The first electronic “push button” telephone was introduced on November 18th 1963 by The Bell System, it was designed by Henry Dryfus.
The magic on this devices comes from the dual-tone multi-frequency (DTMF) technology that provides a “touch-tone” feature that will be the world standard in telecommunications to the date. The device uses multi-sound tones on each key that sends an identificable signal to the other end. When a key is pressed it sends a particular tone that is then processed by the switch center office that will decode the sound and determine which key was pressed.
The first touch tone telephone was the Western Electric model 1500, it only has 10 buttons. The engineers designed and tested 15 keypad layouts until they decided to stay with the setting with the 1 on the top and the 0 in the middle center bottom. The * and # keys were introduced later.
Diverse mechanical relays and coils were used to provide different taps and sounds, when a key was pressed it disconnected the microphone to disable interference when the DTMF sound tones were transmitted to the central office.
The touch tone phone totally displaced the rotary dial invention, however it wasn’t until the 1980’s that most of houses in the US replaced them with the dial tone system.
Related article: From Bell to VoIP – Where VoIP was Born?
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