This App generates DTMF Tones of a 4x4 keypad and It can be used in Robotics and Embedded Systems also .

What is DTMF?
Dual-tone multi-frequency signaling (DTMF) is used for telecommunication signaling over analog telephone lines in the voice-frequency band between telephone handsets and other communications devices and the switching center. The version of DTMF that is used in push-button telephones for tone dialing is known as Touch-Tone.

How it Works?
The DTMF keypad is laid out in a 4×4 matrix in which each row represents a low frequency and each column represents a high frequency. Pressing a single key sends a sinusoidal tone for each of the two frequencies. For example, the key 1 produces a superimposition of tones of 697 and 1209 hertz (Hz). Initial pushbutton designs employed levers, so that each button activated two contacts. The tones are decoded by the switching center to determine the keys pressed by the user.