Hello All,



I have a signal that is composed of the following:



It is a 30Hz Signal at 38 Volts A.C that is Interrupted every 2 Seconds
like a Ringing Signal on a Telephone but has no D.C component involved.
This signal does ring a telephone.



Here is my Problem.



When the above signal is ringing the phone the voltage across the phone
is measured during the ring cycle at 38 volts A.C, when the phone is
taken off hook the voltage drops to 7.2 volts A.C.



What I need to do is detect this drop or off-hook condition and reset
the Pic processor in my design. The problem I see is that I only want to
reset the processor when the phone is taken off hook and not during the
non-ringing cycles and also how to actually convert the voltage drop
into a usable logic level for a Pic reset.



Therefore



30 Hz @ 38.0v A.C with 2 sec Interruptions = On Hook No reset

30 Hz @ 7.20v A.C with 2 sec Interruptions = Off Hook Reset Pic



I know I can detect an off hook on a regular telephone line but this
circuit has no dc component involved to use for this detection. Does
anyone have any ideas for a simple way to do this simple reset?



Regards,

Steve.

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