Insanely Complicated “Unstuck in Time” Seven Segment Display

This is one of those electronic components that leaves you wondering “What were they thinking?” Functionally, it is a seven segment display, which shows the digits from 0 to 9 and an optional decimal point, There is no indication of the manufacturer, but the date code on the label and internal components indicate it was made in the 1980s. Now, since the 1970s, inexpensive, low-power LED seven segment displays which could be directly driven by TTL integrated circuits were commonplace, but none of that here! The digits on the face are made up of round dots which turn out to be the ends of “light pipes” which carry light from a bank of eight tiny incandescent lamps, each of which drives the pipes that illuminate the dots that make up each segment (or decimal point). These are all moulded into a resin block, with the lamps housed in a machined aluminium block that presumably serves as a heat sink and is gold plated because why not? The bulbs touch gold plated pins which go to a connector leading to another module. This contains two military-grade ceramic integrated circuit packages and a rat’s nest of wiring, not on a circuit board, but assembled (obviously manually and with great care and expense) between two circuit boards as in 1950s style cordwood circuitry. The two integrated circuits are a seven segment decoder-driver and a four bit latch, which allow a number of these displays to be multiplexed on a bus and individually addressed, sending the 4 bit binary coded decimal value to each digit serially.

Does it work? Well, building a custom driver for the multiplex electronics doesn’t seem worth it, but driving the individual segments can be easily accomplished. Amazingly, the incandescent lamps are able to be driven directly by 54/7447 open-collector TTL [PDF] seven segment decoder/drivers ICs.

Everything about this screams “aerospace”, as in “Cost is no object—we’ll just squeeze the taxpayers harder”. One YouTube commenter identifies the manufacturer from the code on the label as Safran, and says that such units are still listed in their catalogue for US$850 a pop.

Want to bet they just threw these units away and replaced them with another when one of the incandescent lamps burned out?

LED seven-segment displays currently go for around US$ 2 in small quantities.