DTMF/GSM(DUAL TONE MULTI FREQUENCY) ROBOT
What is DTMF?
DTMF is a signaling system for identifying the keys or better say the number
dialed on a pushbutton or DTMF keypad. The early telephone systems used
pulse dialing or loop disconnects signaling. This was replaced by multi frequency(MF) dialing. DTMF is a multi-frequency tone dialing system used
by the push button keypads in telephone and mobile sets to convey the number or key dialed by the caller. DTMF has enabled the long distance signaling of dialed numbers invoice frequency range over telephone lines. This has eliminated the need of telecom operator between the callers and evolved automated dialing in the telephone switching centers.
DTMF(Dual tone multi frequency
) as the name suggests uses a
combination of two sine wave tones to represent a key. These tones are called row and column frequencies as they correspond to the layout of a telephone keypad. A DTMF keypad (generator or encoder) generates a sinusoidal tone which is mixture of the row and column frequencies. The row frequencies are a group of low group frequencies. The column frequencies belong to high group frequencies. This prevents misinterpretation of the harmonics. Also the frequencies for DTMF are so chosen that none have a harmonic relationship with the others and that mixing the frequencies would not produce sum or product frequencies that could mimic another valid tone. The high-group frequencies (the column tones) are slightly louder than the low-group to compensate for the high-frequency roll off of voice audio systems. The row and column frequencies corresponding to a DTMF keypad have been indicated in the above figure. DTMF tones are able to represent one of the 16 different states or symbols on the keypad. This is equivalent to 4 bits of data, also known as nibble.