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'Telephone system question'
1997\12\17@162402 by SHAWN ELLIS

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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?

Mabye by apllying an alternating current to "even out" the ring wave,
or shunting the ring wire to ground or something like that?

Thanks,

Shawn Ellis
spam_OUTsellisTakeThisOuTspamrx.uga.edu

1997\12\17@163739 by Sean Breheny

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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?
>
>Mabye by apllying an alternating current to "even out" the ring wave,
>or shunting the ring wire to ground or something like that?
>
>Thanks,
>
>Shawn Ellis
>.....sellisKILLspamspam@spam@rx.uga.edu
>

If you are talking about regular phone service (POTS) in the US, I think
that simple shorting the line at any extension would diable ringing and all
phone service throughout the house. If you want to disable just the ring,
it might still be possible, depending on how the house is wired, to put
some type of zener or TVS device on one of the extensions and short just
the ring signal, and this might work throughout the entire house. In the
US's regular phone system, there is no separate ring signal line, the ring
is simply transmitted as an approx. 90V ac signal on the same twisted pair
as the voice is transmitted. The line is normall at about 40V dc and a
phone presents something like 500 ohms resistance when off the hook.

Sean


+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
+--------------------------------+
http://www.people.cornell.edu/pages/shb7
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Phone(USA): (607) 253-0315

1997\12\17@175855 by Wayne Foletta

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Shawn:

If you are asking about a standard (POTS or plain old telephone service
in the USA) telephone - try damping the ringing output transducer. I
have used tape on the both old mechanical bell type and the piezo type.
If a mechanical bell tape the clanger - you still will hear a muffled
clanking from the armature. If you have an electronic phone that does
not have the mute function - with the enclosed piezoelectric type - tape
over the air vent holes. With the open piezo type - put tape right on
the piezo disk or use silicon rubber (RTV).

You can't shunt the ring signal on the telephone line itself without
stopping all phones from ringing because, of course, all extensions are
on the same two wires. If you have a common pair to the extension phones
that can be separated from the main phone input telephone service - you
could add a network that passes on to the extensions the voice + 48VDC
but not the higher voltage (90VAC) low frequency (20Hz) ringing signal.

- Wayne Foletta
BMI - Santa Clara

{Quote hidden}

1997\12\17@190210 by Dmitry Kiryashov

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SHAWN ELLIS 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?
>
> Mabye by apllying an alternating current to "even out" the ring wave,
> or shunting the ring wire to ground or something like that?

Shawn, descript DC/AC line characteristics more detaily and i can help
you.
I done devices like you asked about but for Russian phone standart.
(DC=60v AC call=120v/25Hz)

The main idea is to control connection the phones to the line through
some
switch and when AC ringing is appear than make this switch open.

WBR Dmitry.

1997\12\17@220844 by richard dellacona

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yes simply connect a neon lamp across the phone line
when a call comes in the lamp glows and completes the circuit and trips
the offhook relay at the co

SHAWN ELLIS wrote:

{Quote hidden}

1997\12\17@221512 by Wynn Rostek

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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

1997\12\17@233835 by Rick Dickinson

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At 10:03 PM 12/17/97 -0500, Wynn Rostek wrote:
>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.

Unfortunately, the circuit drawn here will clip the voltage down to about
0.7 volts.  You have forgotten that zeners still are normal diodes in the
forward direction....  Simply place the zeners in series instead of
parallel, and your circuit should work fine, however.

- Rick "Go with the flow" Dickinson


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1997\12\17@234451 by Sean Breheny

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At 08:37 PM 12/17/97 -0800, you wrote:
{Quote hidden}

Rick, you are absolutely right, but I think that one more clarification is
in order, the zeners should be in series, but the series combination of
zeners should be placed in parallel with the line:

<copying an ascii drawing because I am so bad at ascii drawing>

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

Hope you don't mind my clarification,

Sean



+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
+--------------------------------+
http://www.people.cornell.edu/pages/shb7
RemoveMEshb7TakeThisOuTspamcornell.edu
Phone(USA): (607) 253-0315

1997\12\18@083033 by Jack Warren

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Hi all.

So from what I see, this circuit SHOULD keep the line seized forever.  Don't
you want to stay above the 48 volt battery voltage the fone company supplies???


Regards,
Jack Warren


{Quote hidden}

1997\12\18@105905 by Sean Breheny

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At 08:15 AM 12/18/97 -0500, you wrote:
>Hi all.
>
>So from what I see, this circuit SHOULD keep the line seized forever.  Don't
>you want to stay above the 48 volt battery voltage the fone company
supplies???
>
>
>Regards,
>Jack Warren
>

<snip>

{Quote hidden}

Jack,

This circuit will never allow the phone line on right end of the diagram to
jump above Vznr+.6 in either polarity, where Vznr is the zener voltage of
the diodes. If you use zeners with Vznr of say 55 V, then this circuit
should allow normal phone operation but should clamp rings.
Now, this circuit will affect the line on the left side of the diagram,
too, however its effect will be reduced slightly due to the resistors, but
if the resistors are low enough,( I guess around 50 to 100 ohms), then this
circuit might be able to stop all ringing in the house. The best value of
the resistors depends on the way the house is wired. Probably trial and
error would be the best way to find out the values.

