Pendulum clocks are wonderful works of art but they aren’t always the most accurate time keepers. Keith, who we featured back in 2009 for his Servo Guitar has built an automated solution to keep pendulum clocks in time. He uses a hall effect sensor to monitor the pendulum swings. An Arduino circuit is configured to count the number of  transitions on the AC power supply that feeds the project. In North America we have 60 hertz AC power which means that there should be  3600 transitions per minute. In the old days clocks used to rely on there being 5,184,000 transitions per day, if the power frequency drifted so would the time on the clocks. Each minute Keith computes how many times the pendulum should have swung compared to what it actually did. A servo controlled metal bar is raised or lowered to add or remove some magnetic drag to slightly adjust the pendulum swing speed.

 A schematic is provided and I am sure the Arduino source code would available to those who ask nicely.