Stepping switch

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 Colossus to cryptanalyse the German Lorenz ciphers.

Stepping switches were widely used in telephony and industrial control systems when electromechanical technology was paramount.

In this configuration, the rotating contacts resembled the head support arms in a modern hard disk drive.

Another pawl, sometimes called a detent spring, pivoted on the frame ensures that the wipers do not move backward; contact friction keeps them in place.

In most applications, such as telephony, it is desirable to be able to return the wipers to a "home" position; this is at the beginning of rotation, at one end of the array of fixed contacts.

This cam operates a set of contacts when the wiper is at home position, which is at the beginning of the span of rotation.

When the circuit is no longer needed, another electromagnet releases the holding pawl; the spring then returns the wipers to their home position.

Typically, a single compact group of wipers could connect to one of 100 (or 200) different fixed contacts, in ten levels.

The coils were typically driven by the electrical pulses derived from a rotary telephone dial.

Such switches were used in a series of Japanese cypher machines during World War 2: CORAL, JADE, PURPLE (the names were American).

The British code-breaking machine called Colossus used rotary stepping switches, which was used to break the German Lorenz cipher.