At 06:43 AM 9/16/2003 -0500, michael brown wrote:

>Mauricio Jancic wrote:
>> Can you please explain to me what is the difference between a "wet"
>> and a "dry" interface?
>
>There is a nifty 20 page modem design guide for the CMX868 located here:
>
>http://www.eetchina.com/ARTICLES/2002OCT/A/2002OCT15_ICD_BD_NTEK_ID_AN01.PDF

most amusing.
this is the first time i've seen line in use sense done by voltage, since i introduced it in verifone point of sale terminals back in 83.

the 'fcc' schematic is 'wet', notice that the off hook current flows through the transformer.

in the 'ctr21' schematic, the dc current is shunted by q1.
it's much the same thing as the two transistor circuit i mentioned, but maybe not as high an impedance. still, should be fine.

ring detect is done properly, all in all, good starting point.

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