63 lines
2.3 KiB
Plaintext
63 lines
2.3 KiB
Plaintext
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This is the schematic I traced for an answering machine stopper
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gadget : it cuts off the answering machine in case any line is picked
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up. Some answering machines have this feature built-in; the older or
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inexpensive ones don't. The gadget is called Message Stopper (R), by
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Design Tech International Inc., Springfield, VA. Several other mfrs
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make this kind of gadget, so this is just one I happened to buy.
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Cost, roughly $10.
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The gadget is in the same form factor as a wall-plug-in Y-splitter.
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That is, it plugs into the wall RJ11 outlet, and has two RJ11 outlets
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on it, one marked TEL, the other marked ANS. There are two LED's, the
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green one on top of the ANS outlet, the red one on top of the TEL outlet.
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The two outer wires of the three RJ11's are wired in parallel. The
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schematic for the center two wires is :
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.-------------- phone
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.-----------------
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C1 ----|
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C2 -| |
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| '----------------- answering machine
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+--|<--+--|<--->|----
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| | two zeners
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+-->|--+
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two leds
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Top led is green, bottom is red.
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It turns out the leds are basically idiot lights. The outside design
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makes it look like the green should light up when the ANS is offhook,
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and the red when TEL is offhook, but actually, depending on the line
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polarity, only one will glow, and only when the ANS outlet is offhook.
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If a load is connected on the ANS outlet, both leds will glow when
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ring voltage comes through.
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I could not read the zener voltage off the diodes, but I measured 11V
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across one of them when operating.
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The theory of operation is straightforward. All telephone extensions
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in the house are in parallel with each other, and with any device connected
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on the TEL outlet. If any of these devices is offhook, the phone line
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voltage is expected to drop below 12V or so, at which point the zeners
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isolate the ANS outlet from the line.
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It's a fairly simplistic design, and will not work in all situations,
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but it mostly works.
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----
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Regards,
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/ Jon Sreekanth
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Assabet Valley Microsystems, Inc. | Fax and PC products
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5 Walden St #3, Cambridge, MA 02140 | (617) 876-8019
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jon_sree@world.std.com |
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