Introduction
DTMF (Dual Tone Multi-Frequency) signaling is used for telecommunication signaling over telephone line in the voice frequency band between communication devices (telephone, mobile).
It is a set of eight audio frequencies transmitted/received in pairs to represent 16 different signals.
The Telephone keypad is 4x4 or 4x3 matrix of push buttons in which rows represents lower frequency component and columns represents higher frequency component which is mapped as follows.