At 01:53 PM 5/2/2003 -0400, A.J. Tufgar wrote:
>Hey everyone,
>              I need a FCC compliant circuit that outputs 5 V when a
>device is plugged into a phoneline.  How does this look?  Anyone see
>any issues?  Suggstions?
>
>Two lines at the top are ring and tip and the lines @ the bottom are
>ground and the signal line.

I did this in a commercial design some years back.
I used a 10M resistor, and 15V zener and optoisolator diode in series with
a dry relay contact.
Activate the relay for 100mS, and look at the opto output. You can sense
the line once a second or so.
If you bridge the relay contacts with a 75V zener, then you also get ring
detect.
You need a CTR of >100 in the optos, and then a light pulldown on the output.



This passed part 68, and worked well in several million devices.

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