Relay to Cut Phone Line

Hello, I am new to circuitry and am looking to build a circuit that will allow me to disable my phone line for different intervals of time (ie 10 mins - 30 mins). My understanding is that is can be done with a normally closed relay, but that's where my knowledge ends...

Look at this, it is about relays and motors but there is no reason why the relay must switch a motor, you can have it disconnect your phone line.

I am not sure where you are in the world but this is illegal in some countries like the UK.

How much current/voltage travels down the phone lines? Why not just find the specific data line and connect it via a transistor?

What you are looking for is a DPDT relay,

Read the " Pole and throw" section on Wikipedia

Basically, when you energize the relay, it cuts the phone line so that no calls come in and any in progress get disconnected. Nobody would be able to dial out either. De-energize the relay and the phone line goes back to normal

*** Check local laws, there are implications in some areas.

The part itself can be something like this:

It can be done quite easily with a DPDT relay with a transistor to drive it. Of course I didn't tell you this because as GM says. they take a dim view of it in this country....... (its pins 2 and 5 in the socket you ahem switch cough on a UK socket) ::slight_smile:

Sorry for the off topic question.

this is illegal in some countries like the UK.

Do i understand correctly that it is illegal to pull the (all) phone plug(s) from the wall in some countries?


No, we can pull the plugs from the wall socket (all of 'em if you want), just not mess with their precious wiring......

Ah ok.

I was thinking in the line of 'You are not allowed to be un-reachable'. :slight_smile:



Nanny state, yes, dictatorship, not really (at least yet). :wink:

I won't respond in-depth as this forum is not the place to go totally berserk on that subject. I'm even a little embarrassed that i was even thinking of the possibility...



Just wanted to clarify on some points.

It is not technically illegal to modify telecommunications equipment... it is illegal to plug in non approved (by the tele communications authority in your country) equipment to your tele com's infrastructure, it's policy to protect the infrastructure...

Imagine if a home made switch box was to somehow inadvertently connect mains power to a phone line, how much damage could it do in your own house let alone the exchange and potentially other customers houses, screwing with telecom infrastructure is not a good idea and can land you in allot of trouble, fines and potentially jail.

PS I've worked in the telecom industry in Australia, i've seen some pretty stupid stuff.

I once spent a lot of my own money on a 30 page specification from the telephone authorities in the U.K. The diagrams were labelled safe side and dangerous side. Only the safe side was the phone network and the dangerous side was the consumer side. Personally I was thinking it was the other way round.

The UK legislation was used for years to enforce the monopoly and total inaction of the state sector. Due to a legislation anomaly the phone lines in Hull were not part of the nationalised phone network and it was there the first computer bulletin boards were allowed. Along with many early innovations that were not permitted in other parts of the country.

I did here of type approval being rejected because some lettering could be removed by applying a solvent to the device. They wouldn't even allow acoustically coupled modems to be attached and you couldn't claim there was a safety reason for that.

Fortunately things are easer now but type approval is still costly, bureaucratic and time consuming.

They wouldn't even allow acoustically coupled modems to be attached

Ahhh, the good old days........

Almost on a par with the witch hunts they organised to catch CB radios in the late 70's and early eighties. :slight_smile: (Post Office aka Busby back then).

Almost on a par with the witch hunts they organised to catch CB radios in the late 70's

Speaking as someone who lost a rather expensive model aircraft to illegal CB, I'd quite happily have seen the witch-hunt carried to its logical conclusion, and have them burnt at the stake.

Not all regulation is bad.

Two sides to every story..... :slight_smile:

My brother had a couple of mates who had their collars felt for having CB gear. I blame 'Smokey and the Bandit'.