The Resurgence of Retro Display Technologies
These days, the designers of electronic systems have a wealth of affordably display technologies to choose from. Even a relatively simple system like a toaster oven typically boasts a small liquid crystal display (LCD) or light-emitting diode (LED) display.
Of course, developers weren't always this lucky. Throughout much of the first half of the twentieth century, the most widely used display technology (apart from small incandescent light bulbs used to indicate the On/Off conditions of switches) was the analog meter.
The first moving-pointer current detecting device was the galvanometer, which was invented circa 1820. It wasn't long before these devices were coerced into displaying values of voltage and resistance. Over time, analog meters were used to display signals sourced from a variety of sensor types, and to use these signals to display values of things like light, sound, and temperature. At their heart, however, all analog meters are current meters.
Eventually, various digital display technologies started to appear on the scene. For one reason or another, some people are of the opinion that digital displays are inherently "better" than their analog counterparts. They may argue that digital displays are more accurate, but the accuracy of the displayed information largely depends on the way in which the source data is gathered and processed. Others might contend that digital displays are easier to read, citing a digital clock as an example, but a fleeting glance at an analog meter in a factory will suffice to tell you if its pointer is in the safe, warning, or danger zones, which could be indicated on the meter's faceplate using green, orange, and red areas and/or annotations, respectively.
Paradoxically, there is an ongoing resurgence in the use of retro displays, including analog meters. Personally, I love to use meters in my steampunk-inspired hobby projects, such as my Vetinari Clock. On the off-chance you haven't heard of this, Lord Havelock Vetinari is the Lord Patrician of the city-state of Ankh-Morpork in the Discworld series of novels, which were gifted to us by the late, great Terry Pratchett (RIP).
There's a clock in Lord Vetinari's anteroom. Although this clock keeps perfect time, sometimes the "tick" is a fraction late, sometimes the "tock" is a little bit early, and occasionally one or the other doesn’t occur at all. As a result, by the time any visitors get to meet Lord Vetinari, their nerves are completely frazzled.
In the case of my Vetinari Clock, I decided to use four meters. A large meter will display the hours; two medium-sized meters will display the minutes and seconds, and a small meter will be used to reflect the "ticks" and "tocks."
I will, of course, be equipping my Vetinari Clock with a variety of sound effects. Depending on my mood of the moment, it may sound like clockwork, or a pneumatic system, or... we are limited only by our imaginations. Furthermore, since I will be controlling the meters using a microcontroller (MCU) and pulse-width modulation (PWM), I can do anything I want. Take the "Hours" meter, for example. I could make its needle gradually transition from one hour to the next in a similar manner to the way in which the hour hand moves on a traditional clock. Alternatively, I could leave it on the current hour until a few seconds before we reach the new hour, at which point the needle could start to quiver accompanied by a squeaking-graunching sound, followed by a sudden release as the needle flips over to the new hour.
You can, of course, purchase new meters, but I prefer to use vintage parts that I acquire for a few dollars apiece at electronic flea markets. I just think these older devices have a better "look-and-feel" when it comes to the aesthetic I'm trying to achieve.
One thing you have to be careful of is that -- depending on what they were designed to display -- these vintage meters may include shunt or series resistors. Another problem is that opening them up and swapping out their faceplates can cause particles of dust or metal to "gum up the works." Fortunately, I have lots of chums and maker friends with different skills, and we are always helping each other out. In the case of the meters for my Vetinari Clock, for example, my friend Denis of CroDesign created the graphics for the new faceplates, after which Jason at Instrument Meter Specialties refurbished the meters, swapped out the faceplates, and inserted appropriate shunt/series resistors to make them all achieve full-scale deflection at 4.5V, which makes my life a whole lot easier.
Another type of display that's starting to make a real comeback is the Nixie tube, which first made an appearance circa 1955. Nixie tubes soon started to appear all over the place, especially in test equipment where their ability to display numerical values in digital form was much appreciated by engineers.
The heyday of the Nixie tube was the 1960s. They started to be superseded in the 1970s by vacuum fluorescent displays (VFDs) and by light-emitting diodes (LEDs), often presented in the form of seven-segment displays. More recently, Nixie tubes have experienced a comeback, especially in the form of clocks, such as those created by my chum Paul at Bad Dog Designs in the UK.
As a point of interest, until recently, it was difficult, if not impossible, to obtain new Nixie tubes. The best you could hope for was to recycle them from vintage test equipment, or to purchase "New Old Stock"; that is, devices created in East Germany or the USSR during the 1960s and 1970s that are still in the original boxes. However, my friend Dalibor in the Czech Republic handcrafts his R|Z568M tubes, which are pin-compatible with the original Z568M tubes. Approximately 2" wide and 4" tall, these bodacious beauties are a joy to behold (Dalibor made me the custom steampunk set -- bronze bases and copper anodes -- shown in the image at the beginning of this column).
Another form of early digital display that shortly pre-dates the Nixie tube was the 481 Edge-Lit display. As shown in this video, each digit comprised eleven clear Lucite plates; each plate was engraved with a single digit from 0 to 9 or a decimal point; and each plate was lit by a small (grain of rice/wheat-sized) incandescent lamp mounted under its bottom edge.
Happily, Connor Nishijima has created a modern LED-based equivalent using acrylic sheets and WS2812B tricolor LEDs (a.k.a. NeoPixels in Adafruit's terminology). Known as Lixie Displays, these little beauties also have a display area of 2" wide by 4" tall. In fact, I'm using 12 of the little scamps in my Countdown Timer.
These 12 displays are presented in six pairs to present the years (YY), months (MM), days (DD), hours (HH), minutes (MM), and seconds (SS) remaining to the commencement of my 100th Birthday celebrations (29 May 2059 -- mark your calendar).
Sad to relate, I fear that we've only touched on the topic of retro displays, because we haven’t even considered the variety of electromechanical beauties that are starting to make a resurgence, but we will leave those for future column. In the meantime, I'd love to hear what you think about the technologies presented here.