I do have one question for all the phone gurus out there, though: How long
does it take, from the time that the handset on a phone is picked up, 'til
the phone company considers that the call has been answered. In other
words, is there a slight chance that this clamping circuit might actually
answer the call in some systems? I doubt it myself, but I think some more
opinions are needed.

Sean


+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
+--------------------------------+
http://www.people.cornell.edu/pages/shb7
TakeThisOuTshb7EraseMEspamspam_OUTcornell.edu
Phone(USA): (607) 253-0315

1997\12\18@141333 by Martin McCormick

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       One should be careful about the type of load presented to a
telephone line pair.  The equipment at the switch to which your phone is
connected may range in complexity from rotary steppers and mechanical relays
which are extremely forgiving of marginal conditions to solid-state switches
that do lots of line quality testing on an automated basis.  If you have
ever heard your telephone bell ding once or twice in the middle of the night,
that was an automated line test.  The system looks for there to be essentially
no current flow between the tip and ring wires and no connection between
either and other things such as Earth.  Those conditions usually mean damage
to the cabling somewhere between the telephone office and your house or
business.  If one of these tests detects leakage and they send a crew out
to check things out and it turns out to be a poorly designed line interface,
they may not be very friendly about it.

       In the little bit of research I did on this, I found out that the
DC voltage can vary quite a bit depending upon the design of the telephone
switching equipment.  While it is usually a nominal 48 volts, it can be
several volts lower or higher with no ill effects.  Modern switches are
supposed to send out .1 A of ringing current or enough to ring five standard
20-mil ringers.  This may dwindle down to something less if there is a long
run of wire, of course.  The ringers are usually isolated from the DC with
a suitable blocking capacitor.

       Telephones usually drop the line voltage to about 8 or 10 volts when
off-hook, but they should not present any DC load when on-hook.

       Party lines are a whole different story.  They use not only the
pair of wires to carry the conversation and dialing signals, but they also
use the path from tip to Earth and ring to Earth to separately ring each
phone or group of phones on the party line.  They have even designed schemes
for sending various frequencies between 20 and 50 HZ on multi-party lines
and each telephone must have a tuned reed that resonates with one of the
frequencies.  I hope this answers some of the phone interface questions
that ahve come up on the list.  Another excellent resource is
the comp.dcom.telecom news group and its archive site whose URL escapes me
at the moment.

Martin McCormick

1997\12\18@154538 by Harold Hallikainen

picon face
       People considering connecting stuff to the PSTN should also have
a look at part 68 of the FCC rules (47 CFR 68).  You can view it at
http://hallikainen.com/FccRules  .

Harold

1997\12\18@155304 by SHAWN ELLIS

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>         One should be careful about the type of load presented to a
> telephone line pair.  The equipment at the switch to which your phone is
> connected may range in complexity from rotary steppers and mechanical relays

So basically, your saying that there is no practical, recommended way
to cut off ringing from one extension on the inside wiring?  I
thought this might be the case, and I would have to set up the ring
blocker on the enterence point to the house.  Any other suggestions?

1997\12\19@005506 by Wynn Rostek

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At 08:37 PM 12/17/97 -0800, you wrote:
>At 10:03 PM 12/17/97 -0500, Wynn Rostek wrote:
>Unfortunately, the circuit drawn here will clip the voltage down to about
>0.7 volts.  You have forgotten that zeners still are normal diodes in the
>forward direction....  Simply place the zeners in series instead of
>parallel, and your circuit should work fine, however.
>

Of course you're right. It was fairly late, and I was working from memory.
I should know better by now!

1997\12\19@005535 by Wynn Rostek

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At 03:47 PM 12/18/97 EST5EDT, you wrote:
>>         One should be careful about the type of load presented to a
>> telephone line pair.  The equipment at the switch to which your phone is
>> connected may range in complexity from rotary steppers and mechanical relays
>
>So basically, your saying that there is no practical, recommended way
>to cut off ringing from one extension on the inside wiring?  I
>thought this might be the case, and I would have to set up the ring
>blocker on the enterence point to the house.  Any other suggestions?
>
>

Nah, even in the bad old days when Ma Bell made a marine drill sargent like
like a cub scout den mother, we used to disable a ringer by taking the case
off the phone, loosening the terminals and pulling a ringer wire off.  The
phone then "disappeared" from the scans. ;-)

Wynn

1997\12\19@005553 by Wynn Rostek

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At 10:58 AM 12/18/97 -0500, you wrote:

>I do have one question for all the phone gurus out there, though: How long
>does it take, from the time that the handset on a phone is picked up, 'til
>the phone company considers that the call has been answered. In other
>words, is there a slight chance that this clamping circuit might actually
>answer the call in some systems? I doubt it myself, but I think some more
>opinions are needed.

God, here it is late at night and me working from memory again.  (It's
official, I'm untrainable.)  Specs call for about 75-90 ma current draw for
the central switch to detect off hook.  (Phone answered)

I think you'll find that the current draw is under half that, so the central
switch doesn't detect off hook.

