Impractical Clock Uses Tuning Fork

Clock projects are so common that they are almost a cliche. After all, microcontrollers have some clock source and are good at counting, so it stands to reason that a clock is an obvious project. [WilkoL’s] clock though has a most unusual clock source: a 440 Hz tuning fork.

A cheap plastic dome really shows off the fork and contributes to this good-looking build. An ATTiny13 divides the input frequency down, handles the display, and obeys the adjustment buttons. It does require a little metalworking, as the tuning fork needed filing and threading, although we bet you could figure out other ways to mount it.

As good as the clock looks, it is apparently impractical. The problem is that 440 Hz tone is audible. If you think a ticking clock will drive you mad, try a constant 440 Hz tone.

We were amused with the fact that the tuning forks were both a little low so they were tuned by filing material off the ends. Of course, the frequency is only set at a particular temperature and as it gets warmer or colder you might see some drift, but apparently not too much.

A more common choice is a crystal, which usually has a much higher frequency. Sometimes the clock source is the power mains.

30 thoughts on “Impractical Clock Uses Tuning Fork

  1. Watchmaker-

    Yup, the Bulova Accutron was a step below quartz oscillators in accuracy, and did use a micro tuning fork, and a very very fine ratchet and pawl mechanism attached to this to keep time.

  2. Clocks and firearms have one thing in common: their theory of operation is very simple, but making one that’s usefully accurate requires an extraordinary level of engineering.

    1. Reasonably accurate RTC implementation doesn’t require “extraordinary level of engineering”. It only requires some minor efforts either by *buying* a RTC module with the required accuracy or implementing one in firmware.

      If you ignore temperature/voltage drift, you can compensate for the frequency by playing with the divider value. For a low frequency source, a simple Phase accumulator can be implemented as a programmable non-integer frequency divider inside an IRQ. Don’t let the long name scare you as the code is only a few lines long.

          1. The point is those “few lines of code” you are talking about allow communication with an embedded RTC chip which was /engineered/ specifically to keep accurate time.

          2. Have you ever actually gone and built an RTC? Like, from scratch? Like, really, really from scratch? Let’s go to the beach to get sand! (uhm, well, and somewhere for quartz too) :D

      1. RTC modules like the DS3231 that has an EMBEDDED TCXO IN IT and that cost SEVEN DOLLARS in single unit quantities. That’s not “extraordinary.” I seeeeee.

        And then in the second paragraph you go on to describe, in fact, extraordinary engineering in order to obtain accuracy. And, yes, those efforts are extraordinary in the sense that they are “unusual or remarkable.” Because an *ORDINARY* level of engineering would be to just slap a 50 ppm 16 MHz crystal onto a microcontroller and have it count time, and you’d wind up with a clock you’d need to reset probably weekly.

  3. Just as a point of interest: There is a measuring device that uses a driven bell [ tuning fork like ] to measure the density of the gas is is immersed in. I designed drive/measurement electronics about 15 years ago for such a device.

    1. In theory if you can accurately produce a know sound you could use that as a means of measuring gas density acoustically.
      Calibration and repeatability would be the tricky part. It may be easier to make a microphone-speaker feedback loop and put it in the test mixture. Then the density will be proportional to frequency rather than volume.

  4. Also “Solari Cifra 3” was built in tuning fork version, but tuning fork mechanic was built form Jako.
    I’m working on a restoration of one of them, circuit uses 2 coils: one to attract fork and other to sense it, instead of photo diode as in this project…
    Very sensitive circuit however, also for strange mechanics solutions used….

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