Telephone Line Monitor (Plans) Telephone Line Monitor (Plans)| DISCLAIMER: I\'ve collected these information from different sources. The author may revise this documentation from time to time without notice. THIS DOCUMENTATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. IN NO EVENT SHALL THE AUTOR BE LIABLE FOR INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES OF ANY KIND ARISING FROM ANY ERROR IN THIS DOCUMENTATION, INCLUDING WITHOUT LIMITATION ANY LOSS OR INTERRUPTION OF BUSINESS, PROFITS, USE, OR DATA. |
Get yourself a low-voltage DC relay, like a 3v relay... Set it up as follows:
Audio Isolation
Transformer
To <--)||(---------------------+
)||( | <==== Relay Contacts
Speaker <--)||(---+ +--------o/ o
600ohm | | mmmmm DC 3v Relay Coil
| | | |
RED -----------|----+-------+ +----------> To Dispatcher's Phone
|
GREEN -----------+-----------------------------> To Dispatcher's Phone
| |
-+- indicates a connection, --- is not connected.
| |
Circuit Theory:
When the Dispatcher picks up the phone (in a standard circuit, I have NO clue what your PBX does.. this will work on standard home phones, and I used to use it for a tape-recording controller) Hey, there's an Idea - spend $25 on a telephone recording device, and hitch it to a nice loud amp and speaker combo, instead of a tape deck. It'll save you loads of time...
Anyhow.. the voltage will turn into DC, approx 6-10VDC when the phone is picked up, (which is why you've gotta put it before the dispatcher's phone) and click the relay. The relay will connect the transformer, and feed the speaker. it might be towards your advantage to use a SPDT relay, and connect BOTH ends of the transformer, and not just switch one end in and out. That might prevent some line noise...
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