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Connecting a Digital System too a Phone Line

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lee_man_tbu

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Hi everyone,

I have an application where i want too use a PIC MCU too dial a phone number, someone at the other end of the phone number answer the phone, maybe talk too the person operating the PIC through a Speaker and then when the user pushes the "9 Key", the PIC will accept that DTMF code and perform the next operation. IE controlled entrance on an apartment building.

I understand how too decode in coming DTMF signals, my problem is the dialing circuit. I need too know if anyone has any idea's on circuits for this application. IE a digital "Hook", Isolating the PIC from the high voltages from phone lines ect. I know i will probably be using the Pulse Width Modulator too generate the DTMF signals or if an acceptable IC is available too generate DTMF's, i am just unsure of the circuits.

if anyone has any idea's for me, that would be great.

Thanks
Lee
 
For DTMF signal generating/decoding use MT8880 IC. DTMF signal interfacing to tel.line use 1:1 audio trafo, for ringing signal use optocoupler. When You call the remote circuit, the ring signal detected, and after 3...4 ring period the PIC activate a relay, and make off hook. In this state can receive DTMF signals. For on-hook use the asterisk.
 
Thanks for the Info,

The only things is, that i am not calling my PIC circuit, i want the PIC too dial a phone number, then i want the PIC the at the most receive One Key pressed, while voice communcations between someone at the PIC end and SomeOne at the Phone End.

Any details on how this circuit would be great.

Thanks

Lee

lee_man_tbu@hotmail.com

P.S.
If you are intrested in making some $$$ for designing this circuit, e-mail me, because i don't really have much time too design the circuit.
 
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