analog telephone voltages

Actually, I do not intend to connect the private line to the telco. It is just between two devices that work on a standard POTS line. I want to be able to generate off-hook, ring, and on hook so that I can use a low end modem between two points that expect to be on a telco line. I hope I have been able to clarify this...if not...give me another shot at it please...

John,

I have seen the specs for one part that seems to indicate it will sense a ring voltage as low as 17Vac rms. Can I generally depend on that?

I read in sci.electronics.design that snipped-for-privacy@edwards.spx.com wrote (in ) about 'analog telephone voltages', on Mon, 13 Dec 2004:

It depends on which instruments you are using. Some ringers will work on much lower voltages than others.

--
Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

jeff posted:

Jeff posted:

Over what distance?

If you are within a few hundred feet you can probably ring a phone with 12V, 60 Hz.

12VDC will give you at least 20mA loop current thru the two phones, so that is adequate.

If the computers are "real close" you could just use No Modem connection, a.k.a. Null Modem.

Don

Not interested in the specifications, but do want to know minimum requirements???

Oh well, do some digging here:

I read in sci.electronics.design that snipped-for-privacy@edwards.spx.com wrote (in ) about 'analog telephone voltages', on Mon, 13 Dec 2004:

No.

--
Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Quick specs from memory:

On-hook: -48 VDC Off-hook: less, down (up?) to maybe -5 VDC Ring: 90 V, 20 Hz at the phone company, maybe down as far as 40 V by the time you get it

I have run two phones using a 9 V battery. I'm not sure what the lower limit is. If you have an AC-powered supply, it has to be filtered pretty well to keep hum off the phones.

For more details, see pages 935-936 of "The Art of Electronics".

Matt Roberds

what POTS are you talking about? USA-Canada?

Telephone systems really don't work on voltage.

For US-Centric systems, you'll find that the CO will see you off-hook if you draw at least 20mA.

There's a book, called "Understanding Telephone Electronics" that is a very good reference.

you

very

However voltage is a very important part ... just try having your little fingers across the ring and tip wires when the telemarketer calls and you get -48v with a 90 volt 20 hz ringer signal ... your ears will wiggle at 20 hz !!! ;-)