Editing Cam timer (section)

==Description==
An [[electric motor]] drives a shaft arranged with a series of [[Cam (mechanism)|cam]]s or a drum studded with pegs along its surface. Associated with each cam is one or more [[switch]]es. The motor rotates at a fixed speed, and the camshaft is driven through a speed-reducing gearbox at a convenient slow speed.  Indentations or protrusions on the cams operate the switches at different times. Complex sequences of opening and closing switches can be made by the arrangement of the cams and switches. The switches then operate different elements of the controlled system - for example, motors, valves, etc.

A [[programmer]] may change or rearrange (reprogram) peg or cam positions. Much like the pegs in a music box cylinder activate the notes, in a drum sequencer, as the drum of the sequencer spins, the pegs run across switches, activating machine processes. The placement of the pegs along the length of the cylinder determines which switch will activate along the length of the drum. Where the peg lies along the circular circumference of the drum determines at what point the peg will activate the switch in the drum's spin. The drum performs repetitive switching operations by controlling the timing and sequence of switches.

Most cam timers use a miniature mains [[synchronous motor]] to rotate the mechanism at an accurate constant speed. Occasionally, more complex timers with two motors are seen.

A drum sequencer is a reprogrammable electromechanical timing device that activates electric switches in repetitive sequences. These sequencers were primarily used in industrial applications to enable automated manufacturing processes.