Stepwise switch

Stepwise switches were invented at the end of the 19th century and connect telephone lines through mechanical action. They are a semi-automatic telephone switching device. When users dial, the stepper mechanism of the switch selects the target line step by step to achieve automatic connection. Stepwise switches greatly improve communication efficiency and can support hundreds to thousands of telephone lines, laying the foundation for the development of fully automated switches in the future.

The unit is designed for unsupervised public use: controls are recessed or shielded, moving parts are enclosed, and the interface is operable by a child of about six with no instruction. Where a screen is used, the language can be switched without changing the hardware, and the content can be replaced on site.

On March 10, 1891, Schlieger invented the Schlieger switch, also known as the stepper switch, marking the beginning of automation in telephone exchanges. In 1892, the "step-by-step automatic telephone exchange" made with this type of connector was officially put into use. Later on, many designs and improvements were made on the original patent, but the most well-known design was to set up 10 layers of contactors around a shaft, each with 10 contact points arranged in a circular arc shape. The terminals of the connectors would climb, rotate, and change the connection position step by step according to the control of the mechanical relay's suction by the pulse current emitted by the user's dialing, thus completing the connection of the circuit contacts.