These analog phone systems use Dual Tone Multi Frequency (DTMF ... LucidScience decided that it would be useful to have a DTMF decoder on hand, and got busy building one. His DTMF decoder box ...

Once you have the audio it is fed into a pair of XR-2211 Tone decoders. This provides just three interface pins for the Arduino to watch. The annoying noise that grabs your attention at the ...

Detects the presence of a single tone at a specified centre frequency. Features 16-bit data samples, programmable tone frequency, adjustable detection bandwidth and a high performance Digital Down ...