On-off switch

[Jim]

I am in the UK.

Can I build a simple device which would switch a pair of contacts on/off
when my landline phone was being used.

Am thinking of something like this. There might be a simple reed switch
(do such things still exist) which would close its contacts if there was
a current on the phone line.

Perhaps I might need to improve the situation and wind the landline (or
maybe just one of the two wires) around the reed switch.

Would something like this work?

Or can I buy a simple plug-in device for something like a fiver which
closes its contacts when the phone line is active?

 

[Palindrome]

Jim wrote:

I am in the UK.

Can I build a simple device which would switch a pair of contacts on/off
when my landline phone was being used.

Am thinking of something like this. There might be a simple reed switch
(do such things still exist) which would close its contacts if there was
a current on the phone line.

Perhaps I might need to improve the situation and wind the landline (or
maybe just one of the two wires) around the reed switch.

Would something like this work?

Or can I buy a simple plug-in device for something like a fiver which
closes its contacts when the phone line is active?

There are many designs on the internet for such a switch, eg:

http://www.elecdesign.com/Files/29/4343/Figure_01.gif

If you want a description of how it works, ask.

AAstra Telecom (www.aastra.com) /apparently/ makes the LumiNET(tm)
line-in-use indicator.

--
Sue

 

[Stevie Boy]

">I am in the UK.

Can I build a simple device which would switch a pair of contacts on/off
when my landline phone was being used.


Or can I buy a simple plug-in device for something like a fiver which
closes its contacts when the phone line is active?

While I'm not to sure what your hoping to achieve but you can buy a priority
(can be called by another name) switch which basically is a 2 outlet
telephone adaptor plug for less than a fiver that isolates the other
connected line when in use. This is achieved from a array of transistors
inside the unit which consumes it's power from the line.
This may be what your looking for.

Steve

 

[Graham]

"Jim" <nomail@riomail.com> wrote in message
news:Xns99526A09F520B5D4AM2@127.0.0.1...

I am in the UK.

Can I build a simple device which would switch a pair of contacts on/off
when my landline phone was being used.

Am thinking of something like this. There might be a simple reed switch
(do such things still exist) which would close its contacts if there was
a current on the phone line.

Perhaps I might need to improve the situation and wind the landline (or
maybe just one of the two wires) around the reed switch.

Would something like this work?

Or can I buy a simple plug-in device for something like a fiver which
closes its contacts when the phone line is active?

As Sue suggests go for a voltage sensor solution rather than
a current one. On-hook a phone line has about 48v across
the wires, Off hook it falls to about 9v so anything below
(say) 20v can be assumed to be off-hook.

You might want to seek out a line interface that has the
necessary approvals, especially if you are working on
somebody else's line.
--

Graham.
%Profound_observation%

 

[Lurch]

On Sun, 17 Jun 2007 10:25:26 +0100, Jim <nomail@riomail.com> mused:

I am in the UK.

Can I build a simple device which would switch a pair of contacts on/off
when my landline phone was being used.

Am thinking of something like this. There might be a simple reed switch
(do such things still exist) which would close its contacts if there was
a current on the phone line.

Perhaps I might need to improve the situation and wind the landline (or
maybe just one of the two wires) around the reed switch.

Would something like this work?

Or can I buy a simple plug-in device for something like a fiver which
closes its contacts when the phone line is active?

<http://cpc.farnell.com/jsp/Office+Supplies+&+Telephone/Accessories/WHITELEY+ELECTRONICS/Call+Alert/displayProduct.jsp?sku=DP26074>

<http://tinyurl.com/39rfj9>
--
Regards,
Stuart.

 

[On Web]

"Jim" <nomail@riomail.com> wrote in message
news:Xns99526A09F520B5D4AM2@127.0.0.1...

I am in the UK.

Can I build a simple device which would switch a pair of contacts on/off
when my landline phone was being used.

Am thinking of something like this. There might be a simple reed switch
(do such things still exist) which would close its contacts if there was
a current on the phone line.

Perhaps I might need to improve the situation and wind the landline (or
maybe just one of the two wires) around the reed switch.

Would something like this work?

Or can I buy a simple plug-in device for something like a fiver which
closes its contacts when the phone line is active?

