Zero-crossing detector?

[dhouston]

I always use an opto for safety. I did try a huge resistor feeding directly into the PIC which seemed to work fine till i connected the PIC to my laptop through serial and the laptop turned itself off.

For ZC, the resistor is adequate given the PIC has clamp diodes on the inputs. If you need mains isolation for RS232, use optos in the RS232 lines.

• http://www.pkfamily.com/users/solson/eeg/isoRS232.gif