home *** CD-ROM | disk | FTP | other *** search
- From telecom@delta.eecs.nwu.edu Wed Jan 27 06:10:48 1993
- Received: from delta.eecs.nwu.edu by gaak.LCS.MIT.EDU via TCP with SMTP
- id AA29057; Wed, 27 Jan 93 06:10:45 EST
- Received: by delta.eecs.nwu.edu id AA10632
- (5.65c/IDA-1.4.4 for ptownson@gaak.lcs.mit.edu); Wed, 27 Jan 1993 05:10:32 -0600
- Date: Wed, 27 Jan 1993 05:10:32 -0600
- From: TELECOM Moderator <telecom@delta.eecs.nwu.edu>
- Message-Id: <199301271110.AA10632@delta.eecs.nwu.edu>
- To: ptownson@gaak.LCS.MIT.EDU
- Subject: answer machine exclusion key
- Status: R
-
-
- >From telecom Mon Jan 25 06:07:25 1993
- Received: by delta.eecs.nwu.edu id AA14620
- (5.65c/IDA-1.4.4 for \telecom); Mon, 25 Jan 1993 06:07:22 -0600
- Received: from world.std.com by delta.eecs.nwu.edu with SMTP id AA00657
- (5.65c/IDA-1.4.4 for <telecom@eecs.nwu.edu>); Mon, 25 Jan 1993 06:06:58 -0600
- Received: by world.std.com (5.65c/Spike-2.0)
- id AA06197; Mon, 25 Jan 1993 07:06:51 -0500
- Date: Mon, 25 Jan 1993 07:06:51 -0500
- From: jon_sree@world.std.com (Jon Sreekanth)
- Message-Id: <199301251206.AA06197@world.std.com>
- To: telecom@eecs.nwu.edu
- Subject: Answering machine exclusion : schematic
- Status: RO
-
-
- Hi Pat :
-
- This is either for publication, or FAQ or what-have-you. I typed it up
- in response to someone's question, so maybe others will find it
- useful.
-
- ----
-
- This is the schematic I traced for an answering machine stopper
- gadget : it cuts off the answering machine in case any line is picked
- up. Some answering machines have this feature built-in; the older or
- inexpensive ones don't. The gadget is called Message Stopper (R), by
- Design Tech International Inc., Springfield, VA. Several other mfrs
- make this kind of gadget, so this is just one I happened to buy.
- Cost, roughly $10.
-
- The gadget is in the same form factor as a wall-plug-in Y-splitter.
- That is, it plugs into the wall RJ11 outlet, and has two RJ11 outlets
- on it, one marked TEL, the other marked ANS. There are two LED's, the
- green one on top of the ANS outlet, the red one on top of the TEL outlet.
-
- The two outer wires of the three RJ11's are wired in parallel. The
- schematic for the center two wires is :
-
-
- .-------------- phone
- .-----------------
- | |
- C1 ----|
- C2 -| |
- | |
- | |
- | '----------------- answering machine
- |
- +--|<--+--|<--->|----
- | | two zeners
- +-->|--+
- two leds
-
- Top led is green, bottom is red.
-
- It turns out the leds are basically idiot lights. The outside design
- makes it look like the green should light up when the ANS is offhook,
- and the red when TEL is offhook, but actually, depending on the line
- polarity, only one will glow, and only when the ANS outlet is offhook.
- If a load is connected on the ANS outlet, both leds will glow when
- ring voltage comes through.
-
- I could not read the zener voltage off the diodes, but I measured 11V
- across one of them when operating.
-
- The theory of operation is straightforward. All telephone extensions
- in the house are in parallel with each other, and with any device connected
- on the TEL outlet. If any of these devices is offhook, the phone line
- voltage is expected to drop below 12V or so, at which point the zeners
- isolate the ANS outlet from the line.
-
- It's a fairly simplistic design, and will not work in all situations,
- but it mostly works.
-
- ----
-
- Regards,
-
- / Jon Sreekanth
-
- Assabet Valley Microsystems, Inc. | Fax and PC products
- 5 Walden St #3, Cambridge, MA 02140 | (617) 876-8019
- jon_sree@world.std.com |
-
-
-
-
-