Dial-Tone Multi-Frequency (DTMF) is a method for instructing a telephone switching system of the telephone number to be dialed, or to issue commands to the switching systems or related telephony equipment.

The sounds used for tone dialing are referred to as DTMF tones. The DTMF keypad is laid out in a 4×4 matrix, with each row representing a low frequency and each column representing a high frequency. Figure 1 shows tones corresponding to the keys 0, 3, 2, 1, 8, 2, 1, 3, 2, 7, 9, separated by silence.

Figure 1: DTMF signaling for 0, 3, 2, 1, 8, 2, 1, 3, 2, 7, 9

At the end of the experiment, students are encouraged to perform dial-tone multi-frequency modulation by pressing different keys from the transmitting FlexTrainer