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In article <6794@cbnews.ATT.COM>, knt@cbnews.ATT.COM (kirk.n.trost) writes:
> Does anyone have a simple circuit to detect and signal (TTL)
> the hang-up pulse that is generated when the other party
> hangs up the phone on you.

	There is no "hang-up pulse", per se.  Some telephone central offices
will produce a momentary line open when the distant party disconnects, but
this is not universally true.  It also depends upon whether the distant
party is the callING party or the callED party.  In some cases where the
momentary open is provided, it will occur within a second or so of the
distant party disconnecting, and in other cases it will occur 15 to 60
seconds later when the intraoffice trunk times out and your connection is
dumped back to dial tone through a dial register.

	In those central offices that do produce a momentary open, the
line open is usually between 200 and 500 milliseconds in duration.

	You can detect this event by using an optoisolator as a loop
current detector.  The collector of the optoisolator can pull a resistor
to ground, and create a TTL level.

<>  Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp.
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