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'[PIC]: Tone busy detector'
2000\11\09@145139 by Mario A. Amaral

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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
LINE BUSY.
Thanks

Mario

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2000\11\09@152852 by Dan Michaels

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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
>LINE BUSY.


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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2000\11\09@153318 by Dan Michaels

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Oops, left this off:

http://www.cisco.com/warp/public/788/signalling/net_signal_control.html


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
>LINE BUSY.


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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2000\11\13@072502 by Russell McMahon

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>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
>LINE BUSY.


Tones and cadences may vary between countries.
In my country most tones are based on 400 Hz with varying cadences.

I got discrimination of all tones with reasonable accuracy by
cross-correlating a 3 second time sample with stored patterns.
I also used a "voice detector" to indicate when the tones were liable to be
corrupted by speech. This was a bandpass filter followed by an energy
detector (could find frequency specs if desired) which was never triggered
by tones alone and almost a;ways triggered by speech.
End results were very good but not perfect.

The correlation was achieved on up to ?8 simultaneous channels in real time
using a 1 MHz cycle time 6800 cpu so a PIC should be up to the task.

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