An Original Electromagnetic Clock

This clock is an original design of an electromagnetic clock. That is to say, it uses electromagnetism to keep the pendulum swinging. It is not a quartz clock, and keeps time by the natural motion of the pendulum.

The clock is 55" tall and has a 7" dial. The case is bird's eye maple with accents in East Indian rosewood. The rod is invar with a polished brass bob. The electronics are contained in a drawer at the bottom of the case. The impulse mechanism is, generally speaking, in the Fedchenko style. That is to say, it uses a permanent magnet to trigger a coil which drives the pendulum. It runs on four "AA" batteries and the rate can be fine tuned by adjusting the voltage in the drive coil.

Click here to see a large closeup of this clock. (It's a big file - about 300K.)


The pendulum suspension of the clock is made from aluminum bar stock. The invar rod terminates in a brass fixture which clamps the bottom of the steel suspension spring. The top half of the spring is clamped to a threaded rod which rests in the main bracket.




The image on the right shows the bottom end of the pendulum rod. The permanent magnet is inside a brass holder. Above this the rating nut supports an aluminum sleeve (for temperature compensation) which supports the brass bob.



The image below shows the electronics drawer at the bottom of the clock. This drawer contains four "AA" batteries to run the clock, a knob with which to make fine adjustments to the rate of the clock, and the electronic circuit which drives the pendulum and the clock dial. The knob will change the rate by about 30 seconds per week.


I'm making the electronic components of this clock available for sale if you'd like to build your own electromagnetic clock. Click here for more information.

The following graph shows the performance of the clock over a 10 day period. Daily fluctuations due to temperature effects can be seen. The average rate over this period was within 1.6 seconds a month.

I sometimes make clocks like this on special order. Send an email if you wish more information.

Bryan Mumford
Santa Barbara, California
April 24, 1999