Couple DTMF signal to phone lines

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?

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!!

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

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

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

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 ..

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