[Gllug] [Fwd: Caller ID on a POTS line]

Christopher Hunter cehunter at gb-x.org
Tue Jan 18 09:32:42 UTC 2011

-------- Forwarded Message --------
From: general_email at technicalbloke.com
<general_email at technicalbloke.com>
Reply-to: Greater London Linux User Group <gllug at gllug.org.uk>
To: GLLUG List <gllug at gllug.org.uk>
Subject: [Gllug] Caller ID on a POTS line
Date: Tue, 18 Jan 2011 09:01:58 +0000

Hi there,

I want to get caller ID info from my POTS line into my computer. It
seems the only commercial system on the market is the CTI Meteor 2 which
looks very capable but also costs £120 which I'd rather not spend if I
can avoid it.

There are some homebrew plans from the 90s and early 00s on teh interweb
but they involve decoder chips salvaged from long defunct caller id
units which are not easily available now. There are plenty of caller id
units on ebay for a quid but these are the more modern single chip
designs which wouldn't be nearly as easy to hack in any useful way.

So, does anyone know if anyone still makes or supplies a UK CID decoder

Apparently the CID burst is 1200 baud FSK'd so...

Does anyone know if there's a general purposed un-FSKing chip out there
that might work instead?

Alternatively I was wondering if it would be possible to capture the CID
burst as audio via my soundcard then decode it in software? If so would
anyone here know how to build a circuit to get this audio from the
phoneline safely (for both my computer AND my line)?

There were, at one point in history, a few modems that would decode UK
CID but they seem to be even harder to track down than the CID units
with the decoder chip in them :/

Of course I could just start saving my pennies but where would be the
fun in that?



£1.50 + £1.20 p&p can't really be beaten.  I'm going to get two of
them.  When I find the hack to get the data out in serial form, I'll let you know.

It strikes me that these units would be ideal for a USB-connected hack - they run from 4.5V, so 5V from the USB will be dropped by a single diode.


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