Make your own precision pendulum clock

Electronic control package for homemade clocks

If you would like to experiment with your own precision pendulum clock, the EM Controller will greatly simplify the task. It provides an electromagnetic impulse driver to keep your pendulum swinging and an electric slave dial to display the time. You provide a seconds beating pendulum of whatever design you like. This produces a true pendulum clock. The electronic circuit does not control the rate of the pendulum. Timekeeping is entirely a product of the natural motion of your pendulum.

You may choose to use an invar rod and cylindrical brass bob. Click here to see a clock like this that I made using this controller. You may prefer to use a carbon fiber rod; or a wooden rod and a lenticular bob. The design is entirely up to you. Click here to see a clock made out of a can of beans and a bit of string.

The controller requires a pendulum with a one second beat time (custom versions for other pendulum lengths are available on special order). The driver circuit works in the basic style used by the Russian F.M. Fedchenko, whose pendulum clocks were among the most accurate ever made. A small coil is placed under the pendulum. A small permanent magnet is placed at the very bottom of your pendulum. As the magnet passes over the sense coil, it causes a current to flow in the drive coil. Very little energy is expended and the four AA batteries last for many months.

The EM Controller has several additional features to help you make an attractive and accurate clock. Pushbuttons on the controller allow you to advance or retard the hands of the dial without opening the clock case or disturbing the pendulm. An alternate output is provided to drive antique slave dials at 30 or 60 second impulse intervals. A cable is provided that plugs directly into the MicroSet Precision Clock Timer so you can easily monitor the performance of your clock. The impulse circuit runs on regulated voltage for stable performance and includes an electronic adjuster for fine tuning of the rate by changing the amplitude of swing. But keep in mind that the actual rate of the pendulum is not controlled by the electronics. It is the natural rate of the free swinging pendulum that you supply.

The controller, shown below, includes everything necessary to drive a free pendulum at a precision rate, and to display the time. Included in the package is:

• microprocessor-based circuit board
• four "AA" batteries and holder
• sense and impulse coil assembly
• permanent magnet to interact with the coil
• output cable to drive the MicroSet clock timer
• clock motor with hour, minute, and second hands
• trimmer for fine adjustment of the pendulum rate
• instructions for setup and use

You will need to provide a clock case, a seconds beating pendulum with suspension, and a dial for the clock motor.