What would you use this for?

At the moment I can only think of the obvious application: bugging other
peoples conversations, something I'd not be happy to assist with..

 

[Lemmo]

On 17 Jun 2007, On Web <a@b.com> wrote:

"Jim" <nomail@riomail.com> wrote in message
news:Xns99526A09F520B5D4AM2@127.0.0.1...
I am in the UK.

Can I build a simple device which would switch a pair of contacts
on/off when my landline phone was being used.

Am thinking of something like this. There might be a simple reed
switch (do such things still exist) which would close its contacts
if there was a current on the phone line.

Perhaps I might need to improve the situation and wind the
landline (or maybe just one of the two wires) around the reed
switch.

Would something like this work?

Or can I buy a simple plug-in device for something like a fiver
which closes its contacts when the phone line is active?

What would you use this for?

At the moment I can only think of the obvious application: bugging
other peoples conversations, something I'd not be happy to assist
with..

Firstly, your mind is too narrow:

(1) The desklight in the study would switch on and I could then use a
notepad.

(2) A strobe/flash is triggered so those who can not hear the phone
above a loud stereo can tell it has run.

(3) etc

---

Secondly, your mind is poorly uninformed:

"Recording and monitoring telephone calls" (Oftel/Ofcom)
http://tinyurl.com/9en95

HTH

 

[mc]

There are 2 basic approaches.

One is to sense current flowing through the line.

The other, probably easier, is to sense the voltage across it. This will be
well above 30 volts when the line is not in use, well below that when it is
in use.

Your sensing circuit needs a very high input impedance (like 10 or 20
megohms) to avoid putting a measurable load on the line.

 

[mc]

What would you use this for?

At the moment I can only think of the obvious application: bugging other
peoples conversations, something I'd not be happy to assist with..

Good point, but he doesn't have to ask us for technical help for that --
there are commercial gadgets available. At one time Radio Shack sold one
(in the USA).

 

[Owain]

Stevie Boy wrote:

While I'm not to sure what your hoping to achieve but you can buy a priority
(can be called by another name) switch which basically is a 2 outlet
telephone adaptor plug for less than a fiver that isolates the other
connected line when in use. This is achieved from a array of transistors
inside the unit which consumes it's power from the line.
This may be what your looking for.

Privacy adapter.

Quite a lot of them come with LEDs showing the line is in use. An LED is
one half of an optoisolator.

Owain

 

[Owain]

On Web wrote:

Can I build a simple device which would switch a pair of contacts on/off
when my landline phone was being used.
What would you use this for?
At the moment I can only think of the obvious application: bugging other
peoples conversations, something I'd not be happy to assist with..

Automatic switching of a recording device is one possibility, although
it is (in the UK) perfectly legal to record one's own calls.

It might also be useful to mute a radio or other sound source
automatically when answering the phone.

Owain

 

[Beachcomber]

On Sun, 17 Jun 2007 09:54:36 -0400, "mc"
<look@www.ai.uga.edu.for.address> wrote:

There are 2 basic approaches.

One is to sense current flowing through the line.

The other, probably easier, is to sense the voltage across it. This will be
well above 30 volts when the line is not in use, well below that when it is
in use.

Your sensing circuit needs a very high input impedance (like 10 or 20
megohms) to avoid putting a measurable load on the line.

If you want to save time doing the research, Viking Electronics
appears to have an off-the-shelf solution.

http://www.vikingelectronics.com/products/view_product.php?pid=169

Relay provides contact closure on ring as well as loop.

Beachcomber
(no affiliation) just found this when I had a similar need for it.

 

[On Web]

"Lemmo" <le@mo.com> wrote in message news:9952940491BD9D5E712@127.0.0.1...

On 17 Jun 2007, On Web <a@b.com> wrote:

"Jim" <nomail@riomail.com> wrote in message
news:Xns99526A09F520B5D4AM2@127.0.0.1...
I am in the UK.

Can I build a simple device which would switch a pair of contacts
on/off when my landline phone was being used.
snip
What would you use this for?

At the moment I can only think of the obvious application: bugging
other peoples conversations, something I'd not be happy to assist
with..



Firstly, your mind is too narrow:

(1) The desklight in the study would switch on and I could then use a
notepad.

