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Because I have not tested all electronic circuits mentioned on this pages, I cannot attest to their accuracy; therefore, I do not provide a warranty of any kind and cannot be held responsible in any manner.
Software DTMF decoder
6. September 2009 - 11:52 — admin
DTMF (the phone dialing tones) is often decoded with a special IC. Here is a pure SW implementation in the PIC18F877 chip.
Cite: The software DTMF Decoder is based on a modified Goertzel algorithm. A good source of explanation for the this algorithm and how to implement it using a DSP can be found in "Modified Goertzel Algorithm in DTMF Detection Using the TMS320C80" – Application Report from Texas Instruments.
In order to implement this algorithm on a such small processor like a 16 series PIC it was necessary to switch to integers, an finally to work with bits. A good source of inspiration was DTMF - Decoding with a 1-bit A/D converter by Scott Datallo
Link: DTMF PIC decoder