Strowger switch

The Strowger switch was the first commercially successful electromechanical stepping switch telephone exchange system. It was invented by Almon Brown Strowger, and first patented in 1891. Because of its operational characteristics it is also known as a step-by-step (SXS) switch.

Strowger, an undertaker, was motivated to invent an automatic telephone exchange after having difficulties with the local telephone operators, one of whom was the wife of a competitor. He was said to be convinced that she, as one of the manual telephone exchange operators, was sending calls "to the undertaker" to her husband.

He first conceived his invention in 1888, and patented the automatic telephone exchange in 1891. It is reported that the initial model was made from a round collar box and some straight pins.

While Almon Strowger may have devised the concept, he was not alone in his endeavors and sought the assistance of his brother Arnold, nephew William and others with a knowledge of electricity and money to realize his concepts. The Strowger Automatic Telephone Exchange Company was founded in 1891.

The company installed and opened the first commercial exchange in his then-home town of La Porte, Indiana on November 3, 1892, with about 75 subscribers and capacity for 99. It used two telegraph type keys on the telephone, which had to be tapped the correct number of times to step the switch, but the use of separate keys with separate conductors to the exchange was not practical for a commercial system. Early advertising called the new invention the "girl-less, cuss-less, out-of-order-less, wait-less telephone".

The Strowger Automatic Telephone Exchange Company became the Automatic Electric Company, which Strowger was involved in founding, although Strowger himself seems not to have been involved in further developments. The Strowger patents were exclusively licensed to the Automatic Electric Company. Strowger sold his patents in 1896 for US$1,800 and sold his share in Automatic Electric in 1898 for US$10,000. His patents subsequently sold for US$2.5 million in 1916. Company engineers continued development of the Strowger designs and submitted several patents in the names of its employees.

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