Measuring The Time Is A Breeze With This Air Flow Clock

If you’ve ever had surgery, and you’re over a certain age, chances are good you’re familiar with the dreaded incentive spirometer. It’s a little plastic device with one or more columns, each of which has a plastic ball in it. The idea is to blow into the thing to float the balls, to ensure that your lungs stay in good shape and reduce the chance of pneumonia. This unique air-powered clock reminds us a little of that device, without all the pain.

Like a spirometer, [Nir Tasher]’s clock has three calibrated tubes, each big enough to hold a foam ball loosely. At the bottom of each tube is a blower whose motor is under PWM control. A laser rangefinder sits below each ball and measures its height; the measurement is used by a PID loop to control the speed of each fan and thus the height of each ball. The video below shows that the balls are actually pretty steady, making the clock easy to read. It doesn’t, however, reveal what the clock sounds like; we’re going to go out on a limb here and guess that it’s pretty noisy. Still, we think it’s a fantastic way to keep time, and unique in the extreme.

[Nir]’s Air Flow clock is an early entry in the 2020 Hackaday Prize, the greatest hardware design contest on Earth. Everyone should enter something, or at least check out the cool things people are coming up with. It’s still early in the process, but there are so many neat projects already. What are you waiting for?

15 thoughts on “Measuring The Time Is A Breeze With This Air Flow Clock

  1. “If you’ve ever had surgery, and you’re over a certain age, chances are good you’re familiar with the dreaded incentive spirometer.”

    Well I don’t know about the AND but yes I’m familiar with it.

  2. Ah yes, it appears to cunningly combine the power draw of a nimo tube clock with the vertical height requirements of a grandfather clock, while simulating the cheery song of a domestic vacuum cleaner. As long as you have those three specific requirements of a timepiece, this is the perfect one for anybody.

    1. Those little fans run pretty quietly. I wouldn’t expect it be be anything like a vacuum cleaner at all.

      Here’s one ball in a tube with a small axial fan blowing it up the tube, lit from below with a green laser that has a diffraction grating dot pattern:

      Now, if you do away with the tubes and just float the ball on the air from the blower, you’re talking full on vacuum cleaner or leaf blower:

  3. This is wonderful.

    I tried the same thing without a distance sensor, and found that it was very difficult to get the balls to fly halfway up the tube. They would basically either be at the bottom or flying out of the top of the tube. However if you put evenly spaced holes in the tube then you will see a stronger airflow – height relationship.

    1. A flow tube has a tapered bore, somewhat larger at the top. Properly calibrated for the fluid, they direct read. In an application like this, the PWM loop can be made a LOT more stable with a small taper to the tube. Even a tapered insert cut from flat stock would help.

      Without the distance sensor (or some other way of providing feedback) or inherent negative feedback (tapered tube), it is impossible (I make the absolute statement here, and any equilibrium other than sitting on the bottom will be unstable, and, due to the compressability and low density of the fluid, turbulence, and imperfect information about the system, trying to control purely predicatively will be foiled).

      1. I was looking into a purely mechanical piece that did something similar a few years ago. My suspicion was that if I drilled holes along the tube at regular intervals, I could vary the ball height purely by varying the motor speed.

        1. That would do it, and give discrete steps, at well.

          A slot narrow slot would give continuous control.

          The key point is that these give inherent negative feedback to the system. With a plain tube of uniform bore diameter, an external feedback loop is needed.

          It is interesting to note that strictly increasing continuous functions, boolean logic, and multistable operations can be done with balls in tubes, as well. Why the functions must be strictly increasing is likely obvious, but boolean logic and multistables are left as an exercise to the reader.

  4. The time isn’t really being measured by the air flow, that’s what I was expecting from the title. It’s simply being displayed via some flowing air. Now how could we actually measure time using flowing air? That might be fun. Find some natural constant in air circulation and use that to count seconds.

  5. A incentive spirometer is not blown into (maybe you are thinking of a peak flow meter). It is used so that a individual inhales and opens their lungs and small airways. This helps to open small areas of atelectasis (small areas of lung collapse), increases oxygenation, and reduces the risk of pneumonia.

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