Editing Stepping switch (section)

{{short description|Electromechanical multi-pole switch controlled by a chain of pulses}}
{{refimprove|date=November 2016}}
In electrical engineering, a '''stepping switch''' or stepping [[relay]], also known as a '''uniselector''', is an [[Electromechanics|electromechanical]] device that [[Switch|switches]] an input signal path to one of several possible output paths, directed by a train of electrical pulses.

The major use of stepping switches was in early automatic [[telephone exchange]]s to route [[telephone call]]s. Later, they were often used in industrial control systems. During [[World War II]], Japanese cypher machines, known in the United States as [[Coral (cypher machine)|CORAL]], [[JADE (cypher machine)|JADE]], and [[Purple (cipher machine)|PURPLE]], contained them. Code breakers at [[Bletchley Park]] employed uniselectors driven by a continuously rotating motor rather than a series of pulses in the Colossus to [[cryptanalyse]] the German Lorenz ciphers.<ref>{{cite web |url=http://www.lightstraw.co.uk/bletchley/colossus/equipment1.html |title=Colossus - The Equipment |website=lightstraw.co.uk}}</ref>

In a uniselector, the stepping switch steps only along or around one axis, although several sets of contacts are often operated simultaneously. In other types, such as the [[Strowger switch]], invented by [[Almon Brown Strowger]] in 1888, mechanical switching occurs in two directions, across a grid of contacts.