Patent Details
Strowger's patent (US 447918 ) specifies dialing equipment at the customer location and the switching equipment at the central office.
The customer device 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.
The central office switching equipment had a two-motion stepping switch. A contact arm could be moved up and down 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.
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