Re: Phone ring circuit
- From: "mkaras" <mkaras@xxxxxxxxxxxxxxxxxx>
- Date: 25 Dec 2006 02:07:20 -0800
Marcin Szczepaniak wrote:
Hi.
I am building some kind of telephone interface (in other words - some kind of my
own telephone central). I have a question about generating ring signal.
I've read that ringing signal is made by switching polarity of 2 wires sonnected
to telephone set.
In my circuit one wire will be connected to ground point and other to -50V. Will
the phone ring if i just made on/off at -50V line? (transistor based swith TTT
at drawning below). Or should i apply +50V to the second (B) wire when ringing
too and switch +50/-50 between A and B wires? This will complicate circut - i
want it to be simple... but it must work :)
-50V
o
|
|
|
TTT
TTT
|
|
oA
oB
|
|
-----
GND
Or maybe you know any already designed circuit that realize ring-generation and
phone hang up/down detection?
Thanks for help:)
The ring generator needs to send a pulse train that matches the ring
cadence you hope to simulate. For example the ring signal may be
present for 2 seconds and then be away during the time between the
pulses for maybe 4 seconds. The ring signal itself is typically a 20
Hertz sine wave signal with a peak to peak voltage of about 90 to 100
volts. This AC voltage rides on the nominal -48 volts of the phone line
such that the average value level of the 20 Hertz sine wave is at -48
volts.
Yes it takes a more complicated circuit to produce a ring signal but be
that as it may the ring signal is often generated by a 90 to 100 volt
p-p oscillator and low output impedance driver and then AC coupled to
the phone line. One method of coupling could use a transformer of the
appropriate type.
- mkaras
.
- References:
- Phone ring circuit
- From: Marcin Szczepaniak
- Phone ring circuit
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