Re: Telephone : Checking for "RTS"

Ryan Weihl <nixnam@xxxxxxxxxx> schreef in berichtnieuws
e1vfdu$l5s$1@xxxxxxxxxxxxxxxx

Hello Ryan,

according to this: http://oshd.sunsite.dk/projects/caller_id/ and the
included schematic, the dutch telecomm uses what we call a modem with a
DAA to detect a loop reversal to get the DTMF signaling of the CID.
Uses a Mitel/Marlink DTMF decoder. Quite a bit different from Bellcore.
searched for "dutch caller id"

Thanks for the URL. And I did find that one myself too (I did spend quite
some time searching for Dutch caller-ID stuff :-) ).

I'm not at all sure what you mean with "a modem and a DAA", (The only
Modem-alike bit in the schematic is the max232, and isn't connected to the
phone-line at all), but if you mean that the opto-coupler (ring-detector)
could allso be used for detecting the line-reversal ... Well, maybe that
could work.

I've thought about using it before, but I'm not at all sure about it's
dependability.

Thanks for the hint/reminder though, I focussed so much on a 100% solution
that I forgot this one :-\

Regards,
Rudy Wieser

P.s.
A few things I have allways have wondered about when looking at this
schematic :

1) What effect do those put into anti-series diodes D1 and D2 have ? Both
together will not pass current in *any* way .... As far as I can see he (the
designer) mixed up his zener-diode schematic (using an anti-series
configuration) with a normal diode schematic (using an anti-parallel
configuration)

2) why did the designer de-couple from the Phone-line with a trafo *and*
capacitors etc. Why did he not just leave-out those capacitors ? Or even
used the simple one-wire (plus ground) input ?


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