In electrical controls, a stepping switch, also known as a stepping relay, is an electromechanical device which allows an input connection to be connected to one of a number of possible output connections, under the control of a series of electrical pulses. The major use for these devices was in early automatic telephone exchanges to route telephone calls. It can step on one axis (called a uniselector), or on two axes (a Strowger switch). As the first automated telephone switch using electromagnets and hat pins, stepping switches were invented by Almon Brown Strowger in 1888. Strowger filed his patent application on March 12, 1889, and it was issued on March 10, 1891.
