Photoelectronics for pendulums
Robert James Matthys · 2004
Abstract Photoelectronics make good sensors for pendulum clocks, because they add no power losses to the pendulum. A swinging pendulum interrupts a light beam, and a light detector provides an electrical signal to compare to a time standard or to incrementally drive the second hand on a clock face. Most photoelectronic circuitry is aimed at very simple applications, such as counting slow-moving cans or boxes on a production line, or detecting the passage of a slow-moving pendulum. For the pendulum application, where the light source and light detector are about a half-inch or so apart, the most suitable light source is an infrared light emitting diode. There are four basic things that can be done to improve the dimensional and time resolutions of a pendulum: narrow the light beam down to just a slit width, use a voltage comparator on the light detector's output signal, better stray light reduction, and use a faster light detector.