iPhoneOgraphy – 27 Sep 2016 (Day 271/366)
A telephone keypad is a keypad that appears on a “Touch Tone” telephone. It was standardised when the dual-tone multi-frequency system in the new push-button telephone was introduced in the 1960s, which gradually replaced the rotary dial. The invention of the keypad is attributed to John E. Karlin, an industrial psychologist at Bell Labs. The contemporary keypad is laid out in a 4×3 grid, although the original DTMF system in the new keypad had an additional column for four now-defunct menu selector keys (see Autovon). Most keypads have a “*” key (called star or asterisk) on the bottom left and a “#” (called hash, pound, or other names) on the bottom right.
When used to dial a telephone number, pressing a single key will produce a dual-tone multi-frequency signaling pitch consisting of two simultaneous pure tone sinusoidal frequencies. The row in which the…
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