How to interface DTMF receiver & phone line w/o transfor

[Free_Will]

capturing DTMF codes

I want to record the dialed numbers from a phone line to a microcontroller.I know about DTMF receiver IC and microcontrollers.My problem is what is the interface between the DTMF receiver IC and the phone line(not phone) without using any transformer.

Can you please advise me?

Thanks

 

[papyaki]

Hi

Have a look at **broken link removed**

They provide DAA for voice and data without transformer, but with optical isolation... See LITELINK III

 

[Free_Will]

I'll be glad if any other advise rather than offering particular IC.

 

[papyaki]

OK man

Have a look here : http://www.hut.fi/Misc/Electronics/circuits/teleinterface.html. Search DTMF on the page

and here : **broken link removed**

 

[kudjung]

Using a differential opamp circuit(Set an input impedance to be more than 200Kohms) and tap it directly to the line(After the relay). This should do the job. I use to do a telephone recorder this way. This is just an idea. I'm not sure wheter it will cause any other problem. But I've done this and it seem to work ok for my application.

 

[kudjung]

This is what I use

This is what I use