1891

Strowger Step-by-Step Switch

Almon Brown Strowger (1839–1902)

The Bell Telephone Company was incorporated in July 1877, and by the 1880s it was quickly expanding. The switchboards that connected phones together and completed calls were manually run by operators.

The early phone system didn’t have dials or buttons. Instead, there was a crank, connected to a tiny electrical generator. Users would pick up the phone and turn the crank, and electricity would travel down the phone line to signal the operator.

Almon Strowger was an undertaker in Kansas City, Missouri. He noticed that his business had declined as the telephone became more popular. Strowger learned that one of the telephone operators was married to his competitor, and whenever a phone call came in for the undertaker, she would direct the call to her husband. Motivated, Strowger invented the step-by-step switch, an electromechanical device that would complete a circuit between one phone and a bank of others depending on a sequence of electric pulses sent down the phone line. Instead of relying on an operator to connect, Strowger envisioned that people would tap out a code using a pair of push buttons.

Working with his nephew, Strowger built a working model and got a patent. Although other inventors had experimented with operator-free dialing systems—thousands of patents were filed—this system “worked with reasonable accuracy,” according to a 1953 article in the Bell Laboratories Record.

Strowger, family members, and investors then created the Strowger Automatic Telephone Exchange Company in 1891. They went to La Porte, Indiana, which had recently lost its telephone system because of a patent dispute between the local independent operator and the Bell Telephone System, and set up the world’s first automated telephone exchange with direct dialing—at least for local calls—in 1892.

The switch was called “step-by-step” because of the way that a telephone call was completed, one dialed digit at a time. Step-by-step exchanges remained in service throughout the United States until 1999, when the last was removed from service, replaced by the #5ESS computerized local exchange.

The friction drive of the Western Electric 7A Rotary, No. 7001 Line Finder. The bevel gear on the right has a steady rotary motion and does not use an electromagnet for stepping.