The first DTMF tone producing telephone was introduced in November of 1963 for the Bell System. Rotary phones interrupt electrical connections while spinning, and the resulting electrical pulses produced are interpreted as commands (such as 'dial this number'). The first commonly used telephony signaling system was pulse dialing. Signalling systems have evolved to fill that role - both for routing and dialing calls as well as for interacting with phone systems once connected.

DTMF Tones for Automating Telecommunications InteractionsĪlmost as long as we've had telegraph and telephony systems, humans have needed a way to reliably interact with the system in a mechanical and reproducible way. Commonly used over telephone lines, DTMF tones are also commonly called Touch Tones. These encoded data can be stored and processed in a microcontroller to perform different tasks.DTMF, or Dual-Tone Multi-Frequency tones, are in-band telecommunications signals sent over voice frequencies. So, knowing how are DTMF tones generated can surely be an interesting bit of info. Button Low DTMF frequency (Hz) High DTMF frequency (Hz) * 941 1209 # 941 1477 Low and high frequencies of each button ConclusionĭTMF signals can be transmitted over the radio to switch ON or switch OFF home appliances, flashlights, motors, cameras, warning systems, irrigation systems, and so on. The frequencies generated on pressing different phone keys are shown in the Table. Each button lies at the intersection of the two tones.

The frequencies generated on pressing different phone keys are shown in the table Frequency 1209 Hz 1336 Hz 1477 Hz 697 Hz 1 2 3 770 Hz 4 5 6 852 Hz 7 8 9 941 Hz * 0 # Dual-frequency for each keyĮach row and column of the keypad corresponds to a certain tone and creates a specific frequency.

This elementary principle can be extended to a range of applications.

So there is a low and high frequency associated with a button, it is essentially the sum of two waves is transmitted.

These two tones will be distinctive and different from tones of other keys.When a button is pressed, both the row and column tones are generated by the telephone or touch tone instrument.Basic Principle | How Are DTMF Tones Generated

Dtmf tone dialer