🚀 go-pugleaf

The telephone line is a balanced system. In order to connect something
to it you have to observe several rules. The first and most imortant
is the GROUND isolation. Because the line caries a FLOATING
voltagage/current any ground reffered attachement will induce
severe HUM. The second the Balance of the line must be preserved
as much possible. Balance in this context is that the amount of
current/voltage flowing into one wire must be faithfully reproduced
in the other.

The simplest way to acheive this is by capacitalively coupling a
transformer  to the line. Ia two capacitors are used then the
transwormer is simetrically DC isolated not alowing line unbalace.
Also the transformer provides the isolation between the line and the
user aparatus. If at the secondary of the transformer
you attach an 1W, 5V Zener diode it will protect your equipmet fron
the ring voltages on the line.
The design could be improuved with the addition of impedance matching
circuitry and ESD protection until a complete Direct Attachment
Arangement (DAA) is achived. For one schiled in the art it is trivial.
Otherwise, as suggested somwhere else, Radio Shack or equivalent
could be used.

Have FUN. We need it so much.
Alex VonYonkers

======================================================================




"Adrian Webb" <awebb@knwebb.globalnet.co.uk> wrote:

>I want to connect my telephone extension socket to an audio lead. On the UK
>domestic phone lead there is 4 wires. Which ones are the audio and audio
>shield? I've heard that telephone leads are digital and so none of them are.
>This can't be true can it? I mean a cheap 7.50ukp phone thats converts
>digital signals into analogue. The power must be separate from audio.
>On a phone doubler, it is like audio isn't it, in that one wire splits off
>into two, sending out two audio signals for two phones? This is what i want
>to do, but one of them connecting to an audio lead.
>--
>Adrian Webb    also at:
>                       Adrian.Webb@discovery.dmpriest.com

Adrian Webb wrote:

> I want to connect my telephone extension socket to an audio lead. On the UK
> domestic phone lead there is 4 wires. Which ones are the audio and audio
> shield? I've heard that telephone leads are digital and so none of them are.
> This can't be true can it? I mean a cheap 7.50ukp phone thats converts
> digital signals into analogue. The power must be separate from audio.
> On a phone doubler, it is like audio isn't it, in that one wire splits off
> into two, sending out two audio signals for two phones? This is what i want
> to do, but one of them connecting to an audio lead.

You need to do some serious reading about how the telephone signal is
carried from CO to your house.  Radio Shack had a good book on that, but
I don't think that's available where you're at.  IN any case, your
assumptions are wrong.

To sum it up, you cannot just connect the telephone jack wires to an
audio input.  If you do, your telephone will quit working, you may be in
for a very, very nasty surprise if a lightning storm comes by, and you
may get charged by the telco if they find that you have caused a major
problem.


> --
> Adrian Webb    also at:
>                        Adrian.Webb@discovery.dmpriest.com

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John Lundgren <NOlundgrejSPAM@mail.rancho.cc.ca.us> writes: 
> Adrian Webb wrote:
> > I want to connect my telephone extension socket to an audio lead. On the UK
> > domestic phone lead there is 4 wires. Which ones are the audio and audio
> > shield? 

Normal analogue telephone uses two wires. In the USA style RJ-11 connector
those are the two center ones (red and green). The audio in both directions
and the telephone power are carried over this wire pair. The audio in
telehone line is balanced and shield is not normally used because it is
not necessary.

>> I've heard that telephone leads are digital and so none of them are.

Most of the telephone lines coming to houses are normal analogue telephone
lines (PSTN). That's the most common telephoeninterface in use. Nowadays
typically everything from your local telephone central are then digital.
If you have ISDN connection coming to your home then the signal
is digital to your telephone.

> > This can't be true can it? I mean a cheap 7.50ukp phone thats converts
> > digital signals into analogue. The power must be separate from audio.

Those cheap telephones are not digital. Digital telephone is much more
expensive. All cheap telephones I have seen are traditional analogue
telephone. Power and audio can be carried using one audio pair
easily: audio is transformer coupled to line and the transformers
can handle some current flowing though their without saturation.
The power is DC current and the audio is a small AC signal over it.
 
> You need to do some serious reading about how the telephone signal is
> carried from CO to your house.  Radio Shack had a good book on that, but
> I don't think that's available where you're at.  IN any case, your
> assumptions are wrong.

