🚀 go-pugleaf

STATRAA@YaleVM.YCC.Yale.Edu writes:

>I need to build a Hold circuit for a phone line.

Easy... just put a 600 ohm (or so) resistor across the line.  The line will
stay connected.  If you put a transformer in series with this resistor,
and then pipe audio into the other end, presto! you've got music on hold.

>Also, if anyone knows how to do this easily, I would like to build a
>multi-line adaptor for my single line phone.

This wouldn't be complicated.  The line is 0V when not connected, about 9V
when in use, about 48V when available, and 90VRMS 20Hz AC when ringing.
These are easy to tell apart!  In fact, if you make a 'window' type
comparator circuit with two comparators so that the "line unavailable" light
comes on whenever the voltage is less than 4V (say) or greater than 25...
the wildly fluctuating ring voltage will make the indicator flutter without
any more effort on your part!  Make sure you use diode clamps to protect the
inputs to your comparators.

I built something like this for two lines.  Each line had a status indicator
and a hold switch (music on hold if you want it).

							David
-- 
I'm a poet and I'm unaware of it.