Hi I remember this article. A pendulum clock was made more accurate by " harmonic locking " the pendulum to a crystal oscillator.
A small magnet was attached to the pendulum and fitted to pass through a solenoid at one end of the pendulum's swing. The solenoid was driven with a signal that was a harmonic of the pendulum's frequency. If the pendulum arrived a little out of phase with the signal driving the solenoid, it was given a small kick. If the pendulum was in phase, no net kick was given. It's a simple and somewhat effective method of locking two oscillators together. Unfortunately it can be a bit fussy to set up. In high school my Physics instructor had a setup with two pendulums suspended from a common beam. If the pendulums where started up with a small difference in phase, they would soon be swinging together. Pendulums who's frequency was related harmonically could also be " locked". This was a grand time sink and no doubt influenced my interest in oscillators and PLL circuits.. The amount of energy transferred was small but over time it would be enough to lock up the two pendulums. Ah, the power of integration. I have never built a harmonically locked pendulum but I have used harmonically locked oscillators a number of times with mixed results. It can provide dead simple circuits but one often finds ones self in a corner fighting the lock in range of the system, feed through of the reference signal and all the usual trade offs found in PLL systems. That said, I would love to give it a hack someday. Perhaps a pendulum locked to a GPS 1PPS signal driving a nixie display........ There are also a number of " perpetual motion" toys on the market, they are in the form of a pendulum of some sort passing over a plastic base with a battery and circuitry concealed inside. As the magnet in the pendulum passes over the circuit's coil, it begins to oscillate and the pendulum is given a small kick as it passes by. Cheap fun, usually no more than one transistor a coil and a couple of passives. Teasing one apart on the bench can provide a pleasant afternoon's distraction when you just can't make your self do anything useful. Search Amazon for "the amateur scientist" there is an article collection available on CD ROM and there was a dead tree collection printed. Great time sink, great gift for the geeky kid in the family. Have fun Steve Bennett Message: 2 Date: Wed, 04 Jan 2006 23:11:07 -0800 From: Hal Murray <[EMAIL PROTECTED]> Subject: Re: [time-nuts] Three subjects. To: Discussion of precise time and frequency measurement <time-nuts@febo.com> Message-ID: <[EMAIL PROTECTED]> Content-Type: text/plain; charset=us-ascii > http://www.telechron.com/ Neat. Thanks. I think we had one like that back in grade school. That was a long time ago. There was an article in Scientific American 20 or 30 years ago. The idea was to make an old grandfather clock keep very good time by adding a magnet to the pendulum so you could gently push/pull it. Anybody remember that one? Anybody build one? _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts