Micro switch

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The internals of a micro switch.

Comparison of some different switches.

A micro switch is a generic term used to refer to an electric switch that is able to be actuated by very little physical force. They are very common due to their low cost and extreme durability, typically greater than 1 million cycles and up to 10 million cycles for heavy duty models. This durability is a natural consequence of the design. Internally a stiff metal strip must be bent to activate the switch. This produces a very distinctive clicking sound and a very crisp feel. When pressure is removed the metal strip springs back to its original state. Common applications of micro switches include computer mouse buttons and arcade game joysticks and buttons. Micro switches are commonly used in tamper switches on gate valves on fire sprinkler systems and other water pipe systems, where it is necessary to know if a valve has been opened or shut. They have also been used as anti-handling devices in boobytrapped improvised explosive devices manufactured by paramilitary groups e.g. the Provisional IRA during the The Troubles.[1][2]

The defining feature of micro switches is that a relatively small movement at the actuator button produces a relative large movement at the electrical contacts, which occurs at high speed (regardless of the speed of actuation). Most successful designs also exhibit hysteresis, meaning that a small reversal of the actuator is insufficient to reverse the contacts; there must be a significant movement in the opposite direction. Both of these characteristics help to achieve a clean and reliable interruption to the switched circuit.

The first micro switch was invented by Peter McGall in 1932 in Freeport, Illinois. McGall was an employee of the Burgess Battery Company at the time. In 1937 he started the company MICRO SWITCH, which still exists as of 2005. It is now owned by Honeywell Sensing and Control.