Also, the ringing is only clamped for the phone(s) to the right of the
circuit.  Phones to the left of the circuit will still ring.  The only real
problem is that the clamping circuit looks like a couple of normal phones,
and so decreases the number of phones you can have on your drop.

Oh, by the way, here in Central Florida, the phone company scans your lines
to see what is hooked up every three to five years.  There is a ringer
equivalence number on every non-bell phone or other device hooked to the
phone line.  They can tell, with pretty good accuracy, how many of what you
have hooked up.

I have not seen as much of this kind of activity in the last 3 or 4 years,
so they may have given up.  With so many third party phones out there, it
must be much harder to do the analysis. :-)

Wynn

1997\12\19@140618 by Chris Eddy

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Do I sense defeat?  Tisk tisk.  Why can't you use that TI ring detect chip (I
forget the number, links a piezo to the phone line).  Then use a PIC (thus I did
not specify OT in the subject line) to detect the pulses, and based upon a
switch
on a pin that indicates ring/ don't ring, re-generate a piezo ring.  Then rig it
into your phones.  Ring signal is 2 seconds on, 4 seconds off.

Chris Eddy
Pioneer Microsystems, Inc.

Wynn Rostek wrote:

> At 03:47 PM 12/18/97 EST5EDT, you wrote:
> >>         One should be careful about the type of load presented to a
> >> telephone line pair.  The equipment at the switch to which your phone is
> >> connected may range in complexity from rotary steppers and mechanical
relays
{Quote hidden}

1997\12\21@060125 by Tom Handley

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  Chris, I loss track of the originator of the topic but I've used the TI
ring detector (TCM1520A) and a PIC16C84 to monitor rings to a BBS for a local
Amiga user group. Basically, if I did'nt receive an `OK' signal from the Amiga
within a certain time, it would reset the BBS. There was a lot more to it but
the TCM1520A simplified the hardware while being fairly `bullet proof'...

  The nice thing about the TCM1520A is that it connects directly to the phone
line, has built-in suppression (1.5KV/200us), low ringer equivalence (< 1),
built-in 5V regulator suitable for logic or optoisolator applications, and the
diode bridge handles ring signals to 150V. In a typical application, you add
two capacitors and one resistor (two if you use an optoisolator).

  Back to the original question, you could use one edge of the ring detector
output to ignore the first ring.

  - Tom

At 02:02 PM 12/19/97 -0500, you wrote:
>Do I sense defeat?  Tisk tisk.  Why can't you use that TI ring detect chip (I
>forget the number, links a piezo to the phone line).  Then use a PIC (thus
I did
>not specify OT in the subject line) to detect the pulses, and based upon a
> switch
>on a pin that indicates ring/ don't ring, re-generate a piezo ring.  Then
rig it
{Quote hidden}

1997\12\21@231042 by Chris Eddy

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To mask off the ring, you could count off a few of the cycles, figure at 20 Hz
(sometimes 30), there are 40 (60) cycles in that first ring.  Count off five to
make sure that the period is right and it ain't noise, and you could be in.  A
crafty individual would then regenerate the ring back out and tack on the lost
five cycles.  You could then look at the hook status and kill the added ringing
cycles if the phone is answered.

Chris
Pioneer Microsystems, Inc.

Tom Handley wrote:

{Quote hidden}

1997\12\22@001811 by Tom Handley

picon face
  Chris, the TCM1520A uses the ring cycles to charge a cap for the internal 5V
regulator so you don't need to (you can't) count cycles. By it's nature, it
ignores the first ring while charging, then switches the output level after the
ring burst.

  - Tom

At 11:09 PM 12/21/97 -0500, you wrote:
{Quote hidden}

chip (I
{Quote hidden}

1997\12\22@134119 by Chris Eddy

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Tom..
I suppose then you would look at the rising edge like you said and just time
shift
the overall ring envelope.  That ought to do it.  Or, you could use the ring
indicate opto circuit used in modems and do a similar thing.  But than again, I
can't even remember who started this thread.  Hope the originator gets some use
from
it.

Chris Eddy
Pioneer Microsystems, Inc.

Tom Handley wrote:

>    Chris, the TCM1520A uses the ring cycles to charge a cap for the internal
5V
> regulator so you don't need to (you can't) count cycles. By it's nature, it
> ignores the first ring while charging, then switches the output level after
the
> ring burst.
>
>    - Tom
>
> At 11:09 PM 12/21/97 -0500, you wrote:
> >To mask off the ring, you could count off a few of the cycles, figure at 20
Hz
> >(sometimes 30), there are 40 (60) cycles in that first ring.  Count off five
to
> >make sure that the period is right and it ain't noise, and you could be in.
A
> >crafty individual would then regenerate the ring back out and tack on the
lost
> >five cycles.  You could then look at the hook status and kill the added
ringing
> >cycles if the phone is answered.
> >
> >Chris
> >Pioneer Microsystems, Inc.
> >
> >Tom Handley wrote:
> >
> >>   <snip>
> >
> >>    Back to the original question, you could use one edge of the ring
detector
{Quote hidden}

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