Packing 10 into 1: A Square Inch Dekatron Replacement

One of the things that always attracts our eye in old movies is how many kinds of displays you see on old gear both real and imaginary. Really old stuff usually had meters or circular recorders. But slightly newer movies often had some kind of exotic digital display with Nixes or Numitron tubes. One of the really exotic display devices was a Dekatron. While these are pretty rare, you can make a stand-in using modern LEDs and [Dave] did just that in an entry into our square inch competition.

These were gas-filled tubes with ten positions. You had to reset the tube and then the tube would visibly count pulses providing a visual indicator from zero to nine. Depending on the tube configuration, you could use them to count or to act as a divider. Those with neon fill looked sort of orange, although there were argon-based ones that had a purple glow. You can see what an older version of the board looks like in the video below or skip to the second video if you want to see the real ones in action.

[Dave’s] device uses orange LEDs to look similar to a neon Dekatron. Luckily, you won’t need the 350V power supply a real tube requires. Although you can still get surplus Dekatrons, [Dave] was building a replica decimal computer and the cost and power requirements would have been significant.

The device uses a 74HC4017 decade counter IC which — on the newer design — shows up in the middle of the LEDs. The original version, seen in the video, hides the chip on the back of the board which makes it much harder to assemble.

This is the second square inch contest we’ve had and if you want to enter, the deadline’s been extended, but not for much longer. There’s real money on the table, including $500 for the winner. Test equipment seems to be a popular theme, although if last time is any predictor, there are plenty of other options.


11 thoughts on “Packing 10 into 1: A Square Inch Dekatron Replacement

    1. I remember seeing a YouTube video, might have even been linked from here, where a guy had made a dekatron kitchen timer, used a clock pulse and this old industrial dekatron counter (Which he thought was part of some sort of machine that punched out parts, and it was a controller that you could set to x number of parts and then the machine would run, incrementing the counter each time until it got to the set point and then it’d stop), you’d set the dials in the box to the time you wanted and then hit start and it’d run until it hit your set point and then stop. https://www.youtube.com/watch?v=sLEViKXtyt8

  1. I saw the Harwell Dekatron at The National Museum of Computing in Bletchley Park when I visited there in June. It’s well worth a visit. In addition to the flashing Dekatron tubes, the control circuitry is made of relays and so the system both looks *and* sounds like a prop from a 50s sci-fi film.

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