Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!lll-lcc!ames!ucbcad!ucbvax!pnet01.CTS.COM!jeh
From: jeh@pnet01.CTS.COM (Jamie Hanrahan)
Newsgroups: comp.dcom.telecom
Subject: Re: Submission for mod.telecom (Ringing Detection Circuits)
Message-ID: <8705031016.AA03924@crash.CTS.COM>
Date: Sun, 3-May-87 06:00:56 EDT
Article-I.D.: crash.8705031016.AA03924
Posted: Sun May  3 06:00:56 1987
Date-Received: Tue, 5-May-87 00:43:47 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: pnet01!jeh
Distribution: world
Organization: The ARPA Internet
Lines: 18
Approved: telecom@xx.lcs.mit.edu

Here is an absurdly simple ring detector which I threw together years 
ago, before hobbyists had access to optoisolators:  

Scrounge an old phone with a conventional bell.  Disconnect and throw
away (or put in the junk box) everything but the 425B network (or 
equivalent), the ringer coil, and the external ringer capacitor (if
present).  (The 425B network is the mysterious box with altogether
too many cryptically-labeled screw terminals on the top.)  Place a 
magnetic reed switch in close proximity to the ringer coil.  Connect
the reed switch to whatever.  

I never had any problem with this detecting dial pulses as rings, and
it is rather likely that it conforms to phone company specs.  
 
        --- Jamie Hanrahan 
        (uucp:  {akgua | hplabs!hp-sdd | sdcsvax | nosc}!crash!pnet01!jeh)
        (arpa:  crash!pnet01!jeh@nosc)
        (internet:  jeh@pnet01.CTS.COM)