Re: Detect busy tone and ring back tone


"cell" <cellterry@xxxxxxxxx> wrote in message
news:dcac48d8-e00d-46ee-836f-6c1c47b914e5@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hi all,

How to detect ring back tone and busy tone by op amps and/or
transistors? Or detect the moment when someone hooks off the phone?

Thanks!




I have looked for IC's that would detect the various telephone signals,
but have not found anything out there. Most of what I found are dedicated
full
function IC's that do it all for telephone use. These IC's don't output the
signals,
they are used interally - geared for telephone application. I don't think
there is much
need anymore for separate function IC's, which is a problem for guys
like you & me. as a mater of fact the only chip I found that would detect
DTMF was the
now obsolete SS1202P. I was lucky enough to have one in my parts
draw, and there is at least one web site that still has them. Obviously
not a part you would want to use for a production design. The good
news is that you can program a PIC chip to detect DTMF tones.

If I were doing it, I would probably use a PIC chip to detect the tones you
are looking at. An eaisier way (if your not a PIC programmer) would be
to use LM567 tone detecting IC's. The tones are dual tones that are switched
on-off at a determined rate. You could AND gate two 567 outputs, and time
the pulses
to detect a valid signal. IE: "Precise" busy signal is 480HZ and 620 HZ
@ -24dBmo
per tone interupted 0.5 sec on, 0.5 sec off. Notice I specified "Precise"
there is also "Modulated"
busy signal which is 600/120 HZ. You need to find what is used by youre'
exchange.

Ring back can be detected the same way, again there are several tone
combinations out there.
As far as detecting off-hook on the far end, I would just detect when the
ring back stops. Good luck!


.

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