A glorious mechanical seven segment display

If you’ve ever wondered why you’ve never seen a mechanical seven-segment display, now you know. They’re fairly complicated and most likely absurdly expensive, especially when a few light bulbs or LEDs would do the same job equally well. This didn’t stop [kiu] from completing his mechanical seven-segment clock he calls SevenBlocks, and for that we are thankful.

Each of the 28 segments in [kiu]‘s clock is made of three layers of acrylic and a short section of a rack gear. Unlike every seven-segment display you’ve ever seen, tiny hobby servos provide the indication for each segment. For the electronics, An ATMega8 is used for the brains of the outfit with a 74HC595 shift register to expand the number of I/O lines. A DS1307 RTC module provides accurate timekeeping, and the dozens of servo outputs visible in the ‘guts shot’ makes you realize why you’ve never seen a mechanical seven segment display before – they’re really friggin’ complex.

If you want to build your own mechanical seven-segment clock, [kiu] put all the files up on Github. Everything is there, from the .DXF files ready to feed to a laser cutter to the schematic and board files for each of the three PCBs. A video showing this clock in action is sort of necessary, so you can check that out after the break.

36 thoughts on “A glorious mechanical seven segment display

  1. not very found of the final result. it shows the wrong information for a looong time until it completely change over.

    despite that it looks good. althought i would have used magnetism in my first try at that.

  2. I’m pretty sure I’ve seen mechanical 7 segment displays. I even have a few:

    They are common, but hard to get for a cheap price.

    1. A novel method and good looking, but “never seen a mechanical … display”? Don’t you guys get out much? Mechanical seven-segment and dot-matrix displays have been around for decades as annunicators on buses, highways, at train stations and airports, &c&c&c.

      Flipping leaf 7-segment displays are currently being phased out for LCD’s after decades of use in petrol pumps across Australia, and my local still has an (old) LPG pump that still uses them; makes a pattering noise as they operate.

      See Wikipedia Vane_display, Flip-disc_display; and please, whenever you are tempted to claim a first, GIYF.

    1. I agree with you. How is this thing any more complex than driving an LED cube or something? The idea to use an arduino with servos and that gear system is a good idea…but very complex..I think not lol

      1. I mean don’t get me wrong, the craftsmanship that went into this is superb. And I guarantee you considerable time was put into its design and construction. In no way am I denigrating that. But the *concept* was touted as extremely complex by the author of the article. I disagree with that sediment / word choice.

    2. Firstly, I think it is gorgeous. Perhaps the reason the idea is toted as complex, is merely because it is complex to them. Absolutely no offense intended. It is merely a function of what you are familiar with.

      Take myself, I enjoy locksmithing, picking, and manipulation; all of the locks on this site are garbage to me. I know very little about electrical engineering or advanced mathematics; even relatively simple circuits and programs based on hard math are really difficult.

  3. It could also have been made a bit more simple. Rather than use the rack gears, one could just have used the servo horns that came with the servos. And by using an AVR with a little more pins, all the servos could be connected directly to the microcontroller, eliminating all the 74HC595-boards.

    On a side note: this watch looks a bit like it is made of lego.

    1. Or he could have used a single Centipede shield. That gives you 64 latchable digital IO pins in one shield for the price of 2 pins (it uses I2C).

  4. Wow… you first three commentors must be really freaking awexome designers / hackers. “Hmm… my dirty underwear looks better than this…”

    *shakes head*

    This is freaking awexome! Very nice work :)

    1. Yea, where’s the love, this is all kinds of awesome, the sound of the gears alone it worth the watching the video, I wish the faces of the numbers lit up some how, but hey I couldn’t build a sundial so I’m not complaining.

      1. A sundial with a solar powered Arduino to adjust for Daylight Savings Time and to shine a light or a series of LEDs on cloudy day or at night. And GPS and flux gate compass to align the dial to True North.

  5. That is awesome and nicely done, and it’s quite cool that he released all of the files for others.

    Comments above astound me. But then again, we are talking about notorious hackaday comment-ers.

  6. Mechanical seven segment displays were very common “back in the day”. They used a folding leaf design where each segment was made of two long pieces of metal or plastic, hinged down the middle.

    When a segment was off, the leaves folded back into the housing. Turn on and they folded out flat to show their light painted surface.

    I suspect they used solenoids with some type of mechanical linkage.

    The display in this article gets points for the analog effect of using servos, but solenoids would be easier, less expensive and faster – but possibly noisier.

  7. I don’t get it. I’ve used 74HC595 shift registers to drive a large number of leds. You tell them which leds you want to light up then they stay that way until you want them to change. Different from multiplexing because you don’t manually have to constantly refresh the signal to keep your leds lit. But a servo is controlled by sending it several pulses per second, varying the length of time that the pulse stays high for (pwm). This has to be pretty precisely timed high and low. How do you do that with 74HC595′s?

  8. Awesome project. Very, very nicely designed, and mad props for not breaking down and using some pre-built system instead (like an Arduino). I can really respect people who custom design their PCBs for the task at hand.

    Only thing I would have loved to see was the red bits on the segments clear instead, with a few LEDs on the back. As the segments extend forwards, the LEDs for that segment fade on- which should cast a nice light around the extended segment, making it more visible in low-light conditions (I’d still keep the front of the segment totally opaque and black though).

    Right now I’m not sure how well that clock would work from a head-on angle or in a darker room.

    -CMPX

  9. Yeah, have to agree.. In the uk most train stations have mechanical 7 seg displays. Flourescent yellow, with black on the reverse.

  10. Most of the complexity is in the rack drive. It could be simplified considerably by spring-loading the segments so they’d return on their own. Then a simple eccentric cam arrangement could activate them. The servo turns half way for ‘on’, another 180 degree rotation (in either direction) for ‘off’.

    That in no way detracts from what he’s done here. Lovely work….

  11. Mechanical 7 segments are very common in the UK both at petrol stations (billboard pricing info) and in train station clocks. Flip Vane design.

  12. Okay, now do it in Lego

    (before any one replies that it has been done before, I didn’t research, so it probably has been done)

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