circuit needed

[cowboy]

I need a little circuit to adapt an ordinary telephone to play computer wav
files over the line.

So for example, if I was talking to my friend on a conventional telephone,
while sitting at the computer, and I told him a joke, I could click a wav
file of Curly of the three stooges, and we would instantly both hear it in
our telephone conversation, just as if Curly was one the line with us. Or
we could have a song playing on the line within our conversation.

where could I buy this device?

or is there a circuit diagram I could build?

assume a standard conventional corded telephone in the USA, and a typical
Windows XP computer with a typical sound card. Also, how would this work
with a typical cordless telephone?


thanks!

cowboy

 

[[email protected]]

I need a little circuit to adapt an ordinary telephone to play computer wav
files over the line.

assume a standard conventional corded telephone in the USA, and a typical
Windows XP computer with a typical sound card. Also, how would this work
with a typical cordless telephone?

A 600 Ohm 1:1 transformer is all you need. You could buy one or tear
apart an old defunct modem to get one.

One winding connects to the soundcard "line out" and the other winding
goes in series with the phone line between the wall plug and the phone you're
going to be using.

The transformer is needed to prevent lots of hum on the line and/or
interfering with the normal operation of the phone.

It shouldn't make any difference whether the phone is cordless or not.

Jim


James P. Meyer
http://home.att.net/~notjimbob

 

[Pooh Bear]

A 600 Ohm 1:1 transformer is all you need. You could buy one or tear
apart an old defunct modem to get one.

One winding connects to the soundcard "line out" and the other winding
goes in series with the phone line between the wall plug and the phone you're
going to be using.

The transformer is needed to prevent lots of hum on the line and/or
interfering with the normal operation of the phone.

It shouldn't make any difference whether the phone is cordless or not.

If you have DSL, make sure it's fitted on the telephone circuit side of the
'splitter'.

British Telecom would go nuts over ppl doing stuff like this though.

Graham

 

[Mac]

A 600 Ohm 1:1 transformer is all you need. You could buy one or tear
apart an old defunct modem to get one.

One winding connects to the soundcard "line out" and the other winding
goes in series with the phone line between the wall plug and the phone you're
going to be using.

The transformer is needed to prevent lots of hum on the line and/or
interfering with the normal operation of the phone.

It shouldn't make any difference whether the phone is cordless or not.

Jim


James P. Meyer
http://home.att.net/~notjimbob

Wouldn't this potentially expose the sound card, and therefore the
computer, to dangerous Voltages under some circumstances? Lightning
strikes and what have you.

--Mac

 

[Brian]

Wouldn't this potentially expose the sound card, and therefore the
computer, to dangerous Voltages under some circumstances? Lightning
strikes and what have you.

--Mac

Eh, computers are cheap.

 

[cowboy]

A 600 Ohm 1:1 transformer is all you need. You could buy one or tear
apart an old defunct modem to get one.

One winding connects to the soundcard "line out" and the other winding
goes in series with the phone line between the wall plug and the phone
you're
going to be using.

could you post a schematic? I am not clear how to hook it up

the 600 ohm transformer has 4 wires correct?

two wires on one side of transformer go to line out & line out shield?

two wires on other side of transformer go inserted into red phone wire or
else green phone wire?
or is it across red & green? (one wire to each)

 

[Pooh Bear]

could you post a schematic? I am not clear how to hook it up

the 600 ohm transformer has 4 wires correct?

It will inded have 4 terminals or wires.

two wires on one side of transformer go to line out & line out shield?

On the sound card. Sure

two wires on other side of transformer go inserted into red phone wire or
else green phone wire?
or is it across red & green? (one wire to each)

The colours in use will depend on your country normally. And possibly also
where exactly you're 'tapping in' to the circuit.

I strongly doubt it will work acceptably with a paralleled connection either.
The '600ohm' transformer will actually present a low impedance to the line
and effectively shunt it making volume levels lower. It'll almost certainly
kill any DSL usage.

Graham

 

[[email protected]]

Wouldn't this potentially expose the sound card, and therefore the
computer, to dangerous Voltages under some circumstances? Lightning
strikes and what have you.

--Mac

Sure. I use a dial-up connection for my computer. You can't get any
more connected to the phone line than that.

I use an AC surge protected multiple outlet adapter for the power to all
my computer connected equipment. The one I have also has a place to plug the
phone cord from the wall in and an outlet to plug a phone cord that goes to my
modem. It's a "star ground" for my whole system that makes sure (as far as is
reasonably possible) that I don't have any ground loops and everybody is (as far
as is reasonably possible) protected from lightning.

Jim

James P. Meyer
http://home.att.net/~notjimbob

 

[[email protected]]

could you post a schematic? I am not clear how to hook it up

the 600 ohm transformer has 4 wires correct?
Correct.

two wires on one side of transformer go to line out & line out shield?

Get yourself a multimeter to make sure that you have identified the
connections on the transformer properly. The "ohms" reading across the
terminals will show which ones are part of each winding. Even a cheap, >$10.00
one, will do the job. Line out and shield to one winding.

two wires on other side of transformer go inserted into red phone wire or
else green phone wire?