The writer of this article is right. Buy a book on telephone
or read UNDERSTANDING TELEPHONES document which is available at
http://massis.lcs.mit.edu/telecom-archives/archives/technical/how.phones.work
I have also described many details of telephone line interface at my
telehone line intewrfacing document at
http://www.hut.fi/Misc/Electronics/circuits/teleinterface.html
 
> To sum it up, you cannot just connect the telephone jack wires to an
> audio input.  If you do, your telephone will quit working, you may be in
> for a very, very nasty surprise if a lightning storm comes by, and you
> may get charged by the telco if they find that you have caused a major
> problem.

That's true. Whatever audio equipment you connect to telephone line make
sure that you have an isolation transformer between telephone line
and your mixer. A best solution for this isolation is an approved telephone
line audio coupler. If you connect telephoen line to your audio
equipments directly, the telephoen line might quyite work, it might
work somehow poorly for some time or you will break your equipment
inputs immediatly (normal equipments don't like 48V DC and
even 100V AC ring signal on telephone line). And in any case you will
suffer and pay for damages. Those damages can be damages to your
equipments, damages to telephone company equipments, amount of work
caused for finding the problem, maybe for the losses you cause to
company because you damaged their telephone network. And in some countries
you will also pay the fines if telephone company finds out that you
have non-approved equipments connected to public telephone network
(it is illegal in many countries). Do not mess up with telephone lines
unless you know exactly what you are doing amd live by the rules.

-- 
Tomi Engdahl (http://www.iki.fi/then/)
I maintain electronics and PC hardware web pages at
http://www.hut.fi/Misc/Electronics/

On Tue, 3 Mar 1998 15:58:32 -0000, "Adrian Webb"
<awebb@knwebb.globalnet.co.uk> wrote:

>I want to connect my telephone extension socket to an audio lead. On the UK
>domestic phone lead there is 4 wires. Which ones are the audio and audio
>shield? I've heard that telephone leads are digital and so none of them are.
>This can't be true can it? I mean a cheap 7.50ukp phone thats converts
>digital signals into analogue. The power must be separate from audio.
>On a phone doubler, it is like audio isn't it, in that one wire splits off
>into two, sending out two audio signals for two phones? This is what i want
>to do, but one of them connecting to an audio lead.
We have often 'knocked' together such devices for persons wanting to
play/record from their sound card down the phone line. Quite easy to
do (of course the're illegal to use but we just sell them).

-------------------------------------
Name: Dr Steve Mace
E-mail: steve@solwise.demon.co.uk
www: http://www.demon.co.uk/solwise/
Tel: +44 1482 473899
Fax: +44 1482 472245
Date: 30/09/97
Time: 13:49:31
-------------------------------------

You can buy them from the larger - Maplin superstores (saw one last week in
Leeds for around 7 quid. They are, however, illegal and have the red sticker
on them - not authorised for direct connection........

A legal way is to go for one of those records from the Innovations Catalogue
which is a small portable tape recorder. The pickup snaps around the outside
of the phone lead - i.e. induction coupling. So no direct connection so
legal - the only snag is the price - around 150 quid.

You can also get pickups which attack with a sucker to the telephone handset
and plug into the rec jack of a tape recorder - quick and dirty solution for
a few pounds.

Gareth
P.S. we only use 2 of the 4 wires in the UK - the red and the white I think.
Transmit and receive over the same pair using different carrier freq..
Careful though as there is also the ring circuit on this pair - 50vDC - with
enough current to ring a couple of bells and so plenty enough to blow up any
homebrew circuits you put on.



Adrian Webb wrote in message <6dh9g7$627$1@heliodor.xara.net>...
>I want to connect my telephone extension socket to an audio lead. On the UK
>domestic phone lead there is 4 wires. Which ones are the audio and audio
>shield? I've heard that telephone leads are digital and so none of them
are.
>This can't be true can it? I mean a cheap 7.50ukp phone thats converts
>digital signals into analogue. The power must be separate from audio.
>On a phone doubler, it is like audio isn't it, in that one wire splits off
>into two, sending out two audio signals for two phones? This is what i want
>to do, but one of them connecting to an audio lead.
>--
>Adrian Webb    also at:
>                       Adrian.Webb@discovery.dmpriest.com
>
>