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/* Written  9:22 am  Oct 16, 1989 by sekoppenhoef@rose.waterloo.edu in m.cs.uiuc.edu:sci.electronics */
/* ---------- "telephone light indicating use" ---------- */

>We have a phone at home that is shared between a computer and a person's
>voice. Furthermore... we have several telephones on that particular phone
>line. Is there some way of attaching an led or something to indicate
>by being on that the phone is IN-USE ? Something to prevent family members
>from interrupting the connection at the tail end of a 250K file transfer
>for example?
>I would ***REALLY*** appreciate any help in this regard!  :-)

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~|       _ _	KLEIN BOTTLE for sale...
	Shawn E. Koppenhoefer |	       |                      enquire within.
 ...watmath!rose!sekoppenhoef |	       -		 
~~~~~~~~~~~~~~~~~sekoppenhoef@rose.uwaterloo.ca sekoppenhoef@rose.uwaterloo.edu
/* End of text from m.cs.uiuc.edu:sci.electronics */

As I recall, this was discussed in this forum a while back, maybe
a year ago.

On multiline push button phones, a light activates in the buttons
when one of the lines is off hook. This is not a low cost system.

For your purpose, at the least cost, the means to take care of the
problem is to go to Radio Shack or other parts supply, get enough
4 conductor wire to go from the entrance block to the room where
the modem is located. Also get a 2 pole single throw relay. Put
the relay in the line so that it will cut off all extensions and
put your 4 conductor ahead of the relay. Use two of the wires to
activate the relay, the other two to carry the phone signal. Use
a DC type relay, so no hum cross talks to the other two wires in
your cable. When you are ready to activate the modem, pick the
relay, which kills all of the other phones down stream from the
phone block. You could even get fancy and pick the relay via a
pin from a parallel port on the computer, such that you write to
the port to set the bit, picking the relay, and again writing to
the port to drop the relay, after you are through, so you do not
forget. Put it in your communications software to handle it.

Al Irwin
Univ of Ill
Comp Sci
irwin@m.cs.uiuc.edu