Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!zaphod.mps.ohio-state.edu!rpi!bu.edu!telecom-request From: john@zygot.ati.com (John Higdon) Newsgroups: comp.dcom.telecom Subject: Re: Why Does Device Cause Ringing to Stop? Message-ID: <74334@bu.edu.bu.edu> Date: 8 Feb 91 17:53:00 GMT Sender: news@bu.edu.bu.edu Reply-To: John Higdon Organization: Green Hills and Cows Lines: 35 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 102, Message 6 of 11 Alan Nishioka writes: > I've been trying to build a box to make key phone's lights flash and > to implement a hold button. Not to throw cold water, but I can think of two reasons for not bothering with this project. The first is that whatever you come up with SHOULD be certified to comply with the various applicable parts of FCC rules, since it will have to connect with the network directly. The other is that genuine 1A2 KSUs can be obtained for next to nothing (or nothing at all if you happen to be in the right place at the right time) and even if you save money you will be wasting your time. > The problem enters when I add a 200ohm resistor and a 2n2222 > transistor across the line to implement the hold button. (Common > emitter, with a 47K base resistor to a CMOS latch output) The transistor is conducting momentarily in the presence of the high ringing voltage. It just takes one spike to stop the ringing and then you have a "trouble" condition. If you do have a 1AESS this would be expected. This particular switch will protect itself from bogus ringing loads by killing the ring current if it exceeds a certain value. A transistor breaking down and putting a 200 ohm load across the line would create such current. Pac*Bell is running slimy ads for it $ENTREX service which shows old phone systems being thrown into this big junk pile. Just find this pile and pull out a KSU :-) Seriously, "fat wire" keys systems are so out of favor now that you should be able to obtain a KSU for nothing. Unfortunately, I have given my last one away. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@zygot.ati.com | San Jose, CA 95150 | M o o !