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Telephone Intercom with 'Proper' Ring

Hi,

I've been looking for a schematic of a telephone intercom that will use a pair of phones, and deliver a proper ring voltage to the phone being called (If I understand correctly, somewhere around 100V, 20Hz AC. I would prefer if it also gives a dial/ring tone to the phone making the call.

So far, what I've found are simple schematics that use a buzzer instead of a ring signal, or line simulator schematics (such as this:

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), which seem to have too many features, and are too complex.

At the same time, I've found circuits to simply ring a phone, like this pair (

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).

Here are my questions:

1) Does anyone have a circuit that will already do what I am looking for? 2) Could (and how would) I combine one of those ringer circuits with a simple intercom circuit? 3) If I were to put the 20Hz AC signal into both the lifted and unlifted phones at the same time, would it ring on the unlifted phone, and give a dial tone on the other?

I should mention that I am trying to get this to work with 'old-style' bell phones, so I would need to use a 20Hz signal, not 60 Hz, which I have read works with new phones.

Thanks,

Ori

Reply to
obarbut
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Hi Ken,

Dial tone would be cool, but it's not absolutely necessary... and from what I've found on EBay, a PABX is a bit on the pricey side (the ones that have a low price come with huge shipping fees).

What if I were to take a simple phone-intercom schematic (

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), the kind with a buzzer, and replace the buzzer with a relay that connects the phone to a ringer circuit (perhaps just have one, with it's outputs running along a third and fourth conductor, making use of the other lines in a phone cord) in parallel. Would that work? When the ringer circuit output is connected to the phone, could it cause the phone to appear "off the hook" prematurely?

Thanks,

Ori

Reply to
Ori

If you want dial tone as well, that is completely separate from the ring tone generating. Unless you're dead keen on building your own, buy a cheap PABX on Ebay or at a surplus store.

Ken

Reply to
Ken Taylor

Here - read this:

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Good Luck! Rich

Reply to
Rich Grise

I'd be surprised if you couldn't find a 2 line by 8 extension PABX surplus for less than US$25, but as I have no idea where you are I'll take your word on it. :-)

Your idea about running the ringing volts around separately are valid, particularly if you are using an old style phone which you can hack into to separate out the bell wiring. If you're using a modern electronic phone it's not as easy though. There is a fair amount of telephone related circuits at QSL (

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) which may be handy.

Cheers.

Ken

Reply to
Ken Taylor

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