This document summarizes DTMF (Dual Tone Multi-Frequency) which is used in phone line transmission. It describes how DTMF works by generating different tones when keys are pressed on the phone. It also lists some applications of DTMF such as using it for remote controls and phone line operations. Finally, it includes a table showing the frequencies generated for each digit and special character in the DTMF system.

1. DTMF
R-tist

2. DTMF
• This circuit decode frequency which is
generated when key is pressed.
• The dial tone we heard when we pick up the
phone set is call Dual Tone Multi-Frequency,
DTMF in short.
• A complete communication consist of the
tone generator and the tone decoder.

3. Application
• As a remote control.
• Phone line transmission operation.

4. C
D3 O
D
N
MOBILE JACK T D2 T
M
D1 R
F
D0 O
LL
ER

5. 1209 Hz 1336 Hz 1477 Hz 1633 Hz
1 2 3 A
697 Hz
4 5 6 B
770 Hz
7 8 9 C
852 Hz
* 0 # D
941 Hz

6. It is used to instruct the modem to operate
AT+CMGF=1 in text mode. AT+CMGF=0 will instruct the
modem to operate in PDU mode.
It is used to send a text message. It accepts
the recipient mobile number. As soon as this
command is accepted the modem waits for
AT+CMGS="mobile number"
the message content. The text message has
to be sent sequentially and terminated by
the char 0x1A.
It is used to store a message in the memory.
After execution it returns an index for the
message stored. Eg: AT+CMGW=1 . Here 1 is
AT+CMGW="mobile number" the index for the saved message. Later this index
is used to process the message like deleting it or
forwarding to the recipient number.
It is used to delete a message from the
storage. The index of the stored message is
AT+CMGD=2