![]() ![]() S ev en-segment numerals viewed without a colored filter, revealing the cathode (horizontal wires) and the grid (wire mesh). Connections between the segments of the numerals and a backplane are also visible.įigure 25-4. This reveals not only the grid but also the horizontal wires that function as the cathode. Figure 25-4 shows two seven-segment numerals from another device, with the filter removed. Thus, the Commodore calculator used a green filter in front of its green numerals. Three digits from the previous figure, show ing the grid that controls their illumination.Ī tinted filter of the same color as the display is usually placed in front of it, to conceal some of its workings. The vacuum-fluorescent display from a 1 9 7 0s Commodore calculator.Ī closeup of three digits from the previous figure appears in Figure 25-3, showing the grid super- imposed above each numeral.įigure 25-3. Purely nu- meric VFD modules are still available as strings of digits, although they are becoming uncommon and have been replaced by alphanumeric dot- matrix modules where each VFD character is mounted in its own glass module on a separate substrate.įigure 25-2 shows the interior of a Commodore calculator from the 1970s, with its nine-digit vacuum-fluorescent display enclosed in one glass capsule.įigure 25-2. How to Use ItĮlectronic calculators used vacuum-fluorescent displays during the 1970s, before LED displays and LCDs became more competitive. Thus, the grid functions in the same way as the grid in a triode vacuum tube, but its conductors are so thin, they are barely visible. If the grid section is positively charged, it encourages electrons to reach the anode. If a grid section is negatively charged, it repels electrons and prevents them from reaching the The polarity of the charge on the grid controls and diffuses electrons emitted by the cathode. ![]() The basic elements of a vacuum-fluorescent display. A simplified view of this arrangement is shown in Figure 25-1. Anode, Cathode, and GridĪ grid consisting of a mesh of very fine wires is mounted in the thin gap between the filaments of the cathode and the segments of the anode. However, the cathodes in a VFD are efficient electron emitters at a relatively low temperature, while the cathodes in a cathode- ray tube require substantial heaters. This behavior can be compared with that of a c athode-ray tube. When electrons strike a positively charged anode segment, it emits visible light in a process of fluorescence. Each segment of the anode is coated with phosphors, and individual segments can be sep arately energized via a substrate. Opposite the cathode, just a few millimeters away, is an anode that is subdivided into visible alphanumeric segments, symbols, or dots in a matrix. A VFD uses DC, and its cathode array has the function that one would expect, being connected with the negative side of the DC power supply. The wires are often referred to as filaments.Ī fluorescent light uses AC, and both of its electrodes are often confusingly referred to as cathodes. A widely spaced series of very fine wires, primarily made of tungsten, functions as a c athode, moderately heated to en- courage electron emission. The display is mounted inside a sealed capsule containing a high vacuum. There is no specific schematic symbol to repre sent a vacuum-fluorescent display. It is often brighter than the other information display systems, and can emit an intense green phosphorescent glow that some people find aesthetically pleasing, even though a grid of very fine wires is superimposed internally over the displayed im age. ![]() Although a VFD does use fluorescent phosphors, they are printed onto light-emitting segments of the display instead of being applied to the inside surfaces of a glass envelope.Ī v acuum-fluorescent display or VFD superficially resembles a backlit monochrome L CD or an LED display, as it can represent alphanumeric characters by using segments or a dot matrix, and can also display simple shapes. A VFD is an informational display, often showing numerals and letters, while a fluorescent light merely illuminates a room or work area. The entry in this encyclopedia dealing with fluorescent lights does not include VFDs, because their purpose and design are very different. In both instances, the acronym is printed without periods be- tween the letters. The acronym VFD is be- coming increasingly popular, although it is ambiguous, being also used to identify a variable frequency drive. Vacuum-fluorescent display The term vacuum-fluorescent display is seldom hyphenated, but the first two words are hyphenated here as they constitute an adjectival phrase. ![]()
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