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Couple DTMF signal to phone lines

E

eeh

Jan 1, 1970
0
Hi,

Could anyone give me a schematic example how to couple the DTMF signal
to the telelphone lines so that I can dial out?
 
M

Michael Black

Jan 1, 1970
0
eeh" ([email protected]) said:
Hi,

Could anyone give me a schematic example how to couple the DTMF signal
to the telelphone lines so that I can dial out?

Get a cheap phone, and use that. It gives you the touch-tone generator,
and it's already coupled to the phone line.

Failing that, you look at the datasheet for the DTMF generator, and
likely that includes how to connect it to the phone line.

Michael
 
D

DaveM

Jan 1, 1970
0
-- "eeh said:
Hi,

Could anyone give me a schematic example how to couple the DTMF signal
to the telelphone lines so that I can dial out?

The simplest (but not recommended) method is to connect the DTMF tones
through a 600:600 ohm transformer connected directly across the phone lines.
The transformer will provide a DC path so you can draw a dial tone.
But that doesn't allow for the switching and audio Tx/Rx if you want to talk
and listen on it too.

But, you didn't ask about that ... . you're only interested in the DTMF
tones.

Cheers!!!!!!!!!!
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in
the address)

Never take a laxative and a sleeping pill at the same time!!
 
E

eeh

Jan 1, 1970
0
If I do not want to use transformer, is it OK to just use capacitor?
 
T

Tim Wescott

Jan 1, 1970
0
eeh said:
If I do not want to use transformer, is it OK to just use capacitor?
What are you trying to accomplish by sending DTMF? Is this part of a
larger system that you're trying to make work, or do you just want to
make noise on the line?
 
P

Pooh Bear

Jan 1, 1970
0
eeh said:
If I do not want to use transformer, is it OK to just use capacitor?

Not really. It may upset the line's performance.

You're not really meant to couple ground referenced signals into phone
lines. Consider also what happens if the line connection gets reversed.

Graham
 
S

Spajky

Jan 1, 1970
0
If I do not want to use transformer, is it OK to just use capacitor?

IMHO no if only using that, because a telefon line needs a DC load
(resistort o transformer of certain DC resistance) to switch to
outgoing line (from 48 drops to 8Vdc) before it can accept DTFM tones
for dialing ..
 
R

Rich Grise

Jan 1, 1970
0
IMHO no if only using that, because a telefon line needs a DC load
(resistort o transformer of certain DC resistance) to switch to
outgoing line (from 48 drops to 8Vdc) before it can accept DTFM tones
for dialing ..

Maybe he wants to put it alongside some phone that doesn't have
buttons or something, albeit I can't imagine where you'd find
something like that these days. ;-)

Anyway, if that's the case, couldn't he use a pair of, say,
..1 or 1 uF caps from something with a differential output?
(the phone will be providing the DC path - it'd be a little
loud in the earpice, though. :) )

Cheers!
Rich
 
M

Michael Black

Jan 1, 1970
0
Rich said:
Maybe he wants to put it alongside some phone that doesn't have
buttons or something, albeit I can't imagine where you'd find
something like that these days. ;-)
If you want that sort of thing, then you feed the touch-tone generator
into a small amplifier, and then feed a speaker, which can be held
up to the phone's microphone for dealing with the menus.

Michael
 
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