"Jim Thompson" wrote
in message ...
On Wed, 26 Jan 2011 20:58:03 -0500, "Martin Riddle"
wrote:



"Jim Thompson"
wrote
in message ...
[snip]

(Existing reject box designers haven't yet figured out how to insert
CID after second ring. Shouldn't it be easy enough with a micro?? )

So you only want to dump incoming 800 numbers, but let every thing
else
thru.
The CID appears between the first and second rings.
http://www.epanorama.net/documents/telecom/cid_bellcore.html

So you should be able to grab it and determine if the number should be
hung up,
Before the second ring.

Then you need a V.23 1200 baud modem to reinsert the CID after the
second ring.

Sounds like its doable, lotsa time between rings. A PIC would work.
You
would need a blocking circuit for when the modem retransmits the CID.
Ma Bell might not be happy with extra CID data on their lines.

Cheers


That re-insertion is the tricky part.


EDN design idea, CID generation.
http://www.edn.com/contents/images/120700di.pdf

Micro of course. Bit banged.

The re-insertion would need a 'Hybrid' circuit. There's an old NatSemi
appnote that I used to make a Hybrid for a hand-set to modem box.
It worked even at 28.8kbs. They're also know as Line echo cancellers.
That would block the CID from entering the POTs line. ( it would be
reversed in this case )

I think this was the appnote
http://www.nbtsc.org/~erek/optimumhybdesign.pdf

Cheers