http://www.epanorama.net/telephone.html#circuits

is a good start. I did something very similar with a PIC16F873, HT9170 DTM
decoder.
HTH

----- Original Message -----
From: "Gabriel Caffese" <gabrielsdi@IMPSAT1.COM.AR>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: 05 March 2002 23:31
Subject: [OT]: PBX using a PIC micro


> Hello there,
>
>   I want to share 16 "internal" telephone to 4 "external" telephone lines.
> The internal phones will only try to get one external line, as to make a
> communication to the outside world, but want ever try to communicate to
> another internal phone.
>   I will also have to know how much time did that communication last, and
> wich number was dialed.
>  So, here comes the question:
>
>    Does anyone know wich analog circuits would simplify my job ? (DTMF
> dialer, etc, etc)
>
>    Hope to receive help,
>
>
>                Gabriel Caffese.-
>
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.
>
>

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