knt@cbnews.ATT.COM (kirk.n.trost) (05/23/89)
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. Thanks, Kirk ...
larry@kitty.UUCP (Larry Lippman) (05/24/89)
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. <> UUCP {allegra|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> TEL 716/688-1231 | 716/773-1700 {att|hplabs|utzoo}!/ \uniquex!larry <> FAX 716/741-9635 | 716/773-2488 "Have you hugged your cat today?"