What is your favorite electronic display?
October 11, 2019 • article
I have always found displays one of the most fascinating things about electronics. There are so many interesting and creative ways to visualize data! In this week's article we will take a look at a lot of different displays, just so see what's out there. Many of these display technologies are quite old and no longer in use. All the more reason to take a look! And who knows, maybe you will come across on of these displays :)
This article has a lot of chapters. In each chapter we will talk about a specific kind of display and briefly list its main properties as well as advantages and disadvantages. Then there are a few example images. When you click on them you will find some additional text as well as the source for the image (if I could find it).
Seven-segment LED displays
LEDs, arranged in a particular format with seven segments, are perhaps the best known example of electronic displays.
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LED matrix displays
Arranging individual LEDs in a matrix of 5×7 allows the user to display more complicated characters and symbols.
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Mechanical displays (flip dot)
Seven-segment displays as well as matrix displays can also be realized using a mechanism where colored discs (or segments) are flipped in and out. The mechanical motion is usually triggered by electromagnets.
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Edge-lit displays and lightguide displays
Edge-lit displays use a transparent carrier into which a symbol is etched or carved. Upon illumination of the edge of that carrier the light is reflected off of the etches symbold and makes it visible. Nowadays we are used to seeing those displays in shop windows or on exhibitions, but in the 1960's and 1970's this was a viable way to display characters and numbers in mostly scientific instruments.
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Projection displays
As curious little devices, projection displays contain of a set of stencils each illuminated by an individual lamp. The lamp casts a shadow on the screen and thereby displays a symbol. Some of these projection displays contain lenses and other optical components to improve the visibility.
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Liquid crystal displays (LCDs)
LCDs are passive displays. When an electric field is applied to a certain type of liquid crystal, the molecules arrange differently and alter the polarization of the light that passes through. In combination with a polarization filter placed behind the LCD screen a partof the light can be filtered out and creates the illusion of an illuminated segment.
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Vacuum fluorescent displays (VFDs)
Vacuum fluorescent displays are vacuum tubes. The heater (filament) emits thermal electrons. When they are accelerated towards a digit, which in turn is coated in a phosphorescent material, they cause that digit to glow in a desired color. These displays are usually multiplexed and may contain hundreds of individual segments.
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Incandescent displays (numitrons)
These nifty little devices contain segments made of filaments. Each filament glows when a voltage is applied, just like a tiny light bulb. The segments combine to form letters and numerals.
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Gas discharge displays (Nixie tubes)
Nixie tubes are glow lamps. They are filled with a mixture of the noble gases neon and argon. A positive high voltage is applied to the anode (the mesh around the digits). When a digit is connected to ground, electrons leave that digit and cause the adjacent gas to glow, which creates the illusion of a letter forming in thin air.
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Planar gas discharge displays (Panaplex)
Panaplex tubes work similarly to Nixie tubes, they just come in a planar form factor.
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Cathode ray displays (NIMO tubes)
In a way this curious vacuum tube is very similar to the projection display mentioned above: electrons are accelerated through a stencil that is shaped like a digit or symbol. The electrons that make it through reach the front part of the tube which is coated in a phosphorescent material. The impinging electrons cause the phosphor to glow and form the shadow of a number.
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Thyratron displays
These are perhaps the most bizarre display device I have seen (yet). Each segment is a thyratron (a tube filled with gas) that in turn causes a phosphorescent segment to glow if a high voltage is applied. Thyratron displays basically contain several NIMO tubes, one for each segment.
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Final thoughts
As you can see: there are myriads of different display devices out there! I am sure I forgot to mention a lot of them. If so, please get in touch and tell me about your favorite display device!