The ring signal goes away and someone says "hello". <GRIN>
How do you detect the (absence of the) ring signal? That's a better
question.

Call Progress Tones in the US
Dial tone: 350+440Hz Continuous

Busy:
Busy tone: 480+620Hz 0.5s ON 0.5s OFF
Reorder: 480+620Hz 0.25s ON 0.25s OFF

Ring and ring back tone:
Most common: 440+480Hz 2.0s ON 4.0s OFF (the initial ring on some telephone
exchanges may range from 0.5s ON to2.0s ON)
Some PBXs: same frequency, but cadence varies from (1.0s to 1.5s ON and 2.0s
OFF to 3.5s OFF)
Mitel PBXs (When calling from outside) same frequency, but 0.5 ON 0.5 OFF
0.5 ON 1.5s off (burr burr burr burr....)
(Internal calls) 1.0s ON 3.0s OFF

This is from:
http://hyperarchive.lcs.mit.edu/telecom-archives/TELECOM_Digest_Online/0208.
html

and the other links at
http://204.210.50.240/techref/default.asp?url=pots.htm

I'm not sure if Speech recognition of the word "Hello" would be useful but:
http://204.210.50.240/techref/default.asp?url=io/speech.htm

James Newton mailto:jamesnewton@geocities.com phone:1-619-652-0593
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-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Alan Aldaba
Sent: Wednesday, November 17, 1999 9:39 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: tel. call detector


Hi everyone,

        I'm quite new to the list but been lurking for sometime now, so pls.
be
gentle... I'm doing a F84 project that involves the telephone, How can i
detect if the called party have answered the call i made ? What control
signals does a typical telco uses to supervise the line ?

All the best,