Mechanical Seven-Segment Display Mixes Art With Hacking

We’re not sure what to call this one. Is it a circuit sculpture? Sort of, but it moves, so perhaps it’s a kinetic circuit sculpture. Creator [Tomohiro Tsuchita] calls it “something beautiful but totally useless,” which we find a tad harsh. But whatever you call it, we think this mechanical seven-segment display is really, really cool.

Before anyone gets to thinking that this is something like the other mechanical seven-segment displays we’ve seen lately, think again. This one is not addressable; it simply goes through the ten digits in order. So you won’t be building a clock from it, although we suppose the mechanism could be modified to allow that. Then again, looking at that drive train of laser-cut acrylic cams, maybe not. Each segment has its own cam with lobes or valleys for each segment. A cam follower lowers and raises the segments as the cams rotate on a common shaft. A full-rotation servo powers the display under the control of a Micro:bit; the microcontroller is overkill for now but will be used in version two, which will allow the speed to change in response to sensors.

Watching this display change at its stately pace is strangely soothing. We love the look of this, but then again, we’re partial to objets d’art-circuit. After all, we ran a circuit sculpture contest earlier in the year, and just wrapped up a Hack Chat dedicated to the subject.

[via Twitter]

28 thoughts on “Mechanical Seven-Segment Display Mixes Art With Hacking

  1. This could very well make a cool clock.
    Clocks only count sequentially in one direction, so having 4 of these with a sensor on each to know when a digit is shown so it will pause until the next hour or minute would work well I think.
    With the limit switches rigged up right, you’d just have to pulse 1 output in minutes, the rest of the digits can be activated by the previous digit a bit like a mechanical casette tape counter.

    1. That (or an optical encoder or something) is probably what I’d do too, but it’s definitely overkill for a basic clock without any self-adjusting (GPS, NTP, etc.). All you really need is a basic clock mechanism or something like a RTC + stepper motor.

  2. This was a lot more fun that I expected. Don’t dismiss it without watching the video.
    Making it in to a clock would be trivial, it would just need a 0 to 5 version and a _1 to 12 version. These could be mechanically linked, but the animation would probably be neater with two more motors.

    1. A display that cycles through numbers in order is PERFECT for a clock! Just have a set of reduction gears between the hours and 10 minutes, and the 10 minutes and 1s minutes. Alternatively, use a single shaft that completes one rotation every 12 hours, with the diameter of the cams scaled up and the pattern repeating more often per rotation. I think the reduction gears are probably the better approach of the two.

      1. I have thought about this quite a lot (I have been working on-and-off on a conceptually similar clock for about 10 years. (much more off than on).)

        You can”t just gear them together, or the hours take an hour to change digits. It has to be some form of clicker / geneva escapement where the moving minutes moves the tens at the same speed, but only 1/6 of a rev, and the tens moves the hours at the same speed, but only 1/12 or 1/24 of a revolution.

        1. You can’t gear them together unless the cams are driving bistable mechanisms that will only be pushed enough to flip at the specified times (rather than being held in place actively by the cam as most of them seem to be) – wouldn’t be easy to get that lovely smooth animation with that method though. Needing to add dampers to slow the transitions down.

          I think that is how I would do it though – one motor for mechanical drive input seems more elegant than using brushes/sensors to drive the the next digit up based on the previous one/current time. Also means you need nothing in the way of electronics beyond a speed controlled motor.

      1. You can make the tens-of-minutes exactly like the existing section, but with only 6 positions on the cam to display 0-5. (Actually, you might keep the existing section to display tens of seconds? I think that counting full seconds might be too frantic)
        Then you need to find a way to connect the tens to the minutes for 1/6 of a revolution so that everything moves at the same speed, when it moves at all.
        I have put a 3D model of one possible way to do it, which vaguely matches your aesthetic of rotating discs here:
        The idea is that a sliding peg rotates with the end-most disc, but a light spring keeps it out of engagement with the input disc of the next stage, except for 1/6 of a revolution when a stationary cam-plate holds it in mesh with the teeth of the input disc of the next stage. I have drawn an internal cam, but an external one would work just as well with the opposite spring bias. There is no reason that the fixed cam disc and the toothed wheel can not be on the same side of the continually-rotating disc.
        The basic idea is to link the adjacent cam assemblies, but only for a fraction of each revolution.

  3. The joys of cam driven mechanisms. So many complex motions are possible with elegantly simple machinery. (Me being old enough to have worked with B&S screw machines and learned to lay out the cams in school, but not old enough to have actually cut cams for them)

    1. I still live in awe of those, having seen one run in the first shop I worked in. Whomever came up with such a complex system of cam driven creation must have been a mad genius.

      This mechanism display is fantastic! It absolutely should be turned into a clock, just make it faster. Seeing this run as a true seconds counter would be frightening indeed, flailing arms everywhere, haha

  4. I’m not quite sure why you would call it ‘circuit’ anything. ‘Automaton’ could make sense — those pretty much always used the same mechanisms (and it just kinda looks like one while it moves). “Digital automaton” would be ironic and accurate too, since, you know, it’s an automaton of a digit!

  5. I thought from the screenshot it was filling with mercury – i.e. syringes at the bottom pushed up by the cams, to fill/drain the parts of the digit as needed.

    Still, very awesome, and a whole lot less poisonous. (as long as you don’t breath in the fumes while laser cutting!)

    1. Now _that_ would be cool. Made as completely sealed glass parts it wouldn’t even be all that dangerous. Raising and lowering reservoirs behind the digits would suffice to move the mercury around.
      Or, how about a phosphorescent liquid which was “charged” in a box out the back and then moved to the digits by the same scheme.
      (Though I am maybe more relaxed about mercury than many, I had some to play with as a kid, and used Hounsfield Tensometers a fair bit at university). I used to have a pint bottle, but I think I gave it to the Tensometer technician when I left.

      1. I still have about 250g in a bottle from way back when I had bikes with slide-type Mikuni carb banks that needed to be flow balanced regularly (CB400F being the most regularly in need). Haven’t been able to make it go away, and really am not sure I want to.

    2. Working off your idea, having bellows holding colored fluid and the cam driving the bellows up and down in sequence with the segments for the digits to fill glass reservoirs shaped into the segments would be awesome! The entire display could be like those microfluidics built between two slabs of glass and each chamber is a segment.

  6. I used to have a desk clock that had a giant 7 segment display on it, but instead of LEDs and circuitry, it had a tiny light bulb for each segment, and a system of wheels and contacts that were driven off a clock mechanism of sorts.

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