Details of The Patent
US 447918 consists of:
- A device for use by the customer — this creates trains of on-off current pulses corresponding to the digits 1-9, and 0 (which sent 10 pulses). This equipment originally consisted of two telegraph keys engaged by knife switches, and evolved into the rotary dial telephone.
- A two motion stepping switch at telephone exchange. A contact arm could be moved up and down in order to select one of ten rows of contacts, and then rotated to select one of ten contacts in that row, a total of 100 choices. The stepping motion was controlled by the current pulses coming from the originating customer's telegraph keys, and later from the rotary dial.
This system was widely used until the advent of the crossbar switch — an electromechanical switch with a matrix of vertical and horizontal bars and simpler motions, that worked more reliably.
Read more about this topic: Strowger Switch
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