klem kedidelhopper writes:


And as soon as you tell them you did that they will have justification
to blame YOU for the whole damn thing, or whatever it is that you're
complaining about. You might even find a charge for a service call on
your bill as well.

Quite True.

If you understand anything about telephone equipment, your line sits
at 48VDC when the phone in on hook, (hung up). When it rings, an AC
voltage, usually at a frequency of 20HZ is superimposed on the line.

Well, ~130VAC atop the -48V.

When you, your fax machine, or modem etc. "answers" the call your line
goes "off hook".

Detected by the line relay looking at the -48.

At this point your line is sitting at about 6VDC until you hang
up, whereupon the line returns to 48VDC.

The exact off-hook loop current is a function of the
length/gauge of the outside plant. It may be ~5-30 ma; seldom
more. Some badly designed phones/systems get upset if the loop
is too short/current high. Distorted audio is one issue.

Another is the busy-detector in some phones/Zon credit card
machines/faxes; it looks at line voltage. If they see ~35V;
they think it's busy. With short outside plant, the off-hook
voltage may only drop to say 40V. I've put 330 ohms in series
with each side as required.

An LED, (along with the appropriate series resistor) will only
draw a few milliamps from a 48V line so I don't think that it
would trigger an off hook detection, however I really don't
understand what it is you are actually trying to accomplish.

ISTM anything more than ~0.5ma may trip, or maintain, the line relay.

Another old wives tale was you should not short the pair to force a busy;
it will start a fire. Piffle. Work out the math. 0 ohms * 30 ma = 0 watts.


--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433