“What does the DTMF buttons on your radio do?”
On November 18, 1963, the first electronic push-button system with touch–tone dialing was commercially offered by Bell Telephone to customers in the Pittsburgh.
John E. Karlin, a New Jersey man is credited with inventing the keypad on phones and ATMs.
#1 Frequencies when a button is pushed
#1A Single Tone & Dual Tone
#2 Examples – Encoders
#2A 4X4 keypad switch
#2B 16 button MA Bell touch-tone encoder pad
#2C DTMF encoder intergrated circuits
#3 Encoder IC
#4 TelcoEncoder Schematic
#5 DTMF Decoders – Telco KT-247B
#5A DTMF Decoder – Telco Inter-office use
#5B Decoder MT8870 type
#6 Decoder Schematic – MT8870 IC
Anyone can use Touch-tone or DTMF tones to provide switching functions to many different circuits.
Radio transmitter, wireline telephone circuits, actually just about any medium that can pass voice range audio can be used to send DTMF tones to a decoder.
It is a stable and a precision form of tone generation.
Your imagination is the limit to your switching or control projects.
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