piclist 2000\11\09\152852a >
Thread: Tone busy detector
face BY : Dan Michaels email (remove spam text)

Mario A. Amaral wrote:
>Hello All,
>Anyone now how I can discover a tone busy of a telephone line, with a pic or
>other chip.
>The DTMF I use a MT8870, but I need to differentiate between OFF HOOK  and

US busy signal is presumably - dual 480 and 620 hz sinewaves,
0.5 sec on, 0.5 sec off. These are below those of the normal DTMF
row and column frequencies, and you should probably use a method
that detects both freqs.

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Subject (change) Tone busy detector

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