DTMF signaling
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Dual-tone multi-frequency signaling is a telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switchi
The Western Electric 2500, a typical late 20th century American touch-tone telephone
Autovon keypads were a typical application for use of all sixteen DTMF signals. The red keys in the fourth column produce the A, B, C, and D DTMF events.
Two CMD CM8870CSI DTMF receivers
Rotary dial
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A rotary dial is a component of a telephone or a telephone switchboard that implements a signaling technology in telecommunications known as pulse dialing. It is used when initiating a telephone call
DTMF signaling
…known as MF4 in the United Kingdom, as MFV in Germany, and Digitone in Canada. Touch-tone dialing with a telephone keypad gradually replaced the use of rotary dials and has become the industry standard in telephony to control equipment and signal user intent. The signaling on trunks in the telephone network uses a…
A traditional North American rotary telephone dial
The LM Ericsson Dialog from the 1960s that remained popular in Sweden and Finland up until the 1980s
Swedish rotary telephone. The 0 precedes 1.
A 1931 Ericsson rotary dial telephone without lettering on the finger wheel, typical of European telephones. The 0 precedes 1.