This Hourglass Flips Itself

Once upon a time, [Mike] bought an hourglass for his sister. He intended to build it into a clock and give it to her as a gift, but life and other projects got in the way. Fast forward a couple of decades to the point when it all came together and [Mike] had everything he needed on hand to build a beautiful wooden clock that automatically flips the hourglass over.

Every 60 minutes, the bulb, which is situated inside a handcrafted maple ring, rotates 180 degrees to restart the flow of sand. Whatever number is at the top of the outer wheel denotes the current hour. The digit for the next hour is always at the five o’clock position relative to the current hour. This works out because the pockets on the outside of the bulb’s ring share a 5:6 ratio with the gear teeth on the outer ring. Confused? Watch the time-lapse video from [Mike]’s that shows it in action.

[Mike] was determined to build this clock using only things he already had on hand, like a cheap digital watch to keep time and a car window motor to rotate the hourglass. He hacked a USB port into the watch so he could use the hourly chime function to trigger the motor through a quad op-amp. The motor runs until it is triggered to shut off optically—a pair of slits cut into the gear that moves the hourglass pass over a sensor. [Mike] built a beautiful box to hold the guts from a nice piece of walnut and spared no detail in the design.

There are a ton of build pictures on the projects site and an in-depth video tour of the clock, which is embedded after the break. Whether they are designed to amaze or confuse, we love a good clock build around here. If you’re into hourglasses, we featured a digital version not too long ago.

37 thoughts on “This Hourglass Flips Itself

    1. An hourglass (or sand-glass, sand timer, sand watch, or sand clock) that moves, re-accommodates and rotates a dial is a hack of both, a clock dial and an hourglass.

      Hack does not equal electronics.

  1. He should’ve had two sets of grooves in the inner wheel that houses the hourglass. Correspondingly, two parallel sets of teeth on the outer wheel that has the numbers. Then, the outer wheel wouldn’t tilt that way,and would be straight.

    1. Yes, nice markings could be done with glass etching. And in addition, so that the markings will make sense, the sand is levelled by short and soft vibrations of the motor when the glass has been swapped. Really a nice watch!

  2. i have a similar project lurking in the back of my brain, but i would want the hourglass to actually be the timekeeper.

    i dont have the time to build it at the moment, but here would be the gist of it:

    1. chose an hourglass of desired length according to the resolution you wish to have on your clock.
    2. put it in a circular frame a lot like this
    3. hook up mechanical dials of desired design with appropriate gearing taking into consideration the hourglass and the chosen indicators.
    4. put an optical sensor around the neck of the hourglass
    5. trigger rotation based on when the sand stops flowing through the hourglass

    1. I wonder if it would be more accurate if the hourglass were actually two separate bulbs, mounted in a carefully designed frame where each bulb has a pressure sensor under it to measure the weight of the sand independently of the other. Maybe I’m overthinking it (<1c coffee here) – but I do think good pressure sensors might be better than using an optical sensor.

      Other ideas? I enjoy my morning HaD, Tested, slashdot, etc. with coffee to jump-start my brain. ;P

      1. Recently built it similar to your idea. Two tennis ball tubes tapers together. Inside is two short water bottles with small hole in cap. Flexible spring separates bottles. Plastic wrap encases bottle cap and spring. Weight of sand in bottle enough to compress spring. Plunger on bottom of bottles projects through end of tennis ball tubes which are inclined to rotate via weight and wheel. Plunger releases stop at top of device when top bottle rises tripping catch. It works. Takes almost 15 minutes for 10 rotations. Took a lot of fiddling.

  3. Is it just a function of the timelapse, or does the sand flow slower one way?

    It seems that one way there is a little sand left, and the other way it has been empty a while when turning.

    1. I guess the circuit wasn’t strictly dead-bugged as I didn’t glue the parts down. I started with the op-amp and soldered components on to that. I bend the wires and pins as I went along so that the over all profile of the circuit was thin. I made a little rectangular tray out of some thin plastic (an old monitor protector IIRC) by folding the edges up and taping them in place. After testing I just put the circuit in the tray and covered it in epoxy. I trimmed it up after the epoxy set but before it fully hardened.

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