The Vintage Technology Association - Incandescent Displays

Incandescent Displays

Dialco Incandescent Display

Devices included in this entry:

Dialco 7 segment with decimal point display, unknown P/N (PCB back with driver socket; pictured in thumbnail)
Dialco 710-0300-009 7 segment display (plastic back with PCB mount lugs)

This archaic bit of hardware is a 7-segment (plus decimal point) display with eight discrete incandescent lamps, one for each display element. Dialco made a myriad different variants of this basic design, some with spade or PCB mount lugs, some with attached drivers, all with an assortment of different bulb voltages. The standard diameter midget flange lamps installed in these devices are held in with screws and spring terminals, and can be easily replaced.

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Alco MSM-5A

Alco manufactured a vast line of "mosaic indicator" incandescent segmented displays. The MSM-5A is a fairly typical example, a functional duplication of a modern LED seven segment display, done with lamps instead of LEDs. The bulbs in the MSM-5A can not be replaced - the entire display is a plug-in unit, designed to be discarded when one of its bulbs burns out. The display is an exercise in Cold War-era manufacturing excess; machine screws, aircraft grade aluminum, and gold traces are all present and accounted for. Of particular note to the home experimenter is that the lamps can be non-destructively replaced with 3mm LEDs, allowing the full color range of modern LED technology to be used in the display.

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MSC 351 Series

Light pipe displays like this one are a close relative of the Dialco display pictured above, in that they use incandescent bulbs to light a seven segment pattern on a single plane surface. Unlike the comparatively economical Dialco display however, a light pipe display uses bundles of fiber optic cables to present a fixed bitmap image of a number. The display seen here is actually equipped with sixteen segment light pipe arrays, but the unused fiber optic cables have been covered with epoxy. Each plastic-encased driver module contains an Intersil 5600 read only ROM chip which functions as a character decoder for the individual lamps. Unlike the Dialco display above, the lamps in this device are non-replaceable.

The lamps in this display can be non-destructively replaced with 3mm LEDs by the modern electronics hobbyist, but the combination of non modular digit construction and awkward digit spacing make this device a poor choice for a project.

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IEE 10000-1819-B

Before the arrival of reliable, easy-to-use LED displays like the Monsanto MAN-1, companies came up with a vast array of impractical methods to display numbers and characters. Projection displays, such as the one shown here, are one of these fringe display types, and were designed to compete directly with the neon filled Nixie tubes that were the leading display of the time. Also known as a "One Plane Readout" or "In Line Display", these devices were invented by IEE in 1956 for use in their proprietary industrial control systems; the devices proved so popular with customers that IEE began producing and selling the displays as a stand-alone product.

A projection display functions like a miniature slide projector, only the "slides" are numbers, each with its own separate lamp for electrical control. In this IEE display, light from one of 12 different lamps is projected through one of 12 focusing lenses, which directs the light beam onto the appropriate number mask. Light exiting the digit mask passes through a second set of lenses, which bends the light to project the image of the digit mask onto the center of a fogged plastic screen at the front of the display.

Projection displays are complex devices with numerous parts, and were expensive to manufacture compared to a Nixie tube. For the modern hobbyist though, projection displays have several significant advantages over shaped cathode displays like Nixie tubes. Projection displays have replaceable bulbs, allowing the color of the displayed number to be changed simply by replacing the bulb with an appropriate LED light source. The digit masks in most projection displays are also replaceable, which allows for many custom display types to be quickly and easily produced. During the Cold War projection displays were quite popular for industrial control systems, since custom symbols and warning messages could be easily added to the digit mask.

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IEE 220H-6409-B-328

IEE was almost surely responding to the hilarious bulk of their earlier projection displays when they designed this more advanced model. Taking up less than half the volume of larger displays like the 10000 series unit shown above, this model also has an easy access clamshell case, which significantly reduces the difficulty of changing the digit mask.

This model provides a perfect example of how projection displays were tailored to industrial control applications: the standard numeric mask has been replaced with a more custom unit that displays entire preset phrases.

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IEE 340 Series Projection Display

Not all projection displays are bulky; this 340 series display, made by IEE, is so small that it does not look out of place mixed in with modern LED display modules. This device is truly minuscule; the digit height is only 13mm and the projection face is 12mm wide and 20mm tall... not much larger than a standard plastic DIP-packaged LED display. The 340 is much deeper than a LED display however, the complex projection lens system of IEE's larger displays has been replicated within in miniature. The display's clamshell case is secured by two threaded screws, which can be removed for easy replacement of the slide containing the projected numbers.

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Signaltron ST-15 Split Flap Display

Another fringe display technology, split flap displays make projection displays seem almost practical. Split flap displays use a synchronous motor and gearbox to rotate a spindle of spring loaded flaps to display numbers. The numeral flaps are split down the middle and held open by small metal fingers, hence the name "split flap display". A rotary switch attached to the spindle of the motor controls power. When power is applied to the pin for the desired number, the motor will rotate the spindle until the desired number is displayed, at which point the rotary switch will open and shut down the motor. The result is a slow, noisy display that fills a room with the sound of flaps slapping together every time it changes, and has the added feature of needing to be oiled regularly.

Although this is obviously not an incandescent display, this is the best location for such a device until we get around to adding a 'Hopeless Split Flap Display' section.

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Ferranti-Packard Flip Dot Display

Flip dot displays are another 'flap' based electromechanical display in the same family as the Signaltron ST-15 flap display shown above. A flip dot display uses an array of magnetic disks suspended above a matrix of coils to display alphanumeric data. Each coil has a U-shaped bar passing through it, which stores the magnetic state imparted when an electric current passes through the coil. The U-bars are connected to the pivot points of each magnetic disk, causing the disks to flip to match the magnetic state of the bars. Much like core memory, the U-bars store a magnetic state even when power is removed, allowing images to be loaded and stored in the display without any external latches secondary memory hardware.

This Ferranti-Packard model is made up of an array of five separate flip dot 'bars' each containing seven dots. The coils operate at 5V, and are attached to a diode matrix that prevents a pulse on a given row from inadvertently flipping adjacent dots.

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Burroughs SD-11

At first glance, the Burroughs SD-11 may appear to be a standard projection display, but it is in fact a sphericular display. The SD-11 operates in a similar manner to a lenticular device, but instead of being composed of bar-shaped elements, it is composed of a grid of circular elements. The front panel of the SD-11 is a complex two-dimensional array of faceted refractors which generate the displayed digit; there are no lenses or digit masks as in a standard projection display. The angle of the light striking the refractor controls which digit is displayed, by applying power to one of eleven bulbs inside the device. The digits zero through nine can be displayed with or without decimal point. Eliminating the bulky lenses used in projection displays allows for the manufacture of a display that is a fraction of the size of competing devices. The displayed characters on the SD-11 are not as clear as those displayed by most projection displays, but the visual appearance of the sphericular characters is quite distinctive.

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