Path: utzoo!attcan!uunet!pyrdc!netsys!vector!nobody From: munnari!stcns3.stc.oz.au!dave@uunet.UU.NET (Dave Horsfall) Newsgroups: comp.dcom.telecom Subject: Re: In use light Message-ID: Date: 18 Oct 88 05:47:48 GMT Sender: chip@vector.UUCP Lines: 30 Approved: telecom-request@vector.uucp X-Submissions-To: telecom@bu-cs.bu.edu (TELECOM Digest Coordinator) X-Administrivia-To: telecom-request@vector.uucp (USENET Telecom Moderator) X-TELECOM-Digest: volume 8, issue 163, message 4 In article , mgrant@cos.com (Michael Grant) writes: [ An "in-use" LED for a telephone extension ] A local electronics hobbyist magazine "Silicon Chip" published such a circuit, involving monitoring the line voltage and triggering an LM3909 LED flasher when it drops to around 12v or so. There was also a companion circuit, which blocked other extensions when one was picked up - useful! This worked on a similar principle, and it fires an SCR across each extension instead. The device has gone a long way to keeping my wife off the phone when I'm on the modem... I see no reason why an Australian design should not work elsewhere; they merely compared the line voltage (50v on-hook) against a reference zener, and did its magic when it dropped (about 12v off-hook). A diode bridge supplied the power, and the LM3909 is quite an efficient flasher. The diagrams won't reproduce too well on a terminal screen, so I'll send photocopies of the articles to anyone who wants them, although I'd prefer not to be inundated... Perhaps the first few enquirers (assuming there are any :-) can supply others in their country. Oh, and Telecom get stroppy when they find you connecting non-approved devices to their network, so y'all are warned. -- Dave Horsfall (VK2KFU), Alcatel-STC Australia, dave@stcns3.stc.oz dave%stcns3.stc.OZ.AU@uunet.UU.NET, ...munnari!stcns3.stc.OZ.AU!dave PCs haven't changed computing history - merely repeated it