Cam timer
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A cam timer is an electromechanical system for controlling a sequence of events automatically.
An electric motor drives, through a reduction gearbox, a shaft on which is arranged a series of cams. Associated with each cam is one or more switches. The motor rotates at a fixed speed, and the camshaft follows, usually very slowly. Indentations or protrusions on the cams operate the switches at different times. By arrangement of the cams and switches, complex sequences of opening and closing switches can be made. The switches then operate different elements of the controlled system - for example motors, valves, etc.
The most common use for cam timers is in automatic washing machines, where they are used to drive the washing sequence according to a preprogrammed pattern. They are gradually being superseded by microprocessor-controlled systems, where greater versatility and feedback is much easier to obtain. For example, a typical cam timer continues to rotate regardless, so if there is a situation that requires a variable amount of time (for example waiting for a tank of water to heat up to a preset temperature), the cam timer is less than ideal, though it is possible to make the cam motor itself subject to control, as most washing machine designs do.
Using feedback and external time delay and other sensory circuits, it is possible to build an electromechanical state machine using a cam timer, which is what such a system within e.g. a washine machine amounts to.
While still fairly popular, cam timers are mechanical and hence subject to wear and reliability problems. Purely electronic systems have largely replaced them for most applications.