Mechanical School Bell
Someone made lights turn on and off with a mechanical timer, then someone else thought, I can make it operate the School Bells. This is how it started. There has been many variations of this timer since about the mid 50′s using a mechanical clock using cams to trigger a micro switch. I remember in college the deputy principle had the job of looking after the school bells. It was a mechanical clock timer, I remember him altering it every tuesday for assembly day because it was different timetable to the other days. If each days timetable was different it would be a chore setting it for each day. He would have need to revert it back the next day. He was the only one that knew how to adjust it. It had a set ring duration and had a setting for every 5 minutes. You needed good eyesight to see where to slide in the pin, because it was a 24 hour cycle on the dial.