Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!decvax!ittatc!dcdwest!sdcsvax!sdcrdcf!hplabs!hao!seismo!rochester!rocksanne!sunybcs!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: net.analog,net.ham-radio
Subject: Re: Telephone ring detector
Message-ID: <898@kitty.UUCP>
Date: Sat, 22-Mar-86 10:32:48 EST
Article-I.D.: kitty.898
Posted: Sat Mar 22 10:32:48 1986
Date-Received: Mon, 24-Mar-86 21:23:49 EST
References: <2032@orca.UUCP>
Distribution: na
Organization: Recognition Research Corp., Clarence, NY
Lines: 27
Xref: dcdwest net.analog:716 net.ham-radio:3169
Summary: Simple ring detector circuit

In article <2032@orca.UUCP>, philb@orca.UUCP (Phil Biehl) writes:
> 	I'm in the process of adding telephone capabilities (autopatch)
> 	to the UHF ham repeater I am working on. I would like to be
> 	able to detect the ringing current produced by an incoming
> 	call. What I need is a CMOS compatible signal indicating that
> 	ringing current is present on the drop. That is, a pulse for
> 	every ring burst.
> 	I would like to have as much isolation from the drop as possible
> 	and have been considering optoisolators to connect the logic to
> 	the line. 

	A simple ring detector can be made from a GE H11AA1 optoisolator,
which is a dual LED device which detects AC. Connect the LED input in series
with a 3.9 K resistor and a 0.68 uF capacitor, and then across tip and ring
of the telephone line.  The optoisolator output is a transistor; overall
sensitivity can be varied by using a resistor between the base and emitter.
Some integration should also be done to minimize dialing transients from
being detected; this can be done with a capacitor across the base and emitter.
For CMOS use, the emitter can be at Vss to sink a logic input using the
collector.

==>  Larry Lippman @ Recognition Research Corp., Clarence, New York        <==
==>  UUCP    {decvax|dual|rocksanne|rocksvax|watmath}!sunybcs!kitty!larry  <==
==>  VOICE   716/688-1231                {rice|shell}!baylor!/             <==
==>  FAX     716/741-9635 {G1, G2, G3 modes}    duke!ethos!/               <==
==>                                               seismo!/                 <==
==>  "Have you hugged your cat today?"           ihnp4!/                   <==