original on 23 July 2023. Retrieved 23 July 2023.
External links
- Noritake's Guide to VFD Operation
- Vacuum Fluorescent Display (VFD) (including How to drive the filament)
- Photos and specs for antique Russian VFD tubes
- Simple VFD Test Circuit
- The DM70 VFD related Magic eye
- The smallest Triode and earliest VFD, the DM160, with size comparisons
- The Russian VFD indicator like a DM160