Hello, for a project I am building a room monitor: you call the line and the relay picks it up upon getting the 90vac, and stays on. My question; how would I go about getting it to detect a hangup? Is there a votlage fluxuation when the party hangs up? A tone? A polarity reverse? It has been troubling me for a while.
-Zach
You must mean the hanging up on the caller end...
The problem in this is that there is no single universal signaling to tell that the caller has hung up. The telephone system has been originally designed for humans that are intelligent enough to hangl up when call seems to end. On some telephone systems very clear signaling is available, some other not...
Usually not...
On some systems there are tones coming after some time after the caller has hanged up...
Some systems use polarity reversal to signal this I think... This is not widely supported feature.
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The signal your hoping for is intercepted by the Central office switch. Nothing comes done the destination line until it times out as a dead connection, (One end only connected) and that is the tone and voice warning signal. To hear it just pick up a phone and hold it for long enough.
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First off, you should be asking this on the appropriate newsgroup, comp.dcom.telecom.tech. You're not telling us which party is "hanging up". If you meant the far end, then most modern telephone switches don't send anything back to you when the calling party disconnects.
Sorry for posting it in the wrong group. But, to answer your question: I want to detect when the other party hangs up, on the other end of the line. My answering machine seems to do this, and stops recording on its cassette immediately after the party hangs up.
I'll try posting it there.
-Zach
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