Stepping switch

In electrical control engineering, a stepping switch or stepping relay, also known as a uniselector, is an electromechanical device that switches an input signal path to one of several possible output paths, directed by a train of electrical pulses.Several views of a Type 206A stepping relayWiring terminals, unit is a 22-position, six-layer switchInternal contactsSolonoid and wiper armTop view, ratchet wheel, pawl and detent spring on the left In electrical control engineering, a stepping switch or stepping relay, also known as a uniselector, is an electromechanical device that 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 exchanges to route telephone calls. Later, they were often used in industrial control systems. During World War II, Japanese cypher machines, known in the United States as CORAL, JADE, and PURPLE contained them. Code breakers at Bletchley Park employed uniselectors driven by a continuously rotating motor rather than a series of pulses in the Bombe machines to cryptanalyse the German Enigma ciphers. 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.