Just an advice :

Before you start pulling your hair off, take an audio signal
generator an see the shit you can pass via a DAMPS phone :-(


On 2 Mar 2002 at 22:07, Alexandre Guimar=E3es wrote:

> Hi,
>
>     I need to make a audio coupled FSK modem for using with cellphones !=
! I
> know it is weird but the client wants something that can couple to any p=
hone
> and receive data at 1200 bps. It does not even have to be bidirectional =
!
>
>     I have seem the Scenix app-note on a bell 202 modem and I am wonderi=
ng
> if there is a better way to handle the decoding. The encoding is straigh=
t
> forward but the decoding may be a problem because the audio levels would=
 be
> varying a lot, specially because of the audio coupling and in some place=
s
> the cellphones would be working at old analog modes. I was thinking of
> implementing special filters like the ones that Scott used for DTMF deco=
ding
> but I am quite sure I cannot do it fast enough.
>
>     I would really like suggestions for the decoding algorithm and input
> conditioning circuit. My basic idea is to use a "frequency meter like" i=
nput
> circuit that just goes and clips the signal and simple pulse counting to
> check the frequencies. I would like to test some time filtering also to =
see
> if I can get better results. Any suggestions ? The project is not going =
to
> be exclusive, so I can publish the results back to the list when it is
> working.
>
> Best regards,
> Alexandre Guimaraes
>
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>

---
Marcelo Puhl
Mensa Brasil member
http://www.mensa.com.br

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