this an MT8870 implementation with an Arduino. Intended to read and write data with DTMF tones, "the tapeDuino" (mine writes to tape.)
This is a bare implementation of an MT8870 IC for decoding DTMF tones from audio input, especially with the goal of reading and writing data.
The schematic provided is a circuit simply to get you going with an 8870 and provide you with a test bed in order to read DTMF. For more info on my "tapeDuino" project (which is a client-server application [and hardware] to read/write data onto cassette tape over ethernet) please visit dougbtv.com