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Thread: [posted] Free Pendulum Clock

  1. #1
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    [posted] Free Pendulum Clock

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    There are plenty of clock projects documented online. This one differs in that timekeeping is controlled by a magnetically driven free pendulum.

    A free pendulum has no mechanical linkage, escapement mechanism or direct mechanical power to keep it going. A small magnet on the bottom of the pendulum induces a voltage on a coil mounted beneath as it swings past. The voltage is detected by Teensy's a/d converter and triggers a propulsion pulse applied to the coil from a digital output pin. This gives the pendulum a tiny nudge to keep it going. The pendulum defies the senses, swinging in eerie silence.

    A Teensy performs all electronic functions—only a couple passive components added. A setup mode measures the pendulum timing using the processor clock as a reference to allow quick pendulum adjustments. Digital outputs can drive two types of modified analog clock movements—the click-click one-second advancing type and the newer silent, continuous motion type.

  2. #2
    Cool idea, thanks for sharing. Just curious in how accurate the clock is. I'm guessing the nudge pulse has to be pretty precise to get the right amount of travel. Is the nudge pulse PWM controlled?

  3. #3
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    Quote Originally Posted by KrisKasprzak View Post
    Cool idea, thanks for sharing. Just curious in how accurate the clock is. I'm guessing the nudge pulse has to be pretty precise to get the right amount of travel. Is the nudge pulse PWM controlled?
    Accuracy is all about the pendulum. I had it going for a week, running slow by a consistent one second per day. It's difficult for me to tweak the adjustment weights without disturbing the pivot position slightly. I'm trying to refine the pendulum and pivot design for easier, finer adjustment. Propulsion is a 28 ms long pulse on a digital I/O pin, timed by the micros() function. No PWM involved. The propulsion pulse occurs every-other second and is indicated by the longer blink of the LED. Pulse duration is not very critical and only has a small effect on the swing amplitude. It's self regulating, to an extent, because an increased swing amplitude means faster speed passing the coil and less time spent in the highest force region of the coil. Furthermore, swing amplitude has very small effect on the period of the swing.

  4. #4
    Quote Originally Posted by jessicawhite999 View Post
    Electronic Pendulum Clock must be better an mechanical one. Good job man
    I think so.

  5. #5
    Administrator Paul's Avatar
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    This one was posted to the website a while ago. Just catching up now to update this thread.

    https://www.pjrc.com/free-pendulum-clock/

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