On-off switch

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?
Reply to
Jim
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There are many designs on the internet for such a switch, eg:
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If you want a description of how it works, ask.
AAstra Telecom
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/apparently/ makes the LumiNET(tm) line-in-use indicator.
Reply to
Palindrome
">I am in the UK.
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
Reply to
Stevie Boy
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.
Reply to
Graham
On Sun, 17 Jun 2007 10:25:26 +0100, Jim mused:
Reply to
Lurch
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..
Reply to
On Web
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
Reply to
Owain
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
Reply to
Owain
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
Reply to
Lemmo
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.
Reply to
mc
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).
Reply to
mc
If you want to save time doing the research, Viking Electronics appears to have an off-the-shelf solution.
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Relay provides contact closure on ring as well as loop.
Beachcomber (no affiliation) just found this when I had a similar need for it.
Reply to
Beachcomber
snip
Very heath-robinson.
Well I do wonder what the OP is up to since they don't say..
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.
Reply to
On Web
Jim is also trying to capture the phone numbers of people calling the line, so maybe that's the application..
Reply to
On Web
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.
Reply to
ian field
On Sun, 17 Jun 2007 11:43:04 GMT, "On Web" put finger to keyboard and composed:
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
Reply to
Franc Zabkar
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.
Reply to
John G
"On Web" wrote in news:j3fdi.5003$ snipped-for-privacy@newsfe7-win.ntli.net:
I only see one post from him, the first one:
Jim wrote in news:Xns99526A09F520B5D4AM2@127.0.0.1:
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.
Reply to
Lostgallifreyan
Franc Zabkar wrote in news: snipped-for-privacy@4ax.com:
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.
Reply to
Lostgallifreyan
Good job my circumstances are not like yours then! :-)
What unsavory uses are there?
I have shown you a link which says that your first unjustified allegation which you call "bugging other peoples conversations" is actually legal in the UK and seems to be a misunderstanding of the law on your part.
I have shown you other uses.
Yet other uses include switching a device by tripping only the ringer (and not having to make a paid call) by calling from a mobile.
It seems you slur my integrity by making endless innuendos about an application of which you have no idea.
Others posters here may be a better role model for you. They do not adopt an unnecessary and incorrect moralistic tone and are less controlling in that they readily provide information without requiring unnecessary conditions designed only to satisfy a somewhat paranoid outlook.
You have said you won't help so what is the point of your posting? Perhaps you are trying to dissuade people who clearly do not share your attitude from posting?
In the end the purpose of your posts seem to be either to slur my intention and/or limit the information I may get.
Reply to
Jim

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