TELECOM Digest OnLine - Sorted: Re: Experts Please Help

Re: Experts Please Help

Robert Bonomi (
Sun, 10 Apr 2005 19:42:52 -0000

In article <>,
sffdsff <> wrote:

> Hi Guys,

> I am trying to develop an application which will connect to the
> telephone line and when I get an incoming line it shall send a voice
> data on the phone line and then look for key entries from the other
> side ... similar to a voice mail system. I have figured out that I
> would need a DAA to interface to the phone line (of course a one that
> would have a DTMF decoder so that I can get the key entries). Now my
> question is how do I send the voice data out (this voice will be
> pre-recorded on a flash). All the places I have looked say that I
> would need PCM data interfaced to a DSP.

> I do not want to complicate the matter -- I want to make it simple by
> using a PIC Microcontroller.

> So basically this is what I plan it would look like:

> RJ11 <---> DAA <---> Serial Interface <---> PIC Micro <-->Flash

> This should take care of both voice and key entries.

> I have looked into tons of options but cannot figure out a "simple" way
> to do this.

The 'simple' way is to buy it 'off the shelf'. It's called "IVR", aka
"Interactive Voice Response". Inexpensive (even _free_) software to
do this on a PC-type box is readily available. It may require a
"voice/data" modem, or a dedicated phone-line interface card.

If you insist on DIY, the answer to "how do i send the voice data out"
is 'generate the analog wave-form and impress it on the phone line.
If that isn't sufficient 'clue', you don't have the requisite skills
to attempt such a project -- use the "simple" way, mentioned in the
previous paragraph.

For 'digitalized voice' stored anywhere, you have to have "something"
to take that digital data, and convert it back to an _analog_
waveform, to send over the POTS circuit. DSP chips greatly simplify
the process.

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