Phone line presence detector

From: MM (mbmsv_at_yahoo.com)
Date: 08/21/04 

Date: Fri, 20 Aug 2004 23:42:25 -0400

Does anyone know if it is possible to design a potentially _certifiable_
circuit that would detect whether a phone is connected to line or not in the
on-hook state? The circuit that I have seen
(http://www.uoguelph.ca/~antoon/circ/cpld.htm) requires a battery to
operate. Would it be OK to use an isolated power supply instead?

Thanks,
/MM

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