DTMF
Dual-tone multi-frequency (DTMF) is used for telecommunication signaling over analog telephone lines in the voice-frequency band between telephone handsets or other communication devices and the switching center. Each DTMF "tone" has actually two tones: a low-frequency tone and a high-frequency tone-combined. (Hence the name "dual tone multi-frequency"). Looking at the standard phone keypad as a grid, the low tone corresponds to the row, while the high tone corresponds to the column.
Compared with SMS or GPRS controlling, DTMF is easier to control and transfer voice more timely. DTMF is very popular in Safety Surveillance, Alarming and Intelligent Monitoring applications.
At present, most producers adopt external DTMF encoding/decoding chipset. Quectel Wireless Solutions not only embeds the encoding/decoding DTMF and sine tone special frequency in GSM/GPRS modules but also offers abundant DTMF transmission interfaces.
Advantages:
● Cost Saving Without peripheral circuit, Quectel modules can intelligently detect DTMF tone and automatically report it via main UART port. Built-in DTMF function dramatically saves customers’ product space and simplifies the design of customers’ products.
● Enhanced AT Commands Quectel Enhanced AT command can minimize losing rate or repeating rate of different periods of source tones.
Source: http://www.quectel.com/technology/dtmf.htm