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Interfacing telephone line to a microcontroller

Hi

I want to interface my telephone line (POTS) to 8051. I just know that the phone line carries DC signalling voltage and the voice communication is also modulated using this DC voltage. I would like to insert my processing circuitry between the phone line and the phone set.

x--------Phone Line---------x|My Circuit|x---------x|Phone Set|

I would just like to digitize the voice, do some processing and then convert it back to the voice signal.

I have been unable to figure out how to interface my circuit to the phone line and to the phone set as the signal levels are not compatible with TTL/CMOS that my circuit would use.

Any help will be appreciated. In particular, I wonder if there is any ADC and DAC that just interfaces directly with the phone set? And how do I do this without interfering with the initial signalling when a number is dialled or a call is coming in?

Thanks in advance!

-- devj

Reply to
devj.nullj
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If it's a one-off, just hack into an old dialup modem.

Otherwise, google "phone line interface" or so.

Good Luck! Rich

Reply to
Rich Grise

A hybrid? Search the Nat Semi app notes for hybrid interface.

Cheers

Reply to
Martin Riddle

I believe what you want is something called a SLIC circuit (for Subscriber Line Interface Circuit).

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There was another company that had these and I'm trying to recall the name from a prior project. I want to say it was CMS Microcircuits, or something like that. The databook is buried -- I'll never get to it.

Anyway, try a Google search on SLIC. Maybe try "SLIC" on Digikey's search engine and see what they have for telecom stock.

In the United States, your device will have to pass Part-68 device testing. Many off-the-shelf SLIC's make that burden a whole lot easier.

Good luck.

-mpm

Reply to
mpm

Arrg, 80's technology is soo simple, any one can do it.

Even google groups types.

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Reply to
don

pdf

Thanks for your reply.

Following your pointers, I have searced and read a bit more. I think SLIC is for the central office and on the user-end i.e. the subscriber you have DAA (Direct Access Arrangement).

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Now, almost half of my problem is solved.

x--------Phone Line---------x[DAA]----My Circuit|x--[What here ?]-------x|Phone Set|

Once I collect signal from DAA and process it with my processor in the circuit, how do I convert it back to a signal that is acceptable to the phone set?

-- devj

Reply to
devj.nullj

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Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

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Reply to
Vladimir Vassilevsky

TI has some nice codecs like the TLV320AIC10 that only requires a transformer and some resistors to make a telephone interface. It helps to have a micocontroller that has an SSI interface. I did a similar design with an NXP LPC2000 series ARM based controller.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
                     "If it doesn\'t fit, use a bigger hammer!"
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Reply to
Nico Coesel

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