Hi
 I'm designing a PIC based A.C. motor controller and am looking for a
reliable and safe mains zero crossing detector. I've seen the scheme of
putting a large (ie. 5 Mohm resistor in series with a port pin. This
means I'd have to have the hot or neurtral line as my PIC ground. This
makes me nervous.  I was wondering if anyone has used a  better scheme
with success. I was thinking perhaps of using an opto isolator but if
this needs 10ma to turn on it won't be very  accurate. Maybe I need a
common emitter transistor driving the opto isolator with the emitter at
the hot side and the base being driven through a resistor by the
neutral. Any ideas?  Thanks!!
                                       Jim