wheels@watmath.waterloo.edu (Gerry Wheeler) (04/14/89)
I need some advice, and perhaps one of the readers can help.
We have a new electronic phone system which includes several "single
line jacks" -- jacks that emulate a normal loop to be used with modems,
FAXes, answering machines, etc. The biggest difference is that these
loops are powered with 24 volts, rather than the more normal 48 volts
one would expect. Most of our equipment is quite happy with this,
except for a credit card validation machine with an autodialer built in.
I did some tests on this device (using several nine-volt batteries in
series with the line!) and determined that it really is the low voltage
causing the problem. As near as I can figure, the dialer tests the line
voltage before going off hook, to avoid connecting to a line that is
already in use. I presume they use a zener diode or something to
provide a reference voltage. If the line voltage is higher than the
reference, it will dial. If not, it gives an error message.
I can see two different solutions. 1) change the zener diode, or 2)
provide some sort of black box to convert the 24 volt loop to 48 volts.
I can't really do option 1, because we don't own the machine. (Still,
if anyone has a short list of part numbers for zener diodes that are
about 30 volts, I may have a look for it.) So, does anyone know of a
simple way to accomplish option 2? As I see it, this box would have to
terminate the 24 volt loop, and provide power for a 48 volt loop, and
patch the audio from one to the other. It would also have to sense the
off hook condition and handle that appropriately.
Any leads, or any ideas for other options I haven't considered, would
be most appreciated.
--
Gerry Wheeler Phone: (519)884-2251
Mortice Kern Systems Inc. UUCP: uunet!watmath!mks!wheels
35 King St. North BIX: join mks
Waterloo, Ontario N2J 2W9 CompuServe: 73260,1043