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?
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Jim wrote:

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



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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%
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">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
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Stevie Boy wrote:

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
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<http://cpc.farnell.com/jsp/Office+Supplies+&+Telephone/Accessories/WHITELEY+ELECTRONICS/Call+Alert/displayProduct.jsp?sku=DP26074
<http://tinyurl.com/39rfj9
--
Regards,
Stuart.
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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..
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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)
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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).
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I am the OP. Just to clarify ....
There are several ready-built gadgets available on the high street here in the UK to record a phone conversation. They cost little and provide an audio feed from a jack plug which can go straight into a basic voice-activated recorder. Simple. Cheap.
So if I actually wanted to record a phone line I would use something like that. Perfectly legal too.
However I have asked about something different. I want to switch an electrical device on when the landline is in use. My question is how to attach to the landline. Something non-invasive is better and I suggested a magnetic switch. If it has to be a plug-in device then that's ok although it limits the location of the point of attachment to only where the sockets are.
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On Web wrote:

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
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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.

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

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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.
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No, but see the other thread by Jim.

There are plenty of legal things I don't think people should do and there are plenty of illegal things people do regardless of the law.

You have the intended context wrong. I was thinking in terms of jury rigging equipment - adapting/customising it if you wish, certainly not a use of the word jury in a legal sense.

Well clearly I can't police people morality, neither do I or anyone else have to aid people either.

The commercial availability of things has no bearing on their final application.
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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.
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You sit in the dark waiting for phone calls?

I suspect there are already purpose-built devices that can do the same.

I haven't alleged that you are pursuing any particular application for this, though it may be related to your quest to capture callers numbers as per your other thread.
Are you referring to the post by "Lemmo?" in which case how would I know that Lemmo == Jim? Otherwise, this is the only reply by "Jim" that I've seen.
I'm actually not interested in the law (though I've always understood that all parties should be aware that a recording is being made, unless you belong to the security forces).

Well, you didn't identify yourself as the OP, nor have you said they are the actual application.

Well that was exactly my point. What is it that you are planning to do with this device? I haven't said you are trying to pursue some unsavoury application of the technology, I have just expressed an opinion that such applications exist and I wouldn't assist this quest for information without knowing the actual application.

Quite honestly I can't imagine any of my friends or associates having a need for such a device and I would be concerned about them if they did ask me. I have no doubt that there are legitimate and benevolent uses for such a device, just as there are malevolent uses. It's the first time I've been described as having a paranoid outlook, somewhat ironical perhaps given your quest in another to log peoples phone numbers?
If I were a landlord, I might use such technology to spy on my tenants, If I were an employee I might use such technology to spy on the company If I were a jealous husband I might spy on my wife
Those are three applications I wouldn't wish to help anyone with. As for others who have been helpful, I don't consider that a good role model considering the possible repurcussions to others if this technology were misused.
I still have little idea why you want this technology and again I personally wouldn't help anyone construct such stuff without knowing more about the application (which from your other post may be logging callers numbers)..

You can clearly state your intention, I just hope that people will consider what they are helping someone to do. If you weren't so coy about this I wouldn't have posted.
It may well be that given the exact application you had in mind people might have been able to suggest a more targeted solution.
What is it you are trying to do?
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You can record for your own private use, without giving notice. This is equivalent to having an excellent memory or taking detailed private notes, which also is not a crime.
Anything involving third parties is usually a matter of consent by both people in conversation, or of officially warranted interception.
Consent can be tacit, in that if an employer records phone calls for business purposes, they cannot be found guilty if an employee decides to complain at the recording of a private call they decided to make out of their employer's phone system, unless they can demonstrate that they had no grounds to beleive a recording was being made.
This is based on what I know of UK law. Beyond that it gets too subtle for me. :)
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This seems far more likely than the bizarre things you suggest.
-- snip --

-- snip --

I have corrected your misunderstanding once already and given you a link (above) to check up the details. It seems that a sneerer like you prefer to carry on with the sneering and false innueundos than read the facts.

Then do not feel you have to help. As I pointed out, you do not even have to post if you havenothing of value to add to this thread.

Even the most innocuous thing can be misused. My bread knife can be used to kill. Someone can drown in a bathful of water. An electric bar fire can be used to burn someone. An electric drill can be used to maim someone. A car tyre & petrol can be used to burn someone to death.
Despite these horros, we stillmanage to live with these appliances. I don't get asked stupid questions when I buy a car tyre or run a bath and it would be better if you didn't ask them either.
There are any number of things which one might want to switch on when a phone call is being made. It's probably best if you stop being coy and accustory through adopting that false facade of innocence. "I only pointed out that it was possible that the OP could electrocute the cat and also activate the microwave in which his puppy was placed and then destroy the building by a timed fuse on some explosives and do all this by remotely calling his phone line and having the call trip his deadly switch". Get real.

I am setting something up to ensure safety for someone in the household who is suffering trauma and I do not feel I need to go into the details.
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wrote:

lots of snips..

Then I wish you luck with it, whatever it is. I can't help but feel that for whatever your trying to accomplish there's a more direct route to the solution, and no I don't want to know any more, I'm done with this.
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