🚀 go-pugleaf

In article <1629@ariel.unm.edu> ee5391aa@hydra.unm.edu.UUCP (Duke McMullan n5gax) writes:
>A real, live, appropriately technocratic solution to this did occur to me....
>
>Build a little black box which detects the ringing voltage (the phone may ring
>...

Well, it sounds like the original poster wanted an undetectable box (small,
un-obtrusive, and low/no power consuming - cheap would be nice too!).  So
my idea is simply build a passive notch filter and place it in series with
the red/green (tip/ring) wires at the tele main connection.

The ringing is (as another poster mentioned) about 30 hz and around 100 Volts.

Well, dropping this to around 10-30 volts might just keep the ringer from
going.  That depends largly on the ringer equivalences of all the phones on
the line, the condition of the wires in the house, the temperature/humidity
outside (yes phone voltages vary with the weather).  You MUST pass the DC
component, otherwise the phones will not be able to dial out; and you MUST
pass everything over about 100 hz to get the voice and in-band signaling
to go through.  A notch filter set between 10 and 100 hz with about 12 db
loss at 30 hz would be ideal.  I'm not an EE, so the design is left as an
excercise to the reader.

One other option would be to fake a PBX.  I'll try to keep my ramblings
coherent here.  1st, have a relay that disconnects the in-house phone lines
from the telco lines and connect them (the in-house lines) to a voltage
source run through about a 600 ohm resister.  Moniter the voltage on the
in house lines.  While the phones are on-hook, the voltage will be about
what the voltage in the DC supply is.  When sombody takes a phone off-hook,
the voltage will drop to about 1/2 the DC voltage (if more the 1 phone go
off-hook together, the voltage will be even lower).  So set up a comparator
with one input connected to a 75% volage divider off the DC supply, and the
other input directly off the in house lines.  When the in house lines drop
below the 75% threshold, the comparater will fire, and you flip the relay.
Now the phone is connected to the telco lines, they will detect the off-hook
condition and produce a dial-tone.  You continue to moniter the voltages.
When they return to normal for on-hook telco lines (about 60vdc - or anything
over about 12vdc) you flip the relay back to the fake PBX, looking for another
off hook condition.  When an outside caller tries to ring the number, the
signal never makes it to the phones, since the relay has the telco lines
isolated from the in-house lines.  If sombody takes a phone off-hook at the
same time as sombody is calling in, it will look to all teh equipment as if
a normal answer had happened.  The net effect is the same as removing the
ringer from all the phones, except that no modification of equipment in
needed.

Hope it helps
 ______________________________________________________________________
| Dean Reece     Member Technical Staff |"The flames are all long gone |
| The Santa Cruz Operation 408/458-1422 | but the pain lingers on"     |
|___________deanr@sco.com_______________|___________________Pink_Floyd_|