Robot Clock Writes Time Over and Over and Over

We’ve seen quite a few clocks that write the time out with a pen or marker. If you think about it, this really isn’t a great solution; every whiteboard marker will dry out in a day or two, and even if you’re using a pen, that’s still eventually going to run out of ink.

[ekaggrat] wanted a drawing clock that didn’t have these problems, and after taking a look at a magnetic drawing board, was struck with inspiration. The result is a clock that will perpetually write the time. It’s a revision of one of his earlier builds and looks to be much more reliable and mechanically precise.

A clock that writes time needs some sort of surface that won’t degrade, but can be written to over and over again. Whiteboards and glass won’t work, and neither will anything with ink. The solution to this problem was found in a ‘magnetic writing board’ or a Magna Doodle. These magnetic writing boards have a series of cells encapsulating iron filings. Pass a magnet over one side of the board, and a dot of filings appear. Pass a magnet over the opposite side of the board, and the filings disappear.

[ekaggrat]’s time-writing robot consists of a small Magna Doodle display, a robotic arm controlled by two stepper motors, and two solenoids on the end of the arm. The kinematics come from a helpful chap on the RepRap forums, and with the ATmega644 and two stepper drivers, this clock can write the time by altering the current flowing through two solenoids.

A video is the best way to experience this project, and you can check that out below.

26 thoughts on “Robot Clock Writes Time Over and Over and Over

  1. How Magna Doodle Works:

    http://entertainment.howstuffworks.com/magna-doodle.htm

    TL;DR: Transparent/translucent honey-comb cells filled with a suspension of dark magnetic particles in a light/clear colored thick liquid – a thick enough suspension to resist the acceleration of the Earth’s gravity on the magnetic particles. A “pencil” has a magnet in the tip who’s polarity is such that the dark magnetic particles are attracted to the cells surface by the magnet thereby making a dark “pixel”. The entire screen is erased by passing a wide magnet across the back of the screen pulling the magnetic particles away from the visible part of the screen.

    It seems to me at first glance this clock hack writes and erases by revercing the polarity of an electromagnet on the “pencil’s” tip.

    1. No, the clock arm has an electromagnet on both sides. On the front side, the electromagnet attracts the particles to the front, so they can be seen. On the back side, the second electromagnet draws the particles away from the front to essentially erase the image. You can’t just have one electromagnet and reverse the polarity. All that would do is attract the ‘other end’ of each magnetic particle.

  2. I like that it only erases the characters it needs to, rather than the whole board and starting again.

    The buddha boards are quite nice as a redrawing surface, but does involve having water around that isn’t always ideal.

      1. You could possibly cut those.. they aren’t LCDs in the conventional sense of being digital displays. Basically you apply pressure to turn pixels on.. and an an electric current resets the pixels when done.

  3. When it changes from 9:09 to 9:10, it should erase both the 0 and the trailing 9 before drawing the 10. As it is, you temporarily get 9:19, which could be confusing if you happen to glance at the display then.

  4. Since the solenoids are only moving magnets back and forth, you COULD put a much larger magnet on the back side so it can erase a whole numeral in a single stroke. Kind of like the Manga-Doodle does with the whole panel.

    And I agree with Savannah – needs to draw smoother.

    Great idea.

      1. Oh I agree, I think half the fun of a project like this is having it be a little ‘clunky’ and not perfectly optimised (I say that with duest respect :))

        I guess I equate perfectly smooth motion etc as, well, kind of boring, you buy a ready made product if you want that perfection.

        Very nice work.

    1. or three magnets on the back side…I wonder if the stuff they use to make car signs works; that’s easy to cut to shape.

      Hmmm….also, too numbers made of the same material, only put up in the front like some manic robotic sign assembler…Would require a LOT more solenoids :-) or one ‘daisy wheel’ of magnets along the front that moves back and forth.

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