The Cam Timer: A Program Cut Into Discs

Before microcontrollers, a washing machine, a dishwasher, a traffic light or an industrial process followed its sequence by turning a shaft of cam discs past a row of switches. A slow synchronous motor turns the stack once per program; each disc switches one function on while its raised arc passes; the dial on the front is simply the end of the shaft, and turning it by hand skips the program forward. Everything about the program lives in the geometry: time is angle, and each function is an arc. This rung turns a washing program into cam arcs, draws the cams, and builds a four-cam timer from printed discs and microswitches that switches four lamps in sequence.