(2) A strobe/flash is triggered so those who can not hear the phone
above a loud stereo can tell it has run.

(3) etc

Very heath-robinson.

Well I do wonder what the OP is up to since they don't say..

Secondly, your mind is poorly uninformed:

"Recording and monitoring telephone calls" (Oftel/Ofcom)
http://tinyurl.com/9en95

I have a phone line, but I doubt the other house occupants would be pleased
if I rigged up some kind of device to start recording in my absence.
Of course, we have no idea what the OP wants to do, but I can certainly
imagine uses that are unsavoury (I'm not suggesting that is the case).

I wouldn't help anyone along with such a device without knowing the end-use,
but clearly that's just me. It also seems sensible to mention the actual
usage since there may be a ready made/alternative solution besides jury
rigging the phone line.

HTH

 

[On Web]

"On Web" <a@b.com> wrote in message
news:OOedi.460$_l6.228@newsfe6-win.ntli.net...

"Lemmo" <le@mo.com> wrote in message news:9952940491BD9D5E712@127.0.0.1...
On 17 Jun 2007, On Web <a@b.com> wrote:

"Jim" <nomail@riomail.com> wrote in message
news:Xns99526A09F520B5D4AM2@127.0.0.1...
I am in the UK.

Can I build a simple device which would switch a pair of contacts
on/off when my landline phone was being used.
snip
What would you use this for?

At the moment I can only think of the obvious application: bugging
other peoples conversations, something I'd not be happy to assist
with..



Firstly, your mind is too narrow:

(1) The desklight in the study would switch on and I could then use a
notepad.

(2) A strobe/flash is triggered so those who can not hear the phone
above a loud stereo can tell it has run.

(3) etc

Very heath-robinson.

Well I do wonder what the OP is up to since they don't say..

Jim is also trying to capture the phone numbers of people calling the line,
so maybe that's the application..

Secondly, your mind is poorly uninformed:

"Recording and monitoring telephone calls" (Oftel/Ofcom)
http://tinyurl.com/9en95

I have a phone line, but I doubt the other house occupants would be
pleased if I rigged up some kind of device to start recording in my
absence.
Of course, we have no idea what the OP wants to do, but I can certainly
imagine uses that are unsavoury (I'm not suggesting that is the case).

I wouldn't help anyone along with such a device without knowing the
end-use, but clearly that's just me. It also seems sensible to mention the
actual usage since there may be a ready made/alternative solution besides
jury rigging the phone line.


HTH

 

[ian field]

"Jim" <nomail@riomail.com> wrote in message
news:Xns99526A09F520B5D4AM2@127.0.0.1...

I am in the UK.

Can I build a simple device which would switch a pair of contacts on/off
when my landline phone was being used.

Am thinking of something like this. There might be a simple reed switch
(do such things still exist) which would close its contacts if there was
a current on the phone line.

Perhaps I might need to improve the situation and wind the landline (or
maybe just one of the two wires) around the reed switch.

Would something like this work?

Or can I buy a simple plug-in device for something like a fiver which
closes its contacts when the phone line is active?

A few years ago Elektor magazine published a constructional project for a
reed relay based self energising latch for dial up internet intended to
defeat internet rogue diallers that break the connection you dialled
yourself and redial a premium rate number.

The circuit consisted of a reed unit with an energising coil round it, wired
in series with the reed, a push button is in parallel with the reed so the
connection is made while dialling, once the hookswitch is closed and current
flows through the coil the reed pulls in and the button can be released. For
a rogue dialler to dial it must first drop the existing connection - which
also drops out the reed making the dial out impossible.

Since this demonstrates that it is possible to wind a coil round a reed
element that can be operated by the telephone line current, it might help if
you can obtain a copy of the article for the coil winding details and modify
the circuit for your use.

 

[Franc Zabkar]

On Sun, 17 Jun 2007 11:43:04 GMT, "On Web" <a@b.com> put finger to
keyboard and composed:

"Jim" <nomail@riomail.com> wrote in message
news:Xns99526A09F520B5D4AM2@127.0.0.1...
I am in the UK.

Can I build a simple device which would switch a pair of contacts on/off
when my landline phone was being used.

