At 04:21 PM 12/17/97 EST5EDT, you wrote:
>Does anybody out there know if it is possible to "shunt" the ring
>from a "home" telephone system.  What I mean by that is is it
>possible to stop all extensions on the system from ringing from a
>single extension?

For US POTS, if you add a series resistor (100 ohm max) in each line, and
then place a pair of zeners (20-30 volt) across the line (both polarities)
you can clip the ring signal at that phone so it will not ring.  It won't
ever ring.

----------/\/\/\--------|-------|--------
                        |       |
                       ___      V
                        ^      ---
                        |       |
                        |       |
---------/\/\/\--------------------------

By cliping the ring voltage below 30 volts, you prevent the ring detect
circuit from being activated.  The series dropping resistors protect the
zeners from
over current conditions.  The actual line impedance is about 600 ohms, but
don't count on it.  There is a 48 DC signal present when the phone is on
hook.  Taking the phone off hook places a load on the line, and the voltage
usually drops to 10-15 VDC.

If you really want to do it right, you should AC couple the zeners with a 22
uf 100 volt non-polarized cap.

The phone company detects off hook by the current draw, so making the series
resistors too high will prevent you from getting a dial tone.  If the series
resisters are too low in value, you sink a lot of current through the
zeners.  Too much will fry the zener, mostly a thermal affect.  Not usually
a problem due to low duty cycle on the rings.

Another problem with making the series resistors too high is that it will
decrease the amplitude of the voice coming into, and going out of the phone.

This can be built on a small breadboard outboard of the phone to make it
easy to play around.

Have fun, but don't do this while bathing. :-)

Wynn Rostek