Show HN: Apple II clock using interrupts from physical pendulum clock

Re:Show HN: Apple II clock using interrupts from physical pe... by geerlingguy on Sunday January 28, 2024 @12:38PM (#39167899)

This is quite interesting; I've been reading up on PLL and chip design lately, as well as VCOs, TCXOs, etc.

And now I'm wondering how accurate someone could make a reference signal from a physical pendulum like this—or what strange quirks you could introduce into a system using such a 'weighty' clock source!

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Re:Show HN: Apple II clock using interrupts from physical pe... by tvb on Sunday January 28, 2024 @01:29PM (#39168362)

Many pendulum clocks are capable of well under 1 ppm accuracy, which is better than many quartz oscillators. Here is a tour of clock precision by orders of magnitude:

http://leapsecond.com/ten/

Here is a world record setting pendulum clock from a few years ago:

http://leapsecond.com/pend/clockb/

Precision pendulum clocks are a very deep rabbit hole.

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Re:Show HN: Apple II clock using interrupts from physical pe... by zokier on Sunday January 28, 2024 @03:50PM (#39169672)

> The Shortt was the first clock to be a more accurate timekeeper than the Earth itself; it was used in 1926 to detect tiny seasonal changes in the Earth's rotation rate. Shortt clocks achieved accuracy of around a second per year

If my math is right, thats about 30ppb

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