DTMF digits are frequency combinations that enable tone dialing on the PSTN. Pulse dialing was historically used with rotary phones. Voice over IP systems have many methods to leverage DTMF digits ...

The last blog entry covered DTMF relay. This blog entry will focus on Cisco IP Phone and Cisco SIP Trunk DTMF relay support. Cisco’s first generation of IP phones do not support RFC2833 DTMF-Relay.

If you’ve ever wondered about the best way to detect dial and DTMF tones from a phone line, [Debraj] is your man. [Debraj] built a DTMF detector using the Goertzel algorithm. Normally, when w… ...

Nice project ! We did a lot of DTMF decoding “in the old ages”, with the 8870 chip (and others) with a C-64 and also via the PC joystick port and the Centronics parallel printer interface.