Am thinking of something like this. There might be a simple reed switch
(do such things still exist) which would close its contacts if there was
a current on the phone line.

Perhaps I might need to improve the situation and wind the landline (or
maybe just one of the two wires) around the reed switch.

Would something like this work?

Or can I buy a simple plug-in device for something like a fiver which
closes its contacts when the phone line is active?

What would you use this for?

At the moment I can only think of the obvious application: bugging other
peoples conversations, something I'd not be happy to assist with..

My immediate thought was that a line in-use indicator could tell you
if someone was talking on the phone before you tried to send a fax or
dialled in to your ISP. Conversely, it could also be used to indicate
that a dialup Internet session was in progress.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[John G]

"Jim" <nomail@riomail.com> wrote in message
news:Xns99526A09F520B5D4AM2@127.0.0.1...

I am in the UK.

Can I build a simple device which would switch a pair of contacts
on/off
when my landline phone was being used.

Am thinking of something like this. There might be a simple reed
switch
(do such things still exist) which would close its contacts if there
was
a current on the phone line.

Perhaps I might need to improve the situation and wind the landline
(or
maybe just one of the two wires) around the reed switch.

Would something like this work?

Or can I buy a simple plug-in device for something like a fiver which
closes its contacts when the phone line is active?

There are about 1200 entries in Google about "Off Hook indicator" for
telephones.

All of which are most likely illegal in some jurisdictions.
--
John G.

 

[Lostgallifreyan]

"On Web" <a@b.com> wrote in
news:j3fdi.5003$tj3.2717@newsfe7-win.ntli.net:

Jim is also trying to capture the phone numbers of people calling the
line, so maybe that's the application..

I only see one post from him, the first one:

Jim <nomail@riomail.com> wrote in news:Xns99526A09F520B5D4AM2@127.0.0.1:

I am in the UK.

Can I build a simple device which would switch a pair of contacts on/off
when my landline phone was being used.

Am thinking of something like this. There might be a simple reed switch
(do such things still exist) which would close its contacts if there was
a current on the phone line.

Perhaps I might need to improve the situation and wind the landline (or
maybe just one of the two wires) around the reed switch.

Would something like this work?

Or can I buy a simple plug-in device for something like a fiver which
closes its contacts when the phone line is active?

There is no claim of any attempt to capture callers' numbers there.

Regarding issues of recording, deriving switch signals, this is legal in
the UK, you just have to watch how the law applies in specific instances.

You talk of 'jury rigging' a phone line, which is as loaded a phrase as I
ever heard, it implies some kind of illicit activity. Any real jury knows
that a person is guilty until proven innocent.

If you want to be cautious, just point the OP to a page that discusses the
regulations governing user connections to the user side of the master
socket wiring, and the laws governing lawful making and use of
recordings. The rest you must leave to their discretion, you can't police
their morality.

The easiest course is to look at what is commercially available in a shop.
If it's on open sale, it is safe to assume that discussing its function is
not only legal, but wise, and it might be cheaper to make than to buy.
Doubtful though, unless you buy from Maplin or other shop that charges
around twice what many shops accept as reasonable.

 

[Lostgallifreyan]

Franc Zabkar <fzabkar@iinternode.on.net> wrote in
news:d0cb731feu4tn647fv9cfne90v09o472rl@4ax.com:

My immediate thought was that a line in-use indicator could tell you
if someone was talking on the phone before you tried to send a fax or
dialled in to your ISP. Conversely, it could also be used to indicate
that a dialup Internet session was in progress.

Indeed. It can actually help with privacy. Without it, what's to stop
someone picking up the line and finding themselves a willing or surprised
eavesdropper, even against their better judgement. Such a device is as
innocuous as an engaged sign on a toilet door. Many people would encourage
its use, that way at least it takes deliberation, with less excuse for
'accident' in shared households if a person picks up a handset to listen.

 

[Lostgallifreyan]

Lostgallifreyan <no-one@nowhere.net> wrote in
news:Xns9953610FDCF07zoodlewurdle@140.99.99.130:

There is no claim of any attempt to capture callers' numbers there.

And incidentally, a caller ID display device is legal in the UK,
commercially available, often used by people who need to know in advance if
it is safe to answer the phone.