Cut either the red or green wire on the phone cord and connect the cut
ends to the other winding.

or is it across red & green? (one wire to each)

Nope. That would sort of work, but wired that way the phone line would
would be connected all the time that the phone cord was plugged into the wall
and none of your other phones could dial out.
Jim


James P. Meyer
http://home.att.net/~notjimbob

 

[cowboy]

Jim, could you look at the schematic at ABSE, that I just posted, and tell
me what you think?

Correct.

<snip>

 

[Genome]

A 600 Ohm 1:1 transformer is all you need. You could buy one or tear
apart an old defunct modem to get one.

One winding connects to the soundcard "line out" and the other winding
goes in series with the phone line between the wall plug and the phone you're
going to be using.

The transformer is needed to prevent lots of hum on the line and/or
interfering with the normal operation of the phone.

It shouldn't make any difference whether the phone is cordless or not.

Jim


James P. Meyer
http://home.att.net/~notjimbob

Ouch!!!!

Don't know how American phone lines work but, here in the UK, off hook is
signalled by drawing line current, through a current sink. If you stick a
signal transformer in series with the line then it will have to carry that
DC current and will saturate and maybe burn.

Bad news

DNA

 

[Mac]

Sure. I use a dial-up connection for my computer. You can't get any
more connected to the phone line than that.

I use an AC surge protected multiple outlet adapter for the power to all
my computer connected equipment. The one I have also has a place to plug the
phone cord from the wall in and an outlet to plug a phone cord that goes to my
modem. It's a "star ground" for my whole system that makes sure (as far as is
reasonably possible) that I don't have any ground loops and everybody is (as far
as is reasonably possible) protected from lightning.

Jim

James P. Meyer
http://home.att.net/~notjimbob

Right, but your modem is designed to accommodate conditions that might
reasonably be encountered on the line. There are applicable specifications
and regulations for this sort of thing.

Just hooking up a transformer without any protection circuitry sounds
dangerous to me. I'm sure the telco wouldn't like it. ;-)

There is also the question of what happens when you put audio on a line
which is not off the hook.

--Mac

 

[Mac]

Ouch!!!!

Don't know how American phone lines work but, here in the UK, off hook is
signalled by drawing line current, through a current sink. If you stick a
signal transformer in series with the line then it will have to carry that
DC current and will saturate and maybe burn.

Bad news

DNA

I think US telephone lines are the same. 50 V/600 Ohms is 30 mA? Is that
right? So the transformer better be able to handle that without
saturating. No worries for the cable. You can't start a fire even if you
short them together.

WARNING: I'm not a telephone guy. Don't trust my calculations or
assumptions.

--Mac

 

[[email protected]]

Ouch!!!!

Don't know how American phone lines work but, here in the UK, off hook is
signalled by drawing line current, through a current sink. If you stick a
signal transformer in series with the line then it will have to carry that
DC current and will saturate and maybe burn.

Bad news

DNA

exactly, you need a capacitor in series with the phoneline side of the
TF. I'd also fit a series resistor, you can expect audio problems
otherwise.

The more basic way to do it is to just talk while sitting next to the
puter speakers. Thats legal too.


NT

 

[Mac]

exactly, you need a capacitor in series with the phoneline side of the
TF. I'd also fit a series resistor, you can expect audio problems
otherwise.

How, exactly, would that work in this case? I mean, how can the cap be in
series with the transformer and not be in series with the telephone?

The more basic way to do it is to just talk while sitting next to the
puter speakers. Thats legal too.


NT

--Mac

 

[[email protected]]

Just hooking up a transformer without any protection circuitry sounds
dangerous to me. I'm sure the telco wouldn't like it. ;-)

A 600 ohm 1:1 transformer is what most dial-up modems use for coupling
to the line simply because it's the safest device available. I've dissected a
couple of lightning damaged modems and in every case it's a failure of the
protective devices that prevent the modem from working. The transformers and
everything downstream of them were completely functional.

There is also the question of what happens when you put audio on a line
which is not off the hook.

--Mac

An on-hook phone presents a very high impedance to the line. When you
put an audio voltage source in series with a very high impedance, the current is
limited to a very low value. You simply can't put audio on the line when the
phone is on-hook using my suggested circuit.

Jim

 

[[email protected]]

Jim, could you look at the schematic at ABSE, that I just posted, and tell
me what you think?

I've posted a reply on ABSE that shows what I tried to say in words
earlier.

Jim

 

[[email protected]]

Ouch!!!!

Don't know how American phone lines work but, here in the UK, off hook is
signalled by drawing line current, through a current sink. If you stick a
signal transformer in series with the line then it will have to carry that
DC current and will saturate and maybe burn.

Bad news

DNA

If Limey phone lines can supply enough current to burn up transformers,
then you have solved the energy crisis. Just plug your houshold appliances into
the phone line and disconnect from the power grid.

Jim